Self-oscillating offset-filtered mode-locked laser and method of use

Abstract

The application discloses a self-oscillating offset filter mode-locked laser, a resonant cavity, and a resonant cavity which is connected with two pump sources and a fiber grating tuning device respectively. The laser can produce mode-locked pulses in the resonant cavity by adjusting the fiber grating tuning device to change the center wavelength and bandwidth of the first fiber grating reflection spectrum, and finally achieve the effect of stable and reliable self-oscillation. The device only needs to adjust the fiber grating tuning device to realize self-oscillation, and does not need to introduce external excitation, thereby simplifying the use condition, being suitable for various application occasions, and having the portable feature. The application discloses a use method of the self-oscillating offset filter mode-locked laser. The method is simple to operate and easy to adjust.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fiber lasers, and relates to a self-oscillating offset-filter mode-locked laser and a use method of the laser. BACKGROUND

[0002] In a communication system, due to the uncertainty of the starting condition and the saturable absorber parameter of a traditional fiber laser, the actual performance of the output laser is quite different from the expected result. When a traditional ultra-short laser pulse is amplified in an optical fiber, the phase of the pulse will be disordered due to the nonlinear effect after the pulse passes through a section of the optical fiber, so that the pulse cannot be compressed. In order to avoid these problems, a mode-locked laser is usually used.

[0003] The mode-locked laser is a laser formed by cascading two pulse regenerators based on the offset-filter effect. The principle of the mode-locked laser is to realize pulse regeneration by using the self-phase modulation effect to broaden the spectrum and a band-pass filter with a wavelength offset. The mode-locked laser is based on the self-phase modulation effect to broaden the spectrum and the offset-filter effect of the filter to realize mode locking, so as to realize the output of the ultra-short pulse. Since each wavelength is converted by the offset-filter and the nonlinear broadening, the pulses of different wavebands are synchronized and coherent, have good stability and anti-noise signal interference ability, allow a very large nonlinear phase shift, and can realize high-energy pulse output. Based on the above advantages, the mode-locked laser has stronger environmental stability, a more compact structure, and does not need to add a complex signal synchronization device, so it has a very broad application prospect.

[0004] However, the offset-filter mechanism of the mode-locked laser cannot realize self-oscillation in a normal state. In the prior art, a picosecond or femtosecond seed pulse from an additional laser is usually used to start, that is, an additional laser is used to introduce an external pulse to start. This starting method needs an external excitation signal and cannot realize self-oscillation, and the operation is complex, which causes many inconveniences in actual application. At the same time, some mode-locked lasers start mode locking by modulating the pump power, but this method has poor reliability. Therefore, how to design a stable and reliable mode-locked laser that can realize self-oscillation is a problem to be solved. SUMMARY

[0005] The application aims to provide a self-oscillating offset-filter mode-locked laser, which has the characteristics of stability, reliability and self-oscillation.

[0006] The second object of the application is to provide a use method of the self-oscillating offset-filter mode-locked laser.

[0007] The first technical solution of the present invention is a self-oscillating offset filter mode-locked laser, including a resonant cavity, wherein the resonant cavity is respectively connected to two pump sources and a fiber grating tuning device.

[0008] The invention is further characterized in that: the resonant cavity includes a first coupled-wavelength division multiplexer (CWDM), the signal output terminal of the first CWDM is sequentially connected to the d port of the first erbium-doped fiber and the first circulator, the e port of the first circulator is connected to the second fiber grating, the f port of the first circulator is connected to the signal input terminal of the second CWDM, the signal output terminal of the second CWDM is sequentially connected to the a port of the second erbium-doped fiber and the second circulator, the b port of the second circulator is connected to the first fiber grating, the c port of the second circulator is connected to the signal input terminal of the first CWDM, the first fiber grating is connected to a fiber grating tuning device, and the first CWDM and the second CWDM are respectively connected to a pump source.

[0009] All connections are made using single-mode fiber optic pigtails.

[0010] The gain coefficient of both the first and second erbium-doped fibers is 6dB / m, the length of both is 15m, the center wavelength of the second fiber grating is 1550nm, and the bandwidth is 4nm.

[0011] The fiber Bragg grating tuning device includes a fiber Bragg grating tuning device housing. A deformable cantilever beam is vertically mounted on the inner side wall of the fiber Bragg grating tuning device housing. A first fiber Bragg grating is bonded to the side wall of the deformable cantilever beam. The angle between the first fiber Bragg grating and the axis of the deformable cantilever beam is less than 90°. The free ends of the deformable cantilever beam are respectively connected to a vertical deformation application arm and a horizontal deformation application arm. Both the vertical deformation application arm and the horizontal deformation application arm are perpendicular to the axis of the deformable cantilever beam. The vertical deformation application arm is parallel to the plane where the first fiber Bragg grating is located, and the horizontal deformation application arm is perpendicular to the plane where the first fiber Bragg grating is located.

[0012] The first coupled-wavelength division multiplexer is also provided with a pump source input terminal j and a laser output terminal k, and the second coupled-wavelength division multiplexer is also provided with a pump source input terminal h and a laser output terminal g. The two pump sources are a first semiconductor laser and a second semiconductor laser, respectively. The first semiconductor laser is connected to the pump source input terminal j of the first coupled-wavelength division multiplexer, and the second semiconductor laser is connected to the pump source input terminal h of the second coupled-wavelength division multiplexer.

[0013] The first and second semiconductor lasers operate at a wavelength of 980nm and have a maximum power of 550MW. The first and second coupled-wavelength division multiplexers operate at wavelengths of 980nm and 1550nm respectively, and both have an output light ratio of 10%.

[0014] The second technical solution of the present invention is a method for using a self-oscillating offset filter mode-locked laser, which is implemented according to the following steps:

[0015] Step 1: Start the resonant cavity to generate continuous light within it;

[0016] Step 2: Apply deformation to the first fiber grating using a fiber grating tuning device to change the center wavelength and bandwidth of the first fiber grating;

[0017] Step 3: The first semiconductor laser and the second semiconductor laser continuously input energy into the two gain fiber segments in the resonant cavity, and finally output the target laser.

[0018] The second technical solution of the present invention is further characterized in that:

[0019] The specific process of starting the resonant cavity in step 1 is as follows:

[0020] Step 1.1: The pump light emitted by the first semiconductor laser enters the resonant cavity through the j port of the first coupled-wavelength division multiplexer and reaches the first erbium-doped fiber. In the first erbium-doped fiber, the pulse filtered by the first fiber grating is amplified and its spectrum is broadened. The broadened pulse enters the second fiber grating 11 through the d port of the first circulator for reflection filtering and is reflected back to the e port of the first circulator. The reflected light enters the main optical path through the f port of the first circulator.

[0021] Step 1.2: The pump light emitted by the second semiconductor laser enters the resonant cavity through the h port of the second coupled-wavelength division multiplexer and reaches the second erbium-doped fiber. In the second erbium-doped fiber, the pulse filtered by the second fiber grating is amplified and its spectrum broadened. The pulse reaches the a port of the second circulator, then enters the first fiber grating and is reflected and filtered, reflected back to the b port of the second circulator. The reflected light enters the main optical path through the c port of the second circulator, completing one cycle.

[0022] The specific operation of applying deformation to the fiber Bragg grating using the fiber Bragg grating tuning device in step 2 is as follows:

[0023] Step 2.1: Adjust the displacement of the vertical deformation application arm so that it acts on the deformable cantilever beam, causing a change in the bandwidth of the fiber grating;

[0024] Step 2.2: Adjust the displacement of the horizontal deformation application arm so that it acts on the deformable cantilever beam, causing a change in the center wavelength of the fiber grating.

[0025] The beneficial effects of this invention are:

[0026] This invention relates to a self-oscillating offset-filtered mode-locked laser. By adjusting the fiber grating tuning device, the center wavelength and bandwidth of the reflection spectrum of the first fiber grating are changed, ultimately generating a mode-locked pulse in the resonant cavity to achieve a stable, reliable, and self-oscillating effect. This device only requires adjustment of the fiber grating tuning device to achieve self-oscillation, eliminating the need for external pulses for startup, thus simplifying usage conditions. It is suitable for various applications and is portable. The components used in this device are all general-purpose, with simple structures, low cost, and are insensitive to the environment, exhibiting strong anti-interference capabilities and simple maintenance. The self-oscillating offset-filtered mode-locked laser of this invention is simple to operate and easy to adjust. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the self-oscillating offset filter mode-locked laser of the present invention;

[0028] Figure 2 This is a front view of the fiber grating tuning device for the self-oscillating offset filter mode-locked laser of the present invention;

[0029] Figure 3 This is a top view of the fiber grating tuning device of the self-oscillating offset filter mode-locked laser of the present invention;

[0030] Figure 4 This is a left view of the fiber grating tuning device of the self-oscillating offset filter mode-locked laser of the present invention.

[0031] In the figure, 1. First coupling-wavelength division multiplexer, 2. First erbium-doped fiber, 3. First circulator, 4. Second coupling-wavelength division multiplexer, 5. Second semiconductor laser, 6. Second erbium-doped fiber, 7. Second circulator, 8. First semiconductor laser, 9. Fiber Bragg grating tuning device, 10. First fiber Bragg grating, 11. Second fiber Bragg grating, 12. Housing of fiber Bragg grating tuning device, 13. Deformable cantilever beam, 14. Vertical deformation application arm, 15. Horizontal deformation application arm. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0033] This invention relates to a self-oscillating offset filter mode-locked laser, such as... Figure 1 As shown, it includes a resonant cavity, which is connected to two pump sources and a fiber optic grating tuning device 9. The two pump sources can respectively input energy to the two gain fiber segments in the resonant cavity to excite the generation of target laser. The fiber optic grating tuning device 9 can tune the center wavelength and bandwidth of the fiber optic grating.

[0034] The resonant cavity includes a first coupled-wavelength division multiplexer 1. The signal output terminal of the first coupled-wavelength division multiplexer 1 is sequentially connected to the d port of the first erbium-doped fiber 2 and the first circulator 3. The e port of the first circulator 3 is connected to the second fiber grating 11. The f port of the first circulator 3 is connected to the signal input terminal of the second coupled-wavelength division multiplexer 4. The signal output terminal of the second coupled-wavelength division multiplexer 4 is sequentially connected to the a port of the second erbium-doped fiber 6 and the second circulator 7. The b port of the second circulator 7 is connected to the first fiber grating 10. The c port of the second circulator 7 is connected to the signal input terminal of the first coupled-wavelength division multiplexer 1. The first circulator 3 and the second circulator 7 respectively introduce the corresponding laser light into the correspondingly connected first fiber grating 10 and second fiber grating 11, and introduce the reflected light from the corresponding first fiber grating 10 and second fiber grating 11 into the resonant cavity. The center wavelength and bandwidth of the second fiber grating 11 are fixed. The wavelength and bandwidth of the first fiber grating 10 are tuned by the fiber grating tuning device 9. When the reflection spectra of the first fiber grating 10 and the second fiber grating 11 overlap, continuous light can appear in the optical path. As the continuous light intensifies, the reflection spectrum of the first fiber grating 10 is gradually changed, so that the reflection spectra of the first fiber grating 10 and the second fiber grating 11 no longer overlap, and finally, Mamishchev laser is output.

[0035] The first fiber grating 10 is connected to the fiber grating tuning device 9. The first coupling-wavelength division multiplexer 1 and the second coupling-wavelength division multiplexer 4 are respectively connected to a pump source. The first coupling-wavelength division multiplexer 1 is also provided with a pump source input terminal j and a laser output terminal k. The second coupling-wavelength division multiplexer (4) is also provided with a pump source input terminal h and a laser output terminal g. The two pump sources are the first semiconductor laser 8 and the second semiconductor laser 5, respectively. The first semiconductor laser 8 is connected to the pump source input terminal j of the first coupling-wavelength division multiplexer 1, and the second semiconductor laser 5 is connected to the pump source input terminal h of the second coupling-wavelength division multiplexer 4. The first coupling-wavelength division multiplexer 1 and the second coupling-wavelength division multiplexer 4 respectively input the corresponding pump light, and at the same time output the laser light reflected back to the resonant cavity by the corresponding first fiber grating 10 and the second fiber grating 11 according to a certain ratio.

[0036] Among them, the first semiconductor laser 8 and the second semiconductor laser 5 operate at a wavelength of 980nm and have a maximum power of 550MW. The first coupled-wavelength division multiplexer 1 and the second coupled-wavelength division multiplexer 4 both operate at wavelengths of 980nm and 1550nm, respectively, and both have an output light ratio of 10%.

[0037] The first erbium-doped fiber 2 and the second erbium-doped fiber 6 both have a gain coefficient of 6dB / m and a length of 15m. The center wavelength of the second fiber grating 11 is 1550nm and the bandwidth is 4nm. When the first fiber grating 10 is not activated by the fiber grating tuning device, its center wavelength is 1550nm and its bandwidth is 4nm.

[0038] The structure of the fiber optic grating tuning device 9 is as follows: Figure 2 , Figure 3 and Figure 4 As shown, the first fiber Bragg grating 10 is connected to the fiber Bragg grating tuning device 9. The fiber Bragg grating tuning device 9 includes a fiber Bragg grating tuning device housing 12. A deformable cantilever beam 13 is vertically mounted on the inner side wall of the fiber Bragg grating tuning device housing 12. The first fiber Bragg grating 10 is bonded to the side wall of the deformable cantilever beam 13. The first fiber Bragg grating 10 and the axis of the deformable cantilever beam 13 have a certain angle, which is less than 90°. The free ends of the deformable cantilever beam 13 abut against a vertical deformation application arm 14 and a horizontal deformation application arm 15, respectively. All extension arms 15 are perpendicular to the axis of the deformable cantilever beam 13. The vertical deformation extension arm 14 is parallel to the plane containing the first fiber grating 10, and the horizontal deformation extension arm 15 is perpendicular to the plane containing the first fiber grating 10. The first fiber grating 10 is tightly bonded to the deformable cantilever beam 13 in the fiber grating tuning device 9. The deformable cantilever beam 13 is a cantilever beam with high fatigue resistance. Applying forces in different directions to the deformable cantilever beam 13 through the vertical deformation extension arm 14 and the horizontal deformation extension arm 15 causes the deformable cantilever beam 13 to deform in different directions. By controlling the deformation of the deformable cantilever beam 13, the deformation of the first fiber grating 10 is controlled, thereby changing the center wavelength and bandwidth of the first fiber grating 10.

[0039] The plane containing the first fiber grating 10 is the m-plane of the deformable cantilever beam 13. The plane perpendicular to the plane containing the first fiber grating 10 is the n-plane of the deformable cantilever beam 13. Adjusting the displacement of the vertical deformation application arm 14 so that it acts on the n-plane of the deformable cantilever beam 13 causes a change in the bandwidth of the first fiber grating 10. Adjusting the displacement of the horizontal deformation application arm 15 so that it acts on the plane parallel to the m-plane of the deformable cantilever beam 13 causes a change in the center wavelength of the first fiber grating 10.

[0040] This invention provides a method for using a self-oscillating offset filter mode-locked laser, which is implemented using the aforementioned self-oscillating offset filter mode-locked laser, specifically according to the following steps:

[0041] Step 1: Start the resonant cavity to generate continuous light within it;

[0042] Step 1.1: The pump light emitted by the first semiconductor laser 8 enters the resonant cavity through the j-port of the first coupled-wavelength division multiplexer 1 and reaches the first erbium-doped fiber 2. In the first erbium-doped fiber 2, the pulse filtered by the first fiber grating 10 is amplified and its spectrum broadened. The broadened pulse enters the second fiber grating 11 through the d-port of the first circulator 3 for reflection filtering and is reflected back to the e-port of the first circulator 3. The reflected light enters the main optical path through the f-port of the first circulator 3.

[0043] Step 1.2: The pump light emitted by the second semiconductor laser 5 enters the resonant cavity through the h port of the second coupling-wavelength division multiplexer 4 and reaches the second erbium-doped fiber 6. In the second erbium-doped fiber 6, the pulse filtered by the second fiber grating 11 is amplified and its spectrum broadened. The pulse reaches the a port of the second circulator 7, and then enters the first fiber grating 10 where it is reflected and filtered, and then reflected back to the b port of the second circulator 7. The reflected light enters the main optical path through the c port of the second circulator 7, completing one cycle.

[0044] Step 2: Apply deformation to the first fiber grating 10 through the fiber grating tuning device 9 to change the center wavelength and bandwidth of the first fiber grating 10;

[0045] Step 2.1: Adjust the displacement of the vertical deformation application arm 14 so that it acts on the n-plane of the deformable cantilever beam 13, causing a change in the bandwidth of the first fiber grating 10;

[0046] Step 2.2: Adjust the displacement of the horizontal deformation application arm 15 so that it acts on the parallel plane of the m-plane of the deformable cantilever beam 13, causing a change in the center wavelength of the first fiber grating 10.

[0047] As the center wavelength and bandwidth of the first fiber grating 10 change, the reflection spectra of the first fiber grating 10 and the second fiber grating 11 gradually change from completely overlapping to completely non-overlapping. In this case, only random pulses with sufficiently high peak power can generate enough spectral broadening to pass through the first fiber grating 10 and the second fiber grating 11, and then be selected from the background noise to generate mode-locked pulses in the resonant cavity.

[0048] Step 3: The first semiconductor laser 8 and the second semiconductor laser 5 continuously input energy into the two gain fiber segments in the resonant cavity, and finally output the target laser.

Claims

1. A self-oscillating offset-filtered mode-locked laser, characterized in that, Includes a resonant cavity, which is connected to two pump sources and a fiber grating tuning device (9). The resonant cavity includes a first coupled-wavelength division multiplexer (1), the signal output terminal of the first coupled-wavelength division multiplexer (1) is connected in sequence to the d port of the first erbium-doped fiber (2) and the first circulator (3), the e port of the first circulator (3) is connected to the second fiber grating (11), the f port of the first circulator (3) is connected to the signal input terminal of the second coupled-wavelength division multiplexer (4), the signal output terminal of the second coupled-wavelength division multiplexer (4) is connected in sequence to the a port of the second erbium-doped fiber (6) and the second circulator (7), the b port of the second circulator (7) is connected to the first fiber grating (10), the c port of the second circulator (7) is connected to the signal input terminal of the first coupled-wavelength division multiplexer (1), the first fiber grating (10) is connected to the fiber grating tuning device (9), and the first coupled-wavelength division multiplexer (1) and the second coupled-wavelength division multiplexer (4) are respectively connected to a pump source; The fiber Bragg grating tuning device (9) includes a fiber Bragg grating tuning device housing (12). A deformable cantilever beam (13) is vertically installed on the inner side wall of the fiber Bragg grating tuning device housing (12). A first fiber Bragg grating (10) is bonded to the side wall of the deformable cantilever beam (13). The angle between the first fiber Bragg grating (10) and the axis of the deformable cantilever beam (13) is less than 90°. The free ends of the deformable cantilever beam (13) are respectively connected to a vertical deformation application arm (14) and a horizontal deformation application arm (15). Both the vertical deformation application arm (14) and the horizontal deformation application arm (15) are perpendicular to the axis of the deformable cantilever beam (13). The vertical deformation application arm (14) is parallel to the plane where the first fiber Bragg grating (10) is located, and the horizontal deformation application arm (15) is perpendicular to the plane where the first fiber Bragg grating (10) is located.

2. The self-oscillating offset filter mode-locked laser according to claim 1, characterized in that, The gain coefficients of the first erbium-doped fiber (2) and the second erbium-doped fiber (6) are both 6dB / m and both have a length of 15m. The center wavelength of the second fiber grating (11) is 1550nm and the bandwidth is 4nm.

3. The self-oscillating offset filter mode-locked laser according to claim 1, characterized in that, The first coupled-wavelength division multiplexer (1) is also provided with a pump source input terminal j and a laser output terminal k, and the second coupled-wavelength division multiplexer (4) is also provided with a pump source input terminal h and a laser output terminal g. The two pump sources are a first semiconductor laser (8) and a second semiconductor laser (5). The first semiconductor laser (8) is connected to the pump source input terminal j of the first coupled-wavelength division multiplexer (1), and the second semiconductor laser (5) is connected to the pump source input terminal h of the second coupled-wavelength division multiplexer (4).

4. The self-oscillating offset filter mode-locked laser according to claim 3, characterized in that, The first semiconductor laser (8) and the second semiconductor laser (5) operate at a wavelength of 980nm and have a maximum power of 550MW. The first coupled-wavelength division multiplexer (1) and the second coupled-wavelength division multiplexer (4) operate at wavelengths of 980nm and 1550nm respectively, and the output light ratio is 10%.

5. A method for using a self-oscillating offset filter mode-locked laser, characterized in that, The self-oscillating offset filter mode-locked laser according to any one of claims 1-4 is implemented specifically according to the following steps: Step 1: Start the resonant cavity to generate continuous light within it; Step 2: Apply deformation to the first fiber grating (10) through the fiber grating tuning device (9) to change the center wavelength and bandwidth of the first fiber grating (10); Step 3: The first semiconductor laser (8) and the second semiconductor laser (5) continuously input energy into the two gain optical fibers in the resonant cavity, and finally output the target laser.

6. The method of using the self-oscillating offset filter mode-locked laser according to claim 5, characterized in that, The specific process of starting the resonant cavity in step 1 is as follows: Step 1.1: The pump light emitted by the first semiconductor laser (8) enters the resonant cavity through the j port of the first coupling-wavelength division multiplexer (1) and reaches the first erbium-doped fiber (2). In the first erbium-doped fiber (2), the pulse filtered by the first fiber grating (10) is amplified and the spectrum is broadened. The broadened pulse enters the second fiber grating (11) through the d port of the first circulator (3) for reflection filtering and is reflected back to the e port of the first circulator (3). The reflected light enters the main optical path through the f port of the first circulator (3). Step 1.2: The pump light emitted by the second semiconductor laser (5) enters the resonant cavity through the h port of the second coupling-wavelength division multiplexer (4) and reaches the second erbium-doped fiber (6). In the second erbium-doped fiber (6), the pulse filtered by the second fiber grating (11) is amplified and the spectrum is broadened. The pulse reaches the a port of the second circulator (7) and then enters the first fiber grating (10) for reflection and filtering. It is reflected back to the b port of the second circulator (7). The reflected light enters the main optical path through the c port of the second circulator (7) to complete one cycle.

7. The method of using the self-oscillating offset filter mode-locked laser according to claim 6, characterized in that, The specific operation of applying deformation to the fiber grating (10) through the fiber grating tuning device (9) in step 2 is as follows: Step 2.1: Adjust the displacement of the vertical deformation application arm (14) so ​​that it acts on the deformable cantilever beam (13), causing the bandwidth of the fiber optic grating (10) to change; Step 2.2: Adjust the displacement of the horizontal deformation application arm (15) so that it acts on the deformable cantilever beam (13), causing the center wavelength of the fiber optic grating (10) to change.

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