Infrared Optics

Silicon Lens

Monocrystalline silicon is an infrared optical material with excellent comprehensive cost performance. Optical grade Czochralski silicon (OCZ-Si) as a transmission grade material is widely used in the mid-infrared (3-5um) band, and the infrared transmittance exceeds 50%. Zone-melted monocrystalline silicon can be used in a wider band (1-14um), and high-purity zone-melted monocrystalline silicon (HPFZ-Si) can even be used in the far-infrared band (greater than 30um).

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Key Features

Specialized Infrared Band

Its effective operating wavelength is 1.2–7 μm, with particular strength in the 3–5 μm mid-infrared range. Within this band, it absorbs almost no light, exhibiting extremely high transmittance.
$Extremely High Refractive Index$
Extremely High Refractive Index

Its refractive index reaches ~3.4. This means that, for the same focal length, the surface of a silicon lens can be made smoother, helping to reduce design complexity and surface shape errors.
Lightweight and Highly Hard

With a density of only 2.33 g/cm³, it is lighter than sapphire, possesses high hardness, is chemically stable, and is insoluble in water.
Good Thermal Conductivity

High thermal conductivity aids in heat dissipation, reducing the thermal lensing effect in high-power applications.

Specification of Silicon Lens

Crystallographic	Growth Method	CZ OR FZ
Crystallographic	Purity	>99.9999%
Optical	Refractive Index at n3.0	3.436
	Refractive Index at n5.0	3.426
	Thermal Coefficient of Refractive Index at 25 ℃	1.50 x 10-4
	Transmission Range, microns	1.2 - 10, 50 - 100
	Thermal Linear Expansion, ℃-1 for 25 ℃	2.55 x 10-6
Thermal	Thermal Conductivity, W/(m * ℃) at 27 ℃	159
	Specific Heat Capacity, J/(kg * ℃)	0.712 x 103
	Melting Point, ℃	1412
Mechanical	Density, g/cm3 at 20 ℃	2.33
	Mohs Hardness	7
	Young Modulus (E), Pa	1.89 x 1010
	Shear Modulus (G), Pa	7.99 x 1010
	Poisson Ratio	0.266
Chemical	Molecular Weight	28.09
Chemical	Molecular Weight	insoluble

Ref. Index vs. Wavelength λ

Wavelength, Microns	Refractive Index
1.5	3.484
2	3.456
3	3.436
4	3.429
5	3.426
6	3.424
7	3.423
8	3.422
9	3.422

Typical Application Areas

Infrared thermal imaging and temperature measurement

It's used in non-contact temperature measurement, body temperature monitoring, security surveillance, and vehicle-mounted night vision thermal imaging systems.
Optical communication and advanced manufacturing

Used as aspherical lenses or array lenses for beam collimation and focusing in high-speed optical modules (such as 400G/800G); also used in LiDAR (Light Detection and Ranging).
Industry and aerospace

Applied to infrared detection systems in industrial temperature measurement, gas detection, and aerospace fields.