阅读说明：本技术 一种大规模集成的电光微环光学相控阵 (Large-scale integrated electro-optic micro-ring optical phased array ) 是由 程立文 张家荣 罗雨中 张曦晨 李侦伟 张嘉仪 杨达 王俊迪 林星宇 于 2021-08-19 设计创作，主要内容包括：本发明公开了一种大规模集成的电光微环光学相控阵,至下而上包括硅衬底、二氧化硅掩埋层和硅芯层；二氧化硅掩埋层附着在硅衬底；在硅芯层这一层上还包括用于接收激光光源并将激光光源引导至光分束网络的光栅耦合器、用于将光栅耦合器输出的光源分成多路信号并传输至相位调谐区的光分束网络、用于产生相位差光束的相位调谐区和用于将产生的相位差光束发射至自由空间的天线阵列；相位调谐区包括由多个阵元构成的调谐阵列、与光分束网络连接的直波导、用于控制阵元的电压输出的控制总线；每个阵元均包括定向耦合器、p-i-n调制器和电极片；定向耦合器将直波导上的光信号耦合至p-i-n调制器,所述p-i-n调制器通过电极片与控制总线连接,用于使各路光产生相位差。(The invention discloses a large-scale integrated electro-optic micro-ring optical phased array, which comprises a silicon substrate, a silicon dioxide buried layer and a silicon core layer from bottom to top; the silicon dioxide buried layer is attached to the silicon substrate; the silicon chip layer also comprises a grating coupler used for receiving the laser light source and guiding the laser light source to the optical beam splitting network, the optical beam splitting network used for splitting the light source output by the grating coupler into multiple signals and transmitting the multiple signals to the phase tuning area, the phase tuning area used for generating phase difference light beams and an antenna array used for transmitting the generated phase difference light beams to a free space; the phase tuning area comprises a tuning array formed by a plurality of array elements, a straight waveguide connected with the optical splitting network and a control bus used for controlling the voltage output of the array elements; each array element comprises a directional coupler, a p-i-n modulator and an electrode plate; the directional coupler couples optical signals on the straight waveguide to the p-i-n modulator, and the p-i-n modulator is connected with the control bus through the electrode plate and used for enabling each path of light to generate phase difference.)

1. A large-scale integrated electro-optic micro-ring optical phased array comprises a silicon substrate, a silicon dioxide buried layer and a silicon core layer from bottom to top; the silicon dioxide buried layer is attached to the silicon substrate; the method is characterized in that: the silicon chip layer also comprises a grating coupler used for receiving the laser light source and guiding the laser light source to an optical beam splitting network, the optical beam splitting network used for splitting the light source output by the grating coupler into multiple signals and transmitting the multiple signals to a phase tuning area, the phase tuning area used for generating phase difference light beams and an antenna array used for transmitting the generated phase difference light beams to a free space;

the phase tuning area comprises a tuning array formed by a plurality of array elements, a straight waveguide connected with the optical splitting network, and a control bus used for controlling the voltage output of the array elements;

each array element comprises a directional coupler, a p-i-n modulator and an electrode plate; the directional coupler couples optical signals on the straight waveguide to the p-i-n modulator, and the p-i-n modulator is connected with the control bus through an electrode plate and used for controlling the transport of carriers in the p-i-n modulator through an external voltage so that each path of light generates phase difference.

2. The large scale integrated electro-optic microring optical phased array of claim 1, wherein: the p-i-n modulator comprises an n-type doped micro-ring resonator, a p-type doped concave waveguide and a lightly doped annular waveguide; the lightly doped ring waveguide is arranged at the periphery of the n-type doped micro-ring resonator, and the p-type doped concave waveguide is arranged at the periphery of the lightly doped ring waveguide.

3. The large scale integrated electro-optic microring optical phased array of claim 2, wherein: the control bus comprises a row array element control bus for controlling the voltage output of the row array elements and an array element control bus for controlling the voltage output of the array elements;

the lightly doped annular waveguide is connected with the array element control bus through an electrode plate, and the n-type doped micro-ring resonator is connected with the array element control bus through the electrode plate.

4. The large scale integrated electro-optic microring optical phased array of claim 1, wherein: the directional coupler is of a mirror image S-shaped structure, and the coupling length of the directional coupler meets the following conditions:

wherein L is_％For coupling length, Δ n is the effective index difference, P0 is the optical power on the straight waveguide, P1 is the optical power on the coupled waveguide, λ₀The center wavelength.

5. The large scale integrated electro-optic microring optical phased array of claim 1, wherein: the optical beam splitting network comprises (N/2-1) cascaded 1x2 multimode interference couplers and N/2 y-type beam splitters, wherein N is the number of the row arrays of the optical phased array; each 1x2 multimode interference coupler comprises a conical input end, a multimode interference coupling section and a conical output end; the tapered input end of the 1x2 multimode interference coupler as the main cascade is connected with the grating coupler, and the tapered output end of the 1x2 multimode interference coupler as the secondary cascade is connected with the grating coupler; the tapered input end of the 1x2 multimode interference coupler as the secondary cascade is connected with the tapered output end of the 1x2 multimode interference coupler at the previous stage, and the tapered output end of the 1x2 multimode interference coupler at the next stage is connected with the tapered input end of the 1x2 multimode interference coupler at the next stage; the cone-shaped output end of the 1x2 multimode interference coupler as the last stage is connected with a y-type beam splitter; the y-type beam splitter comprises an input straight waveguide and an output straight waveguide; the input straight waveguide is connected with the tapered output end of the 1x2 multimode interference coupler, and the output straight waveguide is connected with the straight waveguide of the phase tuning area.

6. The large scale integrated electro-optic microring optical phased array of claim 5, wherein: the tapered input end is connected with the tapered output end of the grating coupler/the previous-stage 1x2 multimode interference coupler through a bent waveguide; and the tapered output end is connected with the tapered input end/y-shaped beam splitter of the next-stage 1x2 multimode interference coupler through the ridge waveguide.

7. The large scale integrated electro-optic microring optical phased array of claim 5, wherein: according to the input waveguide width, the broadband transmission and the optical loss parameters, the width of the tapered input end, the width of the tapered output end, the coupling length of the multimode interference coupling section and the coupling width of the multimode interference coupling section of the 1x2 multimode interference coupler are obtained.

8. The large scale integrated electro-optic microring optical phased array of claim 1, wherein: the antenna array spacing is less than one operating wavelength.

Technical Field

The invention belongs to the technical field of laser radar communication, and particularly relates to a large-scale integrated electro-optic micro-ring optical phased array.

Background

With the continuous development of intelligent automobiles, unmanned driving has become a popular development project of automobile enterprises in recent years. The laser radar is one of key core components of the intelligent automobile, and the main function of the laser radar is to transmit detected information to a cloud computing system, so that the perception of a land complicated traffic environment is realized. Laser radars generally fall into two broad categories: mechanical lidar and solid state lidar. Mechanical type laser radar adopts mechanical rotating part as the implementation of light beam scanning, can realize wide-angle scanning, but scanning frequency is low, the assembly is difficult, and mechanical type laser radar has obtained preliminary application on intelligent automobile in recent years, nevertheless because can't realize batch production, and the cost is high under, can't realize extensive popularization. Because the price of the existing mechanical laser radar can not be reduced in a short time, the solid laser radar gradually becomes a favorite of the market in order to be matched with the popularization of automatic driving. Current implementations of solid-state lidar are micro-electromechanical systems (MEMS), Flash area array (Flash) technology, and Optical Phased Array (OPA) technology. Micro-scanning galvanometers are adopted in a micro-electro-mechanical system (MEMS), so that a certain integration level is achieved, but the micro-scanning galvanometers are limited in deflection range; the area array Flash (Flash) technology is commercially available, but the field angle is limited, the scanning rate is low, and the detection distance is short; the Optical Phased Array (OPA) technology is a novel light beam pointing control technology developed based on the optical wave phased array scanning theory and technology, has the advantages of no inertial device, accuracy and stability, random direction control and the like, and is also called as an all-solid-state laser radar technology.

Currently, the phase operation modes of the optical phased array are mainly divided into three types: one is based on thermo-optic phase modulation (TO), which is more effective, but has slow modulation speed and is not suitable for large-scale integrated optical phased arrays; the other one is MEMS modulation, the integration level is high, the response speed is higher than that of thermo-optic modulation, but the stability is not high due to a mechanical structure, and the operating environment is limited; the last one is electro-optic modulation (EO), which has the most outstanding advantages of response speed, high controllability, high integration level, but small scanning angle and phase shift range of modulation.

More phase shifters represent higher integration of the optical phased array, and the structure thereof is more complicated. Generally, the spacing between array elements is about one wavelength, and the side lobe is close to the main peak position due to overlarge spacing, so that the scanning range is influenced; too small, in turn, can lead to crosstalk between adjacent waveguides, degrading the beam quality in the far field.

Therefore, on the premise of ensuring the quality of far-field light beams, the problems of small scanning range, low modulation efficiency and low integration level are solved, which is always a significant problem of large-scale optical phased arrays.

Disclosure of Invention

The purpose of the invention is as follows: the invention provides a large-scale integrated electro-optic micro-ring optical phased array, which aims to solve the problems of small scanning range, low modulation efficiency and low integration level of the large-scale optical phased array.

The technical scheme is as follows: a large-scale integrated electro-optic micro-ring optical phased array comprises a silicon substrate, a silicon dioxide buried layer and a silicon core layer from bottom to top; the silicon dioxide buried layer is attached to the silicon substrate; the silicon chip layer also comprises a grating coupler used for receiving the laser light source and guiding the laser light source to an optical beam splitting network, the optical beam splitting network used for splitting the light source output by the grating coupler into multiple signals and transmitting the multiple signals to a phase tuning area, the phase tuning area used for generating phase difference light beams and an antenna array used for transmitting the generated phase difference light beams to a free space;

the phase tuning area comprises a tuning array formed by a plurality of array elements, a straight waveguide connected with the optical splitting network, and a control bus used for controlling the voltage output of the array elements;

each array element comprises a directional coupler, a p-i-n modulator and an electrode plate; the directional coupler couples optical signals on the straight waveguide to the p-i-n modulator, and the p-i-n modulator is connected with the control bus through an electrode plate and used for controlling the transport of carriers in the p-i-n modulator through an external voltage so that each path of light generates phase difference.

Further, the p-i-n modulator comprises an n-type doped microring resonator, a p-type doped concave waveguide and a lightly doped annular waveguide; the lightly doped ring waveguide is arranged at the periphery of the n-type doped micro-ring resonator, and the p-type doped concave waveguide is arranged at the periphery of the lightly doped ring waveguide.

Furthermore, the control bus comprises a row array element control bus for controlling the voltage output of the row array elements and an array element control bus for controlling the voltage output of the array elements;

the lightly doped annular waveguide is connected with the array element control bus through an electrode plate, and the n-type doped micro-ring resonator is connected with the array element control bus through the electrode plate.

Further, the directional coupler is of a mirror image S-shaped structure, and the coupling length of the directional coupler meets the following conditions:

wherein L is_％For coupling length, Δ n is the effective index difference, P0 is the optical power on the straight waveguide, P1 is the optical power on the coupled waveguide, λ₀The center wavelength.

Further, the optical beam splitting network comprises (N/2-1) 1x2 multimode interference couplers and N/2 y beam splitters which are cascaded, wherein N is the number of the row arrays of the optical phased array; each 1x2 multimode interference coupler comprises a conical input end, a multimode interference coupling section and a conical output end; the tapered input end of the 1x2 multimode interference coupler as the main cascade is connected with the grating coupler, and the tapered output end of the 1x2 multimode interference coupler as the secondary cascade is connected with the grating coupler; the tapered input end of the 1x2 multimode interference coupler as the secondary cascade is connected with the tapered output end of the 1x2 multimode interference coupler at the previous stage, and the tapered output end of the 1x2 multimode interference coupler at the next stage is connected with the tapered input end of the 1x2 multimode interference coupler at the next stage; the cone-shaped output end of the 1x2 multimode interference coupler as the last stage is connected with a y-type beam splitter; the y-type beam splitter comprises an input straight waveguide and an output straight waveguide; the input straight waveguide is connected with the tapered output end of the 1x2 multimode interference coupler, and the output straight waveguide is connected with the straight waveguide of the phase tuning area.

Further, the tapered input end is connected with the tapered output end of the grating coupler/the previous-stage 1x2 multimode interference coupler through a bent waveguide; and the tapered output end is connected with the tapered input end/y-shaped beam splitter of the next-stage 1x2 multimode interference coupler through the ridge waveguide.

Further, according to the input waveguide width, the broadband transmission and the optical loss parameters, the taper of the tapered input end, the taper of the tapered output end, the coupling length of the multimode interference coupling section and the coupling width of the multimode interference coupling section of the 1x2 multimode interference coupler are obtained.

Further, the distance between the antenna arrays is smaller than one working wavelength.

Has the advantages that: compared with the prior art, the invention has the following advantages:

(1) the electro-optic micro-ring optical phased array overcomes the problem of crosstalk caused by the space between each array element of an antenna in the traditional optical phased array, also overcomes the problem of insufficient electro-optic modulation light beam phase shift amount in the two-dimensional light beam deflection process, can further improve the performance of a large-scale integrated optical chip, and has the advantages of small size, compact and simple structure, low power consumption, expandability, compatibility with the modern CMOS process, high modulation efficiency and the like;

(2) the electro-optical micro-ring optical phased array works in a 1550nm laser radar, and due to the high signal-to-noise ratio and the high robustness to noise factors, compared with a mature 905nm laser radar, the electro-optical micro-ring optical phased array has the advantages of wider detection range, higher safety to human eyes and higher practicability to severe weather;

(3) the invention can realize phase modulation and beam scanning of 1500 nm-1600 nm beam wave band, with 15 degree of longitudinal scanning range and 50 degree of transverse scanning range.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic cross-sectional view of the present invention;

FIG. 3 is a schematic structural diagram of a 1x2 multimode interference coupler;

FIG. 4 is a schematic diagram of a y-type beam splitter;

FIG. 5 is a diagram of the optical field distribution of the optical transmission at 1550nm wavelength of a multimode interference coupler with 1.1um taper and a y-splitter with a splitting ratio of 50/50 simulated based on the finite difference time domain method using a spatial FDTD solution according to the present invention;

FIG. 6 is a transmission diagram of a y-splitter of the present invention using a fluorescence FDTD solution to simulate a splitting ratio of 50/50 based on the finite difference time domain method at different wavelengths for optical transmission at 1550 nm;

FIG. 7 is a transmission diagram of a multimode interference coupler with 1.1um taper based on finite difference time domain method using a parametric FDTD solution to simulate different wavelengths of optical transmission at 1550 nm;

FIG. 8 is a schematic diagram of a phase tuning section;

FIG. 9 is a graph of the effective refractive index and transmission efficiency of a p-i-n modulator simulated using a parametric FDTD solution based on the finite difference time domain method as a function of different wavelengths according to the present invention;

FIG. 10 is a graph of a light field distribution at 1550nm wavelength for a 50% duty cycle of a stripe grating simulated by a parametric FDTD solution based on a finite difference time domain method and an etching depth of 0.1 according to the present invention;

fig. 11 is a far field scan of a beam at 1550nm for an electro-optic micro-ring optical phased array of the present invention using Matlab calculations for 64x64 antenna arrays.

Detailed Description

The invention is further illustrated below with reference to the figures and examples.

FIG. 1 shows an overall layout of a phased array, and FIG. 2 shows a cross-sectional view of the phased array down and up the material; as can be seen from fig. 2, the present invention discloses a large scale integrated electro-optical micro-ring optical phased array, which comprises a silicon substrate 11, a buried silica layer 12, a cladding layer 13 and a silicon core layer 14 from bottom to top; wherein, the buried silicon dioxide layer 12 is attached to the silicon substrate 11, and the grating coupler 2, the optical splitting network 3, the phase tuning area 7, the antenna array 9, the control bus and the digital-to-analog converter 6 are all on the silicon core layer 14 in the figure. Referring to fig. 1, a specific structure of the electro-optical micro-ring optical phased array of the present invention is further described, which includes:

the laser light source 1 is a tunable light source and is used for longitudinal control of light beams;

the grating coupler 2 is used for receiving an optical signal at an input end;

the optical beam splitting network 3 is used for splitting the light source output by the grating coupler 2 into multiple paths of signals and transmitting the signals to the phase tuning area 7;

the phase tuning area 7 is used for coupling the optical signals of the respective branches into the modulation area through the directional coupler array and generating phase difference in the coupling waveguide by adopting an external voltage mode;

the antenna array 9 is composed of a strip grating and is used for emitting light beams generating phase differences to a free space;

a row array element control bus 8 for controlling voltage output of the row array elements;

the array element control bus 10 is used for controlling the voltage output of the array elements;

a digital-to-analog converter 6 for providing the drive current.

An optical signal generated by a laser light source 1 passes through a grating coupler 2, and a light beam is coupled into a chip; when the laser light signals are input into the light beam splitting network 3, the laser light signals are evenly split into multiple paths of light signals, the multiple paths of light signals are transmitted to the phase tuning area 7, the modulation proportion is distributed by the external digital-to-analog converter 6, the row array element control bus 8 and the array element control bus 10, phase difference occurs to the light signals of all the paths, and finally the modulated light signals are turned from the antenna array 9 to be emitted, so that two-dimensional light beam deflection is realized.

As shown in fig. 3, 4 and 5, the optical splitting network 3 includes (N/2-1) 1 × 2 multimode interference couplers (MMI)4 and N/2 y-type beam splitters 5, where N is the number of rows and columns of the optical phased array, and (N/2-1) 1 × 2 multimode interference couplers 4 are cascaded, and each multimode interference coupler 4 includes a tapered input end 402, a multimode interference coupling section 405 and a tapered output end 403, where the tapered input end 402 is connected to the curved waveguide 401, and the tapered output end 403 is connected to the ridge waveguide 404. The tapered input end of the 1x2 multimode interference coupler as the main cascade is connected with the grating coupler, and the tapered output end of the 1x2 multimode interference coupler as the secondary cascade is connected with the grating coupler; the tapered input end of the 1x2 multimode interference coupler as the secondary cascade is connected with the tapered output end of the 1x2 multimode interference coupler at the previous stage, and the tapered output end of the 1x2 multimode interference coupler at the next stage is connected with the tapered input end of the 1x2 multimode interference coupler at the next stage; the tapered output end of the 1x2 multimode interference coupler as the last stage is connected with a y-type beam splitter.

Each y-splitter 5 comprises an input straight waveguide 501, a first output straight waveguide 502 and a second output straight waveguide 503. The input straight waveguide is connected with the tapered output end of the 1x2 multimode interference coupler, and the output straight waveguide is connected with the straight waveguide of the phase tuning area.

In designing the multimode interference coupler 4, the input waveguide width is first selected according to the fundamental mode distribution, that is:

wherein L is_πCharacteristic imaging length, n_fIs the refractive index of the core layer, λ₀Is a central wavelength, W_mmi ²Is the effective width of the fundamental mode.

Then calculating broadband transmission and optical loss parameters at a wave band of 1500 nm-1600 nm, and finding out the optimal parameters suitable for the wave band, wherein the parameters comprise the width of a cone input end, the width of a cone output end, the coupling length of a multimode interference coupling section and the coupling width of the multimode interference coupling section; the optimal parameters calculate the scanning result of each parameter item through formula (1) and simulation software logical to obtain the optimal value: the taper of the tapered input 402 and the taper of the tapered output 403 are optimally 1.1um, the loss is 0.3dB, the coupling length of the multimode interference coupling section 405 is optimally 32um, and the coupling width is optimally 6 um. When optimizing the y-splitter 5 with a splitting ratio of 50/50, the insertion loss and transmission efficiency in this band need to be calculated to ensure that the optical signal can be distributed uniformly.

As shown in fig. 6 and 7, when the coupling length is 32um and the coupling width is 6um, the maximum transmission efficiency of the multimode interference coupler 4 in 1500 nm-1600 nm can reach 46.5%; the transmission efficiency of the y-type beam splitter 5 with the splitting ratio of 50/50 can reach 48.5% at most after being optimized in a TE mode of 1500-1600 nm, and the insertion loss is 0.1dB in a working wavelength interval. The simulation of the normalized transmission efficiency of the y-splitter is shown in fig. 6, which shows that the simulation results of S21 and S31 are consistent whether the y-splitter is in TE mode or TM mode, and the splitting ratio of the y-splitter is about 50/50. And the y-line beam splitter of this size has proved to have very little loss in the band from 1500nm to 1600 nm.

As shown in fig. 8, the phase tuning region 7 includes a directional coupler array 703, an n-type doped microring resonator array 706, a p-type doped concave waveguide 701, a lightly doped annular waveguide 702, an electrode slice 705, and a straight waveguide 704. The directional coupler array 703 is two sections of folded devices, and is configured to couple an optical signal on the straight waveguide 704 to the modulation region, where a coupling length L and a coupling gap g of the directional coupler array 703 determine optical coupling efficiency, the coupling length needs to be defined according to an effective refractive index difference of a fundamental mode when the directional coupler array 703 is designed, and the coupling gap g is set to 0.05um in this embodiment, that is:

wherein L is_％For the coupling length, Δ n isEffective index difference, P0 is optical power on straight waveguide, P1 is optical power on coupled waveguide, λ₀Is the center wavelength; if 100% of the light is to be coupled from the straight waveguide 704 to the coupling waveguide, the required length is 12.9 um.

The n-type doped micro-ring resonator array 706, the p-type doped concave waveguide 701 and the lightly doped annular waveguide 702 are doped to form a p-i-n modulator, and the split optical signals are modulated to generate phase difference; aluminum electrode plates 705 are respectively arranged in the n-type doped region and the p-type doped region, and applied voltage is applied to control the transport of carriers in the p-i-n modulator, so that the effective refractive index in the waveguide is changed, and phase difference is generated in each path of light.

FIG. 9 shows the respective doping concentrations of 10¹⁸/cm³The effective index and modulation transmission response in the optical mode of (a) with respect to the variation of the bias voltage, for a voltage range of 0.5-4V, the required voltage at a phase shift amount of pi is:

wherein λ is₀At the center wavelength,. DELTA.neff is the effective index, L_piIs the length of the arm;

the extinction ratio is:

insertion loss IL-10 log₁₀(maxT)。

Where T is the transmission rate, calculated in conjunction with the data of FIG. 9, and V_pi1.02V, ER 21dB, and IL 0.03 dB. Therefore, as can be seen from fig. 9, the p-i-n modulator has the advantages of obvious modulation performance, low modulation power consumption and small insertion loss, and is suitable for large-scale optical phased arrays.

FIG. 10 is a graph of light field distribution of a bar grating antenna simulated using a parametric FDTD solution based on a finite difference time domain method, where the transmittance of the antenna array 9 of the bar grating is greater than 40% at 1550 nm; wherein the duty cycle of the grating is 50%, the etching depth is 0.1um, the interval of each antenna array is less than one working wavelength, and the interval is 1.5 um.

Fig. 11 is a far field scan of 64x64(4096) antenna arrays 9 at 1550nm using Matlab calculations for a beam at scan angles of up to ± 50 °, with significant suppression of grating lobes within this range.

In conclusion, the finally designed large-scale integrated electro-optic micro-ring optical phased array numerically simulates a phased array in which a laser signal is uniformly divided into 64 paths of optical signals, wide-field two-dimensional beam scanning of 1500-1600 nm can be realized through phase tuning, the longitudinal scanning angle is 15 degrees, and the transverse scanning angle can reach +/-50 degrees; the whole size of the chip is changed along with the number of array elements, the size of the unit array is 2.5umx2.5um, the invention is suitable for large-scale integration of the optical phased array, the structure is simple and compact, the modulation response is fast, the power consumption is low, the performance can be effectively improved, and the cost can be reduced.