850nm Bandpass Filter

The 850nm wavelength falls within the near-infrared spectrum, exhibiting strong penetrating power, low atmospheric attenuation, and excellent compatibility with silicon-based detectors due to their high responsivity at this wavelength.

  • Application 1: In biomedical detection—such as blood oxygen saturation monitoring—850nm bandpass filters precisely isolate this wavelength, enabling light to penetrate biological tissues while minimizing interference from other spectral components, thus facilitating non-invasive measurement of physiological parameters.
  • Application 2: For security surveillance in night-vision systems, infrared cameras integrated with 850nm bandpass filters effectively block visible light, allowing only ambient infrared radiation at this wavelength to be captured. This ensures clear imaging in low-light conditions by leveraging the wavelength's minimal scatter in atmospheric conditions.
  • Application 3: In short-distance fiber optic communications and data center interconnects, 850nm bandpass filters are critical for multimode fiber systems. They ensure efficient transmission of this specific wavelength by reducing modal dispersion and signal loss, optimizing performance in high-speed data transfer environments.

850nm Filter Selection Guide

This guide focuses on selecting 850nm filters for two critical applications, deriving configuration requirements from real-world use cases and explaining the technical rationale behind each specification.

1. Security Surveillance Night Vision Systems

Application Context

In low-light or nighttime environments, security cameras rely on 850nm infrared (IR) illuminators to capture clear images. The filter must selectively transmit IR light while suppressing visible light and interfering near-infrared (NIR) wavelengths.

Filter Configuration Requirements

Spectral Characteristics

  • Central Wavelength: 850nm ±2nm (precisely matched to the IR light source)
  • Passband Range: 840–860nm (half-bandwidth ≤20nm), ensuring efficient transmission of 850nm IR light (transmittance ≥90%)
  • Cut-off Ranges:
  • Visible Light (400–700nm): Transmittance ≤5% to prevent color distortion caused by ambient light
  • NIR Interference (e.g., 940nm): Transmittance ≤5% to avoid crosstalk from other IR light sources
  • Cut-off Depth: OD ≥3 (transmittance ≤0.1%) for robust stray light suppression

Material & Process

  • Substrate Options:
  • Blue Glass (Absorptive): Suitable for high-resolution cameras (8MP+), using copper ion absorption to eliminate IR reflection interference
  • Quartz Glass with Coatings (Reflective): Cost-effective for low-resolution applications, requiring anti-reflective (AR) coatings to achieve ≥98% transmittance
  • Coating Technology: Vacuum evaporation (non-chemical coating) to ensure uniform, durable film layers resistant to temperature-induced performance degradation

Selection Rationale

  • Interference Resistance: Stringent cut-off of visible and unwanted NIR wavelengths eliminates daytime color distortion from ambient light and nighttime crosstalk from multi-source IR illumination.
  • Image Quality Enhancement: Narrow bandwidth (≤20nm) improves signal-to-noise ratio, reducing IR light scattering that blurs image clarity. Blue glass effectively suppresses IR reflection, ideal for high dynamic range scenarios.
  • System Compatibility: Works with IR CUT switches (using visible-light-transmitting filters during daytime and 850nm passband filters at night) to balance color rendering and IR imaging across day-night cycles.

2. Iris Recognition Systems

Application Context

Iris recognition requires 850nm IR light to penetrate the cornea and capture iris texture features. The filter must enable efficient target wavelength transmission while blocking ambient and stray light that could interfere with biometric data acquisition.

Filter Configuration Requirements

Spectral Characteristics

  • Central Wavelength: 850nm ±2nm (strictly aligned with the IR light source)
  • Passband Range: 830–870nm (half-bandwidth ≤40nm), balancing signal strength and interference resistance
  • Cut-off Ranges:
  • Visible Light (400–700nm): Transmittance ≤0.1% (OD ≥3) to prevent pupil constriction under visible light, which distorts iris imaging
  • NIR Interference (e.g., 780nm, 940nm): Transmittance ≤1% to avoid misidentification from overlapping biometric features (e.g., blood vessels)

Material & Process

  • Substrate Selection: Ultra-thin glass (0.3–0.75mm) to fit compact optical modules, combined with dual-side coatings (primary passband + cut-off layers) to achieve high cut-off depth within limited thickness
  • Coating Design:
  • Primary Passband Layer: 40–55 alternating layers of high/low refractive index materials (e.g., TiO₂/SiO₂) to create narrowband transmission
  • Cut-off Layer: 30–45-layer stacks for full-band suppression (400–630nm), enhancing system immunity to ambient light

Selection Rationale

  • Signal Purity: Narrowband design (≤40nm) minimizes spectral diffusion from iris surface reflections, ensuring sharp texture capture. High cut-off depth (OD ≥3) suppresses noise from ambient light sources like sunlight.
  • Biometric Safety & Specificity: 850nm IR light is eye-safe and penetrates effectively to capture iris stroma layer textures. Strict suppression of other NIR wavelengths prevents cross-triggering of unrelated biometric functions (e.g., vein recognition).
  • System Miniaturization: Ultra-thin substrates and dual-side coatings reduce module thickness for compact devices (e.g., access control systems, mobile terminals), with stress-balanced designs to avoid glass warping that could degrade imaging accuracy.

3. Core Selection Logic Summary

ParameterSecurity SurveillanceIris RecognitionCentral WavelengthStrict alignment with IR source (850nm ±2nm)Strict alignment with IR source (850nm ±2nm)BandwidthNarrowband (≤20nm) for high SNRModerate bandwidth (≤40nm) for signal-interference balanceVisible Light Cut-offHigh cut-off depth (OD ≥3) to suppress ambient lightUltra-high cut-off depth (OD ≥4) to prevent pupil constrictionNIR SuppressionBlock 940nm and other interfering NIR wavelengthsSuppress 780nm/940nm to avoid biometric crosstalkMaterial & ProcessBlue glass (high-res) or coated quartz (low-res)Ultra-thin glass with dual-side vacuum coatings

Key Problem Solutions

  • Security Surveillance: Precise spectral filtering resolves day-night color distortion and enhances low-light image contrast, ensuring consistent surveillance performance.
  • Iris Recognition: Narrowband high-cutoff filters guarantee unique iris feature identification, eliminating misreads caused by ambient light or overlapping biometric signals.

By adhering to these configurations, 850nm filters achieve an optimal balance between signal enhancement and interference suppression, serving as a critical performance enabler for target applications.

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