Narrow linewidth 1.52 µm InAs/InP quantum dot DFB lasers

We have grown, fabricated, and tested single mode ridge-waveguide distributed feedback lasers utilising InAs/InP quantum dots as the gain medium. The growth of quantum dots on InP substrates allows us to reach the important 1.55 μm telecommunications wavelength range, in this case lasing at 1.52 μm. The quantum dot gain medium was grown using chemical beam epitaxy, and the top cladding regrown after grating patterning using metal-organic-chemical vapour-deposition. No shift in the photoluminescence peak wavelength of the dots was observed following top cladding regrowth. Ridge waveguide lasers were fabricated with ridge widths of 3 μm and cleaved to 500 μm and 1 mm cavity lengths. The facets were coated to provide reflectivities of 65% and 2%. In continuous wave (cw) operation single-mode output was observed with a side mode suppression ratio greater than 61 dB, and an output power of 9.7 mW at an injection current of 150 mA. Operation up to 80°C was achieved. The relative intensity noise was measured to be less than -154 dB/Hz from 10 MHz to 10 GHz, and the optical linewidth to be less than 150 KHz for the best devices.