In optical applications—particularly in the manufacturing of lenses, filters, displays, and decorative optical components—color deviation control has become a critical metric to ensure product consistency and visual performance. Color deviation mainly originates from non-uniform film thickness, refractive index variations, and process fluctuations. Therefore, mastering effective control techniques is essential for enhancing the quality of optical coatings.
No.1 Mechanisms of Color Deviation
Optical coatings are typically deposited through thermal evaporation or magnetron sputtering, forming multilayer stacks. The film thickness and refractive index directly influence reflectance and transmittance across different wavelength ranges, thereby affecting perceived color. The primary mechanisms include:
Film Thickness Variation: Uneven deposition rate or improper substrate rotation/fixturing leads to local thickness differences, altering optical interference effects.
Refractive Index Shift: Variations in material purity, gas composition, or substrate temperature can change the refractive index, resulting in reflectance/transmittance color shifts.
Multilayer Interference Coupling: In high-reflective or interference filter stacks, thickness errors accumulate, causing interference peak shifts that manifest as color deviation.
No 2. Optical Coating Color Control Techniques
1. Precise Thickness Control
Quartz Crystal Microbalance (QCM) or optical monitoring systems are employed for real-time deposition rate and thickness measurement.
Closed-loop control systems adjust evaporation source power or sputtering target current, maintaining thickness accuracy within ±1%.
2. Refractive Index Consistency
Material purity and high-vacuum process control are crucial to reduce residual gas incorporation and stabilize refractive indices.
For reactive materials such as TiO₂ and SiO₂, reactive gas feedback control ensures stoichiometric stability.
3. Uniformity Enhancement
Substrate rotation, planetary motion, or multi-target configurations improve film uniformity.
For large-area substrates, multi-source evaporation or cylindrical/annular sputtering targets reduce center-to-edge deviation.
4. Post-deposition Correction
For multilayer interference coatings, laser-based thickness metrology can guide corrective re-coating to minimize deviation.
Thermal annealing optimizes film stress and optical constants, improving color uniformity.
No.3 Industrial Applications and Practices
In high-end display devices, AR/VR optics, camera lenses, and decorative optical films, color deviation control directly determines product yield and visual quality. For example:
AR/VR lenses require multilayer anti-reflection coatings with color uniformity across viewing angles, demanding thickness accuracy within ±2 nm.
Display filters consisting of alternating high/low refractive index layers are highly sensitive to color shifts, requiring precise uniformity and index stability.
Color deviation control in optical coatings relies on film thickness precision, refractive index stability, and uniformity optimization. By integrating QCM or optical monitoring, vacuum process optimization, multi-source deposition, and post-deposition correction, manufacturers can achieve high-fidelity color consistency. These techniques not only ensure optical performance but also enhance end-product visual quality and market competitiveness.
—This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Aug-21-2025