Resolving group delay of narrowband optical filters from their transmission characteristics

In the paper, the factors affecting the accuracy of calculating the optical filter group delay basing on the measured power transmission characteristic are analyzed. Having the phase characteristic of the filter recovered from its transmission, the group delay is usually calculated via differentiation. The new, direct formula is proposed giving more accurate results when the characteristic of the filter is available in the limited frequency range. Also the limitations arising from the noise of the optical spectrum analyzer are examined.