2016 Vol. 45, No. 7
column
- Invited paper
- Infrared technology and application
- Laser technology and application
- Terahertz technology
- Laser radar technology
- Atmospheric optics
- Adaptive optics
- Advanced optical material
- Advanced optical imaging
- Photoelectric devices and microsystem
- Optical design and simulation
- Optical communication and optical sensing
- Photoelectric measurement
- Information acquisition and identification
- Photoelectric navigation and control
The scientific method research is more basic than to get results. This article was a summary of the author's 30 years of scientific research path and the research results. The researches began from some fundamental problems of laser principle, and the laser resonator structure was changed by inducing special optical elements intro/extra cavity. Then various physical phenomena were found with tuning resonator of the two mirrors laser and the three mirrors laser. And we had developed several kinds of precision measuring instruments based on the newly designed laser itself. In this paper, the basic idea of the author's scientific research was summarized, and the physical phenomena found in the laser were introduced briefly, and the scientific system of the laser resonance instruments was established.
2016, 45(7): 703002.
Spherical dome usually works in the state of turbulent convection heat transfer for the penetration infrared guidance system flying at low altitude and high speed. In this paper, the sphere-cone at zero attack corner was focused on. Numerical calculation engineering method of turbulent convection heat transfer for dome was proposed by using SST model, which was implemented by generating the structure grid, setting physical property parameter of inflow and compared with the engineering formula of heat transfer at stagnation point and turbulent region. Firstly, based on Billig's results, detached shock was generated in flow field by use of multi-block structured grid in order to reduce the numerical dissipation. In order to analyze the sensitivity of the calculation results to near-wall grid, several numerical experiments were performed with grid of different near-wall node heights. Then, the influence of SST model parameters on the calculation results was analyzed and Bradshaw number only had an obvious impact on the computation of peak heat flux. The result of heat flux at stagnation point calculated by SST model was consistent with Klein's formula by using the correction approach of equivalent thermal conductivity for inflow. At the region of turbulent flow over dome, the Bradshaw number was modified by applying the engineering formula of turbulent heat transfer over the sphere at high speed. The result of heat flux computed by SST model was consistent with this engineering formula. The results calculated by modified SST model could satisfy the requirement of engineering applications and could be applied to analyze thermal shock resistance of dome, aero-optic effects, non-uniformity correction of infrared images and trajectory design of terminal guidance for infrared or laser guidance system. This numerical calculation method plays an important role in engineering design of optical guidance system at high speed.
HgCdTe plane array detector is a key component in infrared space camera. The scale of detector is enlarging continuously due to the unending requirements of better performance. HgCdTe plane array detector needs to be mounted on loading board in room temperature, and it needs to work at deep cooling environment, temperature fluctuation at about 200 K should be endured. Temperature fluctuation leads to warping deformation of detector due to mismatch of CTE between detector and loading board, and large warping deformation results in damage in detector. Then thermal adapter of HgCdTe focal plane arrays based on carbon fiber with high heat conductivity was proposed. High axial heat conductivity of carbon fiber was adopted to reduce thermal resistance of adapter, and minimal section bending modulus of carbon fiber was adopted to decouple the stiffness between two end faces of thermal adapter. Compared with direct bonding assembly between detector and loading board, after the adoption of thermal adapter based on carbon fiber with high heat conductivity, thermal resistance between detector and loading board was increased by merely about 1 percent, but warping deformation of detector due to mismatch of CTE was reduced by more than 99.9 percent. Problem of damage on large scale detector due to mismatch of CTE was resolved. Manufacture process of thermal adapter based on carbon fiber was briefly introduced.
2016, 45(7): 704002.
doi: 10.3788/IRLA201645.0704002
The infrared imaging technology can acquire the intensity information of targets, and polarization imaging technology can acquire the polarization information of targets. Combination of the two technology is more conducive to the target detection and recognition. Experiments focused on typical targets under typical backgrounds, such as the plane in the sky, the ship on the sea, and the vehicle on the grass. In Experiments, the four-channel long wave infrared polarization imaging (LWIPI) system developed was employed to acquire images. Experimental results show that, compared with traditional long-wave infrared images, LWIPI has the following advantages:(1) the long wave infrared polarization degree image has a higher image contrast in a certain situation, which is beneficial to the target detection and recognition; (2) the long wave infrared polarization angle image can highlight target details, which is beneficial to the viewer's understanding of the content of the scene; (3) the long wave infrared polarization degree image and angle image can suppress clutter in a certain situation, which is beneficial to target imaging studies under the condition of a clutter.
For the above 2000 K temperature field, due to the saturation problem of thermal imager, the reconstruction of thermal imager temperature field of this measurement method is no longer applicable. Using a plurality of optical probe and through the optical fiber transmission, data measurements were realized under the multi-channels and multi-spectral. On the basis of the proposed model without the assumption of the relationship between the emissivity and wavelength, the true temperature of the surface was obtained by the iterative algorithm. By arranging a cross temperature structure of the multi spectral method to the turbocharged boiler, multi-points temperature measurement were achieved and the temperature distribution of the temperature field was constructed. The results show the method can be used to measure the temperature field distribution of the turbocharged boiler and the prediction error is small, which can be used as a reference for the analysis and diagnosis of high temperature field.
2016, 45(7): 704004.
doi: 10.3788/IRLA201645.0704004
The simulation of realistic infrared scene in space infrared down-looking system has always been a difficult problem in the research. A new kind of infrared scene simulation method of space down-looking system based on remote sensing inversion was presented in this paper. Firstly, infrared texture of the terrain was extracted from the data of infrared remote sensing inversion by using matching algorithm. Secondly, an infrared detecting model of down-looking system was proposed, which simulated resampling of infrared texture on FPA. Finally, by using radiation and transmission theory, scene radiance image in front of the entrance pupil was calculated. The simulation results show that the proposed method can realistically simulate infrared texture feature of earth surface. In this paper, thermal infrared remote sensing technology is applied to infrared scene simulation, which greatly simplifies the simulation process of large scale terrain scene, and provides an intuitive and effective new method for infrared scene simulation of space down-looking system.
The pressure recovery system is one of the key techniques for the high energy chemical lasers. Total pressure losses affect the key specification of lasers, such as the output ability, the size and weight of laser systems. The total pressure losses for combustion-driven continuous wave DF/HF chemical lasers were proposed according to the theory analysis of one dimensional gas exhausting. The analysis of the main factors of total pressure losses in the gain generator of the laser is the foundation of the research of recovering the gain generator with high pressure. Two major factors of total pressure losses caused by viscous friction and the temperature rise caused by chemical reaction in optical cavity were discussed in this paper. The result shows that temperature rise caused by burning has obvious influence on system's performance of pressure recovery.
2016, 45(7): 705002.
doi: 10.3788/IRLA201645.0705002
As the rapid development of high-power TEA CO2 laser technology and its extensive application on industrial production, scientific research, aeronautics and astronautics and other fields, higher performance demand on control system for high-power TEA CO2 laser was put forward. A control system based on Digital Signal Processor(DSP) was designed for the high-power TEA CO2 laser, and the core module was introduced on hardware and software in detail. To overcome the severe electromagnetic interference generated during the working process of laser, shielding enclosure, power filter, safety ground, digital filter, storage and recovery of critical data, resisting reset interference and other designs were taken measure on the control system. After long term run-time test on the high-power TEA CO2 laser, the control system works stably and firmly, controlling and responding quickly, meanwhile satisfying the design request of resisting strong electromagnetic interference, with good application and popularization value.
Both 6 kW fiber laser deposition repair system and electromagnetic induction heating equipment were utilized, laser deposition repair experiments were respectively done by TA15 titanium powder under substrate without preheating and preheating at 200℃ and 400℃. Then microstructure, microhardness and residual stress were tested and analyzed through optical microscope, microhardness tester and indentation stress tester, the influence of microstructure, microhardness and residual stress in different substrate preheating temperature on the laser deposition repair sample was achieved. Results show that microstructure of lamella becomes thicker and primary grow more fully; microhardness of material is slightly reduced; residual stress is effectively reduced with the increasing of preheating temperature. The guidance basis for laser deposition repair assisted by induction heating is provided.
2016, 45(7): 705004.
doi: 10.3788/IRLA201645.0705004
Dual-wavelength laser fuse has significant value in the anti-interference of frog and aerosols. In order to decrease the size of the fuze, guarantee the adequacy of the inner space of the missile and optimize the performance of all the system, an ASIC chip for the dual-wavelength laser fuse based on BCD technology was proposed. First, the structure and working principles of the dual-wavelength laser fuse were presented in detail. Then, the design strategy of the chip was deduced and the simulation result of the sub-circuits of the chip was proposed afterwards. The chip is fabricated with a 0.25 m BCD process. Used in driving the dual-wavelength lasers, when the supply voltage of the chip is 5 V and the supply voltage of the branch of the circuits with lasers is 27 V, the peak power of infrared laser reaches above 30 W, and the peak power of violet laser reaches above 25 W. The pulse width is adjustable in a range of 50-500 ns. The repetition frequency is adjustable in a range of 1-100 kHz. The time window is adjustable at a range of 1-100 s. The echo signals are separated at the receiving end. Replacing the role of the 4 chips, the dual-wavelength laser fuse ASIC can simplify the structure of the system and optimizes the function of the fuze.
2016, 45(7): 705005.
doi: 10.3788/IRLA201645.0705005
In order to measure the absolute spectral responsivity of mid-infrared detectors with high accuracy, the improvement of power stability and beam quality of mid-infrared laser was theoretically and experimentally demonstrated. The power stability of mid-infrared laser was improved to be better than 0.1% by using acousto-optic modulator and feedback-control electronics. Based on propogation properties of Gaussion beam, the parameters were calculated and experimental setup of spatial filter was constructed. Owing to the spatial filter, the beam quality of mid-infrared laser was improved. A stable and reliable laser source is provided for the measurement of absolute spectral responsivity of mid-infrared detectors.
2016, 45(7): 703001.
Three kinds of probiotics in the biological food additives which are respectively Bacillus licheniformis, Bacillus subtilis and Bacillus coagulans have been tested and investigated with the terahertz time-domain spectroscopic(THz-TDS) technique at room temperature in nitrogen environment in the paper. The absorption coefficient and refraction index of three probiotics samples were calculated in the frequency of 0.2-1.6 THz. Test reveal that the absorption coefficients is increased as frequency increases and has considerable different absorption trend and characteristic absorption peaks among the samples, which means the vibration information made up of different molecular vibration and multi-molecular group is different in the THz spectrum of three samples. Furthermore, the average refractive indices were 1.71, 1.67 and 1.64 corresponding to Bacillus licheniformis, Bacillus subtilis and Bacillus coagulans, respectively. The refractive value indicates that abnormal dispersion, which meant three samples had the characters of strong selective absorption in this wave band. In contrast, the Fourier transform infrared spectroscopy(FTIR) in the 400-4000 cm-1 was utilized to measure the IR absorption spectra, and the results revealed that the probiotics is more active in the range of Terahertz than in the IR band and terahertz can be a good supplementary means of IR test. Meanwhile, some explanation on mechanism was put forward in this paper. The experiments showed that THz-TDS is a powerful tool to complement the conventional analytical approaches and can be applied to detect and identify the features of the constituent in probiotics or other biological food additives.
2016, 45(7): 703002.
doi: 10.3788/IRLA201645.0703002
By utilizing optical pump terahertz probe spectroscopy, the optical modulated properties of three samples were investigated with terahertz subwavelength structures, which were derived from classical split ring resonators. The obtained results show in the metamaterials design, it is needed to avoid the same length bar in the middle of the symmetric samples due to the fact that the middle bar has less influence on the resonant property when the terahertz electric field vector is parallel to the bottom bar. However, the asymmetric samples exist coupling and splitting phenomenon in transmission spectra. For the different resonance mechanisms, it is found the LC resonance has higher sensitivity than the dipole resonance to the pump excitation. Although different designed structures will exhibit different resonant positions in frequency, the optical modulation behaviors of those samples have one same characterization. That is, when the terahertz electric field vector is parallel to the bilateral bar, there is only one transmission dip because of the structure design and this transmission dip from the dipole resonance is not sensitive to the pump excitation.
2016, 45(7): 703003.
doi: 10.3788/IRLA201645.0703003
In order to improve the THz imaging speed, an image surface scanning THz fast imaging system was designed. It was a single pixel imaging system basing on the reflection type. The system collected THz by an off axis parabolic mirror which was used to realize the imaging of large caliber, high transmittance, high quality imaging. The optical parameters of system were that F/# was 2.93, the aperture diameter was 120 mm, the field angle was 1, the focus length was 293.45 mm, the size of imaging window was 64 mm64 mm, the diameter of circular hole was 2 mm, the imaging speed of 1616 pixels was 0.1 min, the imaging speed of 3232 pixels was 0.47 min, the imaging speed of 6464 pixls was 1.7 min, and the spatial resolution was 10 mm. The system combined with compressed sensing theory and image surface scanning theory realized the fast imaging property. A rotation plate with holes was inserted at image surface position, which scanned the THz intensity. Then a light cone was employed to collect energy to the Golay detector. The device output image by a special situation of compressed sensing theory that the sample number equaled to the image pixels. Sequentially, the regular least squares algorithm was used to reconstruct intensity distribution. The system has the property of high imaging speed and resolution, low costs, and small structure.
2016, 45(7): 730001.
doi: 10.3788/IRLA201645.0730001
LiDAR is a potential technology in mapping field. Especially, the LiDAR systems applying streak tube have attracted great attention recently due to their special properties about detection sensitivity and distance resolution. The simulation of the stripe principle array LiDAR system with broom scanning and the results of the flight experiment were described. Firstly, the establishment of the new LiDAR simulation platform and the typical simulation results were introduced. The simulation platform can guide the design of the new LiDAR, and simulate the setting of the airborne flight experiment parameters. The simulation result which was based on experimental design parameters was that the distance measuring accuracy of the new LiDAR is 0.5 meters. Finally, the airborne flight experiment of the new LiDAR was carried out, then original streak images of the typical area and the cloud points of the images were given. The result of the airborne flight experiment is that the distance measuring accuracy of the new LiDAR is better than 1 m. The accuracy of airborne flight experiment is consistent with the result of simulation analysis. It proves that the correctness of the simulation system is verified. Compared with the images of the passive optical camera, the technical feasibility of the new LiDAR in aerial mapping is verified.
2016, 45(7): 711001.
doi: 10.3788/IRLA201645.0711001
The expression for the scintillation index of radial Gaussian array beams propagation in non-Kolmogorov turbulence was derived by using the extended Huygens-Fresnel principle and Rytov method. The influences of the ring radius r0, beam number N, general exponent and propagation distance L on the on-axis and off-axis scintillation index were studied. The results show that both the on-axis and off-axis scintillation index rise initially as becomes larger, but later the scintillation reduce as grows further. It is worth noting that beams with different r0 reach its maximum scintillation correspond to different . The scintillation index values of array beams are smaller than that of a Gaussian beam around the on-axis point, but with the increase of the transverse coordinate px the scintillation index values become larger than that of a Gaussian beam. Scintillation index decreases with the increase of N, but the dependence of scintillation on r0 is not monotonic.
2016, 45(7): 732001.
doi: 10.3788/IRLA201645.0732001
Considering the wavefront aberration in active imaging with coherent light illumination and spatial heterodyne detection, a digital fast correction technique was proposed. An experimental setup was established, and the target scattering optical complex amplitude on the detection aperture was divided into four sub regions through the numerical segmentation. The high order aberrations in the sub regions were corrected in parallel with tochastic parallel gradient descent algorithm, and then the piston, tip and tilt wavefront aberration among the sub regions were corrected in parallel. The experimental results show that, 600 iterations is needed when the stochastic parallel gradient descent algorithm is used directly, while only 100 iterations is needed for this method proposed in the paper, and the amount of computation is smaller, so that the efficiency of correction is greatly improved.
2016, 45(7): 721001.
doi: 10.3788/IRLA201645.0721001
The transmission model of vortex beam within multilayer dielectric coating has been established, and the temperature property of multilayer dielectric coating irradiated by optical vortex has been discussed. The results show that the temperature property is closely related to the incident plane of vortex beam. When irradiated by the initial plane of optical vortex, the region of temperature rise of coating was focused on the incident center. When irradiated by the optical vortex with a certain transmission distance in space, the temperature rise regions of coating spread on both sides of the incident center. When the transmission distance is far enough, the maximum temperature decreases with the increase of transmission distance. Moreover, the maximum temperature increases as the topological charges increase within a certain transmission distance. Nevertheless, the maximum temperature decreases as the topological charges increase when the transmission distance is far enough.
2016, 45(7): 721002.
doi: 10.3788/IRLA201645.0721002
Dye-doped polymer dispersed liquid crystal film was designed and fabricated, and the random laser action was studied. The mixture of laser dye, nematic liquid crystal, chiral dopant and PVA were used to prepare dye-doped polymer-dispersed liquid crystal by the method of microcapsule. Under frequency doubled 532 nm Nd:YAG (Yttrium Aluminum Garnet) laser-pumped optical excitation, a plurality of discrete and sharp random laser radiation peak can be measured in the range of 582-607 nm. The threshold of the random lasing is about 9 mJ and the line-width is 0.3-0.4 nm. The theory of ring cavity is used to prepare dye-doped cholesteric liquid crystal laser. Comparison with doped one dye polymer dispersed liquid crystal film. The experimental results show that the polymer dispersed liquid crystal film of doped different types of laser dye, it is possible to achieve broad band random lasing.
2016, 45(7): 721003.
doi: 10.3788/IRLA201645.0721003
Bio-printing can be described as an innovative technology that fabricates 3D functional multi-cellular tissue in vitro, namely deposited biological cells on biological scaffolds. Such efforts are being undertaken in many laboratories around the world. Agarose gel and its composite hydrogel are ideal material for scaffolds with superior biological, mechanical and structural properties. In order to research the optical properties of Agarose gel,which is applied to bio-printing, different concentration of Agarose gel were prepared by mixing up Agarose powder with distilled water in certain ratio after heating, dissolving and cooling. During the cooling procress, the refractive index of Agarose solution at 55℃ and Agarose gel was measured with Abbe refractometer. By comparing the refractive index of cell culture medium, the concentration of 0.00786 g/mL was proved to be the best concentration for Agarose hydrogel as bio-printing substrate materials and biological scaffolds. Visible transmittance spectrum, near infrared transmittance spectrum and attenuated total reflectance-Fourier transform infrared spectrum of Agarose gel and cell culture medium were measured, which shows that there is no absorption peak in the spectrum of agarose gel at the wave band from 400 nm to 1100 nm, and the maximum absorption is only 0.1711Abs; In the range of infrared spectrum, Agarose gel has the same absorption properties with cell culture medium, except for an unique absorption property at 2966 cm-1 in the spectrum of cell culture medium. The experiments of the laser scattering characteristic of the surface of Agarose gel show that the 440 nm laser has the strongest laser scattering intensity, while the 532 nm laser has the weakest one. Meanwhile, the smaller the concentration of Agarose gel, the stronger the scattering is.
2016, 45(7): 721004.
doi: 10.3788/IRLA201645.0721004
Laser-induced damage in optical film remains a great challenge in high power laser systems. The mechanism of inclusion damage to film had been studied:firstly, the film damage morphologies had been observed and then the effects of inclusions on film had been analyzed. The research results show that the damage effects of inclusions on film can be divided into thermodynamic effects, interference effects due to scattering and laser plasma effects, the combined action of those damage effects determine the characteristics of damage points. The effects above are closely related to the particles radius:for smaller radius, the deposited laser energy is less and temperature is lower, as the heat diffusion range is smaller and damage points are mainly due to the melting. While for larger radius, the energy deposition and temperature are higher, and the laser plasma can be formed easily and cause big ablated pits.
2016, 45(7): 724001.
doi: 10.3788/IRLA201645.0724001
Planar waveguide spectrometer is a compact spectrometer, which has an asymmetrical crossed Czerny-Turner optical structure within a planar waveguide structure. The multiply diffracted light of this spectrometer is large, so it needs to be carefully studied in order to find a suitable method to reduce it. The formed of the multiply diffracted light could be derived from the diffraction characteristic of grating. Then the stray light problem was identified by using the TracePro software. Then based on the difference of the spatial property and wavelength of stray light, different suppression methods were used. Filters and baffles were involved to suppress the multiply diffracted light, without changing the original optical structure. Finally, stray light coefficient was introduced to evaluate the effect using stray light suppression structure. Simulation and analysis results show that the multiply diffraction light of spectrometer has been well suppressed. The maximum of the stray light coefficient is reduced form 5.3% to 0.033%, and the average of it is dropped from 1.9% to 0.0018%.
2016, 45(7): 720001.
doi: 10.3788/IRLA201645.0720001
A tunable optical filter(TOF) based on MEMS technology was designed. The broadband optical signal was first dispersed by a grating and then the wavelength corresponding to the passband of the TOF was selectively reflected to the output by a MEMS torsion mirror, thus the optical filtering and wavelength tuning functions were realized. A single mode fiber(SMF) was employed as the input and a multimode fiber (MMF) or few mode fiber(FMF) was employed as the output, thus the passband of the TOF was characterized by narrow-band and flat-top. After parameter optimization, the simulation results show that the 0.5 dB and 20 dB bandwidth are 0.95 nm/0.29 nm and 1.39 nm/0.69 nm with MMF and FMF employed, which meet the requirements by DWDM systems of 100 GHz and 50 GHz channel spacing, respectively. The output is MMF or FMF, the optical signal passing through the TOF cannot be further transmitted in SMF. The output can just be received by a photo detector, thus this TOF is usually applied as the outputs of the nodes in all optical network.
2016, 45(7): 720002.
doi: 10.3788/IRLA201645.0720002
Performance differences between Offner convex grating imaging spectrometer and Dyson concave grating imaging spectrometer, both with concentric structure, was analyzed under different grating constants. The diffraction angle expressions of the two spectrometers were obtained, and their diffraction characteristics were acquired. Both of the spectrometers were designed and analyzed by ZEMAX, under F number of 2.5, spectral rage of 8-12 m, spectral resolution of 15.6 nm, and grating constants of 100 m and 50 m. The two structures could both meet the system requirements using spherical mirrors in the case of a higher grating constant. Offner's volume is 7 times larger than Dyson's, and Offner's weight is about Dyson's 1/13. When grating constant turned lower, Dyson could still meet the requirements just with spherical mirrors, while Offner must adopt aspherical mirrors and make an off-axis design for the requirements. The Offner's volume is 7 times larger than Dyson's, and Offner's weight is about Dyson's 1/11. The results show that Offner form and Dyson form have advantages and disadvantages in the aspect of operability of machining, volume, and weight. In the selection of spectrometer, the choice should be made depending on the specific application requirements.
2016, 45(7): 720003.
doi: 10.3788/IRLA201645.0720003
Surface-plasmon-enhanced GaN-LED was proposed based on the multilayered rectangular nano-grating, which was deposited by periodic raster silver thin film in the gas material. A model was theoretically established, which was enhancing the internal luminous efficiency of LED, the SPPs radiant matching and the SPPs radiant declining. The experiment shows that the structure of the deposited silver thin film can improve the luminous efficiency because of the SPPs enhancement. Polarized mode of the emergent light has no effect on the luminous efficiency of LED; Metal raster absorptivity will achieve the peak if the duty ratio is about 0.87; SPPs potentiation can dramatically improve the luminous efficiency and nonlinear process. The research on the improvement of the LED luminous efficiency has theoretical and practical significance.
2016, 45(7): 720004.
doi: 10.3788/IRLA201645.0720004
Because of the high electron mobility and two-dimensional electron gas concentration, InP based pseudomorphic high electron mobility transistors(PHEMTs) become one of the most promising three-terminal devices which can operate in terahertz. The InAs composite channel was used to improve the operating frequency of the devices. The two-dimensional electron gas(2DEG) showed a mobility of 13000 cm2/(Vs) at room temperature. 70 nm gate-length InAs/In0.53Ga0.47As InP-based PHEMTs were successfully fabricated with two fingers 30 m total gate width and source-drain space of 2 m. The T-shaped gate with a stem height of 210 nm was fabricated to minimize parasitic capacitance. The fabricated devices exhibited a maximum drain current density of 1440 mA/mm(VGS=0.4 V) and a maximum transconductance of 2230 mS/mm. The current gain cutoff frequency fT and the maximum oscillation frequency fmax were 280 and 640 GHz, respectively. These performances make the device well-suited for millimeter wave or terahertz wave applications.
2016, 45(7): 718001.
doi: 10.3788/IRLA201645.0718001
The aberration correcting ability of deformable mirror is directly affected by the performance of its supporting structure. A structure form of deformable mirror for space camera was described, and different structures of support base were analyzed from the aspect of material properties and manufacturing process, it proves that solid structure made of CFRP is superior to rib-board structure made of TC4, and stiffness ratio of support base material is the main factor of deformation caused by gravity, while the difference of CTE between the materials of support base and reflector affects thermal deformation mostly. Comparing with three-point edge support, the scheme of three-point back support was used to improve the collapse phenomenon caused by gravity, with the RMS value of gravity in z direction decreased by 73%, from 15.38 nm to 4.17 nm, and homogenize the thermal deformation, with the RMS value of 4℃ rise decreased by 12.5%, from 3.68 nm to 3.22 nm, and its first order frequency is also improved from 1513 Hz to 1982 Hz. This indicates that the dynamic and static stiffness and thermal stability of this deformable mirror satisfies the application requirement for space camera.
Large diameter chalcogenide glasses play an important role in developing high resolution infrared imaging systems for various military and civil applications. However, it lacks an effective measure for inspecting the internal artifacts (including non-uniformity of refractive indices, impurities, and cracks) of bulk chalcogenide glasses and thus the application of such glasses was limited. A near infrared lens was developed for inspecting the internal artifacts of large diameter chalcogenide glasses. Considering the spectral characteristics of the chalcogenide glasses and a currently available infrared camera, the performance of the lens was optimized for the spectral band of 0.95-1.05 m. A group of three achromatic doublets was utilized to eliminate the chromatic aberration and realize an imaging performance that is close to a diffraction-limited system. Off-the-shelf glasses of K9 and F6 were used in this design. The proposed lens was tested in experimental settings for inspecting internal artifacts of chalcogenide glasses. According to the experimental results, the resolution of the proposed lens matches the design parameters well and many kinds of internal artifacts of chalcogenide glasses, including non-uniformity of refractive indices, impurities, and cracks, are clearly observed in images captured by the proposed lens.
2016, 45(7): 718003.
doi: 10.3788/IRLA201645.0718003
Large SiC mirror is a new kind of primary mirror. There is no success support example for study. In order to support SiC larger mirror, the merits and drawbacks of different active supports methods were analyzed. Finally the hydraulic system parallel connection with force actuator ways was chosen. The free harmonic oscillation model scaling method was used to study the active correction force of some 4 m SiC mirror. It was found that the smallest correction force is 0.1 N. To design a force actuator with such a small force resolution, the method of how to design high precision actuator was studied. Main factors that affect the precision of force actuator were discussed. The force actuator was designed with a step motor/harmonic drive combination to drive lead screw/floating nut to produce small displacement. A complex spring system was used to transform the stroke of the screw into a force. The force actuator was produced and tested. It was found that force output range is -400 N-400 N, the displacement resolution is 0.96 m and the force resolution is 0.05 N. These test results suggested that this force actuator can satisfied the need.
2016, 45(7): 722001.
doi: 10.3788/IRLA201645.0722001
Based on the combination model of total variation and wavelet transform, an improved method was proposed to rapidly evaluate the optical properties of actual Photonic Crystal Fibers(PCFs). Firstly, the total variation model in the wavelet domain was set up in this paper. Secondly, the split Bregman algorithm was used iteratively to denoise the cross-section images of PCFs, and thus the edge structures of air holes of PCFs image was kept. Thirdly, the optical properties of practical PCFs were evaluated rapidly by the adoption of the finite element method. By analyzing microscope images of cross sections of commercial and homemade PCFs, it is proved that the proposed method can achieve higher evaluation accuracy of optical properties of PCFs and the Gibbs and staircase effect can be eliminated efficiently in the extraction process of the edges of air holes in PCFs image.
In this paper, a novel orthogonal frequency division multiplexing(OFDM)-based indoor visible light communication(VLC) system was proposed that can provide a high reliability transmission performance while maintaining ambient light stability by using multicolor LEDs. This solution combines Spatial Modulation(SM) and Metameric Modulation(MM) with OFDM-VLC communication system. Along with all of the promising advantages of OFDM, SM and MM, the proposed system will be applicable for high-speed indoor white communication. Through the simulation results, it is known that the proposed indoor visible light transmission system has significant advantages over DC-biased Optical OFDM (DCO-OFDM) and Asymmetrically Clipped Optical OFDM(ACO-OFDM). Moreover, it is robust to the nonlinear distortion caused by a large peak-to-average power ratio(PAPR) of OFDM signal in comparision with other NDC-OFDM VLC transmission systems, and hardly generate intensity fluctuation.
2016, 45(7): 722003.
doi: 10.3788/IRLA201645.0722003
Combining the advantages of OFDM technology with the coherent detection, the bit error rate(BER) performance of coherent OFDM FSO system was studied, and the influence of OFDM mapping mode and mapping order on the symbol error of the system was taken into account. In Gamma-Gamma atmospheric turbulence channel model, the bit error performance of three cases of weak, moderate and strong turbulence were taken into consideration separately from the perspective of the average signal-to-noise ratio and the required average received optical power. On this basis, the closed form expression of the symbol error rate was deduced. Simulation results show that the coherent detection OFDM FSO system can better overcome the effects of atmospheric turbulence, in weak and moderate turbulence, the system BER performance with QAM mapping mode is obviously better than that of PSK mapping mode, however, under the strong turbulence the advantage is not very obvious. In addition, with the increase of mapping order, system symbol error rate increases, so in practice it can improve the system BER performance by reducing the number of mapping order.
2016, 45(7): 717001.
doi: 10.3788/IRLA201645.0717001
In order to improve the spot position detection accuracy for 1550 nm near infrared band,an innovative infinite integral model was proposed. At first, the relationship between InGaAs four-quadrant detector(QD) output signal and the spot real position was deeply analyzed where the laser spot energy displayed a Gaussian profile. By taking into account the error effects of detector diameter and gap size, and introducing the position error compensation factor, an effective spot radius was obtained with a best fit using the least square method, and then a new analytical expression was proposed. Finally, the experiment was made for verifying the performance of our new model in the established InGaAs QD spot detection system. The results of simulation and experiment show that the new model could effectively reduce the spot position detection error for different radii; when the total energy of incident light is about 10 W, the beam radius is 0.75 mm, in the detection range of[-0.75-0.75 mm], the root-mean-square error of 0.003 mm and the maximum position error of 0.009 mm with the new model, are reduced 78.6% and 52.6% than the original model, respectively. Therefore, the new model would have a good prospect in the engineering practice of laser communication or laser radar.
2016, 45(7): 717002.
doi: 10.3788/IRLA201645.0717002
A new method for retardation measurement of a quarter-wave plate was proposed. It was realized by calculating the long and short axes' values of the output elliptical polarized light based on computer simulations. The optical measuring system was simply composed of a laser, a polarizer, the quarter-wave plate to be measured, an analyzer and an optical detector. The real retardation can be obtained by a data processing with Mathcad. The principle of this new method was theoretically analyzed and an application example and its error analysis were demonstrated in this paper. The experiment results show that the absolute error is less than 0.26. Therefore the main advantages of the method are a few optical devices required, very easy to run and a big improvement in measuring accuracy.
2016, 45(7): 717003.
doi: 10.3788/IRLA201645.0717003
Spatial distribution of the beam is an important factor of affecting range indicators for satellite laser altimeter. According to the distribution characteristic of received pulse signal and definition of the received pulse signal's time-centroid and its variance, the influence models of elliptic Gaussian footprint on range and range error for satellite laser altimeter were built, by modeling theoretically the elliptical Gaussian footprint and the linear target. Based on parameters of Geoscience Laser Altimeter System(GLAS), as for three typical observation target with slope degree and roughness(3, 1.7 m), (12.5, 8.9 m) and (28.2, 14.5 m), the influences of the elliptical Gaussian footprint's ellipticity and azimuth on the range and range error were discussed systematically with the ways of numerical simulation. The results show that laser range almost has no relation with the elliptical Gaussian footprint's ellipticity and azimuth, its maximal difference is less than 1 mm. However, laser range error will fluctuate markedly with the elliptical Gaussian footprint's ellipticity and azimuth, corresponding maximal difference reaches 47.04 cm. The conclusions provide practical application values for hardware design and performance assessment of satellite laser altimeter.
2016, 45(7): 717004.
doi: 10.3788/IRLA201645.0717004
In allusion to the intersection error of workspace Measurement and Positioning System (wMPS) and the occlusion problem in the complicated measurement spot, a new circumference receiver was designed based on multi-angle circumference constraint location method and the calibration method was presented. With scanning laser plane measurement principle and feature, the receiver consisted of six photoelectric receiving elements was fixed on a cyclinder. The structure and the calibration method of the circumference receiver were elaborated in detail based on two laser transmitters in this paper. The calibration method was verified with wMPS experimental platform designed by Tianjin University. The experiment results show that the measurement repeatability of the calibration is within 0.2 mm and the accuracy is within 0.3 mm. This method solves the complicate measurement system space scene occlusion and eliminates the impact of intersection error on the measurement result in principle.
2016, 45(7): 717005.
doi: 10.3788/IRLA201645.0717005
A compound target for camera calibration in wind tunnels is developed, solving problems of low precision and high costs caused by a large field of view, small object distance and severe distortions of optical images. Moreover, a camera calibration method for close range photogrammetry system based on different constraints in different regions was presented in this paper. The 1-D calibration frame and 2-D planar in the compound target were utilized to divide the field-of-view into two regions. Based on distinguished constraints offered by the two calibration references, camera intrinsic, extrinsic and distortion parameters for the two regions were calculated respectively. Then the 3-D coordinates of targets can be reestablished with high precision according to the image region where interesting features lie in. In the end, accuracy contrast test and verification test with respect to the proposed calibration method had been conducted. The results show that the root mean square calibration error of inner region is 0.165 and the root mean square calibration error of exterior region is 0.276, verifying that this method is simple, effective and of high accuracy, meeting the precision requirements.
2016, 45(7): 717006.
doi: 10.3788/IRLA201645.0717006
A method for measuring the residual phase noise(RPN) of long microwave optical links(MOLs)and individual components in the MOL was proposed in this paper. Compared with the previous RPN measurement methods, the two-tone correlation-based method suppressed the noise contributions of the uncorrelated noise sources except that of the device under test(DUT). By this method, the RPN of externally modulated long MOLs was measured, the RPN of a 6 km MOL was successfully measured to be -130 dBc/Hz at 1 kHz offset and -140 dBc/Hz at 10 kHz offset, compared with a 1 m short MOL, the RPN deteriorated about 10 dB. In addition, in order to find out the relationship between the RPN and the RF power compression due to the nonlinearity of the photo-electric detector (PD), the RPNs of the PD with different incident optical powers and bias voltages were also measured by this method. The experimental results reveal that the nonlinearity of PD can deteriorate its RPN.
2016, 45(7): 726001.
doi: 10.3788/IRLA201645.0726001
Traditional imaging methods are subject to limitations on information acquisition, which brings about the deficiency of image quality. Therefore, a depth photography model was proposed here. This model contains a depth matrix, a decomposition function, a defocus operator, and an adaptive regularization term. The depth matrix could be estimated using the binocular stereo vision method, the structured light approach, or the time-of-flight algorithm. The decomposition function was used to segment the image into pieces according to the distinct depth values. The defocus operator was calculated through a defocus-from-depth method. The adaptive regularization term reduces the staircase effect and enhances image smoothness. Local standard deviations and local average gradients were used to evaluate the effectiveness of depth photography model. Experimental results demonstrate that the proposed model is effective.
2016, 45(7): 726002.
doi: 10.3788/IRLA201645.0726002
In recent years, digital holographic microscopy has attracted intensive attention for its capability of measuring complex shapes. There are two parts in digital holographic microscopy, hologram recording and digital diffractive reconstruction. Speckles are inevitable in the recorded interferometric patterns, thereby polluting the reconstructed surface topographies. Three reconstruction algorithms, i.e. Fresnel transform, Fresnel-wavelets and the proposed Fresnel-NSCT algorithms were compared. Three typical structures, rectangular, spherical and triangular surfaces were adopted for analysis. The performance of the three reconstruction algorithms on speckle removal and feature preservation was investigated comprehensively. Signal-Noise-Ratio(SNR) and Peak-Signal-Noise-Ratio(PSNR) were used as the numerical criteria. It is found that the Fresnel-NSCT algorithm has great superiority over the other two, subsequently it is promising for applications in the diffractive reconstruction of structured surfaces.
2016, 45(7): 726003.
doi: 10.3788/IRLA201645.0726003
A real-time, accuracy and robustness multi-resolution mountain climb servo (MCS) auto focus method was proposed in order to solve real-time auto focus problem, and was obtained high clear high quality image because low clear low light images was difficult to realize auto focus in range-gated imaging system for underwater. The merits of this method were outstanding as follows. It reduced the amount of processing data and time by taking advantage of the image multi-resolution theory by spatial sampling of the current image and then formed different resolution sampling layers, which made the system possible to deal with auto focus more quickly as 1/2 time as traditional method. Thereby, the method calculated current frame weighted average edge detection image definition, which was determined by the correlation between current frame and two adjacent frames with 0.5, 0.3 and 0.2 coefficients before solving the error judge of interference maximum local peak. At last, the method realized the last operation auto focus by MCS. The repeated experimental verification of range-gated imaging system for underwater shows that the algorithms is capable of guaranteeing the auto focus speed and accuracy and improving the real-time, accuracy and robustness in focus determination.
2016, 45(7): 726004.
doi: 10.3788/IRLA201645.0726004
The classical dynamic Allan variance(DAVAR) can describe the non-stationary of random error of fiber optical gyroscope(FOG) effectively. However, the method has defects such as poor confidence on the estimation of long-term -values due to the reduced amount of data captured by the fixed length windows. Besides, the method is difficult to make a satisfactory tradeoff between dynamic tracking capabilities and variance reduction. An improved DAVAR algorithm based on kurtosis and data extension was proposed to solve the problems. Firstly, the kurtosis of data inside the windows was introduced as characterization of signal's instantaneous non-stationary, and the window length function which was utilized to truncate the signal was built by taken kurtosis as variables, the function can make window length change with the non-stationary of the signal automatically. Secondly, the random error of FOG was truncated with the function. Then the data in the windows were extended by the total variance method to improve the confidence. At last the Allan variance of extended data was computed and arranged by three-dimensional. The measured data of FOG start-up signal was analyzed with the proposed algorithm and DAVAR. The results show that the proposed algorithm is an effective way to characterize non-stationary of FOG and can also obtain a lower estimation error at long-term -values.
2016, 45(7): 726005.
doi: 10.3788/IRLA201645.0726005
In order to ensure accuracy and security of unmanned aerial vehicle(UAV)landing, a UAV autonomous landing with visual navigation pose parameters calculateion method was proposed. Firstly, the airborne camera was calibrated to get the camera parameters, then the important influence of landmark shape and size, angular point geometry distribution and number of points on pose estimation precision were considered, a T type landing landmark was designed with given size parameters, landmark contour extraction with corner detection algorithm was combined to get eight corners with good geometric distribution and the number was reasonable for pose estimation to guarantee the posture calculation accuracy. To reduce the processing time of Lucas-Kanade(LK) optical flow method tracking landmarks stably, the extracted eight corners were used as LK optical flow method input to detect and track, ensuring real-time performance of the algorithm. Finally, real-time flight pose parameters of UAV through the projection relationship between 3D space and 2D image plane were estimated. The results of simulation experiment show that the algorithm has high precision,and the average period is 76.756 ms (about 13 frames per second). The real-time requirements of visual aided navigation of autonomous landing at low speeds of landing stage is satisfied basically.
2016, 45(7): 726006.
doi: 10.3788/IRLA201645.0726006
Multi-pulse laser radar emits hundreds of high repetition frequency laser echo to accumulate, and needs dynamic target signal simulation to verify the detection performance based on target echo waveform model. Pulse laser echo waveform can be modeled through the convolution relationship among the laser emission, channel propagation and target reflection. Firstly, the mathematical descriptions of each component part were established, and the echo waveform model was given by continuous convolution. Then, for the problem that the analytical model was not conducive to the engineering implementation, the discrete algorithm of target echo waveform sequence was presented based on transmitted pulse range resolution. According to the echo signal simulation of long-range aircraft target, the intrinsic relationship between the echo waveform and the target characteristic was pointed out, and the reliability was verified by the experiment. Finally, the development and implementation of the multi-pulse laser radar dynamic target simulator was presented, which provided the necessary verification test conditions for the research of multi-pulse laser target detection.
2016, 45(7): 731001.
doi: 10.3788/IRLA201645.0731001
In order to design optics-eletricity system for high speed vehicle, the mirror is replaced by fast steering mirror, and stabilization platform of complex axes is designed for optics-eletricity system with upside mirror. Through theory analysis, vector equation of line of sight for the platform was calculated, movement characteristic and compensation theory of stabilization for complex axes was analyzed, and controlling method of complex platform was presented. In the end, influence of assembly axes error to system error was studied for engineering application. The research result indicate that, Stabilization platform of complex axes for optics-eletricity system with upside mirror implement compensation to error of first platform, bandwidth of system is 200 Hz, which is approximately equal to bandwith of fast steering mirror, and stabilization precision of system is upgraded, but assembly error of second platform should less than 0.05 mrad.
2016, 45(7): 731002.
doi: 10.3788/IRLA201645.0731002
In order to obtain an accurate model of the photoelectric tracking servo system, the identification using adaptive differential evolution algorithm based on the identification error sum was adopted. The mutation and crossover factor of the algorithm was automatically adjusted. The discrete model of system was identified under the situation of discretely sine digital signal input. Furthermore, the output of the first-order and second-order model using the sweeping frequency method in the frequency domain was compared with the output of the reality to prove the validity of the algorithm. Experimental result shows that under the same discretely sine signal input, the result of the identification is same with the real-life result and reduced about 20.33% in the RMSE compared with the sweeping frequency method. The second-order model has a bigger deviation in the high frequency domain and the first-order model has the same output with the real-life output. The adaptive differential evolution algorithm has a smaller amount of calculation and an accurate identification, besides, this method is simple enough. In summary, this method has a certain value in the engineering application.
2016, 45(7): 731003.
doi: 10.3788/IRLA201645.0731003
Reducing the deviation of light path in cavity can improve mechanically dithered RLG vibration performance. The mechanism of the deviation of light path in the cavity of mechanically dithered RLG was analyzed and simulated. According to the results, the main reasons of light path deviation were dithered tangential inertial force and vibration impact inertial force. Meanwhile, the deviation of light path in cavity of RLG could change the RLG bias produced by Langmuir flow. The two main effective means of reducing Langmuir flow bias produced by vibration and improving gyro vibration performance were decreasing working current and improving stability of light path in cavity. The mechanism of mechanically dithered RLG light path deviation was validated by test. Compared with vibration test results of different working current, the vibration performance of RLG is improved obviously by reducing working current. The means of improving vibration performance by decreasing working current and increasing stability of light path is put forward, which is useful to improve vibration performance of mechanically dithered RLG and reform for the further development of RLG.
