Philip Kiely

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.

Integrated inversion channel optoelectronic devices and circuit elements for multifunctional array applications

An approach to laser-based optoelectronic integration is described. It is shown that by using a single epitaxial growth structure and a common processing sequence, all the electrical and optical devices required for a complete optoelectronic integrated circuit (OEIC) are realized. The demonstrated individual device performance and the implementation of an integrated combination of devices are discussed. Such applications as the implementation of a basic building block for a 2*2 smart-pixel switching node are discussed. A comparison to other laser- and modulator-based approaches is presented. >

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.

Automatic power control of a VCSEL using an angled lid TO56 package

Many applications of semiconductor lasers require that the output power from the laser is maintained at a fixed level independent of temperature and aging, this is typically accomplished with edge emitting lasers using a back facet monitor photodiode which is incorporated into the laser package. The signal from the photodiode is used to drive the feedback control circuit. In the absence of a back facet it is necessary to develop an alternate packaging scheme for VCSELs that allows for the generation of a signal for use in maintaining a fixed output power. In this paper we present a VCSEL packaged in a TO56 can with a silicon pin photodetector. A portion of the emitted beam from the VCSEL is reflected from the lid onto the photodetector. Results demonstrating an auto-power control capability of /spl plusmn/3 percent are presented.

A quantum-well inversion channel heterostructure as a multifunctional component for optoelectronic integrated circuits

An approach to optoelectronic integration utilizing a universal heterostructure with a single GaAs quantum-well active region is presented. The inversion channel forms the basis of a heterojunction field-effect transistor, a lateral current injection laser, a field-effect modulator, and a waveguide photodetector by simple reconfiguration of the electrodes and device geometry. The fabrication technology has been developed for gigahertz bandwidth applications by utilizing ion implantation techniques for interdevice electrical isolation and surface planarization, and reactive ion-etching to realize a self-aligned transistor-based heterostructure. The design, fabrication, and characterization of various heterostructures are discussed in the context of optoelectronic integration and the implementation of ion implantation disordering to realize low-loss self-aligned waveguides for on chip signal routing. The ultimate performance of the devices using a GaAs quantum well is considered, as well as the development of this technology for improved performance using strained InGaAs wells. >

Vertical cavity surface emitting laser packaging with auto power control

We will discuss a discrete VCSEL packaging method using a monitoring photodiode for auto power control. We have demonstrated a VCSEL package with an output power variation within /spl plusmn/1% over a temperature range from 0 to 65/spl deg/C.

Vertical cavity surface emitting laser-based parallel optical data link

Vertical cavity surface emitting laser (VCSEL) arrays are designed and used for 10-channel parallel optical data links, OPTOBUS™, to transmit data at a speed of up to 800 Mbits/s per channel. The interface between the VCSELs and the optical fiber ribbons is based on molded plastic waveguide technology. A bit error rate of 10-15 is demonstrated.

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.