All-optical Gain Research Articles

All-optical gain control for bidirectional optical add-drop multiplexer using ASE noise path through multi-port circulators

An all-optical gain control method for a bidirectional optical add-drop multiplexer using an amplified spontaneous emission noise path through multi-port circulators is reported. The device provides constant gain and low noise figure over a large input power range, has low crosstalk and removes Rayleigh backscattered and back-reflected light.

Theoretical analysis of spectral hole burning and relaxation oscillation in all-optical gain stabilized multichannel erbium-doped fiber amplifier (EDFA)

The spectral hole burning effects and gain dynamics of all-optical gain clamped multichannel erbium-doped fiber amplifiers (EDFAs) are modeled. The two-level laser model is used to write the propagation and rate equations of the inhomogeneous laser medium. The governing equations are an uncountable system of partial differential equations (PDEs). After some mathematical manipulations, averaging over the fiber length and introducing an approximation method, the system of PDEs is converted to a finite system of ordinary differential equations (ODEs). The gain dynamics and hole burning of an all-optical stabilized multiwavelength EDFA and the transient response of an optical fiber inverter are analyzed by the solution of the system of ODEs. Theoretical results are in good agreement with the published experimental result.

Effectiveness of gain control in EDFAs against traffic with different levels of bursty behaviour

Previous publications have addressed the impact of bursty, self-similar traffic on erbium-doped fibre amplifiers (EDFA). Several gain control techniques have been suggested to combat the gain fluctuations of EDFA with this type of traffic. The effectiveness of two such methods are investigated, namely highly inverted amplifiers and all-optical gain clamping, while varying the parameters characterising the burstiness of the sources. While previous publications have focused on the effect of the average load or activity factor, the paper further investigate the dependence on the relative variability of the packet burst lengths (ON times), and lengths of the interburst idle times (OFF times). Both gain control methods reduce the output power and signal-to-noise ratio excursions with respect to a standard amplifier chain. The authors find that, for an eight channel WDM system and a cascade of six EDFAs, all-optical gain clamping can reduce the variations by a factor of five, provided adequate power is present in the clamping laser, while highly inverted amplifiers have variations reduced by a factor of two. The authors find that, in a clamped chain, the source activity factor does not uniquely determine the required level of lasing power. The authors also deduce that information on the relative variability of ON and OFF times is essential.

Gain-clamped fibre amplifier using an ASE end reflector

All-optical gain clamping in an erbium-doped fibre amplifier is demonstrated using a broadband fibre Bragg grating that reflects the amplified spontaneous emission centred at 1530 nm with a 14 nm bandwidth. Experiments on an eight-channel wavelength division multiplexing system show promise when the gain is clamped at 21 dB. Gain flatness is less than 0.6 dB across all channels and gain variation is about 0.2 dB over the input signal power range.

All-optical gain control of in-line erbium-doped fiber amplifiers for hybrid analog/digital WDM systems

Automatic gain control using an all-optical feedback loop in in-line erbium-doped fiber amplifiers (EDFA's) used in hybrid analog/digital wavelength division multiplexing (WDM) systems was studied. It is found that the signal level variation for the digital channels can be maintained within a range /spl les/3-dB between the presence and dropout of the analog channel when the narrowband feedback is centered at the amplified spontaneous emission (ASE) peak (/spl sim/1532 nm) with loop loss ranging between 13-22 dB. Robust transmission at 2.5 Gb/s without measurable power penalty was obtained for the digital channels when the EDFA was saturated by either the analog or the control lasing signal.

Low noise, all-optical gain controlled Er3+ doped fibre amplifier using asymmetric control laser cavity design

The authors demonstrate an Er3+ doped fibre amplifier with all-optical, automatic gain control and with near quantum limited, 1480 nm pumped noise performance. The amplifier gain is controlled by in-band laser action, and two design considerations are established for optimum noise performance: the control laser wavelength should be located in a region of high amplifier gain, and the laser cavity should be constructed to be as asymmetric as possible, ensuring minimum laser power at the signal input end of the amplifier.

Remote all-optical nanosecond gain switching of an erbium-doped fiber amplifier

Abstract All-optical gain switching of an erbium-doped fiber amplifier located up to 50 km away from the signal and control lasers is demonstrated. The amplifier is deactivated by optical control pulses within the amplifier bandwidth that strongly saturate the gain at the signal Wavelength. Fall times are approximately equal to the control pulse duration of 21 ns. From 25 km, a maximum extinction ratio of 16 dB is demonstrated with the signal at 1527 nm and the control pulse at 1554 nm. The dynamic range for remote switching is limited by a stimulated Raman scattering of the control pulses.

Nanosecond all-optical gain switching of an erbium-doped fibre amplifier

Optical gain switching of an erbium-doped fibre amplifier (EDFA) with short pulses at wavelengths within the amplifier bandwidth is demonstrated. Gain compression of 20 dB in 40 ns was experimentally obtained. Theoretical modelling agrees well with experimental results and concludes that gain compression is determined by pulse energy. Optimization of fibre length as well as signal and switching wavelengths predicts that 10 dB nanosecond switching can be obtained with sub-picojoule switching pulse energy. Theory also shows that a pump pulse can accelerate recovery to microseconds. The proposed switching scheme offers optical gain control many orders of magnitude faster than the fluorescence lifetime of erbium ions in a glass host, which limits the switching speed of an EDFA controlled by pump power modulation alone.

Ultra-high-speed PLL-type clock recovery circuit based on all-optical gain modulation in traveling-wave laser diode amplifier

A new phase lock loop (PLL) is developed for very-high-speed optical timing extraction using traveling-wave laser-diode amplifier (TW-LDA) as a phase detector. The all-optical gain modulation of the TW-LDA is utilized to detect the relative phase difference between an optical signal and an optical clock The frequency response of the optical gain modulation measured with the optical heterodyne technique agrees with the theoretical results based on a rate equation model. With the developed PLL, 10-GHz optical timing clock is successfully extracted from randomly modulated optical signal pulses and the measured bit-error-rate performance shows no power penalty. Influence of the received optical noise on the phase variance of the PLL is also evaluated and it is concluded that 100 GHz operation is possible by increasing the input optical power to 10 mW.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

All-optical remote gain switching in Er-doped fibre amplifiers

A novel, all-optical feedback scheme that allows remote optical gain switching in Er-doped fibre amplifiers is demonstrated. A selected wavelength of the amplified spontaneous emission (ASE) at the output of the amplifier is fed back to the input through an unpumped Er-doped fibre acting as a saturable absorber. Off and on switching of ring lasing (and hence, respectively, on and off switching of the amplifier gain) is achieved by remotely injecting optical control signals at appropriate wavelengths over the transmission fibre. A gain bistability (on–off ratio) of 26 dB at 1530 nm is demonstrated. A switching time of 10–50 ms was observed, inherent to the erbium fluorescence lifetime. This scheme could be useful in directing traffic flow in optical networks.