Rayzer Optical’s Mode Field Adaptors MFA is designed to makes two fiber to keep mode field diameter matched with low fundamental mode signal loss and minimal degradation of beam quality (M2). It can also be used to absorb residual pump light in the reverse direction, preventing damage to the seed or isolator. Usually, mode field is different in fibers with different core diameter and NA, and splicing loss is large between two fibers with different mode field. In order to reduce splicing loss, mode field must be similar. MFA can optimize splice loss significantly, usually <0.5dB, even <0.3dB between different fibers.