Flexible frequency comb generation in a periodically poled lithium niobate waveguide enabling optical multicasting

Abstract

We propose and demonstrate a technique for the generation of a coherent optical comb, with tunable line spacing in a periodically poled lithium niobate (PPLN) waveguide. A single continuous wave laser is modulated to generate three phase-locked seed lines, which are injected into a PPLN waveguide, to obtain line multiplication. The line spacing is set acting on the frequency of the electrical signal driving the modulator. The quality of the comb is verified measuring the autocorrelation, the phase noise, and the linewidth of the generated lines. With the same scheme, we demonstrate optical multicasting. From a single quadrature phase shift keying signal, modulated at 12.5 and 25 GBaud, five replicas are generated, with spacing 25 and 37.5 GHz. The performance of each signal replica is measured after transmission through 80 km of a single-mode fiber, demonstrating operation with a bit error rate value lower than the forward error correction threshold.

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“…In the experiments described in [201], the seeds are sourced from independent lasers, thus resulting in a comb, whose lines were not coherent. Vercesi et al [202] introduced a seed generator based on a nonlinear element, such as a MZM driven by an RF signal. The PPLN was fed with frequency and phase locked seed generators, instead of independent lasers, thus resulting in a coherent comb, with FSRs of 25 GHz and 37.5 GHz.…”

“…Here again 8 clearly resolved 10.664 GHz coherent tones within 3 dB of the spectral envelope peak were generated. 7 sub-carriers with a flatness of 2 dB (improved via filtering) were modulated resulting in a 74.648 Gb/s (7× 10.664) DPSK CoWDM signal Ϯ͗ &' ǁŝƚŚ F igure 21: Multicast using PPLN comb, S, signal to be multicast; vQPM, quasi phase matching frequency; ∆v, wavelength de-tuning with respect to vQPM; f, spacing between comb lines [202].…”