阅读说明：本技术 一种通用型硅基集成光波导模式转换器 (Universal silicon-based integrated optical waveguide mode converter ) 是由 周林杰 卢平 许维翰 陆梁军 陈建平 刘娇 于 2020-07-24 设计创作，主要内容包括：本发明属于通讯模式的技术领域,公开了一种通用型硅基集成光波导模式转换器,包括输入波导,所述输入波导与输入模式转换模块相连,所述输入模式转换模块与中间连接波导的一端相连,所述中间连接波导的另一端与输出模式转换模块相连,所述输出模块转换模块与输出波导相连,所述输入波导用于传输输入光波,所述输入模式转换模块用于将输入光波的模式转换为基模模式,所述中间连接波导用于传输基模模式的光波,所述输出模式转换模块用于将基模模式的光波转换为输出光波所要求的模式,所述输出波导用于传输输出光波。本发明的转换器可实现任意同偏振光场模式之间的转换,具有更好的通用性,灵活度和编程重构能力。(The invention belongs to the technical field of communication modes, and discloses a universal silicon-based integrated optical waveguide mode converter which comprises an input waveguide, wherein the input waveguide is connected with an input mode conversion module, the input mode conversion module is connected with one end of an intermediate connection waveguide, the other end of the intermediate connection waveguide is connected with an output mode conversion module, the output module conversion module is connected with an output waveguide, the input waveguide is used for transmitting input optical waves, the input mode conversion module is used for converting the mode of the input optical waves into a basic mode, the intermediate connection waveguide is used for transmitting the optical waves of the basic mode, the output mode conversion module is used for converting the optical waves of the basic mode into the mode required by the output optical waves, and the output waveguide is used for transmitting the output optical waves. The converter can realize conversion between any light field modes with the same polarization, and has better universality, flexibility and programming reconstruction capability.)

1. A general silicon-based integrated optical waveguide mode converter is characterized in that: the optical waveguide module comprises an input waveguide, the input waveguide is connected with an input mode conversion module, the input mode conversion module is connected with one end of an intermediate connection waveguide, the other end of the intermediate connection waveguide is connected with an output mode conversion module, the output module conversion module is connected with an output waveguide, the input waveguide is used for transmitting input optical waves, the input mode conversion module is used for converting the mode of the input optical waves into a basic mode, the intermediate connection waveguide is used for transmitting optical waves in the basic mode, the output mode conversion module is used for converting the optical waves in the basic mode into a mode required by the output optical waves, and the output waveguide is used for transmitting the output optical waves.

2. The universal silicon-based integrated optical waveguide mode converter according to claim 1, wherein: the input conversion module comprises an input star coupler connected with an input waveguide, the input star coupler is connected with an input array waveguide, the input array waveguide is connected with an input array optical switch, and each waveguide is provided with a phase shifter;

the output conversion module comprises an output array optical switch connected with the middle connecting waveguide, the output array optical switch is connected with the output array waveguide, each waveguide is also provided with a phase shifter, the output array waveguide is connected with an output star coupler, and the output star coupler is connected with the output waveguide.

3. The universal silicon-based integrated optical waveguide mode converter according to claim 2, wherein: each waveguide in the input array waveguide and the output array waveguide is a single-mode waveguide, the optical switches in the input array optical switch and the output array optical switch are both set to be in a 1 × 2 multimode interference structure or a 1 × 2Y-type branched structure, and the input star coupler and the output star coupler are both set to be in a Rowland circle structure.

4. A generic silicon-based integrated optical waveguide mode converter according to claim 3, wherein: the waveguide is made of silicon, silicon nitride or the mixed integration of silicon and silicon nitride.

5. The universal silicon-based integrated optical waveguide mode converter according to claim 1, wherein: the input light wave and the output light wave have the same polarization mode.

Technical Field

The invention relates to the technical field of communication modes, in particular to a universal silicon-based integrated optical waveguide mode converter.

Background

In recent years, as the demand of the human society for the data transmission capacity and bandwidth of the communication network increases day by day, a trend that people cannot meet the demand has been developed based on the conventional integrated circuit technology, and the all-optical communication technology can avoid the problems of noise, bit error, power consumption and the like generated in the photoelectric conversion process, can improve the transmission capacity and bandwidth of communication to a great extent, and is developed rapidly. The silicon-based photonic technology has the advantages of large refractive index difference between a silicon waveguide core layer and a cladding layer, compatibility of a processing technology and a traditional CMOS (complementary metal oxide semiconductor) technology, easiness in realization of a super-large-scale integrated optical path and the like, so that the silicon-based photonic technology becomes a research hotspot in the field of photonic integration. In the field of optical communication technology, mode division multiplexing is used as a space division multiplexing technology, and information is independently transmitted in different modes as different transmission channels by utilizing the orthogonality of different modes in a multimode optical fiber, so that the transmission capacity of a single optical fiber can be greatly improved. Similarly, in the field of integrated photonics, mode division multiplexing has also received a great deal of attention and research from those skilled in the art to greatly increase the information transfer capacity in waveguides. The different modes need to be mutually converted, and more flexible signal routing and switching are realized, so that the mode converter is one of core devices in the mode division multiplexing.

The silicon-based optical waveguide has strong light beam-binding capability, the silicon waveguide can support transmission of a plurality of different guided modes such as a transverse electric basic mode (TE0), a transverse electric first-order mode (TE1), a transverse electric second-order mode (TE2), a transverse magnetic basic mode (TM0), a transverse magnetic first-order mode (TM1), a transverse magnetic second-order mode (TM2) and the like, and the larger the waveguide size is, the more the modes capable of supporting transmission are. Just because the waveguide can support a plurality of modes, different modes can be converted, and the signal transmission capacity and the switching flexibility of the silicon-based optical waveguide are greatly improved. The research on the silicon-based optical devices for realizing the mutual conversion among different modes becomes a popular field of the silicon-based photoelectronic research. The nano fang Yu research group of the university of columbia in 2017 (Nature Nanotechnology,2017,12(7)) can realize the conversion from one specific waveguide mode to another waveguide mode within a plurality of wavelengths by adopting a plasma or dielectric nano antenna array to form a gradient super-surface structure on a waveguide, while the traditional method for realizing the mode conversion needs a device with the length of tens of wavelengths to realize the waveguide mode conversion. The method has higher process requirements and general yield, and more importantly, the device with the design can only realize the conversion between specific modes and does not have certain universality.

Disclosure of Invention

The invention provides a universal silicon-based integrated optical waveguide mode converter, which solves the problems that the existing mode converter can only realize conversion among specific modes, and has poor universality and the like.

The invention can be realized by the following technical scheme:

a universal silicon-based integrated optical waveguide mode converter comprises an input waveguide, wherein the input waveguide is connected with an input mode conversion module, the input mode conversion module is connected with one end of an intermediate connection waveguide, the other end of the intermediate connection waveguide is connected with an output mode conversion module, the output module conversion module is connected with an output waveguide, the input waveguide is used for transmitting input optical waves, the input mode conversion module is used for converting the mode of the input optical waves into a basic mode, the intermediate connection waveguide is used for transmitting optical waves in the basic mode, the output mode conversion module is used for converting the optical waves in the basic mode into a mode required by output optical waves, and the output waveguide is used for transmitting the output optical waves.

Further, the input conversion module comprises an input star coupler connected with an input waveguide, the input star coupler is connected with an input array waveguide, the input array waveguide is connected with an input array optical switch, and each waveguide is provided with a phase shifter;

the output conversion module comprises an output array optical switch connected with the middle connecting waveguide, the output array optical switch is connected with the output array waveguide, each waveguide is also provided with a phase shifter, the output array waveguide is connected with an output star coupler, and the output star coupler is connected with the output waveguide.

Further, each of the input array waveguide and the output array waveguide is a single mode waveguide, the optical switches in the input array optical switch and the output array optical switch are both set to be in a 1 × 2 multimode interference structure or a 1 × 2Y-type bifurcated structure, and the input star coupler and the output star coupler are both set to be in a rowland circle structure.

Furthermore, the waveguide is made of silicon, silicon nitride or the mixed integration of silicon and silicon nitride.

Further, the input light wave and the output light wave have the same polarization mode.

The beneficial technical effects of the invention are as follows:

1) the method can realize conversion between any light field modes with the same polarization, namely TEi → TEj/TMi → TMj, and has better universality, higher flexibility and programming reconstruction capability compared with the conventional fixed mode converter which can only realize specific mode conversion.

2) By adopting the array optical switch and the phase shifter array, the flexible regulation and control of the amplitude and the phase of the optical field can be realized, the mode conversion efficiency is improved, and the conversion loss is reduced.

3) The silicon-based integrated circuit has the advantages of flexible structure, strong expansibility and easiness in silicon-based integration.

Drawings

FIG. 1 is a schematic diagram of the general structure of the present invention;

FIG. 2a is a schematic diagram of a Rowland circle structure used in the star coupler of the present invention;

FIG. 2b is a schematic diagram of the present invention light being routed from an input waveguide through an input star coupler to an input arrayed waveguide;

FIG. 3 is a schematic diagram of the unit structure of the optical switch of the present invention, wherein FIG. 3a shows a structure based on multi-mode interference FIG. 3b shows a Y-branch structure;

fig. 4 is a schematic cross-sectional structure of the phase shifter of the present invention, wherein fig. 4a is based on the electro-optic effect, and fig. 4b is based on the thermo-optic effect.

Detailed Description

The following detailed description of the preferred embodiments will be made with reference to the accompanying drawings.

As shown in FIG. 1, the invention provides a universal silicon-based integrated optical waveguide mode converter, which adopts two star couplers and an array optical switch composed of an independent phase shifter on an array waveguide and a cascaded optical switch to realize the conversion TEi → TEj/TMi → TMj between any same-polarization optical field modes, thus realizing the conversion from any input waveguide mode to any same-polarization output waveguide mode, having strong structure reconfigurability and meeting the mode conversion requirements of different application occasions. Specifically, the device comprises an input waveguide, the input waveguide is connected with an input mode conversion module, the input mode conversion module is connected with one end of an intermediate connecting waveguide, the other end of the intermediate connecting waveguide is connected with an output mode conversion module, the output module conversion module is connected with an output waveguide, the input waveguide is used for transmitting input light waves, the input mode conversion module is used for converting the TEi/TMi mode of the input light waves into the basic mode, namely TE0/TM0 mode, the intermediate connecting waveguide is used for transmitting light waves in the basic mode, the output mode conversion module is used for converting the light waves in the basic mode into the mode required by the output light waves, namely TEj/TMj mode, and the output waveguide is used for transmitting the output light waves.

The input conversion module TEi → TE0/TMi → TM0 comprises an input star coupler connected to an input waveguide, the input star coupler is connected to an input arrayed waveguide, the input arrayed waveguide is connected to an input arrayed optical switch, each of the waveguides is provided with a phase shifter, and thus, after the phase is compensated by the phase shifters on the input arrayed waveguide, the coherent beam combination is transmitted to the intermediate connection waveguide portion by means of the cascaded optical switch, i.e., the arrayed optical switch.

The output conversion module TE0 → TEj/TM0 → TMj includes an output array optical switch connected to the intermediate connection waveguide, the output array optical switch being connected to an output array waveguide, each of which is also provided with a phase shifter, the output array waveguide being connected to an output star coupler, the output star coupler being connected to an output waveguide, so that the output star coupler is phase-shifted by the phase shifters and then transmitted to the output star coupler and converted to tej (tmj) mode output at the output waveguides.

The input waveguide has a dimensional width that can support transmission of a plurality of different guided modes, and accordingly the output waveguide also meets the requirements. Input light enters the star coupler of the input mode conversion module from the input waveguide in a TEi/TMi mode, and output light is output from the output waveguide in an TEj/TMj mode.

The star coupler is structurally embodied as a Roland circle structure as shown in FIG. 2a, and the Roland circle is a tangent circle with the radii R and R, and the radius R of the large circle is just twice the radius R of the small circle. If the selected waveguide material is silicon nitride and the number N of the array waveguides connected with the star coupler is 32, the large circle radius is about 60 um; if silicon is chosen as the waveguide material, the corresponding radius R will be smaller, but the losses will rise slightly, since the refractive index is larger than that of the silicon nitride material.

As shown in fig. 2b, after the input mode TEi/TMi passes through the star coupler, the diffracted optical field thereof is input into the arrayed waveguide for sampling, the wavefront amplitude distribution and the phase distribution of the input mode itself are mapped into amplitude distribution and phase difference between different channels in the input arrayed waveguide, and by recording the corresponding amplitude and phase distribution of different input modes at the position where the input modes are propagated to the input arrayed waveguide through the star coupler, a relation lookup table of one-to-one mapping between the input mode type and the amplitude and phase at the arrayed waveguide can be established. Accordingly, according to the principle of reversible optical paths, if the star coupler is excited by the same amplitude distribution and the opposite phase distribution from the direction of the input array waveguide, the current input mode TEi/TMi is obtained at the output end of the star coupler. Therefore, the mapping relationship can be further expanded and applied, and according to the established mapping relationship lookup table, the amplitude and the phase on each output array waveguide can be correspondingly adjusted by the output mode conversion module, so that other modes TEj/TMj required by the user can be synthesized at the output end.

To facilitate a better understanding, the TEi → TEj transformation process will be illustrated here: assuming that the number of input array waveguides is n and the number of output array waveguides is m, the numbers of the input array waveguides and the output array waveguides may be the same or different, and the propagation direction of the waveguides is set as the Z axis, and the input ports and the outputs are set as the input portsThe Z-axis coordinates of the input array waveguide, the intermediate connection waveguide, the output array waveguide and the output port are set as Z in sequence₀、z_1n、z₂、z_3m、z₄. When light in the TEi mode is input from the input star coupler, the relationship between the amplitude and phase of the light at the input arrayed waveguide and the input mode TEi can be expressed as:then, each phase is compensated to an equal phase through a phase shifter input on the array waveguide, so that the amplitude of the TE0 after coherent beam combination can be maximum, and the conversion relation between the coherent beam combination and the mode at the array waveguide is as follows:the redistribution of the amplitude and the corresponding adjustment of the phase are performed on the basis of the amplitude and the phase distribution corresponding to the output mode designated by a user in the output mode conversion module through the output array optical switch and the phase shifter, and the following steps are performed:

based on the mapping lookup table established by the one-to-one mapping described above, the amplitude and phase are adjusted so that the user-specified pattern TEj is excited at the output of the output star coupler:the same applies to the transition between TM modes.

As described above, the coherent beam combining and power splitting network between the input star coupler and the output coupler is responsible for converting the amplitude distribution and the phase distribution in the input arrayed waveguide into the amplitude distribution and the phase distribution in the output arrayed waveguide with low loss. For coherent combining, the beams can be coherently combined into the TE0/TM0 mode of the intermediate light wave by adjusting the input array optical switches and the phase shifter array on the input array waveguides. For power splitting, the required corresponding amplitude and phase distribution in the output array waveguide is output through the output array optical switch and the phase shifter array on the output array waveguide, and then the output is output from the output waveguide through an output star coupler synthesis TEj/TMj mode.

The phase distribution is adjusted by a phase shifter array, and the phase shifter enables a thermal field/electric field to interact with an optical field in the waveguide through a thermo-optic effect or an electro-optic effect, so that the phase of an optical mode in the waveguide is changed. The amplitude distribution is adjusted through an optical switch structure based on a Mach-Zehnder interferometer, the two interference arms of the optical switch structure both comprise the thermo-optic/electro-optic phase shifter, the interference result on the output side can be changed by introducing a phase difference between the two arms, and coherent beam combination or power beam splitting in any proportion is further realized.

The input star coupler and the output star coupler are similar to an optical lens in function, waveguide optical modes are subjected to Fourier transform and then sampled by the arrayed waveguide, and different waveguide modes correspond to different amplitude and phase distributions in the arrayed waveguide. Therefore, the light beams with specific amplitude and phase distribution in the output array waveguide can be integrated into a target TEj/TMj mode by using a mirror image star coupler at the output mode conversion module and then output from the output waveguide.

The input array waveguide and the output array waveguide are conventional single-mode waveguides, and the manufacturing material thereof can be set to be silicon, silicon nitride or mixed integration of silicon and silicon nitride, for example, when silicon is selected as the waveguide material for transmission, the dimensions are generally as follows: width 400nm and height 220 nm.

The input array optical switch and the output array optical switch are both of a 1 × 2 multimode interference structure or a 1 × 2Y-type branched structure, and the specific structure of the respective optical switch array units is shown in fig. 3a and fig. 3 b.

The phase shifter is based on an electro-optic effect or a thermo-optic effect, and the attached drawings 4a and 4b are cross-sectional views of the electro-optic phase shifter of a p-i-n diode and the thermo-optic phase shifter of a silicon thermal resistor respectively, and the phase adjusting range of the phase shifter is 0-2 pi. When the selected phase shifter is a thermo-optical phase shifter, the power consumption can be as low as about 2 mW/pi, and the phase shift speed can reach hundred microseconds magnitude.

Although specific embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that these are merely examples and that many variations or modifications may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is therefore defined by the appended claims.