ABINGDON, U.K. -- Bookham Technology plc (LSE: BHM; NASDAQ: BKHM) will launch at this month’s Optical Fiber Communication (OFC) 2004 Exposition in Los Angeles the industry’s first 2.5Gbit/s directly modulated laser (DML) that is tunable over eight adjacent 50GHz ITU DWDM channels. The LC25FT laser has a 360km reach and is available in 2, 3 and 4mW peak-power versions.
The 360km reach is a record for an eight channel thermally tunable DML, and mounts a serious challenge to the electro-absorption (EA) modulation designs that currently dominate this transmission distance. EA modulated lasers are more expensive than the new device, which is better suited to automated card set-up, tuning and high optical output power.
The LC25FT uses three key Bookham technologies to achieve its 50GHz compliance: an ultra-low-chirp thermally tuned DFB laser, co-packaged with a wavelength locker, and a cooler technology that reduces wavelength drift as the device case temperature changes. Bookham’s unique integration and packaging technologies are crucial to realising the high-performance device within a small 14-pin butterfly package with optical isolator.
“A key to the design of the laser is to maintain the reach performance over full range of laser tuning temperatures,” says John Severn, Product Line Manager for Directly Modulated and EA Lasers, Bookham Technology. “A problem with many lasers on the market is that, when you change the wavelength, the laser dynamics change and the reach falls. The LC25FT, however, keeps a constant-reach performance over a large temperature range.”
50GHz tunability has significant benefits for carriers and systems vendors, especially for metro and regional metro DWDM, and CATV and multiservice networks. Reducing the channel spacing from the commonly used 100GHz to 50GHz doubles the number of channels available, relieving capacity bottlenecks and allowing increased use of wavelength routing and network meshing for remotely provisioned wavelength services and network resilience, as well as giving an overall increase in traffic handling.
Because an LC25FT can be tuned over eight different wavelengths, 87% fewer laser wavelength-code types are needed in manufacturing and sparing inventories. And it makes one-for-eight optical-channel back-up possible, overcoming the exorbitant cost of providing full one-for-one back-up to cover an optical linecard failure.
50GHz tunability in the metro also gives carriers greater flexibility in network design, as it makes it easier to share fibre between the metro and long-haul networks, which commonly use 50GHz DWDM.
“Perhaps surprisingly, a laser that tunes over part of the optical window offers many advantages over lasers that tune over the full band,” says Severn. “It has a simpler technology, making the laser lower cost, simpler to implement, more reliable, smaller in size and with lower power dissipation. These are important features in the cost- and space-sensitive metro and multiservice markets.”