2006 Vol. 27, No. 4
Display Method:
2006, 27(4): 259-263.
Abstract:
Based on the condition of the maximized laser gain, the laser gain, the optimal optical crystal length and width of quasithreelevel solidstate slab lasers, which variate with pump power,are analyzed and optimized. At the same time we found that the the concentration of doping medium and the width of the slabs satisfied a certain relation under the condition of diodesidepumped mode in lower pump power. The laser gain, the optical length and width of the slabs are optimized and simulated when pump power changes from 0 to 2kW. These results can also be applied to the design for other quasithreelevel solidstate lasers.
Based on the condition of the maximized laser gain, the laser gain, the optimal optical crystal length and width of quasithreelevel solidstate slab lasers, which variate with pump power,are analyzed and optimized. At the same time we found that the the concentration of doping medium and the width of the slabs satisfied a certain relation under the condition of diodesidepumped mode in lower pump power. The laser gain, the optical length and width of the slabs are optimized and simulated when pump power changes from 0 to 2kW. These results can also be applied to the design for other quasithreelevel solidstate lasers.
2006, 27(4): 264-267.
Abstract:
The continuous telecentric zoom lens for a digital light processor (DLP) projector with prisms is presented. The total internal reflection (TIR) prisms between the zoom lens and the digital micromirror device (DMD) are analyzed. To obstruct the false light, it is preferable that the projector zoom lens has a telecentric incident side. To study the structure of telecentric beam path for zoom lens system，the axial displacement equation for the stop was deduced, which keep the system telecentric in all zoom position. A thin lens group fixed with the stop shares the power of the others and makes the cam curve smooth.
The continuous telecentric zoom lens for a digital light processor (DLP) projector with prisms is presented. The total internal reflection (TIR) prisms between the zoom lens and the digital micromirror device (DMD) are analyzed. To obstruct the false light, it is preferable that the projector zoom lens has a telecentric incident side. To study the structure of telecentric beam path for zoom lens system，the axial displacement equation for the stop was deduced, which keep the system telecentric in all zoom position. A thin lens group fixed with the stop shares the power of the others and makes the cam curve smooth.
2006, 27(4): 268-273.
Abstract:
The definitions of strictoptimal and quasioptimal (ν, k, 1) optical orthogonal codes are introduced. The relationship between optimal optical orthogonal code and cyclic difference family is given. Based on Wilson’s lemma on evenly distributed differences and primary number theory, a simple and practical construction method for optimal (ν, k, 1) cyclic difference family is proposed. Furthermore, this method was applied to the construction of optical orthogonal codes, and some strictoptimal (ν, k, 1) optical orthogonal codes could be constructed efficiently, in which, the code length ν was a prime number. Finally, through an example of the construction of strictoptimal (ν, k, 1) optical orthogonal codes, the computer assistant design method is given. The work can provides an effective approach for the construction of strictoptimal (ν, k, 1) optical orthogonal codes.
The definitions of strictoptimal and quasioptimal (ν, k, 1) optical orthogonal codes are introduced. The relationship between optimal optical orthogonal code and cyclic difference family is given. Based on Wilson’s lemma on evenly distributed differences and primary number theory, a simple and practical construction method for optimal (ν, k, 1) cyclic difference family is proposed. Furthermore, this method was applied to the construction of optical orthogonal codes, and some strictoptimal (ν, k, 1) optical orthogonal codes could be constructed efficiently, in which, the code length ν was a prime number. Finally, through an example of the construction of strictoptimal (ν, k, 1) optical orthogonal codes, the computer assistant design method is given. The work can provides an effective approach for the construction of strictoptimal (ν, k, 1) optical orthogonal codes.
2006, 27(4): 274-280.
Abstract:
Silicon carbonitride (SiCN) films were prepared with microwave electron cyclotron resonance plasma enhanced unbalance magnetron sputtering technique (MWECR PEUMST). FTIR and XPS characterization results indicate that the amount of CSiN subchemical structure in deposited film increases from 14.3% to 43.6%, when the silicon target sputtering power increases from 150W to 350W. Moreover, larger N2gas flow rate is beneficial to the formation of sp2C＝N and sp1C≡N chemical structure. The optical gap of deposited SiCN films deduced from the Tauc method shows that the maximum optical gap of 2.8eV can be obtained when the silicon target sputtering power is 300W, the carbon target sputtering voltage is 600V and the N2 gas flow rate is set at 6sccm.
Silicon carbonitride (SiCN) films were prepared with microwave electron cyclotron resonance plasma enhanced unbalance magnetron sputtering technique (MWECR PEUMST). FTIR and XPS characterization results indicate that the amount of CSiN subchemical structure in deposited film increases from 14.3% to 43.6%, when the silicon target sputtering power increases from 150W to 350W. Moreover, larger N2gas flow rate is beneficial to the formation of sp2C＝N and sp1C≡N chemical structure. The optical gap of deposited SiCN films deduced from the Tauc method shows that the maximum optical gap of 2.8eV can be obtained when the silicon target sputtering power is 300W, the carbon target sputtering voltage is 600V and the N2 gas flow rate is set at 6sccm.
2006, 27(4): 281-284.
Abstract:
Theoretical research on the record of every incident output of the singlemolecule photon source responded by two SPCM with standard HanburyBrownTwiss technique is presented. The photon statistic measurement of a single molecule photon source based on the HBT configuration with an unbalanced detection system is studied. The photon counting statistics character of the real single molecular photon source with a Poisson statistics background is theoretically investigated. It is shown that the unbalanced detectors, the unbalanced beamsplitter and the unbalanced linear propagation efficiencies will cause the single event Mandel parameter to be less than that of balance system. In addition, the correction expression to the Mandel parameter based on unbalanced detection is given.
Theoretical research on the record of every incident output of the singlemolecule photon source responded by two SPCM with standard HanburyBrownTwiss technique is presented. The photon statistic measurement of a single molecule photon source based on the HBT configuration with an unbalanced detection system is studied. The photon counting statistics character of the real single molecular photon source with a Poisson statistics background is theoretically investigated. It is shown that the unbalanced detectors, the unbalanced beamsplitter and the unbalanced linear propagation efficiencies will cause the single event Mandel parameter to be less than that of balance system. In addition, the correction expression to the Mandel parameter based on unbalanced detection is given.
2006, 27(4): 285-288.
Abstract:
The new method of image matching based on feature extraction and transform domain correlation is proposed in this paper. By extracting long edge information from image and analyzing its geometric feature, the edge directionangle curve can be constucted as an important parameter for image matching. By calculating difference and comparing with relative chain codes of two images’ edge direction curves, the possible rotation angle between the two images will be obtained. After rotating images and transforming them with 2D Fourier, the phase correlation will be gained in frequency domain and the maximum of the correlation coefficient will be found in that position which indicates the displacement of two images. So the two images can be matched accurately. Experimental results prove that this matching method is accurate, fast and automatic, it decreases the disturbance caused by artificial factors and could achieve a satisfactory matching between the two images with low grey difference and noise.
The new method of image matching based on feature extraction and transform domain correlation is proposed in this paper. By extracting long edge information from image and analyzing its geometric feature, the edge directionangle curve can be constucted as an important parameter for image matching. By calculating difference and comparing with relative chain codes of two images’ edge direction curves, the possible rotation angle between the two images will be obtained. After rotating images and transforming them with 2D Fourier, the phase correlation will be gained in frequency domain and the maximum of the correlation coefficient will be found in that position which indicates the displacement of two images. So the two images can be matched accurately. Experimental results prove that this matching method is accurate, fast and automatic, it decreases the disturbance caused by artificial factors and could achieve a satisfactory matching between the two images with low grey difference and noise.
2006, 27(4): 289-292.
Abstract:
With the progress of information technology and the everincreasing information demands from antiterrorism war as background, the application status of electrooptical technology in light weapons is analyzed. The development of weapons triggered by the change of the operation concept in different nations under new military revolution caused by high technology is described briefly. Based on the fundamental role played by electrooptic technology in improving the performance of light weapons， e.g. improving the shooting accuracy of the light weapons by adding optical systems or electrooptical sights, the relation between light weapon and electrooptical technology is summarized under the new defense demand. The paper elaborates the design features for rifle with elbow structure design, future small weapon mounted on human arm, remote light weapon control station for integrated electrooptical sight, smart ammunitions controlled by situation awareness devices, metal storm weapon system launched in a new concept and etc. The roles that electrooptical technology plays in target acquisition and fire control and ballistic correction are pointed out.
With the progress of information technology and the everincreasing information demands from antiterrorism war as background, the application status of electrooptical technology in light weapons is analyzed. The development of weapons triggered by the change of the operation concept in different nations under new military revolution caused by high technology is described briefly. Based on the fundamental role played by electrooptic technology in improving the performance of light weapons， e.g. improving the shooting accuracy of the light weapons by adding optical systems or electrooptical sights, the relation between light weapon and electrooptical technology is summarized under the new defense demand. The paper elaborates the design features for rifle with elbow structure design, future small weapon mounted on human arm, remote light weapon control station for integrated electrooptical sight, smart ammunitions controlled by situation awareness devices, metal storm weapon system launched in a new concept and etc. The roles that electrooptical technology plays in target acquisition and fire control and ballistic correction are pointed out.
2006, 27(4): 293-297.
Abstract:
In order to overcome the jitter,which appears in an electrooptical pod during high speed tracking, an improved lead and lag compensation filter network is proposed. A mathematical model for the pod′s mechanical transmission system was established with MATLAB. The improvement on system dynamic performance made by the filtering network was analyzed. Compared to the traditional filter, such filter takes care of both central resonance frequency′s impact on system dynamic performance and other resonances′ impact on system performance. The experiment results indicate that such filter can improve the system dynamic performance significantly, effectively reduce the jitter amplitude and make digital filering easier to be implemented.
In order to overcome the jitter,which appears in an electrooptical pod during high speed tracking, an improved lead and lag compensation filter network is proposed. A mathematical model for the pod′s mechanical transmission system was established with MATLAB. The improvement on system dynamic performance made by the filtering network was analyzed. Compared to the traditional filter, such filter takes care of both central resonance frequency′s impact on system dynamic performance and other resonances′ impact on system performance. The experiment results indicate that such filter can improve the system dynamic performance significantly, effectively reduce the jitter amplitude and make digital filering easier to be implemented.
2006, 27(4): 298-302.
Abstract:
In order to do the same distribution test for sea target detection accuracy, a statistic analysis was carried out for onsite target detection data. The result indicates that many error data conform with the same distribution or the same normal distribution. In comparison with the method χ2 test, the symbol test and the sum of order test, it is concluded that χ2 test is suitable to the same distribution test for sea target detection. A series of tests indicate that if a reasonable confidence level is selected, the voyages necessary for testing are decreased to 10%～50% of the original voyages. The test method can improve the confidence and accuracy of the test data, shorten the test period, and expand the application of weapon test for data processing and analysis.
In order to do the same distribution test for sea target detection accuracy, a statistic analysis was carried out for onsite target detection data. The result indicates that many error data conform with the same distribution or the same normal distribution. In comparison with the method χ2 test, the symbol test and the sum of order test, it is concluded that χ2 test is suitable to the same distribution test for sea target detection. A series of tests indicate that if a reasonable confidence level is selected, the voyages necessary for testing are decreased to 10%～50% of the original voyages. The test method can improve the confidence and accuracy of the test data, shorten the test period, and expand the application of weapon test for data processing and analysis.
2006, 27(4): 303-307.
Abstract:
Lowlightlevel (LLL) night vision technology, as one of main high military optoelectronic technologies, will become more and more outstanding and important, and will possess enormous potential and wide application in the modern or future high technology war and night fighting along with the technologies fast developing and the performances continuous improving for LLL night vision devices and systems. Based on the detailed analyses of the tube characteristics，main ideas and key technologies of the Super Gen. Ⅱ, Gen. Ⅲ and Gen.Ⅳ image intensifiers, the development status and uptodate progress are introduced and expatiated in this paper. Simultaneously, some prospects and suggestions about developing direction and main research work for domestic LLL night vision technology are put forward according to the internal situation such as the condition of equipments, the performance of devices and the level of technologies.
Lowlightlevel (LLL) night vision technology, as one of main high military optoelectronic technologies, will become more and more outstanding and important, and will possess enormous potential and wide application in the modern or future high technology war and night fighting along with the technologies fast developing and the performances continuous improving for LLL night vision devices and systems. Based on the detailed analyses of the tube characteristics，main ideas and key technologies of the Super Gen. Ⅱ, Gen. Ⅲ and Gen.Ⅳ image intensifiers, the development status and uptodate progress are introduced and expatiated in this paper. Simultaneously, some prospects and suggestions about developing direction and main research work for domestic LLL night vision technology are put forward according to the internal situation such as the condition of equipments, the performance of devices and the level of technologies.
2006, 27(4): 308-311.
Abstract:
To improve the imaging quality of lens used in the helmetmounted LLL nightvision system and make lens small in size, light in weight, the lens with the high order aspheric surface is designed. According to the theory of the aberration, the lens of the helmetmounted nightvision imaging system is designed to meet the demand. When spatial frequency is 40lp/mm, onaxis MTF can reach 0.62 and offaxis MTF 0.42. On the other hand, its total weight is about 300g，the number of lens is reduced from 9 to 6, the total length of the system from 81mm to 72mm. The analyzed results show that the construction of the aspheric surface for helmetmounted LLL nightvision systems can make its lens configuration simple.
To improve the imaging quality of lens used in the helmetmounted LLL nightvision system and make lens small in size, light in weight, the lens with the high order aspheric surface is designed. According to the theory of the aberration, the lens of the helmetmounted nightvision imaging system is designed to meet the demand. When spatial frequency is 40lp/mm, onaxis MTF can reach 0.62 and offaxis MTF 0.42. On the other hand, its total weight is about 300g，the number of lens is reduced from 9 to 6, the total length of the system from 81mm to 72mm. The analyzed results show that the construction of the aspheric surface for helmetmounted LLL nightvision systems can make its lens configuration simple.
2006, 27(4): 312-314.
Abstract:
In order to provide a theoretical base for high resolution optical coherent imaging, the interference of laser beam transmitting in the turbulent atmosphere for a certain distance is studied. The approximation method of phase screen was used to simulate laser beam transmission in turbulent atmosphere, and its interference in turbulent atmosphere was investigated. The simulation indicates that the longer the distance between apertures is， the closer the interference fringes are; good interference fringes are formed when transmission distance is two kilometers and atmospheric turbulence refractive index structure coefficient C2nis 10-14, which is close to strong turbulence. The interference fringes are clear if the apertures are closer. Therefore, proper distance between the transmit apertures could be selected to get better interference fringes and high resolution images.
In order to provide a theoretical base for high resolution optical coherent imaging, the interference of laser beam transmitting in the turbulent atmosphere for a certain distance is studied. The approximation method of phase screen was used to simulate laser beam transmission in turbulent atmosphere, and its interference in turbulent atmosphere was investigated. The simulation indicates that the longer the distance between apertures is， the closer the interference fringes are; good interference fringes are formed when transmission distance is two kilometers and atmospheric turbulence refractive index structure coefficient C2nis 10-14, which is close to strong turbulence. The interference fringes are clear if the apertures are closer. Therefore, proper distance between the transmit apertures could be selected to get better interference fringes and high resolution images.
2006, 27(4): 315-318.
Abstract:
Theoretical analysis and experiment of endpumped Yb3+ doped doubleclad fiber laser are presented in this paper. Based on rate equations, the distribution of pump power and laser power in the fiber, the effect of fiber length and reflectivity of cavity minor on output power are studied. The maximum output laser power can be obtained with the optimum fiber length and fiber end as output coupling. That is, the higher the reflectivity of rearcavity mirror is, the lower the laser output power will be. For short fiber, the output laser power and slope efficiency can be improved when a reflective mirror is set at output end to reflect the pump light. In the experiment, the laser with a central wavelength of 1088.3nm, the slope efficiency of 33.7% and the maximal output power of 1.75W were obtained.
Theoretical analysis and experiment of endpumped Yb3+ doped doubleclad fiber laser are presented in this paper. Based on rate equations, the distribution of pump power and laser power in the fiber, the effect of fiber length and reflectivity of cavity minor on output power are studied. The maximum output laser power can be obtained with the optimum fiber length and fiber end as output coupling. That is, the higher the reflectivity of rearcavity mirror is, the lower the laser output power will be. For short fiber, the output laser power and slope efficiency can be improved when a reflective mirror is set at output end to reflect the pump light. In the experiment, the laser with a central wavelength of 1088.3nm, the slope efficiency of 33.7% and the maximal output power of 1.75W were obtained.
2006, 27(4): 319-322.
Abstract:
In order to carry out nondestructive test by laser holography and to get the test data of phase object, nondestructive test of phase objects by secondary exposure laser holography is studied. The disadvantages of the traditional beam path test for phase objects with the method of secondary exposure were analyzed. Therefore, an improved scheme, which suggests that the object light wave should pass through the sample twice, is put forward. This scheme was applied to the nondestructive test for some phase objects such as normal glass and organic glass, and satisfactory results were achieved. In comparison with the traditional test methods, this scheme has some features such as high precision, high reliability and nondestructive direct test, etc. With a little change, the device can be used in online quality control for plastic and glass production.
In order to carry out nondestructive test by laser holography and to get the test data of phase object, nondestructive test of phase objects by secondary exposure laser holography is studied. The disadvantages of the traditional beam path test for phase objects with the method of secondary exposure were analyzed. Therefore, an improved scheme, which suggests that the object light wave should pass through the sample twice, is put forward. This scheme was applied to the nondestructive test for some phase objects such as normal glass and organic glass, and satisfactory results were achieved. In comparison with the traditional test methods, this scheme has some features such as high precision, high reliability and nondestructive direct test, etc. With a little change, the device can be used in online quality control for plastic and glass production.
2006, 27(4): 323-326.
Abstract:
In order to accurately evaluate the performance of an infrared thermal imager, it is necessary to test its modulation transfer function (MTF). In this paper, a CEDIT ⅡA thermal imaging system is measured and analyzed by the equipment with dual blackbody and reflective target system. The new testing method utilizes the theory of edge target test. The edge is differentiated to obtain the line spread function and Fouriertransformed to get the MTF. It is discovered that the primary factors which affect MTF test are the signal intensity for the testing system incidence, impulse noise suppression and acquisition filtering, etc. The equipment can keep even and steady radiation, and is not affected by ambient temperature, so the accuracy and reliability of measurement can be improved.
In order to accurately evaluate the performance of an infrared thermal imager, it is necessary to test its modulation transfer function (MTF). In this paper, a CEDIT ⅡA thermal imaging system is measured and analyzed by the equipment with dual blackbody and reflective target system. The new testing method utilizes the theory of edge target test. The edge is differentiated to obtain the line spread function and Fouriertransformed to get the MTF. It is discovered that the primary factors which affect MTF test are the signal intensity for the testing system incidence, impulse noise suppression and acquisition filtering, etc. The equipment can keep even and steady radiation, and is not affected by ambient temperature, so the accuracy and reliability of measurement can be improved.
2006, 27(4): 327-331.
Abstract:
Because the sensitivity of the fiber Bragg grating (FBG) sensor to the strain and temperature is observed through the variation of its reflected light wavelength, it is important for FBG sensor to measure the change of the wavelength. Although there are many demodulation methods nowadays, filtering demodulation technique finds more applications because the measurement devices are easy to make, simple in structure and convenient to operate. Eight kinds of filter based demodulation methods are introduced in order to select an optimum demodulation method for the specific application, these demodulations are compared in terms of cost, accuracy, measurement range, manufacture of the devices and applicable environment, their advantages and disadvantages are analyzed. The optical wavelet transform filtering is introduced emphatically, the principle of the measurement system is discussed in depth and its potential applications are pointed out.
Because the sensitivity of the fiber Bragg grating (FBG) sensor to the strain and temperature is observed through the variation of its reflected light wavelength, it is important for FBG sensor to measure the change of the wavelength. Although there are many demodulation methods nowadays, filtering demodulation technique finds more applications because the measurement devices are easy to make, simple in structure and convenient to operate. Eight kinds of filter based demodulation methods are introduced in order to select an optimum demodulation method for the specific application, these demodulations are compared in terms of cost, accuracy, measurement range, manufacture of the devices and applicable environment, their advantages and disadvantages are analyzed. The optical wavelet transform filtering is introduced emphatically, the principle of the measurement system is discussed in depth and its potential applications are pointed out.
2006, 27(4): 332-335.
Abstract:
he Maxwell equations for the propagation of electromagnetic waves in photonic crystal fibers are solved with plane wave method. The cross section of the photonic crystal fiber is taken as a big unit cell and an infinite twodimensional periodic system is generated, thus the core is regarded as a defect in photonic crystal. The properties of a new model of high birefringence photonic crystal fibers (PCB) and that of dispersion flattened PCB are studied respectively with the supercell model described above. It is found that birefringence in the model is higher than that in conventional fibers when the diameter of the holes in the same line with the core varies. Moreover, in the new model of dispersion flattened PCB, a zero dispersion flattened fiber can be obtained when the diameter of the holes closest to the core takes a specific value. The new dispersion flattened PCB will have great potential in optical communication systems.
he Maxwell equations for the propagation of electromagnetic waves in photonic crystal fibers are solved with plane wave method. The cross section of the photonic crystal fiber is taken as a big unit cell and an infinite twodimensional periodic system is generated, thus the core is regarded as a defect in photonic crystal. The properties of a new model of high birefringence photonic crystal fibers (PCB) and that of dispersion flattened PCB are studied respectively with the supercell model described above. It is found that birefringence in the model is higher than that in conventional fibers when the diameter of the holes in the same line with the core varies. Moreover, in the new model of dispersion flattened PCB, a zero dispersion flattened fiber can be obtained when the diameter of the holes closest to the core takes a specific value. The new dispersion flattened PCB will have great potential in optical communication systems.
2006, 27(4): 336-339.
Abstract:
To calculate the refractive index of every layer accurately in coating process, two methods are introduced to determine the refractive index of layers in real time monitoring. The first method calculates the refractive index of the film inversely with the measured transmittance spectrum. The other one fits the refractive index of the film with the estimation algorithm in the least square method (LSM). The results of the test indicate the online inverse calculation method is more suitable for single point monitoring and the error of calculated refractive index is less than 2%. However, in real coating process, the first method is not preferred because the layers’ parameters differ a lot from each other, which makes the error greater than 25%. Meanwhile, the latter one can collect the information from whole wideband spectrum and make the error smaller, which is normally less than 10%. Therefore, it can improve the precision of the film thickness monitoring significantly.
To calculate the refractive index of every layer accurately in coating process, two methods are introduced to determine the refractive index of layers in real time monitoring. The first method calculates the refractive index of the film inversely with the measured transmittance spectrum. The other one fits the refractive index of the film with the estimation algorithm in the least square method (LSM). The results of the test indicate the online inverse calculation method is more suitable for single point monitoring and the error of calculated refractive index is less than 2%. However, in real coating process, the first method is not preferred because the layers’ parameters differ a lot from each other, which makes the error greater than 25%. Meanwhile, the latter one can collect the information from whole wideband spectrum and make the error smaller, which is normally less than 10%. Therefore, it can improve the precision of the film thickness monitoring significantly.
2006, 27(4): 340-343.
Abstract:
To meet the ever increasing applications of femtosecond laser pulse, it has to be measured more precisely. Based on the spectral phase interferometry of direct electricfield reconstruction (SPIDER), the spectral phase of femotosecond laser pulse was reconstructed with numerical simulations. The crucial parameters that include the time delay τ between the tested pulse replicas, the frequency shear Ω and the width of filter window were analyzed to choose their values properly. With the Gauss linearly chirped pulse whose full width at half maximum (FWHM) is about 20fs, the phase is reconstructed with different time delay and different frequency shear Ω/Δω. The optimum phase curve is about at τ=1210fs and relative shear is Ω/Δω=0.09. The width of filtering window is about τ/3.
To meet the ever increasing applications of femtosecond laser pulse, it has to be measured more precisely. Based on the spectral phase interferometry of direct electricfield reconstruction (SPIDER), the spectral phase of femotosecond laser pulse was reconstructed with numerical simulations. The crucial parameters that include the time delay τ between the tested pulse replicas, the frequency shear Ω and the width of filter window were analyzed to choose their values properly. With the Gauss linearly chirped pulse whose full width at half maximum (FWHM) is about 20fs, the phase is reconstructed with different time delay and different frequency shear Ω/Δω. The optimum phase curve is about at τ=1210fs and relative shear is Ω/Δω=0.09. The width of filtering window is about τ/3.
2006, 27(4): 344-349.
Abstract:
The spatial encoding technique is one of the key techniques in 3D measurement. The spatial encoding method,which plays an important role in resolution, speed and reliability in measurement,is introduced. The measurement principle of structured light method based on a triangular algorithm is described. The influence and functions of spatial encoding technique are studied, the principle of encoding is introduced and the condition which should be satisfied by the encoding scheme are summarized. Several typical encoding methods investigated in recent years and the stripe boundary encoding proposed by this laboratory are analyzed and compared. Their advantages, drawbacks and development trend are introduced. The proposed colorencoding methods, their unique advantages and common drawbacks are introduced. Finally, based on the study, the spatial encoding technique is reviewed and its prospect is pointed out.
The spatial encoding technique is one of the key techniques in 3D measurement. The spatial encoding method,which plays an important role in resolution, speed and reliability in measurement,is introduced. The measurement principle of structured light method based on a triangular algorithm is described. The influence and functions of spatial encoding technique are studied, the principle of encoding is introduced and the condition which should be satisfied by the encoding scheme are summarized. Several typical encoding methods investigated in recent years and the stripe boundary encoding proposed by this laboratory are analyzed and compared. Their advantages, drawbacks and development trend are introduced. The proposed colorencoding methods, their unique advantages and common drawbacks are introduced. Finally, based on the study, the spatial encoding technique is reviewed and its prospect is pointed out.
2006, 27(4): 350-354.
Abstract:
For getting superior quality and denser WDM device, a new method to make demultiplexing device with volume holographic technology is studied. Based on coupledmode theory, the fundamental principle that photorefractive volume grating is used as a wave filter for WDM is discussed. The equations of optimum beam ratio,strength of coupling and corresponding maximum diffraction efficiency are described. The effects of the relation on recording geometry with effective electrooptical coefficient and space charge field, wavelength of diffraction beam and diffraction angle on exposure sequence are taken into account, and the perfect exposure sequence is discussed based on recurrence method. A highluminosity halogen lamp is considered as the multiplex photosource and an experimental scheme of 16 channels wave demultiplex based on volume holographic technology is designed. The device can separate the line which wavelength space out 0.8mm to 1.0mm distance and fit in demultiplexing for crowed wave.
For getting superior quality and denser WDM device, a new method to make demultiplexing device with volume holographic technology is studied. Based on coupledmode theory, the fundamental principle that photorefractive volume grating is used as a wave filter for WDM is discussed. The equations of optimum beam ratio,strength of coupling and corresponding maximum diffraction efficiency are described. The effects of the relation on recording geometry with effective electrooptical coefficient and space charge field, wavelength of diffraction beam and diffraction angle on exposure sequence are taken into account, and the perfect exposure sequence is discussed based on recurrence method. A highluminosity halogen lamp is considered as the multiplex photosource and an experimental scheme of 16 channels wave demultiplex based on volume holographic technology is designed. The device can separate the line which wavelength space out 0.8mm to 1.0mm distance and fit in demultiplexing for crowed wave.
2006, 27(4): 355-358.
Abstract:
The passive quenching method is used to characterize InGaAs/InP avalanche photodiode (APD) operating in Geiger mode. Based on the feature that the voltages of APD terminals tend to be stabilized after avalanche, a new passive quenching method is put forward to determine dark breakdown voltage. The experiment indicated, with the decrease of the temperature, the optimum operating area of APD became wider, the optimum gain of APD was increased, and APD’s sensitivity was improved. By comparing the dark current and the signaltonoise ratio of EGG with those of Epitaxy APD, it is discovered that Epitaxy APD is preferable for single photon detection due to its low noise level and high signaltonoise ratio. The study on characteristics of different APDs is helpful to choose proper type of single photon detector for quantum communication.
The passive quenching method is used to characterize InGaAs/InP avalanche photodiode (APD) operating in Geiger mode. Based on the feature that the voltages of APD terminals tend to be stabilized after avalanche, a new passive quenching method is put forward to determine dark breakdown voltage. The experiment indicated, with the decrease of the temperature, the optimum operating area of APD became wider, the optimum gain of APD was increased, and APD’s sensitivity was improved. By comparing the dark current and the signaltonoise ratio of EGG with those of Epitaxy APD, it is discovered that Epitaxy APD is preferable for single photon detection due to its low noise level and high signaltonoise ratio. The study on characteristics of different APDs is helpful to choose proper type of single photon detector for quantum communication.
2006, 27(4): 359-362.
Abstract:
A novel digital portable optical experimental instrument is introduced, which can be used for optical experiment，demonstration in class，research and test. It can fulfil interference, diffraction and holography in wave optics, as well as imaging in geometic optics. The instrument is designed with an orbit in “又” form and a bracket in “工” form to realize a smooth and accurate adjustment. An image processing software and a multilayer instrument which connects the PC mother board with an optical bench were developed base on RGB average method. The image can be gathered and processed in real time. Compared to the traditional experiment set up, this instrument could expand the scope of the digital optical experiment significantly.
A novel digital portable optical experimental instrument is introduced, which can be used for optical experiment，demonstration in class，research and test. It can fulfil interference, diffraction and holography in wave optics, as well as imaging in geometic optics. The instrument is designed with an orbit in “又” form and a bracket in “工” form to realize a smooth and accurate adjustment. An image processing software and a multilayer instrument which connects the PC mother board with an optical bench were developed base on RGB average method. The image can be gathered and processed in real time. Compared to the traditional experiment set up, this instrument could expand the scope of the digital optical experiment significantly.
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