Optics, Volume 5, Issue 3 (September 2024) – 4 articles

Recovery after visual loss is a key goal of neuroscience and treatments able to improve visual function are still largely lacking. Glaucoma, one of the leading causes of visual disability in the world, is usually associated with elevated intraocular pressure (IOP), but a subset of “normal tension glaucoma” patients develop damage without ever manifesting high IOP. Sometimes, even in patients with good control of IOP, retinal ganglion cell degeneration can progress to forward blindness. Moreover, usually the damage already caused by the disease remains. These considerations underline the need to find new, effective treatments and solutions to add to the standard ones. In this paper, we expose the most important data supporting the use of alternating current stimulation, including the theoretical bases of this approach, in glaucoma. Full article

A symmetric laser beam pair can provide unique control over light–matter interactions. When propagating within a symmetric slab waveguide, its non-conical diffraction at a specially designed symmetric leaky waveguide grating can be completely suppressed, a phenomenon we term zero diffraction. This allows for infinite contrast control of light detrapping from the slab waveguide. In this paper, we demonstrate the electric control of the local deflection of a beam pair while preserving its properties. This introduces a novel method for routing optical signals across a planar waveguide. We utilize a waveguide structure that enables zero diffraction under non-conical incidence on a 1D grating and design a grating geometry capable of deflecting the beam pair by approximately 90 degrees. This design is experimentally realized using three different diffractive elements for trapping, deflection, and detrapping. The deflection is controlled by an electric field, allowing the deflected intensity to be tuned by a factor of 21. Full article

Higher-dimensional communications are of interest for multiple reasons, including increasing the classical transmission capacity and, more recently, the quantum state transfer through fibers using the many modes within the fiber. For quantum communications, this enables an increase in the number of bits per photon, increasing quantum fidelity, increasing error thresholds and enabling hyperentanglement transfer, among other possibilities. A high-dimensional quantum state transfer can be transported through multimode fiber using the many modes available. However, this transfer of information through multimode optical fiber is limited by attenuation and mode coupling among the various spatial and polarization modes. Here, we consider how this mode coupling impacts the transfer process. We consider the fiber’s modal properties, including orbital angular momentum, modal group numbers, and principal modes. We also investigate and propose input and output optical components, as well as fiber properties, which better mitigate the deleterious effects of mode coupling. We use the WKB approximation to the scaler wave equation as a guidance to quantify this coupling and then implement corrections to this approximation using exact solutions to the scaler wave equation. We consider methods to circumvent this mode coupling using optical fiber designs, holographic optical components and devices that are commercially available today. Some of these components, such as the holographic gratings and lenses, could be implemented using flat optics. Full article

Over the years, there has been much speculation to understand whether (and how) it was possible to go below the diffraction limit. An advance in knowledge was achieved with the development of microwave techniques. In fact, more than fifty years after the publication of Toraldo’s article dealing with this topic, some experimental measurements in the range of microwaves confirmed the validity of his model. Since some measurements were performed in the region of near field, while Toraldo’s model refers to the far field, the need for a theoretical analysis in the framework of the Fresnel optics arose. The main goal of the present paper is to describe the problem of propagation in the near field (Fresnel optics) by using the same theoretical model already proposed by Toraldo. In order to test the validity of this new approach, the theoretical model has been compared with the FEKO simulation. The comparison of the theoretical model with the FEKO simulation in the far field for an open pupil (an open circular aperture) shows perfect agreement, as expected. We will demonstrate that there is also good agreement in the near field, although it is limited to the region around the main lobe, which is usually the region of main physical interest. Moving away from the main lobe, namely away from the optical axis, the agreement becomes less significant. Full article