Statically scanned single and tandem low-coherence interferometers

Abstract

Statically scanned single and tandem Michelson interferometer configurations are compared for the remote measurement of thermally induced group delay change in optically dispersive glass samples. A broadband tungsten filament bulb was used to illuminate the single interferometer, and a much narrower spectral bandwidth superluminescent diode (SLD) was used to illuminate the tandem interferometer. For a BK7 glass sample, measurements of thermally induced group delay changes were made with <0.5 fs root mean square error for optical path delay (OPD) scan lengths of only 260 µm when applied to low-coherence interferograms with signal-to-noise ratios as low as 6.5 dB. These results demonstrate the power of dispersive Fourier transform spectrometry (DFTS) applied to noisy, dispersion distorted low-coherence interferograms captured with non-mechanical, short path length scans. Further, following experimentally observed source bandwidth-induced measurement resolution limitations between the different illuminating sources, simulations were performed to examine this feature.