High repetition rate figure-9 cavity fiber laser

Abstract

The application belongs to the technical field of lasers, and specifically provides a high-repetition-frequency 9-shaped cavity fiber laser, which comprises a wavelength division multiplexing coupler, a laser output assembly and a non-reciprocal phase shift component for generating a nonlinear phase shift; the non-reciprocal phase shift component comprises a phase shifter and a polarization maintaining fiber; the phase shifter is located on an outgoing light path of the wavelength division multiplexing coupler; an input end of the polarization maintaining fiber is located on an outgoing light path of the phase shifter, and an output end of the polarization maintaining fiber is connected with the wavelength division multiplexing coupler; the laser output assembly is connected with the wavelength division multiplexing coupler; the laser output assembly is used for reflecting part of input laser of the wavelength division multiplexing coupler back to the wavelength division multiplexing coupler and outputting the other part. The high-repetition-frequency 9-shaped cavity fiber laser can generate sufficient nonlinear phase shift for mode locking without a long passive optical fiber by integrating the polarization maintaining fiber region in the non-reciprocal phase shift section, and then the cavity length is shortened and the repetition frequency is improved, so that the fiber laser can output laser with high repetition frequency.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a high repetition rate 9-shaped cavity fiber laser. Background Technology

[0002] Ultrashort pulse fiber lasers, due to their compact structure, high stability, and excellent beam quality, have broad application prospects in precision machining, biomedical imaging, high-speed optical communication, lidar, and nonlinear frequency conversion. Among these, mode-locking technology is the core means to achieve ultrashort pulse output. Among various mode-locking structures, the "Figure-9 cavity" constructed from a nonlinear optical loop mirror (NALM) has attracted much attention due to its unique self-starting mode-locking capability, environmental stability, and structural simplicity.

[0003] Traditional figure-9 cavity fiber lasers typically consist of a long nonlinear passive fiber and a linear feedback arm containing a gain medium, resulting in a relatively long overall cavity length. Their mode-locking mechanism relies on the nonlinear phase shift difference accumulated by forward and reverse propagating pulses in the nonlinear fiber loop, achieving intensity modulation through interference to reach a mode-locked state. However, since increasing nonlinear amplification primarily involves increasing fiber length and reducing fiber mode area, the inherent characteristics of this structure lead to a significant problem in improving the repetition rate. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that it is difficult to improve the repetition rate of the 9-cavity fiber laser in the prior art.

[0005] To address this, the present invention provides a high repetition rate (PRF) 9-cavity fiber laser, comprising a wavelength division multiplexing (WDM) coupler, a laser output component, and a non-reciprocal phase shifting component for generating a nonlinear phase shift. The non-reciprocal phase shifting component includes a phase shifter and a tapered fiber. The phase shifter is located in the output optical path of the WDM coupler. The input end of the tapered fiber is located in the output optical path of the phase shifter, and the output end of the tapered fiber is connected to the WDM coupler. The laser output component is connected to the WDM coupler. The laser output component is used to reflect a portion of the laser input to the WDM coupler back to the WDM coupler and output the other portion.

[0006] Specifically, the differential of the diameter and length of the transition taper region of the aforementioned tapered optical fiber is less than 0.01, and the minimum diameter of the taper region is greater than half the wavelength of the laser.

[0007] Specifically, the aforementioned wavelength division multiplexing coupler includes a first collimator, a dichroic mirror, and a second collimator arranged sequentially along the optical path; the phase shifter is located on the reflected optical path of the dichroic mirror; the output end of the tapered optical fiber is connected to the first port of the second collimator; and the laser output component is connected to the second port of the second collimator.

[0008] Specifically, the lens surface of the aforementioned second collimator is coated with a beam-splitting film.

[0009] Specifically, the spectral dispersion ratio of the aforementioned spectrophotometer is 30-70%.

[0010] Specifically, the wavelength division multiplexing coupler also includes a half-wave plate; the half-wave plate is disposed between the dichroic mirror and the second collimator.

[0011] Specifically, the aforementioned laser output component includes a fiber Bragg grating; the fiber Bragg grating is connected to the wavelength division multiplexing coupler.

[0012] Specifically, the aforementioned laser output component also includes an optical fiber isolator; the optical fiber isolator is located on the transmission optical path of the fiber grating.

[0013] Specifically, the aforementioned high repetition rate 9-cavity fiber laser also includes a gain fiber; the gain fiber is located in the output optical path of the wavelength division multiplexing coupler; the laser generated by the gain fiber enters the phase shifter.

[0014] Specifically, the aforementioned high repetition rate 9-cavity fiber laser also includes a pump source; the wavelength division multiplexing coupler is located in the output optical path of the pump source.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] The high repetition rate 9-cavity fiber laser provided by this invention integrates a tapered fiber region in the non-reciprocal phase shift section, which can generate sufficient mode-locked nonlinear phase shift without a long passive fiber, thereby shortening the cavity length and increasing the repetition rate, thus enabling the fiber laser to output high repetition rate laser.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a high repetition rate 9-cavity fiber laser in one embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of a high repetition rate 9-cavity fiber laser in another embodiment of the present invention.

[0020] Figure reference numerals: 100, laser excitation beam splitter; 110, pump source; 120, wavelength division multiplexing coupler; 121, first collimator; 122, dichroic mirror; 123, half-wave plate; 124, second collimator; 130, gain fiber; 200, non-reciprocal phase shifter; 210, phase shifter; 220, tapered fiber; 300, laser output assembly; 310, fiber grating; 320, fiber isolator. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Although representative embodiments of the present invention have been described in detail, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the embodiments, but should be defined by the appended claims and their equivalents.

[0022] Reference Figure 1 This invention provides a high repetition rate (PRF) figure-9 cavity fiber laser, comprising a wavelength division multiplexing (WDM) coupler 120, a laser output component 300, and a non-reciprocal phase shifting component 200 for generating a nonlinear phase shift. The non-reciprocal phase shifting component 200 includes a phase shifter 210 and a tapered fiber 220. The phase shifter 210 is located in the output optical path of the WDM coupler 120. The input end of the tapered fiber 220 is located in the output optical path of the phase shifter 210, and the output end of the tapered fiber 220 is connected to the WDM coupler 120. The laser output component 300 is connected to the WDM coupler 120. The laser output component 300 is used to reflect a portion of the laser input to the WDM coupler 120 back to the WDM coupler 120, and output the other portion. By integrating tapered fiber 220 and phase shifter 210 into the non-reciprocal phase shift section to form a non-reciprocal phase shift component 200, the high nonlinearity of tapered fiber 220 is used to enhance the nonlinear phase shift efficiency. Combined with the non-reciprocity of phase shifter 210, the non-reciprocal phase is dynamically adjusted, thereby achieving a stable mode-locked state under low pump conditions. Furthermore, the phase shift difference generated by the laser emitted from wavelength division multiplexing coupler 120 after entering the non-reciprocal phase shift component 200 can be controlled. Sufficient nonlinear phase shift for mode-locking can be generated without a long passive fiber, thereby shortening the cavity length and increasing the repetition frequency.

[0023] The wavelength division multiplexing coupler 120 integrates the functions of a wavelength division multiplexer and a coupler, effectively shortening the length of the laser resonant cavity and increasing the output laser repetition frequency. However, NALM mode-locking requires asymmetry to provide sufficient phase shift difference. Therefore, in order to increase the repetition rate, shortening the passive fiber will prevent the laser from accumulating enough phase shift difference and thus fail to successfully lock the mode. Tapered fiber, due to its small core diameter, short length, and adjustable characteristics, shortens the length of the passive fiber, lowers the mode-locking threshold, and increases the repetition rate. It can achieve stable mode-locking of a high repetition rate figure-9 cavity under low pump conditions.

[0024] The tapered fiber 220 can be integrated into the device, with the length and diameter of the tapered region precisely controlled according to the repetition frequency and mode-locking threshold requirements. Specifically, to ensure stable transmission of optical signals in the tapered region, reduce loss, and maintain mode characteristics, the tapered transition of the fiber 220 must satisfy a differential of diameter and length of less than 0.01, and the minimum diameter of the tapered region must be greater than half the wavelength of the laser. By controlling the tapered slope to be less than 0.01, the diameter of the tapered region changes slowly with the length, achieving a "gradual transition" of the structure. This allows the optical field to "gradually adapt" to the size changes during transmission, avoiding energy reflection and mode disorder caused by abrupt structural changes, reducing insertion loss, and improving mode stability. The minimum diameter of the tapered region being greater than half the wavelength of the laser ensures effective confinement of light by the tapered region, preventing optical field leakage, reducing transmission loss, and ensuring device performance stability.

[0025] To amplify the energy of the optical signal, the high repetition rate 9-cavity fiber laser also includes a gain fiber 130; the gain fiber 130 is located in the output optical path of the wavelength division multiplexing coupler 120; the laser generated by the gain fiber 130 enters the phase shifter 210.

[0026] Furthermore, refer to Figure 2 The wavelength division multiplexing coupler 120 includes a first collimator 121, a dichroic mirror 122, and a second collimator 124 arranged sequentially along the optical path; the phase shifter 210 is located on the reflected optical path of the dichroic mirror 122; the output end of the tapered fiber 220 is connected to the first port of the second collimator 124. Figure 1-2 The laser output assembly 300 is connected to the second port (a) of the second collimator 124; Figure 1-2 The middle reflection end (b) is connected. The first collimator 121 is used to collimate the laser, the dichroic mirror 122 is used to reflect the pump laser and transmit the signal laser, and the second collimator 124 is used for collimation and beam splitting.

[0027] In one embodiment, the wavelength division multiplexing coupler 120 further includes a half-wave plate 123; the half-wave plate 123 is disposed between the dichroic mirror 122 and the second collimator 124. The half-wave plate 123 is used to adjust the polarization state.

[0028] After passing through the first collimator 121, the pump laser is reflected by the dichroic mirror 122 and enters the gain fiber 130. The reverse laser passes through the first collimator 121, the dichroic mirror 122, the half-wave plate 123 and the second collimator 124 in sequence, while the forward laser passes through the second collimator 124, the half-wave plate 123, the dichroic mirror 122 and the first collimator 121 in sequence.

[0029] Specifically, the surface of the second collimator 124 lens is coated with a beam-splitting film to split the laser beam; preferably, the beam-splitting ratio of the beam-splitting film is 30-70% to balance the requirements of the main and auxiliary optical paths and ensure stable ratio and low loss.

[0030] Furthermore, the laser output component 300 includes a fiber Bragg grating 310; the fiber Bragg grating 310 is connected to the wavelength division multiplexing coupler 120. The fiber Bragg grating 310 is preferably a polarization-maintaining chirped fiber Bragg grating 310. After the laser beam undergoes dispersion compensation through the fiber Bragg grating 310, a portion is output, and the other portion is reflected back into the wavelength division multiplexing coupler 120 for beam splitting and cycling.

[0031] In another embodiment, the laser output assembly 300 further includes an optical fiber isolator 320; the optical fiber isolator 320 is located in the transmission optical path of the fiber grating 310. The optical fiber isolator 320 is preferably a polarization-maintaining optical fiber isolator 320. After dispersion compensation by the fiber grating 310, part of the laser light enters the output of the optical fiber isolator 320, and the other part is reflected back into the wavelength division multiplexing coupler 120 for beam splitting and cycling.

[0032] Furthermore, the high repetition rate 9-cavity fiber laser also includes a pump source 110; the wavelength division multiplexing coupler 120 is located on the output optical path of the pump source 110.

[0033] In an optimized implementation, the high-repetition-rate 9-cavity fiber laser includes a laser excitation and splitting assembly 100 consisting of a pump source 110 (pump laser), a wavelength division multiplexing coupler 120, and a gain fiber 130. This assembly converts pump energy into laser pulse energy to achieve gain amplification. The wavelength division multiplexing coupler 120 is located in the output optical path of the pump source 110, and the gain fiber 130 is located in the output optical path of the wavelength division multiplexing coupler 120. The laser generated by the gain fiber 130 enters the non-reciprocal phase assembly, and the laser reflected from the laser output assembly 300 enters the wavelength division multiplexing coupler 120, where it is split and the cycle continues.

[0034] Optionally, the pump source 110 is a semiconductor laser diode, and the pump light power is controlled by adjusting the magnitude of its driving current; the gain fiber 130 is a quartz glass matrix doped with trace amounts of rare earth element ytterbium ions, used to pump the pump light, excite electrons to a high energy level to achieve population inversion, and generate stimulated emission to achieve amplification; the wavelength division multiplexing coupler 120 is used to transmit the pump laser and signal light to the gain fiber 130, providing conditions for optical amplification, and the wavelength division multiplexing coupler 120 also provides a coupler function, by placing a section of gain fiber asymmetrically on one side of the wavelength division multiplexing coupler 120, so that the light entering the coupler is split into two beams with opposite propagation directions, one of which is amplified by the gain fiber as soon as it enters the loop, and the other is amplified by the gain fiber when it leaves the loop. Due to the effect of self-phase modulation, the two beams of light propagating in opposite directions obtain different nonlinear phase shifts after one round trip in the NALM, and repeat cyclically, finally forming a stable mode-locked laser output.

[0035] Example 1: Refer to Figure 2 As shown, this embodiment provides a high repetition rate (PRR) 9-cavity fiber laser, including a laser excitation beam splitter 100, a non-reciprocal phase shifter 200, and a laser output component 300. The first end of the laser excitation beam splitter 100 is connected to the first end of the non-reciprocal phase shifter 200, the second end of the non-reciprocal phase shifter 200 is connected to the second end of the laser excitation beam splitter 100, and the third end of the laser excitation beam splitter 100 is connected to the laser output component 300. The laser excitation beam splitter 100 converts pump energy into laser pulse energy to achieve gain amplification. The non-reciprocal phase shifter is used to improve the repetition rate and self-starting performance of the fiber laser. The laser output component 300 is used for outputting laser light and dispersion compensation, and enables the fiber laser to operate in a closed-loop cycle.

[0036] Specifically, the laser-excited beam splitting assembly 100 includes a pump source 110, a wavelength division multiplexing coupler 120, and a gain fiber 130; the wavelength division multiplexing coupler 120 includes a first collimator 121, a dichroic mirror 122, a half-wave plate 123, and a second collimator 124 arranged sequentially along the optical path; the lens surface of the second collimator 124 is coated with a beam splitting film;

[0037] The non-reciprocal phase shifting component 200 includes a phase shifter 210 and a tapered fiber 220;

[0038] The laser output assembly 300 includes a polarization-maintaining chirped fiber grating 310 and a polarization-maintaining fiber isolator 320;

[0039] The first collimator 121 is located on the output optical path of the pump source 110, the gain fiber 130 is located on the reflection optical path of the dichroic mirror 122, and the laser generated by the gain fiber 130 enters the phase shifter 210; the input end of the tapered fiber 220 is located on the output optical path of the phase shifter 210, and the output end is connected to port a of the second collimator 124; the polarization-maintaining chirped fiber grating 310 is connected to the transmitting end b of the second collimator 124; and the polarization-maintaining fiber isolator 320 is located on the transmission optical path of the polarization-maintaining chirped fiber grating 310.

[0040] A pump source 110, a wavelength division multiplexing coupler 120, a gain fiber 130, a phase shifter 210, a tapered fiber 220, and a laser output assembly 300 form a NALM loop. The pump laser emitted from the pump source 110 passes through a first collimator 121 and is reflected by a dichroic mirror 122 into the gain fiber 130, exciting oscillating light that propagates bidirectionally along the fiber loop. The reverse laser sequentially passes through the first collimator 121, the dichroic mirror 122, the half-wave plate 123, and the second collimator 124, while the forward laser sequentially passes through the second collimator 124, the half-wave plate 123, the dichroic mirror 122, and the first collimator 121. After passing through the second collimator 124, the laser enters a polarization-maintaining chirped fiber grating 310 for dispersion compensation. A portion of the laser then enters the polarization-maintaining fiber isolator 320 for output, while the other portion is reflected back into the wavelength division multiplexing coupler 120 for beam splitting and cycling.

[0041] The laser emitted from the laser-excited beam splitter 100 enters the non-reciprocal phase shifter 200, generating a phase shift difference. Since the non-reciprocal phase shifter 200 is composed of a phase shifter 210 and a tapered fiber 220, it can generate a sufficient nonlinear phase shift for mode locking without a long passive fiber, thereby shortening the cavity length and increasing the repetition frequency. After passing through the non-reciprocal phase shifter 200, the laser enters the laser output 300, enabling the fiber laser to output a high repetition frequency laser. It can also effectively reduce the mode-locking threshold, increase the laser's lifetime and start-up performance.

[0042] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A high repetition rate 9-cavity fiber laser, characterized in that: The system includes a wavelength division multiplexing coupler (120), a laser output component, and a non-reciprocal phase shifting component (200) for generating a nonlinear phase shift. The non-reciprocal phase shifting component (200) includes a phase shifter (210) and a tapered fiber (220). The phase shifter (210) is located on the outgoing optical path of the wavelength division multiplexing coupler (120). The input end of the tapered fiber (220) is located on the outgoing optical path of the phase shifter (210), and the output end of the tapered fiber (220) is connected to the wavelength division multiplexing coupler (120). The laser output component is connected to the wavelength division multiplexing coupler (120). The laser output component is used to reflect a portion of the laser input to the wavelength division multiplexing coupler (120) back to the wavelength division multiplexing coupler (120) and output the other portion.

2. The high repetition rate 9-cavity fiber laser as described in claim 1, characterized in that: The differential of the diameter and length of the transition tapered region of the tapered fiber (220) is less than 0.01, and the minimum diameter of the tapered region is greater than half the wavelength of the laser.

3. The high repetition rate 9-cavity fiber laser as described in claim 1, characterized in that: The wavelength division multiplexing coupler (120) includes a first collimator (121), a dichroic mirror (122), and a second collimator (124) arranged sequentially along the optical path; the phase shifter (210) is located on the reflected optical path of the dichroic mirror (122); the output end of the tapered fiber (220) is connected to the first port of the second collimator (124); and the laser output component is connected to the second port of the second collimator (124).

4. The high repetition rate 9-cavity fiber laser as described in claim 3, characterized in that: The lens surface of the second collimator (124) is coated with a beam-splitting film.

5. The high repetition rate 9-cavity fiber laser as described in claim 4, characterized in that: The spectral dispersion ratio of the spectral film is 30-70%.

6. The high repetition rate 9-cavity fiber laser as described in claim 3, characterized in that: The wavelength division multiplexing coupler (120) further includes a half-wave plate (123); the half-wave plate (123) is disposed between the dichroic mirror (122) and the second collimator (124).

7. The high repetition rate 9-cavity fiber laser as described in claim 1, characterized in that: The laser output component includes a fiber optic grating (310); the fiber optic grating (310) is connected to the wavelength division multiplexing coupler (120).

8. The high repetition rate 9-cavity fiber laser as described in claim 7, characterized in that: The laser output assembly also includes an optical fiber isolator (320); the optical fiber isolator (320) is located on the transmission optical path of the fiber grating (310).

9. The high repetition rate 9-cavity fiber laser as described in claim 1, characterized in that: It also includes a gain fiber (130); the gain fiber (130) is located in the outgoing optical path of the wavelength division multiplexing coupler (120); the laser generated by the gain fiber (130) enters the phase shifter (210).

10. The high repetition rate 9-cavity fiber laser as described in claim 1, characterized in that: It also includes a pump source (110); the wavelength division multiplexing coupler (120) is located on the outgoing optical path of the pump source (110).

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