Introduction | Types of Planar Etalons | Fabry-Perot Etalon Theory

Types of Planar Etalons and Typical Specifications*

Air-Spaced Etalons
Air-Spaced Etalons have appropriate grade fused silica (UV-visible or IR) substrates. Outside-face AR coatings and wedges on the substrates prevent extraneous interference patterns from forming. Spacers, optically contacted to the substrates, determine the parallelism of the mirrored surfaces and the etalon’s free spectral range. Depending upon the application, the spacers can be fused silica or a low thermal expansion material such as Zerodur
Æ or ULE.
Plate Material Fused Silica
Spacer Material Fused Silica, ZerodurÆ, or ULE
Flatness l/100
Parallelism l/100
Gap 5m to 65mm
Clear Apertures 2mm to 100mm
Outside Diameter Clear Aperture + 15%
Wavelengths 157nm to 3m
Finesse Up to 100
Coatings Standard and Custom
Housing Acetal or Aluminum

Solid Etalons
Solid Etalons typically have fused silica substrates with the material grade (e.g. UV-visible or IR) dependent on the spectral region. The faces are ground, polished, and figured typically to better than
l/100 flatness with similar quality parallelism between the faces. Dielectric (or, rarely, metallic) coatings provide the reflectivity necessary for the required finesse.
Material Fused Silica
Flatness l/100
Parallelism l/100
Clear Aperture 2mm to 125mm
Diameters 3mm to 150mm
Thickness 50m to 20mm
Wavelengths 157nm to 3m
Finesse Up to 50
Coatings Standard and Custom
Housing Acetal or Aluminum

Fiber optic communication requires extreme miniaturization of optical components. It is for applications such as DWDM (dense wavelength division multiplexing), line narrowing, and channel monitoring that TecOptics introduced its new line of MicroEtalons. Newly developed manufacturing techniques enable TecOptics to supply large quantities of these miniature air-spaced and solid etalons at low prices. Air-spaced versions have dimensions as small as 4.5mm x 2mm x 3mm while solid MicroEtalon cross-sections can be as small as 2mm. Finesse values can be greater than 100.
Plate Material Fused Silica
Spacer Material ZerodurÆ or ULE
Flatness l/100
Parallelism l/100
Gap 100to 3mm
Clear Aperture 2mm
Dimensions Down to 4.5mm x 2mm x 3mm
Finesse To 100
Wavelengths All standard fiber optic regions
Housing None

Deposited Etalons
To overcome the limit of the thinness of a solid etalon yet retain its mechanical strength, TecOptics offers its unique Deposited Etalons. On one side of a precision substrate our sophisticated coating plants sequentially deposit a mirror coating, a silicon dioxide spacer, and the other mirror coating. Deposited etalons' applications include intracavity laser wavelength tuning.
Substrate Fused Silica
Spacer Thickness 2to 25m
Clear Aperture 2mm to 100mm
Wavelengths 193nm to 2.5m
Finesse To 50
Coatings Custom Design
Housing Acetal or Aluminum

* Note that for any etalon it is not always possible to attain all combinations of specifications simultaneously.

Ultra-Narrow Tuned Etalon Filters
Frequently, standard interference filters are not able to attain the resolution required for precision applications. TecOptics Tuned Etalon Filters fill this gap by adding an order of magnitude or more of resolving power. A normal narrow-band interference filter has a resolution of approximately 10‰. By adding the Tuned Filter to the interference filter, the resolution improves to sub-angstrom levels. The basis of the Tuned Filter is our ability to fabricate etalon substrates and spacers with their thickness precisely tuned so an integral number of wavelengths matches the optical path length, including the mirror coatings, of the light inside the etalon. Their specifications are similar to the Air-Spaced and Solid Etalons above with the additional tight tolerance on spacer or plate thickness to tune the desired wavelength.
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