A polarization-maintaining distributed feedback fiber laser with orthogonal polarization beam splitting and polarization maintaining output
By fabricating a π phase-shifting grating in a DFB fiber laser and utilizing polarization alignment technology, stable operation with dual linear polarization and orthogonal beam splitting output with high extinction ratio were achieved. This solves the problem of unstable dual polarization mode output in existing technologies and is suitable for fields such as high-speed coherent optical communication and precision optical measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LASER RES INST OF SHANDONG ACAD OF SCI
- Filing Date
- 2026-04-28
- Publication Date
- 2026-05-29
AI Technical Summary
Existing DFB fiber lasers suffer from problems such as insufficient stability during dual polarization operation, lack of in-situ integration of polarization beam splitting with the laser body, low polarization alignment accuracy, poor beam splitting effect, system redundancy, and complex fabrication, making it difficult to achieve orthogonal beam splitting output of narrow-linewidth laser dual polarization modes.
A π-phase-shifting grating was fabricated by side-exposure of the optical fiber with ultraviolet laser to construct a stable dual-polarization DFB operation. The polarization alignment technique was used to achieve precise matching between the laser's dual linear polarization mode and the fast and slow axes of the polarization-maintaining fiber. Then, the polarization-maintaining fiber PBS was used for in-situ beam splitting to construct a compact and stable orthogonal dual-polarization mode output.
It achieves stable operation with dual linear polarization, orthogonal beam splitting output with high extinction ratio, has a compact structure, simplifies the fabrication process, and is suitable for high-speed coherent optical communication, precision optical measurement, and lidar.
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Figure CN122118504A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of fiber laser technology, and in particular to an orthogonal polarization splitting and polarization-maintaining distributed feedback fiber laser. Background Technology
[0002] Distributed feedback fiber lasers, due to their core advantages such as intrinsic single longitudinal mode, narrow linewidth, small size, and good compatibility with fiber optic systems, have been widely used in important fields such as high-speed coherent optical communication, precision optical measurement, lidar, and microwave photonics. As these fields iterate towards higher capacity, higher precision, miniaturization, and integration, the demand for narrow-linewidth light sources with stable polarization characteristics is becoming increasingly urgent. In particular, orthogonally dual-polarized output lasers can effectively improve the spectral utilization of optical communication systems, enhance the anti-interference capability of precision measurements, optimize the target recognition accuracy of lidar, and generate stable microwave spectra through beat frequency generation, etc. Therefore, the development of narrow-linewidth fiber lasers that combine stable orthogonal dual-polarization operation with high polarization extinction beam-ratio capabilities has become a research hotspot in the field of laser technology.
[0003] Currently, there are three main approaches to generating orthogonal dual-polarization modes in DFB fiber lasers. The first is to apply stress to the fiber to induce birefringence, such as by applying pressure from the side or twisting the DFB grating. This modulates the birefringence of the DFB grating region through external force, altering the laser polarization mode loss and enabling the switching of single and dual polarization lasers. However, the dual polarization generated in this way lacks stable operation capability, and the DFB grating is easily damaged under external force. The second approach utilizes a composite cavity structure and polarization hole burning effect, or directly fabricates the DFB grating cavity using polarization-maintaining gain fiber. However, these approaches are relatively complex and make it difficult to control the laser threshold conditions of the orthogonal polarization modes separately, hindering stable output of orthogonal dual polarization modes. The third approach uses femtosecond fiber grating writing technology. This method can generate a significant birefringence effect, but its application in DFB resonant cavity fabrication is still in its infancy, and many problems remain to be solved.
[0004] In the field of DFB fiber laser dual-polarization orthogonal beam splitting output technology, the main approach is to use polarization devices such as PBS (polarization beam splitter) or in-line polarizers for modulation. However, existing technologies still have shortcomings and deficiencies, specifically: First, conventional external cavity PBS beam splitting schemes are not designed to adapt to the polarization characteristics of dual-polarization DFB lasers, making it impossible to achieve precise alignment between the laser linear polarization mode and the polarization-maintaining fiber. The resulting orthogonal polarization extinction ratio of the split beam is low, which is difficult to meet the requirements of high-capacity communication, high-precision measurement, and other application scenarios. Second, although some schemes use polarization-maintaining fiber in combination with PBS, they do not achieve in-situ integration of the beam splitting function with the laser body, and still suffer from insufficient stability and polarization extinction ratio fading, and cannot meet the application requirements of miniaturization and integration.
[0005] Therefore, addressing the technical problems of existing DFB fiber lasers, such as insufficient stability of dual-polarization operation, lack of in-situ integration of polarization beam splitting with the laser body, low polarization axis accuracy, poor beam splitting effect, system redundancy, and complex fabrication, this patent proposes a method for achieving orthogonal dual-polarization operation and polarization-maintaining output of a distributed feedback fiber laser. During the fabrication of gratings using ultraviolet laser side exposure of fiber, refractive index polarization occurs in the single-mode fiber, leading to a probability of dual-polarization mode operation within the DFB resonant cavity composed of π-phase-shifted fiber gratings. This characteristic can be utilized to construct a stable dual-polarization DFB operation. By precisely matching the laser's dual linear polarization modes with the fast and slow axes of the polarization-maintaining fiber through polarization axis alignment, and then using the polarization-maintaining fiber PBS to achieve in-situ beam splitting of the orthogonal dual polarization modes, a compact, stable, and easily fabricated distributed feedback fiber laser with high polarization characteristics can be constructed. This solves the current technical problem of difficult orthogonal beam splitting output of narrow-linewidth laser dual polarization modes, providing a high-performance light source for high-speed coherent optical communication, precision optical measurement, lidar, microwave photonics, and other fields. Summary of the Invention
[0006] To address the aforementioned technical problems in existing technologies, the present invention aims to provide an orthogonal polarization-splitting and polarization-maintaining distributed feedback fiber laser. This invention provides an intrinsic control method for achieving stable operation of a single longitudinal mode dual-linear polarization in a DFB fiber laser. Furthermore, based on this method, it proposes an all-fiber orthogonal polarization mode coupling beam splitting technique. Through closed-loop polarization alignment, it achieves high extinction ratio orthogonal beam splitting and polarization-maintaining output of the dual-linear polarization mode in the distributed feedback fiber laser in situ, solving the problem of difficult stable dual-polarization mode orthogonal beam splitting output for narrow-linewidth lasers.
[0007] This invention is achieved through the following technical solution: An orthogonal polarization beam-splitting polarization-maintaining distributed feedback fiber laser includes a semiconductor pump source and an active π-phase-shifting fiber grating, with the semiconductor pump source connected to the active π-phase-shifting fiber grating; it also includes a polarization-maintaining wavelength division multiplexer and a polarization-maintaining polarization beam splitter, with the common end of the active π-phase-shifting fiber grating and the polarization-maintaining wavelength division multiplexer connected via a polarization alignment process, and the signal end of the polarization-maintaining wavelength division multiplexer connected to the input end of the polarization-maintaining polarization beam splitter.
[0008] Furthermore, in order to better realize the present invention, it also includes a first polarization-maintaining isolator and a second polarization-maintaining isolator, which are respectively connected to the first output terminal and the second output terminal of the polarization-maintaining polarization beam splitter.
[0009] Furthermore, in order to better realize the present invention, the active π phase-shifting fiber grating is a π phase-shifting fiber grating that is etched on a rare earth-doped fiber using ultraviolet light side exposure, and the active π phase-shifting fiber grating has a grating coupling strength value that enables the distributed feedback fiber laser to operate stably in a dual polarization mode state.
[0010] Furthermore, in order to better realize the present invention, the pump end of the polarization-maintaining wavelength division multiplexer is suspended to export the remaining pump light of the distributed feedback fiber laser.
[0011] Furthermore, in order to better realize the present invention, the input end, the first output end and the second output end of the polarization-maintaining beam splitter are all polarization-maintaining fibers, and the slow axis of the polarization-maintaining fibers at the first output end and the second output end is coupled to the fast axis and the slow axis of the polarization-maintaining fiber at the input end, respectively.
[0012] Furthermore, to better realize the present invention, the polarization alignment process is as follows: Under the pumping excitation of a semiconductor pump source, the pigtail of the active π phase-shift fiber grating is coupled to the polarization-maintaining pigtail at the common end of the polarization-maintaining wavelength division multiplexer. The laser power is monitored from the back end of the first polarization-maintaining isolator and the second polarization-maintaining isolator, respectively. By causing the axial direction of the pigtail of the active π phase-shift fiber grating to rotate relative to the polarization-maintaining pigtail at the common end of the polarization-maintaining wavelength division multiplexer, the polarization alignment is completed when the monitored laser power at the back end of the first polarization-maintaining isolator and the second polarization-maintaining isolator both reach their maximum values. At this time, the dual linear polarization of the distributed feedback fiber laser is aligned with the fast axis and slow axis of the polarization-maintaining optical path composed of the polarization-maintaining wavelength division multiplexer and the polarization-maintaining polarization beam splitter, respectively, to achieve orthogonal polarization beam splitting of the two optical paths.
[0013] Furthermore, to better realize the present invention, the operating wavelength of the orthogonal polarization beam-splitting and polarization-maintaining distributed feedback fiber laser is 1550 nm, the grating Bragg wavelength of the active π phase-shifting fiber grating is 1550.16 nm, and the refractive index modulation is 1.75 × 10⁻⁶. -4 The polarization refractive index difference is 1.1 × 10⁻⁶. -5 The grating coupling strength value is 13.56.
[0014] Furthermore, in order to better realize the present invention, the rare earth doped optical fiber includes any one of erbium-doped optical fiber, ytterbium-doped optical fiber or thulium-doped optical fiber, corresponding to fiber lasers of different wavelengths.
[0015] The beneficial effects of this invention are: This invention first realizes a distributed feedback fiber laser with stable operation of dual-linear polarization through simulation design, which can stably achieve dual-linear polarization operation and effectively suppress polarization jumps and mode competition. Then, by using in-situ polarization alignment and polarization-maintaining beam splitting (PBS), polarization-maintaining beam splitting output of orthogonal polarized lasers is achieved without the need for additional polarizers or polarization control devices, while maintaining a high polarization extinction ratio and low polarization disturbance. At the same time, the laser dual-polarization mode oscillation and polarization beam splitting functions are integrated into one compact structure with low insertion loss. While ensuring single longitudinal mode, narrow linewidth, and high wavelength stability, it can achieve balanced output of two orthogonally polarized beams. The overall system is simple and reliable, which is more conducive to engineering and miniaturization applications. Attached Figure Description
[0016] Figure 1 This is a graph showing the variation of fiber refractive index modulation caused by side exposure in the DFB fiber laser of this invention. Figure 2 This is a graph showing the relationship between the output power of the dual polarization mode of the DFB fiber laser and the value of the grating coupling strength kL. Figure 3 The image shows a typical spectrum of the DFB fiber laser with single longitudinal mode and dual polarization operation constructed in this invention. The red and blue curves represent two laser wavelengths measured by the spectrometer from two orthogonal polarization directions, indicating that the DFB fiber laser is a dual polarization mode. Figure 4 This is a schematic diagram of the orthogonal polarization beam splitting and polarization-maintaining output distributed feedback fiber laser of the present invention; Figure 5 The above are the measured orthogonal polarization beam splitting laser spectra of the two output ports of the laser of the present invention. The red curve is the output spectrum of the first polarization-maintaining isolator, and the blue curve is the output spectrum of the second polarization-maintaining isolator. Figure 6 The polarization state of the output laser from the first polarization-maintaining isolator of the orthogonal polarization beam splitting and polarization-maintaining output distributed feedback fiber laser of the present invention is linear polarization with a direction of approximately 30°. Figure 7 The polarization state of the output laser from the second polarization-maintaining isolator of the orthogonal polarization beam splitting and polarization-maintaining output distributed feedback fiber laser of the present invention is linear polarization with a direction of approximately 120°.
[0017] In the picture, 1. Semiconductor pump source; 2. Active π phase-shift fiber grating; 3. Polarization-maintaining wavelength division multiplexer; 3-1. Common terminal; 3-2. Pump terminal; 3-3. Signal terminal; 4. Polarization-maintaining beam splitter; 4-1. Input terminal; 4-2. First output terminal; 4-3. Second output terminal; 5. First polarization-maintaining isolator; 6. Second polarization-maintaining isolator. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0020] like Figures 1-7 The illustration shows a specific embodiment of the present invention. This embodiment is a 1550nm band orthogonal polarization-splitting, polarization-maintaining, distributed feedback fiber laser. It mainly consists of a resonant cavity formed by a π phase-shift grating inscribed on erbium-doped fiber. The erbium-doped fiber has an absorption coefficient of 7.5dB / m@980nm and an effective core refractive index of 1.4472. A polarization mode operation analysis model was established for this fiber, thereby obtaining the refractive index polarization law of the phase-shift fiber grating as a function of exposure intensity, as shown below. Figure 1 As shown, further analysis of the variation of laser dual polarization modes with grating coupling strength KL is as follows: Figure 2 As shown, stable dual-polarization mode operation can be obtained when the grating coupling strength KL reaches 13.74.
[0021] A π-phase-shift grating was etched onto this erbium-doped fiber using a combination of conventional side-scan exposure and a dynamic phase mask method. The grating length is 38 mm, the Bragg wavelength is 1550.16 nm, and the refractive index modulation Δn is 1.75 × 10⁻⁶. -4 Polarization refractive index difference Δn x-y 1.1*10 -5 The grating coupling strength kL is 13.56. Under a 300mW 980nm pump, the laser spectrum is as follows: Figure 3 As shown in the figure, the red and blue curves represent two laser wavelengths measured by the spectrometer from two orthogonal polarization directions, with a wavelength interval of 12.5 pm. This DFB fiber laser has stable dual-polarization mode laser output characteristics.
[0022] Therefore, an orthogonal polarization-splitting, polarization-maintaining, distributed feedback fiber laser is constructed using an erbium-doped π-phase-shift fiber grating, such as... Figure 4 As shown, it mainly consists of a 980nm semiconductor pump source 1, an erbium-doped π-phase-shifting fiber grating 2, a polarization-maintaining wavelength division multiplexer 3, a polarization-maintaining polarization beam splitter 4, a polarization-maintaining isolator 5, and a polarization-maintaining isolator 6.
[0023] One end of the erbium-doped π-phase-shifting fiber grating 2 is connected to the 980nm semiconductor pump source 1 via a single-mode fiber, and the other end is cut flat along the grating using a fiber cleaver. The polarization-maintaining pigtail at the common end 3-1 of the polarization-maintaining wavelength division multiplexer 3 is also cut flat using a fiber cleaver, and the erbium-doped π-phase-shifting fiber grating 2 and the polarization-maintaining pigtail at the common end 3-1 of the polarization-maintaining wavelength division multiplexer 3 are aligned and coupled using a polarization-maintaining fusion splicer. The pump end 3-2 of the polarization-maintaining wavelength division multiplexer 3 is left suspended to guide the remaining 980nm pump light from the laser, thus maintaining the polarization wavelength division multiplexing. The signal terminal 3-3 of the polarization wavelength division multiplexer 3 is fused with the input terminal 4-1 of the polarization-maintaining beam splitter 4 for polarization maintenance. Both the input and output terminals of the polarization-maintaining beam splitter 4 are polarization-maintaining pigtails. At the same time, the slow axis of the polarization-maintaining pigtails at the two output terminals is coupled to the fast and slow axes of the polarization-maintaining fiber at the input terminal 4-1, respectively. Its input terminal 4-1 is fused with the signal terminal 3-3 of the polarization-maintaining wavelength division multiplexer 3 for polarization maintenance. The polarization-maintaining isolators 5 and 6 are fused with the two output terminals 4-2 and 4-3 of the polarization-maintaining beam splitter 4 for polarization maintenance, respectively.
[0024] Under 300mW 980nm pump excitation, the erbium-doped π-phase-shifted fiber grating 2 emits as shown in the image. Figure 3 The dual-polarized laser shown is monitored for power after the first polarization-maintaining isolator 5 and the second polarization-maintaining isolator 6. A polarization-maintaining fusion splicer causes relative rotation of the axial direction of the polarization-maintaining pigtail at the common end 3-1 of the erbium-doped π-phase-shifting fiber grating 2 and the polarization-maintaining wavelength division multiplexer 3. The laser power after the first and second polarization-maintaining isolators 5 and 6 changes periodically with the angle. When both reach their maximum values, it indicates that the dual linear polarization of the DFB fiber laser is aligned with the fast and slow axes of the polarization-maintaining optical path formed by the polarization-maintaining wavelength division multiplexer 3 and the polarization-maintaining beam splitter 4, respectively. The laser spectra output from the first and second polarization-maintaining isolators 5 and 6 at this time are as follows: Figure 5 As shown, the red curve represents the output spectrum of the first polarization-maintaining isolator 5, and the blue curve represents the output spectrum of the second polarization-maintaining isolator 6. Both lasers are single-polarized light, and the laser wavelength interval is maintained at 12.5 pm. Further, a polarization analyzer is used to measure the polarization state of the output laser from the first polarization-maintaining isolator 5, as shown... Figure 6 As shown, in the Bonga sphere composed of polarization components s1s2s3, the yellow indicator point representing the laser polarization state is located on the equator of the s1s2 plane, indicating that the laser polarization state is linearly polarized light, and the linear polarization direction is approximately 30°; simultaneously, the laser polarization state output by the second polarization-maintaining isolator 6 is measured, as shown... Figure 7 As shown, in the Bonga sphere composed of polarization components s1s2s3, the yellow indicator point representing the laser polarization state is also located on the equator of the s1s2 plane, indicating that the laser polarization state is linearly polarized light, and the linear polarization direction is approximately 120°, which differs from the polarization direction of the laser output from the first polarization-maintaining isolator 5 by 90°. The polarization directions of the two lasers are orthogonal. The above scheme achieves orthogonal polarization beam splitting and polarization-maintaining output of a 1550nm band dual polarization distribution feedback fiber laser.
[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.
Claims
1. An orthogonal polarization beam-splitting polarization-maintaining output distributed feedback fiber laser, comprising a semiconductor pump source (1), an active π-phase-shifting fiber grating (2), a polarization-maintaining wavelength division multiplexer (3), and a polarization-maintaining polarization beam splitter (4), characterized in that: The semiconductor pump source (1) is optically connected to the active π phase-shift fiber grating (2); the active π phase-shift fiber grating (2) is connected to the common terminal (3-1) of the polarization-maintaining wavelength division multiplexer (3) through a polarization alignment process; the signal terminal (3-3) of the polarization-maintaining wavelength division multiplexer (3) is connected to the input terminal (4-1) of the polarization-maintaining polarization beam splitter (4).
2. The orthogonal polarization beam splitting and polarization-maintaining output distributed feedback fiber laser according to claim 1, characterized in that: The laser also includes a first polarization-maintaining isolator (5) and a second polarization-maintaining isolator (6), which are connected to the first output terminal (4-2) and the second output terminal (4-3) of the polarization-maintaining polarization beam splitter (4), respectively.
3. The orthogonal polarization beam splitting and polarization-maintaining distributed feedback fiber laser according to claim 1, characterized in that: The active π phase-shifting fiber grating (2) is a π phase-shifting fiber grating that is etched onto a rare earth-doped fiber using ultraviolet light side exposure. The active π phase-shifting fiber grating (2) has a grating coupling strength value that enables the distributed feedback fiber laser to operate stably in a dual polarization mode.
4. The orthogonal polarization beam splitting and polarization-maintaining distributed feedback fiber laser according to claim 1, characterized in that: The pump end (3-2) of the polarization-maintaining wavelength division multiplexer (3) is suspended to export the remaining pump light of the distributed feedback fiber laser.
5. The orthogonal polarization beam splitting and polarization-maintaining distributed feedback fiber laser according to claim 1, characterized in that: The input end (4-1), the first output end (4-2) and the second output end (4-3) of the polarization-maintaining beam splitter (4) are all polarization-maintaining fibers. The slow axis of the polarization-maintaining fibers of the first output end (4-2) and the second output end (4-3) is coupled to the fast axis and the slow axis of the polarization-maintaining fiber of the input end (4-1) respectively.
6. The orthogonal polarization beam splitting and polarization-maintaining distributed feedback fiber laser according to claim 1, characterized in that: The polarization alignment process is as follows: under the pumping excitation of the semiconductor pump source (1), the pigtail of the active π phase-shift fiber grating (2) is coupled to the polarization-maintaining pigtail of the common end (3-1) of the polarization-maintaining wavelength division multiplexer (3). The laser power is monitored from the back end of the first polarization-maintaining isolator (5) and the second polarization-maintaining isolator (6). The axial direction of the pigtail of the active π phase-shift fiber grating (2) and the polarization-maintaining pigtail of the common end (3-1) of the polarization-maintaining wavelength division multiplexer (3) is rotated relative to each other. When the laser power at the back end of the first polarization-maintaining isolator (5) and the second polarization-maintaining isolator (6) reaches the maximum value, the polarization alignment is completed. At this time, the dual linear polarization of the distributed feedback fiber laser is aligned with the fast axis and slow axis of the polarization-maintaining optical path composed of the polarization-maintaining wavelength division multiplexer (3) and the polarization-maintaining polarization beam splitter (4).
7. The orthogonal polarization beam splitting and polarization-maintaining distributed feedback fiber laser according to claim 3, characterized in that: The rare earth-doped optical fiber includes any one of erbium-doped optical fiber, ytterbium-doped optical fiber, or thulium-doped optical fiber.