Why does an MFD mismatch cause significant loss when splicing single-mode fibers from different manufacturers?
An MFD (Mode Field Diameter) mismatch between single-mode fibers from different manufacturers causes significant splicing loss primarily due to inefficient power coupling.
Here’s why:
- Mode Field Diameter Definition: The MFD represents the effective diameter of the light propagating in the fiber core. Even though the physical core diameter might be similar, the way the light is guided and spread within the core can vary due to differences in refractive index profiles and fiber designs.
- Imperfect Mode Field Overlap: When two fibers with different MFDs are spliced, the propagating light from the first fiber does not perfectly overlap with the fundamental mode of the second fiber. If the MFD of the transmitting fiber is larger than the receiving fiber, some of the light will spill outside the core of the receiving fiber. Conversely, if the transmitting fiber has a smaller MFD, the light will not fully illuminate the core of the receiving fiber, leading to power loss.
- Power Loss: This imperfect overlap results in a portion of the optical power being converted into higher-order modes (which are typically not guided in single-mode fiber and radiate away) or simply being lost at the splice joint, leading to insertion loss. The larger the MFD difference, the greater the power loss.
- Manufacturer Variations: Different manufacturers may use slightly different glass compositions, doping profiles, and drawing processes, leading to variations in the refractive index profile and thus varying MFD specifications within the permissible tolerances for standard single-mode fibers (e.g., G.652D). While they adhere to standards, minor differences can become significant when high precision splicing is required.
For further technical details on optical fiber characteristics, you may refer to our OFSCN® G.652D Optical Fiber and OFSCN® G.657 Optical Fiber product pages.