Abstract

In the next-generation optical network, WDM channels are envisioned to be add/dropped or cross-connected in the optical layer frequently.¹ For the proper operation of these networks, it is essential to monitor the optical signal-to-noise ratio (OSNR) of each channel. However, in such a dynamically reconfigurable network, the conventional linear interpolation technique could not monitor the OSNR accurately since each WDM channel may traverse through different optical paths and EDFA’s.² Recently, several OSNR monitoring techniques have been proposed to overcome this problem.^3–5 For example, it has been demonstrated that the OSNR could be monitored by the polarization-nulling technique using the different polarization properties of the optical signal and ASE noise.^3,4 The other technique monitored the OSNR by analyzing the low-frequency noise characteristics at the receiver.⁵ Although this technique is simple and cost-effective, it becomes erroneous when the pattern length of optical signal becomes longer than 2¹⁵ −1. In this paper, we eliminate only the signal components at a specific frequency within modulation bandwidth by using orthogonal delayed-ho-modyne method and then measure the receiver noise. The result confirms that this technique could measure the receiver noise within the modulation bandwidth even when the pattern length becomes much longer than 2¹⁵ − 1.

© 2002 Optical Society of America