Rosly Abdul Rahman

FIBER BRAGG GRATING BASED SYSTEM FOR TEMPERATURE MEASUREMENTS

In this study, a fiber Bragg grating sensor for temperature measurement is proposed and experimentally demonstrated. In particular, we point out that the method is well-suited for monitoring temperature because they are able to withstand a high temperature environment, where standard thermocouple methods fail. The interrogation technologies of the sensor systems are all simple, low cost and effective as well. In the sensor system, fiber grating was dipped into a water beaker that was placed on a hotplate to control the temperature of water. The temperature was raised in equal increments. The sensing principle is based on tracking of Bragg wavelength shifts caused by the temperature change. So the temperature is measured based on the wavelength-shifts of the FBG induced by the heating water. The fiber grating is high temperature stable excimer-laser-induced grating and has a linear function of wavelength-temperature in the range of 0–285°C. A dynamic range of 0–285°C and a sensitivity of 0.0131 nm/°C almost equal to that of general FBG have been obtained by this sensor system. Furthermore, the correlation of theoretical analysis and experimental results show the capability and feasibility of the purposed technique.

Fibre optic Bragg grating sensors: a new technology for smart structure monitoring in Malaysia

Optical fibres are well known for their importance as transporter of information. However, much has been said and proved that optical fibres are essential and play their role as producers of information, that is as sensors. Recent research has proved that fibre optic sensors can be integrated in structure such as multistorey buildings, dams and bridges with the capability to monitor their strength and integrity. One component that is increasingly being used in communication and sensing is Bragg grating. A study in the implementation of a fibre optics Bragg grating (FOBG) sensors system is discussed in this paper. This study concentrates on the issues related to the utilization of FOBG sensors in smart structures.

Growth dynamics and characteristics of fabricated Fiber Bragg Grating using phase mask method

In this paper, Fiber Bragg Gratings (FBGs) are written by photoinduced refractive index changes in optical fibers. Experimental setup and results are presented to show the growth dynamics and the characteristics of the FBG that are written using phase mask method with different exposure time. In this paper, the effect of various UV exposure times and pulse energy during fabrication onto the reflectivity and Bragg wavelength has been defined.

Effect of laser and mechanical parameters on strength of fiber bragg gratings

The length of the optical fiber which contains the sensor must be able to withstand the tensile loads that will be placed on it during the duration of its service lifetime. It is important to assess the effect of the UV radiation and removal of coating on the strength of the fiber within the region where the grating has been written. In this study, we have identified the various mechanical and laser fabrication parameters which constrain the strength of fiber gratings. These factors include the laser pulse rate, laser energy per pulse, UV exposure time, methods of coating removal and environmental degradation (moisture). The variation in strength with respect to these factors is discussed in detail. However, it is observed in all the investigations that the average strength of all the fiber grating samples decreased. Finally, the enhancement of mechanical strength of fiber gratings can be achieved by adjusting the laser settings and improving the coating removal methods.

The comparative study of optical fiber coupling scheme in pigtailing of semiconductor optical amplifiers

In this paper we present analysis on three different coupling systems, i.e., butt, single ball lens, and two ball lenses between the tips of two coupled single mode fiber in semiconductor optical amplifier (SOA) module. The coupling components inside the module can be aligned in an active alignment process and attached by means of dual beam from an Nd: YAG laser welding system. The tips of the coupled fiber are ferruled inside metallic tubes to enable the attachment to the substrates through saddle-shaped welding clips. Investigations of the variations of coupling efficiency with the with working distance for the three schemes showed that two ball lenses is more efficient with coupling efficiency of 75% followed by single ball lens at 55% and butt coupling mode at 20% maximum. In addition dual ball lens configuration have shown to have better longitudinal tolerant even with an elliptical beam profile from the source fiber. This is however not the case in single ball lens and butt coupling scheme. We also observe however the optimum separation between the two lenses at in the range between 0.35 mm - 0.45 mm. This is to ensure the coupling efficiency is the highest possible within the acceptable tolerant misalignments.

Relationship between fiber gratings reflectivity and laser fabrication parameters

This study concentrates to investigate the relationship between laser fabrication parameters and reflectivity of fiber gratings. The fiber Bragg grating system, comprising Excimer Laser, Mask Aligner, Optical Spectrum Analyzer and Tunable Laser Source was utilized to fabricate the fiber gratings. A series of experiments were carried out for the fabrication of fiber gratings and to observe the effect of laser fabrication parameters on the reflectivity of fiber gratings. These samples were fabricated with different reflectivitys ranging from 27 to 93% at constant pulse rate i.e. 1Hz. The amount of reflectivity is the extent to which the index modulation in the fiber core changes. The higher the reflectivity of a fiber grating, the more microstructural changes occur within the lattice of the photosensitive core and the more the residual axial stress builds up within the cross section of the fiber. Here, we discussed only two laser fabrications parameters i.e. effect of pulse energy on reflectivity of fiber grating and effect of exposure time on reflectivity of fiber grating/Bragg wavelength. Based on the results of this study, it is inferred that reflectivity is exponentially increased, as the pulse energy increase at constant UV exposure time and attained saturation at pulse energy i.e. 165mJ. The low pulse energy produces a low reflectivity fiber Bragg grating even after a longer UV exposure time. It is also concluded that both reflectivity and Bragg wavelength are increased rapidly in the beginning with the increase of UV exposure time and then become saturated at UV exposure time i.e. 110min, even though pulse energy is constant. It means that the induced index of modulation was increased with the increasing of UV exposure time.

A partial coupling power of single mode fiber fusion

Coupled fibers are successfully fabricated by injecting hydrogen flow at 1bar and fused slightly by unstable torch flame in the range of 800-1350°C. Optical parameters may vary significantly over wide range physical properties. Coupling coefficient and refractive index are estimated from the experimental result of the coupling ratio distribution from 1% to 75%. The change of structural and geometrical fiber affects the normalized frequency (V) even for single mode fibers. Coupling ratio as a function of coupling coefficient and separation of fiber axis changes with respect to V at coupling region. V is derived from radius, wavelength and refractive index parameters. Parametric variations are performed on the left and right hand side of the coupling region. At the center of the coupling region V is assumed constant. A partial power is modeled and derived using V, normalized lateral phase constant (u), and normalized lateral attenuation constant, (w) through the second kind of modified Bessel function of the l order, which obeys the normal mode, LP01 and normalized propagation constant (b). Total power is maintained constant in order to comply with the energy conservation law. The power is integrated through V, u and w over the pulling length range of 7500-9500 μm for 1-D where radial and angle directions are ignored. The core radius of fiber significantly affects V and power partially at coupling region rather than wavelength and refractive index of core and cladding. This model has power phenomena in transmission and reflection for industrial application of coupled fibers.