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298nm. The results show that the freeform surface with high-precision and large-steepness can be machined by UASTS turning technology on mold steel.We present an ultrasensitive enhanced fabrication-tolerance refractometer utilizing the polarimetric interference of a tapered PANDA-air-hole fiber (PAHF). To obtain high birefringence and unique group birefringence, the PAHF is specially designed by introducing double air holes into the cladding. Ultrahigh sensitivity can be achieved by reducing the group birefringence difference to zero, defined as birefringent dispersion turning point (BDTP). By modifying the diameter of PAHF, the birefringent dispersion can be effectively manipulated to reduce the group birefringence difference. In this way, the workable diameter range for realizing the ultrahigh sensitivity is twice as large as that of conventional microfibers. Additionally, the ultrasensitive wavelength band is dramatically expanded by at least 600 nm, enabling a compact structure and a flexible fiber-length design. Due to the tunable dispersion optimization, the distinctive properties of ultrahigh sensitivity, enhanced fabrication tolerance, and broadband operation can be achieved. We experimentally verified the ultrahigh refractive index sensitivity of 47223 nm/RIU around the BDTP, and the experimental results matched well with the simulations.Yellow Luminescence (YL) band and blue luminescence (BL) band in a studied unintentionally doped GaN sample show a transient behaviour where the observed luminescence intensities change with the exposure time of the sample under 325 nm laser beam excitation at 10-300 K. Such an intensity variation is accompanied with a red-shift for YL peak at 10-140 K and one for BL peak at 140 K. We propose that such behaviours are related to the chemical transformations of YL-related CN and CNON defects, and BL-related CN-Hi and CNON-Hi defects during the exposure.In this paper, we propose chaotic compressive sensing (CS) encryption algorithms for orthogonal frequency division multiplexing passive optical network (OFDM-PON), aiming at compressing the transmitted data and enhancing the security of data transmission. Bitstream transmission using CS directly is restricted due to its inability to satisfy the sparsity in neither time nor frequency domain. While the sparsity of the transmitted data can be constructed when transmitting the multimedia. A sensor can be then used to identify whether the data is multimedia. If it is, the CS technique is used, and the sensor's result is set as side information inserted into the pilot and transmitted to the terminal simultaneously. For encryption processing, a 2-dimensional logistic-sine-coupling map (2D-LSCM) is used to generate pseudo-random numbers to construct the first row of a measurement matrix to encrypt the system. Four transform formats are then applied to generate the sparsity of the transmitted data. Due to the restriction of data transmission in the physical layer, the discrete cosine transform (DCT) is chosen to conduct the CS technique. Four approximation algorithms are also proposed to optimize the performance of compressing the length of bits. We find that 'Round + Set negative to 0' shows the best performance. The combination of this chaotic CS encryption technique with the OFDM-PON systems saves the bandwidth and improves the security.In this paper, we propose a generalized Kretschmann configuration that employs a metagrating to replace the prism, realizing polarization-controlled efficient and unidirectional surface plasmon polariton (SPP) excitation. This dielectric phase gradient metagrating on the top surface of a silica substrate is designed to deflect incident light, which subsequently launches SPP wave by means of momentum matching on the metal film coated on the bottom surface. A series of metagratings is designed to enable the SPP excitation by circularly or linearly polarized incident light. The flexibility and tunability of this design to efficiently control SPPs show potential to find wide applications in diverse integrated optics and SPP devices.Metasurface color filters (MCFs) have attracted considerable attention thanks to their compactness and functionality as a candidate of an optical element in a miniaturized image sensor. However, conventional dielectric and plasmonic MCFs that have focused on color purity and efficiency cannot avoid reflection in principle, which degrades image quality by optical flare. Here, we introduce absorptive-type MCFs through truncated-cone hyperbolic metamaterial absorbers. By applying a particle swarm optimization method to design multiple parameters simultaneously, the proposed MCF is theoretically and numerically demonstrated in perceptive color on CIELAB and CIEDE2000 with suppressed-reflection. Then, a color filter array is numerically proven in 255 nm of sub-pixel pitch.As 5G communication matures, the requirement for advanced radio access networks (RAN) drives the evolution of optical access networks to support these needs. Basic RAN functions, mobile front-haul to the backbone and interconnected front-end remote radio units, must support and enable data rate surges, low-latency applications, RF coordination, etc. Wavelength division multiplexed optical access networks (WDM-OANs) provide sufficient network capacity to support the addition of RAN services, especially in unused portions of WDM. We propose and demonstrate a method for RAN overlay in WDM-OANs that employ distributed carriers. In such systems, the carrier is modulated at the central office for direct-detected downstream digital data services; later the same carrier is remodulated for the uplink. We propose the use of silicon photonics to intercept the downstream and add 5G signals. We examine the distributed-carrier power budget issues in this overlay scenario. The carrier power must be harvested for direct detection of both digital and RoF services, and yet hold in reserve sufficient power for the uplink remodulation of all services. We concentrate on the silicon photonics subsystem at the remote node to add RoF signals. We demonstrate the overlay with a fabricated chip and study strategic allocations of carrier power at the optical network units housing the radio units to support the overlay. After the successful drop and reception of both conventional WDM-OAN and the newly overlaid RoF signals, we demonstrate sufficient carrier power margin for the upstream remodulation.From a physical-optics point of view, the far-field light-shaping problem mainly requires a Fourier pair synthesis. The Iterative Fourier Transform Algorithm (IFTA) is one of the algorithms capable of realizing this synthesis, however, it may lead to stagnation problems when the fields of the Fourier pair exhibit a homeomorphic behavior. To overcome this problem, we use a mapping-type relation for the Fourier pair synthesis. [https://www.selleckchem.com/products/elacestrant.html see more] This approach results in a smooth phase response function in a single step, without requiring an iterative procedure. The algorithm is demonstrated with examples and the results are investigated via physical-optics modeling techniques.Optical 3D shape measurements, such as fringe projection profilometry (FPP), are popular methods for recovering the surfaces of an object. However, traditional FPP cannot be applied to measure regions that contain strong interreflections, resulting in failure in 3D shape measurement. In this study, a method based on single-pixel imaging (SI) is proposed to measure 3D shapes in the presence of interreflections. SI is utilized to separate direct illumination from indirect illumination. Then, the corresponding points between the pixels of a camera and a projector can be obtained through the direct illumination. The 3D shapes of regions with strong interreflections can be reconstructed with the obtained corresponding points based on triangulation. Experimental results demonstrate that the proposed method can be used to separate direct and indirect illumination and measure 3D objects with interreflections.We experimentally demonstrate an improved orthogonal frequency division multiplexing (OFDM) into the pulse width modulation (PWM) scheme for the X-ray communication (XCOM). The scheme is insensitive to the nonlinearity of the grid-controlled X-ray tube with switching 'on' and 'off' between two points. The dependence of this system's bit-error-rate (BER) performances on the data rates and the working parameters including the anode voltage and filament current of the grid-controlled X-ray tube are studied. The OFDM-PWM scheme reaches the data rate of 360 kbps at a BER of the forward error correction threshold of 3.8 × 10-3 over a 5 cm air channel. In addition, an experiment aided by density-based spatial clustering of applications with noise nonlinear compensation is carried out, and the results demonstrate the improvements in Q-factor by 0.62 dB.Germanium (Ge) is an attractive material for monolithic light sources on a silicon chip. Introduction of tensile strain using a silicon nitride (SiNx) stressor is a promising means for Ge-based light sources due to the enhancement of direct band gap recombination. We propose a device structure that enables current injection from a silicon-on-insulator (SOI) diode to a Ge waveguide with a SiNx stressor formed by a simple fabrication process. Direct-band-gap electroluminescence and direct-band-gap shrinkage due to the applied SiNx stressor was confirmed. Intensity of electroluminescence from the Ge waveguide with the SiNx stressor was about three times higher than that corresponding to the device without the SiNx stressor.We describe a mid-infrared pump - terahertz-probe setup based on a CO2 laser seeded with 10.6 μm wavelength pulses from an optical parametric amplifier, itself pumped by a TiAl2O3 laser. The output of the seeded CO2 laser produces high power pulses of nanosecond duration, which are synchronized to the femtosecond laser. These pulses can be tuned in pulse duration by slicing their front and back edges with semiconductor-plasma mirrors irradiated by replicas of the femtosecond seed laser pulses. Variable pulse lengths from 5 ps to 1.3 ns are achieved, and used in mid-infrared pump, terahertz-probe experiments with probe pulses generated and electro-optically sampled by the femtosecond laser.Rhenium disulfide (ReS2) has emerged as a promising material for future optoelectric applications due to its extraordinary electrical, mechanical, and optoelectrical properties. However, the ReS2-based photodetectors are severely restricted by their slow response speed (&gt;10 s). Here, we demonstrate a high-performance polarization-sensitive photodetector based on suspended ReS2. Such a transistor shows an n-type behavior with the mobility of about 14.1 cm2V-1s-1, an on/off ratio of 105, and a responsivity of 0.22 A/W. Benefitting from well-developed contact between Au and the ReS2 channel and reduced interface scattering from the Si substrate, the response time of the device can be as short as 83.5 and 325.3µs, respectively, which are three orders of magnitude faster than that reported earlier. Furthermore, the suspended ReS2 photodetector also has the capability to detect polarized light (Imax/Imin ≈ 1.4 at 532 nm) due to the robust in-plane anisotropy of the material. These findings offer an efficient approach for improving the performance of ReS2-based photodetectors.