W.H. Chung

Fiber Bragg grating sensor for simultaneous measurement of displacement and temperature

A new approach to measuring displacement and temperature simultaneously by use of a specially designed isosceles triangular cantilevered beam as a strain agent is demonstrated. A fiber Bragg grating epoxied onto the beam surface is experimentally demonstrated to have a temperature sensitivity of ~0.113 nm/ degrees C below 60 degrees C and a displacement sensitivity of 9.24x10(-2) nm/mm .

Cladding-mode-assisted recouplings in concatenated long-period and fiber Bragg gratings.

We investigate new types of mode recouplings in a concatenated grating structure comprising a long-period grating and a fiber Bragg grating. It is demonstrated that the light coupled out to the cladding mode by one of these gratings can be recoupled back to the guided mode by the other grating. Theoretical analysis based on the coupled-mode theory is presented, together with experimental results.

Chirp-Free Tuning of Fiber Bragg Grating Using a Cantilever Beam

A new approach for tuning the wavelength of a fiber Bragg grating without chirping is demonstrated. Tuning is achieved by bending a triangular cantilever beam with the grating was epoxied on its surface. The isosceles triangle was firmly fixed at its base and bending was realised by exerting a force to its vertex. Chirp-free tuning of a fiber Bragg grating over a wavelength range of 4.52 nm is demonstrated. Using a correction index of 0.7, the experimental results are in good agreement with the theoretical values.

Spectral tunable reflector based on concatenated long-period and fiber Bragg gratings

In this paper, a spectral tunable reflector based on concatenated long-period and fiber Bragg gratings, in which the cladding-mode-assisted recouplings occur is presented and the effect of grating phase on the mode recoupling mechanism is discussed.

Wavelength- and bandwidth-tunable reflective filter based on a novel fiber Bragg grating chirping technique

We demonstrate a wavelength- and bandwidth-tunable reflective filter based on a novel fiber Bragg grating chirping technique. The new technique allows grating to be chirped in a wide range without center Bragg wavelength shift. The tunabilities of the new band reflective filter are based on the responses of the grating pitch to the temperature and the applied strain gradient. It enables wavelength and bandwidth tuning ranges up to 5.2 nm and 10.9 nm, respectively.

Active interrogation technique for wavelength-division-multiplexed fiber Bragg grating sensor system

An active interrogation technique for a 16-cascaded wavelength-division multiplexing fiber Bragg grating sensor system is proposed. The system has been demonstrated using a combination of a feedback control technique, which makes the transmission of an employed tunable F-P filter track the Bragg wavelength of the interrogated sensor automatically, and a technique for choosing the output wavelength of a ring- compounded-cavity fiber laser by tuning the applied voltage of the filter. Demodulated by using an unbalanced scanning Michelson interferometer, a sensitivity of 1.682 Deg/(mu) (epsilon) has been achieved.

Improved tuning accuracy of fiber grating lasers using LVDT

A microprocessor controlled feedback system using a linear variable differential transformer to measure the compression of a fiber Bragg grating with a view to improve the tuning accuracy of a fiber grating laser is reported. This technique overcomes the large hysteresis of the PZT actuator normally used to compress the grating. A tuning range of about 20 nm with a readout wavelength accuracy of better than +/- 0.05 nm was achieved.