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     

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.     

10 Gbit/s, 100 km nonrepeatered fibre transmission experiment using a high-sensitivity semiconductor optical preamplifier

10 Gbit/s, 100 km nonrepeated fibre transmission has been demonstrated using a high-sensitivity receiver with two-stage cascade-connected semiconductor optical amplifiers and a pin PD front end. The sensitivity and its improvement were -23.5 dBm and 12.2 dB respectively, resulting in the allowable span-loss of 24.5 dB.<>     

Gain and noise performance of fibre amplifiers operating in new pump configurations

New configurations of erbium-doped fibre amplifiers have been investigated for the 0.98 mu m and 1.48 mu m pump wavelengths. A doubling of the gain coefficient has been predicted for reflective type amplifiers at the cost of a noise figure increase of 1.5 dB.<>     

Gain flattened and improved EDFA using microbending long-period fibre gratings

A new method for flattening the gain spectrum of erbium-doped fibre amplifiers (EDFAs) is proposed. This method is based on microbending long-period fibre gratings, that are simply fabricated by bending the fibre. By adjusting the spectral profiles of the filters mechanically, a gain flatness of <1 dB has been obtained, and gain improvement of <5.32 dB over the 33 nm wavelength range at two different pump powers of 34 and 86 mW, respectively.     

Fibre transmission of 10 Gbit/s signals following wavelengthconversion using a travelling-wave semiconductor optical amplifier

The wavelength of an intensity-modulated signal at 10 Gbit/s was translated from 1546 to 1531 nm using cross gain-compression in a semiconductor optical amplifier. The shifted signal was transmitted with less than 1 dB penalty over a 121 km span of dispersion-shifted fibre with two in-line amplifiers. A dispersion penalty of nearly 2 dB is measured for transmission of 6 Gbit/s data over 20 km conventional fibre     

400 Mbit/s optical heterodyne DPSK system experiment with inline1.5 μm amplifiers

Reports a 400 Mbit/s differential phase shift keying (DPSK) heterodyne optical transmission system experiment using two inline packaged resonant type amplifiers. The optical amplifier gave a 14.5 dB net gain from fibre to fibre at λ=1.488 μm with no significant system penalty     

光接收机中跨阻抗反馈放大器的最佳设计

本文通过对跨阻抗传输函数的极点轨迹的分析,提出光接收机中跨阻抗反馈放大器的最佳设计方法。采用本设计方法于彩色电视光纤传输系统,与当前流行的同类放大器相比较,可使系统得到8 dB 的信噪比改善。     

Experimental optimisation of central wavelength and bandwidth of reflective FBG for efficiency improvement of low-noise L-band EDFAs

Operation of L-band erbium-doped fibre amplifiers (EDFAs) incorporating a reflective amplified spontaneous emission filter (fibre Bragg grating (FBG)) was emulated with a tunable source. The experimental optimisation of the FBG bandwidth and central wavelength led to a low noise (<5.2 dB) 20 dBm single-pumped WDM EDFA.     

High gain limiting erbium-doped fibre amplifier with over 30 dB dynamic range

A limiting optical amplifier is demonstrated using three cascaded stages of erbium-doped fibre amplifiers. A constant output power of +12.9 dBm was obtained for an input power ranging from -30 to 1.5 dBm. The optical noise figure of the amplifier has been measured over the >30 dB dynamic range. Design guidelines for optical limiting amplifiers are also presented.<>     

Optical amplification at 0.54 /spl mu/m by Er/sup 3+/-doped fluoride fibre

Demonstrated is a 16.5 dB all-fibre optical amplifier at 546 nm using Er³⁺-doped fluoride fibre for a signal power of -30 dBm by forward upconversion pumping of a 974 nm laser diode. Results show Er ³⁺-doped fluoride fibre is a promising candidate for 0.54 mum optical amplifiers     

Efficient pump wavelengths of erbium-doped fibre optical amplifier

By choosing pump wavelengths at which excited state absorption does not occur, efficient high gain operation of erbium-doped fibre amplifiers is possible. Practical pump wavelengths of 532 nm and 980 nm are identified as optimal, giving gains as high as 1.35 dB/mW and 2.2 dB/mW of pump at the two wavelengths, respectively.<>     

Twincore erbium-doped fibre amplifier with passive spectral gain equalisation

Automatic spectral gain equalisation is demonstrated using controlled spatial hole-burning in an erbium-doped twincore fibre. Gain equalisation rates up to 0.11 dB difference between input signal levels are demonstrated and should increase the useful bandwidth of cascaded amplifiers.<>     

Erbium-doped fibre amplifiers with an extremely high gain coefficient of 11.0 dB/mW

A gain coefficient of 11.0 dB/mW is obtained using 0.98 mu m laser diode pumped erbium-doped fibre amplifiers with a low erbium concentration of 81 p.p.m. and a high relative refractive index difference of 1.88%.<>     

New configuration of polarisation-independent isolator using a polarisation-dependent one

In optical communication systems using fibre amplifiers, polarisation-independent isolators with high isolation are desirable. A simple effective method to realise polarisation-independent optical isolators is proposed. The isolator consists of spatial walk-off polarisers, half-wave plates, and a conventional polarisation-dependent isolator. The measured forward loss of the assembled isolator is 0.38 dB and 0.32 dB at 1.3 and 1.55 mu m wavelengths, respectively. The backward loss is 55.5 dB and 63.5 dB at 1.3 and 1.55 mu m wavelengths, respectively.<>     

1.3 μm GaInAsP near-travelling-wave laser amplifiers made bycombination of angled facets and antireflection coatings

1.3 μm GaInAsP near-travelling-wave laser amplifiers have been realised by the combination of angled facets and antireflection coatings. Without in situ monitoring on the device itself during dielectric coatings, one can routinely obtain a low effective modal facet reflectivity of 5-8×10^-4. The devices had an internal gain of 24±1.5 dB for the TE mode and a single-mode fibre coupling loss of 5 dB/facet     

Pump wavelength independent gain with bidirectionally pumped alumino-silicate erbium-doped fiber amplifiers in the 800 nm pump band

Using a comprehensive computer model, it was shown that the effects of excited state absorption (ESA), in the 800 nm pump band, in alumino-phosphate-silicate (APS) erbium-doped fiber amplifiers (EDFAs) can be reduced significantly by using bidirectional pumping. If a band optimum length (BOL) is selected, a near optimum small signal gain (SSG) can be constant over broad pump wavelength regions due to the combined effects of ESA and ground state absorption (GSA). Hence, multilongitudinal mode, high power, reliable and inexpensive GaAlAs laser diodes can be used as pumping sources for EDFAs having SSG > 40 dB, noise figures of <4 dB, and output signal powers approaching 100 mW. These fibre amplifiers could be used as line repeaters, preamplifiers, and power amplifiers in different lightwave systems.<>     

Existence of intrinsic 'background loss' in rare-earth doped fibres: drawbacks and usefulness

Estimates are given of the intrinsic multiphonon absorption of trivalent rare earth (RE) dopants in glasses. The orders of magnitude of 1.5 dB/km in ZBLAN glass and 3.5 dB/km in silica glass as far as 2000 cm/sup -1/ from an electronic transition can contribute to what is generally called the 'background loss' and could explain why fibre lasers and amplifiers can be pumped outside usual electronic RE transitions.<>     

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     

Automatic gain control in cascaded erbium doped fibre amplifier systems

Automatic gain control for erbium doped fibre amplifiers is achieved via active stabilisation of the amplifier output power. This technique automatically compensates for any changes in the amplifier gain caused by local environmental and optical effects. Output power is also stabilised for changes in optical input signal, allowing for a full 5 dB repair margin per link in long span systems.<>