A time-delayed integration charge-coupled device (TDI CCD) in an aerial panoramic camera compensates the sweep image motion correctly on the premise that the TDI charge shifting direction is coincident with that of the sweep image motion. The coordinate transformation method is used to find out how the included angle between the two directions originated. Then the precise alignment method of the TDI charge shifting direction is proposed to eliminate the included angle. TDI CCD is operated in area mode, nodding the scan mirror, the trajectory of the image point is derived to be a hyperbola, which could be equivalent to an obliquely straight line. The tilt angle of the line is exactly the included angle between the two directions. Meanwhile, the tilt angle can be calculated by the least square method. Then the scan head or the focal plane assembly is precisely rotated to eliminate the included angle between the two directions. The assembling error after precise alignment is calculated at −16.4 s, which could hardly influence the MTF of TDI CCD. The panoramic imaging experiment and the flight test show that the precise alignment method is feasible and completely satisfies the operating requirement of the aerial panoramic camera.
The radius of curvature (ROC) is one of the most important parameters of sphere optic components. In optic fine grinding process, radius of curvature accuracy requires up to 0.1%. We propose a method based on high precision CNC grinding machine, develop ROC online measurement method for fine grinding optics. This rapid method only takes few measurement points based on spiral route path, attaining enough accuracy and reduce the time cost, furthermore, can greatly reduce the repeated installation error. Analyzing the uncertainty sources that affect to the ROC measurement results, calculates the combined standard uncertainty 32.8 micron. Completed comparison experiments with CMM, the standard deviation of the experiment result are about 18 micron that approaches to CMM results.
Method of smoothing an aspheric surface was studied and discussed in this paper, and a new design of smoothing tool called bonnet-like polishing tool was used to smooth out Mid-Spatial-Frequency (MSF) errors. A concave surface with F# 0.8 and a huge departure of 1mm from best fit radius was polished by this new bonnet-like polishing tool in this paper. The tool can be well matched to the changing radius of the aspheric surface and can effectively restrain MSF errors on the surface. After pre-polishing, the surface was first smoothed by the tool and then was corrected by the bonnet polishing method. This iteration was continued until the MSF errors were nearly gone. In this process, the aspheric surface was first tested by Luphoscan and then tested by CGH when the surface was good enough, which can ensure the accuracy of the surface. This new tool was successfully used to polish a 240mm aperture asphere. Finally, after two iterations between surface smoothing and figure correction, the surface accuracy converged to 5.7nm RMS as well as the period between 1mm to 10 mm converged to around 4nm RMS. The result shows that this method can realize the valid polishing of high-accuracy aspheric surface with mm-scale departure.
Lithography projection objective is one of the most precise optical systems in optical manufacture field. The required accuracy of the asphere in the objective is down to nanometer and sub-nanometer, which is a great challenge for optical fabrication and testing. In this paper, the theories and technologies of sub-nanometer asphere fabrication and testing are studied and developed. Combined the sub-nanometer interference testing method and atom level polishing technologies, sub-nanometer aspheres are realized. Two kinds of testing methods are used for the measurement of the asphere and the difference of the results is less than 1nm (RMS).
The reasons and methods for generating and suppressing mid-spatial frequency (MSF) errors were deeply studied, and a new method of combining multiple small tools was used to smooth out MSF errors. First, an elastic tool was employed to pre-polish the aspheric surface after grinding, aiming at fast removing sub-surface damage as well as correcting surface figure. Then a second tool-self-designed smoothing tool -was mainly used to smooth the surface, which was followed by an air bonnet tool to continue figure correction until Zernike residual was not convergent. The effective combination of the three small tools was not only able to avoid the high slope fabrication difficulty of the aspheric surface, but also to suppress the MSF errors. The surface was tested by CGH, which can ensure the accuracy of the surface. This method was successfully used to polish a 150mm asphere with a maximum departure of 0.26mm. After five iterations, the surface accuracy converged to 4.05nm RMS. The result shows that this method can realize the valid polishing of high-accuracy aspheric surface.
We presented the self-planar mesa structure for improving the performances of 850-nm oxide-confined vertical cavity
surface emitting lasers (VCSELs). Thermal simulation results demonstrated that the enhanced lateral heat dissipation and
decreased series resistance within VCSELs could be gained using the self-planar mesa structure. By employing the selfplanar
mesa, the maximum output power was increased from 8mW to more than 11mW, and the maximum wall-plug
efficiency was improved from 26% to 36% for the VCSEL with an oxide aperture size of 13 μm at 15°C.
Design of the active region and analysis of temperature sensitivity of high-temperature operating 795-nm special
VCSELs for Chip-Scale Atomic Clock (CSAC) are presented. Composition and thickness of the InAlGaAs multiple
quantum wells (MQWs) are optimized at room and elevated temperatures. Temperature sensitivity of the threshold
current is analyzed by calculating the temperature dependence of cavity-mode gain over a broad temperature range
(25°C-150°C). A self-consistent VCSEL model based on quasi 3D finite element analysis is employed to investigate selfheating
effects and temperature distribution in the proposed structure. Output power of 2.5mW is expected from 10μm
aperture VCSELs at 10mA current at ambient temperature of 358K.
Power scaling and beam divergence compression of 980 nm bottom-emitting vertical-cavity surface-emitting lasers
(VCSELs) are presented in this paper. First, the relationships among the reflectivity of the n-doped distributed Bragg
reflector, threshold current, and output power were analyzed, and the n-DBR reflectivity was optimized to achieve higher
slope efficiency in a relatively low threshold current. Second, the influence of the p-contact on the current density
distribution inside the active region was analyzed using the three-dimensional finite-element method. Uniform current
distribution was achieved by optimizing the diameter of the p-contact, and a consequent improvement in beam
divergence was observed. A low divergence of 5.4° was obtained for a single device with continuous-wave (CW) of 1.46
W at room temperature. The 8×8 VCSEL array showed a divergence angle of 10.2° at 4A. This array afforded a CW
output power of 1.95 W under an injected current of 4 A and a pulse output power of 115 W under a pulse drive current
of 130 A, a pulse width of 100 ns, and a repetition frequency of 100 Hz. VCSEL array chips were packaged in series to
form a “quasi-array” to further increase the output power. This series achieved a peak output power of 475 W under a
pulse drive current of 120 A.
The method of bonnet polishing is successfully used to polish an aspheric surface with an aperture of 200 mm and a
maximum departure of 700 μm. Based on the principle of bonnet polishing, we employ one IRP 600 machine to finish
the aspheric surface which was previously ground to an asphere by Satisloh. According to the analysis of error map
obtained by the help of CGH after each iteration, several technological parameters are well verified and the whole
precession process is proved to be under good control when the material to be polished is fused silica. With total 12
iterations of 30 hours including 5 pre-polishing iterations and 7 corrective iterations, the surface form accuracy of 80nm
(PVq) and 15nm (RMS) over the full aperture is achieved. The results indicate that bonnet polishing can not only realize
good form accuracy, but also eliminate a certain mid-frequency effect left by grinding.
The nonlinear response of the PZT for the integrating bucket method is studied by our proposed method: discrete
chirp Fourier transform (DCFT) and maximum likelihood estimation (MLE) techniques for the integrating bucket
method. Based on the signal processing theory, the intensity obtained from CCD is processed by the DCFT and
thus nonlinear response and chirp coefficient of the PZT can be coarsely estimated. This is followed by the MLE
method, in which an iterative optimization process is complemented for accurately estimating the nonlinear
response and chirp coefficient of the PZT. One key advantage of the proposed method is that not only the nonlinear
response and chirp coefficient of the PZT can be acquired, but also initial phase acquired. Our method is tested by
simulating conditions under which a certain magnitude of nonlinearity is assumed. Nonlinear response attained by
the DCFT is compared to that attained by the MLE, and a difference between the actual nonlinear response of the
PZT and our accurate estimation by the proposed method is revealed. Several factors that will have influence on
the nonlinear response of the PZT are discussed.
To obtain a number of advantages in fabrication, testing and alignment, many designs in which spherical mirrors
replace classical Cassegrain-form aspheric mirrors are present in the literature. However, spherical mirrors suffer from
substantial spherical aberration and thereby require some form of corrector group. But in this case, the question
encountered is that of making the basic optical configuration more complex. In this paper, a new design based on Cooke
corrector group is presented for eliminating spherical aberration, which is believed to provide higher performance with
less complexity than previous approaches. Besides, the cost and fabrication period will be extremely decreased. The
telescope system using corrector group here can achieve good optical performance with f# of 10, full field of 0.5°,
obscuration of 1/3 and MTF (Modulation Transfer Function) of 0.48 corresponding to 50@lp/mm.
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