With the increase of communication frequency, terahertz (THz) communication technology has been an important research field; particularly the terahertz modulator is becoming one of the core devices in THz communication system. The modulation performance of a THz communication system depends on the characterization of THz modulator. THz modulators based on different principles and materials have been studied and developed. However, they are still on the way to practical application due to low modulation speed, narrow bandwidth, and insufficient modulation depth. Therefore, we review the research progress of THz modulator in recent years and evaluate devices critically and comprehensively. We focus on the working principles such as electric, optical, optoelectrical, thermal, magnetic, programmable metamaterials and nonlinear modulation methods for THz wave with semiconductors, metamaterials, and 2D materials (such as graphene, molybdenum disulfide, and tungsten disulfide). Furthermore, we propose a guiding rule to select appropriate materials and modulation methods for specific applications in THz communication.

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS₂ and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS₂ on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS₂-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS₂ and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

This article presents a 50-Gb/s optical transmitter (TX), consisting of a 40-nm distributed CMOS driver and a 180-nm silicon-photonic modulator. A lumped-segment Mach–Zehnder modulator (LS-MZM) is developed for high bandwidth (BW) four-level pulse amplitude (PAM-4) modulation. A multi-segment driver with limiting outputs is co-designed, which is distributed into each LS-MZM segment. By grouping these LS-MSM segments in a thermometer code, high-linearity modulation is realized without the need of power-hungry high-swing linear drivers. To improve the optical PAM-4 signal integrity, in-segment multiplexing along with clock phase interpolation is adopted to synchronize the electrical and optical signals across all segments. The hybrid coupling between the driver and modulator is devised to boost the BW of the high-speed data path, while a half-rate clock and data recovery (CDR) circuit is integrated to remove the accumulated jitter. Measurements show that the TX exhibits an extinction ratio (ER) of up to 9.8 dB and a 0.99 ratio of the level mismatch. A figure-of-merit (FoM) of 1.39 pJ/bit/dB corresponds to a 682-mW power, which can be further reduced by 40%, at the cost of a degraded ER of 4 dB. The PAM-4 CDR helps to achieve $< 10^{-12}$ BER and >0.1- $\text{U}I_{\mathrm {pp}}$ jitter tolerance (JTOL) from 10 to 100 MHz.

Memristors are widely used in hardware security applications. Research progress in memristor‐based physical unclonable functions (PUFs), random number generators (RNGs), and chaotic circuits is reviewed. To enhance device security, PUFs and RNGs apply randomness of memristors and incorporate 3D crossbars to amplify the number of challenge‐response pairs and provide proof of the destruction of the key, which enables the administrator to firmly control the device information. In addition, the image encryption technique based on the chaotic system is summarized. Furthermore, an assessment of the research advancement in PUFs, RNGs, and chaotic circuits is conducted. This Review examines the characteristics, applications, progress, and challenges of memristors in hardware security and compares the benefits and limitations of different schemes as accelerators for hardware information protection.

This article presents a discrete-time second-order ΔΣ modulator for the audio applications. In this modulator, a novel dynamic amplifier is proposed to realize the switched-capacitor (SC) integrators. To eliminate the common-mode (CM) voltage drop in a closed-loop dynamic amplifier during the integration phase, without the use of additional load capacitance, the reset method for the amplifier is modified. Two auxiliary branches are introduced to enhance the settling speed of the integrator. Two different flicker noise reduction techniques (FNRTs) are developed to improve the signal-to-noise-and-distortion ratio (SNDR) (about 2 dB in the audio bandwidth). The prototype modulator is fabricated in 65-nm CMOS technology with a 0.12-mm² core area, which achieves a dynamic range (DR) of 91 dB and a peak SNDR of 89.6 dB in the 24-kHz signal bandwidth. It consumes only 49-μW power from a 0.8-V supply, translating into a Schreier figure of merit (FoM) of 176.5 dB.