Reconfigurable Low-Emissivity Optical Coating Using Ultrathin Phase Change Materials

Abstract

A method for controlling the optical properties of a solid-state film over a broad wavelength range is highly desirable and could have significant commercial impact. One such application is smart glazing technology where near-infrared solar radiation is harvested in the winter and reflected it in the summeran impossibility for materials with fixed thermal and optical properties. Here, we experimentally demonstrate the first spectrally tunable, low-emissivity coating using a chalcogenidebased phase-change material (Ge 20 Te 80 ), which can modulate the solar heat gain of a window while maintaining neutral-coloration and constant transmission of light at visible wavelengths. We additionally demonstrate the controlled transfer of absorbed nearinfrared energy to far-infrared radiation, which can be used to heat a building's interior and show fast, sub-millisecond switching using transparent electrical heaters integrated on glass substrates. These combined properties result in a smart window that is efficient and aesthetically pleasingcrucial for successful adoption of green technology.

Ultra-compact nonvolatile phase shifter based on electrically reprogrammable transparent phase change materials

“…Single-doped heaters can therefore be used for waveguides, but also for larger PICs components such as MMIs and even to fit large metasurfaces. Other alternatives for transparent microheaters, already demonstrated to switch PCMs, might be considered to avoid doping losses overall and extend the transparency window to shorter wavelengths, such as graphene, [38,40] fluorine-doped tin oxide, [41] and indium-tin-oxide; [39,42] however, their full integration and reversible cyclability on integrated waveguides is yet to be demonstrated. We draw a direct comparison between our PCM approach and other phase-shifting approaches in Table 1 considering 10-90% rise time, the total change in the effective index, ∆n eff , the total length and voltage to achieve a π phase shift, L π and V π , and the insertion loss (IL).…”

Reversible Switching of Optical Phase Change Materials Using Graphene Microheaters

“…In particular, electro-thermal methods that enable scalable onchip integration have been explored in several recent studies. [39][40][41][42][43][44] The heater materials used include metals, [45] transparent conducting oxides (TCOs), [46][47][48][49] and doped silicon. While metals are useful for free-space reflective devices, they introduce significant optical losses in transmissive or waveguide components.…”

Opportunities and Challenges for Large-Scale Phase-Change Material Integrated Electro-Photonics

“…There are predominantly two types of electrical heaters: (1) doped intrinsic semiconductor, such as silicon, on which the PICs are fabricated; ,, and (2) extrinsic heaters, such as metal, graphene, , indium-doped tin oxide (ITO), , or fluorine-doped tin oxide (FTO) . A detailed simulation study of different heaters revealed that graphene heaters are much more electrical energy-efficient than doped semiconductors (such as PIN diode-based silicon heaters) or ITO heaters, primarily because of graphene’s much smaller active volume.…”

“…There are predominantly two types of electrical heaters: (1) doped intrinsic semiconductor, such as silicon, on which the PICs are fabricated; 45,83,87 and (2) extrinsic heaters, such as metal, 85 graphene, 88,89 indium-doped tin oxide (ITO), 84,86 or fluorine-doped tin oxide (FTO). 90 A detailed simulation study of different heaters revealed that graphene heaters are much more electrical energy-efficient than doped semiconductors (such as PIN diode-based silicon heaters) or ITO heaters, 91 primarily because of graphene's much smaller active volume. On the other hand, PIN silicon heaters have a better heating efficiency than metal heaters 92 because the latter must be placed far from optical modes to avoid high absorption loss, reducing the thermal efficiency and optical contrast.…”