Resonance scanning interferometer for group delay dispersion measurements

Accurate measurements of group delay (GD) and group delay dispersion (GDD) characteristics play a crucial role in achieving top performance of ultra-fast optical systems based on dispersive mirrors (DM). Currently GD and GDD measurements are typically performed with white-light interferometers (WLI). However, the resolution and accuracy of WLI is not sufficient for many present-day challenging applications, especially in cases when ultra-broadband spectrum spanning over more than an optical octave is considered, or very high levels of dispersion need to be controlled. An alternative approach for GD and GDD measurements based on inter-mirror cavity resonances was developed. The idea to use setups similar to Fabry-Pérot and Gires-Tournois interferometers for this purpose was initially proposed in. In that work a single measurement with a fixed spacer thickness was performed. In order to increase the spectral resolution, it was necessary to increase the spacer thickness. However, that caused a rapid decrease of the measured signal level and soon the resonance peaks became masked by unavoidable noise. A “golden middle” spacer thickness often was unable to provide a good balance between resolution and signal-to-noise ratio. In contrast, this paper carried out measurements at a set of different spacer thicknesses, then the acquired data was combined together and processed using a regularization theory of the solution of inverse problems.