C-band tunable broadband light source system with wavelength and power locking function

Abstract

The invention discloses a C-band tunable broadband light source system with a wavelength and power locking function. The C-band tunable broadband light source system comprises a tunable laser array chip, a main control module, a laser chip current driving module, a temperature control module, an optical splitter, a wavelength locking module and a power adjusting module, the temperature control module reads and adjusts the working temperature of the tunable laser array chip; the laser chip current driving module applies current excitation to each laser in the tunable laser array chip; emergent light of the tunable laser array chip is respectively transmitted to the wavelength locking module and the power adjusting module through the optical splitter; the wavelength locking module carries out wavelength locking on the emergent light based on two F-P etalon with the same response curve period and complementary response curve peak values; and the power regulation module adopts a PID algorithm to carry out power regulation and locking on the emergent light. According to the invention, any wavelength lasing can be realized in the C wave band, and the method has the advantages of rapidness, accuracy and the like in the aspect of wavelength and power deviation correction.

Description

Technical Field

[0001] The invention belongs to the field of light source equipment, and in particular relates to a C-band tunable broadband light source system with wavelength and power locking functions. Background Art

[0002] Research shows that light waves in the range of 1530nm-1565nm (C band) have the lowest transmission loss in optical fibers. Therefore, in practical applications, DWDM (Dense Wavelength Division Multiplexing) technology divides multiple independent optical carriers in the C band to transmit multiple different information. Since traditional lasers can only provide fixed wavelengths, multiple lasers need to be integrated in an optical module to meet the requirements of the DWDM system, which greatly increases the size and cost of the optical module and is not conducive to later maintenance and replacement. For this reason, people hope to use semiconductor lasers with adjustable wavelengths in the C band in DWDM systems, so that only one laser can be used as a light source in a DWDM system, which can greatly reduce the complexity and maintenance costs of the system.

[0003] The birth of tunable lasers was a milestone event in the field of optics in the second half of the 20th century, breaking through the limitations of fixed emission wavelengths of traditional lasers. With the continuous advancement of materials, structural design, and processing technology, various types of tunable lasers are developing in the direction of miniaturization and integration, and have made leaps and bounds in many indicators such as wavelength scanning range, wavelength control accuracy, wavelength switching speed, line width and power, and their cost-effectiveness is gradually emerging. Therefore, tunable lasers are considered to be excellent light sources for many application fields such as optical communications, optical switching, and optical coherence tomography, and are the key to the success of future photonic integration and optoelectronic fusion routes.

[0004] Generally speaking, tunable lasers can be divided into discrete and monolithic integrated types according to the integration method. The discrete type mainly includes the external cavity type (ELC), and the monolithic integrated type mainly includes the distributed Bragg reflector type (DBR), the vertical cavity surface emitting type (VCSEL) and the distributed feedback type (DFB).

[0005] ELC tunable lasers have two structural types: Littrow and Littman-Metcalf. The wavelength is selected based on the diffraction grating. This type of semiconductor laser has a simple structure, is easy to manufacture, and has excellent light output performance - a large tuning range, narrow line width, and good single-mode characteristics. However, whether it is the Littrow structure or the Littman-Metcalf structure, the wavelength is selected by mechanical tuning, so the speed and accuracy of wavelength tuning are limited by the mechanical device. More importantly, photonic integration is becoming a trend in the development of information science and technology in the future. Since the ELC tunable laser is a discrete structure, the supporting mechanical tuning device is not conducive to the integration of the laser, so it is likely to be eliminated in the future.

[0006] DBR tunable lasers usually contain an active region, a phase region, and two front and rear Bragg grating regions. The structure works based on the Vernier effect: the two Bragg gratings will have two different multi-peak comb spectra after being excited by current. By adjusting the injected current in the grating region and the phase region, the two comb spectra will overlap at a certain peak, and laser output will be generated at the wavelength corresponding to the peak. DBR tunable lasers have the advantages of a large tuning range, narrow line width, and high power, but they achieve wavelength tuning based on the "vernier effect" and can only emit at fixed wavelength intervals, and cannot achieve true continuous tuning. In addition, the single-mode characteristics are poor, mode hopping is prone to occur, and the stability is poor.

[0007] VCSEL tunable lasers generally use gallium arsenide materials as substrates, with two DBR reflection areas and an active area stacked on the substrate. The DBR reflection area close to the substrate is an n-type semiconductor material, and the DBR reflection area far from the substrate is a p-type semiconductor material. The two DBR reflection areas actually constitute a resonant cavity, and the active area is between the two, and its thickness is generally tens to hundreds of nanometers. The direction of the emitted light of the VCSEL tunable laser is perpendicular to the surface of the active area and the DBR reflection area. Its advantages are small size, easy integration, good single-mode characteristics, and low manufacturing cost. However, its threshold current is too small, the power is too low, and it is restricted by the development of semiconductor material science. There are few VCSEL products working in the C band, so it is currently not suitable for important fields such as optical communication and optical switching.

[0008] DFB tunable lasers usually include an active region, a Bragg grating region, etc. High-reflection films and anti-reflection films are coated on both ends of the active region to form a resonant cavity. Its biggest feature is that the Bragg grating is set inside the resonant cavity. According to the Bragg formula, the effective refractive index of the Bragg grating can be changed by changing the temperature and the magnitude of the excitation current, thereby achieving wavelength selection. Studies have shown that a single DFB laser based on indium phosphide (InP) material can achieve a wavelength tuning range of about 2nm, a temperature tuning coefficient of about 0.1nm / ℃, and a current tuning coefficient of about 0.01nm / mA. In addition to a small tuning range, DFB tunable lasers have many advantages such as precise wavelength, narrow linewidth, good single-mode characteristics, and simple tuning methods. Research shows that with the advancement of semiconductor epitaxial design and processing technology, the new DFB laser array can integrate up to dozens of DFB lasers, Y-type combiner or S-type combiner, semiconductor optical amplifier (SOA) and other structures, which can greatly broaden the wavelength tuning range while retaining the advantages of the DFB structure. Based on this innovative structure, a C-band broadband tunable light source with a wide tuning range, high wavelength accuracy, fast tuning speed, small size, low cost and good stability is developed, which has important scientific research value and practical value, and is expected to solve the current problem of high dependence on imported light sources in optical sensing, optical communication and other fields. Summary of the invention

[0009] In view of the deficiencies in the prior art, the present invention provides a C-band tunable broadband light source system with wavelength and power locking function. Through coordinated control of software and hardware modules, laser output with adjustable power and any wavelength can be achieved in the C-band. It has many advantages such as precise wavelength control, fast tuning speed, high side mode suppression ratio, no mode hopping, high cost performance, etc. It can be used as a C-band universal broadband light source in optical laboratories, optical sensing, optical communications and other fields.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A C-band tunable broadband light source system with wavelength and power locking functions, characterized in that it comprises: a tunable laser array chip, a main control module, a laser chip current driving module, a temperature control module, a spectrometer, a wavelength locking module and a power adjustment module; the main control module is connected to the temperature control module, the laser chip current driving module, the wavelength locking module and the power adjustment module; the temperature control module reads and adjusts the internal operating temperature of the tunable laser array chip; the laser chip current driving module applies current excitation to each laser in the tunable laser array chip; the output light of the tunable laser array chip is transmitted to the wavelength locking module and the power adjustment module respectively through the spectrometer; the wavelength locking module performs wavelength locking on the output light based on two FP standards with the same response curve period and complementary response curve peaks; the power adjustment module uses a PID algorithm to adjust and lock the power of the output light.

[0012] Optionally, the tunable laser array chip internally encapsulates a DFB laser array, a switch chip, a Y-combiner structure and a semiconductor optical amplifier. The DFB laser array is connected to the laser chip current driving module through the switch chip. The DFB laser array includes M×N DFB lasers distributed in a series-parallel structure, where M is the number of parallel waveguides, and N is the number of lasers connected in series on a single waveguide. The M parallel waveguides are combined by a k-level Y-combiner structure and sent to the semiconductor optical amplifier for power amplification, and then connected to the light output port through lens coupling.

[0013] Optionally, a thermistor and a semiconductor cooler are also packaged inside the tunable laser array chip, the thermistor is used to collect the thermistor voltage value corresponding to the chip temperature, and the semiconductor cooler is used to adjust the chip temperature.

[0014] Optionally, the temperature control module includes a digital-to-analog converter, an analog-to-digital converter and a PID hardware and software control loop; the digital-to-analog converter converts the digital voltage corresponding to the target temperature set by the main control module into an analog voltage, and transmits it to the input end 1 of the PID hardware and software control loop; the input end 2 of the PID hardware and software control loop receives the thermistor voltage value corresponding to the chip temperature collected by the thermistor; the PID hardware and software control loop generates a driving current to control the operation of the semiconductor refrigerator by comparing the voltage values ​​of input end 1 and input end 2; the analog-to-digital converter converts the thermistor voltage value into a digital voltage and sends it to the main control module.

[0015] Optionally, the laser chip current driving module includes a DAC chip and a voltage-current conversion circuit; the DAC chip adopts an AD5683RBRMZ-3-RL7 chip, and the main control module writes the Code value into the output control register of the DAC chip to control the DAC chip to generate a voltage output; the voltage-current conversion circuit adopts an AD8531ARTZ-REEL7 chip, and by setting the amplification factor of the operational amplifier's in-phase feedback loop and the reverse end feedback loop, the laser driving current generated by the circuit is only related to the output voltage of the DAC chip and has nothing to do with the internal resistance of the series-connected laser.

[0016] Optionally, the main control module is configured with an on-chip FLASH or an external memory for storing the corresponding relationship λ between the emission wavelength λ of each of the M×N lasers and the laser drive current I_LD output by the laser chip current drive module and the operating temperature T MN (I_LD, T); After the main control module reads the target wavelength set by the user, it MN (I_LD, T) controls the laser chip current driving module and temperature control module to adjust the laser driving current and operating temperature.

[0017] Optionally, the wavelength locking module includes an FP etalon 1, an FP etalon 2, a photodetector 1, a photodetector 2 and an IV conversion circuit 1; the response curves of the FP etalon 1 and the FP etalon 2 have the same period and complementary peak values; the outgoing light of the tunable laser array chip is incident on the FP etalon 1 and the FP etalon 2 respectively after passing through a spectrometer, and then is input into the IV conversion circuit 1 after passing through the photodetector 1 and the photodetector 2 respectively; the IV conversion circuit 1 converts the optical power signal into a voltage signal, and transmits it to the main control module through ADC voltage acquisition;

[0018] After the main control module reads the target wavelength λ0 set by the user, the main control module selects the working FP etalon according to the position of the target wavelength λ0 in the response curves of the FP etalon 1 and the FP etalon 2: if the target wavelength λ0 is in a position where the trend of the response curve of the FP etalon 1 is relatively steep, or is near the peak / valley value of the FP etalon 2, the wavelength locking module works based on the FP etalon 1; if the target wavelength is in a position where the trend of the response curve of the FP etalon 2 is relatively steep, or is near the peak / valley value of the FP etalon 1, the wavelength locking module works based on the FP etalon 2;

[0019] After the tunable laser array chip emits light at the target wavelength λ0 and the target power P0, the main control module adjusts the laser drive current I_LD so that the tunable laser array chip emits light at the target wavelength λ0+λ x and λ0-λ xThe light is emitted one after another, and the optical power P at the output end of the selected FP standard is recorded respectively. x1 and P x2 And the corresponding photodetector response voltage value V x1 and V x2 , by comparing V x1 and V x2 The size of λ determines whether the target wavelength λ0 is on the left or right side of the peak of the selected FP etalon to determine the direction of subsequent wavelength correction; where λ x is a wavelength parameter that depends on the period of the etalon response curve.

[0020] Optionally, the main control module is configured with an on-chip FLASH or an external memory for storing the corresponding relationship P between the output power P of the tunable laser array chip and the driving current I_SOA of the semiconductor optical amplifier. MN (I_SOA).

[0021] Optionally, the power regulation module includes a photodetector 3 and an IV conversion circuit 2; the output light of the tunable laser array chip is partially incident on the photodetector 3 after passing through the spectrometer, and the response current of the photodetector 3 is amplified by the IV conversion circuit 2 to become a response voltage V2; after the main control module reads the target power set by the user, according to the corresponding relationship P MN (I_SOA) inverts the response voltage V1 of the photodetector 3 corresponding to the target power, and corrects the driving current of the semiconductor optical amplifier based on the dichotomy method so that V1-V2→0.

[0022] Optionally, the spectrometer includes spectrometer 1, spectrometer 2 and spectrometer 3; the spectrometer 1 transmits 90% of the output light of the tunable laser array chip to spectrometer 2, and 10% to spectrometer 3; the spectrometer 2 uses 90% of the received light as the final output light, and inputs 10% to the power regulation module; the spectrometer 3 divides the received light into equal parts and inputs them into two standards of the wavelength locking module respectively.

[0023] The core functions of the present invention include three parts: wavelength tuning, power adjustment and locking, and wavelength locking.

[0024] The wavelength tuning method includes:

[0025] 1. Perform wavelength calibration on M×N DFB lasers distributed in series-parallel structure, and record the corresponding relationship between each laser's emission wavelength λ and the laser drive current I_LD and operating temperature T MN (I_LD, T), and stored in the on-chip FLASH or external memory in the main control module, requiring no wavelength interval breakpoints between adjacent wavelength lasers;

[0026] 2. The target wavelength set by the user is transmitted to the main control module, and the main control module calculates the target wavelength according to the relationship λ MN (I_LD, T), determine the laser channel that can produce the target wavelength lasing, control the DAC in the laser chip current drive module to generate the corresponding voltage output, and generate the corresponding laser drive current I_LD through the voltage (V)-current (I) conversion circuit, and then switch I_LD to the corresponding laser channel through the switch chip to complete the rough wavelength tuning;

[0027] 3. The main control module completes the relationship λ according to the above calibration MN (I_LD, T), controls the DAC and corresponding PID hardware and software control loop inside the temperature control module, drives the semiconductor cooler to correct the internal operating temperature of the laser array chip, and completes the wavelength fine tuning.

[0028] It is particularly noted that the wavelength tuning function of the present invention can also be implemented entirely based on current tuning without the assistance of temperature tuning. For example, when the DAC accuracy in the laser chip current driving module is high enough, the laser driving current I_LD can be controlled with sufficiently high accuracy, thereby achieving sufficiently high-precision wavelength control. In this process, the operating temperature of the laser chip is kept constant as much as possible.

[0029] The implementation methods of power regulation and locking include:

[0030] 1. Perform power calibration on M×N DFB lasers distributed in series-parallel structure, and record the corresponding relationship between the output power P of each laser and the semiconductor optical amplifier drive current I_SOA MN (I_SOA) and stored in the on-chip FLASH or external memory in the main control module. The power of each laser is required to be adjustable within the range of 7-10dBm;

[0031] 2. Calibrate the response curve of the photodetector (PD3) in the power regulation module, record the relationship between the response voltage of the PD3 response current after amplification by the current (I)-voltage (V) conversion circuit and the incident light power of PD3 at intervals of 0.5 mW, and store it in the on-chip FLASH or external memory in the main control module; generally, the response voltage of PD3 and the incident light power are approximately linearly related under unsaturated conditions, and this relationship can be appropriately corrected according to the wavelength response characteristics of PD3 under different wavelength conditions, but the correction amplitude is extremely small;

[0032] 3. The target power set by the user is transmitted to the main control module, and the main control module calculates the target power according to the relationship P MN(I_SOA), controls the semiconductor optical amplifier power supply circuit in the laser chip current drive module to generate the corresponding SOA drive current, and adjusts the output power of the corresponding channel laser to near the target power;

[0033] 4. After the outgoing laser passes through the two-way beam splitter, 9% of the outgoing light is incident on the photodetector PD3 in the power regulation and locking module based on the PID algorithm. PD3 converts the incident light power into a response current, which is then converted into a voltage signal by a current (I)-voltage (V) conversion circuit and then transmitted to the main control module by an ADC voltage acquisition circuit;

[0034] 5. The main control module inverts the output power of the laser based on the response curve of the calibrated PD3 mentioned above, and locks the output power near the target power for a long time based on the PID algorithm after comparing it with the target power.

[0035] The methods for achieving wavelength locking include:

[0036] 1. Calibrate the response curve of the two standard tools (FP standard tool 1 and FP standard tool 2) with the same period and peak-valley complementary characteristics in the wavelength locking module based on the dual FP standard tool. Record the ratio of the output power to the incident power of the two standard tools at different wavelengths in the C band at an interval of 2pm (unit: dBm) and store it in the on-chip FLASH or external memory in the main control module;

[0037] 2. Similar to the response curve calibration of the photodetector (PD3) in the aforementioned power adjustment and locking, the response curves of the two photodetectors (PD1, PD2) in the wavelength locking module based on the dual FP standard need to be calibrated and stored in the on-chip FLASH or external memory in the main control module;

[0038] 3. After the outgoing laser passes through the spectrometer 1, 10% of the outgoing light enters the spectrometer 3 in the wavelength locking module based on the dual FP standard. After the spectrometer 3 divides the 10% of the outgoing light equally, 5% of the outgoing light enters the FP standard 1 and the FP standard 2 respectively, and then passes through the corresponding photodetectors (PD1, PD2) and the current (I)-voltage (V) conversion circuit to convert the optical power signal into a corresponding voltage signal, which is transmitted to the main control module by the ADC voltage acquisition circuit;

[0039] 4. The main control module determines which FP etalon the wavelength locking module is to work on, based on the position of the target wavelength in the response curves of FP etalon 1 and FP etalon 2: if the target wavelength is at a position where the trend of the response curve of FP etalon 1 is relatively steep (rapidly monotonically increasing or rapidly monotonically decreasing), or near the peak / valley of FP etalon 2, the wavelength locking module is to work on FP etalon 1; if the target wavelength is at a position where the trend of the response curve of FP etalon 2 is relatively steep (rapidly monotonically increasing or rapidly monotonically decreasing), or near the peak / valley of FP etalon 1, the wavelength locking module is to work on FP etalon 2; the purpose of this step is to ensure that the target wavelength is always at a position where the trend of the response curve of the FP etalon is relatively steep, thereby improving the wavelength locking accuracy and preventing locking failure;

[0040] 5. After determining which FP standard tool the wavelength locking module is based on to work, the main control module will, with the help of the wavelength tuning module and the power locking module, lasing at the target wavelength and target power, and at the same time record the PD response voltage value V0 corresponding to the optical power at the output end of the FP standard tool when the target wavelength is emitted, and adjust the laser drive current I_LD in real time through the PID algorithm, so that during the subsequent working time (the target wavelength remains unchanged), the PD response voltage value corresponding to the optical power at the output end of the FP standard tool is always maintained near V0, thereby overcoming the influence of the wavelength drift of the laser with temperature or other factors when the laser works for a long time, and realizing wavelength locking.

[0041] The beneficial effects of the present invention are:

[0042] (1) The M×N series-parallel structure DFB laser array chip used in the present invention is designed and manufactured based on REC technology. The structure is flexible and adjustable and can be designed on demand. Compared with the traditional electron beam exposure process, it greatly reduces the processing cost and processing time. It has outstanding advantages in wavelength control accuracy, side mode suppression ratio, tuning speed, and yield rate, and provides a domestic alternative to the currently expensive C-band imported tunable light source.

[0043] (2) The software and hardware modules of the present invention are all independently developed. Based on a large amount of previous calibration work, the current tuning and temperature tuning schemes are combined to control the M×N series-parallel structure DFB laser array chip to achieve arbitrary wavelength lasing within the C band. The switch chip in the laser chip current drive module can realize multiplexing of the same current source circuit, which greatly saves hardware resources and system costs.

[0044] (3) The present invention introduces a PID algorithm into the power adjustment module, and inverts the output power of the laser based on the input-output relationship between the photodetector and the current-voltage conversion circuit. The output power is stabilized near the target power for a long time through a negative feedback mechanism. The power adjustment and locking are achieved by adjusting the driving current of the semiconductor optical amplifier, which has almost no effect on the output wavelength, and the wavelength tuning and power adjustment can be independent of each other.

[0045] (4) The present invention introduces a wavelength locking mechanism based on two FP standards with the same period and peak-valley complementary characteristics and a corresponding negative feedback loop. It can effectively deal with the wavelength drift problem under long-term working conditions by directly changing the laser driving current, and does not require the assistance of a reference optical signal. Compared with the traditional method of achieving wavelength locking through TEC temperature control, the present invention has the advantages of precision and speed, and has broad application prospects in scientific research instruments, optical fiber sensing, optical communications, lidar and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the overall architecture block diagram of a C-band tunable broadband light source system with wavelength and power locking functions.

[0047] Figure 2 It is a schematic diagram of the structure of an M×N series-parallel structure DFB laser array chip.

[0048] Figure 3 This is the schematic diagram of the current source circuit in the laser chip current drive module.

[0049] Figure 4 This is a relationship diagram between the laser drive current I_LD and the DAC chip output voltage.

[0050] Figure 5 Schematic diagram of the wavelength automatic calibration solution.

[0051] Figure 6 It is a relationship diagram between the laser emission wavelength and the laser driving current calibrated under fixed temperature conditions.

[0052] Figure 7 is a flow chart of the wavelength tuning algorithm.

[0053] Figure 8 This is a graph showing the relationship between the laser output power and the semiconductor optical amplifier drive current.

[0054] Fig. 9 It is a flow chart of the power regulation and locking PID algorithm.

[0055] Fig.10 It is the response curve diagram of two FP standards with the same period and complementary peak and valley characteristics.

[0056] Fig.11 Flowchart of the wavelength locking algorithm.

[0057] Fig.12 It is a user interface design diagram. DETAILED DESCRIPTION

[0058] The present invention will now be described in further detail with reference to the accompanying drawings.

[0059] like Figure 1 As shown, the present invention provides a C-band tunable broadband light source system with wavelength and power locking functions, which specifically includes: a tunable laser array chip, a main control module, a power module, a laser chip current drive module, a temperature control module, a spectrometer, a wavelength locking module based on a dual FP standard, a power adjustment module based on a PID algorithm, a user interaction interface, etc.

[0060] The main control module is connected with the laser chip current driving module, the temperature control module, the wavelength locking module, the power adjustment module, and the user interaction interface;

[0061] The tunable laser array chip is internally encapsulated with a DFB laser array, a 1-way to 8-way switch chip, a thermistor and a semiconductor cooler (TEC). The DFB laser array is connected to the laser chip current drive module through the 1-way to 8-way switch chip, and the thermistor and the semiconductor cooler are connected to the temperature control module.

[0062] The light outlet of the tunable laser array chip is connected to the spectrometer 1, the first output end (90% light) of the spectrometer 1 is connected to the input end of the spectrometer 2, the second output end (10% light) of the spectrometer 1 is connected to the wavelength locking module, the first output end (90% light) of the spectrometer 2 is the final output light, and the second output end (10% light) of the spectrometer 2 is connected to the power adjustment module.

[0063] like Figure 2 As shown in FIG. 1 , the tunable laser array chip includes M×N DFB lasers distributed in a series-parallel structure, where M is the number of parallel waveguides in the laser array chip, and N is the number of lasers connected in series on a single waveguide. The chip also integrates a Y-wave combining structure and a semiconductor optical amplifier (SOA). The M parallel waveguides are combined by the k-level Y-wave combining structure and then sent to the semiconductor optical amplifier for power amplification, and then connected to the optical fiber output port of the laser array chip through lens coupling. Generally, M=2 k , k value should not be too large to prevent the laser light power from being lost too much after passing through the multi-stage Y-combiner structure; the tunable laser array chip also integrates and packages thermistor R th and semiconductor cooler (TEC), thermistor R thUsed to read the internal working temperature of the laser chip, the semiconductor cooler is used to adjust the internal working temperature of the laser chip.

[0064] The laser chip current drive module includes a digital-to-analog converter (DAC), a voltage (V)-current (I) conversion circuit, and a switch chip. Figure 3 As shown in the figure, the DAC and the voltage (V)-current (I) conversion circuit together form an independent current source. The main control module can use the chip select signal ( Figure 3 SPI1_CS1) and related communication protocols (such as SPI, IIC, etc.) write the Code value into the output control register of the DAC chip to control the DAC chip ( Figure 3 The AD5683RBRMZ-3-RL7) generates a high-precision voltage output; the voltage (V)-current (I) conversion circuit uses a rail-to-rail input / output single-supply amplifier ( Figure 3 The AD853 1ARTZ-REEL7 in the circuit converts low bias current input into high current output I_LD (i.e. laser drive current). This circuit structure cleverly sets the amplification factor of the operational amplifier's in-phase feedback loop and the reverse feedback loop (the two are equal), so that the laser drive current it generates is only related to the DAC output voltage and has nothing to do with the series laser internal resistance. This can effectively avoid the difficulties caused by the different laser internal resistances of different process batches in circuit design. Figure 3 As an example, the high current output terminal (1 port) of AD8531ARTZ-REEL7 is connected through four parallel resistors ( Figure 3 R5, R6, R7, R8) are connected to the input port of the switch chip. According to the virtual short and virtual break characteristics of the operational amplifier, U i -U P =U P -U0, from R1=R3 we can get U1=2U N =2U p =U i +U0, let the equivalent resistance of the four parallel resistors R5=R6=R7=R8 be R0, then the laser drive current Only with DAC output voltage U i The voltage value U of the port can be easily read by the ADC chip working in conjunction with the main control module. i and U0, and calculate the laser drive current I_LD provided by this current source. This design provides a current monitoring hardware foundation for the wavelength automatic calibration process, eliminating the process of manually measuring the actual drive current. The corresponding relationship between the laser drive current I_LD and the DAC output voltage value is shown in Figure 4, showing an approximately linear relationship; the switch chip switches the driving current generated by a single current source to multiple different lasers according to the address information set by the main control module; the laser chip current driving module can apply current excitation to each laser in the M×N structure DFB tunable laser array according to any waveform (DC signal, triangle wave, sawtooth wave, sine wave, etc.) according to actual needs; the laser chip current driving module also includes multiple other independent current sources with the same structure as above, which are used to power structures such as Y-combiner and semiconductor optical amplifier in the DFB laser array chip.

[0065] The temperature control module includes a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), a PID hardware and software control loop and other parts, and works in coordination with the main control module; the DAC is responsible for converting the digital voltage corresponding to the target temperature set by the main control module into an analog voltage, and transmitting it to the input terminal 1 of the PID hardware and software control loop; the thermistor is responsible for collecting the thermistor voltage value corresponding to the temperature of the laser array chip, and transmitting it to the input terminal 2 of the PID hardware and software control loop, and the ADC converts the thermistor voltage value into a digital voltage and transmits it to the main control module; the PID hardware and software control loop is responsible for comparing the voltage values ​​of input terminal 1 and input terminal 2, and generating a drive current to control the operation of TEC.

[0066] The main control module contains on-chip FLASH or external memory, which can save the corresponding relationship between the emission wavelength λ of M×N lasers and the laser drive current I_LD and the operating temperature T MN (I_LD, T), the corresponding relationship between the output power P and the semiconductor optical amplifier drive current I_SOA MN (I_SOA) and use it as the basis for subsequent wavelength tuning and power adjustment.

[0067] The wavelength locking module based on dual FP standards includes two FP standards, a photodetector (PD), a current (I)-voltage (V) conversion circuit, an ADC voltage acquisition circuit, etc. The power-wavelength response curves of the two FP standards should have the same period and have peak-valley complementary characteristics, that is, the peak point of one standard corresponds exactly to the valley point of the other standard.

[0068] The power regulation module based on PID algorithm includes a photodetector (PD), a current (I)-voltage (V) conversion circuit, an ADC voltage acquisition circuit and other parts.

[0069] The user interaction interface includes a display screen, buttons (or knobs), etc., and the user can automatically set the target wavelength and power within the system performance range.

[0070] The specific implementation of the present invention includes three parts: wavelength tuning, power adjustment and locking, and wavelength locking.

[0071] 1. Wavelength tuning

[0072] Wavelength tuning is achieved by table lookup method: wavelength calibration is performed on M×N DFB lasers distributed in series-parallel structure, and the corresponding relationship between each laser's emission wavelength λ and the laser drive current I_LD and operating temperature T is recorded. MN (I_LD, T) and stored in the on-chip FLASH or external memory in the main control module. The main control module reads the target wavelength set by the user and automatically adjusts the laser drive current and operating temperature according to the relationship to achieve the target wavelength emission.

[0073] Wavelength automatic calibration solution Figure 5 :Based on Visual Studio, a wavelength automatic calibration test program (host computer) was developed. The host computer communicated with the main control module through the UART protocol, controlled the laser chip current driver module to generate the laser drive current I_LD, and controlled the semiconductor refrigerator to keep the working temperature of the laser chip at temperature T. After the laser array chip emits light, it is connected to the wavelength meter. The wavelength meter monitors the light wavelength in real time and transmits it to the host computer through the GPIB communication protocol. The corresponding relationship λ between the laser's emission wavelength λ and the laser drive current I_LD and the working temperature T is recorded in steps of 50pm MN (I_LD, T). Taking LD1-1 as an example, the relationship between the laser emission wavelength λ and the laser drive current I_LD calibrated under fixed temperature conditions is as follows: Figure 6 As shown, it is approximately linear, with a slope k 11 =0.02524, intercept b 11 =1549.03569. In order to save the resources of on-chip FLASH or external memory, the wavelength automatic calibration test program (host computer) only calculates the fitting result (slope k) of the relationship between the output wavelength and the driving current of each laser. MN With intercept b MN ) Save and delete the large amount of data recorded above MN (I_LD, T).

[0074] The wavelength tuning algorithm process is as follows Figure 7 , the target wavelength is λ0, the actual wavelength is λ i First, calculate the absolute value of the difference between the actual wavelength and the target wavelength Δλ=|λ0-λ i|; If Δλ<2pm, the wavelength tuning is considered to be completed; if Δλ≥25pm, a current tuning scheme is used for large-scale (rough) rapid tuning, and a suitable laser channel is selected to make the actual wavelength roughly reach the target wavelength; if 2pm≤Δλ<25pm, a temperature tuning scheme is used for small-scale fine tuning, so that the difference between the actual wavelength and the target wavelength is gradually reduced to within 2pm, and the wavelength tuning is completed. In particular, the wavelength tuning function of the present invention can also be completely implemented based on current tuning without the assistance of temperature tuning. For example, when the DAC accuracy in the laser chip current drive module is high enough, the laser drive current can be controlled with sufficiently high accuracy, thereby achieving sufficiently high-precision wavelength control. This process tries to keep the operating temperature of the laser chip constant.

[0075] 2. Power regulation and locking

[0076] Power regulation and locking are implemented based on PID algorithm.

[0077] First, the power of M×N DFB lasers distributed in series-parallel structure is calibrated, and the output power P of each laser is recorded. MN The corresponding relationship between the semiconductor optical amplifier drive current I_SOA and P MN (I_SOA) and stored in the on-chip FLASH or external memory of the main control module. The power of each laser is required to be adjustable within the range of 7-10dBm. Taking LD1-1 as an example, the laser output power P calibrated under fixed wavelength conditions is 11 The relationship with SOA drive current I_SOA is as follows Figure 8 As shown, it is approximately a quadratic curve relationship (P 11 =a·I_SOA 2 +b·I_SOA+c), where a=-0.000432251, b=0.159828571, c=-6.043848485.

[0078] The photodetector in the power regulation module based on the PID algorithm also needs to be calibrated for the response curve. The relationship between the response voltage of the PD after amplification by the current (I)-voltage (V) conversion circuit and the incident light power of the PD is recorded at intervals of 0.5 mW and stored in the on-chip FLASH or external memory in the main control module. Generally, the response voltage of the PD and the incident light power are approximately linearly related under unsaturated conditions. This relationship can be appropriately corrected according to the wavelength response characteristics of the PD under different wavelength conditions, but the correction amplitude is extremely small.

[0079] Power lock algorithm Fig. 9The main control module inverts the PD response voltage V1 corresponding to the target power according to the calibrated photodetector (PD) response curve mentioned above. The output light of the laser array chip is partially incident on the photodetector (PD) after passing through the spectrometer. The PD response current is amplified by the current (I)-voltage (V) conversion circuit and becomes the response voltage V2. The driving current of the SOA is corrected based on the dichotomy method so that V1-V2→0, so that the actual light output power can continuously approach the target power.

[0080] 3. Wavelength locking

[0081] Wavelength locking is achieved based on dual FP etalons and PID algorithm.

[0082] First, the response curves of the two etalons (FP etalon 1 and FP etalon 2) in the wavelength locking module based on the dual FP etalons are calibrated. The ratios of the output power to the incident power of the two etalons at different wavelengths in the C band are recorded at intervals of 2 pm (unit: dBm) and stored in the on-chip FLASH or external memory in the main control module. Some response curves of the dual FP etalons are shown in Figure 2. Fig.10 , the solid line is FP etalon 1, the dotted line is FP etalon 2, the response curve period of the two etalons is 100.1pm, and they have peak-to-valley complementary characteristics, showing a Lorentzian line shape within a single period, which can be expressed as Perform the fitting.

[0083] like Figure 1 In the wavelength locking module based on dual FP standards, after the outgoing laser passes through the spectrometer 1, 10% of the outgoing light enters the spectrometer 3 in the wavelength locking module based on dual FP standards. After the spectrometer 3 divides the 10% of the outgoing light into equal parts, 5% of the outgoing light enters the FP standard 1 and FP standard 2 respectively, and then passes through the corresponding photodetector (PD) and current (I)-voltage (V) conversion circuit to convert the optical power signal into a corresponding voltage signal, which is transmitted to the main control module by the ADC voltage acquisition circuit.

[0084] The specific algorithm flow of wavelength locking is as follows: Fig.11The main control module determines which FP etalon the wavelength locking module will work based on according to the position of the target wavelength λ0 in the response curves of FP etalon 1 and FP etalon 2: if the target wavelength is in a position where the trend of the response curve of FP etalon 1 is relatively steep (rapidly monotonically increasing or rapidly monotonically decreasing), or is near the peak / valley value of FP etalon 2, the wavelength locking module will work based on FP etalon 1; if the target wavelength is in a position where the trend of the response curve of FP etalon 2 is relatively steep (rapidly monotonically increasing or rapidly monotonically decreasing), or is near the peak / valley value of FP etalon 1, the wavelength locking module will work based on FP etalon 2; the purpose of this step is to ensure that the target wavelength is always in a position where the trend of the FP etalon response curve is relatively steep, thereby improving the wavelength locking accuracy.

[0085] Furthermore, after the laser array chip emits light at the target wavelength λ0 and the target power P0, the laser drive current I_LD is adjusted so that the laser array chip emits light at λ0±λ x The light is emitted one after another, and the optical power P at the output end of the selected FP standard is recorded respectively. x1 and P x2 The corresponding PD response voltage value V x1 and V x2 , by comparing V x1 and V x2 The size of can determine whether the target wavelength λ0 is on the left or right side of the peak of the selected FP etalon, and thus the direction of subsequent wavelength correction can be known; where λ x It depends on the period of the etalon response curve. Taking the 12.5GHz etalon as an example, its period is about 100.1pm, λ x Just pick it up at 1-2pm.

[0086] Furthermore, the laser array chip emits light according to the target wavelength λ0 and the target power P0, and the main control module records the PD response voltage value V0 corresponding to the optical power P0 at the output end of the FP etalon selected at this time, and directly corrects the driving current of the laser through a PID algorithm similar to that in the power adjustment module, so that the PD response voltage value corresponding to the optical power at the output end of the FP etalon is always kept near the target value V0 during the subsequent working time (the target wavelength remains unchanged), thereby overcoming the influence of the wavelength drift of the laser with temperature under the condition of long-term operation, and realizing wavelength locking. It can be seen that, because the laser array chip can generate very accurate initial laser output according to the target wavelength λ0 and the target power P0 under the control of the wavelength tuning and power locking module, the wavelength locking module based on the dual FP etalon only needs the signal light passing through the FP etalon, and does not need a reference optical signal.

[0087] In particular, the wavelength locking function of the present invention can also be implemented based on a single FP etalon. However, when the target wavelength is at a position where the trend of the FP etalon response curve is relatively steep (rapid monotonically increasing or rapidly monotonically decreasing but not near the peak), the wavelength locking accuracy is high; when the target wavelength is near the peak of the FP etalon response curve, it is necessary to combine the optimization algorithm to determine the polarity of the difference between the actual wavelength and the target wavelength to determine the wavelength correction direction; when the target wavelength is near the valley of the FP etalon response curve, the wavelength locking accuracy is low.

[0088] User interface such as Fig.12 The left LCD screen contains information such as target wavelength λ, target power P and frequency F, and the four buttons on the right are ▲, Key, Set and Confirm. The Set key is used to select wavelength tuning / power adjustment and can also be used to set the digits that need to be adjusted; ▲ key / The key is used to increase / decrease the selected digit; the confirm key is used to exit the adjustment mode and update the display.

[0089] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A C-band tunable broadband light source system with wavelength and power locking function, characterized in that: include: A tunable laser array chip, a main control module, a laser chip current driving module, a temperature control module, a spectrometer, a wavelength locking module and a power adjustment module; the main control module is connected to the temperature control module, the laser chip current driving module, the wavelength locking module and the power adjustment module; the temperature control module reads and adjusts the internal operating temperature of the tunable laser array chip; the laser chip current driving module applies current excitation to each laser in the tunable laser array chip; The outgoing light of the tunable laser array chip is transmitted to a wavelength locking module and a power adjustment module respectively through a spectrometer; the wavelength locking module performs wavelength locking on the outgoing light based on two FP standards with the same response curve period and complementary response curve peaks; the power adjustment module uses a PID algorithm to adjust and lock the power of the outgoing light.

2. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 1, characterized in that: The tunable laser array chip encapsulates a DFB laser array, a switch chip, a Y-wave combining structure and a semiconductor optical amplifier. The DFB laser array is connected to the laser chip current driving module through the switch chip. The DFB laser array includes M×N DFB lasers distributed in a series-parallel structure, where M is the number of parallel waveguides, and N is the number of lasers connected in series on a single waveguide. The M parallel waveguides are combined by a k-level Y-wave combining structure and sent to the semiconductor optical amplifier for power amplification, and then connected to the light outlet through lens coupling.

3. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 2, characterized in that: The tunable laser array chip further includes a thermistor and a semiconductor cooler encapsulated therein. The thermistor is used to collect the thermistor voltage value corresponding to the chip temperature, and the semiconductor cooler is used to adjust the chip temperature.

4. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 3, characterized in that: The temperature control module includes a digital-to-analog converter, an analog-to-digital converter and a PID software and hardware control loop; the digital-to-analog converter converts the digital voltage corresponding to the target temperature set by the main control module into an analog voltage, and transmits it to the input terminal 1 of the PID software and hardware control loop; the input terminal 2 of the PID software and hardware control loop receives the thermistor voltage value corresponding to the chip temperature collected by the thermistor; the PID software and hardware control loop generates a driving current to control the operation of the semiconductor refrigerator by comparing the voltage values ​​of the input terminal 1 with the input terminal 2; The analog-to-digital converter converts the voltage value of the thermistor into a digital voltage and sends it to the main control module.

5. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 2, characterized in that: The laser chip current driving module includes a DAC chip and a voltage-current conversion circuit; the DAC chip adopts an AD5683RBRMZ-3-RL7 chip, and the main control module writes the Code value into the output control register of the DAC chip to control the DAC chip to generate a voltage output; the voltage-current conversion circuit adopts an AD853 1ARTZ-REEL7 chip, and by setting the amplification coefficient of the operational amplifier's in-phase feedback loop and the reverse end feedback loop, the laser driving current generated by the circuit is only related to the output voltage of the DAC chip and has nothing to do with the internal resistance of the series-connected laser.

6. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 2, characterized in that: The main control module is configured with an on-chip FLASH or external memory, which is used to store the corresponding relationship λ between the emission wavelength λ of each of the M×N lasers and the laser drive current I_LD output by the laser chip current drive module and the operating temperature T MN (I_LD,T); After the main control module reads the target wavelength set by the user, it MN (I_LD,T) controls the laser chip current drive module and temperature control module to adjust the laser drive current and operating temperature.

7. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 2, characterized in that: The wavelength locking module comprises an FP etalon 1, an FP etalon 2, a photodetector 1, a photodetector 2 and an IV conversion circuit 1; the response curves of the FP etalon 1 and the FP etalon 2 have the same period and the peak values ​​of the response curves are complementary; the outgoing light of the tunable laser array chip is incident on the FP etalon 1 and the FP etalon 2 respectively after passing through a spectrometer, and then is input into the IV conversion circuit 1 after passing through the photodetector 1 and the photodetector 2 respectively; the IV conversion circuit 1 converts the optical power signal into a voltage signal, and transmits it to the main control module through ADC voltage acquisition; After the main control module reads the target wavelength λ0 set by the user, the main control module selects the working FP etalon according to the position of the target wavelength λ0 in the response curves of the FP etalon 1 and the FP etalon 2: if the target wavelength λ0 is in a position where the trend of the response curve of the FP etalon 1 is relatively steep, or is near the peak / valley value of the FP etalon 2, the wavelength locking module works based on the FP etalon 1; If the target wavelength is at a relatively steep position of the response curve trend of FP etalon 2, or near the peak / valley value of FP etalon 1, the wavelength locking module operates based on FP etalon 2; After the tunable laser array chip emits light at the target wavelength λ0 and the target power P0, the main control module adjusts the laser drive current I_LD so that the tunable laser array chip emits light at the target wavelength λ0+λ x and λ0-λ x The light is emitted one after another, and the optical power P at the output end of the selected FP standard is recorded respectively. x1 and P x2 And the corresponding photodetector response voltage value V x1 and V x2 , by comparing V x1 and V x2 The size of λ determines whether the target wavelength λ0 is on the left or right side of the peak of the selected FP etalon to determine the direction of subsequent wavelength correction; where λ x is a wavelength parameter that depends on the period of the etalon response curve.

8. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 2, characterized in that: The main control module is configured with an on-chip FLASH or an external memory for storing the corresponding relationship P between the output power P of the tunable laser array chip and the driving current I_SOA of the semiconductor optical amplifier. MN (I_SOA).

9. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 8, characterized in that: The power regulation module includes a photodetector 3 and an IV conversion circuit 2; the output light of the tunable laser array chip is partially incident on the photodetector 3 after passing through the spectrometer, and the response current of the photodetector 3 is amplified by the IV conversion circuit 2 and converted into a response voltage V2; after the main control module reads the target power set by the user, according to the corresponding relationship P MN (I_SOA) inverts the response voltage V1 of the photodetector 3 corresponding to the target power, and corrects the driving current of the semiconductor optical amplifier based on the dichotomy method so that V1-V2→0.

10. The C-band tunable broadband light source system with wavelength and power locking function as claimed in claim 1, characterized in that: The optical splitter includes an optical splitter 1, an optical splitter 2 and an optical splitter 3; the optical splitter 1 transmits 90% of the output light of the tunable laser array chip to the optical splitter 2, and transmits 10% to the optical splitter 3; The optical splitter 2 uses 90% of the received light as the final output light, and inputs 10% into the power adjustment module; the optical splitter 3 divides the received light into equal parts and inputs them into two etalons of the wavelength locking module respectively.

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