LiDAR Evaluation System: Measurement of Transmittance of Bandpass Filters

Significance of the Topic

LiDAR technology plays a pivotal role in remote sensing for geoscience, aerospace and autonomous driving applications. Precise knowledge of optical properties of sensor covers, such as transmittance and angular dependence, is essential to optimize LiDAR performance and ensure accurate detection of objects under varying incident angles and polarization conditions.

Goals and Study Overview

This study aimed to evaluate the transmittance behavior of 905 nm and 1550 nm bandpass filters used in LiDAR sensor covers. By measuring how transmittance varies with incident angle and polarization, the work provides insights into filter performance critical for extending detection range and ensuring eye safety in automotive and research LiDAR systems.

Methodology and Instrumentation

The optical evaluation employed a Shimadzu SolidSpec-3700i UV-VIS-NIR spectrophotometer equipped with a variable angle absolute reflectance measurement unit and a large polarizer set. Key measurement parameters included:

• Wavelength range: 300–2000 nm
• Scan speed: Medium
• Sampling pitch: 1 nm
• Slit width: 8 nm (UV-VIS), 20 nm (NIR)
• Light source switching wavelength: 310 nm

Baseline correction was performed without the sample, then transmittance spectra were recorded at incident angles from 0° to 70° in 10° increments, for both s- and p-polarized light.

Main Results and Discussion

Measurements revealed a pronounced decrease in transmittance of s-polarized light as the incident angle increased. In contrast, p-polarized light showed a smaller angular dependence. Both filters, being interference types, exhibited a shift in center wavelength toward shorter values with increasing angle, confirming theoretical expectations for thin-film interference.

Benefits and Practical Application

The described approach enables comprehensive characterization of filter performance under realistic LiDAR illumination conditions. Automotive and airborne LiDAR developers can apply these results to select and optimize sensor cover materials, maximizing detection range and angular coverage while maintaining eye-safe operation.

Future Trends and Applications

• Integration of automated angle scanning for high-throughput filter screening
• Extension to wider infrared ranges beyond 2000 nm for next-generation LiDAR
• Assessment of environmental effects (temperature, humidity) on coating stability
• Development of real-time monitoring systems for in-field LiDAR calibration

Conclusion

Using variable-angle spectrophotometry, this work successfully quantified the angular and polarization dependence of 905 nm and 1550 nm bandpass filters. The findings support enhanced design and quality control of LiDAR sensor covers, ultimately improving performance in automated driving and remote sensing.

Reference

• Under the Hood of Luminar’s Long-Reach Lidar. IEEE Spectrum (accessed Feb. 12, 2020)