Ricardo E. Silva

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.

Numerical characterization of piezoelectric resonant transducer modes for acoustic wave excitation in optical fibers

The control of light in optical fibers by acoustic waves often requires a piezoelectric transducer as acoustic driver. As the fiber acoustic excitation depends on the deformation and frequency of the transducer, the analysis of the resonances and piezo mechanical behavior provides more efficient operation for acousto-optic devices. In this paper, an acousto-optic modulator is modeled using a three-dimensional finite element method in order to investigate the effect of the vibration modes of a piezoelectric disc in the excitation of acoustic waves in a fiber segment. The results indicate that in specific resonances, transducer radial and thickness modes are useful for the excitation of flexural and longitudinal acoustic waves in optical fiber.

Characterization of flexural acoustic waves in optical fibers using an extrinsic Fabry–Perot interferometer

A setup for the characterization of flexural acoustic modes in optical fibers is reported. An optical system based on an extrinsic Fabry–Perot interferometer is developed in order to measure the mechanical deformations of the fiber caused by a standing acoustic wave. Measurement of the excitation frequency and period allow estimation of the acoustic phase velocity propagating in a standard single mode and in a photonic crystal fiber.

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.

Characterization of longitudinal acoustic waves in a fiber using an extrinsic Fabry-Perot interferometer

Longitudinal acoustical modes propagating in a fiber are characterized using an extrinsic Fabry-Perot interferometer. The method allows the detection of the fiber axial deflection peaks which correspond to the acoustic resonances. The method can be further used for estimating properties of acoustic excited fibers, such as acoustic frequency and wavelength, which are essential in the design of acousto-optic devices employing Bragg gratings.

Fiber Fabry-Perot interferometer sensor for measuring resonances of piezoelectric elements

The development of a fiber extrinsic Fabry-Perot interferometer for measuring vibration amplitude and resonances of piezoelectric elements is reported. The signal demodulation method based on the use of an optical spectrum analyzer allows the measurement of displacements and resonances with high resolution. The technique consists basically in monitoring changes in the intensity or the wavelength of a single interferometric fringe at a point of high sensitivity in the sensor response curve. For sensor calibration, three signal processing techniques were employed. Vibration amplitude measurement with 0.84 nm/V sensitivity and the characterization of the piezo resonance is demonstrated.

Optical fiber sensor for characterization of piezoelectric transducers

The development of an optical fiber sensor for measuring resonances and characterizing the amplitude response of piezoelectric transducers is reported. The method based on the use of an extrinsic Fabry-Perot interferometer allows the detection of the transducer deflection peaks which correspond to the piezo resonances. Amplitude response for 1–10 V excitation range is achieved by monitoring the piezoelectric amplitude variations. Linear response with 9.7% amplitude variation/V sensitivity and resonances measurement with a < 1% error comparing with the impedance analysis method are achieved.

3D numerical investigation of double-core optical fiber properties modulated by flexural acoustic waves

The acousto-optic properties of a double-core optical fiber are numerically investigated. The behavior of the power propagation, the transmission spectrum and the acoustically induced strain in the fiber is simulated using the 3D finite element method. The results indicate a promising first approach for the design of acousto-optic devices in complex fiber geometries.

Wideband notch filter acoustically induced in a chirped fiber Bragg grating

A notch filter acoustically induced in a 1 cm long chirped fiber Bragg grating is experimentally investigated. The notch reflectivity (2.5 dB - 25 dB) and bandwidth (9 nm - 3 nm) are tuned by an electrical signal. The reduction of the grating and modulator size for achieving the acousto-optic modulation compared to previous works, points out for more efficient acousto-optic devices in standard optical fibers.

Suspended core size effect in interaction of longitudinal acoustic waves and fiber Bragg gratings

The interaction between longitudinal acoustic waves and Bragg gratings is numerically investigated for suspended core fibers. The encircle core is increased from 1 to 6.6 μm and the mechanical properties and the grating properties are calculated using a finite element method and a transfer matrix method. Interestingly, while the generated strain in the core increases with decreasing core diameter, the achievable side lobe reflectivity of the Bragg gratings is reduced.