Biomedical optical sensors such as fiber optic immunosensors, pH, pC02 and pO2 sensors and temperature sensors are increasingly being developed for clinical application due to the advantages of optical detection. Many of these biomedical sensors can be improved by the use of wavelength-dependent detection rather than intensity-modulated detection, thereby eliminating problems due to source drift and propagation losses. Unfortunately, current wavelength-modulated sensors have the disadvantage of requiring large, research spectrometers for high resolution and large dynamic range. An integrated optics Fourier transform (IO-FT) spectrometer would potentially be an economical, small, sensor- compatible spectrometer to replace more conventional, but bulky, spectrometers. The availibility of such a rapid, easily operated spectrometer is essential to the transfer of many biomedical sensors from the research laboratory into clinical application. The purpose of this proposal is to investigate the feasibility of fabricating a key element of the role IO-FT spectrometer, a multimode integrated optic phase shifter. Single mode, single wavelength phase modulators have previously been developed as fast optical switches. Multimode waveguides are necessary for broad band spectrometer operation, but they have the complication of intermode phase differences and have yet been tested. Therefore, the feasibility of the IO-FT spectrometer depends upon the successful development of a multimode and multi-wavelength electro-optic phase modulator. In this study, titanium indiffused waveguides in a lithium niobate substrate will be fabricated, and electrodes for electro-optically induced refractive index changes will be deposited around the waveguides in a push-pull configuration. Laser light at 442nm (HeCd), 488nm (Ar+), 514.4nm (Ar+), 543.5 nm (HeNe) and 632.8nm (HeNe) will be prism coupled into the waveguides for each waveguide mode and the relative phase shifts measured with interference techniques. The phase shifts will be investigated as a function of voltage (including breakdown voltage of the waveguide), mode and wavelength. Based on these results, the potential resolution and dynamic range of the IO-FT spectrometer will be evaluated, and improvements in a second generation design will be implemented.
