1. An apparatus comprising: a path computation element (PCE) configured to: communicate with a node comprising a plurality of wavelength converters (WCs); and compute a lightpath that passes through the node using a WC pool information based on a dynamic WC pool model, wherein the dynamic WC pool model comprises information regarding WC pool usage state represented using a WC pool usage state vector, wherein the information regarding WC pool usage state is communicated to the PCE using a WC usage state Type-Length-Value (TLV) that indicates whether each of the WCs is reserved for wavelength conversion or idle at a specified time, and wherein the WC usage state TLV comprises a WC set field that specifies at least one WC and a WC usage state bitmap that indicates whether each WC in the WC set field is available for wavelength conversion.