Laser intensity low-pass filtering method and device

Abstract

The invention discloses a laser intensity low-pass filtering method and device, and the method comprises the steps: enabling an input laser to be connected to an energy transmission optical fiber through determining the length range of the energy transmission optical fiber capable of enabling an output light field to be stable, and enabling the optical fiber length of the energy transmission optical fiber to be within the length range of the energy transmission optical fiber capable of enabling the output light field to be stable. High-intensity signals in traditional multi-longitudinal-mode fiber laser can be converted through the Raman effect, and therefore the effect of intensity low-pass filtering is achieved. According to the invention, the purpose of effectively filtering the high-intensity part of the light wave signal is achieved, the method is relatively suitable for scenes with high requirements on the distribution uniformity of laser intensity, and a new solution is provided for related scientific research fields and engineering application.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of fiber laser, in particular to a laser intensity low-pass filtering method and device. Background Art

[0002] The laser generated by a traditional laser oscillator usually contains a large number of longitudinal mode components, which are prone to phenomena such as self-pulsation and partial mode locking, thus forming a time-domain component with a high peak power. From the perspective of time-domain intensity statistics, at this time, the intensity probability density distribution of the laser is relatively wide and contains components far higher than the average power. Due to the large power density of this part of the laser, it is extremely easy to induce the generation of nonlinear effects, which has become an important limitation in some high-power laser generation and application fields.

[0003] One solution is to use a time-domain stable single-frequency laser, which is further amplified after the spectrum is broadened by a certain phase modulation. However, for this high-power laser generation scheme, the system structure is complex and the cost is relatively high.

[0004] Another solution is to perform filtering processing on the laser output time domain. However, filtering the laser time-domain signal is more difficult than filtering electrical signals. The main reason is the lack of high-speed execution devices that match the optical wave frequency. Therefore, there are few direct filtering methods for near-infrared laser time-domain signals at present. Summary of the Invention

[0005] In view of the requirement of the seed source of the high-power laser amplifier for high concentration of time-domain intensity and the lack of existing laser time-domain filtering technology, the present invention proposes a laser intensity low-pass filtering method and device.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: On the one hand, the present invention provides a laser intensity low-pass filtering method, including: Determine the time-domain signal of the input laser; Obtain the corresponding input optical field based on the time-domain signal of the input laser; Based on the calculated input optical field, use the bidirectional nonlinear Schrödinger equation to calculate the output optical field after the input optical field is transmitted through different lengths of energy transfer fibers; Judge whether the output optical field is stable based on the output optical field situation after the input optical field is transmitted through different lengths of energy transfer fibers. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through a certain length of energy transfer fiber, it is determined that the length of the corresponding energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable; Connect the input laser to the energy transfer fiber, and the length of the energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable. Convert the high-intensity signal in the input laser through the Raman effect, so as to achieve the purpose of low-pass filtering.

[0007] On the other hand, a laser intensity low-pass filtering device is provided, which includes an input fiber laser light source and an energy transmission fiber of a certain length. The input fiber laser light source is connected to the energy transmission fiber. The input fiber laser light source is used to generate input laser. The input laser is input into the energy transmission fiber of a certain length. Through the transmission of the energy transmission fiber of a certain length, the purpose of low-pass filtering is achieved. The length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable, and is determined through the following steps: Determine the time-domain signal of the input laser; Obtain the corresponding input optical field based on the time-domain signal of the input laser; Based on the calculated input optical field, use the bidirectional nonlinear Schrödinger equation to calculate the output optical field after the input optical field is transmitted through different lengths of the energy transmission fiber; Based on the output optical field situation after the input optical field is transmitted through the energy transmission fiber of different lengths, determine whether the output optical field is stable. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through the energy transmission fiber of a certain length, it is determined that the corresponding length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable.

[0008] Compared with the prior art, the technical effects of the present invention are as follows: By determining the length range of the energy transmission fiber that can make the output optical field stable, the present invention connects the input laser to the energy transmission fiber with the length of the energy transmission fiber that can make the output optical field stable, and can convert the high-intensity signal in the input laser through the Raman effect, so as to achieve the effect of intensity low-pass filtering. The present invention solves the purpose of effectively filtering the high-intensity part of the optical wave signal, and is more suitable for scenarios with high requirements for the uniformity of the laser intensity distribution, providing a new solution for related scientific research fields and engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0010] Figure 1 is a schematic structural diagram of a laser intensity low-pass filtering device in an embodiment; Figure 2 is a schematic diagram of the input time-domain signal in an embodiment; Figure 3 is based on Figure 2 the schematic diagram of the output time-domain signal after filtering by the laser intensity low-pass filtering device of the time-domain signal shown; Figure 4 is based onFigure 2 Probability density distribution diagram of the time-domain signal shown after being filtered by the laser intensity low-pass filtering device; Markings in the figure: 1. Input fiber laser light source, 2. Energy transmission fiber, 3. Filtering device, 4. Stripping port, 5. Isolation device. Specific implementation mode

[0011] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0012] In one embodiment, a laser intensity low-pass filtering method is provided, including: Determine the time-domain signal of the input laser; Obtain the corresponding input optical field based on the time-domain signal of the input laser; Based on the calculated input optical field, use the bidirectional nonlinear Schrödinger equation to calculate the output optical field after the input optical field is transmitted through different lengths of the energy transmission fiber; Based on the output optical field situation after the input optical field is transmitted through different lengths of the energy transmission fiber, determine whether the output optical field is stable. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through a certain length of the energy transmission fiber, then determine that the corresponding length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable; Connect the input laser to the energy transmission fiber, where the length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable, and convert the high-intensity signal in the input laser through the Raman effect, so as to achieve the purpose of low-pass filtering.

[0013] Obtain the time-domain signal of the input laser S ( t ), and then preprocess the time-domain signal of the input laser S ( t ): including normalizing the detected time-domain signal of the input laser S ( t ) and then multiplying it by the average power of the input laser P 0, dividing by the core area of the energy transmission fiber (the core radius of the energy transmission fiber is ), then taking the square root, and then performing interpolation processing to make its data interval meet the requirements of subsequent calculations, and using this as the amplitude term of the input optical field. Finally, add specific phase noise , such as Gaussian random noise, as the input optical field for calculation (that is, the optical field at the starting position of the energy transmission fiber ); ;

[0014] wherein is the time-domain signal of the input laser, is the average power of the input laser, is the core radius of the energy transmission fiber, represents the phase noise.

[0015] Based on the calculated input optical field, using the bidirectional nonlinear Schrödinger equation, calculate the output optical field after the input optical field is transmitted through different lengths of the energy transmission fiber A ( L,t ).

[0016] The bidirectional nonlinear Schrödinger equation is as follows:

[0017] wherein, A ( z,t ) is the envelope of the optical field. The superscripts "+" and "-" respectively represent the forward-propagating and backward-propagating light, and the subscripts "p" and "s" respectively represent the pump wave and the Raman Stokes light. is the group velocity; β 2 is the second-order dispersion coefficient; α is the loss coefficient; γ is the nonlinear Kerr coefficient; is the Raman gain coefficient; ε is the Rayleigh backscattering coefficient.

[0018] Based on the output optical field situation after the input optical field is transmitted through different lengths of the energy transmission fiber, determine whether the output optical field is stable. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through a certain length of the energy transmission fiber, then determine that the corresponding length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable. In this way, the available range of the length of the energy transmission fiber can be obtained.

[0019] The input laser is input into the energy transmission fiber, and the fiber length of the energy transmission fiber is within the available range of the length of the energy transmission fiber to achieve the purpose of low-pass filtering.

[0020] In another embodiment, a laser intensity low-pass filtering device is provided, which includes an input fiber laser light source and a certain length of energy transmission fiber. The input fiber laser light source is connected to the energy transmission fiber. The input fiber laser light source is used to generate an input laser. The input laser is input into a certain length of the energy transmission fiber, and through the transmission of a certain length of the energy transmission fiber, the purpose of low-pass filtering is achieved. The length of the energy transmission fiber is the length of the energy transmission fiber that can make the output optical field stable, and is determined by the following steps: Determine the time-domain signal of the input laser; Obtaining a corresponding input light field based on a time domain signal of an input laser; Based on the input light field, the output light field after the input light field is transmitted through different energy transmission fiber lengths is calculated using the bidirectional nonlinear Schrödinger equation. Based on the output light field of the input light field after being transmitted through different lengths of the energy transmission optical fiber, it is judged whether the output light field is stable. If there is no self-pulse in the output light field time domain after the input light field is transmitted through a certain length of the energy transmission optical fiber, the corresponding energy transmission optical fiber length is determined to be the energy transmission optical fiber length that can stabilize the output light field. The length of the energy transmission optical fiber in the laser intensity low-pass filter device is selected to be the energy transmission optical fiber length that can stabilize the output light field, and the high-intensity signal in the input laser is converted through the Raman effect, thereby achieving the purpose of low-pass filtering.

[0021] Reference Figure 1 The laser intensity low-pass filtering device in one embodiment includes an input fiber laser light source 1, an energy transmission fiber 2, a filter device 3, a stripping port 4, and an isolator 5. The input fiber laser light source 1 is connected to the energy transmission fiber 2, the energy transmission fiber 2 is connected to the filter device 3, and the filter device 3 is connected to the isolation device 5 for output. The length of the energy transmission fiber 2 is selected to stabilize the output light field, and the high-intensity signal in the input laser is converted through the Raman effect, thereby achieving the purpose of low-pass filtering. The length of the energy transmission fiber 2 is determined according to the method provided in the above embodiment, which will not be repeated here.

[0022] The filter device 3 has the function of separating the long wavelength laser generated by the Raman scattering effect from the input laser, and its splitting ratio is greater than 20dB, and the fiber size matches the energy transmission fiber. The filter device 3 has a stripping port 4, which is used to export the Stokes light generated by the Raman effect, and its end cap feedback is very small, and the reflectivity is less than 10 -4 .

[0023] The input fiber laser light source 1 is a laser light source output by a fiber pigtail, and the time domain signal includes pulses with different intensity distributions.

[0024] The energy transmission optical fiber 2 adopts large mode field germanium-doped optical fiber, which is a passive energy transmission optical fiber. Its core size matches the input optical fiber laser system. The length of the energy transmission optical fiber is determined according to the method provided in the above embodiment and will not be repeated here.

[0025] The function of the isolation device 5 is to reduce the subsequent output of the signal laser or to generate feedback when connected to other systems. Its isolation is greater than 20 dB, and the fiber size matches the fiber of the filter device.

[0026] In this embodiment, by utilizing the fast response and intensity correlation characteristics of stimulated Raman scattering, the high-intensity components in the laser time-domain signal are filtered out, and then useful signal light is obtained through spectral filtering.

[0027] Based on the structure of the laser intensity low-pass filtering device provided below, a specific embodiment is proposed: Refer to Figure 1 As shown in Figure 2 , which is a schematic diagram of the input time-domain signal. The central wavelength of the input fiber laser source 1 is 1070 nm, the output fiber is a 10 / 125 μm double-clad fiber, and the average power is 150 W. The fiber length of the energy transfer fiber 2 is determined according to the method provided in the above embodiment. Specifically, when the calculated energy transfer fiber length is 200 m, a better filtering effect can be achieved for the output time-domain signal. Therefore, the energy transfer fiber length is set to 200 m. The filtering device 3 is a wavelength division multiplexer (WDM). The input fiber is a 10 / 125 μm double-clad fiber. The optical transmission spectral range of the output fiber is <1100 nm, and the optical transmission spectral range of the stripping port 4 is ≥1100 nm. Anti-feedback treatment is performed on the output end of the stripping port 4, such as cutting an 8° bevel. The passing wavelength of the isolation device 5 is 1070 nm, the optical transmission 3 dB bandwidth is ±10 nm, the isolation degree is 22 dB, and the fiber type is a 10 / 125 μm double-clad fiber. Using the above structure, the time-domain characteristics of the output signal after the time-domain signal is filtered by the laser intensity low-pass filtering device can be obtained as shown in Figure 3 shown. Figure 4 Based on Figure 2 As shown in the probability density distribution diagram of the time-domain signal after being filtered by the laser intensity low-pass filtering device, after filtering, the high-intensity signals in the time-domain signal can be better filtered out, thereby achieving the effect of time-domain filtering.

[0028] Matters not covered in this invention are well-known technologies.

[0029] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0030] The above-described embodiments only represent several implementation manners of this application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application should be subject to the appended claims.

[0031] ​​The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for low-pass filtering of laser intensity, characterized in that, Including: Determine the time-domain signal of the input laser; Obtain the corresponding input optical field based on the time-domain signal of the input laser; Based on the calculated input optical field, use the bidirectional nonlinear Schrödinger equation to calculate the output optical field after the input optical field is transmitted through different lengths of energy transfer fibers; Judge whether the output optical field is stable based on the output optical field conditions after the input optical field is transmitted through different lengths of energy transfer fibers. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through a certain length of energy transfer fiber, it is determined that the corresponding length of the energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable; Connect the input laser to the energy transfer fiber, and the length of the energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable. Convert the high-intensity signal in the input laser through the Raman effect, so as to achieve the purpose of low-pass filtering.

2. The laser intensity low-pass filtering method according to claim 1, wherein Obtain the corresponding input optical field based on the time-domain signal of the input laser , as follows: ； wherein is the time-domain signal of the input laser, is the average power of the input laser, is the core radius of the energy transmission fiber, represents phase noise.

3. The laser intensity low-pass filtering method according to claim 2, wherein The phase noise adopts Gaussian random noise.

4. Laser intensity low-pass filtering device, characterized in that, Including an input fiber laser light source and a certain length of energy transfer fiber. The input fiber laser light source is connected to the energy transfer fiber. The input fiber laser light source is used to generate the input laser. The input laser is input into a certain length of energy transfer fiber and transmitted through a certain length of energy transfer fiber to achieve the purpose of low-pass filtering. The length of the energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable, and is determined by the following steps: Determine the time-domain signal of the input laser; Obtain the corresponding input optical field based on the time-domain signal of the input laser; Based on the calculated input optical field, use the bidirectional nonlinear Schrödinger equation to calculate the output optical field after the input optical field is transmitted through different lengths of energy transfer fibers; Judge whether the output optical field is stable based on the output optical field conditions after the input optical field is transmitted through different lengths of energy transfer fibers. If there is no self-pulse in the time domain of the output optical field after the input optical field is transmitted through a certain length of energy transfer fiber, it is determined that the corresponding length of the energy transfer fiber is the length of the energy transfer fiber that can make the output optical field stable.

5. The laser intensity low-pass filtering device according to claim 4, characterized in that, Obtain the corresponding input optical field based on the time-domain signal of the input laser , as follows: ； wherein is the time-domain signal of the input laser, is the average power of the input laser, is the core radius of the energy transmission optical fiber, represents phase noise.

6. The laser intensity low-pass filtering device according to claim 5, characterized in that The phase noise adopts Gaussian random noise.

7. The low-pass filtering device for laser intensity according to claim 4 or 5 or 6, characterized in that, It also includes a filtering device, a stripping port, and an isolator. The input fiber laser light source is connected to the energy transfer fiber, the energy transfer fiber is connected to the filtering device, and the filtering device is connected to the isolation device and then outputs.

8. The laser intensity low-pass filtering device according to claim 7, wherein, The filtering device is used to separate the long-wavelength laser generated by the Raman scattering effect from the input laser, and its splitting ratio is greater than 20 dB, and the fiber size matches that of the energy transfer fiber.

9. The laser intensity low-pass filtering device according to claim 8, characterized in that, The filtering device has a stripping port, which exports the Stokes light generated by the Raman effect, and the reflectivity of its end cap is less than 10 -4 .

10. The laser intensity low-pass filtering device according to claim 8, characterized in that, The energy transfer fiber adopts a large-mode-field germanium-doped fiber, and its core size matches that of the input fiber laser light source.

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