Silicon photonics holds great promise for low-cost large-scale photonic integration. In its future development, integration density will play an ever-increasing role in a way similar to that witnessed in integrated circuits. Waveguides are perhaps the most ubiquitous component in silicon photonics. As such, the density of waveguide elements is expected to have a crucial influence on the integration density of a silicon photonic chip. A solution to high-density waveguide integration with minimal impact on other performance metrics such as crosstalk remains a vital issue in many applications. Here, we propose a waveguide superlattice and demonstrate advanced superlattice design concepts such as interlacing-recombination that enable high-density waveguide integration at a half-wavelength pitch with low crosstalk. Such waveguide superlattices can potentially lead to significant reduction in on-chip estate for waveguide elements and salient enhancement of performance for important applications, opening up possibilities for half-wavelength-pitch optical-phased arrays and ultra-dense space-division multiplexing.

An ultracompact silicon electro-optic modulator was experimentally demonstrated based on silicon photonic crystal (PhC) waveguides for the first time to our knowledge. Modulation operation was demonstrated by carrier injection into an $80\mu \mathrm{m}$ -long silicon PhC waveguide of a Mach-Zehnder interferometer (MZI) structure. The $\pi$ phase shift driving current, $I_{\pi }$ , across the active region is as low as $0.15\mathrm{mA}$ , which is equivalent to a $V_{\pi }$ of $7.5\mathrm{mV}$ when a $50\Omega$ impedance-matched structure is applied. The modulation depth is 92% operating at $1567\mathrm{nm}$ .

A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density $(\sim {10}^4\mathrm{A}∕{\mathrm{cm}}^2)$ exists for achieving gigahertz modulation in the $p\text{-}i\text{-}n$ diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage $\left(2\mathrm{V}\right)$ by scaling down the interaction length to $80\mu \mathrm{m}$ .

Unmanned aerial vehicle (UAV)-assisted multiaccess edge computing (MEC) technology has garnered significant attention and has been successfully implemented in specific scenarios. The optimization of the network energy consumption in the relevant scenarios is essential for the whole system performance due to the constrained energy capacity of UAVs. However, the dynamic changes in MEC network resources make the energy consumption optimization a challenge. In this paper, a multi-UAV-multiuser MEC model is established to assess the system energy consumption, and the optimization problem of multi-UAV cooperation strategies is formulated base on the model. Then, a multi-agent deep deterministic policy gradient (MADDPG) algorithm based on deep reinforcement learning (DRL) is employed to resolve the above optimization problem. Each UAV is equivalent to a single agent that cooperates with other agents to train actors and critic evaluation networks to accomplish collaborative decision-making. In addition, a prioritized experience replay (PER) scheme is used to improve the convergence of the training process. Simulation results show that the impact of changes in different network resources on the network energy consumption by comparing the performance of different algorithms. The findings presented in this paper serve as a valuable reference for future work on system performance optimization, specifically in terms of energy efficiency.

Ultracompact thermooptically tuned photonic crystal waveguide (PCW) silicon-on-insulator Mach-Zehnder interferometers (MZIs) have been proposed and fabricated. A novel thermal design was employed to improve the device switching performance. Both steady-state and transient thermal analyses were performed to evaluate the thermal performance of the thermooptic MZIs. A switching time less than 20 mus has been experimentally achieved, which clearly demonstrated the speed advantage using the new heating approach. The active length of the PCW-based MZIs was 80 mum, nearly one order of magnitude shorter than the conventional silicon waveguide-based MZIs. A maximum modulation depth of 84% for a switching power of 78 mW was obtained at a wavelength of 1548 nm

To study the size effects in ferroelectric thin film, we measured the optical transmittance and Raman spectra in BaTiO₃ thin films deposited by the rf-magnetron sputtering technique on fused quartz and (111) Si substrates. A variation in the energy gap and Raman peaks with film thickness and grain size was observed and the possible origin was analyzed.