Circuits to improve the frequency modulation resolution of lasers
By controlling the voltage at the DAC output and the thermistor RT feedback terminal using operational amplifiers U2 and U1, combined with a voltage divider network and PID control loop, the problem of insufficient laser wavelength adjustment step size was solved, improving the laser frequency modulation resolution and system stability, and meeting the temperature regulation requirements for mass production of lasers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHANDONG ZHONGKEJILIAN OPTOELECTRONIC INTEGRATED TECH RES INST CO LTD
- Filing Date
- 2025-09-29
- Publication Date
- 2026-07-03
AI Technical Summary
Existing technologies cannot meet the requirement of wavelength adjustment steps of less than 0.016 pm for 1550 nm wavelength lasers, resulting in insufficient stability of communication systems.
By using operational amplifiers U2 and U1 to increase the voltage control range at the DAC output control terminal and the thermistor RT feedback terminal respectively, and by using a voltage divider network and PID control loop, the TEC temperature control range is ensured to be within 15℃-30℃, thus achieving precise temperature adjustment of the 14-bit DAC.
This achieved an improvement in laser frequency modulation resolution, enhanced system stability, met the temperature regulation requirements for mass production of lasers, and reduced costs and weight.
Smart Images
Figure CN224458940U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of laser temperature control, and more specifically, to a circuit for improving the frequency modulation resolution of a laser. Background Technology
[0002] For coherent communication via spaceborne lasers, the wavelength difference between lasers on satellites needs to be maintained within a certain range to achieve coherent communication. To accommodate wavelength shifts caused by the Doppler effect between satellites, the laser wavelength needs to be adjusted in real time. The smaller the wavelength adjustment step, the less interference the communication system experiences, resulting in more stable communication. Currently, for 1550nm wavelength lasers, a wavelength adjustment step of less than or equal to 0.016 pm is required to meet system requirements. The highest precision DAC commonly used in current aerospace devices that meets these requirements is 14 bits, with an output voltage range of 0-1V.
[0003] The laser wavelength is adjusted by regulating its internal TEC (Controlled Temperature Regulator). For every 1°C change in the TEC temperature, the laser wavelength changes by approximately 15 pm. To meet the requirement of a wavelength adjustment step of less than or equal to 0.016 pm for a 1550nm laser, the TEC temperature step needs to be less than or equal to 0.001067°C. To achieve the required laser wavelength, the laser TEC temperature needs to be controlled within a specific range. Different lasers have different operating temperature requirements; to meet the needs of mass production, the laser temperature regulation temperature needs to be adjustable within the range of 15°C to 30°C. Utility Model Content
[0004] The purpose of this invention is to provide a circuit that improves the frequency modulation resolution of a laser. At the output control terminal of the DAC, the output voltage is increased by an operational amplifier U2, and the output voltage of the DAC is controlled within a certain range by a voltage divider network. At the feedback terminal of the thermistor RT, the feedback voltage of the thermistor RT is controlled by an operational amplifier U1 to be consistent with the range of the DAC output voltage, so that when the 14-bit DAC is adjusted from 0 to 16384, the TEC temperature control range is exactly 15℃-30℃.
[0005] This utility model is achieved through the following technical solution:
[0006] A circuit for improving the frequency modulation resolution of a laser includes operational amplifier U1 and operational amplifier U2. The non-inverting input of operational amplifier U2 is connected to the output of DAC_OUT_SEED1 via resistor R10. The output of operational amplifier U2 is connected to a TEC temperature control chip via a voltage divider network. The non-inverting input of operational amplifier U1 is connected to a thermistor RT, which is also connected to an RC filter and a pull-up resistor R3. The output of operational amplifier U1 is connected to the TEC temperature control chip.
[0007] Furthermore, the TEC temperature control chip includes operational amplifier U2 and operational amplifier U3. The output terminal of operational amplifier U2 is connected to the non-inverting input terminal of operational amplifier U3 through a voltage divider network. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U3. The output terminal of operational amplifier U3 is connected to the inverting input terminal of operational amplifier U2 through resistor R2. The ISET terminal of operational amplifier U2 is connected to a current-limiting resistor R14, and the ISET terminal of operational amplifier U3 is connected to a current-limiting resistor R13, so as to limit the temperature control execution current to within 1A and prevent excessive current from impacting the power supply.
[0008] Furthermore, the voltage divider network includes resistors R11 and R12. The output terminal of operational amplifier U2 is connected to resistor R11. Both resistors R11 and R12 are connected to the non-inverting input terminal of operational amplifier U3. Resistor R12 is also connected to a 2.5V reference voltage.
[0009] Furthermore, the RC filter includes a resistor R17 and a capacitor C1, which are connected in series to a thermistor RT.
[0010] Furthermore, it also includes a PID control loop, which includes resistors R9 and R1, capacitors C11 and C4. Capacitor C11 and resistor R9 are connected in parallel and then connected to the output terminal of operational amplifier U1 and the inverting input terminal of operational amplifier U3, respectively. The inverting input terminal of operational amplifier U3 is also connected to resistor R1 and capacitor C4 in series. Capacitor C4 is connected to resistor R2. Resistor R5 and capacitor C2 are connected in parallel across resistor R1 and capacitor C4, respectively.
[0011] Furthermore, a resistor R4 is connected between the inverting input terminal and the output terminal of the operational amplifier U3.
[0012] Compared with the prior art, the beneficial effects of this utility model are:
[0013] 1. The solution is simple and easy to implement, requiring no additional chips, thus reducing weight and cost.
[0014] 2. The tuning accuracy and resolution are better than the system requirements, improving system stability.
[0015] 3. At the DAC output control terminal, the output voltage is increased by operational amplifier U2, and the DAC output voltage is controlled within a certain range by a voltage divider network; at the thermistor RT feedback terminal, the thermistor RT feedback voltage is controlled by operational amplifier U1 to be consistent with the DAC output voltage range, so that when the 14-bit DAC is adjusted from 0 to 16384, the TEC temperature control range is exactly 15℃-30℃. Attached Figure Description
[0016] Figure 1 This is the circuit diagram of this utility model. Detailed Implementation
[0017] The present invention will be further described below with reference to the accompanying drawings.
[0018] like Figure 1 As shown in Embodiment 1, a circuit for improving the frequency modulation resolution of a laser includes operational amplifier U1 and operational amplifier U2. The non-inverting input terminal of operational amplifier U2 is connected to the output terminal DAC_OUT_SEED1 of a DAC through a current-limiting resistor R10. The output voltage range of the DAC is 0-1V. The output terminal of operational amplifier U2 is connected to a TEC temperature control chip through a voltage divider network. The non-inverting input terminal of operational amplifier U1 is connected to a thermistor RT. The thermistor RT is also connected to an RC filter and a pull-up resistor R3. The output terminal of operational amplifier U1 is connected to the TEC temperature control chip.
[0019] Specifically, to improve the laser's frequency modulation resolution, operational amplifier U2 is used to increase the DAC's output voltage at the DAC output control terminal. A voltage divider network is then used to control the DAC output voltage within a certain range, meeting the TEC temperature control requirement of 15℃-30℃. Simultaneously, at the thermistor RT feedback terminal, operational amplifier U1 controls the thermistor RT feedback voltage to match the DAC output voltage range. This ensures that when the 14-bit DAC is adjusted from 0-16384, the TEC temperature control range is exactly 15℃-30℃. The voltage value of the thermistor RT serves as feedback for the TEC temperature control chip and is connected to the input terminal of operational amplifier U1.
[0020] After the DAC output is amplified by operational amplifier U2, the output voltage range changes to 0-2.3V. Operational amplifier U2 serves two purposes: voltage amplification and isolating the DAC output from subsequent circuits, thus stabilizing the DAC output voltage.
[0021] Example 2: A circuit for improving the frequency modulation resolution of a laser. The TEC temperature control chip includes operational amplifier U2 and operational amplifier U3. The output terminal of operational amplifier U2 is connected to the non-inverting input terminal of operational amplifier U3 through a voltage divider network. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U3. The output terminal of operational amplifier U3 is connected to the inverting input terminal of operational amplifier U2 through resistor R2. The ISET terminal of operational amplifier U2 is connected to a current-limiting resistor R14, and the ISET terminal of operational amplifier U3 is connected to a current-limiting resistor R13, so as to limit the temperature control execution current to within 1A and prevent excessive current from impacting the power supply.
[0022] In this embodiment, the voltage divider network includes resistors R11 and R12. The output terminal of operational amplifier U2 is connected to resistor R11. Both resistors R11 and R12 are connected to the non-inverting input terminal of operational amplifier U3. Resistor R12 is also connected to a 2.5V reference voltage.
[0023] Specifically, the output of operational amplifier U2 is connected to a reference voltage of 2.5V via resistors R11 and R12, forming a voltage divider network. The voltage divided between resistors R11 and R12 serves as the input for controlling the TEC temperature. After passing through the voltage divider network, the minimum voltage at the setting terminal of the TEC temperature control chip is (2.5-0) / (100+240)*240=1.76V, and the maximum voltage at the output terminal is (2.5-2.3) / (100+240)*240+2.3=2.44V.
[0024] In this embodiment, the RC filter includes a resistor R17 and a capacitor C1, which are connected in series to a thermistor RT.
[0025] Specifically, the voltage across the thermistor RT passes through an RC filter and then enters the ADC. The MCU acquires the voltage across the thermistor via the ADC and calculates the current temperature. When the maximum temperature fluctuation frequency is 24kHz, according to the Nyquist sampling theorem, the RC bandwidth should be higher than 48kHz to avoid signal mixing. Therefore, based on the bandwidth calculation formula: BW≤1 / (2πRC), a 100Ω resistor R17 and a 33nF capacitor C1 are selected, which meets the current sampling requirements.
[0026] In this embodiment, a PID control loop is also included. The PID control loop includes resistors R9 and R1, capacitors C11 and C4. Capacitor C11 and resistor R9 are connected in parallel and then connected to the output terminal of operational amplifier U1 and the inverting input terminal of operational amplifier U3, respectively. The inverting input terminal of operational amplifier U3 is also connected to resistor R1 and capacitor C4 in series. Capacitor C4 is connected to resistor R2. Resistor R5 and capacitor C2 are connected in parallel across resistor R1 and capacitor C4, respectively.
[0027] Specifically, the PID control loop ensures that the input and output voltages of operational amplifier U3 are consistent, meaning the laser temperature control setpoint matches the feedback value. Capacitor C2 and resistor R5 prevent saturation of the high-frequency and low-frequency component amplification factors. Here, (R9 / R1+C11 / C4) is the proportional coefficient, R9 / C4 is the integral coefficient, and R1*C11 is the derivative coefficient. Through hardware PID control, a fast and stable temperature response is achieved in the laser, reaching the setpoint. The above is existing technology and will not be elaborated further.
[0028] In this embodiment, a resistor R4 is also connected between the inverting input terminal and the output terminal of the operational amplifier U3.
[0029] The feedback value of the thermistor RT is amplified by 1.59 times by operational amplifier U1 before being output. When the temperature is controlled from 15℃ to 30℃, the resistance Rr of the thermistor RT corresponds to 15.71Ω-8.58kΩ, and the voltage across it is 2.5 / (Rr+10)*Rr, which is 1.1545V-1.5276V. After passing through the operational amplifier, the voltage range is 1.83V-2.43V.
[0030] When the DAC outputs 0V and the TEC control chip voltage setting is 1.83V, the thermistor RT is controlled to 30℃ by the TEC temperature control chip; when the DAC outputs 1V and the TEC control chip voltage setting is 2.43V, the thermistor RT is controlled to 15℃ by the TEC temperature control chip.
[0031] When a 14-bit DAC is selected, its output can be set from 0 to 16384. Then, the TEC temperature control step temperature = 15 / 16384 = 0.000915℃, which meets the requirement that the laser tuning step is 0.0137pm, satisfying the requirement that the tuning step is less than or equal to 0.016pm. When the software malfunctions, the DAC output range is 0-1V, and the set value is 15-30℃, so there will be no phenomenon of excessively high or low temperature that could damage the laser.
Claims
1. A circuit for improving the frequency modulation resolution of a laser, comprising an operational amplifier U1 and an operational amplifier U2, characterized in that: The non-inverting input of operational amplifier U2 is connected to the output of DAC via resistor R10. The output of operational amplifier U2 is connected to the TEC temperature control chip via a voltage divider network. The non-inverting input of operational amplifier U1 is connected to a thermistor RT. The thermistor RT is also connected to an RC filter and a pull-up resistor R3. The output of operational amplifier U1 is connected to the TEC temperature control chip.
2. The circuit for improving the frequency modulation resolution of a laser as defined in claim 1, wherein: The TEC temperature control chip includes operational amplifier U2 and operational amplifier U3. The output terminal of operational amplifier U2 is connected to the non-inverting input terminal of operational amplifier U3 through a voltage divider network. The output terminal of operational amplifier U1 is connected to the inverting input terminal of operational amplifier U3. The output terminal of operational amplifier U3 is connected to the inverting input terminal of operational amplifier U2 through resistor R2. The ISET terminal of operational amplifier U2 is connected to a current-limiting resistor R14, and the ISET terminal of operational amplifier U3 is connected to a current-limiting resistor R13.
3. The circuit for improving the frequency modulation resolution of a laser as defined in claim 2, wherein: The voltage divider network includes resistors R11 and R12. The output terminal of operational amplifier U2 is connected to resistor R11. Both resistors R11 and R12 are connected to the non-inverting input terminal of operational amplifier U3. Resistor R12 is also connected to a 2.5V voltage.
4. The circuit for improving the frequency modulation resolution of a laser according to claim 1 or 2, characterized in that: The RC filter includes a resistor R17 and a capacitor C1, which are connected in series to a thermistor RT.
5. The circuit for improving the frequency modulation resolution of a laser of claim 2, wherein: It also includes a PID control loop, which includes resistors R9 and R1, capacitors C11 and C4. Capacitor C11 and resistor R9 are connected in parallel and then connected to the output terminal of operational amplifier U1 and the inverting input terminal of operational amplifier U3, respectively. The inverting input terminal of operational amplifier U3 is also connected to resistor R1 and capacitor C4 in series. Capacitor C4 is connected to resistor R2. Resistor R5 and capacitor C2 are connected in parallel across resistor R1 and capacitor C4, respectively.
6. The circuit for improving the frequency modulation resolution of a laser of claim 2, wherein: A resistor R4 is also connected between the inverting input terminal and the output terminal of the operational amplifier U3.