Abstract: A semiconductor laser diode comprises a p-n junction. The p-n junction comprises a substrate, an n-type semiconductor layer, a p-type semiconductor layer, and a quantum well. The quantum well is disposed between the n-type semiconductor layer and the p-type semiconductor layer. The substrate is formed from a first material system, the n-type semiconductor layer is formed from a second material system, the p-type semiconductor layer is formed from a third material system, and the quantum well is formed from a fourth material system. The second material system is different from the third material system. The second material system and the third material system are selected such that there is an increase in the rate of recombinations of the electrons from the n-type semiconductor layer and the holes from the p-type semiconductor layer in the quantum well. This results in a lower turn-on voltage for the semiconductor laser diode.

Abstract: A second-order multi-mode partial distributed feedback (p-DFB) laser having increased electrical-to-optical power conversion efficiency, stabilized wavelength and narrowed emission linewidth. The laser includes an abbreviated grating housed in the laser cavity that is separated from both the front-end and the back-end of the laser facets.

Abstract: The invention provides a grating for a distributed feedback laser having decreased diffraction loss with reduced +/?1 order diffraction and scattering loss resulting from the reduced imperfections in the grating fabrication. In various embodiments, the grating has a low duty cycle wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is less than 0.5. Further, in some preferred embodiments, the invention includes a laser, the laser comprising a distributed feedback laser wherein the laser includes a grating having less diffraction and less scattering loss. In various exemplary embodiments, the grating is further a partial grating, thereby providing increased efficiency resulting from a decrease in first-order diffraction loss due to the grating being separated from the front and rear facets and in some exemplary embodiments being situated at the area of lowest electric filed.