Fibre optical parametric amplifiers with circularly-polarised pumps

A fibre optical parametric amplifier with orthogonal circularly-polarised pumps requires only half the pump power of an amplifier with linearly-polarised pumps to achieve a given gain. The gain is also independent of the polarisation of the input signal.     

Nonlinear suppression of autoregressive impulse noise in on-off binary communications

A novel method is proposed to combat an impulse noise in on-off binary communication. The method is based on modeling of the impulse noise using the autoregressive model. This approach does not require explicit a priori knowledge of the impulse noise statistics. The performance of the resulting algorithm is analyzed using computer simulation. It is shown that essentially power-independent reception may be achieved under conditions of impulse noise. It is also shown that the proposed technique greatly improves the system performance even when the Gaussian noise is added to the receiver input mixture. However, the improvement diminishes as the impulse-noise-to-Gaussian-noise ratio decreases.     

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.     

Miniature Nd:YAG lasers: noise and modulation characteristics

The frequency and intensity noise spectra, as well as the frequency modulation (FM) response, of 1320-nm laser-diode-pumped miniature Nd:YAG ring lasers have been measured. The frequency noise spectrum has a resonance peak at the relaxation oscillation frequency of the laser (between 123 and 150 kHz) and is flat beyond 200 kHz with a spectral density of 613 rad²-Hz, much smaller than that of semiconductor lasers; the corresponding laser linewidth is less than 49 Hz. The relative intensity noise is -140 dB/Hz at the valley and has a resonance peak at the relaxation oscillation frequency of the laser. The FM response is flat from DC to 110 kHz and is in the 0.65-3 MHz/V range; the modulation frequency is limited by the relaxation oscillation frequency of the laser     

Experimental relative frequency stabilization of a set of lasersusing optical phase-locked loops

A relative frequency stabilization technique using optical phase locking of miniature diode pumped Nd:YAG ring lasers is described. The master laser is RF phase modulated with a modulation index up to 7.4, and slave lasers are locked up to 21 master laser sidebands with a frequency stability better than 3 kHz     

ASK and FSK coherent lightwave systems: a simplified approximateanalysis

A simplified approximate analysis of amplitude shift keying (ASK) and frequency shift keying (FSK) coherent optical communication systems is presented. The analysis accounts for the phase noise of the transmitter and the local oscillator lasers and for the additive Gaussian noise stemming from the shot noise and thermal noise. The analysis yields a closed-form estimate of the bit error rate (BER) and allows an immediate physical insight and appreciation of the impact of the IF filter bandwidth, laser linewidth, and bit rate on the system performance. The theory also yields reasonably accurate estimates of the optimum IF bandwidths and of the sensitivity penalty stemming from the phase noise     

Estimation of parameter drift rate for detection and prediction of faults

System faults may be detected and predicted via estimation of trajectories of the system dynamic parameters in the parameter space. During normal operation, the parameters exhibit random motion around their nominal values. A drift of one (or more) parameters may indicate a fault. Two algorithms are developed here for the estimation of the parameter drift rate. The performance of the developed algorithms is also evaluated.     

Gain-clamped thulium-doped fibre amplifier with single pump at 1050 nm

The large homogeneous bandwidth of a thulium-doped fibre amplifier makes it suitable for optical gain clamping. This has been demonstrated experimentally. Gain variation of 1.2 dB for 15 dB input dynamic range has been achieved, with less than 1 dB gain ripple over 20 nm, and no noise figure degradation, while pumped at 1050 nm.     

On Noise Immunity of Feedback Communication Systems

This paper compares the noise immunities of feedback communication systems for two particular types of systems noise: Gaussian white noise, which is typical of radio and telephone communication, and Poisson-distributed noise, which is typical of laser communication. The comparison shows that as the error probability requirement is made more stringent, the use of feedback will save commensurately more energy in both cases.