| 摘要 |
<p>An optical fibre apparatus measures an external parameter, e.g., temperature, at any of a number of different locations using time-domain reflectometry techniques. Sensor devices (30, 31), each comprising a chip or plate of ruby glass, are interconnected by optical fibers (32, 33). A laser (50) launches along the fiber string short pulses of light at a first wavelength on the absorption edge of the ruby glass and a second wavelength in the transmission region away from the edge. A timer (55) controls sampling circuits (58, 59) to measure back scattered energy at each wavelength at spaced times corresponding to spaced points (62, 63) along the fibre on opposite sides of a selected sensor device (31). A processor (64) calculates the absorption loss in the sensor device at each wavelength by comparing the back scattered energy from the two points on opposite sides of the device, and calculates the differential absorption loss by comparing the losses at the two wavelengths. Embodiments employing a wedge shaped absorber are used to measure displacement. Signal to noise ratio is improved by incorporating retro-reflectors in the fibre lengths between sensor devices. </p> |
