Almost all communication through optical fiber takes place at infrared wavelengths, so the ability to visualize radiation beyond the visible spectrum is a great asset to companies that assemble and test optical networking equipment. Sensors Unlimited has developed a lightweight IR imager, the MiniCamera, which measures just 5 6 9.5 cm and weighs less than 350 g without its lens (see ). It operates in the near-IR band at 9001700 nm, and is based around a 320 240 InGaAs detector array, which is bump-bonded to a silicon readout circuit. There are two keys to achieving such a compact unit. One is to incorporate a large amount of functionality into the readout IC of the imager, which in turn reduces the amount of separate support electronics. The other is to manufacture high-quality arrays that minimize the need for post processing. "We use a proprietary material structure for our imagers which is very different from the device structure used for our high-speed detectors," says Marshall Cohen, executive vice-president of Sensors Unlimited. "This gives the imaging arrays higher uniformity and a much lower dark current." The camera runs off batteries or a small wall transformer. It can easily be hooked up to a TV or a computer, and is compatible with microscopes and laser alignment stations. A wide spectrum of applications A major application for the camera is in the assembly of large optical switches; here, the ability to "see" in the infrared facilitates the active alignment of, for example, multi-channel arrayed waveguides (AWGs) with multiple fibers. Such cameras are also used to align and monitor large MEMS-based crosspoint switches. Another application is laser beam profiling; the cameras have high dynamic range and can handle a high intensity of light without being damaged, so they can be used to measure features such as beam shape and spatial modes (see ). In the silicon industry, IR cameras can be used to view ICs through the back of the wafer (since silicon is transparent at NIR wavelengths) to see damage, hot spots, broken lines etc. At OFC, Sensors Unlimited unveiled its first receiver product for telecom, namely a 10 Gbit/s InGaAs PIN photodiode integrated with a GaAs HBT amplifier in a fiber-coupled, Bellcore-certified package. This is the company s first product for the network itself; its IR cameras are used for monitoring functions, as are its linear arrays that are used to measure the performance of individual DWDM channels (see Compound Semiconductor September/October 2000, p41). "Our detector array work for WDM monitors and cameras has made us one of the largest processors of InGaAs wafers in the world," says Marshall Cohen. "This allows us to produce high-speed photodiodes very cost-efficiently, and to deliver products immediately in high volume." The Finisar connection In October 2000, Sensors Unlimited was acquired by Finisar, one of the leading volume manufacturers of transceiver modules for datacom and data storage applications. In fact, Sensors Unlimited has already started to ship avalanche photodiodes (APDs) for incorporation into some of Finisar s coarse WDM transceiver products. "We are shipping 2.5 Gbit/s APDs in volume to Finisar," explains Chris Dries, director of high-speed product development. "We expect to ship 10 Gbit/s products later this year. APDs are ideal for coarse WDM applications in the metro environment, where there are lots of passive components; the APD provides a simple way to make up for passive losses." Finisar offers course solutions for WDM Finisar, located in Sunnyvale, CA, is an established supplier of modules for gigabit-speed connectivity, serving applications such as Gigabit Ethernet and Fibre Channel. Recently, Finisar announced a full range of modules, including transceivers for coarse WDM, which target metro access networks requiring multiple wavelengths. Coarse WDM uses four or eight widely spaced wavelength channels. Finisar s Gigabit CWDM transceiver has eight channels, and incorporates uncooled DFB lasers with wavelengths separated by 20 nm in the 14701610 nm range. Eight identical PIN-based receivers are used, providing a link budget of 21 dBm. "Since the lasers are uncooled, their wavelengths drift with temperature, but only by 0.09 nm/C over the operating range," says Mike Farley. "The 20 nm wavelength separation easily accommodates this drift. It s not possible to have tight spacing as in DWDM, but in the metro/access area, where a high density of wavelengths is not typically a criterion, this approach is much more cost-effective." Finisar has also introduced a GBIC transceiver operating at rates from 100 Mbit/s to 2.5 Gbit/s; the module incorporates avalanche photodiodes to increase the link budget to 28 dBm. In addition to Sensors Unlimited, which manufactures photoreceivers, Finisar has another subsidiary that makes active devices. Demeter Technologies, based in El Monte, California, was acquired in November 2000. The company is a vertically integrated laser manufacturer, with in-house epitaxy and wafer fabrication facilities. Demeter will continue to provide lasers to its external customers as well as beginning to serve Finisar s internal needs. Multiplex and Agere demo tunable EMLs Multiplex and Agere Systems (formerly Lucent Microelectronics) have introduced 10 Gbit/s tunable transmitters containing lasers with monolithically integrated electroabsorption modulators. Single chip tunable lasers and integrated electroabsorption modulated lasers (EMLs) are available from a number of suppliers, but increasing on-chip functionality represents the next step towards reducing the package size and power consumption of tunable transmitters. These devices will play an increasingly important role in DWDM systems, optical routers and OADMs used in short- and long-haul high-speed optical networks, not least because network operators will need to keep fewer lasers in stock as backups. Both companies use electronic tuning of DBR lasers to select wavelengths across the C-band. Multiplex s device integrates a gain section with phase and Bragg sections to achieve quasi-continuous wavelength tuning. The data signal is then applied to the laser emission by the integrated modulator situated close to the front facet (see ). As well as the gain, Bragg and modulator sections, Agere s single chip features a semiconductor optical amplifier (SOA) section to boost the output power, as well as a detector to monitor the power prior to modulation. Agere s C92 tunable transmitter is housed in a small-form factor package that also contains a wavelength stabilizer in addition to the requisite physical layer processing ICs. Inside the chip, the Fabry Perot mode can be tuned to up to 20 channels by applying a current to the Bragg mirror. The wavelength is stabilized using Agere s on-board LambdaLock device, which is a patented system that locks the laser emission to 50 GHz channel spacings with a wavelength stability of 20 pm. Agere says the transmitter is suited to terminal equipment in DWDM applications from metro to extended-reach systems up to 40 km. The company introduced a 2.5 Gbit/s tunable transmitter and 20-channel tunable laser module last year. The C92 will be sampled in the second quarter of 2001, with production expected by the fourth quarter. Transponder sends and receives Multiplex s MTX-TEML transmitter is a 10 Gbit/s variant of its earlier 2.5 Gbit/s transmitter that can be tuned to any one of 16 channels in under 10 ms. Multiplex also introduced a packaged transponder (see ) which contains the new tunable EML together with a 10 Gbit/s receiver. The MTRX192L receiver features an integrated limiting amplifier and achieves a sensitivity of 19 dBm at a bit rate error of 1E-10. Eye patterns from the transponder typically indicate rise and fall times of 30 ps. Also built into the module as separate components are current sources, a temperature controller and a modulator driver. The package measures only 2 3 0.59 inches. Multiplex will begin shipping samples of the transponder in the second half of the year, with production expected three to six months later.