Pulsed fiber laser device

Abstract

The present invention relates to a pulse fiber laser device, comprising a laser seed light source emitting pulse signal light; a multimode pump laser emitting pump light; a low-doped erbium ytterbium double-clad active fiber, a multimode pump bridge, and a high-doped erbium ytterbium double-clad active fiber connected in sequence; the multimode pump bridge separates the pump light from the signal light; a high-reflection fiber grating filters and reflects the signal light; a low-reflection fiber grating reflects part of the signal light into the high-doped erbium ytterbium double-clad active fiber and amplifies it; a reflection grating reflects part of the pump light into the high-doped erbium ytterbium double-clad active fiber, and transmits the other part of the pump light into the low-doped erbium ytterbium double-clad active fiber. The pulse fiber laser device of the present invention is adopted, and the production time is shortened to half of the traditional pre-amplification double-stage solution, which greatly improves the production efficiency, reduces the labor cost of the laser, and greatly reduces the cost of components, is convenient for commercial batch use, and has ultra-high reliability.

Description

Technical Field

[0001] The present invention relates to the field of pulse fiber lasers, in particular to the field of master oscillator power amplified fiber lasers, and specifically refers to a pulse fiber laser device. Background Art

[0002] Pulse master oscillator power amplifier (MOPA) fiber lasers are widely used in laser radar, laser ranging, laser mapping and other fields due to their advantages such as high peak power and good beam quality. However, since the seed light source in the MOPA laser is usually directly modulated into nanosecond pulses by a circuit, the output power of its seed light is only about hundreds of picojoules. With such a low seed light power, if it is directly amplified by erbium-ytterbium co-doped double-clad fiber (EYDCF), it is very easy to produce a large amount of ASE and the amplification effect is not good. In addition, since the EYDCF has a very high absorption and radiation coefficient at 1530NM, the MOPA laser is very likely to cause the spontaneous emission light (ASE) power at 1530NM to increase and reduce the signal-to-noise ratio (OSNR) of the signal light under high-power pumping. On the other hand, the extremely high ASE energy density at 1530NM is very likely to cause the self-excitation effect of the ASE signal light, resulting in jitter of the spectrum and output light power.

[0003] In order to obtain high peak power and high signal-to-noise ratio, people usually use erbium-doped fiber amplifiers as the first stage of amplification. After the seed is amplified to a certain power, it is input into EYDCF for high-power amplification. Although this method can obtain high-quality laser output, the full set of EDFA fiber components and pump lasers are single-mode components, which have the disadvantages of high cost, large device size, and large number. It not only doubles the cost, but also directly affects the production efficiency and restricts mass production. In addition, more devices have brought great restrictions on reliability and compactness of equipment structure. This is contrary to the requirements of fiber lasers that require high output power and signal-to-noise ratio while meeting the requirements of high production efficiency, low cost, compact structure, and high reliability. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a pulse fiber laser device which meets the requirements of high production efficiency, low cost and compact structure.

[0005] In order to achieve the above object, the pulse fiber laser device of the present invention is as follows:

[0006] The pulse fiber laser device has the following main features:

[0007] A laser seed light source, used for emitting pulse signal light;

[0008] A multi-mode pump laser for emitting pump light;

[0009] A low-doped erbium-ytterbium double-clad active optical fiber connected to the laser seed light source and used to amplify the signal light;

[0010] A highly doped Er-Yb double-clad active optical fiber connected to the multi-mode pump laser for amplifying signal light;

[0011] A multimode pump bridge connected between the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, used for separating the pump light from the signal light;

[0012] A high-reflection fiber Bragg grating is connected to the highly doped erbium-ytterbium double-clad active optical fiber, and is used to filter the signal light and reflect the signal light into the highly doped erbium-ytterbium double-clad active optical fiber for re-amplification;

[0013] A low-reflection fiber Bragg grating is connected to the high-reflection fiber Bragg grating and the multi-mode pump laser, and is used to reflect part of the signal light into the highly doped erbium-ytterbium double-clad active optical fiber and amplify it;

[0014] The reflection grating is connected to the multimode pump bridge, the low-doped erbium ytterbium double-clad active optical fiber and the high-doped erbium ytterbium double-clad active optical fiber, and is used to reflect part of the pump light into the high-doped erbium ytterbium double-clad active optical fiber and transmit the other part of the pump light into the low-doped erbium ytterbium double-clad active optical fiber.

[0015] Preferably, the device also includes an optical circulator and a low-doped erbium-ytterbium double-clad active optical fiber, which are connected to the laser seed light source and the low-doped erbium-ytterbium double-clad active optical fiber, and are used to allow the signal light emitted by the laser seed light source to enter the active optical fiber and output the signal light returned from the active optical fiber.

[0016] Preferably, the device further comprises:

[0017] A separator, connected to the optical circulator, for separating signal light from noise light;

[0018] The output port is connected to the separator and serves as the output port of the laser.

[0019] Preferably, the device further comprises an optical fiber node connected to the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, and used for looping the optical fiber to prevent light leakage.

[0020] Preferably, the low-reflection fiber Bragg grating adopts a 6nm broadband grating.

[0021] Preferably, the high-reflection fiber grating and the low-reflection fiber grating are both arranged inside the core of the active optical fiber by laser direct etching.

[0022] Preferably, the pulse signal light emitted by the laser seed light source is 1550nm; the pump light emitted by the multi-mode pump laser is 940nm.

[0023] The pulse fiber laser device of the present invention can obtain ultra-high output power and spectral OSNR, avoiding the use of traditional EDFA as a two-stage structure of preamplifier + power amplifier. The fiber laser amplification design can be completed with a very simple optical path design scheme: only three passive optical devices are used in the optical path scheme. The extremely simple optical path structure shortens the production time of the fiber laser to half of the traditional preamplifier two-stage scheme, greatly improving production efficiency and reducing laser labor costs. The extremely simple optical path structure greatly reduces the component cost of the fiber laser, reducing the cost by more than half compared to traditional solutions. The laser can be integrated into an ultra-small structure, which is convenient for commercial mass use and has ultra-high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the pulse fiber laser device of the present invention.

[0025] Figure 2 It is a schematic diagram of the optical fiber structure of the pulsed optical fiber laser device of the present invention.

[0026] Figure 3 It is a schematic structural diagram of an embodiment of a pulse fiber laser device of the present invention.

[0027] Figure 4 This is an output power waveform diagram of the pulse fiber laser device of the present invention. DETAILED DESCRIPTION

[0028] In order to more clearly describe the technical content of the present invention, further description is given below in conjunction with specific embodiments.

[0029] The pulse fiber laser device of the present invention comprises:

[0030] A laser seed light source, used for emitting pulse signal light;

[0031] A multi-mode pump laser for emitting pump light;

[0032] A low-doped erbium-ytterbium double-clad active optical fiber connected to the laser seed light source and used to amplify the signal light;

[0033] A highly doped Er-Yb double-clad active optical fiber connected to the multi-mode pump laser for amplifying signal light;

[0034] A multimode pump bridge connected between the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, used for separating the pump light from the signal light;

[0035] A high-reflection fiber Bragg grating is connected to the highly doped erbium-ytterbium double-clad active optical fiber, and is used to filter the signal light and reflect the signal light into the highly doped erbium-ytterbium double-clad active optical fiber for re-amplification;

[0036] A low-reflection fiber Bragg grating is connected to the high-reflection fiber Bragg grating and the multi-mode pump laser, and is used to reflect part of the signal light into the highly doped erbium-ytterbium double-clad active optical fiber and amplify it;

[0037] The reflection grating is connected to the multimode pump bridge, the low-doped erbium ytterbium double-clad active optical fiber and the high-doped erbium ytterbium double-clad active optical fiber, and is used to reflect part of the pump light into the high-doped erbium ytterbium double-clad active optical fiber and transmit the other part of the pump light into the low-doped erbium ytterbium double-clad active optical fiber.

[0038] As a preferred embodiment of the present invention, the device also includes an optical circulator and a low-doped erbium ytterbium double-clad active optical fiber, which are connected to the laser seed light source and the low-doped erbium ytterbium double-clad active optical fiber, and are used to allow the signal light emitted by the laser seed light source to enter the active optical fiber and output the signal light returned from the active optical fiber.

[0039] As a preferred embodiment of the present invention, the device further comprises:

[0040] A separator, connected to the optical circulator, for separating signal light from noise light;

[0041] The output port is connected to the separator and serves as the output port of the laser.

[0042] As a preferred embodiment of the present invention, the device also includes a fiber node connected to the low-doped erbium-ytterbium double-clad active fiber and the high-doped erbium-ytterbium double-clad active fiber, which is used to loop the fiber to prevent light leakage.

[0043] As a preferred embodiment of the present invention, the low-reflection fiber Bragg grating adopts a 6nm broadband grating.

[0044] As a preferred embodiment of the present invention, the high-reflection fiber Bragg grating and the low-reflection fiber Bragg grating are both disposed inside the core of the active optical fiber by direct laser etching.

[0045] As a preferred embodiment of the present invention, the pulse signal light emitted by the laser seed light source is 1550nm; the pump light emitted by the multi-mode pump laser is 940nm.

[0046] In a specific embodiment of the present invention, a MOPA fiber laser based on dual FBG noise reduction technology and dual-stage EYDCF amplification technology is proposed, which can achieve high power and high signal-to-noise ratio output without using traditional EDFA as a preamplifier.

[0047] The device includes the following elements:

[0048] 1550nm laser seed light source Seed, providing signal light for pulse laser;

[0049] The optical circulator allows the signal light emitted by the seed light source to enter the EYDCF and outputs the signal light returned from the EYDCF, while preventing the output return light from returning to the laser, thus acting as an isolator.

[0050] Low-doped erbium-ytterbium double-clad active fiber EYDCF1, used as the gain medium for signal light amplification;

[0051] Highly doped erbium-ytterbium double-clad active fiber EYDCF2, used as the gain medium for signal light amplification;

[0052] Multimode pump bridge MM-WDM, which splits the pump light and then integrates it with the signal light;

[0053] Highly reflective fiber Bragg grating FBG1, for reflection filtering of signal light;

[0054] The low-reflection fiber Bragg grating FBG2 reflects a part of the 1530nm signal light into the EYDCF;

[0055] The reflection grating FBG3 reflects part of the 940 pump light into the highly doped erbium-ytterbium double-clad active fiber EYDCF2, and transmits part of the 940 pump light into the low doped erbium-ytterbium double-clad active fiber EYDCF1;

[0056] 940nm multi-mode pump laser PUMP provides energy for signal amplification;

[0057] The splitter WDM separates the 1550nm signal light from the 1530nm noise light.

[0058] Output end OUT: optical fiber, laser output port, usually using FC / APC interface;

[0059] Fiber node: Loop the fiber to prevent 1530nm light leakage and noise burning of surrounding fibers.

[0060] The parameters of the component are as follows:

[0061] Technical parameters of high-reflection fiber Bragg grating: central wavelength: 1550nm, 0.5db bandwidth: 4nm, reflectivity>99%, grating position: EYDCF core;

[0062] Technical parameters of low-reflection fiber Bragg grating: center wavelength: 1530nm, 3dB bandwidth: 6nm, reflectivity>80%, grating position: EYDCF core;

[0063] Technical parameters of reflection grating FBG3: central wavelength: 940nm, 3dB bandwidth: 10nm, reflectivity: about 50%, grating position: EYDCF fiber core;

[0064] Low-doped erbium-ytterbium double-clad active fiber EYDCF1 model and parameters: EYDCF-10 / 125, core diameter: 10um, cladding diameter: 125um, length 2m, low doping concentration and absorption coefficient.

[0065] Highly doped erbium-ytterbium double-clad active optical fiber EYDCF2 model and parameters: EYDCF-10 / 125, core diameter: 10um, cladding diameter: 125um, length 2.2m, high doping concentration and absorption coefficient.

[0066] Working method:

[0067] The seed light source emits a 1550nm pulsed laser which enters the active fiber low-doped erbium ytterbium double-clad active fiber EYDCF1 through a circulator, and then enters the highly doped erbium ytterbium double-clad active fiber EYDCF2 through a multimode pump bridge. The pump laser emits a pump laser which is directly input into the highly doped erbium ytterbium double-clad active fiber EYDCF2, and is separated from the signal light after being transmitted to the multimode pump bridge. After passing through the reflection grating FBG3, a part of the laser is reflected to the highly doped erbium ytterbium double-clad active fiber EYDCF2, and a part of the laser is transmitted to the low doped erbium ytterbium double-clad active fiber EYDCF1.

[0068] During the transmission process, the gain medium absorbs the pump light energy, and the signal light is amplified by atomic stimulated radiation during the active fiber transmission process. At the same time, the EYDCF spontaneously radiates a large amount of ASE light (such as Figure 2 After the 1550nm signal and ASE are transmitted to the high-reflection fiber Bragg grating, the high-reflection fiber Bragg grating performs reflection filtering, that is, the 1550nm signal and a very small part of the ASE light are reflected, and the remaining ASE light is transmitted to the low-reflection fiber Bragg grating, which reflects about 80% of the 1530NM ASE light (as shown in Figure 2The 1530nm spectrum in the middle) is transmitted through the low-reflection fiber Bragg grating and then transmitted again together with the reversely transmitted 1550NM, such as an active fiber. The 1550nm signal light is amplified again while being transmitted in the active fiber, realizing the high-power output of the laser. At the same time, the 1530nm ASE laser absorbs particles at 1530nm, reduces the number of upper energy level particles at 1530nm, and effectively reduces the ASE self-excitation effect at 1530NM. Finally, the 1550nm and 1530nm lights are split by the circulator and separator and output as fiber lasers. Among them, the 1530nm ASE light is lost at the fiber node.

[0069] This design adopts a series of technologies to control the noise in EYDCF and simplify the processing of optical devices, realizing a MOPA fiber laser that can achieve high OSNR and high-power laser output by using the EYDCF two-stage amplification solution.

[0070] By adopting a multi-mode pump bridge to realize the EYDCF bridged two-stage solution, the solution can greatly improve the spectral signal-to-noise ratio and conversion efficiency. At the same time, the pump bridge solution avoids the technical bottleneck of the traditional technical solution that requires two sets of pump lasers and combiners to realize the EYDCF two-stage amplification, effectively reducing the number of devices and reducing costs.

[0071] The 940nm FBG is used to reflect the remaining pump light in the highly doped erbium-ytterbium double-clad active fiber EYDCF2 again into the highly doped erbium-ytterbium double-clad active fiber EYDCF2 with a high absorption coefficient, which effectively improves the absorption efficiency of the pump and effectively shortens the length of the active fiber. Part of the pump light is transmitted into the low-doped erbium-ytterbium double-clad active fiber EYDCF1. Due to its low doping concentration, a lower pump power can achieve an effective inversion of the particle number, achieve pump power saturation to achieve a pre-release effect, and adjust the pump distribution through the grating, which effectively improves the conversion efficiency and shortens the active fiber.

[0072] High-reflection fiber Bragg grating is used to filter the signal light, and the signal light is reflected into the active optical fiber for re-amplification, while the ASE light generated by the forward amplification is directly filtered out.

[0073] The low-reflection fiber Bragg grating is used to reflect the 1530nm light and then transmit it into the active optical fiber for amplification, which consumes the upper energy level particles at 1530nm. On the one hand, it can reduce the ASE power at 1530nm and improve the signal light OSNR. On the other hand, it can reduce the energy density of the optical fiber core and prevent self-excited oscillation in the optical fiber, which causes spectral instability.

[0074] Among them, the grating adopts a broadband grating with a bandwidth of 6nm, which effectively improves the reflected power of ASE light, fully improves the effect of consuming the number of particles, and effectively avoids the traditional gain-pinning technology solution of adding an external semiconductor laser to input denoised seed light or resonant amplification through a grating pair.

[0075] Both high-reflection fiber Bragg gratings and low-reflection fiber Bragg gratings are prepared inside the fiber core by laser direct etching technology, and have no effect on the 940nm pump light.

[0076] The pump laser is directly fused with the active optical fiber to avoid the use of a fiber combiner for beam combining in the traditional process. This not only avoids the use of a fiber combiner, but also avoids the pump light loss and thermal effect caused by the intrinsic loss when using a traditional combiner, saving device costs while effectively improving the electro-optical conversion efficiency and reliability of the equipment.

[0077] The single-fiber dual-pass amplification design scheme is adopted, and the active optical fiber length is relatively short, which effectively increases the nonlinear threshold and avoids the influence of the optical fiber nonlinear effect on the signal-to-noise ratio and absorption efficiency. At the same time, it increases the pump absorption efficiency, improves the electro-optical conversion efficiency, and reduces the cost of raw materials.

[0078] The use of a circulator can achieve the effect of an isolator, avoiding the need for traditional lasers to use optical fiber isolators for isolation and preventing external return light from interfering with the laser. This reduces costs and processing difficulty while meeting isolation requirements.

[0079] Based on the main optical path design of this invention, the optical path of the complete MOPA fiber laser is as follows Figure 1 As shown,

[0080] The output fiber of the laser seed light source is fused to the first port of the optical circulator, the second port of the optical circulator is fused to the low-doped erbium ytterbium double-clad active fiber EYDCF1, the low-doped erbium ytterbium double-clad active fiber EYDCF1 is connected in series with the multimode pump bridge, the end of the EYDCF grating is fused to the multimode pump laser, the second port of the circulator is fused to the single end of the separator, the 1550nm end of the separator is fused to the output jumper, and the 1530nm end is knotted.

[0081] In a specific embodiment of the present invention, the optical path design of the minimalist MOPA fiber laser can achieve high OSNR and high-power laser output by adopting a two-stage EYDCF amplification scheme. The experimental data are as follows: under the test conditions of seed light source repetition frequency: 500khz, pulse width: 3ns, output peak power 80mw; pump output power: 6W, the pulse peak power is 1.0KW, OSNR = 40dB.

[0082] The pulse fiber laser device of the present invention can obtain ultra-high output power and spectral OSNR, avoiding the use of traditional EDFA as a two-stage structure of preamplifier + power amplifier. The fiber laser amplification design can be completed with a very simple optical path design scheme: only three passive optical devices are used in the optical path scheme. The extremely simple optical path structure shortens the production time of the fiber laser to half of the traditional preamplifier two-stage scheme, greatly improving production efficiency and reducing laser labor costs. The extremely simple optical path structure greatly reduces the component cost of the fiber laser, reducing the cost by more than half compared to traditional solutions. The laser can be integrated into an ultra-small structure, which is convenient for commercial mass use and has ultra-high reliability.

[0083] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be regarded as illustrative rather than restrictive.

Claims

1. A pulsed fiber laser device, characterized in that: The device comprises: A laser seed light source, used for emitting pulse signal light; A multi-mode pump laser for emitting pump light; A low-doped erbium-ytterbium double-clad active optical fiber connected to the laser seed light source and used to amplify the signal light; A highly doped Er-Yb double-clad active optical fiber connected to the multi-mode pump laser for amplifying signal light; A multimode pump bridge connected between the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, used for separating the pump light from the signal light; A high-reflection fiber Bragg grating is connected to the highly doped erbium-ytterbium double-clad active optical fiber, and is used to filter the signal light and reflect the signal light into the highly doped erbium-ytterbium double-clad active optical fiber for re-amplification; A low-reflection fiber Bragg grating is connected to the high-reflection fiber Bragg grating and the multi-mode pump laser, and is used to reflect part of the signal light into the highly doped erbium-ytterbium double-clad active optical fiber and amplify it; A reflection grating connected to the multimode pump bridge, the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, for reflecting part of the pump light into the high-doped erbium-ytterbium double-clad active optical fiber and transmitting the other part of the pump light into the low-doped erbium-ytterbium double-clad active optical fiber; The device also includes an optical circulator connected to the laser seed light source and the low-doped erbium-ytterbium double-clad active optical fiber, used to allow the signal light emitted by the laser seed light source to enter the active optical fiber and output the signal light returned from the active optical fiber; The device also includes: A separator, connected to the optical circulator, for separating signal light from noise light; An output port, connected to the separator, serving as an output port of the laser; The output optical fiber of the laser seed light source is fused with the first port of the optical circulator, the second port of the optical circulator is fused with the low-doped erbium ytterbium double-clad active optical fiber, the low-doped erbium ytterbium double-clad active optical fiber is connected in series with the multimode pump bridge, the end of the low-reflection fiber grating is fused with the multimode pump laser, the second port of the optical circulator is fused with the single end of the separator, and the 1550nm end of the separator is fused with the output jumper.

2. The pulse fiber laser device according to claim 1, characterized in that: The device also includes an optical fiber node connected to the low-doped erbium-ytterbium double-clad active optical fiber and the high-doped erbium-ytterbium double-clad active optical fiber, which is used to loop the optical fiber to prevent light leakage.

3. The pulse fiber laser device according to claim 1, characterized in that: The low-reflection fiber grating adopts a 6nm broadband grating.

4. The pulse fiber laser device according to claim 1, characterized in that: The high-reflection fiber grating and the low-reflection fiber grating are both arranged inside the core of the active optical fiber through laser direct etching.

5. The pulse fiber laser device according to claim 1, characterized in that: The pulse signal light emitted by the laser seed light source is 1550nm; the pump light emitted by the multi-mode pump laser is 940nm.

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