The densification of radio access and the massive deployment of radio heads calls for efficient optical fronthaul technologies. The adoption of analogue radio-over-fiber schemes promises greatly simplified equipment that can be distributed at the antenna sites for the purpose of radio signal conditioning and electro-optic conversion. Towards this direction, we propose and experimentally evaluate a full-duplex interface at the intersection between the optical and the radio frequency layer, aiming at bidirectional radio signal transmission over a single wavelength (1577 nm) and a single carrier frequency (5.375 GHz). Analogue coherent optical reception is performed through an electro-absorption modulated laser, which is employed as multi-functional element that accomplishes wavelength re-use for full-duplex radio-over-fiber transmission. The directional split is shifted to the electrical domain through adoption of a crosstalk-cancelling circulation stage, ensuring compatibility with a high dynamic power range for the simultaneous transmission and reception of up- and downlink radio signals, respectively, without the need for further duplexing methods subject to frequency translation or time slotting. We prove that margins of >2% in terms of error vector magnitude can be accomplished for an unpaired spectral configuration, where down- and uplink radio signals share the same spectrum in the optical and electrical domains.
- Enabling Digital Technologies