Ashok M. Prabhu

Ultracompact SOI Microring Add–Drop Filter With Wide Bandwidth and Wide FSR

We report the design and fabrication of an ultracompact silicon-on-insulator add-drop microring filter with a 1.5-mum radius for wavelength-division-multiplexing on-chip interconnect applications. The fabricated device was measured to have a wide free-spectral range of 52 nm and a wide channel bandwidth of 210 GHz, with a 2.9-dB insertion loss and a deep through-port extinction of nearly 25 dB.

Extreme Miniaturization of Silicon Add–Drop Microring Filters for VLSI Photonics Applications

We theoretically and experimentally investigated the performance of silicon-on-insulator (SOI) microring add-drop filters in the limit of extreme miniaturization for potential application in very dense integration of silicon photonic devices. Rigorous numerical analyses were performed to predict the theoretical limit of achievable intrinsic quality factors as the microring radius is scaled down to 1 μm. Experimental measurements of fabricated SOI microring resonators showed that ultracompact add-drop microring filters with radii as small as 1 μm can be achieved with a free spectral range exceeding 80 nm and an insertion loss of only 1 dB. These devices are also shown to exhibit intrinsic quality factors approaching the theoretically achievable limit set by the bending loss in ultracompact microring resonators.

Realization of asymmetric optical filters using asynchronous coupled-microring resonators.

General filter architectures based on asynchronously-tuned, coupled-microring resonators are proposed for realizing optical filters with asymmetric spectral responses. Asymmetric filters enable more complex spectral shapes to be realized which can better meet the demands of more advanced applications than symmetric filters. By adjusting individual transmission zeros of the filter transfer function, the transition bands on the low and high-frequency sides of the passband can be separately optimized to achieve an optimum filter response. A method for synthesizing asymmetric spectral responses based on the energy coupling matrix will also be presented along with numerical examples of high-order asymmetric optical filters. These devices represent new microring-based architectures that can be explored for advanced applications in optical spectral shaping and dispersion engineering.

Compact silicon microring-assisted directional couplers for optical signal processing applications

We propose and demonstrate a compact microring-assisted directional coupler in the silicon-on-insulator material system. An analytical model based on the strongly coupled mode theory shows that the device can be designed to have a wide range of spectral characteristics, including sharp asymmetric Fano line shapes, which can be used for WDM, switching, and sensing applications. The measured transmission spectra of the fabricated device with a 5-mum-radius microring resonator exhibited an asymmetric spectral response characteristic of the Fano resonance as predicted by the analytical model.

Femtosecond laser tuning of silicon microring resonators.

Femtosecond laser modification is demonstrated as a possible method for postfabrication tuning of silicon microring resonators. Single 400 nm femtosecond laser pulses were used to modify the effective index of crystalline silicon microring waveguides by either amorphization or surface nanomilling depending on the laser fluence. Both blue- and redshifts in the microring resonance could be achieved without imparting significant degradation to the device quality factor.

Experimental determination of coupled-microring filter parameters via pole-zero extraction

A method for directly extracting the coupling coefficients, the resonant frequency detunings and the loss of an N(th)-order serially-coupled microring resonator filter from the measured power spectral responses is presented. The device parameters are obtained from the through-port complex transfer function, which is constructed from the experimentally extracted poles and zeros of the filter. We applied the method to determine the parameters of a symmetric microring doublet fabricated in the Silicon-on- Insulator material platform. Simulated spectral responses using the extracted parameters showed good agreement with the measured data. The extracted parameters along with the poles and zeros of the device provide important information about the fabrication process and can be used to guide the post-fabrication trimming of high-order microring filters.

Post-fabrication tuning of Silicon microring resonators by femtosecond laser modification

We investigated the feasibility of post-fabrication tuning of Silicon microring resonators by fs laser modification at 400nm wavelength. Red and blue shifts were obtained for different laser fluences, with a maximum resonance shift of 10nm/shot.

Wideband 1.5µm-radius SOI add-drop microring filter for WDM on-chip interconnects

We report an ultracompact SOI add-drop microring filter with a 1.5µm-radius, a wide FSR of 52nm, a wide bandwidth of 210GHz, with 2.9dB insertion loss and nearly 25dB extinction for on-chip optical interconnect applications.

Compact silicon microring-assisted directional couplers for WDM and optical signal processing applications

We propose and demonstrate a compact SOI microring-assisted directional coupler. The device can be designed to have a wide range of spectral responses, including sharp asymmetric Fano line shapes, for WDM, switching and sensing applications.