Complex method for angular-spectral analysis of volume phase diffraction gratings recorded in photopolymers

Abstract

Photopolymer recording materials are nowadays widely used for recording of diffraction gratings and other diffraction elements. For obtaining the best performance of these diffraction gratings for desired applications, it is important to assess these gratings from many different perspectives. In this contribution, we present an experimental and characterization approach to an analysis of diffraction gratings recorded into photopolymer materials. This approach is able to provide a complex and very illustrative description of these gratings response and, with accordance to the theory, information about some important grating parameters, such as a spatial period, slant angle, etc., as well. This approach is based on the measurement of a grating response for a wide range of angles and wavelengths and then on the construction and subsequent analysis of maps in the angular-spectral plane. It is shown that the measurements are in a good agreement with the theoretical predictions based on either approximate (Kogelnik's coupled wave theory) or rigorous (RCWA) techniques and that this approach provides complex and detailed characterization of the grating response which can be used for additional optimization or decision of applicability of measured sample gratings.

Tunable Waveguides Couplers Based on HPDLC for See-Through Applications

“…Two important facts that can be observed from Bragg’ detuning are the small deviation from the Bragg’s ideal condition and the attenuation of the grating, refractive index modulation, with depth [ 22 ]. The fact that the predicted Bragg angle coincides with the measured one means also that there is no shrinkage or swelling in this case [ 23 , 24 ].…”

Dimensional changes in slanted diffraction gratings recorded in photopolymers

“…Once we have recorded the grating, we measure the Bragg's angles of the orders ± 1, to obtain the value of K and to check possible variations of Kx component. In order to measure possible deviations from the sinusoidal profile of the gratings, we measured the second and third diffracted orders at second and third Bragg's angles respectively [19,25], this will be analyzed in the next section 4.4. We control the initial Bragg's angles in air for the diffracted orders ± 1, and we measured the new ones with an error of ± 0.002°, this accuracy give us an error of 0.09% in the determination of the shrinkage.…”

“…Nevertheless, nowadays choosing a method to measure the amount of the shrinkage in holographic recording materials can still be considered a hot topic. This year it has been published an interesting work that report a complete analysis of the problem combining the Bragg's angle detuning and Bragg's wavelength detuning, using the Kogelnik's wave coupled theory, KCW, and the rigorous analysis, RCW, proposed by Moharam et al [19]. Nowadays new alternative techniques have been proposed in order to measure the shrinkage in photopolymers [20][21][22][23] and the influence of different parameters on the changes observed in the spatial period [24].…”

“…As we commented before, one of the most studied photopolymers is the one based on polyvinyl alcohol acrylamide (PVA/AA) [19][20][21]24]. Along this work, we have analysed three different types of photopolymers, firstly PVA/AA and secondly one of the greenest photopolymers whose patent belongs to the Alicante University called Biophotopol [26] and on the last place a holographic-dispersed liquid crystal photopolymer (H-PDLC) [27].…”

Roadmap on holography

“…Different techniques have been proposed in order to quantify the shrinkage in photopolymers [35,[46][47][48][49]. The maximum shrinkage has placed when there is no diffusion [46].…”