Coherent High Q Micro-resonator Blue Light Sources – COMBO

A complete characterization of the linear and third order nonlinear response of high-Q resonators will be investigated in the 400- 420 nm range. This study will be held with the use of a cavity ringdown technique extensively developed at the FOTON Institute and broadly adopted by various groups for infrared high-Q resonators characterizations. This technique enables within a single acquisition to determine intrinsic losses, dispersion, coupling regime and even nonlinear properties such as Kerr effect.
This study will allow the lack of knowledge about the linear and nonlinear optical properties in high-Q WGM resonators in the blue range to be overcome.

We demonstrate a compact and low-cost all-fiber-based locking setup for fast-frequency-noise suppression of a 420 nm external-cavity diode laser. Frequency noise reduction in the 100 Hz to 300 kHz range is demonstrated up to 30 dB associated with a linewidth narrowing from 800 kHz to 35 kHz for 10 ms integration time. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.

Two main breakthroughs are targeted: the first demonstration of a Kerr frequency comb in the blue range using a high-Q resonator; and an electrically-pumped sub-kHz linewidth single mode Fabry-Perot (SFP) laser based on resonant optical feedback. Combining these two contributions should yield to the demonstration of a compact blue Kerr frequency comb generator.

G. Perin, et al. «?Stabilisation d'une diode laser à cavité externe émettant à 420 nm sur un anneau de fibre?» JCOM 2021 (Paris)

G. Perin, et al. «?Stabilisation d'une diode laser à cavité externe émettant à 420 nm sur un anneau de fibre?» JNOG 2021 (Dijon)

The development of compact coherent sources has been strongly triggered by the emergence of optical telecommunications in the 70’s. Continuous wave single mode lasers or frequency comb sources are unavoidable photonic tools for a wide variety of applicative domains ranging from trace gas detection to optical clocks. A trend consists in harvesting the know-how acquired in the near infrared band to spread it to surrounding regions of the optical spectrum. The COMBO project is part of this process addressing the blue range of the spectrum between 405 and 480 nm. Linear and nonlinear spectroscopies based on coherent blue sources are relevant for metrology sensing, and trace gas detection. Since few years, the optical telecommunication community manifest a growing interest for the development of compact blue laser for visible light communication and underwater transmission. To be commercially viable, sources have to address several compromises regarding the size, the price, the weight, the power, the coherence and the bandwidth. Nowadays no compact and coherent sources exist in that wavelength domain. Currently, blue single frequency lasers are based on frequency doubling of solid state laser in the near infrared region. This approach gives interesting performances but are bulky and energy consumer. Commercial external cavity diode lasers (ECDL) exist but are costly and not compact. Comb frequency sources in the blue domain are usually based on a bulky 800 nm femtosecond Ti:Sapphire laser frequency doubled in a nonlinear media. An alternative approach to generate compact coherent sources (lasers or frequency combs) can be based on the use of high quality (Q) factor whispering-gallery mode resonators (WGMRs). WGMR based coherent sources in the infrared region have been demonstrated with even commercial sources already available.
COMBO aims to unveil the opportunity to develop coherent sources by use of whispering-gallery mode resonators in an unexplored wavelength range. The ambition of the COMBO project is to develop a WGM resonator platform in the blue range (405-480 nm) for the demonstration of compact single frequency laser diodes and blue Kerr frequency comb. The project is divided in three main objectives. The first objective will draw up a panorama of the linear and nonlinear properties of WGMR in the blue range. A particular focus will be done on fluoride crystalline resonators identified as best candidates for the realization of either linear or nonlinear optical functions. Indeed, the second objective consists in the demonstration of WGMR based laser stabilization and narrowing taking advantage of the impressive linear properties of such resonators as a large Q factor in excess to 10^9 and a Finesse over 10^5. The third objective involves the study of degenerate four-wave mixing leading to frequency comb generation in high-Q WGMRs.
Two main breakthroughs are targeted: the first demonstration of a Kerr frequency comb in the blue range using a high-Q resonator; and an electrically-pumped sub-kHz linewidth single mode Fabry-Perot (SFP) laser based on resonant optical feedback. Combining these two contributions should yield to the demonstration of a compact blue Kerr frequency comb generator.