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J. Eur. Opt. Society-Rapid Publ. 22, 53( 2026)
Fig
. 5. Electric-field intensity of the uncoated microresonator coupled to the optical fiber at the resonance wavelength 786.92 nm, and zoomed mode profiles, including the z-component of the electric field around the microresonator surface.
Fig. 4. Schematic of the biosensor: a 30 lm microdisk with a 100 nm coating in aqueous medium. Light is coupled into the microdisk via an optical fiber, where the coupling distance d x is the key coupling parameter.
with an average mesh quality of 0.89. Each simulation run takes about 328 min( approximately 5 h 28 min) on a workstation equipped with an AMD Ryzen 9 7950X 16-core processor, and 96 GB of RAM.
5 Effects of the nanocoating
As a first step, the uncoated microresonator is modeled and simulated. It is found that the optimal coupling distance between the core of the optical fiber and the microresonator is d x, u = 350 nm, for which 85.6 % of the incoming power is coupled into the microresonator. The corresponding resonance wavelength is k res, u = 786.92 nm with a quality factor of Q f = 1.81 10 4 [ 38 ]. The electric-field intensity of this configuration at k res, u is shown in Figure 5, together with a zoomed view of the z-component of the electric field that clearly illustrates the excited mode.
5.1 PS coating
Figure
6. The electric-field at the resonance wavelength k res,
PS = 789.38 nm for the PS-coated microresonator coupled to the optical fiber, with zoomed mode profile of the E z field near the
microresonator surface.
Next, the PS-coated microresonator is modeled and simulated. In this case, the best coupling is obtained for the distance d x, PS = 400 nm, for which 92.4 % of the incoming power is coupled into the microresonator. The resonance wavelength is k res, PS = 789.38 nm, and the electric-field intensity at resonance is shown in Figure 6. It can be observed that the presence of the coating attracts the optical mode towards the coating layer and thereby amplifies the evanescent tail of the electric field in the water region.
The sensing figures of merit for this configuration are summarized in Table 1. The results show that the PS nanocoating enhances the biosensor performance compared to the uncoated case by increasing Q f by about 15 %, reducing the mode volume by 25.8 %, and amplifying the electricfield intensity at the sensing location by a factor of 1.75, as already reported in [ 38 ]. These results demonstrate that the addition of the 100 nm PS coating significantly improves the sensing functionality of the microresonator.
5.2 CsPbI 3 coating
Finally, the CsPbI 3-coated microresonator is modeled and numerically analyzed. Here, the first and most important step is to identify the desired excitonic – photonic coupling between the microresonator WGM and the perovskite nanocoating. Based on the eigenmode simulations in Ref. [ 41 ], a wavelength range from 886 nm to 900 nm with a step size of 0.01 nm is explored. It is observed that at k res; CsPbI3 ¼ 886:60 nm an effective excitonic – photonic coupling between the microresonator photonic mode and the CsPbI 3 coating excitonic mode is achieved. In this configuration, the hybrid excitonic – photonic mode is mainly confined within the nanocoating rather than in the silica core. However, since the refractive index of the CsPbI 3