Temperature-compensated high strain measurement based on a Fabry-Perot interferometer with the virtual-assisted Vernier effect.

A highly sensitive optical fiber Fabry-Perot interferometer (FPI) for strain measurement with temperature compensation is proposed. Instead of using another actual reference interferometer, a virtual FPI is constructed to superpose with the sensing FPI to form the Vernier effect. The fundamental and the first-order harmonic Vernier effect are generated to increase the sensitivity by adjusting the parameter of the virtual FPI. In order to separate the strain from the environment temperature, an FBG is cascaded to distinguish the applied temperature. Experimental results demonstrate that, with the help of the fundamental Vernier effect, the sensitivity and temperature of the FPI increases from 1.05 pm/°C to 10.63 pm/°C in the temperature range of 40-120°C, and the sensitivity of strain increases from 2.635 pm/µÎµ to 33.11 pm/µÎµ in the strain range of 0-400 µÎµ. In order to access the tracking points more easily and further enhance the sensitivities, the first-order harmonic Vernier effect is generated by modifying the virtual FPI. Results show that the temperature and strain sensitivities are 21.25 pm/°C and 62.25 pm/µÎµ, respectively. In addition, with the help of the FBG, the strain can be separated from the temperature by solving the cross-sensitivity matrix.

Christiansen filters realized with cylindrical lenses of even symmetry.

A type of Christiansen filter that takes the form of a smooth cylindrical lens of even symmetry is proposed. By varying the shape of the lens, the filter can be made to realize many common filtering responses, including the polynomial function response, the Gaussian function response, and the sinc function response. A systematic design technique based on inverse scattering is established, and a desired, prescribed response can be tailored by properly shaping the lens of the filter. Three prototypical Christiansen filters, namely, a second-order all-real-roots filter, a second-order sinc filter, and a Gaussian filter, are synthesized using the proposed method. A prescribed response at 545 nm with a FWHM of 2 nm is achieved systematically by all of the three Christiansen filters.