Technical Details of Hermetic Windows and Lens Caps

SCHOTT can manufacture its range of hermetic windows, lenses, caps and discs in a variety of geometric shapes, with options for different emitting angles, glass types and coatings. We can also provide customized high-performance products according to your application requirements.

Gas-tight

Gas-tight windows and lens caps give components a sturdy defense against water, moisture, humidity, chemicals, mechanical impact, and other environmental effects. This results in an improved performance and extended lifetime.

Excellent optical properties

SCHOTT’s optical glass and coating competence is a large advantage for customers who demand the highest quality and precision. Thanks to our unique expertise in glass, our windows and lenses provide full light-spectrum emission, from the UV to the visible to the IR range.

Weldability and solderablity

Our customers receive products with excellent surface quality thanks to the strict monitoring and control of technical properties, as well as superior material quality. This enhances the weldability of the caps for a reliable hermetic seal.

Incredibly customizable

Customers benefit from a broad range of options, including product shape, optical glass type, metal material, AR or UV coating, and lens refractive indices ranging from 1.5 to 2.0.

Transmission

Coatings

Ball Lens

Sealing technology

Transmission

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 usual glass type used for making window caps with solder glass technology is SCHOTT D263 glass (PI). The following chart shows the glass transmittance spectrum for these glasses. All data is for uncoated glass.

Graph showing the glass transmittance spectrum for St, UV and PI glass

Coatings

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

AR (anti-reflective) coating

Beam splitter (interference or metal attenuation coating)

Filter coating

Ball lens

Ball lens caps can be manufactured using a large variety of optical glasses. Ranging from a refractive index of 1.5 to 2.0, widely used glasses include:

N-BK7
N-LaSF44
Sapphire
LaSFN9
LaSF35

A diagram showing the definition of terms for a ball lens cap

Optical properties for lens caps

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

Because of the highly 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.

SCHOTT can also help with questions concerning how to effectively couple the light into fibers for data communication.

Graph showing the achievable coupling efficiency of different optical glasses

Sealing technology

Hermetic windows and lens caps are often distinguished by their production method – whether the glass and metal components are joined together by molding or soldering.

Molded or 'Direct Seal' caps

Glass and metal are sealed without the use of any other interface material.
The sealing process must be designed in a way that ensures the glass cools down without the formation of bubbles or inclusions, and obtains the correct optical properties.
The highly robust glass-to-metal connection of SCHOTT caps provides excellent mechanical stability and processability during the customer production process.
This production method is typically used for all conventional types of optical signal transmission.

Find out more about glass-to-metal sealing technology.

Cross-section of a SCHOTT Molded Window Cap Cross-section of a SCHOTT Integrated Mini Lens Cap

Solder caps

Metal and glass are fused with the aid of a solder glass.
This production method is typically used for ultra-high precision applications with special optical components.
To ensure that extremely narrow tolerances of the optical properties can be met, the components are soldered together in a cleanroom environment.
Our technological leadership ensures that the lenses and windows are developed and processed to an extremely high quality standard.

Cross-section of a SCHOTT Angled Window Cap Cross-section of a SCHOTT Solder Ball Lens Cap Cross-section of a SCHOTT Machined TO Cap Cross-section of a SCHOTT Wedge Window Cap Cross-section of a SCHOTT Flat Window Cap