Radiation-pressure-mediated control of an optomechanical cavity

Abstract

We describe and demonstrate a method to control a detuned movable-mirror Fabry-Pérot cavity using radiation pressure in the presence of a strong optical spring. At frequencies below the optical spring resonance, self-locking of the cavity is achieved intrinsically by the optomechanical (OM) interaction between the cavity field and the movable end mirror. The OM interaction results in a high rigidity and reduced susceptibility of the mirror to external forces. However, due to a finite delay time in the cavity, this enhanced rigidity is accompanied by an antidamping force, which destabilizes the cavity. The cavity is stabilized by applying external feedback in a frequency band around the optical spring resonance. The error signal is sensed in the amplitude quadrature of the transmitted beam with a photodetector. An amplitude modulator in the input path to the cavity modulates the light intensity to provide the stabilizing radiation pressure force.

Observation of an optical spring with a beam splitter

“…as described in [6] where the first term is for the fundamental mode and the second term is for the yaw mode with Γ my = 2000 Hz.…”

“…For a blue-detuned cavity in which the cavity's resonance frequency is less than the laser frequency, the linear relationship between the radiation pressure force and cavity length creates a positive restoring force with an effective spring constant K OS and an antidamping force Γ OS . The combination of the optical spring constant and the mechanical spring constant of the device combine to shift the resonance frequency of the system from Ω m to Ω 2 m + Ω 2 OS where Ω m is the resonance frequency of the mechanical oscillator and Ω OS is the optical spring frequency [4][5][6]. This frequency shift is an experimental signature of the optical spring.…”

“…The Michelson-Sagnac topology was used to simplifiy the alignment of the laser beams onto the microresonator. The microresonator is similar to the one used in [6,11] and described in [21,22] but consists only of a 358.1-nm thick GaAs cantilever without the highly reflective stack of crystalline Al 0.92 Ga 0.08 As/GaAs layers. The GaAs microresonator has a power reflectivity of R osc = 65% for the laser wavelength of λ = 1064nm.…”

“…The antidamping force created by the optical spring can overwhelm the mechanical damping and lead to dynamic instabilities [7][8][9] and is usually controlled with feedback loops [6][7][8].…”

Broadband reduction of quantum radiation pressure noise via squeezed light injection

“…24,25 The optical spring effect is stabilized by monitoring the cavity reflection and transmission field, and providing active feedback around the optical spring frequency to the laser power and frequency via an electrooptic amplitude modulator (AM) and phase modulator (PM). 18,26 In the final measurement configuration, only the reflected light and PM feedback loop is used to lock the cavity at a detuning of about 0.6 linewidths, with the optical spring pushing the mechanical resonance frequency above 100 kHz.…”