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Issue 5 ， 2004
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Fabrication and experimental characterization of high power bottom-emitting VCSELs
Abstract：High power bottom emitting vertical-cavity surface-emitting lasers(VCSELs)emitting at 980 nm was fabricated and characterized. Through enlarging the active diameter, improving the fabrication technology and using Al2O3 and HfO2 as passivation layer and antireflection coating respectively, the output power was greatly increased. The dependence of maximum output power on device diameter and injected current was investigated, which is in good agreement with theoretical simulation. A continuous-wave(CW)output power as high as 1.95 W for devices with diameters of 500 μm and 600 μm has been achieved, which is the highest value reported for a single device. The detailed analysis of the nearfield and farfield images of a 200 μm diameter device exhibits a homogeneous current distribution and a single transverse mode operation.Keywords：VCSELs;bottom-emitting;980 nm;output power;nearfield and farfield- 58
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Published：2020-08-12 -
Ion beam etching of HfO2 film
Abstract：The ion beam etching of HfO2 film and AZ1350 photoresisit mask were investigated in argon. The etch rate and mechanisms were measured and analyzed as a function of ion energy, ion beam density and ion incidence angle. The equations of etch rate versus such parameters were developed by the least-square-fit. The fidelity pattern transfer of mask and substrate were analyzed with the etching depth. The surface quality before and after etching were examined with AFM tapping mode. The details of etch rate have been interpreted in terms of mechanism of etching. The results show that etch rate has linear dependence on square root ion energy and ion density and varies versus incidence angle. Compared with the unetched substrate the etching process slightly lowers RMS roughness and the fidelity pattern transfer degrades with the etched depth on HfO2 film as a result of poor selectivity towards photoresisit. So it is necessary to improve the selectivity to achieve high fidelity pattern transfer. These results have been applied in the fabrication of HfO2/SiO2 multiplayer diffractive grating patterns.Keywords：HfO2 film;ion beam etching;etch rate;pattern transfer;surface morphology- 38
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Published：2020-08-12 -
Noise characteristics of laser diode pumped solid-state laser by intracavity sum-frequency of KTP phase matching II
Abstract：The laser diode pumped Nd:YVO4 crystal and intracavity sum-frequency by KTP nonlinear crystal phase matching II to generate the orange-yellow laser of 593.5 nm from the wavelengths of 1064 nm and 1342 nm is presented. The noise characteristics of laser has been measured and analyzed in different pumping power. According to the longitudinal mode structure of sum-frequency output, which is measured by F-P scanning interferometer and coupled-wave equationship of sum-frequency generation, the relations between the noise of intracavity sum-frequency laser and the longitudinal mode structure of fundamental frequency has been researched. The results show that the output is low noise operating if the one of wavelengths in intracavity sum-frequency generation is single longitudinal mode in the sum-frequency laser with Nd:YVO4 as gain materials and KTP phase matching II as sum frequency crystals. The cross sum-frequency generation between different modes of different wavelengths and gain saturation between different mode of the same wavelength cause noise and instability, which is the same as "green problems", but noise amplitude is lower than intracavity-doubled laser with the same crystals.Keywords：laser diode pump;intracavity sum-frequency generation;all-solid-state;noise characteristics- 72
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Published：2020-08-12 -
Laser interferometer with isolator function
Abstract：A laser interferometer with isolator function is proposed. It can be used to carry out interference measurement, and at the same time can be prevent reflected light from returning into the laser source to stabilize the source as an isolator does, thus the measurement accuracy can be guaranteed. So, the structure of the device is formed by organic combing two structures of the conventional interferometer and two-stage isolator, in which some elements can be combined two into one with double function. And the optical paths of the interference measurement and isolating are overlapped. Theoretic analysis and experiment results show that the device is effective, the isolation is agrees with that of a two-stage isolator, about 48 dB up to now. The results also show that the accuracy of the interference measurement depends on the wavelength of the laser like that of the general interferometer. But with compact structure, it simplifies the measurement system and is convenient for practical uses.Keywords：laser interferometer;isolating function;interference measurement- 60
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Published：2020-08-12 -
Accurate phase recovery algorithm in lateral shearing interferometry
Abstract：A phase recovery algorithm with improved accuracy and efficiency is proposed for test wavefront phase recovery from obtained phase differences in shearing interferometry. The algorithm is based on complete pixel by pixel mapping relationship between test phase and its differences, together with the least square principle. In the algorithm, a special linear equation set is firstly built, from which the test phase can be obtained directly by equation solving. Since the coefficient matrix of the equation is sparse, it is transferred to a small new matrix to reduce memory need and calculation amount. In the meantime, since the matrix is a positive-defined matrix, Choleski's factorzation is adopted for convenient equation solving. Reduced time cost and computer memory need and improved recovery accuracy and efficiency have been demonstrated by computational and experimental testing on the proposed algorithm and its comparison with others. Good noise suppression ability is proved by error propagation characteristic analysis.Keywords：shearing interferometry;phase recovery;algorithm;phase difference- 71
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Published：2020-08-12 -
Reflectivity measuring device the in national synchrotron radiation laborator
Abstract：The reflectometer in the National Synchrotron Radiation Laboator(NSRL)radiometry metrology experimental station was designed and developed. The wavelengh range is 500～100 nm,and the angle differentiate is 0.005°. Sample table can be adjusted six dimensions. The together-axis feed-through is employed by sample scanner and detector scanner,so that the scan precision of movement and measurement are improved greatly. The sample and detector can both move and rotate, not only rotating singly but also together at θ-2θ angle, and they can exit from light path. By using beamline difference system and reflectometer difference feed-through system, 10-6～10-8 Torr vacuum is obtainable. The sample reflectivity can be measured by wavelengh scan and angle scan.Keywords：synchronization radialization;reflectometer;measurement- 28
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Published：2020-08-12 -
Optoelectronic method for measuring the straightness of the bore with a diameter of 25 mm
Abstract：Based on the principle and technology of laser collimation and optoelectronic inspection, an optoelectronic measuring method is presented to measure the straightness of the bore with a diameter of 25 mm by using the quadrant detection method, technique of laser collimation, optoelectronic detection, precision machine, servocontrol and computer for reference. The overall structure of system is discussed, and the measuring principle of the system is analyzed. Then, the corresponding formula to calculate the straightness of the bore and the mathematics model to solve eccentricity of the optical drone are obtained. Then the system is used to measure a hole standard piece with the length of(1.15 m)and inner diameter of 25 mm, by sampling two groups of the data of straightness with the pedometer of 100 mm each. The results show that the system resolving power can reach 0.005 mm, the measuring error is not more than 0.015 mm, and the measuring repetition error superior to ?0.009 mm,Which indicates that the measuring method is applicable.Keywords：bore;Straightness;laser collimation;optoelectronic target- 48
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Published：2020-08-12 -
Highly sensitive micromachined tunneling sensors
Abstract：Highly sensitive silicon micromachined tunneling sensors with small size and light mass have been widely explored in the last 15 years. Many types of tunneling sensors have been developed. This paper presents a review of silicon micromachined tunneling sensors. Four types of tunneling sensors including accelerometers, gyroscopes, infrared sensors, and magnetic sensors are reviewed. Various designs, fabrication procedures, performance, control systems, and noise constraints of silicon tunneling sensors are described and discussed. Novel polymer-based tunneling accelerometers fabricated by PMMA and hot embossing technique are introduced. The structure, fabrication process and characterization of the polymer-based sensor are presented. We can expect that the polymer tunneling sensor has the potential to become the basis for the next generation of highly sensitive MEMS-based sensors in many areas.Keywords：tunneling sensor;sensitivity;resolution;polymer;hot embossing;low frequency noise- 58
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Published：2020-08-12 -
Single axis double flywheels integrated power and attitude cortrol system
Abstract：A single axis double flywheels integrated power and attitude control system(IPACS), including its working principle and configuration, are given to simulate the charge, discharge and attitude control process during the full sun, eclipse and their interim. Based on the experiment, the system models during the energy storage and release are obtained and their corresponding control arithmetic is given. Experiments show that the system can be used to store and release energy while adjusting the attitude of the platform, as well as of the satellite. The angle of the platform can be controlled to stabilize within 3° and 1.2′, respectively. To the satellite in which the flywheels can be used, the attitude affection should be less than 3.6′ and 1.5″, respectively. After eliminating unbalance affections, such as the difference from motors, the scheme using flywheels to perform the energy storage and attitude control in the satellite is efficiency.- 44
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Published：2020-08-12 -
Analysis and simulation of enveloping grasp stability of the multi-phalange underactuated robot hand
Abstract：The grasp stability of underactuated robot hand is discussed. The definition of grasp configuration is proposed, and the relationship between the numbers of phalanges and grasp configuration is deduced. The transition difficulty in grasp configuration is employed to evaluate the stability of enveloping grasp. The main factors which influence the grasp stability are investigated. Some cases of stimulation are given to validate the evaluation when the underactuated robot hand grasps different objects. The results show that the theory is in accord ance with the simulation, and the multi-grasp-configurations are the primary reasons that lead to unstable grasp.Stable grasp is decided by object shape and initial posture, among which the length of the convex contact line is the most important factor for the grasp stability. The grasp is most unstable when the object shape resembles circle, while the grasp is the most stable when the object shape wholly conforms to the grasp configuration convex with long margin line. The longer the line is, the more stable the grasp is.Keywords：underactuaed robot hand;grasp stability;grasp configuration;simulation- 42
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Published：2020-08-12 -
Deformation sensing and incremental shape reconstruction for intelligent colonoscope
Abstract：This paper analyzes a shape detecting system for colonoscope, especially gives the detecting principle of a curvature sensor, the design of an inserting device and its control system. Two Fiber Bragg Gratings(FBGs)with central wavelength of 1539.234 nm and 1538.882 nm are mounted on a cylindrical slim string, which compose a detecting sensor with a diameter of 3 mm. The string sensor moves step by step along the biopsy channel by the inserting device, the average velocity of which is 30 mm/sec. In the insertion process, the data of the Bragg wavelength change on the sensor is picked up every 50 mm of insertion and memorized at equidistance points, on which the space curvature information is calculated. At last, the shape of the colonoscope is reconstructed by the use of the space curve fitting method, which is based on curvature information of discrete points. The experiment results verify the proposed shape reconstruction method is effective and efficient. Experiment with a circular model shows that the far end positioning error is 0.5 mm, 0.8 mm and -3.4 mm for x, y, and z directions, respectively, while inserting 1000 mm sensing string. The display of the colonoscope shape inside human body will greatly increase the inspection safety during colonoscopy operation.Keywords：colonoscope;fiber Bragg grating;pushing device;shape reconstruction- 56
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Published：2020-08-12 -
Push force analysis of a cylinder linear motor
Abstract：The structure of a cylinder linear motor is presented. And the axial symmetric vortex analytical equation, which fits for its structure characters, is established and the solution is given. This axial symmetric FEM model is set up with the variation theory. Simulation results reveal that these two methods are consistent, and the analytical model is effective and efficient. Moreover, based on the analysis, a cylinder linear motor model was manufactured with appropriate structure parameters, and the change of the start pushing force measured. The test results and the calculations have the same tendency and approximate value. It proves that the analytical model meets the calculation of the cylinder linear motor. Therefore, it verifies the reliability of this method. Furthermore, the above research reveals that the cylinder linear motor meets the demand of driving the mobile sculpture shadily. The main structure parameters, such as the air gap, the thickness of the secondary end and those may affect the performances of the linear motor were also investigated. It is found that when the air gap increases, the pushing force decreases. When the thickness of the secondary is 10 mm, the pushing force reaches its maximal value of 198.5 N.Keywords：mobile sculpture;linear motor;electromagnetic field;analysis;FEM- 63
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Published：2020-08-12 -
Experimental research and analysis of automatic focusing function for imaging measurement
Abstract：Several general automatic focusing functions for imaging measurement are put forward, compared and analyzed in defail. The main parameters of automatic focusing, including sensitivity, consistency, stability and calculating speed, were tested and validated through a series of experiments under different conditions, such as different lighting or different background. The results of experiments show that in the background lighting, the gray functions all have better performance than others, the Variance function and the sum of gray-change function have a large focusing range, good linearity and low sensitivity, so they are propitious to focusing in large range with lower accuracy. The Laplacian and Tenengrad functions both have sharp peak, good sensitivity and small focusing range, which make them applicable to accurate focusing in small range. But in reflection lighting, only the Tenengrad and Brenner functions have fine single peak and low sensitivity. All of these focusing functions will be disabled when the complex backgrounds exist. So, when it comes to practical application, background lighting should be chosen instead of reflection lighting, also interference coming from background should be reduced to minimum level.Keywords：imaging measurement;automatic focusing function;Algorithm- 49
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Published：2020-08-12 -
Research on auto-focused function based on the image entropy
Abstract：Based on the definition of entropy in image, the application of the image entropy in auto-focused function is studied. It is found that there are two different rules in focusing function while using the image entropy. When the image is in the state of focus, one with the entropy is the largest, and the other with the entropy is the least. Through calculating and analyzing different kinds of test images, the existence of rule variance is confirmed, and the reason is analyzed. As the peak value and its shift are small, it is difficulty to find the largest in the four corners. Based on mean-square judge-function, a method weighted in condition is given, and an auto-focus judge-function with coherence rule is obtained. The experiment proves that the mean-square judge-function weighted in condition can enhance the peak of function and does not increase amount of calculation, so it can improve the veracity of judgement. If the test-condition does not change a lot, image entropy can be acted as an auto-focus judge-function through human-computer interface, otherwise the conditional weighted mean-square function is recommended.Keywords：entropy;focusing function;mean-square- 51
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Published：2020-08-12 -
Singular value decomposition-based approach for face recognition
Abstract：A method to extract algebraic features of a face image based on the Fourier transform and Singular Value Decomposition(SVD)is introduced, then the method with the algebraic feature is proposed to recognize faces. First, face images are processed by a 2D Fourier transform that has some effective properties such as a linear transform, and is invariant against spatial translation. The amplitudes of the transform coefficients are used to represent the image in the frequency domain. Second, the amplitude representation of the face image is projected onto the two compressed orthogonal matrixes, which come from the SVD of the standard face image obtained by averaging all training samples and then the projecting coefficients are used as the algebraic feature of the face image. The robustness of this feature is proved and used for face recognition. In the matching stage, the traditional Nearest Neighbor Classifier(NNC)is improved to recognize the unknown faces by using Euclidean distance as the similarity measurement. Finally, the standard face database from Olivetti Research Laboratory(ORL)is selected to evaluate the recognition accuracy of the proposed face recognition algorithm. This database includes face images with different expressions, small occlusions, different illumination conditions and different poses, etc. The recognition accuracy is up to 100.00% by selecting appropriate values of the parameters. The effectiveness of the proposed face recognition algorithm and its insensitivity to the facial expression, illumination and posture are shown in terms of both the absolute performance indices and the comparative performance against some popular face recognition schemes such as Singular Value decomposition-based method.Keywords：face recognition;Fourier transform;SVD;NNC- 44
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Published：2020-08-12 -
Theoretical simulations of the mechanical characteristics of laser induced plasma for monatomic target
Abstract：Based on a magneto-hydrodynamics model, the plasma characteristics for the elements Xe, He, C, N, O, Ne, Al and Ar are studied. And, numerical simulations were introduced to the relationship between the ablation-velocity and -pressure with the wavelength of the imported laser beam by using element Al as an example. These analyses show that under the same condition of the imported laser beam, the ablation-pressures and -velocities of He, C, N, O, Ne, Al and Ar are roughly equal, which means that the Air-breathing-Mode will be the profitable one to improve the effective load of the rocket. These simulations reveal that the ablation-velocity and -pressure of the target goes down and gradually tends to flatness with the increase of the imported laser wavelength. This change goes very rapidly when the wavelength is less than a certain value. If only considering the wavelengths of the induced laser beams,the shorter ones will be better to increase the thrust-force. But a laser beam with a shorter wavelength will be heavily scattered by atmosphere, leading to great energy loss. So in the practical application, the laser beam's wavelength should be chosen according to the different flying height of the aircraft.Keywords：monatomic target;laser;plasma- 35
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Published：2020-08-12
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