Glen Walden Johnson

Low-cost fabrication of optical subassemblies

The optical subassembly is a major contributor to the cost of a fiberoptic computer data link. A technology for low-cost fabrication of optical subassemblies is described, with emphasis on the transmitter subassembly. A factor of three cost reduction is achieved by limiting the parts count to only three: a laser or receiver chip packaged in a TO-can, a plastic housing, and a plastic aspheric lens; and by employment of a fast, automated active-alignment and subsequent fixing technique. Key enabling features include the rise of precision injection molding of specially chosen plastics, an aspheric lens design which permits wide positional variations in the axial direction, and curing of a fast setting epoxy through the use of RF power. A tool was constructed which produced subassemblies at high yield having satisfactory performance.

Evolution of optical subassemblies in IBM data communication transceivers

Optical subassemblies (OSAs) are the highest-cost component of datacom transceivers, and therefore the component that is most constrained by production cost concerns. While transceiver costs have declined, operating rates have increased from 266 Mb/s to 10.3 Gb/s. Corresponding OSA designs, based on multimode fiber, have evolved incrementally through several generations, to 2.4 Gb/s. Costs have been lowered in successive generations by reducing the number of parts, material costs, and complexity of assembly, and by using lower-cost optoelectronic devices--vertical-cavity surface-emitting lasers (VCSELs). This paper traces the mechanical aspects of OSAs that have been developed and introduced into products or developed as demonstration projects.

Packaging aspects of the Litebus/sup TM/ parallel optoelectronic module

The Litebus module is an optoelectronic transceiver and the key component in a parallel fiber optic data link. The module is designed to extend computer-to-computer communications to data rates and link distances beyond those achievable in copper at comparable cost. A transceiver configuration was selected to keep the modules size compact (45 mm/spl times/32 mm/spl times/ 9.8 mm) and to facilitate the integration of an IEC Class 1 laser safety strategy. The Litebus module consists of various packaging components and both CMOS and optoelectronic dies. It is designed to accept a single connector, having one receive and one transmit section, that is mounted on the end of a dual 12 channel fiber optic ribbon cable. Channel-to-channel spacing is 250 /spl mu/m throughout and standard multimode fiber is used. The transmitter consists of a VCSEL (Vertical Cavity Surface Emitting Laser) source having a wavelength of 850 nm. The receiver consists of a transimpedance amplifier with integrated Metal-Semiconductor-Metal (MSM) detector. The modules transmit and receive sections were designed to operate at data rates greater than 1.25 Gb/s (gigabits per second) per channel, yielding a maximum aggregate data rate in excess of 15 Gb/s. In one mode of operation, byte-wide data is simultaneously transmitted from and received by the module at 1.25 GB/s (gigabytes per second), with the four remaining channels on each side being assigned to user-defined overhead functions. The maximum cable length is 400 m in asynchronous mode and 200 m in synchronous mode.

Packaging aspects of the Jitney parallel optical interconnect

The Jitney parallel optical interconnect is a prototype 20-channel wide, low cost data link, designed for operation at speeds up to one Gbyte/s over distances approaching 100 meters. The package is based on (1) an inexpensive overmolded leadframe, (2) passive optical alignment, and (3) plastic molded parts. The packaging challenges in the fabrication of the components, their assembly, and in the achievement of the performance goals are described.

Bilinear noncoherent imaging of patterns on translucent scattering substrates

We treat the imaging of thin absorbing patterns on translucent substrates that are noncoherently illuminated from the side of the imaging lens. Examples of such objects are circuitry on ceramic and ink on paper. With a translucent substrate, the thin-object approximation commonly used in the theory of image formation is invalid, even if the surface pattern is thin. In the process of image formation, part of the incoming light passes through the surface pattern and penetrates into the substrate. The light is scattered, and a portion returns to the surface and passes again through the pattern. The image formed from this light depends linearly on the scattering characteristics of the substrate and bilinearly on the transmittance of the pattern.

Laser-formed structures to facilitate TAB bonding

A laser heating process was used to form structures which facilitate tape automated bonding (TAB). Uniform metal spheroids were created by melting the end of each TAB conductor intended for connection to the terminal pads of an integrated circuit (IC). A fully automated laser tool designed and built to fabricate these structures is described. Results for ICs bonded using this technology are presented.