October 2021
Spotlight Summary by Francesco Morichetti
Hybrid-integrated diode laser in the visible spectral range
Integration of new laser sources on a chip has always been considered a key milestone in the evolution of photonic integrated platforms. With respect to systems with external light sources, having the laser on board not only enables higher device portability and scalability, but it also provides better performance in terms of power stability and linewidth. In the near-infrared range, a well-established approach exploits the hybrid-integration of a semiconductor amplifier with a spectrally-selective passive feedback chip. This strategy is much more challenging for the visible range, where two-photon absorption and roughness-induced scattering loss are critical issues for the realization of the passive feedback chip. This is why the step towards a visible-light hybrid-integrated laser was still waiting to be done.
In their work, Franken and coworkers achieved this goal by integrating an AlGaInP optical amplifier with an ultra-low-loss (0.07 dB/cm at a wavelength of 685 nm) feedback chip realized on a Si3N4 platform. The feedback chip boasts high quality factor (Q = 9.5 · 105) microring resonators arranged in a highly frequency-selective Vernier architecture and provides an effective optical cavity roundtrip length of 49 cm. The result is a single longitudinal mode laser with a linewidth of only 2.3 kHz, wavelength tuneability of 10.8 nm around 684.4 nm, and an output power of 4.8 mW (at a pump current of 90 mA).
And this is just the beginning. Thanks to the wide spectral transparency of Si3N4 we can expect that solutions covering different portions of the visible range will be coming soon. Chip-scale multi-color laser arrays are not too far, and they are likely to open new avenues in many applications, like sensing, imaging, metrology, and quantum processing.
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In their work, Franken and coworkers achieved this goal by integrating an AlGaInP optical amplifier with an ultra-low-loss (0.07 dB/cm at a wavelength of 685 nm) feedback chip realized on a Si3N4 platform. The feedback chip boasts high quality factor (Q = 9.5 · 105) microring resonators arranged in a highly frequency-selective Vernier architecture and provides an effective optical cavity roundtrip length of 49 cm. The result is a single longitudinal mode laser with a linewidth of only 2.3 kHz, wavelength tuneability of 10.8 nm around 684.4 nm, and an output power of 4.8 mW (at a pump current of 90 mA).
And this is just the beginning. Thanks to the wide spectral transparency of Si3N4 we can expect that solutions covering different portions of the visible range will be coming soon. Chip-scale multi-color laser arrays are not too far, and they are likely to open new avenues in many applications, like sensing, imaging, metrology, and quantum processing.
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Article Information
Hybrid-integrated diode laser in the visible spectral range
C. A. A. Franken, A. van Rees, L. V. Winkler, Y. Fan, D. Geskus, R. Dekker, D. H. Geuzebroek, C. Fallnich, P. J. M. van der Slot, and K.-J. Boller
Opt. Lett. 46(19) 4904-4907 (2021) View: Abstract | HTML | PDF