Table 2 Optical materials for DOEs
Materials | CTE (ppm/°C) | Spectral Range (nm) | n | Note(s) |
|---|---|---|---|---|
High-purity fused silica62 | 0.55 | 150–3000 | ~ 1.5 | High transparency and extremely low CTE. Thermally stable and chemically inert. High strength and scratch resistance. |
Silicon (Si)66 | 2.6 | 1000–7000 | ~ 3.5 | Good for IR applications. Moderate CTE. High n translates into tight tolerances for fabrication (etch depth). |
Germanium (Ge)66 | 5.8 | 2000–20,000 | ~ 4.0 | Good for mid-IR applications. Extensively used as a substrate for the production of optical filters. |
Polymer (Plastics)67 | 130 | 400–1600 | ~1.5 | Inexpensive but typically higher CTE and lower mechanical strength, and environmental resilience. |
Sapphire (Al2O3)68 | 4.0 | 150–6000 | ~1.8 | High transparency. High CTE, chemically inert. High cost and limited wafer sizes. Difficult to etch. |
