1 Metro-Access and Short Range Systems, Department of Photonics Engineering, Technical University of Denmark2 Networks Technology and Service Platforms, Department of Photonics Engineering, Technical University of Denmark3 Department of Photonics Engineering, Technical University of Denmark4 University of California
QAM modulation utilizing subcarrier frequency lower than the symbol rate is both theoretically and experimentally investigated. High spectral efficiency and concentration of power in low frequencies make sub-cycle QAM signals attractive for optical fiber links with direct modulated light sources. Real-time generated 10-Gbps 4-level QAM signal in a 7.5-GHz bandwidth utilizing subcarrier frequency at a half symbol rate was successfully transmitted over 20-km SMF using an un-cooled 1.5-μm VCSEL. Only 2.5-dB fiber transmission power penalty was observed with no equalization applied.
Optics Express, 2013, Vol 21, Issue 2, p. 1830-1839