| 摘要 |
A laser diode comprises an optically active planar waveguide and a volume refractive index grating for providing distributed optical feedback of stimulated radiation to the waveguide. According to the invention, the grating comprises a stack of alternating thin layers each layer being less than 300 nm. thick) of two materials having different indices of refraction. At least one side of the stack provides a smooth, planar surface composed of the respective edges of each grating layer. The active waveguide, together with optional cladding and separate-confinement heterostructure (SCH) layers, are epitaxially grown atop the smooth grating surface, whereby the respective planes of such layers are substantially perpendicular to the respective planes of the grating layers. The smooth surface of the grating is advantageous in that it promotes good crystalline growth of the subsequently grown layers of the laser diode structure and reduces the number of non-radiative recombination sites. According to a perferred embodiment, the active waveguide material is a multiple quantum well layer which is comprised of alternating layers of p-Al0.7Ga0.3 As and P-Al0.5Ga0.95As, and the two grating materials comprise AlxGa1-zAs, where x is between about 0.04 and 0.3, and Aly, Ga1-yAs, where y is between about 0.4 and 0.8.
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