Strong circular dichroism for the HE₁₁ mode in twisted single-ring hollow-core photonic crystal fiber

Abstract

Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX We report a series of experimental, analytical and numerical studies demonstrating strong circular dichroism in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing. In the SR-PCFs studied, the hollow core is surrounded by a single ring of non-touching capillaries. Coupling between these capillaries results in the formation of helical Bloch modes carrying orbital angular momentum. In the twisted fiber, strong circular birefringence appears in the ring, so that when a core mode with a certain circular polarization state (say LC) phase-matches to the ring, the other (RC) is strongly dephased. If in addition the orbital angular momentum is the same in core and ring, and the polarization states are non-orthogonal (e.g., slightly elliptical), the LC core mode will experience high loss while the RC mode is efficiently transmitted. The result is a single-circular-polarization SR-PCF that acts as a circular polarizer over a certain wavelength range. Such fibers have many potential applications, for example, for generating circularly polarized light in gas-filled SR-PCF and realizing polarizing elements in the deep and vacuum ultraviolet.

Angular momentum supercontinuum from fibre rings

“…Twisting the fibre ring also allows these resonant frequrncies to be tailored. Our results could be also be useful to researchers working on twisted solid-core and hollow-core photonic crystal fibres [13,42]…”

“…[12]. Twisted ring arrays of fibres and other helical waveguides have been developed to explore new ways to manipulate optical AM in a discrete fashion [13,14]. Optical AM may be exploited for a plethora of applications including astronomical observation [15][16][17], classical [18,19] and quantum [20,21] communication, optomechanics [22,23] and microscopy [24].…”

Bragg reflection and conversion between helical Bloch modes in chiral three-core photonic crystal fiber

“…This has been explored both in freespace [2] and in optical fibers with circularly symmetric cylindrical or annular cores [3]. In recent years it has been shown that optical fibers with N-fold rotationally symmetric structures (such as most photonic crystal fibers -PCFs) support helical Bloch modes (HBMs) that consist of superpositions of Bessel beams with azimuthal order A (m) = A (0) + mN where m is an integer [4]. These may be viewed as HBM harmonics that are coupled together by Bragg scattering in the azimuthally periodic fiber structure.…”

“…Twisted PCFs are also circularly birefringent [5], making them of interest in Faraday-effect current sensing when preservation of circular polarization state is highly desirable [6]. They can also provide strong circular dichroism [4], allow generation of broad-band circularly polarized supercontinuum light [7] and even permit guidance of light in the absence of any structural core [8,9].…”

Effect of cladding geometry on resonant coupling between fundamental and cladding modes in twisted microstructured fibers

“…Numerically obtained relations between n′ cl and dominating orbital angular momentum L D = J D −σ cannot be accurately described using analytical formulas derived for the modes guided in similar but simpler structures, like thin cylindrical layers [35] or cylindrical arrays of weakly coupling waveguides [36,37]. However, similarly as in case of annular modes guided in thin cylindrical layers, the effective index of the cladding modes in microstructured fiber n cl decreases for greater L and increases for greater ρ, regardless of λ.…”