Method and device for generating short optical pulses

#High power laser systems emitting short optical pulses are useful for many emerging applications in materials processing, biotechnology, instrumentation, metrology and medicine, representing one of the fastest growing laser markets nowadays. In particular, semiconductor laser based systems can benefit from the higher efficiency, compactness, wavelength tunability, lower cost, as well as the reduced complexity and footprint of laser diodes when compared to commercially available Ti:sapphire and fiber lasers.

#The generation of optical pulses in semiconductor laser diodes is commonly achieved by means of gain switching, by driving the laser diode with an electrical injection of high peak current pulses having a duration of a few hundred picoseconds. The minimum pulse width that can be achieved with this technique is typically of a few tens of picoseconds which is in many cases longer than required by most applications. Besides, the average power is typically limited to a few mW due to the low duty cycle of the electrical pulse train used to forward bias the laser diode.

#Passive mode locking is another well-established technique from which less than 10 ps optical pulses are commonly attained. It makes use of a two-section laser configuration used for separately pumping a gain and an absorber section. The technique has the advantage of only requiring DC sources without any fast electronics, therefore being a compact and cost-effective alternative.

#In order that the manner in which the above-recited and other advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended figures and tables. Understanding that these figures and tables depict only typical embodiments of the invention and are therefore not to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail by the use of the accompanying drawings in which

#FIG. 1 shows a schematic diagram of a prior art laser: (a) Cross-section view of a standard semiconductor edge-emitting laser waveguide in the vertical and longitudinal directions (vertical and horizontal directions of the drawing, respectively) consisting of n- and p-type contacts designated (1) and (7), n-doped substrate (2), waveguide layers (3) and (5), waveguide layer (4) containing the active region and p-doped contact layer (6). (b) Near field profile of the fundamental mode versus the vertical distance showing narrow width due to a tight localization at the waveguide layer (4). (c) Far field profile of the fundamental mode showing large divergence as a function of the vertical angular coordinate. This figure as well as FIGS. 2-8 below in parts (a) is not to scale. FIGS. 2-6 in parts (b) illustratively present the modifications of the near field, in parts (c) illustratively present the divergence narrowing of the far field of the fundamental mode relative to the case of the edge-emitting laser of FIG. 1.

#FIG. 2 shows a schematic diagram of a prior art laser [2]: (a) Cross-section view of an edge-emitting laser in the vertical and longitudinal directions as in FIG. 1 and with additional mode expanding layers (11), (12) below and above the active layer, respectively. Refractive index, thicknesses and positions of the mode expansion layers (11) and (12) are adjusted to obtain the mode expansion. (b) Near field profile of the expanded fundamental mode with additional expansion peaks (21) and (22) versus the vertical distance. (c) Far field profile of the fundamental mode with narrower divergence as compared to FIG. 1 versus the vertical angular coordinate.

#The preferred embodiments of the present invention will be best understood by reference to the drawings, wherein identical or comparable parts are designated by the same reference signs throughout.

#It will be readily understood that the present invention, as generally described herein, could vary in a wide range. Thus, the following more detailed description of the exemplary embodiments of the present invention, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.

#FIG. 13 shows an optical device 100 for generating short optical pulses Pcomp. The device 100 comprises a single section semiconductor laser 110, an electrical control unit 120, and a dispersive element 130.