Abstract: A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity. To amplify and compress optical pulses in a multi-mode (MM) optical fiber, a single-mode is launched into the MM fiber by matching the modal profile of the fundamental mode of the MM fiber with a diffraction-limited optical mode at the launch end, The fundamental mode is preserved in the MM fiber by minimizing mode-coupling by using relatively short lengths of step-index MM fibers with a few hundred modes and by minimizing fiber perturbations.

Abstract: A novel polarization maintaining optical fiber, which can be used as a high-power polarization maintaining fiber laser or amplifier, is described. Insensitivity of the polarization state to external fiber bending and temperature changes is accomplished by minimizing polarization mode-coupling via reducing stresses inside the fiber core via increasing the fiber diameter. Alternatively, polarization mode-coupling can be minimized by an optimization of the fiber coating to minimize stresses at the interface between the fiber and the coating. As a result insensitivity to polarization mode-coupling is obtained at greatly reduced values of birefringence compared to small-diameter fibers. The fiber is of significant use in any application where polarization stability is important, and will be useful in telecommunications applications in particular for reducing polarization mode dispersion. An implementation in a parabolic pulse-producing fiber laser is also described as one specific high power example.

Abstract: A method is presented for writing a permanent spatially periodic phase-matching second-order non-linearity grating in an optical waveguide. Single frequency exciting radiation is launched in a pair of guided modes of the waveguide in the presence of an external DC electric field applied in a direction transverse to the waveguide. The exciting radiation may be either co-propagating or counter-propagating. The above method may be refined by performing it once for an estimated value of exciting radiation frequency, testing the waveguide to determine error in the chosen estimate, erasing the grating and re-performing the method using a corrected value for the frequency of the exciting radiation.