Huiye Qiu

Silicon Add-Drop Filter Based on Multimode Bragg Sidewall Gratings and Adiabatic Couplers

A silicon photonic add-drop filter is demonstrated with sidewall Bragg gratings in a multimode strip waveguide. The operating principle is based on the contradirectional coupling between the TE0 mode and different higher-order modes inside the multimode waveguide, which depends on the symmetry property of the periodic refractive-index perturbations. In order to relax the fabrication tolerance, a pair of adiabatic couplers is used to add/drop the optical signal at the output/input ports of the multimode waveguide. Experimental results show that the functionality of add/drop filtering is successfully achieved with a low insertion loss of 0.6 dB. We also show that by sweeping the multimode waveguide width from 700 to 1400 nm, the bandwidth can be flexibly tuned from 16 to 2 nm.

Analysis and Design of Refractive Index Biosensors Based on Single Silicon Nanobeam Cavity

Single silicon nanobeam photonic crystal cavity based sensors are systematically analyzed and designed. By using perturbation theory and numerical simulations, both dielectric-mode and air-mode cavities are extensively investigated in terms of sensitivity (S), figure of merit (FOM), detection limit (DL), footprint size, and coupling scheme. The analytical study reveals a sensitivity limit of 1176 nm/RIU and a maximum figure of merit of 5070 for nanobeam cavity based sensors, due to the absorption of light near 1550 nm wavelength. when water is used as the carrier fluid. Design of high FOM (> 4800) nanobeam cavities is demonstrated with S of 291 and 232 nm/RIU for air modes and dielectric modes, respectively. The calculation results indicate that on a 220-nm-thick-silicon SOI platform, it is possible to design a nanobeam cavity based biosensor with DL on the order of 4 × 10-6 RIU, insertion loss of -30 dB, and cavity length less than 40a (a is the lattice constant). To approach the absorption bounded DL, the presented design is adequate when analyte absorption dominates the loss, regardless if it is for dielectric modes or air modes. These results would be conducive to clarification of the confusion on the priority of air mode and dielectric mode in designing nanobeam cavities based sensors, as well as recent considerable efforts to maximize Sand FOM.

Broadband tunable filter based on the loop of multimode Bragg grating

A broadband tunable silicon filter has been demonstrated on silicon-on-insulator platform. The device is based on the loop of multimode anti-symmetric waveguide Bragg grating. A wide bandwidth tunability about 1.455 THz (0.117-1.572 THz) is achieved. The device, functions like a ring, can realize the bandwidth tunable of the drop port and the through port. And, its feature has simultaneous wavelength tuning and no free space ranges limitation. A high out-of-band contrast of 30 dB is achieved with a bandwidth of 1.572 THz (Δλ = 13 nm). The out-of-band contrast is 18 dB at the minimum bandwidth 0.117 THz (Δλ = 1.0 nm).

Silicon Add-Drop Filter Based on Multimode Grating Assisted Couplers

We demonstrate the design, fabrication, and characterization of a two-mode silicon add-drop filter, which is based on multimode grating-assisted contra-directional couplers. The mode conversions between two asymmetry strip waveguides are realized by using spatially periodic corrugations in one side wall of a multimode waveguide at the phase-match condition. Experimental results show that the fundamental mode of a single-mode waveguide is successfully coupled to the first two modes of the multimode waveguide in the opposite direction. The corresponding mode conversion bandwidths and extinction ratios are also measured. The demonstrated add-drop filter may find their applications in a hybrid multiplexing system by combing wavelength-division multiplexing technology and mode-division multiplexing technology for on-chip optical interconnect.

High-

We demonstrate the design, fabrication, and characterization of side-coupled airmode nanobeam photonic crystal cavities in silicon-on-insulator platform. Results show that repeatable devices achieve similar high loaded quality factors (>104) and large optical energy ratio in low refractive region. The unload Q-factors of the fabricated cavities are estimated to exceed 105. With side-coupled configuration, high transmission of through port is achieved with typical insertion loss less than 0.5 dB. Wavelength shifts of the measured resonances with respect to the designed values are observed and well explained by considering the fluctuation of etching depth. The demonstrated side-coupled airmode nanobeam photonic crystal cavities may find their applications in ultracompact integrated photonics, especially for on-chip photonic sensor, notch filter, or optical switch.

Q

A silicon photonic filter based on asymmetric sidewall Bragg gratings in a multimode SOI strip waveguide is demonstrated. Experimental results show that the presented Bragg gratings have a bandwidth of 2.8 nm and an extinction ratio of −23 dB.