A fiber laser

Abstract

This invention relates to the field of laser technology and discloses a fiber laser. The laser includes: a linewidth modulation module, a frequency-doubling waveguide module, a beam splitter, a temperature control module, and a control module. The linewidth modulation module performs initial modulation of the linewidth of the fundamental frequency laser according to a first modulation command. The frequency-doubling waveguide module frequency-doubles the linewidth-modified laser to generate a target wavelength laser, and, according to a temperature control command, changes the phase mismatch during the frequency doubling process to perform secondary linewidth modulation and wavelength detuning of the target wavelength laser. The beam splitter splits the target wavelength laser into a monitoring beam and a main output laser, with the main output laser being output through a high splitting ratio end. The temperature control module generates a temperature control command according to a second modulation command. The control module receives the monitoring beam and collects laser linewidth information to output the first and second modulation commands. The laser provided by this invention can achieve laser linewidth modulation and laser wavelength detuning.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more specifically to a fiber laser. Background Technology

[0002] Atomic sensors based on the spin-exchange-without-relaxation (SERF) effect hold promise for achieving ultra-high sensitivity and precision in magnetic field and inertial measurements, thereby driving breakthrough research in fundamental physics and medical diagnostics. In SERF-based magnetic field / inertial measurement devices, narrow-linewidth lasers are typically used to pump a K-Rb-²¹Ne mixture to achieve atomic SERF states. Narrow-linewidth, high-power pump laser sources can effectively improve the nuclear spin polarization efficiency of ²¹Ne, enhancing the system's measurement sensitivity. However, high-power pump lasers also induce AC-Stark frequency shifts in the gas, reducing the sensitivity and long-term stability of the measurement system. Further optimization of the pump laser's linewidth and wavelength detuning can suppress the AC-Stark effect, significantly improving the measurement sensitivity and long-term stability of SERF atomic sensors. Therefore, there is an urgent need for a laser that combines high power, tunable linewidth, and wavelength detuning capability to support higher-sensitivity SERF magnetic field and inertial measurement devices.

[0003] In recent years, fiber laser technology has developed rapidly. In high-power, narrow-linewidth fiber laser systems based on nonlinear frequency conversion technology, the laser linewidth is broadened mainly by introducing a phase modulation module or noise source at the front end of the fundamental frequency fiber laser amplifier. However, this method can only broaden the laser linewidth and cannot further narrow it. The narrowest output laser linewidth is determined by the seed laser in the laser system, and wavelength detuning cannot be achieved. Summary of the Invention

[0004] This invention provides a fiber laser to solve the problem that fiber lasers cannot achieve laser linewidth modulation and wavelength detuning during the nonlinear frequency conversion stage.

[0005] In a first aspect, the present invention provides a fiber laser, the laser comprising: a linewidth modulation module, a frequency doubling waveguide module, a beam splitter, a temperature control module, and a control module, wherein... The input terminal of the linewidth control module is used to input the fundamental frequency laser, and the control terminal of the linewidth control module is connected to the first output terminal of the control module. The linewidth control module is used to perform initial control of the linewidth of the fundamental frequency laser according to the first control command output by the control module. The input terminal of the frequency doubling optical waveguide module is connected to the output terminal of the linewidth modulation module, and the temperature control terminal of the frequency doubling optical waveguide module is connected to the output terminal of the temperature control module. The frequency doubling optical waveguide module is used to perform frequency doubling conversion on the fundamental frequency laser after linewidth modulation to generate target band laser, and to receive the temperature control command applied by the temperature control module. By changing the phase mismatch during the frequency doubling conversion process through temperature, the linewidth of the target band laser is modulated and the wavelength is detuned. The input end of the coupling beam splitter is connected to the output end of the frequency doubling optical waveguide module. The coupling beam splitter is used to split the target band laser into a monitoring light and a main output laser. The monitoring light is output to the control module through the low splitting ratio end of the coupling beam splitter, and the main output laser is output as the output of the laser through the high splitting ratio end of the coupling beam splitter. The input terminal of the temperature control module is connected to the second output terminal of the control module, and the temperature control module is used to generate the temperature control command according to the second adjustment command output by the control module; The input terminal of the control module is connected to the low beam splitting ratio terminal of the coupled beam splitter. The control module is used to receive the monitoring light and collect laser linewidth information in real time, and output a first control command to the linewidth control module and a second control command to the temperature control module according to the collected laser linewidth information.

[0006] In one optional embodiment, the laser further includes: a power amplification module, the input terminal of which is connected to the output terminal of the linewidth modulation module, and the output terminal of which is connected to the input terminal of the frequency doubling waveguide module. The power amplification module is used to amplify the power of the linewidth-modulated fundamental frequency laser and to transmit the amplified fundamental frequency laser to the frequency doubling waveguide module.

[0007] In one optional embodiment, the frequency doubling optical waveguide module includes: an input coupling terminal, a waveguide body, and an output coupling terminal arranged sequentially along the light transmission direction; The input coupling terminal is used to couple the amplified fundamental frequency optical signal into the waveguide body; The waveguide body is divided into multiple temperature control sections along the light transmission direction. Each temperature control section is connected to the output end of the temperature control module. By adjusting the temperature of each temperature control section, the phase mismatch during the frequency doubling conversion process is changed, so as to perform secondary modulation of the linewidth and wavelength detuning of the target band laser. The output coupling terminal is used to couple the target band laser output after the waveguide body has undergone frequency doubling conversion.

[0008] In one optional implementation, when it is necessary to narrow the linewidth of the target wavelength laser and achieve wavelength detuning, the temperature of each temperature control section is set to the same temperature value, and the temperature value deviates from the optimal phase matching temperature of the frequency doubling optical waveguide module, so that the frequency doubling optical waveguide module is at the phase matching mismatch edge. The phase matching filtering effect and the laser gain edge abrupt effect are used to narrow the linewidth of the target wavelength laser and achieve wavelength detuning at the same time.

[0009] In one optional implementation, when it is necessary to broaden the linewidth of the target wavelength laser, a portion of the temperature control section is set to the working state and the remaining temperature control section is set to the non-working state, so as to effectively shorten the effective working length of the waveguide body and increase the frequency doubling phase matching temperature bandwidth. Furthermore, based on the output spectral characteristics of the target wavelength laser, the temperature of the temperature control zone in operation is adjusted to optimize the phase mismatch, and the abnormal intensity points of the target wavelength laser spectrum are modulated to broaden the linewidth of the target wavelength laser.

[0010] In one alternative implementation, when the laser needs to output the highest power, the temperature of each of the temperature control zones is set to the optimal phase-matching temperature.

[0011] In one optional embodiment, each temperature control section includes a heat insulation cover and a cooling element; each temperature control section of the waveguide body is respectively disposed in the corresponding heat insulation cover, and adjacent heat insulation covers are isolated by a heat insulation element; each heat insulation cover is thermally coupled to the corresponding cooling element, and each cooling element is independently connected to the control output terminal of the temperature control module.

[0012] In one alternative embodiment, the frequency doubling waveguide module further includes a heat dissipation element through which the heat from each of the cooling elements is dissipated.

[0013] In one optional embodiment, the waveguide body is a nonlinear crystal waveguide; the input coupling end is an input polarization-maintaining fiber, the end of which is tapered to form a lens fiber, and the mode field of the lens fiber matches the mode field of the waveguide body; the output coupling end is an output polarization-maintaining fiber; the front end of which is tapered to form a coupling lens fiber, and the mode field of the coupling lens fiber matches the mode field of the waveguide body.

[0014] In one alternative embodiment, the laser further includes an optical fiber seed laser module for generating a fundamental frequency laser.

[0015] The technical solution provided by this invention has at least the following beneficial effects: This invention provides a fiber laser with a dual-stage linewidth modulation system. A linewidth modulation module is introduced at the front end of the frequency doubling waveguide module to achieve initial modulation of the fundamental frequency laser linewidth. By designing the temperature of the frequency doubling waveguide module, fine control of the laser frequency doubling phase mismatch is achieved. Based on the phase-matching narrowband filtering characteristics, the laser linewidth is further modulated. The fiber laser provided by this invention has the ability to switch between laser linewidth narrowing and broadening, and can also achieve laser wavelength detuning. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a first structure of a fiber laser according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a second structure of a fiber laser according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the internal structure of the frequency doubling optical waveguide module; Figure 4 This is a schematic diagram illustrating the principle of achieving linewidth narrowing and wavelength detuning; Figure 5 The results are from experiments on laser linewidth modulation and wavelength detuning when a 1540nm laser is frequency-doubled to a 770nm laser. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0020] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] In recent years, fiber laser technology has developed rapidly. In high-power, narrow-linewidth fiber laser systems based on nonlinear frequency conversion technology, the laser linewidth is broadened mainly by introducing a phase modulation module or noise source at the front end of the fundamental frequency fiber laser amplifier. However, this method can only broaden the laser linewidth and cannot further narrow it. The narrowest output laser linewidth is determined by the seed laser in the laser system, and wavelength detuning is not possible. To solve this problem, this invention provides a fiber laser with a dual-stage linewidth modulation system. A linewidth modulation module is introduced at the front end of the frequency doubling waveguide module to achieve initial modulation of the fundamental frequency laser linewidth. By designing the temperature of the frequency doubling waveguide module, fine control of the laser frequency doubling phase mismatch is achieved. Based on the narrowband filtering characteristics of phase matching, the laser linewidth is further modulated. The fiber laser provided by this invention has the ability to switch between laser linewidth narrowing and broadening, and can also achieve laser wavelength detuning.

[0023] This embodiment provides a fiber laser. Figure 1 This is a schematic diagram of a first structure of a fiber laser according to an embodiment of the present invention, as shown below. Figure 1 As shown, the laser includes: a linewidth control module 1, a frequency doubling waveguide module 2, a coupler beam splitter 3, a temperature control module 4, and a control module 5.

[0024] The input terminal of the linewidth control module 1 is used to input the fundamental frequency laser, and the control terminal of the linewidth control module 1 is connected to the first output terminal of the control module 5. The linewidth control module 1 is used to perform initial control of the linewidth of the fundamental frequency laser according to the first control command output by the control module 5.

[0025] The input end of the frequency doubling optical waveguide module 2 is connected to the output end of the linewidth modulation module 1, and the temperature control end of the frequency doubling optical waveguide module 2 is connected to the output end of the temperature control module 4. The frequency doubling optical waveguide module 2 is used to perform frequency doubling conversion on the fundamental frequency laser after linewidth modulation to generate target band laser, and receives the temperature control command applied by the temperature control module 4. By changing the phase mismatch in the frequency doubling conversion process through temperature, the linewidth of the target band laser is modulated and the wavelength is detuned.

[0026] The input end of the coupling beam splitter 3 is connected to the output end of the frequency doubling optical waveguide module 2. The coupling beam splitter 3 is used to split the target band laser into monitoring light and main output laser. The monitoring light is output to the control module 5 through the low splitting ratio end of the coupling beam splitter 3, and the main output laser is output as the output of the laser through the high splitting ratio end of the coupling beam splitter 3.

[0027] The input terminal of the temperature control module 4 is connected to the second output terminal of the control module 5. The temperature control module 4 is used to generate a temperature control command based on the second regulation command output by the control module 5.

[0028] The input end of the control module 5 is connected to the low beam splitting ratio end of the coupled beam splitter 3. The control module 5 is used to receive the monitoring light and collect the laser linewidth information in real time. Based on the collected laser linewidth information, it outputs the first control command to the linewidth control module 1 and the second control command to the temperature control module 4.

[0029] In this embodiment, the linewidth control module 1 adjusts the linewidth of the input fundamental frequency laser and inputs the linewidth-adjusted fundamental frequency laser into the frequency doubling optical waveguide module 2. The frequency doubling optical waveguide module 2 performs frequency doubling conversion on the input linewidth-adjusted fundamental frequency laser to generate a target band laser, and inputs the target band laser into the coupling beam splitter 3. The coupling beam splitter 3 splits the input target band laser into beams. The main output laser is output through the high splitting ratio end of the coupling beam splitter 3 and serves as the output laser of the laser. The monitoring light is output through the low splitting ratio end of the coupling beam splitter 3. The control module 5 detects the monitoring light. The laser linewidth information is acquired in real time by photometry. Based on the acquired linewidth information, a first control command is output to the linewidth control module 1 and a second control command is output to the temperature control module 4. The linewidth control module 1 performs initial control of the linewidth of the fundamental frequency laser according to the received first control command. The temperature control module 4 sends a temperature control command to the frequency doubling waveguide module 2 according to the received second control command. The frequency doubling waveguide module 2 changes the phase mismatch during the frequency doubling conversion process by changing the temperature, thereby performing secondary linewidth control and wavelength detuning of the target wavelength laser. By constructing a two-stage linewidth control system, the linewidth control module 1 is introduced at the front end of the frequency doubling waveguide module 2 to achieve initial control of the fundamental frequency laser linewidth. By designing the temperature control of the frequency doubling waveguide module 2, the laser frequency doubling phase mismatch can be precisely controlled. Based on the narrowband filtering characteristics of phase matching, the laser linewidth is further controlled. This fiber laser has the ability to switch between laser linewidth narrowing and broadening, and can also achieve laser wavelength detuning.

[0030] In one alternative implementation, Figure 2 This is a schematic diagram of a second structure of a fiber laser according to an embodiment of the present invention, as shown below. Figure 2 As shown, the laser also includes a power amplification module 6. The input end of the power amplification module 6 is connected to the output end of the linewidth control module 1, and the output end of the power amplification module 6 is connected to the input end of the frequency doubling optical waveguide module 2. The power amplification module 6 is used to amplify the power of the linewidth-controlled fundamental frequency laser and transmit the amplified fundamental frequency laser to the frequency doubling optical waveguide module 2.

[0031] Furthermore, the laser may also include: an optical fiber seed laser module 7, which is used to generate a fundamental frequency laser.

[0032] In this embodiment, the fiber seed laser module 7 generates a fundamental frequency laser and inputs it to the linewidth control module 1. The linewidth control module 1 controls the linewidth of the input fundamental frequency laser and inputs the linewidth-controlled fundamental frequency laser to the power amplification module 6. The power amplification module 6 amplifies the power of the input linewidth-controlled fundamental frequency laser and inputs the power-amplified fundamental frequency laser to the frequency doubling optical waveguide module 2. The frequency doubling optical waveguide module 2 performs frequency doubling conversion on the input linewidth-controlled fundamental frequency laser to generate a target wavelength laser and inputs the target wavelength laser to the coupling beam splitter 3. The coupling beam splitter 3 splits the input target wavelength laser and outputs the main output laser through the high splitting ratio end of the coupling beam splitter 3. The output laser light from the laser is output as monitoring light through the low splitting ratio end of the beam splitter 3. The control module 5 collects laser linewidth information in real time through the detection light. Based on the collected laser linewidth information, it outputs a first control command to the linewidth control module 1 and a second control command to the temperature control module 4. The linewidth control module 1 performs initial control on the linewidth of the fundamental frequency laser according to the received first control command. The temperature control module 4 sends a temperature control command to the frequency doubling waveguide module 2 according to the received second control command. The frequency doubling waveguide module 2 changes the phase mismatch during the frequency doubling conversion process by changing the temperature according to the received temperature control command, so as to perform secondary linewidth control and wavelength detuning on the target band laser. By constructing a two-stage linewidth control system, a linewidth control module 1 is introduced at the front end of the frequency doubling waveguide module 2 to achieve initial control of the fundamental frequency laser linewidth. By designing the temperature control of the frequency doubling waveguide module 2, the laser frequency doubling phase mismatch can be precisely controlled. Based on the phase-matching narrowband filtering characteristics, the laser linewidth can be further controlled. This fiber laser has the ability to switch between laser linewidth narrowing and broadening, and can also achieve laser wavelength detuning.

[0033] In one optional implementation, the optical functional devices in the fiber seed laser module 7, the linewidth control module 1, the power amplification module 6, and the pigtails of the frequency doubling waveguide module 2 all use polarization-maintaining optical fibers and have the characteristics of fast-axis cutoff and slow-axis transmission.

[0034] Specifically, the fundamental frequency laser generated by the fiber seed laser module 7 is a fundamental frequency single-frequency continuous laser with a laser linewidth typically in the kHz range. Its output power is less than the maximum power that the linewidth control module 1 can withstand, and the output pigtail is a polarization-maintaining fiber that is transmitted along the slow axis of the fiber.

[0035] The linewidth control module 1 can be based on an electro-optic phase modulator or a white noise signal generator to achieve laser linewidth tuning covering kHz-GHz of the fundamental frequency laser linewidth, while increasing the threshold for stimulated Brillouin scattering in the power amplification module 6 and suppressing the sensitivity of the frequency doubling efficiency of the frequency doubling optical waveguide module 2 to temperature fluctuations.

[0036] Temperature control module 4 operates in dual-channel mode, with each channel independently acquiring and controlling the temperature. The temperature control accuracy is 1mK, and the absolute temperature fluctuation is less than 1mK even under long-term conditions of continuous operation for 24 hours.

[0037] The gain of the frequency-doubled laser output power combination control power amplifier module 6 and the phase mismatch of different sections of the frequency-doubled optical waveguide module 2 are adjusted to meet actual requirements.

[0038] The laser output linewidth retuning and wavelength mistuning need to be adjusted by combining the parameters of the linewidth control module 1 and the phase mismatch of the frequency doubling waveguide module 2 to meet the actual requirements.

[0039] In one alternative implementation, such as Figure 3 As shown, the frequency doubling optical waveguide module includes: an input coupling terminal, a waveguide body, and an output coupling terminal arranged sequentially along the light transmission direction.

[0040] The input coupling terminal is used to couple the amplified fundamental frequency optical signal into the waveguide body.

[0041] The waveguide body is divided into multiple temperature-controlled sections along the light transmission direction. Each temperature-controlled section is connected to the output end of the temperature control module. By adjusting the temperature of each temperature-controlled section, the phase mismatch during the frequency doubling conversion process is changed, so as to perform secondary control of the linewidth and wavelength detuning of the target wavelength laser.

[0042] The output coupling terminal is used to couple the target band laser output after the waveguide body has undergone frequency doubling conversion.

[0043] Furthermore, each temperature control section includes an insulation cover and a cooling element; each temperature control section of the waveguide body is respectively set inside a corresponding insulation cover, and adjacent insulation covers are isolated by thermal insulation elements; each insulation cover is thermally coupled to a corresponding cooling element, and each cooling element is independently connected to the control output terminal of the temperature control module. For example... Figure 3 As shown, the frequency doubling optical waveguide module 2 includes three temperature control sections. Each temperature control section is set in a corresponding metal insulation cover 2-4, 2-5, 2-6. The metal insulation covers 2-4, 2-5, 2-6 are thermally coupled to the corresponding thermoelectric cooling chips 2-7, 2-8, 2-9, respectively.

[0044] The waveguide body is a nonlinear crystal waveguide; the input coupling end is an input polarization-maintaining fiber, the end of which is tapered to form a lens fiber, the mode field of which matches the mode field of the waveguide body; the output coupling end is an output polarization-maintaining fiber, the front end of which is tapered to form a coupling lens fiber, the mode field of which matches the mode field of the waveguide body. The output termination of the output polarization-maintaining fiber can be an FC / APC fiber optic connector or a fiber collimator.

[0045] The frequency doubling waveguide module also includes heat dissipation components, through which the heat from each cooling component is dissipated. For example... Figure 3 As shown, the heat dissipation element is a metal heat dissipation base plate 2-14.

[0046] Figure 3 This is a schematic diagram of the internal structure of the frequency doubling optical waveguide module 2, as shown below. Figure 3 As shown, the polarization-maintaining fiber 2-1 for fundamental frequency laser transmission is coupled to one end of the frequency-doubled waveguide 2-3, which is tapered into a lens fiber. Its mode field distribution is highly matched to that of the frequency-doubled waveguide 2-3, and its slow axis is precisely aligned with the polarization direction of the frequency-doubled waveguide 2-3. Under a high-power microscope, a six-axis fine-tuning frame is used to precisely align the lens fiber and the frequency-doubled waveguide 2-3 to achieve maximum coupling efficiency. The fiber is gold-plated using soldering and then soldered onto a metal sleeve or shell. The polarization-maintaining fiber 2-1, located 10 mm from the tapered fiber lens, is fixed to an insulating plate 2-2 using UV-curable adhesive to prevent fiber stretching at the front end from affecting laser coupling efficiency. The main body of the frequency-doubled waveguide 2-3 is divided into three (or more) parts, each completely embedded in square metal insulation covers 2-4, 2-5, and 2-6. The insulation covers are 2 mm thick and separated by 1 mm aerogel to prevent temperature crosstalk. Each insulation cover has a thermoelectric cooler at its bottom. Each insulation cover 2-4, 2-5, and 2-6 uses independent thermoelectric coolers 2-7, 2-8, and 2-9 for temperature control, which controls the laser frequency doubling phase mismatch and the effective nonlinear action length of the laser frequency doubling. The temperature control accuracy is 1 mK, and the absolute temperature fluctuation is less than 2 mK. The frequency-doubled laser and the residual fundamental frequency light are then coupled into the polarization-maintaining fiber 2-13 for frequency-doubled light transmission. The residual fundamental frequency light dissipates during transmission. Typically, the power of the residual fundamental frequency light and the power of the frequency-doubled laser are high, making them prone to significant heat accumulation and even burning through the coupling end face when coupled into the polarization-maintaining fiber 2-13. Therefore, a six-axis fine-tuning frame is used for precise adjustment to improve laser coupling efficiency, and the coupling ports are fixed to both sides of a heat-conducting metal block 2-11 for heat dissipation control. The temperature of the heat-conducting metal block 2-11 is stabilized by a thermoelectric cooler 2-10. Meanwhile, UV-curable adhesive is used to fix the frequency-doubled polarization-maintaining optical fiber 2-13, located 10mm from the coupling output port, to the heat-insulating fixing plate 2-12 to prevent the back-end fiber from being stretched and affecting the laser coupling efficiency. The heat from the thermoelectric cooling elements 2-7, 2-8, 2-9, and 2-10 is naturally dissipated through the metal heat sink base plate 2-14.

[0047] In this embodiment, with Figure 3Taking a frequency-doubling crystal with three temperature-controlled zones as an example, when the frequency-doubling waveguide module 2 achieves the highest laser frequency doubling efficiency, before the laser modulated by the linewidth control module 1 enters the frequency-doubling waveguide module 2, the three temperature-controlled zones of the frequency-doubling crystal are all set to the optimal phase-matching temperature corresponding to the highest laser frequency doubling efficiency. When the three temperatures reach the set target values ​​and tend to stabilize, and the temperature fluctuation is less than 2mK, the effective working length of the nonlinear frequency-doubling crystal is effectively increased, thereby improving the laser frequency doubling efficiency. Each temperature-controlled zone is also equipped with a temperature sensor to monitor the temperature within that zone, and all temperature sensors are calibrated using a unified standard.

[0048] The frequency doubling optical waveguide module 2 has temperature-dependent phase mismatch control characteristics, such as periodically polarized lithium niobate optical waveguides and lithium triborate crystals. The length of the frequency doubling optical waveguide used in the frequency doubling optical waveguide module 2 is determined by the actual laser frequency doubling efficiency requirements.

[0049] Specifically, when it is necessary to narrow the linewidth of the target wavelength laser and achieve wavelength detuning, the temperature of each temperature control section is set to the same temperature value, and the temperature value deviates from the optimal phase matching temperature of the frequency doubling optical waveguide, so that the frequency doubling optical waveguide is at the phase matching mismatch edge. The phase matching filtering effect and the laser gain edge abrupt change effect are used to narrow the linewidth of the target wavelength laser and achieve wavelength detuning at the same time.

[0050] It should be noted that when the temperature value in the temperature control section is close to the optimal phase matching temperature of the frequency doubling waveguide, the effective working length of the nonlinear frequency doubling crystal is effectively increased, thereby improving the laser frequency doubling efficiency; when the temperature value in the temperature control section deviates from the optimal phase matching temperature of the frequency doubling waveguide, the effective working length of the nonlinear frequency doubling crystal is effectively reduced, thereby reducing the laser frequency doubling efficiency.

[0051] Figure 4 A schematic diagram illustrating the principle by which this invention achieves linewidth narrowing and wavelength detuning is provided. For example... Figure 4As shown, the initial fundamental frequency laser linewidth is relatively narrow, typically in the kHz range, as indicated by the solid black line. After modulation by the linewidth control module 1 and amplification by the power amplification module 6, the laser linewidth is broadened (as indicated by the dashed black line), and the laser power is increased. In the laser frequency doubling stage, the core of temperature phase matching is the quasi-phase matching condition. Temperature adjusts the phase mismatch by changing the crystal's refractive index (thermo-optic effect) and polarization period (thermal expansion effect). Only when the phase mismatch is close to zero does the nonlinear conversion efficiency reach its maximum, equivalent to the passband of a filter. When the temperature deviates from the optimal value, the phase mismatch becomes non-zero, and the conversion efficiency drops sharply. When frequency doubling a broadband laser, changing the temperature is equivalent to shifting the working center wavelength of the filter formed by phase matching, scanning the broadband laser frequency, and simultaneously achieving laser wavelength detuning, i.e., the center wavelength changes from wavelength 1 to wavelength 2 or wavelength 3. When the phase matching temperature changes significantly, there exists a specific temperature inflection point that causes the linewidth of the frequency-doubled laser to be smaller than the theoretical frequency-doubled laser linewidth, thus achieving laser linewidth narrowing.

[0052] In this embodiment, when the laser is required to have an output linewidth smaller than the theoretical minimum, under the power level that the frequency doubling waveguide module 2 can withstand, the temperature of the multiple temperature control segments of the frequency doubling waveguide module 2 is set to the same value, and the set temperature is changed at the same time to increase the phase detuning. When the set temperature is at the edge of phase detuning, the phase matching filtering effect and the laser gain edge abrupt change effect work together to narrow the laser linewidth, and at the same time the laser wavelength is detuned. Further optimization of the parameters of the linewidth control module 1 can expand the wavelength detuning.

[0053] When it is necessary to broaden the linewidth of the target wavelength laser, some temperature-controlled sections are set to the working state and the rest are set to the non-working state to effectively shorten the effective length of the waveguide body and increase the temperature bandwidth of the frequency doubling phase matching. Furthermore, according to the output spectral characteristics of the target wavelength laser, the temperature of the temperature-controlled sections in the working state is adjusted to optimize the phase mismatch and modulate the abnormal intensity points of the target wavelength laser spectrum to broaden the linewidth of the target wavelength laser.

[0054] In this embodiment, when the laser is required to have the widest laser linewidth and the highest laser power output, the parameters of the linewidth control module 1 are first optimized to achieve the widest fundamental frequency laser linewidth. Then, the multi-segment temperature control of the frequency doubling waveguide module 2 is set to single-segment temperature control to increase the temperature bandwidth for efficient frequency doubling phase matching. Based on this, the phase mismatch is further optimized according to the characteristics of the frequency doubling laser output spectrum, and the abnormal intensity points of the frequency doubling laser spectrum are modulated to further increase the laser linewidth and further optimize the process.

[0055] When the laser needs to output the highest power, the temperature of each temperature control zone is set to the optimal phase-matching temperature.

[0056] In this embodiment, when the laser is required to have the highest laser output power, the parameters of the linewidth control module 1 are first optimized so that the power amplification module 6 achieves maximum power output without significant nonlinear effects. At the same time, the multi-segment temperature control of the frequency doubling waveguide module 2 is set to the optimal phase matching temperature to maximize the frequency doubling efficiency and achieve high-power laser output.

[0057] The following describes the working process of the laser in detail using a 1540nm single-frequency laser frequency doubled to a 770nm single-frequency laser as a specific example.

[0058] In this embodiment, the fiber seed laser module 7 generates a 40mW 1540nm fundamental frequency laser, which then enters the linewidth control module 1 for linewidth adjustment. The linewidth control module 1 can employ a fiber-coupled electro-optic phase modulator. By setting parameters such as the RF signal frequency, RF amplifier gain, and electro-optic phase modulator drive voltage, the desired fundamental frequency laser linewidth output is achieved. For example, the initial RF frequency is set to 4GHz, the RF signal power is set to -0.5dBm, and the electro-optic phase modulator drive voltage is fixed at 12V. The linewidth-adjusted fundamental frequency laser is coupled into the power amplification module 6 for laser power amplification. A 27W 976nm multimode pump laser reverse-pumps a 10 / 130 double-clad erbium-ytterbium co-doped gain fiber, increasing the laser power to 10W. The passive components of the amplifier are all PM-GDF1550 fiber pigtails. The amplified laser is coupled into the frequency doubling waveguide module 2 for laser frequency doubling to obtain a 770nm laser. The frequency-doubled waveguide module 2 uses a PM1550 pigtail at the input coupling end and a PM780 pigtail at the output coupling end. It has three temperature control ports, all using thermoelectric coolers for temperature control. The initial temperature of each port is set to the optimal phase-matching temperature of the frequency-doubled waveguide module 2, with a temperature control accuracy of 1 mK and an absolute temperature fluctuation of less than 2 mK. The maximum withstand power for the 1540nm fundamental frequency laser is 10W, and the maximum withstand power for the 770nm frequency-doubled laser is 4W. The frequency-doubled laser enters the coupling beam splitter 3, with 0.5% of the output coupled to the control module 5 for real-time laser linewidth monitoring and parameter optimization control, and the remaining 99.5% of the output laser serving as the main laser output.

[0059] Typically, the linewidth of a frequency-doubled laser is about twice that of a fundamental laser. Therefore, when a laser needs to output a linewidth smaller than the theoretical minimum, the three temperature control stages of the frequency-doubled waveguide module 2 are set to the same value, while simultaneously changing the set temperature to increase the phase mismatch. When the set temperature is at the edge of the phase mismatch, the phase-matching filtering effect and the laser gain edge abrupt change effect work together to narrow the laser linewidth. At the same time, the laser wavelength becomes detuned. Further optimization of the parameters of the linewidth control module 1 can extend the wavelength detuning.

[0060] When the laser needs to have the widest laser linewidth and the highest laser power output, the parameters of the linewidth control module 1, such as the RF frequency, RF amplifier, and electro-optic phase modulator driving voltage, are first optimized to maximize the fundamental frequency laser linewidth. Then, the temperature control of the frequency doubling optical waveguide module 2 is set to single-segment temperature control, while the other dual-segment temperature control is turned off. This effectively shortens the frequency doubling wavelength to increase the temperature bandwidth of the efficient frequency doubling phase matching. Based on this, and according to the characteristics of the frequency doubling laser output spectrum, the phase mismatch is further optimized, and the abnormal intensity points of the frequency doubling laser spectrum are modulated to further increase the laser linewidth.

[0061] When the laser needs to have the highest laser output power, the parameters of the linewidth control module 1 are first optimized so that the power amplification module 6 can achieve the maximum power output without any obvious nonlinear effect. At the same time, the three temperature control sections of the frequency doubling waveguide module 2 are all set to the optimal phase matching temperature (usually around 50℃) to make the most of the frequency doubling waveguide length to improve the laser frequency doubling conversion efficiency and achieve high-power laser output.

[0062] Figure 5 Experimental results on laser linewidth modulation and wavelength detuning based on a single-segment temperature-controlled frequency-doubled waveguide module 2 are presented in a laser that frequency doubles from 1540nm to 770nm. The 1540nm fundamental frequency laser, based on a phase-shifting grating, outputs 40mW of laser light with a linewidth of ~2kHz. After modulation by an electro-optic phase modulator, modulation frequency sidebands are generated on both sides of the center wavelength laser, widening the laser linewidth envelope. The electro-optic phase modulator has a maximum withstand power of 100mW and a half-wave voltage <4V. The RF signal source driving frequency is set to 9GHz, and the RF signal power is -0.5dBm. The linewidth-widened laser enters the power amplification module 6 for power amplification. A 27W 976nm wavelength-locked semiconductor laser is used to reverse-pump a double-clad erbium-ytterbium co-doped gain fiber (PM-EYDF-10 / 130) for laser power amplification, achieving a maximum fundamental frequency laser power close to 10W. The amplified laser beam, after being output through an isolator, is coupled into a periodically polarized lithium niobate frequency-doubled waveguide with single-segment temperature control for laser frequency doubling. The optimal phase-matching temperature is 44°C. With the electro-optic phase modulator inactive, the 770nm laser power exceeds 3W, and the laser power gradually decreases with increasing RF signal driving frequency, while its sensitivity to the phase-matching temperature decreases. With the RF frequency set to 9GHz, the phase mismatch is altered by changing the phase-matching temperature of the periodically polarized lithium niobate frequency-doubled waveguide. As shown in the figure, the laser spectral width and center wavelength exhibit significant differences at different temperatures, demonstrating the simultaneous achievement of laser linewidth modulation and wavelength detuning, proving the feasibility of the fiber laser provided by this invention.

[0063] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A fiber laser, characterized in that, The laser includes: a linewidth modulation module, a frequency doubling waveguide module, a beam splitter, a temperature control module, and a control module, wherein... The input terminal of the linewidth control module is used to input the fundamental frequency laser, and the control terminal of the linewidth control module is connected to the first output terminal of the control module. The linewidth control module is used to perform initial control of the linewidth of the fundamental frequency laser according to the first control command output by the control module. The input terminal of the frequency doubling optical waveguide module is connected to the output terminal of the linewidth modulation module, and the temperature control terminal of the frequency doubling optical waveguide module is connected to the output terminal of the temperature control module. The frequency doubling optical waveguide module is used to perform frequency doubling conversion on the fundamental frequency laser after linewidth modulation to generate target band laser, and to receive the temperature control command applied by the temperature control module. By changing the phase mismatch during the frequency doubling conversion process through temperature, the linewidth of the target band laser is modulated and the wavelength is detuned. The input end of the coupling beam splitter is connected to the output end of the frequency doubling optical waveguide module. The coupling beam splitter is used to split the target band laser into a monitoring light and a main output laser. The monitoring light is output to the control module through the low splitting ratio end of the coupling beam splitter, and the main output laser is output as the output of the laser through the high splitting ratio end of the coupling beam splitter. The input terminal of the temperature control module is connected to the second output terminal of the control module, and the temperature control module is used to generate the temperature control command according to the second adjustment command output by the control module; The input terminal of the control module is connected to the low beam splitting ratio terminal of the coupled beam splitter. The control module is used to receive the monitoring light and collect laser linewidth information in real time, and output a first control command to the linewidth control module and a second control command to the temperature control module according to the collected laser linewidth information.

2. The fiber laser according to claim 1, characterized in that, The laser further includes a power amplification module, the input of which is connected to the output of the linewidth modulation module, and the output of which is connected to the input of the frequency doubling waveguide module. The power amplification module is used to amplify the power of the linewidth-modulated fundamental frequency laser and transmit the amplified fundamental frequency laser to the frequency doubling waveguide module.

3. The fiber laser according to claim 2, characterized in that, The frequency doubling optical waveguide module includes: an input coupling terminal, a waveguide body, and an output coupling terminal arranged sequentially along the light transmission direction; The input coupling terminal is used to couple the amplified fundamental frequency optical signal into the waveguide body; The waveguide body is divided into multiple temperature control sections along the light transmission direction. Each temperature control section is connected to the output end of the temperature control module. By adjusting the temperature of each temperature control section, the phase mismatch during the frequency doubling conversion process is changed, so as to perform secondary modulation of the linewidth and wavelength detuning of the target band laser. The output coupling terminal is used to couple the target band laser output after the waveguide body has undergone frequency doubling conversion.

4. The fiber laser according to claim 3, characterized in that, When it is necessary to narrow the linewidth of the target wavelength laser and achieve wavelength detuning, the temperature of each temperature control section is set to the same temperature value, and the temperature value deviates from the optimal phase matching temperature of the frequency doubling optical waveguide module, so that the frequency doubling optical waveguide module is at the phase matching mismatch edge. The phase matching filtering effect and the laser gain edge abrupt effect are used to narrow the linewidth of the target wavelength laser and achieve wavelength detuning at the same time.

5. The fiber laser according to claim 3, characterized in that, When it is necessary to broaden the linewidth of the target wavelength laser, some of the temperature control sections are set to the working state and the rest of the temperature control sections are set to the non-working state, so as to effectively shorten the effective working length of the waveguide body and increase the frequency doubling phase matching temperature bandwidth. Furthermore, based on the output spectral characteristics of the target wavelength laser, the temperature of the temperature control zone in operation is adjusted to optimize the phase mismatch, and the abnormal intensity points of the target wavelength laser spectrum are modulated to broaden the linewidth of the target wavelength laser.

6. The fiber laser according to claim 3, characterized in that, When the laser needs to output the highest power, the temperature of each temperature control zone is set to the optimal phase-matching temperature.

7. The fiber laser according to claim 3, characterized in that, Each temperature control section includes a heat insulation cover and a cooling element; each temperature control section of the waveguide body is respectively disposed in the corresponding heat insulation cover, and adjacent heat insulation covers are isolated by a heat insulation element; each heat insulation cover is thermally coupled to the corresponding cooling element, and each cooling element is independently connected to the control output terminal of the temperature control module.

8. The fiber laser according to claim 7, characterized in that, The frequency doubling optical waveguide module also includes a heat dissipation element, through which the heat from each of the cooling elements is dissipated.

9. The fiber laser according to claim 3, characterized in that, The waveguide body is a nonlinear crystal waveguide; the input coupling end is an input polarization-maintaining fiber, the end of which is tapered to form a lens fiber, and the mode field of the lens fiber matches the mode field of the waveguide body. The output coupling end is an output polarization-maintaining fiber; the front end of the output polarization-maintaining fiber is tapered to form a coupling lens fiber, and the mode field of the coupling lens fiber matches the mode field of the waveguide body.

10. The fiber laser according to claim 1, characterized in that, The laser also includes an optical fiber seed laser module, which is used to generate a fundamental frequency laser.

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