Imaging laser diodes with a lightwave circuit

A method for imaging light from a plurality of laser diodes (504) onto a multi-channel light valve (6) includes applying light from the plurality of laser diodes to a fiber waveguide (508) wherein each of the plurality of laser diodes is coupled to the fiber waveguide; guiding the light from the fiber waveguide through a planar lightwave circuit (PLC) (408) wherein light from the plurality of laser diodes is combined in the PLC; splitting the combined light in the PLC; and directing the split light from the PLC onto the multi-channel light valve.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned U.S. patent application Ser. No. 13/038,688 (now U.S. Publication No. 2012/0224802), filed Mar. 2, 2011, entitled IMAGING LASER DIODES WITH A LIGHTWAVE CIRCUIT, by Zheng; the disclosure of which is incorporated herein.

FIELD OF THE INVENTION

The present invention relates to multi-channel modulators in general and in particular to connecting individually addressable multi-element laser diodes to the modulator with a planar lightwave circuit.

BACKGROUND OF THE INVENTION

In order to increase the power and data rates available from laser diodes, multi-element, individually addressable arrays of laser diodes are sometimes used. These can be of the diffraction-limited single-mode type or arrays of broad area emitters. The broad area emitters are diffraction-limited in one dimension, referred to as the “narrow” dimension and act as a wide area source in the other or “wide” dimension.

The advantage of the broad area emitters, also referred to as “stripe” laser diodes, is the much higher output power possible. Because of this high power, these devices are manufactured with their positive side bonded to a heat sink since the thermal conductivity of the substrate material is much lower than that of the heat sink. Since the connections to the individual diodes also have to come out of the positive side, there is a conflict and a compromise between the heat sinking needs and the interconnections.

U.S. Pat. No. 5,517,359 (Gelbart) depicts an apparatus for imaging light from a laser diode onto a multi-channel linear light valve.FIG. 1shows a high power laser, wide emission area, laser diode1which emits a light beam2which is collimated in the vertical dimension by a cylindrical micro-lens3. A second micro-lens4is a linear array of cylindrical lenslet arrays4′ aligned with the multiple emitters l′ of laser diode1. The light from cylindrical lenslet arrays4′ is collimated by cylindrical lens5and imaged as a line on linear light valve6.

When a high power laser is used, linear light valve6is a polarized lead zirconiom titanate (PLZT) device, causing the state of the polarization of the light to rotate when a voltage is applied to electrodes on the PLZT material. A polarizer prism7transmits the light of horizontal polarization and reflects the polarized light11with polarization changed by passing through the activated PLZT cells. An imaging lens8images linear light valve6onto heat sensitive or on light sensitive material9, forming an image10. Image10is a reduced image of the linear light valve6.

The part designated as light pipe104inFIG. 1, shows an area where light propagates from lenslet array4in the direction of light valve6. The light emitted from emitters1′ through light pipe104may lose uniformity when it reaches light valve6. An apparatus which overcomes the problem described above would be desirable.

SUMMARY OF THE INVENTION

Briefly, according to one aspect of the present invention an apparatus for imaging light from a plurality of laser diodes onto a multi-channel light valve includes a plurality of laser diodes each coupled to at least one fiber waveguide. A planar lightwave circuit (PLC) is couple to at least one waveguide on a first side, and to the multi-planar light valve on a second side.

DETAILED DESCRIPTION OF THE INVENTION

The present invention describes an imaging head of a laser processing system which is part of a computer-to-plate (CTP) imaging device200shown inFIG. 2.FIG. 3shows the main part of the imaging head which is replaced by this invention.

The structure of light pipe104described in U.S. Pat. No. 5,517,359 causes a non-uniform distribution of power laser array that results in imaging artifacts on imaging material9. An improvement to the light pipe104is accomplished by using a planar lightwave circuit (PLC), shown inFIG. 4. The PLC408referred in this invention is a structure based on optical waveguides to form a light combiner structure412and a light splitter structure. The structures could be implemented by for example ridge, channel or photonic crystal waveguides and replaces several of the components in pipe104, providing a light pipe arrangement that improves the uniformity of the light emitted from the laser source.

FIG. 4shows PLC408. The PLC408includes a fiber waveguide structure to form an emission combiner element412. The combiner element412is configured to receive light emitted by laser source arrangement through inlets404. The received light is then combined by combiner element412and further split by splitter element416into plurality of outlets420via outlet waveguides418. Outlets420are coupled to light valve6. Each of the outlets420are selected or deselected by light valve6according to image data (not shown) thus forming an image on imaging material9. The number of inlets404used is dependent upon the total power required for imaging.

FIG. 5depicts several single high-power laser diodes (LDs)504. The laser diodes504are coupled to fiber waveguides508, which are further coupled to inlets404of PLC408. The fiber waveguides508may be a single mode fiber, multi-mode fiber or polarization maintained fiber. The laser diodes504replace laser diode bar1which is used in U.S. Pat. No. 5,517,359. The number of laser diodes504used, depends upon the total imaging power requirement. The arrangement shown inFIG. 4andFIG. 5limits the need for cylindrical lenslet array4′ (in prior art). The laser output guided through PLC408provides a naturally uniform and non collimated light before entering into light valve6.

FIG. 6shows single laser diode or laser diode array coupled into a PLC combiner/splitter408by a micro-lens or micro-lens array604.FIG. 7shows a PLC combiner/splitter408emitting light onto the direction of a light valve6. The emitted light is reshaped by a lens array704.

PARTS LIST