All-optical wavelength conversion of NRZ and RZ signals using a nonlinear optical loop mirror

Abstract

Wavelength conversion using a nonlinear optical loop mirror (NOLM) is investigated. Our interest is in considering nonreturn-to-zero (NRZ) and return-to-zero (RZ) signals with a high-duty ratio resulting in a nonlinear phase shift of the counterpropagating wave that is not negligible and reduces the extinction ratio considerably compared to signals with a low-duty ratio. It is shown how the NOLM can be used for high-duty signals anyhow by configuring/adjusting the NOLM, particularly the polarization controller inserted in the loop. This paper gives a mathematical description of the NOLM utilizing the Jones calculus and considers different ways of adjusting the polarization controller. The nonlinear phase shifts are calculated and a reasonable confinement for the walk-off is given. Furthermore, the probability density function of the extinction ratio depending on the duty ratio of the control signal and the configuration of the NOLM for either parallel or orthogonal polarizations of the counterpropagating signal waves is derived and evaluated for some exemplary parameters.

All-optical wavelength conversion of short pulses and NRZ signals based on a nonlinear optical loop mirror

“…We will demonstrate that also NRZ wavelength conversion based on an NOLM can be realized meaning that wavelength conversion in a NOLM is transparent to RZ and NRZ format. The conclusion in [11] that the nonlinear phase of the counterpropagating waves can be easily compensated just by adjusting the state of the polarization controller in the NOLM, and high ER of the converted signal can be obtained is confirmed by our experimental results. This paper is divided into four sections.…”

“…But, owing to the relatively slow carrier recovery time of SOA's ( 1 ns), nonreturn-to-zero (NRZ)-like output signals are obtained when the wavelength conversion is performed in SOA's by XGM or XPM, and this is not suitable for return-to-zero (RZ)-based networks [5]. However, nonlinear optical loop mirror (NOLM) based on silica fiber has the potential of attaining terabits per second switching operation due to the ultrafast optical nonlinearity; our experiments will demonstrate that the pulsewidths can be maintained, and even compressed when the walkoff defined in [11] between the CW waves and the control pulses is small. So, wavelength conversion based on a NOLM will be suitable for RZ based networks.…”

“…To achieve all-optical wavelength conversion, various strategies have been investigated. There are mainly two kinds of media: one medium is based on semiconductor optical amplifiers (SOA's), and methods are cross-gain modulation (XGM) [3], [4], cross-phase modulation (XPM) [5], [6], and four-wave mixing (FWM) [7]- [9]; the other medium is based on fibers, and methods are FWM [10] and XPM [11]- [13] in dispersion shifted fibers (DSF's). FWM is transparent to both modulation format and signal bit-rate [7]- [10].…”

40-Gb/s all-optical wavelength conversion based on a nonlinear optical loop mirror

“…In this case, the nonlinear phase of the counterpropagating wave will have some effect on the ER of the converted signal. Like nonreturn-to-zero (NRZ), this problem can easily be solved by adjusting the state of polarization controller in the NOLM [11], [14]. In order to obtain a switching efficiency of 1, the peak power of the control pulse should be 242 mW; it means an average power of about 40 mw.…”

2R regeneration based on dispersion-imbalanced loop mirror and its applications in WDM systems

“…By using and , where is the dispersion parameter, is the wavelength, is the speed of light, and is the dispersion slope, the power difference is given by (see Appendix ) (6) Assuming the nonlinear phase shift of channel 1 is equal to , which could be realized by adjusting the polarization controller [21], the normalized power difference assumes the simple expression (7) If the power difference between these two channels should be smaller than 3 dB, the accumulated dispersion and slope should satisfy (8)…”