Figure 1: OD-Wavelength Curve of Near-Infrared Absorptive Filters (1.0–2.6 μm)
From the OD-wavelength curve in Figure 1:
•General Trend: All OD curves show a gradual decline as wavelength increases.
•Key Node: At 1550 nm (communication band), each curve is precisely calibrated with a tolerance of ±5%.
•Typical Performance:
•OD 0.1 curve: Drops from 0.1 at 1000 nm to ≈0.08 at 2600 nm.
•OD 6.0 curve: Drops from 6.0 at 1000 nm to ≈5.2 at 2600 nm.
•Engineering Significance: Wavelength drift effects on attenuation must be considered in fiber optic communication system design.
Figure 2: OD-Wavelength Curve of ZnSe Reflective Filters (2.0–16.0 μm)
Figure 2 reveals unique characteristics of reflective filters:
•Initial Fluctuation: The OD 3.0 product shows an unusually high density of 4.0 at 2 μm, indicating significant over-attenuation.
•Stable Range: All curves stabilize after 5 μm (marked as a key reference point).
•Typical Performance:
•OD 0.3 curve: Maintains excellent stability at 0.3 ± 0.05 across the entire band.
•OD 3.0 curve: Stabilizes between 2.5 and 2.8 after 5 μm.
•Special Phenomenon: The abnormal peak in the shortwave region suggests special attention is needed for actual OD values in CO₂ laser (10.6 μm) applications.
Table 1: Comparison of Key Parameters Between Reflective and Absorptive Filters
| Product Name | Diameter | OD Specifications | Working Wavelength |
|---|---|---|---|
| Infrared Reflective ND Filters | Ø12.7 mm Ø25.4 mm | 0.3±5%@5 μm 1.0±5%@5 μm 2.0±5%@5 μm 3.0±5%@5 μm | 2.0 μm - 16.0 μm |
| Near-IR Absorptive ND Filters | Ø25.4 mm | 0.3±5%@1550 nm 0.5±5%@1550 nm 1.0±5%@1550 nm 1.5±5%@1550 nm 2.0±5%@1550 nm 3.0±5%@1550 nm 4.0±5%@1550 nm 5.0±5%@1550 nm 6.0±5%@1550 nm | 1.0 μm - 2.6 μm |
A comparative analysis based on the parameter table:
| Comparison Dimension | Reflective Type (ZnSe) | Absorptive Type |
|---|---|---|
| Diameter Options | Ø12.7/25.4 mm (suitable for integrated designs) | Ø25.4 mm (standard size) |
| OD Accuracy | ±5% @ 5 μm (mid-wave infrared reference) | ±5% @ 1550 nm (communication band reference) |
| OD Range | 0.3–3.0 (for moderate attenuation needs) | 0.3–6.0 (for high attenuation scenarios) |
| Wavelength Range | 2.0–16.0 μm (covers long-wave infrared) | 1.0–2.6 μm (short-wave infrared specific) |
| Temperature Characteristics | Thermal drift must be considered (ZnSe material property) | Lower temperature sensitivity |
Based on spectral characteristics and product parameters, we recommend the following selection logic:
1.Wavelength Priority:
•Working wavelength < 2.6 μm → Choose absorptive type.
•Working wavelength > 2.6 μm → Choose ZnSe reflective type.
2.OD Value Selection:
3.System Integration Considerations:
•Space constraints → Choose Ø12.7 mm reflective type.
•Cascading required → Prefer absorptive type (OD can be stacked up to 6.0).
•Problem: Saturation occurs when imaging high-temperature targets.
•Solution:
1.Confirm working band: 3–5 μm mid-wave infrared.
2.Select ZnSe reflective OD 1.0 filter.
3.Verify actual attenuation: Ensure 10x attenuation at 5 μm.
•Problem: Insufficient dynamic range for 1550 nm signals.
•Solution:
1.Choose absorptive OD 3.0 filter.
2.Measure actual attenuation at 1550 nm: 1000x.
3.Fine-tune attenuation by tilting the filter (±15%).
1.Angle Sensitivity:
•Reflective type: Significant OD changes at incident angles > 15°.
•Absorptive type: Minimal impact (<5% at 30°).
2.Surface Maintenance:
•ZnSe filters require regular cleaning (ethanol + lint-free cloth).
•Avoid mechanical scratches on absorptive types (surface softening treatment).
3.Temperature Compensation:
•ZnSe OD values drift +0.1 per 50°C in high-temperature environments.
•Absorptive types should operate in environments <80°C.
1.Hybrid Filters:
•Combine absorptive and reflective mechanisms.
•Achieve ultra-high attenuation (OD > 8.0).
2.Tunable Smart Filters:
•Dynamic OD adjustment based on MEMS technology.
•Fast attenuation control with response times <1 ms.
3.Metasurface Filters:
•Nanostructures enable precise attenuation at specific wavelengths.
•Zero-thickness integration solutions.
