OPTICAL SENSOR FOR DETECTING OPENING AND SHUTTING OF HAND HOLE LID

PROBLEM TO BE SOLVED: To provide an optical sensor for detecting opening and shutting of the lid of a hand hole, having a simple structure, whose loss is small is which is low-cost. SOLUTION: A signal light is made incident on each sensor body 10 by using an approach cable 12, which and connected to an optical cable via an optical connection part. The signal light, which is reflected by an FBG 16, is received by a measuring device. The reflected light can be always received, irrespective of whether the lid 11 of the hand hole is open or shut. Since strain according to the opened or shut of the lid 11 is applied to the FBG 16 by the strain application member 21 of a strain application means 14, the center frequency state of the reflected light changes. By detecting a change in center frequency, the open or shut state of the lid 11 can be detected without having to use optical couplers, the connection loss of the optical detection sensor is reduced by its portion and the cost of the sensor can be reduced.