Carrier-suppressed return-to-zero modulation (CS-RZ), in which there is a 180-degree phase shift between successive pulses, reduces the effects of intrachannel impairments. However, there are a number of variants of CS-RZ that differ in their method of generation, their bandwidth requirements, and their performance. It is shown that a recently proposed technique, in which the RZ signal is generated by filtering a CW signal that is square wave phase modulated (termed CWSW), performs comparably or better than alternative techniques. Relative to a modified duobinary system that results in alternate mark inversion( AMI), CWSW achieves better performance in systems with small dispersion, but slightly poorer performance in systems with larger dispersion and dispersion compensation. The small improvement in performance of AMI relative to CWSW in this latter case is achieved at the expense of requiring a larger transmission bandwidth and more complex transmitter. The physical basis of the impairments in these systems, a peak intensity enhancement phenomenon in CWSW that counters the effects of dispersion, and factors affecting the bandwidth of alternative techniques is discussed.
We propose and evaluate a new return-to-zero (RZ) transmission format, which simplifies the transmitter and produces significantly improved eye diagrams at the receiver compared with other formats. By applying synchronous square wave phase modulation (PM) to a continuous wave (CW) signal, with a 180 degrees phase shift (phase reversal) between adjacent bit slots, and followed by an optimally tuned optical filter, we generate a train of RZ pulses which is inherently stable and resistant to dispersive and nonlinear effects. Separate amplitude modulation (AM) is unnecessary in this approach to shape the RZ pulses. This format (which we term CWSW) not only suppresses the growth of spurious pulses on adjacent "1" states, but also results in a peak intensity enhancement where waveform distortion caused by fiber dispersion initially improves the eye opening during transmission. Single-channel 40 Gbits/s systems employing dispersion-shifted fibers are investigated by computer simulations. We show that spurious pulse suppression and peak intensity enhancement increase the maximum transmission distance and improve the eye profile at the receiver relative to alternative transmission formats.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.