Broadband wavelength control for optical parametric oscillation in radially-poled whispering gallery resonators

We demonstrate that optical parametric oscillators (OPOs) in radially poled whispering gallery resonators (WGRs) can be used for broadband infrared spectroscopy. Identifying the whispering gallery modes of pump, signal and idler waves by comparing the cavity spectra and the tuning capabilities with theoretical estimates allows us to predict the generated wavelengths in the spectral range 1.7-2.5 µm. Controlled wavelength tuning over more than100 nm is achieved by increasing the temperature of the WGR in well-defined steps, addressing one longitudinal mode after the other and keeping the radial and polar pump mode fixed.