Band 5, Heft 4

The modulation characteristics of integrated optical directional couplers have been analyzed theoretically and supported by experiments. Two new effects influencing the modulation behaviour arc presented: the intrinsic mismatch Δβ 0 due to unequal waveguides and Δκ-effect, i.e. the electrooptic variation of the coupling coefficient κ. Couplers with special modulation characteristics can be designed by combining all modulation effects.

ATTL driving optical arbiter module which consists of a hybrid combination of optical devices has been fabricated to demonstrate the performance of a parallel data processing arbiter. The optical arbiter module is assembled by a ten-port guided-wave optical arbiter circuit, fiber-connected laser diodes and fiber-connected avalanche photo diodes. Optical arbitration is shown through connecting ten processors to this module. It is confirmed that priority is decided by the connected input terminal position when many processors request common resource use simultaneously. Applying feasibility for parallel signal processing systems is verified by using this prototype optical arbiter module.

For accurate refractive-index profile measurements of optical fibers with the refracted near-field method the output signal of the instrument has to be extremely stable. It has been found that some instability is caused by beam shifts due to “mode sweeping” in the laser resonator. By active stabilization of the laser cavity the residual fluctuations are reduced to 10 -4 .

Distributed mode-selective losses in a multimode fiber transmission link cause an accumulation of modal noise. A theory has been developed which gives an approximation of the signal-to-noise ratio at the end of the link due to the accumulated modal noise; it shows how this ratio is improved by mode-coupling in the fiber.

In this paper the performance of a digital optical receiver consisting of an avalanche photodiode has been evaluated in the presence of noise and the intersymbol interference (ISI). The ISI levels have been computed for a multimode step index fiber for various lengths and data rates and the results are presented in the graphical form. Improvement in the receiver performance with an equalizer has also been worked out.