Contents
2007
Volume: 27 Issue 2
33 Article(s)
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Atmospheric Optics and Oceanic Optics
Estimation of the Optical Turbulence in the Marine Atmospheric Surface Layer Based on Meteorological Data
[in Chinese], and [in Chinese]
A model used to estimate the optical turbulence in the marine atmospheric surface layer is developed based on the similarity theory and some modifications of the theory under the extremely stable and unstable conditions, and some numerical analyses are done. It is found that the temperature fluctuation dominates the coA model used to estimate the optical turbulence in the marine atmospheric surface layer is developed based on the similarity theory and some modifications of the theory under the extremely stable and unstable conditions, and some numerical analyses are done. It is found that the temperature fluctuation dominates the contributions to the optical turbulence when the temperature difference between the air and the sea surface is large. As the temperature difference becomes smaller, the moisture fluctuation contribution becomes dominative, especially in the infrared windows, with the lower air moisture, and the lower the air moisture, the stronger the optical turbulence. Accompanying the strengthening of the surface wind, the optical turbulence first becomes stronger with the weaker surface wind, then weaker with the stronger surface wind when the air is cooler than the sea surface, but generally becomes weaker with the air being warmer than the sea. The optical turbulence is stronger in the infrared window than that in the visible and near-infrared band when the air is cooler or slightly warmer than the sea, but they are comparable when the air is much warmer than the sea. Under the neutral and near-neutral conditions, the dependence of the vertical profile of the structure parameter of the air refractive index, C2n, on the vertical height obeys the -2/3 power law. As the surface stability becomes more stable (unstable), the absolute value of the negative power of the profile becomes smaller (bigger), and approaches to 0 (-4/3)..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 191 (2007)
Fiber Optics and Optical Communications
Cross Sensitivity of Brillouin Scattering Distributed Fiber Sensor
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Brillouin frequency shift in a Brillouin scattering-based fully distributed fiber sensor is the combined effects of strain and temperature. A single Brillouin frequency shift can't achieve the information of strain and temperature, respectively, and the cross sensitivity limits the practice of the sensor. The preseBrillouin frequency shift in a Brillouin scattering-based fully distributed fiber sensor is the combined effects of strain and temperature. A single Brillouin frequency shift can't achieve the information of strain and temperature, respectively, and the cross sensitivity limits the practice of the sensor. The present methods and working principles for solving the cross sensitivity are introduced. The relationship between Brillouin-scattering spectrum and strain or temperature of large effective area non-zero dispersion-shifted fiber (LEAF) is investigated. It is found that there are three Brillouin scattering peaks in the spectrum, which are linear with strain and temperature. The difference of Brillouin intensity between the first peak and the third peak is independent of temperature but is linear with strain. A resolution to solve the cross-sensitivity problem based on experimental results is given, and about 130 με strain and 8 ℃ temperature measurement resolution is achieved..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 197 (2007)
Novel-High Birefringence Photonic Crystal Fiber
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new type of high-birefringence photonic crystal fiber is brought forward, and the method introducing circinal holes with different sizes or elliptical holes which is used to design high-birefringence photonic crystal fiber is replaced by introducing fluorine-doped solid circles. Then the characteristics of fundmentalA new type of high-birefringence photonic crystal fiber is brought forward, and the method introducing circinal holes with different sizes or elliptical holes which is used to design high-birefringence photonic crystal fiber is replaced by introducing fluorine-doped solid circles. Then the characteristics of fundmental mode field distribution, mode cutoff, and the effect of all structure parameters on the birefringence are analyzed and discussed in detail by full-vector plane wave method. It is concluded that this type of photonic crystal fiber can offer birefringence higher than 10-3 in a rather broad wavelength range, and moreover, the peak of birefringence can be moved to the demanded wavelength by adjusting the hole spacing. Otherwise, it also has some advantages in the aspects of fiber drawing technique, fiber strength and fiber splicing..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 202 (2007)
Light Intensity-Referred and Temperature-Insensitive Fiber Bragg Grating Dynamic Pressure Sensor
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The temperature-insensitive fiber Bragg grating (FBG) dynamic pressure sensing based on reflection spectrum bandwidth modulation and differential optical power detection is proposed and experimentally demonstrated. A specially designed double-hole cantilever beam is presented to locate the FBG into the linear strain-grThe temperature-insensitive fiber Bragg grating (FBG) dynamic pressure sensing based on reflection spectrum bandwidth modulation and differential optical power detection is proposed and experimentally demonstrated. A specially designed double-hole cantilever beam is presented to locate the FBG into the linear strain-gradient region, resulting in FBG reflection spectrum symmetrical broadening and optical power linear increasing with pressure enhancing. Based on the theory of optical waveguide and material mechanics, the causation of FBG spectrum broadening under the linear strain-gradient is analyzed, and the corresponding force-to-bandwidth broadening relation and force-to-optical power relation are formulized. By replacing the traditional wavelength demodulation with optical power detection technique, the demodulating process is simplified and immune to temperature variation. For a temperature range of -10～80 ℃, the measured pressure fluctuates less than 1.8% without any temperature compensation. The system acquisition time is up to 80 Hz for dynamic pressure measurement. The experiment demonstrates the system is stable and applicable..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 207 (2007)
Impact of Aperture Averaging on Bit-Error Rate for Free-Space Optical Communication
[in Chinese], [in Chinese], and [in Chinese]
In free-space optical communication, the impact of aperture averaging of the receiver on the bit-error rate is studied. The log-irradiance variance is a parameter that reflects the log-intensity fluctuation of a certain point on the receiving aperture. If the bit-error rate solely depends on log-irradiance variance, thIn free-space optical communication, the impact of aperture averaging of the receiver on the bit-error rate is studied. The log-irradiance variance is a parameter that reflects the log-intensity fluctuation of a certain point on the receiving aperture. If the bit-error rate solely depends on log-irradiance variance, the result is just for the instance of point receiver. The covariance of log-irradiance is a parameter which is fluctuating related to the spacing between two points at the receiver plane. The aperture averaging effect connects the bit-error rate and covariance of log-irradiance. Two kinds of models are considered, spherical wave and plane wave, and the diameter of the receiving aperture is supposed as the first Fresnel zone length. The result shows that the bit-error rate decreases significantly when the aperture averaging effect is taken into account..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 212 (2007)
Fourier Optics and Signal Processing
Fast Phases Retrieval for Diffraction Optical Devices Optimal Design
[in Chinese], [in Chinese], and [in Chinese]
The shortcoming that the iterative Fourier transform algorithm (IFTA) is sensitive to initial phases is discussed. An improved IFTA algorithm with the initial phases generated by the pseudorandom phases encoding method is proposed to overcome the shortcoming. The improved method has the merits of fast iterative convergThe shortcoming that the iterative Fourier transform algorithm (IFTA) is sensitive to initial phases is discussed. An improved IFTA algorithm with the initial phases generated by the pseudorandom phases encoding method is proposed to overcome the shortcoming. The improved method has the merits of fast iterative convergence and higher precision for image retrieval. When the retrieval kinoform generated from the improved algorithm is input into a phase-only liquid crystal spatial light modulator, the expected far-field image is obtained again. A kinoform with the diffractive efficiency of 85% can be generated within 10 loops. As a quick phase retrieval algorithm, it is of value in the fields of phased array laser radar and agile beam steering..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 219 (2007)
Analysis of New Phase and Height Algorithm in Fourier Transform Profilometry
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to obtain a correct height distribution of a measured object using the conventional Fourier transform profilometry (FTP), the connecting line between the exit pupil of the projecting system and entrance pupil of the imaging device must parallel to the reference plane and in the same horizontal. Otherwise, seveIn order to obtain a correct height distribution of a measured object using the conventional Fourier transform profilometry (FTP), the connecting line between the exit pupil of the projecting system and entrance pupil of the imaging device must parallel to the reference plane and in the same horizontal. Otherwise, severe error will be introduced. We propose a new height calculation method in Fourier transform profilometry for the case of nonparallel, deduce the expression of the reference fringe and deformed fringe, and then obtain the phase-height mapping formula. As a result, we find that the conventional Fourier transform profilometry method, in which the projector and CCD camera are at the same height, is a special example of our method. The new method improved the flexibility in Fourier transform profilometry. It is easier to obtain the full-field fringes through moving either the projector or the camera. Therefore the height distribution in the case that the projector and camera are not at the same height. Both computer simulations and experiments have proved our methods..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 225 (2007)
Holography
Vectorial Analyses and Recording Direction Optimization in Two-Center Holographic Recording
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Vectorial analysis is done for Kukhtarev equations describing the nonvolatile holographic recording in doubly doped crystals, and the bulk photovoltaic effect and external electrical field are considered. On the basis of small signal approximation, the vectorial analytic solutions to the space-charge field for two-centVectorial analysis is done for Kukhtarev equations describing the nonvolatile holographic recording in doubly doped crystals, and the bulk photovoltaic effect and external electrical field are considered. On the basis of small signal approximation, the vectorial analytic solutions to the space-charge field for two-center holographic recording in the recording and readout phases are deduced. Considering the anisotropy of the space-charge field and effective electro-optic coefficient, an optimal recording direction of the two-center holographic recording is given. The optimal recording direction is determined mainly by the effective electro-optic coefficient, in (Fe, Mn):LiNbO3 crystal recording with 633 nm ordinary polarization beams, and the grating vector has a 22° angle to the optical axis and a 30° azimuth angle to x axis. But the optimal recording direction is determined mainly by the fixed space-charge field, in (Fe, Mn):LiNbO3 crystals recording with 633 nm extraordinary polarization beams, and the grating vector has a 44° angle to the optical axis and a 90° azimuth angle to x axis..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 230 (2007)
Image Processing
Robustness of Projection Algorithm for Under-Exposured Images
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A stabilization imaging system is proposed, and the feasibility of design and realization is verified by studying the robustness of gray scale projection algorithm for under-exposured images. The effect of under-exposure on the performance of gray scale projection algorithm is studied by synthetic and real video experiA stabilization imaging system is proposed, and the feasibility of design and realization is verified by studying the robustness of gray scale projection algorithm for under-exposured images. The effect of under-exposure on the performance of gray scale projection algorithm is studied by synthetic and real video experiments. The results show that, even with 1/25 exposure time and certain random noise, a favorable estimation performance of motion vector is also achieved. The projection algorithm is proved to be a fast and robust digital image stabilization technique even for under-exposured images. The projection algorithm can be used in aerial photography and spatial remote sensors to obtain stable and high resolution images, thanks to its small computational burden and robustness for under-exposured images..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 238 (2007)
Fusion of Multispectral and Panchromatic Images Based on the Physical Characteristics of Imaging System
[in Chinese], and [in Chinese]
A novel algorithm for multispectral and panchromatic images based on the physical characteristics of the imaging systems is proposed. In the new algorithm, the à trous wavelet transform is used to extract the detail information of the panchromatic image, and after being adjusted with a certain injection model, theA novel algorithm for multispectral and panchromatic images based on the physical characteristics of the imaging systems is proposed. In the new algorithm, the à trous wavelet transform is used to extract the detail information of the panchromatic image, and after being adjusted with a certain injection model, the extracted information is injected into the original multispectral images. Multispectral images with high spatial resolution are obtained. Some physical characteristics of the imaging system, including the relative spectral response of multispectral sensors, reflectance of the objects on the earth surface and radiometric calibration coefficient of each band, have been taken into account in the proposed injection model. With the proposed algorithm, the spatial quality of fused multispectral images is improved, and meanwhile the spectral characteristics of original multispectral images are preserved as much as possible. We have used the method to merge a set of IKONOS images. The results demonstrate that the proposed approach performs significantly better than other wavelet transform-based methods in the spatial resolution improvement and spectral information preservation..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 243 (2007)
Instrumentation, Measurement and Metrology
Laser Detection by Electronic Instead of Optical Using Two-Frequency Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A ranging system using two-frequency laser was demonstrated, and the lidar-radar system concept was introduced. The two-frequency coherent laser beam carrying 100 MHz radio beat frequency was obtained by a monolithic nonplanar ring single-frequency oscillator and an acousto-optical modulator, and used as a probe. ThrouA ranging system using two-frequency laser was demonstrated, and the lidar-radar system concept was introduced. The two-frequency coherent laser beam carrying 100 MHz radio beat frequency was obtained by a monolithic nonplanar ring single-frequency oscillator and an acousto-optical modulator, and used as a probe. Through the optical transmitting and collecting system, the displacement of the object mounted on a motorized translation stage was detected. In the signal processing, the electronic heterodyne demodulation method was adopted to deal with the signals received by high-speed photodiodes. The displacement was obtained by calculating the phase difference between reference and detection signal achieved by a high-frequency lock-in amplifier. The ranging system turns optical heterodyne into electronic heterodyne demodulation, and the repetition error is less than 3%. The system takes advantage of the signal processing technologies of radar, and meanwhile, maintains the advantages of laser detection. The ranging system provides a good repetition..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 249 (2007)
Fast and Precise Center Location for Circle Target of CCD Laser Autocollimator
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
To meet the requirements for measuring accuracy and real-time performance of CCD laser autocollimators in fields of high-accuracy metrology and aiming and tracing system, a fast and precise center location method for circle target of CCD laser autocollimator is proposed. The specific characteristics of the circle targeTo meet the requirements for measuring accuracy and real-time performance of CCD laser autocollimators in fields of high-accuracy metrology and aiming and tracing system, a fast and precise center location method for circle target of CCD laser autocollimator is proposed. The specific characteristics of the circle target edge are fully extracted by using multiple structuring elements-based generalized morphological edge detection, while the influences of the noises in images are diminished. Then, the edge is quickly located in subpixel precision by adopting the polynomial interpolation method, and the center position of the circle target is acquired accurately by using circle fitting method based on least square fitting method. Experimental results show that the proposed method is fast, stable and accurate, and the measuring accuracy of the modified CCD laser autocollimator is improved from 2 arcsec to ±0.25 arcsec in 0.23 s (a single measurement process) using the proposed method. The proposed method can efficiently fulfill the requirements for high accuracy and real-time performance of CCD laser autocollimators in small angle measuring and tracing systems..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 253 (2007)
Numerical Simulation of Surface-Roughness Measurement Based on Angular Speckle-Correlation Method Using Spatial Average
[in Chinese], [in Chinese], and [in Chinese]
Angular speckle correlation is a method of surface-roughness measurement about amplitude parameter independent on spacing characteristic of the surface roughness profile. The mathematic model of this method is usually based on ensemble average. Through simulating the speckle intensity distribution in the far field of aAngular speckle correlation is a method of surface-roughness measurement about amplitude parameter independent on spacing characteristic of the surface roughness profile. The mathematic model of this method is usually based on ensemble average. Through simulating the speckle intensity distribution in the far field of a random rough surface, we compute the degree of angular speckle correlation by substituting spatial average in speckle pattern for conventional ensemble average, and determinate the surface roughness by the mathematic model of ensemble average. The study proves the applicability of this angular speckle-correlation method using spatial average to roughness measurement. Enough measuring precision can be got, as long as a few parts of area on the same surface are measured and the results are averaged. For surfaces with a mean root square error Rq larger than 2 μm, the relative measuring error is less than 15%. According to the best measuring criterion, this method fits the surface with large roughness..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 259 (2007)
Improved Algorithm of Electromagnetic Scattering by a Multilayered Cylinder of Infinite Length for Normal Incidence and Its Application
[in Chinese], [in Chinese], and [in Chinese]
On the basis of the improved algorithm for electromagnetic scattering of plane waves by multilayered spheres, a stable, efficient numerical algorithm to compute the scattering coefficients of a multilayered cylinder of infinite length is proposed. Compared with previous algorithms, the computation for scattering field On the basis of the improved algorithm for electromagnetic scattering of plane waves by multilayered spheres, a stable, efficient numerical algorithm to compute the scattering coefficients of a multilayered cylinder of infinite length is proposed. Compared with previous algorithms, the computation for scattering field in the proposed one is extended to fairly large parameters, up to 10000 and 106 in number of layers, and the operating time is not more than several seconds. The algorithm can also be used for absorbing or nonabsorbing cylinders of infinite length in different wavebands and different fields. At last, the algorithm is used in the study on scattering of gradient refractive-index polymer optical fiber, which supplies theoretical base for non-intrusive on-line measurement of refractive index by light scattering..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 265 (2007)
Lasers and Laser Optics
Kilowatt Laser Diode-Pumped Solid-State Heat Capacity Slab Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A kilowatt laser diode stack pumped solid state heat capacity laser is studied theoretically and fabricated respectively with single slab and double Nd:YAG slabs. Using the theoretical model of heat capacity laser, the output characteristic for a certian time, the relation of the output power, temperature and time, is A kilowatt laser diode stack pumped solid state heat capacity laser is studied theoretically and fabricated respectively with single slab and double Nd:YAG slabs. Using the theoretical model of heat capacity laser, the output characteristic for a certian time, the relation of the output power, temperature and time, is obtained. The Nd:YAG slab size is 59 mm×40 mm×4.5 mm. The average pump power is 5.6 kW for single slab and 11.2 kW for double slabs, repetition rate of 1 kHz and duty cycle of 20%. In the 1 s running time, the output energy of the laser shows a fluctuation. And the maximal output energy is 1.3 J for one slab laser and 2.06 J for two slabs laser respectedly. After the 1 s process the output energy declines to 70% and 50% of the original values for two lasers respectively. The thermal effects have been minished for one slab cooled by water. The experimental results match well with the calculation data..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 280 (2007)
Er:Glass Laser with LaMgAl11O19:Co2+Passive Q-Switch
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The progress of the Er:glass lasers with passive Q-switch is discussed. The analytical expressions of the output energy and pulse width are derived. The energy, pulse width and peak power of the output pulse as functions of the cavity loss are numerically simulated. The relation between the output pulse energy and inpuThe progress of the Er:glass lasers with passive Q-switch is discussed. The analytical expressions of the output energy and pulse width are derived. The energy, pulse width and peak power of the output pulse as functions of the cavity loss are numerically simulated. The relation between the output pulse energy and input pumping energy is numerically simulated. An Er:glass laser with LaMgAl11O19:Co2+ passive Q-switch was built to verify the numerical results. The results show that the increase of cavity loss results in widening of pulse width, decling of pulse energy and peak power of the output pulse. There is only single-pulse output when the input energy is less than 12 J. When the energy is over 12 J, it brings double-pulse output. 1.535 μm laser output with energy of 2.7 mJ and peak power of 50 kW was gained in the experiments by the power supply of 8 J. In the end, the methods to increase the output pulse energy are discussed..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 287 (2007)
Materials
Beam Threshold Characteristics of Beam Fanning Effect in Ce:KNSBN Crystal
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A two-wave coupling experimental system is used to study the beam fanning effect in a Ce:KNSBN crystal under a non-synchronous readout condition. The influence of the incident beam polarization state, intensity and incident angle on the beam fanning effect is studied with single beam incidence. The results show that whA two-wave coupling experimental system is used to study the beam fanning effect in a Ce:KNSBN crystal under a non-synchronous readout condition. The influence of the incident beam polarization state, intensity and incident angle on the beam fanning effect is studied with single beam incidence. The results show that when the beam has extraordinary polarization, the beam fanning effect is more evident and there exists an obvious intensity threshold of 38.2 mW/cm2. For a constant incident angle, the steady beam fanning intensity increases with the incident beam intensity. For a constant incident beam intensity, the steady beam fanning intensity increases with the incident angle to a peak value with 15° incident angle, and then declines with the rise of incident angle. The incident beam intensity threshold characteristic and the influence of the incident beam polarization state, intensity and incident angle on the steady beam fanning intensity are physically explained..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 291 (2007)
4f5d Transition and Energy Transfer of Tb3+Doped Y2O3Nanocrystalline
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Nanocrystal powders of Y2O3:Tb with different Tb3+ doping concentrations and average sizes were prepared by chemical self-combustion, and the bulk samples of corresponding concentrations were also obtained by annealing nano-materials at high temperatures. The emission spectra, excitation spectrum, X-ray diffraction, trNanocrystal powders of Y2O3:Tb with different Tb3+ doping concentrations and average sizes were prepared by chemical self-combustion, and the bulk samples of corresponding concentrations were also obtained by annealing nano-materials at high temperatures. The emission spectra, excitation spectrum, X-ray diffraction, transmission electron microscopy images and fluorescence decay curves of Y2O3:Tb nanomaterials and bulk materials were measured. Then the 4f8 →4f75d1 transition of Tb3+ ions in Y2O3:Tb nanocrystal powders was studied. Great difference in the excitation spectral line shapes for different sized Y2O3:Tb nanocrystal powders was observed. The change of excitation spectral line shapes is because that the Tb3+ ions exist in two very different local environments——the low crystallization degree of close surface and high crystallization degree inside the particles. The absorption peaks of 4f5d transition are different in these two environments. Also the 5D3→5D4 and 5D4→5D4 energy transfer and luminescence concentration quenching caused by energy transfer were investigated. The (5D3, 7F6) →(5D4, 7F0) energy transfer is caused by interaction of electric dipoles, which is greatly affected by the quantum confinement effect. The concentration quenching of 5D4→7F5 luminescence is resulted by the energy transfer of exchange interaction among 5D4 (Tb) energy levels of different Tb3+ ions. The quantum confinement showed little influence on this type of energy transfer..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 295 (2007)
Medical Optics and Biotechnology
New Simple Method of X-Ray Beam Hardening Correction for CT Reconstruction
[in Chinese], [in Chinese], and [in Chinese]
Based on practical experiments, a new method to eliminate beam hardening effect causing cup-like artifacts in CT reconstruction, is demonstrated. The digital X-ray set FAXITRON MX-20 with a high resolution, of which the focal length of the X-ray tube is 20 μm, and the gray scale of the detecting board is 16 bit, is adoBased on practical experiments, a new method to eliminate beam hardening effect causing cup-like artifacts in CT reconstruction, is demonstrated. The digital X-ray set FAXITRON MX-20 with a high resolution, of which the focal length of the X-ray tube is 20 μm, and the gray scale of the detecting board is 16 bit, is adopted to detect samples with different thickness. Intensities of the X-ray transmitting samples of different thickness are recorded. The exponential fitting method is used to fit the related curves, and by the fitting curves the exponential correction formula is derived. By taking photons of a cylindrical sample by the micro-CT system, we reconstruct a slice of the sample with the fan-beam filtered back-projection algorithm and validate the method. The error of the exponential fitting is less than 1/3 of the results by the conventional two-order polynomial fitting. In the CT reconstruction, the clear cup-like artifact and gray scale ununiformity of the slice before hardening correction are eliminated by the exponential fitting..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 302 (2007)
Brain Signal Analysis of Functional Near-infrared Imaging Based on Hilbert-Huang Transform
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Near-infrared spectroscopy (NIRS) has been widely used to access the brain functional activity non-invasively, but traditional signal analysis methods are unsuitable for non-linear and non-stationary data. A novel signal processing method is developed by using Hilbert-Huang transform (HHT) to perform spectral analysis Near-infrared spectroscopy (NIRS) has been widely used to access the brain functional activity non-invasively, but traditional signal analysis methods are unsuitable for non-linear and non-stationary data. A novel signal processing method is developed by using Hilbert-Huang transform (HHT) to perform spectral analysis of functional NIRS signals sampled in a vision stimulation experiment based on event-related design. Compared with wavelet based multi-resolution analysis (MRA) and Fourier spectral analysis, we demonstrate that the HHT method is better in the extraction of task related signal for observation of activation in the prefrontal cortex. This method indicates a new analytical tool for functional NIRS signals and enables us to understand the episode of functional NIRS more precisely..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 307 (2007)
Nonlinear Optics
Influence on Crystal Matching Length by Group Velocity Delay in Optical Parametric Process
[in Chinese], and [in Chinese]
The theoretical model of type-Ⅰ and type-Ⅱ phase matching conditions for second harmonic generation, group velocity delay of fundamental and second harmonic, and limitation of nonlinear crystal matching length by group velocity mismatch, was obtained by using energy conservation and three-wave coupled equations in optiThe theoretical model of type-Ⅰ and type-Ⅱ phase matching conditions for second harmonic generation, group velocity delay of fundamental and second harmonic, and limitation of nonlinear crystal matching length by group velocity mismatch, was obtained by using energy conservation and three-wave coupled equations in optical parametric process of ultra-short pulses. The relation of the group velocity matching length of the harmonic and fundamental wavelength is analyzed by numerical simulation for a negative uniaxial crystal CsLiB6O10 with an 100 fs pulse. The maximum group velocity matching length of nonlinear crystal is 19.1 mm for fundamental wavelength 642 nm in type-Ⅰ and 0.89 mm for wavelength 767 nm in type-Ⅱ, which correspond to the minimum group velocity delay time, respectively..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 313 (2007)
Influences of Residual F-P Cavity Mode on Non-Degenerated Four-Wave Mixing in Distributed-Feedback Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
All-optical wavelength conversion based on four-wave mixing (FWM) is one of the key technologies in future multi-wavelength telecommunication systems. Besides semiconductor optical amplifiers, semiconductor lasers are also good candidates for wavelength conversion. The influences of the residual F-P cavity mode on the All-optical wavelength conversion based on four-wave mixing (FWM) is one of the key technologies in future multi-wavelength telecommunication systems. Besides semiconductor optical amplifiers, semiconductor lasers are also good candidates for wavelength conversion. The influences of the residual F-P cavity mode on the non-degenerated FWM in a distributed-feedback (DFB) laser have been investigated from small to large range frequency detuning, as well as the conversion efficiency of conersion FWM. The experimental results show that the conversion efficiency of FWM can be enhanced obviously by the cavity resonance when the probe wavelength matches the F-P cavity mode; the FWM with high conversion efficiency can be achieved when the frequency detuning between the injection probe frequency and free-running frequency of DFB laser is up to terahertz..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 318 (2007)
Numerical Simulation on Propagation of Ultra-Short Laser Pulse in Photonic Crystal Fibers with Different Group Velocity Dispersion Parameters
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
For a more accurate numerical simulation, the generalized nonlinear Schrdinger equation is adopted to describe the evolution of ultra-short laser pulse propagating in photonic crystal fibers, and solved by using the second-order split-step Fourier method. The nonlinear propagation of ultra-short pulse with the same puFor a more accurate numerical simulation, the generalized nonlinear Schrdinger equation is adopted to describe the evolution of ultra-short laser pulse propagating in photonic crystal fibers, and solved by using the second-order split-step Fourier method. The nonlinear propagation of ultra-short pulse with the same pulse width and energy, and generation of super-continuum spectrum are numerically simulated in different dispersion regions of photonic crystal fibers. In the different dispersion regions, the influence of high-order dispersion and nonlinear effects on the generation of super-continuum spectrum and pulse profile evolution are analyzed. The results show that, when the central wavelength of the input pulse is in the normal or abnormal dispersion regions, the super-continuum spectrum of short-wave band or long-wave band is obtained respectively (respect to the central wavelength). When the central wavelength is at the zero dispersion wavelength point of photonic crystal fibers, a flat super-continuum spectrum of the whole wave-band can be generated by combining the influence of high-order dispersion and nonlinear effect..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 323 (2007)
Physical Optics
Theoretical Simulation and Experimental Research of Cholesteric Liquid Crystal Optical Rotatory Characteristic
[in Chinese], [in Chinese], and [in Chinese]
The relationship between specific rotation of one kind cholesteric liquid crystal for CH-LCD and incidence wavelength, screw-pitch is simulated with the general cholesteric liquid crystal optical rotation theory and analyzed quantitatively. The specific rotation-temperature characteristic of this kind cholesteric liquiThe relationship between specific rotation of one kind cholesteric liquid crystal for CH-LCD and incidence wavelength, screw-pitch is simulated with the general cholesteric liquid crystal optical rotation theory and analyzed quantitatively. The specific rotation-temperature characteristic of this kind cholesteric liquid crystal is measured by means of magneto-optic modulate frequency multiplication, and the variations of screwpitch, refractive index and birefringence with temperature of this kind cholesteric liquid crystal' are simulated by using its experimental specific rotation values. The simulated results are validated by experiment finally..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 329 (2007)
Analysis of Structure Design of Flashlight Using Monte Carlo Photon Tracing Method
[in Chinese], [in Chinese], and [in Chinese]
Better distribution of the light energy in the field of view is the aim of the structure design of flashlight. Instead of the geometrical optics approaches, the Monte Carlo photon tracing method was used to analyze the structure design of flashlight. After analyzing and modeling of the camera flashlight structure (suchBetter distribution of the light energy in the field of view is the aim of the structure design of flashlight. Instead of the geometrical optics approaches, the Monte Carlo photon tracing method was used to analyze the structure design of flashlight. After analyzing and modeling of the camera flashlight structure (such as the light source, reflectors and Fresnel lens), and introducing cosine random number and other methods, we built up the model of a flashlight. At first, a single photon was traced using Monte Carlo method to simulate the behavior of the flights. Then, a large sum of photons were generated to simulate the real situation happened in the flashlight. At last, the light intensity and direction vector of photon distribution in the orthogonal coordinates was achieved. The simulated result meets the requisition and is very close to the measured one. The feasibility of using the Monte Carlo photon tracing method in the design of flashlight is proved..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 335 (2007)
Quantum Optics
Influence of Entangled-Atoms Pair on Squeezing of Field Entropy
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The entropy squeezing properties of the coherent field interacting with a pair of entangled atoms are studied by means of quantum theory. With the numerical method, the influence of two-atom's entanglement and field intensity on the field entropy squeezing properties is discussed. The results show that the initial The entropy squeezing properties of the coherent field interacting with a pair of entangled atoms are studied by means of quantum theory. With the numerical method, the influence of two-atom's entanglement and field intensity on the field entropy squeezing properties is discussed. The results show that the initial entanglement of atoms and initial intensity of field as well affect intensively both time and depth of field entropy squeezing. The greater depth and longer time of field entropy squeezing appear when the pair of atoms are initially in the maximally entangled state. The weaker the field is, the better the entropy squeezing of field is..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 340 (2007)
Superluminal Group Velocity and Effective Velocity of Information Transfer
[in Chinese], and [in Chinese]
The influence of pulse distortion on superluminal group velocity in an anomalous dispersive medium is researched. The result shows that superluminal group velocity does not disappear even if there is no distortion for light pulse. But the group velocity of a pulse is not equal to the signal velocity. An effective velocThe influence of pulse distortion on superluminal group velocity in an anomalous dispersive medium is researched. The result shows that superluminal group velocity does not disappear even if there is no distortion for light pulse. But the group velocity of a pulse is not equal to the signal velocity. An effective velocity of information transfer is defined based on the information theory, and is applied to explain the experiment that a negative group velocity was observed by Wang, Kuzmich and Dogariu (WKD). Calculation of the information content of input and output pulse shows that the information content of output pulse will decrease due to diffraction of light wave and noise of photon. The effective velocity of light propagation is not greater than the light velocity in vacuum..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 344 (2007)
Rapid Communications
Wavefront Curvature Sensor with Phase Defocus Grating
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The wavefront curvature sensor comprising a phase defocus grating is designed and fabricated. The influence of zero-order diffraction is prohibited, and the high diffractive efficiency of 49% for the ±1 diffraction orders is verified experimentally. Wavefront deformation is introduced by a phase plate. The initialThe wavefront curvature sensor comprising a phase defocus grating is designed and fabricated. The influence of zero-order diffraction is prohibited, and the high diffractive efficiency of 49% for the ±1 diffraction orders is verified experimentally. Wavefront deformation is introduced by a phase plate. The initial wavefront measurement experiment is carried out. The Green function algorithm is used for wavefront reconstruction. The reconstructed wavefront is compared with the measurement result of the Veeco interferometer. It is verified that the measurement of the self-designed curvature sensor is correct, the error percent of peak-valley value (PV) is 10%, and the error percent of root mean square (RMS) is 2%..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 377 (2007)
Spectroscopy
Autobalanced Detection Based on Tunable Diode Laser Absorption Spectroscopy
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect target gas concentration, based on the wavelength tunable characteristic of diode laser, by obtaining the absorption spectra in the characteristic absorption region. Autobalanced detection based on TDLAS can effectively eliminate laser intensTunable diode laser absorption spectroscopy (TDLAS) is a new method to detect target gas concentration, based on the wavelength tunable characteristic of diode laser, by obtaining the absorption spectra in the characteristic absorption region. Autobalanced detection based on TDLAS can effectively eliminate laser intensity noise and other common mode noise. The experiment shows that autobalanced detection could obtain ideal result. The detection limit is below volume ratio 1.2×10-6, and the precision is improved by one order of magnitude contrast to the direct absorption spectroscopy. This autobalanced detection method gains absorption spectra directly, and without signal modulation and lock-in amplifiers, so the excess laser noise is avoided. The noise-cancelling circuit is simple, and it could reduce the cost and system fit volume, and make the system apt to integrate..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 350 (2007)
Ultrafast Optics
New Method of Chirped-Pulse Spectrum Shaping Using Phase Mismatched Optical Parametric Chirped Pulse Amplification
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Phase matching is one of the important keys for high-efficiency energy conversion in optical parametric chirped pulse amplification (OPCPA). With simulation on the OPCPA process of several conventional nonlinear crystals, it is found that the spectra of output signal from phase mismatched OPCPA is broadened, and the cePhase matching is one of the important keys for high-efficiency energy conversion in optical parametric chirped pulse amplification (OPCPA). With simulation on the OPCPA process of several conventional nonlinear crystals, it is found that the spectra of output signal from phase mismatched OPCPA is broadened, and the center of spectra is depressed. It is proposed that the phase mismatched OPCPA can be a novel method for spectra shaping of chirped pulses The parameters influencing the spectra shaping process is given. The amplifying characteristics with OPCPA phase mismatching for several conventional nonlinear crystals under degenerate, quasi-degenerate and non-degenerate conditions are compared..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 354 (2007)
Vision, Color, and Visual Optics
Fast Target Recognition and Tracking Method Based on Characteristic Corner
[in Chinese], [in Chinese], and [in Chinese]
A fast target recognition and tracking method based on characteristic corner is introduced, which is efficient in target tracking and holds corners very well during tracking. The contrast of the corner-pick-up methods based on gray histogram and based on edge indicates the necessity of a new characteristic model, and aA fast target recognition and tracking method based on characteristic corner is introduced, which is efficient in target tracking and holds corners very well during tracking. The contrast of the corner-pick-up methods based on gray histogram and based on edge indicates the necessity of a new characteristic model, and a simple tracking model based on characteristic corners is advanced, with improved processing efficiency and simplified tracking target. Throughout the simulation on 11 frames of the video sequence of a battleplane, whose speed is 300 m/s in the environment of computer with Pentium 4, 80 G random access memory, software Matlab2006a, the processing speed reaches 0.7 s, and the result indicates that this method is effective and simple compared with other tracking methods..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 360 (2007)
Clapper-Yule Spectral Reflection and Transmission of Halftone Color Fluorescent ImageZ
[in Chinese], and [in Chinese]
The color prediction law of fluorescent ink half tone is a pivotal problem in the region of color imaging processing. The reflective law of color fluorescent ink half tone is generalized by utilizing the idea that the reflected light by fluorescent print is divided into two parts: primary streams which consist of origiThe color prediction law of fluorescent ink half tone is a pivotal problem in the region of color imaging processing. The reflective law of color fluorescent ink half tone is generalized by utilizing the idea that the reflected light by fluorescent print is divided into two parts: primary streams which consist of originally incident light and fluorescent streams which are created by absorption of the primary stream. And an exponential matrix modelizing the layer of fluorescent ink is utilized to compute the energy of fluorescence. The weighted factor is introduced to describe the phenomenon that the proportion is different between the exit light from the same colorant and from whole surface by taking into account the fact that proportionally more incident light through a given colorant surface is reflected back onto the same colorant surface than onto other colorant surfaces. And an improved spectral reflection Clapper-Yule model is presented for the fluorescent ink halftone..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 365 (2007)
Accuracy of Colorimetric Characterization and Effect of Black Point for CRT Monitor
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The accuracy of colorimetric characterization using the look-up table (LUT) method and effect of the black point were studied, and experiments were performed on a colorful CRT monitors of SONY G520. The experimental accuracy of characterization is presented as three kinds of color difference units of CIELAB, CIE94 and The accuracy of colorimetric characterization using the look-up table (LUT) method and effect of the black point were studied, and experiments were performed on a colorful CRT monitors of SONY G520. The experimental accuracy of characterization is presented as three kinds of color difference units of CIELAB, CIE94 and CIEDE2000: (1)0.84, 0.40 and 0.42 at considering the black point, and 1.87, 0.74 and 0.76 at not considering one in the characterization equation when the intensity of the black point is larger (i.e. CIE XYZ=1.31/1.19/0.97 in experiments); (2) 0.87, 0.41 and 0.38 at considering the black point, and 1.06, 0.47 and 0.44 at not considering one when the intensity of the black point is smaller(CIE XYZ=0.08/0.10/0.12). This result denotes that whether the effect of the black point should be considered in the characterization equation is related to the intensity of the black point. When the intensity is stronger (weaker) its effect on the accuracy of colorimetric characterization is larger (smaller)..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 27, Issue 2, 371 (2007)
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