Injection locking of optomechanical oscillators via acoustic waves

Injection locking is a powerful technique for synchronization of oscillator networks and controlling the phase and frequency of individual oscillators using similar or other types of oscillators. Here, we present the first demonstration of injection locking of a radiation-pressure driven optomechanical oscillator (OMO) via acoustic waves. As opposed to previously reported techniques (based on pump modulation or direct application of a modulated electrostatic force), injection locking of OMO via acoustic waves does not require optical power modulation or physical contact with the OMO and it can easily be implemented on various platforms. Using this approach we have locked the phase and frequency of two distinct modes of a microtoroidal silica OMO to a piezoelectric transducer (PZT). We have characterized the behavior of the injection locked OMO with three acoustic excitation configurations and showed that even without proper acoustic impedance matching the OMO can be locked to the PZT and tuned over 17 kHz with only -30 dBm of RF power fed to the PZT. The high efficiency, simplicity and scalability of the proposed approach paves the road toward a new class of photonic systems that rely on synchronization of several OMOs to a single or multiple RF oscillators with applications in optical communication, metrology and sensing. Beyond its practical applications, injection locking via acoustic waves can be used in fundamental studies in quantum optomechanics where thermal and optical isolation of the OMO are critical

Brownian noise in radiation-pressure-driven micromechanical oscillators

The authors demonstrate Brownian-noise-limited operation of an optomechanical oscillator, wherein mechanical oscillations of a silica optical microcavity are sustained by means of radiation pressure. Using phase noise measurement above threshold, it has been shown that the short-term linewidth of mechanical oscillations is fundamentally broadened, limited by thermal equipartition of energy

Fiber-taper coupling to Whispering-Gallery modes of fluidic resonators embedded in a liquid medium

We demonstrate efficient coupling to the optical Whispering-Gallery (WG) modes of a fluidic resonator consisting of a droplet embedded in a liquid medium. Unlike previous experiments the droplet is not levitated in an optical or electrostatic trap and free space coupling is replaced by phase-matched, waveguide coupling using a fiber-taper. We have observed critical coupling to fundamental WG modes of a 600 μm diameter water droplet at 980 nm. The experimental challenges towards making, stabilizing and coupling to the droplet resonators are addressed in this paper

Observation of injection locking in an optomechanical rf oscillator

Injection locking of a radiation-pressure optomechanical oscillator is demonstrated through external modulation of the optical pump power near the optomechanical oscillation frequency. It is shown that the frequency and phase of a microtoroidal optomechanical oscillator can be locked to those of an electronic oscillator (or any other signal) that can modulate the optical input power and whose frequency is within the lock range

Importance of Intrinsic-Q in Microring-Based Optical Filters and Dispersion-Compensation Devices

We investigate the impact of the intrinsic-Q of the resonant poles on the performance of multiring-based optical filters and dispersion-compensating devices. We highlight the role of quality factor by defining figures-of-merit for some specific filter configurations

Photonic RF Down-Converter Based on Optomechanical Oscillation

We demonstrate all-optical radio-frequency (RF) down-conversion in a silica microtoroid optomechanical (OM) oscillator. Preliminary results show that the OM oscillator can simultaneously serve as mixer and local oscillator in a photonic homodyne RF-receiver architecture

An Optomechanical Oscillator on a Silicon Chip

The recent observation on radiation-pressure-driven self-sustained oscillation in high-Q optical microresonators has created new possibilities for development of photonic devices that benefit from unique functionalities offered by these “optomechanical oscillators” (OMOs). Here, we review the physics, fundamental characteristics, and potential applications of OMOs using the silica microtoroidal OMO as an example

Free ultra-high-Q microtoroid: a tool for designing photonic devices

We describe techniques that enable fabrication of a new class of photonic devices based on free UH-Q microresonators. Preliminary results show that free silica microtoroids with Qs above 30 million can be fabricated and transferred to different platforms for integration with a variety of photonic devices

Observation of optical spring effect in a microtoroidal optomechanical resonator

We present experimental evidence of the optical spring effect in a silica microtoroid resonator. The variation of the measured mechanical resonant frequency as a function of optical power, optical coupling, and optical detuning is in very good agreement with a model for radiation-pressure-induced rigidity in a silica microtoroid

A fast approach for overcomplete sparse decomposition based on smoothed L0 norm

In this paper, a fast algorithm for overcomplete sparse decomposition, called SL0, is proposed. The algorithm is essentially a method for obtaining sparse solutions of underdetermined systems of linear equations, and its applications include underdetermined Sparse Component Analysis (SCA), atomic decomposition on overcomplete dictionaries, compressed sensing, and decoding real field codes. Contrary to previous methods, which usually solve this problem by minimizing the L1 norm using Linear Programming (LP) techniques, our algorithm tries to directly minimize the L0 norm. It is experimentally shown that the proposed algorithm is about two to three orders of magnitude faster than the state-of-the-art interior-point LP solvers, while providing the same (or better) accuracy.Comment: Accepted in IEEE Transactions on Signal Processing. For MATLAB codes, see (http://ee.sharif.ir/~SLzero). File replaced, because Fig. 5 was missing erroneousl