Design of a broadband Ge1-xSix electro-absorption modulator based on the Franz-Keldysh effect with thermal tuning.

We present the design of an adiabatic taper coupled Ge1-xSix electro-absorption modulator, which is based on Franz-Keldysh effect. The device has an active region of 0.8×50 µm2, an extinction ratio of more than 6 dB and an insertion loss less than 3 dB at the wavelength of 1550 nm. The operating bandwidth can be broadened to more than 90 nm by an AlN block assisted heater with only 6.2 mW energy consumption. Moreover, the operating wavelength shift caused by material composition deviation can be compensated to the expected wavelength by thermal tuning. This design may play an important role in next-generation, high-density optical integrations for datacom and high-performance computing.

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.

Design and fabrication of 3µm silicon-on-insulator waveguide integrated Ge electro-absorption modulator.

We present the design and fabrication of a waveguide-based Ge electro-absorption (EA) modulator integrated with a 3 µm silicon-on-isolator (SOI) waveguide. The proposed Ge EA modulator employs a butt-coupled horizontally-oriented p-i-n structure. The optical design achieves a low-loss transition from Ge to Si waveguides. The interaction between the optical mode of the waveguide and the bias induced electric field in the p-i-n structure was maximized to achieve high modulation efficiency. By balancing the trade-offs between the extinction ratio and the insertion loss of the device, an optimal working regime was identified. The measurement results from a fabricated device were used to verify the design. Under a -4Vpp reverse bias, the device demonstrates a total insertion loss (including the transition loss) of 2.7-5.2 dB and an extinction ratio of 4.9-8.2 dB over the wavelength range of 1610-1640 nm. Subtracting the contribution of the transition loss, the Δα/α value for the fabricated device was estimated to be between 2.2 and 3.2 with an electric field around 55 kV/cm.

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.

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.

30GHz Ge electro-absorption modulator integrated with 3 µm 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.