Spectral Beam Combining Research Articles

Spectral beam combining using superimposed reflective volume Bragg grating

It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. In this paper, a simple SBC system based on the superimposed reflective volume Bragg grating (RVBG) is proposed to reduce the scale of the SBC system. Considering the cross-coupling between the two gratings in a volume, two structure models of the superimposed RVBG-the superimposed RVBG with the same period and the superimposed RVBG with a different period-are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG is easy to be fabricated and has the potential to combine multiple lasers with one volume. Cross-coupling can be neglected for the same period structure when the slant angle divergence is larger than 0.01 rad and for the different period structure when the spectral separation is larger than 1.0 nm. The superimposed RVBG with a different period can achieve high diffraction efficiency simultaneously for each grating with a small slant angle divergence, and is convenient to combine multiple beams with small spectral separation. The effect of wavelength shift on diffraction efficiency can be ignored.

Channel Spectral Separation Narrowing for Spectral Beam Combining by Apodisation of the Reflecting Volume Bragg Grating

The sidelobe in diffraction efficiency of reflecting volume Bragg grating (RVBG) limits the wavelength channel spectral separation, which determines the combining power output in spectral beam combining (SBC) systems. A novel SBC system based on the apodised RVBG has been proposed to suppress the sidelobe. Several apodised RVBGs have been compared and the optimal apodised RVBG is obtained by using the chain-matrix approach. Numerical results show that the sidelobe could be suppressed excellently with Blackman apodised RVBG. In the numerical example, the minimal channel spectral separation was 1.0 nm for SBC system based on the RVBG and it decreased to 0.6 nm for the novel SBC system based on the Blackman apodised RVBG when the spectral combining efficiency of both systems achieves the same maximum value. Defence Science Journal, 2011, 61(3), pp.201-205 , DOI:http://dx.doi.org/10.14429/dsj.61.528

高功率光纤激光器谱合成系统的输出特性分析

高功率光纤激光器谱合成系统的输出特性分析

高功率光纤激光器谱合成系统的输出特性分析

高功率光纤激光器谱合成系统的输出特性分析

Linearly polarized operation of Yb-doped fiber laser by Brewster's angle-polished fiber end

A new method to obtain linear polarization operation by Brewster's angle-polished fiber end is demonstrated. By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity, a cladding-pumped linear polarization and single-transverse-mode (M2<1.1) Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm (FWHM) is less than 0.2 nm, is obtained in a simple configuration. The output power is up to 10 W which is continuouswave output at 1085 nm, and the slope eciency is 63% with respect to the coupled pump power and 75% with respect to the absorbed pump power, respectively. The measured 21-dB polarization extinction ratio does not degrade with the output power. The simplicity of such an approach is highly beneficial for a number of applications, including the use of a fiber laser for the nonlinear wavelength conversion (especially for the intracavity frequency doubling) and for the coherent and spectral beam combination.

Er3+/Yb3+共掺双包层光纤激光器谱组束实验研究

Er³⁺/Yb³⁺共掺双包层光纤激光器谱组束实验研究

Spectral beam combination of fiber amplified

In this paper we introduce a simple scheme to spectrally combine four single beams using three low-cost dielectric interference filters as combining elements. 25 ns pulses from four independent and actively Q-switched fiber seed-sources are amplified in a single stage fiber-amplifier. Temporally and spatially combined 208 W of average power and 6.3 mJ of pulse energy are obtained at two different repetition frequencies. A detailed analysis of beam quality as well as the thermal behavior of the combining elements is carried out and reveals mutual dependency.

Analysis of beam quality for the laser beams after spectral beam combining

The beam quality of the laser beams after spectral beam combining (SBC) has been analyzed in this paper. Based on the propagation model of the spectral beam combining system, the expression for the output field of an individual beam passing through the spectral beam combining system with lens aberration has been given and the intensity distribution of the combined beam has been studied by the principle of incoherent superposition. Consequently, according to the intensity second-order moments method, the M 2-factor of the combined beam has been calculated and the effect of lens aberration on the characteristics of the combined beam has been analyzed quantitatively. It can be shown that the SBC system can improve the beam quality of laser array significantly, and the M 2-factor of the combined beam passing through the ideal spectral beam combining system is almost the same as that of an individual beam. For the spectral beam combining system with lens aberration, the spherical aberration has greater effect on the off-axis beam than on the on-axis beam, and the beam quality of combined beam degrades with increase in lens aberration.

Beam combining of lasers with high spectral density using volume Bragg gratings

Incoherent combining of multiple laser beams with offset wavelengths into a single near-diffraction-limited beam is an effective solution to increasing energy brightness and scaling output power of high-power lasers. Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass allow spectral beam combining with a remarkably high spectral density of channels. Spectral beam combining (SBC) of five channels within 1–2 nm bandwidth around 1064 and 1550 nm into a single near-diffraction-limited beam with absolute efficiency 92–94% is demonstrated. Scaling of this technique to multi-kW power level is discussed.

Spectral Combining and Coherent Coupling of Lasers by Volume Bragg Gratings

The use of volume Bragg gratings (VBGs) recorded in photo-thermo-refractive (PTR) glass for laser beam control is described. These new optical elements provide extremely narrow spectral and angular selectivity and have a high level of resistance to high-power pulsed and continuous-wave laser radiation. These features of PTR volume gratings are used for transverse and longitudinal mode selection, passive coherent coupling, and spectral beam combining (SBC) of semiconductor, solid state, and fiber lasers.

Dual-Grating Spectral Beam Combination of High-Power Fiber Lasers

We describe a dual-grating spectral beam combination (SBC) system to combine multiple high-power fiber laser outputs while maintaining near-diffraction-limited beam quality. The two gratings are parallel in a grating rhomb configuration, with input and output beams that are parallel but shifted with wavelength, rather than the typical angular dispersion of a single grating. The resulting advantage of the dual-grating SBC over other beam combination systems is the relaxation of the linewidth requirement. We combined two fiber lasers with output powers of 115 W each and linewidths of about 0.15 nm ( ~40 GHz) to produce a combined beam of 190 W power with near-diffraction-limited beam quality ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ~ 1.18).

Expansion of the channel number in spectral beam combining of fiber lasers array based on cascaded gratings

Aiming at the problem that the channel number in spectral beam combining (SBC) of fiber lasers array is limited by the narrow spectral selectivity of grating, a new scheme based on cascaded volume Bragg gratings (VBG) is proposed to expand the channel number. A system cascaded by two VBGs is presented and analyzed. A formula used to accurately determine the angle of incidence of all the channels is derived using rigorous coupled-wave analysis (RCWA). The channel number can be multiplied with increasing the number of VBGs. Numerical results show that the system based on cascaded VBGs is a good SBC combiner that has the ability to combine a large number of channels.

基于级联体光栅的光纤激光阵列谱组束

基于级联体光栅的光纤激光阵列谱组束

522 W average power, spectrally beam-combined fiber laser with near-diffraction-limited beam quality

We report a three-channel, spectrally beam-combined (SBC), 1 mum fiber laser that produces 522 W of average power with near-diffraction-limited (M2 ~ 1.2) beam quality. The laser features a SBC power combining efficiency of 93%, versatile master-oscillator, power-amplifier fiber channels with up to 260 W of narrow-band, polarized, and near-diffraction-limited output that is tunable over nearly the entire 1 micro m Yb(3+) gain bandwidth, and excellent prospects for significant power scaling. To our knowledge, these results represent the highest beam quality and average power achieved to date for a beam-combined fiber laser system.

Spectrally Beam-Combined Fiber Lasers for High-Average-Power Applications

Spectrally beam-combined (SBC) laser systems, wherein multiple laser outputs are spectrally multiplexed into a single high-quality beam, are rapidly advancing the power scaling frontier for high-average-power beam-combined fiber lasers with near-perfect beam quality. We describe two- and three-channel SBC fiber lasers featuring 93% power-combining efficiency, near-diffraction-limited beam quality, average output powers in excess of 500 W, and excellent prospects for additional power scaling. To our knowledge, this level of optical performance represents the highest combination of beam quality and average power obtained so far for a beam-combined fiber laser system.

High brightness spectral beam combination of high-power vertical-external-cavity surface-emitting lasers

High brightness spectral beam combination of two high-power vertical-external-cavity surface-emitting laser (VECSEL) using volume Bragg grating in a photo-thermo-refractive (PTR) glass is demonstrated. High efficiency beam combination in excess of 90% is achieved, providing an efficient method for power scaling of diffraction limited beam. The beam quality of each starting lasers was 1.68 and 1.35, and that of combined beam was 1.9. Scaling opportunities based on the parameters of VECSELs and PTR Bragg gratings are discussed