Abstract

When a phase modulated optical signal at the wavelength of 1.55 μm is transmitted through a 1.3-μm zero dispersion fiber, phase modulation (PM) is converted to amplitude modulation (AM) by fiber chromatic dispersion.¹ In optical heterodyne detection, the PM-AM conversion can be compensated by a delay equalizer.² However, in a repeatered transmission system in which the fiber input power is large after in-line amplifiers. i.e., Er⁺³-doped optical fiber amplifiers (EDFAs) are used as in-line amplifiers, the refractive index of the fiber is modulated by the amplitude modulation resulting from the PM-AM conversion. This self-phase modulation (SPM) degrades the receiver sensitivity.³

© 1992 Optical Society of America