In the fields of science and engineering you have to deal with what you have or what you can fabricate. Any math-ematical study that does not have some physical relevance is useless except as an object of calculational art–to be appreciated, but not used. As G. H. Hardy noted in A Mathematician’s Apology, ‘‘ ‘Imaginary’ universes are so much more beautiful than this stupidly constructed ‘real’ one; and most of the finest products of an applied math-ematician’s fancy must be rejected, as soon as they have been created, for the brutal but sufficient reason that they do not fit the facts.’’ The principle in this mathematics example applies to the serious feasibility design study be-ing done to combine OSA and SPIE into a unified society. When trying to combine these two strong, vigorous soci-eties in the field of optics, you cannot make the new or-ganization as streamlined as you might want. You have to deal with the history and current status of our societies. You have work with what’s available.

This PDF file contains the editorial “Guest Editorial: Special Section on Optical Data Communication” for OE Vol. 37 Issue 12

An overview of optical data communications is provided, beginning with a brief history and discussion of the unique requirements that distinguish this subfield from related areas such as telecommunications. Each of the major datacom standards is then discussed, including the physical layer specification, distances and data rates, fiber and connector types, data frame structures, and network considerations. These standards can be categorized by their prevailing applications, either storage [Enterprise System Connection (ESCON), Fiber Channel Connection (FICON), and Fibre Channel], coupling (Fibre Channel), or networking [Fiber Distributed Data Interface (FDDI), Gigabit Ethernet, and asynchronous transfer mode/synchronous optical network (ATM/ SONET)]. We also present some emerging technologies and their applications, including parallel optical interconnects, plastic optical fiber, wavelength multiplexing, and free-space optical links. We conclude with some cost/performance trade-offs and predictions of future bandwidth trends.

Numerical analysis of the current spreading and carrier diffusion problem for four popular long wavelength vertical-cavity surfaceemitting lasers (VCSELs) structures is presented. The results show that current confinement for p-mirror VCSELs is twice as effective as the corresponding n-mirror VCSELs. We also demonstrate the design, fabrication and device characterization for long wavelength 1.3 ?m VCSELs, where oxygen-implanted current-confinement regions were formed in a GaAs/AlGaAs Bragg reflector bottom mirror, which was wafer-bonded to an AlGaInAs/InP cavity consisting of nine straincompensated quantum wells. Room temperature continuous-wave (cw) operation of 1.3 ?m VCSELs with a record low threshold current density of 1.57 kA/cm2 and a record low threshold current of 1 mA is realized. Also, a record low pulsed threshold current density of 454 A/cm2 and a threshold current of 0.83 mA at 20°C are achieved. The maximum cw and pulsed operating temperatures are 40°C and above 100°C, respectively.

Taper and truncation loss calculations, experimental internal reflections, and far-field characteristics and coupling efficiencies into single-mode fiber are reported for a 1.3-?m large spot laser design with laterally tapered active region and a weakly guiding passive waveguide underneath. In the front passive section, the taper is truncated. Modeled taper loss and truncation loss at the end of the taper are compared. It is shown that for taper lengths exceeding 125 ?m, truncation loss dominates taper loss unless the truncated active width is smaller than ~ 0.2 mm. Reflectometer experiments show that for a truncated active width of 0.2 ?m, reflections at the truncation point are negligible, in agreement with modeling results. Experimental far fields are shown to become narrower and smoother as the taper length or the passive section length is increased. Coupling efficiencies into a single-mode fiber are reported. Up to 56% butt-coupling is achieved, with 1 dB lateral fiber positional tolerance of up to 2.4 ?m horizontally and 2.3 ?m vertically.

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.

A 12-fiber unidirectional parallel optical link called PAROLI with discrete Tx and Rx modules and a total bandwidth exceeding 12 Gbits/s is presented. The Tx and Rx module dimensions are 50 mm length, 18 mm width, and 10.5 mm height. The packages have 72 pins with 0.65-mm pitch in surface mount technology. The optical port is an MT-compatible 62.5-mm core graded-index multimode fiber array connector. The supply voltage is 3.3 V. The electrical signal interface is compatible to the Low Voltage Differential Signal Standard (LVDS, IEEE P1596-3 standard).

A small form factor fiber optic connector called the Fiber Jack and defined in Telecommunications Industry Association (TIA) FOCIS-6 is introduced that reduces the center spacing of the ferrules from 1.27 mm (0.5 in.) as in a duplex SC to 0.63 mm (0.25 in.) to enable it to fit within a standard RJ-45 port spacing. The Fiber Jack (FJ™) connector is the combination of two de facto standards: 2.5 mm ferrules and the RJ-45 style plug and jack. The standard 2.5 mm diameter ferrules take advantage of industry investment in termination equipment and techniques. The plug and jack design eliminates the use of an adapter such that the jack mounts flush with an outlet or patch panel. The FJ is designed for both multimode and single-mode fiber and has been tested according to EIA/TIA (Electrical Industry Association/ Telecommunications Industry Association) defined Fiber Optic Test Procedures (FOTPs), the results of which are included. The Fiber Jack interface was developed by Panduit Corporation and is marketed as the OPTI-JACK™ fiber optic connector.

The SC-DC™ and SC-QC™ (SC-DC/SC-QC are registered trademarks of Siecor) are multifiber optical connectors for conventional optical network applications. The SC-DC and SC-QC connectors were designed to provide a new interface technology that is significantly smaller than the duplex SC interface. The small SC-DC and SC-QC connector interfaces occupy half the space of an SC connector, effectively doubling the number of fiber ports in a given space. In addition, SC-DC and SC-QC connectors are simpler to install as well as offering greater packing density for both electronics and cable management. The connector design and performance of the SC-DC/SC-QC connector for both single-mode and multimode applications are described.

A novel fiber optic interconnect technology based on injection molded V-grooves that uses the fiber’s inherent precision to provide a reliable, robust and consistent optical connection is described. This technology has been expanded and applied to optical transceivers that can now achieve the same port density as that of current copper-based systems. Both the interconnect and the optical transceivers are shown to have performance levels similar to current ferrule-based multimode technology. Testing was performed in an effort to accurately measure performance and qualify the connector design for field use. Test results for the interconnect met the performance requirements of Electronics Industry Association/Telecommunications Industry Association (EIA/TIA) 568, which represent test standards for local area networks. Results of insertion loss and return loss performance of the duplex ferrule-less connector design were measured when 400 unique links were tested using 62.5 mm multimode fiber. Mating durability performance tests were performed in which plugs were reconnected to the socket 500 times. A new generation of small form factor transceivers is discussed that were developed using the same V-groove technology. Optomechanical tests are reported that show the performance level of these new transceivers is comparable to existing ST transceiver technology.

The TerraLink laser communication (lasercom) system was developed as a cost-effective, high-bandwidth, wireless alternative to fiber optic transmission. The advantages of lasercom over fiber optic cabling are primarily economic. However, free-space lasercom is subject to atmospheric effects, such as attenuation and scintillation, which can reduce link availability and may introduce burst errors not seen in fiber transmission. The TerraLink transceivers use large receive apertures and multiple transmit beams to reduce the effects of scintillation. By designing the lasercom link with sufficient margin for atmospheric attenuation and scintillation, a bit error rate (BER) of 1029 or better can be achieved. Since we designed the TerraLink transceivers to be eye-safe at the transmit aperture, each system is range-limited. Link power budgets for the TerraLink systems are presented, and link margin data are shown that quantitatively describe how the effective laser link range varies in different weather conditions. Since the TerraLink transceivers act as simple repeaters, they are protocol-independent. Examples of TerraLink installations transmitting wireless fast ethernet (125 Mbits/s), fiber distributed data interface (FDDI) (125 Mbits/s), asynchronous transfer mode (ATM) (155 and 622 Mbits/s), and Enterprise Systems Connection (ESCON) (200 Mbits/s) protocol data are presented.

The experimental work carried out by members of the Gigabit Ethernet Standard’s Modal Bandwidth Investigation group are reviewed to provide an understanding and to propose a solution to the bandwidth reduction observed in high-speed fiber optic test links based on laser transmitters and multimode fiber. The reduced bandwidth values, as compared to the manufacturers specified values, were caused by differential mode delay (DMD) in the optical signal. The cause of the DMD is linked to a combination of the launch conditions established between the laser source and multimode fiber. The criteria for developing a solution with the goal of modifying the launch conditions to eliminate DMD in laser transmission over 99% of multimode fibers are established.

Optoelectronic very large scale integrated (OE-VLSI) circuits are a basic component of optical interconnects proposed to overcome the limitations of high-speed electrical interconnects. Epitaxy-onelectronics (EoE), a monolithic integration technology capable of combining thousands of optoelectronic devices with VLSI-complexity GaAs Electronics, is reviewed. The fundamental assumptions on which the EoE technology is founded are explained and the development of the EoE integration process is reviewed. Then, the recently completed OPTOCHIP research foundry project, which made LED-based optoelectronic integrated circuits (OEICs) available to optical interconnect researchers, is described. Finally, integrated LED, photodetector, and circuit characterization results are detailed. These results show the utility of EoE OEICs in implementing optical interconnect architectures and point out current performance limitations.

A short review of smart pixel technology is followed by an application of one specific smart pixel technology to a 2-D application of analog-to-digital conversion called digital image halftoning. A novel approach to digital image halftoning is described based on a symmetric error diffusion algorithm, a new form of artificial neural network called an error diffusion neural network, and a smart pixel optoelectronic architecture. Two generations of smart pixel architectures are described that incorporate self-electro-optic effect device (SEED) modulators flip-chip bonded to submicrometer feature size complementary metal-oxide semiconductor (CMOS) silicon circuitry to produce CMOS-SEED implementations of the error diffusion neural network. Simulations and experimental characterizations demonstrate that this hardware approach provides sufficient computational accuracy for the analog neural network while simultaneously providing switching speeds that support halftoning at video rates.

Ultrafast processing techniques for the implementation of high-speed all-optical packet-switched networks are reviewed. Some of the key technologies required for building the next generation of highspeed interconnection networks include ultrafast packet generation, high-speed packet demultiplexing, and efficient packet routing. A review of recent component, subsystem, and system development as well as experimental demonstrations being conducted at Princeton University is presented to illustrate some of the capabilities of these technologies.

Ring networks made of fiber-ribbon point-to-point links are proposed. The first network is a control-channel based network in which one fiber in each link joins with others to form a control-channel ring. This ring improves performance of the network by sending medium access control information immediately before the data transmissions. High throughputs can be achieved in the network due to pipelining, i.e., several packets can travel through the network simultaneously but in different segments of the ring. The network can meet tough performance demands in, e.g., massively parallel signal processing systems, which is shown by example. Also, real-time demands can be met using slot reserving. The network, called CC-FPR (control-channel based fiberribbon pipeline ring), can be built today using off-the-shelf fiber optic components. The increasingly good price/performance ratio for fiberribbon links indicates a high potential for the success of the proposed kind of networks; a prototype is currently under development. The second network is similar to first except that it divides the network into two subnetworks, one for packet-switched traffic and one for circuit-switched traffic. When the main data flow in the network does not change rapidly, this is a good choice for a simple but powerful network.

We present the design of new photonic asynchronoustransfer- mode (ATM) switches that use optical code-division multiple access (CDMA) and strict optical orthogonal codes (OOCs). All the peaks of cross-correlation functions and all the sidelobes of any autocorrelation functions for a strict OOC are always limited to be a unit pulse-amplitude (i.e., 1 in the normalized case) for incoherent optical processing, regardless of whether an aperiodic or a periodic pulse sequence is input to optical CDMA decoders. Since the coding and correlation of strict OOCs are performed in the optical domain by using optical delay lines, the processing speed of the proposed photonic ATM switch can be very high. This, in turn, can support real-time broadband communications. Owing to the correlation characteristics of strict OOCs, the proposed ATM switch can flexibly handle both equal-rate and variable-rate/ multirate communication services without violating the cross-correlation and autocorrelation constraints of 1 and with no change of optical CDMA encoders and decoders. This, in turn, can substantially improve the switch flexibility without increasing system complexity.

The Corporate Optical Backbone Network (COBNET) project is a joint research project within the ACTS program of the European Commission. The COBNET consortium is considering the use of advanced optical networking technologies for the backbones of future corporate networks. In particular, multichannel add/drop ring networks based on wavelength division multiplexing (WDM) as well as on optical space-division multiplexing (SDM) technologies are being pursued. An overview is given of the system concept, the device technology, and the demonstration network that was developed within COBNET. The WDM ring option and specifically the related add/drop devices are focused on in more detail. These devices are fabricated in a newly developed highrefractive- index contrast planar silica-on-silicon technology by using silicon-oxynitride (SiON) as the core waveguide material. Compact add/ drop components based on the resonant coupler concept are realized. The filter characteristic can be tailored and tuned by thermo-optic heaters, which enables the selection of any given wavelength out of a series of wavelengths from the WDM ring using the same device.

Since its introduction in 1994, the Parallel Sysplex architecture for mainframe computer systems has attracted a great deal of interest because of its high performance, continuous availability, scalability, and lower cost of ownership. Recently, it has become possible to interconnect the building blocks of a Parallel Sysplex (host processor, coupling facility, sysplex timer, and disk storage) at extended distances using fiber optic data links. In particular, optical wavelength-division multiplexing (WDM) has been an enabling technology for the extension of this architecture to a geographically dispersed Parallel Sysplex (GDPS). We describe the use of WDM in GDPS configurations, including distance limitations and typical performance considerations. Experimental results of testing a GDPS with WDM channel extensions up to 40 km are presented, and some test results on the IBM 9729 Optical Wavelength Division Multiplexer used in these configurations are also discussed.

Microelectromechanical deformable mirrors (MEM-DMs) are attractive for optical phase modulation applications primarily because of their inherently low cost and low drive voltages. Two problems limiting widespread use of segmented piston MEM-DMs are low optical efficiency (fill factor) and undesired amplitude modulation resulting from interference with the static background structure. Using a lenslet array to focus the incident light onto only the reflective surface of the MEM-DM greatly improves the effective fill factor with a corresponding decrease in interference effects. A refractive lenslet array is used with a very low fill factor MEM-DM ( ~ 7%) to comprise a correcting element that behaves like a 70 to 80% fill factor device. The MEM-DM has 128 active piston micromirror elements. Experiments employing the hybrid correcting element demonstrate single beam steering, dual beam steering, and optical aberration correction. A comprehensive model of the lenslet/MEM-DM geometry is developed. Measured data shows good agreement with model predictions. A thermal circuit model is developed to estimate optical power handling capability of the MEM-DM. A conservative estimate of maximum optical power for this particular MEM-DM is 4 W/element when operated in a helium ambient, suggesting that relatively high power laser control applications are feasible.

New results from buffered interfacing techniques used with short-wavelength IR photodiode arrays at room temperature are presented and analyzed. Performance of linear Ge and InGaAs arrays is shown not to be limited by detector characteristics at room temperature, but instead by on-focal-plane hybrid interfacing electronics. Two key issues associated with Si complementary metal-oxide semiconductor (CMOS) interfacing circuitry are input offset voltage, which results in excessive dark currents, and input voltage noise with excessive 1/f characteristics. An analysis of white and 1/f noise generated by both detector and preamplifier is presented. Improved noise performance models give excellent agreement with experimental data. Proposed improvements in readout electronics will result in improved sensitivity and will relax costly cooling requirements associated with detectors.

Proposed here is a method of measuring the state of charge of lead-acid batteries based on the assumption that the addition of sulfuric acid to water will reduce the optical absorption at certain absorption peaks of pure water. This reduction is expected to result from the accompanying drop in the concentration of water molecules. Measurements of the absorption in the vicinity of 0.97, 1.20, and 1.45 ?m indicate that this is indeed the case, although deviations from a linear dependence on water concentration are noted. Two ways of implementing this phenomenon in a lead-acid battery are presented; one involves an absorption cell in a flooded battery, while the second involves an optical fiber woven into an absorbed-glass-mat battery. In the second case, the absorptive electrolyte serves as the cladding of the optical fiber and introduces attenuated total internal reflection into what would otherwise be perfectly guided modes.

The authors present an application of a simulated annealing global optimization method for the structural design of doublet lenses in accordance with a prespecified set of Gaussian characteristics and primary aberration targets. This approach eliminates the need for any prescription for the starting point in the optimization procedure. An identical approach is implemented for the structural design of both cemented and broken contact doublets. Boundaries for the design variables are taken care of by constraining the random walk of this Monte Carlo algorithm entirely within the feasible configuration space. For the sake of accelerating convergence in optimization, few modifications of the basic simulated annealing technique are attempted. Some illustrative examples are given.

The optical response of a Motohiro-Taga biaxial interface (MTBI) that separates two biaxial columnar thin films is explored analytically as well as computationally. Empirical equations based on experimental measurements of the principal effective refractive indices and the columnar inclination angle enable characteristic reflectances to be computed for MTBIs made of titanium oxide. Null-reflection conditions occur for any equicolumnar MTBI (EMTBI) wherein identical columns are inclined at equal angles but on opposite sides of the normal. Then all reflectances at the EMTBI are zero for light obliquely incident in the common deposition plane, but both co- and cross-polarized reflection occur for light obliquely incident in any other plane.

An adaptive bit-reduced mean absolute difference (ABRMAD) is presented as a criterion for the block-matching algorithm (BMA) to reduce the complexity of the very large scale integration (VLSI) implementation and to improve the processing time. The ABRMAD uses the lower pixel resolution of the significant bits instead of full-resolution pixel values to estimate the motion vector (MV) by examining the pixels in a block. Simulation results show that the 4-bit ABRMAD has competitive mean square error (MSE) results and a half less hardware complexity than the mean absolute difference (MAD) criterion. It has also better characteristics in terms of both MSE performance and hardware complexity than the MiniMax criterion and has better MSE performance than difference pixel counting (DPC), binary block matching with edge map (BBME), and bit-plane matching (BPM) with the same number of bits.

A new Er3+-doped phosphate glass exhibiting an excellent durability in both boiling water and NaNO3 molten salt is developed. The ion-exchange process of this glass is investigated by treating glass samples in a variety of salt baths with various exposure times. A planar waveguide with one mode at 1.54 ?m and three modes at 632.8 nm is demonstrated. The spectral properties of Er3+ in this glass are characterized by measuring absorption and emission spectra and fluorescence lifetimes. The emission cross section of Er3+ in this glass is calculated to be 0.76X1020 cm2 using McCumber theory.

This PDF contains the errata for the paper, "Evaluation of a scale-space filter for speckle noise reduction in electronic speckle pattern interferometry."