| 摘要 |
PURPOSE:To directly measure a coupling length, by allowing visible laser beam to be incident to a polarization surface preserving optical fiber for an infrared wavelength from one terminal thereof and bending said optical fiber, until the emitting pattern at the other terminal thereof only comprises an LP01 mode, to measure a light and shade pattern by scattering light. CONSTITUTION:The visible laser beam from He-Ne laser 1 is incident to a polarization surface preserving optical fiber (SPF)2 from one end thereof. At first, when SPF2 is not bent, the emitted pattern 4 projected to a screen 3 contains a higher-order mode. Subsequently, a bent loop 2a is provided on the way of SPF2 and the number of patterns of the loop 2a are increased to constitute the pattern 4 only from an LP01 mode. Herein, a 1/2 wavelength plate 5 is provided between the laser 1 and the incident terminal of SPF2 and linear polarized beam is incident at an angle of 45 deg. to the inherent polarization axis of SPF2. When SPF2 is observed from the lateral direction, a clear light and shade pattern by scattering light is observed. The distance between parts high in scattering intensity is measured to make it possible to directly measure a coupling length. |
