A proper amount of group delay dispersion of a dispersion compensating fiber or a single mode fiber reduces chirping of the optical pulse generated by an electroabsorption modulator. Evaluation of the amount of dispersive wave (nonsoliton components) contained in the output of the fiber by means of the inverse scattering transform provides the condition to minimize the dispersive wave generation although it does not generally agree with the condition to minimize the pulse width.Index Terms-Eigenvalues/eigenfunctions, electrooptic materials/devices, nonlinear equations, optical communication, optical fiber dispersion, optical pulse compression, optical pulse generation.
A 50W pico-second dual Nd:GdVO4 bounce amplifier system with a phase-conjugate mirror is demonstrated. The system has also been extended to generate pico-second mid-infrared radiation with frequency ranges of 1.55-1.57µm and 3.4-3.3 µm.
High intense optical vortex pulses, exhibiting an orbital angular momentum, have potentially to be applied in various fields, such as optical tweezers, laser micro-fabrication, and laser acceleration. Several researchers have successfully demonstrated ways to produce vortex outputs through mode-conversion in an optical fiber, including a stressed optical fiber as well as a hollow fiber. However, they used mostly a passive fiber as well as a continuous-wave laser. In this paper, we present the production of intense pico-second vortex pulses by selectively coupling a pico-second master laser into LP 11 modes in a stressed large mode-area fiber amplifier with an off-axis fiber injection method, for the first time.The experimental setup is shown in Fig. 1. A continuous-wave mode-locked Nd:Gd 0.6 Y 0.4 VO 4 laser with a pulse-width of 4.5 ps and a pulse repetition frequency of 150 MHz was used for the master laser, and its output power was 100 mW. The master laser output was off-axially injected to a large-mode-area Yb doped double-clad fiber (core diameter, φ30 µm, NA 0.06; clad diameter, 400 µm, NA 0.46) amplifier, thereby yielding highly efficient coupling into two orthogonal LP 11 modes. Stress was appropriately applied along a specific direction, so that the two orthogonal LP 11 modes were 90° out of phase at the end of the fiber. The output from the fiber was then converted to a circularly annular beam. The fiber amplifier was also pumped by a 30 W fiber-coupled 975 nm laser diode. The output power reached up to 4.4 W at the maximum pump power, corresponding to a peak power of ~6 kW (Fig. 2). To confirm that the annular output exhibited a phase singularity, we also analyzed interferometric fringes formed by the laser output beam and its laterally sheared copy. Then, a branch like a fork, due to a phase singularity, was observed (Fig. 2).In conclusion, we have produced intense pico-second vortex pulses by selectively coupling a pico-second master laser into the LP 11 mode in a stressed large mode-area fiber amplifier with an off-axis fiber coupling method. In particular, this method is capable of directly producing amplified intense pico-second vortex pulses from a simple fiber amplifier without any phase elements.
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