Experimental determination of 2nd order phase matching turning points in long period gratings

The fabrication of optical fibre long period gratings (LPGs) displaying 2
^nd
order resonant bands operating at the phase matching turning point (PMTP) is explored. Previous reports that exploited 2
^nd
order attenuation bands in sensing schemes did not access the highly sensitive PMTP region. To overcome this limitation, LPGs with periods between 167-177 μm were fabricated using UV irradiation. The spectra acquired were subsequently analyzed and the development of the 2
^nd
order PMTP was identified utilizing peak tracking software. This work has provided the platform for LPG design focused on the prospect of sensitive multi-parameter discrimination.