Point-by-point inscription of phase-shifted fiber Bragg gratings with electro-optic amplitude modulated femtosecond laser pulses

Abstract

Femtosecond laser pulses were used for the direct point-by-point inscription of phase-shifted fiber Bragg gratings (FBGs) in a single fabrication step without postprocessing. An electro-optic amplitude modulator is used in the setup to generate a defined delay between two identical laser pulse trains for the grating inscription. The grating structure with a central phase shift is formed by focusing the modulated laser pulses into the core of a fiber, while the fiber is translated with a constant velocity. The induced phase shift leads to a narrow transmission band with a bandwidth considerably below 10 pm within the stop band of the FBG. The inscribed FBGs show a birefringence of 3.9×10(-5) whereas their temperature and strain sensitivities are 10.4 pm/K and 1.4 pm/μstrain, respectively. The fabrication process is fast and offers a high grade of flexibility for the control of all grating parameters.

High-temperature stable π-phase-shifted fiber Bragg gratings inscribed using infrared femtosecond pulses and a phase mask

“…Alternatively, phase-shifted FBGs can be fabricated using infrared (IR) femtosecond (fs) lasers. The primary techniques in this case are based on point-by-point/line-by-line writing [6,14,15] and displacing a uniform phase mask during the inscription [16,17]. Uniform phase masks were also used to produce phase-shifted FBGs when i) a uniform FBG was overexposed in the center [18], ii) the central part of the fs-laser beam was blocked [19] and iii) a uniform FBG was written in a length of fiber that incorporates a fusion splice [20].…”

Femtosecond Transient Bragg Gratings

“…The PbP method offers the highest flexibility in grating fabrication. Uniform gratings, phase-shifted gratings [30], apodization [31], and more [32] have been demonstrated. The tight focusing condition also enables inscription through the fiber jacket without damage [33].…”

Phase-shifted fiber Bragg grating inscription by fusion splicing technique and femtosecond laser

“…By modulating the phase and frequency of the femtosecond laser with two triggers [16] or an electro-optical modulator [17] and moving a high precise translation stage, the PS-FBG can be inscribed by point-bypoint technique. This technique is versatile and repeatable; however, it requires the synchronization of laser pulse train with writing position.…”