2014 Vol. 7, No. 2
In this paper, our recent theoretical and experimental results on silicon hybrid nanoplasmonic waveguides and integrated devices are reviewed. First, we present several types of silicon hybrid nanoplasmonic waveguides, which enable the confinement of optical field within the lateral scale of 100 nm, as well as a ~102 m propagation distance. Second, several kinds of submicron photonic integrated devices like power splitters, ultra-compact polarization beam splitters and resonators are presented by using silicon hybrid nanoplasmonic waveguides. Finally, the coupling between silicon hybrid nanoplasmonic waveguides and silicon nanowires, as well as the loss compensation of silicon hybrid nanoplasmonic waveguides with gain mediums has also been discussed.
Short-pulse CO2 laser has significant applications in many fields such as laser ranging, environmental detection, space communication and laser interaction with matter. Q-switch techniques are important approach for generating short-pulse CO2 laser and have been extensively studied by researchers. Main Q-switch techniques for CO2 laser are reviewed in this paper, including mechanical Q-switch, electro-optically Q-switch, acousto-optically Q-switch, passively Q-switch and double Q-switch. The key technical points and problems of each Q-switch technique are summarized and analyzed. In addition, the tendencies of Q-switch techniques for CO2 laser are proposed.
In this paper, the developing status and primary characteristics of several remote sensing cameras for Mars observation in recent years, including Mars Observer Camera(MOC), High Resolution Science Imaging Experiment(HiRISE), and High Resolution Stereo Camera(HRSC), were summarized. Meanwhile, the imaging resolution requirements for different objectives were also discussed. It is concluded that the tendency of Mars remote sensing is to develop detailed observation with sub-meter resolution. Near infrared imaging and 3D stereo imaging should also be paid attention to. These analyses will provide references for the design of Chinese Mars observation plans in the future.
We discuss the development of thermo-pneumatic micro-optics and illustrate this progress using examples from our own research as well as recent literature. Pneumatic actuation is used for tuning micro-fluidics based optics, including micromirrors and membrane microlenses, which rely on pressure applied to liquids or liquid/gas interfaces for operation. Thermo-pneumatic actuation uses on-chip temperature changes to generate the requisite pressure differences. We discuss the variety of devices, structures, liquids and membrane materials used for these micro-optical structures and provide typical operating characteristics.
In order to solve the problems that low light level image has low contrast and it is difficult to distinguish objective, it is necessary to research on low light level image enhancement algorithm. A multiple sub-histogram equalization enhancement algorithm is proposed. Initially, in the proposed algorithm, the histogram are separated into four parts according to the area equally. Then, the resultant sub-histograms are clipped according to the average number of pixels of input image to reduce the enhancement phenomenon. In addition, the scale factor is adopted to adjust dynamic range. Finally, each sub-histogram is equalized. The algorithm is implemented on FPGA with verilog language, and is given subjective and objective evaluation. With this algorithm good results can be achieved in real-time on the hardware platform, and the delay of an image processing is about 0.45 ms. Experimental results show that with this proposed algorithm no saturation and noise amplification phenomenon appear, and image details of the processed image are well preserved and highlighted. The algorithm meets the real-time requirement and the enhanced images of better visual effect can be achieved.
The laser intensity could be stabilized by using opto-electrical feedback based on the acoustic optical shifted modulator outside the laser. Due to the Bragg diffraction effect of an acousto-optical modulator(AOM) on controlling of the laser intensity, the feedback electrical signal from a portion of laser was applied to control the driving power of the AOM realizing the stabilization of laser intensity. The experiment results show that the laser intensity noise under the frequency of 47 kHz can be reduced by 15 dB. In addition, the time response in whole feedback loop is analyzed, and the delay phase curve beside the feedback circuit in the loop is also measured.
In order to meet the real-time and anti-noise requirements of auto-focusing system, a definition evaluation function based on SUSAN is proposed. This function is derived from the SUSAN edge detection algorithm, which makes the sum of squared edge point's USAN values as the definition evaluation value, and applies to the auto-focusing system, making use of the high accuracy and strong anti-noise characteristics of SUSAN algorithm. The definition evaluation function performance is compared between SUSAN function and the other classical functions. Experiment results show that the SUSAN definition evaluation function has the characteristics of clear single apex, good unbiased, high sensitivity for the image sequences before and after the introduction of noise. In addition, the running time of the function on the TMS320C6416 hardware platform is 15 ms. It can satisfy the definition evaluation function requirements of single apex, unbiased and sensitivity characteristics, as well as strong real time and anti-noise abilities.
A small size free space optical communication system is introduced, including the hardware structure and the hardware specified physical layer protocol. The rapid synchronization technology applied in protocol is introduced in detail. The technology could reduce waste of bandwidth in the synchronization process between the communication terminals. The hardwares of the system include the laser driver system, the signal amplifying and shaping system, the data interface system. The hardware specified physical layer protocol is used for external signal interface, serialization and de-serialization of the data stream, checking transmission errors and scheduling the data transmission. The system is designed mainly for terrestrial FSO link whose signal channel is the atmosphere. In our system, the sampling clock is generated locally by using multi-phase sampling technique rather than PLL-based clock recovery, which can obtain more rapid synchronization speed and improve the utilization efficiency of bandwidth in the wireless optical communication system and reduce the Bit Error Rate(BER) in the communication.
To investigate the errors brought about by common formula of peak power in pulsed lasers, the peak powers of pulsed laser types of Gaussian, Sech2, Lorentzian, asymmetric Sech2 were calculated analytically. The results demonstrate that the errors introduced by common formula of peak power for Gaussian, Sech2, Lorentzian, asymmetric Sech2 were 6.3%, 13.6%, 22.1%, 20.9% respectively. Furthermore the peak power of irregular pulse was discussed by numerical method based on practical experiments and a method to precisely calculate peak power was proposed.
In the field of laser applications, in order to meet the need of high laser beam quality, correct the wave-front aberration generated during the transmission of laser beam and improve the laser phase distribution, thereby increase the energy concentration of the beam focusing spot, a set of laser beam shaping experimental system is built based on a 79-channel micromachine membrane deformable mirror(MMDM). By using stochastic parallel gradient descent(SPGD) algorithm, the laser beam shaping experiment is carried out respectively with three performance indexes:radius of the focused spot, encircled energy ratio with geometric center as the center, and encircled energy ratio with centroid as the center. In the three cases, convergences come forth after about 58 times, 197 times, 133 times of iterations, respectively, but the evolution curve of spot radius oscillates seriously. Encircled energy ratios increase from 0.200 5, 0.127 7, 0.200 5 before shaping to 0.669 9, 0.733 9, 0.864 0 after shaping, respectively. The results of experiments show that MMDM can be used for laser beam shaping with well results. The shaping speed is fastest with spot radius as the performance index, followed by encircled energy ratio of centroid and encircled energy ratio of geometric center. The shaping effect is best with encircled energy ratio of centroid, followed by the encircled energy ratio of geometric center and spot radius. After synthetical comparison, it is best to choose encircled energy ratio of centroid as the performance index.
In plasmon-sensitized solar cells, layer self-assembly of gold nanoparticles surface plasmon resonance can produce photoelectric current. Photoelectric conversion efficiency of gold nanoparticles layer increases with the intensity of surface plasmon resonance. The efficiency is up to 0.75%. We use the model to simulate the phenomenon of charge separation, produce of photoelectric current and relationship between surface plasmon resonance and the photoelectric currents to explain the experimental results. In the future, these nanoparticle materials have considerable potential applications in surface plasmon activated solar cells and solar cells plasmon.
We carried out a series of basic research for a kind of Si based novel luminescent materials, Er-Yb/Y silicate compounds. We study the structure, optical and electrical properties of these high erbium compound materials including Er silicate, Er-Yb silicate and Er-Y silicate. Through the optimization of Er-Yb-Y composition and structure of Er-Yb/Y silicate compound material, 2 orders of magnitude enhancement of photoluminescence is obtained. We prepare optical waveguide amplifier based on Er-Yb/Y silicate thin films, and observe more than 5 dB/cm light amplification. We develop a metal-insulator-semiconductor structure of electroluminescent devices, and obtain Er-Yb/Y silicate compounds electroluminescence, and theoretically prove the possibility that this material can be electrically pumped laser.
Ternary Zn2GeO4 nanowires were prepared by VLS law and the Chemical Vapor Deposition(CVD) method on 1 cm1 cm silicon wafer sputtered by metal Au catalyst. Zn2GeO4 structure was obtained under the condition that the mass ratio of zinc source and germanium source was 8:1wt% as the X-ray diffraction(XRD) shown. The Scanning Electron Microscopy(SEM) result showed that the diameter of the nanowires was 100 nm and the length was approximately 10-11 m. The photoluminescence(PL) spectra showed two emission peaks at 432 nm and 480 nm, respectively. Finally, the growth mechanism of the Zn2GeO4 nanowires was analyzed.
In order to satisfy all-frequency error quality controlling and high-precision test during the process of the convex asphere, double laps with polar coordinate polishing technique and the measuring poles method used for the alignment of Hindle test are proposed. Firstly, the double laps with polar coordinate polishing technique for manufacturing the aspheric mirror and the numerical control machine for processing aspheric surface are presented. Then, the measuring poles method used to control the distances between vertex of the standard sphere and the vertex and focus of the tested asphere is introduced, and the controlling precision is analyzed. Finally, for a convex asphere with the aperture of 158 mm, the test results and precision of the Hindle test are described. The results indicate that the double laps polishing technique can make the low-frequency surface error convergence quickly, and the mid-frequency surface error is restrained at the same time. The controlling precision of the low-frequency surface error is about /30(=633 nm). The limit error using the measuring poles to control the distance is 0.065 mm, and the tolerances of the two space parameters are 0.22 mm and 0.30 mm, respectively. The fast manufacture and all-frequency controlling of the convex asphere are realized by the double laps with polar coordinate polishing technique, and the test result of low-frequency surface error is 0.022(RMS,@633 nm) in the Hindle test, which satisfies the specification requirements of the optical design.
Based on the R-C system a cooled infrared swith-zoom optical system with long effective focal length is designed. The initial parameters are calculated and the components' focal power is deduced. Secondary imaging structure is adopted, and relay lens is used to match the cold stop. Zoom is realized by switching the relay lens of the short focal length system and the long focal length system. The optimized design of optical system aberration is made. The optimized imaging results of the long effective focal length optical system and the short effective focal length optical system at different field of view are presented, and the modulation transfer functions within 0.8 field of view at 17 lp/mm of spatial frequency are greater than 0.4. Finally, corresponding precision analysis of the main structure is made and the results show that the structure is rational and the imaging quality is good. The optical system can meet actual requirement.
The stress distribution on gating ruling tool edge is analyzed by finite element analysis software DEFORM. Combined with the diamond crystal cleavage theory, the wear resistant edge orientation of tool is designed. As the max friction direction on tool tip is parallel with periodic bond chain of diamond crystal and the load in Z direction is vertical to (111) crystal plane, the angle between the blaze plane of tool and (111) crystal plane is 27 and the angle between non-blaze plane of tool and (111) crystal plane is 63. The ruling distance is more than 17 km under the tool load of 72 g, and no defects occur on tool edge such as collapse, etc. The life of grating ruling tool designed by this method far exceeds that of traditional ruling tool(ruling distance is about 0.8 km), which illustrates that the wear resistant design method of grating ruling tool for echelle is feasible and effective.
In this paper, a hardware design method of binocular vision system is proposed for the pose tracker of surgery. The working principle of the system components and the needs of the surgical navigation are analyzed firstly. Then according to the situation of market supply, each component is ascertained, and the system's structure is affirmed based on the binocular vision positioning principle. At last, a simulation experiment of surgical navigation is developed by prototype of binocular vision system. The experimental results show that with the aid of this system, the layout of the surgery can be carried out. At the same time, the positioning precision for the implant can reach 2 mm, which can satisfy the requirement of clinical application.
In order to complete recognition and detection tasks of the aircraft seeker, a high precision, miniaturization of the zoom optical system is designed. Targets are searched and identified at short focal length, wide field, and recognized at long focal length, narrow field. The mechanical compensation method is selected using three kinds of common optical materials. At the location of the long focal length, combinatorial design of the front group and the zoom group can make the system compact, and meet seeker miniaturization requirements. The zoom optical system with optimization focal length about 12.9010.25~2.592.07 and lene tube length only 174 mm is designed by using the CODEⅤ optical design software. For the each focal length and each field of view, the average MTF is 0.695, and tested result is 0.562 at 50 lp/mm, which can meet performance requirements of the system.
The mirror interval and radius of curvature of optical system including three mirrors are often changed due to the impact of space microgravity, which has a greater impact on the back focal length, and causes camera defocus and imaging quality reduction. Through the equivalent Gauss optical system analysis of three-mirror system, back focal length formula can be obtained. By homogeneous coordinate transformation, the reflection mirror rigid-body displacement formula is obtained, and a mirror radius is obtained in the microgravity environment using the least squares fitting algorithm. Finally, by calculating the camera in space microgravity environment, the defocusing amount is 0.04 mm. Results provide a theoretical basis for the design of focusing mechanism.
In order to realize a high-precision and wild area measurement for the surface profile of photoresist, we studied on a new measurement method. First, based on the physical properties of soft thin film, we proposed a method combining white light interferometer with mechanical ball cantilever to measure the surface profile. Then using this system, we did the measurement experiments on the notch and transparent material. The results show that for the notch, the precision of the system's measuring error is less than 2% and the measuring standard deviation is less than 1 nm, indicating that it is possible to measure the surface with high accuracy. For the transparent material, it shows that with this system the effect of multiple reflection on profile measurement can be overcome.
In order to fulfill the requirement to extract miss distance of moving target in real time in optoelectronic tracking system, a Mean-shift image tracking algorithm based on gray histogram is designed. The target model and the candidate model of the algorithm are improved, and the impact of background pixels on target tracking is suppressed. The algorithm is implemented in the Visual C++ 6.0 platform in the upper computer of the system. When the optoelectronic tracking system captures the moving target, the system uses the Mean-shift image tracking algorithm to track the moving target. The miss distance is used as the input signal of the servo control system to drive the tracking device to track the target. Experiment results show that the proposed Mean-shift algorithm is able to track the moving target in real time precisely and effectively so that the angle deviation can be limited within 30 arc sec.