Comments on "On the Self-Generation of Electrical Soliton Pulses"

Gary J. Ballantyne
2008 IEEE Journal of Solid-State Circuits  
A recent paper on soliton oscillators gave a parsimonious account of earlier work and omitted a critical reference. In [1]- [4], an electrical soliton oscillator was reported. We called it the Baseband Soliton Oscillator (BSO) because [4] also considered a similar device that supported envelope solitons (the ESO). A recent paper remarked that the BSO lacked "robustness, reproducibility and controllability" and claimed priority for such a device [5]. This is difficult for readers to assess for
more » ... emselves as [1] (the only published record of the bulk of our work) is not cited. A few words of clarification are thus required. A single soliton oscillation, where one pulse circulates endlessly in the loop, was easy to arrange in the BSO (for example, Fig. 2 of [1]). We were careful to identify the fundamental stability mechanism (tall solitons are narrow, and experience greater loss), and to form and solve the governing nonlinear partial differential equation. The steady-state solution showed how to control the soliton with respect to the device's parameters (which we verified with repeatable experiments). Many types of robustness may be contemplated for the BSO: for example, structural robustness (e.g., the number of circulating solitons) and amplitude robustness (e.g., the sensitivity of the soliton amplitude to the loop gain). As to structural robustness, we found that if the loop gain was increased beyond a critical level, multiple pulses could be observed in some configurations, and we identified subtle behavior corresponding to the double-cnoidal solutions of the Korteweg-De Vries equation. 1 However, even these were well-behaved (i.e., reproducible and controllable)-and absent if the loop gain was below the threshold value. Furthermore, it was observed in Sec. 2.2.2 of [4] that doublepulse waveforms could be eliminated using either the length of the loop or the strength of the nonlinearity. Unfortunately, [5] unfairly equates the mere presence of multiple pulses to an "oscillation instability" without noting the legitimate double-cnoidal solution, and omits entirely the existence of structurally robust single soliton oscillations. This is significant, as structural stability is a major element of [5]. As to amplitude robustness, [5] correctly identifies the sensitivity of the BSO oscillation amplitude to the loop gain. Unfortunately, [5] does not mention that this conclusion is based on a single design instance, or explore options given by the steady-state analysis in [1] Manuscript
doi:10.1109/jssc.2008.923729 fatcat:e7mkgku57bgljhjw7svzwwpysy