Mid-IR transparent waveguide + phase-change programmable photonics
Physics / mechanism
Chalcogenide glasses contain group VI elements (S, Se, Te) bonded with As, Ge, or Sb. Two distinct uses:
1. Mid-IR waveguide platform. As₂S₃ and As₂Se₃ are transparent from ~0.6 μm out to 8-12 μm — the molecular-fingerprint mid-IR band where silicon absorbs. Loss best-case ~0.1-0.5 dB/cm. Ideal for breath analysis, gas sensing, biomedical spectroscopy, hyperspectral imaging.
2. Phase-change programmable photonics. GeSbTe (GST), the same alloy used in optical-disc storage and emerging electronic phase-change memory, has dramatically different refractive index in amorphous vs crystalline phases. A photonic switch with a GST element can be electrically programmed (set/reset cycles, like FeRAM) and remain non-volatile — opening programmable photonic processors, optical neural networks, and reconfigurable filters.
Competitive landscape
Mid-IR ChG production: IRflex, CorActive, Schott (specialty fibre + bulk), no integrated photonic foundry. Programmable photonics with GST: Oxford (Bhaskaran group), EPFL, IBM Zurich, Cambridge (Wright group). Commercial scale-up: Salience Labs (Oxford spinout, photonic compute), Lightelligence and Lightmatter (different photonic compute approaches but adjacent thesis).
Frontier (open questions)
See frontmatter frontier: block.