Strain engineering at a crystal fiber laser–metal alloy interface: an ultra-sensitive crystal-fiber-based sensor

The strain-activated tuning of a continuous wave Cr4+:Y3Al5O12 crystal-core glass-clad hybrid Raman fiber laser with low-threshold operation and a Cu-Al-alloy packaging was demonstrated. The cascaded Raman resonating scheme significantly reduces the effective Raman pump intensity required to reach the stimulated Raman threshold. This reduction in threshold intensity leads to continuous wave low-threshold lasing with high quantum efficiency. In addition, we demonstrate that such strain-dependent Raman tuning is useful for highly sensitive thermal and stress sensors, with a temperature sensitivity of 0.273 nm/°C and a temperature-strain crosstalk of 530 μe/°C. These sensitivities are at least one order of magnitude higher than the sensitivities achieved by conventional silica fiber-based thermal sensors and polymer fiber-based stress sensors. The large temperature-dependent Raman shift was achieved through the enhanced piezospectroscopic effect of the fiber packaged with the Cu-Al alloy.