阅读说明：本技术 N×n硅基偏振无关光开关系统 (N × N silicon-based polarization independent optical switch system ) 是由 陆梁军 李晓蕊 周林杰 陈建平 于 2020-05-14 设计创作，主要内容包括：一种N×N硅基偏振无关光开关系统,包括芯片和控制模块,所述的芯片包括N路光输入偏振分束器、N路光偏振控制器、N×N光开关阵列和N路光输出耦合器,所述的控制模块包含跨阻放大器TIA、模数转换器芯片、单片机控制芯片、数模转换器芯片和驱动放大器。本发明将任意偏振的输入光经过偏振分束器后分解为两个正交偏振,通过调节光偏振控制器中的移相器相位将光全部调节为横电模输入到光开关阵列中。通过光功率探测器和外部控制电路实现光偏振的自动反馈控制。N×N光开关阵列通过若干个2×2开关单元和波导交叉结以无阻塞拓扑结构排布实现。本发明将控制电路与光路进行结合,对任意偏振输入光实现了无阻塞光交换,对于硅基光开关芯片的实际应用有重要的价值。(The invention discloses an N × N silicon-based polarization independent optical switch system, which comprises a chip and a control module, wherein the chip comprises an N path light input polarization beam splitter, an N path light polarization controller, an N × N light switch array and an N path light output coupler, and the control module comprises a trans-impedance amplifier TIA, an analog-digital converter chip, a single chip microcomputer control chip, a digital-analog converter chip and a driving amplifier.)

1. An N × N silicon-based polarization independent optical switch system, comprising a chip and a control module, wherein the chip comprises N paths of optical input polarization beam splitters (101), N paths of optical polarization controllers (102), N × N optical switch arrays (103) and N paths of optical output couplers (104), the output ends of the N paths of optical input polarization beam splitters (101) are respectively connected with the input ends of the N paths of optical polarization controllers (102), the output ends of the N paths of optical polarization controllers (102) are respectively connected with the N paths of input ends of the N × N optical switch arrays (103), the N paths of output ends of the N × N optical switch arrays (103) are respectively connected with the input ends of the N paths of optical output couplers (104), finally, optical signals are output through the N paths of optical output couplers (104), the electrical input ports of the control module (105) are connected with the electrical output ports of the N paths of optical polarization controllers (102), and the electrical output ports of the control module (105) are respectively connected with the electrical input ports of the N paths of optical input ports (102) and the N paths of optical output couplers (×).

2. The N × N silicon-based polarization independent optical switch system according to claim 1, wherein the N-path optical input polarization beam splitter (101) is constructed by using a two-dimensional grating coupler structure, and an external optical fiber inputs light into the chip through vertical coupling, or is constructed by using an inverted cone-shaped mode spot converter connected to a polarization beam splitter rotator, and an external optical fiber inputs light into the chip through horizontal coupling, and both structures decompose an input optical signal into two orthogonal polarizations and convert the two orthogonal polarizations into two Transverse Electric (TE) modes to be output from two output waveguides.

3. The N × N si-based polarization independent optical switch system of claim 1, wherein the optical polarization controller of the N-way optical polarization controller (102) is composed of two input waveguides (1001), two phase shifters (1002), a 2 × 2 mach-zehnder interferometer (1003), an on-chip optical power detector (1004), and an output waveguide (1005), wherein one phase shifter (1002) controls the relative phase of the input optical signals, and the other phase shifter (1002) controls the operating state of the mach-zehnder interferometer (1003), the on-chip optical power detector (1004) converts light from one port of the mach-zehnder interferometer (1003) into photocurrent, and the output optical current of the on-chip optical power detector (1004) is minimized by changing the phase shift of the two phase shifters (1002), so that the light is completely converted into the TE mode and output from the output waveguide (1005), and the output end of the on-chip optical power detector (1004) is connected to the input end of the control module (105).

4. The N × N silicon-based polarization independent optical switch system of claim 3, wherein the phase shifter (1002) of the optical polarization controller (102) is connected to the output of the control module (105) using thermo-optic effect and carrier dispersion effect.

5. The N × N silicon-based polarization independent optical switch system of claim 3, wherein the on-chip optical power detector (1004) employs a sige PIN diode structure.

6. The N × N Si-based polarization independent optical switch system of claim 1, wherein the N × N optical switch array (103) is formed by a plurality of 2 × 2 switch units and waveguide cross-junctions, the 2 × 2 switch units adopt a Mach-Zehnder structure, a micro-ring resonant cavity structure or a double-ring auxiliary Mach-Zehnder structure, and the waveguide cross-junctions adopt a multimode interference structure or a multilayer waveguide structure.

7. The N × N silicon-based polarization independent optical switch system of claim 6, wherein the 2 × 2 switch cells are integrated with phase shifters, and the routing states of the N × N optical switch array are changed by changing the states of the phase shifters to switch the switch cells to cross or through states, respectively, to realize different switched optical paths, and the phase shifters in the switch cells are connected to the output terminals of the control module.

8. The N × N silicon-based polarization independent optical switch system according to claim 1, wherein the N-path optical output coupler (104) outputs light by vertical coupling with an external optical fiber using a grating coupler or by horizontal coupling with an external optical fiber using an inverse tapered spot-size converter.

9. The N × N silicon-based polarization independent optical switch system of claim 1, wherein the control module (105) comprises a transimpedance amplifier (2001), an analog-to-digital converter chip (2002), a single-chip microcomputer control chip (2003), a digital-to-analog converter chip (2004) and a driver amplifier (2005), an input terminal of the transimpedance amplifier (2001) is connected to an output terminal of an on-chip optical power detector (1004) in the polarization controller (102), an output terminal of the transimpedance amplifier (2001) is connected to an input terminal of the analog-to-digital converter chip (2002), an output terminal of the analog-to-digital converter chip (2002) is connected to an input terminal of the single-chip microcomputer control chip (2003), an output terminal of the single-chip microcomputer control chip (2003) is connected to an input terminal of the digital-to-analog converter chip (2004), an output terminal of the digital to an input terminal of the driver amplifier (2005), and an electrical signal is output through an output terminal of the driver amplifier (2005).

10. The N × N si-based polarization independent optical switch system of claim 9, wherein the transimpedance amplifier (2001) amplifies an input photocurrent to convert it into a voltage value, the analog-to-digital converter chip (2002) reads the voltage and feeds the voltage back to the single-chip microcomputer control chip (2003), the single-chip microcomputer control chip (2003) responds to the feedback value to instruct the digital-to-analog converter (2004) to output a suitable voltage value, which is output to the N-way optical polarization controller (102) and the phase shifter in the N × N optical switch array (103) after passing through the driving amplifier (2005), the magnitude range of the read optical power is determined according to the amplification factor of the transimpedance amplifier (2001) and the number of bits of the analog-to-digital converter chip (2002), the accuracy of the applied voltage is determined according to the number of bits of the digital-to-analog converter chip (2004), and the control algorithm of the single-chip microcomputer control chip (2003) is mainly based on the concept of global minimum search, which can be implemented by using a hill-climbing algorithm, an analog annealing algorithm, a particle swarm optimization algorithm, or the like.

Technical Field

The invention relates to the field of integrated optics of optical communication, in particular to an N × N silicon-based polarization independent optical switch system.

Background

With the increasing demand of people for big data and cloud computing, the improvement of the optical fiber communication capacity becomes a crucial factor. The optical switch plays an important role in cloud computing, data centers and other applications, and is used for establishing an internet to perform high-speed data exchange. The optical switch array chip and the optical switch module have one or more optional transmission ports, perform physical switching or logical operation on optical signals in an optical transmission line or an integrated optical circuit, and play an important role in an optical network.

However, due to the large birefringence of the silicon waveguide structure, the induced Polarization Mode Dispersion (PMD), polarization dependent loss (PD L) and polarization dependent wavelength characteristics (PD λ) are not negligible, and these disadvantages limit the range of applications of silicon-based optical switches.

However, in practical applications, polarization mismatch occurs when coupling a non-polarization maintaining fiber with a silicon waveguide, and a polarization controller is usually used to solve the problem, so it is important to design a large-scale optical switch network that realizes polarization independence to improve the practicability of an optical network.

The polarization diversity mode needs more switch units and more complicated topological networks; the method for designing the waveguide size needs high-precision waveguide size control and has small process error. To this end, we propose to combine the polarization beam splitter, polarization controller and external hardware control circuit to achieve the polarization independent property of the optical switch.

Disclosure of Invention

Aiming at the wide practical application scenes of the polarization-independent optical switch and the respective defects of the existing two polarization-independent optical switches, the invention provides an N × N silicon-based polarization-independent optical switch system which avoids the problems of large-scale increase of optical switch units and crosstalk caused by the optical switch units, has no particularly high requirement on process tolerance and has extremely high application value.

In order to achieve the above object, the technical solution of the present invention is as follows:

an N × N silicon-based polarization independent optical switch system comprises a chip and a control module, and is characterized in that the chip comprises N paths of optical input polarization beam splitters, N paths of optical polarization controllers, an N × N optical switch array and N paths of optical output couplers, wherein output ends of the N paths of optical input polarization beam splitters are respectively connected with input ends of the N paths of optical polarization controllers, output ends of the N paths of optical polarization controllers are respectively connected with N paths of input ends of the N × N optical switch array, N paths of output ends of the N × N optical switch array are respectively connected with input ends of the N paths of optical output couplers, finally optical signals are output through the N paths of optical output couplers, an electrical input port of the control module is connected with an electrical output port of the N paths of optical polarization controllers, and an electrical input port of the N × N optical switch array.

The N paths of light input polarization beam splitters adopt a two-dimensional grating coupler structure, and external optical fibers input light into a chip through vertical coupling; or the inverted cone-shaped spot-size converter is connected with the polarization beam splitting rotator, and the external optical fiber inputs light into the chip through horizontal coupling; both structures decompose an input optical signal into two orthogonal polarizations, convert the two orthogonal polarizations into two Transverse Electric (TE) modes, and output the two orthogonal polarizations from two output waveguide ends.

The optical polarization controller of the N-path optical polarization controller comprises two input waveguides, two phase shifters, a 2 × 2 Mach-Zehnder interferometer, an on-chip optical power detector and an output waveguide, wherein one phase shifter controls the relative phase of an input optical signal, the other phase shifter controls the working state of the Mach-Zehnder interferometer, the on-chip optical power detector converts light from one port of the Mach-Zehnder interferometer into photocurrent, the output photocurrent of the on-chip optical power detector is minimized by changing the phase shift of the two phase shifters, the light is completely converted into a TE mode and is output from the output waveguide, and the output end of the on-chip optical power detector is connected with the input end of the control module.

The phase shifter of the light polarization controller adopts thermo-optic effect and carrier dispersion effect and is connected with the output end of the control module.

The on-chip optical power detector adopts a germanium-silicon PIN diode structure.

The N × N optical switch array is composed of a plurality of 2 × 2 switch units and waveguide cross junctions, wherein the 2 × 2 switch units adopt a Mach-Zehnder structure, a micro-ring resonant cavity structure or a double-ring auxiliary Mach-Zehnder structure, and the waveguide cross junctions adopt a multimode interference structure or a multilayer waveguide structure.

The 2 × 2 switch unit is integrated with a phase shifter, the switch unit is switched to a cross state or a through state respectively by changing the state of the phase shifter, so that the routing state of the N × N optical switch array is changed, different exchange optical paths are realized, and the phase shifter in the switch unit is connected with the output end of the control module.

The N-path optical output coupler adopts a grating coupler to output light with an external optical fiber through vertical coupling; or the inverted cone-shaped spot-size converter is adopted to output light with an external optical fiber through horizontal coupling.

The control module comprises a transimpedance amplifier, an analog-digital converter chip, a single-chip microcomputer control chip, a digital-analog converter chip and a drive amplifier, wherein the input end of the transimpedance amplifier is connected with the output end of an on-chip optical power detector in the polarization controller, the output end of the transimpedance amplifier is connected with the input end of the analog-digital converter chip, the output end of the analog-digital converter chip is connected with the input end of the single-chip microcomputer control chip, the output end of the single-chip microcomputer control chip is connected with the input end of the digital-analog converter chip, the output end of the digital-analog converter chip is connected with the input end of the drive amplifier, and an electric signal is output through the output end of the drive amplifier.

The transimpedance amplifier amplifies and converts input light current into a voltage value, the analog-digital converter chip reads the voltage and feeds the voltage back to the single chip microcomputer control chip, the single chip microcomputer control chip reacts according to the feedback value, commands the digital-analog converter to output a proper voltage value, the proper voltage value is output to the N-path light polarization controller and the phase shifter in the N × N optical switch array after passing through the driving amplifier, the size range of the read light power is determined according to the amplification factor of the transimpedance amplifier and the digit of the analog-digital converter chip, the precision of the applied voltage is determined according to the digit of the digital-analog converter chip, the control algorithm of the single chip microcomputer control chip is mainly used for searching the global minimum value, and the searching algorithm such as a hill climbing algorithm, an analog annealing algorithm or a particle swarm optimization algorithm can be adopted for realizing.

Compared with the prior art, the invention has the following beneficial effects:

1. the N × N silicon-based polarization-independent optical switch chip system of the invention realizes monolithic integration by adopting the silicon-based substrate, has compact structure, is compatible with CMOS process, is beneficial to mass production and reduces the cost.

2. The polarization-independent function of the optical switch is realized by an optical input polarization beam splitter, an optical polarization controller, a control algorithm and an external circuit; the overall structure does not require many switching cells nor does it require a high requirement on the polarization insensitivity of the switching cells.

3. The invention decomposes the input light with any polarization into two orthogonal polarizations after passing through the polarization beam splitter, adjusts the phase of the phase shifter in the light polarization controller to input the light into a transverse electric mode and inputs the light into the optical switch array, realizes the automatic feedback control of the light polarization through the optical power detector and the external control circuit, and realizes the non-blocking topological structure arrangement of the N × N optical switch array through the cross connection of a plurality of 2 × 2 switch units and waveguides.

Drawings

FIG. 1 is a general architecture diagram of an N × N Si-based polarization-independent optical switch chip system according to the present invention.

Fig. 2 is a structural diagram of an optical polarization controller in the N × N si-based polarization independent optical switch chip system according to the present invention.

Fig. 3 is a structural diagram of a control module in the N × N si-based polarization independent optical switch chip system according to the present invention.

Fig. 4 is an overall architecture diagram of a polarization independent D L N optical switch chip according to embodiment 4 × 4 of the present invention.

Fig. 5 is a block diagram of a polarization control circuit of a polarization independent optical switch chip according to embodiment 4 × 4.

FIG. 6 is a diagram of a simulation result of an algorithm of an embodiment of an N × N Si-based polarization-independent optical switch chip system based on a hill-climbing algorithm.

Detailed Description

To further clarify the objects, technical solutions and core advantages of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings and examples. It should be noted that the following specific examples are for illustrative purposes only and are not intended to limit the invention. Meanwhile, the technical features related to the respective embodiments may be combined with each other as long as they do not conflict with each other.

Referring to fig. 1, 2, and 3, it can be seen from the figure that the N × N silicon-based polarization independent optical switch system of the present invention includes a chip and a control module, where the chip includes N paths of optical input polarization beam splitters 101, N paths of optical polarization controllers 102, N × N optical switch arrays 103, and N paths of optical output couplers 104, output ends of the N paths of optical input polarization beam splitters 101 are respectively connected to input ends of the N paths of optical polarization controllers 102, output ends of the N paths of optical polarization controllers 102 are respectively connected to N paths of input ends of the N × N optical switch arrays 103, N paths of output ends of the N × N optical switch arrays 103 are respectively connected to input ends of the N paths of optical output couplers 104, and finally, optical signals are output through the N paths of optical output couplers 104, an electrical input port of the control module 105 is connected to an electrical output port of the N paths of optical polarization controllers 102, and an electrical output port of the control module 105 is respectively connected to an electrical input port of the N paths of optical input ports of the N paths of optical polarization controllers 102 and an electrical input port of the N paths of optical output couplers ×.

The N-path optical polarization controller 102 is composed of two input waveguides 1001, two phase shifters 1002, a 2 × 2 mach-zehnder interferometer 1003, an on-chip optical power detector 1004, and an output waveguide 1005, output ends of the N-path optical polarization controller 102 are respectively connected to N-path input ends of the N × N optical switch array 103, N-path output ends of the N × N optical switch array 103 are respectively connected to input ends of the N-path optical output couplers 104, and finally, optical signals are output through the N-path optical output couplers 104.

The control module 105 is composed of a transimpedance amplifier (TIA)2001, an analog-to-digital converter chip (ADC)2002, a single-chip microcomputer control chip 2003, a digital-to-analog converter chip (DAC)2004 and a Driver amplifier (Driver)2005, an input end of the transimpedance amplifier 2001 is connected to an output end of an on-chip optical power detector 1004 in the polarization controller 102, an output end of the transimpedance amplifier 2001 is connected to an input end of the analog-to-digital converter chip 2002, an output end of the analog-to-digital converter chip 2002 is connected to an input end of the single-chip microcomputer control chip 2003, an output end of the single-chip microcomputer control chip 2003 is connected to an input end of the digital-to-analog converter chip 2004, an output end of the digital-to-analog converter chip 2004 is connected to an input end of the Driver amplifier 2005, and finally, an electric signal is output through an output end of the Driver amplifier 2005 to power up the N-path optical polarization controller 102 and.

Fig. 4 is a general architecture diagram of an embodiment of a 4 × 4 polarization independent Double L eye Network (D L N) optical switch array chip and control module of the present invention, referring to fig. 4, first, 4 optical signals of arbitrary polarization states are input to a polarization beam splitter 101 through an optical fiber array, the polarization beam splitter 101 includes a tapered coupler and a polarization beam splitter rotator (PSR), the optical signals are divided into TE light and TM light, and the TM light is rotated into the TE polarization, then the optical signals are input to an optical polarization controller 102, a first phase shifter 1002 controls the relative phases of the two polarized lights, and a second phase shifter 1002 controls the amplitude of an output port, referring to fig. 5, one of the output ports is connected to an on-chip PD1004, which is referred to as a feedback port, and the other output port is connected to an input end of the optical switch array, which is referred to as an output port, and at the feedback port, the PD1004 converts the optical power signal into a current signal, which is then amplified, sampled and processed by the control module 105.

Through a transmission matrix method, the output optical power P of a feedback end and the phase change amount of two phase shifters in an optical polarization controller under different polarization input light can be establishedThe relationship (2) of (c). It can be obtained that when the initial phases of the TE and TM mode lights after the fraction are the same, the feedback end P has two centrosymmetric global minimum points, so that the power at the output port can be maximized by changing the phases of the two phase shifters to minimize the optical power at the feedback end, and thus the input lights are all converted into the TE polarized lights.

In the control module, a current signal output by a feedback end is amplified and converted into a voltage signal through TIA, the input current signal range of the trans-impedance amplifier is 10pA-2mA, 3 stages of amplification gears are provided, the amplification gears are 1000M, 10M and 1M respectively, and the gear can be adjusted according to actual requirements. The electrical signal is then sampled by the ADC and then sent to the single chip control chip. Then, a global minimum power search algorithm is applied in the single chip microcomputer control chip to search the optimal phase shift value of the phase shifter, so that the photocurrent output by the feedback end is minimum. In this process, the phase shifters in the optical polarization controllers are powered up through the DACs and the driver amplifiers.

In addition, the implementation process and feasibility of the global minimum power search algorithm are illustrated by randomly generating 20 sets of input light with different polarization ratios, and randomly generating 50 initial phases in each set to form 1000 samples. For the 1000 samples, firstly, large step length is adopted near an initial point to carry out global search for 5 times, the searched values are compared, after a smaller value is selected, hill climbing algorithm search is adopted near the smaller value, the step length is adjusted according to the power variation of a feedback section, the global minimum value can be searched through several iterations, and the generation of local optimum is effectively avoided. Matlab software is used for simulating the algorithm, the global minimum value searched finally and the iteration number are counted, and the result is shown in FIG. 6. It can be seen that the average number of iterations is 6, and after the number of iterations of the global search is added, the total average number of iterations is 11. And the searched global minimum value can realize that 99% of input optical signals are converted into TE mode light to be output from the output port.

The method comprises the steps that an algorithm structure part is finished, automatic regulation and control of input optical signals are achieved, 4 paths of TE polarized optical signals are input into a 4 × switch array, then units in the 4 × switch array are adjusted and are respectively electrified and regulated to a cross state or a bar state, voltages required by each switch unit in the cross state and the bar state can be recorded through a table look-up method, then a routing table and a state required to be switched are switched, and a control circuit in a control module conducts electrification on switch units in a 4 × 4 switch network.

Experiments show that the input light with any polarization is decomposed into two orthogonal polarizations through a polarization beam splitter, the light is completely adjusted into a transverse electric mode through adjusting the phase of a phase shifter in a light polarization controller and is input into an optical switch array, the automatic feedback control of the light polarization is realized through an optical power detector and an external control circuit, and the N × N optical switch array is realized through the arrangement of a non-blocking topological structure through the cross-connection of a plurality of 2 × 2 switch units and waveguides.

On the basis of the scheme, the optical switch chip can perform polarization beam splitting and rotation on input light based on the polarization beam splitting rotator, and realizes rapid optical polarization control and a low crosstalk optical switch array through a control algorithm and an external circuit, so that a 4 × 4 polarization-independent silicon-based optical switch is realized, and the optical switch can be expanded according to practical application.

The present invention is not limited to the above-described embodiments, and it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements are also considered to be within the scope of the present invention. Details not described in this specification are within the skill of the art that are well known to those skilled in the art.