Imaging head with laser diode array and a beam-shaping micro light-pipe array
An optical imaging heads that produce a plurality of light spots on light sensitive media such as photographic film or printing plate. The optical head incorporates an array of multi-mode laser diodes as a light source, a Micro Light-Pipe Array (MLPA) as a beam-shaping element, means for reducing the divergence of the laser diode beam in the fast axis direction and means for imaging the laser diode emitters on a surface close to the micro light-pipe entrance aperture.
1 . An optical imaging head comprising:
an array of multi-mode laser diode emitters;
an array of micro light-pipes (MLPs), each of said individual micro light-pipes being associated with one of said laser diode emitters; and
means for imaging the exit aperture of each of said micro light-pipes on a photosensitive medium.
2 . An optical imaging head according to claim 1 , wherein said means for imaging comprises a telecentric lens.
3 . The optical imaging head of claim 1 , additionally comprising means for reducing the divergence of the laser diode beam in the fast axis direction.
4 . The optical imaging head of claim 3 , wherein said means for reducing the divergence is an anamorphic lens.
5 . The optical imaging head of claim 4 , wherein said anamorphic lens is cylindrical.
6 . The optical imaging head of claim 3 , wherein said means for reducing the divergence is common for all said laser diode emitters.
7 . The optical imaging head of claim 3 , wherein said means for reducing the divergence is separate for each of said laser diode emitters.
8 . The optical imaging head of claim 7 , wherein said means for reducing the divergence is a micro-lens array.
9 . The optical imaging head of claim 1 , additionally comprising means for imaging the laser diode emitters on a surface close to the micro light-pipe entrance aperture.
10 . The optical imaging head of claim 1 wherein the micro light-pipes are tapered.
11 . The optical imaging head of claim 3 wherein the micro light-pipes are of funnel type.
12 . An external-drum electro-optical plotter comprising the optical head of claim 1 .
13 . A flatbed electro-optical plotter comprising the optical head of claim 1 .
14 . A method of producing a plurality of writing spots on a photosensitive medium, comprising the steps of:
providing an array of multi-mode laser diode emitters;
providing an array of micro light-pipes, each of said individual micro light-pipes being associated with one of said laser diode emitter; and
imaging the exit aperture of each of said micro light-pipes on said photosensitive medium.
15 . The method of claim 14 , additionally comprising, before said step of imaging, the step of providing means for reducing the divergence of the laser diode beam in the foist axis direction.
16 . The method of clam 15 , additionally comprising, after said step of providing means for reducing the divergence of the laser diode beam in the fast axis direction, the step of imaging the laser diode emitter in a surface close to the micro light-pipe entrance aperture.