• 1710487672923
  • Ge-PCX
  • PCX-Lenses-Ge-1

Germanium (Ge)
Plano-Convex Lenses

Plano-convex (PCX) lenses have a positive focal length and can be used to focus collimated light, to collimate a point source, or reduce the divergent angle of a diverging source. When image quality is not critical, plano-convex lenses can also be used as a substitute for achromatic doublets. To minimize the introduction of spherical aberration, a collimated light source should be incident on the curved surface of the lens when being focused; Similarly, a point light source should be incident on the planar surface when being collimated.

When deciding between a plano-convex lens and a bi-convex lens, both of which cause collimated incident light to converge, it is usually preferable to choose a plano-convex lens if the desired absolute magnification is either less than 0.2 or greater than 5. Between these two values, bi-convex lenses are generally preferred.

Due to its broad transmission range ( 2 – 16 µm) and stable chemical properties, Germanium is well suited for IR laser applications, it is excellent for security, military and imaging applications. However Ge’s transmission properties are highly temperature sensitive; in fact, the absorption becomes so large that germanium is nearly opaque at 100 °C and completely non-transmissive at 200 °C.
Paralight Optics offers Germanium (Ge) Plano-convex (PCX) Lenses available with a broadband AR coating for the 8 µm to 12 μm spectral range deposited on both surfaces. This coating greatly reduces the high surface reflectivity of the substrate, yielding an average transmission in excess of 97% over the entire AR coating range. Check the Graphs for your references.




Germanium (Ge)

Coating Options:

Uncoated or with DLC & Antireflective Coatings Optimized for the 8 - 12 μm Range

Focal Lengths:

Available from 15 to 1000 mm


Excellent for Security, Military, and Imaging Applications


What you get with a Paralight Optics Germanium Plano-Convex Lens

● Each lens goes through a thorough inspection process before leaving our factory.
● Diameters ranging from 25.4-50.8mm and additional options upon request.
● Effective Focal Lengths (EFL) range from 25.4-200mm.
● Additional optical coatings available upon request.
● OEM is always welcome.

Common Specifications:


Reference Drawing for

Plano-convex (PCX) Lens

Dia: Diameter
f: Focal Length
ff: Front Focal Length
fb: Back Focal Length
R: Radius
tc: Center Thickness
te: Edge Thickness
H”: Back Principal Plane

Note: The focal length is determined from the back principal plane, which does not necessarily line up with the edge thickness.


Ranges & Tolerances

  • Substrate Material

    Germanium (Ge)

  • Type

    Plano-Convex (PCX) Lens

  • Index of Refraction

    4.003 @ 10.6 μm

  • Abbe Number (Vd)

    Not defined

  • Thermal Expansion Coefficient (CTE)

    6.1 x 10-6/℃

  • Diameter Tolerance

    Precison: +0.00/-0.10mm | High Precision: +0.00/-0.02mm

  • Thickness Tolerance

    Precison: +/-0.10 mm | High Precision: +/-0.02 mm

  • Focal Length Tolerance

    +/- 1%

  • Surface Quality (Scratch-Dig)

    Precison: 60-40 | High Precision: 40-20

  • Surface Flatness (Plano Side)


  • Spherical Surface Power (Convex Side)

    3 λ/4

  • Surface Irregularity (Peak to Valley)


  • Centration

    Precison: <3 arcmin | High Precision: <30 arcsec

  • Clear Aperture

    > 80% of Diameter

  • AR Coating Range

    8 - 12 μm

  • Transmission over Coating Range (@ 0° AOI)

    Tavg > 94%, Tabs > 90%

  • Reflectance over Coating Range (@ 0° AOI)

    Ravg < 1%, Rabs < 2%

  • Design Wavelength

    10.6 μm

  • Laser Damage Threshold

    0.5 J/cm2 (1 ns, 100 Hz, @10.6 μm)



♦ Transmission curve of 10 mm thick, uncoated Ge substrate: transmission range from 2 to 16 μm
♦ Transmission curve of 1 mm thick AR-coated Ge: Tavg > 97% over the 8 - 12 μm spectral range
♦ Transmission curve of 2 mm thick DLC + AR-coated Ge: Tavg > 90% over the 8 - 12 μm spectral range
♦ Transmission curve of 2 mm thick Diamond-Like coated (DLC) Ge: Tavg > 59% over the 8 - 12 μm spectral range


Transmission Curve of 1 mm thick AR-coated (8 - 12 μm) Germanium


Transmission curve of 2 mm thick DLC + AR-coated (8 - 12 μm) Germanium


Transmission curve of 2 mm thick Diamond-Like coated (DLC) (8 - 12 μm) Germanium