Realization of a Multichannel Chemical and BiologicalSensor Using 6x6 Multimode Interference Structures

Abstract

A new mirroring resonators (MRR) based on 6x6 multimode interference (MMI) couplers for multichannel and highly sensitive chemical and biological sensors is proposed in this paper. The proposed sensor structure has advantages of compactness, high sensitivity compared with the reported sensing structures. By using the transfer matrix method (TMM) and numerical simulations, the designs of the sensor based on silicon nanowires are optimized and demonstrated in detail. Current approaches to the real time analysis of chemical and biological sensing applications utilize systematic approaches such as mass spectrometry for detection. Such systems are expensive, heavy and cannot monolithically integrated in one single chip (1). Electronic sensors use metallic probes which produces electro magnetic noise, which can disturb the electro magnetic field being measured. This can be avoided in the case of using optical sensors. Optical sensors are very attractive due to their advantages of high sensitivity and ultra-wide bandwidth. A large class of optical sensors based on optical fibre and waveguides uses evanescent wave to monitor the presence of the analyte in the environment. Detection can be made by the optical absorption of the analytes, optic spectroscopy or the refractive index change (1). The two former methods can be directly obtained by measuring optical intensity. The third method is to monitor various chemical and biological systems via sensing of the change in refractive index (2). Optical waveguide devices can perform as refractive index sensors particularly when the analyte becomes a physical part of the device, such as waveguide cladding. In this case, the evanescent portion of the guided mode within the cladding will overlap and interact with the analyte. The measurement of the refractive index change of the guided mode of the optical waveguides requires a special structure to convert the refractive index change into detectable signals. A number of refractive index sensors based on optical waveguide structures have been reported, including Bragg grating sensors, directional coupler sensors, Mach- Zehnder interferometer (MZI) sensors, microring resonator sensors and surface plasmon resonance sensors (1-5).