A planar-integrated optical system (PIOS) represents powerful optical imaging and information processing techniques and is a potential candidate for the realization of a three-dimensional (3D) integrated optoelectronic intelligent system. Coupling the optical wave carrying information into a planar transparent substrate (typically fused silica) is an essential prerequisite for the realization of such a PIOS. Unlike conventional grating couplers for nano-waveguides on the silicon-on-insulator platform, the grating couplers for PIOS enable to obtain a higher design freedom and to achieve much higher coupling efficiency. By combining the rigorous coupled wave algorithm and simulated annealing optimization algorithm, a high-efficiency asymmetric double-groove grating coupler is designed for PIOS. It is indicated that, under the condition of the normal incidence of TE polarization, the diffraction efficiency of the -1st order is over 95%, and its average value is 97.3% and 92.8% in the C and C+L bands. The simulation results indicate that this type of grating coupler has good tolerance and is expected to be applied in optical interconnections, waveguide-based augmented reality glasses, and planar-integrated 3D interconnection optical computing systems.

A spectrally sliced heterodyne coherent receiver (SHCR) employing four balanced photodetectors and analog-to-digital converters with half of the signal bandwidth is proposed to complete the signal reception and field recovery. We first numerically characterize the performance of SHCR compared with an intradyne coherent receiver and then validate the principle of the SHCR in a proof-of-concept single-polarization experiment. A 60 GBaud 16-quadrature amplitude modulation transmission is experimentally demonstrated over 80 km standard single-mode fiber with a bit-error-rate of 8.5×10-4 below the 7% hard-decision forward error correction threshold of 3.8×10-3. The SHCR offers a low-cost, hybrid-free, and channel-skew-tolerant candidate for data center interconnects.

A real-time imaging system based on a compact terahertz laser is constructed by employing one off-axis parabolic mirror and one silicon lens. Terahertz imaging of water, water stains, leaf veins, human hairs, and metal wire is demonstrated. An imaging resolution of 68 µm is achieved. The experiments show that this compact and simplified imaging system is suitable for penetration demonstration of terahertz light, water distribution measurement, and imaging analysis of thin samples.

Snapshot spectral ghost imaging, which can acquire dynamic spectral imaging information in the field of view, has attracted increasing attention in recent years. Studies have shown that optimizing the fluctuation of light fields is essential for improving the sampling efficiency and reconstruction quality of ghost imaging. However, the optimization of broadband light fields in snapshot spectral ghost imaging is challenging because of the dispersion of the modulation device. In this study, by judiciously introducing a hybrid refraction/diffraction structure into the light-field modulation, snapshot spectral ghost imaging with broadband super-Rayleigh speckles was demonstrated. The simulation and experiment results verified that the contrast of speckles in a broad range of wavelengths was significantly improved, and the imaging system had superior noise immunity.

Bilayer graphene, which is highly promising for electronic and optoelectronic applications because of its strong coupling of the Dirac–Fermions, has been studied extensively for the emergent correlated phenomena with magic-angle manipulation. Due to the low energy linear type band gap dispersion relationship, graphene has drawn an amount of optoelectronic devices applications in the terahertz region. However, the strong interlayer interactions modulated electron-electron and electron-phonon coupling, and their dynamics in bilayer graphene have been rarely studied by terahertz spectroscopy. In this study, the interlayer interaction influence on the electron-electron and the electron-phonon coupling has been assigned with the interaction between the two graphene layers. In the ultrafast cooling process in bilayer graphene, the interlayer interaction could boost the electron-phonon coupling process and oppositely reduce the electron-electron coupling process, which led to the less efficient thermalization process. Furthermore, the electron-electron coupling process is shown to be related with the electron momentum scattering time, which increased vividly in bilayer graphene. Our work could provide new insights into the ultrafast dynamics in bilayer graphene, which is of crucial importance for designing multi-layer graphene-based optoelectronic devices.

Film thickness measurement can be realized using white light interferometry, but it is challenging to guarantee high precision in a large range of thicknesses. Based on scanning white light interferometry, we propose a spectral-temporal demodulation scheme for large-range thickness measurement. The demodulation process remains unchanged for either coatings or substrate-free films, while some adjustments are made according to the estimated optical thickness. Experiments show that the single-point repeatabilities for 500 nm SiO2 coating and 68 µm substrate-free Si film are no more than 0.70 nm and 1.22 nm, respectively. This method can be further developed for simultaneous measurement of surface profile and film thickness.

Beam quality improvements by a large margin for signal and idler beams of a high energy 100 Hz KTiOAsO4 (KTA) non-critical phase matching (NCPM) optical parametric oscillator (OPO) were demonstrated using an unstable resonator configuration instead of a plane-parallel one. Theoretically, influences of cavity lengths and transmission of an output coupler on the OPO conversion efficiency for both were numerically simulated. For OPO based on an unstable resonator with a Gaussian reflectivity mirror, the maximum pulse energies at the signal (1.53 µm) and idler (3.47 µm) were about 75 mJ and 26 mJ, respectively. The corresponding beam quality factors of the signal were Mx2 = 9.8 and My2 = 9.9, and Mx2 = 11.2 and My2 = 11.5 for the idler. As a comparison, 128 mJ of signal and 48 mJ of idler were obtained with the plane-parallel resonator, and the M2 factors of the signal were Mx2 = 39.8 and My2 = 38.4, and Mx2 = 32.1 and My2 = 31.4 for the idler. Compared with a plane-parallel cavity, over eight times and three times brightness improvements were realized for the signal and idler light, respectively.

Large-size Al3+/Nd3+ co-doped silica glass with 5000 ppm Nd3+ and 50,000 ppm Al3+ doping concentrations was prepared by the modified sol-gel method combined with high-temperature melting and molding technology. Electron probe micro-analyzer tests indicated that high doping homogeneity was achieved with this sample preparation method. The spectral properties of the Nd3+ ions were evaluated. Nd3+-doped silica fiber (NDF) with a core-to-clad ratio of 20/125 μm was drawn from the preform with the Al3+/Nd3+ co-doped silica glass as the core. In the laser oscillation experiment, a maximum output power of 14.6 W at 1.06 μm with a slope efficiency of 39.6% was obtained from the NDF pumped by a commercial 808 nm laser diode. To the best of our knowledge, this is the highest laser power reported for an NDF operated at 1060 nm and prepared by a non-chemical vapor deposition method. In the master oscillator power amplifier experiment, a maximum power of 16.6 W corresponding to a slope efficiency of 30.5% at 1061 nm was also demonstrated. The laser performance of the NDF exhibited the great advantages and potential of the modified sol-gel method in fabricating Nd3+-doped silica glass for a new type of NDFs like large mode area fibers and fibers with large diameter ratio of core/cladding.

We demonstrate the dynamic coloration of polymerized cholesteric liquid crystal (PCLC) networks templated by the “wash-out/refill” method in the presence of organic compounds. The reflection colors were modulated by two key approaches, that is, the injection of mutually soluble organic fluids into a microfluidic channel and the diffusion of volatile organic compounds (VOCs). The reversible tuning of reflected colors with central wavelengths between ∼450 nm and ∼600 nm was achieved by alternative injection of nematic liquid crystal E7 (nav = 1.64) and benzyl alcohol (n = 1.54) using syringe pumps. The fascinating iridescence with reflection centers from ∼620 nm to ∼410 nm was presented from the volatilization and diffusion of alcohol as a model VOC. Additionally, the flow velocity of fluid and the diffusion time were adjusted to explore the underlying mechanism for the dynamic coloration of cholesteric networks. This work is expected to extend the study of PCLCs as a dynamically tunable optofluidic reflector, visually readable sensor, or compact anti-counterfeit label in response to organic compounds.

Zeolitic imidazolate framework-8 (ZIF-8), a metal-organic framework (MOF) with a non-centrosymmetric crystal structure, exhibits nonlinear optics (NLO) properties and can act as the nanoporous matrix of guest molecules. Amorphization of ZIF-8 can be achieved by pressure or high temperature. Both crystalline and amorphous states have their inherent features for optical applications. The effects of the crystalline-amorphous transition on the structural and optical properties under pressure were investigated in detail. Amorphization leads to the destruction of the ZIF-8 lattice structure, collapse of pores, and the change of spatial symmetry, which in turn alters the NLO properties of ZIF-8 and the luminescence properties of the guest Eu cations. Our results establish the structure–optical properties relationship in the amorphization process and provide new clues in designing novel MOFs optical materials.

Lommel beams have been potential candidates for optical communication and optical manipulation, due to their adjustable symmetry of transverse intensity distribution and continuously variable orbital angular momentum. However, the wavefront of the Lommel beam is scrambled when it transmits through highly scattering media. Here, we explore the construction of Lommel beams through highly scattering media with a transmission matrix-based point spread function engineering method. Experimentally, various Lommel beams with different parameters were generated through a ZnO scattering layer by use of a digital micromirror device. The construction of Lommel beams under high scattering is expected to benefit the optical applications behind highly scattering media.

Reference frame independent and measurement device independent quantum key distribution (RFI-MDI-QKD) has the advantages of being immune to detector side loopholes and misalignment of the reference frame. However, several former related research works are based on the unrealistic assumption of perfect source preparation. In this paper, we merge a loss-tolerant method into RFI-MDI-QKD to consider source flaws into key rate estimation and compare it with quantum coin method. Based on a reliable experimental scheme, the joint influence of both source flaws and reference frame misalignment is discussed with consideration of the finite-key effect. The results show that the loss-tolerant RFI-MDI-QKD protocol can reach longer key rate performance while considering the existence of source flaws in a real-world implementation.

Conventional wavelength modulation spectroscopy (WMS) is vulnerable to the influence of low-frequency noise. Accuracy of the method highly depends on the performance of the costly lock-in amplifier. In this article, we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform (FFT). This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave. Formulation and detection procedures were presented. The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method. Second-harmonic waveforms acquired by the two means are generally consistent. The experimental study validates the obtained gas concentration from 5% to 30%, showing a good linear relationship by the proposed method. The maximum relative error on concentration extraction is 2.87%; as for conventional WMS, this value is 4.50%. The developed measurement method may have potential in computed tomography.

The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method. A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser air plasma channel. The hydrodynamic effect on plasma evolution at 1 kHz filament is included and analyzed. The measured initial peak electron density of ∼1018 cm-3 in our experimental conditions decays rapidly by nearly two orders of magnitude within 200 ps. Moreover, the plasma channel size rises from 90 µm to 120 µm as the delay time increases. The experimental observation is in agreement with numerical simulation results by solving the rate equations of the charged particles.