A Highly Sensitive Fiber-Optic Fabry–Perot Interferometer Based on Internal Reflection Mirrors for Refractive Index Measurement

Abstract

In this study, a new type of highly sensitive fiber-optic Fabry–Perot interferometer (FFPI) is proposed with a high sensitivity on a wide refractive index (RI) measurement range based on internal reflection mirrors of micro-cavity. The sensor head consists of a single-mode fiber (SMF) with an open micro-cavity. Since light reflections of gold thin films are not affected by the RI of different measuring mediums, the sensor is designed to improve the fringe visibility of optical interference through sputtering the gold films of various thicknesses on the inner surfaces of the micro-cavity, as a semi-transparent mirror (STM) and a total-reflection mirror (TRM). Experiments have been carried out to verify the feasibility of the sensor’s design. It is shown that the fabricated sensor has strong interference visibility exceeding 15 dB over a wide measurement range of RI, and the sensor sensitivity is higher than 1160 nm/RIU, and RI resolution is better than 1.0 × 10−6 RIU.

Recent Developments in Micro-Structured Fiber Optic Sensors

“…The cantilever FP structure was sensitive to vibrations and able to measure frequencies in the range of 1Hz to 40 kHz. Coating was also put onto the FPI walls to increase the mirror reflectivity by a factor of about 26 [211], which has been demonstrated with a high sensitivity on a wide RI measurement range [212]. Recently, a multi-cavity structure was fabricated by the FIB technique by combining the concepts of solid silica cavity and gap cavity [207].…”

A Novel High-Performance Beam-Supported Membrane Structure with Enhanced Design Flexibility for Partial Discharge Detection

“…From the above description, as the most important sensing element, the membrane plays a vital role in the overall performance of the fiber optic EFPI sensor; e.g., the sensitivity and linear range, as well as the flatness of the central reflective region of the membrane which will influence the light intensity of Fabry-Perot interference [13,14]. …”

“…In most cases, the IM structure, as shown in Figure 2a, is extensively adopted for sensing the acoustic signals, normally made of single crystal silicon with the membrane thickness of tens of micrometers [12,13,14,15,16,17]. Obviously, only two geometrical parameters are involved in designing the structure, i.e., film thickness h and radius R , both dependent on the fundamental frequency of membrane required for a certain magnitude of PDs.…”

“…The fundamental frequency f of a circular membrane can be expressed by [18]: $f=\frac{ah}{4\pi R^2}\sqrt{\frac{E}{3\rho false(1-{\mu }^{2}false)}}=\alpha \frac{h}{R^2}$ where a is the coefficient of vibration mode, E , μ and ρ is the elastic modulus, Poisson’s ratio, and density of the membrane material, respectively, and α is the equivalent coefficient. In general, the fundamental frequency of membrane is selected in the range of 70–180 kHz, considering the influence of the noise frequency distribution in normal transformers and the attenuation of the high-frequency ultrasonic waves in the oil [1,4,6,12,13,15]. …”

Mn4+-Doped Magnesium Titanate—A Promising Phosphor for Self-Referenced Optical Temperature Sensing

“…Among the LOF technology platforms, “Lab-on-Tip” devices are particularly attractive because of the simplicity of the integration of the sensing material on the fiber tip [4]. The application of LOF approach to temperature sensing has been demonstrated using several measuring principles, like for example Fabry-Perot interferometers [5,6], Fiber Bragg gratings [7,8] or surface plasmon resonance [9,10]. Although often moderate sensitivities are reported, with resolutions of 0.55 ${}^{\circ }$C [5], the response time may be several seconds [5,8].…”