Optical components

Cielo Pushes the Limits on Lasers

One of the first components to be based on 1310-nanometer vertical cavity surface emitting lasers (VCSELs) was announced by Cielo Communications Inc. earlier this week, suggesting that this type of technology is about to bear fruit (see Cielo Unveils OC192 Transponder).

Cielo’s first device, a 10-Gbit/s serial transponder, promises to be lower in cost than equivalent products based on older technology, such as 1310nm distributed feedback (DFB) lasers. It also promises to deliver higher-quality light.

And that, as they say, is just for starters. Cielo is planning to launch a second product based on an array of its 1310nm VCSELs next Monday (June 25). It’s an optical interconnect, something capable of linking together equipment at speeds of up to 30 Gbit/s .

Shorter wavelength VCSELS, at 850nm, have already become the lasers of choice for short transmissions because of their low cost and high light quality. Now it looks as though their success could be repeated at longer wavelengths (see Laser Blazers).

The new VCSELs will address the segment of interconnect market that that goes beyond 300 meters -- the distance limit for 850nm devices -- says Jeff Bisberg, Cielo's product marketing manager. Most central offices are already running optical links at 1310nm. Cielo's products will offer a cheaper solution, he says.

"It's not just the cost of the VCSEL, it's the fact that it enables a low-cost manufacturing technique to put the module together," says Bisberg. The tolerance of aligning a VCSEL output beam and a fiber is about 1 micron, which is achievable with automated manufacturing machines. That has big implications for throughput, he says.

Another big cost saver is the fact that VCSELs can be directly modulated, eliminating the need for an external modulator. As a result of this, it also consumes less power. "Less power means less heat and greater reliability for all components," Bisberg notes.

The main drawback of Cielo's 1310nm VCSEL is its low power, resulting from the use of gallium arsenide nitride to make it. This limits its maximum reach to 15 kilometers, according to Bisberg.

Cielo's 10-Gbit/s serial transponder takes in parallel signals at 622 Mbit/s and muxes them up to a single OC192 (10 Gbit/s) channel. On the transmit side, it contains jitter filters, high-speed serializer, laser driver, and a VCSEL. On the receive side, it incorporates a pin photodiode, transimpedance amplifier, limiting amplifier, clock and data recovery (CDR) circuit, and a deserialiser.

The transponder will be released in versions that support the Sonet/SDH, Ethernet, Fiber Channel, and Optical Internetworking Forum (OIF) Very Short Range (VSR) Sonet standard, OIF-SFI4-01.0. It will also comply with the 200-pin small footprint OC192 transponder multisource agreement. It is priced at $8,000 in small volumes and will start sampling to selected customers in Q3 2001.

The array products are less complex internally, containing no mux/demux capabilities or clocking. They comprise either 8 or 12 channels, operating at up to 2.5 Gbit/s per channel, and channels can act independently. The units are priced at less than $600 per channel and should start sampling this summer.

If Cielo can stick to its schedule, then it looks like it will be first to market. However, shipping samples is one thing and convincing system vendors to buy large quantities of VCSEL-based components is another, according to Warner Andrews, VP of marketing at Picolight Inc., a competitor. Customers will want plenty of reliability testing and proof of being able to manufacture lasers in large volumes before they'll commit, he says.

Picolight has an edge in this respect because it's already a big supplier of tranceivers and other components based on 850 nm VCSELs, Andrews contends. Picolight demonstrated a 1310 nm VCSEL at the OFC conference earlier this year and expects to ship samples of first products by the end of 2001, Andrews says.

"We're actually pleased that there's an entrant [like Cielo] in this space because it helps validate the market," he adds. Other players that have recently announced 1310 nm VCSEL developments include E2O Communications Inc. (see E2O Claims VCSEL 'Milestone').

-- Pauline Rigby, Senior Editor, Light Reading http://www.lightreading.com"

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