C. P. Michael

Actuation of micro-optomechanical systems via cavity-enhanced optical dipole forces

Optical forces can produce significant mechanical effects in micro- and nanophotonic systems. Here we demonstrate a novel optomechanical system using a movable, micrometre-scale waveguide evanescently coupled to a high-Q optical microresonator. Micrometre-scale displacements of the waveguide are observed for milliwatt-level optical input powers. Measurement of the spatial variation of the force on the waveguide indicates that it arises from a cavity-enhanced optical dipole force resulting from the stored optical field of the resonator. This force is used to realize an all-optical tunable filter operating with submilliwatt control power. A theoretical model of the system shows that the maximum achievable force is independent of the intrinsic Q of the optical resonator and scales inversely with the cavity mode volume, suggesting that such forces may become even more effective as devices approach the nanoscale.

A proposal for highly tunable optical parametric oscillation in silicon micro-resonators.

We propose a novel scheme for continuous-wave pumped optical parametric oscillation (OPO) inside silicon micro-resonators. The proposed scheme not only requires a relative low lasing threshold, but also exhibits extremely broad tunability extending from the telecom band to mid infrared.

Wavelength- and material-dependent absorption in GaAs and AlGaAs microcavities

The quality factors of modes in nearly identical GaAs and Al0.18Ga0.82As microdisks are tracked over three wavelength ranges centered at 980, 1460, and 1600 nm, with quality factors measured as high as 6.62×10^5 in the 1600 nm band. After accounting for surface scattering, the remaining loss is due to sub-band-gap absorption in the bulk and on the surfaces. The observed absorption is, on average, 80% greater in AlGaAs than in GaAs and is 540% higher in both materials at 980 nm than at 1600 nm.

Growth, processing, and optical properties of epitaxial Er_2O_3 on silicon

Erbium-doped materials have been investigated for generating and amplifying light in low-power chip-scale optical networks on silicon, but several effects limit their performance in dense microphotonic applications. Stoichiometric ionic crystals are a potential alternative that achieve an Er(3+) density 100 x greater. We report the growth, processing, material characterization, and optical properties of single-crystal Er (2)O(3) epitaxially grown on silicon. A peak Er(3+) resonant absorption of 364 dB/cm at 1535 nm with minimal background loss places a high limit on potential gain. Using high-quality microdisk resonators, we conduct thorough C/L-band radiative efficiency and lifetime measurements and observe strong upconverted luminescence near 550 and 670 nm.

Surface encapsulation for low-loss silicon photonics

Encapsulation layers are explored for passivating the surfaces of silicon to reduce optical absorption in the 1500 nm wavelength band. Surface-sensitive test structures consisting of microdisk resonators are fabricated for this purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and SiO2 are applied under varying deposition and annealing conditions. A short dry thermal oxidation followed by a long high-temperature N2 anneal is found to be most effective at long-term encapsulation and reduction of interface absorption. Minimization of the optical loss is attributed to simultaneous reduction in sub-band-gap silicon surface states and hydrogen in the capping material.

Adiabatic self-tuning in a silicon microdisk optical resonator

We demonstrate a method for adiabatically self-tuning a silicon microdisk resonator. This mechanism is not only able to sensitively probe the fast nonlinear cavity dynamics, but also provides various optical functionalities like pulse compression, shaping, and tunable time delay.

Investigations of a Coherently Driven Semiconductor Optical Cavity QED System

Abstract : Chip-based cavity quantum electrodynamics QED devices consisting of a self-assembled InAs quantum dot QD coupled to a high quality factor GaAs microdisk cavity are coherently probed through their optical channel using a fiber taper waveguide. We highlight one particularly important aspect of this all-fiber measurement setup, which is the accuracy to which the optical coupling level and optical losses are known relative to typical free-space excitation techniques. This allows for precise knowledge of the intracavity photon number and measurement of absolute transmitted and reflected signals. Resonant optical spectroscopy of the system under both weak and strong driving conditions are presented, which when compared with a quantum master equation model of the system allows for determination of the coherent coupling rate between QD exciton and optical cavity mode, the different levels of elastic and inelastic dephasing of the exciton state, and the position and orientation of the QD within the cavity. Pump-probe measurements are also performed in which a far off-resonant red-detuned control laser beam is introduced into the cavity. Rather than producing a measurable ac Stark shift in the exciton line of the QD, we find that this control beam induces a saturation of the resonant system response. The broad photoluminescence spectrum resulting from the presence of the control beam the cavity points to sub-band-gap absorption in the semiconductor, and the resulting free-carrier generation, as the likely source of system saturation.

Prospects for epitaxial c-Er 2 O 3 as a CMOS-compatible lasing material

The emission of high-Q c-Er₂O₃ resonators displays little inhomogeneous broadening, robust vacuum-Rabi splitting, and strong upconversion. Considering these effects and a rate-equation model, we analyze the prospects for optically pumped on-chip lasing using c-Er₂O₃.

c-Er 2 O 3 Microdisks on Silicon: Fabrication and Photoluminescence

Microdisks are fabricated from c-Er₂O₃. Surface scattering presently limits the quality of whispering-gallery modes around the 980 nm and 1480 nm Er³⁺ pump bands. Photoluminescence is observed at 1550 nm while resonantly pumping cavity modes.

Ultrafast self-pulsation in a silicon microdisk

We demonstrate a novel scheme for the self-generation of ultrashot pulses inside a silicon microdisk. We report the generation of pulses as short as 96 ps, close to the cavity photon lifetime.