Observation of thermal feedback on the optical coupling noise of a microsphere attached to a low-spring-constant cantilever

Abstract

Original citationWu, Y., Ward, J. and Nic Chormaic, S. (2012) A silica microsphere on a low-spring-constant cantilever (pendulum) is fabricated and evanescently coupled to a tapered optical fiber. The motion of the pendulum is detected as variations in the transmitted laser power through the tapered fiber. The optical coupling noise created by the pendulum motion is recorded by taking a fast Fourier transform of the transmitted laser power and the fundamental mechanical mode of the pendulum at 1.16 kHz is observed. The thermal damping and amplification of the coupling noise is investigated and the effect of the thermal feedback on the noise spectrum is examined. The response of the thermo-optical feedback to small transient and driven variations in the taper-pendulum separation for different values of laser detuning is demonstrated. Preliminary results on the optical force between the pendulum and the tapered fiber are also presented. Microspherical pendulums, with low mechanical spring constant, could be used for studying nanoscopic optical and mechanical forces, or optical cooling.

Optomechanical transduction and characterization of a silica microsphere pendulum via evanescent light

“…This is similar to the effect of dispersion on the system. In order to uncover the fundamental dissipative and dispersive mechanisms in the micropendulum system, we redid our earlier experiments [15] using an input power of about 100 nW. The laser was scanned in steps of 0.6 MHz, spanning more than one full WGM linewidth, and FFT peaks were recorded for each value of ∆ 0 .…”

“…Furthermore each data point for the critical (over) coupled plot (as in Fig. 3(b) and (c)) is an average of four (15) data points.…”

Asymmetric response function of the transduction spectrum for a microsphere pendulum

“…However, the actual trapping and control of a microcavity system has yet to be realized [10][11][12][13] . One simple optomechanical system is a microsphere pendulum coupled to an optical waveguide such as a tapered optical fiber 10,11 . In a delineative manner, a microsphere i.e., a bob, attached to a thin cantilever i.e., a stem, acts as a pendulum.…”

“…Applications such as the actuation of optomechanical systems through optical attractive or repulsive forces have been realized 1,[8][9][10][11][12][13] . However, the actual trapping and control of a microcavity system has yet to be realized [10][11][12][13] . One simple optomechanical system is a microsphere pendulum coupled to an optical waveguide such as a tapered optical fiber 10,11 .…”

“…In this rather simple system, the motion of the pendulum due to various environmental effects such as temperature, air currents, electrostatics, vibrations, and even the forces due to light itself can be transduced. In order to achieve trapping or corralling of a microcavity with optical fields [8][9][10][11][12][13] , the complete details about the pendulum behavior in the evanescent fields are required. Here, we try to understand the observed optical output due to the pendulum-like motion of a microsphere in the evanescent field of a tapered fiber.…”