810 W continuous-wave and single-transverse-mode fibre laser using 20 /spl mu/m core Yb-doped double-clad fibre

It is shown that continuous-wave kW-power fibre lasers can be built using double-clad fibres with relatively small cores. 810 W in a single-transverse-mode output (M/sup 2/=1.27) is demonstrated experimentally with 20 /spl mu/m core low-NA (NA=0.06) Yb-doped double-clad fibre. A laser numerical model matches experimental results and predicts scalability of achievable powers into a multi-kW range.     

Phase-locking of two photonic crystal fibre lasers by mutual injection scheme

In recent years, exciting progress has been made in the upscaling of high-power fibre lasers, owing to the advance in cladding pump and fibre fabrication technologies. Especially, with the advent of photonic crystal fibres (PCFs), Yb-doped PCFs are rapidly being developed and utilised in the study of high-power fibre lasers, the reported output power of PCF laser having exceeded kW levels [1]. Compared with the conventional fibres, PCFs have many unique properties such as endless singlemode guiding, large singlemode area, small nonlinearity, and high numerical aperture of inner cladding, etc., which make PCFs especially suitable for producing high-power lasers with good beam quality. However, as in the case of the conventional fibre lasers, nonlinear effects and onset of catastrophic thermo-optical damage are the main limitations of the upgrading of high-power PCF lasers. Thus, coherent addition schemes are also desired for PCF lasers to achieve higher output power with higher brightness.     

Cavity design for highly efficient singlemode laser in Yb-dopeddouble clad fibre

A novel cavity for a Yb-doped clad-pumped silica fibre laser was designed to enhance the lasing efficiency and the pump absorption into the Yb-doped core, and to provide efficient packaging with low pump power leakage for fibres with totally different parameters. From this cavity setup, we obtained a high power singlemode laser over 3.8 W with a sharp line-width and a slope efficiency of 85%     

Multi-coupler side-pumped Yb-doped double-clad fibre laser and pump light leakage at coupler

A multi-coupler side-pumped Yb-doped double-clad fibre laser with output power of 1.38 W and slope efficiency of 48.9% by the fibre angle-polished method is demonstrated. Its pump light leakage at the fibre coupler is also investigated experimentally and theoretically.     

1 W single-transverse-mode Yb-doped double-clad fibre laser at 978nm

A novel all-glass Yb-doped double-clad fibre laser that emits over 1 W of single-transverse-mode output at 978 nm is described. This device is efficiently pumped with 2.5 W of launched power from a single 200 μm broad-area laser diode at 915 nm     

Mitigating the risk of high power damage to the BT network

Optical powers used in optical telecommunications networks have increased over time with the advent of technologies such as erbium doped fibre amplifiers, dense WDM, and fibre Raman amplifiers. Erbium fibre and Raman amplifiers with output powers up to 1 W and 2 W respectively are now available for deployment giving optical power densities of ≈14 000 MW/m² per Watt launched into a single mode fibre. This compares with 74 MW/m² for the surface of the sun. It is thus essential to ensure that the risk of optical damage to the fibre is understood and steps are taken to mitigate it where necessary. Research carried out by BT over the last few years has shown that fibres carrying relatively modest optical powers, as low as 200 mW for the most sensitive fibres, can be catastrophically damaged at tight fibre bends. Damage is caused by some of the optical power lost at the bend being absorbed by the fibre coating that may over time lead to a sudden increase in temperature to over 700 °C causing either the silica to kink mimicking a fibre break, or the coating to burn off at the bend leading to fibre failure on subsequent handling. This paper describes factors that increase the risk of short-term catastrophic damage at fibre bends, presents experimental results to show the variation in sensitivity between different fibres, and discusses new important theoretical results modelling the temperature rise in the fibre.     

Mitigating the risk of high power damage to the BT network

Optical powers used in optical telecommunications networks have increased over time with the advent of technologies such as erbium-doped fibre amplifiers, dense WDM, and fibre Raman amplifiers. Erbium fibre and Raman amplifiers with output powers up to 1 W and 2 W respectively are now available for deployment giving optical power densities of ≈ 14 000 MW/m² per Watt launched into a single mode fibre. This compares with 74 MW/m² for the surface of the sun. It is thus essential to ensure that the risk of optical damage to the fibre is understood and steps are taken to mitigate it where necessary. Research carried out by BT over the last few years has shown that fibres carrying relatively modest optical powers, as low as 200 mW for the most sensitive fibres, can be catastrophically damaged at tight fibre bends. Damage is caused by some of the optical power lost at the bend being absorbed by the fibre coating that may over time lead to a sudden increase in temperature to over 700 °C causing either the silica to kink mimicking a fibre break, or the coating to burn off at the bend leading to fibre failure on subsequent handling. This paper describes factors that increase the risk of short-term catastrophic damage at fibre bends, presents experimental results to show the variation in sensitivity between different fibres, and discusses new important theoretical results modelling the temperature rise in the fibre.     

All-glass high NA Yb-doped double-clad laser fibres made by outside-vapour deposition

The first all-OVD, all-glass, high-NA (/spl ges/0.3), double-clad, Yb-doped laser fibres are reported. Yb is incorporated via vapour-phase transport. These fibres yield low passive loss (<3/10 dB/km in core/innerclad at 1310 nm) and high-conversion efficiency, suitable for power scaling and higher reliability. Fibre lasers with output power of 110 W, M/sup 2//spl sime/1.07 and slope efficiency near 80% have been demonstrated.     

Ytterbium-doped large-core fibre laser with 272 W output power

A highly efficient cladding-pumped Yb-doped large-core fibre laser, generating up to 272 W of continuous-wave output power at 1.08 /spl mu/m with a beam quality (M/sup 2/) of 3.2, is reported. The slope efficiency was 83% with respect to the launched pump power. No saturation (roll-off) was observed in output power with increasing pump power.     

980nm波段连续光纤激光器的研究进展

980nm波段掺镱光纤激光器在高亮度抽运源和蓝绿光源方面具有广泛的应用前景。首先介绍了980nm波段连续光纤激光器的研究价值、研究难点。然后,介绍了国内外研究机构在980nm波段连续光纤激光器和放大器方面的研究进展和存在的问题。最后对980nm波段连续光纤激光器和放大器未来发展方向进行探讨。     

Helical-core ytterbium-doped fibre laser

An Yb-doped fibre laser with a helical core trajectory in the cladding material has been demonstrated for the first time. The laser yields 350 mW of linearly-polarised, single-spatial-mode output at 1047 nm from a multimode core of diameter, 26 /spl mu/m, and numerical aperture, 0.14, when core-pumped by an Yb:YAG laser at 1030 nm.     

百皮秒激光脉冲的全光纤放大及应用

为了得到高单脉冲能量的百皮秒激光脉冲,采用自制的被动锁模掺镱光纤激光器获得了100ps的激光脉冲输出,在此基础上采用两级全光纤结构主振荡功率放大器进行功率放大,其中预放大级采用7m纤芯的双包层掺镱光纤做增益介质,得到平均功率160mW的稳定脉冲输出;主放大级采用20m纤芯的双包层掺镱光纤做增益介质,在抽运功率逐步增加到35.37W时,输出功率达到了16.60W,相应的单脉冲能量为1.63J,峰值功率为16.61kW。此外,主放大级输出的激光通过自制的模场转换器与光子晶体光纤(纤芯4.6m)成功熔接,得到了2.85W的白光超连续光谱,光谱波长覆盖了600nm~1700nm的检测范围。结果表明,此激光可用于超连续谱光源的产生。     

New polarisation-state control device: rotatable fibre cranks

A new all-fibre device for controlling the state of polarisation (SOP) in a single-mode fibre is proposed. It consists of two fibre elements called rotatable fibre crank (RFC) elements, each of which is equivalent to a rotatable phase plate. It features a very low insertion loss when used in a fibre circuit, because it can be spliced with input and output fibres, and that the control is endless as in a rotatable phase plate. The effectiveness of the SOP control using this device is verified experimentally.     

Photonic bandgap fibre oscillators and amplifiers

In the search for ever higher output power or energy from fibre oscillators or amplifiers a nowadays mature technology relies on enlarging the fibre mode area. Broadening of the core diameter, all other things being equal, inevitably yields a multimode fibre, thereby dramatically limiting the device usefulness. Various strategies have been deployed to design and manufacture single transverse mode fibre oscillators and amplifiers, among which making use of the so-called photonic bandgap effect to restrict the modal population seems promising. Helped by efficient and reliable numerical tools the design of large mode area singlemode photonic bandgap fibres is presented. Two fibres with 20-μm and 40-μm core diameter, both of them heavily doped with Yb³⁺ ions, have been fabricated by the widespread modified chemical vapour deposition process and are shown to behave properly when used as the core element of either continuous wave oscillators or femtosecond amplifiers. Good output beam quality (M² parameter spanning from 1.12 to 1.5 for the set of fibres studied) and high slope efficiency of 80% in cw oscillation regime are demonstrated. Furthermore the 40-μm core diameter fibre is shown to be resilient to tight bending down to 7.5-cm radius. The stack-and-draw process makes it easy to tailor the outer cladding so that a large numerical aperture can be reached. Subsequently, from this air-clad fibre, 500 fs 47 W pulses at 35 MHz are obtained from a two-stage chirped pulse amplification system.     

Polarisation-maintaining single-mode fibre cable design

Guidelines for the design of a circular-polarisation-maintaining single-mode fibre cable are given. The use of circular polarisation allows use of low birefringence fibres and there is no need for orienting the fibres at splices. Quarter-wave plates at input and output of the fibres achieve the desired linear-circular polarisation conversion, and vice versa.     

Power spectrum of fibre output fluctuation in polarisation-preserving optical fibres

The power spectrum of fibre output intensity fluctuation was measured over 1.0 × 10?3 to 1.0 Hz for elliptical-jacket, PANDA and twisted fibres. Peaks peculiar to the mode conversion effect were observed for the linearly birefringent fibre, while the twisted fibre showed flat frequency characteristics with a reduced fluctuation level.     

Coherent combining of Q-switched fibre lasers

The power rising of an actively Q-switched erbium-doped fibre laser by using two coupled cavities with amplifying fibres in an interferometer configuration is reported. This study shows that the pulse peak power obtained is 1.7 higher than in a case of a unique laser. This concept brings some novel perspectives for scaling the output peak power of singlemode Q-switched fibre lasers.     

端面泵浦掺镱双包层光纤激光器功率输出特性研究

基于端面泵浦掺镱双包层光纤激光器的速率方程,应用MATLAB语言编程,分别数值模拟了功率为60瓦前端泵浦、后端泵浦和双端都为30瓦泵浦时掺镱双包层光纤激光器对应的功率输出特性和粒子数密度值特性,增大不同端面输入功率观察输出功率特性,研究得到后端泵浦上能级粒子数分布平坦,输出功率较大,为50.4705瓦。并且增大输入功率时得到双端泵浦输出功率较大。研究结论为提高掺镱双包层光纤激光器功率输出提供理论和实验参考。     

Tunable doped-fibre vertical cavity surface emitting laser

A simple way to improve the output power of singlemode tunable VCSELs is demonstrated. It is based on a master oscillator power amplifier (MOPA)-like embodiment of a fibre-VCSEL. The reported device, operating at 1.55 μm, uses a single pump source to photoexcite both a semiconductor structure and a doped fibre without compromise in compactness. Initial results show continuous tunability over 11 nm and fibre-coupled output power of 3.1 mW. It is noted that this approach can be extended to any part of the spectrum for which rare-earth doped optical fibres are available.     

30 dB optical net gain at 1.543 mu m in Er/sup 3+/ doped fluoride fibre pumped around 1.48 mu m

A 30 dB optical net gain and 12 dBm maximum output power for -1 dBm signal input have been measured at a signal wavelength of 1.54 mu m with an erbium doped ZBLAN fibre pumped at 1.47-1.48 mu m. The results confirm the great potential of ZBLAN fibres for hosting rare earth ions to generate optical amplification. The discussion points out the parameters to be studied to improve the fibre amplifier performance.<>