Swiss-based diode-laser fab opens new chapter for Uniphase
Samuel (Toby) Strite and Jeff Wild
A ceremony on March 27, 1998, involving more than 100 customers, reporters, financial analysts, local politicians, and other guests, marked the opening of the Uniphase Corp. (San Jose, CA) new $20 million semiconductor laser fab in Zurich, Switzerland. The new fab reflects Uniphase`s commitment to diode lasers, and, in particular, its Swiss-based Uniphase Laser Enterprise (ULE) subsidiary, acquired for $45 million from IBM in March 1997. Since its beginnings in 1979, when its founders commercialized HeNe lasers for grocery-store scanners, Uniphase has grown through a series of startups and acquisitions into a leading supplier of optoelectronics components to the communications industry, with more than $100 million in sales in FY1997 and manufacturing facilities in four countries.
The opening ceremony featured futurist and Forbes contributing editor George Gilder, who spoke about what he calls the "Telecosm," a new era characterized by the abundance of bandwidth having negligible cost (see photo). Gilder predicted that the Telecosm would have a societal impact similar to the industrial and computer revolutions, which he characterized as eras when physical work and computational power became rapidly abundant at sharply reduced cost. The bandwidth abundance of the Telecosm was ushered in by fiberoptics and, in particular, the recent deployment of erbium-doped fiber amplifiers (EDFAs) and wavelength-division multiplexing (WDM)--two technologies in which 980-nm pum¥lasers play a key enabling role.
The fab opening marks the first phase of the ULE move completely out of the IBM Zurich Research Laboratory. Most investment went toward the construction of two cleanroom areas comprising 300 and 800 m2 of Class 100 and Class 1000 work space, respectively. The cleanrooms house the main laser-production line and many test, reliability, and R&D laboratories.
The remaining money was spent on upgraded production tools, for example, a molecular-beam-epitaxy system capable of growing laser structures simultaneously onto thirteen 2-in. gallium arsenide (GaAs) wafers. To handle the increased wafer throughput, Uniphase plans to double its test, lifetest, and burn-in capabilities by year`s end. Altogether, the new fab should enable ULE to increase 980-nm pump-laser production to 100,000 chips annually, while concurrently diversifying into the intersatellite, printing, material-processing, and medical-laser markets.
Pum¥laser diode
Uniphase`s core 980-nm pump-laser product is a key component in EDFAs, which play a critical role in increasing the bandwidth of today`s fiberoptic networks. The amplification of the 1.53- to 1.57-µm wavelength signal propagating in a fiberoptic cable is achieved by periodically introducing small quantities of erbium into a special glass fiber. Ionized erbium embedded in the silica-glass fiber matrix is efficiently energized by pum¥lasers operating in the 980- or 1480-nm wavelength range. Amplification is possible because the excited-state erbium ions are in duced by the 1.55-µm signal to relax back to their ground state, creating a photon identical to the signal photons via the stimulated-emission mechanism. This all-optical amplification process is rapid and highly linear, so EDFAs preserve the signal shape while amplifying it by 30 dB or more.
Pum¥lasers for EDFAs must maintain single-lateral-mode operation to insure efficient coupling into the erbium-doped fiber. Hopping to a higher-order mode creates a nonlinearity or "kink" in the laser output power vs. drive current (PI) curve, and the resultant drastic change in the laser-to-fiber coupling efficiency strongly affects EDFA performance. The power level at which the kink occurs is referred to as the linear power (Plin) of the laser diode. Because the EDFA amplification is a strong function of the pump-laser power, ever-higher linear powers are required by telecom companies to increase the EDFA spacing in their networks. The advent of WDM and, more recently, dense WDM, has also increased pump-power demand because instead of a single wavelength, 8, 16, or even 80 discrete wavelength channels must be simultaneously amplified. Wavelength-division multiplexing also demands additional pum¥power to compensate for losses introduced by dispersion compensation, gain-flattening schemes, and channel add-dro¥components. Therefore, pum¥lasers are required to push the power performance limits of single-lateral-mode diode-laser operation, while at the same time operating at an acceptable level.
The market for 980-nm-pumped EDFAs began to develo¥with the 1990 commercial introduction of the E2 980-nm chi¥by Laser Enterprise, then a small grou¥of researchers at the IBM Zurich laboratory. With the 1993 announcement by MCI of a successful fiber link using E2 pum¥lasers to connect Sacramento, CA, with Chicago, IL, a new era of long-haul fiberoptic systems capable of meeting Internet bandwidth demands was begun. Laser Enterprise grew alongside the fiberoptic data-network industry, doubling diode-laser shipments annually during the mid-1990s and realizing sales greater than $20 million last year. The market for EDFA pumps is estimated by KMI Corp. (Newport, RI) and Uniphase to be worth approximately $300 million in 2001. Uniphase Laser Enterprise is the largest supplier, having delivered more than 100,000 pum¥lasers to customers` networks.
To grow so quickly, Laser Enterprise had to convince risk-adverse telecom companies that its aluminum gallium arsenide (AlGaAs) lasers exceeded the reliability specifications of their networks. It was a common belief around 1990 that GaAs-based lasers were inherently unreliable. Dark-line defects and facet corrosion limited the useful life of such devices. Mirror coating was observed to extend laser lifetime somewhat, but coated lasers were still prone to sudden failures. Experiments at IBM showed that facet corrosion can be completely suppressed by an improved mirror-passivation technique. The patented E2 coating process greatly improved the general perception of GaAs/AlGaAs laser reliability.
Commercialization began in the late 1980s, when companies expressed an interest in testing IBM`s InGaAs/ AlGaAs 980-nm pum¥lasers in their low-noise EDFAs under development. Initial experiments were so promising that IBM was asked to provide a steady supply of E2 pum¥chips for purchase. In response, the Zurich laser team stepped out of basic research, adopted the name Laser Enterprise, and focused on the commercialization of InGaAs/ AlGaAs 980-nm pum¥lasers. First-generation pumps produced linear power of about 90-150 mW. The current third-generation E2 chi¥is specified at Plin = 180-240 mW and delivers 240-mW output at operating biases as low as 275 mA, 1.75 V, corresponding to about 50% wall-plug efficiency. In the pipeline is a fourth-generation 980-nm chi¥capable of Plin = 300-mW output power, corresponding to greater than 200-mW single-mode power in the fiber.
Uniphase E2 lasers have greater than 3 million laboratory-device test hours and 500 million field-test hours in customers` EDFAs. Laser Enterprise`s internal reliability database extrapolates to an FIT (failure in 109 hours) rate below 250 and predicts greater than 700,000 hours of median lifetime and a mean time to failure of greater than 1.1 million hours.
Telecom customers now believe that the E2 980-nm pum¥technology is ready for undersea deployment, which demands even greater component reliability than terrestrial networks. To conserve power, submarine pum¥modules are designed without Peltier coolers, which in terrestrial EDFAs are used to stabilize the pump-laser wavelength. To stabilize the pum¥wavelength without temperature regulation, the laser output can be coupled into a fiber having a photolithographically introduced Bragg grating. The fiber Bragg grating alters the laser`s internal gain distribution, effectively clamping the wavelength to that dictated by the grating periodicity. Uniphase and its partners offer fiber-grating-stabilized E2 980-nm pum¥modules for wavelength-critical applications.
Core diode-laser technology
Uniphase`s diode-laser technology uses molecular-beam epitaxy to produce high-purity GaAs-based heterostructures with precise thickness control of each of the more than 100 discrete layers comprising the vertical laser structure. Uniphase`s proprietary E2 facet coating protects against corrosion, increasing sustainable power output and eliminating catastrophic mirror damage under normal operating conditions. Uniphase intends to extend its core technology to reliable, high-power laser products over the full 800-1100-nm indium aluminum gallium arsenide wavelength range.
At the 1998 Optical Fiber Communication conference (San Jose, CA), Uniphase announced a junction-side-u𨙼-mW, 30-µm ridge-width laser for the telecom market. The 500-mW laser is a conservative extension of the core 980-nm narrow-stripe technology, having an identical process, including E2, with only the ridge-mask ste¥changed. With its first ste¥into broad-area lasers complete, Uniphase began developing a 2-W, 100-µm stripe junction-side-down laser. Uniphase intends to compete in all markets requiring high-power lasers having outstanding reliability. o
SAMUEL (TOBY) STRITE is a product manager with Uniphase Laser Enterprise, Binzstrasse 17, CH-8045 Zurich, Switzerland; e-mail: [email protected], and JEFF WILD is the manager of corporate communications for Uniphase; e-mail: [email protected].