Optical wireless communication (OWC) is expected to play a crucial role in future wireless communication networks due to its several advantages, including a license-free spectrum, robustness to electromagnetic interference, and ultra-wide bandwidth that enables very high transmission data rates. In most OWC systems, the received light typically requires amplification in the optical domain using lenses or compound parabolic collectors (CPCs). However, these approaches are constrained by the conservation of étendue, which results in a limited field of view (FOV) of the optical receiver.

Recent studies have shown that fluorescent concentrators/antennas can effectively concentrate light without being limited by étendue. Since the concentration principle of these antennas is based on fluorescence, they can achieve both high concentration gain and a wide FOV. Nevertheless, the photoluminescence (PL) lifetime of these antennas introduces an additional bandwidth-limiting factor. Fortunately, advancements in materials science techniques have significantly reduced the PL lifetime to just a few nanoseconds or even lower, thereby supporting the transmission of data at a high rate . This talk reviews the recent trend of exploring new fluorescent concentrators in various OWC applications, including visible light communications (VLCs) and underwater OWCs. These concentrators include those made from commercially available fluorescent fibers, as well as organic and inorganic fluorescent materials.

Compared with conventional planar electromagnetic waves, vortex electromagnetic waves carrying orbital angular momentum (OAM) are unique beams with a helical phase structure and a toroidal amplitude field. Due to the infinity of OAM modes and orthogonality between different modes, a completely new degree of freedom independent of time, frequency, and polarization domains is provided. OAM waves have great potential in terms of channel expansion and improving spectral efficiency. And with the progress of research, how to transmit more information and have more channel capacity has been a hot issue. In this paper, a novel single-layer dual-band orbital angular momentum (OAM) multiplexed reflective metasurface array antenna is proposed. We firstly design a metasurface that can realize dual-band nearly 360° phase coverage at 7 and 12 GHz, and realize 2-bit coding metasurface cells by obtaining suitable geometrical parameters through simulation optimization, and then we obtain the position of each cell in the array away from the feed source by computing. Afterwards, the corresponding phase compensation and the phase gradient required for specific mode OAM beam generation are calculated from the position of each cell in the array, and a 30×30 reflective metasurface array is obtained, which can independently generate different modes of OAM beams in the C and Ku bands, and complete flexible beam control in each operating band, providing a new possibility for realizing more transmission frequency bands and larger channel capacity in communication applications.

Three-dimensional waveguide structure forming mode manipulating devices

Mode multiplexing technology is a promising technology to increase the optical communication capacity, where a 3D waveguide structure is a neat solution for manipulating the modes with their symmetry in horizontal and vertical direction or their combination. Three-dimensional photonic-integrated vertical directional couplers are applied to form the mode multiplexer, where the mode (de)multiplexer serves for spatial (de)multiplexing the spatial guide modes in a few-mode waveguide. These guide modes are the waveguide modes such as the E11, E21, and E12 modes. In addition, the directional couplers (either the horizontal directional couplers or the vertical directional couplers) can be formed by using adiabatic tapered waveguides. The usage of the tapered waveguide can be functioned as a wavelength expander. In addition, the fabrication of the 3D waveguide structure can be utilized by using the multi-step photolithography processing methodology. For example, we have demonstrated the fabrication of a hybrid-core planar waveguide forming mode multiplexer by using multi-step photolithography processing for the realization of a high-order-mode band-passed function. Also, the passive device can be further developed to be an active device for dynamically manipulating the guided modes. In conclusion, the 3D waveguide structure forming mode manipulating devices are powerful in a mode division multiplexing system for the optical communication.

Ultrafast all-optical computing is essential for overcoming the speed and efficiency limitations of electronic systems, enabling rapid data processing and transmission with minimal energy consumption. The main challenges in all-optical computing include developing materials with strong, fast, and reversible nonlinear optical properties, as currently used materials often require high power and lack durability. Managing optical losses and maintaining signal integrity over distances and components is crucial, necessitating low-loss waveguides and efficient light confinement. Integrating nanoscale optical components with high precision and miniaturization demands advanced fabrication techniques and innovative designs for scalable all-optical circuits. Developing novel materials with enhanced nonlinear optical properties, including organic materials, graphene, plasmonic nanostructures, transition metal dichalcogenides, MXenes, and advanced metal–organic frameworks, can significantly improve the performance of optical switches and logic gates.

In this paper, we present a theoretical model and comprehensive analysis of ultrafast transitions between reverse saturable absorption and saturable absorption in CoTCPP surface-supported metal–organic framework (SURMOF) nanofilms with femtosecond (fs) laser pulses at 400 nm.

The effects of laser input intensity, thickness, concentration, and nonlinear absorption coefficients on transmittance have been studied to optimize all-optical switching in recently reported CoTCPP SURMOF nanofilms. We demonstrate ultralow-power and ultrahigh-contrast all-optical switching in SURMOF nanofilms and use the results to design all-optical fs AND, OR, NOT, universal NOR, and NAND logic gates. The percentage modulation of the Boolean all-optical NAND logic gate with CoTCPP SURMOF nanofilms is greater compared to MoTe₂ nanofilms and BODIPY derivative compound ZL-61. A passive photonic diode with CoTCPP/ZL-61 has also been designed, which results in a nonreciprocity of 17 dB.

Based on CoTCPP SURMOF nanofilms, various combinational circuits that include an adder, subtractor, multiplexer, and encoder can be designed and explored using ultrafast all-optical logic gates. The remarkable nonlinear optical properties of CoTCPP SURMOFs open exciting prospects for ultrafast all-optical computing.

Introduction

A methodology suitable for analyzing strong IBG (Integrated Bragg Grating) is presented using the Transfer Matrix Method (TMM) based on the translation of any waveguide's physical structure into a matrix of effective refractive indexes, n_eff, which is wavelength-dependent and describes the behavior of light in the IBG while avoiding the use of approximations like in Coupled Mode Theory.

IBGs have special characteristics that require a methodology that considers any tiny variation in geometry. These have a notable impact on the value of n_eff because of the high refractive index contrast of SOI (Silicon on Insulator) and therefore on the spectrum of the transfer function.

Method

Starting with a given IBG geometry, we mapped the waveguide structure into a matrix, N’, of effective refractive indices, which are functions of the wavelength and position along the IBG, n_eff(λ,z). Subsequently, the TMM was applied using N’ to characterize each layer and interface of the IBG. Finally, the reflectivity and phase spectra were obtained, i.e., the transfer function.

Using this methodology, four apodization methods (corrugation width, lateral delay, duty cycle, and periodic phase modulations) and different chirp methods are presented and compared. Also, the presence of additional Bragg orders is demonstrated as a result of the Fourier transform equivalence between the IBG apodization and its transfer function in reflection. To demonstrate the generality of the methodology, two technological platforms, SOI and Al₂O₃, are analyzed.

Results

Simulations allow us to obtain the reflectivity and phase spectra, i.e., the IBG transfer function. The goodness of each method is observed, as well as the second and third Bragg order spectra. The Al₂O₃ platform shows more robustness against fabrication errors.

Conclusions

TMM is the most suitable methodology for analyzing an IBG. Apodization, chirp methods, and higher Bragg orders are demonstrated to improve transfer functions.