阅读说明：本技术 一种光栅型偏振不敏感的多通道波分复用接收器 (Grating type polarization insensitive multi-channel wavelength division multiplexing receiver ) 是由 戴道锌 刘大建 于 2020-05-22 设计创作，主要内容包括：本发明公开了一种光栅型偏振不敏感的多通道波分复用接收器。偏振旋转分束器的两端分别连接第一、第二连接波导的一端,第一、第二连接波导之间串接有N个接收单元,每个接收单元包括双向光栅滤波器、滤模器和双端口探测器,N个双向光栅滤波器、N个滤模器依次交替串接相连后连接在偏振旋转分束器的直通端和交叉端之间,每个双向光栅滤波器的正向和反向下载端波导均连接到一个双端口探测器。本发明实现了多通道波分复用接收器的偏振不敏感,获得了一个低插损、低串扰且各通道均有平顶响应的多通道波分复用接收器,具有与CMOS工艺兼容、结构简单、低插损和低串扰等优点。(The invention discloses a grating type polarization insensitive multi-channel wavelength division multiplexing receiver. The two ends of the polarization rotation beam splitter are respectively connected with one end of a first connecting waveguide and one end of a second connecting waveguide, N receiving units are connected between the first connecting waveguide and the second connecting waveguide in series, each receiving unit comprises a bidirectional grating filter, a mode filter and a dual-port detector, the N bidirectional grating filters and the N mode filters are sequentially connected in series in an alternating mode and then connected between a straight-through end and a cross end of the polarization rotation beam splitter, and forward and reverse download end waveguides of each bidirectional grating filter are connected to one dual-port detector. The invention realizes the polarization insensitivity of the multichannel wavelength division multiplexing receiver, obtains the multichannel wavelength division multiplexing receiver with low insertion loss and crosstalk and flat-top response of each channel, and has the advantages of compatibility with CMOS (complementary metal oxide semiconductor) process, simple structure, low insertion loss, low crosstalk and the like.)

1. A grating-type polarization insensitive multi-channel receiver, characterized by: the polarization rotating beam splitter comprises a polarization rotating beam splitter (a), a first connecting waveguide (5), a second connecting waveguide (6) and N receiving units, wherein two ends of the polarization rotating beam splitter (a) are respectively connected with one end of the first connecting waveguide (5) and one end of the second connecting waveguide (6), N receiving units with similar structures are connected between the other ends of the first connecting waveguide (5) and the second connecting waveguide (6) in series, each receiving unit comprises a bidirectional grating filter, a mode filter and a dual-port detector, the bidirectional grating filter and the mode filter of each receiving unit are sequentially connected in series along the direction from the other end of the first connecting waveguide (5) to the other end of the second connecting waveguide (6), the first bidirectional grating filter (b1), the first mode filter (c1), the …, the Nth bidirectional grating filter (bN) and the Nth mode filter (cN) are sequentially connected end to end; and the receiving unit further comprises a dual-port detector (dn) which is positioned beside the bidirectional grating filter and is coupled with the bidirectional grating filter.

2. A grating-type polarization insensitive multi-channel receiver as claimed in claim 1, wherein: the polarization rotation beam splitter comprises an input waveguide (1), a polarization rotation working area (2), a straight-through end output waveguide (3) and a cross end output waveguide (4), the input end of an input waveguide (1) is used as an input port of an optical signal, the output end of the input waveguide (1) is connected to the input end of a polarization rotation working area (2), two output ends of the polarization rotation working area (2) are respectively connected with the input end of a straight-through end output waveguide (3) and the output end of a cross end output waveguide (4), the output end of the straight-through end output waveguide (3) is connected with the input end of a first bidirectional grating filter (b1) of a first receiving unit through a first connecting waveguide (5), the output end of the Nth mode filter (cN) of the Nth receiving unit is connected with the input end of the cross-end output waveguide (4) of the polarization rotation beam splitter (a) through a second connecting waveguide (6).

3. A grating-type polarization insensitive multi-channel wavelength division multiplexing receiver as claimed in claim 1, wherein: the dual-port detectors (dn) of the N receiving units have the same structure, N is 1,2, …, N-1, N, each dual-port detector (dn) is mainly formed by sequentially connecting a forward input waveguide (N12), a detector (N13) and a reverse input waveguide (N14), wherein the forward input waveguide (N12) serves as a forward input end of the dual-port detector and a forward download end of the bidirectional grating filter, and the reverse input waveguide (N14) serves as a reverse input end of the dual-port detector and a reverse download end of the bidirectional grating filter.

4. A grating-type polarization insensitive multi-channel receiver as claimed in claim 1, wherein: each bidirectional grating filter (bn) of the receiving unit has the same structure, wherein N is 1,2, …, N-1, N, and comprises a front-mode demultiplexer (bn1), a multimode waveguide grating (bn2) and a rear-mode demultiplexer (bn 3); the output end of the front mode demultiplexer is connected with the input end of the rear mode demultiplexer through the multimode waveguide grating; the front mode demultiplexer and the rear mode demultiplexer are identical in structure but are symmetrically arranged on both sides of a multimode waveguide grating (bn 2).

5. A grating-type polarization insensitive multi-channel receiver as claimed in claim 4, wherein: the multimode waveguide grating (bn2) is mainly formed by sequentially connecting a front graded grating (n05), an antisymmetric multimode waveguide grating (n06) and a rear graded grating (n07), wherein the input end of the front graded grating (n05) is used as the input end of the multimode waveguide grating, and the output end of the rear graded grating (n07) is used as the output end of the multimode waveguide grating.

6. A grating-type polarization insensitive multi-channel receiver as claimed in claim 4, wherein: the front gradient grating (n05) of the multimode waveguide grating (bn2) has the depth of grating teeth linearly graded from zero to the depth of the antisymmetric multimode waveguide grating; the back graded grating (n07) of the multimode waveguide grating (bn2) has grating teeth which are linearly graded from the depth of the antisymmetric multimode waveguide grating to zero.

7. A grating-type polarization insensitive multi-channel receiver as claimed in claim 5, wherein: the antisymmetric multimode waveguide grating (n06) realizes TE₀Mode back coupling to TE₁Pattern, satisfying phase matching condition (n)₀+n₁) λ/Λ is defined as 2, where n₀Is TE₀Effective refractive index of mode, n₁Is TE₁the effective refractive index of the mode, λ is the resonant wavelength, and Λ is the grating tooth period.

8. A grating-type polarization insensitive multi-channel receiver as claimed in claim 4, wherein: the multimode waveguide grating (bn2) in each of the two-way grating filters employs an apodized grating, and incorporates a graded grating.

9. A grating-type polarization insensitive multi-channel receiver as claimed in claim 4, wherein: the front mode demultiplexer (bn1) is formed by connecting an input waveguide, a download waveguide, a mode multiplexing working area and an output waveguide in a propagation direction, wherein the input end of the input waveguide is connected with the output end of a mode filter of a receiving unit, one end of the download waveguide is connected with the input end of a dual-port detector of the current receiving unit, the output end of the input waveguide and the other end of the download waveguide are respectively connected with one end of the mode multiplexing working area, the other end of the mode multiplexing working area is connected with one end of the output waveguide, and the other end of the output waveguide is connected with the input end of a multimode waveguide grating (bn 2).

10. A grating-type polarization insensitive multi-channel receiver as claimed in claim 4, wherein: the post-mode demultiplexer (bn3) is formed by connecting an input waveguide, a mode multiplexing working area, a download waveguide and an output waveguide in the propagation direction, wherein the input end of the input waveguide is connected to the output end of the multimode waveguide grating (bn2), the output end of the input waveguide is connected to one end of the mode multiplexing working area, the other end of the mode multiplexing working area is respectively connected to one ends of the output waveguide and the download waveguide, the other end of the output waveguide is connected to the input end of the mode filter of the current receiving unit, and the other end of the download waveguide is connected to the output end of the dual-port detector of the current receiving unit.

Technical Field

The invention belongs to a receiver in the field of optical communication, and particularly relates to a grating type polarization insensitive multi-channel receiver.

Background

With the rapid development of broadband China and the arrival of the 5G era, the demand of data services for ultrahigh-capacity optical interconnection is increasingly urgent. As is well known, Wavelength Division Multiplexing (WDM) technology is one of the important technologies in which interconnection of data communication is enhanced. The WDM technology combines two or more optical carrier signals with different wavelengths together at a sending end through a multiplexer and couples the optical carrier signals into the same optical fiber for transmission; at the receiving end, the optical carrier signals of all wavelengths are separated through a demultiplexer, and the original signals are recovered. Typical WDM techniques include Dense wavelength division multiplexing (Dense WDM, DWDM) with small channel spacing (e.g., 0.8nm) and sparse wavelength division multiplexing (Coarse WDM, CWDM) with large channel spacing (e.g., 20 nm).

At present, most of wavelength division multiplexing-demultiplexing devices in practical application are formed by coupling separated elements, have the defects of large size, difficult packaging, high cost and the like, and can not meet the development of future optical communication devices. The wavelength division multiplexing-demultiplexing device based on the planar optical waveguide is concerned by the characteristics of integration miniaturization, low energy consumption, low cost and the like. In an optical fiber communication system, since the polarization state of an optical signal after being transmitted through an optical fiber is random, a polarization insensitive demultiplexer is required at a receiving end for demultiplexing. However, due to the high refractive index difference and the submicron cross-sectional size of the silicon nanowire, the silicon nanowire tends to have large birefringence, and most silicon-based wavelength division demultiplexing devices are polarization-sensitive, so that they cannot be applied to practical optical fiber communication systems. In addition, in order to ensure the excellent overall performance of the communication system, the wavelength division demultiplexer needs to ensure flat-top response, low insertion loss and low crosstalk of the overall device while meeting the requirement of polarization insensitivity.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a grating type polarization insensitive multi-channel wavelength division multiplexing receiver.

The technical scheme adopted by the invention is as follows:

the invention comprises a polarization rotation beam splitter, a first connecting waveguide, a second connecting waveguide and N receiving units, wherein two ends of the polarization rotation beam splitter are respectively connected with one end of the first connecting waveguide and one end of the second connecting waveguide, N receiving units with similar structures are connected between the other ends of the first connecting waveguide and the second connecting waveguide in series, each receiving unit comprises a bidirectional grating filter, a mode filter and a dual-port detector, the bidirectional grating filters and the mode filters of the receiving units are sequentially connected in series along the direction from the other end of the first connecting waveguide to the other end of the second connecting waveguide, namely, the first bidirectional grating filter, the first mode filter, …, the Nth bidirectional grating filter and the Nth mode filter are sequentially arranged in series from the other end of the first connecting waveguide to the other end of the second connecting waveguide, namely, the first bidirectional grating filter, the first mode filter, the Nth bidirectional grating filter and the Nth mode filter are obtained, …, the Nth bidirectional grating filter and the Nth mode filter are sequentially connected end to end; and the receiving unit also comprises a dual-port detector which is positioned beside the bidirectional grating filter and is coupled with the bidirectional grating filter.

The polarization rotation beam splitter comprises an input waveguide, a polarization rotation working area, a through end output waveguide and a cross end output waveguide, wherein the input end of the input waveguide is used as an input port of an optical signal, the output end of the input waveguide is connected to the input end of the polarization rotation working area, two output ends of the polarization rotation working area are respectively connected with the input end of the through end output waveguide and the output end of the cross end output waveguide, two ends of the polarization rotation beam splitter are respectively provided with the through end output waveguide and the cross end output waveguide, the output end of the through end output waveguide is connected with the input end of a first bidirectional grating filter of a first receiving unit through a first connecting waveguide, and the output end of an Nth mode filter of an Nth receiving unit is connected with the input end of the cross end output waveguide of the polarization rotation beam splitter through a second connecting waveguide. After the optical signal enters the input waveguide, the component of the transverse electric mode passes through the working area and is output from the straight-through end output waveguide, and the component of the transverse magnetic mode passes through the working area and is converted into the transverse electric mode and is output from the cross end output waveguide.

The dual-port detectors of the N receiving units have the same structure, where N is 1,2, …, N-1, N, and each dual-port detector is mainly formed by sequentially connecting a forward input waveguide, a detector and a reverse input waveguide, where the forward input waveguide serves as a forward input end of the dual-port detector and is connected with a forward download end of the bidirectional grating filter (i.e., connected with a download end waveguide N04 of a front mode demultiplexer of the bidirectional grating filter), and the reverse input waveguide serves as a reverse input end of the dual-port detector and is connected with a reverse download end of the bidirectional grating filter (i.e., connected with a download end waveguide N11 of a rear mode demultiplexer of the bidirectional grating filter).

The mode filter filters a high-order transverse electric mode in the waveguide and retains a transverse electric fundamental mode, but is not limited to a structure adopting a bent waveguide and the like. The high-order transverse electric mode refers to a transverse electric mode of first order and higher order.

Each bidirectional grating filter of the receiving unit has the same structure, wherein N is 1,2, …, N-1, N, and each bidirectional grating filter comprises a front-mode demultiplexer, a multimode waveguide grating and a rear-mode demultiplexer; the output end of the front mode demultiplexer is connected with the input end of the rear mode demultiplexer through a front gradient grating, an antisymmetric multimode waveguide grating and a rear gradient grating of the multimode waveguide grating in sequence; the front mode demultiplexer and the rear mode demultiplexer are identical in structure but are symmetrically arranged on two sides of the multimode waveguide grating.

The multimode waveguide grating is mainly formed by sequentially connecting a front gradient grating, an antisymmetric multimode waveguide grating and a rear gradient grating, wherein the input end of the front gradient grating is used as the input end of the multimode waveguide grating, and the output end of the rear gradient grating is used as the output end of the multimode waveguide grating.

The mode demultiplexer comprises a front mode demultiplexer and a rear mode demultiplexer and adopts structures such as an asymmetric directional coupler, an adiabatic evolution coupler, a grating auxiliary coupler and the like.

The front gradient grating (n05) of the multimode waveguide grating is linearly graded from zero to the depth of the antisymmetric multimode waveguide grating; the depth of grating teeth of the rear graded grating (n07) of the multimode waveguide grating is linearly graded to zero from the depth of the antisymmetric multimode waveguide grating. Mode mismatch of a waveguide mode and a grating mode is reduced through the front gradient grating, loss caused by the mode mismatch is reduced, and device loss is further reduced.

The antisymmetric multimode waveguide grating realizes TE₀Mode back coupling to TE₁Pattern, satisfying phase matching condition (n)₀+n₁) λ/Λ is defined as 2, where n₀Is TE₀Effective refractive index of mode, n₁Is TE₁effective refractive index of the mode, λ resonance wavelength, and Λ gratingThe tooth period. TE₀Mode and TE₁The modes refer to a transverse electric fundamental mode and a transverse electric first-order mode, respectively.

The multimode waveguide grating in each bidirectional grating filter adopts apodization grating and is added with gradual change grating, in particular, the antisymmetric multimode waveguide grating adopts apodization grating, and the front gradual change grating and the rear gradual change grating adopt gradual change grating, thereby reducing Fabry-Perot effect between the gratings and crosstalk between channels.

The sawtooth of the multimode waveguide grating adopts the shapes of rectangle, triangle, cosine and the like.

The front mode demultiplexer is formed by connecting an input waveguide, a download waveguide, a mode multiplexing working area and an output waveguide in the propagation direction, the input end of the input waveguide is connected with the output end of a mode filter of a receiving unit, one end of the download waveguide is connected with the input end of a dual-port detector of the current receiving unit, the output end of the input waveguide and the other end of the download waveguide are respectively connected with one end of the mode multiplexing working area, the other end of the mode multiplexing working area is connected with one end of the output waveguide, and the other end of the output waveguide is connected with the input end of a multimode waveguide grating.

The rear mode demultiplexer is formed by connecting an input waveguide, a mode multiplexing working area, a download waveguide and an output waveguide in the propagation direction, wherein the input end of the input waveguide is connected to the output end of the multimode waveguide grating, the output end of the input waveguide is connected with one end of the mode multiplexing working area, the other end of the mode multiplexing working area is respectively connected with one end of the output waveguide and one end of the download waveguide, the other end of the output waveguide is connected with the input end of the mode filter of the current receiving unit, and the other end of the download waveguide is connected with the output end of the dual-port detector of the current receiving unit.

The Polarization rotating beam splitter comprises a Polarization rotating beam splitter (PSR), a first connecting waveguide, a second connecting waveguide, a first bidirectional grating filter, an … Nth bidirectional grating filter, a first two-Port Detector (PD), a … Nth two-port detector, a first mode filter and a … Nth mode filter; the input end of the polarization rotation beam splitter is an input waveguide, the straight-through output end of the polarization rotation beam splitter is connected with the input end of a first connecting waveguide, the cross output end of the polarization rotation beam splitter is connected with the output end of a second connecting waveguide, and the output end of the first connecting waveguide is connected with the input end of a first bidirectional grating filter; the plurality of bidirectional grating filters and the plurality of mode filters are sequentially connected, namely the output end of the first bidirectional grating filter is connected with the input end of the first mode filter, the output end of the first mode filter is connected with the input end of the second bidirectional grating filter, the output end of the … (N-1) th mode filter is connected with the input end of the Nth bidirectional grating filter, and the output end of the Nth grating filter is connected with the input end of the Nth mode filter; the output end of the Nth mode filter is connected with the input end of the second connecting waveguide; the forward download ends and the reverse download ends of the bidirectional grating filters are respectively connected with the forward input waveguides and the reverse input waveguides of the dual-port detectors. The input end of the polarization rotation beam splitter is used as an input port of a signal, the forward downloading end of the bidirectional grating filter is used as an output port of a Transverse electric mode (TE) of a corresponding channel (wavelength), the reverse downloading end of the bidirectional grating filter is used as an output port of a Transverse Magnetic mode (TM) of the corresponding channel (wavelength), and finally the Transverse Magnetic mode and the Transverse electric mode of an optical signal under the same channel (wavelength) are received by the same detector, so that the polarization insensitivity of the multichannel wavelength division multiplexing receiver is realized.

The invention has the beneficial effects that:

the invention realizes the wavelength division demultiplexing insensitive to polarization by introducing the polarization rotating beam splitter and cascading a plurality of bidirectional grating filters, and finally obtains the multichannel wavelength division multiplexing receiver insensitive to polarization by connecting each bidirectional grating filter with each dual-port detector.

The bidirectional grating filter of the invention obtains the required channel center and channel bandwidth by adjusting the period and tooth depth of the grating, and can completely meet the requirements of wavelength, bandwidth and the like in various communication protocols.

The invention can reduce the crosstalk among channels by a specially designed and constructed waveguide structure combining the mode filter, the apodization grating and the gradual-change grating, and obtains the multichannel wavelength division demultiplexing with low crosstalk, low loss and flat-top response.

The invention can be manufactured by a planar integrated optical waveguide process, has simple and convenient process, low cost, high performance and small loss, is compatible with the traditional CMOS process and has great production potential.

In summary, the invention realizes the polarization insensitivity of wavelength division demultiplexing, obtains a multi-channel wavelength division multiplexing receiver with low insertion loss and crosstalk and flat-top response of each channel, and has the advantages of compatibility with CMOS process, simple structure, low insertion loss and crosstalk and the like.

Drawings

Fig. 1 is a schematic diagram of the overall structure of a grating-type polarization insensitive multi-channel wavelength division multiplexing receiver.

Fig. 2 is a schematic diagram of a bi-directional grating filter.

Fig. 3 is a sawtooth pattern employed by a multimode waveguide grating, including, but not limited to, (a) rectangular sawtooth, (b) triangular sawtooth, and (c) cosine-shaped sawtooth.

Fig. 4 is a schematic diagram of the operating principle of a grating type polarization insensitive multi-channel wavelength division multiplexing receiver.

FIG. 5 is a graph showing simulation results of antisymmetric multimode waveguide gratings of the device according to the embodiment.

In the figure: a is a polarization rotation beam splitter, b1 is a first bidirectional grating filter, …, bN is an nth bidirectional grating filter, c1 is a first mode filter, …, cN is an nth mode filter, d1 is a first dual-port detector, …, dN is an nth dual-port detector, 5 is a first connecting waveguide, and 6 is a second connecting waveguide;

1 is an input waveguide of the polarization rotation beam splitter, 2 is a working area of the polarization rotation beam splitter, 3 is a straight-through end output waveguide of the polarization rotation beam splitter, and 4 is a cross end output waveguide of the polarization rotation beam splitter;

in the bidirectional grating filter, bn1(N ═ 1,2, …, N-1, N) is a front mode demultiplexer of the nth bidirectional grating filter, bn2 is a multimode waveguide grating of the nth bidirectional grating filter, and bn3 is a rear mode demultiplexer of the nth bidirectional grating filter;

n01 is an input waveguide of the front mode demultiplexer in the nth bidirectional grating filter, n02 is a mode multiplexing working area of the front mode demultiplexer in the nth bidirectional grating filter, n03 is an output waveguide of the front mode demultiplexer in the nth bidirectional grating filter, and n04 is a download waveguide of the front mode demultiplexer in the nth bidirectional grating filter;

n05 is a front tapered grating of the multimode waveguide grating in the nth bidirectional grating filter, n06 is an antisymmetric multimode waveguide grating of the multimode waveguide grating in the nth bidirectional grating filter, and n07 is a rear tapered grating of the multimode waveguide grating in the nth bidirectional grating filter;

n08 is an input waveguide of the post-mode demultiplexer in the nth bidirectional grating filter, n09 is a mode multiplexing working area of the mode demultiplexer in the nth bidirectional grating filter, n10 is an output waveguide of the post-mode demultiplexer in the nth bidirectional grating filter, and n11 is a download waveguide of the post-mode demultiplexer in the nth bidirectional grating filter.

n12 is the forward input waveguide of the nth two-port probe, n13 is the probe of the nth two-port probe, and n14 is the reverse input waveguide of the nth two-port probe.

Detailed Description

The invention is further illustrated by the following figures and examples.

As shown in fig. 1, the embodiment of the present invention includes a polarization rotating beam splitter a, N cascaded bidirectional grating filters, i.e., a first bidirectional grating filter b1, … and an nth bidirectional grating filter bN, and a mode filter c1, …, cN and N dual-port detectors d1, …, dN are included between two connected bidirectional grating filters.

The polarization rotation optical fiber polarization beam splitter specifically comprises a polarization rotation beam splitter a, a first connecting waveguide 5, a second connecting waveguide 6, an nth bidirectional grating filter bn, wherein N is 1,2, …, N-1, N, an nth mode filter cn and an nth dual-port detector dn; the straight-through output waveguide 3 of the polarization rotation beam splitter a is connected with the input end of a first bidirectional grating filter b1 through a first connecting waveguide 5; the first bidirectional grating filter b1, the first mode filters c1, …, the Nth bidirectional grating filter bN and the Nth mode filter cN are connected in sequence; the output end of the Nth mode filter cN is connected with the cross end output waveguide 4 of the polarization beam splitter a through a second connecting waveguide 6; the forward input waveguide n12 and the backward input waveguide n14 of the nth dual-port detector dn are connected to the download waveguide n04 of the front mode demultiplexer of the nth bidirectional grating filter and the download waveguide n14 of the rear mode demultiplexer of the nth bidirectional grating filter, respectively.

Wherein the polarization rotating beam splitter a comprises an input waveguide 1, an active region 2, a straight-through output waveguide 3 and a cross-over output waveguide 4.

Where the n two-port detectors dn include a forward input waveguide n12, a detector n13 and a reverse input waveguide n 14.

As shown in fig. 2, each of the N bidirectional grating filters includes a front mode demultiplexer bn1, a multimode waveguide grating bn2, and a rear mode demultiplexer bn3, the front mode demultiplexer bn1 includes an input waveguide N01, a mode demultiplexing work area N02, an output waveguide N03, and a download waveguide N04; the post-mode demultiplexer bn3 comprises an input waveguide n08, a mode demultiplexing work area n09, an output waveguide n10 and a download waveguide n 11; the multimode waveguide grating bn2 includes a front graded grating n05, an antisymmetric multimode waveguide grating n06 and a rear graded grating n 07.

The multimode waveguide grating bn2 of the N bidirectional grating filters is formed by sequentially connecting a front tapered grating N05, an antisymmetric multimode waveguide grating N06 and a rear tapered grating N07, wherein the other end of the front tapered grating N05 is used as the input end of the multimode waveguide grating, and the other end of the rear tapered grating N07 is used as the output end of the multimode waveguide grating.

As shown in fig. 2, the basic structure of the bidirectional grating filter is as shown in the figure. The front mode demultiplexer bn1 is connected in series with the multimode waveguide grating bn2 and the rear mode demultiplexer bn 3. In the figure, the upper left port is an input port, the upper right port is an output port (also a reverse input port), the lower left port is a forward download port, and the lower right port is a reverse download port.

The front mode demultiplexer bn1 and the rear mode demultiplexer bn3 may be, but are not limited to, formed of asymmetric directionally coupled waveguides, adiabatically evolving waveguides, grating assisted coupled waveguides. TE at right-hand input in front-mode demultiplexer₁TE whose modes can be multiplexed to the lower left port₀Mode(s)Outputting; TE input at left end in rear mode demultiplexer₁TE whose modes can be multiplexed to lower right port₀And (6) outputting the mode.

Multimode waveguide grating satisfies TE₀Mode and reverse TE₁Phase matching condition of pattern, input TE₀Modes can be back-coupled to TE near the Bragg resonance condition₁The mode can obtain the required central wavelength and bandwidth by selecting the total width, tooth depth and period of the grating. By using an apodized grating structure (such as, but not limited to, a laterally shifted gaussian distribution of grating teeth on both sides in the axial direction), a filter with a high side-mode suppression ratio is obtained, and thus crosstalk between signal channels can be reduced.

As shown in fig. 3, the multimode waveguide grating may adopt various forms of saw teeth, including a rectangular saw tooth in fig. 3(a), a triangular saw tooth in fig. 3(b), a cosine saw tooth in fig. 3(c), and the like.

The operation of the present invention as a polarization insensitive wavelength division multiplexing receiver is described below:

the working principle of the invention is shown in fig. 4, carrying the information of each wavelength (lambda)₁…λ_N) An optical signal is Input from an Input end and enters a polarization rotation beam splitter (PSR), a TE polarization component in the optical signal is output from a straight-through end waveguide, namely, a left waveguide in the figure, and a TM polarization component in the optical signal is converted into TE polarization after passing through the polarization rotation beam splitter and is output from a cross end waveguide, namely, a right waveguide in the figure; the light output from the through-end waveguide passes through each of the bidirectional grating filters (b1, …, bN) in turn, and light (λ) of each wavelength₁…λ_N) Sequentially outputting the data at each forward downloading end and entering each detector (PD); the light output from the cross-port waveguide passes in reverse through each bi-directional grating filter (bN, …, b1), light (λ) of each wavelength_N…λ₁) And the data are sequentially output from each reverse download end and enter each detector. Finally, the TE polarization component and the TM polarization component of the optical signal with the same wavelength enter the same detector, and finally polarization insensitive multichannel wavelength division multiplexing receiving is achieved. By introducing apodizing lightThe grating, the mode filter and the gradient grating restrain Fabry-Perot resonance among the gratings and reduce crosstalk among channels, thereby obtaining wavelength division multiplexing reception with low crosstalk and low insertion loss.

The specific embodiment of the invention is as follows:

silicon nanowire optical waveguides based on silicon-on-insulator (SOI) materials are selected: the core layer is made of silicon material, the thickness is 220nm, and the refractive index is 3.4744; the lower cladding material is SiO₂A thickness of 2 μm and a refractive index of 1.4404; the upper cladding material is SiO₂The thickness is 1.2 μm, and the design and simulation are carried out on a CWDM4 device in an O-band communication wave band, wherein N is 4.

An adiabatic evolution coupling structure is employed for the mode demultiplexer (front/rear mode demultiplexer including respective bidirectional grating filters).

For four multimode waveguide gratings, parameters are selected such that the total width of the grating is 850nm, the depth of grating teeth is 170nm, the number of grating cycles is 200, the number of cycles of a front/back gradient grating is 20, the duty ratio of the grating is 0.5, and the periods of the four multimode waveguide gratings are 250nm, 256nm, 262nm and 268nm respectively. The four multimode waveguide gratings adopt a phase apodization scheme, and the apodization mode is that the axial traversing is in Gaussian distribution apodization.

Four multimode waveguide gratings of the device are subjected to simulation verification through a three-dimensional finite difference time domain algorithm. Fig. 5 is a simulation result of the first, second, third, and fourth multimode waveguide gratings, and it can be seen that the device of the present invention has a 1dB bandwidth of 16.5nm in the 1271nm, 1291nm, 1311nm, and 1331nm channels, four channels have flat-top response, insertion loss is less than 0.15dB, and crosstalk in each channel is less than-20 dB. Therefore, the device of the invention can obtain a wavelength division demultiplexer with low insertion loss, low crosstalk and flat-top response, and the connection detector can form a multi-channel wavelength division multiplexing receiver.

The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.