CN113985521A - Silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip - Google Patents
Silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
- G02B6/3554—3D constellations, i.e. with switching elements and switched beams located in a volume
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
- G02B6/3554—3D constellations, i.e. with switching elements and switched beams located in a volume
- G02B6/3556—NxM switch, i.e. regular arrays of switches elements of matrix type constellation
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12145—Switch
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
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 selective optical switch array chip.
Background
With the rapid development of internet technology since the 90 s of the 20 th century, the demand of users for internet traffic has been increasing, and along with this, there has been an urgent growing demand for optical fiber communication capacity. Switches are used to interconnect servers of data centers and various end devices in a global fiber optic communications network. Most of the existing optical networks still adopt an electrical switching technology at a data switching node, and are limited by an electronic bottleneck, so that the transmission rate and the capacity cannot meet the development requirements, and the optical switching with large port number and low power consumption becomes the research focus in the field.
The development of Wavelength Division Multiplexing (WDM) technology provides an effective solution for network expansion, which can simultaneously transmit information through respective channels by more than two optical wavelength signals in the same optical fiber. The wavelength selective optical switch (WSS for short) can independently exchange each wavelength in the multi-wavelength optical signal, supports the allocation of any wavelength channel to any path, and can reduce the use amount of optical fibers. WSS based on liquid crystal on silicon (LCoS) technology has been widely researched and commercialized to separate optical signals of different wavelengths in free space through liquid crystals and diffraction gratings. Although LCoS-based WSS can achieve higher-dimensional wavelength switching, the device size is still large. The device structure can be compact by integrating on a chip, the silicon-based photoelectrons can realize large-scale production by means of mature microelectronic processing technology, and the silicon-based photoelectrons have the advantages of high integration level, low cost, high reliability and the like. The most common WSS reported on a silicon-based platform at present is based on the structure of a micro-ring resonator, and the switching of a transmitted optical signal can be performed by adjusting the resonant wavelength of the micro-ring by using the wavelength selection characteristic of the micro-ring. However, the micro-ring formed by the silicon-on-insulator waveguide has a small size, is easily affected by process errors, is sensitive to temperature, and is not suitable for practical application. In addition, the silicon waveguide commonly used on the silicon-based integrated platform has a size of 500nm × 220nm, and the width and height of the waveguide are unequal, so that the waveguide is sensitive to polarization, and an additional polarization control device is required to adjust the polarization state.
Disclosure of Invention
Aiming at the practical application requirements of the large-scale optical switch chip and the defects of the existing optical switch implementation scheme, the invention provides 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 expandability. More importantly, the invention utilizes the advantages of silicon-silicon nitride three-dimensional integration to greatly reduce the performance deterioration caused by waveguide crossing, and simultaneously constructs and forms a wavelength selection optical switch system irrelevant to polarization, thereby playing an important role in a future ultra-large capacity optical communication system.
In order to achieve 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 by comprising N paths of optical input couplers, N paths of polarization rotation beam splitters, N multiplied by N M wavelength selective optical switch arrays, N paths of polarization rotation beam combiners and N paths of optical output couplers, wherein each path of input optical signal comprises M wavelengths, each N multiplied by N M wavelength selective optical switch array comprises 2N symmetrically distributed input ports and 2N symmetrically distributed output ports, 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 ith input single-mode fiber is connected with the input end of an ith optical input coupler, the output end of the optical input coupler is connected with the input end of the ith polarization rotation beam splitter, 2 output ends of the polarization rotation beam splitter are respectively connected with 2 input ports of an ith pair of the NxNxM wavelength selective optical switch array, 2 output ends of an ith pair of the NxNxM wavelength selective optical switch array (103) are respectively connected with 2 input ends of an ith polarization rotation beam combiner, the output end of the polarization rotation beam combiner (105) is connected with the input end of an ith optical output coupler (106), the output end of the optical output coupler (106) is connected with the ith single-mode fiber, and i is 1, 2, … … and 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 2 output ends of each path of polarization rotation beam splitter (102) have the same polarization, and the NxNxM 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; the N-path polarization rotation beam combiner (105) converts the 2N beams of optical signals with the same polarization state into orthogonal polarization states again, combines the orthogonal polarization states and outputs the N paths of optical signals into N paths of optical signals, and finally outputs the N paths of optical signals to the output single-mode optical fiber for emission.
The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip is realized on an SOI wafer through a silicon-silicon nitride three-dimensional integrated waveguide, and comprises three layers of waveguides, namely a bottom layer silicon waveguide, a middle layer silicon nitride waveguide and a top layer silicon nitride waveguide, wherein the waveguides are isolated by silicon oxide, the distance between the silicon waveguide and the top layer silicon nitride waveguide in the height direction is more than 0.8 mu m, and the distance between the silicon nitride waveguide in the middle layer and the distance between the silicon waveguide in the bottom layer and the silicon waveguide in the top layer are less than 0.5 mu m in the height direction. The NxNxM wavelength selective optical switch array randomly routes optical signals with any wavelength input from the input end of each pair of bottom silicon waveguides to different output ends of the top silicon nitride waveguides for output, converts the optical signals in the top silicon nitride waveguides to the bottom silicon waveguides through the waveguide interlayer coupler, and transmits the optical signals to the polarization rotation beam combiner.
In the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip, each path of input optical signal comprises M wavelengths; splitting each optical signal into 2 orthogonally polarized beams at said polarization rotating beam splitter and wherein one of the beams has its polarization state rotated by 90 degrees so that the optical signals at the 2 outputs of the polarization rotating beam splitter have the same polarization; the NxNxM wavelength selective optical switch array provides dynamic routing for the 2 NxM wavelength optical signals; the 2N-path waveguide interlayer coupler assists optical signals to be transmitted between the silicon-silicon nitride three-dimensional waveguide layers; the N-path polarization rotation beam combiner can convert 2N beams of optical signals with the same polarization state into orthogonal polarization states again, combine the orthogonal polarization states and output the N-path polarization rotation beam combiner as N paths, and finally output the N paths of optical signals to a single-mode optical fiber for emission.
The N paths of optical input couplers and the N paths of optical output couplers respectively comprise N optical input couplers and N optical output couplers, and the structure adopts a two-dimensional grating coupler or an inverted cone-shaped spot-size converter to couple multi-wavelength optical signals containing random polarization states from a single-mode optical fiber to an input/output optical chip in a vertical or horizontal coupling mode.
The N paths of polarization rotation beam splitters and the N paths of polarization rotation beam combiners both comprise N polarization rotation beam splitters, wherein when the polarization rotation beam combiners are used, only the input ports and the output ports of the polarization rotation beam splitters are required to be replaced; the polarization rotation beam splitter can be realized by combining a gradual change ridge waveguide with an asymmetric directional coupler structure.
The 2N-path waveguide interlayer coupler is composed of 2N three-dimensional waveguide interlayer couplers, and comprises a silicon nitride-silicon nitride interlayer coupler composed of a top silicon nitride waveguide and a middle silicon nitride waveguide, and a silicon nitride-silicon interlayer coupler composed of a middle silicon nitride waveguide and a bottom silicon waveguide, wherein the two interlayer couplers are connected through the middle silicon nitride waveguide. And mode field coupling is completed between any two adjacent waveguide layers by using two tapered waveguide structures in opposite directions, so that optical signals are transmitted between the three layers of waveguides.
The N multiplied by M wavelength selective optical switch array is formed by connecting N multiplied by N2 multiplied by 2 wavelength selective optical switch units according to a cross-bar topological structure.
The 2 x 2 wavelength selective optical switch unit adopts a silicon-silicon nitride three-dimensional integrated micro-ring structure and comprises a bottom silicon waveguide, a top silicon nitride waveguide and M groups of Q-level series silicon nitride micro-rings (M is more than or equal to 2, Q is more than or equal to 2), wherein the two ends of the bottom silicon waveguide are respectively an input end (west) and a through end (east), and the two ends of the top silicon nitride waveguide are respectively a cross end (north) and an upload end (south). The silicon waveguide and the silicon nitride waveguide on the top layer form a three-dimensional waveguide cross junction, so that loss and crosstalk caused by waveguide cross are inhibited; and the silicon nitride waveguide at the middle layer forms a cascade micro-ring, and the cascade micro-ring is vertically coupled with the silicon waveguide and the silicon nitride waveguide at the top layer to form a three-dimensional integrated cascade micro-ring resonator.
M groups of Q-grade serial silicon nitride micro-rings (M is more than or equal to 2, Q is more than or equal to 2) in the cascade micro-rings of the 2 multiplied by 2 wavelength selective optical switch unit, and each group of cascade micro-rings Cm(M is 1 to M) comprises Q silicon nitride microrings of the same structure connected in series; coupling coefficients among the Q series-connected silicon nitride micro-rings and between the Q series-connected silicon nitride micro-rings and the bottom layer silicon waveguide and the top layer silicon nitride waveguide 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 groups of the cascade micro-rings corresponds to the number of channels capable of realizing wavelength routing, and each group of the cascade micro-rings CmThe resonance wavelengths of all Q silicon nitride micro-rings are the same; the micro-heater is integrated on each silicon nitride micro-ring of the cascade micro-ring, the resonance wavelength of the silicon nitride micro-ring can be adjusted, the micro-heater 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-shifting power consumption, and the silicon substrate at the bottom and the cladding silicon oxide can be etched to form an air groove, so that the thermal phase-shifting efficiency is further improved.
The 2 x 2 wavelength selective optical switch unit has the same resonance wavelength of all the silicon nitride micro-rings in the initial state, which is lambda0With the input wavelength (λ)1～λM) 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 groupsnThe micro-heater on (n 1-M) is energized, C can be addednShift of resonance wavelength of middle micro-ring and certain input wavelength lambdanThe same holds true for the wavelength λ input from the input end (through end)nThe 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 to the micro-heaters on different groups of cascade micro-rings to electrically tune, the resonant wavelengths are respectively aligned with the corresponding input wavelengths, so as to realize the purpose of adjusting the resonant wavelengths of the micro-heatersAll input wavelengths can be randomly routed from an input end (a through end) to a cross end and a through end (an uploading end and an input end) to be output in the 2 x 2 wavelength selection optical switch unit, and wavelength dynamic routing is realized.
The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip enables the resonant wavelength of the micro-heaters on the mth group of series micro-rings of the pth row and the qth column to be red-shifted to the corresponding wavelength lambda by electrifying the micro-heatersmThe channel (p is less than or equal to N, q is less than or equal to N, M is less than or equal to M) can input the wavelength of lambda from the p input portmTo q output ports; by powering up multiple sets of micro-rings in series, arbitrary routing of wavelength-granular optical signals can be handled.
Compared with the prior art, the invention has the advantages that:
1. the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip is realized by depending on a silicon-silicon nitride three-dimensional integrated platform, and has the advantages of simple device structure, high integration level, compatible manufacturing process and CMOS (complementary metal oxide semiconductor) process, large port number, low loss, low crosstalk, low power consumption and low cost.
2. The invention uses the silicon nitride micro-ring as the basic unit of the optical switch, has higher process tolerance, does not need extra power consumption to calibrate the resonance wavelength of the micro-ring, and reduces the control complexity of the optical switch system.
3. The optical switch array chip supports the transmission and exchange of multi-wavelength optical signals, has the characteristic of simultaneously transmitting two optical signals, can increase the capacity of the optical signals in two dimensions by utilizing polarization multiplexing and wavelength multiplexing, and has practical significance for the development of high-capacity optical communication.
Drawings
FIG. 1 is a general structure diagram of a silicon-silicon nitride-based three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to the present invention;
FIG. 2 is a schematic diagram of a 2 × 2 wavelength selective optical switch unit according to the present invention and its operation principle;
FIG. 3 is a schematic diagram of a 4 × 4 × 2 polarization independent wavelength selective optical switch array chip according to an embodiment of the present invention;
FIG. 4 is a schematic cross-sectional view of a phase shifter according to the present invention;
FIG. 5 is a schematic structural diagram of an embodiment of a waveguide interlayer coupler according to the present invention;
fig. 6 is a schematic diagram of several representative operating states of a 4 × 4 × 2 wavelength selective optical switch array according to an embodiment of the present invention.
Detailed Description
In order to further illustrate the core technical solution and the application object of the present invention, the following description is made with reference to the accompanying drawings and examples. It is to be noted, however, that the scope of the present invention is not limited to the embodiments mentioned herein.
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 an N-way optical input coupler 101, an N-way polarization rotation beam splitter 102, an N × M wavelength selective optical switch array 103, a 2N-way waveguide interlayer coupler 104, an N-way polarization rotation beam combiner 105, and an N-way optical output coupler 106. The input end of the N-path optical input coupler 101 is connected to the input N-path single-mode optical fiber, and the input end of the N-path polarization rotation beam splitter 102 is connected to the output end of the N-path optical input coupler 101; the nxnxnxm wavelength selective optical switch array 103 comprises 2N input ports and 2N output ports, wherein the 2N input ports are distributed on the east and west sides and are respectively connected with the 2N output ends of the N polarization rotation beam splitters 102, and the 2N output ports are distributed on the north and south sides and are respectively connected with the input ends of the 2N waveguide interlayer couplers 104; 2N input ends of the N-path polarization rotation beam combiner 105 are respectively connected with an output end of the 2N-path waveguide interlayer coupler 104; the output end of the N-path polarization rotation beam combiner 105 is connected with the input end of the N-path optical output coupler 106, and the output end of the N-path optical output coupler 106 is connected with the N-path single-mode optical fiber;
the silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array 103 is realized on an SOI wafer through a silicon-silicon nitride three-dimensional integrated waveguide, and referring to fig. 2, the silicon-silicon nitride three-dimensional integrated wavelength selective optical switch array 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 the waveguides are isolated by silicon oxide, 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 distance between the middle layer silicon nitride waveguide 202 and the bottom layer silicon waveguide 201 and the distance between the middle layer silicon nitride waveguide 203 in the height direction are both less than 0.5 μm.
Each path of input optical signal comprises M wavelengths; the polarization rotation beam splitter 102 splits each optical signal into 2 orthogonally polarized beams, and the polarization state of one of the beams is rotated by 90 degrees, so that the optical signals at the 2 output ends of the polarization rotation beam splitter 102 have the same polarization; the nxnxnxm wavelength selective optical switch array 103 provides dynamic routing for the 2N × M wavelength optical signals; the 2N-path waveguide interlayer coupler 104 assists optical signals to be transmitted between the silicon-silicon nitride three-dimensional waveguide layers; the N-path polarization rotation beam combiner 105 converts the 2N-beam optical signals with the same polarization state into orthogonal polarization states again, combines and outputs the orthogonal polarization states into N paths, and finally outputs the N paths of orthogonal polarization states through the output end of the N-path optical output coupler 106 to be transmitted through the N paths of single-mode optical fibers O at the output end.
Example (b):
fig. 3 shows an embodiment of a silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of the present invention, i.e., a 4 × 4 × 2(N ═ 4, and M ═ 2) polarization-independent wavelength selective optical switch array chip. The embodiment is realized by using a silicon-silicon nitride three-dimensional integrated waveguide, and comprises three layers of waveguides: a bottom layer of silicon waveguides 201 and an intermediate layer of silicon nitride waveguides 202 and a top layer of silicon nitride waveguides 203 thereon. The distance between the silicon waveguide 201 and the top silicon nitride waveguide 203 in the height direction is larger than 0.8 μm, so that the three-dimensional waveguide cross junction has lower loss (less than 0.01dB), the distance between the silicon nitride waveguide 202 in the middle layer and the distances between the silicon nitride waveguide 201 in the bottom layer and the silicon nitride waveguide 203 in the top layer in the height direction are both less than 0.5 μm, and the loss of optical signals in coupling transmission between the three layers of waveguides is smaller (less than 0.1 dB).
In this embodiment, the 4 optical input couplers 101 and the 4 optical output couplers 106 are horizontal structures, and couple two-wavelength optical signals including orthogonal polarization states into/out of an optical chip by end-face coupling; 8 polarization rotation beam splitters 102 or 106 adopt a structure of combining a gradient ridge waveguide with an asymmetric directional coupler, 4 polarization rotation beam splitters 102 are used for converting an input optical signal into a signal with the same polarization state and splitting the signal, the input and the output of the other 4 polarization rotation beam splitters are reversely placed to form 4 polarization rotation beam splitters 105, and the signal with the same polarization state is converted into an orthogonal polarization state again and combined; the 4 × 4 × 2 wavelength selective optical switch array 103 includes 16 2 × 2 wavelength selective optical switch units connected by a cross-bar topology, each optical switch unit includes 2 groups of silicon nitride double microrings (Q ═ 2) capable of simultaneously transmitting optical signals of two WDM channels, and each silicon nitride microring integrates a microheater for thermal phase shifting.
FIG. 4 is a cross-sectional view of a thermal phase shifter according to this embodiment. There are two ways to implement thermal phase shift for silicon nitride microrings: low power consumption thermal phase shifting is achieved by fabricating a metal thermal resistor above the silicon nitride microring (fig. 4(a)) or doping the silicon waveguide directly below the silicon nitride microring with the same microring structure (fig. 4(b)), respectively. In this embodiment, the silicon dioxide cladding layer near the phase shifter and the silicon substrate at the bottom are both etched to form air slots, so that heat is concentrated in the phase shifter region and prevented from diffusing to the periphery and the substrate, and the thermal phase shifting efficiency can be further improved.
Fig. 5 shows the structure of the waveguide interlayer coupler 104 in this embodiment, which includes a silicon nitride-silicon nitride interlayer coupler D composed of a top silicon nitride waveguide 203 and an intermediate silicon nitride waveguide 202, and a silicon nitride-silicon interlayer coupler E composed of an intermediate silicon nitride waveguide 202 and a bottom silicon waveguide 201. Mode field coupling is completed between any two adjacent waveguide layers by using two tapered waveguide structures in opposite directions, so that optical signals are transmitted among 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 m-th group of serial micro-rings in the p-th row and q-th column are energized to red-shift the resonant wavelength to the corresponding wavelength λmWhen the channel (p is less than or equal to 4, q is less than or equal to 4, and m is less than or equal to 2), the wavelength input from the p input port is lambdamMay be routed to the q output ports; by powering up multiple sets of micro-rings in series, arbitrary routing of wavelength-granular optical signals can be handled. Fig. 6 shows a schematic diagram of the operation of several representative 4 × 4 × 2 wavelength selective optical switch arrays.
The operation of the silicon-silicon nitride polarization-independent wavelength selective optical switch array chip of the present invention will be described in detail below by taking the state of fig. 6(3) as an example.
In the 4 × 4 × 2 polarization-independent wavelength selective optical switch array chip of fig. 3, one beam contains two-wavelength optical signals (TE + TM, λ) with random polarization states1λ2) Through I1The coupler 1001 is coupled to the optical chip from the single-mode fiber, and after passing through the polarization rotation beam splitter 1021, the optical chip is divided into two beams of optical signals with the same polarization, which are the original TE → TE polarized optical signal and TM → TE polarized optical signal. The TE → TE polarized optical signal is transmitted to the West 1 port of the 4 × 4 × 2 wavelength selective optical switch array, and the TM → TE polarized optical signal is transmitted to the east 1' port of the 4 × 4 × 2 wavelength selective optical switch array. Under the condition of no power supply, the resonance wavelength of the silicon nitride micro-ring is connected with two wavelength channels lambda of the input optical signal in series1、λ2Are all inconsistent. Heating and electrically tuning a first group of series-connected silicon nitride micro-rings in a first row and a second column in a 4 × 4 × 2 wavelength selective optical switch array to red shift the resonant wavelength to λ1The second group of series-connected silicon nitride micro-rings in the first row and the first column are also electrically tuned to red shift the resonant wavelength to lambda2At this time, the optical signal λ input from the West 1 port1、λ2Optical signals lambda respectively routed to north 2, north 1 waveguides, east 1' ports input1、λ2Counterclockwise to the south 2 ', south 1' ports, respectively. The optical signals of the four output ports are respectively transmitted to the silicon waveguide from the top silicon nitride waveguide through the waveguide interlayer coupler, wherein the optical signals lambda of the north 1 port and the south 1' port2Combined by a polarization rotation beam combiner 10501 and output from O1The coupler 10601 outputs an optical signal λ having two ports, north 2 and south 21Combined by polarization rotating beam combiner 105022The coupler 10602 output. To sum up, I1Input orthogonal polarization stateThe dual wavelength optical signals are routed to O1And O2Two output terminals. Similarly, optical signals input by other ports are transmitted between the input-output ports in the same manner.
The embodiments of the present invention are not limited to the above-described embodiments, and can be easily understood by other persons skilled in the art. The foregoing embodiments have been provided for clarity of presentation, but the described embodiments may be modified or equivalents may be substituted for some of the features described. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
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 into N paths, and finally outputs the N paths of optical signals to an output single-mode optical fiber for transmission.
2. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 1, comprising 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 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).
3. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of claim 1 or 2, wherein the nxnxnxm wavelength selective optical switch array (103) is formed by N2The 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, and the bottom layer silicon waveguide (201) and the top layer silicon nitride waveguide (1)203) The three-dimensional integrated cascade micro-ring resonator is characterized in that a three-dimensional waveguide cross junction (B) for inhibiting loss and crosstalk caused by waveguide cross is formed, the middle layer silicon nitride waveguide (202) forms a cascade micro-ring (C), and the cascade micro-ring (C) is vertically coupled with the bottom layer silicon waveguide (201) and the top layer silicon nitride waveguide (203) respectively to form the three-dimensional integrated cascade micro-ring resonator.
4. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 2, 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 Cm(M is 1 to M) comprises Q silicon nitride microrings of the same structure connected in series; coupling coefficients among the Q series silicon nitride micro-rings and between the Q series silicon nitride micro-rings and 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 CmThe 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), the resonance wavelength of the silicon nitride micro-ring can be adjusted, 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 cladding silicon oxide and the silicon substrate at the bottom can be etched to form an air groove, so that the thermal phase-shift efficiency is further improved.
5. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 2, 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 state0With the input wavelength (λ)1～λM) All are different, and the optical signal input from the input end (through end) is directly output from the through end (input end); by aligning one of the sets of stagesCombined micro ring CnThe micro-heater on (n 1-M) is energized, C can be addednShift of resonance wavelength of middle micro-ring and certain input wavelength lambdanThe same holds true for the wavelength λ input from the input end (through end)nThe 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.
6. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 1 or 5, wherein the micro-heaters on the m-th set of serial micro-rings on the p-th row and q-th column are powered to shift the resonant wavelength thereof to the corresponding wavelength λmWhen 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 lambdamMay 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.
7. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip of claim 2, wherein the waveguide interlayer coupler (104) is a three-dimensional waveguide interlayer coupler comprising a first silicon nitride-silicon nitride interlayer coupler (D) formed by a top silicon nitride waveguide (203) and a first middle silicon nitride waveguide (202-1), and a second silicon nitride-silicon interlayer coupler (E) formed by a second middle silicon nitride waveguide (202-2) and a bottom silicon waveguide (201), the first silicon nitride-silicon nitride interlayer coupler (D) and the second silicon nitride-silicon interlayer coupler (E) are connected by a third middle silicon nitride waveguide (202-3), the first middle silicon nitride 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).
8. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to claim 2 or 7, wherein the distance between the bottom silicon waveguide (201) and the top silicon nitride waveguide (203) in the height direction is greater 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 less than 0.5 μm.
9. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to any one of claims 1 to 8, 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.
10. The silicon-silicon nitride three-dimensional integrated polarization-independent wavelength selective optical switch array chip according to any one of claims 1 to 8, 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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