FIELD-INDUCED WAVE-GUIDES AND THEIR APPLICATION TO MODULATORS

Field-induced waveguides (FIG) as well as guide/antiguide modulators w hich utilize the FIG concept have been developed and characterized. Us ing proton implantation to render the implanted regions electrically i nactive, an electrically controllable channel can be formed at the uni mplanted region because only this region may contain a high electric f ield. When a reverse bias is applied to one such region, a high electr ic field will be developed at the junction in the guide layer, increas ing the index relative to the adjacent implanted insulating regions su ch that lateral optical confinement is provided. Unlike conventional f ixed waveguides, lateral guiding of this field-induced waveguide can b e turned on or off electrically, since the index change can be adjuste d via electrooptical effects. Both theoretical and experimental result s promise that a relatively strong confined, low-loss optical waveguid e can be achieved using this method. Based on the field-induced wavegu ide concept, guide/antiguide optical intensity modulators are created. These devices are formed with a central straight FIG electrode sandwi ched between two similar FIG electrodes which function as the antiguid es. With electrical isolation between them, the electrodes can be driv en individually such that different lateral index profiles can be crea ted. For operation in the on-state, a channel waveguide can be created , and the input light will propagate through the modulator. For the of f-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.