Ultrafast IR Laser Writing of Strong Bragg Gratings Through the Coating of High Ge-Doped Optical Fibers

Strong fiber Bragg gratings were written through the standard polymer coatings of "off-the-shelf" high numerical aperture single-mode optical fibers after a few seconds exposure with femtosecond pulse durations of infrared radiation through a phase mask. While writing through the acrylate coating, we obtained index modulations of up to 1.4 x 10^-3 and 7 x 10^-4 with and without H₂ -loading, respectively.     

Efficient grating writing through fibre coating with femtosecond IR radiation and phase mask

Bragg gratings have been written through the polymer coating into hydrogen loaded SMF-28 fibres with ultrafast 800 nm radiation and a phase mask. Index modulations of up to 3.5times10^-4 were induced with fibre strengths remaining at ~85% of the pristine fibre value     

Femtosecond laser fabrication of Bragg gratings in borosilicate ion-exchange waveguides

Ultrafast 800-nm radiation from a Ti : sapphire amplifier was used to write high reflectivity Bragg gratings in silver ion-exchange waveguides made in a borosilicate glass substrate. The fabrication and visual/spectral characterization of the grating structures are presented. The measurements show low polarization effects in the grating spectral characteristics.     

Bragg gratings written in all-SiO/sub 2/ and Ge-doped core fibers with 800-nm femtosecond radiation and a phase mask

Femtosecond laser pulses at 800 nm and 120 fs were used to fabricate high-quality retroreflecting fiber Bragg gratings in standard Ge-doped telecom fiber (Corning SMF-28) and all-silica-core Fluorine doped cladding single-mode fiber using a deep-etch silica zero-order ed phase mask. Induced index modulations of 1.9/spl times/10/sup -3/ were achieved with peak power intensities of 2.9/spl times/10/sup 12/ W/cm/sup 2/ without any fiber sensitization such as hydrogen loading. The fiber gratings have annealing characteristics similar to type II damage fiber gratings and demonstrate stable operation at temperatures as high as 950/spl deg/C. The grating devices exhibit low polarization dependence. The primary mechanism of induced index change results from a structural modification to the fiber core.     

Fiber Bragg gratings with suppressed cladding modes made in SMF-28 with a femtosecond IR laser and a phase mask

High reflectivity fiber Bragg gratings (FBG) with strong cladding mode suppression were written in standard telecom fiber (SMF-28) with femtosecond 800-nm laser pulses and a phase mask. No special fiber photosensitization or fiber design was required. Induced index modulations were created by two-beam interference from the phase mask in both the core and cladding region, which resulted in cladding-mode coupling loss <0.1 dB for a high reflecting -30 dB in transmission FBG.     

Bragg Gratings Made in Highly Nonlinear Bismuth Oxide Fibers With Ultrafast IR Radiation

High-quality Bragg gratings with refractive index modulations $>7times 10^{-4}$ were induced in highly nonlinear bismuth oxide glass fibers using ultrafast infrared radiation and a phase mask. Grating reflectivities approaching 95% for a 6-mm-long grating were achieved. Annealing tests show good thermal stability of the grating structure below 220 $^{circ}hbox{C}$ . The Bragg resonance shift with temperature is observed to be 3–4 times higher than similar gratings in silica fiber.      

Localized High Birefringence Induced in SMF-28 Fiber by Femtosecond IR Laser Exposure of the Cladding

A process for creating a local high fiber birefringence and large variation in refractive-index modulation with a polarization in fiber Bragg gratings using post writing exposures with femtosecond pulses is presented. A birefringence as high as ~8 times 10^-4 was obtained in the core of SMF-28 fiber by exposing the cladding of the fiber in close proximity to the core/cladding interface with a modulated multibeam interference field created by a phase mask. The birefringence is likely due to the induced stress rather than the direct asymmetric refractive index modification.     

High birefringence fibre Bragg gratings written in tapered photonic crystal fibre with femtosecond IR radiation

High birefringence Bragg gratings were written with ultrafast 800 nm radiation in non-birefringent pure silica core photonic crystal fibres (PCF) that were tapered with an oxy-hydrogen flame. The grating spectra indicate that a birefringence above 10^-3 was created in the tapered PCF     

Femtosecond IR laser fabrication of Bragg gratings in photonic crystal fibers and tapers

Fiber Bragg gratings were written in pure silica photonic crystal fibers (PCFs) and PCF tapers with 125-fs 800-nm infrared radiation. High reflectivities were achieved with short exposure times in the tapers. Both multimode and single-mode grating reflections were achieved in the fiber tapers.