Tunable DBR laser driving system based on FPGA and GaN device

Abstract

The invention discloses a tunable DBR (Distributed Bragg Reflector) laser driving system based on an FPGA (Field Programmable Gate Array) and a GaN device, which is used for solving the problems of low temperature control precision, large power supply ripple, nonlinear wavelength sweep frequency and large multi-path driving crosstalk in the traditional driving scheme. The system comprises a GaN switching power supply module, a multi-channel precision current driving module, a temperature control module, a laser module, an optical feedback module and a cooperative control module. The cooperative control module adopts a heterogeneous system chip integrated with a processor system and programmable logic; the processor system is responsible for communication with an upper computer and parameter management, and the programmable logic is responsible for real-time control; and the programmable logic is configured to calculate the instantaneous wavelength of the laser in real time according to the signal acquired by the optical feedback module, compare the instantaneous wavelength with an ideal sweep frequency curve, and dynamically adjust the driving current by inquiring a predistortion compensation table so as to compensate sweep frequency nonlinearity in a closed-loop manner. According to the invention, high-precision temperature control, ultralow-noise power supply and high-linearity wavelength tuning are realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser driving and control technology, specifically to a tunable distributed Bragg reflector (DBR) laser driving system based on field-programmable gate arrays (FPGAs) and gallium nitride (GaN) devices. Background Technology

[0002] Tunable semiconductor lasers, especially distributed Bragg reflector (DBR) lasers, play an important role in modern optoelectronic systems due to their wide tunable wavelength range, stable output, and high integration. Their excellent heat dissipation and ease of fiber coupling make them widely used in high-performance DBR laser modules.

[0003] However, existing tunable DBR laser drive systems still have many limitations in performance: 1) Insufficient temperature control accuracy (usually only reaching ±0.1℃), leading to core temperature fluctuations in the laser, causing output wavelength drift, and affecting the long-term stability and repeatability of the system; 2) The drive power supply typically uses traditional silicon-based MOSFET switching devices, which have limited switching speed and efficiency, resulting in large power supply output ripple (often higher than 50mV), which is directly coupled to the laser drive current, introducing low-frequency noise and deteriorating the laser's side-mode rejection ratio and spectral purity; 3) In wavelength sweep (tuning)... In operation mode, due to the nonlinearity of the current-wavelength response of each functional region of the laser (especially the grating region and the phase region) and the device response delay, the sweep frequency output wavelength changes nonlinearly with time, which seriously restricts the performance in applications such as high-precision ranging and spectral measurement; 4) DBR lasers usually contain multiple functional regions such as semiconductor optical amplification (SOA) region, gain region, grating region and phase region, which require multiple independent current drives. Existing drive systems are prone to crosstalk and insufficient accuracy (usually resolution >1mA) between multiple outputs, which affects the ability of each functional region to be independently and accurately tuned. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a DBR laser driving system with high integration, excellent control precision, fast response speed and good frequency sweep linearity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A tunable laser driving system based on FPGA and GaN devices includes: a GaN switching power supply module, a multi-channel precision current driving module, a temperature control module, a collaborative control module, a DBR laser, an optical feedback module, and a data acquisition module. Each module is electrically and optically connected to form a complete driving and closed-loop control link. Among them, the GaN switching power supply module is used to provide low-ripple DC power; A multi-channel precision current drive module, whose input terminal is connected to the output terminal of the GaN switching power supply module, is used to generate at least four independently adjustable drive currents. Temperature control module, used to monitor and adjust the die temperature of DBR laser; The collaborative control module is connected to the multi-channel precision current drive module and the temperature control module respectively, and is used to output current control signals and temperature control signals. The DBR laser has its power input terminal, current input terminals of each functional area, and temperature sensing terminal connected to the GaN switching power supply module, each output terminal of the multi-channel precision current drive module, and the temperature control module, respectively. An optical feedback module, whose input terminal receives the output light of the DBR laser, is used to convert the change in light wavelength into an electrical signal; The data acquisition module has its input end connected to the output end of the optical feedback module, and its output end connected to the feedback input end of the collaborative control module, forming a closed-loop control loop for wavelength linearity compensation.

[0006] Furthermore, the system also includes a host computer, which is connected to the collaborative control module via wired or wireless communication to provide a human-machine interface for configuring working parameters, controlling the system, and monitoring data.

[0007] Furthermore, the GaN switching power supply module, serving as the main power supply unit of the system, adopts a synchronous buck topology based on gallium nitride high electron mobility transistors (GaN HEMTs), with a switching frequency of no less than 500kHz. GaN devices possess high electron saturation velocity, high breakdown voltage, and extremely low gate charge, enabling higher frequency switching operations. This module, through optimized layout and the use of a multi-stage LC filter network, combined with voltage feedback closed-loop regulation control, can provide a stable 5V / 3A DC output, with an effective output ripple voltage of less than 50mV, providing a clean power supply environment for subsequent precision analog circuits.

[0008] Furthermore, the collaborative control module includes a heterogeneous system chip, which integrates a processor system and programmable logic; the processor system is responsible for communicating with the host computer, parsing parameters and scheduling tasks, and interacting with the programmable logic through an internal bus. The programmable logic is responsible for executing the real-time control algorithm and directly controlling at least one high-speed current channel in the multi-channel precision current drive module. The processor system and the programmable logic interact with each other via an AXI bus for data and instructions.

[0009] Furthermore, the programmable logic is configured to execute a real-time predistortion compensation algorithm, including the following steps: During the wavelength sweep process, the optical feedback signal digitized by the data acquisition module is acquired synchronously. The instantaneous wavelength of the DBR laser output is calculated in real time based on the optical feedback signal. Calculate the error value between the instantaneous wavelength and the ideal sweep wavelength at the current moment; Based on the error value, the corresponding drive current compensation amount is obtained by querying the pre-stored compensation lookup table. Based on the aforementioned drive current compensation amount, the current control signal output to the multi-channel precision current drive module is adjusted in real time.

[0010] Furthermore, the multi-channel precision current drive module includes a first digital-to-analog converter (DAC) unit and a second DAC unit; the first DAC unit is connected to the processor system of the collaborative control module via a serial interface to provide multiple high-precision static or slowly varying drive currents; the second DAC unit is directly connected to the programmable logic of the collaborative control module via a parallel bus to provide one high-speed dynamically updated drive current.

[0011] Furthermore, the driving current provided by the first digital-to-analog converter is used to drive the gain region, semiconductor optical amplification region, and grating region of the DBR laser; the driving current provided by the second digital-to-analog converter is used to drive the phase region of the DBR laser.

[0012] Furthermore, the temperature control module includes a temperature sensor interface, a PID controller, and a thermoelectric cooler driver; it collects the signal of the thermistor inside the DBR laser, compares it with the set temperature, and drives the thermoelectric cooler to heat or cool the laser die after PID calculation.

[0013] Furthermore, the optical feedback module includes a Mach-Zehnder interferometer and a balanced photodetector; the Mach-Zehnder interferometer splits the output light of the DBR laser into two paths to generate an optical path difference and then combines them to form interference light; the balanced photodetector converts the interference light into a differential electrical signal.

[0014] This invention's collaborative control module utilizes the ZYNQ7010 heterogeneous core development platform, which integrates an ARM dual-core processor and FPGA programmable logic. The ARM processor handles upper-level task scheduling, communication with the host computer, parameter parsing, data storage, and the execution of non-real-time control algorithms. The FPGA, on the other hand, handles tasks requiring high real-time performance, including: execution of the temperature control PID algorithm, real-time generation and updating of four DAC control signals, real-time computation of a frequency sweep nonlinear compensation algorithm based on MZI feedback signals, and high-speed interface control with the ADC acquisition module. The ARM and FPGA interact via an internal high-performance bus (AXI), achieving an optimized hardware-software collaborative control architecture.

[0015] The host computer of this invention is control software running on a PC, which communicates with the ZYNQ7010 development board via Ethernet and serial port. The host computer provides a graphical user interface, allowing users to flexibly configure the laser's operating mode, set the current values ​​for each channel, temperature setpoints, frequency sweep parameters, etc.

[0016] System working principle: After the system powers on and initializes, the host computer sends the user-configured operating parameters to the ZYNQ7010's ARM processor. After parsing the parameters, the ARM processor transmits the control instructions to the FPGA logic via the AXI bus.

[0017] The beneficial effects of the system of the present invention include: 1) Provides a clean power supply with ultra-low ripple through optimized GaN power supply and filtering design; 2) High-precision multi-channel current drive and PID temperature control are used to achieve precise stability of the laser's operating point; 3) By using a real-time optical feedback closed loop based on FPGA, the frequency sweep nonlinearity is effectively compensated to obtain a high linearity wavelength tuning output.

[0018] The system of this invention, through innovative hardware architecture and software algorithms, organically integrates high-performance GaN power supply, multi-channel precision current drive, precise temperature control and high-speed optical feedback closed loop on a platform controlled by ARM+FPGA intelligent collaboration, achieving a leapfrog improvement in the performance of DBR lasers. Attached Figure Description

[0019] Figure 1 This is a block diagram of the overall architecture of the system of the present invention; In the diagram, 1. GaN switching power supply module, 2. Multi-channel precision current drive module, 3. Temperature control module, 4. Collaborative control module, 5. DBR laser, 6. Optical feedback module, 7. Data acquisition module, 8. Host computer; Figure 2 This is a schematic diagram of the filter network for a GaN switching power supply module. Figure 3This is a circuit diagram of a multi-channel precision current drive module. Figure 4 This is a circuit diagram of the temperature control module; Figure 5 This is a flowchart of a real-time predistortion compensation algorithm executed in programmable logic. Figure 6 This is a schematic diagram showing the relationship between the output wavelength and optical power of a DBR laser after being driven by the system of this invention; Figure 7 for Figure 6 A magnified schematic diagram showing the relationship between the output wavelength and optical power of the DBR laser in the box; Figure 8 This is a schematic diagram showing the relationship between the output wavelength and signal-to-noise ratio (SNR) of a DBR laser after being driven by the system of this invention; Figure 9 This is a schematic diagram of the laser operating temperature control curve implemented by the system of the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this is not intended to limit the scope of the invention.

[0021] like Figure 1 As shown, the overall architecture of the system of the present invention includes a GaN switching power supply module 1, a multi-channel precision current drive module 2, a temperature control module 3, a collaborative control module 4, a DBR laser 5, an optical feedback module 6, a data acquisition module 7, and a host computer 8. Each module is electrically and optically connected to form a complete drive and closed-loop control link.

[0022] The collaborative control module 4 uses a Xilinx ZYNQ-7010 SoC chip, which internally includes an ARM Cortex-A9 dual-core processor system (PS) and programmable logic (PL). The PS runs an embedded operating system and is responsible for communicating with the host computer 8 via an Ethernet interface, parsing the current, temperature, and frequency sweep parameters sent by the user. The PL is programmed using a hardware description language to implement high-real-time control logic. The PS and PL exchange data at high speed via the AXI4 bus.

[0023] like Figure 1 and Figure 3 As shown, the multi-channel precision current drive module 2 includes two digital-to-analog converters (DACs). One is an LTC2672, a 12-bit, 5-channel current output DAC. In this system, three of its channels are configured in current output mode to drive the gain region, semiconductor optical amplification region (SOA), and grating region of the DBR laser 5, respectively. The output current range of each channel is set to 0-100mA using an external 0.1% accuracy, 25mΩ sampling resistor, achieving a theoretical resolution of approximately 0.01mA.

[0024] The LTC2672 connects to the PS pin of the ZYNQ via the SPI bus and is responsible for outputting three high-precision currents to drive the DBR laser's gain region, SOA region, and grating region.

[0025] The other chip is the MS9714, which is used to drive the phase region, which has extremely high requirements for noise and dynamic response. Its output current range is set to 0-20mA through a precision resistor network, with a resolution of approximately 1.22μA.

[0026] The MS9714 connects directly to the general-purpose I / O pins of the ZYNQ's PL terminal via a 14-bit parallel bus, write enable, and address lines. It is dedicated to high-speed, real-time driving of phase region current, enabling the FPGA to directly control its output with nanosecond-level delay and a refresh rate of up to 50MHz, which is crucial for real-time predistortion compensation algorithms.

[0027] like Figure 4 As shown, temperature control module 3 is based on the MAX1978 chip. This chip integrates a high-resolution (0.1℃) temperature sensor input circuit, a PID compensator, and an H-bridge TEC driver with a ±2.5A drive capability.

[0028] The thermistor (NTC) signal inside the DBR laser 5 is input to the MAX1978. The target temperature value is written to the MAX1978's internal setpoint register via the SPI bus from the ZYNQ PS pin. The chip's internal PID controller outputs a control signal based on the temperature error, driving the external thermoelectric cooler (TEC) to form a stable temperature closed loop.

[0029] like Figure 2 As shown, GaN switching power supply module 1 uses the domestically produced HJW650D150A GaN HEMT as the power switch, and the control chip is KP2206SSG, forming a synchronous buck circuit. By designing a multi-stage LC filter network, the ripple caused by the switching frequency (500kHz) is effectively suppressed to below 50mV, providing a clean power supply for the subsequent precision analog circuit.

[0030] The optical feedback module 6 includes an unbalanced Mach-Zehnder interferometer (MZI) and a balanced photodetector. The optical path difference between the two arms of the MZI is approximately 10 meters, corresponding to a free spectral range (FSR) of approximately 20 MHz in the 1550 nm band. The output light from the laser 5 interferes with the MZI and is converted into a differential voltage signal by the balanced detector.

[0031] The data acquisition module 7 in this embodiment uses the AD9238BCPZ-65 from Analog Devices, a 12-bit, dual-channel, 65MSPS analog-to-digital converter. One channel is used to acquire the MZI interference signal output from the balanced photodetector, and the other channel can be used to monitor the temperature and voltage values ​​of the laser 5. The ADC module is directly connected to the ZYNQ PL terminal via a high-speed parallel LVCMOS interface, ensuring that the sampled data can be input to the FPGA logic for processing with minimal latency. System closed-loop control and predistortion compensation algorithm flow: After the system is powered on and initialized, the host computer software sends the user-configured operating parameters to the ZYNQ PS terminal. The ARM processor parses the parameters and transmits the control commands and data (temperature setpoint, static current values ​​of each channel, and frequency sweep parameters) to the user logic storage area of ​​the PL terminal via the AXI4-Lite bus.

[0032] In constant temperature and constant current operating mode, the FPGA logic control state machine is relatively simple. The PS terminal configures the LTC2672 to output constant current for each channel via SPI, and configures the target temperature of the MAX1978 via another SPI. The PL terminal writes a fixed phase region bias current control word to the MS9714. The system enters a steady state, and the laser outputs a fixed wavelength and power.

[0033] In wavelength sweep frequency operation mode, the real-time predistortion compensation algorithm process executed by the PL terminal involves the PS terminal converting the preset ideal linear sweep frequency curve (wavelength-time relationship) into the corresponding "ideal driving current sequence in the phase region" and preloading it into the block RAM of the PL terminal via DMA.

[0034] like Figure 5 As shown, one of the core innovations of this invention lies in the real-time predistortion compensation algorithm process executed at the PL end, which specifically includes: Step S501: Synchronous signal acquisition. Under the control of the FPGA, while starting wavelength sweep (i.e., updating the MS9714 output), the MZI interference signal after being digitized by the ADC is acquired at a fixed sampling rate (e.g., 20 MSPS). Step S502: Real-time wavelength calculation. The digital signal processing logic inside the FPGA processes the acquired interference signal (approximately sine wave) in real time. By calculating its instantaneous phase Φ(n), and according to the formula Δλ = (λ² / (2π * ΔL)) * ΔΦ, the actual instantaneous wavelength λ_actual(n) of the laser is calculated, where ΔL is the optical path difference between the two arms of the MZI. Step S503: Error calculation. Compare the calculated λ_actual(n) with the preset ideal linear sweep wavelength λ_ideal(n) corresponding to the current time n to obtain the instantaneous wavelength error Δλ(n) = λ_ideal(n) - λ_actual(n). Step S504: Compensation amount query. Using Δλ(n) as the address, query the pre-distortion compensation lookup table (LUT) pre-stored in the FPGA block RAM. This LUT was established through the previous calibration experiment and stores the mapping relationship between "wavelength error" and "required phase region current correction amount ΔI_phase". Step S505: The drive signal is updated in real time. The obtained ΔI_phase(n) is superimposed with the basic sweep frequency current value to generate a new control word, which is immediately written to MS9714 in the next clock cycle to correct the drive current in real time. Step S506: Closed-loop loop. The above process is continuously pipelined within the frequency sweep cycle, forming a high-speed closed loop with microsecond-level delay, thereby achieving dynamic correction of frequency sweep nonlinearity.

[0035] Through the collaborative work of the aforementioned hardware architecture and software algorithms, the system ultimately achieves high-precision, high-stability, and high-linearity driving of the DBR laser.

[0036] After being driven by the system of this invention, the relationship between the output wavelength and optical power of the DBR laser is as follows: Figure 6-7 As shown in the figure, the DBR laser has a good spectral effect in this phase modulation region and continuous single-mode output.

[0037] Figure 8 The relationship between the output wavelength and signal-to-noise ratio (SNR) of a DBR laser after being driven by the system of this invention is as follows: Figure 8 As shown in the figure, it can be seen that the DBR laser outputs a side-mode suppression ratio (SMSR) greater than 48dB in this phase modulation region, indicating good single-mode characteristics.

[0038] The laser operating temperature control curve achieved using the system of this invention is as follows: Figure 9 As shown in the figure, the temperature of the laser chip inside the DBR laser is fed back to the FB-pin of the temperature control chip and compared with the preset operating temperature. Then an error signal is generated. Through the PID control algorithm, a negative feedback control is formed on the TEC inside the laser to achieve controlled cooling and heating, so that the laser operating temperature is always kept at about 25℃.

[0039] Advantages of the system of this invention: 1. Achieved ultra-high precision temperature control: By adopting a high-precision temperature sensor, a dedicated TEC control chip, and an optimized digital PID algorithm, the operating temperature stability of the laser is improved to ±0.01℃, effectively suppressing long-term wavelength drift caused by temperature drift and improving the accuracy and repeatability of the laser output wavelength.

[0040] 2. Provides an extremely clean power supply: Employing GaN HEMT-based high-frequency switching power supply technology, combined with multi-stage filtering and closed-loop voltage regulation, the output ripple is suppressed to below 50mV, significantly reducing the coupling of power supply noise to the laser drive current and improving the spectral purity and power stability of the laser output.

[0041] 3. Achieved multi-channel high-precision independent current drive: The current resolution of all four drive channels is better than 0.01mA, covering the range from mA to hundreds of mA, and the isolation between channels is good with low crosstalk. This enables more precise and independent control of each functional area (SOA, gain, grating, phase) of the DBR laser, optimizing the laser's operating state.

[0042] 4. Significantly improved sweep frequency linearity: Innovatively utilizing an MZI interferometer as a high-sensitivity wavelength scale, and implementing real-time signal acquisition and nonlinear compensation algorithms through FPGA, it can dynamically correct sweep frequency distortion caused by factors such as device response and current-wavelength nonlinearity, obtaining near-ideal linear wavelength scanning, and greatly improving performance in applications such as OFDR and spectral measurement.

[0043] 5. High system integration and flexible configuration: Adopting an ARM+FPGA collaborative architecture, it combines a flexible upper-level management interface with powerful low-level real-time processing capabilities. Coupled with feature-rich host computer software, it supports visual configuration and data monitoring for multiple working modes. The system is highly scalable, facilitating function upgrades and secondary development.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tunable DBR laser driving system based on FPGA and GaN devices, characterized in that, include: GaN switching power supply module (1) is used to provide low ripple DC power; A multi-channel precision current drive module (2) has its input terminal connected to the output terminal of the GaN switching power supply module (1) and is used to generate at least four independently adjustable drive currents. Temperature control module (3) is used to monitor and adjust the die temperature of the DBR laser; The collaborative control module (4) is connected to the multi-channel precision current drive module (2) and the temperature control module (3) respectively, and is used to output current control signals and temperature control signals; The DBR laser (5) has its power input terminal, current input terminals of each functional area and temperature sensing terminal connected to the GaN switching power supply module (1), the output terminals of the multi-channel precision current drive module (2) and the temperature control module (3), respectively. The optical feedback module (6) receives the output light from the DBR laser (5) at its input end and is used to convert the change in light wavelength into an electrical signal; The data acquisition module (7) has its input end connected to the output end of the optical feedback module (6) and its output end connected to the feedback input end of the collaborative control module (4), forming a closed-loop control loop for wavelength linearity compensation.

2. The system according to claim 1, characterized in that, The collaborative control module (4) includes a heterogeneous system chip, which integrates a processor system and programmable logic; the processor system is responsible for communicating with the host computer, parsing parameters and scheduling tasks, and interacting with the programmable logic through an internal bus. The programmable logic is responsible for executing the real-time control algorithm and directly controlling at least one high-speed current channel in the multi-channel precision current drive module (2).

3. The system according to claim 2, characterized in that, The programmable logic is configured to execute a real-time predistortion compensation algorithm, including the following steps: During the wavelength sweep process, the optical feedback signal digitized by the data acquisition module (7) is acquired synchronously; Based on the optical feedback signal, the instantaneous wavelength of the DBR laser (5) output is calculated in real time; Calculate the error value between the instantaneous wavelength and the ideal sweep wavelength at the current moment; Based on the error value, the corresponding drive current compensation amount is obtained by querying the pre-stored compensation lookup table. Based on the driving current compensation amount, the current control signal output to the multi-channel precision current drive module (2) is adjusted in real time.

4. The system according to claim 1, characterized in that, The multi-channel precision current drive module (2) includes a first digital-to-analog converter unit and a second digital-to-analog converter unit; the first digital-to-analog converter unit is connected to the processor system of the cooperative control module (4) through a serial interface and is used to provide multiple high-precision static or slow-changing drive currents; the second digital-to-analog converter unit is directly connected to the programmable logic of the cooperative control module (4) through a parallel bus and is used to provide one high-speed dynamically updated drive current.

5. The system according to claim 4, characterized in that, The driving current provided by the first digital-to-analog converter is used to drive the gain region, semiconductor optical amplification region and grating region of the DBR laser (5); the driving current provided by the second digital-to-analog converter is used to drive the phase region of the DBR laser (5).

6. The system according to claim 1, characterized in that, The temperature control module (3) includes a temperature sensor interface, a PID controller and a semiconductor cooler driver; it collects the signal of the thermistor inside the DBR laser (5), compares it with the set temperature and performs PID calculations, and then drives the semiconductor cooler to heat or cool the laser die.

7. The system according to claim 1, characterized in that, The optical feedback module (6) includes a Mach-Zehnder interferometer and a balanced photodetector; the Mach-Zehnder interferometer splits the output light of the DBR laser (5) into two paths to generate an optical path difference and then combines them to form interference light; the balanced photodetector converts the interference light into a differential electrical signal.

8. The system according to claim 1, characterized in that, The GaN switching power supply module (1) adopts a synchronous buck topology based on gallium nitride high electron mobility transistors, and its switching frequency is not less than 500kHz.

9. The system according to claim 2, characterized in that, The processor system and the programmable logic interact with each other via the AXI bus for data and instructions.

10. The system according to claim 1, characterized in that, It also includes a host computer, which is connected to the collaborative control module (4) via wired or wireless communication, and is used to provide a human-machine interface for configuring working parameters, system control and data monitoring.

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