Observation of Optical Bistability in Oppositely Directed Coupler

Abstract

Nonlinear directional couplers (NDCs) find wide interest in optical communication system because of its potential application in signal processing including optical switching and logic operation. In couplers, if any one of the channel of NDCs is replaced with negative index material (NIM), then the coupler is called as oppositely directed coupler (ODC) because of the opposite direction of input and output fields. The electromagnetic wave entering in one channel of the coupler leave through other channel in opposite direction. Optical bistability (OB) is a nonlinear phenomenon observed in optical systems such that, the system possesses two output intensities for the same input intensity. The importance of optical bistability arises due to its potential application for the development of devices such as optical switches, memories, and amplifiers. The primary requirements of OB are the intensity dependent refractive index and optical feedback mechanism. A two core directional coupler with channels made of nonlinear and homogeneous materials is not bistable. However, ODC shows the phenomenon of OB and admit gap solitons due to effective feedback mechanism in NIM channel arising as a result of opposite directionality of phase velocity and energy flow.