J. Eur. Opt. Society-Rapid Publ. 22, 23( 2026) 239
Fig. 8. Evaluation of the Fano-FBG, with q = �1, as an optical fiber sensor: a) simulated spectrum and b) comparison between the simulation predictions and the experimental results.
Table 1. RI sensors based on FBGs.
|
Detection Limit( RIU) |
Ref |
FBG and etch-eroded fiber Fabry-Pérot interferometer |
1.4 10 �5 |
[ 96 ] |
Thinned fiber Bragg gratings |
10 �4 |
[ 97 ] |
Dual Fabry-Perot FBG |
10 �5 |
[ 98 ] |
End-face of a glass fiber connected to FBG |
10 �3 |
[ 99 ] |
In this Work( Fano-FBG) |
6 10 �4 |
|
signal, and an Optical Spectrum Analyzer( YOKOGAWA AQ6370C, Osaka, Japan) for spectral interrogation. The fiber-tip cleaving process was achieved using a polishing machine, with the support of the OSA, the fiber tip can be polished until the desire asymmetry is obtained( Table 1).
The validation of the mathematical model was performed by comparing the intensity variation within the defined refractive-index range. The simulations resulted in an FBG with 1 % reflectivity, Dn = 2.6 10 �4, andN = 8452. Experimentally, a linear sensitivity of 4.1 ± 0.4 RIU �1 was obtained( r 2 = 0.980), while the simulation yielded a linear sensitivity of 4.18 ± 0.01 RIU �1( r 2 = 0.99997). The experimental results also indicated a detection limit of 6 10 �4 RIU. A deviation of approximately 1 % was observed between the real sensor performance and the simulation predictions, as demonstrated in Figure 8b. This demonstration shows the potential of a Fano-like FBG as a sensing element, both for wavelengthbased measurements as temperature measurement and for self-referenced intensity measurements. In this case, it is possible to use two lasers with wavelengths set at each peak and apply filtering to separate the wavelength contributions. Thus, by using two photodetectors, we obtain a low-cost system. A comparison with other RI sensors reveals that this system provides measurement capabilities comparable to other intensity-based interrogation FBG systems. Also, it offers a simpler implementation for achieving higher sensitivity than many existing approaches, highlighting its potential as an effective optical sensing device.
5 Conclusion
The chronological evolution of studies on Fano resonance in optical fiber systems – from its early conceptual demonstrations in the mid-2000s to the highly integrated and tunable devices developed after 2020 – illustrates a clear trajectory toward functional maturity and application-oriented design. Early works focused on demonstrating the physical existence of Fano interference in guided-wave structures and microresonators, whereas more recent contributions have emphasized engineering control, spectral reconfigurability, and hybrid material integration. The demonstration of the Fano-like FBG highlights the potential of this structure as a simple device capable of exciting a Fano-like resonance. When demonstrated as a RI sensor with a resolution of 6 10 �4 RIU, the sensitivity is not remarkable; however, the self-referencing method is useful for reducing the influence of external noise on the measurement. Looking to the future, research is expected to converge on several key directions. First, the integration of intelligent control mechanisms, such as thermo-optic, electro-optic, and opto-mechanical tuning, will likely enable adaptive Fano resonance devices capable of self-calibration and real-time environmental compensation. These developments may render Fano-based sensors and filters not only highly sensitive but also self-stabilizing and field-deployable for operation in harsh or dynamic environments. The ongoing miniaturization trend in photonic integration suggests that Fano-resonant fiber systems may evolve toward chip-scale architectures, maintaining the low-loss advantages of