A modified Sagnac interferometer-based fiber temperature sensor is proposed. Polarization independent operation and high temperature sensitivity of this class of sensors make them cost effective instruments for temperature measurements. A comparison of the proposed sensor with Bragg grating and long-period grating fiber sensors is derived. A temperature-induced spectral displacement of 0.99 nm/K is demonstrated for an internal stress birefringent fiber-based Sagnac interferometer.

Structural and upconversion emission properties of $\mathrm{Zr}{\mathrm{O}}_2:{\mathrm{Yb}}^{3+}\text{–}{\mathrm{Ho}}^{3+}$ nanocrystals were analyzed as function of ${\mathrm{Yb}}^{3+}$ concentration. Structural characterization shows a crystallite size up to 80 nm and tetragonal and cubic phase as the main crystalline structures. Strong green (540 nm) and weak red (670 nm) and near infrared (760 nm) emission bands were observed with 968 nm excitation. The upconversion is based on two photons absorption either by the energy transfers from ${\mathrm{Yb}}^{3+}$ ion or by the excited state absorption. The energy transfer efficiency was calculated to be 50% for 2 mol % of ${\mathrm{Yb}}^{3+}$ diminishing to less than 20% for higher concentration. The ${\mathrm{Yb}}^{3+}$ concentration also affects the decay time of the green emission of ${\mathrm{Ho}}^{3+}$ ion diminishing from $140\mu \mathrm{s}$ for 2 mol % of Yb to $76\mu \mathrm{s}$ for higher concentration.