Distributed Bragg Reflectors Employed in Sensors and Filters Based on Cavity-Mode Spectral-Domain Resonances

Abstract

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.

One-Dimensional Photonic Crystal with a Defect Layer Utilized as an Optical Filter in Narrow Linewidth LED-Based Sources

“…The transmission spectrum was normalized with respect to the signal recorded by the spectrometer without the 1DPhC. Because narrow spectral resonance peaks are lowered and broadened due to the limiting resolving power of the spectrometer [19], the method of Fourier transform interferometry was applied to overcome this limitation. The method is based on the measurement of the amplitude of a coherence function, or equivalently, a visibility function [62] from which the linewidth (full-width at half-maximum) ∆λ can be obtained.…”

“…When compatible defects are introduced in the structure, defect modes appear within the PBG, and the 1DPhCs thus represent an electromagnetic counterpart of semiconductor crystals with many promising applications. These include optical filters [2][3][4][5][6], along with tunable ones [7][8][9][10][11][12], lasers [13], light-emitting diodes [14], active cavities [15], including optical field enhanced nonlinear absorption [16], optical sensors [17][18][19], fiber-optic sensors [20], humidity sensors [21], gas sensors [22][23][24][25], and photonic biosensors [26][27][28][29][30][31][32]. In addition, alternative designs to the 1DPhC-based optical filters are represented by the 2DPhC-based ones [33][34][35].…”

“…TPs represent waves at the interface between a metal and a 1DPhC, and this concept has a number of sensing applications [55][56][57][58][59]. Defect modes are related to all-dielectric 1DPhCs with defect layers or optical cavities [2][3][4][5][7][8][9][10][11][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. A defect layer introduced in the 1DPhC permits the existence of defect states that are characterized by strong confinement of light in the resonant cavity.…”

“…1DPhCs with cavity mode resonances represent an effective alternative to various applications, as experimentally confirmed [2][3][4][5][7][8][9][10][11][13][14][15][16][17][18][19][20][21][22][23][24]. One of them refers to narrowband transmission filters and their potential applications in narrow linewidth sources.…”

Lab-on-a-chip sensor based on 1DPhC resonant cavity

“…They can be used as planar waveguides, and the guided waves can be used in sensing applications [3]. Moreover, the Bloch surface waves (BSWs) propagating along the interface of the 1DPhC and external medium are widely used in sensing area [4,5]. In this paper, we proposed cavity formed by two Bragg mirrors created by 1DPhCs at the normal incidence of light.…”