Abstract

Wavelength shifting may play an important role in future wavelength-division multiplexed (WDM) optical networks by allowing for dynamic routing and wavelength reuse. Several all-optical wavelength shifting schemes have been proposed, including cross-gain saturation in a semiconductor optical amplifier (SOA),¹ saturable absorption in a DBR laser,² and four- wave mixing in an SOA.³ The cross-gain saturation method has a wide continuous conversion range (~40 nm), high conversion efficiency, and can be implemented in a straight forward manner. However, the contrast ratio is significantly degraded upon shifting, especially for upshifting,⁴ and the prospects for network cascadability with this method are poor. Recently, a two-stage configuration was demonstrated, which alleviated the problem of poor contrast ratio performance.⁵ Also, the standard SOA gain is polarization-dependent: TE mode gain is ~5–6 dB larger than TM mode gain. This will cause the wavelength shifting performance dependent on the polarization of the incoming signal. In this paper, we demonstrate a polarization- independent and contrast-ratio-enhancing wavelength shifting module, which consists of two polarization-dependent SOAs. With proper polarization alignment, we perform 1 Gbit/s wavelength upshifting over 19 nm and reduce the power penalty for the shifter module from 5 dB to 1.5 dB and polarization dependence from 3.5 dB to 0.5 dB in comparison to a wavelength shifter compost of a single SOA.

© 1996 Optical Society of America