Optical Filters for Optical Communication Modules

Common Types of Optical Filters for Optical Modules:

1. Bandpass Filters (BPF) – Allow a specific wavelength band to pass while blocking others. Used in DWDM/CWDM systems.

2. Edge Filters (Longpass/Shortpass) – Transmit wavelengths above (longpass) or below (shortpass) a cutoff. Used for pump/signal separation in EDFAs.

3. Notch Filters (Bandstop) – Block a narrow band of wavelengths. Used for laser protection or ASE suppression.

4. Gain Flattening Filters (GFF) – Equalize gain across wavelengths in EDFAs or Raman amplifiers.

5. Thin-Film Filters (TFF) – High stability, low loss, widely used in transceivers (e.g., 100G/400G modules).

6. Arrayed Waveguide Gratings (AWG) – Multi-channel filtering for high-density wavelength routing.

   Key Specifications:

   • Center Wavelength (CWL) – e.g., 1310 nm, 1550 nm, or specific ITU grid channels.

   • Bandwidth (FWHM or 0.5 dB/3 dB width) – e.g., 0.4 nm for DWDM, 13.5 nm for CWDM.

   • Insertion Loss (IL) – Typically < 1.0 dB.

   • Ripple – ≤ 0.3 dB (in-band flatness).

   • Isolation/Rejection – e.g., > 25 dB at adjacent channels.

   • Return Loss (RL) – ≥ 45 dB.

   • Thermal Stability – < 2 pm/°C for DWDM.

   • Reliability – Telcordia GR-1221/1209 compliant.

   Applications in Optical Modules:

   • Transceivers (SFP, QSFP, OSFP) – WDM multiplexing/demultiplexing.

   • Coherent Modules – Linewidth narrowing and sideband filtering.

   • PON OLT/ONU – Upstream/downstream wavelength separation.

   • Optical Amplifiers – Pump rejection, gain flattening, ASE filtering.

   Stock vs. Custom Filters:

   • Standard stock – OD4@200-1700nm&OD7@1553.33nm,T>90%@1536.61nm, AOI 0°

   • Standard stock – OD4@200-1700nm&OD7@1536.61nm,T>90%@1553.33nm, AOI 0°

   • Custom options – Non-standard center λ, ultra-steep edges, temperature-compensated designs, smaller footprint (e.g., 10*10 mm).