Abstract: A watertight structure in a flap gate 1 provided with a weight-balance supported door 2 to open an opening 200 of a floodgate 100 in a state in which no external force other than gravity is applied, wherein the structure has: a gap opening-closing member 72 that oscillates in the water flow direction and opens and closes a gap C, wherein the gap C is provided between the lower edge 23 of the door 2 and the bottom face 300 of the floodgate 100 in a state in which the door 2 is blocking the floodgate 100; and an opening operation assist means 73 for operating the gap opening-closing member 72 so as to be in an open state by lifting same toward the outer water side.

Abstract: A photonic frequency routing type time division highway switch which requires no conflict control at the input side, and incorporates no inherent splitting loss of the optical signal power. The switch is formed by a plurality of tunable frequency convertors for allocating frequency channels to the optical signals on the input highways at each timeslot; a frequency router for connecting the optical signals outputted from the frequency convertors to its outputs according to the frequency channels allocated to the optical signals at each timeslot; and a plurality of frequency multiplexed output buffers for outputting the optical signals outputted from the frequency router to the output highways such that a plurality of optical signals with different frequency channels which are in an identical timeslot are outputted at different timeslots.

Abstract: A photonic frequency division multiplexed FIFO buffer capable of realizing a multiple input one output FIFO buffer or a one input one output FIFO buffer by using only a small number of buffers. This buffer is formed by a plurality of loop shaped optical waveguide delay lines for storing the input optical signals from the time division multiplexed input highway, which are connected in series by a plurality of 2.times.2 optical switches for selectively transferring the input optical signals among the loop shaped optical waveguide delay lines. This buffer also includes a 1.times.2 frequency channel selector, connected at a last stage of the loop shaped optical waveguide delay lines, for selectively outputting optical signals in specific frequency channels among the input optical signals stored by the last stage of the loop shaped optical waveguide delay lines as the output optical signals to the timeslots on the time division multiplexed output highway.

Abstract: A photonic frequency division multiplexed FIFO buffer capable of realizing a multiple input one output FIFO buffer or a one input one output FIFO buffer by using only a small number of buffers. This buffer is formed by a plurality of loop shaped optical waveguide delay lines for storing the input optical signals from the time division multiplexed input highway, which are connected in series by a plurality of 2.times.2 optical switches for selectively transferring the input optical signals among the loop shaped optical waveguide delay lines. This buffer also includes a 1.times.2 frequency channel selector, connected at a last stage of the loop shaped optical waveguide delay lines, for selectively outputting optical signals in specific frequency channels among the input optical signals stored by the last stage of the loop shaped optical waveguide delay lines as the output optical signals to the timeslots on the time division multiplexed output highway.

Abstract: A FIFO buffer in which respective portions are controlled in a distributed manner is provided. In the FIFO buffer, a number of loop circuits having delay elements are provided in which respective loop circuits are connected to one another in cascade manner. Additionally provided are a number of traffic control units for controlling the signal traffic between respective neighboring loop circuits. In the case where no signal is fed back to a traffic control unit from the output side and also a new signal is transmitted thereto from the input side, the traffic control unit transmits the new signal to the loop circuit which is on the output side. In the case where any signal is fed back to a traffic control unit from the output side and also a new signal is transmitted thereto from the input side, the traffic control unit again transmits the fed-back signal to the loop circuit which is on the output side and transmits the new signal to the loop circuit which is on the input side.