Abstract

The frequency-shift-keyed (FSK) modulation technique has been extensively studied in both direct¹ and coherent detection systems. The main advantage of FSK modulation is that both the required modulation current and the resulting frequency chirp are small. This makes close optical channel spacing in an optical frequency-division-multiplexing (FDM) system feasible and therefore enables efficient use of the available bandwidth of a single-mode fiber. The disadvantage, however, is that the nonuniform low-frequency FM response of a single-section distributed-feedback (DFB) laser owing to thermal effect significantly limits the length of the data pattern.

© 1991 Optical Society of America