Abstract

Phase elements transform optical beams without losses. However, in the plane of conversion, the wavefront is changed, but the intensity profile remains the same. Shaping the beam profile is accomplished by propagation (Fraunhofer or Fresnel diffraction). Therefore, two phase elements, one close to the near field and one close to the far field, must be used for efficient beam shaping. In the case of collimating coherent beams emitted by high power laser diode arrays (LDA), conversion of the multilobed (supermode) emission into a single-lobed Gaussian beam is desired. This is achieved by correcting the phase distribution in the near field, using a phase plate, so that one gets in the far field a smooth Gaussian intensity profile with minimized intermodulation. In that far field, a phase grating acts as a fan-in element to produce a single collimated Gaussian beam. We have shown theoretically that, in the case of a LDA with nine phase locked stripes emitting equal intensities, 99.3% of the output power can be converted into a single-lobed beam. The same principle can also be used to record and optimize fan-out elements for optical interconnections. Either equally spaced N × M arrays or irregularly spaced fan-out patterns can be produced.

© 1989 Optical Society of America