How Much Blocking OD Do You Really Need for LiDAR? (905, 1064, 1550 Compared)
If you're shopping for a LiDAR filter, you've probably wondered: how much out-of-band blocking OD do you actually need? Here's a 'don't overpay but don't get burned' guide that focuses on real SNR, detector, and cost trade-offs for 905 nm, 1064 nm, and 1550 nm LiDAR—plus some table-based recommendations for practical spec writing.
Quick Reference Table — 'Good Enough' Blocking OD
| Application | Laser λ | Detector Type (Typical Range) | Blocking Range to Cover | Recommended OD (outside passband) | Why / Notes |
|---|---|---|---|---|---|
| Automotive ToF (scanning/flash) | 905 nm | Si APD (≈ 350–1100 nm) | 400–1100 nm | OD5 baseline, OD6 for harsh sun / cross-talk | OD4–6 is industry standard; OD6 is ideal for high sun or cross-LiDAR. Extra care near 808–980 nm traffic. |
| Automotive FMCW | 1550 nm | InGaAs (≈ 900–1700 nm) | 900–1700 nm | OD4–OD6, bias OD6 near 905/940/1064 nm | Lower solar background, but block other LiDAR bands. |
| Airborne Topographic / Mapping | 1064 nm | Si APD (≈ 350–1100 nm) | 400–1300 nm | OD6 typical | >OD6 from ~300–1300 nm is frequent to keep out skylight/stray light. |
| Bathymetric LiDAR | 532 nm | Si APD | 300–1100 nm | OD6 | Strong daylight and surface reflections — default to OD6. |
| Atmospheric Raman LiDAR | 355/532/1064 nm + shifted Raman | Matched to detector | Detector range | OD7–OD8 | Raman needs deeper suppression — literature: ≥OD7/OD8. |
Two Money-Saving Design Rules
1. Only block what your detector can see.
Don't spec 'UV-to-SWIR' blocking if your system is Si-only. Tailor blocking range to your detector's wavelength sensitivity — saves budget and complexity.
2. Pick the minimum OD that gets below your system's background floor.
For most LiDAR filters, OD4–6 blocking 'over the detector band' is normal. OD6 for tough outdoor or cross-talk; OD4–5 suffices for indoor/controlled setups. Remember: OD5 → OD6 is 10× extra rejection — and higher cost.
Why the Numbers Look This Way
905 nm vs 1550 nm:
Solar irradiance is much higher at 905 nm, raising your background. This is why most automotive 905 nm specs emphasize OD6 for outdoor and cross-talk immunity. 1550 nm sits in a lower-solar background but you still need to cut out neighboring laser lines.
What Common Practice Looks Like:
Industry will often quote 'OD6 from 300–1300 nm' for narrowband altimetry filters, or OD5 over the detector's key range, especially if baffling or detector specs help with stray light.
TL;DR: Specs to Copy-Paste
- 905 nm automotive (Si APD): Blocking: 400–1100 nm; OD5 typical, OD6 for harsh sun/cross-talk.
- 1550 nm automotive (InGaAs): Blocking: 900–1700 nm; OD4–OD6, with OD6 emphasis near other laser lines.
- 1064 nm mapping (Si APD): Blocking: 400–1300 nm; OD6.
- 532 nm bathymetric (Si APD): Blocking: 300–1100 nm; OD6.
- Raman LiDAR channels: Blocking: match detector; OD7–OD8.
Key Takeaways
- Don't pay for blocking OD you don't need — match your filter blocking range and depth to your detector and background requirements.
- OD6 is a typical 'safe' choice outdoors, but you save money with OD4 or OD5 where conditions allow.
- Raman channels always need deeper blocking — usually OD7–OD8.
- Always check your detector's true range before signing off on a filter spec.
