FIELD-INDUCED WAVE-GUIDES AND THEIR APPLICATION TO MODULATORS

Field-induced waveguides (FIG) as well as guide/antiguide modulators which utilize the FIG concept have been developed and characterized. Using proton implantation to render the implanted regions electrically inactive, an electrically controllable channel can be formed at the unimplanted region because only this region may contain a high electric field. When a reverse bias is applied to one such region, a high electric field will be developed at the junction in the guide layer, increasing the index relative to the adjacent implanted insulating regions such that lateral optical confinement is provided. Unlike conventional fixed waveguides, lateral guiding of this field-induced waveguide can be turned on or off electrically, since the index change can be adjusted via electrooptical effects. Both theoretical and experimental results promise that a relatively strong confined, low-loss optical waveguide can be achieved using this method. Based on the field-induced waveguide concept, guide/antiguide optical intensity modulators are created. These devices are formed with a central straight FIG electrode sandwiched between two similar FIG electrodes which function as the antiguides. With electrical isolation between them, the electrodes can be driven individually such that different lateral index profiles can be created. For operation in the on-state, a channel waveguide can be created, and the input light will propagate through the modulator. For the off-state, on the other hand, an antiguide can be created such that the input light will diffract out of the central guide region. Extinction ratios of 160:1 (> 22 dB), internal losses of approximately 1 dB, and a record wide optical bandwidth from 1 to 1.55 mum have been obtained for the modulator.