Optical coating glossary

Engineered low surface energy without C–F bonds, achieved through silane chemistry, methylated siloxanes, or hierarchical micro/nano structures. The PFAS-free path forward for mass-market AF coatings.

Resistance to wetting and adhesion of oils. Measured as oil contact angle (OCA), typically with hexadecane. OCA > 60° is the practical threshold for fingerprint-resistant surfaces.

A class of synthetic fluorinated chemicals containing C–F bonds. Historically used for hydrophobic / oleophobic coatings due to low surface energy. Now globally restricted (EU REACH, US EPA, Japan, Korea) due to environmental persistence and health risks.

A formulation containing no per- or polyfluoroalkyl substances. Becoming a regulatory hard requirement (EU universal PFAS restriction proposal, US state laws). Kriya's entire RI platform 1.16–2.00 is PFAS-free.

The angle at which a droplet of given volume begins to slide off a tilted surface. Lower slip angle indicates better self-cleaning behaviour. Closely tied to contact-angle hysteresis.

The thermodynamic energy required to create a unit area of new surface, measured in mJ/m². Low surface energy (≈10–20 mJ/m²) gives hydrophobicity and oleophobicity. PFAS surfaces reach ~10 mJ/m²; PFAS-free hybrid silanes 15–20 mJ/m².

The angle a water droplet makes with a surface, measured by goniometry. WCA > 90° = hydrophobic, > 150° = superhydrophobic. Higher WCA correlates with better anti-fingerprint performance and easier cleaning.

The unit of specular gloss, defined so polished black glass with refractive index 1.567 reads exactly 100 GU at 60°. Anti-glare coatings typically deliver 30–95 GU depending on haze target.

An instrument that measures angular distribution of reflected or transmitted light. Used to characterise BRDF, BTDF, and the angular signature of anti-glare coatings beyond simple scalar gloss.

An instrument that measures total transmittance, haze, and clarity of transparent samples by collecting forward-scattered light in an integrating sphere. BYK Haze-Gard is the industry-standard model.

Arithmetic mean surface roughness measured over a small profile length, typically nm to μm scale. AG coatings use controlled Ra in the 50–500 nm range to scatter specular reflection.

A multi-function appearance instrument measuring 20°/60°/85° gloss, distinctness of image (DOI), and reflected haze in a single reading. Standard for surfaces where both gloss and DOI matter.

A pixel-level scintillation visible when an anti-glare surface sits over a pixelated display. Caused by the AG micro-structure modulating the light from individual sub-pixels. A key trade-off in AG haze tuning.

The angle of incidence at which p-polarised light is fully transmitted with zero reflection from a non-absorbing dielectric interface. Foundational for polarisation-discriminating AR design. For absorbing media, replaced by a pseudo-Brewster minimum.

A multilayer anti-reflection design that suppresses reflectance across a wide spectral range (e.g., 400–700 nm visible, 905–1550 nm NIR). Typically 3–5 layers tuned by numerical optimisation.

Reflection at a planar dielectric interface, derived from Maxwell's equations. Polarisation-dependent: s-pol (perpendicular) and p-pol (parallel) reflectance differ. The Fresnel equations are the foundation for AR-coating design.

The practice of choosing layer materials so the refractive indices change gradually rather than abruptly across an interface, suppressing Fresnel reflection. Critical for OLED extraction layers and waveguide cladding.

An optical assembly of two or more thin-film layers with alternating high and low refractive indices, designed to engineer broadband reflectance, transmittance, or filter response. Computed via the transfer-matrix method (TMM).

A complex quantity that combines refractive index and angle, used in TMM to compute reflection and transmission. Reflectance R = |(Y₀ − Y)/(Y₀ + Y)|² where Y₀ is admittance of the incident medium.

A thin-film layer with optical thickness equal to one quarter of the design wavelength. A single QWL of refractive index √(n_air × n_substrate) gives zero reflection at the design wavelength — the simplest single-layer AR.

s-polarised light has its electric field perpendicular to the plane of incidence (German "senkrecht"); p-polarised light has its electric field in the plane (parallel). Reflectance differs significantly between the two, especially near the Brewster angle.

A numerical technique for computing the complex amplitude reflectance and transmittance of arbitrary multilayer thin-film stacks. Each layer is represented as a 2×2 matrix; the stack matrix is the product. Standard tool in AR coating design.

A two- or three-layer AR stack tuned for a single narrow wavelength band, named for its V-shaped reflectance curve. Common in laser optics and LiDAR sensor windows.

The 3D region in which a user's pupil can be placed and still see the full virtual image. Constrained by exit pupil expansion gratings. Larger eye-boxes accommodate diverse interpupillary distances and head positions.

The angular extent of the world a user can see through an optical instrument. AR/VR FOV is bounded by the waveguide TIR envelope and grating bandwidth. Increasing FOV often requires higher refractive-index substrates.

A volume Bragg grating recorded as a refractive-index modulation inside a photopolymer or dichromated gelatin film. Unlike SRG, no surface relief; tunable angular and spectral selectivity. Used in select AR/VR products and HUD combiners.

Diffractive elements at the entry and exit of a waveguide that couple display light into TIR propagation and back out toward the user's eye. Efficiency, uniformity, and angular bandwidth are critical design parameters.

The wavevector representing direction and spatial frequency of a light wave. Used in waveguide and grating analysis to describe coupling, dispersion, and TIR conditions in k-space.

A waveguide design technique that uses successive grating bounces to enlarge the exit pupil from the projector's small native pupil to a useful eye-box. 1D and 2D pupil expanders are standard in modern AR glasses.

A periodic micro/nano-structured surface that diffracts light. In AR/VR waveguides, SRGs serve as in/out-couplers and pupil expanders. Pitch typically 200–500 nm; fabricated by NIL on Kriya HRI substrates.

When light inside a denser medium hits an interface with a less-dense medium beyond the critical angle, all light reflects back. The basis of waveguide light confinement and fibre optics.

A set of camera-, radar-, and LiDAR-based safety features (lane keeping, emergency braking, adaptive cruise). Camera and LiDAR sensor windows demand AR coatings with high transmission across the operating wavelengths.

A protective transparent cover over an automotive camera (front-facing, surround-view, driver monitoring). Demands broadband AR for low ghosting, hardcoat for stone-chip resistance, and AF chemistry for self-cleaning behaviour.

A faint duplicate of the primary HUD image caused by reflection at the second surface of the windshield. Suppressed by wedge-angled PVB inserts and tightly-controlled multilayer AR on the inner glass surface.

An automotive optical system projecting information (speed, navigation, ADAS warnings) into the driver's line of sight via the windshield. Multilayer AR + selective reflection on the glass-air and glass-PVB interfaces is essential to suppress double images.

Time-of-flight 3D-mapping sensor using pulsed laser light, typically at 905, 940 or 1550 nm. Sensor windows need narrow-band AR (V-coat) to maximise transmission and minimise reflection back into the detector.

The fraction of 700–2500 nm light passing through a coating or substrate. Critical for LiDAR (905/940/1550 nm), driver-monitoring cameras (940 nm), and night-vision systems. Most automotive solar-control coatings reject NIR but must transmit at sensor-specific bands.

A HUD design that accounts for the polarised nature of LCD projector output and the polarising effect of polarised sunglasses. Without compensation, drivers wearing polarised glasses lose the HUD image — solved by quarter-wave retarders or s-pol projection.

A self-limiting CVD variant that grows films one atomic layer at a time via alternating precursor pulses. Sub-nm thickness control and conformal coverage. Used for ultra-thin AR layers, gate dielectrics, and pinhole-free barriers.

A wet-chemical coating method where the substrate is immersed in a solution and withdrawn at controlled speed, leaving a uniform film. Thickness scales with viscosity, density, and withdrawal speed (Landau-Levich). Cost-effective for prototyping and small-volume optical parts.

A vacuum PVD method where source material is heated (resistive or e-beam) and vapour deposits on the substrate. Slower-line-of-sight; common for prototype optical coatings. Substrate heating limits use on plastics.

An R2R coating method using an engraved cylinder transferring metered fluid pockets to the substrate. Best for thicker (~1–20 μm) functional layers; not ideal for sub-100 nm AR layers.

Chemical vapour deposition using a plasma to lower required substrate temperature. Common for SiO₂, SiN_x, and SiO_xN_y films on temperature-sensitive substrates. Faster than ALD with thicker films but less precise.

Continuous wet-chemical coating of flexible substrates (PET, TAC) on a roll. Slot-die, gravure, or spray applicators followed by inline cure (UV, thermal, or dual). High throughput; preferred for AR/AG/AF on automotive and display films.

A precision wet-coating method using a metered fluid extruded through a thin slot onto a moving web. Premier R2R technique for thin (~100 nm to ~10 μm) optical coatings with cross-web uniformity below ±1%.

A wet-chemical synthesis route forming an inorganic oxide network from molecular precursors via hydrolysis and condensation. Enables low-temperature processing of optical coatings (silica, titania, zirconia) on plastic substrates. Kriya's core platform.

A wet-chemical method dispensing fluid on a spinning substrate; centrifugal force flings excess off, leaving a thin uniform film. Standard for wafer-scale optics and lab-scale prototyping. Thickness scales with √(viscosity / spin speed).

A wet-chemical method using atomised droplets directed at the substrate. Suited to large or curved parts (automotive bezels, AR/VR optics housings) where dip and spin are impractical. Requires careful nozzle and overspray control for thickness uniformity.

Physical vapour deposition where ions bombard a target and ejected atoms condense on the substrate. Produces dense optical films (TiO₂, SiO₂, Ta₂O₅) with precise thickness. High capex; vacuum-only; standard for camera and laser optics.

The ITU-R recommendation for ultra-HD television, defining a colour space ~75% of the visible CIE 1931 area. Achievable only with quantum-dot or laser primaries. AR cover lenses must avoid wavelength-selective reflection that distorts the wide gamut.

The range of colours a display can reproduce, plotted on a chromaticity diagram. Wider gamuts (DCI-P3, BT.2020) require pure narrow-band primaries and are sensitive to cover-lens reflection coloration — uniform AR is critical.

The ratio of peak white luminance to deepest black luminance. AR coatings on the cover lens reduce ambient light reflection (which adds to black-state luminance) and dramatically improve daylight CR.

A wide-gamut colour space defined for digital cinema (SMPTE 431-2), approximately 25% larger than sRGB. Adopted by Apple displays and modern smartphones. Tightens AR coating colour-neutrality tolerances.

A non-emissive display modulating polarised light from a backlight via voltage-controlled liquid crystals. Dominant in TVs, monitors and most automotive panels. Cover lens commonly receives Kriya AR/AG/AF coatings.

An emissive display using arrays of microscopic inorganic LEDs (typically GaN). Higher luminance and lifetime than OLED. Index-matching encapsulation and AR cover-lens coatings critical for optical efficiency.

A measure of how well an optical system preserves spatial detail, expressed as contrast vs spatial frequency (cycles/mm or lp/mm). Cover-lens scattering (haze, AG roughness) directly degrades MTF.

An emissive display where each pixel emits its own light, eliminating the backlight and enabling true black. Strong demand for index-matched extraction layers (Kriya HRI 1.85+) to boost EQE 20–40%.

The default colour space for the web and most consumer displays, defined by IEC 61966-2-1. Smaller gamut than DCI-P3 or BT.2020. Typical legacy reference for cover-lens reflectance neutrality requirements.

The off-axis angle at which display luminance drops below 50% of normal incidence (CR 10:1 or 50% in spec). Cover-lens AR/AG coatings preserve viewing-angle uniformity by managing reflection at oblique angles.

An oscillating-sand abrasion test originally developed for ophthalmic lenses. Bayer ratio = (Δhaze of reference) / (Δhaze of sample). Higher = better. Used for hardcoat ranking.

A qualitative adhesion test where the coating is cut into a 5×5 or 6×6 lattice and tape is applied/pulled. Rated 0–5 by % of squares retained. ISO 2409 Class 0 (no flaking) is industry minimum.

The increase in haze (%) after a wear test relative to the unworn sample. The standard scalar metric for coating durability after Taber, steel wool, or Bayer abrasion.

A scratch-hardness test that pushes graphite pencils of escalating hardness (6B–9H) across a surface at a defined load and angle. Reported as the hardest pencil that does not mar the surface. Hardcoats target 3H–4H.

A quantitative adhesion test using a dolly bonded to the coating and pulled normal to the surface. Reported in MPa. Captures cohesive vs adhesive failure mode and absolute strength.

A surface's ability to retain optical and aesthetic integrity under sliding contact. Quantified by pencil hardness, Taber, steel wool, or Bayer tests; visualised by scratch density and Δhaze.

A scratch test using #0000-grade steel wool pressed against a surface at fixed load (typically 1 kg/cm²) for a defined number of cycles. Surface failure measured as Δhaze or visual scratch density. Common for cover-glass and AG/AF qualifications.

A standardised wear test using a rotating sample disc and two abrasive wheels under specified load. Reported as Δhaze (%) after a number of cycles (typically 100 or 500). Quantifies real-world cleaning-cycle durability.

The ratio of feature width to pitch in a periodic structure. Affects diffraction efficiency, bandwidth, and angular response. Typical SRG duty cycles 0.3–0.7 depending on application.

In photovoltaics, the ratio of maximum-power-point power to (Voc × Isc), reflecting cell quality. In nanostructure design, the fraction of unit-cell area occupied by structured material.

The radial phase function required to focus a collimated beam to a point at focal length f. Implemented in metalens designs by spatially varying nanopillar height or diameter to engineer local phase delay.

A flat optical lens consisting of an array of sub-wavelength nanopillars that locally tailor phase. Replaces refractive lenses for ultra-thin imaging. Requires HRI (n ≥ 1.85) substrate or dielectric pillars patterned by NIL or e-beam.

A wafer-scale or roll-to-roll patterning technique where a master mould transfers sub-100 nm features into a curable resin. Cost-effective alternative to e-beam or DUV lithography for AR/VR waveguides and metalens prototyping.

The center-to-center spacing of periodic features (gratings, nanopillars). Sub-wavelength pitch (~λ/2) avoids unwanted diffraction orders. AR/VR waveguide pitches typically 200–500 nm.

Continuous nanoimprint patterning on flexible substrates using a roller-mounted master. Enables wafer-equivalent throughput at lower capex than wafer NIL. Critical for cost-effective AR/VR waveguide manufacturing.

Manufacturing at the scale of standard semiconductor wafers (typically 200 mm or 300 mm). Required throughput level for AR/VR waveguides and metalenses to compete with conventional lenses on cost.

A transparent conductive oxide nanoparticle (Sb-doped SnO₂) absorbing strongly in the NIR while transmitting visible light. Key heat-rejecting filler in automotive solar-control coatings; alternative to indium-based ITO.

A high-refractive-index ceramic oxide (n ~2.2 visible) used as nanoparticle filler in HRI coatings and as a UV absorber in protective films. Stable under solar exposure.

A resin combining UV and thermal curing chemistry. UV provides instant green-state cure for line speed; subsequent thermal step completes crosslinking inside shadowed regions or curved geometries. Standard for automotive curved-display coatings.

A material combining an inorganic backbone (Si–O, Ti–O, Zr–O networks) with organic side chains for crosslinking. Provides ceramic hardness with polymer flexibility, the foundation of Kriya's sol-gel coating chemistry.

The international standard for quality management systems. Certifies that a manufacturer maintains documented processes for design, production, and continuous improvement. Kriya is ISO 9001:2015 certified.

South Korea's Act on Registration and Evaluation of Chemical Substances (2015, revised 2019). Substances at ≥1 t/yr must be registered. Mirrors EU REACH structure with Korea-specific tonnage thresholds and authorisation list.

OECD principles for organising and conducting non-clinical health and environmental safety studies. Required for many regulatory submissions (REACH, EPA TSCA). Defines lab accreditation, study traceability, and data integrity.

The EU regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals. Substances above 1 t/yr must be registered with ECHA; SVHCs face Annex XIV authorisation. Driver of PFAS-free transition.

EU directive restricting hazardous substances in electrical and electronic equipment. Limits Pb, Hg, Cd, Cr(VI), PBB, PBDE, and four phthalates. Kriya coatings are RoHS-compliant by design.

Sub-micron amorphous silica particles (n ~1.46) used as the low-refractive-index filler in AR coatings, hardcoat reinforcement, and as a controlled-roughness creator in AG coatings.

A chemical identified by ECHA under REACH as posing serious health or environmental risks. Listed on the Candidate List; Article 33 requires customer notification when present at ≥0.1% in articles. PFAS substances increasingly added.

A resin that polymerises at elevated temperature, typically 80–150 °C for sol-gel hybrids. Slower than UV but produces denser networks and is compatible with thicker coatings.

The US federal law (administered by EPA) regulating commercial chemicals. New substances require pre-manufacture notification (PMN); existing substances are inventoried. PFAS regulations are tightening rapidly under the 2024–2026 actions.

A liquid resin that polymerises rapidly under UV illumination via photo-initiator chemistry. Cures in seconds, ideal for R2R lines and NIL pattern fixing. No solvent emissions.

A high-refractive-index ceramic oxide (n ~2.1) widely used as filler for HRI sol-gel coatings, particularly for AR/VR waveguides and OLED extraction layers. Excellent mechanical and thermal stability.

The standard solar reference spectrum representing direct + diffuse sunlight at sea level after passing through 1.5 atmospheres of air mass. Used to certify solar-cell efficiency. Total irradiance ~1000 W/m².

The increase in solar-cell power output (typically 2.5–4%) achieved by adding broadband AR to the cover glass. Computed by integrating the AR transmittance gain over the AM1.5G spectrum weighted by cell EQE(λ).

For solar cells, the wavelength-dependent fraction of incident photons that produce a collected electron. AR coatings on cover glass directly improve EQE in the visible by reducing surface reflection.

The international standard defining design qualification and type-approval testing for crystalline-silicon photovoltaic modules. Includes accelerated weathering, mechanical load, and hot-spot tests. AR cover-glass coatings must survive these protocols.

A thin metallic or oxide coating that reflects far-infrared (heat) radiation while transmitting visible light. Drops glazing emissivity from ~0.84 (uncoated) to <0.10. Standard for energy-efficient windows.

The fraction of incident solar radiation that becomes heat inside a building or vehicle, including direct transmission and absorbed-and-re-radiated portions. Lower SHGC means better heat rejection. Critical for automotive glazing and building façades.

The thermal transmittance of a glazing assembly, expressing how much heat conducts through per unit area per degree of temperature difference. Lower U = better insulation. Modern double-glazing with low-e coatings reaches U < 1.0 W/m²K.

The fraction of visible light (380–780 nm) transmitted through a glazing, weighted by the photopic eye response. Automotive windshields require VLT ≥ 70% in most jurisdictions.

The refractive-index difference between two principal axes in an optically anisotropic material. Critical for stretch-induced birefringence in PMMA / PC cover lenses, and for liquid-crystal alignment layers.

The fraction of light scattered within ±2.5° of the incident direction — small-angle complement to haze. High clarity preserves image sharpness through the coating.

A measure of how clearly a reflected image appears in a coated surface. DOI ranges 0–100; high-gloss displays target 95+, anti-glare surfaces deliberately drop DOI to scatter the reflected image.

Specular reflectance measured at 60°, 20° (high-gloss) or 85° (matte) and reported in gloss units (GU). 100 GU is the polished black-glass standard. AR coatings target 95–100 GU at 60°; AG coatings deliberately reduce gloss.

The fraction of transmitted light scattered by more than 2.5° from the incident direction, expressed as a percentage. AG coatings introduce controlled haze (typically 1–25%) for diffuse uniformity; AR coatings keep haze < 0.5%.

The fraction of incident light power reflected by a surface or interface, expressed 0–1 or 0–100%. AR design minimises R(λ) over the application bandwidth and operating angle.

The total light scattered into the hemisphere away from a surface, normalised to incident power. For smooth surfaces TIS ∝ (σ/λ)² where σ is RMS roughness — the Bennett-Porteus relation.

The fraction of incident light power that passes through a sample, expressed 0–1 or 0–100%. Wavelength-dependent T(λ) is measured by spectrophotometer. Total T = direct + diffuse (haze).

A measure of optical material dispersion expressed as a single number. Computed from refractive indices at three Fraunhofer wavelengths (d, F, C). High V_d means low dispersion (chromatic aberration).

A surface chemistry that reduces the visibility and adhesion of skin oils and fingerprints. Achieved through low surface energy (high water and oil contact angles), traditionally with fluorinated chemistry; PFAS-free routes use silane-engineered hybrid networks.

A surface treatment that scatters specular reflection to reduce mirror-like glare. AG works by introducing controlled micro-roughness (haze) on the surface, trading gloss for diffuse uniformity.

A coating or multilayer stack designed to suppress optical reflection at an interface, increasing transmittance. Single-layer AR achieves zero reflection at one wavelength; broadband AR uses multiple layers tuned for a wide spectral and angular range.

A simple empirical model of normal dispersion in transparent dielectrics. Three coefficients A, B, C fit n(λ) over the visible spectrum. Standard for thin-film design and ellipsometry pre-fits.

The full complex-valued representation N = n + ik that captures both refraction (n) and absorption (k) at a wavelength. Used in Fresnel and TMM calculations for accurate handling of metals, semiconductors, and absorbing dyes.

The wavelength dependence of refractive index, n(λ). Normal dispersion has n decreasing with increasing wavelength. Quantified by Cauchy or Sellmeier coefficients fitted to ellipsometry or spectrophotometry data.

The imaginary part of the complex refractive index N = n + ik. Quantifies optical absorption per wavelength. For dielectric coatings k ≈ 0; for metals k can be larger than n.

A scratch- and abrasion-resistant coating applied over softer plastic substrates (PMMA, PC). Typical performance metrics: pencil hardness 3H–4H, low Δhaze after Taber abrasion or steel wool cycles.

Optical materials with refractive index typically above ~1.65, used as the high-n layer in AR multilayer stacks, as the substrate or core for AR/VR waveguides, and as photonic structures (metalens nanopillars). PFAS-free HRI up to n=2.00 is rare — Kriya delivers it.

Optical materials with refractive index typically below ~1.40, used as the low-n layer in AR multilayer stacks, as cladding in waveguides, and as anti-reflection top layers. Achieving low n PFAS-free is technically challenging — Kriya covers down to 1.16.

The ratio of the speed of light in vacuum to the speed of light in the medium. Determines how much a ray bends at an interface (Snell's law) and the magnitude of Fresnel reflection.

A physically grounded dispersion model derived from oscillator theory. Uses pole-pair coefficients Bᵢ and Cᵢ. More accurate than Cauchy across wider spectral ranges and near absorption resonances.