Order Fiber Bragg Gratings Research Articles

An intrinsic sensitivity calibration scheme for high temperature measurements using femtosecond point-by-point written fiber Bragg gratings

A calibration method is presented for temperature measurements using fiber Bragg grating transducers written with the point-by-point technique and femtosecond laser impulsions in silica optical fibers. This method is based on the determination of the wavelength-independent thermal sensitivity coefficients of the waveguide over the temperature range of interest. The calibration law is calculated using the wavelength comb-like spectrum of high order fiber Bragg gratings, allowing measurement accuracy comparable to type N thermocouples up to 900°C. The effects of thermal cycling and annealing on measurement errors are also discussed.

Line-by-line fiber Bragg grating fabrication by femtosecond laser radiation

We report on the fabrication of second order and fourth order fiber Bragg gratings (FBGs) in standard single mode telecom fiber through the polymer coating made line-by-line technique using femtosecond laser radiation. Measurement of spectral characteristics were performed in the reflection mode of the input signal of tunable laser.

Femtosecond laser filaments for rapid and flexible writing of fiber Bragg grating.

A new beam delivery method is introduced for controlling filament formation in optical fiber that enables point-by-point writing of 1st order fiber Bragg gratings (FBGs) with single femtosecond laser pulses. Uniform filament tracks with azimuthal symmetry were formed fully through the 9.3 µm core waveguide by a modified immersion focusing method to eliminate astigmatism by the cylindrical fiber shape. Filament arrays were precisely assembled inside of single-mode fiber, generating strong FBG resonances in the telecommunication band. Laser exposure control within this unique thin-grating geometry were key to manipulating the relative strength of the Bragg and cladding mode resonances while also independently tailoring their spectral resolution and features. This filament-by-filament writing rapidly forms gratings with highly flexible pattern control to tune wavelength, or introduce optical defects, demonstrated by a π-shifted FBG having a sharp 25pm resonance embedded within a broader Bragg peak.

Point-by-point femtosecond laser micro-processing of independent core-specific fiber Bragg gratings in a multi-core fiber.

Four 3rd order fiber Bragg gratings were inscribed into separate cores of a 7 core multi-core fiber using the point-by-point inscription technique. A 1030 nm, 206 ± 5 fs laser was used, operating at a frequency of 1 kHz and pulse energy of 2.1 ± 0.2 µJ. Independent Bragg resonances at λB = 1541.01 ± 0.02, 1547.82 ± 0.02, 1532.66 ± 0.02, and 1537.42 ± 0.02 nm and extinction ratios of 13.97 ± 0.4, 16.02 ± 0.4, 10.08 ± 0.4 and 13.40 ± 0.4 dB were recorded. Our data analysis shows that refractive index changes, Δn, of the order 10-3 were induced. Core-specific inscription of fiber Bragg gratings in a multi-core fiber can provide a flexible and versatile platform to address the needs of recent space division multiplexed transmission and optical sensor networks.

Analysis of ultraviolet fringes contrast on first and second order Fiber Bragg gratings written by prism interferometers

A numerical analysis on the refractive index modulation in first and second order of type I fiber Bragg gratings (FBGs) written by prism interferometer fringes is presented. The analysis of FBG written by biprism interferometers has been carried out to optimize the writing position and by Lloyd prism interferometer to optimize FBG length with respect to ultraviolet (UV) beam parameter. It is analytically shown that in the biprism fringe depth, the fiber positions of maximum reflectivity in first and second orders are different and both are less than the distance of maximum beam overlap. The refractive index modulation of FBGs written by Lloyd prism varies along the FBG length. The evolution and saturation of the FBGs written by biprism and Llyod prism are different due to difference in magnitude and/or profile of the UV fringes contrast in the FBG writing plane.

Role of the 1D optical filamentation process in the writing of first order fiber Bragg gratings with femtosecond pulses at 800nm [Invited

The role of the optical filamentation of ultra-short infrared pulses at 800nm in the inscription of highly reflective and low loss fundamental order fiber Bragg gratings is investigated. The onset of the filamentation process is first evidenced through the observation of the spectra of both supercontinuum generation and plasma emission as well as through the precise measurement of the plasma-induced refractive index change. Typical samples of FBG obtained with this approach are presented.

Generation and characterization of first order fiber Bragg gratings with Bragg wavelengths in the visible spectral range

Using a combination of phase mask and interferometric inscription technique we have generated 1st order fiber Bragg gratings (FBGs) with resonance wavelengths in a wide range of the visible spectrum (VIS). We use a modified Talbot interferometer which offers great flexibility in Bragg wavelength, spatial grating length and reflectivity. Gratings with shortest grating lengths of less than 1mm and with reflectivities of more than 70% have been produced. Peak reflectivities of up to 99% have been achieved in the visible spectrum. FBGs in the visible spectral range require structure sizes in the sub 100 nm scale. Potential applications are in the field of laser and sensor technology.

The Effect of Radiation Coupling in Higher Order Fiber Bragg Gratings

The Effect of Radiation Coupling in Higher Order Fiber Bragg Gratings