Hybrid FFPI with Other Fiber-Optic Structures
It is a good strategy for multi-parameter sensing to combine the FFPI with other types of fiber-optic structures. In this way, the advantages of different kinds of fiber-optic structures can be integrated and the capability can be enhanced while the size remains small. Rao et al. developed a hybrid structure by integrating a long-period fiber grating (LPFG) and an EFFPI together . The reflective spectra of the EFFPI and the transmission spectra of the LPFG were detected at the same time for the multi-parameter sensing. High temperature and strain were measured simultaneously. Due to the fact that only pure silica fibers were used, temperature up to 650°C was measured. Strain was also measured at a temperature of 500°C. This work made use of both the reflective and transmission spectra of two different kinds of fiber-optic structures for sensing.
Frazao et al.  demonstrated multi-parameter sensing by using hybrid FFPI and a Michelson interferometer. Both temperature and strain were measured. The device was highly integrative by using a dual asymmetric core microstructured fiber. The two interferometers had different sensitivities for strain and temperature measurement. By using the matrix of the strain and temperature coefficients, multiparameter sensing was achieved.