A wavelength tunable SGDBR frequency-stabilized laser based on FPGA control

Abstract

The present invention belongs to the field of photoelectric control technology, and specifically relates to a wavelength tunable SGDBR frequency-stabilized laser based on FPGA control, including an FPGA control module, a voltage-controlled constant current source, an SGDBR laser, a spectrometer, a TEC drive module and a wavelength locking module; a temperature control module, a PID control module and a current control module are arranged in the FPGA control module; the current control module is used to send a corresponding control voltage signal to the voltage-controlled constant current source according to an internally stored wavelength-current relationship table, and the voltage-controlled constant current source converts the control current signal into a control current signal and sends it to the SGDBR laser; the wavelength feedback module is used to obtain a voltage signal related to the wavelength and send it to the PID module, the PID module calculates a frequency-stabilized feedback voltage signal according to the voltage signal, and the voltage-controlled constant current source converts the frequency-stabilized feedback voltage signal into a feedback current signal and sends it to the phase node of the SGDBR laser. The present invention can realize the rapid tuning of the output wavelength of the SGDBR laser, and improve the stability of the output wavelength.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric control, and in particular relates to a wavelength-tunable SGDBR frequency-stabilized laser based on FPGA control. Background Art

[0002] In recent years, Dense Wavelength Division Multiplexing (DWDM) has become a new generation of research hotspot in the field of optical communications due to its advantages such as large capacity, transparent transmission, flexible networking, and efficient realization of all-optical network switching. In DWDM systems, tunable lasers are core components. Changing the output wavelength of tunable lasers can achieve wavelength switching, but laser drift may occur during the wavelength switching process, causing channel crosstalk. In order to reduce channel crosstalk, tunable lasers are needed to achieve fast and stable wavelength conversion, but the current control methods for achieving tunable laser wavelength conversion cannot meet the above requirements.

[0003] At the same time, if the laser control temperature is unstable, the output wavelength and output frequency will change. On the one hand, as the working time increases, the internal temperature of the tunable laser will rise, causing the output wavelength to drift, affecting the stability of the output wavelength and the output accuracy, reducing the service life of the laser, and may even cause damage to the laser. On the other hand, in the process of switching the wavelength of the tunable laser, the change in current will cause a slow thermal drift inside the tunable laser, which will cause the laser output wavelength to change. Therefore, it is of great significance to keep the laser control temperature stable. The traditional solution is to use temperature compensation, but this method is too slow and has poor control accuracy, and it is impossible to quickly and stably control the internal temperature of the laser. Summary of the invention

[0004] The present invention overcomes the shortcomings of the prior art and aims to solve the technical problem of providing a wavelength tunable SGDBR (Sampled Raster Distributed Bragg Reflector) frequency-stabilized laser based on FPGA control to achieve fast and high-precision tuning of the laser output wavelength and improve the stability of its output wavelength.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a wavelength tunable SGDBR frequency-stabilized laser based on FPGA control, including an FPGA control module, a voltage-controlled constant current source, an SGDBR laser, a beam splitter, a TEC drive module and a wavelength locking module;

[0006] The FPGA control module is provided with a temperature control module, a PID control module and a current control module;

[0007] The SGDBR laser comprises an SOA amplification region, a front grating section, a gain section, a phase section and a rear grating section which are arranged in sequence, and the current control module is used to send a corresponding control voltage signal to the voltage-controlled constant current source according to an internally stored wavelength-current relationship table, and the control voltage signal is converted by the voltage-controlled constant current source into a control current signal and then sent to the SOA amplification region, the front grating section, the gain section, the phase section and the rear grating section of the SGDBR laser;

[0008] The laser signal output by the SGDBR laser is partially split by a beam splitter and then incident on the wavelength locking module. The wavelength feedback module obtains a voltage signal related to the wavelength and then sends it to the PID module. The PID module calculates and obtains a frequency stabilization feedback voltage signal according to the voltage signal. The voltage-controlled constant current source is used to convert the frequency stabilization feedback voltage signal into a feedback current signal and then sends it to the phase node of the SGDBR laser.

[0009] The wavelength locking module includes an FP standard, a 50 / 50 coupler, a photoelectric converter and a signal amplifier. The laser signal output by the SGDBR laser is divided into two paths through a 50 / 50 coupler after a part is split by a spectrometer. One signal is directly output to the photoelectric converter as a reference signal, and the other signal is output as a transmission signal to the photoelectric converter after passing through the FP standard. The photoelectric converter performs photoelectric conversion on the two signals and sends them to the signal amplifier. The signal amplifier outputs the two signals to the FPGA control module.

[0010] The FPGA control module also includes an ADC control module;

[0011] The ADC control module is used to perform calculations based on the two signals sent by the signal amplifier, and then send the obtained voltage difference signal to the PID module.

[0012] The ADC control module uses the ADC128S022 chip and communicates with the FPGA through the SPI interface.

[0013] The optical splitter is a 1:99 optical fiber coupler.

[0014] The FPGA control module also includes a DAC control module, which is used to convert the control signal sent by the current control module into a control voltage signal and then send it to the voltage-controlled constant current source.

[0015] The DAC control module uses the TLV5618 chip and communicates with the FPGA through three-wire SPI communication.

[0016] The FPGA control module is also provided with a RAM storage module, and the RAM storage module is used to store the wavelength-current relationship table;

[0017] The wavelength-current relationship table includes the values ​​of the front grating node current Iq, the rear grating node current Ih and the phase node current Ix corresponding to each output wavelength of the SGDBR laser.

[0018] The voltage-controlled constant current source includes an operational amplifier A1, an operational amplifier A2, a sampling resistor R3, a resistor R2, a resistor R1, a resistor R4, a field effect transistor Q1 and a field effect transistor Q2,

[0019] The operational amplifier A1 has a non-inverting input terminal connected to a control voltage signal, a reverse input terminal connected to ground via a resistor R1, an output terminal connected to a gate of a field effect transistor Q1, a drain of the field effect transistor Q1 connected to a positive electrode of a power supply via a resistor R2, and a source connected to an inverting input terminal of the operational amplifier A1;

[0020] The non-inverting input terminal of the operational amplifier A2 is connected to the source of the field effect transistor Q1, and the output terminal is connected to the gate of the field effect transistor Q2. The source of the field effect transistor Q2 is connected to the positive electrode of the power supply through the resistor R3, and is also connected to the reverse input terminal of the operational amplifier A2 through the resistor R4. The drain of the field effect transistor Q2 outputs a constant output current.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides a wavelength-tunable SGDBR frequency-stabilized laser based on FPGA control, which adopts FPGA chip and high-precision voltage-controlled constant current source design, directly stores the wavelength-current relationship table into the RAM storage module, and directly calls the wavelength-current relationship table by configuring a high-frequency clock signal, so that the output wavelength of the SGDBR laser can be switched quickly, with good stability and high precision.

[0023] 2. The present invention obtains the error signal of wavelength drift through the wavelength locking module, and uses the PID control module set in the FPGA chip to calculate the wavelength locking feedback signal, which can quickly realize the wavelength locking of the laser and eliminate the wavelength drift phenomenon that occurs during the operation of the laser, so that the laser can not only quickly switch the wavelength, but also keep the output wavelength stable.

[0024] 3. The present invention utilizes the TEC and NTC thermistor inside the laser, and controls the TEC drive module by integrating a temperature control module designed by Quartus II software inside the FPGA chip to form a temperature control system to control the internal temperature of the laser. The temperature regulation response speed is fast and the stability is good.

[0025] 4. The present invention uses FPGA chip as the core control device, integrating the temperature control module required for laser constant temperature, the voltage-controlled constant current source module required for wavelength adjustment, and the PID control module described in wavelength locking, which simplifies the structure of the laser system and facilitates integration, and reduces the design cost and has high cost performance. At the same time, FPGA chip can realize data parallel computing, and can adjust the output wavelength of the tunable laser more quickly and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the overall structure of a wavelength-tunable SGDBR frequency-stabilized laser based on FPGA control provided by the present invention;

[0027] Figure 2 Schematic diagram of a voltage-controlled constant current source circuit in an embodiment of the present invention;

[0028] Figure 3 is a schematic structural diagram of a wavelength locking module in an embodiment of the present invention;

[0029] Figure 4 Schematic diagram of the structure of a wavelength-locked loop in an embodiment of the present invention;

[0030] Figure 5 1 is a circuit schematic diagram of a DAC control module in an embodiment of the present invention;

[0031] Figure 6 4 is a circuit schematic diagram of the ADC control module in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] like Figure 1As shown, an embodiment of the present invention provides a wavelength tunable SGDBR frequency-stabilized laser based on FPGA control, including an FPGA control module, a voltage-controlled constant current source, an SGDBR laser, a spectrometer, a TEC drive module and a wavelength locking module; a temperature control module, a PID control module and a current control module are arranged in the FPGA control module. The SGDBR laser includes an SOA amplification area, a front grating section, a gain section, a phase section and a rear grating section arranged in sequence. The current control module is used to send corresponding five control voltage signals to the voltage-controlled constant current source according to an internally stored wavelength-current relationship table. After being converted into five control current signals by the voltage-controlled constant current source, they are respectively sent to the SOA amplification area, the front grating section, the gain section, the phase section and the rear grating section of the SGDBR laser; a part of the laser signal output by the SGDBR laser is split by a spectrometer and then incident on the wavelength locking module. After the wavelength feedback module obtains a voltage signal related to the wavelength, it is sent to the PID module. The PID module calculates a frequency stabilization feedback voltage signal according to the voltage signal. The voltage-controlled constant current source is used to convert the frequency stabilization feedback voltage signal into a feedback current signal and then send it to the phase section of the SGDBR laser.

[0034] like Figure 1 As shown, the SGDBR laser includes an optical SOA amplification region, a front grating section, a gain section, a phase section, and a rear grating section. Among them, wavelength tuning is mainly achieved by adjusting the front grating section current Iq, the rear grating section current Ih, and the phase section current Ix. The gain section current Iz is generally a fixed value. Changing the SOA section current Is can change the output power of the laser. The wavelength locking is mainly achieved by adjusting the phase section current Ip through the wavelength locking loop. In the SGDBR laser of this embodiment, the phase section current and the wavelength drift are linearly related within a certain range. The splitter can be a coupler with a splitting ratio of 1:99.

[0035] Specifically, in this embodiment, a RAM storage module is further provided in the FPGA control module, and the RAM storage module is used to store the wavelength-current relationship table; the wavelength-current relationship table includes the values ​​of the front grating node current Iq, the rear grating node current Ih and the phase node current Ix corresponding to each output wavelength of the SGDBR laser. Specifically, the wavelength-current relationship table can be obtained by testing the SGDBR laser. During the test, the current of each zone is changed to measure the value of its output wavelength. It should be noted that although a certain output wavelength may correspond to multiple current combinations, in the final wavelength-current relationship table, only the current combination value with a relatively high side mode suppression ratio is saved, which can improve the quality of the laser signal output by the SGDBR laser. The FPGA is configured with a 50MHz clock signal, and the system clock frequency reaches 200MHz by using the PLL phase-locked loop multiplication to achieve fast wavelength tuning. The RAM storage module stores the wavelength-current relationship table internally, and the relationship between the output wavelength and the current combination is unique. The FPGA can be directly and quickly called, which greatly improves the switching speed compared to calling from the PC host computer.

[0036] like Figure 2 As shown, in this embodiment, the sampling voltage-controlled constant current source realizes constant current output to the SGDBR laser. It includes: operational amplifier A1, operational amplifier A2, sampling resistor R3, resistor R2, resistor R1, resistor R4, field effect tube Q1 and field effect tube Q2; the in-phase input terminal of the operational amplifier A1 is connected to the control voltage signal, the reverse input terminal is grounded through resistor R1, the output terminal is connected to the gate of the field effect tube Q1, the drain of the field effect tube Q1 is connected to the positive pole of the power supply through resistor R2, and the source is connected to the inverting input terminal of the operational amplifier A1; the in-phase input terminal of the operational amplifier A2 is connected to the source of the field effect tube Q1, the output terminal is connected to the gate of the field effect tube Q2, the source of the field effect tube Q2 is connected to the positive pole of the power supply through resistor R3, and is also connected to the reverse input terminal of the operational amplifier A2 through resistor R4, and the drain of the field effect tube Q2 outputs a constant output current. The operational amplifier A1 and the operational amplifier A2 use high-precision low-temperature drift operational amplifier LT1466L.

[0037] The stability of the voltage-controlled constant current source directly affects the accuracy of the entire system. This embodiment uniformly adopts low-temperature drift component design to reduce temperature drift and ensure high-precision output current of the constant current source. The principle of making a constant current source with an op amp is the addition and subtraction operation circuit of the op amp. The constant current source uses a high-precision low-temperature drift op amp LT1466L. The operational amplifier A1 gives a variable reference voltage relative to the positive power supply. The operational amplifier A2 makes the voltage across the sensitive resistor R3 equal to the reference voltage. The circuit includes a reference power supply and a sampling resistor for determining the output current. The potential at both ends of the sampling resistor is compared and the sampling output is controlled to ensure that the voltage on the sampling resistor remains constant, thereby ensuring the constant output current. The circuit parameters of the designed voltage-controlled constant current source circuit are fixed, and the corresponding voltage and current conversion relationship is also fixed. When a voltage signal is input, the circuit can quickly output the corresponding current signal. The constant output current of this circuit can be adjusted within the range of 0 to 50mA, and the corresponding voltage-controlled voltage range is 0 to 2.5V.

[0038] Specifically, if Figure 1 As shown, in this embodiment, the FPGA control module also includes an ADC control module; the ADC control module is used to perform calculations based on the two signals sent by the signal amplifier, and then send the obtained voltage difference signal to the PID module.

[0039] Specifically, in this embodiment, Figure 3 As shown, the wavelength locking module includes an FP standard, a 50 / 50 coupler, a photoelectric converter and a signal amplifier. After a part of the laser signal output by the SGDBR laser is split by the optical splitter, it is divided into two paths through the 50 / 50 coupler. One signal is directly output to the photoelectric converter as a reference signal, and the other signal is output to the photoelectric converter after passing through the FP standard. The photoelectric converter performs photoelectric conversion on the two signals and sends them to the signal amplifier. The signal amplifier outputs the two signals to the FPGA control module. In this embodiment, the laser signal Δλout input to the wavelength locking module is divided into two signals through the 50:50 coupler. One signal is directly output as a reference signal, and the reference signal is converted into a reference current signal Ic through the photoelectric converter. The other signal is output as a transmission signal after passing through the FP standard, and the transmission signal is converted into a transmission current signal It through the photoelectric converter. According to the filtering characteristics of the FP standard, It will change with the change of the wavelength of light. The detection of the wavelength of light can be achieved by detecting the two currents output by the PD.

[0040] Specifically, in this embodiment, Figure 4The structure diagram of the wavelength locking loop in this embodiment is shown. The SGDBR laser outputs laser light λout through a 1:99 coupler to input a small amount of light Δλout into the wavelength locker, and the remaining majority of the light is directly output. The input optical signal Δλout is split into two signals through a 50:50 coupler. One signal is directly output as a reference signal, and the reference signal is converted into a reference current signal Ic through a PD, and the reference current signal Ic is converted into a reference voltage signal Vc through a signal amplifier; the other signal is output as a transmission signal after passing through an FP standard device, and the transmission signal is converted into a transmission current signal It through a PD, and the transmission current signal It is converted into a transmission voltage signal Vt through a signal amplifier. The reference voltage signal Vc and the transmission voltage signal Vt are calculated by the ADC control module to obtain a voltage difference Vd, and the voltage difference Vd is obtained by the PID control module to obtain a feedback voltage signal Vp, and the feedback voltage signal Vp is converted into a feedback current signal Ip through a voltage-controlled constant current source. The feedback current signal Ip is input to the SGDBR laser phase node to change the laser output wavelength, eliminate the wavelength drift caused by thermal drift, and keep the output wavelength stable.

[0041] The PID control module is used to obtain the feedback signal: when the SGDBR laser outputs a stable wavelength, the feedback voltage signal Vp is zero; when the laser output wavelength deviates from the target wavelength, the feedback voltage signal Vp is converted into a feedback current signal Ip, and the phase current is adjusted to achieve negative feedback of the laser output wavelength to stabilize the laser wavelength.

[0042] like Figure 5 As shown, the FPGA control module also includes a DAC control module, which is used to convert the control signal sent by the current control module into a control voltage signal and then send it to the voltage-controlled constant current source. The DAC control module uses the TLV5618 chip, which is a voltage-output dual-channel 12-bit single-power digital-to-analog converter with an output voltage range of 0 to 4.096V. It communicates with the FPGA using a three-wire SPI. The FPGA sends a control signal to make the DAC chip output five signals in parallel, and can simultaneously adjust the five-way current of the SGDBR laser in real time. By controlling the voltage-controlled constant current source, different current combinations are input into the SGDBR laser, so that the laser can quickly and accurately tune the wavelength.

[0043] like Figure 6 As shown, in this embodiment, the ADC control module contained in the FPGA control module adopts the ADC128S022 chip, has a 12-bit resolution, and also uses the SPI interface to communicate with the FPGA. The conversion rate is 50 to 200ksps. The ADC control module is mainly used to quickly process the two-way voltage signal input by the transimpedance amplifier, and outputs the voltage difference Vd after calculation.

[0044] The working principle of the present invention is as follows: a high-frequency clock signal is configured through FPGA, a wavelength-current relationship table in a RAM storage module is called, a control signal is sent to a DAC control module, and the DAC control module sends five parallel voltage signals to a voltage-controlled constant current source, which are converted into corresponding current values ​​by the voltage-controlled constant current source and input into the SGDBR laser, thereby controlling the output wavelength and output power of the SGDBR laser. The output wavelength in the wavelength-current relationship table in the RAM storage module corresponds to each current value of the SGDBR laser, and different current combinations are controlled to be input into the laser, so as to achieve the purpose of fast and accurate wavelength switching. The TEC inside the SGDBR laser is controlled by a TEC drive module, so that the inside of the laser is always kept at a suitable working temperature point; by establishing a wavelength locking loop, the laser phase node current is adjusted in real time to eliminate wavelength drift, so that the laser output wavelength remains stable.

[0045] In summary, the present invention provides a wavelength-tunable SGDBR frequency-stabilized laser based on FPGA control, including an FPGA control module and a high-precision voltage-controlled constant current source, wherein the wavelength-current relationship table is directly stored in a RAM storage module built into the FPGA control module, and the wavelength-current relationship table is directly called by configuring a high-frequency clock signal, and a control voltage signal is directly output to the voltage-controlled constant current source, which is converted into a control current signal by the voltage-controlled constant current source and sent to the SGDBR laser to control its current. The present invention enables the SGDBR laser to output a wavelength with fast switching speed, good stability and high precision. Moreover, the present invention obtains an error signal of wavelength drift through a wavelength locking module, and calculates a wavelength locking feedback signal using a PID control module provided in an FPGA chip, so as to quickly realize wavelength locking of the laser, eliminate the wavelength drift phenomenon occurring during the operation of the laser, and enable the laser to not only quickly switch wavelengths, but also maintain a stable output wavelength.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wavelength tunable SGDBR frequency-stabilized laser based on FPGA control, characterized in that: Including FPGA control module, voltage-controlled constant current source, SGDBR laser, optical splitter, TEC drive module and wavelength locking module; The FPGA control module is provided with a temperature control module, a PID control module and a current control module; the input end of the TEC drive module is connected to the temperature control module, and the output end is connected to the SGDBR laser, so as to control the TEC inside the SGDBR laser to keep the internal temperature of the laser at the operating temperature point; The SGDBR laser comprises an SOA amplification area, a front grating section, a gain section, a phase section and a rear grating section which are arranged in sequence, and the current control module is used to send a corresponding control voltage signal to the voltage-controlled constant current source according to an internally stored wavelength-current relationship table, and the control voltage signal is converted into a control current signal by the voltage-controlled constant current source and then sent to the SOA amplification area, the front grating section, the gain section, the phase section and the rear grating section of the SGDBR laser; After a part of the laser signal output by the SGDBR laser is split by the spectrometer, it is incident on the wavelength locking module, and the wavelength locking module obtains a voltage signal related to the wavelength and then sends it to the PID control module. The PID control module calculates a frequency stabilization feedback voltage signal according to the voltage signal, and the voltage-controlled constant current source is used to convert the frequency stabilization feedback voltage signal into a feedback current signal and then send it to the phase node of the SGDBR laser; the wavelength locking module includes an FP etalon, a 50 / 50 coupler, a photoelectric converter and a signal amplifier. After a part of the laser signal output by the SGDBR laser is split by the spectrometer, it is divided into two paths by the 50 / 50 coupler, one path of the signal is directly output to the photoelectric converter as a reference signal, and the other path of the signal is output as a transmission signal to the photoelectric converter after passing through the FP etalon. The photoelectric converter performs photoelectric conversion on the two paths of signals and then sends them to the signal amplifier, and the signal amplifier outputs the two paths of signals to the FPGA control module; the FPGA control module also includes an ADC control module; The ADC control module is used to perform calculations based on the two signals sent by the signal amplifier, and obtain a voltage difference signal and send it to the PID control module; The voltage-controlled constant current source includes an operational amplifier A1, an operational amplifier A2, a sampling resistor R3, a resistor R2, a resistor R1, a resistor R4, a field effect transistor Q1 and a field effect transistor Q2, The operational amplifier A1 has a non-inverting input terminal connected to a control voltage signal, a reverse input terminal connected to ground via a resistor R1, an output terminal connected to a gate of a field effect transistor Q1, a drain of the field effect transistor Q1 connected to a positive electrode of a power supply via a resistor R2, and a source connected to an inverting input terminal of the operational amplifier A1; The non-inverting input terminal of the operational amplifier A2 is connected to the source of the field effect transistor Q1, and the output terminal is connected to the gate of the field effect transistor Q2. The source of the field effect transistor Q2 is connected to the positive electrode of the power supply through the resistor R3, and is also connected to the reverse input terminal of the operational amplifier A2 through the resistor R4. The drain of the field effect transistor Q2 outputs a constant output current.

2. The wavelength tunable SGDBR frequency-stabilized laser based on FPGA control according to claim 1, characterized in that: The ADC control module uses the ADC128S022 chip and communicates with the FPGA through the SPI interface.

3. The wavelength tunable SGDBR frequency-stabilized laser based on FPGA control according to claim 1, characterized in that: The optical splitter is a 1:99 optical fiber coupler.

4. The wavelength tunable SGDBR frequency-stabilized laser based on FPGA control according to claim 1, characterized in that: The FPGA control module also includes a DAC control module, which is used to convert the control signal sent by the current control module into a control voltage signal and then send it to the voltage-controlled constant current source.

5. The wavelength tunable SGDBR frequency-stabilized laser based on FPGA control according to claim 4, characterized in that: The DAC control module uses the TLV5618 chip and communicates with the FPGA through three-wire SPI communication.

6. The wavelength tunable SGDBR frequency-stabilized laser based on FPGA control according to claim 1, characterized in that: The FPGA control module is also provided with a RAM storage module, and the RAM storage module is used to store the wavelength-current relationship table; The wavelength-current relationship table includes the values ​​of the front grating node current Iq, the rear grating node current Ih and the phase node current Ix corresponding to each output wavelength of the SGDBR laser.

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