Huimin Ding

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.

Sapphire fiber Bragg grating sensor made using femtosecond laser radiation for ultrahigh temperature applications

We report for the first time the inscription of retro-reflective Bragg gratings in multimode crystalline sapphire fiber. The gratings were fabricated using 800-nm femtosecond laser radiation and a phase mask. The grating behavior was investigated up to 1500/spl deg/C with no detectable reduction in the grating reflectivity or hysteresis in the Bragg resonance. Measurements of the change in the effective index of the fiber as a function of temperature are reported and the performance of the grating as a temperature sensor is evaluated.

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

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.

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.

Single and low order mode interrogation of a multimode sapphire fibre Bragg grating sensor with tapered fibres

Multimode sapphire fibre Bragg gratings (SFBG) made with an ultrafast Ti:sapphire 800 nm laser and a phase mask were probed using a tapered single mode fibre of different taper diameters to produce single and low order mode reflection/transmission responses. A configuration made of an input single mode tapered fibre and multimode silica fibre used for output coupling was also tested and has delivered a filtered multimode transmission spectrum. The tapered coupling improved the spectral resolution of the SFBG. Such improvements facilitate the utilization of the SFBG as a high temperature sensor. Wavelength shifts of the single mode response were monitored as a function of temperature up to 1500 °C with no detectable degradation in the grating strength or hysteresis in the Bragg resonance.

Bragg grating evanescent field sensor made in biconical tapered fiber with femtosecond IR radiation

Retro-reflective Bragg gratings were made with a phase mask and femtosecond radiation from a Ti : sapphire infrared laser into the core and cladding region of a tapered single-mode fiber. The evanescent field in the taper interacts with the ambient environment and the intensity of the reflected signal is used to measure the refractive index changes of the ambient environment as low as 2.5/spl times/10/sup -5/. By controlling the immersion depth of the grating taper, use of the taper as a single port point sensor for measuring fluid levels is also demonstrated.

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.

Direct measurement of the zero-dispersion wavelength of tapered fibres using broadband-light interferometry

The group velocity dispersion (GVD) curves of tapered fibres are characterized by using two-beam near infrared interferometry. Broadband light emitting diodes (LEDs) are selected to measure the tapers zero-GVD wavelength in the near infrared region of interest. The interference patterns at wavelengths near the tapered fibres zero-GVD wavelength are measured and discussed in detail. It is shown that the zero-GVD wavelength can be obtained directly from the interference pattern.

Characterization of the growths of UV-induced birefringence in effective mode index and index modulation in fiber Bragg gratings

The ultraviolet-induced polarization-mode dispersion and polarization-dependent loss of fiber Bragg gratings in single-mode fibers (SMF-28) are characterized in a real-time and in situ fashion during grating inscription. For the first time, the growths in birefringence of both the effective mode index and the index modulation are presented.