Collection: TOF Filter

In Time-of-Flight (TOF) cameras, optical filters play a crucial role in optimizing performance and accuracy. They serve two primary functions:

1. Blocking ambient light:

  • Wavelength Selection:
    • In most TOF systems, near-infrared (NIR) light is used due to its lower sensitivity to ambient light than visible wavelengths. Common choices include 850nm and 940nm lasers.
    • Filters are chosen to block visible light and other unwanted NIR wavelengths, leaving only the specific laser line used for distance measurement. This reduces noise and improves signal-to-noise ratio (SNR), leading to more accurate depth information.
    • Longpass filters with a cutoff wavelength slightly above the laser line are commonly used.

2. Filtering reflected light:

  • Noise Reduction:
    • In addition to ambient light, reflections from nearby objects other than the target can create noise and interfere with signal processing.
    • Bandpass filters centered around the expected return signal wavelength can be used to selectively transmit the desired reflected light while attenuating unwanted reflections.
    • This improves the clarity and accuracy of the resulting depth map.

Additional Features:

  • Steepness: The sharper the transition between passband and stopband, the higher the selectivity. This can be crucial for reducing noise from nearby objects with slightly different reflection wavelengths.
  • Peak Transmission: Higher transmission allows stronger signals, but needs balancing with steepness for optimal performance.
  • Material and Construction: Consider factors like cost, durability, and compatibility with your system and environment.

Types of Filters:

  • Longpass Filters: Block wavelengths shorter than a specific cutoff, typically used for blocking most ambient light and focusing on the NIR laser line.
  • Bandpass Filters: Transmit a specific range of wavelengths around the expected return signal, helping reduce noise from unwanted reflections.
  • Dichroic Filters: Can reflect specific wavelengths (e.g., visible light) while transmitting others (e.g., NIR) in one filter, offering a compact solution.

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