Supercontinuum generation in low-loss chalcogenide waveguide and its application to spectroscopy

Abstract

The supercontinuum generation (SCG), which has broad bandwidth and high spatial coherence enabled the applications into fields such as spectroscopy, optical clock, and tomography. As a media for SCG, the waveguides using various nonlinear materials have been attracting attention. However, it is still challenging in many cases to develop the fabrication process of each material and to engineer dispersion by controlling the dimension of the waveguide. Our research group had previously implemented a high-Q resonator by depositing a non-linear material on a wetetched silica structure, which does not require direct etching of nonlinear material film. In this paper, we propose that this platform can be used as the media for SCG as well as a low-loss waveguide.

For the broadband SCG, the $As_2S_3$ film waveguide was delicately designed and fabricated using the proposed platform. we experimentally demonstrated that the 100 nm bandwidth of the pulse can be extended to 1050 2700 nm (more than 1.5 octaves), by pumping the pulse whose energy and center wavelength is 77 pJ and 1560 nm respectively. Second, we demonstrated that the SCG can be utilized for the quantification of the gas. We detected the CO gas by transmitting generated supercontinuum into CO gas-filled cell. We also quantified the pressure of the gas with the error of 2.36 %, using cepstrum analysis and post-processing such as bandpass filtering. Finally, we demonstrated that the suggested waveguide platform can be also exploited for SCG in the midinfrared region. We showed that a temporally coherent supercontinuum can be generated even in the region beyond 4000 nm, by injecting a pulse with a center wavelength of 2350 nm into a highly nonlinear $As_2S_3$ film waveguide. In this paper, we provide simulation and the initial experimental demonstration of SCG extending to 3400 nm.