A Sagnac loop sensor with a long-period grating (LPG) inscribed in polarization maintains fiber (PMF) for
simultaneous strain and temperature measurement is proposed. Taking using of the different responses of the LPG and
the Sagnac loop to strain and temperature, simultaneous measurement can be achieved by monitoring the wavelength
shifts and the intensity changes of resonance peaks. The experiments show that sensitivity of strain and temperature are
6.4×10-3 dB/με and 0.65 nm/°C, respectively.
A Long-Period Fiber Grating (LPFG) fabricated by CO2 laser in a symmetrical two-hole single-mode fiber (STHSMF)
for refraction index (RI) measurement is demonstrated. The solved sugar liquid of different concentration was filled into
the holes by capillary force and its RI was experimentally measured. The results show that resonant peak shifts toward
shorter wavelengths with its resonance peak intensity changes a little when the external refractive index increases. RI
sensitivity of 141.67 nm/RIU have been achieved with R2 of 0.975.The temperature sensitivity of the STHSMF is also
investigated.
In this paper, an optical Long-period fiber grating (LPG) fabricated by CO2 laser in side-hole single-mode fiber (SHLPG)
for cantilever deflection measurement was demonstrated according with LPG flexural character. resonance wavelength
of SHLPG (1547.3nm) has a total blue shift of approximately -0.83nm for deflection ranging from 0 to 40mm, and a red
shift of 0.74nm with deflection ranging from 0 to -40mm. The results indicated that the SHLPG owns higher deflection
sensitivity than that of normal LPG and fiber Bragg grating. The deflection sensitivity coefficient of SHLPG is
-0.202nm/mm. The resonance wavelength shift has a good linear with the deflection increasing. The correlative
coefficient is 0.9966. Factual deflection measuring can be got with high sensitivity through SHLPG easily.
In the paper, we propose one new type sensor with light modulation method. Having learned to delay a light signal by means of optical fibers, the temperature field may be detected by this way. According to the light speed which can be modulated in a photorefractive material in which written steady volume-index grating by two laser beams in opposite direction, the light signal may transmit with phase modulating due to intervening of another frequency shifting laser beam. In the experiment, the inner grating would be written in an optical fiber in which suitable Stannum has been doped. The periodic structure in the fiber can make the light signal reflect and the value of phase shift corresponds to the effective length of the periodic grating. According to magneto-optical Faraday effect, temperature may changes polarization direction by shifting Verdet constant. During testing period, a Sn-doped fiber is exposed to measured temperature environment and certain uniform steady field. Under this environment, the more the temperature increases, the shorter the effective interference area is in the fiber. Comparing with light delayed signal that transmits through fiber with different temperature, the delaying value may be corresponded to temperature. This research work is supported by the National Natural Science Foundation of China under grant No.60472023.
Mostly, the principle of FGB strain sensor is to detect the shift of the central wavelength of FBGs. Now, we propose a new strain sensor using light speed extraordinary controlled method in a periodic structure modulated optical fiber. According to light speed which can be modulated in a photorefractive material in which written volume-index grating by two laser beams in opposite direction of fiber, the light signal may transmit with phase modulating due to intervening of another frequency shifting laser beam. In the experiment, the inner grating would be written in an optical fiber in which suitable little Stannum has been doped. Based on quantum theory, the energy-band structure has a zero slope at the edges of Brillouin zone and the group velocity of photons at the band structure of a periodic structure is zero. Due to the effect of stress, optical principal axle rotation angle of each beam is shifted, inducing the inner effective grating changed. During the testing period, pressure is put to a point of the fiber and fiber would be partly in uniform magnetic field. Under this environment, according to elasto-optical effect and magneto-optical effect, the pressing position and pressure value can be determined. This research work is supported by the National Natural Science Foundation of China under grant No.60472023.
Under special environment, usually the magnetic intensity must be tested with full optical system. The purpose of the paper is to present theoretical analysis about testing magnetic parameter using light speed modulating and indicate the advantages to obtain new method of optical test. According to the light speed can be modulated in a photorefractive material in which written steady volume-index grating by two laser beams in opposite direction, so as to the light signal may transmit with phase modulating because of the intervening of another frequency shifting laser beam. In the experiment, the inner grating would be written in an optical fiber in which the suitable little Stannum has been doped. The periodic structure in the fiber can make the light signal reflect and the value of the phase shift is corresponding to the change of the periodic structure. With the quantum theory, the energy-band structure has a zero slope at the edges of the Brillouin zone and the group velocity of the photons at the band structure of a periodic structure is zero. According to the magneto-optical effect, the magnetic field may make the polarization plane change. After the two laser beams come into two ends of a fiber, the magnetic field can make their polarizations direction rotate and the interfering effect should be decreased simultaneously. During the testing period, a Sn-doped fiber is exposed to a magnetic field with linear distribution. Under this environment, the more increasing of magnetic intensity, the shorter length of effective steady grating in fiber is. Compared with light delayed signals transmitting through fiber in or not in the magnetic field, the delaying value may be correspondent to average magnetic intensity. This research work was supported by the National Natural Science Foundation of China under grant No.60472023.
The principle of the most of the FGB strain sensor is to detect the shift of the central wavelength in FBGs. Now, we
propose a new strain sensor using light speed extraordinary controlled method in a periodic structure modulated optical
fiber. According to the light speed can be modulated in a photorefractive material in which written volume-index grating
by two laser beams in opposite direction of fiber, so as to the light signal may transmit with phase modulating due to
intervening of another frequency shifting laser beam. In the experiment, the inner grating would be written in an optical
fiber in which the suitable little Stannum has been doped. With the quantum theory, the energy-band structure has a zero
slope at the edges of the Brillouin zone and the group velocity of the photons at the band structure of a periodic structure
is zero. Due to the effect of stress, the optical principal axle rotation angle of each beam is shifted, inducing the inner
effective grating changed. During the testing period, pressure is put to a point of the fiber and fiber would be partly in
uniform magnetic field. Under this environment, according to the elasto-optical effect and magneto-optical effect, the
pressing position and pressure value can be determined. The output signal light could be processed by various smart way.
This research work was supported by the National Natural Science Foundation of China under grant No.60472023.
During some special processing or under the special environment, usually the magnetic intensity must be tested with full
optics system. According to the light speed can be modulated in a photorefractive material in which written
volume-index grating by two laser beams in opposite direction, so as to the light signal may transmit with phase
modulating due to intervening of another frequency shifting laser beam. In the experiment, the inner grating would be
written in an optical fiber in which the suitable little Stannum has been doped. The periodic structure in the fiber can
make the light signal reflect and the value of the phase shift is corresponding to the change of the periodic structure. With
the quantum theory, the energy-band structure has a zero slope at the edges of the Brillouin zone and the group velocity
of the photons at the band structure of a periodic structure is zero. According to the magneto-optical effect, the measured
magnetic field may make the polarization plane change. After the two laser beams come into two ends of a fiber, the
magnetic field can make their polarizations direction rotate and the interfering effect should be decreased simultaneously.
During the testing period, a Sn-doped fiber is exposed to a magnetic field with linear distribution. Under this
environment, the more increasing of magnetic intensity, the shorter effective interference area is in the fiber. Comparing
with the light delayed signal that transmits through fiber that in or not in the magnetic field, the delaying value may be
corresponded to the average magnetic intensity. The output signal light could be processed by various smart way. This
research work was supported by the National Natural Science Foundation of China under grant No.60472023.
In the paper, we propose one new type sensor with using light modulation method. Having learned to delay a light signal
by means of optical fibers, the temperature filed may be detected by this way. According to the light speed can be
modulated in a photorefractive material in which written steady volume-index grating by two laser beams in opposite
direction, so as to the light signal may transmit with phase modulating due to intervening of another frequency shifting
laser beam. In the experiment, the inner grating would be written in an optical fiber in which the suitable Stannum has
been doped. The periodic structure in the fiber can make the light signal reflect and the value of the phase shift is
corresponding to the effective length of the periodic grating. According to magneto-optical Faraday effect, the
temperature may changes polarization direction by shifting the Verdet constant. During the testing period, a Sn-doped
fiber is exposed to measured temperature environment and certain uniform steady field. Under this environment, the
more increasing of temperature, the shorter effective interference area is in the fiber. Comparing with the light delayed
signal that transmits through fiber with different temperature, the delaying value may be corresponded to the temperature.
This research work was supported by the National Natural Science Foundation of China under grant No.60472023.
KEYWORDS: Crystals, Laser crystals, Modulation, Signal processing, Stereolithography, High speed photography, Electromagnetic radiation, Argon ion lasers, Modulators, Signal detection
During some high processing, such as high-speed photography and so on, the encode pulse or driving signal must be
compressed with full optics system. According to the light speed can be slowed down in a photorefractive crystal bar in
which written volume-index grating by two laser beam, so as to the light signal may be transmitted in slow speed under 1/
7 of light speed in vacuum. Because the genesis of the phenomenon is the inner index periodic structure, so the out put
signal compressed may be realized through erasing the periodic structure in the opposite direction of signal beam using
another laser beam when the signal light transmitting the crystal bar. However, every finite signal stream can be further
compressed by the same way again. Different erasing method would get many kinds of out put signal to adapt to various
design.
During some high precision measuring, the LD light beam on frequency modulating would be carried time marks using frequency, such as FMCW test system. In this system, the frequency is shifted usually by changing the injection current of a LD. In the same time, the intensity of the laser beam must be changed. This change have no use for the test. In our experiment, the intensity change can be controlled by a modulator through electronic circuits according to a high speed response detector. This is a closed-loop control system using opti-electronic method, but not a signal clipper. Then, the laser beam can be modulated on intensity through another modulator to carry available signal in the measuring system for another testing value.
Free space optical communication system is competent for its large bandwidth, the agility and short fixing time. The bandwidth is affected by many factors, and the optical system is one. This paper firstly introduces the FSO system and the constitution of its optical system, and then analyzes the impact of the lens dispersion on system communicating bandwidth. On the basis of the bandwidth limitation discussion, this paper puts forward a means to use a couple of cemented-doublets group as the transmitting lens, and use the dense whorl lens as the receiving lens. In the end, the use of such design in our own system proved the feasibly of it.
In this paper, a Michelson form interferometer not only acts as a pure unit of measurement, but also as part of the digital encoder. When a normal beam splitter is taken place of the special one which made of photorefractive material, the orders of the diffraction correspond the path light intensity and its fringe. The out put field is shown as array form. Signal would be sent by optical fiber and all system is full optical with quasi-digitized code.
Particles suspended in a fluid exhibit Brownian motion. This motion is due to collisions of the fluid molecules with the suspended particles. The smaller the particles are, the higher their frequency is. The laser light scattered by particles exhibiting Brownian motion will also fluctuate with time. The fluctuation frequency of the intensity of the scattered light will therefore depend on the size of the particles. Therefore the measured light signal contains information about the particle size. Photon correlation spectroscopy (PCS) is an important method for studying fluctuation frequency of the intensity of the scattered light, in which autocorrelation function estimation plays a key role. Accurate particle size measurements are possible only when the autocorrelation function is of high quality. Based on the character of software correlation, two measures, subtracted average from the signal and adopted non-bias estimation, were taken in this paper to improve the quality of software estimation. The results indicate that it is feasible for getting better autocorrelation estimation using the software autocorrelation method.
KEYWORDS: Modulation, Signal processing, Diffraction, Computer programming, Holography, Control systems, Interferometers, Signal to noise ratio, Electronic components, Crystals
During the high speed processing, the intensity of the light beam must be detected and converted into some digital signals without electronic device for system controlling. The A/D converting should be in full optics way. The interferometer may make some fringes correspond the input light, while the fringe intensity contains some important information. When a photorefractive material was put into the interference field, another reading-laser beam would be diffracted. The order of the diffraction can be controlled because the nonlinear reactivity of photorefractive materials. Then, the reading laser beam goes into an encoder to demodulate signals. Through the demodulating processing in light speed, the group-codes may be output as the input signals of other control system. The speed of the modulating should be tied from the photorefractive materials. The important step is how to change the time domain information into space domain information. If the responding speed of the photorefractive material is suitable to react on the input signal light, the conversion is successful. In that process, organic photorefractive materials or crystal photorefractive materials have different application features.
In this paper, a He-Ne laser not only acts as a pure light source in the interferometer, but also as part of the interferometer. When an interning system may put into the cavity of the laser, the numbers of the laser oscillating modes may be changed. If the change is detected, the distance is determined appropriately. Further accuracy data is obtained by driving the mirror moving with electric-mechanical method. Because of optical gain, the output signal is very easy to further process.
In this paper, we introduce a new method to inspect the soft and smooth surface, especially the corneal topography. The method is based on the fact that smooth surfaces have the property of reflecting light. Special-shaped gratings are used as projecting device, that is, different grating for different inspected object, according to the topographic condition. For example, a grating with the form of a series of concentric circular rings is good for corneal topography inspection. When the image which contains the topographic information of the object being tested is reflected, it is recorded by a CCD camera. Then the 2D image obtained is processed and calculated by a computer to make out a 3D profile of the surface. This article emphatically reckons a new algorithm which can deduce the corneal topography.
A synthetic type of distance ranging system is described in this paper. In this system, one frequency-modulated laser beam and two multimode laser beams that come from different lasers, having different wave length, are input to a Michelson interferometer together with the same path. When the systems start to run, the computer may send out signals driving the reference reflector to find or keep the zero optical path difference, according to the principle of frequency-modulated ranging and quasi-white light positioning with the interferometer. In the meantime, the shifted value of the reference reflector would be measured by another interferometer. Lastly, the distance can be accurately detected by that value and the environment parameters through calculating with computer. Some fundamental experiments have been done, proving the feasibility of this synthetic method.
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