ISMOT 2009, Dec 16-19, New Delhi, India Investigation of Insertion Loss due to Fresnel Reflection at the Lithium Niobate–Air Interfaces via Output Characteristic Curve of Electro-Optic Modulation Morteza. A. Sharif 1* 1 Electrical Engineering Group Urmia University of Technology, Band Road, Urmia, Iran Tel: 98-441-3554181; E-mail: m.abdolahisharif@ee.uut.ac.ir Abstract- Recent progresses in fiber optics communications are strictly indebted to utilization of electro-optic crystal of LiNbO3 which has shown fair electro-optic characteristics while utilizing in fiber optics devices. In spite of this, they have been observed some undesired properties of it; one of these properties is known as insertion loss due to Fresnel reflection at the lithium niobate–air interfaces which is a result of light beam reflection at LiNbO3-air interfaces; this effect causes undesired changes in the output intensity of LiNbO3 electro-optic modulator; designers try to minimize the effect of this property. In recent experiment, the electro-optic behavior of LiNbO3 is investigated experimentally via applying a DC bias voltage on it and the effect of insertion loss due to Fresnel reflection at the lithium niobate–air interfaces is observed. Afterward the effect is justified via obtaining Output Characteristic Curve of electro-optic modulation and related equations. Theoretical model is also provided to describe the effect; The experimental setup contains a 17 mW He-Ne laser as a light source, two polarizers as the analyzer and polarizer, a LiNbO3 Z-cut crystal uncoated with any antireflection layer, a DC voltage generator in order to applying DC bias voltage on LiNbO3 crystal -in the form of transverse modulation- and a photodetector in order to detecting, monitoring and recording the Output Characteristic Curve of the electro-optic modulation. In order to remove this effect, antireflection coatings or index matching can be helpful. Description in details is given in manuscript containing the experimental data, diagrams, equations and more references. Index Terms- Insertion loss, Lithium Niobate, Electro-optic Modulation, Output Characteristic Curve. I. INTRODUCTION For the fabrication of functional devices in waveguide geometries, lithium niobate (LiNb03) was rapidly recognized as one of the most promising alternatives during two passed decades. The waveguide fabrication in LiNb03 via titanium in-diffusion was demonstrated at the AT&T Bell Laboratory, and gave rise to the development of channel waveguides with very low losses in a material that possesses valuable electro-optic and acousto-optic effects. In the mid-1980s the viability of waveguide devices based on LiNb03, such as integrated intensity modulators of up to 40 GHz, and with integration levels of up to 50 switches in a single photonic chip had already been demonstrated in laboratory experiments. A few years later, the standard packaging required in communication systems was obtained, and so the devices were ready to enter the market [1]. Recent progresses in fiber optics communications are strictly now indebted to utilization of electro-optic crystal of LiNbO3 since it has shown fair electro-optic characteristics in the fiber optics communication zone. In spite of this, they have been observed some undesired properties of this crystal while utilizing it in photonics devices; [2-4]. One of these properties is known as insertion loss due to Fresnel reflection at the lithium niobate–air interfaces. This effect is a result of light beam reflection at LiNbO3-air interfaces which causes undesired changes in the intensity of output light beam from the photonics devices and especially from the LiNbO3 electro-optic modulator; hence, that is considered as an important parameter in designing process of electro-optic modulator which is desired to be so low[2,5,6] . In recent experiment, the electro-optic behavior of