Compact and broadband silicon TE-pass polarizer based on tapered directional coupler.

We demonstrate a novel TE-pass polarizer, to the best of our knowledge, on a silicon-on-insulator (SOI) platform. The device's working principle is based on the phase-matched coupling of the unwanted TM0 mode in an input waveguide to the TM1 mode in a tapered directional coupler (DC), which is then guided through a low-loss bend (180-degree) and scattered in a terminator section with low back reflections. However, the input TE0 mode is routed through the tapered section uncoupled with negligible loss. An S-bend is added before the output for filtering any residual TM0 mode present in the input waveguide. Tapering the DC helps maintain phase matching for broadband operation and increases the tolerance toward fabrication errors. The measurement shows low insertion loss (IL < 0.44 dB), high extinction ratio (ER > 15 dB), and wide bandwidth (BW = 80 nm). The overall device length is only 13 µm. A high performing TE-pass polarizer (IL < 0.89, ER > 30, and BW = 100 nm) is also demonstrated by cascading two proposed polarizers.

CMOS compatible ultra-compact MMI based wavelength diplexer with 60 Gbit/s system demonstration.

We design and experimentally demonstrate an ultra-compact 1310/1550 nm wavelength diplexer based on a multimode interference (MMI) coupler. The proposed device is designed at the first imaging length for 1550 nm wavelength resulting in an MMI length of only 41 µm. In order to improve the extinction ratio, the output ports are made asymmetric in width. A low insertion loss (< 1dB) and high extinction ratio (> 20 dB) is measured at the two operating wavelengths. It also displays a wide 3-dB bandwidth of 100 nm centered around 1310 nm and 1550 nm wavelengths. Furthermore, an on-chip wavelength demultiplexing experiment carried out on the fabricated device, with a non-return-to-zero (NRZ) on-off keying (OOK) signal at 60 Gbit/s, shows clear eye diagrams for both the wavelengths.

Robust broadband athermal 2 × 2 Mach-Zehnder interferometer with sub-wavelength grating adiabatic couplers.

We report an all-silicon thermally insensitive (-1.5pm/∘C) 2×2 Mach-Zehnder interferometer (MZI) over a spectral range from 1540 to 1620 nm. Additionally, the proposed MZI exhibits no imbalance in its extinction ratio with temperature. The broadband spectral range with minimal temperature sensitivity is achieved by slightly overcompensating the MZI design for temperature variations. At the same time, the uniformity in the extinction ratio is controlled using sub-wavelength grating adiabatic couplers for splitting and combining.

Monolithic Multi Degree of Freedom (MDoF) Capacitive MEMS Accelerometers.

With the continuous advancements in microelectromechanical systems (MEMS) fabrication technology, inertial sensors like accelerometers and gyroscopes can be designed and manufactured with smaller footprint and lower power consumption. In the literature, there are several reported accelerometer designs based on MEMS technology and utilizing various transductions like capacitive, piezoelectric, optical, thermal, among several others. In particular, capacitive accelerometers are the most popular and highly researched due to several advantages like high sensitivity, low noise, low temperature sensitivity, linearity, and small footprint. Accelerometers can be designed to sense acceleration in all the three directions (X, Y, and Z-axis). Single-axis accelerometers are the most common and are often integrated orthogonally and combined as multiple-degree-of-freedom (MDoF) packages for sensing acceleration in the three directions. This type of MDoF increases the overall device footprint and cost. It also causes calibration errors and may require expensive compensations. Another type of MDoF accelerometers is based on monolithic integration and is proving to be effective in solving the footprint and calibration problems. There are mainly two classes of such monolithic MDoF accelerometers, depending on the number of proof masses used. The first class uses multiple proof masses with the main advantage being zero calibration issues. The second class uses a single proof mass, which results in compact device with a reduced noise floor. The latter class, however, suffers from high cross-axis sensitivity. It also requires very innovative layout designs, owing to the complicated mechanical structures and electrical contact placement. The performance complications due to nonlinearity, post fabrication process, and readout electronics affects both classes of accelerometers. In order to effectively compare them, we have used metrics such as sensitivity per unit area and noise-area product. This paper is devoted to an in-depth review of monolithic multi-axis capacitive MEMS accelerometers, including a detailed analysis of recent advancements aimed at solving their problems such as size, noise floor, cross-axis sensitivity, and process aware modeling.