Actively stabilized optical feedback scheme for very stable, high sensitivity shear-force measurement

Abstract

We present here an active feedback control scheme which can maintain the distance between a laterally vibrating tapered optical fiber tip (TOFT) and a one facet of a laser diode (LD) at optimum value to measure the vibration amplitude of the TOFT in an optical feedback shear-force measurement scheme. Extremely good sensitivity for measuring the vibration amplitude, 9.58×10−2 pm/√Hz for a metal coated TOFT, can be maintained for at least 6 h by use of an active stablization scheme. Using a linearized lasing model of the LD in the presence of optical feedback, we are able to determine the vibration amplitude and effective reflection coefficient of the TOFT.