At Alcatel, engineers have developed a laser that can be mass-produced while still providing customized wavelengths that are stable with temperature. This is achieved by using a single basic laser with an interchangeable external cavity to provide the amplification and set the wavelength. So far, researchers have demonstrated an average output power of 1 mW over four different wavelengths in the C-band, and a modulation speed of 622 Mbit/s. With optimization of the electrical lines, researchers said, the laser should work at 2.5 Gbit/s.1
Standard indium phosphide (InP) lasers are coupled into a lensed fiber. These components are held in a silicon mount that includes a V-groove so that fibers can be aligned passively, and then packaged in an MT-connector. The other half of the system is a fiber Bragg grating that controls the emitted wavelength.
To give the system its stability with temperature, the team used two materials with different thermal-expansion coefficients: as one expands, the other contracts, thus keeping the fiber Bragg wavelength relatively constant. This doesn't work to 100%: the thermal behavior of the two materials does not quite match perfectly (see figure). But the mode-hopping and wavelength changes that result do not significantly add to the overall wavelength variation, which is less than 50 pm.
The Alcatel team showed that the generic InP device could be used to produce a consistent output at 1530, 1537, 1550, and 1560 nm. For all of these, the threshold current was below 9 mA, and the efficiency above 0.11 W/A. In other experiments, researchers were also able to show that, for temperatures from 0°C to 70°C, the transmission penalty compared to the conventional device is just 0.5 dB (over 90 km and at 6.22 Mbit/s) for the four wavelengths.
For more information contact Arnaud Leroy at arnaud.leroy@alcatel.fr.
Sunny Bains
REFERENCE
- A. Leroy et al., Elect. Lett. 37 (16) 1012 (Aug. 2, 2001).
