Davis H. Hartman

A low cost, high performance optical interconnect

Optobus is a ten channel parallel bi-directional datalink based on multimode fiber ribbons. The design represents a series of tradeoffs between cost and performance to produce a low cost interconnect solution with a minimum of 1.5 Gbit/s of aggregate throughput.

Characteristics of VCSEL arrays for parallel optical interconnects

The use of vertical cavity surface emitting lasers (VCSELs)in a parallel optical interconnect for Motorolas OPTOBUS/sup TM/ interconnect was made public over 1 year ago. This was the first time VCSELs were introduced into a product which took advantage of the excellent qualities of VCSELs over edge-emitting lasers. Motorolas OPTOBUS/sup TM/ interconnect is a ten channel parallel bi-directional data link based on two 10 channel multimode fiber ribbons. One of the key differences in this type of interconnect compared with previous data link designs is the use of the VCSELs as the optical source for the links fiber optic transmitter. A single 1/spl times/10 VCSEL array from a GaAs wafer is die attached to a 10 channel GUIDECAST/sup TM/ optical interface unit which couples the emission from each laser device to its corresponding fiber ribbon channel and thus negates the use of expensive manufacturing techniques such as active alignment and pigtailing. The OPTOBUS/sup TM/ interconnect achieves its performance goals (which include low cost) via the unique characteristics of the GaAs VCSELs arrays. For example, the 850 nm devices produce a circular symmetric beam with a half angle of about 10 degrees allowing the coupling loss into the waveguide to be less than 3 dB. In addition, to maintain low manufacturing costs, each VCSEL array is individually and automatically probe tested (just as in the silicon industry) to verify that each VCSEL achieves the OPTOBUS/sup TM/ interconnects stringent electrical, optical, thermal and mechanical specifications. Typical computer generated wafer maps from automated production tooling and statistical parametric results are discussed. The combination of low threshold currents with superior thermal and optical performance allow the devices to be modulated under fixed bias conditions. Typical drive currents of 3X threshold are used to obtain nominal FDA Class 1 safety optical power levels from the GUIDECAST/sup TM/ optical interface unit.

Use of VCSEL arrays for parallel optical interconnects

The use of vertical cavity surface emitting lasers (VCSELs) in a parallel optical interconnect for Motorolas OPTOBUSTM interconnect was made public over 1 year ago. This was the first time VCSELs were introduced into a product which took advantage of the excellent qualities of VCSELs over edge-emitting lasers. Motorolas OPTOBUSTM interconnect is a ten channel parallel bi-directional data link based on two 10 channel multimode fiber ribbons. One of the key differences in this type of interconnect compared with previous data link designs is the use of the VCSELs as the optical source for the links fiber optic transmitter. A single 1 X 10 VCSEL array from a GaAs wafer is die attached to a 10 channel GUIDECASTTM optical interface unit which couples the emission from each laser device to its corresponding fiber ribbon channel and thus negates the use of expensive manufacturing techniques such as active alignment and pig-tailing. The OPTOBUSTM interconnect achieves its performance goals (which include low cost) via the unique characteristics of the GaAs VCSELs arrays. For example, the 850 nm devices produce a circular symmetric beam with a half angle of about 10 degrees allowing the coupling loss into the waveguide to be less than 3 dB. In addition, to maintain low manufacturing costs, each VCSEL array is individually and automatically probe tested (just as in the silicon industry) to verify that each VCSEL achieves the OPTOBUSTM interconnects stringent electrical, optical, thermal and mechanical specifications. Typical computer generated wafer maps from automated production tooling and statistical parametric results are discussed. The combination of low threshold currents with superior thermal and optical performance allow the devices to be modulated under fixed bias conditions. Typical drive currents of 3X threshold are used to obtain nominal FDA Class 1 safety optical power levels from the GUIDECASTTM optical interface unit.

Low-cost high-performance optical interconnect

Summary form only given. The optical waveguides have a uniformity of 1 dB. The resulting optical links have a jitter of no more than 150 ps not including pulse-width distortion, static skew between channels of less than 200 ps and dissipate 1.5 W. A representative multichannel eye pattern at 400 Mbit/s is shown. In this presentation we focus on the design approach and subsystem requirements that make this performance possible without sacrificing manufacturability or cost.

A low-voltage low-noise digital buffer system

A novel low-voltage CMOS digital buffer is proposed. The primary characteristic of this digital buffer is the low voltage operation (V/sub DD/ between one and two transistor threshold voltages (V(/sub T//sup B/)), with a typical V/sub DD/ = 1.5V/sub T/). While operating at this reduced power supply, low noise and high overall performances are achieved.

Parallel optical interconnects using VCSELs

Optobus is a ten channel parallel bi-directional datalink based on multimode fiber ribbons. The design represents a series of tradeoffs between cost and performance to produce a low cost interconnect solution with a minimum of 1.5 Gbit/s of aggregate throughput.