905nm Bandpass Filter

905nm light is in the near-infrared spectrum, offering good atmospheric transmission, low eye safety risk, and suitability for distance measurement and sensing due to its ability to penetrate certain materials and avoid strong visible light interference.

  • Application 1: In LiDAR (Light Detection and Ranging) systems, the filter blocks unwanted wavelengths, allowing only 905nm light to pass through, which enhances the accuracy of distance measurements by minimizing ambient light interference and improving the signal-to-noise ratio for precise object detection and mapping.
  • Application 2: In optical communication and sensing devices, such as proximity sensors or industrial automation equipment, the filter ensures that only the 905nm wavelength is detected, enabling reliable signal reception and reducing false triggers caused by other light sources, thus improving the device's operational stability and sensitivity.
  • Application 3: In night vision systems and surveillance cameras, the filter isolates the 905nm near-infrared light emitted by illuminators, blocking visible light and other infrared wavelengths to enhance the clarity of monochrome night images, enabling effective monitoring in low-light or completely dark environments without being affected by irrelevant light sources.

905nm Filter Selection Guide for Key Applications

1. LiDAR (Light Detection and Ranging) Systems

Filter Configuration Requirements

a. Central Wavelength & Bandwidth

  • Must precisely match the laser source wavelength (typically 905±5nm). Bandwidth ranges from 10-66nm based on system design. For autonomous driving LiDARs, which need to compensate for temperature drift (≈1nm red-shift per 10°C) and large measurement angles (e.g., 20°), the central wavelength may adjust to 922±3nm with an expanded bandwidth of 66±6nm.

b. Blocking Depth & Transmittance

  • Requires OD4-6 (optical density 4-6, <0.01% out-of-band transmittance) across 200-1100nm, with peak transmittance >90% at the central wavelength.

c. Material & Coating

  • Constructed from optical glass (e.g., K9, BK7) or fused silica, coated with anti-reflective layers to minimize reflection loss (<0.2% reflectivity) and enhance scratch resistance.

d. Dimension & Angle of Incidence

  • Customized dimensions (e.g., 1-inch diameter) to fit optical designs, supporting 0-35° angle of incidence to maintain high transmittance during wide-angle measurements.

Selection Rationale and Application Benefits

  • Ambient Light Suppression: Narrow-band filters restrict the passband (10-66nm), allowing only laser signals to pass through, improving signal-to-noise ratio (SNR) by 10-20dB. An OD6 blocking depth effectively blocks 700-1100nm ambient light, ensuring detectors only receive laser echo signals.
  • Temperature & Angular Compensation: Adjusting central wavelength and bandwidth compensates for laser source drift (temperature-induced red-shift and angle-induced wavelength shift), enabling stable operation across -40°C to 85°C.
  • Cost-Effectiveness & Durability: 905nm filters utilize mature glass coating processes, costing 1/3 to 1/5 of 1550nm filters, while offering impact resistance and weather durability suitable for harsh automotive environments.

2. Surveillance Night Vision Systems

Filter Configuration Requirements

a. Spectral Characteristics

  • Available in narrow-bandpass (central wavelength 905±5nm, 20-30nm bandwidth, OD4+ visible light blocking at 400-700nm) or long-pass (cutoff at 700nm, transmitting 700-1100nm infrared light).

b. Transmittance & Durability95% transmittance at 905nm, fabricated from K9 glass or PMMA with hard coatings (hardness >6H) to resist scratches and oil contamination.c. Dimension & Integration

  • Compatible with camera lens sizes (e.g., 6x6mm, 25mm diameter), supporting integration with ICR (Infrared Cut-off Filter) switches for automatic day-night mode transitions.

Selection Rationale and Application Benefits

  • Covert Surveillance: 905nm laser illumination produces no visible red glow (unlike 850nm/940nm), and narrow-band filters ensure cameras only capture 905nm reflected signals, enabling completely covert monitoring. A 20nm bandwidth filter eliminates 850nm/940nm ambient light interference, boosting image SNR by over 15dB.
  • Low-Light Imaging Enhancement: Long-pass filters allow 700-1100nm IR light to pass, enabling imaging at 0.001lux ultra-low 照度 when paired with high-sensitivity sensors. OD4 visible light blocking prevents overexposure in night scenes. For example, a 905nm narrow-band filter-equipped night vision camera can clearly identify license plates at 200m range.
  • System Compatibility: Seamlessly integrates with existing surveillance camera modules without hardware changes. Upgrading an 850nm night vision camera to 905nm only requires filter replacement, reducing retrofit costs by 30%.

3. Critical Selection Principles

a. Source Matching

  • Laser wavelength tolerance (±5nm) and temperature drift must be compensated by filter bandwidth. A 10nm bandwidth filter is suitable only for lasers with extreme wavelength stability.

b. Blocking-Transmittance Balance

  • While OD6 provides superior ambient light suppression, it may reduce peak transmittance below 85%. Choose parameters based on environment: OD4 for urban areas (moderate light) vs. OD6 for wilderness (strong ambient light).

c. Mechanical & Environmental Considerations

  • Automotive LiDAR filters must pass -40°C to 85°C thermal cycling (ΔT<±2nm wavelength shift), while surveillance filters require salt spray resistance (5% NaCl solution, 48-hour corrosion test).

By following these configurations, 905nm filters effectively address core challenges in LiDAR and surveillance systems—ambient light interference, temperature instability, and covert operation needs—delivering significant performance and reliability improvements.

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