Enhanced Tunability of Polarization Volume Gratings Using Dual Rotating Mask

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Optical properties of reflective polarization volume grating and exposure method with easily tunable period via dual rotating polarization grating mask Kapil Kumar Gangwar. Polarization volume gratings (PVGs) are used to selectively diffract light based on polarization state with the angle of diffraction dependent on the grating film design. They show high diffraction efficiency and unique polarization selectivity.

This work presents the compare between two different configuration of polarization volume grating (planar and slanted structure) and the optical properties of PVGs with depends on their polarizing nature.

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Here a new approach develops, to record polarization grating (PGs) based on dual rotating polarization grating mask. This approach can easily tune the PGs period while maintaining the compact size of the setup. By this technique, the large- period PGs easily fabricated. Introduction The self-organized liquid crystal helical structures are known as PVGs. They are different from surface-relief grating and volume Bragg gratings (holographic gratings).

The unique polarization sensitivity of PVGs arises due to difference, the modulation of PVGs is based on the spatially anisotropic liquid crystal (LCs), while other two are based on the spatially distributed refractive index of isotropic material.

Here the optical properties of two different types of PVGs (planar and slanted PVGs) are studied.

PGs with a first grating period are creates by several methods, holography, proximity or projection lithography of single mask and nanoimprinting. These techniques must be reconfigured to create a second grating period, which involves a significant time delay or the substitution of potentially expensive optical element or both.

These methods require substantial equipment cost. Here, a new technique to fabricate 1 PGs by which easily tuning the arbitrary large grating periods.

Now easily scaled for large area recording while no change in setup by this technique [9]. Background The horizontal periodicity (Px) is define as the distance by which liquid crystal (LC) director rotates 1800 along the horizontal direction and the distance by which LC director rotates 1800 along the vertical direction is known as vertical periodicity (Py).

The Bragg periodicity (PB) is as follows: 1 𝑃𝑥 2 + 1 𝑃𝑦 2 = 1 𝑃𝐵 2 (1) where the slant angle 𝜙, is related to Px and Py as follows: tan𝜙 = 𝑃𝑦 𝑃𝑥 (2) Now the corresponding wavelength is defined as 𝜆𝐵 = 2𝑛𝑃𝐵 cos𝜙 (3) where n is average refractive index of LC.The step of PVGs fabrication as, a photo-alignment material brilliant yellow spin coated on to a glass substrate whose thickness is 10nm, and the exposed with two coherent and circularly polarized laser beams (𝜆 = 457) with opposite handedness. The two beam aligned at an angle 31.30 to normal to the substrate in symmetric manner and generated a polarization interference pattern with a horizontal periodicity.

To obtain the thin PVG single or multiple times coating work, but for a thick PVG multiple times is required. To characterize the polarization properties, the PVG was fixed on a rotation stage and set to the center of a glass cylinder that contains index matching oil (n=1.58). The incident light (a) Planar PVG and (b) Slanted PVG, 𝜃𝑝 is the angle of liner polarizer. 2 was perpendicular to the PVG at the initial state. The angle of incidence (in the x-y plane) can then be adjusted by rotating the PVG, and the Stokes parameter S3 of the diffracted beam was directly measured by a polarimeter (PAX100VIS, Thorlabs).

A conventional holographic arrangement to achieve the interference pattern. The period created by holographic interference pattern is define as Λ = 𝜆 sin 𝜃 (4) where λ is the recording wavelength and θ is the half-angle of the recording beams. The disadvantage of conventional approach is the practical upper limit of achievable Λ, e.g., periods Λ ≫ 20μm. Period created by this approach is depend on the half angle θ, so the setup scales according to angle.

This is not feasible due to the large no of elements, the complexity, volume and cost of recording setup. A rearrangement of the setup is need to modify  while at same time ensuring the high quality polarization state of beams, which is essential to achieve the desired period with good quality of the recorded pattern. Results and discussion The optical efficiency and polarizing properties of two reflective PVG is simulate. The diffraction efficiency increases as the film thickness increases and the rate is very similar for planar (dashed line) and slanted PVGs (solid lines) as shown.

The polarization property of diffracted light characterize by stokes parameter S3 (degree of circular polarization of light). In Fig. 3(b), S3 is decreases as film thickness increases but there is extreme difference in S3 between planar and slanted (solid line) PVGs. S3 is almost near to unity for slanted PVG, so it indicates the diffracted light is nearly circularly. The conventional holographic setup to create the PG profile, which includes mirrors (M), beam splitter (BS) and quarter-wave plate (QWP). 3 polarized. While for Planar PVG, the diffracted light significantly deviates from the circular polarization.

The shows the simulated grating efficiency for different input polarization with a film thickness 2.0µm. This indicates that the slanted PVG are sensitive to polarization angle of a linearly polarized light while planar are not. For both configuration, we simulate the transmittance variation as a function of input linear polarization angle. In the experiment, the grating transmission is measured as function of input polarizer angle and good agreement is found between simulation and experiment for slanted PVG. Hence by this method simply differentiate slanted and planar PVGs.

There is a concept to control the output beam by use of two rotating grating mask over to each other [10-11]. By rotating their grating axis, the two grating for particular wavelength can make any output angle with in the field of view. Angle of output can be tune as simply ro- tating two grating mask as shown in (a) Optical efficiency of PVGs as function of film thickness, (b) Stokes parameter as function of film thickness.

The Transmittance of PVGs is a function of input linear polarization angle. Dual rotating mask set up 4 Here the grating period of mask grating to be same (i.e. the same diffracted angle, θd). To achieve the very large grating period, the two mask PG are aligned parallel and angle between output beam can be very small. Another way when the mask PG are aligned antiparallel to each other, the output beams have the maximum angle (i.e. =2d). Hence from this easily create various grating period by controlling the relative grating orientation.

The grating period of replicated grating PG is determined as follows: Λ𝑟𝑒𝑝𝑙𝑖𝑐𝑎 = 𝜆0 2sinΘ (5) where 𝜆0 is the recorded wavelength of the dual rotating PG mask. The splitting angle  of the output beam could be easily tune by controlling the rotation angle  of the setup. Hence we can achieve the large grating period (>20μm) without significant effort. The setup parameter and corresponding grating Λreplica are shown in Table 1 (the ηn is the efficiency of order n).

Conclusion

A significant difference observes in their optical properties while there is similarity in between diffraction efficiency between planar and slanted PVG. The planar configuration delivers more retardance towards the diffracted light while the diffracted light from slanted structure tends to maintain the circular polarization state.

A new technique proposed for PG exposure by which the grating period of sample can easily tune, while in conventional holography approach lots of difficulty on tuning the grating period due to the scaling size of sample, complexity of setup and several optics included that are needs to aligned carefully. Using this technique, we can easily determine PG fabrication with large grating periods (>20μm).

References

T. Levola, “Novel diffractive optical components for near to eye displays,” SID Symp. Dig. Tech. Pap. 37, 64–67 (2006).
T. Rasmussen, “Overview of high-efficiency transmission gratings for molecular spectroscopy,” Spectroscopy 29, 32–39 (2014).
Yun-Han Lee, Ziqian He, and Shin-Tson Wu, ‘’Optical properties of reflective liquid crystal polarization volume gratings,” J. Opt. Soc. Am. B 36(5), D9-D12 (2019).
G. Crawford, J. Eakin, M. D. Radcliffe, A. Callan-Jones, and R. Pelcovits, “Liquid- crystal diffraction gratings using polarization holography alignment techniques,” J. Appl. Phys. 98, 123102 (2005).
C. Provenzano, P. Pagliusi, and G. Cipparrone, “Highly efficient liquid crystal based diffraction grating induced by polarization holograms at the aligning surfaces,” Appl. Phys. Lett. 89, 121105 (2006). ї
M. J. Escuti, “Methods of fabricating liquid crystal polarization gratings on substrates and related devices,” U.S. patent application 60/912,036 (April 16, 2007).
S. R. Nersisyan, N. V. Tabiryan, D. M. Steeves, and B. R. Kimball, “Characterization of optically imprinted polarization gratings,” Appl. Opt. 48, 4062–4067 (2009).
Z. He, Y. Lee, R. Chen, D. Chanda, and S. T. Wu, “Switchable Pancharatnam–Berry microlens array with nano-imprinted liquid crystal alignment,” Opt. Lett. 43, 5062–5065 (2018).
Jihwan Kim and Michael J. Escuti, “Polarization grating exposure method with easily tunable period via dual rotating polarization grating masks,’’ J. Opt. Soc. Am. B 36(5), D42-D46 (2019).
C. Oh, J. Kim, J. F. Muth, S. Serati, and M. J. Escuti, “High-throughput, continuous beam steering using rotating polarization gratings,” IEEE Photon. Technol. Lett. 22, 200– 202 (2010).
Y. Zhou, D. Fan, S. Fan, Y. Chen, and G. Liu, “Laser scanning by rotating polarization gratings,” Appl. Opt. 55, 5149–5157 (2016).