The Design of Bending Long Period of Photonic Crystal Fiber Grating Sensors

The bending photonic crystal fiber grating sensor is an important role in underwater monitoring and fire alarm systems. It is studied that the resonant wavelength expression of bending long period photonic crystal fiber gratings is deduced, it is designed that a bending long period photonic crystal fiber grating sensor system, it is calculated in theory that between the bending long period photonic crystal fiber gratings sensor resonance wavelength and the grating period and the bending strain. The result is shown by calculating and analysing in theory, the grating curvature is increased by the increase of the bending strain of the grating, and the resonance wavelength of the grating sensor is drifted, the drift amount is increased, one in this grating, the drifted amount of the resonant wavelength is 0.014 nm.

Gamma-radiation effects in pure-silica-core photonic crystal fiber

We investigated the steady state gamma-ray radiation response of pure-silica-core photonic crystal fibers（PSC-PCFs）under an accumulated dose of 500 Gy and a dose rate of 2.38 Gy/min. The radiation-induced attenuation（RIA） spectra in the near-infrared region from 800 nm to 1700 nm were obtained. We find that the RIA at 1550 nm is related with hydroxyl（OH^-） absorption defects in addition to the identified self-trapped hole（STH） defects. Moreover, it is proposed and demonstrated that reduced OH^-absorption defects can decrease the RIA at 1550 nm. The RIA at 1550 nm has effectively declined from 27.7 d B/km to 3.0 dB/km through fabrication improvement. Preliminary explanations based on the unique fabrication processes were given to interpret the RIA characteristics of PSC-PCFs. The results show that the PSC-PCFs,which offer great advantages over conventional fibers, are promising and applicable to fiber sensors in harsh environments.

Photonic crystal fiber Mach-Zehnder interferometer with microholes ablated by a femtosecond laser for refractive index sensing

A new structure of the photonic crystal fiber（PCF）based Mach-Zednder interferometer（MZI）is fabricated and presented.The structure has microholes ablated by a femtosecond laser.The fringe visibility can be enhanced more than 10 dB compared with the interferometer without a microhole.The interferometer is characterized by sodium chloride solutions for refractive index（RI）sensing.The RI sensitivities are greatly increased by the hole fabrication since it directly changes the cladding modes of the PCF.For the interferometer sensor with two holes,the RI sensitivity is 157.74 nm/RIU,which is 5 times than that of the sensor without a microhole.Microholes ablation with a femtosecond laser on PCF can increase the sensor＇s sensitivity dramatically.Femtosecond laser has a wide application prospect in the field of performance improvement of the sensors.

Intermodal interference based refractive index sensor employing elliptical core photonic crystal fiber

A refractive index(RI)sensor based on elliptical core photonic crystal fiber(EC-PCF)has been proposed.The asymmetric elliptical core introduces the polarization-dependent characteristics of the fiber core modes.The performances of intermodal interference between the intrinsic polarization fiber core modes are investigated by contrast in two interferometers based on the Mach-Zehnder(M-Z)and Sagnac interference model.In addition,the RI sensing characteristics of the two interferometers are studied by successively filling the three layers air holes closest to the elliptical core in the cladding.The results show that the M-Z interference between LP_(01)and LP_(11)mode in the same polarized direction is featured with the incremental RI sensing sensitivity as the decreasing interference length,and the infilled scope around the elliptical core has a weak correlation with the RI sensing sensitivity.Due to the high birefringence of LP11 mode,the Sagnac interferometer has better RI sensing performance,the maximum RI sensing sensitivity of 12000 nm/RIU is achieved under the innermost one layer air holes infilled with RI matching liquid of RI=1.39 at the pre-setting EC-PCF length of 12 cm,which is two orders of magnitude higher than the M-Z interferometer with the same fiber length.The series of theoretical optimized analysis would provide guidance for the applications in the field of biochemical sensing.