Nonlinear chirped fiber grating preparation structure based on speed regulation and control

Abstract

The invention discloses a nonlinear chirped fiber grating preparation structure based on speed regulation and control, and belongs to the field of laser technology and nonlinear optics. Comprising a light source displacement control scheme, a phase mask plate displacement control scheme and a grating inscribing and monitoring scheme. The optical, electrical and mechanical devices comprise a laser light source, a diaphragm, a plano-concave mirror, a plano-convex mirror, a cylindrical lens, an electric control displacement platform, a control program, a signal generator, a function editor, a precise displacement platform, an optical isolator, an optical circulator, a photosensitive optical fiber and an optical fiber analyzer. According to the non-linear chirp fiber grating preparation scheme based on speed regulation and control, the adjustable displacement speed is introduced while the uniform phase mask plate is used, flexible chirp regulation and control are achieved while simple and stable preparation is guaranteed, the preparation scheme of the non-linear chirp tube fiber grating is widened, and the preparation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of laser technology and nonlinear optics, and in particular relates to a nonlinear fiber grating preparation scheme based on speed regulation. Background Art

[0002] Fiber Bragg gratings have very important applications in the fields of fiber lasers, fiber communications and sensors due to their small size, low splicing loss and easy integration. In particular, chirped fiber Bragg gratings have made great progress in the field of high-energy fiber lasers due to their large dispersion and high integration.

[0003] At present, the preparation of fiber gratings mainly includes standing wave writing method, phase mask method and femtosecond point-by-point writing method. The standing wave writing method is to couple the laser from the end face into the photosensitive optical fiber, and after reflection by the reflector on the other end face of the optical fiber, the incident and reflected lasers in the optical fiber interfere to form a standing wave, so that the core refractive index of the photosensitive optical fiber changes periodically to form a grating. However, this method is easily affected by mechanical vibration or temperature drift, and it is not easy to make fiber gratings with complex interfaces, so it is not often used. The femtosecond point-by-point writing method uses a femtosecond laser as the light source, uses precision machinery to control the movement displacement of the laser, and writes the grating point by point. By controlling the movement speed of the laser, gratings of any period can be written, but the writing beam must be focused to a very dense point, so this method can only write gratings of shorter lengths. The phase mask method is to place a glass phase mask made by holographic interference in front of the optical fiber, and then pass 248nm ultraviolet light through the phase mask. Relying on the phase mask's function of suppressing the zero-order and enhancing the first-order diffraction, the ultraviolet light is diffracted onto the optical fiber after passing through the phase mask to form interference fringes, and a grating with a writing period of half the mask period is written. This method greatly simplifies the production process of fiber gratings and is currently the only way to achieve commercial mass production of fiber gratings. However, the grating parameters prepared by the phase mask method are limited by the structure of the phase mask, so it has the disadvantage of being inflexible and difficult to prepare special gratings.

[0004] In recent years, with the development of laser technology, several methods for preparing chirped fiber Bragg gratings have been proposed, such as: (1) using a chirped phase mask, (2) using a linear mask, but changing the exposure time along the grating length direction, (3) in the case of external stress gradient, making the uniform grating produce a change in the grating modulation period along the grating axis direction, thereby introducing the nonlinear chirp of the fiber Bragg grating. However, the chirped mask is expensive, and the chirp amount is fixed and cannot be flexibly tuned; changing the exposure time and stress is easily affected by factors such as vibration, making it difficult to achieve stable, emergent, and flexible nonlinear chirped fiber Bragg grating preparation.

[0005] In order to overcome these challenges, the present invention proposes an innovative nonlinear chirped grating preparation scheme, which applies a freely programmable movement speed to the light source and the mask while utilizing a uniform phase mask, aiming to achieve flexible and adjustable nonlinear chirped grating preparation, which has broad application prospects in the fields of nonlinear amplification, pulse shaping, etc. Summary of the invention

[0006] In order to solve the problem that the existing nonlinear chirped fiber grating is difficult to prepare flexibly at low cost, the present invention proposes a nonlinear chirped fiber grating writing scheme that uses a uniform phase mask and introduces an adjustable displacement speed. The light source in the scheme is an ultraviolet pulse laser, and a slit is placed in front of the phase mask to change the light source from a line light source to a point light source. The slit is fixed on an electrically controlled displacement platform, and the control program on the computer drives the moving speed and position of the electrically controlled displacement platform; the phase mask is fixed on a precision displacement platform, and the moving speed of the phase mask is controlled by the driving degree. The relative speed difference between the slit and the mask can change the Bragg reflection wavelength written at the current moment, and the nonlinear distribution of the relative speed difference realizes the introduction of nonlinear chirp.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A nonlinear chirped fiber grating preparation structure based on speed control includes a light source displacement control system, a phase mask displacement control system, and a grating writing and monitoring system.

[0009] The light source displacement control system includes: a first laser light source, a first aperture, a plano-concave mirror, a plano-convex mirror, a cylindrical lens, a second aperture, an electrically controlled displacement platform and a control program. After the laser is emitted from the first laser light source, the light beam is filtered by the first aperture, then expanded and shaped by the plano-concave mirror and the plano-convex mirror, and focused by the cylindrical lens. The second aperture is fixed on the electrically controlled displacement platform, and the displacement is controlled by the control program.

[0010] The phase mask template displacement system solution includes: a signal generator, a function editor, and a precision displacement platform. The first laser light source is connected to the signal generator, and the function editor is also connected to the signal generator; the signal generator outputs a signal connected to the precision displacement platform; the phase mask template is installed on the precision displacement platform to realize the displacement control of the phase mask template. The function editor can realize complex functions such as logarithms and exponentials, and the precision displacement platform can read these complex functions, so it can drive the precision displacement platform, that is, the phase mask template performs variable acceleration motion in addition to uniform motion and uniform variable speed motion.

[0011] The grating writing and monitoring system includes: a second laser light source, an optical isolator, an optical circulator, a photosensitive optical fiber, and a spectrum analyzer. The output end of the second laser light source is connected to the input end of the optical isolator, the output end of the optical isolator is connected to a port of the optical circulator, the second port of the optical circulator is connected to the photosensitive optical fiber, the photosensitive optical fiber is connected to the spectrum analyzer through an optical fiber jumper, and the third port of the optical circulator is also connected to the spectrum analyzer through an optical fiber jumper.

[0012] The present invention is based on the preparation of fiber Bragg grating by using a uniform phase mask plate in the ultraviolet exposure method, and controls the displacement of the ultraviolet light source and the phase mask plate to achieve chirped fiber grating writing. The light source is an ultraviolet pulse laser, and the control program on the computer drives the electric control displacement platform with the slit fixed to move at a uniform speed; the motion trajectory function of the precision displacement platform is edited by the function editor, and the trajectory function is loaded into the signal generator, and the signal generator outputs a signal to drive the precision displacement platform with the phase mask plate fixed to move with variable acceleration. The relative speed difference between the slit and the mask plate changes the Bragg reflection wavelength written at the current moment, and the nonlinear distribution of the relative speed difference realizes the introduction of nonlinear chirp.

[0013] Preferably, the first laser light source is an ultraviolet band laser, the laser type is an excimer pulse laser, and the output mode is spatial output.

[0014] Preferably, the electric displacement platform can move at a constant speed.

[0015] Preferably, the function editor that controls the precise displacement platform that fixes the phase mask can realize the editing of complex functions.

[0016] Preferably, the second laser light source is a broad spectrum light source, such as a supercontinuum light source or an ASE light source.

[0017] Preferably, the photosensitive optical fiber is a highly germanium-doped, boron-germanium co-doped or hydrogen-loaded optical fiber.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] The present invention provides a nonlinear chirped fiber grating preparation scheme based on speed control, which realizes the writing of various fiber gratings by adding movement to the light source and the phase mask and regulating the movement speed of the two. Wavelength tuning, linear chirp and nonlinear chirped fiber gratings can all be realized. The present invention has an obvious effect on realizing flexible and adjustable nonlinear chirped fiber gratings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of a nonlinear chirped fiber grating preparation solution based on speed control provided for the implementation of the present invention.

[0021] Figure 2It is a logical process diagram of the grating writing scheme of the present invention.

[0022] Among them, 1. the first laser light source, 2. the first aperture, 3. the plano-concave lens, 4. the plano-convex lens, 5. the cylindrical lens, 6. the second aperture, 7. the electrically-controlled displacement platform, 8. the precision displacement platform, 9. the second laser light source, 10. the optical isolator, 11. the optical circulator, 12. the photosensitive optical fiber, 13. the spectrum analyzer, 14. the signal generator, 15. the computer (including the electronically-controlled platform control software and the function editor). DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described below in conjunction with several drawings and embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form a new embodiment. The specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

[0024] like Figure 1 As shown, a preparation scheme of nonlinear chirped fiber grating based on speed control includes: a first laser light source 1, a first aperture 2, a plano-concave lens 3, a plano-convex lens 4, a cylindrical lens 5, a second aperture 6, an electrically controlled displacement platform 7, a precision displacement platform 8, a second laser light source 9, an optical isolator 10, an optical circulator 11, a photosensitive optical fiber 12, a spectrum analyzer 13, a signal generator 14, and a computer 15 (including electronically controlled platform control software and a function editor).

[0025] like Figure 2 As shown, the above laser scheme logic flow chart includes the following steps:

[0026] The second aperture movement speed is set by the electric displacement platform controller to achieve the light source displacement speed exposed on the photosensitive optical fiber. First, the motion function of the precision displacement platform is edited on the function editor on the computer and imported into the signal generator. The signal generator is set to external triggering. The output signal of the first light source is connected to the signal generator, and the output signal of the signal generator is connected to the precision displacement platform. When the first light source starts to output, the precision displacement platform starts to make the set movement. The introduction and regulation of chirp are achieved by changing the speeds of the two.

[0027] The present invention provides a nonlinear chirped fiber grating writing scheme with stable structure, high reproducibility and flexible adjustment. Compared with the traditional fiber grating preparation method, this nonlinear chirped fiber grating preparation scheme based on speed control does not require the customization of different nonlinear chirped phase masks. Through a set of displacement control schemes, fiber gratings with various chirp characteristics can be prepared, and stable batch production can be achieved. It further expands the nonlinear chirped fiber grating preparation scheme and reduces costs.

Claims

1. A nonlinear chirped fiber Bragg grating preparation structure based on speed control, characterized in that: Including light source displacement control system, phase mask displacement control system, grating writing and monitoring system; The light source displacement control system comprises: a first laser light source, a first aperture, a plano-concave mirror, a plano-convex mirror, a cylindrical lens, a second aperture, an electrically controlled displacement platform and a control program; after the laser is emitted from the first laser light source, the light beam is filtered by the first aperture, then expanded and shaped by the plano-concave mirror and the plano-convex mirror, and focused by the cylindrical lens; the second aperture is fixed on the electrically controlled displacement platform, and the displacement is controlled by the control program; The phase mask displacement control system comprises: a signal generator, a function editor, and a precision displacement platform; the first laser light source is connected to the signal generator, and the function editor is also connected to the signal generator; the signal generator outputs a signal connected to the precision displacement platform; the phase mask is mounted on the precision displacement platform to realize the displacement control of the phase mask; the function editor is a complex function capable of realizing logarithmic and exponential functions, and the precision displacement platform reads the complex function and drives the precision displacement platform, that is, the phase mask performs variable acceleration motion in addition to uniform motion and uniform variable speed motion; The grating writing and monitoring system includes: a second laser light source, an optical isolator, an optical circulator, a photosensitive optical fiber, and a spectrum analyzer; the output end of the second laser light source is connected to the input end of the optical isolator, the output end of the optical isolator is connected to one port of the optical circulator, the second port of the optical circulator is connected to the photosensitive optical fiber, the photosensitive optical fiber is connected to the spectrum analyzer through an optical fiber jumper, and the third port of the optical circulator is also connected to the spectrum analyzer through an optical fiber jumper.

2. The nonlinear chirped fiber grating preparation structure based on speed control according to claim 1, characterized in that: Based on the preparation of fiber Bragg grating using uniform phase mask by ultraviolet exposure method, chirped fiber grating is written by controlling the displacement of ultraviolet light source and phase mask; the light source is ultraviolet pulse laser, and the control program on the computer drives the electric control displacement platform with fixed slit to move at uniform speed; the motion trajectory function of the precision displacement platform is edited by function editor, and the trajectory function is loaded into signal generator, and the output signal of signal generator drives the precision displacement platform with fixed phase mask to move with variable acceleration; the relative speed difference between the slit and the mask changes the Bragg reflection wavelength written at the current moment, and the nonlinear distribution of relative speed difference realizes the introduction of nonlinear chirp.

3. The nonlinear chirped fiber grating preparation structure based on speed control according to claim 1, characterized in that: The first laser light source is an ultraviolet band laser, the laser type is an excimer pulse laser, and the output mode is spatial output.

4. The nonlinear chirped fiber Bragg grating preparation structure based on speed control according to claim 1, characterized in that: The electric displacement platform can move at a constant speed.

5. The nonlinear chirped fiber Bragg grating preparation structure based on speed control according to claim 1, characterized in that: The function editor that controls the precision displacement platform that fixes the phase mask can realize the editing of complex functions.

6. The nonlinear chirped fiber grating preparation structure based on speed control according to claim 1, characterized in that: The second laser light source is a broad spectrum light source, which is a supercontinuum light source or an ASE light source.

7. The structure for preparing a nonlinear chirped fiber Bragg grating based on speed control according to claim 1, characterized in that: Photosensitive optical fiber is highly doped germanium, boron-germanium co-doped or hydrogen-loaded optical fiber.

8. The nonlinear chirped fiber Bragg grating preparation structure based on speed control according to claim 1, characterized in that: The implementation process of this structure is as follows: the second aperture movement speed is set through the electric displacement platform controller to achieve the light source displacement speed exposed on the photosensitive optical fiber. The motion function of the precision displacement platform is first edited on the function editor on the computer and imported into the signal generator. The signal generator is set to external triggering. The output signal of the first light source is connected to the signal generator, and the output signal of the signal generator is connected to the precision displacement platform. When the first light source starts to output, the precision displacement platform starts to perform the set movement. The introduction and regulation of chirp are achieved by changing the speeds of the two.

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