Joan Fong

High-speed Ge photodetector monolithically integrated with large cross-section silicon-on-insulator waveguide

We demonstrate a compact, high speed Ge photodetector efficiently butt-coupled with a large cross-section silicon-on-insulate (SOI) waveguide in which the Ge p-i-n junction is placed in the horizontal direction to enable very high speed operation. The demonstrated photodetector has an active area of only 0.8×10 μm2, greater than 32 GHz optical bandwidth, and a responsivity of 1.1 A/W at a wavelength of 1550 nm. Very importantly the device can readily be integrated with high performance wavelength-division-multiplexing filters based on large cross-section SOI waveguide to form monolithic integrated silicon photonics receivers for multichannel terabit data transmission applications.

30GHz Ge electro-absorption modulator integrated with 3μm silicon-on-insulator waveguide

We demonstrate a compact waveguide-based high-speed Ge electro-absorption (EA) modulator integrated with a single mode 3 µm silicon-on-isolator (SOI) waveguide. The Ge EA modulator is based on a horizontally-oriented p-i-n structure butt-coupled with a deep-etched silicon waveguide, which transitions adiabatically to a shallow-etched single mode large core SOI waveguide. The demonstrated device has a compact active region of 1.0 × 45 µm(2), a total insertion loss of 2.5-5 dB and an extinction ratio of 4-7.5 dB over a wavelength range of 1610-1640 nm with -4V(pp) bias. The estimated Δα/α value is in the range of 2-3.3. The 3 dB bandwidth measurements show that the device is capable of operating at more than 30 GHz. Clear eye-diagram openings at 12.5 Gbps demonstrates large signal modulation at high transmission rate.

Low loss shallow-ridge silicon waveguides

We demonstrate low loss shallow-ridge silicon waveguides with an average propagation loss of 0.274 + or - 0.008 dB/cm in the C-band (1530 nm - 1565 nm). These waveguides have a cross section of 0.25 microm by 2 microm and are fabricated by standard photolithography and dry etching. We also investigate a compact double-level taper which adiabatically couples light from these waveguides to silicon strip waveguides enabling tight bends.

36 GHz submicron silicon waveguide germanium photodetector

We present two effective approaches to improve the responsivity of high speed waveguide-based Ge photodetectors integrated on a 0.25 μm silicon-on-insulator (SOI) platform. The main cause of poor responsivity is identified as metal absorption from the top contact to Ge. By optimizing Ge thickness and offsetting the contact window, we have demonstrated that the responsivity can be improved from 0.6A/W to 0.95 A/W at 1550 nm with 36 GHz 3 dB bandwidth. We also demonstrate that a wider device with double offset contacts can achieve 1.05 A/W responsivity at 1550 nm and 20 GHz 3 dB bandwidth.

High speed GeSi electro-absorption modulator at 1550 nm wavelength on SOI waveguide

We demonstrate a high speed GeSi electro-absorption (EA) modulator monolithically integrated on 3 µm silicon-on-insulator (SOI) waveguide. The demonstrated device has a compact active region of 1.0 × 55 μm(2), an insertion loss of 5 dB and an extinction ratio of 6 dB at wavelength of 1550 nm. The modulator has a broad operating wavelength range of 35 nm and a 3 dB bandwidth of 40.7 GHz at 2.8 V reverse bias. This compact and energy efficient modulator is a key building block for optical interconnection applications.

Power-efficient III-V/Silicon external cavity DBR lasers

We report the design and characterization of external-cavity DBR lasers built with a III-V-semiconductor reflective-SOA with spot-size converter edge-coupled to SOI waveguides containing Bragg grating mirrors. The un-cooled lasers have wall-plug-efficiencies of up to 9.5% at powers of 6 mW. The lasers are suitable for making power efficient, hybrid WDM transmitters in a CMOS-compatible SOI optical platform.

Silicon-on-Insulator-Based Planar Circuit for Passive Optical Network Applications

A novel design of a silicon-on-insulator (SOI) filter for passive optical network applications is described. The SOI filter comprises a monolithically integrated planar reflective grating and a multistage Mach-Zehnder interferometer. The fabricated device showed low insertion losses and high optical isolation. To the best of our knowledge, this letter describes the first demonstration of an SOI circuit comprising monolithically integrated planar reflective grating and cascaded Mach-Zehnder interferometer

Fabrication Insensitive Echelle Grating in Silicon-on-Insulator Platform

We demonstrate a compact, low crosstalk, low loss, and flat passband demultiplexer based on an echelle grating fabricated in the silicon-on-insulator (SOI) platform. The demonstrated 12 channel demultiplexer has an 8-nm channel spacing, 5.5-nm flat passband, 1.7-dB on-chip loss, and better than 25-dB optical crosstalk. By arranging the output waveguides very close to the zero degree angle of the echelle grating, the performance of the demonstrated device is made insensitive to the vertical angle of the grating facet. The fabricated devices have a very small footprint and have the potential to provide a low-cost demultiplexer solution for multichannel data transmission applications.

Low loss silicon waveguides for application of optical interconnects

We present low loss shallow-ridge silicon waveguides with an average propagation loss of 0.274 dB/cm in the C-band, which can find applications in chip-level optical interconnects.

Compact single-chip VMUX/DEMUX on the silicon-on-insulator platform

We demonstrate a compact, single-chip 40-channel, dense wavelength division multiplexing (DWDM) variable attenuator multi/demultiplexer (VMUX/DEMUX) by monolithic integration of an echelle grating and high-speed p-i-n VOA on the silicon-on-insulator (SOI) platform. The demonstrated device has a flat-top filter shape, on chip loss of 5.0 dB, low PDL of 0.3 dB after compensation of the polarization dependent frequency (PDF) shift, a fast attenuation response speed of 3 MHz, and an area of only 25 mm by 10 mm.