Simultaneous optical pulse compression and wing reduction

Abstract

In the optical fiber pulse compressor, the intensity-dependent refractive index n2 in the fiber provides the necessary self-phase modulation for subsequent temporal compression in the dispersive delay line. One drawback of using this compressor to obtain subpicosecond pulses is that compared with the pulses obtained directly from mode-locked lasers, the compressed pulses have proportionately more extensive wings. Another effect in optical fibers arising from the same third-order nonresonant nonlinear susceptibility is the intensity-dependent polarization rotation. On propagation through an optical fiber, the higher intensity portion of the pulse will acquire a different polarization than the low-intensity pulse wings. This effect has previously been used in intensity discrimination and nonlinear pulse reshaping. In this presentation we report the successful combination of both self-phase modulation and polarization rotation in a modified optical pulse compressor to achieve pulse compression with a significant reduction in the wings of the compressed pulse. An important feature of this combination is our ability to adjust the strength of the polarization rotation independent of the degree of self-phase modulation. With this situation, compression ratios of typically 20 are achieved with pulse shapes comparable with those obtained directly from mode-locked lasers.