Fiber Bragg grating inscription by high-intensity femtosecond UV laser light: comparison with other existing methods of fabrication

Abstract

By use of high-intensity (Ϸ200 GW/cm 2) femtosecond 264-nm laser light and a phase mask technique, Bragg grating inscription in a range of different photosensitive and standard telecom fibers (both H 2-free and H 2-loaded) was studied. The dependences of the induced refractive index modulation versus the incident fluence as well as the thermal decay curves were compared with similar dependences for gratings fabricated by other existing methods. It was shown that with high-intensity UV laser irradiation, two-quantum photoreactions occur in the irradiated fiber core, that result in a significant photosensitivity enhancement of the investigated fibers in comparison with conventional low-intensity 248-nm exposure (by 6-128 times, depending on fiber type and irradiation intensity).

High order Bragg gratings for short wavelengths operation

“…When exposure time increases from 200 s to 1400 s on a total inscribed fiber length of 1 cm, the strength of the second order grating firstly presents an exponential increase, and then a fast degradation after reaching the saturation point. In the meantime, the center wavelength of the grating moves towards the longer wavelengths through all the process, which is induced by the change of the average mode effective index [12,13]. These experiments results perfectly verify the theoretical analysis.…”

“…The method for producing the Bragg gratings is similar to that described by Stephen A. et al [13]. The fourthharmonic radiation of a femtosecond laser emitting 220 fs pulses at 258 nm is used for the inscription of FBGs.…”

Femtosecond pulse written fiber gratings: a new avenue to integrated fiber technology

“…Such gratings are therefore called Type I-IR by some [82]. However, if the inscribing wavelength lies in the UV, one-photon processes compete with nonlinear absorption [83,84]. Thus, a sub-classification does not make much sense here.…”

Surface-corrugated microfiber Bragg grating

“…FBGs are based on a periodic variation in the refractive index of the fiber core and allow for the reflection of a narrowband signal centered at a specific Bragg wavelength. Over the last two decades, FBGs have been manufactured mainly by modifying the core refractive index using interferometric or point-by-point techniques; most of interferometric techniques use a phase mask and an ultraviolet (UV) laser [1] (typically excimer or frequency doubled Ar+ ion) or femtosecond (fs) lasers (near IR [2] or UV [3]). Gratings based on surface corrugations have also been demonstrated in etched fibers using photolithographic techniques [4].…”