Polarization noise places severe constraints on coherence of all-normal dispersion femtosecond supercontinuum generation

Abstract

Supercontinuum (SC) generated with all-normal dispersion (ANDi) fibers has been of special interest in recent years due to its potentially superior coherence properties when compared to anomalous dispersion-pumped SC. However, care must be taken in the design of such sources since too long pump pulses and fiber length has been demonstrated to degrade the coherence. To assess the noise performance of ANDi fiber SC generation numerically, a scalar single-polarization model has so far been used, thereby excluding important sources of noise, such as polarization modulational instability (PMI). In this work we numerically study the influence of pump power, pulse length and fiber length on coherence and relative intensity noise (RIN), taking into account both polarization components in a standard ANDi fiber for SC generation pumped at 1064 nm. We demonstrate that the PMI introduces a power dependence not found in a scalar model, which means that even with short ~120 fs pump pulses the coherence of ANDi SC can be degraded at reasonable power levels above ~40 kW. We further demonstrate how the PMI significantly decreases the pump pulse length and fiber length at which the coherence of the ANDi SC is degraded. The numerical predictions are confirmed by RIN measurements of fs-pumped ANDi fiber SC.

Amplitude noise and coherence degradation of femtosecond supercontinuum generation in all-normal-dispersion fibers

“…In ANDi SC generation, it has been shown that the pulse duration, fiber length, and peak power have a critical influence on the noise properties [12,14], e.g., the anticipated coherent spectra are only obtained for sufficiently short pulse durations and fiber lengths. To see the effect of pump laser amplitude noise on the coherence and the requirements on the fiber length and pulse parameters, we simulate a wide parameter space and calculate for each case the spectrally averaged coherence given by [12,20]:…”

“…Unfortunately Gonzalo et al just briefly mentioned the effect of pure amplitude noise of the pump laser for one specific pulse duration and fiber length and no specific simulation including the amplitude noise was shown and no general study conducted [14]. In this work, we therefore present a comprehensive study of the influence of the noise of a mode-locked pump laser on the coherence and RIN of the SC spectrum generated in an ANDi fiber.…”

“…The reason for this high coherence comes from the coherent spectral broadening mechanisms of self-phase modulation (SPM) and optical wave-breaking (OWB) [12,13]. In fspumped ANDi SC generation these mechanisms are considerably more efficient than the incoherent nonlinear effects of noise-seeded modulation instability and stimulated Raman scattering [1], allowing for octave spanning SC generation in which these incoherent effects are suppressed for sufficiently short fiber lengths and input pulse durations [12,14].…”

“…Several theoretical studies about SC coherence have been reported in anomalous dispersion fiber, covering pulse durations from fs up to continuous wave, and including several kinds of noise, such as one-photon-per-mode (OPM) quantum noise added as pure phase noise in the frequency domain, Wigner-representation based quantum noise added in the time domain as amplitude and phase noise, Raman noise, and polarization noise [15][16][17][18][19][20][21][22][23][24][25][26]. This is not the case for theoretical studies of ANDi SC generation, which have mostly considered only the OPM noise [1,12,20], except for a recent work of Gonzalo et al [14], in which relative intensity noise (RIN) was experimentally and numerically compared, for ANDi SC generation with 170 fs pump pulses. In this study, it was found that OPM noise was too weak to describe the experimentally observed noise, whereas adding 1 % amplitude fluctuations of the laser gave better agreement with the experimental results.…”

Chalcogenide-glass polarization-maintaining photonic crystal fiber for mid-infrared supercontinuum generation

“…On the other hand, there is particular interest in combining the chalcogenide fiber platform with polarization-preserving properties as this will enable polarization-dependent applications in interferometric techniques, gas and pressure sensing, integrated-optic devices and also polarization-sensitive OCT [25][26][27][28][29][30]. Polarization-maintaining fibers also help in minimizing detrimental effects such as polarization noise and instability [31]. There are several ways of introducing strong birefringence in the fiber for polarization maintaining propagation.…”