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Distributed refractive index sensing with cascaded TFBGs via derivative spectrum analysis.
Optics Express
|February 20, 2026
Summary
Multiple tilted fiber Bragg gratings (TFBGs) can now be multiplexed for refractive index sensing. A novel derivative spectrum analysis method enables independent interrogation of cascaded TFBGs, overcoming previous limitations.
Area of Science:
- Fiber optic sensing
- Nanotechnology
- Spectroscopy
Background:
- Tilted fiber Bragg gratings (TFBGs) are sensitive refractometric probes.
- Their broad cladding-mode spectra limit them to single-point sensing due to incompatibility with wavelength-division multiplexing.
Purpose of the Study:
- To demonstrate multiplexed sensing using cascaded TFBGs.
- To overcome the spectral overlap limitations of TFBGs for multipoint sensing applications.
Main Methods:
- Cascading multiple bare, uncoated TFBGs with distinct grating periods and tilt angles in a single-mode fiber.
- Utilizing first-order derivative spectrum analysis to isolate local slopes of cut-off modes.
- Suppressing envelope distortions caused by upstream gratings.
Main Results:
- Independent interrogation of cascaded TFBGs over an 80-nm bandwidth.
- Achieved sensitivities of 52-58 nm/RIU, consistent with intrinsic TFBG performance.
- Enhanced demodulation accuracy by up to 65% with preserved linearity (R² = 0.94-0.98) and minimal cross-talk (<0.03 nm).
Conclusions:
- Multiplexing of TFBG refractometers is feasible, challenging previous assumptions.
- The derivative spectrum analysis method enables reliable, decoupled multipoint refractive-index sensing.
- This breakthrough enables scalable, cost-effective quasi-distributed sensing networks for chemical and biological applications.
