Free-space optical communications hold promising advantages, including a large bandwidth, access to license-free spectrum, high data rates, quick and simple deployment, low power consumption, and relaxed quality requirements. Nevertheless, key technical challenges remain, such as a higher transmission efficiency, a lower transmission loss, and a smaller form factor of optical systems. Here, we demonstrate the viability of circular-polarization-multiplexed multi-channel optical communication using metasurfaces alongside a photonic-crystal surface-emitting laser (PCSEL) light source at wavelength of 940 nm. Through the light manipulation with metasurface, we split the linearly polarized incidence into left and right circular polarizations with desired diffraction angles. Such orthogonal polarization states provide a paradigm of polarization division multiplexing technique for light communication. The PCSEL light source maintains a low divergence angle of about 0.373 degrees after passing through an ultra-thin metasurface without further bulky collimator or light guide, making end-to-end (E2E) and device-to-device (D2D) communications available in a compact form. Both light source and modulated polarized light exhibit a − 3 dB bandwidth over 500 MHz, with successful 1 Gbit/s transmission demonstrated in eye diagrams. Our results affirm that metasurface effectively boosts transmission capacity without compromising the light source's inherent properties. Future metasurface designs could expand channel capacity, and its integration with PCSEL monolithically holds promise for reducing interface losses, thereby enhancing efficiency.
It is published in Discover Nano.
自由空間光通訊具有許多有利特點，包括大帶寬、使用無需許可的頻譜、高數據傳輸速率、快速簡便的部署、低功耗以及較寬鬆的質量要求。然而，仍然存在一些關鍵的技術挑戰，如提高傳輸效率、降低傳輸損耗以及光學系統體積更小等。在這裡，我們展示了使用「超穎介面 (metasurface)」和「光子晶體面射型雷射（PCSEL）」光源（波長 940 nm）實現的圓偏振多通道光通信的可行性。通過 metasurface 對光的操控，我們將線性偏振入射光分成具有所需繞射角的左右圓偏振。這樣的正交偏振狀態提供了一種光通訊的偏振多路複用技術範例。PCSEL 光源通過超薄 metasurface 後的發散角度僅約為 0.373 度，無需進一步龐大的聚焦鏡或光波導，實現了超微小型的端對端（E2E）和設備對設備（D2D）通訊。光源和調製的偏振光都表現出超過 500 MHz 的 -3 dB 帶寬，並在眼圖中成功演示了 1 Gbit/s 的傳輸。我們的結果證實了 metasurface 有效地提升了傳輸容量，而不影響光源固有屬性。未來的 metasurface 設計可能擴大通道容量，並與 PCSEL 的積體化有望減少界面損耗，從而提高效率。
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