Contents
2005
Volume: 25 Issue 9
27 Article(s)
Export citation format
Fiber Optics and Optical Communications
A Novel High-Sensitivity Chirp Tuning Device of Fiber Grating
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A novel and simple chirp tuning device of fiber Bragg grating (FBG) is proposed, which possesses a “C” shape and consists of a straight beam and two half-round arches. A linear strain field is induced over the straight beam by applying stress on the arches. As a result, the uniform FBG bonded on the surface of the beamA novel and simple chirp tuning device of fiber Bragg grating (FBG) is proposed, which possesses a “C” shape and consists of a straight beam and two half-round arches. A linear strain field is induced over the straight beam by applying stress on the arches. As a result, the uniform FBG bonded on the surface of the beam is converted to a linearly chirped fiber grating. The bandwidth of the FBG is tuned linearly by applied stress with the sensitivity up to 0.34 nm/N and a linearity of 0.9982. In the experiment, a chirp bandwidth of about 7 nm can be obtained with the stress of 20 N. Additionally, the reflective spectra are quite flat. The experimental results are in good agreement with the analyses. Due to the characteristic of the bandwidth immunity to environmental temperature variation and large tunable range of bandwidth, the device can be applied in fields such as measurement of stress (strain, curvature, etc.), fiber laser, chromatic dispersion compensation..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1153 (2005)
Theoretical Study of Silicon-Based Two-Dimensional Photonic Crystal Coupler
[in Chinese], [in Chinese], and [in Chinese]
Photonic crystal is a new artificial material. Its unique optical properties enable it to be used in fabricating novel optical devices. In this work, a 4-port coupler is proposed theoretically in silicon based on two-dimensional silicon photonic crystals. The optical properties of the 4-port coupler device have been dePhotonic crystal is a new artificial material. Its unique optical properties enable it to be used in fabricating novel optical devices. In this work, a 4-port coupler is proposed theoretically in silicon based on two-dimensional silicon photonic crystals. The optical properties of the 4-port coupler device have been demonstrated for TM polarization by finite-difference time-domain method. Transmittivity in each output port of the device is given as a function of coupling length. Results show that propagation direction of the input light beam can be controlled by changing coupling length of the device. Further studies indicate that the output optical power in each output port of the device can be tuned by reducing the radii of the silicon rods in the photonic crystals. The properties make the device find its potential applications in all-optical switching systems with wavelength-selective and tunable properties..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1157 (2005)
Coupling Among Three Nonparallel Waveguides
[in Chinese]
A novel concise analytical method of the coupling among three nonparallel waveguidesextended coupling coefficient method is reported. The change of nonparallel-waveguide geometric shape is directly translated into the one of the interval among the parallel waveguides in the coupling coefficient, in other words, the couA novel concise analytical method of the coupling among three nonparallel waveguidesextended coupling coefficient method is reported. The change of nonparallel-waveguide geometric shape is directly translated into the one of the interval among the parallel waveguides in the coupling coefficient, in other words, the coupling coefficient is extended technologically, the change of the distance among parallel waveguides is included in coupling equations by exponent, and the novel coupling-mode equations are derived for three nonparallel waveguides. These coupling-mode equations include all information such as the amplitude and phase of the nonparallel waveguides, the distances among input ports and the angle, the propagation distance and the power translating with these parameters, etc.. Using the skilled mathematic conversion, the perfect analytical solutions are obtained by solving the equations. The coupling among three nonparallel waveguides is analyed and discussed for symmetrical and asymmetrical initial conditions. In accordance with these analytic solutions, the optimum parameters can be presented for the nonparallel waveguide structures..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1161 (2005)
Experimental Study of Fiber Grating Smart Layer System Based on Fiber Bragg Grating Sensors
[in Chinese], [in Chinese], and [in Chinese]
One of the final research goals for smart structures is to integrate sensing elements with composite materials. It is the most potential technical approach that the standardization and modularization of fiber optic smart layer system with function of self-diagnosing is designed. The fiber grating smart layer (FGSL) witOne of the final research goals for smart structures is to integrate sensing elements with composite materials. It is the most potential technical approach that the standardization and modularization of fiber optic smart layer system with function of self-diagnosing is designed. The fiber grating smart layer (FGSL) with embedded fiber Bragg grating (FBG) sensors is fabricated using dielectric substrate of polyimide. The calibration test of embedded FBG sensors is conducted and the models of strain measurements and temperature measurements for FBG sensors embedded inside FGSL are set up. The experimental results show that the wavelength shift of Bragg grating is excellently linear with strain and temperature by embedded FBG sensors, but it is noted that the thermal characterization of the structure built-in FGSL should be investigated. The active and real time monitoring system would be established by fiber Bragg grating networks embedded inside FGSL and advanced information treatment technology..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1166 (2005)
Improving Composite Second Oorder Distortion Performances of Externally-Modulated CATV Systems by Optical Fiber Raman Amplifiers
[in Chinese], [in Chinese], and [in Chinese]
The composite second order distortion (CSO) induced by self-phase modulation (SPM) in a vestigial sideband amplitude modulation (AM-VSB) externally modulated CATV system employing optical fiber Raman amplifier is studied theoretically. Firstly, the SPM-induced CSO expression is obtained analytically by solving SchrdinThe composite second order distortion (CSO) induced by self-phase modulation (SPM) in a vestigial sideband amplitude modulation (AM-VSB) externally modulated CATV system employing optical fiber Raman amplifier is studied theoretically. Firstly, the SPM-induced CSO expression is obtained analytically by solving Schrdinger equation with the help of perturbation method. Subsequently the corresponding numerical results are presented and discussed. According to the calculation results, it is shown that, compared with using EDFA, the CSO performance can be improved by more than 10 dB by using distributed Raman amplification in the system..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1171 (2005)
Image Processing
Multi-Scale Mathematical Morphology Fusion Filtering and the Evaluation of the Filtered Image
[in Chinese], and [in Chinese]
The algorithm based on multi-scale mathematical morphology fusion filter is presented to resolve the infrared and TV image detection polluted by heavy yawp in the shipboard infrared search and track system. First the target image is filtered through multi-scale mathematical morphology operators, bigger morphology operaThe algorithm based on multi-scale mathematical morphology fusion filter is presented to resolve the infrared and TV image detection polluted by heavy yawp in the shipboard infrared search and track system. First the target image is filtered through multi-scale mathematical morphology operators, bigger morphology operator eliminating noise and smaller morphology operator picking up image detail. The simultaneity transacted results are fused based on wavelet transform. Across resolution evaluation operator of target and background is presented to solve the performance of match filtering arithmetic. The experimental results show that the algorithm can eliminate the strong clutter of clouds, ocean waves, sea level and strong noise and is better than median and wavelet transform algorithm. The experimental results also show that the quantative evaluation algorithm of filtered image reasonable and effective. The algorithmis suited for shipboard infrared surveillance system..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1176 (2005)
Imaging Systems
Axial Superresolution in Optical Coherence Tomography Through the Combination of Apodization and Coherence Gating
[in Chinese], [in Chinese], and [in Chinese]
Axial resolution in optical coherence tomography (OCT) imaging is determined by the coherence length of light source and the beam-focusing condition. The most adopted approach for achieving high axial resolution in OCT is using a light source with a broaden bandwidth. A method to increase the axial resolution in OCT byAxial resolution in optical coherence tomography (OCT) imaging is determined by the coherence length of light source and the beam-focusing condition. The most adopted approach for achieving high axial resolution in OCT is using a light source with a broaden bandwidth. A method to increase the axial resolution in OCT by combining coherence gating with apodization through an appropriate pupil filter is introduced. In the proposed OCT system, the width of central lobe of axial point spread function is apodized to be within the coherence length of light source, while its side-lobes are lying outside without contributing to coherence imaging. It is in this way that improved resolution can be obtained in OCT system without recurring to broadening the bandwidth of light source, which is nevertheless costing and inconvenient in implementation..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1181 (2005)
Range Estimation by Optical Differentiation
[in Chinese], [in Chinese], and [in Chinese]
The application of optical differentiation method in passive range estimation was discussed. The concept of optical differentiation is extended to a more general model based on the linear property of imaging system. In this model, the distribution of the images' intensity for depth recovery can be formulated as an The application of optical differentiation method in passive range estimation was discussed. The concept of optical differentiation is extended to a more general model based on the linear property of imaging system. In this model, the distribution of the images' intensity for depth recovery can be formulated as an arbitrary order linearly differential form and it gives us more selections of the optical differential form between the two processes of imaging. For the improvement of the ranging system, the influence of the optical system's parameter on the ranging precision and the longitudinal resolution is analyzed. The design and optimization of the optical masks are also briefly investigated..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1186 (2005)
Instrumentation, Measurement and Metrology
Polarization-Induced Fading Elimination Technique for Coherent Detection of Brillouin Scattering Spectrum
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to reduce the effect of polarization mismatch on detection of Brillouin scattering spectrum in the coherent detection system for Brillouin optical time-domain reflectometry (BOTDR), based on the feature of Brillouin scattering light and the principles of the polarization spreading and the polarization diversitIn order to reduce the effect of polarization mismatch on detection of Brillouin scattering spectrum in the coherent detection system for Brillouin optical time-domain reflectometry (BOTDR), based on the feature of Brillouin scattering light and the principles of the polarization spreading and the polarization diversity, the time-domain polarization diversity (TDPD) technique is introduced. The TDPD is implemented easily and effectively for BOTDR. The theoretical analysis shows that with TDPD more than half of signal power is heterodyned with the local light no matter how their polarizations vary, and the received signals are insensitive to the random variation of the polarization of Brillouin backscattering light. The TDPD is implemented by performing simple and non-feedback polarization control on the local light, and the original architecture of BOTDR is less changed. The comparison between the system with and without TDPD shows that the fluctuation of the received signal light power with TDPD is 4.2 times less than that without TDPD..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1191 (2005)
Three-Dimensional Defect Detection Based On Single Measurement Image
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to acquire overall three-dimensional (3D) defect information, a new 3D defect detection method is designed. It only needs single image captured from real-time measurement line. From the single image, 3D data of the work piece shape ranged from 0° to 180° can be got. Moreover, it can give an overall rIn order to acquire overall three-dimensional (3D) defect information, a new 3D defect detection method is designed. It only needs single image captured from real-time measurement line. From the single image, 3D data of the work piece shape ranged from 0° to 180° can be got. Moreover, it can give an overall recognition of plane dimensions and depth information of the defect. The key technique is made use of the 3D clues——“shading value”, which left in the single measurement image, to process luminance analysis and conversion, thus to calculate the depth information by slant and tilt. In the application of defect detection for magnetic work piece, the resolution in X and Y direction can reach 0.1 mm, and the resolution in Z direction can reach 0.007 mm. This experiment proves that the designed 3D defect detection method has the merits of simple operation, low cost, high speed and high precision. This 3D method is fit to use in industrial application..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1195 (2005)
Inspection for the Status of Collimating Mirror in Synchrotron Radiation——Wavefront Inspection of Spot with Small Output Width But Long Curvature Radius
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new approach is described to detect the position status of collimating mirror with a shearing interferometer based on micro-wedge. Laser beam having the same divergence as the synchrotron radiation can be created with a lens and a pinhole, and by measuring the parallelism of the laser beam reflected by the collimatinA new approach is described to detect the position status of collimating mirror with a shearing interferometer based on micro-wedge. Laser beam having the same divergence as the synchrotron radiation can be created with a lens and a pinhole, and by measuring the parallelism of the laser beam reflected by the collimating mirror with the shearing interferometer, the best status of the collimating mirror about its position, pitch, curvature and bending force can be determined. This interferometry scheme is easily aligned, every interference pattern corresponds with only one status of the collimating mirror. Therefore this approach can determine the whole status of the mirror. The approach is especially fit for measuring the wavefront with small output width but long curvature radius, and not only has high accuracy but also is valuable in practice..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1201 (2005)
Integrated Optics
Design and Optimization of a New Type 3×3 Silicon-on-Insulator Multimade Interference Optical Switch
[in Chinese], [in Chinese], and [in Chinese]
In this paper, a new type 3×3 SOI multimode interference optical switch was presented. The index-modulated regions were introduceed in the multimode waveguide with the plasma dispersion effect (PDF) of silicon to change the regional index of the multimode waveguide, the phase of the light field was modified to detIn this paper, a new type 3×3 SOI multimode interference optical switch was presented. The index-modulated regions were introduceed in the multimode waveguide with the plasma dispersion effect (PDF) of silicon to change the regional index of the multimode waveguide, the phase of the light field was modified to determine the position of the output light field. The various states of the switch were simulated and analyzed using the finite difference beam propagation method (FD-BPM), the structure parameters of the switch was also designed and optimized. The peak extinction ratio of the switch reaches -17.27 dB with the optimized structure parameters..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1208 (2005)
Lasers and Laser Optics
Influence of TO Packaging on the High-Frequency Response of Semiconductor Laser: Analysis and Experiment
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The parasitics from packages can obviously degrade the overall performance of the packaged laser diode at high frequencies. Two novel equivalent methods, namely predication method and evaluation method, which can be used to analyze the influence of through-hole (TO) packaging on the high frequency response of laser dioThe parasitics from packages can obviously degrade the overall performance of the packaged laser diode at high frequencies. Two novel equivalent methods, namely predication method and evaluation method, which can be used to analyze the influence of through-hole (TO) packaging on the high frequency response of laser diode, are deduced from the relation between the scattering parameters of laser diode before and after packaging. In the experiment, TO packaged laser module is taken as an example to investigate the high-frequency influence of the TO packaging. The coherence between the experimental results from the novel method and that from traditional comparison method show the effectivity of the methods. It also can be seen that the TO packaging does not reduce the bandwidth of the packaged laser diode, which means that TO packaging can achieve a frequency bandwidth of 10 GHz, furthermore, the resonance among the circuit elements of TO packaging provides compensation for the frequency response of the devices. The two methods are useful for screening and optimizing the packaging of high-speed optoelectronics devices..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1214 (2005)
The Influence of Non-Instantaneous Phase Conjugate Optical Feedback on the Dynamics of Semiconductor Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Based on the physical origin of phase conjugation generated by four wave mixing, the response time of phase conjugate mirror is defined and the external cavity model for laser diode under non-instantaneous phase conjugate optical feedback is set up. Numerical analysis is given to discuss the influence of response time Based on the physical origin of phase conjugation generated by four wave mixing, the response time of phase conjugate mirror is defined and the external cavity model for laser diode under non-instantaneous phase conjugate optical feedback is set up. Numerical analysis is given to discuss the influence of response time and frequency detuning on the characteristics of bifurcation and noise. The results indicate that the numbers and the range of chaotic bands can be restrained greatly by increasing the phase conjugate mirror's response time when the influeme of noise is considered. When the response time reaches 1.5 ns, all the instabilities of laser diode are suppressed. If noises considered, the intensity of relative intensity noise decreases by several dB or even tens dB with the increase of response time and its spectrum peak moves to higher frequency , the feedback rate for coherence collapse also increases by one order. Since the frequency detuning is smaller compared to laser diode lasing frequency by more than three orders of magnitudes, it only influences the bifurcation diagram and almost have no influence on relative intensity noise..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1219 (2005)
Machine Vision
Research on Autofocus Technique in Micro-Vision
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
An evaluation method of autofocus function based on spatial domain is presented. Four features are proposed to evaluate the function on computation time and sharpness of the focus curve. An optimum can be filtrated from many classic functions. Entropy function is the evaluating result through experiments on the developAn evaluation method of autofocus function based on spatial domain is presented. Four features are proposed to evaluate the function on computation time and sharpness of the focus curve. An optimum can be filtrated from many classic functions. Entropy function is the evaluating result through experiments on the developed autofocus system of micro assembly workcell. A novel focus searching algorithm——positioning algorithm (PA) which is different from hill climbing searching alorithm (HCSA) and Fibonacci Searching Algorithm (FSA) is put forward. Setting up the relation between defocus value and focus function value is key factor of the algorithm. Three methods: polynomial fitting, Gaussian function fitting and cubic spline interpolation fitting are presented to realize PA. Then an autofocus system comprising entropy function and PA is set up. Experimental results indicate that focusing precision can reach 6.992 μm and one focusing processing can be done within 3.4 s. It proves that the evaluation method and the PA can realize autofocus accurately and quickly..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1225 (2005)
Study on the Novel Intelligent Robotics Sensitive Skin Suitable for Real-Time Obstacle Avoidance
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In an uncertain environment, real-time obstacle avoidance is key technology for a intelligent robot to work autonomously. Sensitive skin endows intelligent robot carrier with an ability to sense surrounding and the ability of real-time decision. The developed robotics sensitive skin is a large-area, flexible, mini-typeIn an uncertain environment, real-time obstacle avoidance is key technology for a intelligent robot to work autonomously. Sensitive skin endows intelligent robot carrier with an ability to sense surrounding and the ability of real-time decision. The developed robotics sensitive skin is a large-area, flexible, mini-type array of infrared sensors with dataprocessing capabilities, which can be used to cover the surface of robot. Depending on the array of infrared sensors, it endows robot carrier with an ability to sense its surrounding. Distance between sensitive skin and obstacle is measured by using geometric optics model. Experimental results show that the sensitive skin can real-timely provide existence and distance information about obstacles for multi-joint robot within sensory area. The development of the sensitive skin means an attempt in sensing and control. It presents a new paradigm in solving problems such as obstacle avoidance for multi-joint robot. It will promote the development of robot and related science in our country and improve intelligent level. This will be of far-reaching significance to the promotion of robot and will have a wide application and promising prospect..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1233 (2005)
Materials
Research on Improving Diffraction Efficiency of Red-Sensitivity Acrylamide-Based Photopolymer
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
At present diffraction efficiency of acrylamide-based photopolymer using polyvinyl alcohol(PVA) as binder is low at high resolution, that is, the photopolymer system has a low resolution. According to mechanism of photopolymerization the main reason is discussed and four novel methods are presented to accelerate monomeAt present diffraction efficiency of acrylamide-based photopolymer using polyvinyl alcohol(PVA) as binder is low at high resolution, that is, the photopolymer system has a low resolution. According to mechanism of photopolymerization the main reason is discussed and four novel methods are presented to accelerate monomers movement so as to improve diffraction efficiency. These methods include adding acrylic acid into the photopolymer system, using low polymerization degree of PVA and optimizing the layer thickness and the dry time, which have been experimentally verified. At a given condition system's diffraction efficiency using polymerization degree 341 of PVA is about 60% higher than that using polymerization degree 1750 of PVA, and diffraction efficiency of adding acrylic acid increases about 10%, system using low polymerication degree and adding acrylic acid is almost not crystaled. Both the layer thickness and the dry time have optimal range. Diffraction efficiencies of over 90% at spatial frequency about 2000 lp/mm and over 55% at 3000 lp/mm were obtained. Transmission holograms and plane reflective holograms can be fabricated by authors' material. So this material is promising to holographic display..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1238 (2005)
Effects of Crystallinity of Raw Material Y2O3 on Luminescent Character of Y2O2S∶Eu3+
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to improve the luminescent character of Y2O2S∶Eu3+, the method of improving crystallinity of primary raw material Y2O3 is used. The emission intensity of red phosphors Y2O2S∶Eu3+ is effectively enhanced 5％ and 10％ respectively at the voltages of 20 kV and 25 kV while the other primary properties of applicationIn order to improve the luminescent character of Y2O2S∶Eu3+, the method of improving crystallinity of primary raw material Y2O3 is used. The emission intensity of red phosphors Y2O2S∶Eu3+ is effectively enhanced 5％ and 10％ respectively at the voltages of 20 kV and 25 kV while the other primary properties of application in chromaticity, granularity and decentralization are not changed. The voltage resistance character (relation between emission intensity and excitation voltage) is elevated. The origins of the emission intensity enhancement and excitation voltage elevation are discussed and analyzed preliminarily. It is likely that the abnormal change and defect of crystal lattice led by the substitution of larger radius Eu3+ ion for smaller radius Y3+ ion are reduced by the better crystal quality of Y2O2S∶Eu3+ from the better crystallinity of raw material Y2O3. Because the crystal field condition of Eu3+ ion is improved, radiationless process and energy loss led by crystal defect are cut down, the emission efficiency of Y2O2S∶Eu3+ phosphors is enhanced and its voltage character is improved. The experiment shows that the decomposing temperature to get the high crystallinity Y2O3 is about 1400 ℃..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1243 (2005)
Investigation of Negative Refraction in a Uniaxial Crystal
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
By relying on dispersion equation, optimal conditions for negative refraction in the interface between isotropic medium and anisotropic crystal are investigated. The negative refraction phenomenon can be very evident when the optical axial angle and anisotropic parameters are arranged appropriately. The optimal opticalBy relying on dispersion equation, optimal conditions for negative refraction in the interface between isotropic medium and anisotropic crystal are investigated. The negative refraction phenomenon can be very evident when the optical axial angle and anisotropic parameters are arranged appropriately. The optimal optical axis angle and corresponding maximum incident critical angle are given. For strong anisotropy crystal, the maximum incident angle that yields the negative refraction could be very large. Further, the difference of negative refraction associated with uniaxial crystal and with negative index media is discussed. In negative index media the negative refraction is caused by a negative refractive index, whereas in the case of anisotropic crystal, the negative refraction is a natural result of dispersion relation in anisotropic media. It is found that the uniaxial crystal slab is not suitable for constructing perfect lens, firstly predicted by Pendry..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1249 (2005)
Medical Optics and Biotechnology
Time Resolved Diffuse Reflection of Three-Layered Mismatched Media Diffusion Equation
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A tissue is multi-layered mismatched medium, but many investigators only study the diffusion equation of matched medium, they take the tissue as media with the same refractive index. In order to understand the light transport in tissue, the solution of the diffusion equation of a three-layered mismatched medium in freqA tissue is multi-layered mismatched medium, but many investigators only study the diffusion equation of matched medium, they take the tissue as media with the same refractive index. In order to understand the light transport in tissue, the solution of the diffusion equation of a three-layered mismatched medium in frequency domain is set up. Through Fourier transform, the time-resolved reflectance is computed. The time-resolved reflectance between the solution of three-layered mismatched media diffusion equation and Monte-Carlo simulation are compared. The result shows the method not only accords with the Monte-Carlo simulation, but also can solve the problem of a two-layered mismatched turbid media model..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1254 (2005)
Optical Devices
Study of Miniature Optical Sensor for Laser Particle Counter
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A miniature optical sensor, the core of a miniature laser aerosol particle counter, has been developed. The optical system of the sensor is a right-angle scattering optics. A high-power laser diode module is used as the light source, and a PIN photodiode with high performance is used as the photo-detector. By using a rA miniature optical sensor, the core of a miniature laser aerosol particle counter, has been developed. The optical system of the sensor is a right-angle scattering optics. A high-power laser diode module is used as the light source, and a PIN photodiode with high performance is used as the photo-detector. By using a reflective spherical mirror with large numerical aperture, the light scattered by individual particles is collected over a large angular range of 20° to 160°. The scattered light signal from the particle is short pulse, which consists mainly of high frequency components. A band-pass preamplifier is used to eliminate lower-frequency eletromagnetic interference from external environment. The light scattering response characteristics of the sensor are calculated based on Mie scattering theory. The sensor performance has been tested with standard par5ticles of polystyrene latex, the results show that the sensor has high signal-to-noise ratio, counting efficiency, and size resolution..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1260 (2005)
Quantum Optics
Evolution of Femtosecond Pulse in Resonant Atomic Medium with Long Distance
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
To study the evolution of femtosecond (fs) laser pulse in a long-distance two-level medium, the Maxwell-Bloch equations of 5 fs carrier interaeting with two-level medium are numerically solved with use of finite-difference time domain procedure. It is found that the 5 fs pulse envelope, obtained within the slowly varyiTo study the evolution of femtosecond (fs) laser pulse in a long-distance two-level medium, the Maxwell-Bloch equations of 5 fs carrier interaeting with two-level medium are numerically solved with use of finite-difference time domain procedure. It is found that the 5 fs pulse envelope, obtained within the slowly varying envelope approximation and rotating-wave approximation, agrees nicely with the carrier field. It is also found that it takes 50000 times longer distance for a pulse with an area of 3.2π to evolve into a stable symmetric hyperbolic-secant pulse than its area varying into a stable value. The evolution process is complicated, for the pulse's spectral width much larger than the atomic linewidth. As a result, an injected pulse with an area of 3.2π could not maintain a shape of symmetric hyperbolic-secant during its area evolving into stable, and must propagate a very long distance to transform into a stable solitary wave. In addition, comparison of the results of the 5 fs and 50 fs pulse has demonstrated that the shorter the pulse is, the more intricate process, the longer distance it needs..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1265 (2005)
Quantum Statistical Property of Radiation Field in Three-Level Electromagnetically Induced Transparency System
[in Chinese], [in Chinese], and [in Chinese]
The second-order coherence of radiation field in Λ-type three-energy level electromagnetically induced transparency (EIT) system is investigated theoretically. The result of calculation indicates that the coherence effect of atom in EIT system induces the second-order coherence of the resonance fluorescence field of upThe second-order coherence of radiation field in Λ-type three-energy level electromagnetically induced transparency (EIT) system is investigated theoretically. The result of calculation indicates that the coherence effect of atom in EIT system induces the second-order coherence of the resonance fluorescence field of upper level to present the quantum statistical property of single photon. And the second-order coherence of the radiation field dependence of intensity of coupling light and detuning of probe light is considered. Under the condition of Ω>(Γ2+Γ3)/2, if the weaker power of coupling light or far-off-resonance of probe light is applied, second-order coherence can retain smaller than 1 in longer time delay, which can make for realizing the quantum statistical action of nonclassical field; contrarily, under the condition of Ω≤(Γ2+Γ3)/2, the smaller off-resonance of probe light is applied, the better the quantum statistical nonclassical field realizes that second-order coherence can retain smaller than 1 in longer time delay. So the quantum statistical property of single-photon field in EIT can be optimized in different conditions when appropriate parameters are chosen..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1271 (2005)
Radiation Pressure on a Ladder-Type Three-Level Atom in a Squeezed Vacuum
[in Chinese], [in Chinese], and [in Chinese]
The Radiation pressure of a moving ladder-type three-level atom in a squeezed vacuum is discussed. From the Hamiltonian of the atomic system, making use of Born-Markoff approximation, the optical Bloch equations are derived. As the time scales for the evolution of internal and external degrees of freedom are highly disThe Radiation pressure of a moving ladder-type three-level atom in a squeezed vacuum is discussed. From the Hamiltonian of the atomic system, making use of Born-Markoff approximation, the optical Bloch equations are derived. As the time scales for the evolution of internal and external degrees of freedom are highly distinct, the steady-state solutions of the optical Bloch equations can be obtained using numerical calculation. Then the graphical method is used to discuss the dependence of the force on various parameters such as two-photon detuning, Rabi frequencies and spontaneous emissions. The result shows that the radiation pressure shows Doppler-shifted resonance peaks resulting respectively from one-photon and two-photon transitions, and the radiation pressure depends strongly on the relative phase of the driving field and the squeezed vacuum. When the phase matching condition is fulfilled, the dissipative force will be diminished..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1277 (2005)
Phosphate Glass Matrices Prepared for Optic Microcavity
[in Chinese], and [in Chinese]
Quantum dot optic microcavity device had potential application in field of quantum information technology using as the low threshold laser and single photon light source etc. High density of quantum dot need be implanted into the glass microsphere with high dielectric constants in order to realize the optic gain and laQuantum dot optic microcavity device had potential application in field of quantum information technology using as the low threshold laser and single photon light source etc. High density of quantum dot need be implanted into the glass microsphere with high dielectric constants in order to realize the optic gain and lasing. The glass formation ability, infrared, crystallization thermal stability and microcavity forming ability in the ZnO-P2O5, CdO-P2O5 and CdS-P2O5 binary phosphate glass system were investigated. The maximum solubility of ZnO in the glass is 0.6 mole fraction, and that of CdO and CdS is 0.4 mole fraction. The glass matrices have a similar light absorption character to those commercial cut-off filter glass, which was not dependent on the composition of the glass. The α-Zn2P2O7 or CdS solid phase was precipitated in the crystallized glass matrices, where CdS phase has a uniform distribution in matrices. The powdered glass matrices can easily be formed into microcavity with a perfectly round sphere using thermal spray method. It was concluded that the ZnO-P2O5 and CdS-P2O5 binary phosphate glass can be formed into optic microcavity and the high density of Ⅱ-Ⅵ group quantum dot can grow in CdS-P2O5 glass matrices..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1283 (2005)
Spectroscopy
A New Derivative Photoacoustic Spectroscopic Technique
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new method for obtain the derivative photoacoustic spectroscopy is proposed. A wavelength-intensity splitter is designed to obtain the derivative spectroscopy of photoacoustic spectroscopy with the help of a monochromator and a prism. Using the wavelength-intensity splitter, two light beams with identical intensity bA new method for obtain the derivative photoacoustic spectroscopy is proposed. A wavelength-intensity splitter is designed to obtain the derivative spectroscopy of photoacoustic spectroscopy with the help of a monochromator and a prism. Using the wavelength-intensity splitter, two light beams with identical intensity but lightly different are obtained in wavelenth at the same time. The two light beams are modulated and then folded in the photoacoustic detector symmetrically, so as to realize the difference of phtoacoustic signal. The derivative photoacoustic spectra is obtained by scanning the wavelength of monochromator. The first-order derivative spectra of photoacoustic spectra is obtained with the method. The derivative photoacoustic spectroscopy is endowed with higher resolution than that of photoacoustic spectroscopy..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1288 (2005)
Thin Films
Effect of N2 Mass Flow Rate On the Optical Property of Titanium Nitride Films Deposited by Magnetron Sputtering
[in Chinese], and [in Chinese]
The titanium nitride thin films were deposited on slides and Al substrates by magnetron sputtering and the variation of N/Ti atom ratios was controlled by selected N2 mass flow rate. The effect of N2 mass flow rate on the optical properties of titanium nitride films was analyzed via spectrophotometer and scanning tunneThe titanium nitride thin films were deposited on slides and Al substrates by magnetron sputtering and the variation of N/Ti atom ratios was controlled by selected N2 mass flow rate. The effect of N2 mass flow rate on the optical properties of titanium nitride films was analyzed via spectrophotometer and scanning tunneling microscopy (STM) methods. The results of reflectivity spectrum and scanning tunneling spectrum (STS) showed that titanium nitride thin films mainly conform to free-carrier absorption mechanism, and as the N content increases, the numbers of free electrons of the films reduce consequently and the plasma frequency keeps shifting to lower energy, so that the reflectivity of films is downhill and the color of films varies regularly. STS spectra of TiN indicated that the TiN film exhibits metallic optical property and the band gap is 1.64 eV..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 25, Issue 9, 1293 (2005)
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20