Enhancing OFDM with index modulation using heuristic geometric constellation shaping and generalized interleaving for underwater VLC.

In this paper, we propose and demonstrate enhanced orthogonal frequency division multiplexing with index modulation (OFDM-IM) schemes for bandlimited underwater visible light communication (UVLC) systems via geometric constellation shaping (GCS) and subblock interleaving. Specifically, two heuristic GCS approaches based on particle swarm optimization (PSO) and hybrid genetic algorithm-PSO (GA-PSO) algorithms are proposed to generate IM-preferable constellations. Moreover, a generalized interleaving technique is further proposed to overcome the low-pass effect of bandlimited UVLC systems, where an optimal step size can be obtained to perform subblock interleaving.

0.5-bit/s/Hz fine-grained adaptive OFDM modulation for bandlimited underwater VLC.

In this paper, we propose and demonstrate a 0.5-bit/s/Hz fine-grained adaptive orthogonal frequency division multiplexing (OFDM) modulation scheme for bandlimited underwater visible light communication (UVLC) systems. Particularly, integer spectral efficiency is obtained by conventional OFDM with quadrature amplitude modulation (QAM) constellations, while fractional spectral efficiency is obtained by two newly proposed dual-frame OFDM designs.

Investigation of mode coupling in strained and unstrained multimode step-index POFs using the Langevin equation.

The Langevin equation (LE) is used to evaluate mode coupling in multimode step-index polymer optical fiber (SI POF) that is both unstrained and strained. The numerical solution of the LE matches the numerical solution of the power flow equation (PFE). Strain-induced mode coupling is noticeably stronger in strained fiber than in unstrained fiber of the same types.

Correction: Savović et al. Power Flow in Multimode Graded-Index Microstructured Polymer Optical Fibers. 2023, , 1474.

The authors wish to make three changes to their published paper [...

Investigation of space division multiplexing in multimode step-index silica photonic crystal fibers.

The feasible distance is presented for space division multiplexed (SDM) transmission along multimode silica step-index photonic crystal fiber (SI PCF) by solving the time-independent power flow equation (TI PFE). These distances for two and three spatially multiplexed channels were determined to depend on mode coupling, fiber structural parameters, and launch beam width in order to keep crosstalk in two- and three-channel modulation to a maximum of 20% of the peak signal strength. We found that the length of the fiber at which an SDM can be realized increases with the size of the air-holes in the cladding (higher NA).

Power Flow in Multimode Graded-Index Microstructured Polymer Optical Fibers.

We investigate mode coupling in a multimode graded-index microstructured polymer optical fiber (GI mPOF) with a solid core by solving the time-independent power flow equation (TI PFE). Using launch beams with various radial offsets, it is possible to calculate for such an optical fiber the transients of the modal power distribution, the length at which an equilibrium mode distribution (EMD) is reached, and the length for establishing a steady-state distribution (SSD). In contrast to the conventional GI POF, the GI mPOF explored in this study achieves the EMD at a shorter length .

Transmission performance of multimode W-type microstructured polymer optical fibers.

By solving the time-independent power flow equation (TI PFE), we study mode coupling in a multimode W-type microstructured polymer optical fiber (mPOF) with a solid-core. The multimode W-type mPOF is created by modifying the cladding layer and reducing the core of a multimode singly clad (SC) mPOF. For such optical fiber, the angular power distributions, the length L at which an equilibrium mode distribution (EMD) is achieved, and the length z for establishing a steady state distribution (SSD) are determined for various arrangements of the inner cladding's air-holes and different launch excitations.

Treatment of Mode Coupling in Step-Index Multimode Microstructured Polymer Optical Fibers by the Langevin Equation.

By solving the Langevin equation, mode coupling in a multimode step-index microstructured polymer optical fibers (SI mPOF) with a solid core was investigated. The numerical integration of the Langevin equation was based on the computer-simulated Langevin force. The numerical solution of the Langevin equation corresponded to the previously reported theoretical data.

Calculation of Bandwidth of Multimode Step-Index Polymer Photonic Crystal Fibers.

By solving the time-dependent power flow equation, we present a novel approach for evaluating the bandwidth in a multimode step-index polymer photonic crystal fiber (SI PPCF) with a solid core. The bandwidth of such fiber is determined for various layouts of air holes and widths of Gaussian launch beam distribution. We found that the lower the NA of SI PPCF, the larger the bandwidth.

Theoretical Investigation of the Influence of Wavelength on the Bandwidth in Multimode W-Type Plastic Optical Fibers with Graded-Index Core Distribution.

The bandwidth of multimode W-type plastic optical fibers (POFs) with graded-index (GI) core distribution is investigated by solving the time-dependent power flow equation. The multimode W-type GI POF is designed from a multimode single-clad (SC) GI POF fiber upon modification of the cladding layer of the latter. Results show how the bandwidth in W-type GI POFs can be enhanced by increasing the wavelength for different widths of the intermediate layer and refractive indices of the outer cladding.

Investigation of bandwidth in multimode graded-index plastic optical fibers.

A new method is proposed for investigating the bandwidth in multimode graded-index plastic optical fibers (GI POFs). By numerically solving the time-dependent power flow equation, bandwidth is reported for a varied launch conditions (radial offsets) of multimode GI POF. Our theoretical results are supported by the experimental results which show that bandwidth decreases with increasing radial offset.

Frequency response and bandwidth in low-numerical-aperture step-index plastic optical fibers.

By experimental measurement and from a numerical solution to the time-dependent power flow equation, the frequency response, bandwidth, mode coupling, and mode-dependent attenuation are determined for a low-numerical-aperture (NA) plastic optical fiber. Frequency response and bandwidth are specified as a function of fiber length. Numerical results are verified against experimental measurements.

Influence of launch-beam distribution on bandwidth in step-index plastic optical fibers.

The power-flow equation is employed to calculate bandwidth of step-index plastic optical fibers (POFs) for different launch conditions. The outcome specifies bandwidth as a function of the mean input angle and width of the launch-beam distribution. For small distribution widths, bandwidth is shown to decrease with increasing mean input angle of the launch-beam distribution.

Influence of depth of intermediate layer on optical power distribution in W-type optical fibers.

For different depth and width of the intermediate layer, a power flow equation is used to calculate spatial transients and steady state of power distribution in W-type optical fibers (doubly clad fibers with three layers). A numerical solution has been obtained by the explicit finite difference method. Results show how the power distribution in W-type optical fibers varies with the depth of the intermediate layer for different values of intermediate layer width and coupling strength.

Numerical solution of the transport equation describing the radon transport from subsurface soil to buildings.

A theoretical evaluation of the properties and processes affecting the radon transport from subsurface soil into buildings is presented in this work. The solution of the relevant transport equation is obtained using the explicit finite difference method (EFDM). Results are compared with analytical steady-state solution reported in the literature.

Equilibrium mode distribution and steady-state distribution in 100-400 μm core step-index silica optical fibers.

Using the power flow equation, the state of mode coupling in 100-400 μm core step-index silica optical fibers is investigated in this article. Results show the coupling length L(c) at which the equilibrium mode distribution is achieved and the length z(s) of the fiber required for achieving the steady-state mode distribution. Functional dependences of these lengths on the core radius and wavelength are also given.

Radon diffusion in an anhydrous andesitic melt: a finite difference solution.

Radon-222 diffusion in an anhydrous andesitic melt was investigated. The melts were glass discs formed artificially from melted volcanic materials. Solutions of the relevant diffusion equations were done by the explicit finite difference method.

Explicit finite difference solution of the diffusion equation describing the flow of radon through soil.

Radon diffusion through soil and into air is investigated. The solution of the relevant diffusion equation is given using the explicit finite difference method. Results from a two-medium model (soil-air) are compared to those from a simplified single-medium model (soil alone).

Mode coupling in strained and unstrained step-index glass optical fibers.

By using the power flow equation, we have examined the state of mode coupling in strained and unstrained step-index glass optical fibers. Strained fibers show stronger mode coupling than their unstrained counterparts of the same type. As a result, the coupling length where equilibrium mode distribution is achieved and the length of fiber required for achieving the steady-state mode distribution are shorter for strained than for unstrained fibers.

Calculation of the coupling coefficient in step index glass optical fibers.

A method for calculating the coupling coefficient in step-index multimode optical fibers is verified for glass fibers by comparison to published data and to an analytical solution for the steady-state mode distribution. The coefficient that the method calculates is used to determine the state of mode coupling along the fiber, including the coupling length for achieving the equilibrium mode distribution when measurement of fiber characteristics (such as linear attenuation or bandwidth) becomes meaningful.

Calculation of the coupling coefficient in strained step index plastic optical fibers.

The coupling coefficient in a strained step index plastic optical fiber is determined using our recent simplified method. This enabled the calculation of the length z(s) at which the steady-state distribution (SSD) is achieved. Results are in good agreement with measurements reported earlier.

Numerical solution of the diffusion equation describing the flow of radon through concrete SEQ CHAPTER.

The process of radon diffusion through slabs of concrete with different thicknesses is investigated. The solution of the relevant diffusion equation is obtained by the explicit finite difference method. It is compared to experimental measurements and to numerical results obtained by the finite element method reported earlier.

Method for calculating the coupling coefficient in step-index optical fibers.

A simple method is proposed for determining the mode coupling coefficient D in step-index multimode optical fibers. It only requires observation of the far-field output pattern for one fiber length with the input light launched centrally along the fiber axis (theta(0)=0). For illustration, the coupling coefficient determined by this simple method for a step-index plastic optical fiber was used to calculate the coupling length L(c) at which the equilibrium mode distribution is achieved, and length z(s) at which the steady-state distribution is achieved.

Mode coupling in strained and unstrained step-index plastic optical fibers.

Using the power-flow equation, we have examined the state of mode coupling in strained and unstrained step-index plastic optical fibers. The strained fibers show much stronger mode coupling than unstrained fibers of the same types. As a result, the coupling lengths where equilibrium mode distribution is achieved and the lengths of fiber required for achieving a steady-state mode distribution for strained fibers are much shorter than the corresponding lengths for unstrained fibers.

Influence of numerical aperture on mode coupling in step-index plastic optical fibers.

Using the power-flow equation, we have examined the state of mode coupling in step-index plastic optical fibers with different numerical apertures. Our results confirm that the coupling rates vary with the coupling coefficient of the fibers as the dominant parameter, especially in the early stage of coupling near the input fiber end. However, we show that the fiber's numerical aperture has a significant influence on later stages of this process.