Abstract

State-of-the-art high brightness LEDs offer optical powers of about one watt and span a wide wavelength range - clearly outperforming usual single mode laser diodes. Thus, LEDs excel in applications where beam quality - the main advantage of lasers - is not the decisive criteria and/or speckle are critical. For a LED illuminated spot array generator a pupil splitting design approach with a lens-array is presented. Contrary to usual laser diode spot array generators with diffractive beamsplitters this design enables individually colored spots, suppresses unwanted speckle and increases beam quality with increasing spot number. Design rules and scaling laws are established, then the resulting system is analyzed with respect to useful transmission, beam quality and chromatic aberrations. We realized a 21x21 spot array generator with 40°x40° FOV using a simple plano-convex lens as projection optics. A chirped lens array with varying focal widths and pre-distorted lenslet positions corrects field curvature and distortion of the projection optics. Additional buried apertures and color filters suppress unwanted straylight and enable individually colored spots, respectively. The lens array is fabricated by replication of reflow master structures into polymer on glass.

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