GUIDED-TO-LEAKY MODE TRANSITION IN UNIAXIAL OPTICAL SLAB WAVE-GUIDES

The guided-to-leaky hybrid mode transition in slab optical waveguides made on uniaxial crystals such as LiNbO3 or LiTaO3 is analyzed. Two di fferent guided-to-leaky transitions have been identified, namely the o rdinary cutoff and the extraordinary cutoff, which occur when consider ing negative and positive birefringent materials, respectively. Analyt ical but transcendental expressions have been obtained, yielding the c ritical optical axis orientation, relative to the waveguide axis, abov e which the totally guided hybrid modes become leaky. The results indi cate that the value of the critical orientation strongly depends on th e waveguide parameters. The possibility of tuning this critical orient ation to a desired value through the waveguide parameters is discussed .