A dynamically adjustable ultra-wideband metamaterial perfect absorber (MPA) is proposed which consists of three resonance rings based on vanadium dioxide (VO₂) and a metal ground layer separated by a dielectric spacer. The simulation results show that the terahertz (THz) absorption bandwidth of more than 90% absorptance reaches 3.30 THz, which covers from 2.34 to 5.64 THz, under different incident polarization angles. The range is better than that of previous VO₂-based reports. Moreover, when the conductivity of VO₂ changes from 200 S/m to 2×10⁵ S/m, the absorption peak intensity can be adjusted continuously from 4% to 100%. The key is to optimize the geometric structure through interference cancellation and impedance matching theory, to achieve better absorption bandwidth and efficiency. Besides, the terahertz absorber has a wide-angle absorption effect both in TE and TM waves. Thus, the designed absorber may have many potential applications in modulating, sensing and imaging technology.

Based on the transverse electric (TE)/transverse magnetic (TM) polarization diversity in plasmonic Bragg gratings, a compact TM-pass/TE-stop polarizer is theoretically proposed on thin-film lithium niobate on insulator (LNOI) platforms. By introducing a large misalignment between metal gratings on both sides of the LNOI waveguide, we demonstrate a polarizer with a high extinction ratio of 20 dB, a low insertion loss of 2.5 dB, a wide waveband from 1.48 to 1.62 μm, and a compact size of only 23 μm on simulation.

A broadband adjustable absorber operating in the terahertz (THz) range is presented based on a vanadium dioxide (VO₂) multiple ring structure with a certain gap design. The dynamic absorption regulation of the absorber is realized by utilizing the phase-change characteristics of VO₂, which is easily affected by external temperature. The simulation results show that when the external temperature reaches 350 K, the conductivity of VO₂ can reach 2 × 10⁵ S/m, and the absorber can obtain an absorption efficiency of over 90% from 3.01 THz to 7.27 THz. At this time, the absorption bandwidth reaches 4.26 THz with 82.9% of the relative bandwidth. When the external temperature reaches 300 K, the conductivity changes to 200 S/m, and the absorption efficiency is less than 4%, indicating the strong THz absorption dynamic adjustable ability. Further, through analyzing the optimal impedance matching and the electric field distribution under different conductivities, the broadband absorption mechanism of the absorber can be obtained. Finally, this paper shows that the absorption spectrum cannot be influenced by small angle incidences in both polarization modes. Therefore, the ultra-wideband adjustable absorber is expected to have applications in the terahertz fields of detecting, modulating, and switching.

A wide-spectrum, ultra-stable optical frequency comb (OFC) module with 100 GHz frequency intervals based on a quantum dot mode locked (QDML) laser is fabricated by our lab, and a scheme with 12.5 Gb/s multi-channel broadcasting transmission for free-space optical (FSO) communication is proposed based on the OFC module. The output power of the OFC is very stable, with the specially designed circuit and the flatness of the frequency comb over the span of 6 nm, which can be limited to 1.5 dB. Four channel wavelengths are chosen to demonstrate one-to-many channels for FSO communication, like optical wireless broadcast. The outdoor experiment is established to test the bit error rate (BER) and eye diagrams with 12.5 Gb/s on-off keying (OOK). The indoor experiment is used to test the highest traffic rate, which is up to 21 Gb/s for one-hop FSO communication. To the best of our knowledge, this scheme is the first to propose the realization of one-to-many broadcasting transmission for FSO communication based on the OFC module. The advantages of integration, miniaturization, channelization, low power consumption, and unlimited bandwidth of one-to-many broadcasting communication scheme, shows promising results on constructing the future space-air-ground-ocean (SAGO) FSO communication networks.

In this paper, a 200-Gb/s free-space optical (FSO) wavelength division multiplexing (WDM) transmission architecture based on multiwavelength directly modulated transmitter optical sub-assemblies for 5G wireless networks has been proposed and demonstrated experimentally. Pulse amplitude modulation-4 (PAM-4) modulation format is adopted in our scheme to further improve system capacity. In order to demonstrate the feasibility of our scheme, the outdoor experiments with 25 Gb/s PAM-4 are tested in free space. With 8 × 25 Gb/s ~50-m outdoor transmission between the two buildings, the eye diagrams and bit error rates (BERs) are tested for one-hop system and forwarding system, respectively. For one-hop system, clear eye diagrams and stable BER performance are demonstrated in all the wavelengths. For the forwarding system, the values of BER with eight channels are measured lasting for 30 min that range from 1E-2 to 1E-3. The experimental results show that the scheme is feasible in FSO transmission system for 5G wireless networks. The advantages of integration, channelization, miniaturization, and low power consumption of the FSO WDM scheme present a promising result on constructing the future fronthaul/backhaul link for wireless cellular networks and optical access network extension.

A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module. Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals. Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion. The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 5.2 GHz and 7.8 GHz or not. Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO. The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible.