A lens of 38 mm in diameter, 23 mm thickness, and 120 mm focal length is nothing special, except the very first one made by Assyrians nearly 3000 years ago, currently on display in the British Museum. About 2000 years ago, Archimedes, as the story goes, used mirrors to burn Roman ships. Notably, the mirror of the Hubble Space Telescope is not fundamentally different from that of Archimedes… Optics, after all, may have been the oldest of professions…

It also has been the hardest to reform. Citing Bernard Kress, Optical Architect at Microsoft Hololens, “Unlike electronics, optics does not follow Moore’s law, and is proving to be one of the hardest challenges to solve in AR/VR hardware” [1]. Indeed, in contrast to generating light, there are only a very few means of controlling it—the most intangible form of matter. It is only shape and refractive index in the case of transparent isotropic materials—the first and the second generations of optics, correspondingly. Anisotropic materials provide two more opportunities. The third generation of optics, modulation of the effective magnitude of optical birefringence, is, literally, in full display in liquid crystal displays. This feature issue of JOSA B on Diffractive Waveplates presents achievements in the new, fourth generation of optical technologies that makes it possible to obtain every variety of optical functions by modulating the orientation of the optical anisotropy axis in the plane of thin films [2].

Figure 1 shows excerpts from a historical document—disclosure of the invention that thin films with varying orientation of the optical anisotropy axis in the plane of the film are capable of broadband 100% diffraction efficiency. Erez Hasman and colleagues suggested and demonstrated the feasibility of a variety of optical components based on the Pancharatnam–Berry phase (or geometrical phase) modulation using subwavelength gratings [3]. The lithographic fabrication process limits performance of such components due to limited resolution, while their discontinuous structure limits diffraction efficiency (which was still amazingly high in those studies). These limitations apply similarly to both multilevel Fresnel lenses [4] and the technology of plasmonic and dielectric metasurfaces [5]. The Lawrence Livermore National Lab statement in [4] that it “…has the only facility in the world that can make precision diffractive optics of more than a few centimeters in diameter” is quite descriptive of the level of cost and complexity of those technologies and raises questions on the commercial value of such components. Hence, none of them are available commercially or have been demonstrated outside a lab after decades of developments.

 

Fig. 1. Photocopy of some parts and figures of the disclosure of the opportunity of 100% broadband diffraction efficiency for components with a periodically modulated orientation pattern.

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The diffractive waveplate technology brought the breakthrough for which optics, particularly, planar and thin film optics, has been longing … well, at least for centuries. Due to large optical anisotropy of liquid crystal and liquid crystalline polymers, their wide availability and technology maturity due to the LCD industry, diffractive waveplate “prisms,” lenses, beam shapers, etc., could be produced at low cost even in large area. Their structural continuity and thinness make possible the use of techniques well developed for waveplates to obtain broadband/achromatic performance without compromising efficiency and transmission. These components are not laboratory artifacts but rather are shown in industry exhibits and are available commercially. Their low-cost fabrication as coatings enables modern applications such as switchable lenses for AR/VR, non-mechanical beam steering systems for self-driving cars, adaptive ophthalmic lenses, ultralight ultrathin space telescopes, and even solar sails.

The technology was the subject of many plenary/keynote and invited talks, and review papers; however, this issue is the first that summarizes ongoing research from many groups active in the area.

The breakthrough made in the technology of modulating the geometrical phase, and the development of materials that allow the performance of such modulation at a high spatial resolution, economically, and in large area are the driving forces of the exploding interest toward the fundamental and practical aspects of diffractive waveplate technology. This issue will further increase awareness of the optics and photonics community in the novel opportunities. The topics covered include all key aspects of the technology: concepts, fabrication, materials, and applications.