Fused silica
SiO₂
The quiet foundation of all of photonics: the fiber that spans oceans at 0.2 dB/km, the cladding on every integrated platform, and the substrate under most free-space optics.
Reference
Materials
The material platforms that photonics is actually built on, one page each: key optical properties with sources, and what those numbers mean when you sit down at the bench. Values are room-temperature unless stated otherwise.
Gallium arsenide
GaAs
The direct-gap workhorse of the 780–1100 nm range: VCSELs, pump diodes, and high-power bars. A strong second-order nonlinearity keeps it interesting for integrated nonlinear optics.
Indium phosphide
InP
The native platform of telecom light. Direct bandgap, lattice-matched quaternaries spanning 1.0–1.65 μm, and monolithic integration of lasers, amplifiers, modulators, and detectors on one substrate.
Lithium niobate
LiNbO₃
The electro-optic material. A strong Pockels effect, wide transparency, and ferroelectric poling made bulk LiNbO₃ the telecom modulator standard for decades; thin-film LiNbO₃ has rebuilt the platform at chip scale.
Silicon
Si
The workhorse of integrated photonics. High index contrast on SOI enables dense circuits at telecom wavelengths, at the cost of two-photon absorption, no native gain, and no second-order nonlinearity.
Silicon nitride
Si₃N₄
The low-loss, high-power passive platform. Moderate index contrast, transparency from the visible into the mid-IR, negligible nonlinear absorption at telecom wavelengths. No gain, detection, or fast modulation of its own.