We introduce and experimentally demonstrate a modified Kramers-Kronig (KK) receiver with direct detection (DD) to realize an accurate optical field reconstruction at low carrier-to-signal power ratio (CSPR) condition. In our scheme, an exponential operation is applied to a single-sideband (SSB) signal, rather than a continuous-wave tone adding method in the conventional KK scheme. By this means, the minimum phase condition (MPC) is inherently satisfied, thus the optical field can be reconstructed accurately through KK relation at a low CSPR, leading to a high receiver sensitivity in a DD system. A proof-of-concept experiment is conducted, in which an SSB signal is generated based on an 8-GBaud 16-quadrature amplitude modulation (QAM) data stream and then is transmitted over an 80-km single mode fiber (SMF). By using the modified KK technique, 1.1- and 0.9-dB sensitivity improvements are achieved in the optical back-to-back and after the fiber transmission cases, respectively. The proposed and the conventional KK schemes show similar BER performances at the optimum CSPR value with a high received optical power. In addition, we perform numerical simulations to study the impacts of bandwidth limitation and chromatic dispersion on the proposed minimum phase signal.

中文翻译：

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基于改进型直接检测 KK 接收器的低 CSPR 条件下的精确场重建

我们介绍并实验证明了一种改进的 Kramers-Kronig (KK) 接收器，它具有直接检测 (DD)，可在低载波信号功率比 (CSPR) 条件下实现精确的光场重建。在我们的方案中，指数运算应用于单边带 (SSB) 信号，而不是传统 KK 方案中的连续波音调添加方法。通过这种方式，固有地满足最小相位条件（MPC），因此可以在低 CSPR 下通过 KK 关系准确地重建光场，从而导致 DD 系统中的高接收器灵敏度。进行了概念验证实验，其中基于 8 GBaud 16 正交幅度调制 (QAM) 数据流生成 SSB 信号，然后通过 80 公里单模光纤 (SMF) 传输。通过使用改进的 KK 技术，1。在光背对背和光纤传输后分别实现了 1-dB 和 0.9-dB 的灵敏度改进。所提出的和传统的 KK 方案在具有高接收光功率的最佳 CSPR 值下显示出相似的 BER 性能。此外，我们执行数值模拟来研究带宽限制和色散对建议的最小相位信号的影响。