We study routing and wavelength assignment for a circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM network. In a conventional WR network, an entire wavelength is assigned to a given session (or circuit). This can lead to lower channel utilization when the individual sessions do not need the entire channel bandwidth. We consider a TDM-based approach to reduce this inefficiency. In this architecture, each wavelength is partitioned in the time-domain into fixed-length time-slots organized as a TDM frame. Multiple sessions are multiplexed on each wavelength by assigning a sub-set of the TDM slots to each session. Thus, given a session request with a specified bandwidth, the goal is to determine the route, wavelength and time-slot assignment (RWTA) that meets the request. This is similar to routing and wavelength assignment in WR networks. We present a family of RWTA algorithms and study the blocking performance. We use the existing shortest-path routing algorithm with a new link cost function, least resistance weight (LRW) function, that incorporates wavelength utilization information. We employ the known least loaded (LL) wavelength selection and present three variations of the least-loaded time-slot (LLT) algorithm. Simulation based analyses are used to compare the proposed TDM architecture to traditional WR networks, both with and without wavelength conversion. The goal is to compare the benefits of TDM and wavelength conversion towards improving performance in WR networks. The results show that the use of TDM provides substantial gains, especially for multi-fiber networks.