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In a reciprocal system, all the wave travels in the same way backward as forward. When the exchange between the source and detectors result in different transmittance, non-Hermiticity is granted but the nonreciprocity needs to be carefully evaluated. Although most of the integrated circuits are reciprocal, unexpected nonreciprocal response may emerge in the system, especially the tunable components containing asymmetrically coupled resonators, traveling wave electrodes and hysteresis response. The nonreciprocity may result in unexpected signal distribution, distortion and errors in analogue circuits of electrical and photonic networks. With proper engineering, the nonreciprocity can be leveraged and optimized for suppressing the laser noise in photonic systems as isolators, reducing the circuits duplication as circulators. The radio-frequency nonreciprocity can be used for protecting the high power amplifiers from oscillation and damage. Asymmetric coupling can also be useful in simplifying the circuit complexity and reducing crosstalk in the optical interconnect transceiver circuits. 

We demonstrated low insertion loss fully integrated photonic crystal cavity with on-chip metalens coupling, with experimentally measured total quality factor of 10⁴. 

Abstract Chalcogenide-based nonvolatile phase change materials (PCMs) have a long history of usage, from bulk disk memory to all-optic neuromorphic computing circuits. Being able to perform uniform phase transitions over a subwavelength scale makes PCMs particularly suitable for photonic applications. For switching between nonvolatile states, the conventional chalcogenide phase change materials are brought to a melting temperature to break the covalent bonds. The cooling rate determines the final state. Reversible polymorphic layered materials provide an alternative atomic transition mechanism for low-energy electronic (small domain size) and photonic nonvolatile memories (which require a large effective tuning area). The small energy barrier of breaking van der Waals force facilitates low energy, fast-reset, and melting-free phase transitions, which reduces the chance of element segregation-associated device failure. The search for such material families starts with polymorphic In₂Se₃, which has two layered structures that are topologically similar and stable at room temperature. In this perspective, we first review the history of different memory schemes, compare the thermal dynamics of phase transitions in amorphous-crystalline and In₂Se₃, detail the device implementations for all-optical memory, and discuss the challenges and opportunities associated with polymorphic memory. 

We observe ultra-low propagation and coupling loss (<2dB) in topological photonic crystal waveguide with integrated metalens coupling. 

Here we performed the first space experiments of photonic integrated circuits, revealing the critical roles of energetic charged particles. The year-long cosmic radiation does not change carrier mobility but reduces free carrier lifetime, resulting in unchanged electro-optic modulation efficiency and well-expanded optoelectronic bandwidth. 

We demonstrated an insertion loss of 2.2 dB and a back-excitation suppression of 5.1 dB over the 35 nm bandwidth with on-chip asymmetric metasurface. 

Abstract Metasurface has emerged as a powerful platform for controlling light at subwavelength thickness, enabling new functionalities for imaging, polarization manipulation, and angular momentum conversion within a flat surface. An integrated asymmetric metasurface simultaneously achieving broadband, low loss forward power transmission, and significant back reflection suppression in multi‐mode waveguides is explored. The tapering along the direction of light propagation leads to low loss and space‐efficient mode conversion. Enhanced by a double‐flipped structure, a thin (2.5 µm) metasurface can simultaneously achieve high conversion efficiency (>80%), and back‐reflection efficiency of 90% over a 200 nm wavelength range. Such single‐side reflectors can be one of the enabling components for gain‐integrated adaptive optics on a chip. 

We demonstrate a silicon photonic passive PT-symmetric structure operating at an exceptional point, with dynamic mode-splitting tunability enabled by a local heater.