Laser wavelength tuning method based on temperature control for FBG (Fiber Bragg Grating) demodulator

Abstract

The invention discloses a laser wavelength tuning circuit based on temperature control for an FBG demodulator. The laser wavelength tuning circuit comprises a current driving module used for providing constant driving current for a laser of the FBG demodulator; the temperature acquisition module is used for acquiring the temperature of the laser by adopting NTC in the laser as a temperature sensor; the temperature adjusting module is used for adjusting the direction and the size of working current of a semiconductor chilling plate TEC in the laser so as to adjust the temperature of the laser; the main control module is used for enabling the target wavelength output by the laser to correspond to the target temperature, calculating the temperature adjusting amount according to the temperature, collected by the temperature collection module, of the laser and the target temperature, generating a corresponding control signal and outputting the control signal to the temperature adjusting module. According to the invention, constant current driving of the laser is realized, the influence of current fluctuation is avoided, high-precision temperature control is realized, the wavelength tuning linearity is ensured, and the performance of the FBG demodulator is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of FBG demodulators, and more specifically, relates to a temperature-controlled laser wavelength tuning method for FBG demodulators. Background Technology

[0002] The FBG demodulator is a core device in a fiber optic grating sensing system. Its core function is to identify and demodulate specific wavelength light signals reflected by the FBG sensor by adjusting the laser's output wavelength, thereby acquiring information about changes in the measured quantity (such as temperature and strain). Currently, most mainstream FBG demodulators use current tuning to adjust the laser's wavelength. This involves changing the laser's drive current to alter its output wavelength, thus completing the wavelength scanning and demodulation process. This current tuning method has the following drawbacks: large output power fluctuations, limited laser lifespan, poor wavelength tuning linearity, and significant temperature drift. Summary of the Invention

[0003] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention proposes a technical solution to achieve wavelength tuning by adjusting the laser temperature. The purpose is to achieve stable adjustment of the output wavelength by precisely controlling the laser temperature while keeping the laser driving current constant, thereby improving the performance of the FBG demodulator.

[0004] To achieve the above objectives, the present invention provides a temperature-controlled laser wavelength tuning circuit for an FBG demodulator, comprising: The current drive module is used to provide a constant drive current to the laser of the FBG demodulator. A temperature acquisition module is used to acquire the temperature of the laser by using the NTC inside the laser as a temperature sensor. The temperature regulation module is used to adjust the direction and magnitude of the operating current of the semiconductor cooling chip TEC inside the laser, thereby regulating the temperature of the laser. The main control module is used to map the target wavelength output by the laser to the target temperature. Based on the laser temperature and the target temperature collected by the temperature acquisition module, it calculates the temperature adjustment amount and generates the corresponding control signal to be output to the temperature adjustment module.

[0005] Preferably, in the laser wavelength tuning device of the present invention, the current driving module includes: The first operational amplifier has its inverting input connected to the reference voltage signal output of the main control module. The first NMOS transistor has its gate (G) connected to the output of the first operational amplifier, its source (S) connected to the non-inverting input of the first operational amplifier, and its source connected to one end of a sampling resistor, the other end of which is grounded. The drain (D) of the first NMOS transistor is connected to the negative terminal of the laser, and the positive terminal of the laser is connected to the positive power supply.

[0006] Preferably, in the laser wavelength tuning device of the present invention, an RC low-pass filter circuit is connected between the inverting input terminal of the first operational amplifier and the reference voltage signal output terminal of the main control module, and one end of a filter capacitor is also connected between the gate of the first NMOS transistor and the output terminal of the first operational amplifier, while the other end of the filter resistor is grounded.

[0007] Preferably, in the laser wavelength tuning device of the present invention, the temperature adjustment module is implemented using an H-bridge TEC drive circuit.

[0008] Preferably, in the laser wavelength tuning device of the present invention, the temperature acquisition module includes a first voltage divider resistor, a second voltage divider resistor, a third voltage divider resistor, a first input resistor, a second input resistor, an input voltage divider resistor, a feedback resistor, and a second operational amplifier; One end of the first voltage divider resistor and one end of the second voltage divider resistor are connected together to the reference voltage. The other end of the first voltage divider resistor is connected to the ground via a third voltage divider resistor in series, and to the inverting input of the second operational amplifier via a second input resistor in series. The other end of the second voltage divider resistor is connected to the non-inverting input of the second operational amplifier via a first input resistor in series. One end of the input voltage divider resistor is connected to the end of the first input resistor closest to the second operational amplifier, and the other end of the input voltage divider resistor is grounded. The output of the second operational amplifier is connected to the inverting input of the second operational amplifier via a feedback resistor in series. The other end of the second voltage divider resistor serves as the signal input of the temperature acquisition module and is connected to one of the RTH pins of the laser. The other RTH pin of the laser is grounded. The output of the second operational amplifier serves as the signal output of the temperature acquisition module and is connected to the ADC interface of the main control module.

[0009] Preferably, in the laser wavelength tuning device of the present invention, the current driving module operates as follows: the reference voltage signal is a fixed-value DC voltage connected to the inverting input terminal of the first operational amplifier. The first operational amplifier compares the voltages at its non-inverting input terminal and the inverting input terminal, and outputs a voltage connected to the gate (G) terminal of the first NMOS transistor. The magnitude of the gate voltage of the first NMOS transistor determines the on-resistance between its drain (DS) and source (DS) terminals. The larger the gate voltage of the first NMOS transistor, the larger the current flowing through its drain (DS) terminals. The sampling resistor monitors the magnitude of the current flowing through the drain (DS) terminals of the first NMOS transistor and converts it into a voltage connected to the non-inverting input terminal of the first operational amplifier, forming a closed-loop control to stabilize the driving current.

[0010] Preferably, in the laser wavelength tuning device of the present invention, the main control module uses a PID control algorithm to calculate the temperature adjustment amount.

[0011] Overall, the above-mentioned technical solutions conceived in this invention have beneficial effects compared with the prior art: This invention achieves constant current driving of the laser through the architecture of "reference voltage + operational amplifier + sampling resistor" to avoid the influence of current fluctuations; it adopts the "NTC detection + H-bridge TEC drive" circuit to achieve high-precision temperature control, ensure wavelength tuning linearity, and improve the performance of the FBG demodulator. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the circuit of the current drive module provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the H-bridge TEC drive circuit provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the temperature acquisition module provided in an embodiment of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0014] In the description of the embodiments of this application, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, apparatus, product or device that includes a series of steps or modules is not necessarily limited to those steps or modules that are explicitly listed, but may include other steps or modules that are not explicitly listed or that are inherent to such process, method, product or device.

[0015] The naming or numbering of steps in the embodiments of the present invention does not mean that the steps in the method flow must be executed in the time / logical order indicated by the naming or numbering. The execution order of the named or numbered process steps can be changed according to the technical purpose to be achieved, as long as the same or similar technical effect can be achieved.

[0016] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0017] This invention provides a temperature-controlled laser wavelength tuning circuit for an FBG demodulator, comprising: The current drive module is used to provide a constant drive current to the laser of the FBG demodulator. A temperature acquisition module is used to acquire the temperature of the laser by using the NTC inside the laser as a temperature sensor. The temperature regulation module is used to adjust the direction and magnitude of the operating current of the semiconductor cooling chip TEC inside the laser, thereby regulating the temperature of the laser. The main control module is used to map the target wavelength output by the laser to the target temperature. Based on the laser temperature and the target temperature collected by the temperature acquisition module, it calculates the temperature adjustment amount and generates the corresponding control signal to be output to the temperature adjustment module.

[0018] refer to Figure 1 , Figure 1 This is a schematic diagram of the circuit of the current drive module provided in an embodiment of the present invention. The laser LD integrates a TEC (thermal cooling chip) and an NTC (negative temperature coefficient thermistor). The LD+ pin of the laser LD is connected to the positive power supply +5V, and the positive power supply is grounded through multiple power supply filter capacitors C137 to C142, thereby filtering out high-frequency noise in the power supply.

[0019] The current drive module includes: a first operational amplifier U32 and a first NMOS transistor Q13.

[0020] The inverting input of the first operational amplifier U32 is connected to the reference voltage signal output of the main control module, and the reference voltage signal DAC_LD is obtained from the main control module. The gate of the first NMOS transistor is connected to the output of the first operational amplifier U32. The source of the first NMOS transistor Q13 is connected to the non-inverting input of the first operational amplifier U32. The source of the first NMOS transistor Q13 is connected to one end of the sampling resistor R156, and the other end of the sampling resistor R156 is grounded. The drain of the first NMOS transistor Q13 is connected to the negative terminal LD- pin of the laser.

[0021] The current drive module works as follows: It uses a first operational amplifier U32, a sampling resistor R156, and a first NMOS transistor Q13 to form a feedback closed loop. It receives the reference voltage signal DAC_LD from the main control module and stabilizes the laser LD's operating current at a preset constant value, ensuring no current fluctuations. The constant current output range can be set to 0-200mA, with current stability ≤0.1mA. The sampling resistor R156 samples the current signal, converts it into a voltage signal, and feeds it back to the inverting input of the first operational amplifier U32, forming a closed-loop control that adjusts the drive current to ensure the laser LD operates normally.

[0022] The reference voltage signal DAC_LD is a fixed-value DC voltage connected to the inverting input of the first operational amplifier U32. The first operational amplifier U32 compares the voltages at its non-inverting and inverting inputs and outputs a voltage connected to the gate (G) of the first NMOS transistor Q13. The magnitude of the gate voltage of the first NMOS transistor Q13 determines the on-resistance between its drain and source (DS) terminals. The larger the gate voltage of the first NMOS transistor Q13, the larger the current flowing through its drain and source terminals. The sampling resistor R15... The 6-ohm resistor has a value of 2Ω. It monitors the current between the drain and source terminals of the first NMOS transistor Q13 and converts it into a voltage, which is then connected to the non-inverting input of the first operational amplifier U32. The voltage at the non-inverting input of the first operational amplifier U32 connected to the sampling resistor R156 must be equal to the reference voltage signal DAC_LD for the entire circuit to be stable. If the voltage is too large or too small, the output voltage of the first operational amplifier U32 will increase or decrease, thereby adjusting the conduction state of the MOS transistor, controlling the current to increase or decrease, forming a closed-loop control, which in turn regulates and stabilizes the drive current.

[0023] In a preferred embodiment of the present invention, an RC low-pass filter circuit is connected between the inverting input terminal of the first operational amplifier U32 and the reference voltage signal output terminal of the main control module. The RC low-pass filter circuit includes a resistor R154 and a capacitor C143. The resistor R154 has a value of 1kΩ, and the capacitor C143 has a value of 100pF. The two ends of the resistor R154 are respectively connected to the reference voltage signal output terminal and the inverting input terminal of the first operational amplifier U32. One end of the capacitor C143 is connected to the end of the resistor R154 away from the reference voltage signal output terminal, and the other end of the capacitor C143 is grounded. The RC low-pass filter circuit is used to filter out high-frequency noise between the main control module and the first operational amplifier U32. A filter capacitor C144 is also connected between the gate of the first NMOS transistor and the output terminal of the first operational amplifier. The other end of the filter capacitor C144 is grounded. The filter capacitor C144 is used to filter out high-frequency signals output by the first operational amplifier.

[0024] refer to Figure 3 , Figure 3 This is a schematic diagram of the temperature acquisition module provided in an embodiment of the present invention. The temperature acquisition module includes a first voltage divider resistor R90, a second voltage divider resistor R91, a third voltage divider resistor R98 / / R99 ( / / indicates parallel connection), a first input resistor R93, a second input resistor R97, an input voltage divider resistor R92, a feedback resistor R94, and a second operational amplifier U15. The values ​​of the first voltage divider resistor R90, the second voltage divider resistor R91, the third voltage divider resistor R98 / / R99, the first input resistor R93, the second input resistor R97, the input voltage divider resistor R92, and the feedback resistor R94 are 10KΩ, 10KΩ, 10KΩ / / 10KΩ, 390KΩ, 390KΩ, 1MΩ, and 1MΩ, respectively.

[0025] One end of the first voltage divider resistor R90 and the second voltage divider resistor R91 are connected together to the reference voltage REF, which is DC 2.5V. The other end of the first voltage divider resistor R90 is connected in series with the third voltage divider resistors R98 / / R99 and then grounded. On the other hand, it is connected in series with the second input resistor R97 and then connected to the inverting input terminal of the second operational amplifier U15. The other end of the second voltage divider resistor R91 is connected in series with the first input resistor R93 and then connected to the non-inverting input terminal of the second operational amplifier U15. One end of the input voltage divider resistor R92 is connected to the end of the first input resistor R93 near the second operational amplifier U15, and the other end of the input voltage divider resistor R92 is grounded. The output terminal of the second operational amplifier U1 is connected in series with the feedback resistor R94 and then connected to the inverting input terminal of the second operational amplifier U15. The other end of the second voltage divider resistor R91 serves as the signal input terminal of the temperature acquisition module and is connected to one of the RTH pins of the laser LD. The other RTH pin of the laser is grounded. The output terminal of the second operational amplifier U15 serves as the signal output terminal of the temperature acquisition module and is connected to one of the ADC interfaces of the main control module.

[0026] The working principle of the temperature acquisition module is as follows: The temperature acquisition module uses the NTC (negative temperature coefficient thermistor) inside the laser LD as a temperature sensor, and together with the voltage divider resistor and the operational amplifier TP2301-TR, etc., to form a signal acquisition circuit. It acquires the temperature signal of the laser LD in real time and converts it into a voltage signal. This voltage signal is input to the main control module through the ADC interface (analog-to-digital converter interface) of the main control module to realize real-time temperature monitoring.

[0027] refer to Figure 2 , Figure 2 This is a schematic diagram of the H-bridge TEC driving circuit provided in this embodiment of the invention. The temperature regulation module is implemented using the H-bridge TEC driving circuit. The main control module outputs four temperature control signals DAC_TEC_L, DAC_TEC_R, TEC_SWA_L_UP, and TEC_SWA_R_UP through four output pins to the H-bridge TEC driving circuit to control it. The core function of the H-bridge TEC driving circuit is to precisely adjust the direction and magnitude of the operating current of the TEC integrated inside the laser according to the temperature control signal from the main control module, thereby realizing the heating / cooling switching and regulation rate control of the laser LD temperature, achieving closed-loop precise temperature control, and ultimately achieving precise wavelength tuning.

[0028] The H-bridge driver circuit controls the on / off logic of two NMOS transistors Q4 and Q5 and two PMOS transistors Q10 and Q2 to switch the direction of the TEC current, thereby switching the heating / cooling mode: when the current flows into the "positive" terminal of the TEC and flows out from the "negative" terminal, the TEC inside the laser is in cooling mode, which lowers its temperature; when the current direction is reversed (negative terminal inflow, positive terminal outflow), the TEC inside the laser is in heating mode, which raises its temperature.

[0029] The main control module maps the target wavelength of the laser LD to the target temperature value. By comparing the actual temperature of the laser LD uploaded in real time by the temperature acquisition module with the target temperature, the module uses a PID (proportional-integral-derivative) control algorithm to calculate the temperature adjustment amount and generate a corresponding control signal to output to the temperature adjustment module. The laser LD's own TEC is used as the core temperature control element in conjunction with the TEC drive circuit to achieve temperature adjustment.

[0030] Overall, the technical solutions conceived in this invention have beneficial effects compared with the prior art: the constant current drive of the laser is achieved through the "reference voltage + operational amplifier + sampling resistor" architecture, avoiding the influence of current fluctuations; the "NTC detection + H-bridge TEC drive" circuit achieves high-precision temperature control, ensuring wavelength tuning linearity and improving the performance of the FBG demodulator.

[0031] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature-controlled laser wavelength tuning circuit for an FBG demodulator, characterized in that, include: The current drive module is used to provide a constant drive current to the laser of the FBG demodulator. A temperature acquisition module is used to acquire the temperature of the laser by using the NTC inside the laser as a temperature sensor. The temperature regulation module is used to adjust the direction and magnitude of the operating current of the semiconductor cooling chip TEC inside the laser, thereby regulating the temperature of the laser. The main control module is used to map the target wavelength output by the laser to the target temperature. Based on the laser temperature and the target temperature collected by the temperature acquisition module, it calculates the temperature adjustment amount and generates the corresponding control signal to be output to the temperature adjustment module.

2. The laser wavelength tuning device according to claim 1, characterized in that, The current drive module includes: The first operational amplifier has its inverting input connected to the reference voltage signal output of the main control module. The first NMOS transistor has its gate (G) connected to the output of the first operational amplifier, its source (S) connected to the non-inverting input of the first operational amplifier, and its source connected to one end of a sampling resistor, the other end of which is grounded. The drain (D) of the first NMOS transistor is connected to the negative terminal of the laser, and the positive terminal of the laser is connected to the positive power supply.

3. The laser wavelength tuning device according to claim 2, characterized in that, An RC low-pass filter circuit is connected between the inverting input terminal of the first operational amplifier and the reference voltage signal output terminal of the main control module. One end of a filter capacitor is also connected between the gate of the first NMOS transistor and the output terminal of the first operational amplifier, and the other end of the filter resistor is grounded.

4. The laser wavelength tuning device according to claim 2, characterized in that, The temperature regulation module is implemented using an H-bridge TEC drive circuit.

5. The laser wavelength tuning device according to claim 1, characterized in that, The temperature acquisition module includes a first voltage divider resistor, a second voltage divider resistor, a third voltage divider resistor, a first input resistor, a second input resistor, an input voltage divider resistor, a feedback resistor, and a second operational amplifier; One end of the first voltage divider resistor and one end of the second voltage divider resistor are connected together to the reference voltage. The other end of the first voltage divider resistor is connected to the ground via a third voltage divider resistor in series, and to the inverting input of the second operational amplifier via a second input resistor in series. The other end of the second voltage divider resistor is connected to the non-inverting input of the second operational amplifier via a first input resistor in series. One end of the input voltage divider resistor is connected to the end of the first input resistor closest to the second operational amplifier, and the other end of the input voltage divider resistor is grounded. The output of the second operational amplifier is connected to the inverting input of the second operational amplifier via a feedback resistor in series. The other end of the second voltage divider resistor serves as the signal input of the temperature acquisition module and is connected to one of the RTH pins of the laser. The other RTH pin of the laser is grounded. The output of the second operational amplifier serves as the signal output of the temperature acquisition module and is connected to the ADC interface of the main control module.

6. The laser wavelength tuning device according to claim 2, characterized in that, The current drive module operates as follows: A reference voltage signal, a fixed-value DC voltage, is connected to the inverting input of the first operational amplifier. The first operational amplifier compares the voltages at its non-inverting and inverting inputs and outputs a voltage connected to the gate (G) of the first NMOS transistor. The magnitude of the gate voltage of the first NMOS transistor determines the on-resistance between its drain and source (DS) terminals. The larger the gate voltage of the first NMOS transistor, the larger the current flowing through its drain and source terminals. The sampling resistor monitors the current between the drain and source terminals of the first NMOS transistor and converts it into a voltage, which is then connected to the non-inverting input of the first operational amplifier, forming a closed-loop control to stabilize the drive current.

7. The laser wavelength tuning device according to claim 1, characterized in that, The main control module uses a PID control algorithm to calculate the temperature adjustment.

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