Temporal coherence characteristics of InGaAsP laser diode with single-longitudinal-mode oscillation

Temporal coherence characteristics of the InGaAsP laser diode in the single longitudinal mode are measured using an unbalanced Michelson interferometer. It is demonstrated that the coherence characteristics can be expressed by the sum of the Fourier transformation of a spectral fine structure, which consists of a main mode and two adjacent submodes. These submodes cause the coherence length to be shorter than would be expected if direct line-width measurements were made.