CN204333584U - Cascade-pumped Ytterbium Ion, Raman Mixed-Gain High Power Fiber Laser Amplifier - Google Patents

Abstract

The utility model relates to a kind of cascaded pump ytterbium ion, Raman hybrid gain high power optical fibre laser amplifier.This amplifier adds the single order stokes light of original signal wavelength in the seed of cascaded pump amplifier, produces stimulated Raman scattering artificially and guides it towards fl transmission, this ensure that the safety of system, make power be able to further lifting.By the design of theoretical model, select concrete wavelength and the power of stokes light, effectively can suppress backward Raman scattering light and next stage Raman stokes light, thus realize the high-power output of cascaded pump fiber amplifier.

Description

Cascade-pumped Ytterbium Ion, Raman Mixed-Gain High Power Fiber Laser Amplifier

technical field

The invention belongs to the technical field of fiber lasers, and relates to a novel technical solution for simultaneously using ytterbium ions and Raman gain to perform laser amplification in cascaded pump fiber amplifiers to suppress stimulated Raman scattering and achieve high power output.

Background technique

High average power lasers have important and extensive uses in the fields of industrial processing, national defense security, and scientific research. Compared with traditional solid-state lasers, fiber lasers have the advantages of compact structure, high conversion efficiency, excellent beam quality and convenient thermal management, and have been developed rapidly in recent years. At present, the single-mode output of a single fiber has exceeded 20,000 watts, and the multi-mode output has exceeded 100,000 watts. Although the fiber laser has a large surface area to volume ratio, which is good for heat dissipation, but at high power, the thermal effect in the fiber is still an important reason that restricts the further increase of laser power. In addition, the brightness and nonlinear effects of the pump source are also the main limitations restricting the power increase of fiber lasers. In recent years, the technical scheme of using fiber lasers to pump cascaded fiber lasers to obtain high power output has attracted more and more attention from researchers. On the one hand, this scheme first converts the energy of the semiconductor pump source with low brightness into high Fiber laser, and then inject the fiber laser as a new pump source into the next-level fiber laser to pump a higher-brightness laser, so that the brightness of the pump source is greatly improved, and more power can be injected into the fiber in theory . On the other hand, since the wavelength of the fiber laser used as the pump source is closer to the wavelength of the final laser, the quantum defect in the energy conversion process is relatively smaller, so that the heat generated in the fiber is relatively less, thus reducing the thermal burden of the system . Taken together, cascaded pumped fiber lasers have obvious advantages in obtaining high power.

At present, the high-power output of fiber lasers is usually achieved by using ytterbium-doped fibers, which is due to the simple energy level structure of ytterbium-doped fibers, wide absorption and emission spectra, and high doping concentration. The traditional Ytterbium-doped fiber laser pumping scheme uses a semiconductor pump source near 915nm or 976nm for pumping to obtain a laser output near 1070~1090nm. As mentioned above, on the one hand, the thermal effect of the quantum deficit is relatively serious, and on the other hand, the brightness of the pump source is too low to inject more pump energy. The cascaded pumping scheme solves the above problems well. Specifically, it first uses a semiconductor pump source near 915nm or 976nm to pump the ytterbium-doped fiber to generate fiber laser at about 1010nm~1030nm, and then uses it to pump to generate Laser near 1060nm~1090nm. It is worth noting that the cascaded pump solution solves the problems of insufficient brightness of the pump source and serious thermal effects in high power acquisition, but the wavelength of the fiber laser used as the cascaded pump source is usually selected around 1010nm~1030nm. At present, the absorption of ytterbium-doped optical fiber in quartz matrix is relatively small in this band, generally 1/20~1/30 near 976nm. Therefore, in the amplifier structure, the length of the gain fiber is usually longer than that of the traditional amplifier, which reduces the threshold value of the nonlinear effect of the system to a certain extent. For broadband light sources, the main nonlinear effect is stimulated Raman scattering, and the threshold of this effect is mainly inversely proportional to the peak intensity of the laser and the effective length of the fiber. Since Raman scattering can be generated from thermal noise, the Stokes light generated in the fiber will be transmitted forward and backward at the same time, and when the power is large enough, the power of the Stokes light will appear Exponential growth produces stimulated Raman scattering. The light transmitted in the backward direction is difficult to effectively isolate in the fiber optic system, so it is very dangerous and must be avoided as much as possible.

Contents of the invention

The invention discloses a cascaded pump fiber amplifier scheme utilizing ytterbium ions and Raman gain to achieve high power output, and provides a calculation method to greatly increase the threshold value of nonlinear effects in cascade pump fiber lasers , so as to give full play to the advantages of the cascaded pumping scheme, and finally obtain high-power fiber laser output.

The purpose of the present invention is to solve the problem that in the cascaded pumping scheme, the stimulated Raman scattering threshold is lowered due to the longer gain fiber and backward light is generated, thereby limiting the acquisition of higher power fiber laser. Its main feature is that the first-order Stokes light of the original signal wavelength is added to the seed of the cascaded pump amplifier to artificially generate stimulated Raman scattering and guide it to transmit forward, which ensures the safety of the system and enables The power can be further increased.

The basic structure of the cascaded pumped ytterbium ion and Raman mixed-gain high-power optical fiber amplifier proposed by the present invention is: the seed source 1 is composed of a light source 8 in a conventional band, and the wavelength range is 1060nm~1090nm (such as the selected wavelength is 1080nm), and the corresponding Stokes-band laser source 9, the wavelength range is 1100nm~1160nm (for example, the selected wavelength is 1120nm), which is combined into the same optical fiber through a wavelength division multiplexer 11; the pigtail fiber of seed source 1 is connected to The signal arms of the pump signal combiner 4 are connected, the high-power fiber laser pump source array 3 is connected to the pump arm of the pump signal combiner 4, and the output end of the pump signal combiner 4 is connected to a section of ytterbium-doped The optical fiber 5 is connected to form an amplifier structure, and a cladding light stripper 6 is connected to the end of the amplifier to filter out excess cladding light, and finally output laser light through an end cap 7 .

Furthermore, the mixed-gain high-power optical fiber amplifier can also be connected to the next-stage amplifier for cascade amplification to obtain higher power.

The wavelength of the fiber laser pumping source array 3 is selected from 1010 nm to 1030 nm. For example, 1018nm can be selected, which is the result of comprehensive consideration of pump absorption and high-power pump source. Further, in order to protect the Stokes-band laser source, an isolator 10 may be added behind the Stokes-band laser source to prevent the influence of backward light.

Another structure of the hybrid-gain high-power fiber amplifier is: the Stokes band laser source 9 is connected to the signal arm of the pump signal combiner 4 through a fusion point, and the semiconductor pump source 14 is connected to the pump signal combiner. The pumping arm of the beamer 4, the output end of the pumping signal beam combiner 4 is connected to a section of ytterbium-doped optical fiber 5 to form an amplifier structure, and the front end and the end of the amplifier are connected to the fiber grating 17 through fusion splicing points.

The seed source 1: this is the core of the present invention, that is, by adding the first-order Stokes light of the traditional signal light to the seed, its wavelength is located in the Raman gain spectrum, and the power ratio of the two wavelength lasers is adjusted, thereby Controls laser output characteristics and suppression effects.

The fiber laser pump source array cascaded pump source: the fiber laser source used to pump the final laser, its wavelength is usually selected around 1010nm~1030nm, which is based on the comprehensive consideration of the optical fiber absorption and the difficulty of obtaining it the result of.

Amplifier stage: The main components are a beam combiner and a section of ytterbium-doped optical fiber. The key point is the selection of optical fiber, which requires not only ensuring enough pump light to be injected but also having a high absorption coefficient for the pump light.

Spontaneous Raman in optical fibers is generated from thermal noise, so both directions exist. When the power density is high, spontaneous Raman light in both directions will be amplified and further evolved into stimulated Raman amplification, consuming Signal light power, and more seriously, the backward light will threaten the safety of the entire laser system. Therefore, injecting the Stokes light corresponding to the signal light into the seed can effectively suppress the backward Stokes light. In theory, although the addition of Stokes light will reduce the threshold of signal light corresponding to Raman scattering, the system can safely output higher power. This is because under the same total power, the input Stokes The power and wavelength of the light can control the power ratio of the signal light and its Stokes light in the output laser, so that it will not produce the next level of Raman scattering. On the other hand, the Raman gain coefficient is inversely proportional to the wavelength. The longer the wavelength, the smaller the Raman gain coefficient, so the Raman threshold will be higher, which also increases the threshold of the next level of Raman to a certain extent.

The key to achieve high power amplifier is to design the wavelength and power ratio design of the light source in the conventional band and the laser source in the Stokes band in the seed source. The specific design method can be analyzed by the following model:

(1)

(2)

(3)

(4)

(5)

(6)

(7)

in, is the fiber doping concentration distribution along the axial direction, is the upper level particle number concentration, is the doping concentration of ytterbium ions in the fiber, is the wavelength Axial power distribution of the laser, subscript corresponding to the first wavelength components, the superscript ± corresponds to the transmission direction, and are the absorption and emission cross sections, respectively, is the area of the fiber core, is the fill factor of the laser, is Planck's constant, is the upper level fluorescence lifetime of ytterbium ion, is the nonlinear coefficient, For the contribution of the Raman effect to the phase modulation, ( , ) represents the Raman gain coefficient, is the phase mismatch, Corresponding to the transmission loss of the optical fiber, is the optical frequency of the kth wavelength, ( , , ) is the wavelength of the kth (1, 2, 3) laser, is the speed of light in vacuum, is the spontaneous emission wavelength interval, is a unit imaginary number, , , are the light field amplitudes of the signal light and its first-order and second-order Stokes light, respectively, , , correspond respectively , , The nonlinear coefficient of ( , , ) is the gain coefficient of the ytterbium ion pair laser, is the axial coordinate, is the ratio of the optical field area of the laser to the doped area of ytterbium ions.

The above model considers the effect of amplified spontaneous emission in Ytterbium-doped fiber lasers, and also includes first-order, second-order Raman effects and four-wave mixing effects. The specific boundary conditions are given according to the experimental design. Using the above model, the wavelength and power of pump light, signal light and first-order Stokes light can be conveniently selected for theoretical analysis. In particular, for the traditional cascaded pumping scheme, the pump laser is 1010nm~1030nm band laser, the signal wavelength is around 1060nm~1090nm, the wavelength range of Stokes light that can be selected is 1100nm~1160nm, and its power can also be Design according to the system requirements to achieve the optimum. The optimum standard here refers to the minimum Stokes optical power of the next stage and the minimum return light. Compared with the prior art solution, the present invention has the advantage that the Stokes light of the original signal light is added to the seed source as a new seed and injected into the amplifier, which can well suppress the backward transmission generated by spontaneous Raman At the same time, the power ratio of the two wavelengths in the forward output light is controlled through fine theoretical analysis and design, thereby effectively increasing the threshold of the next-level Raman light and overcoming the severe Raman effect in the cascaded pump fiber laser. At the same time, it combines the advantages of high pump brightness and small thermal burden, and is expected to develop into a high-power fiber laser solution with great potential and market prospects.

Description of drawings

Fig. 1 is the basic structural diagram of cascade pumping ytterbium ion of the present invention, Raman mixed-gain high-power optical fiber amplifier;

Figure 2 is another possible injection of the amplifier seed of the present invention.

Detailed ways

Fig. 1 is a basic structural diagram of the cascaded pumped ytterbium ion and Raman mixed gain high-power optical fiber amplifier proposed by the present invention. A structure of the seed source is: the light source 8 of the conventional band, the wavelength range is 1060nm~1090nm (if the wavelength is selected as 1080nm), and the corresponding Stokes band laser source 9, the wavelength range is 1100nm~1160nm (if the wavelength is selected The wavelength is 1120nm), the power level can be optimized by the aforementioned theoretical model, and combined into the same optical fiber through a wavelength division multiplexer 11. The pigtail of the seed source 1 is connected to the signal arm of the pump signal combiner 4 through the fusion point 2, and the high-power fiber laser pump source array 3 is connected to the pump arm of the combiner 4, and the output end of the combiner It is connected with a section of ytterbium-doped fiber 5 to form an amplifier structure, and a cladding light stripper 6 is connected to the end of the amplifier to filter out excess cladding light, and finally output laser light through an end cap 7 . In order to obtain higher power, it can also be connected to the next stage amplifier for cascade amplification. For the fiber laser pump source 3, its wavelength can be selected from 1010nm to 1030nm, for example, 1018nm can be selected, which is the result obtained by comprehensive consideration of pump absorption and high-power pump source. Wherein, in order to protect the seed source in the Stokes band, an isolator 10 may be added behind it to prevent the influence of backward light.

Figure 2 is another possible injection of the amplifier seed of the present invention. The Stokes light seed source 9 is directly connected to the conventional band laser through the signal arm of the pump signal beam combiner 4 . The laser is composed of a semiconductor pump source 14 , a pump signal beam combiner 4 , an ytterbium-doped fiber 5 and a fiber grating 17 . This way can ensure the stability of the output seed power.

Claims (5)

1. The cascade pump ytterbium ion and Raman mixed gain high-power optical fiber laser amplifier is characterized in that a tail fiber of a seed source (1) is connected with a signal arm of a pump signal combiner (4) through a fusion point (2), a high-power optical fiber laser pump source array (3) is connected with the pump arm of the pump signal combiner (4), the output end of the pump signal combiner (4) is connected with a section of ytterbium-doped optical fiber (5) to form an amplifier structure, a cladding light stripper (6) is connected to the tail end of the amplifier to filter redundant cladding light, and finally laser is output through an end cap (7);

the seed source (1) is formed by combining a light source (8) with a conventional waveband in the wavelength range of 1060 nm-1090 nm and a corresponding Stokes waveband laser source (9) in the wavelength range of 1100 nm-1160 nm into the same optical fiber through a wavelength division multiplexer (11).

2. The cascade pump ytterbium-ion Raman hybrid-gain high-power fiber laser amplifier according to claim 1, wherein the wavelength of the fiber laser pump source array (3) is selected to be 1010 nm-1030 nm.

3. The cascade pump ytterbium ion, Raman mixed gain high power fiber laser amplifier of claim 1, further characterized in that, in order to protect the Stokes band laser source, an isolator (10) is added after the Stokes band laser source (9) to prevent the effect of backward return light.

4. The cascade pump ytterbium-ion, raman-hybrid-gain high-power fiber laser amplifier of claim 1, wherein the amplifier has another structure: the Stokes wave band laser source (9) is connected with a signal arm of the pumping signal combiner (4) through a fusion point, a semiconductor pumping source (14) is connected with the pumping arm of the pumping signal combiner (4), the output end of the pumping signal combiner (4) is connected with a section of ytterbium-doped optical fiber (5) to form an amplifier structure, and the front end and the tail end of the amplifier are connected with the fiber grating (17) through the fusion point.

5. The cascade pump ytterbium-ion, raman mixed-gain high-power fiber laser amplifier of claim 1, wherein the amplifier is further connected to a next-stage amplifier for cascade amplification to obtain higher power.