Studies concerning the dynamic range of the integrated optic spectrum analyser

The work described in this thesis is concerned with some of the factors which can influence the dynamic range of the Integrated Optic Spectrum Analyser. Chapter 1 considers the various types of spectrum analyser device based on the interaction of acoustic waves with optical waves. The main features of the hulk acousto-optic spectrum analyser and the integrated optic spectrum analyser (IOSA) are considered. Two types of IOSA device are considered. The working of the IOSA device as well as its dynamic range is considered. In Chapter 2 the physical properties of Lithium Niobate are considered. The choice of Y-cut LiNbO3 as a substrate material for the IOSA is considered. The fabrication of titanium indiffused LiNbO3 optical waveguides are described. Chapter 3 considers the importance of in-plane light scattering in integrated optical devices and especially in the IOSA device. The study of in-plane light scattering in optical waveguides in relation to titanium thickness, diffusion time, diffusion temperature is considered. The evolution and disappearance of surface roughness during the diffusion process is considered and also the evolution of defects in the waveguides. Chapter h deals with the importance of surface acoustic waves (SAW) in signal processing devices. The interdigital transducer as a source for the excitation of SAW is considered. IDT delay line design parameters, fabrication and characterisation are described. Chapter 5 considers the theory of acousto-optic interaction. The dependence of the diffraction efficiency on various material parameters is considered. Experimental results obtained in the study of acousto-optic interaction are described. The discrepancy in the experimentally obtained results and the results already published by various authors is considered. Chapter 6 deals with the theory of multifrequency acousto-optic diffraction as given by D.L. Hecht. Experimental results (conforming to the phase matching conditions used for the theory) along with the difficulties involved in the observational of third order intermodulation signals are described. The experimentally obtained results for this thesis are compared with the theoretical results as well as with the limited results obtained by other authors. The dependence of the dynamic range of the IOSA on in-plane light scattering and third order intermodulation effects is considered. During work described in Chapter 5 and 6, changes in the waveguide index due to r.f. power were observed. In Chapter 7, the dependence of the changes in the refractive index of the waveguide on the r.f. power to the IDT and optical power in the waveguide is considered. From the study carried out in Chapter 7 it is concluded that changes in the index due to r.f. power at the IDT are due to the thermo-optic effect arising because of heat dissipation at the IDT. However the effect of the presence of optical power is probably not the photo-refractive effect. The main conclusions of the work done for this thesis are described in Chapter 8 along with suggestions for future work arising out of this study