Dispersion in nonlinear interferometry: implications for optical coherence tomography with undetected photons

TL;DR

This paper investigates how dispersion affects nonlinear interferometry used in optical coherence tomography with undetected photons, proposing a novel empirical method to compensate for dispersion and significantly improve imaging resolution.

Contribution

It introduces a new empirical numerical dispersion compensation technique based on phase extraction from time-domain data for OCT with undetected photons.

Findings

Achieved a 2.2-fold improvement in axial resolution.

Demonstrated the effectiveness of the proposed compensation method.

Outperformed alternative numerical correction techniques.

Abstract

Nonlinear SU(1,1) quantum interferometers based on non-degenerate optical parametric down-conversion exhibit strong unbalanced group velocity dispersion (GVD). This feature is intrinsic to this type of interferometer as correlated photons of vastly different frequencies propagate through a dispersive nonlinear crystal; consequently, the dispersion arises from the source itself. The resulting GVD degrades the axial point-spread function (PSF) in optical coherence tomography (OCT) with undetected photons; and physical compensation is less straightforward, in particular for non-degenerate broadband regimes due to the limited number of suitable materials. In this contribution, we analyze dispersion in bulk nonlinear interferometry and describe its implications for OCT imaging. Aspects of hardware compensation are addressed, and a novel empirical numerical method of compensation is proposed. The approach is based on the extraction of the phase component directly from the time-domain modality (high precision linearized quantum Fourier transform infrared spectrometer) and its injection into the mid-IR spectral-domain OCT signals (central wavelength of around 3770 nm) before the Fourier transform. The proposed method is compared with an alternative numerical technique. The results demonstrate a 2.2-fold improvement in axial resolution and outperform the alternative correction method in overall imaging performance.