| 摘要 |
PURPOSE:To obtain high resolution by measuring group delay due to dispersion that a single mode optical fiber has as the phase of a beat signal. CONSTITUTION:The oscillation wavelength of a laser 1 is set fixedly to lambda0 and the oscillation wavelength lambda of a laser 2 is variable. The output light beams of the lasers 1 and 2 are coupled 3 mutually, passed through a half-mirror 5, and demultiplexed by an acoustooptic modulator 6 into light which is varied in angular frequency by omegam and light which is not. The demultiplexed beams are reflected by a corner cube 7 and a reflecting mirror 8, multiplexed 6, and then demultiplexed 5. One demultiplexed light beam is guided to a grating 9 through a polarizer 10 and a half-mirror 4 and light which shifts in angular frequency from the wavelength lambda0 by 2omegam is selected and photodetected 15, so that an AC signal of angular frequency 2omegam is outputted. The light transmitted through the half-mirror 4 is guided to the signal mode optical fiber 13 to be measured and demultiplexed 14 into light beams with wavelengths lambda0 and lambda, which are passed through polarizers 11 and 12 and photodetectors 16 and 17 to find the phase difference by a phase processing circuit 18, thereby performing group delay. |
