Evanescent-absorption coefficient for diffuse source illumination: uniform- and tapered-fiber sensors

Area of Science:

• Photonics
• Optical Sensing
• Fiber Optics

Background:

• Evanescent-wave fiber-optic sensors offer sensitive detection methods.
• Uniform and tapered fiber designs present different optical characteristics.

Purpose of the Study:

• To comparatively analyze the performance of uniform versus tapered fiber-optic absorption sensors.
• To derive expressions for effective evanescent-absorption coefficients under diffused illumination.
• To investigate the influence of sensor design and fluid properties on sensitivity.

Main Methods:

• Theoretical derivation of evanescent-absorption coefficients.
• Comparative analysis of sensor performance based on numerical aperture, taper ratio, and fluid refractive index.
• Modeling of sensor response under Lambertian source illumination.

Main Results:

• Sensor sensitivity is dependent on fiber numerical aperture, taper ratio, and the absorbing fluid's refractive index.
• Increased sensitivity correlates with a reduced range of functional refractive indices.
• For tapered fibers, optimal numerical aperture for maximum sensitivity is fluid-dependent.

Conclusions:

• Both uniform and tapered fiber-optic sensors are viable for absorption sensing.
• Tapered fibers offer tunable sensitivity, but require careful selection of numerical aperture based on the target fluid.
• Understanding these dependencies is crucial for optimizing sensor design for specific applications.