Simulated Characteristics of a Nonlinear Directional Coupler Based Optical Switch. Characteristics of Nonlinear Directional Coupler

Abstract-This paper presents a nonlinear directional coupler for optical power switching. The theoretical study has been done to study the coupling characteristics of the nonlinear directional coupler. Variation of the coupling coefficients with wavelength have been done, and found that, out of all four coupling coefficients, nonlinear coupling coefficient (equivalent to selfphase modulation) decreases with the wavelength. The wavelength dependency of the critical power is studied. We have study the variation of coupling coefficients with the width of waveguide and realized that single mode waveguide with smaller core width have lower critical power. Here, we have proposed a noble design of NLDC with asymmetric waveguide along the length with lower critical power as compare to the symmetric waveguide directional coupler. Characteristics of Nonlinear Directional Coupler

Keywords: Directional coupler, waveguide, critical power, optical switch, coupling coefficient

I. INTRODUCTION

The nonlinear directional coupler (NLDC) has many interesting applications in integrated optical system, such as in optical computing and ultra-fast communication systems. Optical switching is very important for high speed telecommunication and silica is a promising material for optical switching. Optical switching using the optical Kerr effect in single mode fiber has been reported in [1-2]; however, silica has very small nonlinear coefficient. Due to small nonlinearity, very long (few kilometers) fibers were used for switching purpose. To overcome the need for long fiber length, materials with high third order nonlinearity have been employed by various researchers. A nonlinear directional coupler with chalcogenide (ChG) material was first proposed by Jensen in 1982 [3]. ChG glasses are low-phonon-energy materials and are transparent from the visible to the infrared region. These glasses have been used in a large number of applications such as fiber amplifiers, diffraction gratings, optical switching, and waveguide fabrication [4-6]. Application of ChG glass fibers in ultrafast optical switches has been reported, and the switching efficiency has been studied with optical Kerr shutter experiments [7].
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