Fiber laser

Abstract

The invention provides a fiber laser. The fiber laser comprises a polarization beam splitter, a first grating, a second grating and an output device, the polarization beam splitter is used for receiving the light source laser and at least dividing the light source laser into a first sub-laser and a second sub-laser; the first grating is used for receiving the first sub-laser and reflecting part of the first sub-laser to form first specific wave laser; the second grating is used for receiving the second sub-laser and reflecting part of the second sub-laser to form second specific wave laser; the output device is used for outputting dual-wavelength laser based on the first specific wave laser and the second specific wave laser; the corresponding sub-lasers are processed through the first grating and the second grating respectively, and part of lasers are reflected by the sub-lasers respectively to form first specific wave laser and second specific wave laser which are different in wavelength; the problem of unstable output caused by factors such as mutual interference of the laser is avoided, so that the dual-wavelength laser can be stably output, and the requirement for a stable dual-wavelength light source is met.

Description

Technical Field

[0001] The present application belongs to the field of laser technology, and in particular relates to a fiber laser. Background Art

[0002] In the field of laser technology, dual-wavelength single-longitudinal-mode fiber lasers have attracted much attention due to their unique performance and application potential. With the continuous development of fields such as laser sensing and precision measurement, the performance requirements for light sources are becoming increasingly higher, especially for those that require high-precision and wide-range frequency tunability.

[0003] In the related art, it is difficult for fiber lasers to stably output dual-wavelength lasers. Summary of the Invention

[0004] The purpose of the present application is to provide a fiber laser, aiming to solve the problem in traditional technologies that fiber lasers are difficult to stably output dual-wavelength lasers.

[0005] A first aspect of an embodiment of the present application provides a fiber laser, comprising:

[0006] a polarization beam splitter, the polarization beam splitter being configured to receive a light source laser and split the light source laser into at least a first sub-laser and a second sub-laser; wherein the polarization directions of the first sub-laser and the second sub-laser are perpendicular to each other;

[0007] a first grating, configured to receive the first sub-laser and reflect a portion of the first sub-laser to form a first specific wave laser;

[0008] a second grating for receiving the second sub-laser and reflecting a portion of the second sub-laser to form a second specific-wave laser; the wavelength of the second specific-wave laser is different from the wavelength of the first specific-wave laser;

[0009] An output device is configured to output dual-wavelength laser light based on the first specific-wave laser light and the second specific-wave laser light.

[0010] In some embodiments of the present application, the fiber laser further includes a mode selection device, which is used to receive the first specific wave laser and the second specific wave laser, and to output a synthetic wave after performing mode selection on the first specific wave laser and the second specific wave laser, and the output device is used to output the dual-wavelength laser according to the synthetic wave.

[0011] In some embodiments of the present application, the mode selection device includes a Sagnac ring and a saturated absorber mode selection element. The Sagnac ring is used to input the first specific wave laser and the second specific wave laser into the saturated absorber mode selection element. The saturated absorber mode selection element is used to output the synthetic wave of a single longitudinal mode after mode selection of the first specific wave laser and the second specific wave laser.

[0012] In some embodiments of the present application, the saturable absorber mode-selective element is an unpumped ytterbium-doped optical fiber.

[0013] In some embodiments of the present application, the mode selection device also includes a first optical fiber coupler, which is used to divide the first specific wave laser and the second specific wave laser into a first optical path and a second optical path according to a preset ratio. The saturated absorber mode selection element is used to perform mode selection and output on the first optical path and the second optical path. After being output by the saturated absorber mode selection element, the first optical path and the second optical path interfere with each other to form the synthetic wave.

[0014] In some embodiments of the present application, a first resonant cavity is formed between the mode selection device and the first grating, and a second resonant cavity is formed between the mode selection device and the second grating; the first resonant cavity and the second resonant cavity are used for back and forth reflection of laser light to form stable laser oscillation.

[0015] In some embodiments of the present application, the output device includes a second fiber coupler, which outputs the dual-wavelength laser and the resonant laser based on the synthetic wave and according to a preset output ratio. The resonant laser is a light source laser input into the polarization beam splitter.

[0016] In some embodiments of the present application, the fiber laser further includes a wavelength division multiplexer, an ytterbium-doped fiber, and a pump source, wherein the wavelength division multiplexer and the ytterbium-doped fiber are arranged between the mode selection device and the polarization beam splitter, and the pump source is connected to the wavelength division multiplexer and is used to output excitation light to the ytterbium-doped fiber;

[0017] The ytterbium-doped optical fiber generates radiated laser light based on the excitation light, and the radiated laser light is a light source laser input to the polarization beam splitter.

[0018] In some embodiments of the present application, the fiber laser further includes a first polarization controller and a second polarization controller, wherein the first polarization controller is arranged between the polarization beam splitter and the first grating; and the second polarization controller is arranged between the polarization beam splitter and the second grating.

[0019] In some embodiments of the present application, the fiber laser includes an electrically controlled tuning mechanism, which is used to adjust the axial stretching of the first grating and the second grating to adjust the wavelengths of the first specific wave laser and the second specific wave laser.

[0020] The beneficial effects of the present application are: the fiber laser of the present application includes a polarization beam splitter, a first grating, a second grating and an output device; the polarization beam splitter is used to receive the light source laser and split the light source laser into at least a first sub-laser and a second sub-laser; the polarization direction of the first sub-laser and the polarization direction of the second sub-laser are perpendicular to each other; the first grating is used to receive the first sub-laser and reflect part of the first sub-laser to form a first specific wave laser; the second grating is used to receive the second sub-laser and reflect part of the second sub-laser to form a second specific wave laser; the wavelength of the second specific wave laser is different from the wavelength of the first specific wave laser; the output device is used to output a dual-wavelength laser based on the first specific wave laser and the second specific wave laser; in the present application, the corresponding sub-lasers are processed respectively by the first grating and the second grating, and each reflects part of the laser to form a first specific wave laser and a second specific wave laser with different wavelengths. This method of beam splitting and specific wavelength selection avoids the output instability problem caused by factors such as mutual interference of lasers in traditional technologies, thereby enabling stable output of dual-wavelength lasers and meeting the demand for stable dual-wavelength light sources. In laser interferometry, stable dual-wavelength lasers can be used to generate more precise interference fringes, improving the resolution and accuracy of measurements. Moreover, since the wavelengths of the first specific wave laser and the second specific wave laser can be flexibly determined by selecting different first gratings and second gratings, it is conducive to better achieving wide-range frequency difference tunability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the structure of a fiber laser provided in one embodiment of the present application;

[0022] Figure 2 A schematic structural diagram of a fiber laser provided in another embodiment of the present application;

[0023] Figure 3 This is a schematic structural diagram of a fiber laser provided in yet another embodiment of the present application.

[0024] Specific element symbol description: 100-polarization beam splitter, 200-first grating, 300-second grating, 400-output device, 500-mode selection device, LD-pump source, WDM-wavelength division multiplexer, YDF-ytterbium-doped fiber, DC1-first fiber coupler, DC2-second fiber coupler, PC1-first polarization controller, PC2-second polarization controller. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0026] It should be noted that when an element is referred to as being “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0027] Furthermore, 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0028] It's important to note that laser sensing, a key branch of modern sensing technology, relies on high-precision light sources to accurately detect various physical and chemical quantities. For example, in distributed fiber-optic sensing systems, the light source must be able to provide stable dual-wavelength lasers with a specific frequency difference. This allows the interference effect generated when the dual-wavelength lasers are transmitted through the fiber to accurately measure subtle changes in parameters such as temperature and stress. For long-distance, large-scale monitoring scenarios, the light source must also be capable of tunable frequency differences over a wide range, allowing for flexible adjustment of measurement accuracy and range based on actual monitoring needs.

[0029] The field of precision measurement also places stringent demands on light source performance. In high-precision measurement facilities such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), in order to detect extremely weak gravitational wave signals, the dual-wavelength laser output by the light source must have ultra-high frequency stability and extremely narrow linewidth, and the frequency difference must be precisely adjusted within a certain range to match the interference fringe resolution requirements in different measurement scenarios. In the lithography technology link of the semiconductor manufacturing process, dual-wavelength single-longitudinal-mode fiber laser is used as the light source. The stability of its output laser and the tunability of its frequency difference directly affect the precision and yield of chip manufacturing.

[0030] However, the current structure and working mechanism of fiber lasers make it easy for lasers of different wavelengths to interfere with each other when generating dual-wavelength lasers, resulting in unstable phenomena such as output power fluctuations and wavelength drift. This is because in the fiber resonant cavity, various factors such as the inhomogeneity of the intracavity gain medium, nonlinear effects, and performance limitations of optical devices make it difficult to maintain the dual-wavelength laser mode stably. When trying to achieve dual-wavelength output by adjusting the intracavity parameters, mode competition often occurs, further destroying the stability of the dual-wavelength laser. For example, in some fiber lasers that use ordinary fiber Bragg gratings as wavelength selection elements, due to the temperature sensitivity and wavelength drift characteristics of the fiber Bragg grating, the stability of the dual-wavelength output drops sharply with changes in ambient temperature or long-term operation, and cannot meet the requirements of high precision and high stability of light sources in fields such as laser sensing and precision measurement.

[0031] Based on this, the embodiments of the present application improve the current fiber laser.

[0032] See also Figure 1 , Figure 1 A structural schematic diagram of the fiber laser provided in this embodiment is shown; the fiber laser of the embodiment of the present application includes a polarization beam splitter 100, a first grating 200, a second grating 300 and an output device 400; the polarization beam splitter 100 is used to receive the light source laser and split the light source laser into at least a first sub-laser and a second sub-laser, and the polarization directions of the first sub-laser and the second sub-laser are perpendicular to each other; the first grating 200 is used to receive the first sub-laser and reflect part of the first sub-laser to form a first specific wave laser; the second grating 300 is used to receive the second sub-laser and reflect part of the second sub-laser to form a second specific wave laser; the wavelength of the second specific wave laser is different from the wavelength of the first specific wave laser; the output device 400 is used to output a dual-wavelength laser based on the first specific wave laser and the second specific wave laser.

[0033] It should be explained that the polarization beam splitter 100 is an optical element that operates based on the polarization properties of light. Light has different polarization directions, and the polarization beam splitter 100 can identify and separate light with different polarization directions. When a laser light source is incident, it will, based on its special internal structure, split the laser light into at least a first sub-laser and a second sub-laser with different polarization states. This beam splitting method provides the basis for the subsequent independent generation of specific wavelength lasers of different wavelengths, preventing interference between multiple wavelength lasers in the same optical path, and plays a key role in improving the stability of dual-wavelength laser output. A grating is an optical device with a periodic structure. When light is incident on a grating, diffraction occurs. For the first grating 200 and the second grating 300, their structural parameters (such as grating period and grating constant) determine the selection of specific wavelengths of light. When the first sub-laser is incident on the first grating 200, the portion of light that meets its specific conditions is reflected back to form the first specific wavelength laser. Similarly, the second sub-laser is reflected by the second grating 300 to form the second specific wavelength laser. By precisely designing the grating parameters, the wavelength of the reflected light can be precisely controlled.

[0034] It can be understood that in the fiber laser technical solution of the embodiment of the present application, the light source laser first enters the polarization beam splitter 100 and is divided into a first sub-laser and a second sub-laser. The separate optical paths avoid the possibility of mutual interference between lasers of different wavelengths, and provide the basic conditions for the subsequent stable output of dual-wavelength lasers. The first sub-laser enters the first grating 200. The grating reflects part of the first sub-laser to form a first specific wave laser according to its own diffraction principle and its specific design parameters; similarly, the second sub-laser forms a second specific wave laser under the action of the second grating 300. Since the parameters of the two gratings are independently designed, the wavelengths of the two specific wave lasers generated are different. This method of independently controlling wavelength generation greatly improves the stability and accuracy of the wavelength compared to the traditional method of attempting to generate dual wavelengths in the same optical path.

[0035] Most current fiber lasers only have one grating and a shared reflection loop, which may cause interference between the reflected lasers, thus easily affecting the stability of the output laser. However, in the present application, the corresponding sub-lasers are processed separately by the first grating 200 and the second grating 300, and each reflects part of the laser to form a first specific wave laser and a second specific wave laser with different wavelengths. This method of beam splitting and specific wavelength selection avoids the output instability problem caused by factors such as mutual interference of lasers in traditional technologies, thereby being able to stably output dual-wavelength lasers and meet the demand for stable dual-wavelength light sources. In laser interferometry, stable dual-wavelength lasers can be used to generate more accurate interference fringes and improve the resolution and accuracy of the measurement; and since the wavelengths of the first specific wave laser and the second specific wave laser can be flexibly determined by selecting different first gratings 200 and second gratings 300, it is conducive to better achieving wide-range frequency difference tunability.

[0036] In some embodiments of this application, please refer to Figure 2 , Figure 2 The figure shows a schematic structural diagram of the fiber laser provided in this embodiment; the fiber laser in this embodiment also includes a mode selection device 500, which is used to receive the first specific wave laser and the second specific wave laser, and to output a composite wave after selecting the mode of the first specific wave laser and the second specific wave laser, and the output device 400 is used to output a dual-wavelength laser according to the composite wave.

[0037] It should be noted that the mode selection device 500 can screen the input first and second specific laser waves, selecting a mode that meets specific requirements from a wide range of possible laser modes. This precise mode selection ensures that the output laser has excellent beam quality and stability, meeting the stringent laser mode requirements of different application scenarios.

[0038] It is understandable that after the first specific wave laser and the second specific wave laser enter the mode selection device 500, the mode selection device 500 can screen the multiple modes of each laser. For example, in some applications, the laser is required to have a single longitudinal mode characteristic to ensure high frequency stability and narrow linewidth. The mode selection device 500 can effectively suppress other non-single longitudinal mode modes, so that the output composite wave only contains the required single longitudinal mode component. In this way, the composite wave after mode selection can output high-quality dual-wavelength laser under the action of the output device 400. For laser sensing applications, stable single longitudinal mode dual-wavelength laser can improve the accuracy and resolution of sensing and reduce measurement errors caused by mode instability. In the field of precision measurement, such as laser interferometry, high-quality dual-wavelength laser can produce clearer and more stable interference fringes, thereby achieving high-precision measurement of physical quantities such as small displacements and vibrations. Through the operation of the mode selection device 500, the problems of mode instability and poor beam quality when traditional fiber lasers output dual-wavelength lasers are solved, greatly expanding the applicability and reliability of fiber lasers in high-end applications.

[0039] In some embodiments of this application, please refer to Figure 3 , Figure 3 shows a schematic structural diagram of the fiber laser provided in this embodiment; Figure 3 In this example, UPYDF (unpumped ytterbium-doped fiber) is used as a saturable absorber mode-selective element, FPBS (fiber polarization beam splitter 100) is used as a polarization beam splitter 100, FBG1 is used as a first grating 200, and FBG2 is used as a second grating 300. The mode-selective device 500 of this embodiment includes a Sagnac ring and a saturable absorber mode-selective element. The Sagnac ring is used to input the first specific wavelength laser and the second specific wavelength laser into the saturable absorber mode-selective element. The saturable absorber mode-selective element is used to select the first specific wavelength laser and the second specific wavelength laser and then output a single longitudinal mode composite wave.

[0040] It should be explained that a Sagnac loop is an optical ring structure based on fiber, consisting of a closed section of optical fiber. Its operating principle is based on the Sagnac effect. When two counter-propagating beams of light travel through this ring structure, interference occurs due to slight differences in optical path length (e.g., due to changes in the external environment or the characteristics of the structure itself). In this fiber laser, the Sagnac loop guides and regulates the optical signal. It efficiently directs the first and second specific-wave lasers to the saturated absorber mode-selective element, ensuring that the two beams interact with the saturated absorber in a suitable manner. The saturated absorber mode-selective element is made of a material with saturated absorption properties. When the light intensity is low, the material strongly absorbs light. However, when the light intensity increases to a certain level, the material's absorption properties reach saturation, significantly reducing the absorption of light. In this embodiment, the saturated absorber mode-selective element utilizes this property to select the mode of the input first and second specific-wave lasers. It preferentially absorbs light with low intensity and multiple longitudinal mode components, and absorbs less light with high intensity and single longitudinal mode components, so that the light passing through it gradually tends to the single longitudinal mode state, and finally outputs a single longitudinal mode synthetic wave.

[0041] It's easy to understand that the combination of a Sagnac ring and a saturable absorber mode-selective element significantly improves the quality and stability of the dual-wavelength output of a fiber laser. The Sagnac ring precisely guides the first and second specific-wave lasers to the saturated absorber mode-selective element. During this process, the interference properties of the Sagnac ring help select light components with specific phase relationships and mode characteristics, preliminarily optimizing the mode distribution of the input light. In a fiber laser, different modes exhibit different intensity distributions and propagation characteristics. Multi-longitudinal-mode lasers, because they contain multiple longitudinal modes, have relatively dispersed light intensity; whereas single-longitudinal-mode lasers have a concentrated intensity on a single longitudinal mode. The saturated absorber mode-selective element preferentially absorbs the low-intensity light from the multi-longitudinal-mode components, gradually suppressing them. However, the higher-intensity single-longitudinal-mode component, once the saturated absorber reaches saturation, is able to pass smoothly through, thus achieving mode selection. The resulting single-longitudinal-mode composite wave exhibits an extremely narrow linewidth and highly stable frequency characteristics.

[0042] In the field of laser sensing, such as distributed fiber optic temperature sensing systems, single-longitudinal-mode dual-wavelength lasers can greatly improve the accuracy and resolution of temperature measurements and reduce measurement errors. In high-resolution spectral analysis, the single-longitudinal-mode characteristic enables clearer resolution of spectral features, improving the accuracy of analysis. In the field of optical communications, single-longitudinal-mode dual-wavelength lasers can be used in wavelength division multiplexing systems to increase communication capacity and signal transmission stability. The design of this mode selection device 500 effectively solves the problems of unstable dual-wavelength output mode and large linewidth of traditional fiber lasers, meeting the stringent requirements of high-end application scenarios for high-precision, high-stability light sources.

[0043] In some embodiments of this application, please continue to refer to Figure 3 In this embodiment, the saturated absorber mode selection element is an unpumped ytterbium-doped optical fiber.

[0044] It's important to explain that unpumped ytterbium-doped fiber is a special type of fiber whose core is doped with the rare earth element ytterbium (Yb). In its unpumped state, meaning without external energy injection to excite the ytterbium ions to high energy levels, it exhibits unique optical properties that allow it to function as a saturable absorber and mode-selective element. Ytterbium ions form a specific energy level structure within the fiber, and when a light signal passes through unpumped ytterbium-doped fiber, the light interacts with the ytterbium ions.

[0045] As can be understood, the unpumped ytterbium-doped fiber, acting as a saturable absorber and mode-selective element, plays a significant role in improving the quality of dual-wavelength output from fiber lasers. When the first and second specific-wavelength lasers enter the unpumped ytterbium-doped fiber, the low-intensity light is preferentially absorbed due to its saturated absorption properties. In multi-longitudinal-mode lasers, the intensity distribution of different longitudinal modes varies. The low-intensity multi-longitudinal-mode component is largely absorbed by the ytterbium ions in the unpumped ytterbium-doped fiber. As the light intensity increases, the absorption of the ytterbium ions gradually reaches saturation, allowing the high-intensity single-longitudinal-mode component to pass more smoothly. For dual-wavelength laser output, this mode selection method effectively suppresses mode noise and improves laser stability. In laser sensing applications, stable single-longitudinal-mode dual-wavelength lasers can significantly improve sensing accuracy. For example, when measuring small strains, the single-longitudinal-mode nature of the lasers enhances wavelength stability, making the measurement results less susceptible to external interference, thereby enabling more accurate detection of subtle strain changes. In the field of high-resolution spectroscopy, single-longitudinal-mode dual-wavelength lasers can provide clearer and more accurate spectral information, facilitating more detailed analysis of the spectral characteristics of materials. By utilizing the saturation absorption characteristics of unpumped ytterbium-doped fiber for mode selection, the problem of unstable dual-wavelength output mode of traditional fiber lasers is solved, providing a high-quality dual-wavelength light source for related fields.

[0046] In some embodiments of this application, please continue to refer to Figure 3 The mode selection device 500 of this embodiment further includes a first optical fiber coupler DC1, which is used to divide the first specific wave laser and the second specific wave laser into a first optical path and a second optical path according to a preset ratio. The saturated absorber mode selection element is used to select and output the first optical path and the second optical path. After being output by the saturated absorber mode selection element, the first optical path and the second optical path interfere with each other to form a synthetic wave.

[0047] It should be explained that a fiber coupler is a passive device that implements optical signal splitting / combining. In this fiber laser mode selection device 500, the function of the first fiber coupler DC1 is to distribute the first specific wave laser and the second specific wave laser to the first optical path and the second optical path according to a preset ratio. The setting of the preset ratio can be determined based on factors such as the power requirements of the two optical paths in the actual application scenario, which allows for more flexible adjustment of the subsequent mode selection and interference process. For example, the preset ratio of the first fiber coupler DC1 can be 5:5.

[0048] It can be understood that the saturable absorber mode selection element performs mode selection for the first and second optical paths separately. Because the saturable absorber has different absorption characteristics for light of different intensities and modes, it preferentially absorbs low-intensity, multi-longitudinal-mode light components while allowing high-intensity, single-longitudinal-mode light components to pass through. This results in both light paths being closer to a single-longitudinal-mode state after mode selection.

[0049] When the two selected light beams interfere with each other to form a composite wave, due to their own single longitudinal mode characteristics, the composite wave also has good single longitudinal mode characteristics. This single longitudinal mode dual-wavelength composite wave has an extremely narrow linewidth and a highly stable frequency. In laser sensing applications, it can greatly improve the accuracy and resolution of measurements and reduce the impact of external interference on measurement results. In the field of optical communications, the single longitudinal mode characteristic helps to improve the stability and bandwidth utilization of signal transmission and reduce the bit error rate. Overall, this technical solution effectively solves the problems of unstable dual-wavelength output mode and large linewidth of traditional fiber lasers, and improves the output quality and application performance of dual-wavelength lasers.

[0050] In some embodiments of this application, please continue to refer to Figure 3 In this embodiment, a first resonant cavity is formed between the mode selection device 500 and the first grating 200, and a second resonant cavity is formed between the mode selection device 500 and the second grating 300; the first resonant cavity and the second resonant cavity are used for laser back and forth reflection to form stable laser oscillation.

[0051] It should be explained that the first resonant cavity is constructed by the mode selection device 500 and the first grating 200. In this closed optical structure, the laser can reflect back and forth between the mode selection device 500 and the first grating 200. With each reflection, the laser will undergo energy replenishment by the gain medium and mode screening by the mode selection device 500. Through multiple reflections, the laser mode that meets the resonance conditions is continuously enhanced to form a stable laser oscillation. Similarly, the second resonant cavity is composed of the mode selection device 500 and the second grating 300. Its working principle is similar to that of the first resonant cavity, and the laser propagates back and forth between the mode selection device 500 and the second grating 300. During the propagation process, the laser obtains energy from the gain medium on the one hand, and accepts the optimization of its mode by the mode selection device 500 on the other hand, thereby establishing a stable laser oscillation.

[0052] In related technologies, the cavity type of fiber lasers is mainly divided into linear structure and ring structure. Linear cavity fiber lasers have the significant advantages of simple structure and small size. Their cavity length can usually reach several centimeters, and fewer optical devices are used in the cavity, which reduces the cost and system complexity to a certain extent. However, this structure has obvious limitations. On the one hand, its wavelength tuning range is small, which makes it difficult to meet application scenarios that require wide-range wavelength tuning, such as certain high-precision spectral analysis fields. On the other hand, the spatial hole burning effect in the linear cavity makes the laser mode competition extremely fierce, seriously affecting the stability and quality of the laser output, resulting in problems such as output power fluctuations and mode instability in practical applications.

[0053] After completing a single rotation, light within a ring cavity returns to its initial position, forming a closed-loop structure. This makes it more stable and more resistant to interference than a linear cavity. Due to this characteristic, ring cavity fiber lasers can be used to achieve wide wavelength tuning, making them valuable in laser sensing applications requiring a wide wavelength tuning range. They are also suitable for the fabrication of high-power fiber lasers, meeting the demands of industrial processing and other applications requiring high-power lasers. Furthermore, ring cavity fiber lasers offer significant advantages in generating multiple wavelengths, enabling them to meet the specific needs of scientific research and industrial applications requiring multi-wavelength light sources. However, ring cavities also present significant challenges. Because their cavity length is much longer than that of linear cavities, typically measuring over ten or even twenty meters, the spacing between longitudinal modes within the laser system decreases, significantly increasing the difficulty of mode selection. In practice, more sophisticated and complex mode selection techniques are required to ensure stable output of the desired mode. Furthermore, ring cavities suffer from mode hopping, whereby the laser mode can suddenly change under certain operating conditions. This severely impacts the stability and reliability of laser output, presenting numerous challenges in practical applications.

[0054] However, in the embodiment of the present application, a resonant cavity is formed between the mode selection device 500 and the grating, and the laser is reflected back and forth in the resonant cavity. Each time it passes through the gain medium, it can obtain energy replenishment to maintain the continuous oscillation of the laser. At the same time, the mode selection device 500 continuously selects modes that meet specific requirements in this process and suppresses other unstable or unnecessary modes. For example, for some application scenarios that require single longitudinal mode output, the mode selection device 500 can gradually suppress the multi-longitudinal mode components during the multiple reflections of the laser, so that the first specific wave laser and the second specific wave laser form stable single longitudinal mode oscillations in their respective resonant cavities, greatly improving the stability of the laser output.

[0055] Furthermore, the presence of the resonant cavity optimizes the laser's frequency, linewidth, and other characteristics. Due to the laser's multiple reflections within the resonant cavity, only light meeting specific frequency conditions can form stable oscillations. This limits the laser's output frequency range and narrows its linewidth. In fields such as high-resolution spectral analysis, narrow-linewidth dual-wavelength lasers can provide more precise spectral information and improve analytical accuracy. Furthermore, stable laser oscillations also result in more stable laser power output, ensuring consistent processing quality for applications requiring precise control of laser power, such as laser machining.

[0056] The two resonant cavities in the embodiment of the present application are interconnected via a mode selection device 500. The mode selection of the first and second specific-wavelength lasers by the mode selection device 500 not only ensures stable oscillation of the lasers in their respective resonant cavities but also enhances the synergy of the two wavelengths' mode characteristics. In applications requiring dual-wavelength laser interference, such as laser interferometry for measuring small displacements, stable and synergistic dual-wavelength lasers can produce clearer and more stable interference fringes, improving measurement accuracy.

[0057] In some embodiments of this application, please continue to refer to Figure 3 The output device 400 of this embodiment includes a second fiber coupler DC2, which is based on a synthetic wave and outputs a dual-wavelength laser and a resonant laser according to a preset output ratio. The resonant laser is a light source laser input to the polarization beam splitter 100.

[0058] It is understandable that the second fiber coupler DC2 can output dual-wavelength laser and resonant laser according to a preset output ratio, which greatly enhances the applicability of the fiber laser in different application scenarios. In the field of laser processing, a higher-power dual-wavelength laser may be required to achieve fine processing of materials. In this case, most of the synthetic waves can be allocated as dual-wavelength laser output. In the self-stabilizing system of the fiber laser, the resonant laser can be fed back into the cavity to adjust the oscillation state of the laser and maintain the stable operation of the laser. By reasonably setting the output ratio, the effective operation of the self-stabilizing system can be guaranteed.

[0059] In some embodiments, the preset output ratio may be 1:9, with the dual-wavelength laser accounting for 10% and the resonant laser accounting for 90%.

[0060] In some embodiments of this application, please continue to refer to Figure 3The fiber laser of this embodiment also includes a wavelength division multiplexer WDM, an ytterbium-doped fiber YDF, and a pump source LD. The wavelength division multiplexer WDM and the ytterbium-doped fiber YDF are arranged between the mode selection device 500 and the polarization beam splitter 100. The pump source LD is connected to the wavelength division multiplexer WDM and is used to output excitation light to the ytterbium-doped fiber YDF; the ytterbium-doped fiber YDF generates radiation laser based on the excitation light, and the radiation laser is a light source laser input to the polarization beam splitter 100.

[0061] It should be explained that the wavelength division multiplexer (WDM) is an optical device that can multiplex and demultiplex optical signals of different wavelengths. In this fiber laser, it is spaced between the mode selection device 500 and the polarization beam splitter 100, and plays the role of merging the excitation light output by the pump source LD with the optical signals in other optical paths, ensuring that the excitation light can smoothly enter the ytterbium-doped optical fiber YDF. As an energy supply device, the pump source LD is connected to the wavelength division multiplexer (WDM) and is responsible for outputting excitation light to the ytterbium-doped optical fiber YDF. The wavelength and power of the excitation light are key factors affecting the generation of radiated laser light by the ytterbium-doped optical fiber YDF. Different application scenarios may require pump source LDs with different parameters.

[0062] It can be understood that after the excitation light output by the pump source LD enters the ytterbium-doped fiber YDF through the wavelength division multiplexer (WDM), the ytterbium ions in the YDF achieve a population inversion distribution, thereby generating stimulated emission and achieving laser gain. This enables the fiber laser to generate a sufficiently intense source laser, providing the energy foundation for subsequent dual-wavelength laser output. For example, in laser processing applications, laser light of sufficient intensity is essential for effective material processing.

[0063] In some embodiments, the characteristics of the laser radiation generated by the ytterbium-doped fiber (YDF), such as power and wavelength, can be precisely controlled by adjusting the parameters of the pump source LD. Different pump powers and wavelengths affect the energy level transitions of the ytterbium ions, thereby changing the output characteristics of the laser radiation. This controllability enables fiber lasers to better adapt to diverse application requirements, improving laser performance and flexibility.

[0064] In some embodiments of this application, please continue to refer to Figure 3 The fiber laser of this embodiment further includes a first polarization controller PC1 and a second polarization controller PC2. The first polarization controller PC1 is arranged between the polarization beam splitter 100 and the first grating 200; the second polarization controller PC2 is arranged between the polarization beam splitter 100 and the second grating 300.

[0065] It should be explained that the first polarization controller PC1 is arranged between the polarization beam splitter 100 and the first grating 200. Its main function is to precisely control the polarization state of the first sub-laser output from the polarization beam splitter 100. In a fiber laser, the polarization state of light is affected by a variety of factors, such as fiber bending, temperature changes, etc. These factors may cause the polarization state of the laser to change, thereby affecting the generation and output of the first specific wave laser by the first grating 200. The first polarization controller PC1 can change the polarization direction and polarization ellipticity of the first sub-laser by adjusting its own parameters, such as the rotation angle and stretching degree, so that it achieves the optimal polarization state to meet the working requirements of the first grating 200.

[0066] The second polarization controller PC2, located between polarization beam splitter 100 and second grating 300, controls the polarization state of the second sub-laser. Similar to the first polarization controller PC1, it compensates for polarization changes in the second sub-laser caused by various factors during transmission, ensuring that the second sub-laser enters second grating 300 with the appropriate polarization state, thereby optimizing the generation and output of the second specific laser wave.

[0067] It can be understood that by precisely controlling the polarization states of the first sub-laser and the second sub-laser through the first polarization controller PC1 and the second polarization controller PC2, the laser output fluctuations caused by changes in the polarization state can be reduced. In the resonant cavity, a stable polarization state helps to maintain the oscillation conditions of the laser, making the output power and wavelength of the first specific wave laser and the second specific wave laser more stable. For example, in laser sensing applications, stable laser output can improve the accuracy and reliability of measurements and reduce measurement errors. And the appropriate polarization state can enable the grating to better play its frequency selection role, improve the reflection efficiency of the specific wavelength laser, and suppress other unnecessary wavelength components. The setting of the first polarization controller PC1 and the second polarization controller PC2 can ensure that the first sub-laser and the second sub-laser enter the corresponding grating with the optimal polarization state, thereby optimizing the output quality of the dual-wavelength laser and making the output dual-wavelength laser have a narrower linewidth and higher purity.

[0068] In some embodiments of this application, please continue to refer to Figure 3 The fiber laser of this embodiment includes an electrically controlled tuning mechanism, which is used to adjust the axial stretching of the first grating 200 and the second grating 300 to adjust the wavelengths of the first specific wave laser and the second specific wave laser.

[0069] It is understandable that the electrically controlled tuning mechanism gives the fiber laser the ability to flexibly adjust its wavelength. In practical applications, different application scenarios often require dual-wavelength lasers of different wavelengths. For example, in the field of laser communications, different communication bands correspond to different communication requirements and transmission characteristics. Through the electrically controlled tuning mechanism, the wavelengths of the first specific wave laser and the second specific wave laser can be adjusted quickly and accurately, so that the fiber laser can adapt to the requirements of various communication bands, improving the versatility and adaptability of the equipment. Due to the use of electrical control, the electrically controlled tuning mechanism has a fast dynamic response capability. It can adjust the axial stretching of the grating in a short time, thereby realizing rapid switching of the laser wavelength. In some application scenarios that require real-time changes in laser wavelength, such as lidar, laser imaging, etc., this fast dynamic response capability can enable the fiber laser to adapt to different measurement and imaging requirements in a timely manner, improving the real-time performance and performance of the system.

[0070] In the examples of this application, please refer to Figure 3 In this embodiment, a fiber polarization beam splitter 100 (FPBS) is used to split the intracavity laser into two paths with a central wavelength of 1064 nm and a bandwidth of ±30 nm. A polarization controller (PC) is used to balance the gain and loss in the dual cavities, thereby achieving simultaneous oscillation of the two wavelengths. A length of unpumped ytterbium-doped fiber (UPYDF) with an absorption coefficient of 80 dB / m is connected to a Sagnac ring composed of a 5:5 3dB directional coupler (first fiber coupler DC1) as a saturable absorber mode selection element. Two fiber Bragg gratings (FBG1 and FBG2) with different central wavelengths are used as wavelength selection elements for the two paths. FBG1 and FBG2 have central wavelengths of 1061 nm and 1064 nm, respectively, with a reflection bandwidth of 0.2 nm and a reflectivity of 99%. The unpumped ytterbium-doped fiber and the fiber Bragg grating embedded in the Sagnac ring serve as two reflectors to form a laser standing wave resonant cavity.

[0071] Optical Principle: When a pump with a central wavelength of 976 nm is introduced into the cavity via a wavelength division multiplexer (WDM), the ytterbium-doped medium undergoes population inversion due to the 976 nm pump light, generating a large amount of stimulated emission. The ytterbium ion emission spectrum covers the 1-1.1 μm band, necessitating wavelength selection. The light is then split into two orthogonally linearly polarized paths by a fiber polarization beam splitter 100: one with P polarization and the other with S polarization. After wavelength selection by a fiber Bragg grating (FBG), the light with the specific central wavelength is reflected back. The leftmost portion of the system shows an unpumped ytterbium-doped fiber embedded in a Sagnac ring. This fiber acts as both a mode-selective element and a resonant mirror. The light reflected from the FBG undergoes mode selection and then returns along the original path. The laser then reflects back and forth within the cavity until stable laser oscillation is achieved. The laser is then output via a 1:9 output coupler (output device 400).

[0072] Tuning process: A dual-wavelength single-longitudinal-mode fiber laser can be used as a wavelength selection device to output the required dual-wavelength laser. At the same time, when the device is subjected to external stimuli, such as transverse stress, axial tension, temperature change, etc., the center wavelength can be tuned and changed. When the fiber Bragg grating is axially stretched, the strain sensitivity is the greatest, and a wider range of wavelength stretching can be achieved. When a 23cm fiber Bragg grating is stretched, the stretching length ΔL is about 0.9mm, and the fiber Bragg grating can achieve wavelength tuning between 3nm. When two fiber Bragg gratings with center wavelengths of 1061nm and 1064nm are selected for wavelength selection and longitudinal mode selection, the wavelength difference can be changed from 0-3nm, and the corresponding frequency difference can reach the terahertz level, thus achieving a dual-wavelength single-longitudinal-mode light source with adjustable frequency difference from 0-1THz, which meets the requirements of an ideal light source for absolute distance interferometry.

[0073] In the embodiment of the present application, the laser wavelength difference tuning range can be continuously tuned between 0.04nm and 2.916nm, corresponding to a frequency difference tuning range of 10.6GHz to 772.74GHz. The use of electric control to achieve fully controllable axial stretching makes experiments more convenient and the data obtained more accurate.

[0074] In some embodiments, the fiber laser in the embodiments of the present application is applied in the field of absolute distance measurement.

[0075] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0076] The basic concepts have been described above. It will be apparent to those skilled in the art that the detailed disclosure above is merely illustrative and does not limit the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and amendments to the present application. Such modifications, improvements, and amendments are suggested in the present application and remain within the spirit and scope of the exemplary embodiments of the present application.

[0077] At the same time, this application uses specific terms to describe the embodiments of this application. For example, "one embodiment," "an embodiment," and / or "some embodiments" refer to a certain feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that "one embodiment," "an embodiment," or "an alternative embodiment" mentioned twice or multiple times in different locations in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application may be appropriately combined.

[0078] Similarly, it should be noted that, in order to simplify the presentation of this application and thus facilitate understanding of one or more embodiments of the invention, the foregoing descriptions of the embodiments of this application sometimes combine multiple features into a single embodiment, figure, or description thereof. However, this disclosure method does not mean that the subject matter of this application requires more features than those recited in the claims. In fact, an embodiment may have fewer features than all of the features of a single embodiment disclosed above.

[0079] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A fiber laser, characterized in that: include: a polarization beam splitter, the polarization beam splitter being configured to receive a light source laser and split the light source laser into at least a first sub-laser and a second sub-laser; wherein the polarization directions of the first sub-laser and the second sub-laser are perpendicular to each other; a first grating, configured to receive the first sub-laser and reflect a portion of the first sub-laser to form a first specific wave laser; a second grating for receiving the second sub-laser and reflecting a portion of the second sub-laser to form a second specific-wave laser; the wavelength of the second specific-wave laser is different from the wavelength of the first specific-wave laser; An output device is configured to output dual-wavelength laser light based on the first specific-wave laser light and the second specific-wave laser light.

2. The fiber laser according to claim 1, wherein: The fiber laser also includes a mode selection device, which is used to receive the first specific wave laser and the second specific wave laser, and to output a synthetic wave after performing mode selection on the first specific wave laser and the second specific wave laser. The output device is used to output the dual-wavelength laser according to the synthetic wave.

3. The fiber laser according to claim 2, characterized in that The mode selection device includes a Sagnac ring and a saturated absorber mode selection element. The Sagnac ring is used to input the first specific wave laser and the second specific wave laser into the saturated absorber mode selection element. The saturated absorber mode selection element is used to output the synthetic wave of a single longitudinal mode after mode selection of the first specific wave laser and the second specific wave laser.

4. The fiber laser according to claim 3, characterized in that The saturated absorber mode selection element is an unpumped ytterbium-doped optical fiber.

5. The fiber laser according to claim 3, wherein: The mode selection device also includes a first optical fiber coupler, which is used to divide the first specific wave laser and the second specific wave laser into a first optical path and a second optical path according to a preset ratio. The saturated absorber mode selection element is used to perform mode selection and output on the first optical path and the second optical path. After being output by the saturated absorber mode selection element, the first optical path and the second optical path interfere with each other to form the synthetic wave.

6. The fiber laser according to any one of claims 2 to 5, characterized in that: A first resonant cavity is formed between the mode selection device and the first grating, and a second resonant cavity is formed between the mode selection device and the second grating; the first resonant cavity and the second resonant cavity are used for back and forth reflection of laser light to form stable laser oscillation.

7. The fiber laser according to claim 6, characterized in that The output device includes a second optical fiber coupler, which outputs the dual-wavelength laser and the resonant laser based on the synthetic wave and in a preset output ratio. The resonant laser is a light source laser input to the polarization beam splitter.

8. The fiber laser according to claim 2, wherein: The fiber laser further includes a wavelength division multiplexer, an ytterbium-doped fiber, and a pump source. The wavelength division multiplexer and the ytterbium-doped fiber are arranged between the mode selection device and the polarization beam splitter. The pump source is connected to the wavelength division multiplexer and is used to output excitation light to the ytterbium-doped fiber. The ytterbium-doped optical fiber generates radiated laser light based on the excitation light, and the radiated laser light is a light source laser input to the polarization beam splitter.

9. The fiber laser according to claim 1, wherein: The fiber laser further includes a first polarization controller and a second polarization controller. The first polarization controller is arranged between the polarization beam splitter and the first grating; the second polarization controller is arranged between the polarization beam splitter and the second grating.

10. The fiber laser according to claim 1, wherein: The fiber laser includes an electrically controlled tuning mechanism, which is used to adjust the axial stretching of the first grating and the second grating to adjust the wavelengths of the first specific wave laser and the second specific wave laser.

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