Foster-Miller is developing a family of low cost active WDM components based on electronically switchable Bragg gratings (ESBG) in holographically polymerized polymer dispersed liquid crystal (H-PDLC). These provide approximate to 50 mu s switching speeds, adequate for many network reconfiguration functions. Space switches, wavelength selective add-drop multiplexers, attenuators and switchable taps may be integrated in a variety of architectures on chip by using ESBGs with different periods and device geometries. ESBG fabrication is a one step, low cost process compatible with standard silicon optical waveguide techniques.

Just as Bragg gratings are a favored technique for wavelength-selective filtering in optical waveguide systems, switchable Bragg gratings are theoretically an optimum active WDM switching mechanism. To date however, few practical methods for switchable waveguide Bragg gratings are available that combine large dynamic range, index compatibility, good optical quality, and ease of fabrication. Recently, Sutherland and coworkers (1993, 1995, 1997) demonstrated a holographic polymerization process in a polymer-dispersed liquid crystal composite that results in efficient electronically switchable Bragg gratings (ESBG) with low scattering. We report the first waveguide WDM applications.

Electronically switchable Bragg gratings (ESBG) based on holographic polymerized polymer/liquid crystal composites have been described by Sutherland et al. We present an overview of potential applications to waveguide based fiber optic NXN crossconnect and waveguide selective (WDM) crossconnect devices. Various proposed waveguide grating devices are described, and silicon and glass/polymer fabrication paths are outlined. Recent experimental results are summarized. ESBGs are a promising new technology for efficient, large N scalable, moderate speed reconfiguration switches for fiber optic networks.

The cost of critical alignment techniques required in the packaging of optoelectronic components has been one of the most important contributors to the high cost of these components. Recently, efforts have been undertaken around the world to develop novel techniques to reduce the complexity of alignment procedures and thereby reduce the costs of optical and optoelectronic components. Most of these aligned packaging techniques utilize platforms that while providing enhanced alignment capabilities, also allow the potential for increased hybrid integration. It is the purpose of this paper to review some of these newly evolving techniques that show particular promise or capture the imagination.

This paper describes the development of laser transmitter arrays for analog optoelectronic link applications up to 2 GHz. These modules have been developed in an attempt to utilize passive assembly and alignment operations for the purpose of reducing costs. To this end, silicon waferboard integration platforms and semiconductor laser arrays have been fabricated with special alignment features that allow passive assembly of flip-chip laser arrays to single-mode optical fiber arrays.

We describe the design of single frequency array transmitters and their application in RF-photonic systems. In addition, we present an array-based packaging technology that is based on passive-alignment with Si-waferboards.

This paper describes the packaging challenges associated with array-based transmitters and receivers used for analog fiber-optic links. The optoelectronic modules are being developed under an ARPA Analog Optoelectronic Module TRP. The paper will focus on the development of optoelectronic array modules using silicon waferboard technology for application to personal communication systems

Since the early 1960s when the semiconductor diode laser was first demonstrated, there has been an almost uninterrupted stream of performance enhancements to this device that is so central to modem optical communications. Today, diode lasers with extremely low threshold currents and high modulation frequencies are common to both the AlGaAs and InGaAsP materials systems. This has been made possible largely by advances in both design and processing technology, especially in crystal growth. Exquisitely complex designs of laser structures can be built, atomic layer by atomic layer, using molecular beam or metal-organic epitaxial techniques. Other elements vital to implementing practical optical communications systems experienced similar performance enhancements. Among these were high-speed, low-noise detectors along with suitable transmitter and receiver electronics. Finally, with the development of low-loss, low-dispersion optical fiber, all the pieces were in place for establishing communications links of almost unlimited capacity. Reliability was an early concern of system integrators, however, mainly because diode lasers showed a disturbing tendency to degrade in relatively short times. This prompted a massive effort by researchers throughout the world to systematically attack the problem, and it is probably now safe to say that laser reliability, at the chip level, is no longer a serious constraint. Unfortunately, reliability remains a system-level issue because advances in device packaging have not kept pace with device performance. This chapter will highlight the challenges specific to optoelectronic device packaging and will explore some new and exciting packaging concepts that promise to satisfy reliability requirements, preserve device performance, and, at the same time, offer a cost-effective approach to integration.

Progress toward the implementations of low-cost and reliable multiple optical fiber I/Os (input/outputs) for high-speed optoelectronics modules based on the use of micromachined silicon platforms is described. This approach, which makes use of conventional silicon processing technology, has built-in capabilities for reducing the labor requirements for packaging modules with multiple optical I/Os. In addition, it provides a natural means of extension to the fabrication of multitechnology modules (MTMs) for future-generation microwave systems, antennas, computers, and telecommunications systems. The assembly tolerances that are possible with this technology and the close connection that silicon waferboard has to existing silicon processing technology make it practical module level packaging technology for multiple optical fiber I/Os.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two new approaches are described for epi-down die bonding of diode lasers. The first approach, based on an acetic acid vapor flux, eliminates complications associated with the use of liquid flux in optoelectronic packaging. Based on this approach, InGaAsP/InP laser arrays were soldered onto silicon substrates. These laser arrays, which were passively aligned to single-mode optical fibers on the silicon substrate, had thermal impedances comparable to those obtained using conventional liquid flux. The second approach, called bridged die bonding, is proposed as a technique for reducing stress associated with epi-down bonding of diode lasers with hard solders. Bridged die bonding seeks to minimize bonding stress by avoiding contact of the laser active region with the hard solder. Thermal modeling indicates that the bridged die bonding approach, which uses a solder pattern with an air gap, can provide a thermal impedance comparable to conventional soldering techniques.<>

The success andwidespreaduse offiberoptic technology in highvolume applications such as telecommunications and computer interconnects is largely dependent upon the availability oflow-cost optoelectronic subsystems. Typical requirements in the case of local loop telecommunications are several parallel optical channels consisting of both receivers and transmitters performing at speeds of 150 to 600 Mb/s. We describe in this paper the fabrication of a four-channel receiver making use of a hybrid integration approach on a silicon substrate. The performance of a receiver channel as well as its components, an InGaAs metal-semiconductormetal photodetector aligned to a single-mode fiber and connected to a GaAs transimpedance amplifier, will be detailed. In addition, we discuss the integration of metal-insulator-metal (MIM) decoupling capacitors into the silicon substrate design.

We have demonstrated the fabrication of two structures achieved by the thin ifim transfer technique: back4lluminated InAlAsfInGaAs metal. semiconducthr-metal (MSM) detectors with buried interdigitated fingers on GaAs substrates; and long wavelength InGaAsP lasers on GaAs or Si substrates. For optoelectromc system applications, one often considers the use of a single material system for both the optical and electronic components on the chip, because it is not complicated by lattice mismatch. Compared to epitaxial growth of latticemismatched material systems, such as GaAs on Si, the thin ifim transfer technique does not result in a substantial number of misfit dislocations which can adversely affect device performance. The results we obtained demonstrate the feasibility of the thin film transfer process and point to the potential integration of OEICs and other components fabricated from a variety of materials on a common host substrate.

A high frequency, low dark current, 1.3 μm metal-semiconductor-metal photodetector on GaAs is reported. The measured frequency response of this photodetector up to 10 GHz agrees with a model that assumes different collection times for electrons and holes.