In this paper, spatial light modulation is proposed to increase the transmission capacity of graded-index multimode fibers. In the method, selected linearly polarized eigenmodes of the fiber are excited using simple binary-phase spatial filters. Numerical results indicate that the selectivity of the method is very high, also for fibers with perturbed profiles. The excess attenuation of the method is very low. In the experiment, a threefold increase of fiber bandwidth for several filters is obtained.

In study, we investigated the influence of lighting light emitting diodes (LED) chip parameters, including the doping concentration, ABC parameters, and bias current, on the kernels of the Volterra representation of the nonlinear dynamic response. The Volterra kernels were obtained from the LED rate equations and transformed from the time domain to the frequency domain using the harmonic input method. An analysis of kernels up to third order for a specific type of lighting LED (the Luxeon Rabel blue LED) demonstrated the dynamic character of LED nonlinearity. We further validated our approach by application to a simulated discrete multitone (DMT) modulation experiment and obtained excellent agreement between the theoretical and simulation results. We also proposed two measures of LED nonlinearity based on the first- and second-order kernels of the frequency Volterra representation. These measures facilitated analysis of the device’s nonlinear behavior for other advanced modulation formats, such as pulse amplitude modulation (PAM), and made subsequent investigation of the impact of the LED chip parameters on the 1st-order frequency response and dynamic nonlinearity easier. The latter analysis demonstrated that with increasing doping concentration, the 3-dB modulation bandwidth increased, whereas the nonlinear distortions were diminished. Similarly, increasing the bias current boosted the modulation bandwidth, as well as the nonlinear distortions (unlike to the trend obtained by increasing the doping concentration). The obtained results may be useful for designing LED chips and selecting a suitable LED modulation format.

In this paper, we present a time domain method for extracting coefficients of nonlinear Volterra-series kernels for white light-emitting diodes (LED) used both for illumination and visible light communications. We show that this method may have several advantages over the thus far more popular frequency domain method. We successfully apply the measured kernel coefficients up to the 3rd order for the modeling of nonlinear distortion impact on advanced modulation formats: pulse amplitude modulation, carrierless amplitude phase and orthogonal frequency division multiplexing. The impact of blue filtering on dynamic nonlinearity is also presented.

In this paper, we investigate how data transmissions may be affected by various types of optical interference introduced into the fiber on purpose, via a clip-on coupler. The research proved that transmissions may be jammed completely using inexpensive equipment readily available on the market, provided that the attacker has physical access to the fiber optic cable. The most dangerous attacks rely on a typical, slowly modulated communication laser with a rectangular waveform. This study urges further research aimed at counteracting such attacks.

Optical beat interference is one of the major problems impairing upstream transmission in passive optical networks. In this letter, a theoretical study indicates that if single mode fibers are replaced with multimode fibers, the interference is reduced at least by the factor of N, where N is the number of modes propagating. In the experiment carried with two types of lasers, a reduction of beating noise ~10 dB is observed. Even greater reduction is expected in the first transmission window.