阅读说明：本技术 光学相控阵列 (Optical phased array ) 是由 J·孙 M·R·瓦茨 A·雅各比 E·提莫尔多甘 于 2014-01-07 设计创作，主要内容包括：一种由大量纳米光子天线元件形成的光学相控阵列可用于将复杂图像投射至远场中。这些纳米光子相控阵列(包括所述纳米光子天线元件及波导)可使用互补金属氧化物半导体(CMOS)工艺形成在单个硅芯片上。方向耦合器将来自所述波导的光倏逝地耦合至所述纳米光子天线元件,所述纳米光子天线元件将光发射为光束,所述光束具有被选择使得发射光束在所述远场干涉以产生期望图案的相位及振幅。在一些情况下,所述相控阵列中的每个天线可光学耦合至相应可变延迟线,诸如热光调谐波导或液体填充单元,其可用于变化所述天线的输出的相位(及所产生的远场干涉图案)。(An optical phased array formed from a large number of nanophotonic antenna elements may be used to project complex images into the far field. These nanophotonic phased arrays, including the nanophotonic antenna elements and waveguides, may be formed on a single silicon chip using Complementary Metal Oxide Semiconductor (CMOS) processes. A directional coupler evanescently couples light from the waveguide to the nanophotonic antenna element, which emits the light as a beam having a phase and amplitude selected such that the emitted beams interfere in the far field to produce a desired pattern. In some cases, each antenna in the phased array may be optically coupled to a respective variable delay line, such as a thermo-tuned waveguide or a liquid filled cell, which may be used to vary the phase of the output of the antenna (and the resulting far-field interference pattern).)

1. For measuring wavelength λ from free space₀Forming a far field with the coherent light beamAn optical phased array of radiation patterns, the optical phased array comprising:

at least one waveguide for guiding the coherent light beam; and

a plurality of antenna elements disposed in a plane of the at least one waveguide and evanescently coupled to the at least one waveguide to emit respective portions of the coherent optical beam to form the far-field radiation pattern.

2. The optical phased array of claim 1, wherein the at least one waveguide comprises:

a column waveguide for guiding the coherent light beam in a first direction; and

at least one row waveguide evanescently coupled to the column waveguide to direct a first portion of the coherent optical beam to at least one antenna element of the plurality of antenna elements.

3. The optical phased array of claim 2, wherein the at least one row waveguide comprises:

a first row of waveguides evanescently coupled to the column waveguides via a first directional coupler having a first coupling efficiency to guide the first portion of the coherent optical beam having a first amplitude; and

a second row waveguide evanescently coupled to the column waveguide via a second directional coupler having a second coupling efficiency to guide a second portion of the coherent optical beam having a second amplitude.

4. The optical phased array of claim 3, wherein the first coupling efficiency and the second coupling efficiency are selected such that the first amplitude is substantially equal to the second amplitude.

5. The optical phased array of claim 1, wherein the at least one waveguide is formed via a Complementary Metal Oxide Semiconductor (CMOS) process.

6. The optical phased array of claim 1, wherein the plurality of antenna elements are arranged at approximately λ₀A pitch interval of an integer multiple of/2.

7. The optical phased array of claim 1, wherein the plurality of antenna elements are arranged at less than or equal to about λ₀A pitch interval of/2.

8. The optical phased array of claim 1, wherein the respective portions of the coherent light beam emitted by the plurality of antenna elements have substantially equal amplitudes.

9. The optical phased array of claim 1, further comprising:

at least one variable optical delay line in optical communication with at least one of the plurality of antenna elements to shift a phase of a respective portion of the coherent optical beam to vary an amplitude distribution of the far-field radiation pattern and/or to compensate for phase errors in the at least one waveguide.

10. The optical phased array of claim 9, further comprising:

at least one heater in thermal communication with the at least one variable optical delay line to heat at least a portion of the at least one variable optical delay line to change a phase offset imparted by the at least one variable optical delay line on the corresponding portion of the coherent light beam.

11. The optical phased array of claim 10, wherein the at least one heater comprises a resistive heater formed in a doped semiconductor.

12. The optical phased array of claim 10, further comprising:

a controller operatively coupled to the at least one heater to control a temperature of the at least one heater to vary the far-field radiation pattern via changes in phase offsets imparted on the respective portions of the coherent light beam by the at least one variable optical delay line.

13. The optical phased array of claim 9, further comprising:

a grating in optical communication with the at least one variable optical delay line to diffract at least a portion of the respective portion of the coherent beam to form the far-field radiation pattern.

14. The optical phased array of claim 13, wherein the grating has a full width half maximum diffraction bandwidth of at least about 100 nm.

15. The optical phased array of claim 13, wherein the grating is configured to suppress resonant back reflection of the respective portion of the coherent light beam.

16. From having free space wavelength lambda₀The method of forming a far-field radiation pattern in a far field of an optical phased array, the optical phased array comprising at least one waveguide and a plurality of antenna elements disposed in a plane of the at least one waveguide, the method comprising:

(A) directing the coherent light beam via the at least one waveguide;

(B) evanescently coupling respective portions of the coherent optical beam from the at least one waveguide to respective antenna elements of the plurality of antenna elements; and

(C) transmitting the respective portion of the coherent light beam from the respective antenna element to produce the far-field radiation pattern.

17. The method of claim 16, wherein:

(A) including evanescently coupling a first portion of the coherent optical beam from the column waveguide to at least one row waveguide, an

(B) Including evanescently coupling the respective portion of the coherent optical beam from the at least one row waveguide to the respective antenna element.

18. The method of claim 17, wherein (a) comprises:

(A1) evanescently coupling the first portion of the coherent optical beam from the column waveguide to a first row waveguide via a first directional coupler having a first coupling efficiency, the first portion of the coherent optical beam having a first amplitude; and

(A2) evanescently coupling a second portion of the coherent optical beam from the column waveguide to a second row waveguide via a second directional coupler having a second coupling efficiency, the second portion of the coherent optical beam having a second amplitude, and the second coupling efficiency selected such that the second amplitude is approximately equal to the first amplitude.

19. The method of claim 16, wherein (a) comprises:

coupling the coherent light beam from the coherent light source into a first waveguide formed via a Complementary Metal Oxide Semiconductor (CMOS) process.

20. The method of claim 16, wherein (B) comprises:

coupling respective portions of substantially equal amplitude from the at least one waveguide to the plurality of antenna elements.

21. The method of claim 16, wherein (C) comprises:

from about equal to λ₀A pitch of an integer multiple of/2 of the plurality of antenna elements transmits the respective portion of the coherent light beam.

22. The method of claim 16, wherein (C) comprises:

from less than or equal to about λ₀A distance of/2Emits the respective portion of the coherent light beam.

23. The method of claim 16, further comprising:

shifting a phase of at least one of the respective portions of the coherent light beam with at least one optical delay line in optical communication with a first antenna element of the plurality of antenna elements to vary the far-field radiation pattern and/or compensate for phase errors in the at least one waveguide.

24. The method of claim 23, further comprising:

heating at least a portion of the at least one optical delay line to change a phase shift imparted by the at least one optical delay line on the at least one of the respective portions of the coherent light beam.

25. One for driving a motor from a voltage of about lambda₀The coherent light beam of free-space wavelengths forming an optical phased array of far-field radiation patterns, the optical phased array comprising:

a substrate;

a column waveguide formed in or on the substrate to guide the coherent light beam;

a plurality of directional couplers formed in or on the substrate to evanescently couple respective portions of the coherent optical beams from the column waveguides to produce a plurality of row optical beams;

a plurality of row waveguides formed in or on the substrate, each of the plurality of row waveguides in optical communication with a respective one of the plurality of directional couplers to guide the plurality of row light beams;

a plurality of phase shifters formed in or on the substrate, each phase shifter of the plurality of phase shifters evanescently coupled to a respective row waveguide of the plurality of row waveguides and configured to impart a respective phase shift to a respective portion of the respective row beam of the plurality of row beams to produce a respective phase-shifted beam;

a plurality of antenna elements formed in or on the substrate, each antenna element of the plurality of antenna elements in optical communication with a respective phase shifter of the plurality of phase shifters and configured to emit the respective phase-shifted beam at an angle relative to the substrate to form the far-field radiation pattern; and

a plurality of independently controllable heaters, each independently controllable heater of the plurality of independently controllable heaters in thermal communication with a respective phase shifter of the plurality of phase shifters and configured to heat the respective phase shifter to vary the respective phase shift to vary the far-field radiation pattern and/or to compensate for phase errors in the column waveguide and/or the plurality of row waveguides.

26. The optical phased array of claim 25, wherein each of the plurality of directional couplers has a length selected such that the row beams of the plurality of row beams have approximately equal amplitudes.

27. The optical phased array of claim 25, wherein the plurality of antenna elements comprises at least approximately 4096 antenna elements.

Background

Radio frequency electromagnetic phased arrays are well known and have achieved applications ranging from communications to radar, broadcasting and astronomy. The ability to generate arbitrary radiation patterns with large scale phased arrays has long been sought. While deploying large-scale radio frequency phased arrays is extremely expensive and cumbersome, optical phased arrays have the unique advantage that much shorter optical wavelengths are promising for large-scale integration. However, short wavelengths of light also place stringent requirements on manufacturing. Thus, while optical phased arrays have been investigated in connection with various platforms and more recently in connection with chip scale nanophotonics, the optical phased arrays presented to date have been one-dimensional arrays or small-scale two-dimensional arrays.

Disclosure of Invention

Embodiments of the invention include methods for recovering a wavelength from free space λ₀And a corresponding method of forming a far-field radiation pattern using the optical phased array. One example of an optical phased array includes at least one waveguide evanescently coupled to a plurality of antenna elements disposed in the same plane as the waveguide. In operation, the waveguide directs a coherent light beam to the antenna elements, which emit respective portions of the coherent light beam to form a far-field radiation pattern.

In some cases, an optical phased array includes a column waveguide evanescently coupled to one or more row waveguides. The column waveguides guide the coherent light beams in a first direction to the row waveguides, which guide respective portions of the coherent light beams to the antenna elements. For example, an optical phased array may include: a first row of waveguides evanescently coupled to the column waveguide via a first directional coupler having a first coupling efficiency; and a second row waveguide evanescently coupled to the column waveguide via a second directional coupler having a second coupling efficiency. Depending on the implementation, the first coupling efficiency may be less than the second coupling efficiency, for example, to ensure that the amount of optical power coupled into the first row of waveguides is approximately equal to the amount of optical power coupled into the second row of waveguides. If desired, the waveguide may be formed via a Complementary Metal Oxide Semiconductor (CMOS) process.

The antenna elements in the optical phased array may be spaced at any suitable spacing, including approximately equal to λ₀A pitch of an integer multiple of/2 or less than or equal to about λ₀A/2 pitch. The antenna elements may also emit respective portions of coherent light beams of approximately equal amplitude. In some cases, each antenna element may include a grating that diffracts at least a portion of a respective portion of the coherent light beam to form a far-field radiation pattern. Each grating may have a full width half maximum diffraction bandwidth of at least about 100 nm. And each grating may be configured to suppress resonant back-reflection of a respective portion of the coherent light beam.

In some cases, the optical phased array may include a plurality of variable optical delay lines, each in optical communication with a respective antenna element. In operation, such a variable optical delay line may be used to shift the phase of a corresponding portion of the coherent optical beam to change the amplitude distribution of the far field radiation pattern and/or to compensate for phase errors in the at least one waveguide. Each variable optical delay line may be activated by a respective heater, such as a resistive heater formed in a doped semiconductor. In operation, the heater heats at least a portion of the variable optical delay line to change the phase shift imparted by the variable optical delay line on the corresponding portion of the coherent light beam. A controller operatively coupled to the heater can control the temperature of the heater to vary the far field radiation pattern via changes in the phase offsets imparted on the respective portions of the coherent light beam by the variable optical delay line.

In another embodiment, an optical phased array includes a substrate, a column waveguide, a plurality of directional couplers, a plurality of row waveguides, a plurality of phase shifters, a plurality of antenna elements, and a plurality of controllable heaters. The column waveguides, directional couplers, row waveguides, phase shifters and antenna elements are formed in or on the substrate. In operation, the column waveguide will have an approximate λ₀The coherent optical beam of free-space wavelengths is directed to a directional coupler that evanescently couples respective portions of the coherent optical beam from the column waveguide to the row waveguide. The row waveguides guide and evanescently couple portions of these "row beams" to phase shifters, each phase shifter imparting a respective phase shift to a respective portion of a respective row beam to produce a respective phase-shifted beam. Each phase shifter couples its respective phase-shifted beam to a particular antenna element of the plurality of antenna elements. The antenna elements emit phase-shifted beams at an angle relative to the substrate to form a far-field radiation pattern. And the heater can be controlled to heat the phase shifter to vary the phase shift, which in turn varies the far field radiation pattern and/or compensates for phase errors in the column waveguides and/or the row waveguides.

It should be appreciated that all combinations of the above concepts and additional concepts discussed in greater detail below (provided that these concepts are consistent with one another) are contemplated as part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. It is also to be understood that the terms explicitly employed herein, which may also appear in any disclosure incorporated by reference, shall control in meaning that is most consistent with the particular concepts disclosed herein.

Drawings

Skilled artisans will appreciate that the figures are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The figures are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of various features. In the drawings, like reference numbers generally refer to like features (e.g., functionally similar and/or structurally similar elements).

Fig. 1A illustrates a 64 x 64 element optical phased array (an inset shows a unit cell or pixel of the optical phased array).

Fig. 1B shows a power feed network suitable for use in the optical phased array of fig. 1A, with a bus waveguide coupling an equal amount of optical power to multiple row waveguides.

Fig. 1C is a graph of coupler length (left axis) and coupling efficiency (right axis) versus row/column index for the bus-row coupler (upper curve) and row-unit coupler (middle curve) in the 64 x 64 nanometer photonic phased array of fig. 1A.

FIG. 1D shows a unit cell (pixel) of the optical phased array of FIG. 1A with directional couplers, phase shifters, and nanophotonic antenna elements.

Fig. 2A is a schematic diagram of an 8 x 8 element active optical phased array using thermo-optic phase tuning.

Fig. 2B is a schematic diagram of thermo-optically tuned pixels in the active optical phased array of fig. 2A.

Fig. 3A is a schematic diagram of a 12 x 12 element active optical phased array using liquid-based phase tuning.

Fig. 3B is a schematic diagram of a liquid tuning pixel in the active optical phased array of fig. 3A.

Fig. 4A is a graph of a three-dimensional, near-field emitted Finite Difference Time Domain (FDTD) simulation suitable for use with nanophotonic antennas in an optical phased array.

Fig. 4B is a polar plot of the far-field radiation pattern of the optical nano-antenna calculated from the near-field emission plotted in fig. 4A using a near-field-far-field transformation.

Fig. 4C is a polar plot of a simulated radiation pattern (here, a mark of the Massachusetts Institute of Technology (MIT)) emitted by the 64 x 64 element optical phased array shown in fig. 2A in the far field.

FIG. 4D is a polar plot of the encircled area of the simulated radiation pattern shown in FIG. 4C.

Fig. 5 is a block diagram illustrating antenna synthesis for a large-scale nanophotonic phased array.

FIG. 6A shows a display panel with λ₀A 64 × 64 optical phased array of a pixel pitch of 2 emits a simulated far field array factor pattern (in this case, the "MIT" flag).

FIG. 6B shows a multi-channel optical beam propagating at different angles, for example, for optical free-space communication, with λ₀64 × 64 optical phased array emission of a pixel pitch of 2 simulated far field array factor pattern.

Fig. 6C is a color plot of the phase distribution across the 64 x 64 optically phased array used to generate the far field array factor pattern shown in fig. 6A.

Fig. 6D is a color plot of the phase distribution across the 64 x 64 optically phased array used to generate the far field array factor pattern shown in fig. 6B.

Fig. 7A to 7D are graphs with gaussian phase noise obtained by subtracting the standard deviations σ ═ 0 (i.e., no phase noise; fig. 7A), σ ═ pi/16 (fig. 7B), σ ═ pi/8 (fig. 7C), and σ ═ pi/4 (fig. 7D)_mnAdding to the desired phaseWhile simulated far-field array factor patterns with different phase noise levels are simulated.

Fig. 8A is a Scanning Electron Micrograph (SEM) of a fabricated 64 x 64 element optical phased array.

Fig. 8B is an SEM of the pixels in the fabricated 64 x 64 element optical phased array shown in fig. 8A.

Fig. 9A is an SEM of a fabricated nanophotonic antenna suitable for use in an optical phased array.

Fig. 9B is a graph of simulated emission efficiency versus emission wavelength for the nanophotonic antenna of fig. 9A in upward emission (top curve), downward emission (middle upper curve), reflection (middle lower curve), and transmission (bottom curve).

FIG. 10A is a diagram of an imaging system for observing the near field and the far field of an optical phased array.

FIG. 10B is a near field image of the optical phased array shown in FIG. 8A obtained using the imaging system of FIG. 10A.

Fig. 10C is a close-up view of the 8 x 8 pixel portion of the near field shown in fig. 10B.

FIG. 10D is a histogram of measured intensity distributions of optical emissions from pixels in an optical phased array.

FIG. 10E is a far field (Fourier plane) image of the optical phased array shown in FIG. 1B obtained using the imaging system of FIG. 10A.

Fig. 10F is a far field (fourier plane) image of the 32 x 32 pixel portion of the optical phased array shown in fig. 8B obtained using the imaging system of fig. 10A.

Fig. 11A-11E illustrate the phase distribution (top row), simulated far field radiation pattern (middle row), and measured far field radiation pattern (bottom row) of the optical phased array of fig. 2A emitting a boresight beam (fig. 11A), a focused beam directed vertically up to 6 ° (fig. 11B), a focused beam directed horizontally up to 6 ° (fig. 11C), a single beam split vertically into two beams (fig. 11D), and a single beam split horizontally into four beams (fig. 11E).

Detailed Description

Examples of the present technology include large-scale, two-dimensional optical phased arrays (also known as Nanophotonic Phased Arrays (NPAs)) having optical nano-antennas densely integrated on a silicon chip within a relatively small footprint. For example, an exemplary NPA may include 4096 antenna elements configured as a 64 x 64 element array in an area of about 576 μm x 576 μm. The robust NPA design disclosed herein, along with state-of-the-art complementary metal oxide semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips.

The NPA, like its radio frequency (rf) counterpart, includes an optical antenna array, also known as a nanowire, nanophotonic antenna, antenna element, or simply element. For example, the NPA may include a set of identical optical antennas configured as a periodic, two-dimensional array in which the elements are separated by a distance of up to about the wavelength of the light. In other examples, the array may be non-periodic (e.g., random or sparse) and/or one-dimensional. Each optical antenna in the array emits light of a particular amplitude and phase. These emissions interfere to form the desired far-field radiation pattern. Changing the amplitude and/or phase of the light beam emitted by the optical antenna results in a change in the far field radiation pattern.

Because light has a relatively short wavelength (e.g., on the order of one micron), NPAs may include thousands or even millions of antenna elements in a compact, low-cost chip. By incorporating a large number of antennas, the NPA can produce a high resolution far field pattern, including the most arbitrary radiation patterns, that imparts NPA functionality beyond traditional beam focusing and steering. However, short optical wavelengths also present challenges in achieving coherent output from these large-scale NPAs, because even nanoscale fluctuations affect the ability to balance the phase and power of light emissions from thousands of nanoantennas that are balanced in power and aligned in phase to form a particular far-field radiation pattern. Thus, the chip-based, two-dimensional NPAs revealed to date have been implemented as small-scale with no more than 16 antenna elements and limited in function to focusing and steering a single beam.

In one example, the NPA includes 64 × 64 optical nanoantennas on a silicon chip, wherein all 4096 optical nanoantennas are balanced in power and aligned in phase to produce a particular radiation pattern (e.g., MIT mark) in the far field (in optics, the far field is generally defined as the area where the Freund and Fisher approximation applies, i.e., the distance is greater than or equal to about L)>W²Lambda, whereinW is the size of the aperture and λ is the wavelength of the emitted light). This power balance and phase alignment may be fixed to ensure repeatable generation of a particular far-field radiation pattern. Experimental results show that despite short optical wavelengths and the corresponding lengths of the phase elements, the phase of the light beams emitted by the antenna elements can be maintained, highlighting the ability to arbitrarily manipulate the phase of the optical field within the nanophotonic chip.

In other examples, each antenna element in the array includes a respective phase tuner for active phase tuning. Tuning the relative phases of the antenna elements in the NPA allows the beam emitted by the NPA to be dynamically steered and/or shaped. Dynamic phase tuning in conjunction with a large number of antenna elements also enables the generation of more complex far-field radiation patterns, extending the functionality of the phased array beyond beam focusing and beam steering.

The large number of nano-antennas and the embedded phase tunability enable NPAs to dynamically generate arbitrary far-field radiation patterns and then impact new areas such as communications, LADAR, three-dimensional holography, biological and environmental sensing, and biomedical sciences. For example, the exemplary NPA may be used in a (low cost) LIDAR adapted for use in automobiles, trucks, satellites, robots, and the like. The ability to utilize CMOS integrated processes also promises the bright future of low cost and compact NPAs.

Optical phased array with evanescently coupled bus and nano-antennas

Fig. 1A to 1D illustrate an optical phased array 100 formed using a CMOS integration process. As shown in FIG. 1A, optical phased array 100 includes a phase modulator at about λ₀The/2 pitch is configured as 4096 unit cells (pixels) 130 of a 64 pixel × 64 pixel grid, where λ₀Is the wavelength of the light beam emitted by the optical phased array 100. The optical fiber 102 couples light from a laser or other coherent light source (not shown) into the column bus waveguide 110, which in turn evanescently couples the light into 64 row bus waveguides 120-1 through 120-64 (collectively, row bus waveguides 120). Each row bus waveguide 120 then evanescently couples light into 64 pixels 130, which emit light to form a predetermined far-field emission pattern.

In this optical phased array 100, the coupling to the row bus waveguides 120 is controlled so that each row bus waveguide 120 achieves the same amount of power as described in more detail below. The optical power in each row bus waveguide 120 is then similarly divided among the 64 pixels 130 coupled to the row bus waveguide 120 such that all 4096 optical nano-antennas in the optical phased array 100 are uniformly excited. Because each pixel 130 receives an equal portion of the optical power provided by the optical fiber 102, the difference in the relative phases of the light beams emitted by the pixels 130 determines the far field emission pattern of the optical phased array. In other examples, the optical power coupled into/or out of each pixel 130 may be weighted, attenuated, or amplified to produce inter-pixel variations in emitted power to produce a particular far-field radiation pattern.

In this example, the pixel pitch is less than the free space wavelength λ of the optical emission in the x and y directions₀Half of that. Because the pixel pitch is less than λ₀/2, then the optical phased array 100 can produce a unique interference pattern in the far field without higher order radiation lobes. For values greater than λ₀A pixel pitch of/2, the optical phased array 100 may produce a (possibly undesirable) high order interference pattern in the far field in addition to the desired far field radiation pattern. In other words, the optical phased array 100 may produce an aliased version of the desired pattern in the far field.

Power management in nanophotonic phased arrays

In a phased array, the amplitude of the individual emissions of the pixels affects the far field radiation pattern. Undesired variations in these amplitudes may damage or otherwise degrade the far-field radiation pattern of the optical phased array. Preventing undesirable amplitude variations often becomes more challenging (and more important) in larger arrays. Thus, in large arrays (e.g., arrays having thousands of pixels), the power feed network should deliver optical power to each antenna element reliably and accurately.

Fig. 1B illustrates the power feed network (column bus waveguide 110 and row bus waveguide 120) of the optical phased array in more detail. As is known in the art of CMOS processing and CMOS electronics, the column bus waveguides 110 and the row bus waveguides 120 may be formed of silicon waveguides (e.g., silicon-on-insulator waveguides). The column bus waveguide 110 is butt-coupled to an optical fiber 102, which optical fiber 102 emits an optical beam into a single transverse mode supported by the column bus waveguide 110.

The optical beams propagate along the column bus waveguide 110 through a series of column-row directional couplers 140-1 to 140-64 (collectively directional couplers 140), each coupling a respective portion of the optical beam into a respective row bus waveguide 120. The directional couplers 140-1 through 140-64 shown in FIG. 1B are four-port, passive devices formed by respective column coupling regions 112-1 through 112-64 (collectively coupling regions 112) of the column bus waveguide 110. In each directional coupler 140, the column coupling regions 112 extend parallel to and spaced apart from the row coupling regions 122-1 through 122-64 (collectively coupling regions 122) in the respective row bus waveguides 120-1 through 120-64.

In operation, light propagating through a given column coupling region 112-m is evanescently coupled into an adjacent row coupling region 122-m, where m represents the number of rows. As will be appreciated by those skilled in the art, the proportion of optical power transferred from the column coupling region 112-m into the row coupling region 122-m depends on the optical path length L of the coupling region_c(m) and the optical path length separating the column coupling region 112-m from the row coupling region 122-m. To provide equal power to each row, the length L of the directional coupler_c(m) is varied to change the coupling ratio so that the m (1) th<m<M) row bus waveguides have a coupling efficiency of 1/(M +2-M), where M is the highest row number (in this case, M-64.) the desired coupling ratio (and coupler length) may be obtained by three-dimensional time-domain finite difference modeling or any other suitable technique for the 64-pixel × 64-pixel optical phased array 100 shown in fig. 1A, the bus-row coupler length L_c(m) varies from about 3.53 μm for m-1 (coupling efficiency of about 1.54%) to about 8.12 μm for m-64 (coupling efficiency of about 50%) to equally distribute power among the row bus waveguides 120.

In other examples, the power distribution across the optical phased array may be non-uniform. For example, the power distribution may have a gaussian or exponential decay envelope to provide a gaussian or lorentzian shape to the light beam emitted by the optically controlled array. Similarly, instead of, or in addition to, varying coupler lengths, the coupling ratio of the directional coupler may be varied by varying the separation distance between coupling regions 112 and 122. However, the coupling efficiency tends to be less sensitive to variations in coupler length than variations in separation distance, and thus, directional couplers 140 having varying lengths tend to have looser manufacturing tolerances than directional couplers having varying separation distances.

Some optical phased arrays may also include a tuning mechanism for varying the power distribution across the array, for example, to alter or scan the far field pattern. For example, each directional coupler may comprise an interferometer, such as a mach-zehnder modulator or a ring resonator, with an input port coupled to a column bus waveguide, a first output port coupled to a column bus waveguide, and a second output port coupled to a row bus waveguide. Tuning the interferometer with an electric field (e.g., via electrodes) or a magnetic field (e.g., via electromagnets) changes its coupling ratio, allowing adjustment of the optical power coupled from the column bus waveguide to the row bus waveguide.

In other embodiments, one or more row bus waveguides may include a variable optical attenuator at or near its optical connection with a column bus waveguide. Actuating the variable optical attenuators reduces the optical power propagating through the respective row bus waveguides. Alternatively or additionally, the column bus waveguide may also comprise one or more variable optical attenuators, for example distributed between successive directional couplers. Actuating the variable optical attenuator in the column bus waveguide reduces the optical power available for coupling into the row bus waveguide downstream of the variable optical attenuator.

Fig. 1C is a graph illustrating the performance of the power feed network in the optical phased array 100 of fig. 1A-1C. It shows the coupler length (left axis) and coupling efficiency (right axis) versus row/column index for the directional coupler connecting the column bus waveguide 110 to the row bus waveguide 120 and for the row-pixel directional coupler connecting the row bus waveguide 120 to the pixels 130 in the optical phased array 100 of fig. 1A (described below with respect to fig. 1D). (the length of the row-pixel directional coupler is different from the length of the column-row directional coupler 140 because the row-pixel directional coupler has a different bend radius than the column-row directional coupler 140.)

Nanoantenna design and phase management

FIG. 1D illustrates the pixel 130 in the optical phased array 100 of FIG. 1A in more detail. The pixel 130 includes a pixel waveguide 132 formed using the same CMOS process used to form the column bus waveguide 110 and the row bus waveguide 120. In some cases, all of these waveguides may be clad with a layer of dielectric (such as silicon oxide (SiO)_x) ) such as silicon or silicon nitride. Depending on their refractive index and cross-sectional dimensions, these waveguides can guide light at visible or infrared wavelengths. To guide light at a wavelength of 1550nm, for example, the waveguide may be about 220nm high and about 400nm wide.

The pixel waveguides 132 are evanescently coupled to the respective row bus waveguides 120 via row-to-pixel directional couplers 150. Like the column-row directional coupler 140 shown in fig. 1B, the row-pixel directional coupler 150 is formed by a coupling region 124 in a row bus waveguide 120 extending parallel to and spaced apart from the coupling region 134 in a pixel waveguide 138. And as with the column-row directional coupler 140, the row-pixel directional coupler 150 has a length (and/or width) selected to couple a predetermined proportion of the optical power from the row bus waveguide 120 into the pixel waveguide 132. This coupling efficiency may be different for each pixel, for example, to ensure that each pixel radiates approximately the same amount of energy to provide a predetermined envelope to the near-field radiation pattern emitted by the optical phased array 100, and so on. In other implementations, the row-pixel directional coupler 150 may comprise an active device that can be used to vary the amount of optical power coupled into (and out of) the pixel 130.

The pixel waveguide 132 couples light into an antenna element 138 (also referred to as a nano-antenna, nano-photonic antenna, or element) via an S-shaped static optical delay line 136. The static optical delay line 136 is formed by a segment of the pixel waveguide 132 having an optical path length selected to shift the phase of a wave propagating through the pixel waveguide 132 by a predetermined amountIn this case, the static optical delay line 136 includes two sections, each of which induces a phase shiftWhere m and n are for the total phase shiftThe row and column indices of the pixels. In other embodiments, a pixel may comprise more or fewer segments of an optical delay line, each segment causing an appropriately selected phase shift (e.g.,and andetc.).

As shown in fig. 1D, the use of a curved or serpentine delay line 136 reduces the pixel size, which in turn allows for more precise pixel pitch. In addition, the delay line design makes the position of the antenna element 138 independent of phase delaySuch that all of the antenna elements 138 may be placed on a periodic grid. The varying coupler length slightly affects the phase of the emitted light and the coupled-out light. This effect may be used to calculate the phase shift for each pixel 130Are considered.

The antenna element 138 shown in fig. 1D is a dielectric grating formed in the same plane as the column bus waveguides 110, the row bus waveguides 120, and the pixel waveguides 132. The grating diffracts light up and down out of the plane of the waveguide and grating. Because the grating has a relatively small number (e.g., 5) of grooves, it may have a diffraction bandwidth of a full width at half maximum of several hundred nanometers (e.g., 100nm, 200nm, etc.). In some cases, the grating may be blazed such that light is diffracted more upward than downward (or vice versa). Furthermore, the grating period may be slightly detuned from the resonant emission to avoid reflecting radiation back into the pixel waveguide 132, where it may cause undesirable interference. Such misalignment may cause the optical axis of the emitted beam to deviate from the surface normal of the grating.

Active optical phased array

FIGS. 2A and 2B illustrate 8 × 8 an active tunable optical phased array 200 and unit cells (pixels) 230, respectively, like the passive phased array 100 shown in FIG. 1A, the active phased array 200 shown in FIG. 2A includes an optical radiation source (in this case, an optical fiber 202 coupled to a laser (not shown)) that will have a free-space wavelength λ₀Into the single mode column bus waveguide 210. Evanescent directional couplers 240-1 through 240-8 (collectively directional couplers 240), as described with respect to FIG. 1B, couple light from column bus waveguide 210 into eight different row bus waveguides 220-1 through 220-8 (collectively row bus waveguides 220). And as described above, the coupling efficiency of the directional coupler may be varied to ensure that each row bus waveguide receives a predetermined amount (e.g., an equal amount) of optical power from the column bus waveguide 210.

Each row bus waveguide 220 guides a light beam from a respective directional coupler 240 to eight unit cells (pixels) 230, each of which may be approximately λ₀(e.g., about 9 μm × 9 μm.) As described above with respect to FIG. 1D, the directional coupler 250 evanescently couples light from the bus waveguide 220 to the respective unit cells 230, each unit cell 230 including a silicon waveguide 232, the silicon waveguide 232 coupling the light into the grating-based antenna element 238. this antenna element 238 emits light having a desired amplitude and phase to form a pattern in the far field of the active optical phased array 200.

In this case, however, the active optical phased array 200 includes a pixel addressing matrix that can be used to independently vary the phase of the light beams emitted by the pixels 230. The pixel addressing matrix is formed by column control lines 260-1 through 260-8 (collectively column control lines 260) and row control lines 262-1 through 262-8 (collectively row control lines 262). In this example, the column control lines 260 and row control lines 262 are disposed in parallel planes above the pixels 230; in other examples, the control lines may instead be routed in a plane below the pixels 230.

As shown in fig. 2A and 2B, each column control line 260 extends over a respective column of pixels 230 and is electrically coupled to a copper-silicon electrical contact 264 in each pixel 230 in the column. Similarly, each row control 262 extends over a respective row of pixels 230 and is electrically coupled to a copper-silicon electrical contact 268 in each pixel 230 in the row. The electrical contacts 264 and 268 in each pixel 230 are electrically coupled to a respective integrated heater 266 formed by doping a portion of the silicon waveguide 232. Each heater 266 may have a resistance of approximately 2.5k Ω, including the resistance of contacts 264 and 268.

Applying voltages to a particular column control line 260-m and a particular row control line 262-n causes a change in the potential of the integrated heaters 266 in the pixels 230-mn across the intersection of the column control line 260-m and the row control line 262-n. This change in potential causes the heater 266 to change temperature (become hotter or colder) resulting in a corresponding change in the optical path length of the doped portion of the silicon waveguide 232 via the thermo-optic effect. And this change in optical path length causes a corresponding phase shift of the light beam propagating through the waveguide 232 to the antenna element 238. In some cases, the heater 266 may operate at a thermal efficiency of about 8.5mW per 7 ° phase shift.

Fig. 3A and 3B illustrate an active optical phased array 300 that uses liquid-based tuning in place of (or in addition to) an integrated heater for varying the phase of the light beam emitted by the pixels. Again, the optical fiber 302 coupled to the laser (not shown) will have a free-space wavelength λ₀Into the single mode column bus waveguide 310. Evanescent directional coupler 340 couples light from column bus waveguide 310 into row bus waveguides 320, where the coupling efficiency is selected to ensure that each row bus waveguide 320 receives a predetermined amount (e.g., an equal amount) of optical power from column bus waveguide 310. Each row bus waveThe guides 320 direct the light beams from respective directional couplers 340 into a respective set of unit cells (pixels) 330, each of which may be approximately λ₀(e.g., about 9 μm × 9 μm.) the directional coupler 350 evanescently couples light from the bus waveguides 320 to the respective unit cells 330, each unit cell 330 including a silicon waveguide 332, the silicon waveguide 332 coupling the light into the grating-based antenna element 338, as shown in fig. 3B.

Like the active optical phased array 200 shown in fig. 2A, the active optical phased array 300 shown in fig. 3A includes column control lines 360 and row control lines 362 in parallel planes above the plane of the pixels 330. As shown in fig. 3B, these column and row control lines 360 and 362 are connected to electrical contacts 374 and 376 in individual pixels 330, much like the control lines shown in fig. 2A and 2B.

The active optical phased array 300 shown in fig. 3A and 3B also includes an array of fluid reservoirs 379 disposed over the unit cells 330. In this case, there is one liquid reservoir 379 for each pixel 330; in other cases, a single reservoir may cover multiple pixels. Each fluid reservoir 379 holds a respective volume of fluid 378, such as an electroactive material or a transparent fluid, having an index of refraction greater than that of air (e.g., n-1.5). In this example, the fluid includes an electroactive liquid crystal material 378 that emits at the emission wavelength λ of the phased array₀The lower side is transparent.

Application of voltages to particular column control lines 360-m and particular row control lines 362-n generates a potential drop across liquid crystal material 378 and fluid reservoirs 379-mn in pixels 330-mn at the intersection of column control lines 360-m and row control lines 362-n. This liquid crystal material 378 aligns itself with the direction of the applied electric field, resulting in a change in the index of refraction experienced by light propagating from the antenna element 338 through the liquid crystal material 378. This increase or decrease in the refractive index of the liquid crystal delays or advances the phase of the emitted light beam.

Alternatively, or in addition, the liquid crystal material may also rotate the polarization of the emitted light beam. In some cases, the emitted beam may then pass through a fixed polarizer (e.g., a linear polarizing film; not shown); if the polarization state of the emitted light beam does not match the polarization state delivered by the polarizer, the polarizer attenuates the emitted light beam, as will be appreciated by those skilled in the art. Thus, the emitted light beam may be selectively attenuated by actuating the liquid crystal material to tune the polarization state of the emitted light beam. In other cases, the polarizer may be omitted and the liquid crystal material may modulate the polarization of the emitted beam, for example to create a polarization multiplexing pattern in the far field and/or to change the polarization of the far field pattern.

In other examples, the phased array may include one or more auxiliary reservoirs coupled to the fluid reservoir via microfluidic channels and/or microfluidic pumps (not shown). These pumps may be used to increase or decrease the amount of fluid in a particular fluid reservoir to produce a corresponding increase or decrease in the optical path length experienced by a light beam emitted by an antenna element below the fluid reservoir. In other words, the fluid-filled reservoir may act as a variable optical delay line for tuning the phase of the emitted light beam.

As those skilled in the art will readily appreciate, the appropriate combination of applied voltages to the column and row control lines shown in fig. 2A and 3A tunes the phase of the light beams emitted by the pixels in the phased array. The voltage may be determined by a processor (not shown) to project a particular image or pattern of radiation into the far field of the phased array. For example, a voltage ramp is applied across one face of the optical phased array via the row electrodes, causing the light beam to point up or down depending on the slope of the voltage ramp.

Optical phased array for arbitrary pattern generation

The ability to integrate a large number of pixels in a nanophotonic phased array within a small footprint opens the possibility of using nanophotonic phased arrays to generate arbitrary, complex far-field radiation patterns. The far field radiation field E (theta, phi) of the phased array is calculated as the far field S (theta, phi) of the individual nanoantenna multiplied by an array factor F_a(theta, phi), the array factor being in phase with the optical emission from all pixelsBit-dependent systematic factors:

E(θ，φ)＝S(θ，φ)×F_aS(θ，φ) (1)

in principle, large scale nanophotonic phased arrays can be used to generate arbitrary radiation patterns in the far field by controlling the emission phase of all pixels. However, given a short wavelength of light (1.55 μm) and a high refractive index of silicon (n ≈ 3.48), slight manufacturing imperfections may lead to large phase errors. Therefore, nanophotonic phased arrays should be resistant to phase errors to be reliably manufactured and to function properly.

Fortunately, the large-scale nanophotonic phased arrays disclosed herein are highly tolerant of phase errors (e.g., as described below with respect to fig. 7A-7D). This high phase tolerance arises from the nature of the nanophotonic phased array as a fourier system, where the phase noise of the near-field emission is averaged in the far-field by interference of the light emissions from all pixels. This high phase tolerance is more efficient in combination with more pixels and enables the nanophotonic phased array to scale up to hundreds, thousands or millions of pixels.

Fig. 4A to 4D illustrate simulations of the same optical phased array as shown in fig. 1A, 2A, and 3A. The pixel pitch of the nanophotonic array was chosen to be 9 μm in the x-direction and y-direction (as used in fabrication), and the free space wavelength was taken to be about 1.55 μm. Because the pixel pitch is a multiple of the half wavelength of free space, the interference condition occurs periodically in the far field to produce higher order patterns that appear as a replica of the desired radiation pattern ("MIT" mark).

Fig. 4A shows a near-field transmission pattern simulated using a three-dimensional time-domain finite difference method from a grating antenna element transmitting 51% optical power up and 30% optical power down at a wavelength of 1.55 μm. The emission is not vertical (perpendicular to the surface) because the grating period is slightly out of tune with the period of a second order grating that will emit vertically. This misalignment suppresses resonant back reflections that might otherwise interfere with light propagating in the phased array. The emission from the nano-antenna is also broadband, with wavelengths of the full-width bandwidth extending across hundreds of nanometers (e.g., greater than 100 nm).

Fig. 4B to 4D illustrate simulated far-field patterns of the optical nano-antenna shown in fig. 4A (fig. 4B) and the array of the optical nano-antenna shown in fig. 4A calculated using a near-field-far-field transformation. These far field patterns appear as projections of a far field hemisphere onto the equatorial plane in a polar coordinate system. They are viewed from the apex of the far-field hemisphere, where θ and φ are the far-field azimuth and polar angles, respectively. In each case, the projected pattern is primarily visible in the vicinity of the apex due to the directional emission of the optical nano-antenna. Varying or assigning a particular optical phase to each pixel in a nanophotonic phased array(where m and n are the row and column indices of the pixels, respectively) so that a predetermined radiation pattern E (θ, φ) may be projected. Phase of each pixelThe determination may be by antenna synthesis, for example using the geiger-saxon algorithm as described below with respect to fig. 5.

Fig. 4C and 4D show simulations of radiation patterns of a 64 x 64 nanometer photonic phased array designed to produce MIT markers in the far field. This radiation pattern is a superposition of the far field of the array factor of the system (as shown in the background) and the far field of the nano-antenna (in fig. 4A). The circle in the center of fig. 4C indicates the viewable area in the micromirror lens (e.g., with a numerical aperture of 0.4), as also shown in fig. 10E and 10F (described below). Fig. 4D shows a close-up view of the visible region showing the far field of the MIT marker. The lower right inset shows the MIT flag pattern.

Synthesis of large-scale nanophotonic phased arrays

Nanophotonic phased array synthesis produces a specific far-field radiation pattern by assigning an optical phase to each pixel in the phased array. As shown in equation (1) above, the far-field radiation pattern is the far-field S (θ, φ) of the individual nanoantenna and the far-field F of the array factor_aThe product of (theta, phi). Although the far field of the individual nano-antennas is fixed, the array factor F_a(θPhi) is related to the emission phase of all pixels in the array:

wherein M × N is the size of the array, and (X)_m，Y_n) The position of each nano-antenna is described. The transmitting amplitude and phase of the nano-antenna are respectively passed through | W_mnI andis described so that

In phased arrays, nanoantennas may be transmitted in conjunction with a desired amplitude pattern, such as uniform amplitude (| W) as used herein_mn1) to make the phase in a far field to form an ideal interference conditionThe interaction can be effected appropriately. Parameter u is sin (θ) cos (φ)/λ₀And v ═ sin (θ) sin (φ)/λ₀Is related to the far-field coordinates (theta, phi), and₀is the wavelength of light in free space. As shown in equation (2), the array factor F_a(θ, φ) is a simple discrete Fourier transform of the transmit phase of the array.

FIG. 5 is a block diagram illustrating an efficient iterative process 500 for finding an optical phase v_nmTo generate a given radiation pattern F using the Geiger-Sakstone algorithm_a(theta, phi). In the k-th iteration, the array factor is approximated(which includes a desired amplitude | F)_a(theta, phi) | and the phase of the experiment) Is inverse fourier transformed (block 510) to obtain a corresponding w for each nanoantenna^k _mn. Far fieldTest phaseMay be arbitrarily selected because it does not necessarily affect the final far-field radiation image (block 520). In block 530, w^k _mnThen set to 1 without changing the phase so that the amplitude of the nanoantenna emission remains uniform across the array. Thus, the updated array factorObtained by Fourier transform (block 540), the phase phi of which^k(θ, φ) is passed to the (k +1) th iteration as the new trial phase φ^k+1(θ, φ) (block 550). The initial trial phase of the radiation field is set to Φ in the first iteration¹(θ, Φ) ═ 0 or another arbitrary value. After several iterations, the phase is passedResulting final array factorConverge to the desired pattern | F_a(θ，φ)|。

FIGS. 6A-6D are shown with λ₀FIG. 6A shows an "MIT" marker as projected in the far field, and FIG. 6C shows the corresponding phase distribution across the array face, similarly FIG. 6B shows multiple beams with different angles in the far field, with the corresponding phase distribution shown in FIG. 6D.

Phase noise analysis of large scale nanophotonic phased arrays

In nanophotonic phased arrays, far field generation relies on precise optical phase for each nanoantennaHowever, due to random manufacturing imperfections, the actual phase on each nanoantenna may be at its expected valueDifferent. This random error can be expressed as phase noise_mnIts effect on the array factor pattern will be analyzed. Assume that random phase noise has a Gaussian probability distribution with zero mean<∈_mn>0 and the standard deviation σ, which is typically the case for noise introduced by manufacturing. The actual resulting array factor pattern in the presence of phase noise is again given by equation (2), which has a phase

Wherein F_a ^ac(theta, phi) represents the actual array factor pattern with noise, F_a ^id(θ, φ) is an ideal array factor pattern, andis a convolution operator. An expectation value (denoted by an angle bracket) is used herein to mean that the average value is taken as a random variable and function. The discrete Fourier transform of the phase noise is given by the following equation

And the expected value in equation (4) is calculated by definition as

Substituting equation (5) into equation (4) and then into equation (3) yields

Equation (6) shows that the shape of the far field array factor pattern reaches exp (- σ) when its amplitude is reduced by phase noise²The/2) times are retained.

More specifically, the simulations show gaussian phase noise at levels σ -0 (no phase noise; fig. 7A), σ -pi/16 (fig. 7B)), σ -pi/8 (fig. 7C), and σ -pi/4 (fig. 7D), which is added to the output of a 64 × 64 nanometer photon phased array, the phase of which is 64 × 64 nanometer photon phased arrayIs set to generate the MIT flag. These figures show that the shape of the desired pattern remains relatively unaffected by the increased phase noise, but the signal-to-noise ratio (SNR) decreases. The increase in background noise results from the fact that the emitted light beam does not fully satisfy the desired interference conditions in the presence of phase noise. The simulation results are consistent with the theoretical analysis in equation (6).

Fig. 7A to 7D show that even under relatively large phase noise (σ ═ pi/4), the desired pattern can be distinguished. This indicates that phased arrays exhibit high phase tolerance, which relaxes the accuracy requirements for fabrication, and implies that large-scale nanophotonic phased arrays can be reliably fabricated and function correctly. Furthermore, this high fault tolerance is not dependent on the size of the array. In fact, statistical considerations suggest that the above analysis is more accurately applicable to arrays having a large number of nano-antennas. Therefore, nanophotonic phased arrays extend beyond 64 x 64 to millions of pixels.

Illustration of

The following examples are intended to highlight aspects of the inventive subject matter and not to limit the claims.

Nanophotonic phased arrays are fabricated in a 300-mm CMOS foundry with 65-nm technology nodes using silicon-on-insulator wafers with 0.22 μm top silicon layer and 2 μm buried oxide. A timed partial silicon etch (0.11 μm) was first performed to make a partially etched grating trench. An all-silicon etch is then applied to form the waveguide and grating nano-antenna. Subsequent toN and n + dopants are implanted for the active array followed by standard silicidation to make copper silicon contacts. The contacts are connected to on-chip probe pads by two metal layers for thermo-optic tuning. SiO with a total thickness of 3.6 μm₂For overlay devices where a final polishing step is used to flatten the surface to avoid additional phase errors due to surface wrinkling.

Fig. 8A and 8B are Scanning Electron Micrographs (SEMs) of portions of a 64 x 64 nm photonic phased array fabricated in a CMOS foundry. Fig. 8A shows several pixels in a nanophotonic phased array, and fig. 8B is a close-up view of the pixels indicated by rectangles in fig. 8A. The pixel size is 9 μm x 9 μm, with the compact silicon dielectric grating acting as an optical nanoantenna, with the first grooves of the grating partially etched to enhance upward emission. The emission phase of each pixel can be adjusted by varying the optical path length of the optical delay line within the pixel.

FIG. 9A is a close-up view of a silicon dielectric nanoantenna in the pixel of FIG. 8B, the nanoantenna is used as a transmitter in each pixel for direct integration with CMOS processes, lighter colored areas represent silicon with a height of 220nm, darker colored areas represent a Buried Oxide (BOX) layer under the silicon, and moderately shaded areas represent partially etched silicon with a height of 110nm the nanoantenna measures 3.0 μm × 2.8.8 μm and includes five grating etches the first grating etch is half way through the 220nm thick silicon layer to create an upper-lower asymmetry to emit more power up and out from the plane to the phased array, the grating period is 720nm, which is slightly out of alignment with the period of the second order grating (at λ)₀1.55 μm for Si-SiO₂581 nm of the grating). This misalignment suppresses resonant back reflections that might otherwise interfere with the propagation of the light beam within the phased array. This misalignment also causes the antenna to emit light along an axis that is angled relative to the surface normal of the optical phased array.

Fig. 9B is a graph of the transmission efficiency of the antenna shown in fig. 9A. It shows that an overall emission efficiency of 86% is achieved at a wavelength of 1.55 μm, with 51% emission upwards and 35% emission downwards. FIG. 9B also shows λ₀Back reflection of only about 5% at 1.55 μm, and emissionThe 3dB bandwidth is over 200nm due to the short grating length of the antenna. By optimizing the partial etch depth (in this case, the partial etch depth is fixed to 110nm for considerations of other devices on the same mask), more efficient upward emission is achieved by adding a reflective ground plane below the grating to emit downward emission or both.

Fig. 10A is a diagram of an imaging system 1000 for viewing the near and far fields of the nanophotonic phased array 1010 shown in fig. 8A, 8B, and 9A emitting light at a wavelength of 1.55 μm. The first lens 1020 alone (numerical aperture 0.40) is used in conjunction with an infrared charged coupled device (IRCCD)1040 to obtain Near Field (NF) images, as indicated by external radiation. A Far Field (FF) image or fourier image (as shown by the internal ray) is taken by moving the first lens 1020 downward (to position 1020') to form a far field image in its back focal plane (fourier plane) and inserting the second lens 1030 to project the far field image onto the IRCCD 1040.

Fig. 10B-10F show data obtained using the system 1000 of fig. 10A. The near field image of the optical phased array plane in fig. 10B shows uniform emission across all 64 x 64 (4096) nano-antennas. The input bus waveguide is located in the upper left corner, resulting in some unwanted scattering noise. The scattering noise is not reflected non-uniformly in the array itself and can be easily addressed with a large separation from the fiber input. FIG. 10C is a close-up view of a portion of the near field, containing 8 × 8 pixels; which shows a high uniformity of the amplitude of the antenna output.

FIG. 10D is a histogram representing a measured intensity distribution of optical emissions from a pixel. Statistics show that the standard deviation (σ) of the emission intensity is 13% of the mean intensity (μ).

Fig. 10E shows the measured far field radiation pattern of the fabricated 64 x 64 nanometer photonic phased array. The image reveals that the desired radiation pattern (in this case, the MIT mark) is present in the far field. The far field image is held by the finite numerical aperture (0.4) of the lens 1020 in fig. 10A. This is also predicted by simulations, as shown by the circles in fig. 4C and 4D, which show that emission can be captured within a small divergence angle from vertical (the surface normal of the nanophotonic phased array chip). The intensity noise in the background of the far field image originates from light scattering caused by fiber-waveguide coupling. The scattered light is also responsible for the concentric fringes in the background by interference of the scattered light between the top and bottom surfaces of the silicon-on-insulator wafer. This noise can be reduced by placing the fiber-waveguide coupler farther away from the NPA system to reduce light scattering captured by the imaging column, and a much cleaner far-field radiation pattern would be expected.

Figure 10F shows the far field radiation pattern of a 32 x 32 nanometer photon phased array on the same chip as a 64 x 64 nanometer photon phased array. FIG. 10F shows less noise because the 32 x 32 nanometer photonic phased array is farther from the fiber coupling point; but the far field pattern resolution is lower because the 32 x 32 nanometer photon phased array contains fewer pixels than the 64 x 64 nanometer photon phased array. The measured images are consistent with the simulations in fig. 4C and 4D in terms of the shape of the pattern (MIT mark) and the relative intensities of all interference levels, highlighting the robustness of the nanophotonic phased array design and the accuracy of fabrication.

Comparing fig. 10B with fig. 10E shows that the near-field image of the nanophotonic phased array contains normal uniform emission anywhere, while the far-field includes an image with MIT markers. Heretofore, image information has been stored and transmitted substantially in terms of the intensity of the pixel; in contrast, this large-scale nanophotonic phased array technique opens up another dimension for imaging: the image information is now encoded in the optical phase of the pixel, like a histogram, but is generated from a single point. Such presentations, such as static phased arrays capable of producing truly arbitrary radiation patterns, are used for complex beam generation and mode matching, for example, in optical spatial division multiplexing.

Fig. 11A-11E show the phase distribution (top row), simulated far-field radiation pattern (middle row), and measured far-field radiation pattern (bottom row) of an active 8 x 8 nanophotonic phased array like the arrays shown in fig. 2A and 3A. The phase and intensity plots appear on the right. In the top row, each point represents a different antenna element/pixel. In the middle and bottom rows, circles indicate the edges of the lens (numerical aperture ═ 0.4), and the boxes specify the area of one interference order. (higher orders of aliasing occur in far fields because the antenna spacing is larger than the free space wavelength).

In fig. 11A, the phase distribution across is uniform at 0, so the array projects a uniform beam at the visual axis (in the center of the dashed box). A vertically and horizontally stepped square wave phase profile applied between 0 and pi directs the focused beam up to 6 deg. to the edge of each interference stage in the vertical direction (fig. 11B) and horizontal direction (fig. 11C), respectively. The application of a vertically stepped square wave phase profile between 0 and pi/2 vertically splits the beam into two beams as shown in fig. 11D. And one period of the horizontally oriented triangular wave applied varying between 0 and pi divides the single light beam into four light beams in the horizontal direction, as shown in fig. 11E.

Fig. 11A to 11E show good agreement between simulations and experiments confirming the robustness of nanophotonic phased arrays and the accuracy of fabrication and active thermo-optic phase tuning. The active NPA architecture can be extended to larger phased arrays (e.g., 64 x 64, as described above), with independent electrical control of each pixel with the assistance of full CMOS control circuitry to electrically access all pixels, in conjunction with applications to project dynamic patterns in the far field, including but not limited to communications, three-dimensional histogram display, laser detection and ranging (LADAR), biomedical imaging, and interferometry.

Unlike other histogram methods, such as meta-surface antennas, the optical phased array disclosed herein allows for individual control of the phase and amplitude of light emission and on-chip, single-point excitation of the nanophotonic emitters, enabling any histogram to be generated entirely on-chip. Furthermore, by guiding light in silicon instead of using free space light, active manipulation of optical phase can be implemented directly to achieve dynamic far field patterns with greater flexibility and wider application by converting pixels to phase thermally tunable pixels in CMOS processes. For example, a portion of the silicon optical path in each pixel may be lightly doped with an n-type implant to form a resistive heater for thermo-optic phase tuning while maintaining low loss of light propagation. Two narrow silicon leads with heavy n-doping (providing electrical connection to and thermal insulation from the heater) may be connected to the heater on the inside of the insulating bend to minimize losses caused by light scattering.

Conclusion

Although various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will be based on the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the above-described embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, provided that such features, systems, articles, materials, kits, and/or methods are mutually consistent, is included within the scope of the disclosed invention.

The above-described embodiments can be implemented in any number of ways. For example, implementations of designing and fabricating the coupling structures and diffractive optical elements disclosed herein can be implemented using hardware, software, or a combination thereof. When implemented in software, the software code can be implemented on any suitable processor or collection of processors, provided in a single computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in any of a variety of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Further, the computer may be embedded in a device not normally considered a computer but having suitable processing capabilities, including a Personal Digital Assistant (PDA), smart phone, or any other suitable portable or fixed electronic device.

In addition, a computer may have one or more input and output devices. These devices may be used, inter alia, to provide a user interface. Examples of output devices that may be used to provide a user interface include printers and display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that may be used as a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible formats.

The computers may be interconnected by one or more networks IN any suitable form, including as a local area network or a wide area network, such as an enterprise network and an Intelligent Network (IN) or the Internet. These networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks, or fiber optic networks.

The various methods or processes outlined herein (e.g., in the design and fabrication of the coupling structures and diffractive optical elements disclosed above) may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Further, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

In this regard, the various inventive concepts may be embodied as a computer-readable storage medium (or multiple computer-readable storage media) (e.g., a computer memory, one or more floppy disks, optical disks, magnetic tapes, flash memories, circuit configurations of field programmable gate arrays or other semiconductor devices, or other non-transitory or tangible computer storage media) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the invention discussed above. One or more computer-readable media may be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above.

The terms "program" or "software" are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. Furthermore, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present invention.

Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

In addition, data structures may be stored in any suitable form on a computer readable medium. For simplicity of illustration, the data structure may be shown with fields associated by location in the data structure. Such relationships may likewise be achieved by assigning storage of the fields with locations in a computer-readable medium that convey relationships between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags, or other mechanisms that establish a relationship between data elements.

In addition, various inventive concepts may be embodied as one or more methods, one example of which is provided. The actions performed as part of the method may be ordered in any suitable way. Thus, implementations may be constructed in which acts are performed in a different order than illustrated, which may include performing some acts concurrently, even though shown as sequential acts in the illustrative implementations.

All definitions, as defined and used herein, should be understood to encompass dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite article "a" or "an" as used herein in the specification and in the claims is to be understood as meaning "at least one" unless clearly indicated to the contrary.

The phrase "and/or" as used herein in the specification and in the claims should be understood to mean "either or both" of the elements so combined, i.e., the elements being present in combination in some cases and separately in other cases. Multiple elements listed with "and/or" should be construed in the same manner, i.e., "one or more" elements so combined. In addition to elements specifically identified by the "and/or" clause, other elements may optionally be present, whether related or unrelated to those elements specifically identified. Thus, by way of non-limiting example, reference to "a and/or B," when used in conjunction with open-ended terms such as "comprising" may refer in one embodiment to a alone (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than a); in yet another embodiment refers to a and B (optionally including other elements), and the like.

As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, where items in a list are separated, "or" and/or "should be interpreted as being inclusive, i.e., including at least one of several elements or lists of elements, and optionally additional unlisted items, but also including more than one. Terms which are only expressly indicated to the contrary, such as "only one" or "exactly one" or "consisting of … … when used in a claim, will refer to exactly one element including several elements or lists of elements. In general, the term "or" as used herein, when used in the foregoing to modify an exclusive term, should be interpreted merely as indicating an exclusive substitute (i.e., "one or the other, but not two"), such as "either," one, "" only one, "or" exactly one. "consisting essentially of … …" when used in a claim shall have its conventional meaning as used in the patent law field.

As used herein in the specification and in the claims, the phrase "at least one," when referring to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the list of elements, but not necessarily including at least one of each element specifically listed within the list of elements and not excluding any combination of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements referred to by the phrase "at least one," whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of a and B" (or, equivalently, "at least one of a or B," or, equivalently "at least one of a and/or B") can refer in one embodiment to at least one (optionally including one or more) a, with no B present (and optionally including elements other than B); in another embodiment refers to at least one (optionally including more than one) B, with no a present (and optionally including elements other than a); in yet another embodiment, at least one (optionally including more than one a) and at least one (optionally including more than one) B (and optionally including other elements); and the like.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "maintaining," "consisting of … …," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. The transitional phrases "consisting of … …" and "consisting essentially of … …" shall be closed or semi-closed transitional phrases, respectively, as specified in the U.S. patent office patent examination program manual, paragraph 2111.03.