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Proceedings Paper

Demonstration of a free-space optical interconnect in a CMOS chip
Author(s): Pablo V. Mena; Robert M. Lammert; Steve M. Kang; James J. Coleman
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Paper Abstract

We have developed a hybrid optoelectronic circuit to demonstrate a free-space optical interconnect in a CMOS chip. Discrete GaAs-based optical devices are hybridly integrated with a 0.8 micrometers CMOS chip fabricated by a MOSIS foundry. The CMOS chip consists of two separate digital modules, an ALU and a ROM, communicating via a pair of optical interconnects. Each interconnect consists of a CMOS laser driver that converts full CMOS logic-level data into a suitable laser drive current, a laser-photodetector pair, and a CMOS transimpedance amplifier that converts a photocurrent from the photodetector into logic-level data. An on-chip clock is used to time the serialization and deserialization of 4-bit words of data across each interconnect at a data rate of 40 Mb/s. In order to account for limitations of the hybrid design as well as process variations, pads are provided for off-chip clock signals to override the built-in clock and therefore operate the interconnect at a transmission rate different from the design value. Each laser-photodetector pair is fabricated from a single laser structure epitaxially grown on semi-insulating GaAs substrate. Similar to a laser-photomonitor arrangement, a dry etch is used to divide the laser structure into a separate laser and photodiode. This device is then hybridly integrated with the CMOS chip to implement the proof-of-principle free-space optical interconnect. Experimental results for the optical elements and simulation results for the CMOS design are presented to demonstrate the operation of the chip.

Paper Details

Date Published: 5 April 1995
PDF: 11 pages
Proc. SPIE 2400, Optoelectronic Interconnects III, (5 April 1995); doi: 10.1117/12.206301
Show Author Affiliations
Pablo V. Mena, Univ. of Illinois/Urbana-Champaign (United States)
Robert M. Lammert, Univ. of Illinois/Urbana-Champaign (United States)
Steve M. Kang, Univ. of Illinois/Urbana-Champaign (United States)
James J. Coleman, Univ. of Illinois/Urbana-Champaign (United States)


Published in SPIE Proceedings Vol. 2400:
Optoelectronic Interconnects III
Ray T. Chen; Harvard Scott Hinton, Editor(s)

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