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Visible diode lasers with wide wavelength tunability and narrow spectral linewidth are of high importance in bio-photonics and metrology. Hybrid integrated diode lasers, using waveguide circuits for spectrally selective feedback, provide wide tunability and sub-100-Hz intrinsic linewidths in a robust chip format. So far, these lasers have only been realized at infrared wavelengths. Here we present the first operation of a hybrid integrated diode laser in the visible. The laser, formed by a diode amplifier which is hybrid integrated with a Si3N4 ring-resonator based feedback circuit, is tunable over 11 nm around 685 nm and delivers 5 mW output power.

We demonstrate a hybrid integrated and widely tunable diode laser with an intrinsic linewidth as narrow as 40 Hz, achieved with a single roundtrip through a low-loss feedback circuit that extends the cavity length to 0.5 meter on a chip. Employing solely dielectrics for single-roundtrip, single-mode resolved feedback filtering enables linewidth narrowing with increasing laser power, without limitations through nonlinear loss. We achieve single-frequency oscillation with up to 23 mW fiber coupled output power, 70-nm wide spectral coverage in the 1.55 $\mu$m wavelength range with 3 mW output, and obtain more than 60 dB side mode suppression. Such properties and options for further linewidth narrowing render the approach of high interest for direct integration in photonic circuits serving microwave photonics, coherent communications, sensing and metrology with highest resolution., Comment: 13 pages, and 11 figures

We present an integrated hybrid semiconductor-dielectric (InP-Si$_3$N$_4$) waveguide laser that generates frequency combs at a wavelength around 1.5 $\mu$m with a record-low intrinsic optical linewidth of 34 kHz. This is achieved by extending the cavity photon lifetime using a low-loss dielectric waveguide circuit. In our experimental demonstration, the on-chip, effective optical path length of the laser cavity is extended to 6 cm. The resulting linewidth narrowing shows the high potential of on-chip, highly coherent frequency combs with direct electrical pumping, based on hybrid and heterogeneous integrated circuits making use of low-loss dielectric waveguides.

Epitaxial growth of rare-earth-ion-activated KY(1-x-y)Gd(x)Lu(y)(WO4)2 co-doped thin layers onto KY(WO4)2 substrates has enabled lattice-matched waveguides with high refractive-index contract and large variation of the active rare-earth-ion concentration. In Yb3+-activated micro-structured channel waveguides, we demonstrated lasers with 418 mW of continuous-wave output power at 1023 nm and a slope efficiency of 71% versus launched pump power at 981 nm. Channel waveguide lasers operating on the 981-nm zero-phonon line were demonstrated under pumping at 934 nm with an output power of 650 mW and a slope efficiency of 76% versus absorbed pump power. Lasing with a record-low quantum defect of 0.7% was achieved. In a feasibility study, a device comprising a tapered active channel waveguide and a passive planar pump waveguide, fabricated by multi-layer growth of lattice-matched layers, was demonstrated as a laser by diode-side pumping with a high-power, multi-mode diode bar. This approach offers the potential for significantly increased output powers from channel waveguide lasers. Tm3+-activated channel waveguide lasers demonstrated a maximum output power of 300 mW and slope efficiency of 70%, when pumping near 800 nm. Lasing was obtained at various wavelengths between 1810 nm and 2037 nm. These lasers were operated with resonators exploiting either butt-coupled mirrors, providing only a non-permanent solution, or based on Fresnel reflection at the waveguide end-facets, resulting in laser emission from both waveguide ends and without control of the laser wavelength. Currently we are inscribing Bragg gratings into the top cladding to provide a stable resonator configuration that allows for effective wavelength selection.