Other

Peter W E Smith

John Edward Sipe

Thomas Szkopek

David J F Cooper

A novel multimode fiber structure with modal propagation characteristics tailored to facilitate the creation of narrowband, high reflectivity, fiber Bragg gratings is disclosed. The fiber structure comprises concentric cylindrical shells of higher and lower refractive index material. A full vector, second order finite element method is used to analyze the proposed multimode fiber structure. Simulations of the modal profiles show that high order modes are localized to particular high refractive index shells. We present the theoretical characterization of the modal propagation constant as a function of inner shell radius, shell separation, and harmonic mode parameter. It is shown that a fiber with a minimum inner shell radius of at least 25&lgr; (where &lgr; is the vacuum wavelength), and a minimum shell separation of at least 10&lgr; provides a reasonable trade off between fiber size and grating performance. A simulation of the multimode fiber grating shows that a grating with a FWHM bandwidth on the order of 10 &lgr; is theoretically possible if optical power is launched strictly into modes with angular harmonic parameter p&equals;1.

Multimode fiber for narrowband bragg gratings

The present invention provides a method and devices for time division multiplexing of a fiber optic serial Bragg grating sensor array containing more than one Bragg grating. The device provides a pulse read-out system that allows for a reduction in system noise and an increase in sensor resolution and flexibility. In one aspect the optical signals reflected from the Bragg grating sensor array are gated by an electronically controlled optical modulator before any wavelength measurement is performed to determine the sensor information. This offers significant advantages since the sensor information is encoded into the wavelength of the optical signal and not its intensity. Therefore the sensor signal information is not distorted by the gating. Since the gating or switching of the optical modulator is performed on the optical signal, the speed of the electronic processing needs only to be performed at the speed of variation of the sensor information and the choice of methods of wavelength measurement is not influenced by the gating action. The device may include one or more optical amplifiers that provide the ability to demultiplex the reflected signals electronically.

Method and devices for time domain demultiplexing of serial fiber bragg grating sensor arrays

The present invention provides a method and device for to implement time division multiplexing of a fiber optic serial Bragg grating sensor array containing more than one Bragg grating. The device provides a pulse read-out system that allows for a reduction in system noise and an increase in sensor resolution and flexibility. The optical signals reflected from the Bragg grating sensors are gated by an electronically controlled optical modulator before any wavelength measurement is performed to determine the sensor information. This offers significant advantages since the sensor information is encoded into the wavelength of the optical signal and not its intensity. Therefore the sensor signal information is not distorted by the gating. Since the gating or switching of the optical modulator between transmission and attenuating states is performed on the optical signal, the speed of the electronic processing needs only to be performed at the speed of variation of the sensor information and the choice of methods of wavelength measurement is not influenced by the gating action.

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Toronto, Canada

Peter W E Smith