Gerhard Winzer

Wavelength multiplexing components - A review of single-mode devices and their applications

State-of-the-art and systems applications of single-mode wavelength-division multiplexing (WDM) devices are described. The performance characteristics required differ depending on whether the method of operation is one-way or two-way. Development trends and problems of the new technology are discussed.

Monolithically integrated detector chip for a two-channel unidirectional WDM link at 1.5 mu m

The fabrication and operation of a monolithically integrated InGaASP/InP wavelength division multiplexing (WDM) detector chip is reported. It consists of a Y-branch grating demultiplexer and two p-i-n photodiodes. Polarization-independent operation for two closely spaced channels ( Delta lambda =3.6 nm) at lambda =1.5 mu m was obtained. In polarization-independent operation, 1.3-mm-long Bragg gratings on buried waveguides showed a peak crosstalk attenuation of 15 dB and a stop bandwidth of 0.2 nm at -10 dB. These values show the high potential of Bragg grating devices for dense wavelength division multiplexing applications. The static electrical properties of the monolithically integrated p-i-n photodiodes (dark current of 2-5 nA at -10 V, breakdown voltage of 45-65 at a 10 mu A leakage current) approach the values obtained for discrete devices. The bandwidth of 420 MHz enables operation in the 600-Mbaud region. The external quantum efficiency of the complete detector chip ( eta =0.08) is still rather small. However, it could be considered sufficient for the operation of such devices in local networks with distances of a few kilometers. >

Epilog-latest advances in dense WDM technology

Since great progress has occurred recently, a short summary is presented of some of the most significant results reported in a period of six months. Topics covered include optical FDM (frequency division multiplexing) transmission/distribution experiments; augmenting dense WDM with subcarrier multiplexing; the feasibility of distributing analog and digital video signals to 4096 subscribers; dense WDM component technology advances; and demultiplexing of WDM signals. >

Character Recognition with a Coherent Optical Multichannel Correlator

A coherent-optical reading method for Optical Character Recognition Set A [OCR(A)]-numerics is derived modifying a customary coding method which has been used in optical correlators that feature signal input via ultrasonic light modulators for time compression of radar pulses. It is shown by computer simulation that unambiguous recognition of these numerics will be possible if combined application of masks for the numeric codes and matched auxiliary masks for significant features are realized.1