We developed a simple and real-time readout autocorrelator for several tens and sub-10fs pulses, based on the two photon absorption phenomena of a commercial GaP photodetector including a transimpedance amplifier. With a suitable gain adjustment, we demonstrated that the interferometric autocorrelation for sub-nJ pulses delivered as a high output voltage as to resolve all fringes in an autocorrelation trace with features of low noise and a low offset voltage. By fitting the measured quadratic power dependence of output voltages, we obtained the quantum efficiency of TPA for the GaP detector comparable with those of a GaAsP diode and an SHG with a thin BBO crystal. The autocorrelator of a TPA based GaP photo detector is highly suitable for sensitively measuring a few cycle pulses with a broad spectral distribution from 600 nm to 1100 nm.
We calculate optical properties of guided modes of a hybrid-guiding photonic crystal fiber. The design and modeling of such hybrid-guiding PCF is made by replacing air holes with inserts of high refractive index material layer by layer in order. The optical properties such as mode intensity profile, mode dispersion, optical birefringence, confinement loss, and chromatic dispersion during transition of the guiding mechanism are analyzed and discussed. The guided modes in the hybrid-guiding region are also compared with those of reference index-guiding and bandgap-guiding photonic crystal fibers.
This study presents an 8x four-group inner-focus zoom lens with one-moving group for a compact camera by use of a focus tunable lens (FTL). In the initial design stage, we obtained the powers of lens groups by paraxial design based on thin lens theory, and then set up the zoom system composed of four lens modules. Instead of numerically analytic analysis for the zoom locus, we suggest simple analysis for that using lens modules optimized. After replacing four groups with equivalent thick lens modules, the power of the fourth group, which includes a focus tunable lens, is designed to be changed to fix the image plane at all positions. From this design process, we can realize an 8x four-group zoom system having one moving group by employing a focus tunable lens. The final designed zoom lens has focal lengths of 4 mm to 32 mm and apertures of F/3.5 to F/4.5 at wide and tele positions, respectively.
Tris-HCl buffer solution is extensively used in biochemistry and molecular biology to maintain a stable pH for biomolecules such as nucleic acids and proteins. Here we report on the high-precision THz dielectric spectroscopy of a 10 mM Tris-HCl buffer. Using a double Debye model, including conductivity of ionic species, we measured the complex dielectric functions of Tris-HCl buffer. The fast relaxation time of water molecules in Tris-HCl buffer is ~20% longer than that in pure water while the slow relaxation time changes little. This means that the reorientation dynamics of Tris-HCl buffer with such a low Tris concentration is quite different from that of pure water.
A single-and dual-wavelength switchable polarized Yb-doped double-clad fiber laser around 1120 nm based on a pair of fiber Bragg gratings (FBGs) is demonstrated. The polarization-maintaining (PM) linear cavity is composed of a double clad PM Yb-doped fiber (YDF) and a pair of PM FBGs. The laser can operate in stable dual-wavelength or wavelength-switching modes due to the polarization hole burning (PHB) and the spatial hole burning (SHB) enhanced by the PM linear cavity. In dual-wavelength operation, the two orthogonally polarized wavelengths are centered at 1118.912 nm and 1119.152 nm, with an interval of 0.24 nm and a signal to noise ratio (SNR) of 35 dB. The maximum output power is 14.67 W when the launched LD pump is 24 W corresponding to an optical efficiency of 61.1%. The lasing lines switchover may be realized by adjusting the polarization controller (PC) fitted in the cavity. The two single-wavelengths are 1118.912 nm and 1119.152 nm. When the injected LD pump is 24 W, the highest output powers are 7.68 W and 8.64 W corresponding to optical efficiencies of 32% and 36% respectively. The spectral linewidth of the lasing lines are 0.075 nm and 0.07 nm, and the average numerical values of PER are 20.3 dB and 19.9 dB, respectively.
This study has investigated the feasibility of 980-nm low-energy pulsed near-infrared laser stimulation to evoke auditory responses, as well as the effects of radiant exposure and pulse duration on auditory responses. In the experiments, a hole was drilled in the basal turn of the cochlea in guinea pigs. An optical fiber with a 980-nm pulsed infrared laser was inserted into the hole, orientating the spiral ganglion cells in the cochlea. To model deafness, the tympanic membrane was mechanically damaged. Acoustically evoked compound action potentials (ACAPs) were recorded before and after deafness, and optically evoked compound action potentials (OCAPs) were recorded after deafness. Similar spatial selectivity between optical and acoustical stimulation was found. In addition, OCAP amplitudes increased with radiant exposure, indicating a photothermal mechanism induced by optical stimulation. Furthermore, at a fixed radiant exposure, OCAP amplitudes decreased as pulse duration increased, suggesting that optical stimulation might be governed by the time duration over which the energy is delivered. Thus, the current experiments have demonstrated that a 980-nm pulsed near-infrared laser with low energy can evoke auditory neural responses similar to those evoked by acoustical stimulation. This approach could be used to develop optical cochlear implants.
In a dual lens stereoscopic camera, a convergence point determines the stereopsis effects of a video. When a user zooms an object, a convergence point is fixed since it is not coupled with a zoom function. Due to the fixed convergence point, it is possible for a zoom to cause the excessive binocular disparity resulting in visual discomfort. In this paper, to solve this problem, we build the relational model including all phenomena possible to arise and propose the adjustment methods of a convergence point by the positions of a focus, an object and a convergence point. We also evaluate the experiments measuring a binocular disparity and the subjective test to investigate the visual comfort. The results show that one of the proposed methods produced more comfortable 3D images to viewers than the others.
A Carbon Fiber Composite (CFC) framework was designed for a small lightweight space camera. According to the distribution characteristics of each optical element in the optical system, CFC (M40J) was chosen to accomplish the design of the framework. TC4 embedded parts were used to solve the low accuracy of the CFC framework interface problem. An integrated optimization method and the optimization strategy which combined a genetic global optimization algorithm with a downhill simplex local optimization algorithm were adopted to optimize the structure parameters of the framework. After optimization, the total weight of the CFC framework and the TC4 embedded parts is 15.6 kg, accounting for only 18.4% that of the camera. The first order frequency of the camera reaches 104.8 Hz. Finally, a mechanical environment test was performed, and the result demonstrates that the first order frequency of the camera is 102 Hz, which is consistent with the simulation result. It further verifies the rationality and correctness of the optimization result. The integrated optimization method mentioned in this paper can be applied to the structure design of other space cameras, which can greatly improve the structure design efficiency.
A dual loop optoelectronic oscillator (OEO) based on an acousto-optic modulator (AOM) for single mode operation with an acousto-optic delay line is demonstrated in this paper. When the OEO operates, the free spectral range is a function of the total loop length of the OEO, which is mainly dependent on the propagation time of the acoustic wave in the AOM. Due to the huge difference in the magnitude between the speed of light and the acoustic velocity in the AOM, the effective loop length converted to light-propagation length of the OEO increases to 3.8 km. With 150 MHz oscillation frequency, phase noise of -118 dBc/Hz at 10 kHz frequency offset, and -140 dBc/Hz at 200 kHz frequency offset, is achieved.
This paper proposes an optical system for complex holographic display that enhances the quality of the reconstructed three-dimensional image. This work focuses on a new design for an optical system and the evaluation of the complex holographic display, using a single spatial light modulator (SLM) and a circular grating. The optical system is based on a 4-f system in which the imaginary and real information of the hologram is displayed on concentric rectangular areas of the SLM and circular grating. Thus, this method overcomes the lack of accuracy in the pixel positions between two window holograms in previous studies, and achieves a higher intensity of the real object points of the reconstructed hologram than the original phase-reconstructed hologram. The proposed method provides approximately 30% less NMRS (Normal Root Mean Square) error, compared to previous systems, which is verified by both simulation and optical experiment.
Surface protein internalin (InlA) is a major virulence factor of the food-borne pathogen L. monocytogenes. It plays an important role in bacteria crossing the host's barrier by specific interaction with the cell adhesion molecule E-cadherin. Study of this protein will help to find better ways to prevent listeriosis. In this study, a monoclonal antibody against InlA was used to detect InlA. The reaction was label-free and monitored in real time with an oblique-incidence reflectivity-difference (OI-RD) technique. The kinetic constants k on and k off and the equilibrium dissociation constant K d for this reaction were also obtained. These parameters indicate that the antibody is capable of detecting InlA. Additionally, the results also demonstrate the feasibility of using OI-RD for proteomics research and bacteria detection.
For visual measurement under dynamic scenarios, a zoom lens camera is more flexible than a fixed one. However, the challenges of distortion prediction within the whole focal range limit the widespread application of zoom lens cameras greatly. Thus, a novel sequential distortion correction method for a zoom lens camera is proposed in this study. In this paper, a distortion assessment method without coupling effect is depicted by an elaborated chessboard pattern. Then, the appropriate distortion correction model for a zoom lens camera is derived from the comparisons of some existing models and methods. To gain a rectified image at any zoom settings, a global distortion correction modeling method is developed with bundle adjustment. Based on some selected zoom settings, the optimized quadratic functions of distortion parameters are obtained from the global perspective. Using the proposed method, we can rectify all images from the calibrated zoom lens camera. Experimental results of different zoom lens cameras validate the feasibility and effectiveness of the proposed method.
An enzyme-free optical method is proposed for estimating high concentrations of glucose in a glucose-lactose mixture, based on a predictive equation that takes advantage of the reflective optical power observed at two discrete wavelengths. Compared to the conventional absorption spectroscopy method based on Beer's Law, which is mainly valid for concentrations below hundreds of mg/dL, the proposed scheme, which relies on reflection signals, can be applied to measure higher glucose concentrations, of even several g/dL in a glucose-lactose mixture. Two probe wavelengths of 1160 and 1300 urn were selected to provide a linear relationship between the reflective power and pure glucose/lactose concentration, where the relevant linear coefficients were derived to complete the predictive equation. Glucose concentrations from 2 to 7 g/dL in a glucose-lactose mixture were efficiently estimated, using the established predictive equation based on monitored reflective powers. The standard error of prediction was 1.17 g/dL.
Terahertz (THz) generation by a GaP ridge waveguide with a collinear modal phase-matching scheme based on cascaded difference frequency generation (DFG) processes is theoretically analyzed. The cascaded Stokes interaction processes and the cascaded anti-Stokes interaction processes are investigated from coupled wave equations. THz intensities and quantum conversion efficiency are calculated. Compared with non-cascaded DFG processes, THz intensities from 11-order cascaded DFG processes are increased to 5.48. The quantum conversion efficiency of 177.9% in cascaded processes can be realized, exceeding the Manley-Rowe limit.
The distributions of (or constraints for) amplitude and phase around C-points, including Lemon, Mon-Star and Star, are studied. A Cartesian coordinate system with origin at the C-point is established. Four curves, where the azimuthal angles of polarization ellipses are 0°, 45°, 90°, and 135° respectively, are used to determine the distributions. Discussions of these constraints illustrate why Mon-Star is rarer than Lemon or Star in experiments. The transformation relationships between these three polarization singularities (PSs) are also discussed. We construct suitable functions for amplitude and phase according to their constraints, and simulate several PSs of particular shapes. With the development of modulation techniques for amplitude and phase, it is clear that this work is helpful for generating arbitrarily shaped C-points in experiments.
We investigated surface-roughness-dependent optical loss in a plasmonic cavity consisting of a semiconductor nanodisk/silver nanopan structure. Numerical simulations show that the quality factors of plasmonic resonant modes significantly depend on the surface roughness of the dielectric-metal interface in the cavity structure. In the transverse-magnetic-like whispering-gallery plasmonic mode excited in a structure with disk diameter of 1000 nm, the total quality factor decreased from 260 to 130 with increasing root-mean-square (rms) surface roughness from 0 to 5 nm. This quantitative theoretical study shows that the smooth metal surface plays a critical role in high-performance plasmonic devices.
We demonstrated the pretilt angle effect on the viewing angle properties of a single-domain fringe-field switching (FFS) liquid crystal (LC) mode. By performing the Poincare sphere analysis, we investigated, in detail, the origin of the viewing angle asymmetry that exists in the single-domain FFS LC mode both in the field-on and field-off states. Using this analysis, we confirmed that the pretilt angle reduces the viewing angle symmetry in the single-domain FFS LC mode. Finally, we examined the effect of a zero pretilt angle on the viewing angle symmetry by evaluating real single-domain FFS LC cells.
We report a new all-optical flip-flop (AOFF) with a quite simple structure, using optical beating in an injection-locked Fabry-Perot laser diode (FP-LD) with optical bistability. While conventional AOFF methods using an injection-locked FP-LD require additional devices such as secondary FP-LDs or polarization controllers for reset operation, the proposed method can be implemented using only a single commercially available FP-LD with set and reset signals. The optical beating induces intensity fluctuations inside the FP-LD, and releases the locking state to the reset state. Even though we demonstrated the AOFF at 100 Mbit/s, we expect that its operation rate could extend to 10 Gbit/s, according to the limit of the FP-LD’s frequency response.
We synthesized Er3+-Yb3+, Pr3+-Yb3+, and Er3+-Pr3+-Yb3+ -doped oxyfluoride glass ceramics containing CaF2 nanocrystals by proper thermal treatments. Spectral characteristics of down- and up-converted emissions in three kinds of glass ceramics under 365-nm and 980-nm excitations were compared and explained by cross relaxations, excited-state absorptions, and energy-transfer processes between different ions. The huge reduction of up -conversion emission in the triply doped glass ceramics under 980-nm excitation compared to the Er3+-Yb3+ codoped one was explained by the split pump power and the direct energy transfer from Er3+ to Pr3+ ions. Increasing Yb3+ concentration from 2% to 10% in the triply doped glass ceramics showed more than quadratic enhancement of the absorbed power, and we explained it by the enhanced energy-transfer efficiency from Yb3+ to Er3+ ions. We also observed enhanced up-converted emissions of Er3+ and Pr3+ ions in three kinds of glass ceramics under
Transparent film heaters (TFHs) based on Joule heating are currently an active research area. However, TFHs based on an indium tin oxide (ITO) monolayer have a number of problems. For example, heating is concentrated in only part of the device. Also, heating efficiency is low because it has high sheet resistance (R-s). To address these problems, this study introduced hybrid layers of ITO/Ag/ITO deposited by magnetron sputtering, and the electrical, optical, and thermal properties were estimated for various thicknesses of the metal interlayer. The R-s, of ITO(40)/Ag/ITO(40 nm) hybrid TFHs were 5.33, 3.29 and 2.15 Omega/rectangle for Ag thicknesses of 10, 15, and 20 nm, respectively, while the R-s, of an ITO monolayer (95 nm) was 59.58 Omega/rectangle. The maximum temperatures of these hybrid TFHs were 92, 131, and 145 degrees C, respectively, under a voltage of 3 V. And that of the ITO monolayer was only 32 degrees C. For the same total thickness of 95 nm, the heat generation rate (HGR) of the hybrid produced a temperature approximately 100 degrees C higher than the ITO monolayer. It was confirmed that the film with the lowest R-s, of the samples had the highest HGR for the same applied voltage. Overall, hybrid layers of ITO/Ag/ITO showed excellent performance for HGR, uniformity of heat distribution, and thermal response time.
