Fiber-tip Fabry-Perot Interferometer Research Articles

All-solid highly sensitive fiber-tip magnetic field sensor based on a Fabry-Perot interferometer with a breakpoint structure.

An all-solid fiber-tip Fabry-Perot interferometer (FPI) coated with a nickel film is proposed and experimentally verified for magnetic field sensing with high sensitivity. It is fabricated by splicing a segment of a thin-wall capillary tube to a standard single-mode fiber (SMF), then inserting a tiny segment of fiber with a smaller diameter into the capillary tube, and creating an ultra-narrow air-gap at the SMF end to form an FPI. When the device is exposed to magnetic field, the capillary tube is strained due to the magnetostrictive effect of the nickel film coated on its outer surface. In addition, owing to the unique breakpoint sensitivity-enhancement structure of the air-gap FPI, the elongation of the capillary tube whose length is over 100 times longer than the air-gap width is entirely transferred to the cavity length change of the FPI, and the sensor is extremely sensitive to the magnetic field as proved by our experiments, achieving a high sensitivity of up to 2.236 nm/mT for a linear magnetic field range from 40 to 60 mT, as well as a low-temperature cross-sensitivity of 56µT/°C. The all-solid stable structure, compact size (total length of ∼3.0 mm), and reflective working mode with high magnetic field sensitivity indicate that this sensor has good application prospects.

A hybrid self-growing polymer microtip for ultracompact and fast fiber humidity sensing

A hybrid self-growing polymer microtip is firstly proposed and fabricated as an ultracompact fiber-tip Fabry-Perot interferometer (FPI) with enhanced figure of merit (FoM). The hybrid microtip FPI is based on a sharp polymer microtip grown on an ultraviolet (UV) cured polymer film at the fiber end, which has exhibited significant interferometric visibility with high fringe contrast up to 30 dB in the reflection spectra. Using this tiny FPI, an optical fiber relative humidity (RH) sensor with the enhanced FoM of ∼ 0.95/%RH was demonstrated, which is ∼30 times higher than the previous optical fiber-based humidity sensors, and the achieved sensitivity is high enough to perform real-time human breath observation. Furthermore, the humidity sensor exhibited excellent performance in monitoring human breath with fast response time of ∼ 0.6 s. This new type of photonic microtip RH sensing element has shown advantages of compactness, flexibility, fast-response and high sensitivity, which provides a promising platform for potential applications in environmental and biological RH sensing, especially in a restricted space environment.

Suppression of parasitic interference in a fiber-tip Fabry-Perot interferometer for high-pressure measurements.

We demonstrate a novel design and fabrication process for fiber-tip Fabry-Perot interferometric (FTFPI) pressure sensors which eliminates fringe envelopes in the reflection spectrum. The outer facet reflectivity and thickness of the FTFPI silica diaphragm were reduced through orthogonal rough-polishing of the fiber end facet. A silica FTFPI sample with a diaphragm thickness of ~10.7 μm was produced and tested under hydraulic pressures ranging from 0 to 30 MPa. The proposed sensor achieved a pressure sensitivity of -284 pm/MPa at 1555 nm and could be a valuable new tool for high pressure measurements.

High-sensitive ultrasonic sensor using fiber-tip PVC diaphragm Fabry-Perot interferometer and its imaging application

A polyvinyl chloride (PVC) diaphragm based on fiber-tip Fabry-Perot interferometer (FPI) is proposed and demonstrated experimentally for ultrasonic wave (UW) three-dimensional imaging. The sensor probe is created by coating the PVC diaphragm to the end facet of a well-cut single mode fiber (SMF) using a plastic welder. The probe performs with an ultra-high UW sensitivity due to high pressure sensitivity of the PVC, and thus is capable of detecting gradient seismic physical models with different angles. By scanning the model using the proposed sensor in water and three-dimensional signals reconstruction, the imaging of the spherical model is achieved.

Growth dynamics of ZnO nanowire on a fiber-tip air bubble

We demonstrate a novel method of online monitoring of ZnO nanowire growth by an optical method. Nanowires were grown on the surface of an optical fiber tip and their effect on the spectral characteristics of a fiber-tip Fabry-Perot interferometer (FPI) was investigated. The interference fringe of the fiber tip yielded a linear red shift against the ZnO nanowire growth. Results also indicated that the ZnO thin layer has a stronger correlation with the reflection spectra variation of the FPI than the ZnO nanowires. The growth rate of the ZnO thin layer was measured by monitoring the free spectral range (FSR) of the reflection spectra, which achieved growth rates of 2 nm/min from 40 to 100 min and approximately 1.1 nm/min from 100 to 120 min in a 0.01-M growth solution, and 6.8 nm/min from 40 to 90 min in a 0.05-M growth solution. The proposed method is simple and cost effective, and has potential for wider applications in nanostructure manufacturing.

Optical fiber-tip Fabry–Perot interferometer for hydrogen sensing

A novel optical fiber-tip Fabry–Perot interferometer (FPI) coated with Pt/WO3 film was demonstrated as a hydrogen sensor. The air-cavity of FPI was formed by inserting a single mode fiber (SMF) into a partially polymer-filled glass capillary. A layer of Pt/WO3 was coated on the capillary of the FPI serving as a reaction heater upon hydrogen exposure. The heat locally raised the FPI temperature, which led to the length of air-cavity decrease due to the volume expansion of polymer. Thus, the dip wavelength of interference spectrum yielded a blue shift. The temperature compensation method based on an optical switch was proposed to eliminate the effect of ambient temperature fluctuation. Experimental investigations demonstrated a high sensitivity of −5.1nm/% at a low hydrogen concentration ranging from 0% to 0.5%.

Sub-micron silica diaphragm-based fiber-tip Fabry-Perot interferometer for pressure measurement.

We demonstrate a sub-micron silica diaphragm-based fiber-tip Fabry-Perot interferometer for pressure sensing applications. The thinnest silica diaphragm, with a thickness of ∼320 nm, has been achieved by use of an improved electrical arc discharge technique. Such a sub-micron silica diaphragm breaks the sensitivity limitation imposed by traditional all-silica Fabry-Perot interferometric pressure sensors and, as a result, a high pressure sensitivity of ∼1036 pm/MPa at 1550nm and a low temperature cross-sensitivity of ∼960 Pa/°C are achieved when a silica diaphragm of ∼500 nm in thickness is used. Moreover, the all-silica spherical structure enhanced the mechanical strength of the micro-cavity sensor, making it suitable for high sensitivity pressure sensing in harsh environments.

Low-cost fiber-tip Fabry-Perot interferometer and its application for high temperature sensing

We propose, fabricate, and demonstrate a compact fiber-tip Fabry-Perot interferometer of microcavity for high-temperature sensing. The microcavity which can be used for temperature or pressure sensing is fabricated by using arc discharge at the end of a multimode fiber, which is processed with chemical etching. Advantages of the sensor based on the fiber-tip Fabry-Perot interferometer are small size, easy fabrication, low cost and may have potential applications in space-limited and high-temperature environment.