Line-width-adjustable distributed feedback fiber laser

Abstract

The invention relates to the technical field of lasers, in particular to a line width adjustable distributed feedback fiber laser, which is characterized in that a phase shift grating and piezoelectric ceramics are mechanically coupled, and a signal generator is configured to output a voltage noise signal with adjustable amplitude or bandwidth to the piezoelectric ceramics so as to apply dynamic strain to the phase shift grating in the working process of laser, so that the phase shift grating can be subjected to dynamic strain; and the effective refractive index or pitch of the phase shift grating is changed, so that the line width of the output laser is broadened, and the controllable adjustment of the line width is realized. By applying a voltage noise signal to the piezoelectric ceramic, a dynamic pulling force can be applied to a phase-shift grating in the distributed feedback fiber laser to realize laser line width broadening of the distributed feedback fiber laser; the line width of the distributed feedback fiber laser can be controlled by applying voltage noise signals with different voltage amplitudes or different bandwidths to the piezoelectric ceramics.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular to a linewidth-adjustable distributed feedback fiber laser. Background Art

[0002] Single-frequency, narrow-linewidth fiber lasers are widely used in lidar, coherent optical communications, underwater acoustic detection, and high-energy laser links due to their narrow linewidth, low intensity noise, high efficiency, and compact structure. In high-power amplification scenarios, stimulated Brillouin scattering (SBS) needs to be suppressed by widening the signal linewidth. Currently, the main means of suppressing stimulated Brillouin scattering (SBS) is to phase or frequency modulate the single-frequency seed laser through a modulator to widen the linewidth of the signal laser, and then achieve power amplification through a fiber amplifier. However, this method has obvious limitations: the controllability and adjustment range of the linewidth are constrained, and sometimes multiple modulators need to be connected in series, which increases the system insertion loss and makes the overall structure more complex.

[0003] To this end, the present application designs a DFB fiber laser solution with a simple structure, low loss and continuously controllable linewidth to solve the above problems. Summary of the Invention

[0004] In order to overcome the deficiencies in the prior art, the present invention provides a distributed feedback fiber laser with adjustable linewidth.

[0005] A linewidth-adjustable distributed feedback fiber laser, comprising a distributed feedback fiber laser, characterized in that: The distributed feedback fiber laser is composed of a phase-shifted grating written in a rare earth ion-doped fiber to form a resonant cavity and provide gain. The single-mode pump is coupled into the phase-shifted grating via a wavelength division multiplexer, and the laser emitted by the phase-shifted grating is output via a fiber isolator. The phase-shift grating is mechanically coupled to a piezoelectric ceramic (PZT), and a signal generator is configured to output a voltage noise signal with adjustable amplitude or bandwidth to the piezoelectric ceramic, so as to apply dynamic strain to the phase-shift grating during laser operation, change the effective refractive index or grating pitch of the phase-shift grating, thereby widening the output laser linewidth and achieving controllable adjustment of the linewidth.

[0006] Furthermore, in order to better implement the present invention, the rare earth ion-doped optical fiber is an erbium-doped optical fiber, the single-mode pump is a 980nm pump, the wavelength division multiplexer is a 980 / 1550nm type, and the optical fiber isolator is a 1550nm isolator.

[0007] Furthermore, in order to better implement the present invention, the phase-shift grating is a π phase-shift grating inscribed on an erbium-doped optical fiber, and the π phase shift is located at the center of the grating or at 0.3 to 0.7 times the grating length.

[0008] Furthermore, in order to better implement the present invention, the piezoelectric ceramic is mechanically coupled to the optical fiber segment where the phase-shift grating is located by gluing; the model of the signal generator is UTG9404T.

[0009] Furthermore, in order to better realize the present invention, the linewidth-adjustable distributed feedback fiber laser also includes a linewidth testing system, which is sequentially connected to a fiber collimator, an adjustable attenuator, a 1×2 Mach-Zehnder fiber interferometer based on the delayed self-heterodyne method with a delayed fiber length of 55 km, a photodetector, a data acquisition card and a computer. The computer is used to perform Lorentz line fitting on the beat frequency power spectral density and calculate the half-maximum full width to obtain the linewidth.

[0010] Furthermore, in order to better implement the present invention, the signal generator increases the amplitude of the voltage noise to increase the line width when the bandwidth remains unchanged, and increases the bandwidth of the voltage noise to reduce the line width when the amplitude remains unchanged.

[0011] The beneficial effects of the present invention are: By applying a voltage noise signal to a piezoelectric ceramic, the present invention applies dynamic tension to the phase-shifted grating in a distributed feedback fiber laser, thereby broadening the laser linewidth of the distributed feedback fiber laser. By applying voltage noise signals of varying voltage amplitudes or bandwidths to the piezoelectric ceramic, the linewidth of the distributed feedback fiber laser can be controlled. The device of the present invention has a simple structure, continuous linewidth control, high laser coherence, and simple control. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic structural diagram of the linewidth-adjustable distributed feedback fiber laser of the present invention; Figure 2 Schematic diagram of the experimental device for linewidth control and testing of the laser of the present invention; Figure 3 The laser linewidth diagrams corresponding to voltage noise signals with a bandwidth of 50 MHz and amplitudes of 0 mV, 10 mV, 20 mV, 50 mV, 100 mV, 200 mV, and 300 mV, respectively, emitted by the UTG9404T signal generator of the present invention are shown in FIG. Figure 4 The laser linewidth diagrams corresponding to voltage noise signals with a bandwidth of 50 MHz and amplitudes of 300 mV, 500 mV, 600 mV, 800 mV, 1000 mV, 1500 mV, 2000 mV, and 5000 mV, respectively, emitted by the UTG9404T signal generator of the present invention are shown in FIG. Figure 5This is a graph of the laser linewidth variation generated by voltage noise signals with an applied bandwidth of 50 MHz and amplitudes of 0 mV, 10 mV, 20 mV, 50 mV, 100 mV, 200 mV, 300 mV, 500 mV, 600 mV, 800 mV, 1000 mV, 1500 mV, 2000 mV, and 5000 mV, in the present invention; Figure 6 These are the laser linewidth diagrams corresponding to voltage noise signals with an amplitude of 1V and bandwidths of 1MHz, 50MHz, 100MHz, 150MHz, and 200MHz, respectively, emitted by the UTG9404T signal generator of the present invention; Figure 7 These are the laser linewidth diagrams corresponding to voltage noise signals with an amplitude of 1V and bandwidths of 200MHz, 250MHz, 300MHz, 350MHz, and 400MHz, respectively, emitted by the UTG9404T signal generator of the present invention; Figure 8 This is a graph showing the laser linewidth variation when a voltage noise signal with an amplitude of 1 V and bandwidths of 1 MHz, 50 MHz, 100 MHz, 150 MHz, 200 MHz, 250 MHz, 300 MHz, 350 MHz, and 400 MHz is applied according to the present invention.

[0013] In the figure, 1. Signal generator, 2. Piezoelectric ceramics, 3. Phase-shift grating, 4. Wavelength division multiplexer, 5. Single-mode pump, 6. Fiber isolator, 7. Fiber collimator, 8. Adjustable attenuator, 9. Fiber interferometer, 10. Photodetector, 11. Data acquisition card, 12. Computer. DETAILED DESCRIPTION

[0014] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in a variety of different configurations.

[0015] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0016] Figures 1-8This is a specific embodiment of the present invention, a distributed feedback fiber laser with adjustable linewidth. The phase-shifted grating 3 is a π-phase-shifted grating directly written onto a section of rare-earth ion-doped optical fiber, forming a distributed feedback structure. The π phase shift is located at 0.4 times the grating length. The phase-shifted grating 3 on this rare-earth ion-doped optical fiber serves as both the laser resonator and the gain medium. The core operating principle of the distributed feedback fiber laser is as follows: pump light is emitted by a single-mode pump 5 and input to the phase-shifted grating 3 through the pump port of a wavelength division multiplexer 4. The laser light emitted by the phase-shifted grating 3 is then transmitted in reverse, passing through the signal port of the wavelength division multiplexer 4 and the fiber isolator 6, and then entering the linewidth measurement system for linewidth measurement. A signal generator 1 generates a voltage input to the piezoelectric ceramic 2, which applies tension to the phase-shifted grating 3. Signal generator 1 applies voltage noise signals of varying amplitudes or bandwidths to the piezoelectric ceramic 2, causing the laser linewidth to vary and achieve controllable linewidth.

[0017] The specific measurement process of this embodiment is as follows: Start the laser under test and the test equipment, and after 20 minutes of stable operation, perform the measurement. In the distributed feedback fiber laser, the single-mode pump 5 is a 980nm pump, the fiber isolator 6 is a 1550nm isolator, the wavelength division multiplexer 4 is a 980 / 1550nm wavelength division multiplexer, and the phase-shift grating 3 is a π phase-shift grating inscribed on the erbium-doped fiber. In this example, the π phase shift of the phase-shift grating is located at 0.4 times the grating length, and the generated laser light can be emitted from both ends of the grating. Alternatively, the π phase shift can be applied to other locations closer to the center of the grating, such as 0.3 to 0.7 times the grating length, to ensure that the laser meets the threshold condition. In this case, the laser power emitted from both ends of the grating will be significantly different. In linewidth measurement system 3, fiber interferometer 9 is a 1x2 Mach-Zehnder interferometer based on the delayed self-heterodyne method. Its delay fiber length is 55 km. The output of fiber interferometer 9 is the beat frequency optical signal of the laser being measured. A photodetector 10 converts the detected beat frequency optical signal of the laser being measured into an electrical signal that is input into a PCI-9812 data acquisition card 11. The digital signal from the PCI-9812 data acquisition card 11 is input into a computer 12, where it undergoes a fast Fourier transform (FFT) to generate the beat frequency power spectral density of the laser being measured. The peak value of the beat frequency power spectral density is found, and half of its corresponding full-width at half-maximum (FWHM) value on the frequency coordinate axis is taken to obtain the linewidth of the laser being measured. For more accurate calculation, a Lorentzian line profile fit can be performed on the power spectral density before FWHM measurement.

[0018] The computer 12 outputs the following Figure 3 Figure 4As shown in the results, it can be seen from the figure that the UTG9404T signal generator 1 emits a voltage noise signal with a bandwidth of 50MHz and amplitudes of 0mV, 10mV, 20mV, 50mV, 100mV, 200mV, 300mV, 500mV, 600mV, 800mV, 1000mV, 1500mV, 2000mV, and 5000mV, which is input into the piezoelectric ceramic 2, whose model is Core Mingtian PSt150 / 2×3 / 7L, to apply dynamic tension to the phase shift grating 3 to achieve the laser linewidth broadening of the distributed feedback fiber laser, which corresponds to <3kHz, 4kHz, 7kHz, 10kHz, 17kHz, 40kHz, 50kHz, 80kHz, 100kHz, 130kHz, 160kHz, 210kHz, 250kHz, and 300kHz. It can be seen that when the voltage amplitude is 0mV, that is, there is no external voltage, the original laser linewidth is <3kHz; when voltage noise of different amplitudes from 10mV to 5000mV is applied, the linewidth is 4kHz to 300kHz, and there is different degrees of broadening. The higher the voltage noise amplitude, the wider the linewidth.

[0019] like Figure 5 As shown, the UTG9404T signal generator 1 applies voltage noise signals of different amplitudes to obtain different line widths to achieve controllable line width.

[0020] Likewise, the computer 12 outputs the following Figure 6 Figure 7 The results shown in the figure show that when a UTG9404T signal generator 2 emits a 1V voltage noise signal with bandwidths of 1MHz, 50MHz, 100MHz, 150MHz, 200MHz, 250MHz, 300MHz, 350MHz, and 400MHz, it is input into a piezoelectric ceramic 2 (model: Core Tomorrow PSt150 / 2×3 / 7L). Dynamic tension is applied to the phase-shifted grating 3 to achieve the laser linewidth broadening of the distributed feedback fiber laser 1, which is 107kHz, 99kHz, 84kHz, 61kHz, 48kHz, 37kHz, 30kHz, 24kHz, and 19kHz, respectively. Applying a noise signal with a bandwidth range of 1MHz-400MHz will cause the laser linewidth to change, and the wider the bandwidth, the smaller the linewidth broadening.

[0021] like Figure 8 As shown, the UTG9404T signal generator 1 applies voltage noise signals of different bandwidths to obtain different line widths to achieve controllable line width.

[0022] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A linewidth-adjustable distributed feedback fiber laser, comprising a distributed feedback fiber laser, characterized in that: The distributed feedback fiber laser is composed of a phase shift grating (3) written on a rare earth ion doped optical fiber to form a distributed feedback resonant cavity and provide gain. A single-mode pump (5) is coupled into the phase shift grating (3) via a wavelength division multiplexer (4). The phase shift grating emits laser light which is output via an optical fiber isolator (6). The phase-shift grating (3) is mechanically coupled to the piezoelectric ceramic (2), and the signal generator (1) outputs a voltage noise signal with adjustable amplitude or bandwidth to the piezoelectric ceramic (2), so as to apply dynamic strain to the phase-shift grating (3) during laser operation, thereby changing the effective refractive index or grating pitch of the phase-shift grating (3), thereby widening the output laser line width and achieving controllable adjustment of the line width.

2. The linewidth-adjustable distributed feedback fiber laser according to claim 1, characterized in that: The rare earth ion-doped optical fiber is an erbium-doped optical fiber, the single-mode pump (5) is a 980nm pump, the wavelength division multiplexer (4) is a 980 / 1550nm type, and the optical fiber isolator (6) is a 1550nm isolator.

3. The linewidth-adjustable distributed feedback fiber laser according to claim 1, wherein: The phase-shift grating (3) is a π phase-shift grating inscribed on an erbium-doped optical fiber, and the π phase shift is located at the center of the grating or at 0.3 to 0.7 times the length of the grating.

4. The linewidth-adjustable distributed feedback fiber laser according to claim 1, wherein: The piezoelectric ceramic (2) is mechanically coupled to the optical fiber segment where the phase-shift grating (3) is located by gluing; the model of the signal generator (1) is UTG9404T.

5. The linewidth-adjustable distributed feedback fiber laser according to claim 1, wherein: The linewidth-adjustable distributed feedback fiber laser is tested for its laser linewidth by a linewidth test system. The linewidth test system is sequentially connected with a fiber collimator (7), an adjustable attenuator (8), a 1×2 Mach-Zehnder fiber interferometer (9) based on a delayed self-heterodyne method, an interferometer with a delayed fiber length of 55 km, a photodetector (10), a data acquisition card (11) and a computer (12). The computer (12) is used to perform Lorentz line fitting on the beat frequency power spectrum density and calculate the full width at half maximum to obtain the linewidth.

6. The linewidth-adjustable distributed feedback fiber laser according to claim 1, characterized in that: The signal generator (1) increases the amplitude of the voltage noise while keeping the bandwidth constant so as to increase the line width, and increases the bandwidth of the voltage noise while keeping the amplitude constant so as to reduce the line width.

Images