256-channel bidirectional optical interconnect using VCSELs and photodiodes on CMOS

Abstract

Two-dimensional parallel optical interconnects (2-D-POIs) are capable of providing large connectivity between elements in computing and switching systems. Using this technology we have demonstrated a bidirectional optical interconnect between two printed circuit boards containing optoelectronic (OE) very large scale integration (VLSI) circuits. The OE-VLSI circuits were constructed using vertical cavity surface emitting lasers (VCSELs) and photodiodes (PDs) flip-chip bump-bonded to a 0.35m complementary metal-oxide-semiconductor (CMOS) chip. The CMOS was comprised of 256 laser driver circuits, 256 receiver circuits, and the corresponding buffering and control circuits required to operate the large transceiver array. This is the first system, to our knowledge, to send bidirectional data optically between OE-VLSI chips that have both VCSELs and photodiodes cointegrated on the same substrate.

Interconnection Networks

“…Prototype interconnects have been constructed with 16 ×16 arrays of VCSELs and photodetectors on a single chip [16]. In this system, the VCSELs arrays and photodiode arrays were flip-chip bonded to a CMOS chip using heterogeneous integration techniques.…”

“…In this system, the VCSELs arrays and photodiode arrays were flip-chip bonded to a CMOS chip using heterogeneous integration techniques. Although the demonstration of [16] used bulk optics to deliver light between ICs, optical paths have been designed using both rigid optical links [5] (useful for chipto-chip links on a board), and flexible fiber imaging guides [9] (useful for board-to-board links).…”

A 90nm CMOS 16Gb/s Transceiver for Optical Interconnects

“…The negligible frequency dependent loss of optical channels provides the potential for optical link designs to fully leverage increased data rates provided through CMOS technology scaling without excessive equalization complexity. Optics also allows very high information density in both free space systems [6]- [8], with the ability to focus short wavelength optical beams into small areas without the crosstalk issues of electrical links, and in fiber based systems, with the added dimension of wavelength division multiplexing (WDM) [9].…”

Breaking the memory bottleneck with an optical data path

“…On chip, the size associated with high-speed (> 1 Gb/s) laser drivers and receivers is small enough to fit in a 125 µm × 125 µm area [3], smaller than half the area typically required for a traditional electrical pad and associated drive circuitry. Combine this with the fact that the I/O is no longer restricted to the periphery of the chip, and the data rate available on and off chip is dramatically increased over all-electrical techniques.…”

“…Prototype chip-to-chip optical interconnects have been constructed by Plant et al [3] with 16 × 16 arrays of VCSELs and photodetectors, and 32 × 32 arrays will soon be available. In these systems, the VCSEL and photodiode arrays are flip-chip bonded to CMOS chips using heterogeneous integration techniques.…”