Abstract: An apparatus and method for depositing multiple layer, thin optical films onto a substrate and an optical filter made thereby. The apparatus includes a vacuum chamber; moving means for moving the substrate between regions of the vacuum chamber; material depositing means within each region for depositing a film of material on the substrate; a reactive substance source for introducing a reactive substance into each region so as to react with the material as it is deposited in that region; and control means for controlling the degree of such reaction in one region relative to the other, to obtain desired stoichiometry in the deposited materials.

Abstract: A dynamic frame length slotted ALOHA communication system has a central station which monitors the traffic congestion and determines the optimum frame length. This is transmitted to the sub-stations in the form of a service information message when there is to be a change in the frame length but not, as is conventional, at the beginning of each frame. The amount of time available for the useful transmission of communication messages is thus optimized.

Abstract: In a dynamic frame length slotted ALOHA system the synchronizing signals are transmitted by a base station at different frequencies (each having a period equivalent to a multiple of the time slot period). The different frequencies denote different frame lengths and the central stations detect these frequencies and select a frame length accordingly.