OBR & LWA Measurement Drift

Customers have reported measuring fiber lengths with a Luna OBR or Lightwave Analyzer (LWA), and observing that the lengths measured are varying by 10's to 100's of microns over time.  In practice, customers may observe slow or step-like changes in reported fiber length over time, even when the physical fiber appears unchanged. These effects are commonly referred to as length drift.

Luna's engineering team has written the attached application note to explain the primary physical and system-level mechanisms that contribute to apparent length drift in OFDR measurements. Rather than indicating an instrument malfunction such as wavelength calibration, most observed drift arises from well-understood effects related to environmental conditions and the intrinsic thermo-optic and mechanical behavior of optical fiber.  

Environmental conditions such as temperature or strain will cause the reported length to change over long time periods. This change in length is real and demonstrates proper operation of the systems. The application note describes various causes of changes in measured lengths and recommended operation to minimize impact on length-sensitive measurements.