Hans F. Mahlein

Single-mode and multimode all-fiber directional couplers for WDM

The theory, production process, and properties of wavelength division multiplexers (WDM) designed on the beam splitting principle are described. Typically these modules require no lenses, and the edge interference filter applied to the oblique polished single-mode or multimode fiber end face exhibits only minimal polarizing effects. Whereas all the fibers of multimode modules are identical in type, single-mode modules require a large-diameter core fiber for coupling out light. The characteristics of the couplers depend on the given type of fiber (single-mode or multimode), the light sources (laser diodes or LEDs), the channel separation, and the channel used (transmission or reflection). Insertion losses vary between 0.7 and 2 dB, far-end cross talk attenuation varies between 11 and 22 dB, and near-end cross talk attenuation exceeds 40 dB.

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. >

Yield and cost model for integrated optical chips

A yield and cost model for integrated optical chips is presented on the basis of easily attainable figures. It allows a prediction to be made of yield and cost for complex optical chips on the basis of currently available processing technology. Both yield and cost area of calculated in absolute terms but in comparison with a simple reference chip from the production line. The model can already be applied when a chip is at an early phase of development, i.e., at the planning stage.