Monolithic integration of a multiwavelength laser array associated with asymmetric sampled grating lasers

We present a novel approach for a monolithically integrated multiwavelength laser array based on asymmetric sampled grating lasers. The asymmetric sampled grating laser combines sampled gratings of different periods with an index shifter to utilize the first-order reflection for lasing operation. With this structure, a simple fabrication procedure as well as high yield could be achieved without using complex and time-consuming e-beam lithography for multiperiod gratings. With numerical analysis based on a transfer matrix method, the effect of grating strength and mirror coating was analyzed to improve single-mode and power extraction performance. By using high-reflection/antireflection coatings on both facets, it was shown theoretically that high-power extraction efficiency as well as high single-mode yield was achieved. A four-channel laser array with 400-GHz wavelength spacing was fabricated and its operation at designed wavelengths was demonstrated. The individual laser showed a threshold current of 9-13 mA and a slope efficiency of around 0.21 W/A. A high sidemode suppression ratio over 44 dB was observed as well.