Abstract
An on–off keying (OOK) to quadrature phase shift keying (QPSK) format conversion scheme has been demonstrated in this paper. Two-channel OOK signals are converted into one-channel QPSK signal, and accompanied with a multicast function. The proposed scheme is based on a cascaded semiconductor optical amplifiers (SOA) configuration where the processes of cross phase modulation (XPM) and nonlinear polarization rotation (NPR) are properly controlled by OOK signals in each SOA. The experimental results show that after conversion, four-channel QPSK signals are successfully obtained with open eye-diagrams, and all the converted signals experience a small power penalty of less than 3.4 dB at a bit error rate (BER) of $10^{-9}$ compared to the original signal. In addition, the optical spectra and the constellation diagrams of the converted signal also indicate the high quality performance exhibited by the proposed format conversion scheme.
Highlights
Phase modulation is a promising technology when it comes to improve the performance of long-distance data transmission systems
When data from metropolitan area network (MAN) comes to the switching node, two on-off keying (OOK) signals of different wavelengths may need to be multiplexed into a single quadrature phase shift keying (QPSK) signal
The two OOK signals are amplified by erbium doped fiber amplifiers (EDFAs), where OOK1 is used as the control signal of SOA1 through a circulator, and OOK2 is used to control SOA2
Summary
Phase modulation is a promising technology when it comes to improve the performance of long-distance data transmission systems. It is likely that between the metropolitan and backbone networks, an intermediate node is needed to convert the modulation formats between quadrature phase shift keying (QPSK) and OOK signals, so as to construct a seamless. AlGaAs waveguide can perform the format conversion function similar to HNLF in shorter device interaction length, but its transmission loss is significantly high [10]. Compared with HNLF and AlGaAs waveguide, semiconductor optical amplifier is considered as a promising device for all-optical signal processing due to its high nonlinearity, small size and gain characteristics [11]–[14].
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