An All-Optical Carrier Recovery Scheme for Access Networks With Simple ASK Modulation

We theoretically investigate and experimentally demonstrate a scheme for all-optical carrier recovery in loopback access networks that avoids orthogonal or complex modulation formats for the downstream or upstream signals. The applied technique is based on a passive resonating circuit that is capable of recovering the optical carrier of the amplitude-shift-keyed downstream signal for remodulation with a reflective modulator as upstream transmitter enabling full-duplex 10 Gb/s operation. The scheme is compared with alternative pattern suppression techniques based on optical gain saturation and electro-optical feed-forward injection for the stringent requirements of next-generation access networks, namely, an extended loss budget and high upstream data rates. Operation at downstream modulation depths of ~3 dB is reported with the feed-forward approach, while higher modulation depths of up to 9 dB are demonstrated with the all-optical carrier recovery technique, for which the dependence on longer sequences of consecutive identical bits is investigated. Finally, the feasibility of the all-optical downstream cancelation technique for optical access networks is evaluated in a wavelength division multiplexed passive optical network, showing full-duplex transmission with margins of at least 9 dB.