Why Bandpass Filters are Essential

In a laser rangefinder, the light received by the detector is a combination of the laser signal reflected from the target and unwanted background radiation (like sunlight).

• Noise Reduction: Sunlight contains significant spectral irradiance, particularly in the NIR region. The BPF acts as a highly selective gate, allowing the signal (which is a strong, narrow spike at the laser's wavelength) to pass while attenuating the broad spectrum of noise, which is critical for accurate ranging, especially over long distances or in bright outdoor conditions.
• Increased Sensitivity: By reducing the total background light that hits the detector, the filter lowers the overall noise floor (e.g., shot noise), effectively increasing the detector's sensitivity to the weak reflected laser pulse.