We report a silicon photonic refractometric CO(2) gas sensor operating at room temperature and capable of detecting CO(2) gas at atmospheric concentrations. The sensor uses a novel functional material layer based on a guanidine polymer derivative, which is shown to exhibit reversible refractive index change upon absorption and release of CO(2) gas molecules, and does not require the presence of humidity to operate. By functionalizing a silicon microring resonator with a thin layer of the polymer, we could detect CO(2) gas concentrations in the 0-500ppm range with a sensitivity of 6 × 10(-9) RIU/ppm and a detection limit of 20ppm. The microring transducer provides a potential integrated solution in the development of low-cost and compact CO(2) sensors that can be deployed as part of a sensor network for accurate environmental monitoring of greenhouse gases.

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We report observation of optical bistability and enhanced thermal nonlinearity in a graphene-silicon waveguide resonator. Photo-induced Joule heating in the graphene layer gives rise to a temperature increase in the silicon waveguide core and a corresponding thermo-optic shift in the resonance of the Fabry-Perot resonator. Measurement of the nonlinear resonance spectra showed a 9-fold increase in the effective thermal nonlinear index due to the graphene layer compared with a bare silicon waveguide.

Harnessing the full complexity of optical fields requires complete control of all degrees-of-freedom within a region of space and time -an open goal for present-day spatial light modulators (SLMs), active metasurfaces, and optical phased arrays. Here, we solve this challenge with a programmable photonic crystal cavity array enabled by four key advances: (i) near-unity vertical coupling to high-finesse microcavities through inverse design, (ii) scalable fabrication by optimized, 300 mm full-wafer processing, (iii) picometer-precision resonance alignment using automated, closed-loop "holographic trimming", and (iv) out-of-plane cavity control via a high-speed µLED array. Combining each, we demonstrate near-complete spatiotemporal control of a 64-resonator, two-dimensional SLM with nanosecond-and femtojoule-order switching. Simultaneously operating wavelength-scale modes near the space-and time-bandwidth limits, this work opens a new regime of programmability at the fundamental limits of multimode optical control.

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We experimentally investigated thermal nonlinear effects in a hybrid Au/SiO(2)/SU-8 plasmonic microring resonator for nonlinear switching. Large ohmic loss in the metal layer gave rise to a high rate of light-to-heat conversion in the plasmonic waveguide, causing an intensity-dependent thermo-optic shift in the microring resonance. We obtained 30 times larger resonance shift in the plasmonic microring than in a similar SU-8 dielectric microring. Using an in-plane pump-and-probe configuration, we also demonstrated all-plasmonic nonlinear switching in the plasmonic microring with an on-off switching contrast of 4 dB over 50 mW input power.

We report a silicon photonic dual-gas sensor based on a wavelength-multiplexed microring resonator array for simultaneous detection of H and CO gases. The sensor uses Pd as the sensing layer for H gas and a novel functional material based on the Polyhexamethylene Biguanide (PHMB) polymer for CO gas sensing. Gas sensing experiments showed that the PHMB-functionalized microring exhibited high sensitivity to CO gas and excellent selectivity against H. However, the Pd-functionalized microring was found to exhibit sensitivity to both H and CO gases, rendering it ineffective for detecting H in a gas mixture containing CO. We show that the dual-gas sensing scheme can allow for accurate measurement of H concentration in the presence of CO by accounting for the cross-sensitivity of Pd to the latter.

Subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform are proposed and demonstrated. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which have critical dimensions greater than 100 nm, are fabricated using a commercial rapid turn-around silicon nitride prototyping foundry process using electron beam lithography. Experimental characterization of the fabricated device reveals excellent ring resonator internal quality factor (2.11 × 10 5 ) and low propagation loss (≈1.5 dB cm −1 ) in the C-band, a significant improvement of both parameters compared to silicon-based SWG ring resonators. These results demonstrate the promising prospects of SWG metamaterial structures for silicon nitride based photonic integrated circuits. IntroductionSilicon photonics (SiP) has become a leading integrated photonics technology by leveraging existing microelectronics manufacturing processes and infrastructure to produce compact, scalable,