Over in Denmark, a team of six scientists claims to have hit on a way of turning Vertical Cavity Surface Emitting Lasers (VCSELs), which are traditionally low-power devices best suited to datacom, into high-power lasers suitable for long-distance telecommunications. And they've started up a company to commercialize their work.

Alight Technologies A/S (Website live but under construction) is yet another spinoff from the COM Research Center, Denmark Technical University. Previous ventures include Ionas, and Cisilias, which have now merged into a single entity called NKT Integration A/S, as well as Crystal Fibre A/S and Micro Managed Photons A/S.

"We think that with our technology we can help bring VCSEL transmitters into high-speed telecom markets and optical storage," claims Alight's CEO John Erland Østergaard. As VCSELs can be significantly less expensive to manufacture than other types of laser, this could be a big deal.

The standard problem with VCSELs, says Østergaard, is that the amount of light and the optical distribution, or "mode," of that light cannot be controlled independently. They are both defined by the aperture of the laser -- the region where light exits the top of the laser (not an actual hole).

It's possible to make higher-power lasers by increasing the size of the aperture -- the power per unit-area produced by the semiconductor is a fixed amount. But as the size of the aperture gets larger, light starts to become multimode. This is undesirable because different modes travel at slightly different speeds in optical fiber, leading to increased Chromatic Dispersion and Polarization Mode Dispersion (PMD). It also makes it more difficult to couple the light into singlemode fiber.

Alight says it can overcome this problem using photonic crystals to implement what it calls "transverse optical-mode control." In other words, it etches microscopic holes into the surface of the laser which constrain the light to be singlemode, even though the aperture is much larger than normal.

Other teams around the world have experimented with etching patterns of holes into the surface of VCSELs but, Østergaard contends, they didn't make the holes the right size to create a true photonic crystal effect. This effect only occurs when multiple reflections in the etched material combine to make it behave like a mirror (see The Hole Thing or The Shape of Things to Come, for example). If the dimensions are not right, the holes merely act like a material with an average refractive index.

Alight has just closed an agreement with the Technical University's technology transfer unit, DTU-Innovation, for seed funding of €0.8 million, and is hoping to increase that total to €1 million (US$0.98 million) with additional funding from the Danish Growth Fund.

Having spent a lot of time perfecting its prototypes, Alight plans to present a paper on its work at the OFC conference next March. It held off from publication until patenting issues were sorted out.

The next step, says Østergaard, is to "get out there and offer this technology to 1310nm VCSEL manufacturers."

— Pauline Rigby, Senior Editor, Light Reading
www.lightreading.com