we propose an electrically driven electro-optical modulator integrated with the phase-change material Ge2Sb2Te5 (GST). This modulator incorporates a hybrid Si-GST-Cu waveguide with input and output Si waveguides. For the waveguide modulator with an active segment of 0.2 μm 2, the switched phase is stable with off/on extinction ratios of >5.4 dB on the entire C-band. Since the phase-change of GST only consumes energy during the stated transitions, the energy consumption per bit for this nano-size device is ideally low on the order of sub-nJ per cycle.

We present the design, fabrication, and characterization of a multi-slot photonic crystal (PhC) cavity sensor on the silicon-on-insulator platform. By optimizing the structure of the PhC cavity, most of the light can be distributed in the lower index region; thus, the sensitivity can be dramatically improved. By exposing the cavities to different mass concentrations of NaCl solutions, we obtained that the wavelength shift per refractive index unit (RIU) for the sensor is 586 nm/RIU, which is one of the highest sensitivities achieved in a non-suspended cavity. Furthermore, the size of the sensing region of the reported sensor is only 22.8 μm × 1.5 μm, making the high-sensitivity PhC cavity sensor attractive for the realization of on-chip sensor arrays.

On-chip nonvolatile photonic switches enabled by phase change materials (PCMs) are promising building blocks for power-efficient programmable photonic integrated circuits. However, large absorption loss in conventional PCMs (such as Ge₂Sb₂Te₅) interacting with weak evanescent waves in silicon waveguides usually leads to high insertion loss and a large device footprint. In this paper, we propose a 2×2 photonic switch based on two-mode interference in a multimode slot waveguide (MSW) with ultralow loss Sb₂S₃ integrated inside the slot region. The MSW supports two lowest order TE modes, i.e., symmetric TE₀₀ and antisymmetric TE₀₁ modes, and the phase of Sb₂S₃ could actively tune two-mode interference behavior. Owing to the enhanced electric field in the slot, the interaction strength between modal field and Sb₂S₃ could be boosted, and a photonic switch containing a ∼9.4 µm-long Sb₂S₃-MSW hybrid section could effectively alter the light transmission between bar and cross ports upon the phase change of Sb₂S₃ with a cross talk (CT) less than −13.6 dB and an insertion loss (IL) less than 0.26 dB in the telecommunication C-band. Especially at 1550 nm, the CT in the amorphous (crystalline) Sb₂S₃ is −36.1 dB (−31.1 dB) with a corresponding IL of 0.073 dB (0.055 dB). The proposed 2×2 photonic switch is compact in size and compatible with on-chip microheaters, which may find promising applications in reconfigurable photonic devices.

We propose a nanogap-enhanced phase-change waveguide with silicon PIN heaters. Thanks to the enhanced light-matter interaction in the nanogap, the proposed structure exhibits strong attenuation (Δα = ∼35 dB/µm) and optical phase (Δn_eff = ∼1.2) modulation at λ = 1550 nm when achieving complete phase transitions. We further investigate two active optical devices based on the proposed waveguide, including an electro-absorption modulator and a 1 × 2 directional-coupler optical switch. Finite-difference time-domain simulation of the proposed modulator shows a high extinction ratio of ∼17 dB at 1550 nm with an active segment of volume only ∼0.004λ³. By exploiting a directional coupler design, we present a 1 × 2 optical switch with an insertion loss of < 4 dB and a compact coupling length of ∼ 15 µm while maintaining small crosstalk less than −7.2 dB over an optical bandwidth of 50 nm. Thermal analysis shows that a 10 V pulse of 30 ns (1×1 modulator) and 55 ns (1×2 switch) in duration is required to raise the GST temperature of the phase-change waveguide above the melting temperature to induce the amorphization; however, the complete crystallization occurs by applying a 5 V pulse of 180 ns (1×1 modulator) and a 6 V pulse of 200 ns (1×2 switch), respectively.

In this article, the chalcogenide slot waveguide is theoretically studied, and the highest power confinement factors of the slot region and the cladding region are obtained to be 36.3% and 56.7%, respectively. A high-sensitivity chalcogenide slot microring resonator sensor is designed and fabricated by electron-beam lithography and dry etching. The structure increases the sensitivity of the sensor compared with the conventional evanescent field waveguide sensor. The cavity has achieved a quality factor of 1 × 10⁴ by fitting the resonant peaks with the Lorentzian profile, one of the highest quality factors reported for chalcogenide slot microring resonators. The sensor sensitivity is measured to be 471 nm/RIU, which leads to an intrinsic limit of detection of 3.3 × 10­⁻⁴ RIU.

We design and fabricate an on-substrate bowtie photonic crystal (PhC) cavity in silicon. By optimizing the bowtie shapes in the unit cells of the PhC cavity, the maximum of the electric field can be highly confined in the bowtie tips. Due to such confinement, an ultra-low mode volume of ∼0.1(λ/n_Si)³ is achieved, which is more than an order of magnitude smaller than the previous on-substrate nanobeam cavities. An ultra-high quality (Q) factor as large as 10⁶ is predicted by simulation, and up to $1.4 \times {10^4}$ is measured in experiment. The observation of pronounced thermo-optic bistability is consistent with the strong confinement of light in the cavities.