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The method for detection and classification of defects in Printed circuit boards using image subtraction has been presented in this paper. Image subtraction method is one of the simplest methods for the inspection of the PCB defects. The defects like missing hole, over and under etching, wrong hole size defects, missing conductor and break lines have been detected and classified in this paper.

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In this paper, Optical Dense Wavelength Division Multiplexed Systems (DWDM) employing Erbium Doped Fiber Amplifiers (EDFAs) are investigated with the main emphasis on the fiber nonlinearities like Stimulated Raman Scattering (SRS) and Four Wave Mixing (FWM). Analysis has been carried out for the calculation of the bit-error-rate (BER) considering receiver noise as well. The dependence of BER on system parameters such as system length, inter-amplifier separation and inter-channel separation has been shown graphically.

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In this work a dispersion-compensated Raman amplifier has been cascaded with a single-pump parametric amplifier to build a dense wavelengthdivision multiplexed (DWDM) system. This hybrid system demonstrates a flat gain in the L-band. Our hybrid has been evaluated for a 25 GHz 96-channel system at 40 Gbps in the band spreading from 189 to 191.375 THz. The results demonstrate the gain larger than 16.9 dB and the gain ripple less than 5.82 dB, with no gainflattening technique used. The novelty of our design lies in combining dispersion compensation with signal amplification in a long-length Raman-amplifier fibre followed by a short-length parametric amplifier implemented on a separate highly nonlinear fibre. For the data rate 10 Gbps, the achievable gain ripple is as low as 1.9 dB, without any gain-compensation technique. The optical signal-to-noise ratio larger than 18 dB and the flat gain confirm that our Raman fibre-optic parametric amplifier can be used as a tunable and broad-gain amplifier for the future long-haul DWDM systems. The results obtained for our system have been compared with those of the L-band optical amplifiers developed recently. The comparison testifies that our amplifier is the best of all existing analogues.

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