阅读说明：本技术 具有1.02-1.06μm包层泵浦方案的大功率镱：铒（Yb:Er）光纤激光器系统 (High power ytterbium with 1.02-1.06 μm cladding pumping scheme: erbium (Yb: Er) fiber laser system ) 是由 艾廉·扎特斯蒂夫 费多尔·谢尔比纳 安德瑞·马史金 于 2019-06-28 设计创作，主要内容包括：一种光纤激光器,配置有：双包层光纤,其具有掺杂铒(Er～(+3))和镱(Yb～(+3))的离子的纤芯。至少两个间隔开的高反射镜和低反射镜,位于纤芯的侧面并在它们之间限定谐振腔。光纤激光器还包括泵浦激光器,该泵浦激光器输出波长范围在1.02-1.06μm内的光并耦合到掺Yb:Er的双包层光纤中。一种光纤放大器包括：双包层光纤,其纤芯掺杂有铒(Er～(+3))和镱(Yb～(+3))的离子；以及泵浦激光器,生成在1.02-1.06μm波长范围内的泵浦波长的辐射；泵浦激光器,输出在1.02-1.06μm波长范围内的光且所述光被耦合到掺Yb:Er的双包层光纤中。所公开的光纤激光器和光纤放大器在1μm波长范围内的激光阈值均比在9xxnm泵浦波长进行操作的已知原理的阈值高得多。(A fiber laser configured with: double-clad optical fiber having erbium (Er) doping +3 ) And ytterbium (Yb) +3 ) Of ions of (a). At least two spaced apart high and low mirrors flanking the core and defining a resonant cavity therebetween. The fiber laser also includes a pump laser that outputs light in the wavelength range of 1.02-1.06 μm and is coupled into a Yb: Er doped double clad fiber. An optical fiber amplifier comprising: double-clad optical fiber having core doped with erbium (Er) +3 ) And ytterbium (Yb) +3 ) The ion of (2); and a pump laser generating radiation at a pump wavelength in the wavelength range 1.02-1.06 μm; a pump laser outputting light in a wavelength range of 1.02-1.06 μm and coupled to the Yb: Er dopedIn the double clad optical fiber of (1). The laser threshold of the disclosed fiber laser and fiber amplifier in the 1 μm wavelength range is much higher than the threshold of the known principle of operation at a pump wavelength of 9 xxnm.)

1. A fiber laser comprising:

double-clad optical fiber having Er doped⁺³Ion and Yb⁺³"a core of ions;

at least two spaced apart high and low mirrors flanking the core and defining a resonant cavity therebetween; and

a pump laser generating radiation at a pump wavelength in the wavelength range 1.02-1.06 μm, the pump laser outputting light in the wavelength range 1.02-1.06 μm, the light being coupled to a light source doped with Yb: double-clad Er fiber.

2. The fiber laser of claim 1, wherein the pump laser is a single mode "SM" fiber laser or a multimode "MM" fiber laser and is configured as a fabry-perot resonator or as a MOPFA.

3. The fiber laser of claim 1, wherein the pump laser is selected from a laser or a semiconductor laser.

4. The fiber laser of claim 1, wherein the double-clad fiber is end-pumped or side-pumped.

5. The laser according to claim 1, wherein the core of the double-clad fiber is configured to support propagation of multiple transverse modes or a single transverse mode.

6. An optical fiber amplifier comprising:

double-clad optical fiber having Er doped⁺³Ion and Yb⁺³"a core of ions; and

a pump laser generating radiation at a pump wavelength in the wavelength range 1.02-1.06 μm, the pump laser outputting light in the wavelength range 1.02-1.06 μm, the light being coupled to a light source doped with Yb: double-clad Er fiber.

7. Amplifier according to one of the preceding claims 6, wherein the pump laser is selected from SM fiber lasers or MM fiber lasers with fabry-perot configuration.

8. The amplifier of claim 6, wherein the pump laser is a laser or a semiconductor laser.

9. The amplifier of claim 6, wherein the optical fiber is end-pumped or side-pumped.

10. The amplifier recited in claim 6 wherein the core is configured to support propagation of multiple transverse modes or a single transverse mode.

11. A fiber laser system comprising:

a master oscillator power fiber amplifier "MOPFA" configuration structure, the MOPFA configuration structure comprising Yb: er fiber laser, Yb: and for the Er fiber laser, Yb: and (3) performing seed injection on the Er fiber amplifier, wherein Yb: er fiber laser and Yb: at least one or both of the Er fiber amplifiers is based on a double-clad fiber configured with Er-doped fiber⁺³Ion and Yb⁺³A core of ions and a cladding surrounding the core; and

a pump laser outputting pump light in a 1.02-1.06 μm wavelength range, the pump light being coupled to at least one of the master oscillator and the amplifier doped with Yb: er in an active fiber.

12. The fiber laser system of claim 11, wherein the pump laser is an SM fiber laser or an MM fiber laser and is configured with a fabry-perot resonator or a MOPFA architecture.

13. The fiber laser system of claim 11, wherein the pump laser is a laser or semiconductor, the laser selected from Nd: YAG or Yb: YAG.

14. The fiber laser system of claim 11, wherein the pump fiber laser pumps the Yb: er fiber laser and Yb: both Er amplifiers supply energy.

15. The fiber laser system of claim 11, wherein the Yb: the Er fiber laser and amplifier have corresponding pump lasers.

16. The fiber laser system of claim 11, wherein the Yb: the Er fiber amplifier is pumped unidirectionally or bidirectionally.

17. The fiber laser system of claim 11, wherein the active fiber is end-pumped or side-pumped.

18. The fiber laser system of claim 11, further comprising a thermostat controllable to switch the Yb-doped fiber to a Yb: the temperature of the Er active fiber was maintained above room temperature.

Technical Field

The present disclosure relates to a high power Yb: Er fiber laser system that suppresses the generation of Yb laser light in the wavelength range of 1 micrometer (nm). In particular, the present invention relates to high power fiber oscillators and amplifiers based on Yb: Er doped fiber in the wavelength range of 1020-1060nm, wherein the Yb: Er doped fiber is cladding pumped.

Background

There is a need for high power, practical, and low cost erbium (Er) doped double clad fiber laser systems operating in the 1.5-1.6 μm wavelength range. Laser operation in this wavelength range is attractive for the following reasons: it is well suited for pumping of thulium (Tm) laser systems, mid-infrared parametric amplifiers and oscillators; in addition, it has low fiber loss, making high power Er lasers a great advantage in many scientific and engineering applications.

The most common laser transitions in Er are concentrated around 1550 nm. Most of the pumping devices of Er-based laser systems operate around the 980nm pump wavelength and are widely used in Er fiber systems. However, Er fiber devices pumped in the 9xx nm wavelength range may not have sufficient power to meet the growing industry demands. The primary reason limiting power scaling of Er fiber devices is the lack of a high power Single Mode (SM) energy source. Generally, known SM energy sources are based on diode lasers with a power not exceeding 2-3W. Another limitation stems from the fact that Er ion doping concentrations are relatively low for the following reasons. First, at high Er concentrations, luminescence may be quenched by energy transfer processes due to the interaction between Er ions and OH ". Second, the well-known "concentration quenching" process, in which Er ions are de-energized by electrostatic dipole-dipole interactions. This phenomenon results in reduced efficiency and reduced gain. Furthermore, if a large pump power is applied, another cooperative up-conversion process can occur, which can lead to very undesirable optical darkening that degrades the fiber.

Co-doped Er⁺³And Yb⁺³(wherein Yb⁺³As a sensitizer) has been used to circumvent the relatively low pump absorption in Er fibers, thereby increasing the power scaling of Er lasers and Er amplifiers. As shown in fig. 2, for the silica fiber, Yb ions have a simple electronic structure having only one metastable state higher than the ground state, a wide absorption spectrum, and large absorption and emission cross sections. Unlike Er, Yb can be used at high doping concentrations and often at high doping concentrations, allowing high power MM diode lasers to utilize cladding pumping schemes. In principle, the pumping can be performed over a wide wavelength range of 910nm to 1064 nm. A large absorption cross section (especially at 976 nm) can achieve high pump absorption, resulting in shorter fiber lengths.

Fig. 3 shows a typical schematic diagram of a high power fiber system configured with an Er laser 10 having a Yb: Er co-doped Double Clad (DC) fiber 12 disposed within an optical resonator defined between a high mirror and a low mirror 15. A diode laser based pump source 14 bi-directionally side-pumps the Yb: Er laser at a wavelength of 9xx nm. In operation, pump light is emitted and confined in the inner cladding and spatially overlaps the core of the optical fiber 12. Yb of⁺³The ions absorb the pump photons over the entire length of the fiber 12 while transferring their energy to Er resonantly⁺³Ions. The optical fiber 12 is a phosphosilicate glass, which is considered to be Yb due to its larger emission cross-section³⁺Er³⁺Good matrix for co-doped systems. The larger photon energy in the phosphate matrix increases the transition probability for the desired relaxation, which prevents energy from Er⁺³Transfer back to Yb⁺³. Furthermore, the spectral overlap between the Yb emission spectrum and the Er absorption spectrum is large, from Yb in phosphosilicate fibers³⁺To Er³⁺The energy conversion efficiency can reach 95%.

There are many limiting factors that hinder the power scaling of the laser 12, and the pump arrangement 14 of fig. 3 operates in the 9xx nm wavelength range. One of these limitations is parasitic Yb emission in the 1 μm wavelength range that may inevitably damage the fiber 12 of an Yb: Er fiber laser due to an undesirably high gain factor in that wavelength range. Fig. 4 shows the parasitic generation of the Yb: Er fiber laser 10 of fig. 2 in the 1 μm wavelength range. The bottom curve 1 shows the Er output pulse at 1570 nm. The top curve 2 shows the superluminescence signal of Yb, which has a lasing peak in the 1 μm wavelength range.

One of the factors explaining the unwanted emission in the 1 μm wavelength range is: there are a finite number of Yb ions in the core of the fiber that are isolated from the Er ions, and these Yb ions do not participate in the energy transfer to the Er ions. Usually, the isolated Yb ions do not exceed a few percent of the total amount of Yb ions. However, the isolated Yb ions contribute much more to the total unwanted population inversion than the Yb ions that participate in the energy transfer at the 9xx pump wavelength, as can be seen by comparing the gain spectra in respective fig. 5 and 6. The high gain of Yb ions in the 1 μm wavelength range is a typical, unwanted phenomenon in Yb: Er fiber laser systems.

Another factor affecting power scaling is parasitic generation in the 1 μm wavelength range. As the temperature of the active fiber increases, the absorption coefficient in this wavelength range and the transition speed between Er and Yb ions also increase. However, if the latter condition is not satisfied, higher spurious generation in the 1 μm wavelength range is exacerbated.

Based on the foregoing, there is a need for a high power, high efficiency Yb: Er laser and amplifier characterized by low gain in the 1 μm wavelength range.

Disclosure of Invention

The high-power Yb: Er fiber laser/amplifier of the invention meets the requirement by realizing at least one Yb fiber laser for pumping Yb: Er-doped fibers within the pumping wavelength range of 1-1.06 mu m.

Er doped fiber pumps Yb in the 1-1.06 μm pump wavelength range with a population inversion of isolated Yb ions limited to about 2-15% compared to 70% population inversion at a 9xx nm pump wavelength. At the same time, compareLong pump wavelengths do not significantly affect the participation in Er⁺³Energy-transferred Yb of ions⁺³The population of the ions is reversed. Due to isolated Yb⁺³The population inversion of the ions is small and the maximum gain coefficient in the 1 μm range at a pump wavelength of 1020 to 1060nm is significantly lower than the maximum gain coefficient at a pump wavelength of 9xx nm. As a result, the laser threshold of the inventive system in the 1 μm wavelength range is much higher than that of the known solution principle operating at a pump wavelength of 9xx nm.

More specifically, according to one aspect of the present disclosure, the inventive system is configured with a Yb: Er fiber laser. In particular, fiber lasers are based on an Er Yb co-doped double-clad (DC) configuration that is pumped by a laser source operating in the 1-1.06 μm pumping wavelength range. The pump light can be coupled into the pump cladding of the DC fiber in one of the forward and backward directions (relative to the direction of signal light propagation) or bi-directionally.

The disclosed Yb: Er DC optical fiber, which outputs signal light at a wavelength of about 15xx nm, may be configured with: single Mode (SM)/Low Mode (LM) core with output M²Signal light in the 15xx nm range below 5 (preferably below 2); or a multimode (MM) fiber.

According to another aspect, the disclosed pump laser may be a SM or a MM. Furthermore, the technique of pumping Yb: Er fibers can be side pumping or end pumping. The particular pumping technique depends on the task at hand and may be used with any or all of the above-described aspects and features of the disclosed system.

An Er system may be configured with: a Yb laser pump operating in the wavelength range of 1000-1060 nm; a seed for outputting signal light having a desired wavelength of 15xx-16xx nm; and one or more amplification cascades. At least one or both of the seed and the amplifier are based on a Yb: Er fiber. The seed and amplifier together form a Master Oscillator Power Fiber Amplifier (MOPFA) architecture.

The Yb-pumped fiber lasers disclosed in all of the above aspects can selectively pump either a seed source or a fiber amplifier, or both, in accordance with all of the above-disclosed pumping techniques. Furthermore, the disclosed Yb fiber pump can be used in conjunction with other pump configurations. For example, one of the seed and amplifier operates in conjunction with diode laser based pumping, while the other is pumped using the disclosed Yb fiber laser.

The single fiber laser and MOPFA configurations disclosed above can be used as Yb: Er pumps for various doped active media. One of the industrial applications of Yb: Er pumping involves pumping an Er fiber laser or amplifier that operates at a longer wavelength than the Yb: Er pump light. Another application of Yb: Er pumping involves outputting pump light coupled into a thulium (Tm) doped gain medium.

The Yb: Er lasers and MOPFA configurations disclosed above may operate under different operating regimes. That is, they may operate in a Continuous Wave (CW), quasi-CW (qcw), or purely pulsed regime.

Drawings

The above and other features and advantages will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which:

FIG. 1 is Er in Yb: Er phosphate glass⁺³The known absorption and emission cross-sections of the ions;

FIG. 2 shows Yb in silica glass⁺³The known absorption and emission cross-sections of the ions;

FIG. 3 is an optical schematic of a known Yb: Er laser pumped at a pump wavelength of 9xx nm;

FIG. 4 shows an example of signal generation at 1.5 μm wavelength and parasitic generation at 1 μm wavelength in a Yb: Er QCW fiber laser;

FIG. 5 shows Er of FIG. 2 participating in Yb: Er fiber at a pump wavelength of 9xx nm⁺³Energy-transferred Yb of⁺³The gain of the ions;

FIG. 6 shows gain-isolated Yb in the Yb: Er fiber of the schematic diagram of FIG. 2⁺³Ions;

FIG. 7 shows all Yb parasitic at a parasitic wavelength of 1 μm in the schematic diagram of FIG. 2⁺³The total gain of the ions;

FIG. 8 is an optical schematic of the disclosed laser system;

FIG. 9 is a diagram of all Yb at a parasitic wavelength of 1 μm in the schematic diagram of FIG. 8⁺³The total gain of the ions;

FIG. 10 is an optical schematic diagram showing the fiber laser system of the present invention of FIG. 8 operating in a master oscillator power fiber amplifier configuration;

FIG. 11 is an optical schematic of the inventive fiber laser system of FIG. 9 pumping a gain medium doped with Tm ions;

fig. 12 shows the dependence of the laser threshold on temperature.

Detailed Description

Fig. 8 shows an inventive schematic of a MM Er fiber laser or amplifier 20 based on a double-clad Yb: Er doped fiber 22, the double-clad Yb: Er doped fiber 22 being disposed in a resonant cavity defined between MM wavelength reflectors 24. In contrast to known techniques, Er fiber lasers are cladding pumped by a pump source such as a Fabry-Perot Yb fiber laser operating at 1020-1060nm pump wavelength or a neodymium (Nd) doped fiber laser at 1050-1060nm pump wavelength to output signal light at a wavelength of about 15 xxnm. The pumping arrangement may be configured according to a side-pumping or end-pumping technique, allowing unidirectional pumping in one of the opposite optical propagation directions, or bidirectional pumping as shown.

The exemplary fiber 22 of fig. 8 is pumped by one or more MM Yb pump fiber lasers 26 laterally pumping the fiber 22 at a pump wavelength of 1028 nm. The optical fiber 22 has a 50 μm MM core doped with Yb: Er ions and is approximately 10 meters in length. A1 kW output at a signal wavelength of 1570nm has been obtained under the QCW mechanism without Yb in the 1 μm wavelength range⁺³Parasitic generation of ions. In contrast, the same exemplary schematic diagram according to the configuration of FIG. 3 operating with a 960-970nm pump source outputs a signal wavelength of 1570nm with a maximum of 300-400W, after which the spurious generation in the 1 μm wavelength range is theoretically determined. In theory, if a 1kW output at a 960nm pump wavelength can be obtained by using the configuration of FIG. 3, then all Yb⁺³The total amplification of 1 μm of ions will exceed 80dB as shown in figure 7. In contrast, theoretically, for the fiber 22 having the above-described content as described above, the inventive structure of fig. 8 will have only 32dB total parasitic amplification for the same 1kW output, as clearly seen in fig. 9.

FIG. 10 shows an optical schematic representation 30 of the QCW Yb: Er fiber laser of the present invention utilizing a pump wavelength range of 1020-1060nm in a Master Oscillator Power Fiber Amplifier (MOPFA) configuration. A filter 32 is placed between the Yb: Er fiber laser 20 and the Yb: Er fiber amplifier or booster 30, the filter 32 configured as a length of Yb doped fiber, further processing spurious signals within the 1 μm wavelength range at the output of the fiber 22. The pumping arrangement comprising the Yb fiber laser 34 is configured as both the pump laser 20 and the booster 30. Pumping of the Yb: Er fiber is accomplished by placing a resonant cavity of the Yb pump 34 between two relatively weak wavelength reflectors 36 and 38, which allows pump light to be coupled into the laser 20 and the booster 30, with the pump light coupled into the laser 20 being much weaker than the pump light coupled into the fiber booster 30. To prevent unwanted leakage of 15xx nm wavelength signal light from the cavity of laser 20, a combination of multiple MM strong wavelength reflectors 40 are installed upstream along the Yb: Er fiber 22.

Turning to fig. 11, the Yb: Er fiber configuration of the present invention may be used as a pumping unit for a Tm fiber laser system 42. As shown, in the MOPFA configuration, the latter can be implemented as a separate Tm fiber laser, or a separate Tm fiber amplifier.

In summary, the pump wavelength range of 1020-1060nm allows for a reduction in isolated Yb⁺³The gain of the ions and the increase of the threshold of parasitic generation at 1 μm wavelength in Yb: Er phosphate fibers is 2-3 times.

The presently disclosed method can help optimize the configuration of Yb: Er fibers for any given task. Typically, the maximum power of the laser system and the quality of the light are set from the beginning. From these a priori known parameters, the maximum acceptable parasitic gain in the 1 μm wavelength range is determined. Depending on the specific application of the Yb: Er laser system, the acceptable parasitic gain may vary. For example, if a Yb: Er fiber laser is used as the pump source for the Tm-doped fiber, the maximum acceptable gain in the 1 μm wavelength range may be higher than that of a Yb: Er fiber used for heat treating a material having a reflective surface. As for the quality of the optical signal output by the Yb: Er fiber laser, it depends mainly on the parameters of the gain medium, i.e., the Yb: Er fiber, such as the core diameter, fiber length, core NA, and other well-known parameters of ordinary skill in the fiber art.

It is assumed that for the desired output power of an Yb: Er laser at a wavelength of 15xx μm, a high power pump source operating at a wavelength of 1 μm is required. Typically, a 1kW system output at 1550nm, assuming a pump efficiency of 50% due to various optical losses, requires about 2kW of pump light at a wavelength range of 1 μm.

According to the foregoing, there are two sets of Yb ions in Yb: Er media. The first group comprises isolated Yb⁺³Ions of composition not exceeding Yb⁺³5% of the total number of ions and a lifetime between 1ms and 1.4 ms. Another group for example comprises the participating Er⁺³95% Yb of ion energy transfer⁺³Ions, and a lifetime of tens of microseconds (μ s). Yb of⁺³The absorption of the pump light by the ions is distributed to 5% to 95%, where Yb⁺³Yb of ion transferred by second energy⁺³And (4) ion absorption.

By the assumptions disclosed above, Yb is determined at the output of a 2kW pump, e.g. 1020nm wavelength, for a given fiber length⁺³Each Yb in the ion set⁺³The level of population inversion in the ion population. Then two sets of Yb are known⁺³Population inversion in ions, determination and accumulation of two sets of Yb⁺³The corresponding gain of the ions. If the maximum parasitic gain exceeds the maximum acceptable level, the following steps may be taken.

First, the length of the doped fiber can be changed and Yb recalculated according to the above procedure⁺³The final gain of the ions. However, the fiber length cannot be increased indefinitely because it leads to unacceptable optical losses and reduced laser efficiency.

Second, the pump wavelength increases. For example, instead of the 1020nm wavelength, a 1030nm wavelength is used. As the pump wavelength increases, the population of the isolated Yb ions inverts and thus the gain in the undesirable wavelength range decreases. As a result, the population inversion of isolated Yb ions is reduced by the same 2kW pump power, while the energy-transferred Yb is⁺³The population inversion of the ions remains unchanged. Thus, the undesirable total Yb gain in the 1 μm wavelength range is also reduced.

The Yb: Er fiber configuration should also be reconsidered as the pump wavelength increases. For example, it may be desirable to reduce the cladding diameter from, for example, 200 μ to 150 μ.

Fig. 12 illustrates another important factor that helps minimize the parasitic generation of 1 μm. The temperature of the active Er: Yb fiber is close to room temperature at the initial stage of laser operation. As the laser continues to operate, the temperature of the gain medium increases. During the so-called cold start, parasitic generation in the 1 μm wavelength range occurs at relatively low temperatures. However, as the laser continues to operate and the temperature increases, this generation almost disappears. Therefore, to further minimize parasitic generation in the 1 μm wavelength range, the fiber laser system of the present invention shown in fig. 8 includes a thermostat that can be controlled to maintain the temperature of the Yb: Er fiber within a specific temperature range from the beginning. The lower limit of this range should obviously be above room temperature and the maximum temperature should obviously not reach a level detrimental to the integrity of the optical fiber. The range of each laser can be determined analytically or experimentally.

One of ordinary skill in the laser arts will readily recognize that many different configurations of the various fiber lasers disclosed may be readily implemented without departing from the intended scope of the present invention. It is clear that the operation mechanism of the inventive structure is not limited to QCW configuration and can be successfully used in CW and pulsed mechanisms. All SM or low mode lasers, pump sources and amplifiers may be substituted for the MM device described above. Although the pumping arrangement preferably comprises a fibre laser, the pumping arrangement may alternatively comprise any other suitable pump source. The disclosed signal light power is merely exemplary and may of course and will increase with optimization of the pump power and cooling arrangement.

It is, therefore, to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.