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Fiber tapering technology has been used to realize low-loss coupling from solid-core fibers to antiresonant hollow-core fibers (AR-HCFs) at low-power level, by inserting the tapered solid-core fibers into the hollow-core of AR-HCFs. Here, we have demonstrated the high-power coupling capacity of this way. For ice-cream type AR-HCF, a transmission efficiency of ~47% is achieved with injected 1080 nm laser power of ~90 W in a ~2 m HCF; for nodeless type AR-HCF, a transmission efficiency of ~40% is achieved with injected 1550 nm laser power of ~32 W in a ~2 m HCF. The output mode field with good beam quality shows the mode filtering characteristics of AR-HCFs.

2-5 μm mid-infrared lasers are of great use in many aspects such as the applications of remote monitoring, free space communication, laser surgery and infrared countermeasures. The fiber gas Raman source, combining the advantages of traditional solid core fiber lasers and gas lasers, firstly demonstrated in 2002, has aroused extensive attentions and now is still a hot topic for having better beam quality, higher damage threshold, higher peak power and narrower linewidth. By particularly designing hollow-core fibers (HCFs), selecting proper gases filled in the HCFs, mid-infrared lasers with various wavelengths can be easily obtained. So far, fiber gas Raman laser sources of different bands such as 1.5 μm, 2.0 μm, 3.0 μm, and 4.0 μm has been demonstrated through the sitmulated Raman scattering (SRS) of different gases such as methane, hydrogen and ethane. However, due to the transmission properties of current low-loss mid-infared HCFs, no efficient mid-infared fiber gas Raman laser sources beyond 4 μm have been reported up to now. In this paper, we provides a method of generating mid-infrared laser through the SRS of gases filled in the HCFs under cascaeded sturcture. In our experiments, two kinds of HCFs with different transmission spectra are used respectively in the first stage and second stage of generating Raman laser. In the first stage, a commercial 1064 nm high peak power laser is coupled into a methan-filled HCF through reflectors and planoconvex lens, and a 1.55 μm high peak power Raman laser is achieved by the first-order vibrational SRS of methane. In the seconde stage, the output 1.55 μm Raman laser is coupled into a hydrogen-filled HCF as the pump source, and finally a 4.3 μm Raman laser is generated by the first-order vibrational SRS of hydrogen. The transmission spectra of the HCF are the key factors in determining whether to generate 1.55 μm laser by the SRS of methane in the first stage or generate 1.9 μm laser by the SRS of hydrogen in the first stage. This work provides a vital way to realize a wide wavelength range of mid-infrared, even far-infrared fiber laser sources from available commercial 1 μm lasers with appropriate HCFs and different active gases.

On-line measurement of fiber core-temperature is very important for the investigations of high-power fiber lasers. Using thermal infrared imager is currently the most common approach to detect the temperature of fiber, even though it only monitor the surface temperature. So the measurement result is greatly different from the actual temperature of fiber core. Fiber Bragg Gratings (FBGs) have been widely used in detecting many physical quantities, such as strain, temperature, compression strength and curvature due to its intrinsic advantages, including simple manufacture technology, low insertion loss. Here, a new method based on FBG for measuring the temperature of fiber core is presented and experimentally demonstrated. We use a mutiple inscription method that inscribe a low reflectivity FBG on the high reflectivity chirp grating location as a fiber core temperature on-line monitor. Due to the resonant wavelength of chirp grating (1080nm) is far away from FBG’s resonance peak (1550nm), it means that the presence of FBG will not impact the performance of the chirp grating. Alongside this composite optical fiber structure is applied to fiber oscillator we inject a amplified spontaneous emission (ASE) light with the wavelength range near 1550 nm from the signal fiber of (2+1)*1 combiner. And then, the reflection spectrum of FBG can be record from the port 2 of circulator. The temperature of chirp grating and low reflectivity FBG can be measure by recording the shift of FBG’s resonance peak after the lineal relation between resonance wavelength and temperature are cofirmed. In order to detect the accuracy of this new structure, we also use Optical Frequency Domain Reflectometer (OFDR) to measure the temperature of the chirp grating. Experiment results prove the high accuracy of proposed temperature monitor. It is strongly believed that the novel proposed structure can be used to achieve measurement of fiber core temperature in high-power fiber lasers. This work also provides a novel idea for manufacturing multi-functional composite fiber structure.

The average power of diode-pumped fiber lasers have developed deep into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting the further power scaling. To date, many methods for SRS suppression have been proposed in fiber systems, such as the application of large-mode-area (LMA) fibers or enlarging the fiber mode area, spectrally selective fibers, or lumped spectral filters like long-period gratings (LPGs). The enlarging of fiber mode area must be combined with controlling numerical aperture (NA) for the operation of fundamental mode. Otherwise it will leads to a decreased transverse modal instability (TMI) threshold in fiber lasers, which also limits further power scaling. It is quite difficult to realize by today’s material and manufacturing technologies of fibers. The designing of spectrally selective fibers is usually very complex. Besides, it is also not easy to manufacture such fibers and it is still limited by the maximum fiber core size that can be employed. The working principle of lumped filters is similar to that of spectrally selective fibers, but it is much easier to design and fabricate such filters. LPGs have good filtering properties, but the filtering characters of LPGs is instable for their high sensitivities to the environment variable such as temperature, strain or humidity. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating (CTFBG) for the first time. The CTFBG is designed and inscribed in LMA fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG being inserted between the seed laser and the amplifier stage, a SRS suppression ratio of ~10 dB is achieved in spectrum at the maximum output laser power of 2.35 kW, and there are no reduce in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.

In this paper, the numerical steady-state model of mode competition in high power ytterbium-doped fiber amplifiers (YDFA) which considering the distributed photodarkening (PD) loss has been studied and developed for the first time. According to the relationship between PD loss and the upper-state population fraction, the formula of saturated PD loss which can distinguish different modes is established. Based on the rate-equation model considering transverse spatial-hole burning, we calculate the longitudinal distribution and quantitative results of each mode’s PD loss for the first time to the best of our knowledge. The dependence of parameters such as pumping direction, fiber length, and fiber doping composition on YDFA is also investigated and discussed. According to our simulation results, the output power of YDFA is strongly affected by PD loss. Meanwhile, PD increases the loss of higher-order mode (HOM), as well as enhances the ratio between fundamental mode (FM) and HOM. Thus, HOM suppression and improvement of beam quality can be expected within PD effect. In our work, the mode competition of high power YDFA under varying degrees of PD loss has been simulated. Obviously the output power will decrease with increasing the PD loss. However the ratio between FM and HOM has no evident changes with varying the PD loss, which providing guideline on appropriately using PD loss to regulate the mode competition between FM and HOM aiming at effective single-mode output of YDFA.

We demonstrated photodarkening induced core laser leakage phenomenon in the long term operation of a 3 kW copumping fiber amplifier. Output power perturbation of 4~6 minutes period was observed in the 6 hours maximum power operation. Despite the perturbation, the maximum power also drops from 3 kW to 2.65 kW due to the leakage of the core laser. This indicates that the co-pumping scheme may not be suitable to achieve high power fiber laser with long term output stability. We also provide a solution by adopting the counter-pumping scheme that shows very stable output power in the 1-hour maximum power operation test.

The side-coupled cladding-pumped fiber has many advantages in terms of system design, ease of pump injection, signal extraction and power scalability over traditional double cladding fiber. We demonstrate a 290-W all home-made side-coupled cladding-pumped fiber laser with the slope efficiency of 67.8%. To the best of our knowledge, the slope efficiency is the highest for the published high power fiber laser based on the DSCCP fiber. The slope efficiency of the home-made side-coupled cladding-pumped fiber amplifier is mainly limited by the background loss, pump light coupling and pump light absorption. The results show that the power ratio of signal light to residual pump light is near 20 dB. The pump light is not absorbed enough that the slope efficiency can be further improved by optimizing the amplifier structure.

A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical pump efficiency of 50% was demonstrated. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Macro pulse operations with square shaped pulses from 100 μs to 1 ms are achieved without relaxation oscillation. The exact wavelength of pump diode is found to be crucial for amplified spontaneous emission and parasitic oscillation in high power 1120 nm fiber laser. Effects of inhomogeneous spectral broadening and temperature dependent absorption are proposed to explain experimental observations.

Improving performance of beam uplink propagation in the relay mirror system has become a very lively area of scientific research. In recent years, many methods were proposed. But most related researches only concerns power coupling efficiency. We propose that both power coupling efficiency and the non-uniformity of the received beam should be considered. Model of the relay mirror system is established. With this model, damage effect of the system is theoretically analyzed in detail. Performances of uplink propagation with optimizations using different evaluation functions are calculated. Results show that uplink propagation with optimization using power coupling efficiency as the evaluation function can't get the optimal performance. For the 25km-altitude relay mirror system, performance of uplink propagation decreases instead of increases with optimization using power coupling efficiency as the evaluation function. The coming results show that taking the product of power coupling efficiency and the influence factor induced by the non-uniformity of the received beam as the evaluation function of the uplink propagation process is reasonable.

Current research on Surface plasmon polaritons (SPPs) is widely spread to surface adsorption, surface roughness and other related phenomena. It has also been used in the chemical and biological high-precision detection fields. More and more high-precision sensors have been created. Supercontinuum (SC) is a laser source with advantages as broad and flat spectra, high brightness and good coherent characters. By researching the SC laser source based surface plasmon resonance (SPR) effect, we can get a more comprehensive reflection of the SPR effect from factors as the light intensity reflectivity and the phase change. The SC laser source based SPR effect is a subject with important theoretical and practical significance. The testing principles and testing methods of the SPR effect in the installations with the Au-coated prism structure were studied. Using a SC laser, the wavelength-scanning and angle-scanning methods can be carried out in one system. The SC laser source based SPR effect in the installations with the Au-coated prism structure was tested. The SPR effect sensors based on SC were designed and realized. The theoretical results matched with the experimental results. Through the relation between the refractive index and the resonance wavelength, we could demarcate different substances.

Because of the diversified properties Fiber Laser affords a wide field of application. But restricted by nonlinear effects, heat damage and other elements, it is impossible to increase the output power unlimitedly. When single fiber can't meet, it needs to use Fiber Laser through beam combination to get high output power. Undoubtedly combiners play an important role for increasing the output power of Fiber Laser. The advent of Photonic crystal fiber (PCF) abound the kinds of combiners. It has numerous benefits and widespread application value. First, build the model of PCF combiners. Then through Finite Difference Method(FDM), calculate the effect of PCF combiners on the whole loss under different lengths of transition zone. Finally, compare the results. Through the results of numerical simulation calculation: when the length of Transition zone L is shorter than the diffraction length of the tapered L0, loss will go down with the increase of L; however, when L is far longer than L0, the increase of L will have negligible effect on the decrease of loss. So the conclusion is significant to both increase the performance of Photonic crystal fiber combiner and decrease the loss.

The laser relay mirror technique has been under extensive research in recent years. The concept and the working process of the relay mirror system are analyzed in this paper. The model of the relay mirror system is established, the effect on 1km-altitude target with 500 m/s flying speed of the relay mirror system and the conventional ground-based laser system are calculated respectively. Obtains that the maximum coverage range of the ground-based laser system is 2.0 km and the maximum coverage range of the relay mirror system is 23.2 km. The relay mirror can largely open up the coverage range of the laser system and strengthen the attacking ability of the ground-based laser.

Combining fiber laser beams are of current interest for scaling lasers to high average output power. The Master Oscillator Power Amplifier (MOPA) configuration is important in fiber laser beam combination. The efficiency of coherent beam combining is depended on the phase control precision of the system mostly, which is equivalent to the closed loop output phase noise. In this paper, a simplified negative feedback model of the phase control system is constructed to study the optimum design of the system. The effects of the transfer function of the system on the phase noise of the optical fiber amplifier, the measured noise and the stability of the system are analyzed. The relationship between the closed loop output noise and the system parameters is analyzed and calculated. The results show that there is a set of system parameters to minimize the closed loop output noise for different phase noise of the optical fiber amplifier, and for a fixed set of system parameters, the closed loop output noise of the system almost changes linearly with the change of the input noise. The effective means to achieve optimal system parameters for higher degree of control precision are obtained.

A two-dimensional program is applied to simulate the chemical dynamic process,gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers.Some important parameters in the cavity are obtained.The calculated results include averaged pressure and temperature,zero power gain coefficient, laser spectrum, output power, chemical efficiency and overtone efficiency.Based on the numerical simulation,the influence of entering gas flow parameter,nozzle structure and nozzle array length on the performance of HF overtone lasers are investigated separately.Because of small zero power gain coefficient of each HF overtone spectral line,the saturation degree of gain medium in the cavity is the most important parameter to influence the overtone efficiency of HF lasers.

A two-dimensional program was applied to simulate the chemical dynamic process, gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers. Some important parameters in the cavity were obtained. The calculated results included HF molecule concentration on each vibration energy level while lasing, averaged pressure and temperature, zero power gain coefficient of each spectral line, laser spectrum, the averaged laser intensity, output power, chemical efficiency and the length of lasing zone.

The He is usually used as diluent in combustion cw hydrogen/deuterium fluoride (HF/DF) chemical lasers. Sometimes, the N2 is also used as diluent in cw HF/DF chemical laser, because N2 is more cheaper than the He. It was thought that the efficiency of cw HF/DF laser with N2 diluent was lower than that of HF/DF laser with He diluent since the molecular weight of N2 is heavier than that of He. In this paper, the performance of cw DF chemical lasers with He and N2 diluent was investigated. The small signal gain, power spectral distributions, cavity pressure, power and efficiency of DF lasers with these two diluents have been calculated using a finite-difference technique for the numerical integration of the steady and unsteady Navier-Stokes equation with reactive flow (compressibility scaling method-CSM), which was developed in the chemical gas dynamic laboratory of the state institute of applied chemistry in Russia. The numerical results show that the efficiency of DF lasers with N2 diluent is not lower than that of the lasers with He diluent.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.