The study of structured light is an important field of investigation in both the quantum and classical regimes.^1,2 In particular, light carrying orbital angular momentum (OAM) different from zero has been used in many applications ranging from quantum simulation^3,4 and quantum engineering^5,6 to quantum and classical communications.^{7 – 14} Recently, OAM modes have been particularly studied for their uses in biomedical applications of imaging and diagnosis.^{15 – 17} In particular, they have been exploited for the development of noninvasive diagnostics on tissues. In this regard, studies comparing the transmittance to the Gaussian spatial mode on scattering media simulating real tissue properties have been carried out.^{18 – 20} In this context, it becomes of fundamental importance to investigate how the structure of OAM modes can be degraded by scattering and turbulent media. In particular, this has been investigated in communications through scattering media,²¹ atmospheric turbulence,^{22 – 24} and underwater.^25,26

Diffuse optical tomography using deep learning is an emerging technology that has found impressive medical diagnostic applications. However, creating an optical imaging system that uses visible and near-infrared (NIR) light is not straightforward due to photon absorption and multi-scattering by tissues. The high distortion levels caused due to these effects make the image reconstruction incredibly challenging. To overcome these challenges, various techniques have been proposed in the past, with varying success. One of the most successful techniques is the application of deep learning algorithms in diffuse optical tomography. This article discusses the current state-of-the-art diffuse optical tomography systems and comprehensively reviews the deep learning algorithms used in image reconstruction. This article attempts to provide researchers with the necessary background and tools to implement deep learning methods to solve diffuse optical tomography.

Quantum key distribution (QKD) is a method for exchanging keys between two parties (Alice and Bob) with an absolute level of security in the ideal scenario. QKD systems are vulnerable to hacking through secondary emissions of photons by SPAD detectors, known as backflash. In this work, we derive an information leakage probability model for the scenario of QKD in a free space communication (FSO) system, and suggest a method for its minimization.

Optical interrogation of tissues is broadly considered in biomedical applications. Nevertheless, light scattering by tissue limits the resolution and accuracy achieved when investigating sub-surface tissue features. Light carrying optical angular momentum or complex polarization profiles, offers different propagation characteristics through scattering media compared to light with unstructured beam profiles. Here we discuss the behaviour of structured light scattered by tissue-mimicking phantoms. We study the spatial and the polarization profile of the scattered modes as a function of a range of optical parameters of the phantoms, with varying scattering and absorption coefficients and of different lengths. These results show the non-trivial trade-off between the advantages of structured light profiles and mode broadening, stimulating further investigations in this direction.

Data centers are crucial elements in modern information technology. In order to implement the next generation of data centers, new challenges must be overcome. These include reducing the energy consumption, increasing the data rates, reducing the communication latency, increasing the flexibility and scalability, and reducing the maintenance time and cost. One promising way for meeting these challenges is to employ multichannel optical wireless communication as part of the data center hybrid communication network. In this paper, we analyze three technologies that could be used in this context: MIMO (Multiple-in-Multipleout), multiplexing through orbital angular momentum of light, and direct modulation through the large number of modes associated with orbital angular momentum. Our results indicate that these technologies could provide an innovative and flexible means of meeting the challenges of the next generation of data centers.