Passive Mode Locking

Table of Contents:

  1. Saturable Absorption
  2. Nonlinear Fiber-Loop Mirrors
  3. Nonlinear Polarization Rotation
  4. Role of Fiber Nonlinearity and Dispersion

SATURABLE ABSORPTION

Efficient graphene saturable absorbers on D-shaped optical fiber for  ultrashort pulse generation | Scientific Reports

NONLINEAR FIBER-LOOP MIRRORS

nonlinear amplifying loop mirror

NONLINEAR POLARIZATION ROTATION

When high intensity light propagates inside of a fiber, the effects of XPM and SPM on the pulses are non-negligible. In nonlinear polarization rotation, the intensity dependent phase changes as a result of the XPM and SPM are exploited in the orthogonally polarized components. An example setup of nonlinear polarization rotation is shown below.

Nonlinear Polarization Rotation for Fiber Lasers with Ultra-High Pulse  Energy

In this case, we have a polarizing isolator that is placed between two polarization controllers. The role of the isolator is to ensure uni-directional propagation and to induce linear polarization. The polarization controller then changes the polarization state to elliptical. SPM and XPM then change the polarization state of the pulse through propagation in the doped fiber. The second polarization controller after propagation then adjusted such that the isolator lets pass the central, high intensity part of the pulse but blocks the lower intensity wings, thereby shortening the pulse.

ROLE OF FIBER NONLINEARITY AND DISPERSION

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