Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-03-10
2001-05-29
Font, Frank G. (Department: 2877)
Coherent light generators
Particular active media
Semiconductor
C372S034000, C372S035000, C372S036000, C372S108000
Reexamination Certificate
active
06240116
ABSTRACT:
BACKGROUND
Generally, the present invention relates to semiconductor laser bars assembled in an array to produce a two dimensional array of output beams and, more particularly, to an arrangement of laser bars that provides for higher thermal conductivity of the assembled laser bars while optimizing their combined brightness.
In the manufacture of assembled semiconductor laser bars, it is customary to stack mount a plurality of laser bars with their respective submounts, as illustrated in U.S. Pat. No. 4,716,568 to Scifres et al. In laser bar stacks, the laser bars are respectively mounted on a submount and the submounts with bonded laser bars are stacked in a repetitive arrangement, possibly interspersed with heat spreaders. This is generally termed a “rack and stack” approach to forming a two dimensional array of laser emitters. The combination of a laser diode bar, a submount and a heat spreader may have a thickness of about 1 mm or more. Thus, the pitch between adjacently stacked laser diode bars may typically be between about 1 mm to 2 mm. The stacking of multiple bars provides a two dimensional array of laser emitters with a pitch between emitters of adjacent bars equal to the thickness of the laser bar/submount arrangement.
Rather than using the “rack and stack” approach, others have suggested the use of a heatsink mount or substrate with a plurality of spatially disposed grooves that are parallel with one another as well as perpendicular with the planar extent of a major surface of the mount in which the grooves are formed. A laser bar is inserted in each groove with its emitters aligned along or extending out of the major surface of the bar facing in a direction away from the grooves. Examples of this “bars in grooves with perpendicular emission” approach are disclosed in U.S. Pat. Nos. 5,040,187; 5,128,951; 5,284,790; and 5,311,535 to Karpinski.
There is a problem with both the “rack and stack” and the “bars in grooves with perpendicular emission” approaches in that the smallest pitch between adjacent laser bars has a lower limit. Thus, it is not possible to improve the density of the two dimensional array of emitters by reducing the dead space between adjacently disposed laser bars. Therefore, it is difficult to improve the optical quality of the total combined beam output, particularly to further enhance the brightness of the output achieved through higher emitter density.
A second problem with the both the “rack and stack” and the “bars in grooves with perpendicular emission” approaches is that the thermal performance of the two dimensional array is limited by dissipating heat from the laser bars principally via the rear regions of the laser bar submounts. As a result, a large pitch is maintained between adjacently mounted laser bars in order to achieve adequate cooling of the bars.
Therefore, there is a need to provide a laser diode array system which produces an output having low size-divergence product and where the dead space between the beams produced by adjacent laser bars is reduced. There is also a need to provide a two dimensional output beam array that permits closer inter-beam spacing of emitters in adjacently mounted laser bars without requiring any change in the original thickness of the laser bars/submount arrangement. There is a further need to provide a laser diode bar array with high cooling efficiency while 2 producing closely spaced output beams from the two dimensional array. Finally, there exists a need to provide a laser diode bar array that permits superior cooling of the assembled laser bars over the cooling possible from conventional the “rack and stack” and the “bars in grooves with perpendicular emission” laser bar arrays.
SUMMARY OF THE INVENTION
According to one embodiment of this invention, a laser diode array package includes a mount and first and second laser diode arrays disposed on the mount. Each of the laser diode arrays defines an optical axis and has an emitting surface lying in an emitting surface plane. The emitting surface plane of the first laser diode array is displaced relative to the emitting surface plane of the second laser diode array in a direction parallel to one of the optical axes. The optical axes of the first and second laser diode arrays are offset from each other in a direction perpendicular to one of the optical axes. First and second lenses are disposed relative to respective emitting surfaces to reduce divergence of light output from the emitting surfaces.
In another embodiment of the invention, a substrate has first and second surfaces that are substantially parallel. A plurality of angled grooves are formed on the first surface, where each of the grooves has a mounting surface disposed at an angle to the second surface, the angle ranging from more than 0° to less than 90°. Laser diode array bars are disposed within respective groove to emit light from an emitting surface at the angle. Lenses are aligned with the laser diode array bars to reduce the divergence of light emitted by the laser diode array bars in at least one dimension.
In another embodiment of the invention, a laser diode array package includes a cooler block and mounting blocks detachably mounted on, and independently removeable from, the cooler block. Laser diode arrays are disposed on diode array mounting surfaces of respective mounting blocks. Divergence-reducing lenses are positioned by respective laser diode arrays to reduce divergence of laser beams output therefrom. Diode array mounting surfaces of adjacent mounting blocks lie in planes separated by a distance approximately equal to a height of a divergence-reduced laser beam at an output of a divergence-reducing lens.
In another embodiment of the invention, a semiconductor laser diode array includes means for producing laser beams from laser diodes, the laser beams having respective optical axes, means for reducing divergence of the laser beams in at least one direction; and means for mounting the laser diodes on a cooler with emitting surfaces of the laser diodes offset from each other in a direction parallel with at least one of the optical axes.
According to another embodiment of the invention, laser diode array bars are stacked and the individual output beam from each bar is collimated using a short focal length, low aberration lens. The resulting collimated beams are treated with reflectors to reduce, or remove, the dead spaces between adjacent collimated beams, thus permitting the use of low aberration lenses, which results in an improved divergence-size product for each beam produced by a bar. Additionally, the total beam output by the array of laser bars is condensed in size.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. Other objects and attainments, together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
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patent: 5373173 (19
Endriz John G.
Haden James M.
Lang Robert J.
Schoenfelder Alexander
Staskus Michael P.
Carothers, Jr. W. Douglas
Font Frank G.
Rodriguez Armando
SDL Inc.
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