ISO 9001 - AS 9100 - ITAR Standard & Custom Optical Filters and Coatings


Optical Coating Capabilities


What is an Optical Filter Coating?

An optical coating is one or more thin layers of material deposited on an optical component such as a lens or mirror, which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating, which reduces unwanted reflections from surfaces, and is commonly used on spectacle and photographic lenses. Another type is the high-reflector coating which can be used to produce mirrors that reflect greater than 99.99% of the light which falls on them. More complex optical coatings exhibit high reflection over some range of wavelengths, and anti-reflection over another range, allowing the production of dichroic thin-film optical filters.


Andover has a variety of optical coating technologies at its disposal, providing customers with solutions tailored to their specific applications. Technologies include:

We can design and manufacture coatings to meet your most demanding requirements. Range of Wavelengths from 193nm to 14 microns, on a wide variety of substrate materials including BK-7, filter glass, borosilicate glass, Silicon, Germanium, Sapphire, Fused Silica, Calcium Fluoride, Zinc Selenide, Zinc Sulfide, and more.

All Andover chambers are internally custom-built, computer-controlled, and use the latest deposition techniques. Ion beam compaction yields high-density coatings, reducing environmental effects and eliminating voids in the coating, which also increases hardness.


We have an extensive back-catalog of optical coating formulas for substrate materials from optical glass and crystalline materials to bare and nickel-plated metals. Our thin-film coatings employ oxide and fluoride dielectric multilayer coating materials including MgF, SiO2, TaO5, and HfO2. We also offer enhanced and protected metallic coatings of gold, silver, and aluminum. Our current coating line-up covers a nominal wavelength range from 193nm - 14µm.

Coating Types

  • Anti-reflective coatings
  • High reflective coatings
  • Partially reflective coatings
  • Polarizing coatings
  • Bandpass coatings for the UV, visible, and infrared
  • Beam splitter coatings for the UV, visible, and infrared
  • Neutral density filters
  • Protective and enhanced aluminum, silver, and gold coatings 


We have the unique ability to provide a diverse range of coatings spanning a broad wavelength range on a wide variety of materials. We produce coatings for a multitude of applications, ranging from environmental monitoring to space-based astronomy. Our AS9100 certification ensures compliance with aerospace as well as military standards.

  • Variety of coating technologies to suit any need
  • Wavelengths from 193nm to 14μm
  • Custom coatings on a wide variety of substrates

Dichroic Filter Coatings

Andover designs and produces custom dichroic filter coatings for a variety of applications. Our in-house engineers can design exotic coatings to meet very stringent spectral and environmental requirements. As with all of our coatings, they can be applied to a wide variety of materials, in a myriad of shapes and sizes.

A hot mirror is a dichroic filter that reflects 90% of near-infrared (NIR) and infrared (IR) light while transmitting up to 80% of the visible light. Hot mirrors transmit shorter wavelengths and reflect infrared energy. Hot mirrors can be specified for an angle of incidence ranging from aero to 45 degrees. They are made by applying a multi-layer dielectric coating to the glass substrate such as borosilicate glass. 

A cold mirror is a dichroic filter that reflects up to 90% of the visible light spectrum while allowing transmission of infrared wavelengths IR and near IR of up to 80%. Cold mirrors reflect the shorter wavelengths and transmit the heat (infrared). A cold mirror can be specified for an angle of incidence ranging from zero to 45 degrees. They are made by applying a multi-layer dielectric coating to the glass substrate such as borosilicate glass.

Anti-Reflective AR Coatings

Andover produces hard oxide AR coatings from 193nm to 14μm. We routinely coat customer-supplied substrate material in all shapes and sizes: lenses, prisms, flats, domes, etc. We can coat a wide variety of materials, ranging from typical optical glass to exotic materials such as Calcium Fluoride, Zinc Sulfide, and Zinc Selenide. The hard coatings not only reduce reflections to <0.1% at angles up to 50°, but also help protect optical surfaces, as the coating is more durable than the uncoated substrate. 

Neutral Density Filters

Andover is a leader in flat response neutral density filters in the UV to near-infrared (250nm-2000nm) and far-infrared (2000-14000nm). These coatings are hard and pinhole-free. Our ND Filters exhibit industry-leading spectral neutrality over a broad wavelength range, with optical densities up to 4.0. (We can deposit A/R coating on the uncoated surface for a nominal fee.) Andover's absorptive ND filters are unique in that they are AR coated to reduce surface reflections. This enables them to be stacked without concern about losses and artifacts due to multiple reflections.

Bandpass Filters

We produce bandpass filters over a much broader range than any other coating firm, from 193nm to 14μm in wavelength. Bandwidths range from very wide, (> 10%) to extremely narrow, (< 0.02%). We can produce semi-custom bandpass filters with short lead times. We also have over 1,500 standard filters.

Specialized Coatings

With our computer-controlled systems, we can quickly produce a variety of high-quality coatings in sizes up to 300mm with excellent repeatability using any process from resistance evaporation to magnetron sputtering. We also offer Ion-assisted e-beam deposition and Hybrid technologies.

Transmittance depends considerably on the light wavelength range: different kind of glasses and coatings helps to improve performance in particular spectral regions, e.g. UV or IR. Generally, good transmission in the UV region is more difficult to achieve.


Contact a technical sales representative for more information.



ISO 9001 and AS 9100 Certified. ITAR Registered.