There is always more than one way to solve the optical problem in AR/VR and smart glasses, and the options are not equally good at everything. This article compares IR filters against the materials, processes and design approaches it competes with, on the criteria that matter commercially: performance, durability, unit cost and lead time.
IR Filters in AR/VR and Smart Glasses
In AR/VR and smart glasses, that translates into a specific set of requirements rather than a general preference for quality. Head-mounted optics are judged by the human eye at a distance of centimeters, so haze, stray light and color shift are immediately visible. Weight and thickness drive the industrial design, which pushes designers toward thin or ultra-thin glass, wafer-scale processing and coatings that survive being worn, dropped and cleaned daily.
The tolerances that actually matter
An IR filter is specified by its curve, so the tolerances that matter are spectral. A typical commercial part holds the cut-on wavelength to plus or minus five nanometers and the visible transmission to within a few percent of nominal; precision imaging parts tighten the wavelength to two nanometers and also constrain the slope of the transition. All of these numbers are only meaningful at a stated angle of incidence, and the acceptance angle belongs on the drawing next to the spectral tolerance. Mechanical tolerances follow the mounting: thickness to plus or minus 0.02 mm for a drop-in window, outline to plus or minus 0.05 mm, and a chamfer on every edge. In AR/VR and Smart Glasses, the specification most often forgotten is the permitted variation of color across the aperture, which is what a user actually notices when a wide lens produces a green frame edge.
How it compares with the alternatives
The direct alternatives to a coated IR filter are absorptive blue glass, an absorptive dye on a polymer film, and removing the band in software. Absorptive glass has the advantage of being angle-independent and rugged but adds thickness, weight and color cast. Films are cheap and thin, which suits consumer modules, but they degrade under UV and heat and cannot be used at elevated flux. Software correction reduces NIR bleed without any component at all, but it cannot recover information the sensor never resolved separately, and it fails entirely in single-channel or monochrome systems. For instruments, machine vision and outdoor imaging in AR/VR and Smart Glasses, a dichroic filter on a thin glass substrate continues to offer the best combination of edge sharpness, transmission and service life.
Substrate and material selection
The substrate decides transmission, thickness and durability. B270 and D263T borosilicate are the standard carriers for camera and sensor windows: clear, dimensionally stable, and thin enough to laminate or to fit behind a lens. Absorptive blue glass is used where the NIR must be removed without an angle-dependent coating, and it can also be combined with a dichroic layer to sharpen the edge. Sapphire enters when the window must resist abrasion - handheld devices and outdoor instruments - and its hardness also brings a wider transmission band, out to about 4.5 micrometers. In AR/VR and Smart Glasses, the substrate is usually specified together with the cut-on wavelength, because the two interact: a dichroic edge deposited on a substrate with some intrinsic NIR absorption will read further blue than the same stack on clear glass.
What drives cost and lead time
Layer count is the main cost lever. A simple IR-cut stack is a routine chamber run; adding a broadband AR on the second surface, a hydrophobic top layer, or tightening the transition from 30 nm to 10 nm each adds chamber time, increases sensitivity to layer thickness error and reduces yield, so prices rise faster than the layer count suggests. Substrate grade and thickness matter less than expected, except for sapphire, which is materially more expensive in every respect. Size is the second lever: parts that fit comfortably inside the chamber's uniform zone cost far less per unit than parts that must be positioned at the edge, where thickness uniformity degrades. In AR/VR and Smart Glasses, the cheapest real saving usually comes from relaxing the angle specification rather than from changing the material.
Requirements specific to AR/VR and Smart Glasses
In AR/VR and smart glasses, that translates into a specific set of requirements rather than a general preference for quality. Head-mounted optics are judged by the human eye at a distance of centimeters, so haze, stray light and color shift are immediately visible. Weight and thickness drive the industrial design, which pushes designers toward thin or ultra-thin glass, wafer-scale processing and coatings that survive being worn, dropped and cleaned daily.
- Haze below 0.1 percent for see-through combiner paths
- Wafer-scale thickness uniformity for thin glass
- Wavelength-selective behavior at defined angles of incidence
- Light weight with impact resistance
ISO 10110 for optical drawings, IEC 62368 context for the finished device, and RoHS and REACH declarations.
Selection data at a glance
| Parameter | Typical value | Notes |
|---|---|---|
| IR-cut cut-on | 630-700 nm | Tuned to the sensor response |
| Visible transmission | T ≥ 90 %, R ≤ 1 % | Average 420-620 nm |
| NIR blocking | OD2 - OD4 (1 % - 0.01 %) | 700-1100 nm |
| Edge steepness | 10-30 nm transition | Dichroic designs |
| Angle of incidence | 0-30 deg specified | Passband shifts blue with angle |
| Wavelength tolerance | ± 5 nm standard, ± 2 nm precision | Measured at stated AOI |
| Substrate | B270, D263T, blue glass, sapphire | Absorptive option removes NIR without angle shift |
| Thickness | 0.3-3 mm | 0.55 - 1.1 mm typical for camera windows |
| Environmental | Humidity, salt spray, abrasion tested | MIL-C-48497 / MIL-PRF-13830B |
Frequently asked questions
Do the filters pass humidity and salt spray testing?
Ion-assisted hard oxide coatings do. Every shipment can include humidity, adhesion, abrasion and salt spray results, and the parts are routinely qualified against MIL-style test methods when the application requires it.
Can you supply the filter laminated to a sensor window or a cover glass?
Yes, coating on thin substrates down to 0.3 mm allows direct lamination or bonding. State the adhesive or bonding method at quotation so the coating stress and the assembly thermal cycle can be considered together.
How tight can the wavelength tolerance be?
Plus or minus five nanometers is routine and plus or minus two nanometers is achievable on precision imaging parts. Tighter than that usually requires sorting parts by measurement, which raises cost sharply.
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