Jeffrey A. Kash

Generation of subpicosecond electrical pulses on coplanar transmission lines

Electrical pulses shorter than 0.6 ps were generated by photoconductively shorting a charged coplanar transmission line with 80 fs laser pulses. After propagating 8 mm on the line the electrical pulses broadened to only 2.6 ps.

Integrated transversal equalizers in high-speed fiber-optic systems

Intersymbol interference (ISI) caused by intermodal dispersion in multimode fibers is the major limiting factor in the achievable data rate or transmission distance in high-speed multimode fiber-optic links for local area networks applications. Compared with optical-domain and other electrical-domain dispersion compensation methods, equalization with transversal filters based on distributed circuit techniques presents a cost-effective and low-power solution. The design of integrated distributed transversal equalizers is described in detail with focus on delay lines and gain stages. This seven-tap distributed transversal equalizer prototype has been implemented in a commercial 0.18-/spl mu/m SiGe BiCMOS process for 10-Gb/s multimode fiber-optic links. A seven-tap distributed transversal equalizer reduces the ISI of a 10-Gb/s signal after 800 m of 50-/spl mu/m multimode fiber from 5 to 1.38 dB, and improves the bit-error rate from about 10/sup -5/ to less than 10/sup -12/.

160 Gb/s Bidirectional Polymer-Waveguide Board-Level Optical Interconnects Using CMOS-Based Transceivers

We have developed parallel optical interconnect technologies designed to support terabit/s-class chip-to-chip data transfer through polymer waveguides integrated in printed circuit boards (PCBs). The board-level links represent a highly integrated packaging approach based on a novel parallel optical module, or Optomodule, with 16 transmitter and 16 receiver channels. Optomodules with 16 Tx+16 Rx channels have been assembled and fully characterized, with transmitters operating at data rates up to 20 Gb/s for a 27-1 PRBS pattern. Receivers characterized as fiber-coupled 16-channel transmitter-to-receiver links operated error-free up to 15 Gb/s, providing a 240 Gb/s aggregate bidirectional data rate. The low-profile Optomodule is directly surface mounted to a circuit board using convention ball grid array (BGA) solder process. Optical coupling to a dense array of polymer waveguides fabricated on the PCB is facilitated by turning mirrors and lens arrays integrated into the optical PCB. A complete optical link between two Optomodules interconnected through 32 polymer waveguides has been demonstrated with each unidirectional link operating at 10 Gb/s achieving a 160 Gb/s bidirectional data rate. The full module-to-module link provides the fastest, widest, and most integrated multimode optical bus demonstrated to date.

Non-blocking 4x4 electro-optic silicon switch for on-chip photonic networks

We present a 4x4 spatially non-blocking Mach-Zehnder based silicon optical switch fabricated using processes fully compatible with standard CMOS. We successfully demonstrate operation in all 9 unique switch states and 12 possible I/O routing configurations, with worst-case cross-talk levels lower than -9 dB, and common spectral bandwidth of 7 nm. High-speed 40 Gbps data transmission experiments verify optical data integrity for all input-output channels.

Chip-to-chip optical interconnects

Terabus is based on a silicon-carrier interposer on an organic card containing 48 polymer waveguides. We have demonstrated 4times12 arrays of low power optical transmitters and receivers, operating up to 20 Gb/s and 14 Gb/s per channel respectively

PICOSECOND HOT ELECTRON LIGHT EMISSION FROM SUBMICRON COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR CIRCUITS

Optical emission consisting of pulses with temporal widths of less than 270 ps has been detected from fully functional silicon integrated circuits fabricated using submicron complementary metal– oxide–semiconductor (CMOS) logic gates. Emission is observed under normal bias conditions and occurs when the gates are switching. The emission arises from the hot electron populations created by the transient current pulses present in the transistors during switching. The speed and spectral characteristics of the emission suggest future applications in the measurement of timing in high speed CMOS circuits.

Terabit/s-Class Optical PCB Links Incorporating 360-Gb/s Bidirectional 850 nm Parallel Optical Transceivers

We report here on the design, fabrication, and characterization of highly integrated parallel optical transceivers designed for Tb/s-class module-to-module data transfer through polymer waveguides integrated into optical printed circuit boards (o-PCBs). The parallel optical transceiver is based on a through-silicon-via silicon carrier as the platform for integration of 24-channel vertical cavity surface-emitting laser and photodiode arrays with CMOS ICs. The Si carrier also includes optical vias (holes) for optical access to conventional surface-emitting 850 nm optoelectronic devices. The 48-channel 3-D transceiver optochips are flip-chip soldered to organic carriers to form transceiver optomodules. Fully functional optomodules with 24 transmitter + 24 receiver channels were assembled and characterized with transmitters operating up to 20 Gb/s/ch and receivers up to 15 Gb/s/ch. At 15 Gb/s, the 48-channel optomodules provide a bidirectional aggregate bandwidth of 360 Gb/s. In addition, o-PCBs have been developed using a 48-channel flex waveguide assembly attached to FR4 electronic boards. Incorporation of waveguide turning mirrors and lens arrays facilitates optical coupling to/from the o-PCB. Assembly of optomodules to the o-PCB using a ball grid array process provides both electrical and optical interconnections. An initial demonstration of the full module-to-module optical link achieved >; 20 bidirectional links at 10 Gb/s. At 15 Gb/s, operation at a bit error ratio of <; 10- 12 was demonstrated for 15 channels in each direction, realizing a record o-PCB link with a 225 Gb/s bidirectional aggregate data rate.

Picosecond imaging circuit analysis

A newly developed optical method for noninvasively measuring the switching activity of operating CMOS integrated circuit chips is described. The method, denoted as picosecond imaging circuit analysis (PICA) can be used to characterize the gate-level performance of such chips and identify the locations and nature of their operational faults. The principles underlying PICA and examples of its use are discussed.

Tapered Fabry-Perot waveguide optical demultiplexer

We describe a novel waveguide spectrometer for use in wavelength division multiplexing (WDM) systems. A high refractive index resonator is coupled to a waveguide and extracts light from the waveguide at its resonance frequency. A taper in the thickness of the resonator allows light of different wavelengths to be extracted at different positions. A structure is fabricated for use at 750 nm with a measured dispersion of 29 nm/cm and a wavelength resolution of 1 nm. The device operation is in good agreement with first-order coupled-mode calculations.<<ETX>>

Electric field induced decrease of photoluminescence lifetime in GaAs quantum wells

Time‐resolved photoluminescence measurements of excitons in GaAs‐Ga1−xAlxAs quantum wells subject to an electric field perpendicular to the well plane have been made. With increasing field, both integrated luminescence (as previously reported) and luminescence lifetime decrease. Thus the electric field increases the exciton nonradiative decay rate. Estimates of several possible mechanisms suggest that Fowler–Nordheim tunneling is responsible for the quenching. With increasing pump laser intensities, larger electric fields are required to quench the lifetime because of exciton screening of the field.