We present the packaging of a large multi-chip energyefficient WDM silicon photonic interconnect prototype enabled by hybrid integration, high-accuracy optical alignment and thermal-mechanical aware design and assembly.

We describe a multiwavelength hybrid-integrated solid-state link on a 3 µm silicon-on-insulator (SOI) nanophotonic platform. The link spans three chips and employs germanium-silicon electroabsorption waveguide modulators, silicon transport waveguides, echelle gratings for multiplexing and demultiplexing, and pure germanium waveguide photo-detectors. The 8λ WDM Tx and Rx components are interconnected via a routing "bridge" chip using edge-coupled optical proximity communication. The packaged, retimed digital WDM link is demonstrated at 10 Gb/s and 10(-12) BER, with three wavelength channels consuming an on-chip power below 1.5 pJ/bit, excluding the external laser power.

Electroabsorption from GeSi on silicon-on-insulator (SOI) is expected to have promising potential for optical modulation due to its low power consumption, small footprint, and more importantly, wide spectral bandwidth for wavelength division multiplexing (WDM) applications. Germanium, as a bulk crystal, has a sharp absorption edge with a strong coefficient at the direct band gap close to the C-band wavelength. Unfortunately, when integrated onto Silicon, or when alloyed with dilute Si for blueshifting to the C-band operation, this strong Franz-Keldysh (FK) effect in bulk Ge is expected to degrade. Here, we report experimental results for GeSi epi when grown under a variety of conditions such as different Si alloy content, under selective versus non selective growth modes for both Silicon and SOI substrates. We compare the measured FK effect to the bulk Ge material.Reduced pressure CVD growth of GeSi heteroepitaxy with various Si content was studied by different characterization tools: X-ray diffraction (XRD), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), Hall measurement and optical transmission/absorption to analyze performance for 1550 nm operation. State-of-the-art GeSi epi with low defect density and low root-mean-square (RMS) roughness were fabricated into pin diodes and tested in a surface-normal geometry. They exhibit low dark current density of 5 mA/cm(2) at 1V reverse bias with breakdown voltages of 45 Volts. Strong electroabsorption was observed in our GeSi alloy with 0.6% Si content having maximum absorption contrast of Delta alpha/alpha similar to 5 at 1580 nm at 75 kV/cm.

We report high-fidelity 10-Gb/s optical-proximity-communication using reflecting mirrors micro-machined into silicon and co-integrated with low-loss silicon-on-insulator waveguides for packaged chip-to-chip communication. Device integration was carried out by dry etching a rib waveguide 8 mum wide that was tapered to a width of 13 mu m and subsequently truncated with a wet-etched, micro-mirror facet forming a 54deg angle with the (100) surface. Light in waveguides on a bottom chip can couple to waveguides on a top chip upon face-to-face positioning so that the reflecting mirrors form a coupled pair and complete an optical proximity hop. High-speed link measurements were accomplished with chips aligned with a six-axis nano-positioner stage and compared with results for a new precision alignment approach that packages silicon chips for proximity signaling. Our new packaging approach is based on the co-integration of pyramidal etch pits micro-machined into silicon that match a precision micro-sphere for accurate chip alignment. Assemblies of chips can self-align in the package using chip placement that is initially coarse. The final chip alignment accuracy of our new packaging approach is limited by photolithographic resolution. Additionally, multichip arrays can be aligned together with global positioning having similar precision. Nonreturn-to-zero data was fiber launched into the waveguides and transported across a package consisting of a three-chip assembly with two optical proximity hops for inter-chip communication. Continuous wave optical losses, eye diagrams, bit error rates, and power penalties were measured. A passively aligned chip-to-chip optical proximity hop in the package was measured to have optical coupling loss of 4.0 dB, which was 1 dB more than when measured with precision-aligned chips with a nano-positioning stage. RMS jitter and amplitude metrics for the eye quality are shown to be nearly identical (to within 1%) when OPxC hops associated with the package is inserted into 10-Gb/s links. This self-aligned mechanism enables chip packages for several classes of proximity communication.

We review 10Gb/sec Optical Proximity Communication realized with packaged chips that carry SOI optical waveguides and reflecting mirrors micromachined in silicon. The high precision chip to chip alignment and placement was enabled by a new packaging concept based on the co-integration of pyramidal pit features defined by anisotropic silicon etch and matching high precision micro-spheres. We support this novel packaging approach with measured optical transmission data and discuss the extent of it towards other applications of Proximity Communication.

Optical proximity communication (OPxC) with reflecting mirrors is presented. Direct optical links are demonstrated for silicon chips with better than -2.5dB coupling loss, excluding surface losses. OPxC is a true broadband solution with little impairment to the signal integrity for high-speed optical transmission. With wavelength division multiplexing (WDM) enabled OPxC, very high bandwidth density I/O, orders of magnitude higher than the traditional electrical I/O, can be achieved for silicon chips.