We report novel optical load sensors utilizing fiber Bragg grating based Fabry-Perot (FBG-FP)
structures. Each transmission peak of a FBG-FP is observed to split into two peaks due to the
birefringence effect caused by the transversal loading. Transversal loading can be measured through
the wavelength separation of the peak split, which shows a good linear relationship. We also
demonstrate a load sensing scheme based on the measurement of the beating frequency of a dualwavelength
laser employing a FBG-FP. Such a scheme also provides a new way to generate
We report a novel liquid level sensor based on a simple uniform fiber Bragg grating by monitoring
both the short-wavelength-loss peaks and its Bragg resonance. The liquid level can be measured from
the amplitude changes of the short-wavelength-loss peaks, while temperature can be measured from
the wavelength shift of the Bragg resonance. Such a scheme has some advantages including robustness,
simplicity, flexibility in choosing sensitivity, and simultaneous temperature measurement capability.
Fiber Bragg gratings (FBGs) have attracted a lot of attention in recent years due to their wide applications in optical telecommunications and smart sensing. They have been used as DWDM filters, dispersion compensators, gain flattening filters, optical switch and connection devices, and temperature/strain sensors. FBGs have been found to exhibit four different type structures according to their different growth mechanisms. Each type of FBG exhibits unique thermal and strain properties. Generally, the Type I gratings in hydrogenated and hydrogen-free fibers are used most for applications. However, some novel devices may be achieved by combinational structure of different types of gratings in the future. In this paper, we propose a novel concept of fabrication and application of FBGs with hybrid grating types. We have observed a complex growth behavior of a hybrid-type grating in the UV exposure to a B/Ge codoped fiber through a phase mask. A new model has been developed to simulate the complex growth behavior of the hybrid-type gratings, giving results in excellent agreement with experiment.
We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23nm and mutually orthogonal polarisation states was achieved by utilising the polarisation hole burning effect. An amplitude variation of less than 0.7dB over 80s period was obtained for both wavelengths.
Long period fiber grating (LPFG) can be used as active gain controlling device in EDFA. However, LPFGs fabricated in the standard telecom fiber only have a typical temperature sensitivity of 3-10nm/100 degree(s)C, which may not be sufficient for implementing tuneable filters capable of wide tuning range and high tuning efficiency. In this paper, we report a theoretical and experimental investigation of thermal properties of LPFGs fabricated in B/Ge co-doped optical fiber. We have found that the temperature sensitivity of the LPFGs in the B/Ge fiber is considerably increased compared with those produced in the standard fiber. The LPFGs written in the B/Ge fiber have achieved, on average, one order of magnitude higher sensitivity than that of the LPFGs produced in the standard telecom fiber. We have also identified that the thermal response of LPFG is strongly dependent on the order of the coupled resonant cladding mode. The maximum sensitivity of 1.75nm/ degree(s)C achieved by the 10th cladding mode of the 240micrometers LPFG is nearly 24 times that of the minimum value (0.075nm/C) exhibited by the 30th mode of the 34micrometers LPFG. Such devices may lead to high-efficiency and low-cost thermal/electrical tunable loss filters or sensors with extremely high temperature resolution.