How LiDAR Works and How Bandpass Filters Supercharge Its Range and SNR

LiDAR (Light Detection and Ranging) is revolutionizing how we map, sense, and understand the world. By sending out a laser pulse and measuring how long it takes to return, LiDAR systems create highly precise 3D models of surfaces, objects, and even underwater landscapes. But did you know that a powerful secret behind LiDAR's range and clarity lies in the optical filter in front of its receiver? Here's how bandpass filters supercharge LiDAR performance.

LiDAR lasers emit a specific wavelength—such as 905 nm, 1064 nm, 1550 nm, or 532 nm—chosen for the application (e.g., terrain mapping, self-driving cars, river depth sensing). These pulses bounce back from objects and are detected by ultra-sensitive detectors (like Si or InGaAs APDs). The timing and intensity of the return allow the system to build a precise point cloud—a digital 3D snapshot of the scene.

To work, LiDAR must pick out its returning laser signal from a sea of background light—mainly sunlight. This is where the ultra-narrow bandpass filter comes in. It lets through only the signal's specific wavelength and blocks all others, massively boosting the system's signal-to-noise ratio (SNR) and enabling accurate, long-range measurements even in challenging lighting.

Key Features of LiDAR Bandpass Filters

• Ultra-narrow bandwidth: Passbands from sub-nanometer up to a few nanometers FWHM, tightly aligned to the LiDAR's laser line.
• High blocking (OD6 or better): Blocks sunlight and interference from other sources by a factor of a million (or more).
• Steep edges: Maintains a sharp transition between passing and blocking, ensuring only the laser line reaches the detector.
• Durability: Multi-layer thin films withstand temperature swings, vibration, and contamination in cars, drones, and field sensors.
• AOI optimization: Designed to handle angle-of-incidence (AOI) shifts, keeping the passband centered even for wide field-of-view receivers.

The sun is vastly brighter than any LiDAR return, threatening to drown out weak reflections from distant or small objects. By blocking all but the laser's wavelength, the filter allows the detector to amplify even the faintest signals—extending range, improving object detection, and enabling use in full daylight.

Without a sharp filter, sunlight and background glare would swamp the receiver, making high-resolution 3D mapping or safe vehicle automation impossible.

• 905 nm systems (cars, consumer ToF): 905 nm narrow bandpass, silicon detectors
• 1064 nm (aerial mapping): 1064 nm bandpass filter, Si APD or InGaAs detectors
• 1550 nm (UAV, long-range, eye-safe): 1550 nm narrow bandpass, InGaAs detectors
• 532 nm (bathymetry): 532 nm green bandpass, silicon detectors

Custom coatings can optimize filters for multiple returns, high-incident angles, or challenging conditions.

• Select a filter tightly matched to your laser's wavelength and beam divergence.
• Account for AOI shift—especially for wide-FOV sensors; request custom filters if needed.
• Review filter specs for out-of-band blocking, especially if operating near other light sources.
• Ensure correct mounting and orientation to maintain passband alignment.

• Ultra-narrow bandpass filters dramatically improve LiDAR's SNR and range, transforming your sensor from 'good' to 'world-class.'
• Always match your filter choice to your laser, detector, and optical path for best possible performance.