The basic theories underlying the reduction of the group velocity of light are introduced and methods for achieving ultraslow light propagation are discussed. The phenomenon of spectral hole-burning in homogeneously broadened media and the experimental slowing of light in ruby are described. We discuss the significance of such research for science and applications.

Ultraslow light propagation in solid media

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 quasi-digitizing interferometer for optical measurement

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.

Research on optical A/D conversion using interference modulators

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.

Research on no-guide distance measurement using internal servo interferometer optics system

The storage of optical signals with a high speed bit-rate is one of the most impotent fields of optical information technology,for which the all-optical buffer is the bottleneck.We review recent advances in the research of all-optical buffers,with emphasis on the principle of slow light and its physical bases.The development of an all-optical buffer using electromagnetically induced transparency in semiconductor quantum dots is discussed.

Slow light and all-optical buffers

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

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 sensor using light speed modulating method in an inner interfering optical fiber

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.

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

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.

Gang Zheng

Papers

Research on quasi-digitizing interferometer for optical measurement

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

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

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

Research of FBG strain sensors based on light speed modulating method