Internet data traffic capacity is rapidly reaching limits imposed by optical fiber nonlinear effects. Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capacity. We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber. Over 1.1 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 1.6 terabits per second using two OAM modes over 10 wavelengths. These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks.
Beams with polarization singularities have attracted immense recent attention in a wide array of scientific and technological disciplines. We demonstrate a class of optical fibers in which these beams can be generated and propagated over long lengths with unprecedented stability, even in the presence of strong bend perturbations. This opens the door to exploiting nonlinear fiber optics to manipulate such beams. This fiber also possesses the intriguingly counterintuitive property of being polarization maintaining despite being strictly cylindrically symmetric, a prospect hitherto considered infeasible with optical fibers.
Light's orbital angular momentum (OAM) is a conserved quantity in cylindrically symmetric media; however, it is easily destroyed by free-space turbulence or fiber bends, because anisotropic perturbations impart angular momentum. We observe the conservation of OAM even in the presence of strong bend perturbations, with fibers featuring air cores that appropriately sculpt the modal density of states. In analogy to the classical reasoning for the enhanced stability of spinning tops with increasing angular velocity, these states' lifetimes increase with OAM magnitude. Consequently, contrary to conventional wisdom that ground states of systems are the most stable, OAM longevity in air-core fiber increases with mode-order. Aided by conservation of this fundamental quantity, we demonstrate fiber propagation of 12 distinct higher-order OAM modes, of which 8 remain low-loss and >98% pure from near-degenerate coupling after kmlength propagation. The first realization of long-lived higher-order OAM states, thus far posited to exist primarily in vacuum, is a necessary condition for achieving the promise of higherdimensional OAM-based classical and quantum communications over practical distances.Quantum numbers are usually assigned to conserved quantities; hence it appears natural that paraxial light travelling in isotropic, cylindrically symmetric media such as free space or optical fibers be characterized by its angular momentum [1]: J = L + S (1) L represents light's orbital angular momentum (OAM) [2], and S represents its spin angular momentum, SAM, commonly known as left or right handed circular polarization, ̂±, such that S = ±1 in units of ħ for left and right handed circular polarization, respectively. L forms a countably infinite dimensional basis, spawning widespread interest in OAM beams [3,4,5]. In particular, this enables a large alphabet of states for hyper-entangled quantum communications or high-capacity classical links. The information capacity of a classical or quantum communications link increases with the number of distinct, excitable and readable orthogonal information channels. Degrees of freedom that conserve their eigenvalues are required, because perturbations which cause eigenstate rotation, conventionally called mode coupling, are debilitating. In classical communications, computational algorithms can partially recover information for some limited perturbations, albeit with energy-intensive signal processing [6]. For low-light level applications such as quantum communications or interplanetary links, the information is lost. With the use of wavelength and polarization as photonic degrees of freedom
Optical vortex beams, possessing spatial polarization or phase singularities, have intriguing properties such as the ability to yield super-resolved spots under focussing, and the ability to carry orbital angular momentum that can impart torque to objects. In this review, we discuss the means by which optical fibers, hitherto considered unsuitable for stably supporting optical vortices, may be used to generate and propagate such exotic beams. We discuss the multitude of applications in which a new class of fibers that stably supports vortices may be used, and review recent experiments and demonstration conducted with such fibers.
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