Optical fiber amplifier with high stimulated Brillouin scattering threshold

Abstract

The invention discloses an optical fiber amplifier with a high stimulated Brillouin scattering threshold value, the amplifier comprises a laser seed source, an intensity modulator, an optical fiber beam splitter, a multi-path optical fiber amplifier and an optical fiber beam combiner, the intensity modulator modulates seed light into pulse laser with a certain repetition frequency, and the pulse width of the pulse laser is smaller than the service life of optical fiber phonons; the optical fiber beam splitter divides the pulse laser into multiple paths and outputs the pulse laser; the first path of the multi-path optical fiber amplifier comprises a multi-stage optical fiber amplification stage, and each path comprises an optical fiber delayer and a multi-stage optical fiber amplification stage from the second path of the multi-path optical fiber amplifier; the optical fiber delayer performs delay processing on each path of pulse laser, so that each path of pulse laser can have any time delay compared with the first path of pulse laser in a time domain; and the optical fiber beam combiner combines multiple paths of pulse laser into one path of continuous wave or arbitrary waveform pulse to be output.

Description

Technical Field

[0001] The invention relates to the field of lasers, and in particular to an optical fiber amplifier with a high stimulated Brillouin scattering threshold. Background Art

[0002] When using a fiber amplifier to increase the laser power, the stimulated Brillouin scattering (SBS) effect is very likely to occur due to the continuous increase in the laser power density in the gain fiber core. [1,2] , causing part of the forward transmitted signal light power to be transferred to the reverse transmitted Stokes light, and with the increase of signal laser power, the Stokes light power also increases rapidly, thereby limiting the increase of signal laser power. At the same time, there is a risk of damaging the preceding optical system, so certain measures need to be taken to suppress it.

[0003] The use of large mode field step-index fiber can reduce the core power density, but the laser will be in a few-mode operation state, and it is difficult to ensure high beam quality. Large mode field microstructure fiber with a specially designed cladding structure supports single transverse mode operation of the laser, but the fiber preparation is difficult, and most of them cannot be coiled, making it difficult to be widely used. In addition, applying a temperature gradient or stress gradient to the gain fiber can reduce the effective gain coefficient of SBS, but it is difficult to control and costly, and it will also shorten the service life of the gain fiber and increase the complexity of the laser system. The essence of the SBS process is the interaction between sound and light. For pulsed lasers, when the action time of the pulse and the dielectric material is less than the phonon lifetime (about 10ns in quartz fiber), the Brillouin gain can be effectively reduced to increase the SBS threshold, but it is not applicable to application scenarios that require continuous wave / quasi-continuous wave lasers or long pulse lasers. Therefore, it is particularly important to explore efficient and easy-to-implement methods to suppress nonlinear effects in fiber amplifiers.

[0004] References

[0005] [1] C.Shi, H.Tian, ​​S.Fu, Q.Sheng, Z.Shi, P.Jiang, W.Shi, and J.Yao, "High-energy single-frequency pulsed fiber MOPAat 1064nm based on a hybrid active-fiber," Opt.Express30(9),15575-15582(2022).

[0006] [2] C. Shi, H. Tian, ​​Q. Sheng, W. Shi, Q. Fang, S. Sun, J. Zhang, and J. Yao, "High-power single-frequency pulsed fiber MOPA via SPM suppression based on atriangular pulse," Results Phys. 28, 104594 (2021). Summary of the invention

[0007] The present invention provides a fiber amplifier with a high stimulated Brillouin scattering threshold. The present invention effectively suppresses the nonlinear effect in the fiber amplifier, obtains a stable high-power continuous wave laser output, or a pulsed laser output of any shape, and improves the laser output power, as described below:

[0008] A fiber amplifier with a high stimulated Brillouin scattering threshold, the amplifier comprising: a laser seed source, an intensity modulator, a fiber beam splitter, a multi-channel fiber amplifier and a fiber beam combiner,

[0009] The intensity modulator modulates the seed light into a pulse laser with a certain repetition frequency and a pulse width less than the fiber phonon lifetime, and the fiber beam splitter divides the pulse laser into multiple outputs;

[0010] The first path of the multi-path optical fiber amplifier includes multiple optical fiber amplification stages, and each path starting from the second path includes an optical fiber delay device and multiple optical fiber amplification stages; the optical fiber delay device performs time delay processing on the pulse laser of each path, so that the pulse laser of each path can be delayed by any time in the time domain compared with the pulse laser of the first path, and form complementarity in the time domain;

[0011] The optical fiber combiner combines multiple pulse lasers into one continuous wave output.

[0012] The output wavelength of the laser seed source is any wavelength in the range from visible light to mid-infrared, and the laser operation mode is continuous wave operation, quasi-continuous wave operation or pulse operation.

[0013] The optical fiber beam splitter divides the laser output by the intensity modulator into multiple outputs according to actual needs, and the laser powers of the multiple outputs are the same or different.

[0014] The number of the multi-stage optical fiber amplification stages in each of the multi-channel optical fiber amplifiers is: a multi-stage core pumping amplification stage, or a multi-stage cladding pumping amplification stage, or a multi-stage core pumping amplification stage connected to a multi-stage cladding pumping amplification stage.

[0015] The optical fiber combiner combines the lasers output from the multi-channel optical fiber amplifiers into one channel and outputs the combined lasers. The number of input ports matches the number of output ports of the optical fiber splitter.

[0016] The beneficial effects of the technical solution provided by the present invention are:

[0017] 1) The present invention uses an intensity modulator to modulate the seed light into a pulse laser with a certain repetition frequency and a pulse width less than the fiber phonon lifetime, and then uses a beam splitter to divide the pulse laser into multiple outputs. Since the pulse width of each pulse laser is less than the phonon lifetime of about 10ns in the quartz fiber, the Brillouin gain can be effectively reduced to increase the SBS threshold, which is beneficial to the improvement of the peak power of the pulse laser, thereby increasing the laser output power after beam combining;

[0018] 2) The present invention uses an intensity modulator to modulate the seed light to obtain a pulsed laser, and can flexibly modulate the repetition frequency and pulse width of the pulsed laser, thereby combining the use of an optical fiber delay device to obtain a continuous wave laser output after beam combining, or a pulsed laser with any repetition frequency and pulse width;

[0019] 3) The present invention uses an intensity modulator to modulate the seed light to obtain a pulsed laser, can pre-shape the pulse waveform, and then reasonably utilize the waveform distortion caused by the gain saturation effect in the multi-stage optical fiber amplifier stage, so as to obtain a continuous wave laser output with stable power or a pulsed laser output of any shape after beam combining. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of a fiber amplifier with a high stimulated Brillouin scattering threshold;

[0021] Figure 2 This is a schematic diagram of the curve showing the variation of the SBS threshold with the pulse width when a 1m long commercial ytterbium-doped fiber with a core diameter / cladding diameter of 30μm / 250μm is used in a fiber amplifier.

[0022] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0023] 1: Laser seed source; 2: Intensity modulator;

[0024] 3: Fiber optic beam splitter; 4: Fiber optic delay device for the second optical path;

[0025] 5: Fiber optic delay device for the third optical path; 6: Fiber optic delay device for the fourth optical path;

[0026] 7: The first multi-stage optical fiber amplifier stage; 8: The second multi-stage optical fiber amplifier stage;

[0027] 9: The third multi-stage optical fiber amplifier stage; 10: The fourth multi-stage optical fiber amplifier stage;

[0028] 11: Fiber combiner. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0030] The embodiment of the present invention provides a fiber amplifier with a high stimulated Brillouin scattering threshold, which uses an intensity modulator to modulate seed light into a pulse laser with a certain repetition frequency and a pulse width less than the phonon lifetime of the fiber material, and then uses a beam splitter to divide the pulse laser into multiple paths; each path contains the same multi-stage fiber amplification stage, and the pulse laser power is increased to the same extent, and then a beam combiner is used to combine the multiple pulse lasers into one path for output. Since the pulse width of each pulse laser is less than the phonon lifetime of the fiber, the Brillouin gain can be effectively reduced to increase the SBS threshold, which is beneficial to the improvement of the peak power of the pulse laser. Starting from the second path, a fiber delay is placed before the multi-stage amplification stage to delay the pulse laser of each path, and the delay time of the fiber delay of each path is adjusted respectively. In this way, the pulse lasers of all paths can be complementary in the time domain, so that the laser after beam combination is a continuous wave output; the intensity modulator can also be used to optimize the pulse waveform, so that after undergoing the multi-stage fiber amplification stage, it evolves into a standard rectangular pulse under the effect of gain saturation, thereby improving the stability of the beam combined output laser. In addition, the pulse laser parameters and the configuration of each amplifier can be flexibly designed, and the delay of each pulse laser can be flexibly adjusted by using an optical fiber delay device to achieve high-power pulse output of arbitrary waveform.

[0031] Example 1

[0032] The embodiment of the present invention provides a fiber amplifier with a stimulated Brillouin scattering threshold, which outputs a continuous wave laser. Figure 1 The amplifier includes: a laser seed source 1, an intensity modulator 2, a fiber splitter 3, a four-way fiber amplifier (the first way includes: a first multi-stage fiber amplifier stage 7, excluding a fiber delay; the second way includes: a second optical path fiber delay 4 and a second multi-stage fiber amplifier stage 8; the third way includes: a third optical path fiber delay 5 and a third multi-stage fiber amplifier stage 9; the fourth way includes: a fourth optical path fiber delay 6 and a fourth multi-stage fiber amplifier stage 10), and a fiber combiner 11.

[0033] Among them, the laser seed source 1 outputs a continuous laser with a central wavelength of 1064nm, an output power of 30mW, a spectral linewidth of 5MHz, and a core / cladding diameter of the output fiber pigtail of 6μm / 125μm respectively; the intensity modulator 2 is based on an electro-optical intensity modulator, and the core / cladding diameters of the input and output fiber pigtails are 6μm / 125μm respectively, the working wavelength range is 980-1150nm, the bandwidth is 12GHz, and the intensity modulation accuracy is 100ps. The pulse width set in the embodiment of the present invention is 5ns, and the repetition frequency is 50MHz; the fiber optic splitter 3 has the same input and output fiber pigtails and the core / cladding diameters are 6μm / 125μm respectively, the number of output ports is 4, and the laser power is evenly distributed; the second optical path optical The input and output pigtails of the optical fiber delay 4, the third optical path optical fiber delay 5 and the fourth optical path optical fiber delay 6 are the same and the core / cladding diameters are 6μm / 125μm respectively, which can make the pulsed laser transmitted by each optical path produce any time delay within the range of 0-1s. In the embodiment of the present invention, the second optical path optical fiber delay 4 is set to have a 5ns delay, the third optical path optical fiber delay 5 is set to have a 10ns delay, and the fourth optical path optical fiber delay 6 is set to have a 15ns delay; the first multi-stage optical fiber amplifier stage 7, the second multi-stage optical fiber amplifier stage 8, the third multi-stage optical fiber amplifier stage 9 and the fourth multi-stage optical fiber amplifier stage 10 are all composed of a first-level core pump pre-amplifier stage, a first-level cladding pump pre-amplifier stage and a first-level cladding pump main amplifier stage.

[0034] In the embodiment of the present invention, the gain fiber used in the core-pumped pre-amplifier stage is an ytterbium-doped single-clad fiber and the core / cladding diameters of all optical fibers are 6μm / 125μm, respectively; the gain fiber used in the cladding-pumped pre-amplifier stage is an ytterbium-doped double-clad fiber and the core / cladding diameters of all optical fibers are 15μm / 250μm, respectively; the gain fiber used in the cladding-pumped main amplifier stage is an ytterbium-doped double-clad fiber and the core / cladding diameters of all optical fibers are 30μm / 250μm, respectively; the input and output pigtails of the optical fiber combiner 11 are the same and the core / cladding diameters are 30μm / 250μm, respectively, the number of input ports is 4, and the output end adopts a bevel design to ensure stable and safe laser output.

[0035] The pulse width after beam combination is 20ns, and the repetition frequency is 50MHz. The two multiplied together are 1s, which is the continuous wave output. Since the Brillouin gains of each channel will not be superimposed, the SBS threshold of the continuous wave laser after beam combination is consistent with that of each pulse laser, which can reach several kW, much higher than the SBS threshold of hundreds of watts in traditional continuous wave amplifiers, achieving a significant increase in the output power of narrow linewidth lasers.

[0036] Example 2

[0037] The embodiment of the present invention provides a fiber amplifier with a high stimulated Brillouin scattering threshold, which outputs pulsed laser. Figure 1 and Figure 2 The amplifier includes: a laser seed source 1, an intensity modulator 2, a fiber splitter 3, a four-way fiber amplifier (the first way includes: a first multi-stage fiber amplifier stage 7; the second way includes: a second optical path fiber delay 4 and a second multi-stage fiber amplifier stage 8; the third way includes: a third optical path fiber delay 5 and a third multi-stage fiber amplifier stage 9; the fourth way includes: a fourth optical path fiber delay 6 and a fourth multi-stage fiber amplifier stage 10), and a fiber combiner 11.

[0038] The laser seed source 1 outputs a continuous laser with a central wavelength of 1064 nm, an output power of 30 mW, a spectral line width of 5 MHz, and a core / cladding diameter of the output pigtail of 6 μm / 125 μm, respectively; the intensity modulator 2 is based on an electro-optic intensity modulator, and the core / cladding diameters of the input and output pigtails are 6 μm / 125 μm, respectively, with an operating wavelength range of 980-1150 nm, a bandwidth of 12 GHz, and an intensity modulation accuracy of 100 ps. The pulse width set in the embodiment of the present invention is 5 ns, and the repetition rate is 2 ms. The frequency is 50kHz; the input and output pigtails of the optical fiber splitter 3 are the same and the core / cladding diameters are 6μm / 125μm respectively, the number of output ports is 4 and the laser power is evenly distributed; the input and output pigtails of the second optical path optical fiber delay 4, the third optical path optical fiber delay 5 and the fourth optical path optical fiber delay 6 are the same and the core / cladding diameters are 6μm / 125μm respectively, and they can each generate any time delay within the range of 0-1s for the passing laser pulse. In the embodiment of the present invention, the second optical path optical fiber delay 4 is set The optical fiber delay device 5 of the third optical path is set to 5ns delay, the optical fiber delay device 5 of the third optical path is set to 10ns delay, and the optical fiber delay device 6 of the fourth optical path is set to 15ns delay; the first multi-stage optical fiber amplifier stage 7, the second multi-stage optical fiber amplifier stage 8, the third multi-stage optical fiber amplifier stage 9 and the fourth multi-stage optical fiber amplifier stage 10 are all composed of a first-stage core pump pre-amplifier stage, a first-stage cladding pump pre-amplifier stage and a first-stage cladding pump main amplifier stage. The gain fiber used in the core pump pre-amplifier stage in the embodiment of the present invention is an ytterbium-doped single-clad optical fiber and the core / cladding diameters of all optical fibers are 1 / 4. The diameters of the core and cladding of the optical fiber are 6μm / 125μm respectively. The gain fiber used in the cladding-pumped pre-amplifier stage is ytterbium-doped double-clad fiber and the core / cladding diameters of all optical fibers are 15μm / 250μm respectively. The gain fiber used in the cladding-pumped main amplifier stage is ytterbium-doped double-clad fiber and the core / cladding diameters of all optical fibers are 30μm / 250μm respectively. The input and output pigtails of the optical fiber combiner 11 are the same and the core / cladding diameters are 30μm / 250μm respectively. The number of input ports is 4, and the output end adopts a bevel design to ensure stable and safe laser output.

[0039] The pulse width after beam combination is 20ns, the repetition frequency is 50kHz, and the multiplication of the two is 0.001s, and the duty cycle is 0.1%, which is the pulse output. Since the Brillouin gain will not be superimposed, the SBS threshold of the pulsed laser after beam combination is consistent with that of the 5ns pulsed laser. Under this pulse width, a single-frequency laser output with a peak power of tens of kW can be achieved, which is much higher than the SBS threshold of hundreds of watts in the traditional amplifier with a pulse width of 20ns, achieving a significant increase in the peak power of the output pulsed laser.

[0040] Example 3

[0041] In the above-mentioned Embodiment 1 and Embodiment 2, the output wavelength of the laser seed source can be any wavelength in the range of visible light to mid-infrared, and the laser operation mode can be continuous wave operation, quasi-continuous operation or pulse operation, which is not limited in the embodiment of the present invention. The optical fiber beam splitter can divide the optical path into 4 paths or more paths, as long as each optical path has its own delay and amplification function, the time domain splicing control of the final laser output can be realized.

[0042] Accordingly, the operating wavelengths of the intensity modulator, the fiber beam splitter, the fiber delay, the fiber amplifier stage, and the fiber combiner only need to match the output wavelength of the seed source, and the embodiments of the present invention do not impose any limitation on this.

[0043] In the above-mentioned embodiment 2, the intensity modulator 2 can modulate pulse sequences with different repetition frequencies, different pulse widths, and different shapes. By using various optical fiber delay devices in combination, pulse laser output with high SBS thresholds and different pulse widths and arbitrary shapes can be achieved after beam combining, thereby achieving a significant increase in the peak power of the pulse laser.

[0044] Except for special instructions on the models of various components in the embodiments of the present invention, the models and specifications of other components, including the modulation principle and modulation step size of the intensity modulator, the number of fiber combiner output ports and fiber splitter output ports, and the number and type of multi-stage fiber amplifier stages, can be any device as long as it can complete the above functions.

[0045] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0046] 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 fiber amplifier with a high stimulated Brillouin scattering threshold, characterized in that: The amplifier comprises: a laser seed source, an intensity modulator, an optical fiber splitter, a multi-channel optical fiber amplifier and an optical fiber combiner. The intensity modulator modulates the seed light into a pulse laser with a certain repetition frequency and a pulse width less than the fiber phonon lifetime, and the fiber beam splitter divides the pulse laser into multiple outputs; The first path of the multi-path optical fiber amplifier includes multiple optical fiber amplification stages, and each path starting from the second path includes an optical fiber delay device and multiple optical fiber amplification stages; the optical fiber delay device performs delay processing on the pulse laser of each path, so that the pulse laser of each path can be delayed by any time in the time domain compared with the pulse laser of the first path; The optical fiber combiner combines multiple pulse lasers into one continuous wave or arbitrary waveform pulse output.

2. The optical fiber amplifier with a high stimulated Brillouin scattering threshold according to claim 1, characterized in that: The output wavelength of the laser seed source is any wavelength within the range from visible light to mid-infrared band, and the laser operation mode is continuous wave operation, quasi-continuous wave operation or pulse operation.

3. The optical fiber amplifier with a high stimulated Brillouin scattering threshold according to claim 1, characterized in that: The optical fiber beam splitter divides the laser output by the intensity modulator into multiple outputs according to actual needs, and the laser powers of the multiple outputs are the same or different.

4. The optical fiber amplifier with a high stimulated Brillouin scattering threshold according to claim 1, characterized in that: The number of the multi-stage optical fiber amplification stages in each channel of the multi-channel optical fiber amplifier is: a multi-stage core pumping amplification stage, or a multi-stage cladding pumping amplification stage, or a multi-stage core pumping amplification stage connected to a multi-stage cladding pumping amplification stage.

5. The optical fiber amplifier with a high stimulated Brillouin scattering threshold according to claim 1, characterized in that: The optical fiber combiner combines the laser beams outputted by the multi-channel optical fiber amplifiers into one channel and outputs the combined laser beams. The number of the input ports matches the number of the output ports of the optical fiber splitter.

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