We present an optical fiber voltage sensor by Michelsion interferometer (MI) employing a Fabry-Perot (F-P) interferometer and the DC phase tracking (DCPT) signal processing method. By mounting a MI fabricated by an optical fiber coupler on a piezoelectric (PZT) transducer bar, a dynamic strain would be generated to change the optical path difference (OPD) of the interferometer when the measured voltage was applied on the PZT. Applying an F-P interferometer to demodulate the optical intensity variation output of the MI, the voltage can be obtained. The experiment results show that the relationship between the optical intensity variation and the voltage applied on the PZT is approximately linear. Furthermore, the phase generate carrier (PGC) algorithm was applied to demodulate the output of the sensor also.
We demonstrate a fiber ring laser for high-resolution torsion measurement, where the laser cavity consists of a
Mach-Zehnder interferometer (MZI) formed with a pair of long-period fiber gratings written in a twisted single-mode
fiber (SMF) by a CO2 laser. The emitting wavelength of the laser provides a measure of the rate of the torsion applied to
the grating pair, while the direction of the wavelength shift indicates the sense direction of the applied torsion. The
narrow linewidth and the large side-mode suppression ratio of the laser can provide a much more precise measurement of
torsion, compared with passive fiber-optic torsion sensors. The torsion sensitivity achieved is 0.084 nm/(rad/m) in the
torsion range ±100 rad/m, which corresponds to a torsion resolution of 0.12 rad/m, assuming a wavelength resolution of
10 pm for a typical optical spectrum analyzer.
A novel fiber temperature sensor with high sensitivity based on a Michelson interferometer in a single-mode fiber is
constructed and demonstrated. The sensor consists of a peanut-shape structure and we demonstrated that the
peanut-shape structure can couple the light energy of the core mode into the cladding and re-couple the light in the
cladding into the core. The experimental results show that the device can be heated up to 900°C with the sensitive of
0.096nm/° when the sensor length L is ~21mm. Such kind of simple, low-cost, and highly sensitive fiber-optic
temperature sensor would find applications in sensing fields.
We present a refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer, which is realized by two
cascaded special long period gratings with rotary refractive index modulation (C-RLPFG). The wavelength shift of the
refractometer behaves good linear response in a RI range of 1.3342 to 1.3362, and the sensitivity of 14.5pm/mm for
0.01SRI change has been obtained. The sensitivity is 4 times higher than that of M-Z interferometer formed by using
normal long period fiber gratings. Such kind of high sensitivity, easy fabrication and simple structure interferometer may
find applications in chemical or biochemical sensing field.
We report the fabrication of a highly sensitive refractive-index sensor based on three cascaded single-mode fiber tapers,
in which a weak taper is sandwiched between the two tapers to improve the sensitivity of the sensor. Experimental
results show that the sensitivity of the device is 0.286 nm for a 0.01 RI change, which is about eleven times higher than
that of the normal two cascaded tapers MZ interferometer. Such kind of low-cost and highly sensitive fiber-optic
refractive index sensors will find applications in chemical or bio-chemical sensing fields.
We report a simple and robust all-fiber in-line Fabry-Perot interferometer (FPI) with bubble cavity, which is fabricated by
directly splicing a mutimode photonic crystal fiber to a conventional single mode fiber by using a commercial splicer.
The fabrication process only involves fusion splicing and cleaving. The high-temperature strain characteristic of such a
device is evaluated and experimental results shows that this FPI can be used as an ideal sensor for precise strain
measurement under high temperatures of up to 750°C. Therefore, such a FPI sensor may find important applications in
aeronautics or metallurgy areas.
Two kinds of novel in-line all-fiber interferometers, including tip Farby-Perot interferometer and compact Mach-Zehnder
interferometer, are proposed and demonstrated by automatically fusion splicing a short section of hollow fiber to the end
of a single-mode fiber (SMF) and sandwiching a section of hollow fiber in two section of SMF with a tiny intentional
lateral offset that induces the optical path difference (OPD) required to form the two interferometers, respectively.
Temperature responses of both the two interferometers are studied experimentally. It is anticipated that such an easy
making, compact and low cost fiber-optic interferometers could find important applications in practice.
A PCF-based MZI with regular and high-contrast fringe pattern is fabricated by splicing a section of PCF in between two
SMFs with a commercial available fusion splicer. Its resonant wavelength is sensitive to external bending with a
sensitivity of 3.046nm/m but independent on temperature. To that end, we also propose another kind of bending sensor
with higher sensitivity of 5.129nm/m. This device is constructed by combining an LPG and an MZI with zero offset at
the second splice. It is anticipated that the high sensitive structures will find applications in robot arms and artificial
limbs.
We present the application of a fiber-optic F-P strain sensor based on hollow-core photonic crystal fiber (HCPCF)
to measurement of stress of engine blades. The blade stress under different rotating speeds is tested by detecting the
reflected wavelength shift of the HCPCF sensor. The experimental results show that the strain has a quadratic
relationship with the rotating speed, which agrees well with the theoretical analysis. As such a HCPCF sensor with
short cavity length can stand high temperature of up to 600°C and has low temperature sensitivity, it would be
possible to realize real-time health monitoring of engine blades during operation.
Spatial-frequency division multiplexing (SFDM)/coarse-wavelength division multiplexing (CWDM) of
in-line fiber-optic etalon (ILFE) strain sensors, formed by a section of hollow-core photonic crystal fiber
(HCPCF), is reported in this paper, for the first time to the best of our knowledge. Due to the low thermal
expansion coefficient of HCPCF, such a strain sensor is much less sensitive to temperature change
compared with conventional ILFE sensors. In the meanwhile, as the transmission loss of HCPCF is very
low, the cavity length of the HCPCF sensor can be much longer than existing ILFEs, making it ideal for
use in SFDM and offering great potential to realize multiplexing of a very large number of ILFE sensors.
A SFDM/CWDM system with four HCPCF-based ILFE strain sensors is demonstrated and the
experimental results show that a strain accuracy of ±5 can be achieved.
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