| 摘要 |
<p>WAVELENGTH SWITCHED PASSIVE INTERFEROMETRIC SENSOR SYSTEM This invention includes a fiber optic interferometer having a reference arm isolated from a physical parameter being monitored and a sensing arm exposed to the physical parameter being monitored. The sensing arm produces changes in the relative phase of the optical signals propagating in the sensing and reference arms in response to changes in the physical parameter. The sensing and reference signals are combined to produce an interference pattern after the sensing signal has been exposed to the physical parameter being monitored. A frequency shifter changes the frequency of the optical signal input to the interferometer, which produces interference signals for the two frequencies. The optical path difference of the sensing and reference arms for the two frequencies produces phase changes that are in quadrature, which permits the interference signal for one frequency to be expressed as a function of the cosine of the phase change and the interference signal for the other frequency to be expressed as a function of the sine of the phase change. A demodulation algorithm uses data from the two interference signals to calculate either the tangent or cotangent of the phase angle to determine the phase change in the sensing signal caused by changes in the parameter.</p> |
