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Technical Insight

Device makers fight it out to share in the 10 Gbit/s action

Despite a lack of customers, there is a lot of activity at the component level of the fiber-optic market. Tim Whitaker and Richard Dixon report from the recent OFC conference in Anaheim, CA.
Fiber-optic component vendors face the fundamental problem that customers are few and far between. None of the device makers among the 1200 exhibitors at this year s Optical Fiber Communication conference, held on March 17-22 in Anaheim, CA, tried to pretend that they are having an easy ride at the moment. However, there is clearly a great deal of product development going on as companies prepare for recovery.

Device makers are focusing a great deal of their current effort on the 10 Gbit/s space, which is the "sweet spot" in the market at the moment. There are several key trends; one is to improve existing products by making them smaller, less power-hungry and of course cheaper. Another trend is to incorporate more functionality into modules while maintaining their cost and footprint. The third trend is to enhance functionality at the device level either through integration or by developing components with enhanced performance.

At OFC there was less evidence of activity in the metro area, which last year was touted as the saviour of the fiber-optic market. The development of 40 Gbit/s components was an area of great interest, but the current downturn has delayed this considerably.

New technologies

One of the most interesting aspects of this year s OFC was the number of companies seeking to bring new technologies to the commercial market. These take the form of advanced devices providing key advantages such as smaller size and lower power consumption and cost. Essient Photonics, a Scottish company founded in February 2002, has received $7 million to develop devices based on resonant tunneling diodes, one example being a modulator requiring a drive voltage of only 100 mV. Meanwhile Zia Laser has reached several milestones in the development of quantum-dot lasers, which are highly temperature-insensitive and have ultra-narrow linewidths. The company, based in Albuquerque, NM, has manufactured a 1310 nm DFB laser on a GaAs substrate, and a 1550 nm tunable gain chip suitable for use in an external cavity laser that allows a maximum output power of 40 mW.

Irish start-up Eblana Photonics revealed that it is using photonic bandgap structures to manufacture pump and transmission lasers without regrowth. Microstructures are etched into the top surface of the laser structure to control the spatial and longitudinal modes, resulting in ultra-narrow linewidths. Nova Crystals is using wafer-bonding technology to fabricate InGaAs-based APDs on silicon, which have much higher performance than conventional APDs on InP.


As well as demonstrations of wafer-scale integration, including both hybrid and monolithic approaches, many companies were showing examples of module integration where more functionality is incorporated into the same package size. Agere Systems introduced what it claims is the industry s first cooled 10 Gbit/s transponder to transmit up to 80 km without any amplification. The CB64L2, measuring 3.5 x 4.5 inches, utilizes a 1550 nm electroabsorption modulated laser and an APD or a pin diode, and also incorporates the necessary electronic components including amplifiers and mux and demux ICs. Agere also introduced an uncooled TB64L1 transponder containing a 1310 nm DFB laser, with a reach of 40 km at 10 Gbit/s. Nortel Networks demonstrated a tunable transmitter module; the LG10M contains a widely tunable VCSEL, a GaAs Mach-Zehnder modulator, a variable optical attenuator, a wavelength locker and a power monitor.

Bookham Technology, which recently acquired Marconi Optical Components, showed several examples of the hybrid integration of active devices onto its silicon-based ASOC platform. As well as integrating Genoa s linear optical amplifier (LOA), Bookham demonstrated a Multi-Channel Link consisting of separate eight-channel transmitters and receivers. Each transmitter contained eight lasers and eight monitor photodiodes hybridized on a single silicon chip, with laser drivers and other circuitry incorporated into the 20 x 55 x 5 mm package. Each receiver contained eight photodiodes hybridized on a silicon chip with transimpedance amplifiers (TIAs) included in the package.

At the monolithic level, Agility conducted a live demo of its widely tunable InP-based lasers. Each device consists of a four-section sampled grating DBR laser with a monolithically integrated semiconductor optical amplifier (SOA) and an electroabsorption modulator. MetroPhotonics showcased a dynamic channel equalizer based on its echelle grating technology (see Compound Semiconductor July 2001, p87). The monolithic InP-based chip, about the size of a dime, contains two echelle gratings. The first grating separates the light by wavelength and distributes each channel into a separate waveguide, after which the light passes through an integrated photodiode. This device acts as both a channel monitor and a variable optical attenuator (VOA) to allow the channels to be equalized. The second echelle grating recombines the light before it leaves the chip.

ThreeFive Photonics has commercialized its first product, a single-chip receiver capable of detecting multiple wavelengths at 2.5 Gbit/s. The InP-based receiver employs a monolithically integrated arrayed waveguide grating (AWG) and features four channels covering 1525-1565 nm with a spacing of 100 GHz, making it suitable for CWDM. The operating temperature range is 0-70 ºC. Samples will ship in the second quarter of 2002, with 16-channel versions and four-channel 10 Gbit/s receivers expected. "Optoelectronic integration using InP not only leads to very small systems at lower price levels - it also yields systems that are more robust, require less maintenance and repair, and consume less power. In some metropolitan areas, power consumption is the most critical consideration," said CEO Wouter Deelman.

New companies

Several new companies made their debut at OFC, including Essient Photonics and Xindium Technologies, which is fabricating high-speed InP-based ICs (see "Xindium uses InP expertise to make commercial 40 Gbit/s ICs"). OEPic, founded in July 2000, designs and manufactures optoelectronic ICs for 10 and 40 Gbit/s systems. The company has an in-house InP wafer fab with gas-source MBE and MOCVD growth capabilities as well as sub-0.1 µm e-beam processing, and also uses external foundries for GaAs-based devices. OEPic has received more than $30 million from several venture capitalists and corporations. Its founders include Yi-Ching Pao, formerly at Litton and Filtronic, and Denny Houng, formerly at Agilent. OEpic s first products are a complete 10 Gbit/s chipset, priced at $99 for bare die or $199 as packaged parts. The chipset consists of an 850 nm VCSEL, a driver, a pin photodetector with an integrated TIA and a limiting amplifier. "These first products are for short-reach applications at 10 Gbit/s, and will soon be followed by our longer-reach products fabricated in our own InP fab in Sunnyvale, CA," said George Bechtel, director of marketing. "We will put more emphasis on 40 Gbit/s parts when the market is ready."

Several new fabless companies are involved in the design of high-speed ICs for 10 and 40 Gbit/s applications. Centellax, based in Santa Rosa, CA, was founded in April 2001 by a team of device engineers including several from Agilent. The company has developed a family of broadband amplifiers that is currently implemented in GaAs PHEMT technology, as well as mixed-signal ICs (mux, demux etc) implemented in SiGe and CMOS. The first product is the DA1A seven-stage traveling-wave amplifier, which can be used as a TIA, a small-signal gain block and as a driver amplifier for electroabsorption modulators. The DA series incorporates the company s patent-pending techniques to extend frequencies to as low as 30 kHz without expensive high-Q inductors and also to cascade two amplifiers on a single chip. "The products reflect the design philosophy of our company - high performance, ease of use, reliability and a competitive price," said Julio Perdomo, Centellax s founder and president. The company is working with R&D groups and is selling products "in small quantities".

iTerra Communications, based in Fremont, CA, designs highly integrated driver amplifier and receiver products for 12.5 and 43 Gbit/s networks. One of its first products is a DC to 50 GHz GaAs MMIC amplifier which provides an output voltage of 8 Vpp to drive a lithium niobate modulator. Another fabless start-up is DA-LightCom, based in Les Loges en Josas, France, which is developing 40 Gbit/s driver amplifiers and TIAs, and has a series of standard products at 10 Gbit/s.

Narrow channel spacing

One way to increase the capacity of a DWDM system is to reduce the spacing between channels. For ultra-dense WDM systems with a spacing of 25 GHz, stability and absolute accuracy are critical. Fiberspace, based in Woodland Hills, CA, has developed a wavelength locker technology, Gridlocker, that provides a wavelength accuracy of ±250 MHz. The company s patented optical phase-locked loop (OPLL) technology incorporates a tuned Fabry-Perot etalon to provide a sharp optical frequency reference. The OPLL stabilizes the laser frequency by utilizing frequency modulation techniques to derive a phase-dependent error signal that locks the laser frequency to the peak of the Fabry-Perot transmission. Fiberspace s product uses standard DFB lasers purchased externally and is tunable across a 3 nm range.

40 Gbit/s systems

Many companies are developing 40 Gbit/s ICs using InP, SiGe or even CMOS. Infineon, Bookham and Agilent jointly demonstrated a 40 Gbit/s system utilizing signal generation and test equipment from Agilent and SiGe mux and demux ICs from Infineon. Bookham supplied the GaAs PHEMT driver and a transmitter containing a DFB laser, broadband GaAs modulator and an integrated wavelength locker.

One of the highlights of the post-deadline session at OFC came from Lucent s Bell Labs, which claims to have doubled the distance record for high-bandwidth, ultra-long-haul transmission by sending 2.56 Tbit/s some 4000 km. The lab experiment used a 64-channel DWDM system, where each channel carried information at 40 Gbit/s. The amplifiers were 100 km apart, and the experiment was made possible by a new coding scheme, differential phase shift keying (DPSK), together with extended L-band amplifiers, Raman amplifiers, forward-error correction (FEC) and optimal dispersion compensation. In related news, Deutsche Telekom has started field trials of Lucent s 40 Gbit/s LambdaXtreme Transport system, which can transport signals 1000 km without regeneration. Tim Sullivan, president of Lucent s Optical Networking Group, reports that the LambdaXtreme 40 Gbit/s system is already more cost-effective than 10 Gbit/s systems.

"The LambdaXtreme system delivers 40 Gbit/s wavelengths for 15% less than the cost of combining four standard 10 Gbit/s wavelengths," he explained. "Our 40 Gbit/s products are shipping now, and offer service providers a system that is able to meet all of their distance and capacity needs, while continuing to deliver significant savings in operational expenses."

Tunable lasers

Many different types of tunable laser were on display at OFC. JDS Uniphase launched a narrowly tunable, high-power laser, while Quantum Devices showed a temperature-tunable DFB laser capable of delivering 15 mW of power and tunable across four adjacent ITU wavelengths using a 100 GHz spacing. Iolon exhibited a 20 mW external cavity device capable of tuning to more than 200 channels with 25 GHz spacing. "The 25 GHz channel spacing results from the integrated wavelength locker technology that Iolon incorporates into the Apollo laser module," said president and CEO John Clark. "This provides better than ±1 GHz frequency accuracy over the entire tuning and operating temperature range, and the fact that our laser is continuously tunable made this possible without changes to the external laser cavity itself."

ADC announced a tunable laser based on its monolithic four-section DBR design with an integrated wavelength locker and proprietary control algorithm. The firm says it is the only manufacturer building widely tunable lasers with built-in wavelength lockers in volume. The laser operates in the C-band and supports the 1529-1561 nm EDFA window, and tunes to a channel in less than 2 ms.

The LG10M, Nortel s new widely tunable 10 Gbit/s transmitter, has a GaAs Mach-Zehnder modulator, variable optical attenuator, wavelength locker and power monitor with a CW widely tunable VCSEL. The module, which covers up to 32 nm in the C- and L-bands, measures 80 x 18 x 12.5 mm and uses a MEMS-based tunable VCSEL designed by Nortel s subsidiary Coretek.

Agility adds functionality

Agility Communications introduced two widely tunable products: the 3105, a 10 Gbit/s laser that delivers 10 mW of output power for long-haul applications, and the 4245, a lower-power 2.5 Gbit/s laser that targets metro applications. The same InP sampled-grating DBR laser is used in both products. Each chip contains six sections; these are gain and phase sections and two gratings for the laser, together with a monolithically integrated SOA and electroabsorption modulator. Tuning is over 100 channels with 50 GHz spacing and available across the full C-band (1530-1565 nm). Production is slated for July.

In the 10 mW long-haul laser, the electroabsorption modulator is left open and a lithium niobate modulator is used instead. The lower-data-rate laser employs the InP modulator and operates at up to 2.7 Gbit/s for FEC support, with +3 dBm (2 mW) of output power in the C-band.

"Most of today s 10 Gbit/s architectures use lithium niobate to modulate the laser signal, and this is what our new 10 mW laser is designed for," said Arlon Martin, VP of marketing. "While lithium niobate is much more expensive, bulky and harder to connect to fiber, it provides excellent drive and on-off signal characteristics compared with InP modulators, and is suited to long-haul links or 10 Gbit/s operation. Our shorter-range device uses the integrated InP modulator because it is cheaper and does an excellent job at 2.5 Gbit/s, where most of the demand is currently situated in metro links." Background information VCSELs target 10 Gbit/s applications and parallel interconnects

A number of VCSEL-based products were on show at OFC. As well as demonstrating its 10 Gbit/s serial transponder, which incorporates a directly modulated 1310 nm VCSEL, Cielo Communications launched several 1310 nm parallel array modules. The new family targets OC-3 (155 Mbit/s), OC-12 (622 Mbit/s) and Gigabit Ethernet (1.25 Gbit/s) applications up to 25 km on singlemode fiber. The separate transmit and receive packages contain arrays of eight or twelve VCSELs and pin photodiodes respectively. The arrays are currently shipping to development partners, with availability slated for the second quarter of 2002.

10 Gbit/s serial VCSELs
The VCSEL Optical Products business of Honeywell exhibited a new family of directly modulated 10 Gbit/s serial VCSELs and receivers designed for applications including 850 nm short-range multimode links compliant with the 10 Gigabit Ethernet standard. The VCSEL source is a directly modulated AlGaAs/GaAs device with a 10 µm diameter oxide-confined aperture. The receiver contains an 850 nm pin detector and pre-amplifier.

During its manufacture, the VCSEL device undergoes "Stabilaze", which Honeywell recently introduced as a method to manufacture 850 nm arrays. This approach includes burn-in procedures that ensure that the parameters of VCSELs in an array are constant within known limits. "The burn-in is done at the wafer level using a proprietary approach, and this guarantees a high level of quality before dicing," said Honeywell s Jim Guenter. "We also perform the standard wafer probing, including electro-optical and spectral measurements."

The new DC to 12.5 Gbit/s emitter features a threshold current of 3 mA and slope efficiency of 0.2 mW/mA measured at a power output of 0.35 mW. Power consumption is typically 10-20 mW. "In the 10 Gbit/s serial area we are introducing three types of device," said Guenter. "These include separate transmit and receive components, connectorized components and what we call optical front-ends. Optical front-ends contain the requisite components needed to mate to the fiber, but not the back-end of the receiver."

Honeywell is also looking to sample 1300 and 1550 nm VCSELs this year.

Large-aperture devices
At OFC, Zarlink released large-aperture 850 nm selectively oxidized VCSELs for 10 Gbit/s operation. The devices are designed for VSR optical interconnects and have a 12 µm. The power penalty is only 0.5 dB over 300 m of high-bandwidth fiber at 80 °C. This provides a significant power margin for the IEEE 802.3ae 10 Gigabit Ethernet standard, which could result in better link performance and reliability, longer reach and lower costs.

The large-aperture design tends to introduce unwanted higher-order frequencies that lead to signal degradation. Zarlink says the design, which deliberately introduces losses that cancel the higher-order lateral modes, is more reliable than small-aperture VCSELs because a lower operating current density can be used.

Alvesta chooses Avalon
Alvesta, whose product range includes 10 Gbit/s four-channel transceivers for short-reach (100 and 300 m) applications, has selected Avalon Photonics as its source of VCSEL arrays. "The performance and reliability of Avalon s VCSELs has enabled Alvesta to deliver in volume the lowest-cost 10 Gbit/s optics solution in the market," said Robert Nalesnik, Alvesta s VP of marketing. "Four-channel VCSEL-based parallel optics provide compelling value for telecom and datacom backplane and multi-vendor optical interconnects." Background information Pump lasers provide higher powers

Just before OFC, Furukawa Electric announced a venture with Mitsui Chemical to produce high-power 980 nm laser chips. A new company, MC Fitel, will be established with 65% of the investment coming from Furukawa and the remainder from Mitsui. Headquartered at Furukawa s site in Chiba, Japan, the venture will be led by Yoshikazu Ikegami of the company s Optical Devices division. The alliance will exploit Furukawa s expertise in output signal stabilization and Mitsui s chip technology to create a de-coupled confinement heterostructure chip with an output power of more than 300 mW.

Furukawa and Mitsui have been jointly developing high-power 980 nm chips since October 2000. MC Fitel aims to address rapidly the increasing market demand for 980 nm pump lasers.

Corning enhances power
Corning Lasertron demonstrated new levels of power and reliability from its pump lasers. The company gave a live demo of the CLT3.0, a 980 nm pump chip that delivers up to 600 mW of kink-free power and 500 mW of operating power over the lifetime of the product - doubling the power of Corning s current chip. The company also demonstrated a new 14XX nm Raman pump providing 420 mW of power.

Both chips are manufactured using a precision-etch process developed at Lasertron s site in Bedford, MA. "The process increases our chip power by an average of 30%, and chip-power efficiencies by more than 10%," said product manager David Bean. "The improvement also injects outstanding consistency into our process."

The process has been fully qualified with the 980 nm Optilock CLT2.2 pump chip, and has logged more than 1.5 million device-hours in reliability testing. Full qualification and acceptance have been received in the 250 mW wavelength-stabilized Gibraltar 2 package. The firm has now introduced a fifth-generation Gibraltar 3 package, which is epoxy- and flux-free. The 980 nm version includes a getter to ensure high reliability.

Axcel unveils 980 nm chips
Founded in mid-2000, Axcel Photonics manufactures diode lasers, and revealed its first products - 980 nm pump lasers - at OFC. Available in chip or chip-on-submount form the pumps provide more than 360 mW of kink-free power, says the company, which is also set to introduce a 1480 nm version with up to 300 mW output later this year. Axcel s 980 nm pump has a typical slope efficiency of 0.85 W/A and operating current of 0.5 A. Axcel grows its lasers by MOCVD and performs wafer processing, burn-in and testing at its facility in Marlborough, MA. The company also demonstrated a 980 nm device with 1030 mW of kink-free singlemode output power during OFC.

MSA guarantees packages
Alcatel, JDS Uniphase and Nortel have signed a multi-source agreement (MSA) for 960-980 nm pump lasers in uncooled mini-DIL packages. Targeting the wavelength range, the agreement covers terrestrial EDFAs. The MSA is expected to reduce significantly the size and power consumption of EDFAs used in metro and long-haul networks. Uncooled Mini-DIL pump modules will offer more than 100 mW, and will maintain this performance over the 0-70 °C temperature range.

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