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In order to separate the multiplexed beams with different wavelengths in an all-fiber network, a novel concept of distinguishing different wavelengths by the orbital angular momentum (OAM) beams [i.e., L(topological charge) =1 and $L=-1$ ] based on the OAM fiber is proposed and investigated in the theory and experiments. Meanwhile, a new OAM fiber supporting the first order vector modes (i.e., TE0,1, HE2,1, and TM0,1) is also designed and fabricated. For the sake of verifying the feasibility of the proposed scheme, an experimental platform is anticipated and established. Bit error rates (BERs) and constellation diagrams are employed to evaluate the performance of the proposed schemes with respect to the transmission rate of data (V) and the difference of wavelength between the two input lasers. The simulated and measured results demonstrate that two different wavelengths (i.e., 1548 and 1545 nm) with the cycle of 14 and 10 nm can be distinguished though two OAM beams (i.e., $L=1$ and $L=-1$), respectively. The measured BERs and constellation diagrams with respect to data rates (V) depict that the performance of the proposed schemes degenerates with the increment of data rates (V) from 5 to 40 Gb/s. Similarly, the measured BERs and constellation diagrams with respect to the difference of wavelengths also demonstrate that the performance of the proposed scheme can be improved by increasing the difference of wavelengths from 1 to 4 nm. [ABSTRACT FROM AUTHOR]

The phenomenon of modal noise, which is typically undesired within fiber optic links, is exploited advantageously to characterize vertical cavity surface emitting lasers (VCSELs) operating in the first optical window (wavelength $\lambda \simeq 850$ nm), in terms of frequency chirping. The proposed method, which can be applied utilizing ordinary laboratory components and instrumentation, contributes to fill an existing gap. Indeed, the methods which are typically exploited to determine this undesired optical frequency modulation can be straightforwardly applied only to sources operating at wavelengths of 1310 and 1550 nm, while they become unpractical or even inapplicable at wavelengths of 850 nm. Through the proposed technique, the evaluation of chirp coefficient $M$ and phase difference $\psi $ between frequency and intensity modulation (or equivalently linewidth enhancement factor $\alpha $ and chirp scaling factor $\kappa $) of VCSELs can be performed. This allows the correct design of various types of fiber optic links, making possible to take advantage of these low-cost and low-consumption optical sources. [ABSTRACT FROM AUTHOR]

We report a large mode area (LMA), Ge11.5As24Se64.5 six-fold symmetry quasi-periodic dual cladding leakage channel fiber (LCF) for supercontinuum generation (SCG) from 2 to 15~\mu \textm wavelengths. The proposed LMA fiber exhibits single-mode behavior by means of higher order mode delocalization for the entire wavelengths. Besides, the LCF possesses two zero dispersion wavelengths at 4.36 and 14.16~\mu \textm . Indeed, we numerically demonstrated the spectral broadening of continuum for the first time from 2 to 15~\mu \textm in the quasi-periodic dual cladding LCF for a length of 10 mm. It is observed that the red-shifted soliton at the centre wavelength of 9.42~\mu \textm obtain an energy of 0.164 nJ for a low input energy of 0.2 nJ. Further, the SCG in the proposed LCF attains a high conversion efficiency of 82 % at the solitonic spectrum and broadest spanning from 2 to 15~\mu \textm for the low input energy of 0.2 nJ. Thus, the proposed LCF-based SC source is the best choice for the applications, such as optical sensing, optical communication, food quality monitoring, and early cancer diagnostics. [ABSTRACT FROM PUBLISHER]

A mathematical framework is presented to study the evolution of multi-point cumulants in nonlinear dispersive partial differential equations with random input data, based on the theory of weak wave turbulence (WWT). This framework is used to explain how energy is distributed among Fourier modes in the nonlinear Schrödinger equation. This is achieved by considering interactions among four Fourier modes and studying the role of the resonant, non-resonant, and trivial quartets in the dynamics. As an application, a power spectral density is suggested for calculating the interference power in dense wavelength-division multiplexed optical systems, based on the kinetic equation of the WWT. This power spectrum, termed the Kolmogorov-Zakharov (KZ) model, results in a better estimate of the signal spectrum in optical fiber, compared with the so-called Gaussian noise model. The KZ model is generalized to non-stationary inputs and multi-span optical systems. [ABSTRACT FROM PUBLISHER]