In this paper, we investigate the design and performance of multi-path routing in optical wavelength division multiplexed (WDM) networks, that support traffic grooming. A circuit-switched network is considered, where connection requests arriving to the network have to be allotted an end-to-end path carrying the requested bandwidth. Traffic grooming implies that the capacity of a wavelength on a fiber link (e.g. OC-48) will be shared among several lower capacity connections (e.g. OC-3). In order to increase the network performance in terms of improved blocking probability and also to support survivable operation, a connection is split into multiple smaller sub-streams and carried on multiple sub-paths from source to destination. This is based on the Virtual Concatenation (VCAT) mechanisms used in SONET/SDH networks. One important constraint is that the differential delay among the sub-paths should be limited (e.g. 25 ms, 45 ms, etc.). In this paper, we consider mechanisms for splitting a connection request while maintaining the differential delay constraint. In particular, we study two schemes: even splitting of connection bandwidth among the constituent sub-paths; and uneven splitting of connection bandwidth. The work also considers sub-paths that are not necessarily link-disjoint. The performance analysis shows that the uneven splitting mechanism can substantially improve performance in terms of blocking probability (and other metrics) compared to the even splitting mechanism. © 2010 IEEE.