FBG Length Research Articles

Quasi-Distributed Temperature and Strain Sensors Based on Series-Integrated Fiber Bragg Gratings.

Two types of series-integrated fiber Bragg gratings (SI-FBGs), i.e., strong and weak SI-FBGs, were inscribed in a standard single-mode fiber (SMF) using the femtosecond laser point-by-point technology. In the SI-FBGs inscribing system, the grating pitch of each FBG and the distance between the two adjacent FBGs in the SI-FBGs can be flexibly controlled by adjusting the inscription parameters. The strong SI-FBGs with different grating pitches and the weak SI-FBGs with an identical grating pitch were employed to successfully measure the temperature distribution in a tube furnace and the strain distribution on a cantilever beam, respectively. A high spatial resolution of less than 1 mm was achieved during the distributed temperature sensing experiment. Moreover, the spatial resolution could be improved by decreasing the distance between the two adjacent FBGs, i.e., decreasing the FBG length and the space between the two adjacent FBGs. Hence, the inscribed high-quality SI-FBGs have great potential to be developed as various quasi-distributed sensors with a high spatial resolution.

Dispersion compensation FBG with optical quadrature phase shift keying (OQPSK) modulation scheme for high system capacity

Abstract The study simulated OQPSK modulation scheme-based FBG compensation for high data rates. The signal power, noise power and output power variations with the FBG length variations are clarified with fiber length of 50 km and amplifier gain of 40 dB. The max Q Factor variations with amplifier gain variations in the presence and absence of FBG device. The eye diagram analyzer for the proposed model under the same operating conditions with the previous model with/without FBG device. Besides the signal power variations is demonstrated against spectral wavelength and time variations for the proposed model with/without FGB device. Max Q and min error rate are clarified for the proposed model with 150 km length, amplifier gain pf 40 dB with FBG device length of 6 m and without FBG device.

Smart Photonic Carbon Brush: FBG Length as Sensing Parameter

This article deals with problem of carbon brush’s length measurements. There are many applications where regular inspection is not feasible because of a number of factors including, for example, time, labor, cost and disruptions due to down time. Thus, there is a need for a system that can monitor the brush’s length to calculate it’s wear rate, while the component is in operation or without removing of the component from its operational position. We propose a novel method for characterization of carbon brush’s length. This method based on the usage of advantages of the multiplicative response of FBGs and FBG arrays: spectral parameters depend on several aspects, such as grating’s period, refractive index, it’s physical length and so on. We are the first, in our point of view, who proposed to use third parameter for sensing application and prospectively all three parameters for complex measurement: the change of FBG’s length is used to measure length of the brush and it’s wear rate, grating’s central wavelength shift for temperature (due to refractive index change) and mechanical stress (due to grating’s period variations) measurements. The results of modelling and experiments are presented.

Performance Analysis of High Speed Optical Communication using FBG

This paper based on study of communication system over fiber optics. To design high speed system with high performance it is necessary to compensate the dispersion with the help of Fiber Bragg Grating. The performance of communication system simulation is done on Optisystem simulator Vr.12 at different parameters of the system. A high speed NRZ signal is transmitted over SSMF. By simulating the design of optical communication system at different values which includes Q-Factor, Min BER, MZM-Extinction Ratio, FBG length is evaluated. With the help of eye diagram get better result.

Reduced length fibre Bragg gratings for high frequency acoustic sensing

In-fibre Bragg gratings (FBGs) are now well established for applications in acoustic sensing. The upper frequency response limit of the Bragg grating is determined by its gauge length, which has typically been limited to about 1 mm for commercially available Type 1 gratings. This paper investigates the effect of FBG gauge length on frequency response for sensing of acoustic waves. The investigation shows that the ratio of wavelength to FBG length must be at least 8.8 in order to reliably resolve the strain response without significant gain roll-off. Bragg gratings with a gauge length of 200 µm have been fabricated and their capacity to measure low amplitude high frequency acoustic strain fields in excess of 2 MHz is experimentally demonstrated. The ultimate goal of this work is to enhance the sensitivity of acoustic damage detection techniques by extending the frequency range over which acoustic waves may be reliably measured using FBGs.

Numerical modeling and design of mid-infrared FBG with high reflectivity

Based on the coupled-mode equations and transfer matrix theory, the reflective spectrums of a silica FBG centered at 1.9μm and a fluoride FBG centered at 2.8μm with different length and refractive index perturbation were calculated, respectively. The results show that the peak reflectivity and the spectrum width increase and decrease with the increasing FBG length, respectively. An increase in refractive index disturbance quantity results in the increase of both reflective peak and spectrum width. Above 99% reflectivity with the spectrum width of ∼0.6nm can be achieved for the silica FBG at 1.9μm when the length and refractive index perturbation are chosen in the range of 4.3–6.4mm and 4.32×10−4–5.36×10−4, respectively. For the fluoride FBG at 2.8μm, above 99% of the reflectivity with the spectrum width of ∼0.75nm can be achieved when the length and disturbance of refractive index are in the range of 6.0–8.0mm and 4.53×10−4–6.0×10−4.

Theoretical investigation into spectral characteristics of a semiconductor laser with dual-FBG external cavity

A new theoretical model of the dual-FBG external cavity based on the couple-mode theory has been proposed for controlling the output spectral characteristics of the semiconductor laser with dual-FBG external cavity. The output spectral characteristics have been studied through the analyses of the external cavity length, the FBG length and the fiber length between the two FBGs. The results reveal that the side mode suppression ratio (SMSR), the full wave at half maximum (FWHM), the longitudinal mode interval (LMI) and the stability of the central wavelength are mainly determined by the effective external transmissivity, the fiber length between the two FBGs and the external cavity length, respectively. Furthermore, the rising/falling tendencies of the SMSR and the FWHM are exactly opposite. There exist the maximum of the SMSR and the minimum of the FWHM in a semiconductor laser with dual-FBG external cavity. The increase of the fiber length between the two FBGs results in the exponential decrease of the LMI. The increase of the external cavity length leads to the better stability of the central wavelength.