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Fiber Bragg gratings (FBGs) inscribed by using femtosecond laser point-by-point (PbP) technology typically have high birefringence due to the elliptical cross-sectional pattern of refractive index modulations (RIMs) created in the fiber core. Additionally, a highly reflective type II PbP FBG, which has a large coupling coefficient, also exhibits large insertion loss due to the limited RIM area induced by a single femtosecond laser pulse. Here we demonstrate a slit beam shaping method for femtosecond laser PbP inscription of high-quality FBGs, featuring by high reflectivity, low insertion loss, and low birefringence. The slit beam shaping method could reduce the ellipticity in the cross-sectional pattern of RIMs without reducing the cross-sectional area, leading to low birefringence and low insertion loss. The experimental results agree well with numerical calculations. Hence, a high-quality type II PbP FBG, which has high reflectivity of 99.12% (i.e., Bragg resonance attenuation of 20.52 dB), low insertion loss of 0.30 dB, and low birefringence of 1.86 × 10−6, was successfully created by use of a slit width of 0.8 mm. Moreover, an enlarged cross-sectional area was created by use of a slit width of 0.2 mm, resulting in a high ratio of 172.46 of the coupling strength coefficient to the scattering loss coefficient in the fabricated PbP FBG, which exhibits very high reflectivity of 99.99% (i.e., a strong Bragg resonance attenuation of 46.65 dB) and low insertion loss of 0.27 dB. Such high-quality FBGs will be promising in many applications, such as optical fiber communications, sensors, and lasers. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate an automatic arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers. The proposed technology has been developed by implementing an embedded program in a commercial fusion splicer, which employs an ultraprecision motorized translation stage while the tensioning mass required by conventional inscribing technology is eliminated. More significantly, the arc-induced H-LPFGs have been reported to have potential usage as sensors in temperature, refractive index, twist stress, and strain. [ABSTRACT FROM PUBLISHER]

An integrated surface plasmon resonance (SPR) based on an Au-film-coated, side-opened suspended core fiber is proposed and simulated to develop a highly sensitive, real-time refractive index sensor. The inner surface of the side-opened hole is supposed to be uniformly deposited with a thin Au film for realizing the SPR operation. Such a sensor not only ensures a fast response time, but also brings up a designing flexibility for SPR biosensing applications. Two potential sensing mechanisms, i.e., monitoring the transmission loss spectrum peak shift and measuring the transmission power change at a fixed wavelength are utilized and analyzed to achieve a better sensitivity. Moreover, our calculation results show that this novel sensor could cover a wide index detection range with an optimized resolution of up to 2.3e−5 refractive index unit. [ABSTRACT FROM PUBLISHER]

We proposed and demonstrated a novel scheme for simultaneous measurement of temperature and refractive index (RI) by cascading a liquid-filled photonics crystal fiber (PCF) to a long period fiber grating (LPFG) written in a single-mode fiber. The liquid-filled PCF showed a high-temperature sensitivity of 1.695 nm/°C, which is two orders of magnitude higher than that of the LPFG (0.0642 nm/°C). The LPFG exhibited a blue shift with the increased RI. In contrast, liquid-filled PCF showed a total immunity to the surrounding RI. So, the temperature was solely measured by the liquid-filled PCF, and the RI information was extracted from the total response of the LPFG with the temperature effect having been compensated by the liquid-filled PCF. [ABSTRACT FROM PUBLISHER]