Demonstration of an InGaN/GaN-based optically pumped multiquantum well distributed feedback laser using holographically defined third-order gratings

We demonstrate an optically pumped InGaN/GaN-based multiquantum well distributed feedback laser in the blue spectral region. The third-order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion-beam etching. When aligning the stripe-shaped pump beam either parallel or perpendicular to the grating grooves, we found a considerably lower pumping threshold, higher slope efficiency, a slightly longer emission wavelength, and a much narrower linewidth for the geometry with the pump beam orthogonal to the grating lines. A nearly constant emission wavelength of 400.85 nm and a linewidth of 0.7 Å were observed under various pump intensities. To the best of our knowledge, this is the narrowest linewidth ever reported for an optically pumped device in this material system.