On-chip integration of 2D Van der Waals germanium phosphide (GeP) for active silicon photonics devices

Non-reciprocal response in silicon photonic resonators integrated with 2D CuCrP2S6 at short-wave infrared

Achieving non-reciprocal optical behavior in integrated photonics with high efficiency has long been a challenge. Here, we demonstrate a non-reciprocal magneto-optic response by integrating multilayer 2D CuCrP2S6 (CCPS) onto silicon microring resonators (MRRs). Under an applied magnetic field, the CCPS intralayer ferromagnetic ordering, characterized by easy-plane magneto-crystalline anisotropy, induces asymmetrical modal responses in the clockwise (CW) and counterclockwise (CCW) light propagation directions. The proposed configuration achieves a low insertion loss ranging from 0.15 dB to 1.8 dB and a high isolation ratio of 28 dB at 1550 nm. Notably, it exhibits a significant resonance wavelength splitting of 0.4 nm between the counter propagation directions, supporting a 50 GHz optical bandwidth. Operating directly in the transverse electric (TE) mode, it aligns with the main polarization used in silicon photonics circuits, eliminating the need for additional polarization management. The device is ultra-compact, with a 2D flake interaction length ranging from 22 µm to 55 µm and a thickness between 39 nm and 62 nm. Its operation range covers the entire C-band with a bandwidth of up to 100 nm. These attributes make our hybrid CCPS/Si device ideal for advanced non-reciprocal optical applications in the short-wave infrared (SWIR) spectrum, crucial for enhancing the resilience of optical systems against back-reflections.

Electro-optic tuning in composite silicon photonics based on ferroionic 2D materials

Tunable optical materials are indispensable elements in modern optoelectronics, especially in integrated photonics circuits where precise control over the effective refractive index is essential for diverse applications. Two-dimensional materials like transition metal dichalcogenides (TMDs) and graphene exhibit remarkable optical responses to external stimuli. However, achieving distinctive modulation across short-wave infrared (SWIR) regions while enabling precise phase control at low signal loss within a compact footprint remains an ongoing challenge. In this work, we unveil the robust electro-refractive response of multilayer ferroionic two-dimensional CuCrP2S6 (CCPS) in the near-infrared wavelength range. By integrating CCPS into silicon photonics (SiPh) microring resonators (MRR), we enhance light-matter interaction and measurement sensitivity to minute phase and absorption variations. Results show that electrically driven Cu ions can tune the effective refractive index on the order of 2.8 × 10-3 RIU (refractive index unit) while preserving extinction ratios and resonance linewidth. Notably, these devices exhibit low optical losses and excellent modulation efficiency of 0.25 V.cm with a consistent blue shift in the resonance wavelengths among all devices for either polarity of the applied voltage. These results outperform earlier findings on phase shifters based on TMDs. Furthermore, our study demonstrates distinct variations in electro-optic tuning sensitivity when comparing transverse electric (TE) and transverse magnetic (TM) modes, revealing a polarization-dependent response that paves the way for diverse applications in light manipulation. The combined optoelectronic and ionotronic capabilities of two-terminal CCPS devices present extensive opportunities across several domains. Their potential applications range from phased arrays and optical switching to their use in environmental sensing and metrology, optical imaging systems, and neuromorphic systems in light-sensitive artificial synapses.

Unexpected doping effects on phonon transport in quasi-one-dimensional van der Waals crystal TiS3 nanoribbons

Doping usually reduces lattice thermal conductivity because of enhanced phonon-impurity scattering. Here, we report unexpected doping effects on the lattice thermal conductivity of quasi-one-dimensional (quasi-1D) van der Waals (vdW) TiS3 nanoribbons. As the nanoribbon thickness reduces from ~80 to ~19 nm, the concentration of oxygen atoms has a monotonic increase along with a 7.4-fold enhancement in the thermal conductivity at room temperature. Through material characterizations and atomistic modellings, we find oxygen atoms diffuse more readily into thinner nanoribbons and more sulfur atoms are substituted. The doped oxygen atoms induce significant lattice contraction and coupling strength enhancement along the molecular chain direction while have little effect on vdW interactions, different from that doping atoms induce potential and structural distortions along all three-dimensional directions in 3D materials. With the enhancement of coupling strength, Young's modulus is enhanced while phonon-impurity scattering strength is suppressed, significantly improving the phonon thermal transport.