ABSTRACTThe transmission reach of signals in opticaltransmission systems is limited. To go beyondthese transparent reach limits, signal regeneration is necessary to re-amplify, reshape, andretime the optical signals. Translucent opticalnetworks are a type of optical transport networkspecifically devised to address such a concern byallowing for sparse but strategic signal regeneration in the network. Translucent optical networksseek a graceful balance between network designcost and service provisioning performance, andcan achieve performance comparable to that ofan all-electronic switching network, but requiringfar fewer signal regenerators. Despite massiveprogress, there are many outstanding issuesregarding the implementation of translucent networks planning and operation. This articlereviews a range of translucent optical networksand discusses various research issues, particularlyinvolving network planning, lightpath routing andwavelength assignment, and network survivability.We also suggest other potential research topicssuch as traffic grooming, fault detection, andmulticasting for translucent networks.