This paper proposes the deconvolution image restoration algorithm, which uses the point spread function constructed by the physical characteristics of the terahertz beam to reconstruct the terahertz image and improve the image resolution[1]. At the same time, by constructing a point spread function with different penetration depths in the sample, the effect of image chromatogram on the sample can also be achieved. The integrated circuit (IC) electronic package terahertz imaging results clearly show the spatial position of the pins, internal chips and defects of the electronic packages, and analyze a variety of failure defect types, which are <1% more than the actual size.
A semi-annular-rectangular cavity based on metal-insulator-metal (MIM) waveguide is proposed. The results show that there are obvious asymmetric transmission peaks in the transmission spectrum due to Fano resonances. The sharp transmission peak with a transmittance of ~ 0.75 occurs at the wavelength of ~1174.99nm . Then a steep dip arises at its right side, and the transmittance is almost 0 at ~1239.22nm . In addition, high sensitivity and figure of merit are also investigated. The performances of the proposed structure are demonstrated by using FDTD method.
Thermal reflow is widely used in the fabrication of microlenses as a simple and low-cost process, which includes the direct contact heating and the upside-down reflow. To compare the difference in the shapes of the microlenses obtained by these two approaches, the cylindrical microstructure arrays obtained rapidly via DMD-based lithography system were used for different thermal reflow processes, and subsequently, two types of high-fill-factor microlens arrays (MLAs) were fabricated and measured in the experiment. Results indicate that the MLAs obtained by these two kinds of thermal reflow have different surface profiles, while these MLAs are good in surface quality because the profile curves of each microlens are very similar and continuous. The comparison results provided in this paper can be used as a reference for selecting the appropriate thermal reflow process for fabrication of other microlenses.
The digital micromirror device (DMD) is the key device in maskless lithography. However, because of the machinery manufacturing limit of DMDs, the gap between the micromirrors may destroy the continuity of the graphic. This work presents a simple way to fill the imaging crack by controlling the partial coherence factor σ of the light source. A crack can be regarded as the image of a dark space. By considering the resolving power for such cracks under partially coherent illumination, the images of such dark spaces can be covered, preventing them from being imaged on the substrate. By using mathematical derivations of the light intensity distribution exposed to the substrate, and by utilizing the diffraction effect induced by the finite aperture of the optical projection system, an appropriate σ value can be determined for eliminating the image of the crack in an actual scene. The numerical simulation results demonstrate that this method can ensure the continuity of the graphic at the critical partial coherence factor σc regardless of the shape of the target graphic.
Based on the two-step phase-shifting interference (PSI) technique in fractional Fourier transform (FRT) domain and random mixed encoding, we present a new scheme for double image encryption. In the proposed scheme, information of each primitive image is recorded in two intensity interference patterns of FRT spectra by PSI technique, from which an encrypted image for each primitive image can be digitally derived. Random mixed encoding is then employed to divide and recombine both encrypted images into a single synthetic encrypted image. During the mixed encoding process, repositioning operations based on shift-variance of FRT are performed on the encrypted images to realize the spatial separation of decoded results in the output plane. By inverse FRT with correct fractional order, any of the primitive images can be easily retrieved directly from the synthetic encoded image with the corresponding phase encoding key. Crosstalk effect due to the overlapping of decoded images is alleviated for their spatial separation. Computer simulation and experimental results are presented to verify the validity and efficiency of our scheme.
We present a hybrid configuration of joint transform correlator (JTC) and joint fractional transform correlator (JFTC) for encryption purpose. The original input is encoded in the joint fractional power spectrum distribution of JFTC. In our experimental arrangement, an additional random phase mask (master key) is holographically generated beforehand by a Mach–Zehnder interferometer with a JTC as the object arm. The fractional order of JFTC, together with the master key, can remarkably strengthen the safety level of encryption. Different from many previous digital-holography-based encryption schemes, the stability and alignment requirement for our system is not high, since the interferometric operation is only performed in the generation procedure of the master key. The advantages and feasibility of the proposed scheme have been verified by the experimental results. By combining with a multiplex technique, an application for multiple images encryption using the system is also given a detailed description.
In conventional interference-based optical encryption schemes, a potential cracker can retrieve partial information (silhouette) of the secret image using only one phase-only mask (POM). We resolve this drawback using a phase-blend operation and piecewise linear chaotic map (PWLCM) to further encode the POMs. One cannot recover a secret image visibly when inverse phase-blend operation and inverse chaotic permutation are not carried out with the correct decryption keys. Chaotic parameters of PWLCM, and random phase-angle function in the phase-blend operation enlarge the key space and improve the security of the proposed system greatly. Numerical simulations and optoelectronic experiments are performed to verify the effectiveness of the proposed scheme.
The morphological joint fractional Fourier transform correlator (MJFTC), as a modified nonlinear joint fractional Fourier transform correlator (JFTC), is introduced in this paper. An optoelectronic setup that can implement such a nonlinear JFTC is advised and constructed. We investigate the correlation properties of the MJFTC using computer simulation and optical experiments. Numerical and experimental results show that the MJFTC exhibits remarkable improvement in terms of discriminability and peak sharpness compared with the classic JFTC. Moreover, the MJFTC provides better noise tolerance to the salt-and-pepper noise or normally distributed white additive noise than the JFTC and the other nonlinear processing or fractional-order filtering JFTC.
Projection imaging is one of the most important steps in the fabrication of Printed Circuit Board. In order to meet the
increasing demand for higher resolution, speed and larger area of imaging, a novel Laser Projection Imaging (LPI) has
been developed to take the place of the conventional Hg lamp exposure. We set up a system with resolution 10μm over
large exposure area of 460mm×610mm on substrate materials. The system is available by the combination of three main
parts: an XeF excimer laser with a wavelength of 351nm and single pulse energy of 120mJ, an illumination system with
numerical aperture (NA) value of 0.02, and a double telecentric optical projection lens with NA value of 0.025. Such
designs can theoretically meet the demand of actual lithography. However, experiments have shown that the propagation
loss ratio of laser power from the light source to the substrate can be up to 50% or more so as to hardly achieve the
expected results. In this paper, we present our results of experiments under different conditions on laser projection
imaging equipment, and meanwhile, parameters such as gas lifetime, pulse repetition rate, exposure dose, as well as the
optical lose of quartz microlens array are analyzed. Finally, we acquired the optimum exposure parameters.
KEYWORDS: Avalanche photodetectors, Sensors, Control systems, HVAC controls, Temperature metrology, Semiconductors, Single photon, Amplifiers, Control systems design, Temperature sensors
The low temperature control system of single photon detection device avalanche photodiode (APD) is researched. Avalanche photodiode is used for photon detector with high sensitivity. In order to reduce dark current, its operating environmental temperature needs to be lowered by a semiconductor thermoelectricity cooling apparatus. In accordance with the peculiarity of single photon detection system and the technology of semiconductor thermoelectric Peltier cooling, an APD cooling control system is designed and produced by properly selecting components and using some necessary control circuits. The accuracy and the lowest temperature of this control system can amount to 0.1oC and -50oC, respectively. Above all, the low temperature can be adjusted successively.
For BaTiO3:Ce to produce bridge mutually-pumped phase conjugation (MPPC), it is not thought to be achievable because the pump beam incident upon crystal's `a'-face can easily result in strong self-pumped phase conjugation (SPPC) in a wide input range. Therefore the more easily a SPPC is undergone; the more difficult a bridge MPPC is made. However we for the first time, to our knowledge, have successfully obtained the bridge MPPC in BaTiO3:Ce by using two He-Ne laser beams. At some an incident normal angle, there is a transmissivity of as high as 40%. We tentatively suggest the formation mechanism and give a possible explanation of the observed effects.
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