Demonstration of an Optical Parametric Oscillator (OPO)-Based High-Power Data Transmitter for a 10-Gbit/s QPSK Mid-IR Coherent Free-Space Link Through Fog

Compared to near-infrared (Near-IR) wavelengths, mid-infrared (Mid-IR) transmission windows typically have lower atmospheric attenuation and better penetration through hazy conditions that can enable efficient free-space communication systems. We demonstrate a 10-Gbit/s Mid-IR coherent link through emulated fog using an optical parametric oscillator (OPO) to generate a Mid-IR quadrature phase shift keying (QPSK) channel. At the transmitter, we generate a QPSK data channel at ∼1064 nm using a phase modulator. Subsequently, the data channel is converted by the OPO to a Mid-IR wavelength (e.g., ∼3400 nm) with ∼100-mW power. At the receiver, the Mid-IR signal is converted to the C-band and detected by a coherent detector. Our results show that bit-error rates (BERs) of the detected Mid-IR QPSK signal can reach below 20% soft-decision forward error correction (SD-FEC) limit under a fog with ∼18-dB Mid-IR power loss, while the same fog causes ∼40-dB loss for a ∼1550-nm Near-IR data channel.