Optomechanical transduction of an integrated silicon cantilever probe using a microdisk resonator

Sensitive transduction of the motion of a microscale cantilever is central to many applications in mass, force, magnetic resonance, and displacement sensing. Reducing cantilever size to nanoscale dimensions can improve the bandwidth and sensitivity of techniques like atomic force microscopy, but current optical transduction methods suffer when the cantilever is small compared to the achievable spot size. Here, we demonstrate sensitive optical transduction in a monolithic cavity-optomechanical system in which a sub-picogram silicon cantilever with a sharp probe tip is separated from a microdisk optical resonator by a nanoscale gap. High quality factor (Q ~ 10^5) microdisk optical modes transduce the cantilever's MHz frequency thermally-driven vibrations with a displacement sensitivity of ~ 4.4x10^-16 m\sqrt[2]{Hz} and bandwidth > 1 GHz, and a dynamic range > 10^6 is estimated for a 1 s measurement. Optically-induced stiffening due to the strong optomechanical interaction is observed, and engineering of probe dynamics through cantilever design and electrostatic actuation is illustrated

Electromagnetically Induced Transparency and Wideband Wavelength Conversion in Silicon Nitride Microdisk Optomechanical Resonators

We demonstrate optomechanically mediated electromagnetically induced transparency and wavelength conversion in silicon nitride (Si_3N_4) microdisk resonators. Fabricated devices support whispering gallery optical modes with a quality factor (Q) of 10^6, and radial breathing mechanical modes with a Q = 10^4 and a resonance frequency of 625 MHz, so that the system is in the resolved sideband regime. Placing a strong optical control field on the red (blue) detuned sideband of the optical mode produces coherent interference with a resonant probe beam, inducing a transparency (absorption) window for the probe. This is observed for multiple optical modes of the device, all of which couple to the same mechanical mode, and which can be widely separated in wavelength due to the large band gap of Si_3N_4. These properties are exploited to demonstrate frequency up-conversion and down-conversion of optical signals between the 1300 and 980 nm bands with a frequency span of 69.4 THz

Overcoming Thermo-Optical Dynamics in Broadband Nanophotonic Sensing

Advances in integrated photonics open exciting opportunities for batch-fabricated optical sensors using high quality factor nanophotonic cavities to achieve ultra-high sensitivities and bandwidths. The sensitivity improves with higher optical power, however, localized absorption and heating within a micrometer-scale mode volume prominently distorts the cavity resonances and strongly couples the sensor response to thermal dynamics, limiting the sensitivity and hindering the measurement of broadband time-dependent signals. Here, we derive a frequency-dependent photonic sensor transfer function that accounts for thermo-optical dynamics and quantitatively describes the measured broadband optomechanical signal from an integrated photonic atomic-force-microscopy nanomechanical probe. Using this transfer function, the probe can be operated in the high optical power, strongly thermo-optically nonlinear regime, reaching a sensitivity of $\approx$ 0.4 fm/Hz$^{1/2}$, an improvement of $\approx 10\times$ relative to the best performance in the linear regime. Counterintuitively, we discover that higher transduction gain and sensitivity are obtained with lower quality factor optical modes for low signal frequencies. Not limited to optomechanical transducers, the derived transfer function is generally valid for describing small-signal dynamic response of a broad range of technologically important photonic sensors subject to the thermo-optical effect

Bound-state-in-continuum guided modes in a multilayer electro-optically active photonic integrated circuit platform

Bound states in the continuum (BICs) are localized states existing within a continuous spectrum of delocalized waves. Emerging multilayer photonic integrated circuit (PIC) platforms allow implementation of low index 1D guided modes within a high-index 2D slab mode continuum; however, conventional wisdom suggests that this always leads to large radiation losses. Here we demonstrate low-loss BIC guided modes for multiple mode polarizations and spatial orders in single- and multi-ridge low-index waveguides within a two-layer heterogeneously integrated electro-optically active photonic platform. The transverse electric (TE) polarized quasi-BIC guided mode with low, <1.4 dB/cm loss enables a Mach-Zehnder electro-optic amplitude modulator comprising a single straight Si3N4 ridge waveguide integrated with a continuous LiNbO3 slab layer. The abrupt optical transitions at the edges of the slab function as compact and efficient directional couplers eliminating the need for additional components. The modulator exhibits a low insertion loss of 2.3 dB and a high extinction ratio of 25 dB. The developed general theoretical model may enable innovative BIC-based approaches for important PIC functions, such as agile spectral filtering and switching, and may suggest new photonic architectures for quantum and neural network applications based on controlled interactions between multiple guided and delocalized modes