Free-space Optical Interconnect System Research Articles

OEIC technologies for high-speed optical interconnection system

As the level of integration and the power of computation increase, methods of interconnecting computational elements attract more attention and the total system performance is bottlenecked by the problems associated with electrical interconnections. Optical interconnections have advantages of practically unlimited bandwidth and absence of crosstalk. To utilize such merits of optical interconnections, a large number of low-cost high-performance optoelectronic integrated circuits (OEICs) are needed. This paper focuses on monolithically integrated receiver OEICs that consist of InP/InGaAs p-i-n photodiodes and fully ion-implanted InP junction field-effect transistors (JFETs). In the formation of shallow InP p-n junctions we use a co-implantation technique in which we implant a group V element together with Be, a dopant, and take advantage of damage and stoichiometry effects. We fabricate a p-i-n/JFET amplifier receiver front-end circuit and a receiver 2×2 crosspoint switch circuit using this technique. We also develop bandwidth enhancement designs using inductive peaking and cascoding. Finally, we demonstrate a single-channel, free-space optical interconnection system with a bandwidth of 1.5 GHz and an interconnection length of 50 cm.

Diffractive optics applied to free-space optical interconnects

The optimum design of free-space optical interconnection systems utilizing diffractive optics is determined from a practical engineering standpoint for systems ranging from space invariant to fully space variant. System volume is calculated in terms of parameters such as the f-number of the diffractive lens, the wavelength of light, and also the total number, size, and separation of the optical sources and detectors. Performance issues such as interconnection complexity, diffraction efficiency, and signal-tonoise ratio are discussed. Diffractive optics fabricated by electron-beam direct-write techniques are used to provide experimental results for both shuffle-exchange and twin-butterfly free-space optical interconnects.

Packaged optical interconnection system based on photorefractive correlation

We present an experimental implementation of a packaged free-space optical interconnection system by photorefractive correlation. The system consists of a phase code, a LiNbO(3) crystal, two computergenerated-hologram Fourier-transform lenses, and a detector, all mounted on a glass substrate. We present experimental results with a prototype packaged system showing interconnections between 25 inputs and 25 outputs, and we discuss the possibility of applying this packaging technology to interconnections between larger arrays.

A scalable optoelectronic neural system using free-space optical interconnects

The design of a scalable, fully connected 3-D optoelectronic neural system that uses free-space optical interconnects with silicon-VLSI-based hybrid optoelectronic circuits is proposed. The system design uses a hardware-efficient combination of pulsewidth-modulating optoelectronic neurons and pulse-amplitude-modulating electronic synapses. Low-area, high-linear-dynamic-range analog synapse and neuron circuits are proposed. SPICE circuit simulations and an experimental demonstration of the free-space optical interconnection system are included.