Songlin Zhuang

Research on light signals extraordinary compressed using periodic structure modulated method in photorefractive materials

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.

Research of FBG strain sensors based on light speed modulating method

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.

Research on magnetic intensity sensor using light speed modulating method in an inner interfering optical fiber

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.

Research on magnetic intensity test based on light speed modulating with inner interfering

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.

Temperature test of photorefractive materials using light speed slowdown method

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.

Research on special modulations combined with intensity and frequency in one LD light beam and its applications

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.

Research on quasi-digitizing interferometer for optical measurement

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.

Research on optical A/D conversion using interference modulators

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.

Distance measurement using internal cavity interferometer

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.