CN113985521B - Silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip - Google Patents

Abstract

A silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip comprises an input coupler, a polarization rotation beam splitter, a wavelength selective optical switch array, a waveguide interlayer coupler, a polarization rotation beam combiner and an output coupler. By utilizing silicon-silicon nitride three-dimensional integration, the silicon nitride micro-ring optical switch with large process tolerance and simple and convenient control, the waveguide cross junction with low loss and low crosstalk and the waveguide interlayer coupler with high efficiency are realized. Micro heaters are integrated on the silicon nitride micro ring to tune the resonant wavelength to match with the wavelength channel of the input optical signal, and wavelength selective routing is supported. By utilizing the polarization rotation beam splitter and beam combiner, polarization-independent operation can be realized only by using a single optical switch array, external polarization control is not needed, the problem that the existing silicon optical chip is sensitive to polarization is solved, and polarization multiplexing signals can be compatible. The chip supports wavelength granularity and routing of polarization multiplexing optical signals among any ports, and has the advantages of compact structure, simplicity and convenience in control and the like.

Description

Silicon-silicon nitride three-dimensional integrated polarization-independent wavelength-selective optical switch array chip

technical field

The invention relates to the technical field of optical communication, in particular to a silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selection optical switch array chip.

Background technique

Since the 1990s, with the rapid development of Internet technology, users' demand for Internet traffic has been increasing, and with it, there has been an urgent growing demand for optical fiber communication capacity. Switches are used to interconnect servers in data centers and various end devices in global fiber-optic communication networks. Most of the existing optical networks still use electrical switching technology at the data switching nodes. Due to the limitation of "electronic bottleneck", the transmission rate and capacity cannot meet the development needs. Optical switching with a large number of ports and low power consumption has become the focus of research in this field. .

The development of wavelength division multiplexing (WDM) technology provides an effective solution for network expansion, which can simultaneously transmit information through two or more optical wavelength signals through their respective channels in the same optical fiber. The wavelength selective optical switch (abbreviated as WSS) can independently switch each wavelength in the multi-wavelength optical signal, and supports the assignment of any wavelength channel to any path, which can reduce the consumption of optical fibers. WSS based on liquid crystal-on-silicon (LCoS) technology has been widely studied and commercialized, and the optical signals of different wavelengths are separated in free space by liquid crystal and diffraction grating. Although LCoS-based WSS can achieve higher-dimensional wavelength switching, the device size is still large. By integrating on a chip, the device structure can be made compact, and silicon-based optoelectronics can be mass-produced with the help of mature microelectronics processing technology, with the advantages of high integration, low cost, and high reliability. The most commonly reported WSS on a silicon-based platform is based on the structure of a microring resonator. Using the wavelength selective properties of the microring, the transmitted optical signal can be switched by adjusting the resonant wavelength of the microring. However, due to the small size of the microring formed by the silicon-on-insulator waveguide, it is easily affected by process errors and is sensitive to temperature, which is not suitable for practical applications. In addition, the commonly used silicon waveguides on silicon-based integrated platforms are 500 nm × 220 nm in size, and the unequal width and height of the waveguides make them sensitive to polarization, requiring additional polarization control devices to adjust the polarization state.

SUMMARY OF THE INVENTION

In view of the practical application requirements of the above-mentioned large-scale optical switch chips and the defects existing in the existing optical switch implementations, the present invention proposes a silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip. The chip has the advantages of simple structure, large process tolerance and strong expansibility. More importantly, the present invention takes advantage of the three-dimensional integration of silicon-silicon nitride to greatly reduce the performance deterioration caused by the crossover of the waveguides, and at the same time constructs a polarization-independent wavelength selective optical switch system, which can be used for ultra-large-capacity optical switches in the future. important role in the communication system.

For achieving the above object, the technical solution of the present invention is as follows:

A silicon-silicon nitride three-dimensional integrated polarization-independent wavelength-selective optical switch array chip is characterized in that it includes N-channel optical input couplers, N-channel polarization rotation beam splitters, N×N×M wavelength-selective optical switch arrays, N channels polarization rotation beam combiner and N optical output couplers, each input optical signal includes M wavelengths, and the N×N×M wavelength selective optical switch array includes symmetrically distributed 2N input ports and symmetrically distributed 2N where N is a positive integer greater than 2, representing the number of input and output optical waveguides, respectively, and M is a positive integer greater than 2, representing the number of optical channels of different wavelengths transmitted;

The i-th input single-mode fiber is connected to the input end of the i-th optical input coupler, and the output end of the optical input coupler is connected to the input end of the i-th polarization rotation beam splitter. The polarization rotation beam splitter The two output ends of the device are respectively connected with the two input ports of the i-th pair of the N×N×M wavelength selective optical switch array, and the N×N×M wavelength selective optical switch array (103) The two output ends of the i-th pair are respectively connected to the two input ends of the i-th polarization rotation beam combiner, and the output end of the polarization-rotation beam combiner (105) is connected to the input of the i-th optical output coupler (106). end connection, the output end of the optical output coupler (106) is connected to the i-th single-mode fiber, i=1, 2, ..., N;

Each polarization rotation beam splitter (102) divides each optical signal into two beams of orthogonal polarization, and the polarization state of one of the beams is rotated by 90 degrees, so that in 2 beams of each polarization rotation beam splitter (102) The optical signals of the two output terminals have the same polarization, and the N×N×M wavelength selective optical switch array (103) arbitrarily routes the optical signals of any wavelength input from each pair of input terminals to different output terminals for output; so The N-way polarization rotating beam combiner (105) re-converts 2N beams of optical signals of the same polarization state into orthogonal polarization states, and combines them to output N-way, and finally outputs them to the output single-mode fiber for emission.

The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip is realized on the SOI wafer by silicon-silicon nitride three-dimensional integrated waveguides, including three layers of waveguides, which are the bottom layer silicon waveguide and the middle layer silicon nitride respectively. The waveguide and the top layer silicon nitride waveguide are separated by silicon oxide. The spacing between the silicon waveguide and the top layer silicon nitride waveguide is greater than 0.8 μm in the height direction. The pitch of the silicon waveguides in the height direction is all less than 0.5 μm. The N×N×M wavelength selective optical switch array arbitrarily routes optical signals of arbitrary wavelengths input from the input ends of each pair of bottom silicon waveguides to different output ends of the top silicon nitride waveguides for output, and passes between the layers of the waveguides. The coupler converts the optical signal in the top layer silicon nitride waveguide to the bottom layer silicon waveguide for transmission to the polarization rotating beam combiner.

In the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip, each input optical signal contains M wavelengths; at the polarization rotation beam splitter, each optical signal is divided into orthogonal polarizations. 2 beams of light, and the polarization state of one beam is rotated by 90 degrees, so that the optical signals at the two output ends of the polarization rotation beam splitter have the same polarization; the N×N×M wavelength selective optical switch array The optical signals of ×M wavelengths provide dynamic routing; the 2N-way waveguide interlayer coupler assists the transmission of optical signals between the silicon-silicon nitride three-dimensional waveguide layers; the N-way polarization rotation beam combiner can combine 2N The optical signals of the same polarization state are re-converted into orthogonal polarization states and combined and output into N channels, and finally output to the single-mode fiber for emission.

The N-way optical input coupler and N-way optical output coupler respectively include N optical input couplers and N optical output couplers, and the structure adopts a two-dimensional grating coupler or an inverted tapered mode spot converter, so as to The multi-wavelength optical signal containing random polarization states is coupled into/out of the optical chip from a single-mode fiber by means of vertical or horizontal coupling.

The N-way polarization rotation beam splitter and the N-way polarization rotation beam splitter both include N polarization rotation beam splitters, and when used as a polarization rotation beam combiner, only the input of the polarization rotation beam splitter needs to be connected. , the output port can be replaced; the polarization rotation beam splitter can be realized by adopting a graded ridge waveguide combined with an asymmetric directional coupler structure.

The 2N-way waveguide interlayer coupler is composed of 2N three-dimensional waveguide interlayer couplers, including a silicon nitride-silicon nitride interlayer coupler composed of a top layer silicon nitride waveguide and an intermediate layer silicon nitride waveguide, There is also a silicon nitride-silicon interlayer coupler composed of an intermediate layer silicon nitride waveguide and a bottom layer silicon waveguide, and the two interlayer couplers are connected through the intermediate layer silicon nitride waveguide. Between any two adjacent waveguide layers, two tapered waveguide structures with opposite directions are used to complete the mode field coupling, so as to realize the transmission of optical signals between the three-layer waveguides.

The N×N×M wavelength selective optical switch array is formed by connecting N×N 2×2 wavelength selective optical switch units according to a cross-bar topology.

The 2×2 wavelength selective optical switch unit adopts a silicon-silicon nitride three-dimensional integrated micro-ring structure, including a bottom layer silicon waveguide, a top layer silicon nitride waveguide and M groups of Q-level series silicon nitride micro-rings ( M≥2, Q≥2), the two ends of the bottom silicon waveguide are the input end (west) and the straight end (east), respectively, and the two ends of the top layer silicon nitride waveguide are the cross end (north) and the upload end (south). The silicon waveguide and the silicon nitride waveguide on the top layer are used to form a three-dimensional waveguide crossing junction to suppress the loss and crosstalk caused by the crossing of the waveguides; the intermediate layer silicon nitride waveguide is used to form a cascaded micro-ring, which passes through the silicon waveguide and the silicon nitride waveguide on the top layer respectively. The vertical coupling constitutes a three-dimensional integrated cascaded microring resonator.

M groups of Q-stage series-connected silicon nitride micro-rings (M ≥ 2, Q ≥ 2) in the cascaded micro-rings of the 2×2 wavelength selective optical switch unit, each group of cascaded micro-rings C _m (m =1～M) contains Q silicon nitride microrings with the same structure connected in series; the coupling coefficients between the Q series silicon nitride microrings and with the bottom silicon waveguide and the top silicon nitride waveguide can be obtained through Design the waveguide spacing and the length of the waveguide in the coupling area to increase the working bandwidth of the device. The number of groups M of the cascaded microrings corresponds to the number of channels that can realize wavelength routing. In each group of cascaded microrings _Cm , all The resonant wavelengths of the Q silicon nitride microrings are all the same; a micro heater is integrated on each silicon nitride microring of the cascaded microrings, which can adjust the resonant wavelength of the silicon nitride microring. It is realized by fabricating titanium nitride metal thermal resistance above the silicon nitride microring or directly doping the silicon waveguide under the silicon nitride microring into the same microring structure, and placing the microheater structure as close as possible to the cascaded microrings to reduce The thermal phase shifting power consumption can also be etched on the cladding silicon oxide and the bottom silicon substrate to form air grooves, which further improves the thermal phase shifting efficiency.

For the 2×2 wavelength selective optical switch unit, the resonant wavelengths of all silicon nitride microrings in the initial state are the same, which is λ ₀ , which is different from the input wavelength (λ ₁ ~λ _M ). The optical signal input from the straight-through end) _is directly output from the _straight -through end (input end); The resonant wavelength shift of the ring is the same as that of one of the input wavelengths λ _n . At this time, the optical signal with wavelength λ _n input from the input end (through end) is output from the cross end (download end), and the input light of other wavelengths remains Output from the straight-through end (input end); by applying different voltage and electrical adjustments to the micro-heaters on different groups of cascaded micro-rings, so that the resonant wavelengths are aligned with the corresponding input wavelengths, so as to select the light at the 2×2 wavelength. The switch unit realizes that all input wavelengths can be arbitrarily routed from the input end (straight-through end) to the output of the crossover end and the straight-through end (upload end and input end) to realize wavelength dynamic routing.

The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip red-shifts its resonance wavelength to the corresponding value by applying power to the micro-heaters on the m-th group of series-connected micro-rings in the p-th row and the q-th column. The wavelength λm channel ( _p≤N , q≤N, _m≤M ) can route the optical signal with wavelength λm input from the p input port to the q output port; Can handle arbitrary routing of wavelength granularity optical signals.

Compared with the prior art, the advantages of the present invention are embodied in the following aspects:

1. The polarization-independent wavelength selective optical switch array chip of the silicon-silicon nitride three-dimensional integration of the present invention is realized by relying on the silicon-silicon nitride three-dimensional integration platform, and has the advantages of simple device structure, high integration degree, manufacturing process compatible with CMOS process, and large number of ports. , low loss, low crosstalk, low power consumption, low cost advantages.

2. The present invention uses the silicon nitride microring as the basic unit of the optical switch, which has high process tolerance, does not require additional power consumption to calibrate the resonant wavelength of the microring, and reduces the control complexity of the optical switch system.

3. The optical switch array chip of the present invention supports the transmission and exchange of multi-wavelength optical signals, and has the characteristics of transmitting two beams of optical signals at the same time, and can use polarization multiplexing and wavelength multiplexing to increase the optical signal capacity in two dimensions. The development of capacity optical communication has practical significance.

Description of drawings

1 is a general structural diagram of an array chip of the present invention based on a silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch;

FIG. 2 is a structural diagram of a 2×2 wavelength selective optical switch unit of the present invention and its working principle;

FIG. 3 is a schematic diagram of an embodiment of a 4×4×2 polarization-independent wavelength selective optical switch array chip according to the present invention;

4 is a schematic diagram of a cross-sectional structure of a phase shifter of the present invention;

FIG. 5 is a schematic structural diagram of an embodiment of the waveguide interlayer coupler of the present invention;

FIG. 6 is a schematic diagram of several representative working states of a 4×4×2 wavelength selective optical switch array according to an embodiment of the present invention.

Detailed ways

In order to further illustrate the core technical solutions and application objectives of the present invention, the following descriptions are made in conjunction with the accompanying drawings and embodiments. However, it should be noted that the scope of the present invention is not limited to the embodiments mentioned here.

As shown in FIG. 1 , the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of the present invention includes N channels of optical input couplers 101, N channels of polarization rotation beam splitters 102, and N×N×M wavelength selective light beams. Switch arrays 103 , 2N channels of waveguide interlayer couplers 104 , N channels of polarization rotation beam combiners 105 and N channels of optical output couplers 106 . The input end of the N-way optical input coupler 101 is connected to the input N-way single-mode fiber, and the input end of the N-way polarization rotation beam splitter 102 is respectively connected with the N-way optical input coupler 101. The output end is connected; the N×N×M wavelength selective optical switch array 103 includes 2N input ports and 2N output ports, and the 2N input ports are distributed on the east and west sides, which are respectively connected with the N channels. The 2N output ends of the polarization rotation beam splitter 102 are connected, and the 2N output ports are distributed on the north and south sides, and are respectively connected with the input ends of the 2N channels of the waveguide interlayer coupler 104; the N channels of polarization rotation beam combining The 2N input ends of the 2N way of the waveguide interlayer coupler 104 are respectively connected with the output ends of the 2N way of the waveguide interlayer coupler 104; The input end is connected, and the output end of the N-way optical output coupler 106 is connected with the N-way single-mode fiber;

The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array 103 is realized by silicon-silicon nitride three-dimensional integrated waveguides on SOI wafers, see FIG. 2 , including three layers of waveguides, which are the bottom silicon waveguides 201 , the middle layer silicon nitride waveguide 202 and the top layer silicon nitride waveguide 203, the waveguides are isolated by silicon oxide, and the distance between the bottom layer silicon waveguide 201 and the top layer silicon nitride waveguide 203 in the height direction is greater than 0.8 μm, and the distances between the silicon nitride waveguide 202 in the middle layer and the bottom layer silicon waveguide 201 and the top layer silicon nitride waveguide 203 in the height direction are all less than 0.5 μm.

Each input optical signal contains M wavelengths; the polarization rotation beam splitter 102 divides each optical signal into 2 beams of orthogonal polarization, and the polarization state of one beam is rotated by 90 degrees, so that in the The optical signals at the two output ends of the polarization-rotating beam splitter 102 have the same polarization; the N×N×M wavelength selective optical switch array 103 provides dynamic routing for the 2N×M wavelength optical signals; the The 2N-way waveguide interlayer coupler 104 assists the transmission of optical signals between the silicon-silicon nitride three-dimensional waveguide layers; the N-way polarization rotary beam combiner 105 reconverts the 2N optical signals of the same polarization state into orthogonal polarizations state and combined output into N channels, and finally output through the output end of the N channels of optical output coupler 106 and transmit through the N channels of single-mode fibers O at the output end.

Example:

FIG. 3 shows an embodiment of the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of the present invention, that is, a 4×4×2 (N=4, M=2) polarization-independent wavelength selective optical switch array chip. This embodiment is implemented using a silicon-silicon nitride three-dimensional integrated waveguide, which includes three layers of waveguides: a bottom layer silicon waveguide 201 , a middle layer silicon nitride waveguide 202 and a top layer silicon nitride waveguide 203 thereon. The distance between the silicon waveguide 201 and the top layer silicon nitride waveguide 203 is greater than 0.8 μm in the height direction, which ensures that the three-dimensional waveguide cross junction has a low loss (less than 0.01dB). The distance between the bottom layer silicon waveguide 201 and the top layer silicon nitride waveguide 203 in the height direction is both less than 0.5 μm, which ensures that the coupling and transmission loss of the optical signal between the three-layer waveguides is small (less than 0.1 dB).

In this embodiment, the four optical input couplers 101 and the four optical output couplers 106 are horizontal structures, and two-wavelength optical signals including orthogonal polarization states are coupled into/out of the optical chip by means of end-face coupling; The 8 polarization rotation beam splitters 102 or 106 adopt the structure of a graded ridge waveguide combined with an asymmetric directional coupler. The input and output of the four polarization rotation beam splitters are placed in opposite directions to form four polarization rotation beam splitters 105, which re-convert the signals with the same polarization state into orthogonal polarization states and combine them; 4×4×2 wavelength selective optical switches The array 103 includes 16 2×2 wavelength selective optical switch units, and the optical switch units are connected through a cross-bar topology. Each optical switch unit includes two sets of silicon nitride double microrings (Q=2), which can simultaneously Transmitting optical signals from two WDM channels, each silicon nitride microring integrates a microheater for thermal phase shifting.

FIG. 4 is a schematic cross-sectional view of the structure of the thermal phase shifter in this embodiment. There are two ways to achieve thermal phase shift for the silicon nitride microring: making a metal thermal resistance above the silicon nitride microring (Fig. 4(a)) or directly doping the silicon waveguide below the silicon nitride microring The same microring structure (Fig. 4(b)) is used to achieve low-power thermal phase shifting. In this embodiment, the silicon dioxide cladding near the phase shifter and the silicon substrate at the bottom are etched to form air grooves to concentrate the heat in the phase shifter area and prevent it from spreading to the surroundings and the substrate , which can further improve the thermal phase shifting efficiency.

5 shows the structure of the waveguide interlayer coupler 104 in this embodiment, including a silicon nitride-silicon nitride interlayer coupler D composed of a top layer silicon nitride waveguide 203 and an intermediate layer silicon nitride waveguide 202 and a silicon nitride interlayer coupler D composed of The silicon nitride-silicon interlayer coupler E constituted by the middle layer silicon nitride waveguide 202 and the bottom layer silicon waveguide 201 . Between any two adjacent waveguide layers, two tapered waveguide structures with opposite directions are used to complete the mode field coupling, so as to realize the transmission of optical signals between the three-layer waveguides 201 , 202 and 203 .

In the 4×4×2 polarization-independent wavelength selective optical switch array chip of this embodiment, the resonant wavelength of the m-th group of micro-rings in the p-th row and the q-th column is red-shifted to the corresponding wavelength λ _m channel ( When p≤4, q≤4, m≤2), the optical signal with a wavelength of λ _m input from the p input port can be routed to the q output port; by powering up multiple groups of serial microrings, the wavelength granularity optical signal can be processed any route. Figure 6 shows a schematic diagram of several representative working states of a 4×4×2 wavelength selective optical switch array.

Taking the state of FIG. 6(3) as an example, the working process of the silicon-silicon nitride polarization-independent wavelength selective optical switch array chip of the present invention will be described in detail as follows.

In the 4×4×2 polarization-independent wavelength selective optical switch array chip of FIG. 3 , a two-wavelength optical signal (TE+TM, λ ₁ λ ₂ ) containing random polarization states passes through the I ₁ coupler 1001 from the single-mode fiber After being coupled into the optical chip, after passing through the polarization rotating beam splitter 1021, it is divided into two optical signals of the same polarization, which are the original TE→TE polarization state optical signal and the TM→TE polarization state optical signal respectively. The TE→TE polarization state optical signal is transmitted to the west 1 port of the 4×4×2 wavelength selective optical switch array, and the TM→TE polarization state optical signal is transmitted to the east 1' port of the 4×4×2 wavelength selective optical switch array. When no power is applied, the resonance wavelength of the series-connected silicon nitride microrings is inconsistent with the two wavelength channels λ ₁ and λ ₂ of the input optical signal. The first group of series-connected silicon nitride microrings in the first row and the second column in the 4×4×2 wavelength selective optical switch array are thermally tuned to red-shift the resonance wavelength to λ ₁ . The second group of serial silicon nitride microrings in the column is heated and adjusted to red-shift its resonance wavelength to λ ₂ . At this time, the optical signals λ ₁ and λ ₂ input from the west 1 port are routed to the north 2 and north 1 waveguides respectively, and the east The optical signals λ ₁ and λ ₂ input to the 1' port are routed counterclockwise to the south 2' and south 1' ports, respectively. The optical signals of the above four output ports are respectively transmitted from the top layer silicon nitride waveguide to the silicon waveguide through the waveguide interlayer coupler, wherein the optical signals λ2 of the north ₁ and south 1' ports are combined and combined by the polarization rotation beam combiner 10501. Output from the O ₁ coupler 10601, the optical signals λ ₁ of the North 2 and South 2' ports are combined by the polarization rotation beam combiner 10502 and output from the O ₂ coupler 10602. In summary, the orthogonal polarization state dual-wavelength optical signals input by I ₁ are routed to the two output terminals of O ₁ and O ₂ , respectively. Similarly, the optical signals input by other ports are transmitted between the input-output ports in the same way.

The specific embodiments of the present invention are not limited to the above-mentioned embodiments, and are easily understood by other persons in the technical field. The foregoing embodiments have clearly described the present invention, but the technical solutions described can still be modified, or some technical features thereof can be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. A silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip is characterized by comprising N paths of optical input couplers (101), N paths of polarization rotating beam splitters (102), N multiplied by M wavelength selective optical switch arrays (103), N paths of polarization rotating beam combiners (105) and N paths of optical output couplers (106), wherein each path of input optical signals comprises M wavelengths, each N multiplied by M wavelength selective optical switch array (103) comprises 2N input ports which are symmetrically distributed and 2N output ports which are symmetrically distributed, N is a positive integer more than 2 and respectively represents the number of input and output optical waveguides, and M is a positive integer more than 2 and represents the number of transmitted optical channels with different wavelengths;

the i-th input single-mode fiber is connected with the input end of an i-th optical input coupler (101), the output end of the optical input coupler (101) is connected with the input end of the i-th polarization rotation beam splitter (102), 2 output ends of the polarization rotation beam splitter (102) are respectively connected with 2 input ports of the i-th pair of the N × N × M wavelength selection optical switch array (103), 2 output ends of the i-th pair of the N × N × M wavelength selection optical switch array (103) are respectively connected with 2 input ends of an i-th polarization rotation beam combiner (105), the output end of the polarization rotation beam combiner (105) is connected with the input end of an i-th optical output coupler (106), the output end of the optical output coupler (106) is connected with the i-th single-mode fiber, and i is 1, 2, … …, N;

each path of polarization rotation beam splitter (102) splits each path of optical signal into two beams of orthogonally polarized light, and the polarization state of one beam of polarization rotation beam splitter is rotated by 90 degrees, so that the optical signals at the 2 output ends of each path of polarization rotation beam splitter (102) have the same polarization, the N multiplied by M wavelength selective optical switch array (103) routes the optical signals with any wavelength input from each pair of input ends to different output ends for output, and the N paths of polarization rotation beam combiner (105) converts the 2N beams of optical signals with the same polarization state into orthogonal polarization states again and combines the orthogonal polarization states and outputs the orthogonal polarization states as N paths, and finally outputs the orthogonal polarization state optical signals to output single-mode optical fibers for emission;

the waveguide structure comprises three layers of waveguides, namely a bottom layer silicon waveguide (201), a middle layer silicon nitride waveguide (202) and a top layer silicon nitride waveguide (203), wherein all the waveguides are isolated by silicon oxide;

the NxNxM wavelength selective optical switch array (103) routes optical signals with any wavelength input from the input end of each pair of bottom silicon waveguides (201) to different output ends of the top silicon nitride waveguides (203) for output, converts the optical signals in the top silicon nitride waveguides (203) to the bottom silicon waveguides (201) through the waveguide interlayer coupler (104), and transmits the optical signals to the polarization rotation beam combiner (105);

the NxNxM wavelength selective optical switch array (103) consists of N ² The 2 multiplied by 2 wavelength selective optical switch units (A) are connected according to a horizontal and vertical crossed topological structure, each 2 multiplied by 2 wavelength selective optical switch unit (A) adopts a silicon-silicon nitride three-dimensional integrated micro-ring structure and comprises a bottom layer silicon waveguide (201), a top layer silicon nitride waveguide (203) and M groups of Q-level series silicon nitride micro-rings (M is more than or equal to 2, and Q is more than or equal to 2); two ends of the bottom layer silicon waveguide (201) are respectively used as an input end and a through end, two ends of the top layer silicon nitride waveguide (203) are respectively used as a cross end and an uploading end, the bottom layer silicon waveguide (201) and the top layer silicon nitride waveguide (203) form a three-dimensional waveguide cross junction (B) for inhibiting loss and crosstalk caused by waveguide cross, the middle layer silicon nitride waveguide (202) forms a cascade micro-ring (C), and the three-dimensional integrated cascade micro-ring resonator is formed by vertical coupling with the bottom layer silicon waveguide (201) and the top layer silicon nitride waveguide (203).

2. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 1, wherein M groups of Q-level serial silicon nitride micro-rings (M ≧ 2, Q ≧ 2) in the cascaded micro-rings (C) of the 2 x 2 wavelength selective optical switch unit (A), each group of the cascaded micro-rings C _m (M-1 to M) comprises Q-stage silicon nitride microrings connected in series; coupling coefficients among the Q series silicon nitride micro-rings, the bottom layer silicon waveguide (201) and the top layer silicon nitride waveguide (203) can be changed by designing the waveguide spacing and the coupling region waveguide length so as to increase the working bandwidth of the device; the number M of the cascade micro-ring (C) corresponds to the number of channels capable of realizing wavelength routing, and each group of cascade micro-ring C _m The resonance wavelengths of all Q silicon nitride micro-rings are the same; the micro-heater (D) is integrated on each silicon nitride micro-ring of the cascade micro-ring (C) and can adjust the resonance wavelength of the silicon nitride micro-ring, the micro-heater (D) is realized by manufacturing a titanium nitride metal thermal resistor above the silicon nitride micro-ring or directly doping a silicon waveguide below the silicon nitride micro-ring into the same micro-ring structure, the micro-heater structure is close to the cascade micro-ring as much as possible to reduce the thermal phase-shift power consumption, and the micro-heater structure can also be used for reducing the thermal phase-shift power consumption of the silicon nitride micro-ringThe cladding silicon oxide and the silicon substrate at the bottom are etched to form an air groove, so that the thermal phase-shifting efficiency is further improved.

3. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 1, wherein the 2 x 2 wavelength selective optical switch cells (a) have the same resonance wavelength λ of all silicon nitride micro-rings in the initial state ₀ With the input wavelength (λ) ₁ ～λ _M ) All are different, and the optical signal input from the input end (through end) is directly output from the through end (input end); by cascading micro-rings C to one of the groups _n The micro-heater on (n 1-M) is energized, C can be added _n Shift of resonance wavelength of middle micro-ring and certain input wavelength lambda _n The same holds true for the wavelength λ input from the input end (through end) _n The optical signal of (2) is outputted from the cross terminal (download terminal), and the input light of other wavelengths is still outputted from the through terminal (input terminal); by applying different voltage and electricity to the micro-heaters on different groups of cascaded micro-rings to align the resonance wavelengths with the corresponding input wavelengths, all the input wavelengths can be randomly routed from the input end (through end) to the cross end and the through end (upload end and input end) to be output in the 2 x 2 wavelength selective optical switch unit (A), and the wavelength dynamic routing is realized.

4. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of claim 3, wherein the dynamic routing comprises energizing the micro-heaters on the m-th set of serial micro-rings of the p-th row and q-th column to shift the resonant wavelength thereof to the corresponding wavelength λ _m When the channel (p is less than or equal to N, q is less than or equal to N, and M is less than or equal to M), the wavelength input from the p input port is lambda _m May be routed to the q output ports; by energizing any set of microheaters in series with the microring, any routing of wavelength-granular optical signals can be handled.

5. The SONOS three-dimensional integrated polarization-independent wavelength-selective optical switch array chip of claim 1, wherein the waveguide interlayer coupler (104) is a three-dimensional waveguide interlayer coupler comprising a first SONOS interlayer coupler (D) formed by a top layer SONOS waveguide (203) and a first middle layer SONOS waveguide (202-1), and a second SONOS interlayer coupler (E) formed by a second middle layer SONOS waveguide (202-2) and a bottom layer SONOS waveguide (201), the first SONOS interlayer coupler (D) and the second SONOS interlayer coupler (E) being connected by a third middle layer SONOS waveguide (202-3), the first middle layer SONOS waveguide (202-1), The second middle layer silicon nitride waveguide (202-2) and the third middle layer silicon nitride waveguide (202-3) are integrated to form a middle layer silicon nitride waveguide (202) with the width gradually changed from small to large; and mode field coupling is completed by two tapered waveguides in opposite directions between any two adjacent waveguide layers, so that optical signals are transmitted among three layers of waveguides, namely the bottom layer silicon waveguide (201), the middle layer silicon nitride waveguide (202) and the top layer silicon nitride waveguide (203).

6. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 1 or 5, wherein the distance between the bottom silicon waveguide (201) and the top silicon nitride waveguide (203) in the height direction is larger than 0.8 μm, and the distance between the silicon nitride waveguide (202) in the middle layer and the distance between the bottom silicon waveguide (201) and the top silicon nitride waveguide (203) in the height direction are smaller than 0.5 μm.

7. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to any one of claims 1 to 5, wherein the optical input coupler (101) and the optical output coupler (106) both comprise N optical couplers, and a two-dimensional grating coupler or an inverted cone-shaped spot-size converter is adopted to couple a multi-wavelength optical signal containing random polarization states from a single-mode optical fiber to an input/output optical chip in a vertical or horizontal coupling manner.

8. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to any one of claims 1 to 5, wherein the N-way polarization rotation beam splitter (102) and the N-way polarization rotation beam combiner (105) are a pair of couplers with opposite structures, and are realized by combining a gradient ridge waveguide with an asymmetric directional coupler.

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