Abstract
Optical sinc-shaped Nyquist pulses are widely used in microwave photonics, optical signal processing, and optical telecommunications due to their numerous advantages, like rectangular shape in the frequency domain, the orthogonality and the consequential possibility to use these pulses to transmit data with the maximum possible symbol rate. Ideal sinc pulses with the rectangular spectrum are just a mathematical construct. However, high-quality sinc pulse sequences offer the same advantages and can be generated by a phase-locked rectangular frequency comb with mode-locked lasers, intensity modulators, and integrated devices. Nevertheless, any non-idealities in the pulse and comb generation might lead to a degradation of the system performance, especially for metrology. Here, we investigate and analyze the effect of three major non-idealities, namely, the roll-off factor, the side band suppression ratio (SSR), and the ripple of sinc-shaped reconfigurable optical Nyquist pulse sequences based on 3, 5, and 9-line optical phase-locked frequency combs. We compare these results with the existing literature for the three-line comb followed by the experimental verification of the simulation results. We illustrate that by increasing the number of comb lines, the pulse sequences have superior performance and contribute to lesser root-mean-square (r.m.s.) error. We also discuss the trade-off between the r.m.s. error and the optical power loss for increasing the SSR.
Highlights
The surge in the worldwide demand for high data rate transmission to drive modern technologies and innumerable applications such as the internet of things (IoT), high-speed global networking, etc., might be attainable by optical signal processing as it provides a larger bandwidth, relatively simpler implementation and more flexibility as compared to the electrical domain
In this work, the effect of non-idealities for sinc-shaped Nyquist pulse generation such as roll-off factor, sideband rejection ratio (SSR), and ripple has been investigated thoroughly for a 3, 5, and 9-line comb which can further be extended for a higher frequency spacing between the comb lines
The effect of Nyquist bandwidth due to different roll-off factors for modulated sinc-pulses has been explored for a 3-line comb, and it is verified that a lower roll-off corresponds to a much higher confinement of the information in the channel bandwidth for some popular modulation schemes
Summary
The surge in the worldwide demand for high data rate transmission to drive modern technologies and innumerable applications such as the internet of things (IoT), high-speed global networking, etc., might be attainable by optical signal processing as it provides a larger bandwidth, relatively simpler implementation and more flexibility as compared to the electrical domain. The ideal sinc-shaped Nyquist pulses with β ∼ 0 are represented in black (dotted line) and the simulated pulses with respective roll-off are shown in orange. The roll-off factor of zero corresponds to the ideal scenario with sinc-shaped Nyquist pulses in the time domain and a rectangular frequency comb. Our work provides a comprehensive analysis of the effect of non-idealities in Nyquist pulses, namely, roll-off factor, SSR and ripple including r.m.s. error for 3-line, 5-line, and 9-line combs. SSR and roll-off factor play a critical role in the accurate generation of sinc-pulse sequences and for optical sampling
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