Uncooled 1310nm DFB delivers across wide temperature range

Details of what is billed as the industry's first directly modulated DFB laser to combines ultra-wide bandwidth and high linearity over 25-85°C (without cooling) were revealed by a team from Bookham Technology and Cambridge University's Department of Engineering at last month's OFC conference in Atlanta.

Such lasers were described as being "crucial" to the realisation of the direct transport of analogue microwave/RF signals over fibre for in-building distributed antenna systems in cellular networks and for the growing market in wireless LANs, such as the IEEE 802.11-series standards and HiperLAN.

"The big advantage of going to uncooled directly modulated lasers is that they are cheaper, more compact and efficient," said Kenton White, Advisor, Modulated Sources Technology, at Bookham and the paper's joint author.

"Typically, you can take up to a Watt of power consumption off, and, in terms of packaging, I would say there is a factor of two in area reduction by removing the cooler. Of course, you don't need an expensive, and potentially complex, external modulator taking up more space and power. This could really help optics to move into the wireless area, for example, by solving the big problem of providing low-cost fibre-fed radio access."

"Cost is the key in RF-over-fibre applications in cellular and wireless-LAN distribution," added professor Ian White of the Photonics Group at Cambridge University. "Hence we are focusing on developing new techniques allowing full RF transmission over multimode fibre using uncooled lasers."

The paper also showed that laser diodes developed by Bookham for data communications applications exhibit "record" linearities up to 20GHz frequencies. Broadband spurious-free dynamic ranges of over 100dB.Hz2/3 are demonstrated over this entire range, sufficient for not only wireless but also radar applications.

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