Simple Self-Homodyne Detection Scheme for Optical OFDM With Inserted Pilot Subframes and Application in Optical Access Networks

In this paper, a simple self-homodyne detection scheme is proposed and experimentally demonstrated for applications in optical access networks. Unmodulated pilot subframes are periodically inserted and interleaved with data subframes to form an orthogonal frequency-division multiplexing (OFDM) signal. Owing to the coherence between the embedded pilot and data subframes, a Mach-Zehnder delay interferometer with a free spectral range equal to the frequency of the subframe is deployed for the self-homodyne detection of the OFDM signal. It saves the local oscillator and optical hybrid, which are usually used in a conventional coherent receiver, thus reducing the hardware complexity and implementation cost. Meanwhile, the digital signal processing (DSP) for the self-homodyne detection is free from carrier-frequency-offset compensation and carrier-phase estimation, reducing the complexity, power consumption, and latency of the system. It also allows the use of a low-cost laser source as the source for the downstream signal. The proposed scheme provides a cost-effective and energy-efficient downstream solution for optical access networks, owing to the hardware saving and complexity reduction in DSP. A 10-Gb/s OFDM downstream transmission over a 20-km standard single-mode fiber is experimentally demonstrated with an error-free operation, using both a 10-MHz distributed feedback laser and a 100-kHz external cavity laser as downstream laser sources.