We propose a simple approach to realize integrated broadband passive optical nonreciprocal transmission (ONT) using a nonlinear attenuator (NA) and a linear attenuator (LA). In a proof-of-concept experiment based on single-mode fiber, we use a conventional erbium-doped fiber (EDF) as a NA and a variable optical attenuator (VOA) as a LA, and realize large nonreciprocal transmission ratio (NTR) up to 25 dB. Signaling performance of 20 Gbit/s quadrature phase-shift keying (QPSK) signal and 2 Gbit/s 4-level pulse amplitude modulation (4-PAM) signal is also examined. Our architecture may provide a practical answer to the challenge of ONT in photonic integrated circuits.
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