Optical Filters in LiDAR and Laser Technology
Andover Corporation. While lasers have long been integral to defense applications, their impact now spans manufacturing, environmental monitoring, biomedical imaging, aerospace, and autonomous systems. At the core of these laser-based systems are optical filters, precision components that control light transmission, block unwanted wavelengths, and enhance measurement accuracy. However, wavelength isn’t the only consideration. Filter selection is driven by multiple factors including system constraints, environmental conditions, laser type, detector characteristics, and wavelength-specific challenges.
Critical Optical Design Considerations for Laser Systems
Effective filter design requires understanding the complete optical system, not just isolated component specifications. Engineers must consider:
- Laser type (continuous wave vs. pulsed) and its impact on coating durability
- Detector sensitivity and spectral response characteristics
- Optical system architecture including beam paths and component integration
- Environmental conditions including temperature extremes, humidity, and contamination exposure
- Angle of incidence (AOI) effects, as AOI sensitivity can be as critical as center wavelength in determining filter performance
- Temperature stability and spectral drift, particularly for outdoor LiDAR and industrial laser systems operating across wide temperature ranges
- Solar background interference in outdoor applications
- Laser damage threshold requirements based on power levels and pulse characteristics
Many advanced laser systems require custom filter designs optimized for the specific combination of laser source, detector, and operating environment.
Understanding Wavelength-Specific Filter Requirements
Different LiDAR and laser applications operate at distinct wavelengths, each presenting unique optical challenges. This guide explores four core wavelengths commonly used in modern laser-based systems: 905 nm for automotive LiDAR and robotics, 940 nm for short-range LiDAR and structured light, 1064 nm for surveying and airborne mapping, and 1550 nm for eye-safe, long-range applications.
905 nm: Automotive LiDAR and Robotics
Automotive LiDAR and short-range time-of-flight (ToF) systems predominantly operate at 905 nm, where high solar background radiation presents significant challenges. Engineers designing for this wavelength must prioritize:
- Narrow bandpass filters with aggressive visible blocking to reject ambient sunlight
- CWL (center wavelength) stability to maintain performance across temperature variations
- High signal-to-noise ratio optimization to distinguish laser returns from solar interference
- AOI shift compensation, as angle of incidence often matters more than center wavelength alone in real-world deployments
The intense solar background at this wavelength requires filters with exceptional out-of-band blocking while maintaining high transmission within the narrow passband.
940 nm: Short-Range LiDAR and Structured Light
Short-range LiDAR, structured light systems, and VCSEL-based applications at 940 nm benefit from reduced ambient sunlight compared to 905 nm, but still demand tight spectral control. Typical specifications include:
- Bandpass or notch filters with precise bandwidth control
- Thermal stability to maintain performance across operating temperature ranges
- Compatibility with illumination sources, as these systems often pair filters with active illumination
While solar interference is lower at 940 nm, engineers cannot compromise on spectral precision, even short-range systems require filters engineered for consistent performance.
1064 nm: Surveying, Mapping, and Airborne LiDAR
Industrial surveying, topographic mapping, and airborne LiDAR systems operating at 1064 nm face distinct challenges related to high pulse energy and demanding environmental conditions. Critical filter specifications include:
- High laser damage threshold capable of withstanding intense pulsed laser power
- Robust thin-film coatings that prevent optical degradation over time
- Bandpass filters with anti-reflection (AR) coatings to maximize transmission efficiency
- Durability for harsh environments, including extreme temperatures, humidity, and mechanical stress
At this wavelength, coating durability is paramount, filters must maintain peak precision and longevity under continuous high-power operation in industrial and aerospace applications.
