Single longitudinal mode blue-violet laser diode for data storage

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Commercially available blue-violet diodes near 405 nm for Blue-ray and HD-DVD disks lase with multiple longitudinal modes and have thus a sub-millimeter coherence length. Optical data storage technologies requiring coherent interference, such as holographic e.g., will benefit from having a compact blue-violet laser diode source with a long coherence length and some level of wavelength tuning. Prior approaches, such as external cavities with diffraction gratings [1], have been used to generate single longitudinal mode tunable lasers near 405 nm. Such cavities require a very low reflectivity front facet coating, precise alignment, occupy a volume on the order of several cm3 and are prohibitively expensive for any mass markets. In contrast, we propose and experimentally demonstrate an ultra-short external cavity laser based on reflective volume holographic gratings.