ImPhys Colloquium | Juan P. Torres | Feb 14

Nonlinear interferometers for optical coherence tomography

In the last few years there has been a growing interest in the use of nonlinear interferometers for imaging, sensing, spectroscopy, microscopy and optical coherence tomography (OCT). While standard interferometers are based on the use of beam splitters, nonlinear interferometers contain several optical parametric amplifiers.

OCT is a highly successful 3D imaging technique that was put forward in 1991. Our group has developed experimentally some OCT schemes based on nonlinear interferometers that we will discuss here. Standard OCT schemes make use of a Michelson interferometer, and achieve high axial resolution using light with a large bandwidth. Some of the OCT schemes based on nonlinear interferometer that we have developed rely on the idea of induced coherence, a particular class of nonlinear interferometer originally introduced the very same year than OCT. Other configurations are based on a SU(1,1) configuration. We will show OCT schemes based on both induced coherence and SU(1,1) configurations

Most experimental demonstrations of nonlinear interferometers have been done in the low parametric gain regime, where the low energy available requires long integration times to achieve high quality images. In this regime one needs to use single photon counting modules or high-sensitive CCD cameras for signal detection. But nonlinear interferometers can also work in the high parametric gain regime. We show an example of OCT scheme that works in this regime. For imaging and sensing applications, this scheme promises to outperform previous experiments working at low parametric gain, since higher photon fluxes provide better sensitivity and lower integration times for obtaining high-quality images. Moreover, there is no need to use single-photon detectors and standard spectrometers can be used instead. Other advantages of the high-parametric gain regime will be discussed.