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Fiber Limits
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Video Transmission, 2013
David R. Goff, Kimberly Hansen, Michelle K. Stull
Polarization mode dispersion (PMD) represents another complex optical effect that can occur in single-mode optical fibers. Single-mode fibers support two perpendicular polarizations of the original transmitted signal. If a fiber were perfectly round and free from all stresses, both polarization modes would propagate at exactly the same speed, resulting in zero PMD. In the real world, fibers are not perfect, so the perpendicular polarizations may travel at different speeds and arrive at the end of the fiber at different times. The fiber is said to have a fast axis and a slow axis. The difference in arrival times, normalized with length, is known as PMD (ps/√km).
Optical Fibers
Published in Johan Meyer, Justice Sompo, Suné von Solms, Fiber Lasers, 2022
Johan Meyer, Justice Sompo, Sune von Solms
Polarization Mode Dispersion (PMD) (Gisin et al. 1991) is related to the birefringence of the fiber. The transverse shape of the fiber is never perfectly cylindrical resulting in orthogonally polarized components of the same mode travelling at different group velocities. As for the other type of dispersion, this situation results in broadened optical pulses. The time delay due to PMD for an ideal fiber with constant birefringence can be written as, ΔT=|Lvgx−Lvgy|=L|β1x−β1y|=L(Δβ1), where Δβ1 represents the difference between group velocities of the two states of polarization of the mode represented by subscripts x and y respectively.
A MATLAB-based modelling and simulation package for DPS-QKD
Published in Journal of Modern Optics, 2022
Anuj Sethia, Anindita Banerjee
Chromatic dispersion (CD): It is the dependence of group velocity associated with the fundamental mode on the frequency of signal. It is also known as group velocity dispersion (GVD). It can be further distinguished as either material dispersion or wave-guide dispersion.Higher-order dispersion: The non-zero higher derivatives of the total dispersion curve causes pulse broadening at zero-dispersion wavelength.Polarization mode dispersion (PMD): The birefringence of optical fibre between two principle polarization axis results in signal delay.
An optical channel modeling of a single mode fiber
Published in Journal of Modern Optics, 2018
Neda Nabavi, Peng Liu, Trevor James Hall
Consequently, an ideal ‘single’ mode fibre (SMF) supports two orthogonally polarized degenerate guided modes. In the case of weakly guiding waveguides, these modes may be considered to be linearly polarized to a good approximation. The effect of small perturbations of the structure of the ideal fibre on light propagation may be described in terms of the ideal modes by a coupling between their overall amplitudes (6). Coupling to higher order modes provides a loss mechanism in which energy leaks away by diffusing to higher order modes. However, provided that the perturbation is very slowly varying, significant coupling only occurs between nominally degenerate modes and there is no radiation loss (7). In a single mode fibre, polarization mode dispersion (PMD) is a random phenomenon that takes place due to birefringence in the fibre that originates from asymmetry caused by an elliptical core, stress, bend or twist. Polarization mode dispersion stems from the random birefringence which yields different group velocities of the two orthogonal polarizations modes (8). This polarization effect causes mode coupling and random changes in state-of-polarization (SOP) in a long haul transmission (8,9). Since polarization mode dispersion, together with chromatic dispersion (CD), is a major source of pulse distortion and pulse spreading in high-speed optical transmission systems, which is also a cumulative effect as a function of the length of the fibre (10–12), it has been studied in detail theoretically and experimentally. Various techniques have been proposed to overcome the PMD barrier, such as the new generation of coherent optical receivers based on digital signal processing (DSP) (13–16) and the deployment of orthogonal frequency-division multiplexing (OFDM) in optical communication systems (17–23). Nevertheless, this phenomenon still needs further investigations in order to allow an improvement of the transmission capacity, speed, and performance level of a fibre optic communication system (8). The effective compensation of the dynamic channel impairments such as PMD and CD, can be achieved with finite impulse response (FIR) filters (24). Hence, a MIMO equalizer which compensates the dynamic impairments of the channel using four filters that have the inverse Jones matrix of the dynamic channel can be used (25).