Paulo de Tarso Neves

Detailed analysis of the longitudinal acousto-optical resonances in a fiber Bragg modulator

The interaction frequencies between longitudinal acoustic waves and fiber Bragg grating are numerically and experimentally assessed. Since the grating modulation depends on the acoustic drive, the combined analysis provides a more efficient operation. In this paper, 3-D finite element and transfer matrix methods allow investigating the electrical, mechanical and optical resonances of an acousto-optical device. The frequency response allows locating the resonances and characterizing their mechanical displacements. Measurements of the grating response under resonant excitation are compared to simulated results. A smaller than <1.5% average difference between simulated-measured resonances indicates that the method is useful for the design and characterization of optical modulators.

Control of the long period grating spectrum through low frequency flexural acoustic waves

We have shown experimental results of the excitation of long period fiber gratings by means of flexural acoustic waves with a wavelength larger than the grating period, validated by numerical simulations. The effect of the acoustic wave on the grating is modeled with the method of assumed modes, which delivers the strain field inside the grating, then used as the input to the transfer matrix method, needed for calculating the grating spectrum. The experimental and numerical results are found to be in good agreement, even though only the strain-optic effects are taken into account.

Analysis of Mechanical Properties of a Photonic Crystal Fiber Bragg Grating Acousto‐Optic Modulator

In this work the mechanical properties of a Photonic Crystal Fiber is achieved using concepts of the rules of mixture of composite materials in order to find the effective area, effective Young’s modulus and the effective density. Results achieved by analytical method are compared to results achieved through a commercial software. Simulation results of acoustic‐induced modulation of a Photonic Crystal Fiber Bragg grating obtained using adapted Finite Element and Transfer Matrix Methods is showed. The methodology applied to study the device consists of the achieving of Photonic Crystal Fiber mechanical properties; the strain field in the whole structure is obtained by using the Finite Element Method. Further, the calculated strain field is used on the Transfer Matrix algorithm to obtain the Fiber Bragg Gratings reflected spectrum. The results are compared with conventional Fiber Bragg Gratings Acousto‐Optic modulator. Numerical results show that, due to its smaller stiffness, compared to conventional Fiber...

Fiber Bragg grating tuning with notch-type spring device

This paper presents a notch-type spring mechanism based on the traction principle for tuning fiber Bragg gratings, which magnifies the displacement of piezoelectric actuators. Practical tuning ranges up to 8 nm and tuning times below 20 ms are demonstrated. Oscillations that affect the device due to the rapid voltage change applied to the actuator are mitigated using either an electronic filter or a viscoelastic neutralizer technique.

Two-channel CWDM OADM Based on Large Bandwidth Fibre Bragg Gratings

We report on the fabrication of large bandwidth (12 nm) FBG and its application in two-channel CWDM optical add/drop multiplexer. The OADM allows complete channel dropping, showing a suppression ratio of over 20 dB between adjacent channels

Modelling the bandwidth behaviour of fibre Bragg gratings excited by low-frequency acoustic waves

A model is presented to explain the dynamically induced bandwidth increase of fibre Bragg grating spectra, when those are excited by acoustic waves at low frequencies. The approach considers the existence of both flexural and longitudinal waves propagating simultaneously in the fibre.

Acousto-optic control of the LPG spectrum for sensing applications

Experimental and numerical demonstration of the acousto-optic effect applied in long period grating by means of flexural waves is presented. The interaction between acoustic and optical waves is modeled with help of the method of assumed modes, which delivers the strain field inside the grating and the transfer matrix method, which, given the strain field as input, calculate the resultant grating spectrum. The experimental and theoretical results are found to be in good agreement. The main effect of the bends in the grating is the break of degeneracy of the circular cladding modes, leading the attenuation band to be changed. Among all the applications of this methodology, it is important to mention the possibility of use as a tunable filter, laser cavity gain controller, switching device and transducer in sensing systems.

Design of a BG-AOM based on the Combined Finite Elements and Transfer Matrix Method

We describe a combined numerical method, using the finite elements and transfer matrix techniques, to estimate the behavior of a FBG under the excitation of acoustic waves.