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We present hybrid-integrated extended cavity diode lasers tunable around 637 nm, with a gain-wide spectral coverage of 8 nm. This tuning range addresses the zero-phonon line of nitrogen-vacancy centers and includes the wavelength of HeNe lasers (633 nm). Best performance shows wide mode-hop free tuning up to 97 GHz and a narrow intrinsic linewidth down to 10 kHz. Also, the maximum output power is 2.5 mW in a single-mode fiber, corresponding to an on-chip power of 4.0 mW. Full integration and packaging in standard housing with fiber pigtails provide high intrinsic stability and enable integration into complex optical systems.
Winkler et al. (Tue,) studied this question.