Resonant and Sensing Performance of Volume Waveguide Structures Based on Polymer Nanomaterials

Abstract

Organic–inorganic photocurable nanocomposite materials are a topic of intensive research nowadays. The wide variety of materials and flexibility of their characteristics provide more freedom to design optical elements for light and neutron optics and holographic sensors. We propose a new strategy of nanocomposite application for fabricating resonant waveguide structures (RWS), whose working principle is based on optical waveguide resonance. Due to their resonant properties, RWS can be used as active tunable filters, refractive index (RI) sensors, near-field enhancers for spectroscopy, non-linear optics, etc. Our original photocurable organic–inorganic nanocomposite was used as a material for RWS. Unlike known waveguide structures with corrugated surfaces, we investigated the waveguide gratings with the volume modulation of the RI fabricated by a holographic method that enables large-size structures with high homogeneity. In order to produce thin photosensitive waveguide layers for their subsequent holographic structuring, a special compression method was developed. The resonant and sensing properties of new resonant structures were experimentally examined. The volume waveguide gratings demonstrate narrow resonant peaks with a bandwidth less than 0.012 nm. The Q-factor exceeds 50,000. The sensor based on waveguide volume grating provides detection of a minimal RI change of 1 × 10−4 RIU. Here we also present the new theoretical model that is used for analysis and design of developed RWS. Based on the proposed model, fairly simple analytical relationships between the parameters characterizing the sensor were obtained.

Diffraction of a Gaussian Beam with Limited cross Section by a Volume Phase Grating under Waveguide Mode Resonance

“…Numerical calculations show that S λ δλ 0.5 ∼ S θ δθ 0.5 > S λG δλ 0.5G ∼ S θG δθ 0.5G . It is consistent with the results of [10,13].…”

“…They are determined based on the curves shown in Figure 3a. The seventh row of the Table 2 contains δλ 0.5α , calculated by the following analytical expression [10,30] δλ 0.5α = α rad λΛ/π (21) There are a good agreement between the data given in rows 6 and 7. It confirms the correctness of the proposed method for calculating the limited beam diffraction by the diffraction grating.…”

“…Rows 16 and 17 of Table 2 show the ratios S λ /δλ 0.5 and S θ /δθ 0.5 for the plane wave, which are calculated based on data from rows 6, 9, 12, and 14. It can be seen that: S λ δλ 0.5 ∼ S θ δθ 0.5 (26) The last equation was obtained in [10] based on Equation (25). Rows 18 and 19 of Table 2 show similar equations for the incidence of the Gaussian beam on the grating using data in rows 8, 11, 13 and 15.…”

“…It is much less than the average refractive index of the grating medium n 20 . The structure under study is essentially a planar waveguide and the following condition must be satisfied under resonance [10,13,17]:…”

“…The resonance appears at the different wavelengths or at the different angles when the refractive index of the tested medium changes. Grating-based sensors can be of two types, namely, the dielectric grating on the dielectric substrate or metal or dielectric grating on the metal substrate [ 9 , 10 , 11 , 12 ]. The description and analyses of various refractive index sensors as well as providing extensive references on the corresponding sensors are presented in the reviews references [ 9 , 11 ].…”