CN-115792763-B - Automatic calibration system and method for silicon-based N x N optical switch chip

CN115792763BCN 115792763 BCN115792763 BCN 115792763BCN-115792763-B

Abstract

A silicon-based N x N optical switch chip automatic calibration system and method monitors the state of an on-chip optical path through a photoelectric detector on an expansion level redundant port in an optical switch array chip, reads the optical power of the photoelectric detector to a microprocessor in a time-sharing manner through an analog selection switch, and utilizes an automatic calibration algorithm deployed in the microprocessor to complete quick and automatic calibration on the states of all units in the optical switch array. The invention can effectively reduce the number of the on-chip photoelectric detectors and the peripheral analog-to-digital converters, realizes the rapid calibration of the state of the silicon-based optical switch chip, and has the advantages of simple method, high calibration speed, low cost and the like.

Inventors

LU LIANGJUN
LIU CHENGHAN
ZHOU LINJIE
LI YU
CHEN JIANPING

Assignees

上海交通大学

Dates

Publication Date: 20260505
Application Date: 20221129

Claims (7)

1. An automatic calibration system for a silicon-based nxn optical switch chip, comprising: the light source is used for generating two paths of input optical signals with equal energy and single wavelength; the two symmetrically arranged programmable polarization controllers are used for respectively receiving the input optical signals and adjusting the polarization states of the input optical signals through the respectively received control signals; Two symmetrical 1 XN optical switches for receiving feedback signals, controlling the input optical signals to be input from 1 input port and any one of N output ports or controlling the input optical signals to be input from any one of N input ports and the 1 output port; The silicon-based N x N optical switch chip comprises 4M photoelectric detectors, a first-stage 2x 2 optical switch, a second-stage 2x 2 optical switch, a third-stage 2x 2 optical switch, a fourth-stage 2T-2 stage 2x 2 optical switch and a fourth-stage 2T-1-stage 2x 2 optical switch, wherein the third-stage 2x 2 optical switch consists of M2 x2 optical switches, each 2x 2 optical switch comprises 4 redundant ports, and the left end and the right end of each 2 optical switches are respectively connected with the photoelectric detectors; Two 1X 2M analog selector switches which are symmetrically arranged, wherein 2M ports of each 1X 2M analog switch are respectively connected with 2M photoelectric detectors and are used for outputting real-time photocurrents of the photoelectric detectors on different paths and transmitting the real-time photocurrents to corresponding transimpedance amplifiers; The two transimpedance amplifiers are symmetrically arranged and are used for amplifying received photocurrent and converting the photocurrent into a voltage signal; The two analog-digital converters are symmetrically arranged and are used for reading the voltage signals output by the transimpedance amplifier and converting the voltage signals into digital signals; the microprocessor is used for realizing a hardware platform of an automatic calibration algorithm, outputting a feedback signal and a feedback voltage value to the digital-to-analog converter by receiving the voltage value fed back by the analog-to-digital converter, automatically switching an output port of the 1 XN optical switch unit according to the automatic calibration algorithm, simulating an output port number of the switch, and feeding back a new voltage value to the digital-to-analog converter; the digital-to-analog converter is used for reading the feedback signal of the microprocessor, converting the feedback signal into an analog signal and feeding the analog signal back to the driving amplifier; And the driving amplifier converts the digital signal fed back by the digital-to-analog converter into a corresponding voltage value and loads the corresponding voltage value on the corresponding 2 multiplied by 2 switch unit.
2. The automatic calibration system of a silicon-based nxn optical switch chip as recited in claim 1, wherein the network topology of the silicon-based nxn optical switch chip includes Benes, expansion Benes, crossbar, a two-layer network (DLN) structure; The 2X 2 optical switches are arranged in a certain network topology structure, the number of the 2X 2 optical switches is determined by the topology structure, and the 2X 2 optical switches are of a 2X 2 Mach-Zehnder interferometer structure or a 2X 2 micro-ring resonator structure; The T-th stage 2 x2 optical switch is formed by cross-connecting 42 x2 optical switches if there is no redundant port.
3. The automatic calibration system of a silicon-based nxn optical switch chip as recited in claim 2, wherein the photodetector is a silicon-germanium PIN type detector.
4. The automatic calibration method of the silicon-based N multiplied by N optical switch chip is characterized by comprising the following steps of: the microprocessor turns on the light source to introduce two paths of input light signals with equal energy and single wavelength into the respective programmable polarization controllers; Selecting a calibration path, namely selecting an mth input port and an nth output port of a silicon-based NxN optical switch chip as one to-be-calibrated path I m -O n （I m and O n respectively, wherein M, n=1, 2, & gt, N, optical signals are input into a1 xN optical switch array from left and right paths, namely left optical signals are input into the NxN optical switch array chip from the mth port, and right optical signals are input into the NxN optical switch chip from the nth port; the path I m -O n to be calibrated passes through an ith (i=1, 2,..M) optical switch of the middle stage, the microprocessor sends control signals to 1X 2M analog switches on two sides, so that the left and right 1X 2M analog switches are respectively switched to a 2X I-2+p and a 2X I-2+q path (p, q=1, 2) to be connected with a p-th photoelectric detector on the left side and a q-th photoelectric detector on the right side of an ith optical switch unit of the middle stage; the calibration path initialization, namely, according to the read voltage signal, a microprocessor sends a control signal to a programmable polarization controller, adjusts the polarization state of an input optical signal to maximize the optical signal of an intermediate-stage optical switch, and sends the control signal to a digital-to-analog converter, and all optical switch units in the path I m -O n to be calibrated are loaded with required initial voltages to make the voltage signal read from the analog-to-digital converter larger; The calibration switch unit is used for calibrating the optical switch units in the path I m -O n to be calibrated in sequence, the microprocessor sends control signals to the corresponding digital-to-analog converters to change the driving voltage loaded on the optical switch units to be calibrated, reads the voltage signal of the left analog-to-digital converter if the optical switch to be calibrated is on the right side of the middle stage, and reads the voltage signal of the right analog-to-digital converter if the optical switch to be calibrated is on the right side of the middle stage; Selecting the next path to be calibrated, repeating the steps until the driving voltage values of all the units of the NxN optical switch are obtained, and writing the obtained driving voltage into a lookup table to complete the calibration.
5. The method for automatically calibrating a silicon-based nxn optical switch chip according to claim 4, wherein the initial voltage of the switch is obtained through previous experience or testing of a test device.
6. The method for automatically calibrating a silicon-based nxn optical switch chip as recited in claim 4 wherein the search algorithm includes one-dimensional golden section, linear scan, gradient descent, particle swarm algorithm.
7. The method of claim 4, wherein the convergence condition is that the voltage signal read from the digitizer is either maximum or minimum, the maximum voltage signal represents the cell in the state required by the calibrated path, and the minimum voltage signal represents the cell in the opposite state of the calibrated path.

Description

Automatic calibration system and method for silicon-based N x N optical switch chip Technical Field The invention relates to the field of optical communication, in particular to an automatic calibration system and method for a silicon-based N multiplied by N optical switch chip. Background With the popularity of 5G technology with high definition video applications, global data traffic has exploded. International data centers (International Data Corporation, IDC) predict that global data traffic will increase from 33ZB to 175ZB in 2018 in 2025. Wherein, the data center internal flow exchange accounts for more than 71.5% of all flows. The traditional electric switching network cannot meet the requirements of low power consumption, high bandwidth and low cost of the current data center. The all-optical switching network directly completes the switching of signals in the optical domain, is not influenced by the traditional electronic technology any more, and has the advantages of high bandwidth, low power consumption, low cost and the like. The optical switch can route high-speed optical signals to different output ports with low power consumption and low delay, and is one of the most core devices of the all-optical switching network. An nxn high speed optical switch chip is the most basic, core device in an optical switch. The traditional optical switching system is mainly built by adopting 2×2,4×4 and other discrete optical switch arrays, and has the problems of large volume, high energy consumption, low reliability and the like. The silicon-based optical switch chip has the advantages of high integration level, low power consumption, compatibility of the manufacturing process and the traditional microelectronic CMOS process, and the like, and is suitable for large-scale optical switch arrays of all-optical switching systems. The topology structure of the silicon-based optical switch chip mainly comprises Benes, crossbar, switches & select (S & S), and the like. Wherein the Benes-based optical switch array can realize an n×n optical switch array by fewer optical switch units, such as a 32×32 optical switch array, and the Benes structure can realize a non-blocking switch array by only 144 switch units. However, since the Benes switch is a reconfigurable non-blocking switch structure, the change of the current routing state affects the transmission of other routing signals, so the control algorithm of the Benes-based switch array is more complex than the strict non-blocking switch structure. The structure of the switching unit mainly includes a Mach-Zehnder interferometer (MZI), a micro-ring resonator, and the like. The MZI structure has the advantages of broadband response, insensitivity to temperature and the like, so that the MZI structure has more application prospect. However, due to process errors, the initial state and the design value of the switch unit are not consistent, and the initial state calibration of the chip is required. In addition, since the phases of two output optical signals of the 3dB optical splitter in the MZI unit are not just different by pi/2, and the optical splitting ratio is uneven, the working voltages of Cross and Bar under different input ports are slightly different. In the same switching state, the voltages for realizing the optimal extinction ratio by the optical signals from different port inputs are different, and the crosstalk of the switch array is further increased. At present, a silicon-based optical switch chip mainly calibrates the state of a switch unit on a path by monitoring the optical power change of a target output port, and the state calibration can be realized only by the aid of the crosstalk switch unit due to the unavoidable existence of interference signals of crosstalk ports in the switch calibration process. The problem (Qiao L,Tang W,Chu T.32×32silicon electro-optic switch with built-in monitors and balanced-status units[J].Scientific Reports,2017,7(1):1-7) of Zhejiang university Chu Tao is to directly calibrate the state of an optical switch unit on a target path by inserting a double directional coupler and a grating coupler at the right side of the middle stage of a Benes structure optical switch, but the use of the grating coupler requires off-chip optical fiber vertical coupling and off-chip optical power detection, so that the packaging difficulty and calibration time of a chip are further increased. The Hua Chen (P.Dumais et al.,"Silicon Photonic Switch Subsystem With 900Monolithically Integrated Calibration Photodiodes and 64-Fiber Package,"in Journal of Lightwave Technology,vol.36,no.2,pp.233-238,15Jan.15,2018.) directly realizes the calibration of the state of the switch unit on the chip by embedding two weak directional couplers and integrated silicon germanium photodetectors on each 2×2 optical switch unit output waveguide, but the output electrodes of the whole 32×32 optical switch chip are thousands of because each switch is connected wi