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.     

Low pump power photonic crystal fibre amplifiers

Designs of low pump power optical amplifiers, based on photonic crystal fibres are presented. The potential of these fibre amplifiers is investigated, and it is demonstrated that such amplifiers may deliver gains of more than 15 dB at 1550 nm with less than 1 mW of optical pump power. We focus on the design of erbium-doped photonic crystal fibre amplifiers operated at very low pump powers. We achieve this by using PCFs with large air holes and thereby large index contrasts. With such high index contrast fibres, we may obtain very small mode field diameters.     

抽运功率配置对双向喇曼放大器性能的影响

为了研究抽运功率配置对双向抽运光纤喇曼放大器性能的影响,基于已有的耦合方程,采用数值仿真方法,分析了不同抽运功率配置对双向抽运光纤喇曼放大器的增益、增益饱和以及抽运功率转换效率的影响。结果表明,双向抽运光纤喇曼放大器的增益、增益饱和以及抽运功率转换效率特性均介于同向和反向抽运光纤喇曼放大器之间,并且随着同向抽运功率在抽运总功率中所占比例的升高,增益、增益饱和功率和抽运功率转换效率的数值增加;大信号、抽运功率较大时,抽运功率配置对双向抽运光纤喇曼放大器性能的影响显著。这对双向抽运光纤喇曼放大器和光纤激光研究具有一定的参考价值。     

Investigation of transient response in cascaded gain-clamped erbium-doped fibre amplifiers

The maximum power overshoot in gain-clamped erbium-doped fibre amplifier has been modelled and investigated from a laser point of view. It is found that by mismatching the relaxation frequency of cascaded amplifiers the transient power excursion and the relative-intensity noise can be tailored.     

Gain limitation of fibre Raman amplifiers considering third Stokes wavelength generation

The use of a fibre Raman amplifier as a repeater amplifier and a power amplifier is studied by considering the third Stokes generation. Due to the multiple Stokes generation, there exists a limit on the achievable amplifier gain. With optimum pump powers, maximum amplifier gains of up to 58 dB and 28 dB are achievable for a repeater amplifier and a power amplifier, respectively.<>     

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.<>     

Photonic crystal fibre for use in fibre Raman amplifiers

A novel photonic crystal fibre is proposed and designed. For this fibre, the variation of its effective core area Aeff via wavelength can be designed to follow the track of its Raman gain coefficient gR, so that a flat Raman gain efficiency rR=gR/Aeff is resulted. A fluctuation of less than 5.5% is obtained for rR between 1565 and 1625 nm (L-band).     

Transfer characteristics of Brillouin fibre amplifiers for use in self-homodyne coherent optical transmission systems

Presents for the first time, the basic input-output characteristics of a Brillouin fibre amplifier, and shows that these are in good agreement with the first experimental results reported recently by other workers on a novel and potentially very important application of Brillouin amplification in a coherent optical fibre transmission system. For this type of application, theoretical results are also presented on the optical pump power dependence of the amplifier gain per unit optical pump power.<>     

Gain-shifted thulium-doped fibre amplifiers employing novel highconcentration doping technique

A novel high thulium concentration doping technique is proposed for shifting the gain band in thulium-doped fibre amplifiers (TDFAs). The gain peak shifts from 1473 to 1505 nm when the Tm³⁺ concentration is increased from 2000 to 8000 ppm. The authors have achieved gains of >18 dB and a noise figure (NF) of <7 dB from 1480 to 1510 nm (30 nm bandwidth) for a total pump power of 500 mW     

Field demonstration of coherent transmission system with diode-pumped erbium doped fibre amplifiers

Reports a field demonstration of 622 Mbit/s DPSK and FSK coherent transmission over 200 km of installed single mode fibre. Diode-pumped erbium doped fibre amplifiers were used as both power amplifiers and repeaters. System loss budgets of more than 68 dB were achieved with an intermediate amplifier repeater gain of 16.5 dB. Both systems incorporated fully automated endless polarisation control.<>     

Limitations in fibre Raman amplifiers imposed by Rayleighscattering of signals

A simple method of Rayleigh scattering noise calculation in fibre Raman amplifiers is proposed. Using the method, it is disclosed that the optimal Raman pump power is lower when the Rayleigh scattering of both signal and amplified spontaneous emission (ASE) are considered than when the Rayleigh scattering of ASE only is considered     

Gain reciprocity in fibre optical parametric amplifiers

A fibre optical parametric ampifier operating in the small-signal gain regime can exhibit the same gain when amplifying in either direction. This is true even in the presence of random dispersion and birefringence variations along the fibre.     

Highly efficient Er-doped fibre amplifiers pumped in 660 nm band

High gain coefficient in an erbium-doped fibre amplifier, 3.8 dB/mW at 1.536 mu m and 2.3 dB/mW at 1.552 mu m, is achieved for a pump wavelength of 664 nm by using an erbium-doped fibre with a high numerical aperture of 0.285 and thermally-diffused expanded core fibre ends. The gain at 1.536 mu m reaches 30 and 35 dB for launched pump powers of 10 and 15 mW, respectively.<>     

Erbium-doped fibre amplifiers: the latest revolution in opticalcommunications

Like many technological advances associated with optical fibre communication, erbium-doped fibre amplifiers have moved from the laboratory to the field with extraordinary speed. They are capable of low-noise, low-distortion, high-gain and high-power operation over a broad bandwidth. The paper describes the physical principles behind their operation and shows how their unique characteristics are set to bring about a qualitative change in the way in which optical fibre is used     

Modeling of spontaneous emission noise in erbium-doped fibre amplifiers using the Green functions method

This article describes a study of the main characteristics of erbium-doped fibre amplifiers based on a non-quantum approach to the phenomenon of amplification in spatially inhomogeneous structures. The noise figure in particular is assessed theoretically and numerically on the basis of various amplifier parameters, including the reflection coefficients at the fibre input and output. The results show the importance of monitoring reflectivity at the amplifier input and the power of the incoming signal.     

Noise figure for erbium-doped optical fibre amplifiers

A rate equation model is used to calculate the excess noise figure for erbium-doped fibre amplifiers. It is shown that erbium amplifiers can operate with high gain and can have noise figures only 0.2 dB above the quantum limit     

High performance single mode OTDR using coherent detection and fibre amplifiers

A high performance single mode OTDR has been constructed at 1.55 mu m using a DFB laser diode, laser diode pumped fibre amplifiers and a coherent detector, all suited to integration into a robust and portable instrument. A dynamic range of 33 dB has been attained with 1 mu s launch pulses, 1 MHz receiver bandwidth and 10/sup 4/ integrations. This result represents an increase of about 13 dB in performance over the standard version of the OTDR using a laser diode as a light source. It is comparable to the best previously reported value attained using a high power glass laser and a cooled detector.<>     

Temperature insensitive Er/sup 3+/-doped optical fibre amplifiers

Temperature dependence of the gain at 1.536 mu m in Er/sup 3+/-doped fibre are reported for 0.98 and 1.48 mu m pumping. The fibre lengths at which gain is temperature insensitive are found for both pump wavelengths. The temperature insensitive gain characteristics for 0.98 mu m and 1.48 mu m pumping are demonstrated to fibres tuned to their temperature insensitive lengths.<>     

Implicit analytical solution for erbium doped fibre amplifier

An implicit analytical solution for the gain and output signal power of a realistic erbium doped fibre amplifier is given as a function of pump power, fibre length, input signal power and various fibre and materials parameters. This solution is shown to accurately predict the gain variation with fibre length and pump power, and the saturation behaviour with increasing signal power. It is a useful block for accurately modelling multiamplifier systems while minimising computation time.<>     

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.