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UBC Theses and Dissertations

Voltage induced optical waveguide modulators in lithium niobate Jaeger, Nicolas August Fleming


Two types of optical modulator were studied, both of the voltage induced optical waveguide type first proposed and demonstrated by Channin in 1971. An optical waveguide was created in an electrooptic substrate by applying voltage between two electrodes deposited on the substrate. Channin used wide electrode spacings which resulted in large operating voltages being necessary. The devices discussed in this thesis had much smaller electrode spacings and therefore operated at much reduced voltages. They are of the planar and ridge types. In the planar type the electrodes were deposited on top of a planar substrate and in the ridge type a ridge of electrooptic material separated thick electrodes. The theory of operation for both types of device was developed and they were modeled, fabricated, and tested. Numerically derived results were obtained for light with wavelengths of 442 and 633 nm which showed that the confinement of the light increased with increasing voltage, decreasing gap width, and decreasing wavelength. The theory was further developed to investigate the performance of the device as a voltage-controlled linking waveguide between two optical fibers. The optimum coupling efficiency, as a function of voltage and interelectrode gap width, from optical fibers to both types of device was calculated in terms of the model. Key aspects of the theory were confirmed by the measurements made on the fabricated devices. A planar device was used as a front-end switch between a laser and an optical fiber using a V-groove etched in silicon to align the voltage induced waveguide with the fiber. One problem was a decay phenomenon in which the induced waveguide disappeared over a period of time during which a constant voltage was applied to the electrodes. This was believed to be due to the photorefractive effect. It was found that the device would recover upon the application of a fly-back cycle.

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