Chi Fan

Power minimization and technology comparisons for digital free-space optoelectronic interconnections

This paper investigates the design optimization of digital free-space optoelectronic interconnections with a specific goal of minimizing the power dissipation of the overall link, and maximizing the interconnect density. To this end, we discuss a method of minimizing the total power dissipation of an interconnect link at a given bit rate. We examine the impact on the link performance of two competing transmitter technologies, vertical cavity surface emitting lasers (VCSELs) and multiple quantum-well (MQW) modulators and their associated driver-receiver circuits including complementary metal-oxide-semiconductor (CMOS) and bipolar transmitter driver circuits, and p-n junction photodetectors with multistage transimpedance receiver circuits. We use the operating bit-rate and on-chip power dissipation as the main performance measures. Presently, at high bit rates (>800 Mb/s), optimized links based on VCSELs and MQW modulators are comparable in terms of power dissipation. At low bit rates, the VCSEL threshold power dominates. In systems with high bit rates and/or high fan-out, a high slope efficiency is more important for a VCSEL than a low threshold current. The transmitter driver circuit is an important component in a link design, and it dissipates about the same amount of power as that of the transmitter itself. Scaling the CMOS technology from 0.5 /spl mu/m down to 0.1 /spl mu/m brings a 50% improvement in the maximum operating bit rate, which is around 4 Gb/s with 0.1 /spl mu/m CMOS driver and receiver circuits. Transmitter driver circuits implemented with bipolar technology support a much higher operating bandwidth than CMOS technology; they dissipate, however, about twice the electrical power. An aggregate bandwidth in excess of 1 Tb/s-cm/sup 2/ can be achieved in an optimized free-space optical interconnect system using either VCSELs or MQW modulators as its transmitters.

Chatoyant: a computer-aided-design tool for free-space optoelectronic systems

Chatoyant is a tool for the simulation and the analysis of heterogeneous free-space optoelectronic architectures. It is capable of modeling digital and analog electronic and optical signal propagation with mechanical tolerancing at the system level. We present models for a variety of optoelectronic devices and results that demonstrate the systems ability to predict the effects of various component parameters, such as detector geometry, and system parameters, such as alignment tolerances, on system-performance measures, such as the bit-error rate.

Digital free-space optical interconnections: a comparison of transmitter technologies

We investigate the performance of free-space optical interconnection systems at the technology level. Specifically, three optical transmitter technologies, lead-lanthanum-zirconate-titanate and multiple-quantum-well modulators and vertical-cavity surface-emitting lasers, are evaluated. System performance is measured in terms of the achievable areal data throughput and the energy required per transmitted bit. It is shown that lead-lanthanum-zirconate-titanate modulator and vertical-cavity surface-emitting laser technologies are well suited for applications in which a large fan-out per transmitter is required but the total number of transmitters is relatively small. Multiple-quantum-well modulators, however, are good candidates for applications in which many transmitters with a limited fan-out are needed.

Transimpedance receiver design optimization for smart pixel arrays

Optical transimpedance receivers implemented in CMOS VLSI technologies are modeled and optimized for freespace optoelectronic interconnections. Sensitivity, bandwidth, power dissipation, and circuit area are analyzed for receivers using three different submicron CMOS processes. A comparison with the circuit noise limited optical power indicates that, for digital computing applications, the receiver sensitivity is limited by the gain-bandwidth product of the receiver amplifiers and the necessary noise margin of logic circuits.

Deposition and characterization of thin ferroelectric lead lanthanum zirconate titanate (PLZT) films on sapphire for spatial light modulators applications

Ferroelectric lead lanthanum zirconate titanate (PLZT) films are deposited on R-plane sapphire using RF triode magnetron sputtering. Perovskite PLZT films with the desired composition (9/65/35) are obtained using compensated deposition techniques around 500 degrees C and postdeposition annealing at 650 degrees C. The deposited films exhibit good optical and electrooptical properties. The room temperature dielectric constant of the films was 1800 at 10 kHz. The refractive index of the films was in the range of 2.2-2.5. The films showed a quadratic electrooptic effect with R=0.6 *10/sup -16/ m/sup 2//V/sup 2/. The development of PLZT on silicon-on-sapphire smart spatial light modulators using these films is also explored.<<ETX>>

Computer-aided design of free-space opto-electronic systems

This paper presents a system capable of static and dynamic simulationsof heterogeneous opto-electronic systems. It is capable ofmodeling Gaussian optical signal propagation with mechanicaltolerancing at the system level. We present results which demonstratethe systems ability to predict the effects of various componentparameters, such as detector geometry, and system levelparameters, such as alignment tolerances, on system performance.

Design issues and development of monolithic silicon/lead lanthanum zirconate titanate integration technologies for smart spatial light modulators

System, device, and material issues for the design and realization of smart spatial light modulators are discussed. Silicon and lead lanthanum zirconate titanate (PLZT) are two promising materials that meet the system requirements. Two different technologies for the integration of Si and PLZT are described. Results show that large-scale smart spatial light modulators can be realized with Si/PLZT technologies.

Small-signal-equivalent circuits for a semiconductor laser.

Passive electrical circuits whose voltage and current equations are exactly equivalent to the small-signal rate equations of a semiconductor laser are derived to model an electrically modulated laser (verified to be the same as that given in the literature), an optically modulated laser (i.e., a laser used as an optical amplifier), and a multimode laser. These circuits offer a fast and efficient simulation tool with little computational complexity in which the small-signal assumption (i.e., small modulation range) is neither violated nor insufficient for the simulation.

Quantum-confined Stark effect modulators at 1.06 mu m on GaAs

Electroabsorption modulation is achieved at or near a wavelength of 1.06 mu m with In/sub x/Al/sub y/Ga/sub 1-x-y/As/In/sub x/Ga/sub 1-x/As multiple-quantum-well (MQW) structures grown on GaAs substrates. The lattice mismatch (close to 2%) between the MQW and the substrate is accommodated by a compositional-step-graded buffer array. A dislocation density of less than 10/sup 7//cm/sup 2/ is estimated for the MQW region. For 80-to-100 AA well widths, a maximum electroabsorption coefficient of 8000 cm/sup -1/ with an applied voltage of 15 V is obtained.<<ETX>>

Heterogeneous integration of optoelectronic components

The heterogeneous integration of optoelectronic, electronic, and micro-mechanical components from different origins and substrates makes possible many advanced systems in diverse applications. Besides the monolithic integration approach, which is the basis for the success of todays silicon industry, various hybrid integration technologies have been explored. These include flip-chip bonding, micro-robotic placement, epitaxial lift-off and direct bonding, substrate removal and bonding, and several self-assembly methods. In this paper, we describe the results of our monolithic integration effort involving a 2 by 2 optoelectronic switching circuit and an 8 by 8 active-pixel sensor array on GaAs substrates, and a 16 by 16 spatial light modulator array produced by flip-chip bonding of III-V multi-quantum-well (MQW) modulators and silicon driver circuits. We also present our preliminary experimental results on the self-assembly of small inorganic devices coated with DNA polymers with self- recognition properties.