Integrated photonic resonators are widely used to manipulate light propagation in an evanescently-coupled waveguide. While the evanescent coupling scheme works well for planar optical systems that are naturally waveguide based, many optical applications are free-space based, such as imaging, display, holographics, metrology and remote sensing. Here we demonstrate an active dielectric antenna as the interface device that allows the large-scale integration capability of silicon photonics to serve the free-space applications. We show a novel perturbation-base diffractive coupling scheme that allows a high-Q planer resonator to directly interact with and manipulate free-space waves. Using a silicon-based photonic crystal cavity whose resonance can be rapidly tuned with a p-i-n junction, a compact spatial light modulator with an extinction ratio of 9.5 dB and a modulation speed of 150 MHz is demonstrated. Method to improve the modulation speed is discussed.
Suspended ring resonators formed by both single-mode waveguide (SMW) and multi-mode waveguide (MMW) are designed, fabricated and characterized near 3.4 μm by thermal tuning and near 4.5 μm and 5.2 μm by tunable quantum cascade lasers. The dispersion property is analyzed by simulation in regards to frequency comb generation. The taper width is optimized for maximum coupling.Measurement setup is built up and described. For the SMW ring resonator, the intrinsic quality factor is fitted to be 6,800 and 16,000 near 5.2 μm and 4.5 μm, respectively. For the MMW ring resonator, it rises to 35,000 near 4.5 μm.Transmission spectrum distortion is observed at high input power, and is modeled as heat effect. Thermal tuning rate is experimentally confirmed at 0.21 nm/°C. Based on the measured distortion and heat simulation, absorption loss is estimated. Alloptical modulation is conducted to estimate the response time of this process. It can be shown that main loss is from surface thus is reducible by improving surface quality. On-chip electrical heater is designed and preliminary experiment indicate the feasibility to pattern it with our Electron Beam Lithography system.
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