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Optical components

Dotty Lasers Draw Investment

It's easy, not to mention fun, to mock startup Zia Laser Inc. for having dotty ideas. The company appears to be the only one to date that's brave (or stupid) enough to try to commercialize quantum dots -- microscopic semiconductor particles that emit light (see Zia Laser's Not-so-Dotty Idea).

However, evidence is mounting that Zia might succeed in its venture, the latest news being the company's announcement of a $5.4 million round of funding today (see Zia Laser Grabs $5.4M). This cash comes from Prism Venture Partners and the RWI Group, the same investors that stumped up for Zia's first round of funding back in July 2001 (see Zia Laser Gets $6 Million Seeding).

What's more, Zia has had a paper accepted for the OFC Conference later this month, describing how quantum dot technology can be used to produce lasers that are more stable at high operating temperatures than standard devices. This advance will enable Zia to produce lasers that don't need thermo-electric coolers to operate, which translates into lower-cost transmitters for access and metro markets.

Zia's original plans called for it to develop widely-tunable lasers using quantum dot technology (see Zia Laser Inc.). The wavelength of light from the dots is determined by their size, rather than just the material composition, which makes it easy to produce plenty of light across a broad wavelength range using a single device.

But although its work on tunable lasers continues -- Zia claims to have sampled tunable gain chips to customers -- the company realised that the ability to make uncooled lasers is going to lead to more immediate returns. "The whole idea is to focus on one product at a time, to minimize cash burn," says the startup's COO, Joe Dixon.

Zia Laser is aiming to produce a 10-Gbit/s uncooled 1310nm laser that delivers higher power than ordinary Distributed Feedback (DFB) Lasers at 85° C -- the maximum operating temperature expected of telecom equipment.

Ordinary DFB lasers deliver high powers when they are first switched on, says Dixon. But as current flows through them they heat up, and as they heat up, the output power starts to fall. There are one of two solutions to this problem: either add a cooler to remove heat from the device, or accept the reduced performance. Adding a cooler adds to the expense of the device considerably, but it's the only acceptable solution for DWDM applications.

Quantum dot lasers, on the other hand, emit less power when first switched on, but their power remains virtually constant with temperature. The result is that their performance exceeds that of ordinary DFB lasers at high temperatures. In its OFC paper, Zia will show results from a batch of devices that deliver 3 mW of output power at 100° C -- a temperature that would fry most DFBs.

It's worth pointing out that plenty of vendors are pursuing uncooled laser technology and that it is improving all the time. Major players include Agilent Technologies Inc. (NYSE: A), JDS Uniphase Corp. (Nasdaq: JDSU; Toronto: JDU), which bought Optronx for its uncooled laser technology, and TriQuint Semiconductor Inc. (Nasdaq: TQNT) through its purchase of Agere's opto business (see Agilent Boosts 10 Gig Ethernet ). Then there are startups such as ASIP Inc. (see Startup Has an 'Uncool' Laser).

Zia says that quantum dot lasers have another advantage that could bring down the cost of laser modules still further -- they can be packaged without an isolator. The isolator is included in standard laser packages to prevent light from being reflected at outside facets, such as the fiber face, back into the laser cavity. Light reflected from surfaces other than the laser's two mirrors can interfere destructively with that reflected by the mirrors, reducing the output power and performance. Quantum dots aren't so vulnerable to this effect, says Dixon, so the isolator isn't needed.

All of this leaves the question: If quantum dots are so good, what's stopping other companies from commercializing them? Dixon says it's because Zia has established a reliable epitaxial process for growing good quality quantum dots, and other outfits haven't.

JDS Uniphase has a slightly different view. Although it is interested in quantum dot technology, the company believes there's still plenty of mileage in plain-vanilla 1310nm DFB laser technology. In fact, JDS is claiming that its 1310nm DFBs deliver better performance with Zia Laser's quantum dots. Acording to spokesman Gerald Gottheil, JDS has shipped products that deliver more than 3 mW of output power at 90° C, and demonstrated prototypes with 3 mW at 110° C.

"Quantum dots pose challenges in manufacturing because they require changes to the processes currently used in the industry, and their performance is not yet proven," says Gottheil. "Therefore, for the near-term, JDS Uniphase believes that quantum well technology for uncooled source lasers is preferable due both to manufacturability and performance."

— Pauline Rigby, Senior Editor, Light Reading

For up-to-date information about the coming OFC Conference, please visit Light Reading’s Unauthorized OFC Preview Site

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