Extreme Broadband Transparent Optical Phase Change Materials for High-Performance Nonvolatile Photonics (1811.00526v2)

Abstract: Optical phase change materials (O-PCMs), a unique group of materials featuring drastic optical property contrast upon solid-state phase transition, have found widespread adoption in photonic switches and routers, reconfigurable meta-optics, reflective display, and optical neuromorphic computers. Current phase change materials, such as Ge-Sb-Te (GST), exhibit large contrast of both refractive index (delta n) and optical loss (delta k), simultaneously. The coupling of both optical properties fundamentally limits the function and performance of many potential applications. In this article, we introduce a new class of O-PCMs, Ge-Sb-Se-Te (GSST) which breaks this traditional coupling, as demonstrated with an optical figure of merit improvement of more than two orders of magnitude. The first-principle computationally optimized alloy, Ge2Sb2Se4Te1, combines broadband low optical loss (1-18.5 micron), large optical contrast (delta n = 2.0), and significantly improved glass forming ability, enabling an entirely new field of infrared and thermal photonic devices. We further leverage the material to demonstrate nonvolatile integrated optical switches with record low loss and large contrast ratio, as well as an electrically addressed, microsecond switched pixel level spatial light modulator, thereby validating its promise as a platform material for scalable nonvolatile photonics.

• The paper demonstrates that GSST decouples refractive index and loss, achieving a figure of merit improvement of over two orders of magnitude.
• The study employs DFT calculations and experimental validations to confirm GSST’s broadband transparency (1–18.5 μm) and high optical contrast (Δn up to 2.0).
• The material enables record-low insertion losses and high contrast ratio switching, paving the way for advanced nonvolatile photonic devices.

Overview of "Extreme Broadband Transparent Optical Phase Change Materials for High-Performance Nonvolatile Photonics"

The paper presents a comprehensive paper of a novel class of optical phase change materials (O-PCMs), Ge-Sb-Se-Te (GSST), which demonstrates significant advancements over traditional phase change materials such as Ge-Sb-Te (GST). This new material showcases exceptional nonvolatile photonic capabilities with low losses and high contrast ratios, positioning it as a promising candidate for various applications in the field of photonic devices.

Key Results and Technical Insights

The authors introduce GSST as a material that decouples the traditionally linked refractive index (Δn) and optical loss (Δk) changes typically seen in conventional O-PCMs. This decoupling is quantitatively characterized by a material figure of merit (FOM), with GSST displaying a FOM improvement of over two orders of magnitude compared to previous materials. Such improvement is achieved by leveraging a compositionally optimized alloy, resulting in broadband optical transparency spanning the 1 to 18.5 μm range. The GSST’s Δn reaches up to 2.0, highlighting its high optical contrast without a corresponding penalty in optical loss.

Experimental Validation and Technological Demonstrations

The researchers employ a combination of density functional theory (DFT) calculations and experimental validations to explore the structural and electronic attributes of GSST. These studies reveal that the substitution of Te with Se in the phase change matrix contributes to a bandgap increase and a reduction in free carrier absorption (FCA). Experimentally, this material was utilized to fabricate nonvolatile integrated optical switches demonstrating record-low insertion losses (<0.5 dB) and high contrast ratios (42 dB) when switching between amorphous and crystalline states.

Furthermore, an electrothermal pixel-level switch illustrating rapid reflectance modulation was developed, showcasing the material's potential in free-space optical devices. These findings suggest significant advancements in pixel switches with applications in infrared light control, metasurfaces, and spatial light modulators.

Theoretical and Practical Implications

From a theoretical standpoint, the paper disrupts conventional paradigms in O-PCMs by effectively utilizing composition and structural design to achieve superior optical performance. Practically, GSST enables new device architectures that could lead to miniaturized photonic circuits, efficient beam steering systems, and advanced metasurfaces with potential applications in telecommunications and optical computing.

Future Outlook

The advancement in O-PCMs as demonstrated by GSST may herald a new era of non-volatile photonic technologies, enabling enhanced device performance in both integrated and free-space optics. As research progresses, further exploration into the integration of such advanced materials into scalable, high-performance photonic systems could be groundbreaking in developing ultrafast all-optical data processing and highly efficient light modulation systems. The methodologies outlined also underscore the value of computationally driven material design using first-principle modeling techniques in furthering material science innovations.