We study the properties of a soliton crystal, an bound state of severaloptical pulses that propagate with a fixed temporal separation through theoptical fibres of the proposed approach for generation of optical frequencycombs (OFC) for astronomical spectrograph calibration. This approach - alsobeing suitable for subpicosecond pulse generation for other applications -consists of a conventional single-mode fibre and a suitably pumped Erbium-dopedfibre. Two continuous-wave lasers are used as light source. The soliton crystalarises out of the initial deeply modulated laser field at low input powers; forhigher input powers, it dissolves into free solitons. We study the solitoncrystal build-up in the first fibre stage with respect to different fibreparameters (group-velocity dispersion, nonlinearity, and optical losses) and tothe light source characteristics (laser frequency separation and intensitydifference). We show that the soliton crystal can be described by twoquantities, its fundamental frequency and the laser power-threshold at whichthe crystal dissolves into free solitons. The soliton crystal exhibits featuresof a linear and nonlinear optical pattern at the same time and is insensitiveto the initial laser power fluctuations. We perform our studies using thenumerical technique called Soliton Radiation Beat Analysis.
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