The proliferation of high-bandwidth applications such as high-speed Internet access and telecommuting has created among network providers a growing interest in upgrading their networks to deliver broadband services to homes and small businesses. This paper describes broadband fiber access (BFA), a fiber-to-the-customer access architecture based on Lucent Technologies' broadband AnyMedia™ interface platform (AIP). The BFA architecture provides asynchronous transfer mode (ATM) connection to customer premises equipment (CPE) and supports full quality-of-service (QoS) and traffic management functions defined by the ATM Forum. The BFA line card, or application pack (AP), is designed to support the concentration of traffic from CPE at the OC-3c/STM-1 rate (155.52 Mb/s). It supports the use of single-fiber drop to CPE using bidirectional coarse wavelength division multiplexing (CWDM). A hardware-based flow-control mechanism, which is applied to low-priority traffic originated from the CPE, allows for fast response to congestion at the feeder multiplexer. This fast response to congestion allows fair and efficient utilization of the feeder bandwidth.

For free-space optical interconnections between optoelectronic chips to reach commercial realization, the technology must provide high-density optical channels in a simple, inexpensive, and easily aligned package. Although point-to-point connections with microlens pairs can provide densities of several thousand channels per square centimeter, the Gaussian nature of the beams limits the connection range to a few millimeters. We propose an arrangement of microlens pairs with an intermediate relay lens that significantly increases the connection distance. This basic setup can be tiled laterally across large chips to form extensible arrays. The optical design is constructed entirely with diffractive elements because of the low chromatic sensitivity over a range of approximately ?10% around the design wavelength. We derive the lateral positioning error at the image by using a simple ray trace, and we show the effect of Gaussian beams. We experimentally demonstrate the low chromatic sensitivity for a system with an interconnection distance of 64 mm. Finally, we demonstrate the interconnection of two linear arrays of multimode fibers with two adjacent channels operating at data rates of hundreds of megabits per second.

We describe a new optoelectronic switching system demonstration that implements part of the distribution fabric for a large asynchronous transfer mode (ATM) switch. The system uses a single optoelectronic VLSI modulator-based switching chip with more than 4000 optical input-outputs. The optical system images the input fibers from a two-dimensional fiber bundle onto this chip. A new optomechanical design allows the system to be mounted in a standard electronic equipment frame. A large section of the switch was operated as a 208-Mbits/s time-multiplexed space switch, which can serve as part of an ATM switch by use of an appropriate out-of-band controller. A larger section with 896 input light beams and 256 output beams was operated at 160 Mbits/s as a slowly reconfigurable space switch.

We describe an optoelectronic switching system demonstration that implements part of the distribution fabric for a large ATM switch. The system uses a single optoelectronic VLSI modulator-based switching chip with more than 4000 optical I/O. The optical system images the input fibers from a two dimensional fiber bundle onto this chip. The optomechanical design allows the system to be mounted in a standard electronic equipment frame. A large section of the switch was operated as a 208 Mb/s time multiplexed space switch, which can serve as part of an ATM switch using the appropriate out-of-band controller. A larger section with 896 input light beams and 256 output beams was operated at 160 Mb/s as a slowly reconfigurable space switch. In this presentation, we will give an overview of the demonstration system, including the motivation, architecture, switching chip, optical system, input lasers, fiber bundle array, opto-mechanics, control software, and experimental results.

The authors describe an optoelectronic switching chip with 1024 differential optical inputs and 1024 differential optical outputs with individual channels tested above 600 Mbit/s. The technology for the chip consists of 850 nm GaAs/AlGaAs multiquantum well (MQW) detectors and modulators, flip-chip bonded onto silicon CMOS with substrate removal to allow access to the optical devices.

As the demand for telecommunications services continues to increase, the need to switch large bandwidths of data becomes important. While purely electronic solutions are possible, photonic solutions, using the integration of electronics with optical I/O (smart pixels), provides the potential for smaller physical volume, lower latency, lower power dissipation, and lower cost. We describe initial results from two opto-electronic switching chips, one with 1024 differential optical inputs and 1024 differential optical outputs with individual channels tested above 600 Mb/s and a second with 512 differential optical inputs and outputs with individual channels tested up to 900 Mb/s. The technology for the chip consists of flip-chip bonding of 850 nm GaAs/AlGaAs multiple quantum well (MQW) detectors and modulators onto silicon CMOS with substrate removal to allow access to the optical devices [1]

We demonstrate the integration of a large (64 × 68) p-i(MQW)-n GaAs diode array to a silicon CMOS chip, using flip-chip solder bump bonding techniques together with concomitant GaAs substrate removal. The capability of removing a relatively large area of GaAs substrate cleanly and uniformly is attributed to the introduction of a new selective etch stop with a smooth isotropic etchant for the GaAs substrate removal. The presence of the lattice matched In0.49Ga0.51P selective etch stop layer has no detrimental effect on the performance of the GaAsAlGaAs optical detector/modulator diodes, which gives the chip the large IO count of 4352.

Anticipation of large scale integration of vertical cavity surface emitting laser (VCSEL) and receiver arrays with CMOS processing circuits is driving the investigation of optical interconnects to find a strategy suitable to deliver this high throughput technology and yet acceptable to conventional electronics system designers who are unfamiliar and perhaps uncomfortable with conventional optics. A short list of desirable system attributes would include: densely packed optical channels, inexpensive and compact packaging, and optomechanical systems without critical micron level alignment tolerances.

A 4096 optical input and 256 optical output chip was used to construct a 155 Mb/s per channel demonstration of an ATM switching fabric. Quickly reconfigurable optoelectronic VLSI permits switching at ATM cell boundaries.

We present the first high-speed optoelectronic very large scale integrated circuit (VLSI) switching chip using LU-V optical modulators and detectors flip-chip bonded to silicon CMOS, The circuit, which consists of an array of 16 x 1 switching nodes, has 4096 optical detectors and 256 optical modulators and over 140K transistors. All but two of the 4352 multiple-quantum-well diodes generate photocurrent in response to light, Switching nodes have been tested at data rates above 400 Mb/s per channel, the delay variation across the chip is less than +/- 400 ps, and crosstalk from neighboring nodes is more than 45 dB below the desired signal, This circuit demonstrates the ability of this hybrid device technology to provide large numbers of high-speed optical I/O with complex electrical circuitry.

The melding of silicon electronic processing circuits with GaAs quantum well optical modulators and receivers provides the opportunity to significantly increase system communication throughput by virtue of integrated high-speed, free-space, optical channels as demonstrated in a recent experiment1. A second accomplishment of this experiment, the mounting of the optical platform in an electronics cabinet, illustrates the progress toward adapting the optical infrastructure to more traditional packaging schemes. The challenge of blending opto-electronic techniques into contemporary electronic architectures lies in further reducing the opto-mechanical system volume and cost.

In the past few years, the demand for telecommunications services beyond voice telephony has skyrocketed. For the growth of these services to continue at this rate, cost effective means of transporting and switching large amounts of information must be found. Although fiber optic transmission has significantly reduced the cost of transmission, switching high bandwidth signals remains expensive. While all electronic switching systems are certainly possible for these high bandwidth systems, considerable effort has been expended to reduce the cost of fiber optic connections between frames or racks of equipment separated by several meters. As an example, one can envision fiber-optic data links connecting the line units that receive and transmit data from the outside world with an electronic switching fabric. Optical data links, ODLs, can perform the optical to electrical conversions. Several of these optical data links can be electrically connected with electronic switching chips on a printed circuit board. As the demand for bandwidth increases, several hundred to several thousand optical fibers might be incident on the switching fabric. Discrete optical data links and parallel data links with up to 32 fibers per data link remain an expensive solution to transporting this information due to their per-link cost, physical size, and power dissipation. Power dissipation on the switching chips is high because of the need for electronic drivers for the high speed electrical interconnections between the switching chips and the data links. By integrating the O/E conversions directly onto the switching chips, lower cost and higher density systems can be built. In this paper, we describe preliminary results of an experimental optoelectronic switching network based on this lower cost solution. The network is designed to be part of an asynchronous transfer mode (ATM) network based on the Growable Packet Architecture. The switching chip consists of GaAs/AlGaAs multiple quantum well modulators and detectors flip- chip bonded to silicon VLSI circuitry. The optical system images the inputs from a two dimensional fiber bundle onto the switching chip, provides optical fan-out of the signals from the fibers to the switching chip, and images the outputs from the chip onto the fiber bundle.

The advent of large-scale, free-space, opto-electronic interconnections, as demonstrated in recent system prototypes, requires new sampling methods to reveal diagnostic information. Several factors contribute to the difficulty of probing optical communications channels without disrupting their operation. High-speed electronic connections to the chip periphery are not available in sufficient number and would contribute an undesirable thermal load. Electronic and optical physical contact probes would obscure many of the optical channels that are relayed to a common surface of the chip in current systems. Optical sampling provides the better method although many standard techniques are either too time consuming or complex to implement. We describe a tool we developed that delivers diagnostic information on a large number of high-speed, optical data channels simultaneously and operates analogously to the conventional sampling electronic oscilloscope. The optical oscilloscope is constructed using CCD cameras and video capture boards that are controlled by a software application resident in a personal computer. Sampling is based on a stroboscopic method of using short pulsed laser probe beam synchronized to a data stream to illuminate optical modulators within the optoelectronic circuit. We have demonstrated and discuss the tool's capability of simultaneously monitoring arrays of broadband optoelectronic devices operating at speeds from several hundred Megabit/s to a few Gigabit/s.

Free-space digital optical systems have demonstrated the capability to provide thousands of optical connections between optoelectronic chips. This dense concentration of channels creates substantial challenges in monitoring individual connections for diagnostic purposes without compromising performance. Prom the concept of stroboscopic techniques, we have designed and constructed a multichannel optical diagnostic tool that operates analogously to an electronic-sampling oscilloscope. The tool is economically constructed by the use of commercially available video cameras and video-enhanced personal computers. An integrated software application operates the tool and displays multiple-channel waveforms. We demonstrate the oscilloscope-sampling optical waveforms of a two-dimensional optoelectronic modulator array operating at data rates from 0.5 to 4 Gbits/s.

An important operation in a communications system is packet header recognition. For future high-speed time-division-multiplexed (TDM) systems, a packet header recognizer needs to distinguish between the various packet headers on a ultrafast time scale to avoid placing a bottleneck on the system. Frequency-domain processing [1,2] of femtosecond optical pulses has been shown to be capable of performing correlations in the frequency-domain in parallel rather than serially in the time-domain. Unfortunately, the input optical pattern can only be compared to a single packet at a time, which forfeits some of the advantages gained by the frequency-domain processing.

An important operation in a communications system is packet header recognition. For future high-speed time-division-multiplexed (TDM) systems, a packet header recognizer needs to distinguish between the various packet headers on a ultrafast time scale to avoid placing a bottleneck on the system. Frequency-domain processing [1,2] of femtosecond optical pulses has been shown to be capable of performing correlations in the frequency-domain in parallel rather than serially in the time-domain. Unfortunately, the input optical pattern can only be compared to a single packet at a time, which forfeits some of the advantages gained by the frequency-domain processing.

Custom designed surface-relief gratings are used to generate two-dimensional, uniform intensity beam arrays in several current digital free-space photonic system demonstrators. Although the design process for creating these gratings depends intrinsically on the size of the beam array; the optimization algorithm and the available computational resources ultimately determine the greatest complexity grating that is easily obtained. A new design algorithm is presented that has proven its ability to quickly design large beam array generators (128 X 128 and larger solutions) composed of either uniform intensity or arbitrary intensity beams. The algorithm produces two-dimensional non-separable binary phase or multiphase level solutions that yield a higher diffraction efficiency than separable dimension designs. Although the algorithm must optimize up to the order of 106 parameters that determine the intensities of from 16 to 32 K beam intensities, a personal computer will generate solutions in a matter of a few minutes to a few hours. We evaluate the algorithm performance for a number of designs and demonstrate several patterns that have been fabricated onto fused silica substrates via microlithography and reactive ion etching.

The principle of transmitting information using free-space optics poses a serious challenge to collecting diagnostic signals within large-scale digital photonic systems 1 . High concentrations of parallel optical channels and localized electronic signals bring about great difficulties in monitoring high speed operations using conventional contact techniques. Up to now, the typical diagnostic procedure was to sample a portion of the light reflected from the output modulators with a system viewport and form a remote magnified image. A high-sensitivity photodetector was then sequentially aligned with each spot to transform the signal to an electronic format that could be monitored using an electronic oscilloscope. This sampling procedure and other electro-optic sampling techniques 2,3 developed for high speed systems are too time consuming when many signals must be actively monitored.