Robert B. Walker

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 nulled 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.

Multiple-beam interference patterns in optical fiber generated with ultrafast pulses and a phase mask

We compare the cladding patterns present in grating structures fabricated with an ultrafast laser and a phase mask with a cw beam interference model. We find that the observed patterns agree well with the model results for picosecond pulses; however, for femtosecond pulses, we show that the full bandwidth and the pulsed nature of the sources must be considered because the pattern can be affected by group-velocity walk-off. An interesting consequence of order walk-off is the possibility of pure two-beam interference generation with a phase mask in the femtosecond pulse regime.

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 grating inscription in various optical fibers with femtosecond infrared lasers and a phase mask

Since its demonstration in 2003, Bragg grating inscription with high-power femtosecond pulse duration infrared sources and phase masks has proven to be an effective and far more versatile approach to grating fabrication than the conventional ultraviolet laser technique. The ultrafast IR laser-based process allows for the creation of grating structures in glassy and crystalline material waveguides that are not typically UV-photosensitive, thereby creating new applications for Bragg gratings. In this paper we will review studies that have been performed on the development and applications of the ultrafast laser technique to fabricate gratings in various optical fibers and waveguides using phase masks.

Bragg Gratings Made With a Femtosecond Laser in Heavily Doped Er–Yb Phosphate Glass Fiber

Bragg gratings made in heavily doped phosphate glass fibers using ultrafast infrared radiation and a phase mask are reported. Refractive indexes >1.5times10-3 were induced in Er-Yb-doped phosphate fiber in a few seconds of exposure corresponding to reflectivity above 99.99% for a 6-mm-long grating. Annealing test up to 400 degC shows good thermal stability of the grating structure

Induced Bragg Gratings in Optical Fibers and Waveguides Using an Ultrafast Infrared Laser and a Phase Mask

Since its development in 2003, the technique of Bragg grating inscription in optical fibers and waveguides with ultrafast infrared radiation and a phase mask has proven to be as simple as the standard UV-laser grating writing techniques but far more versatile. The ultrafast IR laser-based process allows for the creation of grating structures in glassy and crystalline materials that are not typically UV photosensitive. In this article, we will review the studies that have been performed at the Communications Research Centre Canada on the grating formation processes as well as applications of the ultrafast laser technique to fabricate gratings in various optical fibers and waveguides.

Multiparameter Sensor Based on Single High-Order Fiber Bragg Grating Made With IR-Femtosecond Radiation in Single-Mode Fibers

Narrowband multiple high-order Bragg resonances from a single Bragg grating structure inscribed using a femtosecond IR laser and a 4.28 mum pitched phase mask are used to demonstrate a multiparameter sensor in standard low cutoff wavelength optical fiber. Six high reflectivity resonances that are observed in the wavelength range from 1 to 2 mum can be used to monitor up to six sensing parameters. Temperature and strain coefficients of the grating at each of the high-order Bragg resonances are evaluated.

All-polymer photonic devices using excimer laser micromachining

A method for preparing endfaces of polymer waveguides on plastic substrates using excimer laser radiation is presented. Using a focussed excimer laser beam at 193 nm, clean vertical cuts have been achieved through plastic substrate, polymer waveguide core, and upper cladding material. This technique allows efficient coupling of light from an optical fiber into all-polymer photonic devices and facilitates dicing and optical fiber alignment groove fabrication.

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

High-quality Bragg gratings with refractive index modulations > 7 × 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°C. The Bragg resonance shift with temperature is observed to be 3-4 times higher than similar gratings in silica fiber.

Narrowband fiber-optic phase-shifted Fabry–Perot Bragg grating filters for atmospheric water vapor lidar measurements

A unique ultranarrowband fiber-optic phase-shifted Fabry-Perot Bragg grating filter for atmospheric water vapor lidar measurements was designed, fabricated, and successfully tested. Customized optical fiber Bragg gratings were fabricated so that two transmission filter peaks occurred: one (89% transmission, 8 pm FWHM) near the 946-nm water vapor absorption line and the other peak (80% transmission, 4 pm FWHM) at a region of no absorption. Both transmission peaks were within a 2.66-nm stop band. Demonstration of tension tuning to the 946.0003-nm water vapor line was achieved, and the performance characterization of custom-made optical fiber Bragg grating filters are presented. These measurements are successfully compared to theoretical calculations using a piecewise-matrix form of the coupled-mode equations.