Optical pattern recognition using two-channel joint transform correlation

A new joint transform correlation (JTC) technique, named two-channel JTC (TJTC), is proposed in this paper for optical pattern recognition applications. The TJTC technique independently evaluates the autocorrelation and crosscorrelation values of the reference and the target images and employs a modified decision algorithm. In addition, optical threshold operation and fringe-adjusted filter are incorporated in the proposed technique to enhance the correlation output and to improve the discrimination performance. The proposed technique shows better recognition performance compared to existing JTC techniques. Computer simulation are presented to investigate the salient features of the proposed TJTC technique with noise-free as well as noisy input scenes. The text was submitted by the authors in English.     

Fiber nonlinearity compensation of WDM-PDM 16-QAM signaling using multiple optical phase conjugations over a distributed Raman-amplified link

In this paper, multiple optical phase conjugation (OPC) devices were used along the optical link to improve the performance of an \(8\times 256\) Gbps polarization-division multiplexing 16-state quadrature amplitude modulation signaling, producing total bit rate of 2.048 Tbps. A 50-GHz spaced, eight-channel wavelength division multiplexing (WDM) communication system was considered using 912 km dispersion-unmanaged standard single-mode fiber link with backward distributed Raman pumps. The performance of a dual-pump highly nonlinear fiber-based OPC was investigated analytically using a set of eight nonlinear Schrödinger equations taking into account the effect of polarization. Simulation results were compared with the case of mid-span optical phase conjugation (MS-OPC) compensation scheme showing better performance in terms of achievable Q-factor, optimal signal launched power, and the total length of the transmission link. In 256 Gbps, single-channel scenario, a Q-factor improvement of 1.35 dB was achieved and the nonlinear threshold was increased by \(\sim \) 4 dB compared to the case of MS-OPC. Moreover, using multiple OPC led to increase the length of the transmission link by 30.7% compared with the case of MS-OPC. In 2.048 Tbps WDM system, a maximum Q-factor of 9.27 dB over the same link was obtained showing an improvement of 0.62 dB over the MS-OPC case. The simulation results were compared with published analogous experimental data showing very good agreement.     

Effect on the performance of staircase APDs of electron impactionization within the graded-gap region

The performance of a staircase avalanche photodiode is usually analyzed assuming that electrons ionize at the steps only while the holes ionize within the graded-gap regions. Here, the analysis is extended in order to consider the effect of carrier (electron and hole) impact ionizations both in the graded-gap regions and at the steps. The modeling procedure adopted represents an expedient simplification, selected to render tractable a complex subject, and appending this to potential physical device models leads to consideration of three extreme cases. The results indicate that electron ionization in the graded region can lead to improved sensitivity when residual hole ionization in both regions is kept to a minimum     

Performance degradation of APD-optical receivers due to darkcurrent generated within the multiplication region

General expressions for the effective gain and effective excess noise factor associated with dark current generated within the high-field region of an avalanche photodiode (APD) are given. The influence of this background current on the performance of a uniformly multiplying APD receiver is evaluated and compared with that due to a dark current component generated outside the multiplication region (diffusion current). The results indicate clearly that the former dark current component has less effect on receiver performance than the latter, especially when hole and electron ionization rates are very different     

Influence of extinction ratio on performance of optical receivers incorporating laser preamplifiers

Reports the performance degradation of optical receivers incorporating semiconductor laser amplifiers (SLAs) caused by the nonzero extinction ratio of the input optical signal. The resulting sensitivity penalty dependencies on bit rate, SLA gain and facet reflectivity are also investigated. The results clearly show that the new receiver can be more affected by a finite extinction ratio compared to a conventional pin or APD receiver. Using a bandpass optical filter to reduce amplifier spontaneous emission noise will increase the extinction ratio penalty.<>