Grid is a resource management technology which provides infrastructures to execute applications. Grid manages resources and provides an infrastructure composed of computing, storage and other resources. While Grid assumes existence of network which connects resources, network used to be considered as a non-manageable resource. However, in these several years, an idea and implementations to use bandwidth of network as a manageable resource have been proposed and demonstrated. Using this kind of schemes together with optical circuit (path) switching technology, a high-performance, energy-efficient and low-cost IT infrastructure can be realized. In this paper, the G-lambda project and its experiments, in which lambdas (optical paths) are reserved and used by requests from applications and middleware, are introduced.