Collection: 1310nm Bandpass Filter

1310nm Filter Selection Guide: Reverse Engineering from Typical Applications

1. Wavelength Division Multiplexing (WDM) Modules in Optical Communication Systems

In fiber optic communication, 1310nm and 1550nm are the two low-loss windows of G.652 fiber, commonly used for single-fiber bidirectional (BiDi) transmission. Taking 1.25/2.5Gbps low-speed BiDi modules as an example, the filter configuration must meet the following core requirements:

Key Configuration Parameters

• Spectral Characteristics:

Use 45° dielectric thin-film interference filters to achieve bidirectional separation: reflecting 1310nm signals and transmitting 1550nm signals. This design leverages the thin-film interference principle, forming multi-layer coatings (e.g., TiO₂/SiO₂) with alternating high/low refractive index materials to enable precise wavelength division at a 45° incident angle.

• Bandwidth Control:

The reflection bandwidth should cover 1310±5nm, and the transmission bandwidth should cover 1550±5nm, with a transition band width exceeding 40nm to avoid wavelength shifts caused by polarization differences between s-polarized and p-polarized light. For instance, when using a 1310nm DFB laser with a typical wavelength tolerance of ±10nm, the filter's narrowband design (full width at half maximum, FWHM < 10nm) ensures precise spectral matching.

• Optical Performance:

Insertion loss must be controlled below 0.5dB, and isolation should exceed 45dB to ensure crosstalk is below -45dB. These metrics directly impact system bit error rate (BER); low-loss characteristics reduce the need for optical amplifiers in long-distance transmission (e.g., 10km), lowering operational costs.

• Environmental Adaptability:

Filters must comply with Telcordia GR-468 certification, withstanding temperature variations from -40°C to 85°C and maintaining stability in high-temperature, high-humidity environments. This is critical as optical modules are often deployed outdoors or in data centers with variable environmental conditions.

Selection Rationale

The 1310/1550nm wavelength combination in low-speed BiDi modules is chosen because low-cost directly modulated lasers (e.g., FP/DFB) exhibit minimal chirp at 1310nm, supporting transmissions over 10km. The filter's narrowband design and high isolation effectively separate dual-wavelength signals, preventing pulse broadening due to chromatic dispersion and solving the signal interference problem in single-fiber bidirectional transmission.

2. Laser Vibration Meters in High-Temperature Environments

In industrial vibration detection, 1310nm infrared lasers are widely used for non-contact measurement due to their strong penetrability and immunity to luminescence from high-temperature objects. The filter configuration for this application requires:

Key Configuration Parameters

• Spectral Characteristics:

Adopt bandpass filters with a central wavelength of 1310±2nm, FWHM of 8-20nm, and peak transmittance >90%. This design efficiently filters out visible and near-infrared ambient light, allowing only the laser signal to pass through and enhancing the signal-to-noise ratio (SNR).

• Blocking Depth:

In the 400-1100nm range, the filter must achieve a blocking depth of OD4 or higher (transmittance < 0.01%) to suppress interference from infrared components in sunlight (e.g., 940nm, 1064nm) on the detector. For example, in high-temperature furnace detection, blackbody radiation in the 900-1100nm range could overwhelm the laser signal; high blocking depth significantly reduces background noise.

• Material & Structure:

Use optical glass substrates (e.g., K9, fused silica) with all-dielectric hard coatings (Ti₃O₅+SiO₂), capable of withstanding temperatures above 500°C. Filters should also be designed in compact sizes (e.g., 3-80mm) to fit integrated photonic chip optical paths, enabling miniaturization and portability of the equipment.

• Polarization Characteristics:

For polarization-sensitive detection systems, polarization-dependent loss (PDL) must be controlled below 0.1dB to avoid signal fluctuations caused by changes in laser polarization states.

Selection Rationale

The 1310nm laser wavelength does not overlap with the thermal radiation wavelength of high-temperature objects (typically >1400nm), eliminating self-interference. The filter's high blocking depth and narrowband design reduce ambient light noise to levels below the detector's dark current, solving the SNR deficiency problem that traditional Doppler vibration meters face in high-temperature scenarios. Additionally, the high-temperature resistance of all-dielectric coatings ensures long-term stability in extreme environments.

3. Critical Dimensions for Selection Decisions

• Spectral Matching:

Choose the filter's central wavelength and FWHM based on the light source's wavelength tolerance (e.g., 1310±10nm) and system bandwidth requirements (e.g., WDM module transition band >40nm).

• Optical Performance Trade-offs:

- In optical communication, prioritize isolation (>45dB) and low loss (<0.8dB).

- In laser vibration measurement, focus on blocking depth (OD4+) and SNR enhancement.

• Environmental Compatibility:

Select temperature-resistant materials for high-temperature scenarios, anti-UV coatings for outdoor applications, and ensure compliance with strict reliability tests for optical communication modules.

By adhering to these configurations, 1310nm filters can precisely adapt to target applications, ensuring system performance while effectively reducing costs and complexity.