2012 Vol. 5, No. 1
To develop and make use of tunable Terahertz(THz) sources with high power, high efficiency and operating in room temperature, this paper researches and analyzes the progress in THz sources by photonics methods, including optically pumped THz lasers, air plasma THz sources, photoconductive antennas and the optical rectification, difference frequency generation, THz parametric generation based on nonlinear optical process. The numerous challenges and key technologies of this THz generation method are also proposed.
Advances in Liquid Crystal Adaptive Optical Systems(LC AOS) are described for Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences(CIOMP, CAS) in this paper. For two bottlenecks of low energy utilization ratio and slow correction frequency in LC AOS problems, a series of effective methods are presented by the LC AOS working group. The low energy utilization ratio has been improved from 5% to 85%, which is similar to that of the deformable mirror based AOSs. Furthermore, the correction frequency of the LC AOS is also greatly improved from 5 Hz to 140 Hz, which is closed to the ability of correction for atmospheric turbulence. According to these research results, two LC AOSs which correspond to a 2.16 meter Telescope(located at Xinglong Station of Beijing Astronomical Observatory) and a 1.2 meter telescope(located at CIOMP, CAS) are designed to correct the stars. Obtained results show that the resolution ability of the star for the 1.2 meter telescope is up to 3 times of the diffraction limitation.
The progress of aerial electro-optic payloads in recent years is introduced. The development of visible and infrared detectors is overviewed, then, the functions and parameters for three kinds of advanced E-O equipment are described, such as Multi-spectral Targeting System-A/B(MTS-A/B sensor pod), Electro-optical Targeting System(EOTS), and DB-110 sensors(generation Ⅲ). The conformal optics, spectral imaging, stabilization and compensation, image processing technologies mentioned above are analyzed, and the key technologies to be solved are further discussed in detail.
To get higher accuracy ground sampled distances and to improve the imaging resolution for aerial remote sensing instruments, this paper analyzes the reasons that a remote sensing instrument is out of focus. Based on the characteristics and structures of the optical system for a push-scan aerial remote sensing instrument, it designs an image plane focusing structure to compensate the motion error of the focusing structure. In design, an eccentric cam with inner and outer curves is used to ensure the position stabilization of the CCD sensor when the remote sensing instrument is imaging. The motion error is tested to verify the validity of the simulation result. The test shows that the error is less than 0.04 mm, which meets using demands. The focusing method of moving focal plane proposed is suitable for aerial remote sensing instruments whose focal length is shorter and size is smaller.
The lightweight structure of a mirror in the Fast-steering Mirror(FSM) System was designed. Due to the high specific stiffness and low thermal deformation rate, SiC was used as a raw material to prepare the mirror. The lightweight mirror with a notched structure was supported by three points on the back. Several lightweight structures were analyzed by finite element method. The results show that the rigid of mirror increases with the width of rib. When the rib is wide enough, the rigid of mirror increases slightly. The stress and deformation of mirror caused by gravity increases with mirror thickness. Structure parameters of 4 mm rid and 4 mm mirror thickness are confirmed considering current mechanical manufacture process. The lightweight rate of mirror is 55%. The RMS value of mirror measured by Zygo interferometer is less than /30, which is in agreement with that of the analysis.
In order to modify the disaccord of output sequency of a double-tap Charge Coupled Device(CCD), an improved design method for software RAM is proposed, and the output of CCD is conformed by this method. Firstly, a dual-port RAM is constructed by using Block RAM of Xilinx Virtex series Field Programmable Gate Array(FPGA). Since the sequence of data from tap1 is the same as that to be conformed before, this paper comes up with an improved method based on the traditional Ping-Pang operation to conform the output data from the CCD. Comparing to the traditional Ping-Pang method, the resource consumption of designed software is greatly reduced by 25%. It is proved to be valid and accurate by the simulation result of ModelSim. The new method which has been applied in the project successfully can save hardware resources and reduce the hardware cost greatly.
In order to improve the detecting speed and accuracy of sub-pixel edges for an Industrial Computed Tomography(ICT) image, a kind of improved edge detecting method based on Zernike moments is studied. First, the Sobel edge operator is used to quickly detect all the possible edges of the image, and then the Zernike moment operator is taken to re-test all the possible edges. Finally, the exact positions of the sub-pixel edges can be detected and calculated. As the possible edges have been detected and the detection range is reduced, the computing amount is shortened and the operation speed is imporved. An experiment is performed on CT images, and the result shows that the absolute error for the accuracy is less than 0.24 pixel,while Zernike moment operator computing speed is increased by about 70%, which ensures the accuracy of edge detection and improves the speed of edge detection.
The nonlinear optical crystal grown from the melt GaSe∶AgGaSe2(10%, mass percent) is identified as acentrosymmetric -GaSe∶Ag(0.04%, mass percent) and is used for phase matched frequency conversion. The silver presence results in 30% increase in microhardness, which allows the crystal to be cut and polished at arbitrary direction. The optical properties from visible to mid-IR and further THz ranges are studied in detail. It demonstrates that the absorption coefficient of GaSe∶Ag(0.04%, mass percent) crystal is twice that of a pure GeSe, and the CO2 laser Second Harmonic Generation(SHG) efficiency is about 1.7 times that of ZnGeP2 crystal.
A method to improve the performance of polymer waveguide devices by Inductively Coupled Plasma(ICP) etching is proposed and the principle and advantages of ICP etching technology are introduced. Polymethyl Methacrylate-glycidyl Methacrylate(P(MMA-GMA)) is chosen as the waveguide material to study the influence of various ICP parameters on the etching results when oxygen is selected to be the process gas. Firstly, the fabrication process of an inverted ridge waveguide device is introduced in detail. Then the variations of etching results with time, powers, pressures, gas flow parameters are analyzed by changing a single process parameter. Finally, the optimized groove and the slab structures are characterized. Experimental results indicate that the waveguide surface morphology can be improved effectively and a good shape of P(MMA-GMA) groove structure can be achieved by using the optimized IPC etching parameters in an antenna RF of 300 W, a bias RF power of 30 W, a gas pressure of 0.5 Pa and a oxygen flow velocity of 50 cm3/min.
By choosing Polymethyl Methacrylate-glycidyl Methacrylate with a low absorption loss at 650 nm as the cladding material of a waveguide, and taking the bisphenol A epoxy resin as the refractive index modifier, the cross section size of a single mode waveguide was designed according to the refractive index of the cladding and core material. Then the layout of a 16-channel Arrayed Waveguide Grating(AWG) was designed and optimized using beam propagation method. The Optiwave software was used to simulate the optical propagation characteristics of the AWG, and results show that the channel spacing is 0.845 01 nm, the device insertion loss is less than 14 dB, and the crosstalk is less than -25 dB.
By taking 4.25 Gbps Small Form-factor Pluggable(SFP) as an example, this paper analyzes theoretically its key parameters in detail, and discusses the module structure composition from the transmitter, receiver and the control part. Then it designs the optical module according to the SFP MSA and SFF-8472 agreement. On the basis of the design, some sample optical transceiver modules are designed. Finally, the optical power, extinction ratio, sensitivity and other performance indicators of the module are tested at -40, 25, 85 ℃, and results indicate that these parameters meet the design requirements, and show good stability in a suitable temperature range. The feasibility of the design is confirmed by experiments, which provides a reference for the actual production of modules.
The design principles and design methods are introduced for a InP-based Quantum Cascade Laser(QCL) with high power and short wavelength. According to the described ideal and real carrier transition paths, the active region designing trends and approaches to enhance the efficiency of the QCL are also proposed. The most advanced design methods, such as two phonon resonance design, nonresonant extraction design, strong coupling design, deep well design, shallow well design and short injector design are reviewed, respectively. The characteristics and advantages of each design method are discussed. With these highly advanced design approaches, the Wall-plug Efficiency(WPE) of the short wavelength QCL exceeds 50% at low temperature and room temperature, continuous wave operation surpasses 3 W and the maximum T0 and T1 reach 383 K and 645 K, respectively. As the most advanced working region, high power, advanced design methods make QCL unlimited usage in both military and civilian fields. Moreover, they could also be served as the highly efficient bandstructure pioneer design methods for other working regions.