Optical Properties

Transmission of Used Glasses

Molded Caps
SCHOTT offers two main glass types as molded glass. The main workhorse (“St”) is usable for visible and NIR light. A second glass expands this range into the UV region (“UV”).

The following chart shows the transmission performance of these glasses. All data indicated are for uncoated glass.

Figure 1. Transmission of typical glass

Soldered Caps

Windows
The usual glass type used for making window caps with solder glass technology is SCHOTT D263 glass. The transmission of this glass is shown in Figure 1 (“Pl”). For more information about this glass type, please visit this page.

For applications which have to extend into the UV and/or further into the infrared regions, we offer solder-sealed window caps with sapphire windows. This material provides a transmission band from 170 nm to 5500 nm. Sapphire with defined crystal orientation (i.e. c-cut) can be offered if the birefringent nature of sapphire is unsuitable for the application.

Ball Lens Caps
Ball lens caps can be made with a big variety of optical glasses. Widely used glasses, ranging from refractive index 1.5 to 2.0 include:

• N-BK7
• N-LaSF44
• Sapphire
• LaSFN9
• LaSF35

Data for the above-mentioned optical glasses are available here.

Coatings
SCHOTT can offer optical coatings on lens and window caps for special applications that require a unique performance. Commonly applied coatings include:

• AR (anti-reflective) coating

Figure 2. Example of broadband AR coating

• Beam Splitter (interference or metal attenuation coating)

Figure 3. Example of interference beam splitter

• Filter Coatings

Figure 4. Example of filter coating

Coatings are applied using PVD techniques such as evaporation or sputtering. All of our coatings meet the requirements of MIL-C-48497 for durability. Transmission measurements are carried out using state-of-the-art spectrophotometers.


Optical Data for Lens Caps
SCHOTT has all necessary equipment to calculate and measure the optical properties of our lens caps. We can supply all necessary data such as effective focal length, position of principal planes in the lens, lens radius etc…

Due to the very accurate sphericity (typical specification: sphericity < 0.5 µm), it is very easy to calculate the effective focal distance (EFL) with respect to the back focal distance (BFL) of the ball lenses.

Figure 5. Definition of terms for Ball Lens
(With courtesy of Edmund Optics, Inc.)

EFL = nD/[4(n-1)]
BFL = EFL - [D/2]

SCHOTT can also assist the customer in questions concerning how to effectively couple the light into fibers for data communication.

Figure 6. Achievable coupling efficiency into single mode fiber of different
optical glasses (refractive index n)