Abstract: An apparatus for measuring a water temperature in a pipe in which water is carried includes: a temperature measuring sensor configured to be installed on an external surface of the pipe to measure an external surface temperature of the pipe; and a water temperature detector configured to receive the external surface temperature from the temperature measuring sensor, and to determine whether there is water-flow in the pipe based on the external surface temperature at a first measurement time and the external surface temperature at a second measurement time.

Abstract: Disclosed is an optical transmission system that executes optical transmission using OSSB (Optical Signal Side Band) modulation. This optical transmission system includes a transmitter having an OSSB modulation optical transmitting unit for selectively generating an OSSB signal in an upper or lower sideband according to an input data signal; an optical transmission medium for transmitting an optical signal output from the transmitter; and a receiver prepared at a receiving end of the optical transmission medium and including an optical filter for selectively passing only a specific sideband of the optical signal transmitted from the transmitter and outputting a digital optical signal corresponding thereto and an optical receiving unit for photo-electrically converting the optical signal output from the optical filter to restore the data signal.