Distributed-feedback laser array provides selectable WDM wavelengths

Researchers at Fujitsu Laboratories and Fujitsu Quantum Devices (both Atsugi, Japan) have designed and fabricated a wavelength-selectable laser by monolithic integration of eight distributed-feedback (DFB) lasers into a quarter-wavelength-shifted, eight-channel DFB array. The 0.6-mm-wide, 2-mm-long device demonstrated performance characteristics comparable to those of discrete DFB lasers. Fiber-coupled output power climbed to +10 dBm with good uniformity, narrow linewidth, and a side-mode suppression ratio of up to 50 dB. Emission wavelengths for the array started at 1535 nm and increased by 3.18 nm for each successive DFB laser, with a standard deviation for wavelength spacing of 0.12 nm. The mean threshold current was 7.9 mA, with a 0.3-mA standard deviation.

The DFB laser array was integrated with a compact, low-loss multimode-interference combiner circuit and a semiconductor optical amplifier. The entire device was fabricated in a high-index-contrast buried-waveguide structure to minimize the insertion loss and length of the optical combiner. The high-index contrast also allowed compact fabrication of the bent waveguides that coupled the DFB laser array to the combiner. The waveguide was fashioned out of a 200-nm-thick gallium indium arsenide phosphide layer with a 1.3-µm bandgap. Contact Martin Bouda at [email protected]. — Paula M. Noaker