Forced pump oscillation at anti-Stokes wavelength of coupled Raman fibre laser resonators

Multi-watt oscillation of a Yb/sup 3+/-doped silica fibre pump laser is demonstrated at two wavelengths when pump-coupled Raman fibre laser resonators are constructed using fibre end reflection and a dielectric mirror, which are common to both the pump and Raman fibre lasers. Using an off-resonant Bragg grating to force the initial oscillation of the Raman fibre laser, pump emission at the anti-Stokes wavelength is demonstrated.     

光纤中的多级斯托克斯及反斯托克斯谱线

本文叙述在多模光纤中产生的多级受激拉曼散射谱，作了两种不同掺杂的SiO2光纤中的受激拉曼散射谱。对掺锗硅光纤得到16级斯托克斯线及10级反斯托克斯线。对掺磁硅光纤获得了13级斯托克斯线及4～5级斯托克斯线。测出了各级谱线的峰值波长及相对强度分布，并作了简单讨论。     

Ultra-low-loss (0.1484 dB/km) pure silica core fibre and extensionof transmission distance

A pure silica core fibre with unprecedented low-loss of 0.1484 dB/km has been successfully fabricated. With a large effective area of 118 μm², this ultra-low-loss fibre extends transmission distance by 33% compared to conventional Ge-SMF, and over 400 km distance transmission is possible with Raman amplification     

Bit error rate evaluation of optical signals amplified via stimulated Raman process in an optical fibre

Gain-stabilised Raman amplification in a silica fibre has been realised by means of backward pumping with a continuously mode-locked Nd:YAG laser. This enabled the first bit error rate evaluation of Raman amplified laser diode light signals. The power penalty owing to gain fluctuation has been suppressed to about 1 dB even at a gain as high as 14 dB.     

Ultra-wide-band Raman amplifier using tellurite and silica fibres

An extremely large seamless gain-bandwidth of 135 nm (1497-1632 nm) with a minimum gain of 22.8 dB is achieved with a novel hybrid tellurite/silica fibre Raman amplifier. The amplifier is used successfully as a pre-amplifier in a WDM transmission experiment     

Efficient backward and forward pumping CW Raman amplification for InGaAsP laser light in silica fibres

By pumping a small-core single-mode silica fibre with a 1.32 ?m CW Nd:YAG laser, continuous-wave Raman amplification of InGaAsP laser diode light, with unsaturated gain as high as 21 dB, has been obtained in both backward as well as forward pumping configurations.     

Fibre-optic Solc filter for use in Raman amplification of light

Fibre-optic Solc filters, in which five consecutive fibre coils are tilted with respect to each other, have been fabricated. The wavelength of maximum transmittance is designed to coincide with 1.24 ?m wavelength, and the half-power bandwidth is 61 nm. To show the feasibility of the fibre-optic Solc filter in Raman amplification of light, the third Stokes line (?=1.24 ?m) of 1.06 ?m Nd:YAG laser light from a silica fibre was successfully extracted, while the pump light and other Stokes lines were suppressed below ?13 dB.     

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.     

Fibre splices with `perfect fibre? strengths of 5.5 GPa, v<0.01

Splices of single-mode fused silica fibre having strengths equivalent to that of the as-drawn fibre of ~800 ksi (5.5 GPa) with a coefficient of variation v of <0.01 are produced by fusion splicing with an H2-Cl2-O2 flame. These results demonstrate that fused silica fibre can be reheated to fusion temperatures and retain original high strength. The results are statistically analysed with respect to variations in breaking load, fibre and splice diameter, and relative humidity.     

Tunable, broad visible range, fibre-based Raman source

Nine Raman orders covering a 130 nm bandwidth in the visible range have been generated in an optical fibre using a visible fibre pump source based on a seeded ytterbium amplifier and second harmonic generation in periodically poled KTP. A tunable, compact, fibre-based visible source has been demonstrated     

Raman amplifier based long-distance, remote FBG strain sensor with EDF broadband source recycling residual Raman pump

A novel and simple Raman amplifier based long-distance fibre Bragg grating (FBG) sensing system without any additional broadband light source is demonstrated. With the simplified system configuration recycling residual Raman pump power for generation of amplified spontaneous emission in an erbium-doped fibre (EDF), the high quality of remote strain sensing operation at a location of 50 km is achieved.     

Multi-wavelength, continuous wave fibre Raman ring laser operatingat 1.55 μm

A four wavelength continuous wave, fibre Raman ring laser has been demonstrated at room temperature using fibre Bragg gratings as the wavelength-selective elements with applications as a multi-wavelength source for optical fibre telecommunications. Channel spacings were ~5 nm between 1551.6 and 1565.1 nm with 14.9 dBm total output power     

Highly efficient linearly polarised Raman generation in a germania-core optical fibre

The letter reports very efficient Raman generation and polarisation switching effects in a high-germania-content optical fibre, with a small 2?m2 core area. 10 dB Raman amplification has been observed in 5 m of fibre at a pump power of 2W. The Raman emission is only generated along the birefringence axes of the fibre.     

Single-polarisation, single-frequency, 2 cm ytterbium-doped fibre laser

A single-polarisation, single-frequency, ytterbium-doped silica fibre laser has been demonstrated in a 2 cm linear cavity. The output power reaches 35 mW with an optical signal-to-noise ratio greater than 65 dB. A polarisation-maintaining fibre Bragg grating is used as the polarisation-dependent reflector to generate the single-polarisation output with the polarisation extinction ratio greater than 20 dB. The laser works stably for 2 h under laboratory conditions     

High-power cascaded Raman fibre laser using phosphosilicate fibre

A 13.2 W second cascade phosphosilicate cascaded Raman fibre using a 450 m phosphosilicate singlemode optical fibre is demonstrated. The lasing wavelength is 1539 nm and the conversion efficiency is 32.5%. This is the highest output power ever reported from a cascaded Raman fibre laser in the 1400-1600 nm range.     

Effect of enhancing the Raman gain factor on the linearity of Raman fibre amplifiers

The effect of enhancing the Raman gain factor on the linearity characteristics of Raman fibre amplifiers is analysed. In addition to providing higher Raman gain per unit pump power, a higher value for the Raman gain factor also results in a lower value for the maximum gain, and therefore the maximum output power, available from the amplifier if it is to operate in the linear regime. This has important implications for optimising the design of Raman fibre amplifiers.<>     

硫化铅掺杂石英玻璃光纤喇曼增强特性研究

普通单模光纤的喇曼增益低,严重制约了喇曼放大器的发展。因此,研究高喇曼增益的光纤具有重要意义。研究了硫化铅掺杂石英玻璃光纤的喇曼散射增强特性。采用改进的化学气相沉积(MCVD)法分别制备出硫化铅掺杂石英玻璃光纤和普通单模光纤样品,并测得其传输损耗谱和喇曼光谱,实验结果表明:硫化铅掺杂石英玻璃光纤具有更强的喇曼散射强度。在不同的泵浦功率条件下,分别进行了喇曼放大实验,相比于普通单模光纤,硫化铅掺杂石英玻璃光纤具有更大的喇曼增益。     

铌酸锂掺杂石英光纤拉曼增强特性研究

为了获得高拉曼增益特种石英光纤,提高拉曼光纤 放大器增益,本文研究了铌酸锂掺杂石英光纤的拉曼散射增强特性,采用改进化学气相沉积(MCVD)法制备出了铌酸锂掺杂石英光纤样品,其在1550nm 波长处的传输损耗为5dB/km。测得了铌酸锂掺杂石英光纤的拉曼光谱,并与相同长度的常 规单模光纤拉曼 光谱进行了对比,发现铌酸锂掺杂石英光纤具有更高的拉曼散射强度,在几个主要峰位处, 铌酸锂掺杂石 英光纤的拉曼散射强度为常规单模光纤的3.8～4.8倍。同时,搭建了 拉曼光纤放大器系统,分别测得铌酸 锂掺杂石英光纤和常规单模光纤的拉曼散射放大增益。实验结果表明,铌酸锂掺杂石英光纤 拉曼放大增益 约是常规单模光纤的2倍。因此,铌酸锂掺杂石英光纤作为拉曼光纤放大器的增益介质将可 取代常规单模 光纤,并能有效地提高拉曼光纤放大器的放大效果。     

Switchable dual-wavelength Raman erbium-doped fibre laser

A fibre Bragg grating feedback fibre laser with both Raman and erbium-doped fibre pumps is proposed. Dual-wavelength switching is achieved by controlling the power of the Raman pump. The characteristics of the dual-wavelength switching are studied experimentally, and the mechanism is explained physically.