Excitation of Orbital Angular Momentum Resonances in Helically Twisted Photonic Crystal Fiber

Abstract

Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.

Optical vortices in fiber

“…This is because constructive and destructive interference (see the "+" and "-" signs in Figure 4) lead to an LP 11 intensity patterns, and light propagation in the constituent true (vector) modes in a fiber will necessarily lead to such beating with a beat length of λ/Δn eff , where λ is the wavelength of operation and Δn eff is the difference in n eff between the vector modes. Although the mathematical description above is only for the circularly symmetric fiber case, experimental observations of the vortex states in the case of non-circularly symmetric fibers (such are photonic crystal and multicore fibers) [29,30] confirm the same intermodal coupling phenomenon. Finally, we note that fiber generation techniques for realizing OAM beams or polarization vortices include a subset of free-space generation techniques that are implemented at the facet of a single mode fiber (SMF).…”

“…Likewise, several of the fiber generation techniques mentioned earlier can also, in principle, be used to generate OAM states in fiber. In addition, given the helical symmetry of these modes, helecoidal gratings in photonic crystal fibers [29], and helically phased inputs into multicore fibers [30] have had success in producing states that resemble the first non-zero OAM state in short ( < 1 m) fibers. One of the lowest loss, high purity techniques to generate OAM in fiber remains acoustooptic gratings [24] mentioned earlier.…”

The Orbital Angular Momentum Modes Supporting Fibers Based on the Photonic Crystal Fiber Structure

“…Almost at the same time, the helically twisted PCF is proposed, as shown in Figure 1b, in which a regular hexagonal lattice of hollow holes is arrayed symmetrically as the fiber cladding around a central glass core [31][32][33][34]. This type of microstructure fiber is continuously twisted to match (mimic) the spiral properties of OAM, in which a fraction of the axial momentum is transformed into azimuthal momentum to form the OAM states.…”

“…Cross section and structure parameters of (a) ring photonic crystal fiber (PCF) (reprinted with permission from [30]. Copyright 2012 Optical Society of America), (b) the twisted air-core PCF (Reprinted from [31] by permission from AAAS), and (c) hollow-core photonic bandgap fiber (HC-PBGF) (reprinted with permission from [41]. Copyright 2016 Optical Society of America).…”

A Research on Static and Dynamic Dispersion Compensation Scheme Based on Optisystem

“…The advantages and disadvantages described above dispersion compensation fiber by dynamic dispersion compensation device of DCF and FBG [5], and they were compared with the use of their different and complementary characteristics. DCF and dispersion compensation fiber single-mode fiber SMF compatibility, and stable performance, and compensation amount remains unchanged.…”