G. Heise et M. Schienle, INVESTIGATION OF DIRECTIONAL COUPLER NEAR-END CROSS-TALK BY LASER-INDUCED REFRACTIVE-INDEX SHIFTS, Applied optics, 32(33), 1993, pp. 6698-6702
The near-end cross talk of InGaAsP-InP waveguide directional couplers
is investigated. It is shown that the cross-talk level is strongly dep
endent on the optical path difference between the two link-end arms of
the coupler. By locally heating one of these arms with an argon laser
beam this path difference, and hence the couplers' near-end cross tal
k, can be tuned. The ultimate limit for the near-end cross talk is det
ermined by stray light and has therefore approximately the same level
as the far-end cross talk.