Dispersion-Induced Delay Deviation and Its Influence on Distributed Strain Measurement Using OFDR

The broad wavelength tuning range in optical frequency-domain reflectometry (OFDR) enables high-spatial-resolution distributed strain sensing. The large wavelength tuning range of over tens of nanometers makes the issue of dispersion non-negligible; however, the influences of dispersion on the sensing performance in OFDR are seldom discussed in the literature. For high performance measurement, it is necessary to compensate strain induced delay to maintain high coherence between the reference measurement and the sensing measurement. In this work, we find out that the presence of group velocity dispersion introduces significant deviations in determining the delay in a distributed manner. The larger the applied strain is, the greater the induced delay deviation becomes. We also investigate the influences of the delay deviation on distributed strain demodulation based on conventional cross-correlation calculation, showing that high-spatial-resolution distributed strain measurement requires dispersion compensation which allows the delay to be accurately determined and compensated along the sensing fiber. The conclusion in this work indicate that for applications requiring specialty fibers or waveguides, or for scenarios demanding ultrahigh spatial resolution, dispersion influence should not be ignored and it needs to be compensated to enhance the performance.