光学反射仪的选读.ppt

10.4.3 Special Consideration Spatial Resolution Measurement Range Reflection Sensitivity Polarization Diversity Detection Spurious Sidelobes Spatial Resolution The spatial resolution: The right equation should be multiplied by 0.44,0.88 and 1.2 for Lorentzian,Gaussian,and rectangular-shaped spectrums. 相干长度 Measurement Range Difficulty: 1.The scan range of more than tens of centimeters is difficult to achieve in a portable instrument. 2. The number of resolvable points in a single scan can easily be greater than 10,000, although this physical distance is sometimes considered small. How to increase the measurement range in OLCR? Measurement Range Methods： Combine the data from many separate mirror scans Fold the optical path between the fiber and the movable reference mirror Reflection Sensitivity The SNR for a single, weak reflector: By making the shot noise the dominant noise source: Reflection Sensitivity Polarization Diversity Detection Problems: As the fibers within the interferometer paths are handled or subjected to Environmental changes, the interference signal can completely fade away because of polarization effects. How can OLCR measurements depend on polarization when their low-coherence sources are unpolarized? Two ways to answer this question: An unpolarized signal can be thought of as the linear superposition of two orthogonal polarization states. The low-coherence source continuously emits very short coherence packets. Each individual packets is polarized, but with a random polarization state compared to all the other packets. Polarization Diversity Detection The reference signal is equally divided on the two detectors by polarizer. Polarization-diversity Receiver to overcome polarization problems: (Polarizing beam splitter) Spurious Sidelobes Two weak reflectors in the detector arm. Two weak reflectors in the source arm. Fake signals or spuri