What's the Best LiDAR Bandpass Filter? (Spoiler: It Depends—Here's How to Choose)
If you're designing or optimizing a LiDAR system, the search for the 'best' bandpass filter is a common quest—and a common misconception. Here's the straight answer: There isn't one single 'best' bandpass filter for LiDAR. The optimal choice depends on your system's laser wavelength, receiver design (Field-of-View/AOI), and how much ambient-light rejection you need.
Why LiDAR Bandpass Filter Selection Is Never One-Size-Fits-AllMost LiDAR applications use hard-coated, laser-line bandpass filters centered on a common laser wavelength (typically 905 nm, 940 nm, or 1550 nm for automotive/industrial; 1064 nm or 532 nm for aerial systems). However, your exact requirements will depend on:
- Laser Wavelength: Match the center wavelength (CWL) to your laser line. For example, 905 nm is popular for Si-APD (silicon avalanche photodiode) receivers, while 1550 nm is common for longer-range and eye-safe designs. Applications like automotive or airborne LiDAR often default to these lines.
- Acceptance Angle/Field-of-View (AOI): The filter's passband can shift (usually 'blue-shift') when the angle of incoming light (AOI) increases—critical for wide-FOV receivers found in automotive LiDAR. Some filters are designed to maintain their spectral profile across a wide AOI (up to 60°), which is ideal if your sensor isn't narrowly collimated. Others are designed for optical stacks with a narrow acceptance angle near 0°.
- Ambient Light Rejection: LiDAR performance rests on the signal-to-noise ratio (SNR)—strong in-band return, deep out-of-band blocking. High peak transmission (≥90–95%) at the laser wavelength and out-of-band optical density (OD) of 6 or above are gold standards.
- 1. Pick the right center wavelength (CWL).
Match the filter to your laser's nominal wavelength (e.g., 905 nm, 940 nm, 1550 nm). Some suppliers offer design flexibility for custom lines. - 2. Choose an appropriate bandwidth (FWHM) to balance SNR and AOI tolerance.
If your detector is narrow-angle (collimated), an ultra-narrow (e.g., ≤1.5 nm) FWHM maximizes sunlight rejection. Wide-angle automotive sensors may require slightly broader filters (e.g., 10–40 nm FWHM at 905/940 nm, ~50 nm at 1550 nm) to maintain overlap with your laser line across the FOV, or special designs to tolerate ±10–60° AOI shifts. - 3. Account for AOI shift.
Bandpass 'blue-shifts' with nonzero AOI. Either choose a filter engineered for your nominal AOI or design your receiver optics to keep the filter close to a pupil or stop, reducing cone angle. - 4. Plan for temperature drift (laser & filter).
Most diode lasers shift roughly 0.25–0.3 nm/°C (even DFBs drift ~0.1 nm/°C). The filter must cover this drift over your full operating temperature range. Hard-coated filters drift far less (2–5 pm/°C), but budget both together when choosing filter width. - 5. Block ambient light—OD and Tpk matter.
Aim for ≥90–95% peak transmission at your laser wavelength. OD 6–8 blocking from UV to out-of-band IR keeps sunlight and room lights from drowning out your return signal. - 6. Durability, LIDT, and customization.
Hard, sputtered coatings survive automotive and outdoor environments and offer better abrasion, humidity, and thermal resistance. For high-peak-power laser pulses, confirm that the filter's laser-induced damage threshold (LIDT) suits your application.
| Use Case | Recommended Filter Choice |
|---|---|
| 905/940 nm automotive ToF | Bandpass centered at nominal AOI; ~10–40 nm FWHM or AOI-tolerant design (OD ≥ 3–4 from 200–1100 nm) |
| 1550 nm long-range/industrial | Broader passbands (approx. 50 nm) when wide AOI is unavoidable; deep blocking into the NIR |
| Aerial/bathymetric (1064/532 nm) | Ultra-narrow ≤1.5 nm, OD 6–7, maximized for SNR in sunlight |
- Wide AOI Tolerance: Filters engineered for 0–60° AOI are available for automotive or scanning LiDAR, with >95% transmission for robust daylight performance.
- Standard Stock Filters: Some providers offer standard near-IR bandpass filters, such as 905 nm or 940 nm, with sharp cut-on/off, supporting customization for AOI and substrate needs.
- Hard-Coated Durability: All examples featured hard (not 'soft') coatings for stable, long-term use in harsh environmental applications.
Instead of hunting for a universal 'best' bandpass filter, start by identifying your system's laser line, FOV/AOI, ambient conditions, and durability requirements. If you can share your laser type, acceptance cone angle, and operating temperature window, then it's possible to precisely specify the center wavelength, bandwidth (FWHM), and OD for your setup—and obtain a filter perfectly tuned for your LiDAR's needs.
Key Takeaway: There is no universal 'best' LiDAR bandpass filter. The optimal choice depends on your system's wavelength, FOV/AOI, and noise rejection needs. Always consider AOI, FWHM, durability, and environmental factors when selecting or specifying your filter.
