Alignment-tolerant broadband compact taper for low-loss coupling to a silicon-on-insulator photonic wire waveguide.

We experimentally demonstrate a broadband, fabrication-tolerant compact silicon waveguide taper (34.2 µm) in a silicon-on-insulator wire waveguide. The taper works on multimode interference along the length of the taper. A single taper design has broadband operation with coupling efficiency >70% over 700 nm that can be used in O-, C-, and L-bands. The compact taper is highly tolerant to fabrication variations; ±100 nm change in the taper and end waveguide width varies the taper transmission by <5%. The footprint of the device, i.e., the taper along with linear gratings, is ≈442 µm2, 11.5× smaller than the adiabatic taper. The taper with linear gratings provides coupling efficiency comparable to standard focusing gratings. We have also experimentally compared the translational and rotational alignment tolerance of the focusing grating with linear grating couplers.

Compact broadband low-loss taper for coupling to a silicon nitride photonic wire.

We demonstrate an ultra-compact waveguide taper on a silicon nitride platform. The proposed taper provides a coupling efficiency of 95% at a length of 19.5 µm in comparison to the standard linear taper of length 50 µm, which connects a 10 µm wide waveguide to a 1 µm wide photonic wire. The taper has a spectral response >75% spanning over 800 nm and resilience to fabrication variations; ±200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally demonstrate taper insertion loss of <0.1 dB/transition for a taper as short as 19.5 µm, and reduce the footprint of the photonic device by 50.8% compared to the standard adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in silicon nitride.

All-optical ultrafast XOR/XNOR logic gates, binary counter, and double-bit comparator with silicon microring resonators.

We present designs of all-optical ultrafast YES/NOT, XOR/XNOR logic gates, binary counter, and double-bit comparator based on all-optical switching by two-photon absorption induced free-carrier injection in silicon 2 × 2 add-drop microring resonators. The proposed circuits have been theoretically analyzed using time-domain coupled-mode theory based on reported experimental values to realize low power (∼ 28 mW) ultrafast (∼ 22 ps) operation with high modulation (80%) and bit rate (45 Gb/s). The designs are complementary metal-oxide semiconductor compatible and provide advantages of high Q-factor, tunability, compactness, cascadibility, scalability, reconfigurability, simplicity, and minimal number of switches and inputs for realization of the desired logic. Although a two-bit counter has been shown, the scheme can easily be extended to N-bit counter through cascading.