I. Introduction
The wavelength-division-multiplexed passive optical network (WDM-PON) is a promising solution to provision broadband access to business and residential subscribers. In order to enable more flexible and reliable data delivery, a self-protected survivable network architecture which can also support simultaneous unicast and multicast data streams is highly desirable. Recently, several interesting schemes [1]–[5] have been proposed to overlay a multicast data stream onto a conventional WDM-PON. The multicast data in either differential phase-shift keying (DPSK) format [1], inverse-return-to-zero (IRZ) format [2], or sub-carrier multiplexed (SCM) form [3], were modulated onto all of the downstream amplitude-shift keying (ASK) unicast data wavelengths by adjusting the extinction ratio of the unicast data. However, the unicast data might suffer from system penalty due to their reduced extinction ratio. In [4], [5], unicast data and multicast data are superimposed onto different sub-carriers generated from a single optical carrier. Such approaches avoid the power penalty from the reduced extinction ratio of the unicast data and therefore improve the system performance. However, none of these schemes have considered the survivability of the whole network, and a single fiber failure may interrupt the high speed services and cause enormous loss in data and business.