2006 Vol. 27, No. 5
Taking one dimensional quadratic congruence code (QCC) as time-spread mode, optical orthogonal code (OOC) and QCC as frequency-hop mode, two types of frequency-hop time spread codes of QCC/QCC and QCC/OOC applicable to two dimensional optical code division multipleaddress (OCDMA) systems were constructed by combining time domain and frequency domain. The correlation and capacity of the codes were analyzed. In comparison with one dimensional QCC, the capacity of QCC/QCC is enlarged p1 times, where p is code weight, and the correlation is improved, outofphase autocorrelation is λa=1 and crosscorrelation isλc=2. QCC/OOC with better correlation and larger capacity are obtained. Its outofphase auto-correlation is λa=0. All the code words can be divided into p1 groups according to a certain law, crosscorrelation of code words in the same group is λa=1 and in different groups is λa=2. The study provides a new method for constructing frequency-hop timespread codes in OCDMA systems.
As Fourier transform is limited in dealing with certain kinds of signals, an improved method of Fourier transform which is called the fractional Fourier transform (FrFT) is put forward. FrFT, a manifestation of the classical Fourier transform, appears to be potentially useful. It depends on a parameter and can be interpreted as a counterclockwise rotation of coordinate system taking the original point as an axis by an angle on the timefrequency plane. It is a normal representation of the classical Fourier transform. Through mathematic ratiocination, a conclusion was reached that FrFT is better than Fourier transform in dealing with signal reconstruction. To explain FrFT systemically, the optimization algorithm of FrFT filter was given，then Matlab was used as a tool, which can provide emulator, to test and analyze FrFT’s implement effects . At last, all kinds of designs of FrFTbased filters was put forward and explained.
The resonant photonic modes in a quantum well (QW) structure composed of three slabs of different photonic crystals with different lattice constants is analyzed with planewave based transfer matrix method (TMM). It is found that the energy band of the well slab submerged into the band gap of barrier slab is discretized into resonant modes and the number of the resonant modes changes with the well slab thickness. A model structure of asymmetrical photonic QW consisting of two slabs of 2D photonic crystals with different lattice constants and one uniform dielectric slab in between is firstly proposed and the resonant modes in it are investigated. A useful numerical simulation method for theoretical discussion as well as for practical application about photonic QW structure of photonic crystals with different lattice constants is proposed.
Largeshearing electronic speckle pattern interferometry (LSESPI) offers many advantages such as good fringe quality and no reference beam needed. The fringe pattern obtained by the LSESPI is easy to be observed. The new electronic speckle pattern interferometer is formed by introducing carrierfrequency modulation for interference fields to LSESPI. The new system does not have strict requirement for environment on isolating vibration. The displacement fields could be quantitatively measured with the system. The principle of carrierfrequency modulation of LSESPI is discussed. A typical experiment is implemented with a centralloaded and peripheralclamped plate. And a step motor system controlled by a computer is designed. With the step motor system the reference object can be rotated accurately so that the electronic speckle pattern can be modulated automatically. At last, Fourier transform is used to demodulate the modulated fringes and obtain the phase of deformed field, then acquire the precision deformation of the object by the transformation calculation of the phase and displacement. The experimental results indicate that the interference field of the speckle pattern can be modulated and the displacement of the object can be measured accurately by this system.
The micromechanism interacting between optical field and high polymer is analyzed, the polarization process of high polymer and small molecule under the effect of the light field is introduced. The distribution of polarization on the high polymer chain which has been polarized is analyzed in narrowbeam optic field. The analysis indicates that for the tensionthinning film made from polymer, the dipole model can not be used to explain the mechanism interacting between high polymer and optic field. An antenna model is adopted and investigated in detail. The polarization formula of high polymer chain of aerial mode is theoretically derived, and its validity is verified through calculating the polarization distribution with DVM. Assuming the polarization distribution is the same as the distribution of the electric current on the aerial, the angle distribution of the aerial secondary radiation is calculated, and the modification factor of electric dipole model is obtained.
A metallicdielectric photonic crystal thinfilm is presented. Its reflectivity and transmissivity are calculated with the transmission matrix method. The numerical results show that the photonic crystal film has an up to 99% reflectivity for millimeter and centimeter waves and about 50% average transmissivity for the visible light in microwave spectrum. The effects of the dielectric layer thickness, the metallic layer thickness and the total thickness of metallic layers on the transmissivity are examined, and the principles of material selection and structure design are presented. Due to these characteristics, the metallicdielectric photonic crystal film can be employed in effective reduction of radar crosssection of scattering on airplane canopy.
The pixel transfer function (PTF) for analyzing microscanning technology′s effect on spatial resolution is given based on the detailed analyses of the aliasing effect decreased by the microscanning technology. The analysis, calculation and discussion on PTF are carried out for two modes of microscanning (2×2，4×4). The result shows that the microscanning technology can increase the focal plane spatial resolution, decrease the image aliasing effectively and improve the imaging quality significantly for FPA thermal imager. It is pointed out that even if highspatialresolution imaging device is not available, high spatial resolution images can still be obtained with lowresolution imaging devices by utilizing the microscanning technology.
The principle, structure and property of optoelectronic position sensitive detector (PSD) are briefly introduced. The nonlinearity caused by PSD is analyzed according to the principle and characteristics of PSD. The location equation of PSD output signal independent of light intensity was derived. PSD nonlinearity modulation circuit was designed to achieve low temperature drift and high precision. The validity of correcting PSD nonlinearity with differential algorithm, optimization method of neural network and analytic method is analyzed. Some of the data obtained during the experiment are also analyzed. The prospects of PSD′s application in optical trigonometry, automatic check and highprecision measurement are discussed.
Feasibility of adding a CCD camera to the gunner′s periscopic sight is analyzed. The principle and scheme of adding the CCD camera are brought forward in this paper. The requirement for keeping the periscopic height at the original point, changing the internal structure of the gunner′s periscopic sight as little as possible and reducing the cost of the whole project was met by selection of suitable mounting position and structure distribution of the CCD camera. The selection of CCD camera, the calculation of the beam path and the variation of laser emission path film are discussed by aid of relative theories. It is pointed out that the automatic video tracking can be realized if an automatic tracking assembly with the function of data processing is mounted on the system after the CCD camera is added to the gunner periscope, and the original observationaiming function in visible light is still retained. The whole research has significant value for improving fire control system function and tactics technique function of whole tanks.
The infrared target simulator is composed of infrared target image transmitter and the optical projection system. The infrared coupling optical system is a middleinfrared system with a long focal length, larger field and telecentric beam path in image space, which is required to match with the parameters of two homing optical systems. The optical design of infrared coupling system applied to infrared target simulator is presented in this paper. The combination of infrared coupling system and homing optical system can constitute an infrared projective optical system with a magnification of 4.5. The IRCRT image can be projected on the receiver of homing optical system through an infrared projective optical system. SiGeSi is selected as optical material based on the design characteristics and technical specification of infrared coupling system, and the design of the optical system with a Cooke threelens structure has been implemented. The design and assessment results indicate that the optical performance and image quality of the system can meet the design specification.
Based on the analysis of the luminous characteristics of typical lasers and optical properties of cylindrical lenses, a novel optical system for laser panoramic fuse, which uses two sets of cylindrical lenses with orthogonal sagittal planes to improve the scattering angle of laser beam and uses four sectors to realize the panoramic function, is proposed in this paper. Since the distribution uniformity of the light energy of the system is satisfactory on the circle of 0.5～10m radius and the beam path of the system offers an advantage of invertibility, it can be used in the fuse of the missile with the feature of WFOV emission and reception. The system is comparable to its counterpart abroad. The system is compact in structure and easy to be fabricated. The demonstration in the test range proves the new optical system is feasible and practical. The reflective optical system available will be replaced by this system in the future.
The principle and calculation method to design shortwavelength pass filters with a concept of equivalent refractive index is presented in this paper. TiO2 was chosen as the material of high refractive index and SiO2as the material of low refractive index based on the principle and method. Periodicity of shortwavelength pass filter at wavelength λ＝950～1150nm was theoretically designed according to the concept of equivalent refractive index. The main film system and the spectrum curve of the shortwavelength pass filterare presented. The design of the film system was corrected since its transmissivity did not meet the requirement at the range of wavelength λ＝750～810nm. The effect of the main processing technology and the film thickness on the optical characteristics of the shortwavelength pass filter is described. As a result of the correction, the best way to make the film system was found. The film system prepared in this way was tested in different environment conditions. The experiment result shows that the specification of this film system can meet the requirement of the design.
The thermal distribution of objects can be transformed into the visual pictures by the infrared thermal imaging system and displayed on the monitor in grey level or pseudocolor, thus the temperature distribution of objects can be obtained. According to the thermal imaging principle of temperature measurement and the characteristics of infrared images, the pseudocolor coding of infrared images is studied in this paper. A new pseudocolor coding, automatic threshold method, is presented. This method was proved by TMS320C6202 and FPGA thermal imaging systems at room temperature. Experimental results show that gradations of infrared images can be discriminated and different temperature regions can be easily resolved by the method.
To overcome the shortcomings of thickfilm capacitors (limited size, low capacity and high dissipation) fabricated by traditional thickfilm technology, which limit their applications to some specific areas, a technology fabricating the thickfilm capacitors on ceramic substrate by laser microcladding rapid prototype is put forward. The novel technology does not take the mask as a necessity as in the former capacitor. The structure and properties of the capacitor fabricated by laser microcladding and the traditional sintering method, which includes capacity, dielectric crystal, quality factor and insulation resistance, are analyzed. The forming mechanism of the capacitor is studied. The results prove that, compared with those made with traditional sintering techniques, the capacitors fabricated by laser microcladding rapid prototype method have better repeatability and higher capacity, it is more compact and also minimizes the composition diffuseness between interfaces.
Through discussion on the damage mechanism of wide-band optical transparent dielectrics and comparison of the damage levels of wideband optical transparent dielectrics ablated by ultra-short laser pulses and long laser pulses, a powerful tool applicable to processing wideband optical transparent dielectrics with ultrashort laser pulse is obtained. When laser pulse with wavelength of 800nm and pulse time of 150fs is focused into the inside of transparent dielectrics (K9 glasses and ZK6 glasses) with different band widths, the gratings with different constants can be made. The far-field relative diffraction efficiency and the diffraction efficiency of the grating were measured under the vertical illumination of He-Ne CW laser at 635nm.
A sapphire fiber fluorescence thermal probe with Cr3+iondoped end was grown from the laser heated pedestal growth method. The fluorescence thermal probe offers the advantages of compact in structure, high performance and ability to detect temperature ranging from the room temperature to 450℃. The data processing based on the wavelet transform can effectively decrease the noise out of the signal so that the signaltonoise ratio can be improved. Based on the theoretical analysis of the fluorescence temperature measurement methodology and fiber technology, a phaselock loop technology is adopted to make the realtime measurement without the interference of the exciting light. Taking advantage of the different features indicated by noise and signal when wavelet transformation is applied, the temperature signal extraction and noise elimination method based on the wavelet transformation theory is given. In comparison with other processing methods, the wavelet transform method overcomes the shortcoming in the fast Fourier transform and can be applied to mutation signals, and it has a variable window that the Gabor transform does not has. Therefore, the method can shorten the process of signal processing and improve the measurement resolution.
A demodulation method for measuring the pressure with the fiber Bragg dualgrating is put forward to improve the precision of fiber Bragg grating (FBG) pressure sensors and reduce the cost of the measurement systems. Under the action of external pressure, the reflected wavelength drift of sensing FBG is transformed into time interval variation of light pulse reflected by the grating, which is modulated by means of driving the equally intense cantilever beam into up and down bending periodically. The experimental result shows that the detection range for the reflected wavelength drift of FBG is 0～3 nm, the uncertainty of wavelength detection is 1 pm, and the uncertainty of the pressure measurement is 0.005 MPa when the measurement range of the pressure sensor is 0～6 MPa.
There is no good solution to the torque measurement of mechanic principal axes working under various loads at home and abroad. Through installing the circular grating and indicative grating at both ends of a principal axis, the noncontact dynamic measurement of the principal axis torque can be realized by computing and subdividing grating Moiré fringes. After the photoelectric conversion of the Moiré fringes, the signal is amplified, filtered and compared with integrated programmable analog devices. Here, a microprocessor of soft core is used to realize data acquisition, processing and controlling, and to substitute the method of FPGA+MCU. During the experiment, the circular grating with 1200 grating lines was adopted, and the precision of the twist angle (less than 0.001°) was acquired while the rotational speed of the principal axis is within the range of 0～1500r/min. The experiment shows that the adoption of Moiré fringes of the circular grating can make highprecision torque measurement of the principal axis meet the requirement, which offers a new noncontact method for the measurement of mechanic principal axes.
The principle of stitching interferometry for testing the large plane optics is presented in this paper. The relative placements of both interferometer and the mirror under test can be adjusted, and interferometric test of subaperture can be done over the whole part of the mirror surface under test. The wavefront data in the overlapping areas of adjacent subapertures are analyzed by using the leastsquare algorithm. The relationship between the tested subapertures is clarified step by step. Finally subapertures are stitched together, and full aperture surface shape under test is synthesized. The error between the spliced surface by stitching interferometry and the actual surface is analyzed, and the accuracy of stitching interferomertry is evaluated. The experiment based on the theory of stitching interferometry was done. The results indicate that the stitching interferometry is an effective means to measure largeaperture optics accurately.
The application of phaseshifting interferometers for measuring angles of the cone cube reflectors (CCR) is studied so as to realize the realtime and high accuracy test for optical elements. The relationship between the dihedral angle errors of CCRs and the interference pattern is obtained by calculating the dihedral angle errors of CCRs. The relationship between the shape of interference wavefront and the synthetic errors of CCRs is analyzed. A program to test the dihedral angle errors and the synthetic errors of CCRs is designed. After lots of experiments and comparison of the results by the digital phaseshifting interferometer and the ZYGO interferometer, it is proved that, in the program of CCR test, the measurement error of the dihedral angular difference is less than 0.3″ and the measurement error of RMS is in λ/50 with the application of digital phaseshifting interferometer.
Laserinduced fluorescence (LIF) spectrum technique is introduced to study combustion process. The experimentation for LIF spectrum of small molecules common in combustion process is described and its results are given. Experimental schemes are designed to measure the spectrum of OH and NO freeradicals by the technique of LIF. OH freeradical in alcohol burner and candle flame and NO freeradical in B/KNO3 pyrolyzing and laser ignition are measured by instruments of YAG laser, dye laser, CO2 laser, spectrometer and ICCD. Experiment results show that fluorescence spectrum is independent with excitation wavelength, but the fluorescence intensity may be decreased when the excitation wavelength changes because the fluorescence deviates from optimal wavelength. The experiment shows that the results agree with fluorescence spectrum characteristics. In comparison with other techniques, the LIF spectrum technique possesses the advantages of superior selectivity and sensitivity.
The spectral responsivity is one of the important parameters of detector. With the development of infrared detect technique, accurate measurement for the spectral responsivity of infrared detector becomes more and more important. The technique on how to measure the spectral responsivity of infrared detector is introduced. Based on an infrared spectral responsivity facility in the institute，the cavity pyroelectric detector is used to calibrate the relative spectral responsivity of infrared detector in several wavelengths on the facility. After repeated measurement，different results are achieved and their average is given in the paper. At last the uncertainty which influences the results is analyzed. Since the wavelength range of infrared spectral responsivity facility is 1～20μm, the relative spectral responsivity of InSb detector and HgCdTe detector can also be measured. The analysis of the uncertainty shows that the measurement accuracy of the spectral responsivity of infrared detector meets the requirement.
In order to measure instantaneous rotation speed， the rotation speed of the shaft in the spatial coordinate system is investigated and the measurement model for measuring instantaneous rotation speed of rotation mechanism is proposed. A novel system for measuring the rotation speed is designed based on linear CCD and the realtime processing of measurement data is carried out by threeorder structure. The test results show that the deficiencies of the instantaneous rotation speed measurement in the instantaneous characteristic analysis of rotation mechanism were solved. A simple speed compression model was build up and the reference for other speed measurement applications was provided.