Laser Doppler velocimetry has the ability to measure speed and surface vibrations non-intrusively with high precision. In
this study the Doppler spectrum shift and spectrum broadening of echo signals by moving targets are investigated. The
interaction between moving object and the laser beam of laser Doppler velocimetry have been described by varying
rotating velocity, the angular velocity, distance and incident facula. By using different scattering surfaces, such as
Polytetrafluoroethylene (PTFE) and sandpaper with different grain sizes, the characteristics of echo signals' Doppler
spectra have been studied experimentally in detail. The results show that Doppler spectrum distribution is changed with
different scattering surfaces. Meanwhile, in order to get a high measuring accuracy, the moving object's scattering
characteristics must be considered carefully.
We propose a novel method to compensate the nonlinear distortion from an optical pulse replicator based on an active optical fiber loop. It could be used to faithfully recover the input optical pulse shape from the sampled results of the replicated pulse train, despite of the distortion in the loop. Thus, the replicator could be applied to the measurement of optical pulses for optical fiber communication applications. Our proposed post-processing technique is based on modelling the nonlinear amplification behaviour of the optical amplifier in the loop. The methodology of our technique is described in detail, as well as the simulated recovered results using the proposed algorithm.
Based on the analyses of the key limiting factors for duobinary signals in dispersion limited fiber systems, we propose a novel optical receiver design that can further overcome the deterministic timing 'jitter' resulted from the dispersion-induced inter-symbol interference. Our idea is based on over-sampling of the received waveform and a novel decoding scheme. Our technique would provide better estimations of the received bits based on a decision feedback and feedforward scheme that takes advantage of the knowledge of adjacent bits. We study, through extensive simulations, the effectiveness of our novel receiver design in increasing the dispersion tolerance, and our promising results show that our innovative solution can provide significantly improvement over even the best reported schemes thus far.
Proc. SPIE. 5628, Semiconductor Lasers and Applications II
KEYWORDS: Signal to noise ratio, Optical fibers, Optical amplifiers, Semiconductor optical amplifiers, Signal attenuation, Interference (communication), Receivers, Distortion, Analog electronics, Active optics
We have proposed a simple and convenient gain control scheme of the semiconductor optical amplifier (SOA) utilizing the amplified spontaneous emission (ASE) from the SOA itself. Based upon this scheme, an optical pulse active replicator using a SOA could be used for high-fidelity replication of short analog optical pulses. Taking into account the ASE noise, a numerical model of the SOA is developed to investigate the optical pulse recirculating propagation in the active replicator. Results indicate that the replicator is feasible and effective. Selecting appropriately operating parameters, such as the loss within the loop, the power of signal pulse and the front-end receiver electrical bandwidth, the replicator can generate a sequence of precise periodic optical pulse trains with low distortion and good SNR.