Generation of a flexible optical comb in a periodically poled lithium niobate waveguide

Abstract

We propose and demonstrate a technique for the generation of an optical comb with tunable line spacing in a periodically poled lithium niobate (PPLN) waveguide. The technique is implemented with four input continuous waves (CWs), which generate a 19-line comb tuned to the spacing of 25 and 20 GHz. We show that each additional CW switched on out of the quasi phase-matching band at the PPLN waveguide input generates the growth of six new lines. The performance of the comb is tested modulating the lines with a 40 Gb/s differential quadrature phase shift keying data, demonstrating error-free operation. Nonuniform spacing of the input seed CWs improves the efficiency of the line generation process.

A Survey of Optical Carrier Generation Techniques for Terabit Capacity Elastic Optical Networks

“…The QPM bandwidth limits the achievable carrier/line spacing and overall bandwidth of the generated comb. Authors in [201] also proved that non-uniform spacing between seed lasers decreases overlapping contributions of SFG and SHG, thus increasing the number of lines (for uniform spacing, N seed lines can produce 2N-1 lines). In the experiments described in [201], the seeds are sourced from independent lasers, thus resulting in a comb, whose lines were not coherent.…”

“…Authors in [201] also proved that non-uniform spacing between seed lasers decreases overlapping contributions of SFG and SHG, thus increasing the number of lines (for uniform spacing, N seed lines can produce 2N-1 lines). 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.…”

“…Scaffardi et al made first demonstration of PPLN based optical frequency combs for optical communication applications [201]. The working principle is shown in Fig.…”

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

“…These techniques typically require high radio frequency (RF) and high optical power, due to large insertion losses. Other techniques, employing integrated circuits, are based on Kerr effects in microrings [11], which need feedback control for stable working conditions, and gain-switched lasers [12], with limited comb spacing tunability.Recently, we proved the generation of noncoherent optical combs, i.e., those without frequency-locked lines, in a periodically poled lithium niobate (PPLN) waveguide, starting from independent laser sources [13].In this Letter we demonstrate, for the first time to our knowledge, the generation of a coherent comb in a PPLN waveguide, by exploiting a single laser source. The proposed scheme is compact, low power consuming, and allows generating tunable-spacing and low phase noise lines.…”

“…Finally, differently from all other implementations (based on [16] and not based on PPLN), multicasting is achieved with a number of input pumps, lower than the number of obtained output replicas, thanks to the nonlinear line multiplication process, taking place into the waveguide, thus being more efficient. With the proposed scheme, multicasting of a 12.5 and 25 Gbaud coherent quadrature phase shift keying (QPSK) signal, through 80 km of single-mode fiber (SMF), is successfully demonstrated.The generation of a frequency comb with a PPLN waveguide can be performed, exploiting second-harmonic generation (SHG) and sum-frequency generation (SFG), cascaded with difference-frequency generation (DFG) [13]. The working principle is shown in Fig. …”