A current-tuned semiconductor laser array linear tuning system

Abstract

The application discloses a current tuning semiconductor laser array linear tuning system, which comprises a DFB laser array, a beat frequency signal processing unit, a linear tuning unit and a laser driving unit which are connected in sequence; the beat frequency signal processing unit converts laser signals emitted by the DFB laser array into beat frequency signals to obtain data of the relationship between the beat frequency signal frequency and time; the linear tuning unit obtains linear tuning control data of the next round; and the laser driving unit performs round scanning on the DFB laser array according to the linear tuning control data output by the linear tuning unit. The application can realize the driving and fast linear tuning of the current tuning semiconductor laser array, improve the overall performance of the system and reduce the cost of the system.

Description

Technical Field

[0001] This invention belongs to the field of laser frequency modulation technology, specifically relating to a linear tuning system for a current-tuned semiconductor laser array. Background Technology

[0002] Linear tunable laser technology works by emitting a linear sawtooth or triangular frequency-modulated light signal and interfering with the frequency-modulated light signal reflected from the target. By measuring the frequency difference caused by time delay and the Doppler effect due to the movement of the target, the position and velocity information of the target can be obtained. Therefore, an ideal linear frequency-sweeping laser plays a very important role in practical applications.

[0003] As a high-quality light source for tunable laser technology, the output wavelength of a DFB laser is primarily affected by temperature and drive current. Due to fluctuations in operating temperature and conditions, the characteristic impedance of a DFB laser fluctuates to some extent during actual operation. Therefore, for a given drive voltage, the corresponding drive current exhibits fluctuations, affecting the linearity of the laser output. Furthermore, because lasers inherently possess a degree of nonlinearity, a linearly input drive current is insufficient to achieve linearly tunable laser output.

[0004] Tunable laser technology, as a key technology in short-range OFDR, optical CT, and lidar, directly relates to important performance characteristics such as system accuracy and resolution. Currently, for the linear tuning problem of tunable lasers, one widely used method is to achieve linear frequency modulation and coherent enhancement through a hybrid analog-digital phase-locked loop (PLL), but this method suffers from high system complexity. Another method is to achieve linear tuning of tunable lasers through digital circuit structures such as resampling and digital predistortion. Summary of the Invention

[0005] Technical problem solved: This invention discloses a linear tuning system for a current-tuned semiconductor laser array, which can realize the driving and rapid linear tuning of the current-tuned semiconductor laser array, helping to improve the overall system performance and reduce system cost.

[0006] Technical solution:

[0007] A current-tuned semiconductor laser array linear tuning system, the linear tuning system comprising a DFB laser array, a beat frequency signal processing unit, a linear tuning unit and a laser driving unit connected in sequence;

[0008] The beat frequency signal processing unit converts the laser signal emitted by the DFB laser array into a beat frequency signal, uses an elliptic filter to filter out the high-frequency components in the beat frequency signal, performs a Hilbert transform on the beat frequency signal after high frequency removal, and then performs median filtering on the transformed beat frequency signal to obtain the relationship data of the beat frequency signal frequency changing with time.

[0009] The linear tuning unit simultaneously reads the relationship data of the beat frequency signal frequency changing with time and the control data of the current scanning round. Based on the relationship data of the beat frequency signal frequency changing with time, it determines the start and end points of the sweep frequency and the corresponding ideal sweep frequency curve. Calibration points are set at preset intervals on the ideal sweep frequency curve. Based on the correspondence between the sweep frequency and the control data on the time axis, the position of the ideal frequency corresponding to each calibration point on the time axis is extracted. The control data corresponding to the same position on the time axis is found and written into the linearly tuned control data sequence. Then, the control data between each calibration point is linearly fitted to obtain the linear tuning control data for the next round.

[0010] The laser driving unit performs a circular scan of the DFB laser array based on the linear tuning control data output by the linear tuning unit.

[0011] Furthermore, the beat frequency signal processing unit includes a self-heterodyne Mach-Zehnder interferometer, a photoelectric balance detector, an analog-to-digital conversion module, and a signal processing module connected in sequence;

[0012] The laser signal emitted by the DFB laser array is converted into a beat frequency signal by a self-heterodyne Mach-Zehnder interferometer, and then converted into a corresponding analog electrical signal by a photoelectric balance detector. The analog-to-digital conversion module converts the analog electrical signal into a corresponding data signal and inputs it into the signal processing module. The signal processing module uses an elliptic filter to filter out the high-frequency components in the beat frequency signal, performs a Hilbert transform on the beat frequency signal after high-frequency filtering, and then performs median filtering on the transformed beat frequency signal to obtain the relationship data of the beat frequency signal frequency changing with time.

[0013] Furthermore, the linear tuning unit includes a search-fit module and a data path module;

[0014] The search-fit module calculates the linear tuning control data for the next round based on the relationship data of the beat frequency signal frequency changing over time and the control data of the current scanning round;

[0015] The data path module includes an AXI bus and a corresponding interface, used to store the next round of linear tuning control data into the memory of the laser driver unit for the laser driver unit to read.

[0016] Furthermore, the linear tuning unit includes a tuning mode setting module, and the tuning modes include single tuning, periodic tuning, and linearity threshold control tuning.

[0017] Furthermore, the linear tuning unit includes a calibration point setting module, which compares the frequency-time relationship data with the ideal sweep frequency curve. When the frequency corresponding to the calibration point differs from the ideal frequency by more than a preset frequency threshold, the first spacing is used for calibration; otherwise, the second spacing is used for calibration. The first spacing is smaller than the second spacing.

[0018] Furthermore, the linear tuning unit fills in the missing control data between calibration points by linear fitting based on the control data of adjacent calibration points, thereby obtaining linear tuning control data of the same length as the original control data.

[0019] Furthermore, the laser driving unit includes an FPGA control module, a digital-to-analog converter module, and a multiplexer; the first output terminal of the FPGA control module is directly connected to the first input terminal of the multiplexer, and the gating data is directly sent to the multiplexer; the second output terminal of the FPGA control module is connected to the second input terminal of the multiplexer through the digital-to-analog converter module, and the linear tuning control data is converted into a format and then sent to the multiplexer.

[0020] The output of the multiplexer is connected to the control terminal of the DFB laser array, and the DFB laser array is controlled according to the received gating data and linear tuning control data.

[0021] Furthermore, the digital-to-analog conversion module includes a DAC chip and an operational amplifier;

[0022] The DAC chip converts 12-bit binary data DATA into corresponding analog current and has two differential current outputs I. OUTA and I OUTB The conversion formula is:

[0023]

[0024]

[0025] Where I OUTFS It is the full-scale current, which is 20mA; Data is the decimal form of DATA;

[0026] The operational amplifier subtracts and biases the two differential current outputs to obtain a single-ended output with twice the amplitude, which is output as a single-ended voltage V. OUT :

[0027]

[0028] The formula contains:

[0029]

[0030] R4, R f R6, R3, and R5 are the resistance values;

[0031] The operational amplifier then converts the single-ended output voltage into a current output I that drives the laser. OUT :

[0032]

[0033] Furthermore, the multiplexer uses a MAX4782 chip to select the output current of the upper-level circuit to four channels based on the gating data, thereby achieving row selection of the DFB laser array.

[0034] Beneficial effects:

[0035] First, the current-tuned semiconductor laser array linear tuning system of the present invention first controls the laser to perform an initial frequency sweep. Based on the frequency sweep curve, the control data after linear tuning is obtained by a search-fit method and used for the next frequency sweep, so that the laser output frequency curve has higher linearity. When using the search-fit method to linearly tune the laser, the laser frequency sweep frequency, algorithm complexity, resource utilization and the requirements for tuning accuracy are fully considered, which is conducive to improving the frequency sweep linearity of existing lasers and providing higher performance in a variety of practical application scenarios. It realizes dynamic, real-time and high-performance linear tuning of the current-tuned semiconductor laser array.

[0036] Secondly, the linear tuning system of the current-tuned semiconductor laser array of the present invention differs from the optoelectronic hybrid phase-locked loop technology. The present invention uses a pure digital circuit structure, which has higher stability and reliability, clearer control links and data paths, easier parameter configuration, and is easy to port to various types of current-tuned semiconductor laser arrays.

[0037] Third, the current-tuned semiconductor laser array linear tuning system of the present invention differs from traditional resampling and digital predistortion techniques. It utilizes the feedback information of the current sampling to perform linear tuning of the laser output frequency by searching instead of calculating, thereby reducing the complexity of the tuning system. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the current-tuned semiconductor laser array linear tuning system of the present invention;

[0039] Figure 2 This is a schematic diagram illustrating the application principle of the current-tuned semiconductor laser array linear tuning system of the present invention;

[0040] Figure 3 This is a schematic diagram illustrating the principle of linear tuning algorithm for current-tuned semiconductor laser arrays.

[0041] Figure 4 This is a comparison chart of the laser array sweep curves before and after linear tuning;

[0042] Figure 5 It is a circuit diagram that uses an operational amplifier to subtract the two differential current outputs and bias them appropriately.

[0043] Reference numerals: 1. DFB laser array; 2. Self-heterodyne Mach-Zehnder interferometer; 3. Photoelectric balanced detector; 4. Analog-to-digital converter module; 5. Signal processing module; 6. Search-fit module; 7. Data path module; 8. FPGA control module; 9. Digital-to-analog converter module; 10. Multiplexer. Detailed Implementation

[0044] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0045] This invention discloses a current-tuned semiconductor laser array linear tuning system, the linear tuning system comprising a DFB laser array 1, a beat frequency signal processing unit, a linear tuning unit and a laser driving unit connected in sequence;

[0046] The beat frequency signal processing unit converts the laser signal emitted by the DFB laser array 1 into a beat frequency signal, uses an elliptic filter to filter out the high-frequency components in the beat frequency signal, performs a Hilbert transform on the beat frequency signal after high frequency removal, and then performs median filtering on the transformed beat frequency signal to obtain the relationship data of the beat frequency signal frequency changing with time.

[0047] The linear tuning unit simultaneously reads the relationship data of the beat frequency signal frequency changing with time and the control data of the current scanning round. Based on the relationship data of the beat frequency signal frequency changing with time, it determines the start and end points of the sweep frequency and the corresponding ideal sweep frequency curve. Calibration points are set at preset intervals on the ideal sweep frequency curve. Based on the correspondence between the sweep frequency and the control data on the time axis, the position of the ideal frequency corresponding to each calibration point on the time axis is extracted. The control data corresponding to the same position on the time axis is found and written into the linearly tuned control data sequence. Then, the control data between each calibration point is linearly fitted to obtain the linear tuning control data for the next round.

[0048] The laser driving unit performs a circular scan of the DFB laser array 1 based on the linear tuning control data output by the linear tuning unit.

[0049] See Figure 1 and Figure 2 The linear tuning system comprises the following three parts:

[0050] The first part is the beat frequency signal measurement and signal processing section, including a self-heterodyne Mach-Zehnder interferometer 2, a photoelectric balance detector 3, an analog-to-digital converter module 4, and a signal processing module 5. The laser beam is converted into a beat frequency signal by the self-heterodyne Mach-Zehnder interferometer; the photoelectric balance detector 3 receives the beat frequency signal and converts it into an electrical signal that can be read by the analog-to-digital converter module 4; the digital signal output from the analog-to-digital converter module is input to the host computer; the signal processing module 5 uses an elliptic filter to filter out high-frequency components, performs a Hilbert transform on the filtered signal, and performs median filtering to remove noise, obtaining the frequency-time relationship of the beat frequency signal.

[0051] The second part is the linear tuning section, which includes the search-fit module 6 and the data path module 7; Figure 3 The diagram illustrates the search-fit algorithm. The Zynq platform's PS terminal simultaneously reads frequency-time relationship data from the beat frequency signal measurement and signal processing sections, along with the current scan control data. Based on the frequency-time relationship data, it determines the start and end points of the sweep frequency, i.e., the sweep range. Based on these points, it determines the ideal sweep frequency curve, and then performs calibration sequentially on this ideal curve. During calibration, the frequency-time relationship data is compared with the ideal sweep frequency curve. When the frequency corresponding to a calibration point differs from the ideal frequency by more than a preset threshold, a smaller calibration interval is used; otherwise, a larger interval is used. The smaller and larger intervals can be flexibly configured in advance through the Zynq platform. Using a smaller calibration interval for segments exceeding the threshold ensures high overall linearity of the sweep frequency curve. After calibration, based on the correspondence between the sweep frequency and control data on the time axis, the position of the ideal frequency corresponding to each calibration point on the time axis is extracted. The control data corresponding to the same position on the time axis is then searched and written into the linearly tuned control data sequence. After the search is complete, linear fitting is performed on the control data between each calibration point to obtain complete linearly tuned control data. Preferably, based on the control data of adjacent calibration points, the missing control data between calibration points is filled by linear fitting to obtain linear tuning control data of the same length as the original control data.

[0052] The third part is the DFB laser module and driver section, including the DFB laser array 1, FPGA control module 8, multiplexer 10, and digital-to-analog converter module 9. The digital-to-analog converter module 9 and multiplexer 10 together constitute the tuning and driving voltage signal source for driving the DFB laser array 1, directly driving it. The FPGA control module 8 reads control data from the BRAM at the PL terminal of the Zynq platform, sends control data to the digital-to-analog converter module 9 according to a preset sequence, and sends selection signals to the multiplexer 10, driving one unit in the DFB laser array 1 to emit laser light of the corresponding frequency, while the remaining units become transparent, achieving a sweeping effect of the DFB laser array.

[0053] The data path module 7 includes an AXI bus and corresponding interfaces, storing complete linear tuning control data in the BRAM for the FPGA control module 8 to read. In this embodiment, the AXI bus in the data path module 7 connects the PS and PL ends of the Zynq platform, transmitting the linear tuning control data obtained by the lookup-fit ​​module 6 from the PS end to the BRAM of the PL end, improving data transmission speed and ensuring scan continuity. The linear tuning section can be configured as single tuning, periodic tuning, or linearity threshold control tuning according to actual needs. The FPGA control module 8 reads control data from the BRAM and generates an enable signal. The control data and enable signal are transmitted to the digital-to-analog converter module 9 and the multiplexer 10, respectively, to generate the drive signal and gating signal for the DFB laser array 1. The DFB laser array 1 outputs frequency-modulated laser, which is converted into an electrical signal by the beat frequency signal measurement module. The signal processing module obtains the frequency-time relationship of the laser output by the laser array. The search-fit module 6 at the PS end in the Zynq platform obtains the ideal sweep frequency curve based on the frequency-time relationship. On the curve, calibration points are set at certain intervals according to the difference between the actual frequency and the ideal frequency. The control data corresponding to the calibration points is searched, and the data between the calibration points is fitted. The data after tuning is stored in the BRAM through the data path module 7 for driving the next scan.

[0054] The specific implementation method of the tuning process is as follows:

[0055] First, set the sweep frequency to 1kHz, manually write the linear control data, and use the single-tuning method.

[0056] The digital-to-analog converter module 9 uses the AD9765 as the DAC chip and the MAX4416 as the operational amplifier. The AD9765's single DAC has two differential current outputs I... OUTA and I OUTB The formula for converting 12-bit binary data DATA to analog current is:

[0057]

[0058]

[0059] Where I OUTFS It is the full-scale current, which is 20mA; Data is the decimal form of DATA.

[0060] See Figure 5 An operational amplifier is used to subtract the two differential current outputs and apply appropriate bias to obtain a single-ended output with twice the amplitude, which is output as a single-ended voltage. The voltage output formula is as follows:

[0061]

[0062] The formula contains:

[0063]

[0064] R4, R f R6, R3, and R5 are the resistance values ​​shown in the circuit diagram.

[0065] Substituting the actual circuit parameters, the voltage output formula is:

[0066]

[0067] An operational amplifier and a BJT are used to convert the single-ended output voltage into a current output IOUT that can directly drive the laser. The specific current output formula is as follows:

[0068]

[0069] The multiplexer 10 uses the MAX4782 chip, which can select the output current of the upper-level circuit to output to 4 channels according to the strobe signal, so as to realize row selection of the laser array.

[0070] The frequency sweep signals of the DFB laser array before and after linear tuning using the method described in this invention are obtained in the host computer, specifically as follows: Figure 4 Using Matlab to calculate the sweep frequency linearity before and after linear frequency tuning, it can be found that before linear tuning, the R² of the sweep frequency curve of the DFB laser array is 0.987629 and the residual norm is 10.1644. After linear tuning, the R² of the sweep frequency curve of the DFB laser array is 0.999795 and the residual norm is 1.2201. This invention simultaneously improves the sweep frequency linearity and reduces the residual norm of the sweep frequency curve for the laser array sweep frequency optical signal, achieving excellent linear tuning effect.

[0071] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A current-tuned semiconductor laser array linear tuning system, characterized by, The linear tuning system comprises a DFB laser array, a beat signal processing unit, a linear tuning unit and a laser driver unit connected in sequence. The beat signal processing unit converts the laser signal emitted by the DFB laser array into a beat signal, filters high-frequency components in the beat signal using an elliptical filter, performs Hilbert transform on the beat signal after filtering the high-frequency components, and performs median filter processing on the transformed beat signal to obtain the relationship data of the beat signal frequency changing with time. The linear tuning unit reads the relationship data of the beat signal frequency changing with time and the control data of the current scanning round simultaneously, determines the sweep start and end points and the corresponding ideal sweep curve according to the relationship data of the beat signal frequency changing with time, sets the calibration points on the ideal sweep curve at a preset interval, extracts the positions of the ideal frequencies corresponding to each calibration point on the time axis according to the corresponding relationship between the sweep frequency and the control data on the time axis, finds the control data corresponding to the same position on the time axis, writes the linearly tuned control data sequence, and performs linear fitting on the control data between the calibration points to obtain the linear tuning control data of the next round. The laser driver unit performs round scanning on the DFB laser array according to the linear tuning control data output by the linear tuning unit.

2. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The beat signal processing unit comprises a self-heterodyne Mach-Zehnder interferometer, a photoelectric balance detector, an analog-to-digital conversion module and a signal processing module connected in sequence. The laser signal emitted by the DFB laser array is converted into a beat signal by the self-heterodyne Mach-Zehnder interferometer, and then converted into a corresponding analog electrical signal by the photoelectric balance detector. The analog electrical signal is converted into a corresponding data signal by the analog-to-digital conversion module and input into the signal processing module. The signal processing module filters high-frequency components in the beat signal using an elliptical filter, performs Hilbert transform on the beat signal after filtering the high-frequency components, and performs median filter processing on the transformed beat signal to obtain the relationship data of the beat signal frequency changing with time.

3. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The linear tuning unit comprises a lookup-fitting module and a data path module. The lookup-fitting module calculates the linear tuning control data of the next round according to the relationship data of the beat signal frequency changing with time and the control data of the current scanning round. The data path module comprises an AXI bus and a corresponding interface, which are used to store the linear tuning control data of the next round in the memory of the laser driver unit for reading by the laser driver unit.

4. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The linear tuning unit comprises a tuning mode setting module, and the tuning modes include single tuning, periodic tuning and linearity threshold control tuning.

5. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The linear tuning unit comprises a calibration point setting module, which compares the frequency-time relationship data with the ideal sweep curve. When the frequency corresponding to the calibration point differs from the ideal frequency by more than a preset frequency threshold, the first interval is used for calibration, otherwise the second interval is used for calibration, and the first interval is smaller than the second interval.

6. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The linear tuning unit fills the missing control data between the calibration points by linear fitting according to the control data of adjacent calibration points, and obtains linear tuning control data with the same length as the original control data.

7. The current-tuned semiconductor laser array linear tuning system of claim 1, wherein, The laser driving unit comprises an FPGA control module, a digital-to-analog conversion module and a multiplexer; a first output end of the FPGA control module is directly connected with a first input end of the multiplexer, and the gating data is directly sent to the multiplexer; a second output end of the FPGA control module is connected with a second input end of the multiplexer through the digital-to-analog conversion module, and the linear tuning control data is sent to the multiplexer after being converted in format; An output end of the multiplexer is connected with a control end of the DFB laser array, and the DFB laser array is controlled according to the received gating data and the linear tuning control data.

8. The current-tuned semiconductor laser array linear tuning system of claim 7, wherein, The digital-to-analog conversion module comprises a DAC chip with a model number of AD9765 and an operational amplifier with a model number of MAX4416. The DAC chip converts 12-bit binary data DATA into corresponding analog current, having two-way differential current output and The conversion formula is: ； ； wherein is full scale current, 20 mA; Data is the decimal form of DATA; The operational amplifier outputs two-way differential current and offsets to obtain a single-end output with double amplitude, and outputs in the form of single-end voltage : ； In the formula, there are: ； R4, R f , R6, R3, R5 are resistance values; The operational amplifier converts the single-ended output voltage into a current output that drives the laser : 。 9. The current-tuned semiconductor laser array linear tuning system of claim 7, wherein, The multiplexer adopts a MAX4782 chip, and the output current of the upper circuit is selected and output to four channels according to the gating data, so that the row selection of the DFB laser array is realized.

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