PHYSICAL REVIEW A 106, 033702 (2022) Analysis of the signal measured in spectral-domain optical coherence tomography based on nonlinear interferometers Arturo Rojas-Santana Tecnologico de Monterrey, School of Engineering and Science, Avenida Eugenio Garza Sada 2501, Monterrey, Nuevo León 64849, Mexico Gerard J. Machado ICFO–Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain Maria V. Chekhova Max-Planck Institute for the Science of Light, Staudtstraße 2, Erlangen 91058, Germany and Friedrich-Alexander University of Erlangen-Nuremberg, Staudtstraße 7/B2, Erlangen 91058, Germany Dorilian Lopez-Mago * Tecnologico de Monterrey, School of Engineering and Science, Avenida Eugenio Garza Sada 2501, Monterrey, Nuevo León 64849, Mexico Juan P. Torres † ICFO–Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain and Departament of Signal Theory and Communications, Universitat Politecnica de Catalunya, 08034 Barcelona, Spain (Received 21 January 2022; accepted 26 August 2022; published 6 September 2022) We analyze and compare the output signals obtained in three different configurations of optical coherence tomography (OCT). After appropriate processing, these signals are used to retrieve an image of the sample under investigation. One of the configurations considered is the common choice in most OCT applications and is based on the use of a Michelson interferometer. For brevity, here we refer to it as standard OCT. The other two configurations are two types of optical coherence tomography based on the use of so-called nonlinear interferometers, interferometers that contain optical parametric amplifiers inside. The goal is to highlight the differences and similarities between the output signals measured in standard OCT and in these two OCT schemes, with the aim of evaluating if retrieval of information about the sample can be better done in one case over the others. We consider schemes where the optical sectioning of the sample is obtained by measuring the output signal spectrum (spectral or Fourier-domain OCT), since it shows better performance in terms of speed and sensitivity than the counterpart time-domain OCT. DOI: 10.1103/PhysRevA.106.033702 I. INTRODUCTION Optical coherence tomography (OCT) is a three- dimensional high-resolution imaging scheme that produces tomographic images of a variety of objects, such as biological systems, by measuring light backscattered from the samples [1]. In order to obtain good transverse resolution (in the plane perpendicular to the beam propagation axis), OCT focuses light into a small spot that is scanned over the sample. To obtain good resolution in the axial direction (optical sectioning along the beam propagation direction), OCT uses light with a large bandwidth. Optical coherence tomography is a highly mature optical imaging technology as well as a very active topic of research (see, for instance, [2] for reports on advances in optical coherence tomography). * dlopezmago@tec.mx † juanp.torres@icfo.eu The first OCT systems were put forward and demonstrated in [3,4] and most of the current OCT systems follow the same general structure of these pioneering experiments. They use a broadband light beam that splits into two beams in a Michelson interferometric setup: the reference and object beams. The output signal results from the combination of the reference beam with the object beam after being reflected from the sample. We will refer to these OCT systems as standard OCT, although we should remark that there is still a rich variety among these conventional OCT systems. In the past few years several research groups have demon- strated new OCT schemes based on nonlinear interferometers [5–8] and interferometers that contain parametric amplifiers [9]. The main advantage of these quantum schemes is that they allow probing the sample at a chosen wavelength, for instance, in the far infrared, to achieve higher penetration depth into the sample, while at the same time using an optimum wavelength for efficient detection. Nonlinear interferometers are key ele- ments in numerous applications, namely, in imaging [10,11], sensing [12], spectroscopy [13–15], and microscopy [16,17]. 2469-9926/2022/106(3)/033702(10) 033702-1 ©2022 American Physical Society