One problem associated with microcavity devices is the significant difference between the reflection spectra of fabricated porous silicon microcavity (PSM) devices and those obtained by theoretical calculation of ideal microcavity devices. To address this problem, studies were carried out to determine the effects of the refractive index dispersion, the absorption of the porous silicon layer and the fluctuation of the dielectric interface on the reflection spectra of PSM devices. The results are in good agreement with those obtained experimentally from the fabricated PSM devices, which provides a theoretical basis for the design of PSM sensors.
A method for improving lateral resolution and reducing imaging distortion of optical subtraction microscopy is proposed. First, an azimuthally polarized (AP) light is modulated by an annular aperture. Then, an image with higher lateral resolution is obtained by subtracting an image obtained by an annular AP beam from an image obtained by a radially polarized beam. The simulation results demonstrate that compared with the case without the annular aperture, negative side-lobes in the effective point spread function are effectively suppressed, and the imaging quality of subtraction microscopy is obviously enhanced.
Due to the limit of the pixel size of the charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensor, the traditional differential algorithm has a limited measuring accuracy by determining the critical angle in integral pixel. In this paper, we present a practical algorithm based on the centroid value of the reflective ratio around the critical angle pixel to address the traditional differential algorithm problem of determining the critical angle under sub-pixel in a critical angle refractometer (CAR). When the change of refractive index (RI) of a liquid sample is beyond the sensitivity of the traditional differential algorithm, the RI of the liquid can be obtained by using the centroid value of reflectivity around the critical angle pixel. The centroid value is associated with the RI change of the liquid in sub-pixel. Demonstrated by both theoretical analyses and experimental results using saline solutions with RI that changes in sub-pixel tested through the reflective CAR, the algorithm is found to be computationally effective and robust to expand the measuring accuracy of the Abbe-type refractometer in sub-pixel.
A switchable dual-wavelength erbium-doped fiber (EDF) laser is proposed and demonstrated. The interference filter is achieved by employing a phase-shifted fiber Bragg grating (PSFBG) combined with Sagnac loop structure. By adjusting polarization controller (PC) states, the birefringence effect is introduced to weaken mode competition, then stable and switchable dual-wavelength fiber laser can be realized. Based on coupled-mode theory and transmission matrix, the Sagnac loop transmission characteristics are studied. The experimental results show that the proposed fiber laser can operate in switchable dual-wavelength output mode at room temperature just by simply adjusting PC. The output wavelength range of fiber laser is 1 556.128–1 556.384 nm, the side mode suppression ratio (SMSR) is over 45 dB, and dual-wavelength spacing as small as 0.048 nm is achieved, which can be used in high-fineness dense wavelength division multiplexing (DWDM) systems and similar structures.
White organic light-emitting devices (WOLEDs) were fabricated by using a highly blue fluorescent dye of 4,4’-bis(2,2’-diphenyl vinyl)-1,1’-biphenyl (DPVBi) and a red fluorescent dye of 5H-benzo[ij] quinolizin-9-yl) ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2), together with a green fluorescent dye of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyroyran-o(6,7-8-i,j) quinolizin-11-one (C545T). The multilayer WOLEDs does not involve the doping process. The structure of the device is indium tin oxide (ITO)/4,4’,4”-tris{N,-(3-methylphenyl)-N-phenylamin}triphenylamine (m-MTDATA) (55 nm)/ N,N’-bis-(1-naphthyl)-N,N’-diphenyl-1,1’-biph-enyl-4,4’-diamine (NPB) (10 nm)/ DPVBi (8 nm)/ C545T (x nm)/ DPVBi (5 nm)/ DCM2 (y nm)/ tris- (8-hydroxyquinoline) aluminum (Alq3) (60nm)/ LiF (1 nm)/ Al, where the DPVBi is introduced as a spacer. By changing the thicknesses of dual ultrathin layers of C545T and DCM2, the WOLED is obtained. When x=y=0.05, the Commission Internationale de 1’Eclairage (CIE) coordinates of the device change from (0.262 6, 0.351 4) at 4 V to (0.214 7, 0.269 3) at 12 V that are well in the white region. Its maximum luminance is 41400 cd/m2 at 13 V, and the maximum current efficiency and the maximum power efficiency are 7.95 cd/A at 6 V and 5.37 lm/W at 5 V, respectively.
Cu2ZnSnSe4 (CZTSe) absorbers were deposited on borosilicate glass substrate using the low-temperature process, and different Na incorporation methods were applied to investigate the effects of Na on the CZTSe growth. Na was diffused into some of the absorbers after growth, which led to strongly improved device performance compared with Na-free cells. With the post-deposition treatment, the effect of Na on CZTSe growth was excluded, and most of Na was expected to reside at grain boundaries. The conversion efficiency of the completed device was improved due to the enhancement of open circuit voltage and fill factor. The efficiency of 2.85% was achieved at substrate temperature as low as 420 °C.
Nonlinear optical properties of tetraphenylporphyrin (H2TPP) and protonated tetraphenylporphyrin (H4TPP2+) in toluene were investigated by Z-scan technique using a nanosecond laser with 5 ns pulse at 532 nm. Results show that H4TPP2+ exhibits weaker nonlinear refraction but enhanced reverse saturable absorption (RSA) and optical limiting performance in comparison with pristine H2TPP. Since no nonlinear scattering is observed in H4TPP2+ under low input fluence, and H4TPP2+ exhibits weaker nonlinear scattering signals than H2TPP under high input fluence, the enhancement of RSA and optical limiting performance can be attributed to the larger ratio of excited state absorption cross-section to that of the ground state of H4TPP2+. H4TPP2+ also exhibits superior optical limiting performance, even better than the benchmark RSA material C60.
A novel optical instrument is proposed and studied to measure the deformation of each connection point for a mirror, which includes 24 multi-matrix base units and can be used in millimeter-scale signal reflection systems. Experimental investigations reveal that the error of measurement is σ=8.7×10−3 mm at a distance of 5 500 mm, which allows to measure the linear deformation of a radiotelescope with the mirror diameter of 70 m.
In the current furniture production line, the level of automation in the stage of loading and unloading is not high enough. In order to improve its automation, a novel integer programming based method for automatically segmenting board is proposed and a multi-sensor configuration is given. In such a configuration, we include multiple cameras and Lidar sensors. The cameras attached on each board are used to collect quick response (QR) code information, while Lidar sensors can obtain each board’s contours information. We then formulate each board’s segmentation as the integer programming problem. The experimental results show that our method can achieve a very high segmentation accuracy of 95% on average.
In order to improve the super-resolution reconstruction effect of the single image, a novel multiple dictionaries learning via support vector regression (SVR) and improved iterative back-projection (IBP) are proposed. To characterize the image structure, the low-frequency dictionary is constructed from the normalized brightness of low-frequency image patches in a discrete-cosine-transform (DCT) domain. Pixels determined by Gaussian weighting are added to the input vector to restore more high-frequency information when training the high-frequency image patch dictionary in the space domain. During post-processing, the improved IBP is employed to reduce regression errors each time. Experiment results show that the peak signal-to-noise ratio (PSNR)and structural similarity (SSIM) of the proposed method are enhanced by 1.6%–5.5% and 1.5%–13.1% compared with those of bicubic interpolation, and the proposed method visually outperforms several algorithms.