Substrates and Discs

Lens elements appear to be very simple products, but appearances can be deceiving. Their surfaces are so smoothly polished that deviations from perfection are measured in millionths of an inch!

The manufacture of a low-volume or prototype lens or colored filter starts with roughly cut discs of glass and ends with precision polishing. Mirrors and thin-film filters require additional processing. Engineers use the term disc to refer to a roughly plane-parallel slice of glass that will be ground and polished. The term substrate refers to a polished piece of glass that will receive a coating.

The manufacture of lenses, mirrors and filters involves several steps. The first step, of course, is the creation of the basic material, such as glass, sold in blocks or "slabs." Manufacturers reduce the blocks to smaller rods or rectangular sections using diamond core drills and diamond bandsaws. Craftsmen slice the rods or sections into discs that are roughly the size of the final component.

The roughly plane-parallel surfaces of the discs are ground with a coarse diamond slurry to bring the optical surfaces into approximate conformance with the final specification. Lensmakers use precision grinding compounds to form the proper surface curvatures, and then use a polishing rouge to create a precision polish. At this point, the surfaces are smooth to a few millionths of an inch, and a lens or colored filter can function as an optical device.

Mirrors and other components, such as thin-film filters, often require a coating to function properly. Polished components serve as substrates for these coatings.

Usually, glass substrates and discs are purchased by companies that manufacture optical components. Nevertheless, important applications for optical materials exist in other branches of engineering. For example, its rigidity (small Poisson’s Ratio) and low coefficient of thermal expansion make Pyrex® and other specialty glass ideal for certain critical parts of mechanical assemblies. Substrates and discs can provide the starting points for the manufacture of these mechanical components.

JML can supply special shapes and various sizes of substrates or discs. The surfaces can be diamond saw cut, ground or precision polished. Please see the following list of available glass types.