A frequency-doubled fiber laser

Abstract

This application relates to a frequency-doubled fiber laser, comprising a seed source, a fiber amplifier, a waveguide, a beam splitter, a pump laser, a controller, and a laser power stabilization system. The output end of the pump laser is connected to the fiber amplifier. The controller is connected to the seed source, pump laser, waveguide, and laser power stabilization system. The system includes a beam splitting input connected to one output end of the beam splitter; a photodiode, the photosensitive portion of which is connected to the beam splitting input; a first temperature control device, in which the photodiode is disposed; and an operational amplifier circuit. The operational amplifier circuit samples and connects to the photodiode and the controller to convert the current collected through the photodiode into a voltage signal, which is then fed back to the controller. The controller then controls the pump laser based on the voltage signal. By controlling the temperature around the photodiode through the first temperature control device, the influence of the surrounding environment, especially temperature, on the photodiode is reduced, improving the accuracy of the output voltage signal. This feedback is then used to control the pump laser, seed source, and waveguide, thereby improving the power stability of the fiber laser.

Description

Technical Field

[0001] This application relates to the field of laser technology, and more particularly to a frequency-doubled fiber laser. Background Technology

[0002] In recent years, with the development of fiber optic devices, the optical performance of fiber lasers has been continuously improved, and their integration level has become increasingly higher, making them irreplaceable in fields such as fiber optic communication, precision measurement, and lidar. Periodically polarized lithium niobate (PPLN) waveguides are nonlinear optical crystals. They can generate sum-frequency and difference-frequency effects using nonlinear second harmonics. With innovations and breakthroughs in lithium niobate thin-film ridge waveguide technology, the sum-frequency and difference-frequency conversion efficiencies have been significantly improved. Therefore, PPLN ridge waveguides are widely used in single-frequency fiber lasers, expanding the laser's operating wavelength range, such as special wavelengths like 532nm and 780nm, making them crucial for applications in atomic and molecular science research, biomedicine, and quantum detection.

[0003] Since the stability of laser power affects the signal-to-noise ratio of the probe signal, the power stability of fiber lasers has become a major concern. Generally, feedback is obtained by probing the optical signal and the laser is controlled by a PID algorithm to achieve power stability. However, in practical engineering applications, the probe optical signal is affected by the environment and generates noise, which affects the accuracy of laser stability control.

[0004] Therefore, how to provide fiber lasers with low-noise power stability systems and improve the power stability of fiber lasers has become an urgent problem to be solved. Utility Model Content

[0005] In view of this, embodiments of this application provide a frequency-doubled fiber laser to solve the problem of how to provide a fiber laser with a low-noise power stabilization system and improve the power stability of the fiber laser.

[0006] This application provides a frequency-doubled fiber laser, comprising a seed source, a fiber amplifier, a waveguide, and a beam splitter connected sequentially in the optical path propagation direction;

[0007] It also includes a pump laser, a controller, and a laser power stabilization system, wherein the optical output end of the pump laser is connected to the fiber amplifier to adjust the amplification factor of the fiber amplifier;

[0008] The controller is connected to the seed source, the pump laser, the waveguide, and the laser power stabilization system;

[0009] The laser power stabilization system includes a beam splitting input terminal, the beam splitting input optical path is connected to one output terminal of the beam splitter, and the other output terminal of the beam splitter outputs photons;

[0010] A photodiode, wherein the photosensitive portion of the photodiode is connected to the beam splitting input terminal, so as to adjust the current passing through the photodiode according to the light entering the beam splitting input terminal;

[0011] A first temperature control device, wherein the photodiode is disposed within the first temperature control device; and

[0012] An operational amplifier circuit is provided, wherein the operational amplifier circuit is connected to the photodiode for sampling, so as to collect the current passing through the photodiode and convert the current into a voltage signal;

[0013] The output of the operational amplifier circuit is connected to the controller to feed back the voltage signal to the controller, so that the controller controls the pump laser according to the voltage signal.

[0014] In one embodiment, the first temperature control device includes a temperature sensor and a temperature control device. The temperature control device is equipped with the photodiode to control the ambient temperature of the photodiode. The temperature sensor is located around the photodiode to collect the ambient temperature of the photodiode.

[0015] In one embodiment, the temperature control device includes at least two copper plates, one of which is provided with a first semiconductor cooling chip, and the photodiode is disposed on the copper plate provided with the first semiconductor cooling chip, and the photodiode is covered by another copper plate.

[0016] In one embodiment, the controller is connected to the temperature sensor to acquire a first temperature, and the controller is connected to each first thermoelectric cooler via a corresponding drive module to perform temperature control on the first temperature control device based on the first temperature.

[0017] In one embodiment, the temperature sensor is a first thermistor temperature sensor.

[0018] In one embodiment, the laser power stabilization system further includes a sampling circuit, which uses a shielded twisted-pair cable, and the operational amplifier circuit is connected to the photodiode through the sampling circuit.

[0019] In one embodiment, the operational amplifier circuit is an operational amplifier zero-bias circuit or an operational amplifier plus-bias circuit.

[0020] In one embodiment, the frequency-doubled fiber laser further includes a second temperature control device, the waveguide is disposed on the second temperature control device, and the controller is connected to the second temperature control device to adjust the temperature around the waveguide.

[0021] In one embodiment, the second temperature control device includes a second thermoelectric cooler and a second thermistor temperature sensor. The controller is connected to the second thermistor temperature sensor to collect a second temperature. The controller is connected to the second thermoelectric cooler through a corresponding drive module to control the temperature of the second temperature control device according to the second temperature.

[0022] In one embodiment, the controller includes a human-computer interaction system, an ADC circuit, an FPGA circuit, and a DAC circuit. The human-computer interaction system is connected to a first terminal of the FPGA circuit. One terminal of the ADC circuit is connected to a second terminal of the FPGA circuit. The other terminal of the ADC circuit is connected to the output terminal of the operational amplifier circuit. A third terminal of the FPGA circuit is connected to one terminal of the DAC circuit. The other terminal of the DAC circuit is connected to the pump laser, the seed source, the waveguide, and the first temperature control device.

[0023] The advantages of this application compared to the prior art are as follows: This application includes a seed source, an optical fiber amplifier, a waveguide, and a beam splitter connected sequentially in the optical path propagation direction. It also includes a pump laser, a controller, and a laser power stabilization system. The optical output end of the pump laser is connected to the optical fiber amplifier to adjust the amplification factor of the optical fiber amplifier. The controller is connected to the seed source, pump laser, waveguide, and laser power stabilization system. This system includes a beam splitting input end connected to one output end of the beam splitter; a photodiode, the photosensitive part of which is connected to the beam splitting input end to adjust the current passing through the photodiode according to the light entering the beam splitting input end; a first temperature control device, in which the photodiode is disposed; and an operational amplifier circuit, the operational amplifier circuit being sampled and connected to the photodiode to collect the current passing through the photodiode and convert the current into a voltage signal. The output end of the operational amplifier circuit is connected to the controller to feed back the voltage signal to the controller, so that the controller controls the pump laser according to the voltage signal. The temperature around the photodiode is controlled by the first temperature control device to reduce the influence of the surrounding environment, especially temperature, on the photodiode, improve the accuracy of the output voltage signal, and then use the feedback to control the pump laser, seed source and waveguide, thereby improving the power stability of the fiber laser. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a frequency-doubled fiber laser provided in one embodiment of this application;

[0026] Figure 2 This is a schematic diagram of the structure of an operational amplifier zero-bias circuit provided in an embodiment of this application. Detailed Implementation

[0027] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0028] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0029] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0030] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0031] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0033] To illustrate the technical solution of this application, specific embodiments are described below.

[0034] like Figure 1 The diagram shown is a schematic of a frequency-doubled fiber laser provided in an embodiment of this application. The frequency-doubled fiber laser includes a seed source, a fiber amplifier, a waveguide, and a beam splitter connected sequentially in the optical propagation direction; as well as a pump laser, a controller, and a laser power stabilization system. The optical output end of the pump laser is connected to the fiber amplifier to adjust the amplification factor of the fiber amplifier; the controller is connected to the seed source, pump laser, waveguide, and laser power stabilization system.

[0035] The laser power stabilization system includes a beam splitter input terminal, a photodiode, a first temperature control device, and an operational amplifier circuit. The beam splitter input optical path is connected to one output terminal of the beam splitter, and the other output terminal of the beam splitter outputs photons. The photosensitive portion of the photodiode is connected to the beam splitter input terminal to adjust the current passing through the photodiode based on the light entering the beam splitter input terminal. The photodiode is housed within the first temperature control device. The operational amplifier circuit is connected to the photodiode for sampling to collect the current passing through the photodiode and convert the current into a voltage signal. The output terminal of the operational amplifier circuit is connected to a controller to feed the voltage signal back to the controller, enabling the controller to control the pump laser based on the voltage signal.

[0036] The temperature around the photodiode is controlled by the first temperature control device to reduce the influence of the surrounding environment, especially temperature, on the photodiode, improve the accuracy of the output voltage signal, and thus improve the power stability of the laser.

[0037] Specifically, in Figure 1In the controller, there are a human-machine interaction system, an ADC circuit, an FPGA circuit, and a DAC circuit. The human-machine interaction system is connected to the first terminal of the FPGA circuit. One terminal of the ADC circuit is connected to the second terminal of the FPGA circuit. The other terminal of the ADC circuit is connected to the output terminal of the operational amplifier circuit. The third terminal of the FPGA circuit is connected to one terminal of the DAC circuit. The other terminal of the DAC circuit is connected to the pump laser, the seed source, the waveguide, and the first temperature control device.

[0038] Of course, the DAC circuit in the controller may also be independent of the first temperature control device, which is controlled by a separate controller.

[0039] The controller employs an FPGA circuit, which communicates with the human-machine interface system to receive commands from the system. The FPGA circuit acquires voltage signals via a single-channel ADC, which are then used to adjust the operating parameters of the pump laser, seed source, and waveguide via a DAC.

[0040] In one embodiment, the ADC circuit can employ a 16-bit 2MHz differential ADC sampling chip. Differential signal input minimizes power supply ripple and external noise interference with the sampling signal. Simultaneously, the high sampling bit depth ensures sampling accuracy, while high data processing speed minimizes system response time, thereby increasing power stability. The DAC circuit uses a single-ended 16-bit 2MHz chip to control the current of the LT3743.

[0041] The seed source amplifies power through an optical fiber amplifier. The amplified fundamental frequency light enters the waveguide. At the same time, the human-machine interaction system sends parameter commands to the second temperature control device. The FPGA circuit adjusts the waveguide operating temperature to maximize the output frequency-doubled light power.

[0042] The beam splitter divides the frequency-doubled light output from the waveguide into two paths: one path illuminates the photodiode, and the other path serves as the laser output. The power of the two beams after passing through the beam splitter is linearly related. Therefore, as long as the power of the feedback beam is kept stable, the power of the output beam can be kept stable.

[0043] Once the waveguide is in stable operation, the power stabilization mode is activated. The output of the photodiode is connected to the zero-bias operational amplifier circuit via a shielded twisted pair cable to amplify the signal. Finally, the signal is processed by the FPGA. The FPGA runs a PID algorithm to calculate the difference between the signal sampled by the ADC and the actual value that needs to be achieved. Finally, the output optical power is stabilized by controlling the pump laser current through the DAC.

[0044] In addition, the pump laser's operating current and the fiber amplifier's output power are linearly related, resulting in a fast response speed and good stability of the system.

[0045] In one embodiment, the first temperature control device includes a temperature sensor and a temperature control unit. A photodiode is disposed on the temperature control unit to control the ambient temperature of the photodiode. The temperature sensor is disposed around the photodiode to collect the ambient temperature. By detecting the ambient temperature using the temperature sensor, the temperature control unit can be accurately controlled based on the ambient temperature, for example, maintaining the ambient temperature at approximately 25°C.

[0046] In one embodiment, the temperature sensor is a thermistor temperature coefficient (NTC) sensor, which can reduce the overall size of the device and accurately collect temperature information.

[0047] In one embodiment, the temperature control device includes at least two copper plates. A first thermoelectric cooler (TEC) is disposed on one of the copper plates, and a photodiode is disposed on the copper plate with the first TEC. The photodiode is covered by another copper plate. By placing the photodiode on one copper plate and covering its upper part with a copper plate, heat conduction is achieved, ensuring temperature uniformity across the entire photodiode. Finally, the first TEC controls the temperature of the copper plate, ensuring that the controlled temperature remains consistent within the operating temperature range. For example, the first TEC maintains a constant temperature of 25°C within the operating temperature range, thus ensuring that the photodiode's responsivity does not change with ambient temperature variations.

[0048] In one embodiment, each first thermoelectric cooler is connected to a controller to control the temperature of the first temperature control device according to the controller's control commands. A temperature sensor is connected to the controller to send the collected temperature data to the controller. The controller controlling the laser can be connected to the first temperature control device for temperature control; alternatively, the first temperature control device can be controlled by an independent controller.

[0049] In one embodiment, a sampling circuit is also included. The sampling circuit uses shielded twisted-pair cable, and the operational amplifier circuit is connected to the photodiode through the sampling circuit. Since the current generated by the photodiode is a small signal, even slight external interference can cause a significant change in the output optical power. Therefore, using shielded twisted-pair cable can minimize EMC interference.

[0050] In one embodiment, the operational amplifier circuit is either a zero-bias operational amplifier circuit or an over-bias operational amplifier circuit. Figure 2 shows a schematic diagram of the zero-bias operational amplifier circuit provided in this embodiment, which is an operational amplifier chip and its components used for converting the current of a photodiode to voltage and amplifying the voltage. The photodiode is a current-type device, requiring the conversion of the current signal into a detectable voltage signal, and amplification of the small signal. The operational amplifier chip itself has a certain amount of noise; therefore, a low-noise chip model is selected here. A low-noise operational amplifier chip refers to an amplifier with extremely low internal noise levels, typically a few nV / Hz. Its purpose is to minimize the additional noise introduced by itself when amplifying weak current or voltage signals.

[0051] Figure 2 illustrates a complete signal transmission path: the photodiode current signal flows through a feedback resistor, is converted into a voltage by a low-noise operational amplifier (LNP), amplified, and then converted into a digital signal by an ADC and output to a digital processor. The LNP and precision resistors ensure the accuracy of signal conversion and amplification, while the ADC performs a high-fidelity conversion from analog to digital.

[0052] In addition, photodiodes generally have two driving methods: biased and zero biased. When using the biased method, the photodiode has a fast response speed but high noise, while the zero biased method sacrifices the response speed but has low system noise. The zero biased method is the preferred option for frequency conversion lasers with a closed-loop response speed of several hundred Hz.

[0053] In one embodiment, the frequency-doubled fiber laser further includes a second temperature control device. A waveguide is disposed on the second temperature control device, and a controller is connected to the second temperature control device to adjust the temperature around the waveguide. The second temperature control device is used to control the temperature of the waveguide to achieve stable operation of the waveguide.

[0054] In one embodiment, the second temperature control device includes a second thermoelectric cooler and a second thermistor temperature sensor. A controller is connected to the second thermistor temperature sensor to acquire a second temperature. The controller is also connected to the second thermoelectric cooler via a corresponding drive module to control the temperature of the second temperature control device based on the second temperature. Similar to the first temperature control device described above, the use of a thermoelectric cooler and a thermistor effectively achieves temperature acquisition and control while also reducing the device's footprint.

[0055] This waveguide can be a ridge waveguide such as PPLN.

[0056] This application employs precise temperature control of the photodiode to ensure that the output optical power does not change significantly when the ambient temperature changes. Furthermore, it uses shielded twisted-pair cables to minimize external interference, and employs low-noise operational amplifiers and matching zero-bias circuits to minimize the circuit's own noise and improve the stability of the output power.

[0057] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A frequency-doubled fiber laser, characterized by, It includes a seed source, an optical fiber amplifier, a waveguide, and a beam splitter connected sequentially in the direction of optical propagation; It also includes a pump laser, a controller, and a laser power stabilization system, wherein the optical output end of the pump laser is connected to the fiber amplifier to adjust the amplification factor of the fiber amplifier; The controller is connected to the seed source, the pump laser, the waveguide, and the laser power stabilization system; The laser power stabilization system includes a beam splitting input terminal, which is connected to one output terminal of the beam splitter, and the other output terminal of the beam splitter outputs photons. A photodiode, wherein the photosensitive portion of the photodiode is connected to the beam splitting input terminal, so as to adjust the current passing through the photodiode according to the light entering the beam splitting input terminal; A first temperature control device, wherein the photodiode is disposed in the first temperature control device; as well as An operational amplifier circuit is provided, wherein the operational amplifier circuit is connected to the photodiode for sampling, so as to collect the current passing through the photodiode and convert the current into a voltage signal; The output of the operational amplifier circuit is connected to the controller to feed back the voltage signal to the controller, so that the controller controls the pump laser according to the voltage signal.

2. The frequency-doubled fiber laser according to claim 1, characterized in that, The first temperature control device includes a temperature sensor and a temperature control device. The temperature control device is equipped with the photodiode to control the ambient temperature of the photodiode. The temperature sensor is located around the photodiode to collect the ambient temperature of the photodiode.

3. The frequency-doubled fiber laser of claim 2, wherein, The temperature control device includes at least two copper plates, one of which is provided with a first semiconductor cooling chip, and the photodiode is disposed on the copper plate provided with the first semiconductor cooling chip, and the photodiode is covered by another copper plate.

4. The frequency-doubled fiber laser of claim 3, wherein, The controller is connected to the temperature sensor to collect a first temperature. The controller is connected to each first semiconductor refrigeration chip through a corresponding drive module to control the temperature of the first temperature control device according to the first temperature.

5. The frequency-doubled fiber laser of claim 2, wherein, The temperature sensor is a first thermistor temperature sensor.

6. The frequency-doubled fiber laser of claim 1, wherein, The laser power stabilization system also includes a sampling circuit, which uses a shielded twisted-pair cable, and the operational amplifier circuit is connected to the photodiode through the sampling circuit.

7. The frequency-doubled fiber laser of claim 1, wherein, The operational amplifier circuit is either a zero-bias operational amplifier circuit or an over-bias operational amplifier circuit.

8. The frequency-doubled fiber laser of claim 1, wherein, The frequency-doubled fiber laser also includes a second temperature control device, the waveguide is disposed on the second temperature control device, and the controller is connected to the second temperature control device to adjust the temperature around the waveguide.

9. The frequency-doubled fiber laser of claim 8, wherein, The second temperature control device includes a second semiconductor cooling chip and a second thermistor temperature sensor. The controller is connected to the second thermistor temperature sensor to collect a second temperature. The controller is connected to the second semiconductor cooling chip through a corresponding drive module to control the temperature of the second temperature control device according to the second temperature.

10. The frequency-doubled fiber laser of any of claims 1 to 9, wherein, The controller includes a human-computer interaction system, an ADC circuit, an FPGA circuit, and a DAC circuit. The human-computer interaction system is connected to the first terminal of the FPGA circuit. One terminal of the ADC circuit is connected to the second terminal of the FPGA circuit. The other terminal of the ADC circuit is connected to the output terminal of the operational amplifier circuit. The third terminal of the FPGA circuit is connected to one terminal of the DAC circuit. The other terminal of the DAC circuit is connected to the pump laser, the seed source, the waveguide, and the first temperature control device.

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