We report an experimental demonstration of an integrated biochemical sensor based on a slot-waveguide microring resonator. The microresonator is fabricated on a ${\mathrm{Si}}_3{\mathrm{N}}_4–\mathrm{Si}{\mathrm{O}}_2$ platform and operates at a wavelength of $1.3\mu \mathrm{m}$. The transmission spectrum of the sensor is measured with different ambient refractive indices ranging from $n=1.33$ to 1.42. A linear shift of the resonant wavelength with increasing ambient refractive index of $212\mathrm{nm}$/refractive index units (RIU) is observed. The sensor detects a minimal refractive index variation of $2\times {10}^{-4}\mathrm{RIU}$.

We demonstrate label-free molecule detection by using an integrated biosensor based on a ${\mathrm{Si}}_3{\mathrm{N}}_4∕{\mathrm{SiO}}_2$ slot-waveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and $3.2\mathrm{nm}∕(\mathrm{ng}∕{\mathrm{mm}}^2)$ for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and $16\mathrm{pg}∕{\mathrm{mm}}^2$ for anti-BSA and BSA, respectively, limited by wavelength resolution.

Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and coupling of optical and mechanical waves at the nanoscale. Among their physical implementations, optomechanical (OM) crystals built on semiconductor slabs enable the integration and manipulation of multiple OM elements in a single chip and provide gigahertz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and gigahertz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap, which should enable longer lifetimes, as acoustic leakage is minimized. Here we demonstrate the excitation of acoustic modes in a one-dimensional OM crystal properly designed to display a full phononic bandgap for acoustic modes at 4 GHz. The modes inside the complete bandgap are designed to have high-mechanical Q-factors, limit clamping losses and be invariant to fabrication imperfections.

Optical nonlinearities, such as thermo-optic mechanisms and free-carrier dispersion, are often considered unwelcome effects in silicon-based resonators and, more specifically, optomechanical cavities, since they affect, for instance, the relative detuning between an optical resonance and the excitation laser. Here, we exploit these nonlinearities and their intercoupling with the mechanical degrees of freedom of a silicon optomechanical nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser we demonstrate accurate control to activate two- and four-dimensional limit cycles, a period-doubling route and a six-dimensional chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between two- and four-dimensional limit cycles, between different coherent mechanical states and between four-dimensional limit cycles and chaos. Our findings open new routes towards exploiting silicon-based optomechanical photonic crystals as a versatile building block to be used in neurocomputational networks and for chaos-based applications.