| 摘要 |
PURPOSE:To determine the presence of propagation of undesired mode accurately and handily, by applying a disturbance to a fiber into which a modulation light is made incident to measure the amplitude and phase of an emission light in a base band frequency range. CONSTITUTION:A single mode optical fiber line 1 to be measured lets light of a light source 2 modulated by a sine wave signal from a high frequency oscillator 4 incident through an optical system 3. An emission light from the line 1 is detected with a light receiver 6, sent to a signal input terminal of a vector voltmeter 8 via an amplifier 7 and the phase and amplitude thereof are compared with a sine wave modulation signal. Then, a disturbance such as bending 5 is applied to the line 1 at a proper position thereof and the amplitude and phase of an output of the light receiver 6 are measured with the meter 8. The same measurement is repeated by varying the frequency of the modulation signal from the oscillator 4 and an a result, when the disturbance will not cause any change in the phase of a base band output, the single mode transmission going on can be checked by this condition. |
