The ripple errors of the lens lead to optical damage in high energy laser system. The analysis of sidelobe on the focal plane, caused by ripple error, provides a reference to evaluate the error and the imaging quality. In this paper, we analyze the diffraction characteristics of sidelobe of optical elements with ripple errors. First, we analyze the characteristics of ripple error and build relationship between ripple error and sidelobe. The sidelobe results from the diffraction of ripple errors. The ripple error tends to be periodic due to fabrication method on the optical surface. The simulated experiments are carried out based on angular spectrum method by characterizing ripple error as rotationally symmetric periodic structures. The influence of two major parameter of ripple including spatial frequency and peak-to-valley value to sidelobe is discussed. The results indicate that spatial frequency and peak-to-valley value both impact sidelobe at the image plane. The peak-tovalley value is the major factor to affect the energy proportion of the sidelobe. The spatial frequency is the major factor to affect the distribution of the sidelobe at the image plane.
A traditional tracking device obtain the attitude angle by analyzing the spots position on photodetector. However, the attainable angular measurement accuracy depends on the field of view (FOV), number of pixels of the photodetector and the centroiding algorithm. In this paper, we present a high-precision attitude angle measuring system based on Talbot interferometry using cross-gratings and four wedge plates, which can acquire the real-time change of incident angle along two axis. The specific structure of the system is introduced, and the formula for calculating the relative angle is derived. The tracking accuracy is analyzed to be better than 0.2 arcsecond, which is dependent on the grating period, the distance between the two gratings and the gray scale of image. The Simulation results show that the RMS error of relative angle is better than 0.1 arcsecond both in x and y direction.
A panoramic long-wave infrared athermal system is introduced in this paper. The proposed system includes a panoramic annular lens (PAL) block providing a stereo field of view of (30 deg – 100 deg) × 360 deg without the need to move its components. Moreover, to ensure the imaging quality at different temperatures, a refractive/diffractive hybrid lens is introduced to achieve optical passive athermalization. The system operates in a spectral band between 8 and 12 μm, with a total length of 175 mm and a focal length of 3.4 mm. To get a bright and clear image, the aperture of the system was set to f/1.15. The introduction of aspherical surface and even-order diffractive surface not only eliminates the differential thermal but also makes the structure simple and lightweight and improves the image quality. The results show that the modulation transfer function below 20 lp/mm of the system is above 0.2 at each temperature ranging from −20°C to +60°C, which is close to the diffraction limit. The system is suitable to be applied in an uncooled infrared focal plane array detector and will serve as a static alert system. It has a number of pixels of 640×480, and the pixel size is 25 μm.
Star-tracker plays an important role in satellite navigation. Considering the satellites on
near-Earth orbit, the system usually has two optical systems: one for observing the profile
of Earth and the other for capturing the positions of stars. In this paper, we demonstrate a
novel kind of dual-channel optical observation system of star-tracker with non-blind area
PAL imaging system based on dichroic filter, which can combine both different
observation channels into an integrated structure and realize the feature of miniaturization.
According to the practical usage of star-tracker and the features of dichroic filter, we set
the ultraviolet band as the PAL channel to observe the Earth with the FOV ranging from
40°-60°, and set the visible band as the front imaging channel to capture the stars far away
from this system with the FOV ranging from 0°-20°. Consequently, the rays of both
channels are converged on the same image plane, improving the efficiency of pixels of
detector and reducing the weight and size of whole star-tracker system.
We propose a novel design of panoramic annular lenses (PAL) for the imaging of 360° surroundings
with a large field of view (FOV) ranging from 30°~105°, which can partly realize the zooming function.
Its wavelength band is between 486 and 656 nanometers. The conventional vari-focal PAL is based on
the axial shift of some optical components, which will make the blind zone larger and out of the
sensing area, while our design is based on the lateral shift, which can make some imaging area zoom in,
keep the area of blind zone stay the same, and minimize the whole scale of this system. In order to
change the focal length of conventional PAL system, we introduce several pairs of free-form surfaces
(Alvarez surfaces) which can be regarded as several plano-spherical lenses and change the focal power
of the whole optical system. As we set two different configurations (long focal length and wide angle),
all of the optical parameters are designed and optimized with the help of the software (Zemax).