An asymmetric Mach-Zehnder fiber filter was used as a substitute for fiber Bragg grating sensor, in order to solve the
problem of cross-sensitivity between strain and temperature, while the characteristics of wavelength encoding were
retained. In this paper, sensing characteristics of an asymmetric Mach-Zehnder fiber filter was analyzed theoretically.
The result showed that the frequency separation of an asymmetric Mach-Zehnder fiber filter had a nearly linear
relationship with the strain pressed on it. This conclusion had been verified by experiments. In our experiment, a
cantilever beam was employed to tune strain on the asymmetric Mach-Zehnder fiber filter. Changing of frequency
separation was used to describe the size of the strain. When variation of strain was about 1300 με, the changing of
frequency separation would be about 6 THz. While, when temperature varied between 20°C and 70°C, the changing of
frequency separation would not more than 0.02 THz. The structure of strain sensors had the advantage of wavelength
encoding. At the same time; temperature change on the effects of strain sensing had been eliminated. It could be used for
fiber-optic sensor to measure strain changes.
In this article, a novel technique of fiber sensor demodulation for fiber Michelson interferometric sensor is proposed. The
output optical signal of the interferometric sensor is processed by a hybrid optical bistable device in frequency domain.
When the optical path difference between the two arms of the sensor changing, it will cause the bistable device switching
on and switching off. The measurement is realized by counting the optoelectronic pulses. The experimental and
simulation results show that this technique with high accuracy, the resolution of the length measurement is nanometer
level.
The optical limiting (OL) properties of the nanocomposites containing highly-dispersed platinum polycrystal particles in
carbon nanoparticles (Pt/C) were studied by using a Q-switched Nd:YAG laser system at 532 nm with pulse width of 8
ns. It is observed that Pt/C water suspension exhibits stronger OL property than that of C60 toluene solution. The OL
experimental results also show that Pt/C has the conversion characteristic from reverse saturable absorption (RSA) to
saturable absorption (SA) with the increasing light intensity. The experimental results were analyzed in detail.
We report a new hybrid optical bistable device by using a 98OnmLD pumped, electrically tunable widely wavelengthswept
fiber laser. We use digital oscillograph observed the optical hysteresis in a fiber Fabry-Perot and analyze the
optical bistable operating principle, keeping the input light power constant and adjusting the bias voltage VB gradually.
We also discuss this optical bistable device applications in demodulate the fiber Fabry-Perot sensor.
In this paper, we propose a novel scheme of fiber Bragg grating interrogation by use of hybrid fiber optical bistable
device (OBD). The OBD is realized in the fiber Bragg grating (FBG) sensing element. Light source is an electronic tuned
widely swept ring fiber laser. In this experiment, FBG's are acting as optical intensity modulator and sensing elements at
same time. Combined with feedback control circuit, the OBD can be used as an optic-fiber sensor working in digital type
through bistable switching phenomenon. We discuss the mechanism of this bistable sensor. Scanning the bias Voltage on
PZT, the bistable pulse signal can be counted by circuit that operates in the manner of a pulse-equivalent. If we use 16 bit
Digital Analog Converter (DAC), the resolution will achieve 1pm level. High accuracy, high speed and high ratio of
signal to noise are the advantages of this scheme.
Utilizing the fused-taper technology, a fiber coupler with sensitive to wavelength and strain is obtained. This type
coupler is fabricated after Nth coupling period. They are usually called overcoupled devices, N is the number of coupling
period, N>>1. The relation between wavelength and coupling ratio of the coupler is analyzed. The maximum sensitive
wavelength can be control by the fused-taper technology. When a Bragg wavelength of the fiber Bragg grating (FBG) is
agreed with the maximum sensitive wavelength of the coupler, the shift of the Bragg wavelength is can be detected. In
this paper we demodulate one FBG which Bragg wavelength is at 1564.69 with the coupler. So the coupler with sensitive
to wavelength can be used to demodulate the FBG. And the sensitive to strain of the coupler is also analyzed. The
experimental data is present as the theory value, sinusoidal curve. So the coupler can also be used to detect the strain and
the temperature with the packaging of the thermal sensitive. The overcoupled couplers have a potential application to the
sensing system.
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