810nm Filter Selection Guide: Key Applications and Configuration Logic
1. Biomedical SpO₂ Monitoring Systems
In non-invasive pulse oximeters, 810nm filters serve as critical components for accurate blood oxygen saturation (SpO₂) measurement. Leveraging a dual-wavelength detection principle, these systems calculate oxygen levels through absorbance differences between 660nm red light and 810nm near-infrared (NIR) light. Filter configurations must meet the following technical requirements:
1.1 Narrow Bandpass Design
Select filters with a central wavelength of 810nm and a full width at half maximum (FWHM) of 10nm. This design strictly confines the detection bandwidth, eliminating interference from hemoglobin absorption at other NIR wavelengths (e.g., 760nm or 850nm). For example, filters procured by the National University of Defense Technology specify a 10nm bandpass to ensure pure optical signal transmission.
1.2 High Optical Density (OD) Cutoff
Filters must provide an OD4 (Optical Density 4) cutoff outside the passband, achieving >99.99% suppression of 660nm red light and other non-target wavelengths. Inadequate cutoff (e.g., OD3) can lead to cross-talk from red light channels or ambient light/LED leakage, causing measurement errors exceeding ±2%—failing medical-grade precision standards.
1.3 Substrate Material and Coating Technology
Optical glass substrates with multi-layer dielectric coatings offer >90% peak transmittance while ensuring mechanical durability. The ams AS7038RB sensor, for instance, integrates an 810nm filter with a photodiode via wafer-level interference coating, achieving medical-grade signal-to-noise ratio in a 0.65mm ultra-thin package.
Selection Rationale:
This configuration addresses signal contamination issues through precise wavelength selection and high rejection capability. Experimental data shows devices using 10nm bandwidth OD4 filters maintain measurement errors within ±1% during motion or low-perfusion conditions—significantly outperforming traditional broadband filters.
2. Security Surveillance Infrared Night Vision Systems
In low-light monitoring scenarios, 810nm filters work with infrared LEDs to enable covert imaging by separating invisible IR light from visible light, ensuring clear grayscale representation. Key configuration criteria include:
2.1 Long-Pass Cutoff Characteristics
Choose long-pass filters with a 700nm cutoff wavelength to fully block 400–700nm visible light while transmitting 810nm and longer IR wavelengths. A security camera adopting this design achieved >30% grayscale contrast in complete darkness (<0.01lux), compared to completely overexposed white images without filtering.
2.2 Anti-Reflective (AR) Coating Optimization
Multi-layer AR coatings reduce surface reflectance at 810nm to <0.2%, minimizing interface reflections between the lens and filter. This enhances IR signal transmission by 15–20%, extending the effective monitoring range of low-power IR LEDs (<50mW) from 10m to 15m.
2.3 Broad Spectral Compatibility
Filters should maintain >85% transmittance across 700–1100nm to accommodate different 810nm/850nm IR light sources. In one case, a camera using such a filter required no recalibration when switching between 810nm and 850nm illumination, achieving brightness consistency within <5% deviation.
Selection Rationale:
The dual design of visible light cutoff and IR enhancement solves the common issues of "daytime overexposure and nighttime blurring" in traditional night vision systems. Field tests show that the 700nm cutoff + AR coating solution achieves <200ms response time for day-night mode switching with a false trigger rate <0.1 times/hour.
3. Critical Considerations for Selection Decisions
3.1 Application-Specific Spectral Environment
In high-fluorescence environments (e.g., biological labs), prioritize OD5-level filters; for outdoor surveillance, focus on weather resistance (e.g., coating adhesion ≥5B per ASTM D3359).
3.2 System Optical Efficiency Balance
Narrow-band filters' high selectivity may reduce signal intensity—adjust light source power based on detector sensitivity. For example, 10nm bandwidth filters in oximeters require >10mW 810nm LEDs, while 20nm bandwidth solutions can use 5mW LEDs for equivalent SNR.
3.3 Mechanical Compatibility
Security applications need tight tolerance control (e.g., thickness tolerance ±0.02mm) for lens integration, whereas medical devices prioritize surface flatness (λ/4@632.8nm) to avoid optical distortion.By following this configuration logic, 810nm filters can achieve optimal performance in target applications while mitigating risks of wavelength drift and optical loss.
