CN220085103U - Polarization insensitive array waveguide grating - Google Patents
Polarization insensitive array waveguide grating Download PDFInfo
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- CN220085103U CN220085103U CN202321462710.7U CN202321462710U CN220085103U CN 220085103 U CN220085103 U CN 220085103U CN 202321462710 U CN202321462710 U CN 202321462710U CN 220085103 U CN220085103 U CN 220085103U
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Abstract
The utility model provides a polarization insensitive array waveguide grating, which comprises an input waveguide, an output waveguide, a flat waveguide, an array waveguide, a polarization rotation waveguide and a reflector, wherein the input waveguide and the output waveguide are arranged at a first port on the same side of the flat waveguide, a second port of the flat waveguide is connected with an input end of the array waveguide, an output end of the array waveguide is connected with a first port of the polarization rotation waveguide, the reflector is arranged at a second port of the polarization rotation waveguide, and light is sequentially output through the polarization rotation waveguide, the second port of the flat waveguide, the first port of the flat waveguide and the output waveguide after being reflected by the reflector. The polarization rotation waveguide is added into the array waveguide grating to realize deflection when light in TE mode and TM mode polarization state is transmitted in the array waveguide, so that polarization compensation is realized, output slab waveguide and half array waveguide are saved, the volume of the array waveguide grating is further reduced by about half, and the space utilization rate of a chip is increased.
Description
Technical Field
The utility model relates to the field of optical communication, in particular to a polarization insensitive array waveguide grating.
Background
AWG (Arrayer Waveguide Grating, arrayed waveguide grating) is widely used in wavelength division multiplexing scenarios in the field of optical communications, where composite light is incident from an input waveguide, enters a slab waveguide, is diffracted, and is then coupled into each waveguide in a waveguide array. Each adjacent waveguide in the array waveguide has a fixed length difference, so that a phase difference is generated after light is transmitted through the array waveguide. The light beams with phase difference are converged at different points on the AWG image plane through the output slab waveguide, and then are coupled to the output waveguides at corresponding positions, so that the light beams with different wavelengths are separated, namely wave decomposition is realized, and otherwise, wave multiplexing is realized.
At present, the silicon-based AWG in the AWG of each material has wider application, and can realize high-density integration mainly because the AWG can be compatible with a mature CMOS process and has small size. But at the same time, due to the material characteristics, the light polarization has a larger influence on the transmission effect. Since the effective refractive indices of the transverse electric mode and the transverse magnetic mode in the waveguide are different, the phase difference generated by the light of the two modes in the waveguide is also different, so that the frequency spectrum of the channel is correspondingly shifted, namely polarization sensitivity is caused, which is particularly serious in the silicon waveguide. Moreover, the polarization state of the light transmitted through the common optical fiber is randomly changed, so that it is important to reduce the polarization sensitivity of the AWG.
The inventor knows that the polarization insensitive AWG schemes disclosed at home and abroad at present mainly comprise the following steps:
1. the non-birefringent waveguide method employs waveguides with square cross sections, which makes it difficult to eliminate the polarization sensitivity of AWG caused by birefringent materials. (Soole J; amersboot M R; polar-independent InP arrayed waveguide filter using square cross-section waveguides [ J ]; electronics Letter, 1996).
2. The idea of the polarization diversity scheme is that the incident light is polarized and split, one path of the incident light is polarized and rotated, so that two paths of the incident light are in a polarization state supported by the device, then the incident light enters the AWG respectively, and finally the two paths of the incident light are combined and output. The two-dimensional photonic crystal vertical coupling grating is adopted to realize the function of polarization beam splitting rotary coupling, so that the design complexity is increased, the size of a device is increased, and the method is not suitable for chip integration. (S.Pathak; M.Vanslemberouck; P.Dumon; D.V. Thourhaout and W.Bogaerts. Compact SOI-based polarization diversity wavelength de-multiplexer circuit using two symmertric AWGs [ C ]; european Conference and Exhibition on Optical communications. OSA, 2012).
3. CN201110219194.0 adopts a slab waveguide region with a special shape, and the optical path difference is determined by the optical path difference of the array waveguide region and the slab waveguide region. This solution has small process tolerances and is not suitable for AWG with large channel numbers.
4. The half-wave plate scheme, which requires a narrow slot to be vertically opened in the center of the AWG, damages the AWG integrity, adds other processes and introduces additional devices, cannot realize the integration of the half-wave plate with the AWG, is not suitable for the silicon-based AWG with ultra-small size, is unfavorable for chip integration, and is only suitable for the AWG with large size (Inoue Y, ohmori Y, kawachi M, et al Polarization mode converter with polyimide half waveplate in silica-based planar lightwave circuits J IEEE Photonics Technology Letters, 1994, 6 (5): 626-628.).
5. The patent application CN03118878.8 adopts a folding array waveguide grating, and the polarization rotation is controlled by a magnetoelectric substance film, so that an additional device is added, the structure is complex, and the chip integration is not facilitated.
Disclosure of Invention
The utility model provides a polarization insensitive array waveguide grating, which comprises an input waveguide, an output waveguide, a flat waveguide, an array waveguide, a polarization rotation waveguide and a reflector, wherein the input waveguide and the output waveguide are arranged at a first port on the same side of the flat waveguide, a second port of the flat waveguide is connected with an input end of the array waveguide, an output end of the array waveguide is connected with a first port of the polarization rotation waveguide, the reflector is arranged at a second port of the polarization rotation waveguide, and light is sequentially output through the polarization rotation waveguide, the second port of the flat waveguide, the first port of the flat waveguide and the output waveguide after being reflected by the reflector. The polarization rotation waveguide is added into the array waveguide grating to realize deflection when the light in TE mode and TM mode polarization state is transmitted in the array waveguide, so that polarization compensation is realized, the light in TE mode and TM mode has the same diffraction angle in the planar waveguide, and the light in different polarization states reaches the array waveguide on the output Roland circle. Meanwhile, the reflector is added in the array waveguide grating, so that the output slab waveguide and half of the array waveguide are simplified, the volume of the array waveguide grating is further reduced by about half, and the space utilization rate of a chip is increased.
The polarization rotation waveguide is provided with through holes sequentially arranged along the light transmission direction, and the centers of the through holes are arranged at the non-axial positions of the polarization rotation waveguide. In some embodiments, the through-hole cross-section is provided as a circle or square.
The reflectors are sequentially provided with air holes along the light transmission direction, and the centers of the air holes are arranged on the axes of the reflectors. In some embodiments the air holes are arranged in a circular or square cross-section.
In some embodiments, the arrayed waveguide grating is provided in 7 channels.
The polarization rotating waveguide achieves 45 degree polarization rotation of light at a time. The input light is reflected by the reflector, and then is reflected by the polarization rotation waveguide again to realize 45-degree polarization rotation, 90-degree polarization rotation is realized by accumulation, and the TE mode is converted into the TM mode and the TM mode is converted into the TE mode.
Drawings
FIG. 1 is a schematic diagram of an arrayed waveguide grating structure according to the inventive concept
FIG. 2 is a schematic diagram of a polarization rotating waveguide according to an embodiment of the present utility model
FIG. 3 is a schematic view of a reflector according to an embodiment of the utility model
FIG. 4 is a schematic diagram of connection of an array waveguide to a polarization rotating waveguide and a reflector in an embodiment of the utility model
FIG. 5 is a schematic diagram of a TE mode and TM mode spectrum simulation in an embodiment of the present utility model.
Detailed Description
The following description of the embodiments of the present utility model will be made with reference to the accompanying drawings.
In the implementation of the present utility model, a polarization insensitive arrayed waveguide grating structure as shown in fig. 1 may be provided, where one input waveguide 1 receives a light beam from a light source, and a slab waveguide 2 receives the light beam input by the input waveguide 1. Kirchhoff diffraction occurs in the slab waveguide 2, the optical field expands and optical power is distributed to each waveguide in the array waveguide 3, and each adjacent waveguide in the array waveguide 3 is provided with a uniform and fixed length difference, so that light in different waveguides can achieve an integral multiple of 2 pi in phase difference, and constructive interference of light can be achieved. Meanwhile, light with different wavelengths has different diffraction angles, light beams in the array waveguide are reflected by the reflector 5 after being subjected to polarization conversion by the polarization rotation waveguide 4, and then return to the slab waveguide 2 to be diffracted and focused at an imaging point to enter the output waveguide 6 arranged at the position, so that the wavelength separation function is realized. The input waveguide 1 and the output waveguide 6 are provided on the same side of the slab waveguide 2, and are used for inputting and outputting light, respectively. The array waveguide 3, the polarization rotation waveguide 4 and the reflector 5 are arranged on the other side of the slab waveguide 2.
The length difference L of each adjacent waveguide in the array waveguide 3 is expressed by the following formula:
（1）
wherein: m represents the diffraction order, λc represents the center wavelength of the transmitted light, n ea Representing the effective refractive index of the arrayed waveguide 3.
The diffraction order m is an integer, which is derived from the following formula:
（2）
wherein N represents the number of channels, and the lambda represents the channel wavelength interval, N g Representing the group index of refraction of the arrayed waveguide 3.
The relationship between the grating radius of the slab waveguide 2 and the pitch of each waveguide in the output waveguide 6 and the pitch of each waveguide in the waveguide array, and is expressed by the following formula.
（3）
Wherein R represents output slab waveguide lightThe radius of the gate circle, denoted by X, represents the pitch of each of the output waveguides 6, n es Represents the effective refractive index, d, of the slab waveguide 2 a Representing the pitch of each of the waveguides in the array waveguide 3.
According to different transmission wavelengths and formulas (1), (2) and (3), parameters such as length difference, spacing, grating radius of the slab waveguide and the like of each waveguide in the embodiment are designed by adopting a simulation technology.
In the embodiment of the present utility model, as shown in fig. 2, the polarization rotation waveguide 4 is designed as a photonic crystal waveguide, and a plurality of circular through holes 21 are provided along the optical transmission direction and the eccentric axis. In one embodiment, the circular through holes 21 are arranged at equal intervals, and the number is 7. In other embodiments, the circular through-holes 21 are designed as squares. The existence of the circular through hole 21 changes the refractive index inside the polarization rotation waveguide 4, and the light beam passes through the polarization rotation waveguide 4 twice, so that TE mode-to-TM mode conversion and TM mode-to-TE mode conversion are realized.
The reflector 5 is designed in the utility model to realize that after the light beam which realizes 45-degree polarization rotation through the polarization rotation waveguide 4 is reflected, the light beam passes through the polarization rotation waveguide 4 again to overlap the second 45-degree polarization rotation, 90-degree polarization rotation is realized in an accumulated way, and finally, the TE mode is converted into the TM mode and the TM mode is converted into the TE mode. The structure of the reflector 5 is shown in fig. 4, and a plurality of circular air holes 31 are arranged at the central axis along the light transmission direction and are equidistantly arranged along the central axis, so that photonic crystal waveguide design is realized, and the refractive index inside the reflector 5 is changed. In one embodiment, the circular air holes 31 are designed to be 9. In other embodiments, the circular air holes 31 are designed as squares. The center of the circular air hole 31 is disposed at the central axis of the reflector in the light transmission direction.
Fig. 4 is a schematic diagram showing a connection structure between the polarization rotation waveguide 42 and the reflector 43 and one waveguide 41 of the array waveguides, and fig. 4 shows that an input end of the polarization rotation waveguide 42 is connected to one waveguide 41 of the array waveguides and an output end of the polarization rotation waveguide 42 is connected to the reflector 43. The light beam is input through waveguide 41, is polarization rotated by 45 degrees through polarization rotating waveguide 42, and is reflected by reflector 43. The reflected light beam passes through the polarization rotation waveguide 42 for the second time, again realizes 45-degree polarization rotation, and integrates to realize 90-degree polarization rotation, so that the TE mode is converted into the TM mode, and the TM mode is converted into the TE mode. The polarization rotating waveguide length in the present utility model is designed to achieve a 45 degree length of beam polarization.
The polarization-rotating waveguide length L' that achieves 90 degree polarization of the light beam is calculated by the following formula:
（4）
（5）
wherein, pi represents the phase difference generated between TE mode and TM mode after L' transmission length, n TE Representing the effective refractive index corresponding to TE mode, n TM Indicating the effective refractive index corresponding to the TM mode.
TE mode center wavelength lambda through polarization conversion waveguide 0TE And the TM mode center wavelength lambda 0TM Is represented by the following formula:
（6）
（7）
（8）
as can be seen from the above, the arrayed waveguide grating with the polarization conversion waveguide structure is added, the TE mode center wavelength is equal to the TM mode center wavelength, and the TE mode and TM mode light wave spectral lines are basically coincident in the spectrum. Spectral simulation as shown in fig. 5, the dashed line indicates that the input light field is TM fundamental mode, and the solid line indicates that the input light field is TE fundamental mode.
The polarization insensitive array waveguide grating provided by the embodiment of the utility model is completely compatible with the traditional array waveguide grating manufacturing process, and no additional element is needed. The reflector is added, half of array waveguide is reduced, the chip size is effectively reduced, and the utilization rate of chip space is improved. The polarization rotation structure and the AWG are integrated integrally, the angle problem of the polarization rotation structure is not considered, the process error is small, the implementation is easy, the AWG is not damaged, and the integrity of the AWG is maintained.
The above embodiments only list preferred specific technical schemes and technical means, but do not exclude other alternatives of equivalent technical means which can solve the technical problem within the scope of the claims of the present utility model, and should be understood as what is claimed in the present utility model.
Claims (7)
1. A polarization insensitive arrayed waveguide grating, comprising: the device comprises an input waveguide, an output waveguide, a flat waveguide, an array waveguide, a polarization rotation waveguide and a reflector, wherein the input waveguide and the output waveguide are arranged at a first port on the same side of the flat waveguide, a second port of the flat waveguide is connected with an input end of the array waveguide, an output end of the array waveguide is connected with the first port of the polarization rotation waveguide, the reflector is arranged at the second port of the polarization rotation waveguide, and light is sequentially output through the polarization rotation waveguide, the second port of the flat waveguide, the first port of the flat waveguide and the output waveguide after being reflected by the reflector.
2. The polarization-insensitive arrayed waveguide grating of claim 1, wherein the polarization-rotating waveguide has through holes arranged in sequence along the light transmission direction, the center of the through holes being disposed at a position other than the axis of the polarization-rotating waveguide.
3. The polarization-insensitive arrayed waveguide grating of claim 1, wherein the reflectors are sequentially aligned with air holes along the light transmission direction, the air holes being centrally disposed on the reflector axis.
4. The polarization insensitive arrayed waveguide grating of claim 1, wherein said arrayed waveguide grating is provided in 7 channels.
5. The polarization insensitive arrayed waveguide grating of claim 1, wherein the polarization rotating waveguide achieves 45 degree polarization rotation for light at a time.
6. The polarization-insensitive arrayed waveguide grating of claim 2, wherein the through-holes are provided in a circular or square shape in cross-section along the polarization-rotating waveguide axis.
7. A polarization insensitive arrayed waveguide grating according to claim 3, wherein the air holes are arranged in a circular or square shape in cross section along the reflector axis.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202321462710.7U CN220085103U (en) | 2023-06-09 | 2023-06-09 | Polarization insensitive array waveguide grating |
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