Note that there may be several cladding modes in the sensing fiber which will results in a relatively complex interference spectrum.
When the gold-coated FMI is inserted to the sealed oil tank, the mode indices of the cladding mode and the core mode of the sensing SMF will change due to the stress-optic effect , which consequently results in the wavelength shift of the interference spectrum of the FMI.
Hydrostatic pressure sensing is achieved by measuring the wavelength shift of the interference spectrum of the FMF-based hydrostatic pressure sensor.
02 nm is used to detect the interference spectrum of the two modes of the FMF.
The wavelength spacing of the interference spectrum (around 1550nm) of the hydrostatic pressure sensor is about 8.
When the pressure increases, the interference spectrum of the hydrostatic pressure sensor has a blue-shift.