Abstract: In order to provide a multi-path monochromator capable of reducing the size of optical parts with a high resolution and a wide dynamic range, the multi-path monochromator has a lens 2 used as a first collimator for converting an incident light into a parallel light, a diffraction grating 4 for diffracting an output light outputted from the lens 2, plane mirrors 3 and 5 for reflecting a diffraction light diffracted by the diffraction grating 4 to return the diffraction light back to a same path, a parabolic mirror 7 used as a second collimator for collecting a diffraction light which is again diffracted by the diffraction grating into which a reflected light is again outputted from the plane mirror, and an output slit positioned at a focal position of the parabolic mirror 7. The parabolic mirror 7 used as the second collimator has a focal length which is longer than a focal length of the lens used as the first collimator.

Abstract: An optical pulse ?0 from a light source section 10 is incident upon an optical fiber 1 through an optical demultiplexer section 20, and its return light is supplied to an optical/electrical processing section 30 as the light of a plurality of different wavelengths ?1 to ?n by the optical demultiplexer section 20, and is respectively converted into electrical signals. Signals of the converted return light are respectively sampled and are averaged by respective processing circuits 402 to 40n of a signal processing section 40 so as to be formed as desired measurement waveforms. In the measurement waveforms, which are the results, data for corresponding sampling points are expressed as measurement data at an identical distance in the optical fiber.