Optical waveguide sensors that use evanescent wave interactions have attracted significant attention from researchers. Such sensors offer advantages for chemical sensing applications, including miniaturization potential, the ability to discriminate surface and bulk effects, suitability for measuring highly absorbing and scattering media due to short effective path lengths, enabling of full or quasi-distributed sensing to measure analyte concentration profiles over distances, and providing designers control over interaction parameters. Evanescent wave fiber optic sensors also offer economic benefits due to the availability of light emitting diodes and sensitive photodetectors.

1. Background of
OFSEWA
The optical waveguide sensors for chemical and biological organisms
dependent on these evanescent wave (EW) interactions have drawn
significant attention from researchers. Compared to other sensing
methods, the evanescent wave sensing technique offers a number of
advantages, especially in chemical sensing applications.
1. As the interrogating light remains directed, no coupling optics are
needed in the sensor region and all fiber approach is feasible.
Considerable miniaturization with EW interaction is commonly
available in integrated optics.
2. Surface and bulk effects can be discriminated by using proper launch
optics and thereby reducing the EW field to a short distance from the
guiding interface.
3. The fiber optic EW sensors are perfectly suited for accurate
absorption measurements on highly absorbing and highly scattering
media due to their short effective path length.
4. If the optical fiber is designed to be sensitive to EW interactions along
its length or in distinct areas, then full or quasi-distributed sensing is

2. possible which enables the measurement of the spatial profile of the
analyte concentration over considerable distances.
5. In comparison to traditional approaches, the EW approach allows the
sensor designer control over interaction parameters such as volume
sensing and response time.
6. By inventing light emitting diodes (LEDs) and highly sensitive
photodetectors, EWFOS offers significant economic benefits [42, 43,
44].