Gryga Michal, Ciprian Dalibor, Hlubina Petr
Department of Physics, Technical University Ostrava, 17. Listopadu 2172/15, 708 00 Ostrava-Poruba, Czech Republic.
Sensors (Basel). 2022 May 10;22(10):3627. doi: 10.3390/s22103627.
Spectral-domain resonances for cavities formed by two distributed Bragg reflectors (DBRs) were analyzed theoretically and experimentally. We model the reflectance and transmittance spectra of the cavity at the normal incidence of light when DBRs are represented by a one-dimensional photonic crystal (1DPhC) comprising six bilayers of TiO2/SiO2 with a termination layer of TiO2. Using a new approach based on the reference reflectance, we model the reflectance ratio as a function of both the cavity thickness and its refractive index (RI) and show that narrow dips within the 1DPhC band gap can easily be resolved. We revealed that the sensitivity and figure of merit (FOM) are as high as 610 nm/RIU and 938 RIU-1, respectively. The transmittance spectra include narrow peaks within the 1DPhC band gap and their amplitude and spacing depend on the cavity's thickness. We experimentally demonstrated the sensitivity to variations of relative humidity (RH) of moist air and FOM as high as 0.156 nm/%RH and 0.047 %RH-1, respectively. In addition, we show that, due to the transmittance spectra, the DBRs with air cavity can be employed as spectral filters, and this is demonstrated for two LED sources for which their spectra are filtered at wavelengths 680 nm and 780 nm, respectively, to widths as narrow as 2.3 nm. The DBR-based resonators, thus, represent an effective alternative to both sensors and optical filters, with advantages including the normal incidence of light and narrow-spectral-width resonances.
对由两个分布布拉格反射器（DBR）形成的腔的光谱域共振进行了理论和实验分析。当DBR由包含六层TiO₂/SiO₂双层且以TiO₂为终端层的一维光子晶体（1DPhC）表示时，我们对光垂直入射时腔的反射率和透射率光谱进行了建模。使用一种基于参考反射率的新方法，我们将反射率比建模为腔厚度及其折射率（RI）的函数，并表明可以轻松分辨1DPhC带隙内的窄凹陷。我们发现灵敏度和品质因数（FOM）分别高达610 nm/RIU和938 RIU⁻¹。透射率光谱在1DPhC带隙内包括窄峰，其幅度和间距取决于腔的厚度。我们通过实验证明了对潮湿空气相对湿度（RH）变化的灵敏度以及FOM分别高达0.156 nm/%RH和0.047 %RH⁻¹。此外，我们表明，由于透射率光谱，带有空气腔的DBR可用作光谱滤波器，这在两个LED光源上得到了证明，其光谱分别在波长680 nm和780 nm处被滤波至窄至2.3 nm的宽度。因此，基于DBR的谐振器是传感器和光学滤波器的有效替代方案，具有光垂直入射和窄光谱宽度共振等优点。
