Introduction of birefringence into photonic crystal fibers

Abstract

Abstract Selective opening and closing of air-holes in photonic crystal fibers (PCFs) are realized by using a femtosecond infrared laser and a CO 2 laser. By heating/tapering the PCFs while pressurizi ng those opened holes, the birefringent properties of the PCFs can be modified. High birefringence of 3.6×10 -4 and 1.5×10 -3 were obtained by post-processing commercial LMA-10 and HC-1550-02 fibers. Keyword: photonic crystal fiber, microstructure optical fiber, fiber taper, birefringence, polarimetric sensor 1. Introduction Photonic crystal fibers (PCFs) are novel optical fibers with periodic arrays of air-holes running along their length. Properties that may not be achieved with conventional optical fibers have been demonstrated by PCFs, including endlessly single mode operation, light-guidance in an air-core, and very high nonlinearity and birefringence [ 1]. Optical fibers with high birefringence have found numerous applications in optical fiber sensors. The stack-and-draw process allows long length of highly birefringent (Hi-Bi) PCFs to be conveniently fabricated. These Hi-Bi PCFs have demonstrated group birefringence of an order of magnitude higher than that of conventional Hi-Bi fiber [ 2]. Apart from the high level of design flexibility in fabrica ting Hi-Bi PCFs from the preform stage, it is also possible to create large birefringence in a sectio n of a commercial low birefringent PCF thro ugh post-processing. In this paper, we report the post-processing of commercial solid-core large mode area (LMA) PCFs and hollow-core photonic bandgap fibers (HC-PBFs) to achieve large birefringen ce in selected sections of these fibers.