Precise and accurate wavelength calibration of spectrographs is essential for key science cases, e.g. the search for extrasolar planets, a possible variation of fundamental constants and the direct observation of cosmic expansion.
A crucial tool for this are laser frequency combs (LFCs), directly linking the accuracy of atomic clocks to optical laser lines.
However, strong material dispersion and large spectral separation from the established infrared laser oscillators so far prevent the use of LFCs for spectrograph calibration in the blue and UV part of the spectrum. At OHP/SOPHIE, we demonstrated for the first time the calibration of an astronomical spectrograph using an astrocomb in the ultraviolet spectral range below 400nm. Key technology used were nano-fabricated, periodically-poled waveguides in lithium niobate photonic chips, fed by either a robust infrared electro-optic comb generator or a chip-integrated microresonator comb. In an end-to-end test, we could demonstrate stable and accurate LFC-based spectrograph calibration, showcasing a viable path towards precision wavelength calibration of spectrographs in the ultraviolet, crucial e.g. for the future ELT/ANDES.
Precision astronomical spectroscopy is vital for seeking life beyond Earth and often relies on detecting very small wavelength shifts over years. Precision of these instruments are ensured by regular wavelength calibration and laser frequency combs stabilized with frequency standards have recently emerged as suitable sources. In this work, we demonstrate wavelength calibration of an astronomical spectrograph in ultraviolet spectrum below 400 nm. This is achieved using second- and third- order nonlinear effects in thin-film, periodically poled lithium niobate waveguides with an infrared electro-optic comb generator at 18 GHz.
This conference presentation, “Parametric phase-sensitive amplification in silicon nitride waveguides” was recorded for the Nonlinear Optics and its Applications 2022 conference at SPIE Photonics Europe 2022.
Many linear and nonlinear optics applications rely on micro-resonators (MRRs) with carefully designed dispersion and coupling rate coefficients. These parameters are however challenging to measure for MRRs based on high-confinement optical waveguides. In this paper, we report on the use of optical frequency domain reflectometry (OFDR) for the measurement of group velocity dispersion (GVD), coupling coefficients and round-trip loss, in high-Q (Qi ∼ 0.3 × 106) silicon-rich nitride MRRs. This technique allows for retrieving the GVD coefficients, intrinsic losses and coupling coefficients for each transverse mode in the resonator, thus providing very valuable feed-back information from experiments to the design flow step.
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