High precision detection of refractive index variation using laser emission from a micro-ring resonator

Abstract

In-situ precise monitoring of refractive index (RI) variations has important applications in studying biomedical and chemical reactions. Using laser emission from a well-designed micro-ring resonator, modeled with a four-level two-electron gain material model, a high-precision RI sensor is proposed that can detect RI variations as small as 0.001. Through the use of the three-dimensional finite-difference time-domain method, we design and numerically analyze the laser dynamics and field distribution in response to the RI variation of the surrounding medium. Unlike most other refractive index sensors, which mostly rely on the frequency shift and spectrum broadening in passive media, here we show that the direction of coupling of the excited laser mode (in the ring waveguide) to the near linear waveguide is highly sensitive to RI. We also demonstrate that by properly tuning the input pump intensity, varying RI can turn the laser mode ON or OFF. Our study offers a new platform for sensing RI variations and controlling laser output, which are potentially suitable for developing chemical and biomedical sensors in lab-on-a-chip devices.