A silicon-on-insulator-based adiabatic waveguide taper with a high coupling efficiency and small footprint is presented. The taper was designed to reduce the incidence of mode conversion to higher-order and radiation modes inside the waveguide. In connecting a 0.5-μm-wide output waveguide and a 12-μm-wide input waveguide of a grating coupler, a compact 120-μm-long taper was demonstrated, achieving a transmission of 98.3%. Previously, this transmission level could only be achieved using a conventional linear taper with a length of more than 300 μm.

In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide. There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as VπLπ~0.07 V cm for straight waveguides and VπLπ~0.0024 V cm for 12 μm radius microring resonators. This phase modulation device uniquely enables a small signal amplitude <1 V with a micrometer-sized footprint for compatibility with CMOS circuit integration. Examples of phase-induced changes are computed for straight waveguides and for microring resonators, showing the possibility of implementing several optoelectronic functionalities as modulators, tunable filters, and switches.

We present photonics technology based on a bulk-Si substrate for cost-sensitive dynamic random-access memory (DRAM) optical interface application. We summarize the progress on passive and active photonic devices using a local-crystallized Si waveguide fabricated by solid phase epitaxy or laser-induced epitaxial growth on bulk-Si substrate. The process of integration of a photonic integrated circuit (IC) with an electronic IC is demonstrated using a 65 nm DRAM periphery process on 300 mm wafers to prove the possibility of seamless integration with various complementary metal-oxide-semiconductor devices. Using the bulk-Si photonic devices, we show the feasibility of high-speed multidrop interface: the Mach–Zehnder interferometer modulators and commercial photodetectors are used to demonstrate four-drop link operation at 10 Gb/s, and the transceiver chips with photonic die and electronic die work for the DDR3 DRAM interface at 1.6 Gb/s under a 1∶4 multidrop configuration.

A hybrid integrated light source was developed with a configuration in which a laser diode (LD) array was mounted on a silicon optical waveguide platform for interchip optical interconnection. This integrated light source is composed of 13-channel stripes with a pitch of 20 or 30 μm. The output power of each LD in the 400 or 600-μm long LD array was over 40 mW at room temperature without cooling. An output power uniformity was 1.3 dB including an LD array power uniformity. The use of a SiON waveguide with a spot size converter resulted in an optical coupling loss of 1 dB between an LD and SiON waveguide. The integrated light source including 52 output ports demonstrated a reduction in the footprint per channel. We also demonstrated a light source with over 100 output ports in which the number of output ports is increased by using a waveguide splitter and multichip bonding. These integrated light sources are practical candidates for use with photonic integrated circuits for high-density optical interconnection.

We describe a polarization rotator based on a parallel-core structure consisting of a silicon nanowire waveguide and a silicon-nitride waveguide. The 60-μm-long rotator provides a polarization extinction ratio of more than 10 dB with excess loss of less than 1 dB. In addition, the extremely wide bandwidth of more than 150 nm expected from calculations is confirmed in experiments. A study of the fabrication tolerance of our rotator indicates that fabrication error of around 25 nm is allowable.

We report uniaxial tensile strains up to 5.7% along <100> in suspended germanium (Ge) wires on a silicon substrate, measured using Raman spectroscopy. This strain is sufficient to make Ge a direct bandgap semiconductor. Theoretical calculations show that a significant fraction of electrons remain in the indirect conduction valley despite the direct bandgap due to the much larger density of states; however, recombination can nevertheless be dominated by radiative direct bandgap transitions if defects are minimized. We then calculate the theoretical efficiency of direct bandgap Ge LEDs and lasers. These strained Ge wires represent a direct bandgap Group IV semiconductor integrated directly on a silicon platform.

One of the most serious challenges facing exponential performance growth in the information industry is the bandwidth bottleneck in interchip interconnects. We propose a photonics–electronics convergence system in response to this issue. To demonstrate the feasibility of the system, we fabricated a silicon optical interposer integrated with arrayed laser diodes, spot-size converters, optical splitters, optical modulators, photodetectors, and optical waveguides on a single silicon substrate. Using this system, 20 Gbps error-free data links and a 30 Tbps/cm2 bandwidth density were achieved. This bandwidth density is sufficient to meet the interchip interconnect requirements for the late 2010s.