Thermally induced sideband generation in silicon-on-insulator cladding modulated Bragg notch filters.

We investigate and experimentally demonstrate a cladding modulated Bragg grating superstructure as a dynamically tunable and reconfigurable multi-wavelength notch filter. A non-uniform heater element was implemented to periodically modulate the effective index of the grating. The Bragg grating bandwidth is controlled by judiciously positioning loading segments away from the waveguide core, resulting in a formation of periodically spaced reflection sidebands. The thermal modulation of a periodically configured heater elements modifies the waveguide effective index, where an applied current controls the number and intensity of the secondary peaks. The device was designed to operate in TM polarization near the central wavelength of 1550 nm and was fabricated on a 220-nm silicon-on-insulator platform, using titanium-tungsten heating elements and aluminum interconnects. We experimentally demonstrate that the Bragg grating self-coupling coefficient can be effectively controlled in a range from 7 mm-1 to 110 mm-1 by thermal tuning, with a measured bandgap and sideband separation of 1 nm and 3 nm, respectively. The experimental results are in excellent agreement with simulations.

Broadband and low-loss TM-pass polarizer using tilted subwavelength structures.

Photonic systems built on the Silicon-on-Insulator platform exhibit a strong birefringence, and must thus be operated with a single polarization for most applications. Hence, on-chip polarizers that can effectively suppress an undesired polarization state are key components for these systems. Polarizers that extinguish TE polarized light while letting TM polarized light pass with low losses are particularly challenging to design for the standard 220 nm Silicon-on-Insulator platform, because the modal confinement is stronger for TE polarization than for TM polarzation. Here, we propose and design a broadband, low loss and high extinction ratio TM-pass polarizer by engineering a Bragg grating that reflects the fundamental TE mode into the first order TE mode using a subwavelength metamaterial which at the same time allows the TM mode to pass. Our device achieves an extinction ratio in excess of 20 dB, insertion losses below 0.5 dB and back-reflections of the fundamental TE mode of the order of -20 dB in a bandwidth of 150 nm as demonstrated with full 3D-FDTD simulations.

Narrowband Bragg filters based on subwavelength grating waveguides for silicon photonic sensing.

Subwavelength grating (SWG) waveguides have been shown to provide enhanced light-matter interaction resulting in superior sensitivity in integrated photonics sensors. Narrowband integrated optical filters can be made by combining SWG waveguides with evanescently coupled Bragg gratings. In this paper, we assess the sensing capabilities of this novel filtering component with rigorous electromagnetic simulations. Our design is optimized for an operating wavelength of 1310 nm to benefit from lower water absorption and achieve narrower bandwidths than at the conventional wavelength of 1550 nm. Results show that the sensor achieves a sensitivity of 507 nm/RIU and a quality factor of 4.9 × 104, over a large dynamic range circumventing the free spectral range limit of conventional devices. Furthermore, the intrinsic limit of detection, 5.1 × 10-5 RIU constitutes a 10-fold enhancement compared to state-of-the-art resonant waveguide sensors.