We proposed a compact design of an optical biochemical sensor based on the Mach-Zehnder interferometer (MZI), which was coupled by a ring resonator (RR) as a sensing tool. The sensor sensitivity has been determined by power difference at the output ports. The sensor enhancement has been optimized by numerically evaluating the geometrical parameters of the MZI and RR. A great sensor sensitivity depicted by Fano resonance characteristic has been demonstrated as a function of the round trip phase in the range of 4×10−4 − 4×10−4, which was changed by the presence of the sample solution in the sensing area. This optimum sensitivity has been obtained for the values of two coupling coefficients of the MZI κ 1 = κ 2 = 0.5/mm and the coupling coefficient between the MZI arm and RR κ R = 0.5/mm. Furthermore, a good profile of sensitivity exchange has been exhibited by inducing the direct current voltage to the coupling region of κ R. Finally, the output power transmission of the ring-coupled arm was depicted as a function of tunable κ R.
In order to realize working state remote monitoring for a passive net, alarm timely and correctly for the rockfall invasion, and solve the disadvantages in the existing means, such as needing power supply in situ, vulnerability to electromagnetic interference and environmental climate impact, a smart passive net structure based on the optical fiber sensing technology was designed which equipped with intercepting and sensing functions. The wire rope net as one part of the smart passive net was weaved with two kinds of optical fiber sensing elements, namely, fiber Bragg grating (FBG) perimeter severity sensors and optical fiber monitoring net with each end of the tail fiber containing an FBG probe. Based on the proposed smart structure, a combination alarm strategy for rockfall was proposed, which can distinguish transmission bug, whether the rockfall invasion or net broken occurs. Through a designed simulation test, the effectiveness of the proposed alarm strategy was certificated.
The author studied and demonstrated the various modeling aspects of long period fiber grating (LPFG) such as the core effective index, cladding effective index, coupling coefficient, coupled mode theory, and transmission spectrum of the LPFG using three-layer fiber geometry. Actually, there are two different techniques used for theoretical modeling of the long period fiber grating. The first technique was used by Vengsarkar et al who described the phenomenon of long-period fiber gratings, and the second technique was reported by Erdogan who revealed the inaccuracies and shortcomings of the original method, thereby providing an accurate and updated alternative. The main difference between these two different approaches lies in their fiber geometry. Venserkar et al used two-layer fiber geometry which is simple but employs weakly guided approximation, whereas Erdogan used three-layer fiber geometry which is complex but also the most accurate technique for theoretical study of the LPFG. The author further discussed about the behavior of the transmission spectrum by altering different grating parameters such as the grating length, ultraviolet (UV) induced-index change, and grating period to achieve the desired flexibility. The author simulated the various results with the help of MATLAB.
We designed and simulated a nano-biosensor to work in wet chemical optical processes for the determination and analysis of gaseous or liquid media. For this purpose, the optical properties of materials have been studied, and by creating the relationship between the refractive index of materials and other optical parameters, the measurement process was carried out. In this work, an optical filter based on the photonic crystal (OFPC) was used. By creating an active environment for the interaction between the substance and electromagnetic light, a situation to measure the properties of available substances in that active environment could be provided. Considering that the defect created in the OFPC may cause disruption in its operation, so the volume of the environment should be limited. Creation of defects in the structure of the nano-biosensors can increase the accuracy and quality of measurements; finally by rearranging the created defects, the output will be placed in the appropriate scope. The accuracy is increased by applying the finite difference time domain (FDTD) modeling approach in order to analyze the wave equations governing the structure of the photonics crystal.
A versatile fiber interferometer was proposed for high precision measurement. The sensor exploited a double-cavity within the unique sensing arm of an extrinsic-type fiber Fabry-Perot interferometer to produce the quadrature phase-shifted interference fringes. Interference signal processing was carried out using a modified zero-crossing (fringe) counting technique to demodulate two sets of fringes. The fiber interferometer has been successfully employed for dynamic displacement measurement under different displacement profiles over a range of 0.7 μm to 140 μm. A dedicated computer incorporating the demodulation algorithm was next used to interpret these detected data as well as plot the displacement information with a resolution of λ/64. A commercial displacement sensor was employed for comparison purposes with the experimental data obtained from the fiber interferometer as well as to gauge its performance, resulting in the maximum error of 2.8% over the entire displacement range studied.
A fiber-optic humidity sensor has been fabricated by coating a moisture sensitive polymer film to the fiber Bragg grating (FBG). The Bragg wavelength of the polyimide-coated FBG changes while it is exposed to different humidity conditions due to the volume expansion of the polyimide coating. The characteristics of sensors, including sensitivity, temporal response, and hysteresis, were improved by controlling the coating thickness and the degree of imidization during the thermal curing process of the polyimide. In the relative humidity (RH) condition ranging from 11.3% RH to 97.3% RH, the sensitivity of the sensor was about 13.5 pm/% RH with measurement uncertainty of ±1.5% RH.
Aluminum metallization using the sprayed coating for exhaust mild steel (MS) pipes of tractors is a standard practice for avoiding rusting. Patches of thin metal coats are prone to rusting and are thus considered as defects in the surface coating. This paper reports a novel configuration of the fiber optic sensor for on-line checking the aluminum metallization uniformity and hence for defect detection. An optimally chosen high bright 440 nm BLUE LED (light-emitting diode) launches light into a transmitting fiber inclined at the angle of 60° to the surface under inspection placed adequately. The reflected light is transported by a receiving fiber to a blue enhanced photo detector. The metallization thickness on the coated surface results in visually observable variation in the gray shades. The coated pipe is spirally inspected by a combination of linear and rotary motions. The sensor output is the signal conditioned and monitored with RISHUBH DAS. Experimental results show the good repeatability in the defect detection and coating non-uniformity measurement.
The excitation of the surface field and evanescent enhancement in the graphene have shown sensitive to the refractive index of surrounding media and potential applications in high-sensitivity biochemical sensing. In this paper, we investigate the graphene-coated microfiber Bragg gratings (GMFBGs) with different diameters for ammonia gas sensing. The maximum sensitivity with 6 pm/ppm was achieved experimentally when the microfiber’s diameter was about 10 μm. Moreover, by adjusting the diameter of the GMFBG, the sensing performance of the GMFBGs could be optimized. Experimental results indicated that GMFBGs with the diameter of 8 μm − 12 μm would show the characteristics of the high sensitivity, relative low attenuation, and large dynamic range.