Site: IBM Optical Interconnect Technology
OEM Technical Support
3605 Highway 52 North
Rochester, Minnesota 55901-7829
Date Visited: October 23, 1994
Report Author: R. Hickernell
R. Jonathan Thatcher
The Rochester IBM site has 5,500 employees who are proud of their teamwork, which has resulted in revenue and profitability for the company. They are also proud of winning the 1990 Malcolm Baldridge National Quality Award, which is displayed prominently in the front lobby and listed on business cards. In 1992, IBM Rochester became the first IBM site to achieve ISO-9000 registration.
JTEC panelists met with members of the Optical Interconnect Solutions Department in the AS/400 and Fiber Channel OEM divisions of IBM. Their optical solutions to data interconnects are mid-range solutions that can be scaled up or down from the particular needs of the AS/400.
As of August 1995, approximately 300,000 AS/400 systems were installed worldwide, two-thirds of which were outside of the United States. Eight thousand firms write software for the AS/400, and 20,000 applications have been written. A new advanced family of AS/400s has been introduced recently, and ten are shipped from the Rochester site every minute, priced at between $12 thousand and $1 million.
In the division, about twenty scientists work on the development of optical link cards for computer interconnection. From 1990 to August 1995, over 250,000 such cards were manufactured and shipped. The main optoelectronic components of the cards are a laser transmitter operating near 780 nm, a large-area (600-micron-diameter) silicon pin or GaAs MSM receiver photodetector, and multimode fiber connector bores (for 50- or 62.5-micron core fiber) built into a molded duplex SC connector configuration. A key to the low-cost production and high-data-rate operation of the links is the use of lasers originally designed for compact disk (CD) player applications. Dual-sided surface-mount technology (transmitter electronics on one side, receiver electronics on the other) is used for low-cost packaging of both optics and electronics.
The primary application of the link card is for fiber channel (FC) at data rates of 1,063, 531, and 266 Mbit/s. The technology allows a growth path to 4 Gbit/s, enabled by the short-wavelength laser and GaAs MSM detector. Another near-term application is for ATM at a data rate of 622 Mbit/s. The links are designed for modest distances, up to 500 m at the FC 1,063 Mbit/s data rate in a fiber with a 50 micron core. (For comparison, the typical AS/400 link length is 10 m.) Multimode fiber is preferred because of the lower cost for connectors and device receptacles, because of the significant installed base, and because multimode fiber is written into premise wiring standards.
The Optical Interconnect Solutions Department overcame four major challenges in developing an optical link using a short-wavelength laser in favor of the long-wavelength (1,300 nm) LED alternative: (1) The cost of the lasers was overcome by using low-cost CD-type lasers. (2) The perception that LEDs have a lifetime 1,000 times that of lasers was countered by improving the reliability of CD-type lasers through process and screening enhancements and by verifying the lifetime of the lasers. IBM's lifetime test facility has logged over 80 million hours of laser operation time. Whereas typical off-the-shelf CD lasers have an average failure rate of 0.6%/khr over 18 khrs at 35 deg. C, the high-reliability CD lasers that IBM uses in its link cards have shown a projected average failure rate of less than 0.007%/khr over a 60 khr period at the higher temperature of 50 deg. C. (3) Problems with modal noise and relative intensity noise in multimode fibers were eliminated by using short coherence lengths and/or self-pulsating lasers. (4) The laser safety issue was overcome by designing and certifying the link card as a class-1 laser product using an open fiber control technique; if light is not sensed by the receiver, the laser is automatically shut off.
IBM has an alliance with Hewlett-Packard to codevelop similar cards for use in fiber channel standard applications. Sun Microsystems is the third party in a Fiber Channel Systems Initiative. As of August 1995, RISC System/6000 and IBM 3090 mainframes were being shipped with an optical link card.
Steve DeFoster gave an overview of optical card manufacturing, followed by a tour of the manufacturing line. The AS/400 card line turns out over 200 different parts of various volumes, a formidable job for cost control and turnaround compared to the typical computer card line that produces high volumes of only a few different types. The advantages of the card line that enable it to produce low-cost products with quick cycle times are the location of development and manufacturing under one roof (with excellent communication between them) concurrent engineering, use of the same hardware in development and manufacturing areas, and vertical integration. Prototype optical links are built on the manufacturing line, so that manufacturing problems are discovered early in the development stage.
On the manufacturing floor the JTEC team observed many of the stages of optical link card production, including automated chip placement, wave soldering of the boards, hand assembly of lasers and receivers in plastic housings, hand soldering of electrical connections from the board to the transmitter and receiver, and extensive, semi-automated optical testing of the finished cards. The department designed its own automated bit-error-rate (BER) tester, which is significantly less expensive and faster than the equivalent Tektronix BER tester.
During the manufacturing line tour, Jonathan Thatcher again emphasized that the key to the success of the product line was the screening of CD lasers for high performance. The screening process is performed to IBM specifications by manufacturers at their own sites. Over 95% of the lasers used in the links are supplied by Japanese manufacturers.
IBM shares data on lifetime and reliability of lasers with manufacturers on an individual basis. It has been asked for data from competitor's products, but refuses, for reasons of maintaining trust. One of the challenges to reliability testing is the issue of accelerated life testing procedures. IBM is working with laser manufacturers to develop guidelines.
Researchers in the Optical Interconnects Solutions Department are investigating the use of vertical cavity surface-emitting lasers (VCSELs) for use in future generation optical links. Most of the work to date has consisted of feasibility studies, although they have been awarded an ARPA contract to develop interconnects using VCSELs. This work will allow VCSEL manufacturers to develop improved manufacturing specifications. VCSELs apparently can meet the requirement of a short coherence length, but the coherence length depends heavily on VCSEL design. As a part of the ARPA contract, IBM is investigating the design of VCSELs for modal noise reduction.