Postfabrication exposure of gap-type bandpass filters in broadly chirped fiber gratings

Abstract

High efficiency in-fiber bandpass filters with arbitrary passband/stop-band combinations have been produced successfully with an UV postfabrication exposure technique in broadly chirped fiber gratings. By further concatenating such a bandpass filter with two additional chirped gratings we achieved a finesse as high as 220 for a 36-nm stop band. This new approach exhibits great advantages in controlling precisely the profiles of bandpass filters in terms of stop-band width, transmission wavelength and linewidth, and spacing of passbands.

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

“…So the induced refractive index modulation Δn m ¼ 4.1 Â 10 À 4 for a dip of À 12.7 dB. After exposure of 60 s, the grating in the fusion spliced region is strong enough to form two cascaded Fabry-Pérot structures [10,11] due to the higher intensity in the center of Gaussian laser beam, though the length of the fusion spliced region is only a few hundreds of micrometers, so a 3rd dip is observed at the central wavelength of 1548.46 nm. It is noted that the real refractive index profile of this PS-FBG in the experiments will be more complicated than that in the schematic.…”

“…The moving fiber/PMscanning beam technique in conjunction with a uniform PM is proposed to inscribe PS-FBG with arbitrary phase shift [8], but it needs relatively long PS-FBG device. The post-processing technique, by which the phase shift is created through exposing the middle of a uniform FBG with focused UV [9,10] or CO 2 laser [11], is also investigated. This technique possesses high quality, whereas it requires a high precise control and is time consuming.…”

“…Finally, the fusion spliced fiber is exposed by femtosecond laser through a cylindrical lens and a uniform PM which is shown in Fig. 1(c), thus a FBG-based FabryPérot structure or PS-FBG is formed [9,10]. The femtosecond laser pulses have a 35 fs duration and are generated by a Ti:sapphire amplifier at wavelength of 800 nm with pulse repetition rate of 1 kHz.…”

<title>Fabrication of highly efficient grating band-pass filters and their applications in soliton propagation system</title>

“…We have carried out a systematic investigation of practical approaches utilising the established UV-sideexposure fibre Bragg grating technique [12], with chirp and resonant grating fabrication and UV post-processing to achieve a range of profiles for fibre bandpass filters [13][14][15]. Utilisation of the chirped grating structure has been a key factor in our experiments.…”

Flat-top, wide-passband filter fabricated by CO 2 laser engraved D-shaped structure within linearly chirped fibre Bragg grating

“…Owing to counterpropagating core modes coupling, FBGs are traditionally used as band-reflection filters unless additional devices such as a coupler or high-cost circulator are employed. By creating a passband peak within the stopband using a thermal head [2], UV exposure [3], external refractive index perturbation [4], a microchannel [5], or by forming a Fabry-Perot resonator [6], several FBG-based bandpass filters have been investigated. However, the Lorentzian shape and ultra-narrow bandwidth (typically in picometres) of these reported passband filters are undesirable in WDM system applications [7], which normally require a wider bandwidth, larger transmissivity and a flatter passband top.…”