Tunable narrow-linewidth Raman fiber laser generation device and method

Abstract

The invention relates to a tunable narrow-linewidth Raman fiber laser generating device and method, the tunable narrow-linewidth Raman fiber laser generating device comprises a pump laser, a Raman fiber, a flat weak reflector and an adjustable narrow-band filter, the pump laser is respectively connected with the Raman fiber and the flat weak reflector, and the adjustable narrow-band filter is connected with the Raman fiber and the flat weak reflector. The light source is used for providing pump light and Stokes light for the Raman optical fiber and the flat weak reflector respectively; the Raman optical fiber is used for converting the pump light into Raman laser and improving the energy level of the Raman laser; the flat weak reflector is used for reflecting Stokes light generated in the Raman laser scattering process back to the Raman optical fiber; and the adjustable narrow-band filter is connected with the flat weak reflector and is used for receiving the Raman laser and providing sub-nanoscale tunable reflection laser to the flat weak reflector. A double-feedback mechanism combining flat weak reflection and narrow-band tunable filtering is provided, more control dimensions are provided for compressing the laser line width, and therefore the frequency doubling efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a tunable narrow-linewidth Raman fiber laser generating device and method. Background Art

[0002] The generation of wavelength-tunable visible light sources based on fiber laser frequency doubling is an indispensable tool in applications such as biological detection, laser display, and frequency measurement. Typical nonlinear crystals have a narrow phase matching bandwidth, and obtaining broadband tunable, sub-nanometer output spectrum linewidth fundamental frequency light sources is an important way to improve frequency doubling efficiency. However, there is a large wavelength gap in the output wavelength of rare-earth-doped fiber lasers, and gain cannot be obtained at all wavelengths. These wavelength gaps can be filled by cascaded Raman fiber lasers, in which rare-earth-doped fiber lasers are used as pumps. Due to stimulated Raman scattering, the photon energy is converted to the Stokes radiation peak with a lower frequency. Through such a cascade process, Stokes light can act as a pump, converting photon energy to a lower frequency, and can also directly provide output, filling the gap between the emission bands of different doped particles. However, the fiber grating reflection wavelength adjustment flexibility of the Raman fiber laser is limited, and the feedback is a fixed wavelength, so the output wavelength of the traditional Raman laser is fixed. In recent years, based on the Rayleigh scattering caused by the random inherent inhomogeneity in the optical fiber, random distributed feedback can be provided to form a random Raman laser resonant cavity. Using point feedback on one side of the random cavity to form a half-open structure can reduce the threshold of Stokes light generation, thereby achieving cascade conversion within a short fiber length. Using a wavelength-independent random feedback mechanism to tunable pump broadband point feedback can achieve wide wavelength tunable output. However, the characteristics of the broadband influence of Rayleigh scattering make it difficult to control the laser linewidth produced by this method, and sub-nanometer linewidth output cannot be achieved. Therefore, it is crucial to further compress the spectral linewidth without affecting the tunability of Raman laser wavelength. Summary of the invention

[0003] To solve the problems raised by the background technology, in a first aspect of the present invention, a tunable narrow-linewidth Raman fiber laser generating device is provided, comprising: a pump laser, a Raman fiber, a flat weak reflector and an adjustable narrowband filter, wherein the pump laser is connected to the Raman fiber and the flat weak reflector, respectively, and is used to provide pump light and Stokes light to the Raman fiber and the flat weak reflector, respectively; the Raman fiber is used to convert the pump light into Raman laser and to increase the energy level of the Raman laser; the flat weak reflector is used to reflect the Stokes light generated in the Raman laser scattering process back to the Raman fiber; the adjustable narrowband filter is connected to the flat weak reflector, and is used to receive the Raman laser and provide a sub-nanometer tunable reflected laser to the flat weak reflector.

[0004] In some embodiments of the present invention, the flat weak reflector includes: an input optical fiber for receiving Rayleigh scattering and Stokes light generated by the Raman optical fiber; and a weak reflection collimating lens for reflecting the cascade Raman laser at a preset reflectivity of 1%-5%.

[0005] Furthermore, the output surface of the weak reflection collimating lens is used to transmit all the cascade Raman lasers, and an angle no greater than 8° is formed between the transmission surface and the reference plane.

[0006] In some embodiments of the present invention, the flat weak reflector includes: an input optical fiber for receiving Rayleigh scattering and Stokes light generated by Raman optical fiber; a weak reflection filter for reflecting cascade Raman laser at a reflectivity of 1%-5%; and a fiber-coupled lens for receiving transmitted light, with an end face angle of no more than 8°.

[0007] Furthermore, the weak reflection filter includes at least one weak reflection filter, and the coating wavelengths of two end faces of the weak reflection filter cover the spectral band generated by the cascade Raman laser.

[0008] In the above embodiment, the pump laser includes: a first output end and a second output end, the first output end has a reflectivity less than 90% and is connected to the Raman optical fiber; the second output end has a reflectivity greater than 90% and is connected to a flat weak reflector.

[0009] The second aspect of the present invention provides a method for generating a tunable narrow-linewidth Raman fiber laser, comprising: a pump laser, a Raman fiber, a flat weak reflector and an adjustable narrowband filter, wherein the pump laser provides pump light and Stokes light to the Raman fiber and the flat weak reflector respectively; the Raman fiber converts the pump light into Raman laser and improves the energy level of the Raman laser; the flat weak reflector reflects the Stokes light generated in the Raman laser scattering process back to the Raman fiber; the adjustable narrowband filter receives the Raman laser and provides a sub-nanometer tunable reflected laser to the flat weak reflector.

[0010] The third aspect of the present invention provides an electronic device, comprising: one or more processors; a storage device for storing one or more programs, when the one or more programs are executed by the one or more processors, the one or more processors implement the tunable narrow-linewidth Raman fiber laser generation method provided in the second aspect of the present invention.

[0011] A fourth aspect of the present invention provides a computer-readable medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the method for generating a tunable narrow-linewidth Raman fiber laser provided in the second aspect of the present invention.

[0012] The beneficial effects of the present invention are: Based on the dual feedback mechanism, wavelength-tunable narrowband feedback is combined with wide-wavelength broadband flat feedback, and the combination of narrowband feedback linewidth compression and flat feedback provides the advantages of high-efficiency Raman conversion. This dual-feedback-assisted Raman laser generation mechanism can compress the linewidth without affecting the wavelength tuning ability of the Raman laser. At the same time, dual feedback with narrower filter bandwidth and higher feedback will provide more control dimensions for compressing the linewidth, thereby improving the frequency doubling efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the basic structure of a tunable narrow-linewidth Raman fiber laser generating device in some embodiments of the present invention; Figure 2 It is a schematic structural diagram of a flat weak reflector of a tunable narrow-linewidth Raman fiber laser generating device in some embodiments of the present invention; Figure 3 A schematic diagram of the working principle of the dual feedback mechanism in some embodiments of the present invention; Figure 4 Schematic diagram of the process of generating a tunable narrow-linewidth Raman fiber laser in some embodiments of the present invention; Figure 5 It is a schematic diagram of the structure of an electronic device in some embodiments of the present invention.

[0014] Reference numerals: Pump laser 101, Raman fiber 102, flat weak reflector 103, tunable narrowband filter 104; Input optical fiber 201, weak reflection collimating lens 202, weak reflection surface 202a, anti-reflection surface 202b; input optical fiber 203, weak reflection filter 204, weak reflection surface 204a, anti-reflection surface 204b, optical fiber coupling lens 205; The flat weak reflector 103 reflects a spectrum curve 301 , and the tunable narrowband filter 104 reflects a spectrum curve 302 . DETAILED DESCRIPTION

[0015] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0016] refer to Figure 1In a first aspect of the present invention, a tunable narrow-linewidth Raman fiber laser generating device is provided, comprising: a pump laser 101, a Raman fiber 102, a flat weak reflector 103 and a tunable narrowband filter 104, wherein the pump laser 101 is connected to the Raman fiber 102 and the flat weak reflector 103, respectively, and is used to provide pump light and Stokes light to the Raman fiber 102 and the flat weak reflector 103, respectively; the Raman fiber 102 is used to convert the pump light into Raman laser and improve the energy level of the Raman laser; the flat weak reflector 103 is used to reflect the Stokes light generated in the Raman laser scattering process back to the Raman fiber 102; the tunable narrowband filter 104 is connected to the flat weak reflector 103, and is used to receive the Raman laser and provide a sub-nanometer tunable reflected laser to the flat weak reflector 103.

[0017] In some embodiments of the present invention, the pump laser 101 includes: a first output end and a second output end, wherein the reflectivity of the first output end is less than 90% and is connected to the Raman fiber 102; the reflectivity of the second output end is greater than 90% and is connected to the flat weak reflector 103.

[0018] Specifically, the pump laser 101 is a standing wave cavity structure, that is, it consists of two output ends, wherein the low reflectivity end (reflectivity is less than 90%) is connected to the Raman fiber 102, and the high reflectivity end (reflectivity is greater than 90%) is connected to the flat weak reflector 103. The pump laser 101 uses rare earth doped fiber as a gain medium, and the low reflectivity end outputs high-power pump laser to provide basic pumping for the generation of Stokes light. The high reflectivity end of the pump laser 102 outputs laser light containing low-power Stokes light, which first passes through the flat weak reflector 103, whose reflectivity is less than 5%, and can reflect the Stokes light back to the Raman fiber 102. Under the action of Rayleigh scattering and stimulated Raman, a Stokes resonant cavity is formed, which reduces the threshold of Raman laser generation, and the reflector has a flat reflectivity curve, which can indiscriminately re-inject Stokes light into the Raman laser, providing broadband Raman feedback gain. The pump light and Stokes light transmitted and output by the flat reflection filter 103 are connected through the adjustable narrowband filter 104. The filter is a reflection filter with a sub-nanometer reflection bandwidth and a tunable reflection center wavelength. The Stokes light with the required bandwidth and center wavelength can be selected and fed back to the Raman laser to form a narrowband Raman resonant cavity, thereby realizing narrowband tunable Raman laser output.

[0019] It should be noted that two methods for realizing the flat weak reflector are provided in the present invention to more clearly express the concept of the present invention.

[0020] In a first implementation, the flat weak reflector includes: an input optical fiber for receiving Rayleigh scattering and Stokes light generated by the Raman optical fiber; and a weak reflection collimating lens for reflecting the cascade Raman laser at a preset reflectivity of 1%-5%.

[0021] Specifically, Figure 2 As shown, it includes an input optical fiber 201, a weak reflection collimating lens 202, a weak reflection surface 202a, and an anti-reflection surface 202b; an input optical fiber 203, a weak reflection filter 204, a weak reflection surface 204a, an anti-reflection surface 204b, and an optical fiber coupling lens 205. The Rayleigh scattering and Stokes light generated by the Raman optical fiber are directly injected into the weak reflection collimating lens 202 through the input optical fiber 201. In order to avoid the formation of FP cavity due to Fresnel reflection at the two end faces of the collimating lens 202 to affect the flatness of light feedback, the following structure is specially designed: the coating wavelength of the weak reflection end face 202a of the collimating lens 202 covers the spectral band generated by the cascade Raman laser, and the reflectivity is controlled within the range of 1%-5%, so as to avoid strong feedback affecting the output power and the laser time domain stability; the Rayleigh scattering and Stokes light transmitted through the weak reflection end face 202a are all transmitted and output by the anti-reflection surface 202b at the output end of the lens, and the transmission surface 202b is not a plane, but an angle of 8°, so as to avoid the generation of Fresnel reflection.

[0022] In the second implementation, a fully fiber-based flat weak reflector is provided, and the end face of the input fiber output 203 is cut at an angle of 8° to prevent Fresnel reflection from interfering with the weak reflection flatness. Then, through the weak reflection filter 204, the coating of the two end faces is the same as 202, that is, the coating wavelength of 204a covers the spectral band generated by the cascade Raman laser, and the reflectivity is controlled within the range of 1%-5%; the anti-reflection surface 204b is fully transmitted and output, and the transmission surface 202b is not a plane, but an angle of 8°. The light beam passing through the weak reflection filter 204 is received by the fiber coupling lens 205, and the lens end face angle is 8°.

[0023] refer to Figure 3 , the reflection spectrum curve 301 of the flat weak reflector 103, the reflection spectrum curve 302 of the adjustable narrowband filter 104, and the reflectivity curve 303 under the dual feedback mechanism.

[0024] Therefore, the principle of the dual feedback mechanism provided by the embodiment of the present invention is that the flat weak reflector 103 provides a lower reflectivity, as shown in 301, but can cover a wider band, and can reflect all Stokes spectrum components generated by the cascade Raman laser back into the Raman laser; combined with the adjustable narrowband filter 104 reflection spectrum curve 302, a reflection spectrum with a wavelength tuning range of several or tens of nanometers and a spectrum width less than 0.5nm is provided, which is superimposed to form a reflection spectrum curve 303 under the overall dual feedback mechanism. Obviously, the superimposed spectrum can generate strong narrowband filter feedback, compress the Raman laser line width, and reflect all backward Stokes light in the cascade Raman laser generation process back into the Raman resonant cavity, thereby improving the Raman laser conversion efficiency.

[0025] Example 2 refer to Figure 4 In a second aspect of the present invention, a method for generating a tunable narrow-linewidth Raman fiber laser is provided, comprising: a pump laser, a Raman fiber, a flat weak reflector and an adjustable narrowband filter, S100. The pump laser provides pump light and Stokes light to the Raman fiber and the flat weak reflector respectively; S200. The Raman fiber converts the pump light into Raman laser and improves the energy level of the Raman laser; S300. The flat weak reflector reflects the Stokes light generated in the Raman laser scattering process back to the Raman fiber; S400. The adjustable narrowband filter receives the Raman laser and provides a sub-nanometer tunable reflected laser to the flat weak reflector.

[0026] Further, in step S300, reflecting the Stokes light generated in the Raman laser scattering process back to the Raman optical fiber includes: receiving the Rayleigh scattering and Stokes light generated by the Raman optical fiber; reflecting the cascade Raman laser at a reflectivity of 1%-5%; and transmitting the transmitted Rayleigh scattering and Stokes light to the Raman optical fiber through the anti-reflection surface of the lens.

[0027] Example 3 refer to Figure 5 According to a third aspect of the present invention, an electronic device is provided, comprising: one or more processors; a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method according to the second aspect of the present invention.

[0028] The electronic device 500 may include a processing device (e.g., a central processing unit, a graphics processing unit, etc.) 501, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 502 or a program loaded from a storage device 508 into a random access memory (RAM) 503. In the RAM 503, various programs and data required for the operation of the electronic device 500 are also stored. The processing device 501, the ROM 502, and the RAM 503 are connected to each other via a bus 504. An input / output (I / O) interface 505 is also connected to the bus 504.

[0029] Typically, the following devices may be connected to the I / O interface 505: an input device 506 including, for example, a touch screen, a touch pad, a keyboard, a mouse, a camera, a microphone, an accelerometer, a gyroscope, etc.; an output device 507 including, for example, a liquid crystal display (LCD), a speaker, a vibrator, etc.; a storage device 508 including, for example, a hard disk, etc.; and a communication device 509. The communication device 509 may allow the electronic device 500 to communicate with other devices wirelessly or by wire to exchange data. Although Figure 5 The electronic device 500 is shown with various devices, but it should be understood that it is not required to implement or possess all the devices shown. More or fewer devices may be implemented or possessed instead. Figure 5 Each block shown in the figure may represent one device, or may represent multiple devices as required.

[0030] In particular, according to an embodiment of the present disclosure, the process described above with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present disclosure includes a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from the network through a communication device 509, or installed from a storage device 508, or installed from a ROM 502. When the computer program is executed by the processing device 501, the above functions defined in the method of the embodiment of the present disclosure are executed. It should be noted that the computer-readable medium described in the embodiment of the present disclosure can be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium can be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to, an electrical connection with one or more conductors, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In an embodiment of the present disclosure, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system, an apparatus, or a device. In an embodiment of the present disclosure, a computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, in which a computer-readable program code is carried. Such propagated data signals may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. A computer-readable signal medium may also be any computer-readable medium other than a computer-readable storage medium, which may send, propagate, or transmit a program for use by or in combination with an instruction execution system, an apparatus, or a device. The program code embodied on the computer readable medium may be transmitted using any appropriate medium, including but not limited to: wire, optical cable, RF (radio frequency), etc., or any suitable combination of the foregoing.

[0031] The computer-readable medium may be included in the electronic device, or may exist independently without being installed in the electronic device. The computer-readable medium carries one or more computer programs. When the one or more programs are executed by the electronic device, the electronic device: Computer program code for performing the operations of embodiments of the present disclosure may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages, such as Java, Smalltalk, C++, Python, and conventional procedural programming languages, such as "C" or similar programming languages. The program code may be executed entirely on a user's computer, partially on a user's computer, as a separate software package, partially on a user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0032] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present disclosure. In this regard, each box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A tunable narrow-linewidth Raman fiber laser generating device, comprising: A pump laser, a Raman optical fiber, a flat weak reflector and an adjustable narrowband filter, characterized in that: The pump laser is connected to the Raman optical fiber and the flat weak reflector, respectively, and is used to provide pump light and Stokes light to the Raman optical fiber and the flat weak reflector, respectively; The Raman optical fiber is used to convert the pump light into Raman laser and to increase the energy level of the Raman laser; The flat weak reflector is used to reflect the Stokes light generated in the Raman laser scattering process back to the Raman optical fiber; The adjustable narrowband filter is connected to the flat weak reflector and is used to receive the Raman laser and provide sub-nanometer-level tunable reflected laser to the flat weak reflector.

2. The tunable narrow-linewidth Raman fiber laser generating device according to claim 1, characterized in that: The flat weak reflector comprises: An input optical fiber, used for receiving Rayleigh scattered light and Stokes light generated by the Raman optical fiber; The weak reflection collimating lens is used to reflect the cascade Raman laser according to a preset reflectivity of 1%-5%.

3. The tunable narrow-linewidth Raman fiber laser generating device according to claim 2, characterized in that: The output surface of the weak reflection collimating lens is used to transmit all the cascade Raman lasers, and an angle no greater than 8° is formed between the transmission surface and the reference plane.

4. The tunable narrow-linewidth Raman fiber laser generating device according to claim 1, characterized in that: The flat weak reflector comprises: An input optical fiber, used for receiving Rayleigh scattered light and Stokes light generated by the Raman optical fiber; A weak reflection filter, used to reflect the cascade Raman laser at a reflectivity of 1%-5%; The optical fiber coupling lens is used to receive the transmitted light, and the end face angle is not greater than 8°.

5. The tunable narrow-linewidth Raman fiber laser generator according to claim 5, characterized in that: The weak reflection filter includes at least one weak reflection filter. The coating wavelengths of the two end faces of the weak reflection filter cover the spectral band generated by the cascade Raman laser.

6. The tunable narrow-linewidth Raman fiber laser generating device according to claim 1, characterized in that: The pump laser comprises: a first output end and a second output end, The reflectivity of the first output end is less than 90%, and is connected to the Raman optical fiber; The second output end has a reflectivity greater than 90% and is connected to a flat weak reflector.

7. A method for generating a tunable narrow-linewidth Raman fiber laser, comprising: A pump laser, a Raman optical fiber, a flat weak reflector and an adjustable narrowband filter, characterized in that: The pump laser provides pump light and Stokes light for the Raman fiber and the flat weak reflector respectively; Raman fiber converts pump light into Raman laser and increases the energy level of Raman laser; The flat weak reflector reflects the Stokes light generated during the Raman laser scattering back to the Raman fiber; The tunable narrowband filter transmits the received Raman laser light and provides sub-nanometer tunable reflected laser light to the weak reflector.

8. The method for generating tunable narrow-linewidth Raman fiber laser according to claim 7, characterized in that: The step of reflecting the Stokes light generated in the Raman laser scattering process back to the Raman optical fiber comprises: Receive Rayleigh scattered light and Stokes light generated by Raman fiber; Reflect the cascade Raman laser at a reflectivity of 1%-5%; The transmitted Rayleigh scattered and Stokes light are all transmitted to the Raman optical fiber through the anti-reflection surface of the lens.

9. An electronic device, comprising: one or more processors; A storage device for storing one or more programs, which, when executed by the one or more processors, enables the one or more processors to implement the tunable narrow-linewidth Raman fiber laser generation method as described in any one of claims 7 to 8.

10. A computer readable medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the method for generating a tunable narrow-linewidth Raman fiber laser according to any one of claims 7 to 8 is implemented.

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