Wide band gap phase change material tuned visible photonics (1808.06459v2)

Abstract: Light strongly interacts with structures that are of a similar scale to its wavelength; typically nanoscale features for light in the visible spectrum. However, the optical response of these nanostructures is usually fixed during the fabrication. Phase change materials offer a way to tune the properties of these structures in nanoseconds. Until now, phase change active photonics use materials that strongly absorb visible light, which limits their application in the visible spectrum. In contrast, Stibnite (Sb2S3) is an under-explored phase change material with a band gap that can be tuned in the visible spectrum from 2.0 to 1.7 eV. We deliberately couple this tuneable band gap to an optical resonator such that it responds dramatically in the visible spectrum to Sb2S3 reversible structural phase transitions. We show that this optical response can be triggered both optically and electrically. High speed reprogrammable Sb2S3 based photonic devices, such as those reported here, are likely to have wide applications in future intelligent photonic systems, holographic displays, and micro-spectrometers.

• The paper introduces Sb₂S₃ as a phase change material that enables tunable refractive index shifts in the visible spectrum with low absorption.
• It demonstrates a refractive index change of approximately 1 at 614 nm and an absorption edge red-shift of 115 nm, highlighting enhanced photonic performance.
• The study shows that Sb₂S₃ undergoes rapid phase transitions on a nanosecond scale, making it promising for reprogrammable optical devices.

Analysis of Wide Band Gap Phase Change Material Tuned Visible Photonics

The paper "Wide Band Gap Phase Change Material Tuned Visible Photonics" introduces a novel approach to leveraging phase change materials (PCMs) for active photonic applications, particularly in the visible spectrum. The paper offers an in-depth exploration of stibnite (Sb₂S₃) as a PCM, highlighting its advantageous properties compared to conventional tellurium-based compounds like Ge₂Sb₂Te₅. This research provides significant insights into enhancing the performance and functionality of photonic devices using Sb₂S₃, which has traditionally been considered unsuitable for rewritable optical data storage due to its large band gap.

Key Findings

1. Material Properties: Stibnite (Sb₂S₃) exhibits a tuneable band gap ranging from 2.0 to 1.7 eV and offers a non-volatile change in optical constants. The paper showcases its suitability for visible photonics by demonstrating its notable band gap and low absorption.
2. Optical Response: The coupling of the Sb₂S₃ band gap with an optical resonator leads to a marked response in the visible spectrum. The authors achieved a dramatic change in refractive index—around $\Delta$n ≈ 1 at 614 nm, manifesting a significant shift in the resonant wavelength.
3. Switching Speed: Sb₂S₃ is capable of amorphizing and crystallizing on a nanosecond scale similar to Ge₂Sb₂Te₅, with a crystallization switching time of approximately 70 ns. This speed complements the high refractive index change crucial for intelligent photonic applications, such as reprogrammable displays and micro-spectrometers.
4. Tuning Mechanisms: The paper elucidates three potential mechanisms for tuning nanostructures' optical properties. Using Sb₂S₃, the focus is placed on switching the material's refractive index via structural phase transitions, which allows for large shifts in the photonic device's spectral characteristics.

Significant Numerical Results

• Refractive Index Shift: The refractive index sees a maximum change of $\Delta$n ≈ 1, essential for modifying the condition for reflection and absorption, pivotal in resonator applications.
• Absorption Edge Shift: From amorphous to crystalline states, Sb₂S₃ shows an absorption edge red-shift of 115 nm, which translates to a band gap adjustment critical for visible photonics.
• Heating Temperatures: The crystallization occurs upon heating above 573 K and amorphization via rapid quenching post heating over 823 K.

Implications and Future Directions

The research underscores the potential of Sb₂S₃ to profoundly impact low-absorption, high-efficiency photonic devices, overcoming the limitations posed by high-loss materials like Ge₂Sb₂Te₅. This advancement situates stibnite as a viable candidate for future developments in intelligent photonics and offers several avenues for practical applications, including holographic displays and adaptive optics.

The next steps likely involve optimizing the integration of Sb₂S₃ in device architectures to harness its full potential for visible spectrum applications. Further investigation may address the scalability of the fabrication process and the durability of these materials under extended use conditions. Additionally, exploring the coexistence of electrical and optical switching capabilities could offer dual-function devices with enhanced performance and multi-modal operation.

Overall, this paper presents a compelling case for Sb₂S₃ as a far superior PCM for visible photonics, encouraging further exploration and refinement to enable advanced, rapid-response photonic systems.