Modulation instability and highly sensitive optical fiber biosensor

Abstract

The modulation instability (MI) is one of the interesting nonlinear phenomena which is used as a sensing mechanism. The performance of this mechanism is based on the shift of generated sidebands when the effective refractive index of the sensor is changed. The use of the MI process as a biosensing mechanism has capabilities such as high sensitivity, label-free and selective operation. In this paper, the novel optical fiber structures are proposed as lab-on-a-chip biosensors. In the proposed biosensors, capturing target biomolecules is achieved by immobilizing a capture layer. Consequently, after attaching the target layer the effective refractive index and the total dispersion of the structure are changed. As a result, the MI gain profile is changed and the generated sidebands (Stokes and anti-Stokes) around pump frequency are shifted. We demonstrate that the maximum sensitivity of these proposed sensors is 34.88 nm/nm. Moreover, the nonlinear material which is used in these biosensors is semiconductor doped glass (CS 3-68). This material due to the high nonlinear refractive index is an appropriate candidate to realize the MI process at low pump power. The used laser is a conventional laser 1550 nm with a power of 100 mW. The maximum length of the proposed biosensors is 0.199 cm which can realize the concept of lab-on-a-chip biosensors.