780nm Bandpass Filter

780nm light, a near-infrared wavelength, features strong tissue penetration capability, minimal visible light interference, and high-efficiency response by specific photodetectors;

  • Application 1: In remote sensing and environmental monitoring, the 780nm bandpass filter isolates characteristic near-infrared light reflected by vegetation to accurately assess chlorophyll content and plant growth status;
  • Application 2: Within biomedical detection, this filter separates 780nm fluorescent labeling signals, eliminating background light noise to enhance sensitivity in flow cytometers or fluorescence microscopes;
  • Application 3: For infrared communication and night-vision devices, the 780nm bandpass filter removes stray light interference, ensuring stable signal transmission and robust anti-interference performance for infrared LEDs or laser diodes.
780nm Bandpass Filter

780nm Filter Selection Guide

I. Wavelength Division Multiplexing (WDM) in Optical Fiber Communication Systems

In optical fiber communication, the 780nm wavelength is commonly used for short-distance optical signal transmission or in specific-band WDM systems. Below are the key configuration requirements for narrowband filters in such applications:

Key Configuration Parameters:

  1. Central Wavelength & Bandwidth
  • Strictly controlled central wavelength: 780±2nm
  • Full width at half maximum (FWHM): 10–24nm
  • Function: Ensures only the target wavelength passes through, preventing crosstalk from adjacent wavelengths (e.g., 850nm or 940nm) and improving signal transmission accuracy.

1. Cutoff Depth & Transmittance

  • Cutoff range: 200–1100nm
  • Non-passband cutoff depth: OD4–OD6 (optical density ≥4, transmittance < 0.01%)
  • Peak transmittance in passband: >90%
  • Function: Suppresses background stray light and noise from non-communication bands, ensuring signal purity and sufficient optical power transmission efficiency.

2. Material & Coating Process

  • Substrate materials: UV-grade fused silica or Schott B270 glass
  • Coating technology: Ion-beam sputtered multi-layer dielectric films (hard coatings for enhanced abrasion resistance)
  • Advantages: Minimizes temperature-induced wavelength drift and withstands long-term stable operation in communication devices.

Problem Solving:

In WDM systems, multiple wavelengths share the same fiber. A narrow bandwidth prevents wavelength crosstalk, while high cutoff depth blocks environmental light interference. This precise wavelength isolation solves signal-to-noise ratio (SNR) degradation issues in multi-wavelength multiplexing, ensuring stable communication and accurate data transmission.

II. Excitation-Emission Separation in Biomedical Fluorescence Imaging

In fluorescence imaging, 780nm is often used for exciting near-infrared fluorescent dyes or detecting specific fluorescent signals. Take confocal micro-Raman spectrometers as an example; their filter configurations require the following:

Key Configuration Parameters:

1. Excitation Filter

  • Central wavelength: 780±2nm, FWHM: 10–24nm
  • Peak transmittance: >90%, cutoff range: 200–750nm
  • Cutoff depth: OD4–OD6 (transmittance < 0.01% in non-passband)
  • Function: Filters 780nm excitation light from lasers, isolating visible and other near-infrared interferences.

2. Emission Filter

  • Long-pass (LP) design with cutoff at 780nm
  • Cutoff depth for <780nm: ≥OD3 (transmittance < 0.1%)
  • Transmittance for >780nm: >85%
  • Function: Separates fluorescent signals from excitation light, reducing background noise.

3. Dichroic Beamsplitter

  • Performance at 45° incidence:
  • Reflectance for 780nm excitation light: >95%
  • Transmittance for fluorescent signals (>780nm): >90%
  • Visible light cutoff depth: OD4+
  • Function: Efficiently splits excitation and emission light paths.

Problem Solving:

Fluorescence imaging faces challenges from minimal wavelength differences (Stokes shift) between excitation and emission signals. A deep-cutoff excitation filter suppresses autofluorescence from biological tissues (predominantly in the visible range), while the emission filter and dichroic beamsplitter ensure precise light separation. This resolves the issue of weak fluorescent signals being overwhelmed by residual excitation light, significantly improving imaging SNR for high-sensitivity applications like tumor detection and cellular labeling.

III. Key Selection Parameters by Application

1. Optical Fiber Communication (WDM)

  • Central Wavelength: 780±2nm
  • Bandwidth (FWHM): 10–24nm
  • Cutoff Depth: OD4–OD6 (200–1100nm non-passband)
  • Peak Transmittance: >90% (passband)
  • Substrate: UV-grade fused silica

2. Biomedical Fluorescence Imaging (Excitation Filter)

  • Central Wavelength: 780±2nm
  • Bandwidth (FWHM): 10–24nm
  • Cutoff Depth: OD4–OD6 (200–750nm non-passband)
  • Peak Transmittance: >90% (passband)
  • Substrate: Schott B270 glass

3. Biomedical Fluorescence Imaging (Emission Filter)

  • Cutoff Characteristic: Long-pass 780nm (>85% transmittance for >780nm, ≥OD3 cutoff for <780nm)
  • Substrate: Float glass

IV. Selection Considerations

1. Angular Sensitivity

  • For applications like fiber coupling, choose filters with low angular dependence (transmittance variation <5% within ±5° incidence).

2. Environmental Adaptability

  • In high-temperature/humidity environments, select hard-coated filters to enhance corrosion and abrasion resistance.

3. System Compatibility

  • Match the filter's damage threshold with the light source power to prevent performance degradation from high-power lasers.

By adhering to these configurations, 780nm filters enable precise wavelength multiplexing in optical communications and enhance fluorescent signal detection in biomedical imaging, meeting the optical performance and environmental requirements of diverse applications.

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