Whispering gallery mode biosensors allow selective unlabelled detection of single proteins and, combined with quantum limited sensitivity, the possibility for noninvasive realtime observation of motor molecule motion. However, to date technical noise
sources, most particularly low frequency laser noise, have constrained such applications. Here we introduce a new technique for whispering gallery mode sensing based on direct detection of back-scattered light. This experimentally straightforward technique is immune to frequency noise in principle, and further, acts to suppress thermorefractive noise. We demonstrate 27 dB of frequency noise suppression, eliminating frequency noise as a source of sensitivity degradation and allowing an absolute frequency shift sensitivity of 76 kHz. Our results open a new pathway towards single molecule biophysics experiments and ultrasensitive biosensors.
We experimentally demonstrate thermo-optic locking of a semiconductor laser to an integrated toroidal optical microresonator. The lock is maintained for time periods exceeding twelve hours, without requiring any electronic control systems. Fast contr
ol is achieved by optical feedback induced by scattering centers within the microresonator, with thermal locking due to optical heating maintaining constructive interference between the cavity and the laser. Furthermore, the optical feedback acts to narrow the laser linewidth, with ultra high quality microtoroid resonances offering the potential for ultralow linewidth on-chip lasers.
We implement a cavity opto-electromechanical system integrating electrical actuation capabilities of nanoelectromechanical devices with ultrasensitive mechanical transduction achieved via intra-cavity optomechanical coupling. Electrical gradient forc
es as large as 0.40 microN are realized, with simultaneous mechanical transduction sensitivity of 1.5 X 10^-18 m/rtHz representing a three orders of magnitude improvement over any nanoelectromechanical system to date. Opto-electromechanical feedback cooling is demonstrated, exhibiting strong squashing of the in-loop transduction signal. Out-of-loop transduction provides accurate temperature calibration even in the critical paradigm where measurement backaction induces opto-mechanical correlations.
