We theoretically and experimentally demonstrated an all-fiber, hundred-watts-level, linearly-polarized, narrow spectral linewidth laser amplifier at a central wavelength of 1018 nm based on master oscillator-power amplifier configuration, which is composed of a laser oscillator and one stage of the fiber amplifier. The laser system can generate 104-W output power with 3- and 20-dB spectral linewidth of ∼0.073 and ∼0.25 nm, respectively, and a higher polarization extinction ratio of ∼17.89 dB at 1018.3 nm was obtained. Theoretical analysis based on the rate equations was used to optimize the parameters of 1018-nm ytterbium-doped fiber laser system for the maximum suppression of amplified spontaneous emission (ASE). The ASE was well depressed based on the optimization for the parameters of the laser system including the seed power, seed spectrum, gain fiber length in the amplifier, etc. And ∼ 27-dB signal-to-noise ratio was achieved at the maximum output power. The slope efficiency for the amplifier stage can reach 79%, and near-diffraction-limited beam quality ( and ) was obtained.
High power and high efficiency random fiber laser working at 1.5μm with mixed Erbium-Raman gain was theoretically proposed. The numerical model based on rating equations was established to analysis the laser performance of Erbium-Raman gain random fiber laser by different pump schemes. The optical-optical conversion efficiency reached 90% when pump power is 100W by forward pump scheme in the 1.5μm regime. Our work supplied an effective design for high efficiency and high power random fiber laser at 1.5μm which can be used for optical fiber sensing, research and communication. In our simulations results we found that forward pump scheme is better than backward pump scheme and bidirectional pump scheme in high power 1.5μm random laser, besides forward pump scheme is better than the other two pump schemes because of its compact, high efficiency and low costs, we also found that long Er-doped fiber (EDF) fiber length had good effect on the laser efficiency, the fiber length of single mode fiber (SMF) from 200m to 1km had little effect on laser efficiency. This design of 1.5μm random fiber laser can be a useful theoretical guidance for experiment and diverse wavelength could be achieved by the seed of 1.5μm random fiber laser.
1018nm Short wavelength Yb3+-doped fiber laser can be widely used for tandem-pumped fiber laser system in 1 μm regime because of its high brightness, high beam quality and low quantum defect (QD). In order to achieve 1018nm short wavelength Yb3+-doped fiber laser or amplifier with high output power and high beam quality, a steady-state rate equations model considering the mode competition, bend loss has been established. We theoretically analyzed the mode competition in 1018nm short wavelength Yb3+-doped fiber laser and amplifier and the simulation results show that the when the bend radius is 5cm, the LP01 mode output power is higher than the other mode power in the fiber laser and amplifier. When the bend radius is larger than 5cm, the beam quality will decrease in fiber laser and amplifier especially for fiber laser, besides we calculated the mode power in the fiber amplifier at different power of seed laser, when the LP01 mode power is higher than the other, the beam quality will increase. At last we analyzed the evolution of transverse gain of every mode along the radial coordinate in fiber laser and amplifier. Our results can provide instructive suggestions when designing bend radius and the power of seed laser based fiber laser and amplifiers and can help to enhance the beam quality.
We present an analytical theory based on a steady-state rate equations that describe pump power, stimulated Brillouin scattering (SBS) power, amplified spontaneous emission (ASE) and output power of a single-frequency 1018nm short wavelength fiber amplifier. A detailed model that accounts for amplified spontaneous emission (ASE) and stimulated Brillouin scattering (SBS) in relation to the ASE gain, Brillouin gain, fiber length, seed power, the linewidth of seed laser, and available pump power in both co-pumped, counter-pumped and bidirectional configurations is developed. It is found that when fiber length is optimized, the amplifier output power will increase with available pump power. In order to mitigate the SBS process, we can shorten the fiber length or reduce the seed laser power. Although higher output power is obtained with higher seed power, the SBS power will increase, and we find that the same amplifier efficiency is obtained with different pumped configuration, counter-pumped configuration mitigate SBS is more effective than co-pumped configuration and bidirectional configuration. We also calculate the output power and SBS power which consider the linewidth of seed laser by different pumped configuration, we also find that broader linewidth of seed laser can achieve lower SBS output power, but the change of laser power is unobvious with increasing the linewidth of seed laser. In order to suppress the ASE waves, we can shorten the fiber length or increase the seed laser power.
Photodarkening(PD) in Yb-doped fiber is one of the power limiting factor for long-time operation in high power fiber lasers and amplifiers. In order to achieve Yb-doped fiber laser and amplifier with high output power, a steady-state rate equations considering the amplified spontaneous emission (ASE) and PD losses has been established. Thermal effects and output power characteristics of high power fiber laser and amplifier are investigated. Transverse and longitudinal temperature distributions in fibers have been calculated by solving thermal conduction equations. We theoretically analyzed the PD losses and temperature in Yb-doped fiber laser and amplifier, the simulation results show that with the PD losses increasing, then the laser power drop quickly and we find that higher doped concentration and larger PD losses will lead higher temperature, so we should choose suitable doped concentration fiber and decrease PD losses to achieve higher output power.
We present result of achieving a random fiber laser at a working wavelength of 1178nm while pumping at 1018nm. The laser power is realized by 200m long cavity which includes three high reflectivity fiber Bragg gratings. This simple and efficient random fiber laser could provide a novel approach to realize low-threshold and high-efficiency 1178nm long wavelength laser. We theoretically analyzed the laser power in random fiber lasers at different pump power by changing three high reflectivity fiber Bragg gratings. We also calculated the forward and backward power of 1st-order stokes, 2nd-order stokes, 3rd-order stokes. With the theoretical analysis, we optimize the cavity’s reflectivity to get higher laser power output. The forward random laser exhibits larger gain, the backward random laser has lower gain. By controlling the value of angle-cleaved end fiber’s reflectivity to 3×10-7, when the high reflectivity increases from 0.01 to 0.99, the laser power increases, using this proposed configuration, the 1178nm random laser can be generated easily and stably.
We demonstrate an all-fiberized, linear-polarized, narrow spectral linewidth laser system with kilowatts-level output power at 1030 nm in master oscillator-power amplifier (MOPA) configuration. The laser system consists of a linear-polarized, narrow linewidth (~28 GHz) fiber laser oscillator and two stages of linear-polarized fiber amplifiers. A 925 W linear-polarized fiber laser with a polarization extinction ratio (PER) of 15.2 dB and a spectral width of ~60 GHz at the central wavelength of 1030.1 nm is achieved. Owing to the setting of the appropriate parameters for the laser, no indication of Stimulate Brillouin Scattering (SBS) is observed in the system. Moreover, thanks to the excellent quantum efficiency of the laser and the thightly coiling of the active fiber in the main amplifier, the mode instability (MI) is successfully avoided. As a result, the near diffraction-limited beam quality (M2<1.3) is achieved.
We present results on Raman fiber laser and random fiber laser. We theoretically analyzed the optical conversion efficiency in core and cladding pumped Raman fiber lasers. For cladding pumped Raman fiber laser, we change the cladding area and core area ration, fiber length, reflectivity of output FBG, Raman gain for improving the laser efficiency. At last we present a study of power output characteristics of random fiber lasers based on the half-open cavity by one or two fiber Bragg gratings, through our theoretical study we can know how to change the laser structure or fiber parameters to obtain the laser power and laser wavelength we want.
We have introduced a theoretical modeling based on arbitrary pump mode, derived the analytic functions of distributed amplifier along the fiber, and constructed a steady state heat equations of Yb-doped double-clad fiber amplifiers with both quantum defect and propagation losses being considered. Thermal effects and output power characteristics of kilowatt all fiber master-oscillator power amplifier (MOPA) are investigated by distributed pumping. Proper designs for reducing the temperature at the end of the fiber are proposed, the effect of the pumping mode and fiber length on the output performance and the temperature of fiber amplifiers is discussed and proposed a method to alleviate the thermal effect and improve amplifier efficiency. At last we also analyzed the output power and temperature characteristics by changing the power of seed laser, the results show that with the increasing the power of seed laser, the output power and temperature increase.
1018nm short wavelength Yb3+-doped fiber laser can be widely used for tandem-pumped fiber laser system in 1 μm regime because of its high brightness and low quantum defect (QD). In order to achieve 1018nm short wavelength Yb3+-doped fiber laser with high output power, a steady-state rate equations considering the amplified spontaneous emission (ASE) and Stimulated Raman Scattering (SRS) has been established. We theoretically analyzed the ASE and SRS effects in 1018nm short wavelength Yb3+-doped fiber laser and the simulation results show that the ASE is the main restriction rather than SRS for high power 1018nm short wavelength Yb3+-doped fiber laser, besides the high temperature of fiber is also the restriction for high output power. We use numerical solution of steady-state rate equations to discuss how to suppress ASE in 1018nm short wavelength fiber laser and how to achieve high power 1018nm short-wavelength fiber laser.