Net 562.5-Gbps/$\lambda$ 2 × 2 MIMO Optical Wireless Transmission System at 322 GHz With Sampling Frequency Offset Compensation

The Terahertz (THz) band as an underdeveloped frequency range, possesses a significant bandwidth and holds great potential for valuable applications. Photonics-aided THz wireless transmission techniques that can generate and detect broadband signal have bright application prospects in the future. While the larger bandwidth usually refers to higher sampling rates of digital-to-analog converter (DAC) and analog-to-digital converter (ADC), which are more difficult to keep the actual sampling frequency align with the nominal frequency. The sampling frequency offset (SFO) between DAC and ADC in the transceiver will seriously degrade the performance of these asynchronous optical communication systems. The SFO-induced impairments and their compensation methods have been widely studied in optical multi-carrier systems, while rarely investigated in signal-carrier systems. In this paper, we successfully realize a 60-GBaud 64-QAM THz-wave signal delivery at 322 GHz in a 2 × 2 MIMO dual-polarization system, with 20-km wired and 3-m wireless distance, achieving a record-breaking single-wavelength net rate of 562.5 Gbps. To achieve this, digital signal processing (DSP) based digital-interpolation (DI) SFO method and other advanced DSP methods are applied. The SFO between DAC and ADC in the transceiver reaching up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>20 parts per million (ppm) in nominal case can be compensated to as if case with SFO of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 0.2 ppm and satisfy the bit error rate (BER) threshold. To the best of our knowledge, this currently represents the highest achievable single-lane net rate in short-range single-wavelength THz wireless transmission systems.