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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. 

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 experimentally demonstrate a low-cost transfer process of GeSn ribbons to insulating substrates for short-wave infrared (SWIR) sensing/imaging applications. By releasing the original compressive GeSn layer to nearly fully relaxed state GeSn ribbons, the room-temperature spectral response of the photodetector is further extended to 3.2 μm, which can cover the entire SWIR range. Compared with the as-grown GeSn reference photodetectors, the fabricated GeSn ribbon photodetectors have a fivefold improvement in the light-to-dark current ratio, which can improve the detectivity for high-performance photodetection. The transient performance of a GeSn ribbon photodetector is investigated with a rise time of about 40 μs, which exceeds the response time of most GeSn (Ge)-related devices. In addition, this transfer process can be applied on various substrates, making it a versatile technology that can be used for various applications ranging from optoelectronics to large-area electronics. These results provide insightful guidance for the development of low-cost and high-speed SWIR photodetectors based on Sn-containing group IV low-dimensional structures.