Process for preparing an optical fiber sensor with enhanced sensitivity

A process for preparing an optical fiber have at least one long period grating with enhanced sensitivity, the process comprising the steps of:

• a) providing a length of optical fiber having a refractive index profile, and wherein the optical fiber supports a core mode and cladding modes for a range of operational wavelengths;
• b) calculating effective indices of the core mode and the cladding modes;
• c) calculating a phase match condition of a long period grating;
• d) generating characteristic modal curves;
• e) identifying a modal cusp by plotting wavelength of light passing through the optical fiber versus grating period and identifying a change in slope of the plot;
• and
• f) writing a long period grating in the optical fiber wherein the long period grating has a period defined by the group indices and wherein the long period grating couples light from the core mode to a cladding mode proximate to the modal cusp.

A process for measuring an environmental perturbation, the process comprising the steps of:

• a) providing an optical fiber having at least one long period grating with enhanced sensitivity, each long period grating having a period defined by group indices and having two coupling points into a single cladding mode, wherein each coupling point has a specific wavelength;
• b) exposing the optical fiber to a perturbation in an environment wherein the exposure causes a change in the wavelength of each coupling point;
• and
• c) measuring a separation difference in the wavelengths of each coupling point.

A process for measuring refractive index, the process comprising the steps of:

• a) providing an optical fiber having at least one long period grating with enhanced sensitivity, each long period grating having a period defined by group indices and having two coupling points into a single cladding mode, wherein each coupling point has a specific wavelength;
• b) exposing the optical fiber to a refractive index change, wherein the exposure causes a change in the wavelength of each coupling point;
• and
• c) measuring a separation difference in the wavelengths of each coupling point.