Harmonic and Intermodulation Distortion Analysis in Directly Modulated Lasers Over Local and Remote Photonically Generated Millimeter-Wave Signals

This paper presents a comprehensive analytical derivation and experimental evaluation of the impact of harmonic and intermodulation distortion on data transmission over local and remote photonically generated millimeter wave (mmW) signals over an optical fronthaul based on a directly modulated laser (DML) and carrier-suppressed (CS) external modulation for frequency up-conversion. Frequency response of different harmonic distortion (HD) and intermodulation (IMD) terms are measured for a 40 GHz signal under back-to-back, local and remote scenarios for the sake of comparison. Furthermore, measurements of error vector magnitude (EVM) of single and multiband QPSK signals are presented in good agreement with the frequency measurements for
$(2{{\boldsymbol{\omega }}_{\mathbf{k}}})$
,
$({{{\boldsymbol{\omega }}_{\mathbf{k}}} - {{\boldsymbol{\omega }}_{\mathbf{l}}}})$
and
$({{{\boldsymbol{\omega }}_{\mathbf{k}}} + {{\boldsymbol{\omega }}_{\mathbf{l}}}})$
-type distortion terms. Wideband signals with in-band distortion and multiband signals with out-of-band distortion are examples that need to be transmitted over local generation mmW approach in cloud-radio access networks (C-RAN), in spite of the high performance achieved by remote generation approach due to the combined effect of fiber dispersion and laser chirp. Results will serve as valuable guidelines for 6G networks deployment in concrete application scenarios.