光電所所訊

Collinear and non-collinear multi-wavelength optical parametric generation in 1D PPLT

Professor Lung-Han Peng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所彭隆瀚教授

We demonstrated multiple wavelengths optical parametric generation (OPG) from a single grating, one dimensional periodically poled lithium tantalate crystal. Such OPG spectra are found in continuous spatial positions symmetrical to the collinear direction, with decreasing signal and increasing idler wavelengths, associated with decreasing powers when the far-field angle increases. These observations were ascribed to the simultaneous collinear and non-collinear optical parametric generation (OPG) processes due to the pump intensity and the resultant wavelength-dependence on the angular bandwidth of the parametric gain.

This work was collaborated with Prof. Boudrioua of U. Paris 13, France and Prof. Simohamed of´ Éole Militaire Polytechnique (Algeria)

Fig. 1. Spatial dispersion of the generated spectrum

Fig. 2. Generated OPG spectra recorded at different symmetrical spatial positions

Fig. 3. Calculated single-pass gain spectra and measured signal wave intensities

Ref: M. Lazoul, A. Boudrioua, L. M. Simohamed, A. Fisher, and L.-H. Peng, “Simultaneous collinear and non-collinear parametric generation in 1D single grating periodically poled lithium tantalate,” Appl. Phys. B 110, 459 (2013).

Spectroscopic measurement of absorptive thin films by spectral-domain optical coherence tomography

Professor Sheng-Lung Huang's Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所黃升龍教授

A non-invasive method for measuring the refractive index, extinction coefficient and film thickness of absorptive thin films using spectral-domain optical coherent tomography is proposed, analyzed and experimentally demonstrated. Such an optical system employing a normal-incident beam of light exhibits a high spatial resolution. There are no mechanical moving parts involved for the measurement except the transversal scanning module for the measurement at various transversal locations. The method was experimentally demonstrated on two absorptive thin-film samples coated on transparent glass substrates. The refractive index and extinction coefficient spectra from 510 to 580 nm wavelength range and film thickness were simultaneously measured. More info can be found at Optics Express, 22, No. 5, pp. 5675–5683, 2014.

Figure: The dispersions of index refraction and extinction coeff. of a yellow (a, b) and a green (c,d) color filters.