Transduction of large optomechanical amplitudes with racetrack-loaded Mach-Zehnder interferometers

Chip-integrated photonic devices have stimulated development in areas ranging from telecommunications to optomechanics. Racetrack resonators have gained popularity for optomechanical transduction due to their high sensitivity and cavity finesse. However, they lack sufficient dynamic range to read out large amplitude mechanical resonators, which are preferred for sensing applications. We present a robust photonic circuit based on a Mach-Zehnder interferometer (MZI) combined with a racetrack resonator that increases linear range without compromising high transduction sensitivity. Optical and mechanical properties of combined MZI-racetrack devices are compared to lone racetracks with the same physical dimensions in the undercoupled, overcoupled and critical coupled regimes. We demonstrate an overall improvement in dynamic range, transduction responsivity, and mass sensitivity of up to 4x, 3x and 2.8x, respectively. Our highly phase sensitive MZI circuit also enables applications such as on-chip optical homodyning.

Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform

We report the experimental realization of horizontal plasmonic slot waveguides capable of subdiffraction modal confinement at IR wavelengths. These waveguides have a propagation length of approximately 6 lambda(g) and are monolithically integrated with conventional silicon photonic waveguides on the same silicon-on-insulator platform. Direct coupling of light from the silicon waveguides to the plasmonic waveguides was achieved with an efficiency of 30% using taper-funnel couplers to obtain mode matching between the two waveguide systems.

Aperture-coupled MIM plasmonic ring resonators with sub-diffraction modal volumes

We propose and investigate ultracompact aperture-coupled plasmonic ring resonators with submicron bending radii based on strongly-confined metal-insulator-metal plasmonic waveguides. Enhanced coupling can be obtained via diffraction by small apertures having typical widths between 50-100 nm in the metallic sidewall between the ring and bus waveguides. Both analytical model and rigorous FDTD simulations show that 500 nm-radius ring resonators can be obtained with low insertion loss, wide free spectral range and sub-diffraction cavity volume of less than 0.1(lambda(0)/n(eff))(3).

Ultrafast all-optical modulation in silicon-based nanoplasmonic devices

A five-layer silicon-based nanoplasmonic waveguiding structure is proposed for ultrafast all-optical modulation and switching applications. Ultrafast nonlinear phase and amplitude modulation is achieved via photo-generated free carrier dynamics in ion-implanted silicon using above-bandgap femtosecond pump pulses. Both an analytical model and rigorous numerical simulations of the structures have shown that a switching time of 5 ps and an on-off contrast of 35 dB can be achieved in these devices.

Specific detection of proteins using photonic crystal waveguides

Specific detection of proteins is demonstrated using planar photonic crystal waveguides. Using immobilized biotin as probe, streptavidin was captured, causing the waveguide mode cut-off to red-shift. The device was shown to detect a 2.5 nm streptavidin film with a 0.86 nm cut-off red-shift. An improved photonic crystal waveguide sensor design is also described and shown to have a 40% improved bulk refractive index response.

Photonic logic NOR gate based on two symmetric microring resonators

We demonstrate an all-optical NOR logic gate based on symmetric GaAs-AlGaAs microring resonators whose resonances are closely matched. Two input pump data streams are tuned close to one resonance of the symmetric microrings to switch a probe beam tuned to another resonance by two-photon absorption. The switching energy of the gate is 20 pJ/pulse, and the switching window is 40 ps, limited by the carrier lifetime. The use of two rings provides for better cascading in photonic logic circuits because of the higher number of available ports.

All-optical time-division demultiplexing and spatial pulse routing with a GaAs/AlGaAs microring resonator

We report what is to our knowledge the first demonstration of all-optical time-division demultiplexing and spatial pulse routing in a compact nonlinear GaAs/AlGaAs microring resonator operating at 1.55 microm . Switching is through the refractive-index change induced by two-photon absorption. The switching time of the device, limited by the ring-charging time and the recombination time of the induced carriers, is measured to be 30 ps. The switching on-off contrast, limited by the slight mismatch between the input and output coupling coefficients, exceeds 8 dB. The device can be used for time-division multiplexing as well.

Vertically coupled GaInAsP--InP microring resonators

Vertically coupled microring resonator channel-dropping filters are demonstrated in the GaInAsP-InP material system. These devices were fabricated without regrowth. In this method, low-loss single-mode waveguides are removed from the growth substrate and bonded to a GaAs transfer substrate with benzocyclobutene. This permits fabrication of vertically coupled waveguides on both sides of the epilayer. Optical quality facets are obtained by cleaving through the transfer substrate. Operation of single-mode, single-ring optical channel-dropping filters is demonstrated.