A computer-implemented method, comprising: identifying a new circuit to be added to a mesh optical network having a plurality of optical links (201, 203, 205, 207, 209, 211, 213, 215), each optical circuit including a source node (102, 104, 106, 108, 110, 702) and a destination node (102, 104, 106, 108, 110, 708) between which an optical signal carried over the optical circuit is not converted to an electrical signal; identifying a set of potential paths for the new circuit through the mesh optical network, wherein identifying the set of potential paths comprises identifying a subset of paths having a path length within a configured percentage of a smallest path length identified between the source node and the destination node, wherein path length is measured in terms of total optical fiber length along the respective paths; for each optical link in each identified potential path, determining respective costs (2001, 2003, 2005, 2007) for a plurality of frequency slots of allocating the new circuit to a potential path including the optical link, wherein the cost of allocating a given frequency slot on a given optical link is determined in part based on the lengths of optical circuits that can traverse the given optical link using that frequency slot; calculating total cost values (3001, 3101, 3201, 3301) for allocating available frequency slots over each of the identified potential paths for the new circuit based on the costs determined for the frequency slots for each optical link along the potential paths; selecting one of the identified potential paths and one or more of the available frequency slots for the new circuit based on the calculated total cost values; and communicating routing and spectrum allocation instructions based on the selected path and the selected one or more frequency slots to a plurality of nodes in the network to implement the new circuit. identifying a new circuit to be added to a mesh optical network having a plurality of optical links (201, 203, 205, 207, 209, 211, 213, 215), each optical circuit including a source node (102, 104, 106, 108, 110, 702) and a destination node (102, 104, 106, 108, 110, 708) between which an optical signal carried over the optical circuit is not converted to an electrical signal; identifying a set of potential paths for the new circuit through the mesh optical network, wherein identifying the set of potential paths comprises identifying a subset of paths having a path length within a configured percentage of a smallest path length identified between the source node and the destination node, wherein path length is measured in terms of total optical fiber length along the respective paths; for each optical link in each identified potential path, determining respective costs (2001, 2003, 2005, 2007) for a plurality of frequency slots of allocating the new circuit to a potential path including the optical link, wherein the cost of allocating a given frequency slot on a given optical link is determined in part based on the lengths of optical circuits that can traverse the given optical link using that frequency slot; calculating total cost values (3001, 3101, 3201, 3301) for allocating available frequency slots over each of the identified potential paths for the new circuit based on the costs determined for the frequency slots for each optical link along the potential paths; selecting one of the identified potential paths and one or more of the available frequency slots for the new circuit based on the calculated total cost values; and communicating routing and spectrum allocation instructions based on the selected path and the selected one or more frequency slots to a plurality of nodes in the network to implement the new circuit.