This disclosure relates to polarizing optical fibers and polarization maintaining optical fibers, including active and/or passive implementations. An embodiment includes a polarizing (PZ) optical fiber that includes stress applying parts (SAPs) disposed in a first cladding region, the SAPs comprising a material with a thermal expansion coefficient, ?.sub.SAP. A core region is at least partially surrounded by cladding features and the SAPs. The core includes glass with a thermal expansion coefficient, ?.sub.core. The arrangement of the SAPs satisfies: R.sub.sc=d.sub.SAP/D.sub.sc, where D.sub.sc is the SAP center to core center distance, and d.sub.SAP is the average SAP diameter, and d?=|?.sub.SAP??.sub.core|, and where Rsc and d? may be sufficiently large to induce stress birefringence into the core and to provide for polarized output. Active fibers in which a portion of the fiber is doped may be implemented for application in fiber lasers, fiber amplifiers, and/or optical pulse compressors.

A photonic crystal fiber (PCF) assembly including a PCF and at least one ferrule structure. The PCF includes a core region and a cladding region and a first fiber end section with a first fiber end. The ferrule structure is mounted to the first fiber end section. The ferrule structure includes an inner ferrule arrangement and an outer ferrule arrangement surrounding the first fiber end section. The inner ferrule arrangement includes an inner ferrule front section proximally to the first fiber end and an inner ferrule rear section distally to the first fiber end, and each of the sections has an inner diameter and in at least a length thereof fully surrounds the PCF. The inner ferrule rear section is anchored in an anchor length section to the first fiber end section and the inner ferrule front section supports the first fiber end section proximally to the first fiber end.

An object of the present invention is to provide a structure of an optical fiber capable of satisfying desired requirements of an output power, a propagation distance, and a beam quality. In the design of the PCF of the present invention, the PCF has air holes having diameters d and intervals in an overlapping region where a region of A.sub.eff of a desired value or more and a cutoff region in a desired higher-order mode overlap each other on a graph where the horizontal axis represents d/ and the vertical axis represents , so that it is possible to sufficiently cut off the mode which is the desired higher-order mode or more, and thus, it is possible to select a region where the A.sub.eff is large.

A method of drawing a material into sheet form includes forming a preform comprising at least one material as a large aspect ratio block wherein a first transverse dimension of the preform is much greater than a second transverse dimension substantially perpendicular to the first transverse dimension. A furnace having substantially linearly opposed heating elements one spaced from the other is provided and the heating elements are energized to apply heat to the preform to create a negative thermal gradient from an exterior surface along the first transverse dimension of the preform inward toward a central plane of the preform. The preform is drawn in such a manner that the material substantially maintains its first transverse dimension and deforms across its second transverse dimension.

The present invention provides a frontal light diffusing device comprising a non-circular core fiber section having a proximal end and a distal end, and a lens; wherein fiber core of the non-circular core section has a top hat core irradiance distribution and the frontal light diffusing device provides a top hat spatial irradiance distribution at a targeted location. The present invention further provides a frontal light diffusing device comprising an optical fiber and a collimation lens assembly wherein the collimation lens assembly includes a variable aperture that blocks portions of light outcoupled from the optical fiber thereby allowing only a central portion of the light to exit through the variable aperture resulting in a flat irradiance distribution.

The present invention provides a cylindrical light diffusing device comprising a non-circular core fiber having (i) a fiber core that provides a top hat core irradiance distribution; (ii) light blocking means that prevent frontal light emisson from distal end of the non-circular core fiber; and (iii) a light diffusing section having a diffusing proximal end, a diffusing distal end, and internal scattering features distributed within the fiber core of the light diffusing section along central axis of the fiber core, wherein the light diffusion section emits irradiance in a radially symmetric longitudinally top hat diffusing irradiance distribution.

The low magnetic sensitivity PM-PCF based on mechanical buffer is obtained by adding buffer structures in the cladding layer of the photonic crystal fiber. In the center of the fiber, the core region contains at least 3 layers of air-holes, enclosed by the cladding layer. The buffer structures are placed in the cladding layer. These buffer structures are formed by replacing silica of any shape by air, and are symmetrically located in X-axis and Y-axis directions to achieve mechanical isotropy. The buffer structures improve the fiber's performance in fiber coiling and stress conditions. Therefore, the fiber optic gyroscope using the PM-PCF can do without a magnetic shield, thus greatly reducing the weight of the fiber optic gyroscope and extending the scope of its application. Compared with the conventional commercial PCF, the PM-PCF provides the fiber optic gyroscope with lower temperature sensitivity and improved accuracy.

An object is to provide a beam propagating method capable of satisfying desired output power and a desired propagation distance and a required condition of beam quality and a method of designing an optical fiber designing the structure of an optical fiber. According to the present invention, an effective core cross-sectional area A.sub.eff is calculated based on desired specification values and, by appropriately adjusting the structure of an optical fiber satisfying the effective core cross-sectional area and the number of modes to be propagated, the structure of the optical fiber is determined. In this way, by controlling the excitation ratio of a high-order mode at the time of coupling laser light in the optical fiber designed as above, light of high-output laser can be propagated a long distance with the beam quality maintained.

A multicore polarization-maintaining fiber 10 includes a plurality of cores 11, a cladding 12 surrounding the plurality of cores 11, and a plurality of stress applying parts 15 provided sandwiching the plurality of cores 11 in a region surrounded by the outer circumferential surface of the cladding 12. The cross sectional area of the stress applying part 15 is greater than the cross sectional area of the core 11. Stress applying parts 15 of the plurality of stress applying parts 15 are disposed in a first direction, and stress applying parts 15 of the plurality of stress applying parts 15 are disposed in a second direction different from the first direction.

A method of producing a microstructured optical fiber is disclosed. The method includes providing a preform and drawing the preform. The preform has a center axis, a length and a first end and a second end and has at least one longitudinal hole extending lengthwise. The method includes inserting a first end of a pressure tube into the hole of the preform at the first end of the preform and subjecting the hole of the preform to a controlled pressure via the pressure tube during the drawing.