Advances in infrared GRIN: a review of novel materials towards components and devices

Abstract

Novel optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. UCF's Glass Processing and Characterization Laboratory (GPCL) with our collaborators have been evaluating compositional design and processing protocols for both bulk and film strategies employing multi-component chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. This paper reviews progress in forming ChG-based GRIN materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and meta-lens structures realized through multiphoton lithography (MPL).

Advances in infrared gradient refractive index (GRIN) materials: a review

“…where n and V correspond to the refractive index and volume fraction of the composite's phases, respectively. 42,45,51,54 While simplistic and approximate, this relationship has been shown to reasonably estimate the effective optical properties observed in optical nanocomposites made up of glass and crystalline phase(s) in the glass ceramics formed from parent glass to spatially transform a medium to realize a new optical function. It is important to note that the remaining residual glass phase will be modified by the departure of the crystal-forming constituents, thus resulting in a modified postprocessed glassy phase refractive index, and due to the subtle nature of this depletion, this composition and index change are difficult to experimentally quantify.…”

“…Recently, optical nanocomposites based upon multicomponent GAP-Se glasses have been shown to yield high-refractive index Pb-containing nanocrystalline phases in an amorphous matrix, which can remain stable at elevated temperatures or under photo/electronically excited states. 14,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] The effective refractive index, n eff , of the resulting glass ceramic nanocomposite increases monotonically with an increase in the volume fraction of the high-refractive index crystalline phase(s), thereby enabling creation of a homogeneous effective refractive index change in the starting glass. The glass ceramic composite's effective index can be approximated by knowledge of the refractive index of the residual amorphous and induced crystal phase(s) formed as well as their respective volume fractions, as calculated by E Q -T A R G E T ; t e m p : i n t r a l i n k -; s e c 2 .…”

“…Recent efforts have demonstrated the ability to engineer the index and dispersion behavior in bulk and thin film forms 62 of GAP-Se materials with precision, including the ability to not only use laser-induced nucleation and/or heat-induced post growth to spatially control the localized crystal phase formation, 14,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] but also the ability to locally induce vitrification (or reamorphization) of previously formed glass ceramics, to create a decrease in refractive index by converting previously formed nanocrystals back toward the initial, glassy state. 54,55 Such flexibility in both compositional design and processing routes will enable a wide variety of materials, which can be tailored to fit applications across the IR.…”

“…14,[40][41][42][43]45,46,49,[51][52][53][54][55] The energetically favorable route to phase separation consistently seen in this material system has gained interest from optical designers and glass scientists since the Pb-rich amorphous phases, once thermally treated, can be exclusively converted into nanocrystallites with an index far greater than that of the surrounding matrix. 14,[41][42][43]45,46,49,51,53,54 This indicates that the effective index of nanocomposites increases upon heat treatment, while maintaining their transparency as an effective medium. Since the number density and the crystallinity of the high-refractive index, Pb-rich phases can be controlled by knowledge of the nucleation and growth rates of these phases, thus a prescribed thermal treatment protocol, a combination of the material chemistry and the process, provides a pathway toward the formation of a GRIN profile within a single component.…”

Diffusion-based gradient index optics for infrared imaging

“…Other IR-GRIN methods have recently been demonstrated that do not rely on diffusion of glass elements. 21 Selective ceramization exploits the refractive index change that occurs when specially formulated chalcogenide glasses undergo crystallization. 22 This can be spatially controlled using laser-induced nucleation 23 and thermally controlled nucleation and growth 24 to create GRIN profiles.…”