A high-sensitivity hydraulic pressure sensor with polydimethylsiloxane (PDMS) film-based Fabry-Perot interferometer (FPI) is experimentally demonstrated. The sensor is fabricated by splicing a single mode fiber (SMF) with a section of hollow core fiber (HCF), then filling PDMS into the HCF. By capillary effect, a thin PDMS film up to 33.75 μm is achieved, which works as a reflector of the FPI. The sensor is compact for the length of the FPI cavity as short as 137.79 μm. Due to excellent elasticity of the PDMS film, the sensor’s sensitivity is enhanced. The experimental results indicate that a hydraulic pressures sensitivity as high as 11.4 nm/kPa can be achieved within the range from 0 to 440 Pa with the detective limitation of 50 Pa. Moreover, ultra-compact device size and optical fiber configuration make it possible to sense hydraulic pressure sensitively under the harsh environment.
An erbium-doped fiber ring laser with embedded Mach–Zehnder interferometer (MZI) is constructed and experimentally demonstrated for strain and refractive index (RI) measurement. The MZI consists of a segment of thin-core fiber sandwiched between two single-mode fibers and acts as both the sensing component as well as a bandpass filter to select the lasing wavelength. The strain sensitivity of ∼-0.97 pm/μϵ and RI sensitivity of ∼44.88 nm/RIU are obtained in the range of 0 to 1750 μϵ and 1.3300 to 1.3537, respectively. The high-optical signal-to-noise ratio of >50 dB and narrow 3-dB bandwidth of <0.11 nm obtained indicate that the fiber ring laser sensor is promising for high-precision strain and RI measurement.
We demonstrate an optical Fabry–Perot interferometer fiber tip sensor based on a glass microsphere glued at the etched end of a multimode fiber. The fiber device is miniature and robust, with a convenient reflection mode of operation, a high temperature sensitivity of 202.6 pm/°C within the range from 5°C to 90°C, a good refractive index sensitivity of ∼119 nm/RIU within the range from 1.331 to 1.38, and a gas pressure sensitivity of 0.19 dB/MPa.
An optical fiber spherical end face coated with zeolite thin film is used together with a fiber Bragg grating (FBG) for simultaneous measurement of trace organic vapor and temperature. The fiber spherical end face is fabricated by using electrical arc discharge on single mode fiber and then coated with zeolite thin film. The FBG is placed in front of the zeolite film-coated fiber spherical end head. The coated fiber spherical end essentially forms an intrinsic Fabry–Perot (F–P) cavity. The trace chemical vapor concentration is measured by monitoring the interference wavelength shift of the coated optical fiber spherical F–P sensor head, due to the zeolite film adsorption to organic vapor molecules. Meanwhile, temperature is measured by monitoring the Bragg wavelength shift of the FBG. The experimental results show that the proposed trace organic vapor sensor exhibits a high sensitivity, which is 1.199 nm/ppm for isopropanol within the range from 0 to 20 ppm, and the temperature sensitivity is 10.2 pm/°C within the range from 30°C to 70°C. Such a sensor has high sensitivity, excellent repeatability, fast response, and real-time monitoring capability.
Passive harmonic mode-locking fiber laser is experimentally demonstrated with high pulse energy and excellent signal-to-noise-ratio by employing monolayer graphene and multi-mode fiber. A repetition rate of 20.26 MHz corresponding to the 3rd harmonic mode-locking has been achieved, with a pulse duration of ~ 603 fs, and a high single-pulse energy of ~1.04 nJ. The spectral width of the pulses is found to be decreased with the increase of the harmonic order. Such a fiber laser is suitable for optical access network or material processing applications.
An optical fiber in-line Mach-Zehnder interferometer based on a fiber internal mirror constructed by use of a hollow ellipsoid fabricated by femtosecond laser micromachining and fusion splicing technique is demonstrated. The interface of the hollow ellipsoid surface and air can act as an internal mirror. The device has been used for refractive index, bending and high temperature measurement and simultaneous multiple parameter sensing.
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