Optomechanical gigahertz oscillator made of a two photon absorption free piezoelectric III/V semiconductor

Abstract

Oscillators in the GHz frequency range are key building blocks for telecommunication and positioning applications. Operating directly in the GHz while keeping high frequency stability and compactness, is still an up-to-date challenge. Recently, optomechanical crystals have demonstrated GHz frequency modes, thus gathering prerequisite features for using them as oscillators. Here we report on the demonstration, in ambient atmospheric conditions, of an optomechanical oscillator designed with an original concept based on bichromaticity. This oscillator is made of InGaP, a low loss and TPA-free piezoelectric material which makes it valuable for optomechanics. Self-sustained oscillations directly at 3 GHz are routinely achieved with a low optical power threshold of 40 µW and short-term linewidth narrowed down to 100 Hz in agreement with phase noise measurements (-110 dBc/Hz at 1 MHz from the carrier) for free running optomechanical oscillators.

Microwave oscillator and frequency comb in a silicon optomechanical cavity with a full phononic bandgap

“…Importantly, our device improves the noise performance of silicon disks fabricated in micro-electro-mechanical systems (MEMS) technology [38]. The OMO reported in a study by Ghorbel et al [12], which makes use of a 1D OM crystal cavity in GaAs, shows a phase noise at 100 kHz more than 10 dB worse that our device for a similar microwave frequency. Since both OM cavities display similar mechanical Q factors at room temperature (limited by material losses), the better performance of our device in terms of phase noise may be due to an improved value of g 0 or a higher driving power.…”

“…Operating at cryogenic temperatures would enormously improve the phase noise [46] as a result of the enhancement of the mechanical Q factor because of the full phononic bandgap [22]. This would also allow us to discern if the phononic bandgap plays a role in the better performance in terms of phase noise in comparison to the OM crystal reported in a study by Ghorbel et al [12]. Tunability of the resulting microwave signal could be achieved by injection locking to an external optically modulated tone [47].…”

“…Since the mechanical vibration can efficiently modulate the intensity of an input optical signal, OM cavities could play a role in microwave photonics, a discipline that addresses the processing of microwave signals in the optical domain [10]. In this sense, some experiments have shown the performance of OM cavities as radio frequency (RF) down-converters [11] or OM oscillators [12], which are essential functionalities in microwave photonics. Moreover, since OM cavities are nonlinear elements, multiple harmonics of the fundamental mechanical vibrations can be over-imposed on the optical signal [11,13,14], a phenomenon that has been recently interpreted theoretically as an optical frequency comb (OFC) [15].…”

Photonic crystal optical parametric oscillator

“…The photonic crystal is created using e-beam lithography, dry etch of the hard mask, inductively coupled plasma etching of the holes and wet etching of the underlying material substrate to release the membrane[ 50 ]. The large electronic gap (1.89 eV) prevents two-photon absorption when operating the telecom spectral band, while the residual absorption rate is very low[ 51 ].…”

Observation of phonon trapping in the continuum with topological charges

“…Based on these results and the scaling rule of Eq. ( 2 ), we expect mechanical BICs with Q ≥ 10 7 can be realized in millimeter-scale PnCs with improved fabrication and material quality, such as using single crystalline silicon 30 or epitaxially grown materials 31 – 33 . The mechanical quality factor can also be further improved using the technique of topological charge merging to suppress scattering losses 19 .…”