Numerical simulations and coherence properties of supercontinuum generation in photonic crystal and tapered optical fibers

J.M Dudley,S Coen

doi:10.1109/jstqe.2002.1016369

Abstract

Numerical simulations have been used to study broad-band supercontinuum generation in optical fibers with dispersion and nonlinearity characteristics typical of photonic crystal or tapered fiber structures. The simulations include optical shock and Raman nonlinearity terms, with quantum noise taken into account phenomenologically by including in the input field a noise seed of one photon per mode with random phase. For input pulses of 150-fs duration injected in the anomalous dispersion regime, the effect of modulational instability is shown to lead to severe temporal jitter in the output, and associated fluctuations in the spectral amplitude and phase across the generated supercontinuum. The spectral phase fluctuations are quantified by performing multiple simulations and calculating both the standard deviation of the phase and, more rigorously, the degree of first-order coherence as a function of wavelength across the spectrum. By performing simulations over a range of input pulse durations and wavelengths, we can identify the conditions under which coherent supercontinua with a well-defined spectral phase are generated.

Highlights

P HOTONIC CRYSTAL FIBERS (PCF) commonly consist of a central-fused silica core surrounded by a regular array of air holes running along the fiber length
The higher nonlinearity associated with PCF and tapered fibers leads to enhanced signatures of nonlinear and dispersive interactions during propagation, we stress that ultrashort pulse propagation in optical fibers has been the subject of extensive research for over 20 years [36], and many of the observed spectral and temporal features seen in the simulation results in Fig. 2 can be readily interpreted in terms of well-understood physics [30], [37]
The dramatic spectral broadening observed during the SC generation process arises from the interaction between the fiber dispersion and various nonlinear processes, including self-phase modulation (SPM), four-wave mixing (FWM), self-steepening, and stimulated Raman scattering [30]

Summary

INTRODUCTION

P HOTONIC CRYSTAL FIBERS (PCF) commonly consist of a central-fused silica core surrounded by a regular array of air holes running along the fiber length. An aspect of SC generation in PCFs which has not yet been the subject of detailed study is the sensitivity of the spectral broadening processes to input pulse noise This is of particular importance, because key applications of octave-spanning SC sources such as precision optical frequency metrology require highly coherent SC light with limited pulse to pulse variations and reduced timing jitter [20]. In this regard, we note that SC generation in standard optical fiber has previously been the subject of much research in a telecommunications context, where spectrally sliced broad-band SC have been proposed as sources for wavelength-division-multiplexing applications [21]–[28].

NUMERICAL MODEL

Results in the Absence of Input Pulse Noise

Results in the Presence of Input Pulse Noise

DISCUSSION AND CONCLUSION