OSNR monitoring technique using polarization-nulling method

Two-Photon-Absorption-Based OSNR Monitor for NRZ-PSK Transmission Systems

“…This out-of-band measurement becomes difficult to use in high density wavelength-division-multiplexed (WDM) systems where the spectral efficiency is high, and for systems where optical filtering renders an in-band noise level which is significantly different from that found out-of-band. including the orthogonal delayed-homodyne method [3], the polarization nulling method [4], and polarization diversity technique [5]. These techniques show great promise, however, they do have some draw-backs.…”

“…The orthogonal delayed-homodyne method requires a high-frequency receiver and radio-frequency (RF) spectrum analyzer, two relatively expensive components. In contrast, [4] and [5] have low component costs but rely on the assumption that the ASE is completely unpolarized; this assumption has been shown to generate significant errors in systems with polarized noise [6]. In this letter, we present a simple technique for monitoring OSNR in nonreturn-to-zero (NRZ)-PSK systems based on two-photon absorption (TPA) in a semiconductor microcavity.…”

Optical performance monitoring in optical packet-switched networks

“…Due to the PC scrambling, there are some coupling angle values whereby the state of polarization of the signal is aligned with one of the polarization axes so that the effect of PMD is completely eliminated. In this case, the detected RF power is maximized and this value is used for normalization, P c [Lee01,Ono00]. On the other hand, the effect of PMD is maximized when the power of both principal polarization states is balanced (i.e.,  =0.5).…”

“…As a result, the performance of this technique is bound to be affected by various polarization effects that occurred in the transmission link [Xie05, Lee06]. In fact, this technique becomes erroneous if the signal is depolarized due to PMD [Lee01]. Apart from the PMD effect, the optical signal could also be depolarized by nonlinear birefringence [Phi99, Phi05].…”

“…Otherwise, when the polarization controller is set to the same polarization state as the signal, the power meter indicates a maximum value (P signal + 0.5P noise ). By comparing the maximum and minimum detected values, the OSNR can be estimated [Lee01].…”