Hollow-core optical fiber incorporating a metamaterial cladding

An optical fiber (100, 200, 300) for guidance of electromagnetic radiation with an operational wavelength l, the fiber (100, 200, 300) having a longitudinal direction along a longitudinal axis and a transverse direction in a plane perpendicular to the longitudinal axis, the fiber (100, 200, 300) comprising: - a core region comprising a hollow core (101, 201, 301, 401, 501, 601, 801) extending along the longitudinal axis, and - a cladding (102, 202, 302, 402, 502, 602, 802) comprising a first cladding region (220, 320, 420, 520, 620, 820) surrounding the core (101, 201, 301, 401, 501, 601, 801) region and comprising a dielectric background material (222, 322, 422, 522, 622, 822), the first cladding region (220, 320, 420, 520, 620, 820) having a total cross-sectional cladding area, the first cladding region (220, 320, 420, 520, 620, 820) further comprising a number of longitudinally extending cladding elements located in the background material (222, 322, 422, 522, 622, 822) and having a total cross-sectional element area, wherein the first cladding region (220, 320, 420, 520, 620, 820) has a filling fraction f being defined as the ratio between the element area and the cladding area wherein - the cladding elements (221, 321, 421, 521, 621, 821) are made of metal and are oriented substantially parallel to the core (101, 201, 301, 401, 501, 601, 801) region in a transverse distance from the core (101, 201, 301, 401, 501, 601, 801), and wherein the distance L between neighbouring cladding elements (221, 321, 421, 521, 621, 821) is smaller than half the wavelength l, and wherein the cladding elements (221, 321, 421, 521, 621, 821) are arranged so that transverse magnetic radiation with a wavelength of l can propagate through the core (101, 201, 301, 401, 501, 601, 801) region. The invention further relates to a method relating to and the use of the inventive fiber.