The unique features of fibre optic sensors have sparked wide spread interest in applications that provide new sensor capabilities or offer cost or performance benefits over existing sensors. Photonic sensors are small, lightweight, electrically passive, and immune to electromagnetic interference, making them attractive for industrial, ocean, military, and medical applications. Many of the attributes of optical sensing can be and are being applied today in a wide spectrum of applications areas. However, the oceans and the human body present many challenges in bringing optical sensing to these unique environments.