In this Letter, we report a combination of non-invasive analysis of the cross-section structure, phase, and chemical composition combining optical coherence tomography (OCT) with spectroscopic methods such as X-ray analytical microscope (μ-XRF) and micro-Raman spectroscopy (μ-RS), which allow us to effectively and conveniently identify the colorants used for each color region and the glass-making process of an ancient multicolored stratified glass eye bead. The results reveal that the sophisticated colors of the glass bead arise from the transition metals and chemical compound crystals deliberately added in the same base glass and carefully adjusted by the glass maker to obtain four colors. We also propose and discuss the provenance of the glass bead. It was probably introduced to China through the Northern Silk Road from Egypt or the Eastern Mediterranean areas about 1400 years ago. The combined multi-analytical technique is the promising approach for precious cultural heritage research.

The gravimeter based on atom interferometry has potential wide applications on building gravity networks and geophysics as well as gravity assisted navigation. Here, we demonstrate experimentally a portable atomic gravimeter operating in the noisy urban environment. Despite the influence of noisy external vibrations, our portable atomic gravimeter reaches a sensitivity as good as 65μGal/Hz and a resolution of 1.1 μGal after 4000 s integration, being comparable to state-of-the-art atomic gravimeters. Our achievement paves the way for bringing the portable atomic gravimeter to field applications.

A plethora of physical-layer techniques aim to enhance the performance of communication systems in several ways. Spectral efficiency and security are on the top of the list of enhancements; however, both are isolated and antagonistic islands of research. Augmented communication (ACom) is introduced in this Letter as the first technique that aims to combine these two enhancements in visible light communications (VLCs). The dividends of the proposed concept are demonstrated via simulations and the performance is experimentally validated. Results show that ACom can simultaneously provide the high spectral efficiency and the resistance to eavesdropping, while introducing minimal signal-to-noise ratio penalties.

We analyze a feasible high-sensitivity homodyne coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK). A fourth-power phase-lock loop based on a digital look-up table is used. Considering the non-negligible loop delay, we optimize the loop natural frequency. Without error correction coding, a sensitivity of ?37 dBm/?35 dBm is achieved, while the bit error rate is below 10^?9 at 2.5 Gbaud/5 Gbaud rate. For the QPSK communication system, the bit rate is twice the baud rate. The loop natural frequency is 0.647 Mrad/s, and the minimized steady-state phase-error standard deviation is 3.83°.

A new architecture, naked-eye ghost imaging via photoelectric feedback, is developed that avoids computer algorithm processing. Instead, the proposed scheme uses a photoelectric feedback loop to first realize the correlation (multiplication) process of the traditional ghost imaging system. Then, the vision persistence effect of the naked eye is exploited to implement the integral process and to generate negative images. Two kinds of feedback circuits, the digital circuit and the analog circuit, are presented that can achieve a feedback operation. Based on this design, high-contrast real-time imaging of moving objects is obtained via a special pattern-scanning architecture on a low-speed light-modulation mask.

Detailed power and spectral analysis of a diode-pumped c-cut Pbnm 3 at.% Tm-doped yttrium aluminum perovskite (Tm:YAP) laser in a continuous wave (CW) operation is presented. The laser was experimentally examined in terms of the dependence on the transmittance and radius of curvature of the output coupling mirrors. At room temperature, for an output coupling transmission of 10.8%, the maximum output power of 6.35 W was obtained under a total absorbed pump power of 13.67 W with an optical-to-optical conversion efficiency of 46.5%. The highest slope efficiency of 60.4% was indicated. A detailed spectral analysis was presented. For its dependence on output coupler transmission, the Tm:YAP laser generates wavelengths at approximately 1940 nm or 1990 nm.

A novel four light ray path test method for measuring residual reflectance has been presented. Residual reflectance spatial distribution at a cladding interface was measured using the technique. Residual reflectance could be on the order of 10^?5 by matching the refractive index of Nd:glass, polymer, and cladding glass and eliminating defects in the adhesive layer. Residual reflection spatial distribution appears to be similar to Newton rings due to the edge surface flatness. The relationship between the residual reflectance and the edge surface flatness was discussed, and the results revealed that the edge surface flatness is very important during the cladding process.

The broadband photochromic effect on undoped and rare-earth-doped lead lanthanum zirconate titanate (PLZT) ceramics was studied under the illumination of ultraviolet light at 360 nm. The photocarriers’ trapping and detrapping processes of thermal disconnected traps played the vital role in both darkening and bleaching processes. The interaction between photocarrier traps and rare-earth ion energy levels was demonstrated, which influenced the photochromatic darkening performance greatly. The transformation of photoluminescence spectra in Er³⁺-doped PLZT ceramics also improved the physical picture of the trap’s distribution of the materials. This work could be used to modulate the photoluminescence and lasing behavior.

The study of structured laser beams has been one of the most active fields of research for decades, particularly in exploring laser beams with orbital angular momentum. The direct generation of structured beams from laser resonators is deeply associated with the formation of transverse modes. The wave representations of transverse modes of spherical cavities are usually categorized into Hermite–Gaussian (HG) and Laguerre–Gaussian (LG) modes for a long time. Enormous experimental results have revealed that the generalized representation for the transverse modes is the Hermite–LG (HLG) modes. We make a detailed overview for the theoretical description of the HLG modes from the representation of the spectral unitary group of order 2 in the Jordan–Schwinger map. Furthermore, we overview how to derive the integral formula for the elliptical modes based on the Gaussian wave-packet state and the inverse Fourier transform. The relationship between the HLG modes and elliptical modes is linked by the quantum Fourier transform. The most striking result is that the HLG modes can be exactly derived as the superposition of the elliptical modes without involving Hermite and Laguerre polynomials. Finally, we discuss the application of the HLG modes in characterizing the propagation evolution of the vortex structures of HG beams transformed by an astigmatic mode converter. This overview certainly provides not only a novel formula for transverse modes, but also a pedagogical insight into quantum physics.

In a single nanoscale device, surface plasmon polaritons (SPPs) have potential to match the different length scales associated with photonics and electronics. In this Letter, we propose an accurate design of a plasmonic metasurface Luneburg lens (PMLL) accommodating SPPs. The simulations indicate that the full width at half-maximum is 0.42 μm, and the focus efficiency is 78%. The characters of a PMLL have robustness to manufacturing errors. The PMLL is applied in a 10 μm long compact coupler model, which couples the SPPs to the 40 nm wide output waveguide. The couple efficiency is higher than that of a conventional taper coupler in a broad bandwidth. The design is compatible with standard lithography technology.

We experimentally demonstrate for the first time an active all-optical ultrafast modulation of electromagnetically induced transparency-like effect in a hybrid device of sapphire/Si/metamaterial. From numerical simulations, it can be deducted that the tuning process is attributed to the coupling between the dark mode existing in split-ring resonators and the bright mode existing in cut wire resonators. The transmission amplitude modulation is accompanied by the slow-light effect. In addition, the ultrafast formation process is measured to be as fast as 2 ps. This work should make an important contribution to novel chip-scale photonic devices and terahertz communications.

We demonstrate a tunable terahertz (THz) absorber based on an indium tin oxide (ITO) metamaterial. The upper ITO cross-shaped metasurface with different arm lengths is fabricated by direct femtosecond laser etching. The thickness of the middle dielectric layer is only 60 μm, which makes the absorber very transparent and flexible. The experimental results show that the THz resonant peaks have a high performance near 1 THz. By setting spacers of different thicknesses between the middle layer and the ITO mirror, a new type of tunable THz absorber is proposed. Its absorption peak frequency can be continuously adjusted from 0.92 to 1.04 THz between TE and TM polarization. This transparent THz metamaterial absorber is expected to be widely used in THz imaging, sensing, and biological detection.

We propose a photonic-assisted single system for measuring the frequency and phase noise of microwave signals in a large spectral range. Both the frequency and phase noise to be measured are extracted from the phase difference between the signal under testing and its replica delayed by a span of fiber and a variable optical delay line (VODL). The system calibration, frequency measurement, and phase noise measurement are performed by adjusting the VODL at different working modes. Accurate frequency and phase noise measurement for microwave signals in a large frequency range from 5 to 50 GHz is experimentally demonstrated.

Inhomogeneity and low efficiency are two important factors that hinder the wide application of laser-induced periodic surface structures. Two-beam interference is commonly used to fabricate gratings with interference periods. This study reports regular and uniform periodic ripples fabricated efficiently by the interference of two femtosecond laser beams via a cylindrical lens. The interference period is adjusted to be an integer multiple of the wavelength of a surface plasmon polariton. Regular and uniform subwavelength nanogratings (RUSNGs) on a silicon wafer of a diameter of 100 mm are fabricated with a scanning velocity of 6–9 mm/s. Bright and pure colors (including purple, blue, and red) are demonstrated on different patterns covered with RUSNGs.

Optical edge detection, a part of image processing, plays an important role in extracting image information used in optical analog computation. In this Letter, we raise a new way to realize optical edge detection. This design is based on two liquid crystal polarization gratings with a period of 2.2 mm, which function as a spatial differentiator. We experimentally demonstrate broadband optical detection and real-time adjustable resolution. The proposed method takes advantage of the convenience to use, simple fabrication process, and real-time tunable resolution. It may guide more significant applications in the optical field and other practical scenarios like machine vision in computers.