Why LIDAR sensor windows need AR coatings
LIDAR sensors for autonomous driving and ADAS emit laser pulses and detect their reflections to build a 3D map of the environment. The sensor window — the cover that protects the LIDAR optics from the environment — introduces reflection losses at each glass-air interface. At approximately 4% reflection per surface, a simple glass window reduces round-trip signal by nearly 15% (two surfaces on transmit, two on receive).
For LIDAR systems operating at the margin of detection — identifying dark objects at maximum range in adverse weather — this 15% signal loss directly reduces detection range and confidence. AR coating the sensor window is one of the most cost-effective ways to recover this lost performance.
Wavelength-specific optimisation
The two dominant LIDAR wavelengths in automotive are 905 nm and 1550 nm. Unlike broadband AR for visible-light applications, LIDAR window AR can be optimised for a narrow spectral band centred on the laser wavelength. This allows the AR stack to achieve near-zero reflection at the target wavelength, maximising signal transmission.
Kriya's tuneable RI platform (1.16 to 2.00) enables precision design of quarter-wave stacks for either wavelength. The same platform supports dual-band designs for systems that combine 905 nm and 1550 nm LIDAR or integrate LIDAR with camera functionality through the same window.
Performance improvement
With optimised AR coating on the sensor window:
- Reflection per surface: reduced from approximately 4% to below 0.5% at the LIDAR wavelength
- Transmission improvement: up to 5% per surface
- Round-trip signal improvement: up to 18% for a two-surface window
- Effective range improvement: proportional to the square root of signal improvement, translating to measurable detection range gains
Environmental durability
Automotive LIDAR sensor windows are exposed to extreme environmental conditions: temperature cycling from -40 to +85 degrees Celsius, UV radiation, salt spray, stone impact, and cleaning chemicals. Kriya's sol-gel AR coatings produce dense oxide films that meet automotive environmental durability standards:
- Temperature cycling: -40 to +85 degrees Celsius, 1000 cycles
- Humidity resistance: 85 degrees Celsius / 85% RH
- Salt spray resistance per automotive specifications
- UV stability: no degradation under accelerated UV aging
ADAS sensor integration
Beyond LIDAR, Kriya's AR coatings serve the broader ADAS sensor suite:
- Camera cover glass — broadband visible AR for improved image clarity and reduced lens flare
- Radar radome — oxide-based dielectric coatings that are 100% RF transparent (unlike metallic AR coatings that attenuate radar signals)
- Multi-sensor windows — combined AR performance across visible, NIR, and radar bands for integrated sensor modules
The critical advantage of Kriya's oxide-based chemistry is full RF/5G/LIDAR transparency. Metallic AR coatings (such as ITO-based approaches) attenuate radio frequencies, making them incompatible with radar and 5G communication in the same optical path.
Processing and supply
LIDAR window AR coatings are applied via spin or dip coating, compatible with standard sensor module production. Kriya supplies coatings ready for application with full process specifications, and works directly with Tier-1 sensor manufacturers to optimise for specific sensor window geometries and production requirements.