frequency offset

IEEE Photonics Technology Letters

The recent decade has witnessed the evolution and enormous demand of the high-capacity data center interconnect (DCI), in such application scenarios spectral efficiency, optical field recovery and cost-effectiveness are highly desirable. Compared to coherent detection, direct detection does not require local oscillators, resulting in a simpler transceiver structure and thus a lower-cost solution for DCIs. To overcome chromatic dispersion induced power fading, field recovery enabled by direct detection has drawn extensive research interests. To date, various proposed direct detection schemes concentrate mainly on single sideband (SSB) modulation. Compared to double sideband (DSB) modulation, however, one sideband of SSB is unfilled and hence SSB poses higher requirement on the receiver bandwidth. Besides, the complexity and cost of implementing precisely aligned optical filtering poses burden for adopting SSB. Accordingly, we recently proposed a novel direct detection scheme called carrier assisted differential detection (CADD), which can realize the field recovery of complex-valued DSB signals with the aid of an optical carrier. In this letter, we carry out the first-time experimental demonstration of the CADD receiver. 54-Gb/s OFDM signals are transmitted over 160-km standard single-mode fiber with digital chromatic dispersion compensation at the receiver, indicating the ability to reconstruct optical field of DSB signals. For signal-signal beat interference (SSBI) which extensively exists in direct detection, experimental results show that merely two iterations of cancellation are sufficient to mitigate SSBI. More importantly, compared to various SSB based receiver schemes, the requirement of receiver bandwidth for DSB based CADD scheme is relaxed by 41%.

Experimental Demonstration of Complex-Valued DSB Signal Field Recovery via Direct Detection