Abstract
We report a method for effective fabrication of Bragg gratings in all-silica photonic crystal fibers (PCF). The problem of cladding-hole scattering in PCF grating inscription is avoided by selectively inflating a section of PCF, resulting a locally suspended-core fiber (SCF) region with relatively simple cladding structure. Hence, the inscription laser can laterally access to the core region with little loss. In the SCF regions with core diameter ranging from 2 to 4.5 μm, first-order Bragg gratings are fabricated by use of a phase mask and a focused infrared femtosecond laser with pulse energy as low as ~200 μJ. For the same grating period, samples with different core sizes exhibit different resonant wavelengths and spectral properties, which would enable a range of applications in grating-integrated PCF sensors and devices.
Highlights
The widely-used fiber Bragg gratings (FBGs) have been realized on various optical fibers by using high power lasers and interferometric or point-by-point inscription methods [1,2]
We report a method for effective fabrication of Bragg gratings in all-silica photonic crystal fibers (PCF)
The problem of cladding-hole scattering in PCF grating inscription is avoided by selectively inflating a section of PCF, resulting a locally suspended-core fiber (SCF) region with relatively simple cladding structure
Summary
The widely-used fiber Bragg gratings (FBGs) have been realized on various optical fibers by using high power lasers and interferometric or point-by-point inscription methods [1,2]. For the new generation fibers with complicate cladding structures, such as the photonic crystal fibers (PCFs), two major challenges existed in applying conventional grating inscription methods: the large cladding scattering and distortion to transvers incident laser beam, and the low photosensitivity of fiber material due to the lack of necessity of the doping process for optical wave guidance [3]. The combination effect of the collapsing and expansion of different hole-columns in a PCF eventually forms a region with SCF structure, which have a micro-/nano-sized core supported inside the fiber by several struts and connected at its both sides to the unprocessed PCF regions via low-loss transitions (typically
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