Abstract
A brief review in the cavity ring-down technique (CRD) is presented. In this review, there will only be considered the conventional fiber CRD configuration, i.e., there will only be presented researches involving cavities with two couplers with 99:1 ratios, due to the large amount of publications involving this spectroscopy method. The presented survey is divided in different topics related to the measurement of physical parameters, such as strain and temperature, curvature, pressure, refractive index, gas and biochemical sensing.

Abstract
The purpose of the present study is to present a prototype of a fiber optic based buckle transducer suitable for measuring strain caused by stretching of a tendon. The device has an E-shape and its central arm is instrumented with a fiber Bragg grating (FBG) sensor. The tendon adjusts to the E-form in a fashion that when it is stretched the central arm bends causing a shift of the Bragg's wavelength (lambda(B)) that is proportional to the amount of strain. This prototype is presented as an alternative to conventional strain gauge (SG) buckle transducers.

Abstract
Focused ion beam milling is used on chemically etched tapered fiber tips to create fiber Bragg gratings. These fiber Bragg gratings are based on a modulation of silica and external medium. This leads to a wide and structured spectrum obtained due to imperfections and the inherent structure of the tip. The fiber Bragg gratings presented are very short and have a length of 27 mu m and 43 mu m and are milled on the tapered fiber tip. They are characterized in the high temperature range 350-850 degrees C and a sensitivity of 14.4 pm/K is determined.

Abstract
This work demonstrates the viability of using a cavity ring-down technique (CRD) for remote sensing. A conventional CRD configuration is used where and optical circulator is added inside the fibre loop to couple 20 km of optical fibre with a gold mirror at its end with the purpose of remote sensing. As a proof-of-concept, an intensity sensor based on an eight-figure configuration is used at the end of the 20 km of fibre for displacement sensing. In this case, a commercial OTDR is used as modulated light source to send impulses down to the fibre ring.

Abstract
The purpose of the present work was to construct a weighing machine based on fiber Bragg gratings (FBGs) for the location of the 2D coordinates of the center of gravity (COG) of objects with complex geometry and density distribution. The apparatus consisted of a rigid equilateral triangular platform mounted on three supports at its vertices, two of them having cantilevers instrumented with FBGs. As an example, two femur bone models, one with and one without a hip stem prosthesis, are used to discuss the changing of the COM caused by the implementation of the prosthesis.

Abstract
This work presents a fiber cavity ring down (CRD) configuration for the measurement of strain. An optical time-domain reflectometer (OTDR) was used to send impulses down into the fiber loop cavity, inside of which a chirped fiber Bragg grating was placed to act as a strain sensing element. This technique could provide strain results with both conventional CRD-based configuration and the OTDR. The CRD configuration provided a linear response to strain applied in the range 0-2000 epsilon, and a sensitivity of 1.34 ns/epsilon was obtained. For the same operation range, the OTDR interrogation allowed obtaining a periodic behavior due to fiber Bragg grating scanning of the wavelength peaks of the multimode laser source while increasing strain. It is shown that the OTDR interrogation method provide a ring-down time response of about 8 s which is a great improvement when compared to the conventional CRD configuration (23 s). (c) 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1442-1444, 2015