LIGHT DELAYING UNIT

PROBLEM TO BE SOLVED: To provide a light delaying unit capable of varying delay quantities at high accuracy. SOLUTION: When air is supplied to an air cylinder 6 as a bobbin moving mechanism, the interval between both bobbins 2, 4 is expanded. When the interval between them is expanded, since a strain in a longitudinal direction is applied to an optical fiber 7, the length of the optical fiber 7 is substaially lengthened and a light propagating in the inside of the optical fiber 7 is delayed. The delay quantity is changed because the pull length of the optical fiber 7 is changed by changing the air supplying amount of the air cylinder 6. When the bobbins 2, 4 are housed in a heat insulating container together with the air cylinder 6, the optical fiber 7 is hardly influenced by the temp. change of the outside to stabilize the length of the optical fiber 7 and, then, the reliability of a light delaying unit 8 is enhanced.