Karen E. Chisholm

Bragg grating fast tunable filter for wavelength division multiplexing

A Bragg grating fast tunable filter prototype working over a linear tuning range of 45 nm with a maximum tuning speed of 21 nm/ms has been realized. The tunable filter system is based on two piezoelectric stack actuators moving a mechanical device thus compressing an apodized fiber Bragg grating. The filter allows both traction and compression and can work in transmission and in reflection. It is designed to work with a channel spacing of 100 GHz according to the ITU specifications for wavelength division multiplexing systems.

Fabrication and characterization of bandpass filters based on concatenated chirped fiber gratings

Practical, low-loss ( 30 dB out-of-band rejection over /spl sim/25 mm spectral widths. The approach adopted is based on the concatenation of two or more tailored broadband chirped gratings fabricated with low short-wavelength loss to maximize the rejection and stopband width in a filter with /spl sim/1 nm passband. The effect of thermal aging for similar complex structures is considered in the context of three different fiber types: standard telecommunication, high germania (Ge)-doped and boron/germania (B/Ge)-codoped. It is shown that while hydrogenated B/Ge-codoped fiber exhibits excellent photosensitivity, the resulting decrease in guiding strength and thermal stability may make germania-doped fiber the more attractive choice.

Highly sensitive transverse load sensing with reversible sampled fiber Bragg gratings

We present the implementation of optical load sensors utilizing mechanically induced reversible sampled fiber Bragg gratings (SFBGs). The load is measured by the reflectivity of the first-order Fourier component of the induced SFBGs. The theoretical and experimental characterization indicates that such SFBGs can be tailored to realize load sensors with high sensitivity of near-linear response and free of influence from environmental and system noises.

Quadratic behavior of fiber Bragg grating temperature coefficients

We describe the characterization of the temperature and strain responses of fiber Bragg grating sensors by use of an interferometric interrogation technique to provide an absolute measurement of the grating wavelength. The fiber Bragg grating temperature response was found to be nonlinear over the temperature range -70 degrees C to 80 degrees C. The nonlinearity was observed to be a quadratic function of temperature, arising from the linear dependence on temperature of the thermo-optic coefficient of silica glass over this range, and is in good agreement with a theoretical model.

Effects of thermal annealing on Bragg fibre gratings in boron/germania co-doped fibre

This paper shows that two annealing processes must be considered when predicting the effect of temperature on fibre Bragg gratings that have been written by UV radiation in boron/germania co-doped fibres. Both the thermal decay of the grating-related refractive index and the annealing of the boron-induced refractive index contribute to the wavelength shift observed. We have combined the theory of these two effects to match data taken experimentally (accuracy nm) and successfully explained a selection of observed wavelength shifts ranging from -2.83 to +0.75 nm.

Chirped fibre Bragg grating optical wear sensor

A novel sensor is demonstrated to allow a real-time measurement of the physical wear applied to the surface of an object. Two different measurement methods are presented, both utilizing the reflected power from a sacrificial chirped fibre Bragg grating to give the wear measurement. The measurement systems are simple to implement with the possibility of low cost designs depending on the application. The sensor can measure wear with a resolution of 120 μm.

Design and realization of dispersion slope compensators using distributed Gires-Tournois etalons

We report the design and realization of novel dispersion slope compensators (DSCs) using fiber Bragg grating-based distributed Gires-Tournois etalons (DGTEs). By offsetting the free spectral range of the DGTEs, both positive and negative DSCs have been realized. Owing to compact all-in-fiber design, such a device is an attractive solution for dispersion slope compensation, which has advantages such as low loss, low cost, low group delay ripples.

Compact FBG array structure for high spatial resolution distributed strain sensing

In this article, we report an implementation of distributed sensors that employ compact-grating-array structure, offering advantages of arbitrary dynamic range, high spatial resolution and simple interrogation by utilizing the established wavelength-division-multiplexing technique. The sensors have been demonstrated for measuring both linearly and non-linearly distributed strain with high spectral and spatial resolutions.

A strain sensing system using a novel optical fibre Bragg grating sensor and a synthetic heterodyne interrogation technique

A potential low cost novel sensing scheme for monitoring absolute strain is demonstrated. The scheme utilizes a synthetic heterodyne interrogation technique working in conjunction with a linearly chirped, sinusoidally tapered, apodized Bragg grating sensor. The interrogation technique is relatively simple to implement in terms of the required optics and the peripheral electronics. This scheme generates an output signal that has a quasi-linear response to absolute strain with a static strain resolution of ~±20 μe and an operating range of ~1000 μe.

Fast and widely tunable Bragg grating reflection filter

A fiber Bragg grating filter device linearly tunable over 45 nm is presented. The device has a maximum tuning speed of 19 nm/ms with a wavelength setting time below 1.5 ms.