Spatially variable waveplates (SVW) fabrication is based on inscription of self-organized nanogratings inside fused silica glass using a femtosecond laser.

Rapid prototyping enables adaptation of every element to the specific needs of end user (slow axis and retardance distribution, structure clear aperture, substrate shape and thickness) without high additional development costs.

SVWs are spatially variable retardance plates which enables tailored control of spatial polarization also for high power lasers. SVWs embedded in bulk of fused silica glass have high damage threshold (up to 20 J/cm2) which is 100 times higher than that of liquid crystal spatial light modulators (0.2 J/cm2).

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Figure 1 “International year of light 2015” logo and interference color calibration pattern fabricated in bulk of fused silica glass using femtosecond laser (left). Calculated interference colors chart developed by initially Auguste Michel-Lévy [source: Bjorn Eske Sorensen” A revised Michel-Levy interference color chart based on first-principles calculations” European Journal of Mineralogy (January 2013)].

 

Current technology allows fabrication of SVW with retardance from R = 200 nm to R = 1000 nm.  The wavelength range for which it is possible to fabricate λ/2 waveplates is λ = 400 nm to λ = 2 µm. Figure 1 shows “International year of light 2015” logo and interference color calibration pattern fabricated in fused silica glass. Different colors in cross polarized light appear due to destructive interference in embedded structures. Interference colors chart (first developed by Auguste Michel-Lévy) defines the interference colors from different orders of birefringence (Figure 1).

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Figure 2 Spatially variable waveplate examples (from left to right) S-waveplate, “soft” aperture, Fresnel lens and sinusoidal phase grating shown in cross polarized light.

 

Orientation of induced nanogratings orientation is always perpendicular to laser beam polarization that is used for writing, therefore it is possible to fabricate predefined slow axis distribution patterns (Figure 2). One of the most common spatially variable waveplate is S-waveplate. S-waveplate is a super-structured waveplate which converts linear polarization to radial or azimuthal polarization. Other patterns, such as Fresnel lens, “soft” aperture, Dammann gratings, flat-top and Airy beam converters, sinusoidal phase and fork-shaped gratings can be easily realized using this technology.

SVWs have a very broad range of applications from material processing to spinoptics in plasmonics. Since its introduction to the market in 2011, Workshop of Photonics has produced over 250 spatially variable waveplates to academic and industrial laboratories worldwide.

 

Dr. Titas Gertus
Project manager at Workshop of Photonics