One or more combiner elements are disclosed for optically combining multiple laser beam bundles, either extra-cavity or intra-cavity to the laser generating array chips, to form higher density bundles of parallel laser beams. The combiner elements can be shared between two or more array chips and include a form of a pellicle combiner, a polarizing beam splitter cube combiner, or some combination of the two devices.
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There are many applications for bundles of laser beams from an array of emitters, whether that array is a stack of edge emitting laser diodes, surface emitting laser diodes, or vertical cavity surface emitting laser (VCSEL) arrays. These applications generally require high optical power, but in a small physical space. VCSELs have the advantage of being used to create monolithic arrays of laser emitters which greatly reduce the assembly cost of end products. A limiting factor when attempting to increase the density of laser emitters in an array so as to create a high-power bundle is the ability to provide sufficient drive current and cooling for the array.
Simply adding more emitters per unit area so as to achieve greater power only compounds the heat extraction and current supply problems. In addition, many of the applications for laser beam bundles, such as converging the bundle into a single fiber optic, requires that the beams in the bundle be in parallel. Simply adding more beams to the periphery of the bundle to make it larger will often be ineffective because there is a limit angle for beams being joined into the converged bundle, such as in a fiber optic coupling. Also, each beam must be of low divergence to allow reasonable distances between the emitter array and the downstream optics, or to facilitate the use of intermediate optical elements such as a micro-lens array, to shape the beams so as to better conform to the optical requirements of the system.
In the case of VCSEL arrays, their inherently low-divergence beams also facilitate the use of intra-cavity optics, where one or more of the resonator mirrors are not on the VCSEL chip. This gives rise to the possibility of placing one or more “optical combining” elements in the laser cavity, which increases the optical bundle density while simultaneously sharing the use of common optical elements among two or even more VCSEL array chips.
Embodiments include one or more elements for optically combining multiple laser beams generated by two or more laser-emitting semiconductor devices so as to form higher density bundles of substantially parallel laser beams. While one-dimensional and two-dimensional arrays of edge-emitting laser diodes could be used as the laser source, such devices have less desirable beam divergence. Beam divergence is a measure for how fast the beam expands in the far field, i.e., far from the beam waist. VCSELs arrays, however, are ideally suited for use with combiners because such arrays generate beams having circular cross-sections and low divergence. For example, a downstream combiner, referred to as a pellicle combiner herein and further discussed below, is more appropriately used with the collimated beams generated by VCSEL arrays than with other more divergent output beam sources.
Embodiments disclosed herein can be used with semiconductor light devices including top emitting vertical-cavity surface emitting lasers (VCSELs), bottom emitting VCSELs, top emitting VCSELs with external cavities (VECSELs), and bottom emitting VECSELs. Embodiments can also be used with light-emitting diodes, edge emitting lasers, organic light-emitting diodes, optically pumped light sources, and electrically pumped light sources.
As noted, one of the combiners disclosed herein is referred to as a pellicle combiner. The term “pellicle” is usually used to refer to a thin film, membrane or skin. In the context of light manipulation, however, the term “pellicle” is usually used in reference to a pellicle mirror, which is a type of thin, semi-transparent mirror employed in the light path of an optical instrument to split a light beam into two separate beams, both of reduced light intensity. In contrast to the pellicle mirror, the pellicle combiner described herein is a thin device, typically formed from a flat glass surface, having a reflective surface, typically formed from a coating of a highly reflective metal, such as chrome, for reflecting a first bundle of beams from a first VCSEL array and having a pattern of holes through the reflective surface for passing through a second bundle of beams from a second VCSEL array so as to combine the first bundle with the second bundle.
As illustrated in
The pellicle combiner illustrated herein can be used either intra-cavity or extra-cavity to combine the beam bundles. In particular,
In
In one embodiment, the second bundle emitted by a second laser chip can be reflected two or more times to ensure that after the two or more reflections, the second bundle is parallel to the first bundle emitted by the first laser chip. For instance, the arrangement of a device may make it necessary for the first laser chip to have a first orientation, resulting in a first bundle of laser beams being emitted in a first direction, and a second laser chip to have a second orientation that is not perpendicular to the first laser chip, resulting in a second bundle of laser beams emitted in a second direction. In such a device, it may be necessary for either the first bundle of laser beams or the second bundle of laser beams, or both the first bundle and the second bundle to be reflected one or more times to ensure that the first bundle and the second bundle are oriented parallel after all of the reflections so that these two laser bundles can be combined into a single bundle of laser beams.
A second type of combiner disclosed herein uses the notion that two beams (or beam bundles) that are optically polarized at 90 degrees to each other can be combined in a “polarizing beam splitter” cube where the vertically polarized bundle (relative to the reflecting surface of the combiner cube) passes through the combiner cube, and the horizontally polarized bundle reflects off the back side of the combiner cube's polarizing reflector to form a set of co-incident and parallel beams having both vertical and horizontal polarization as well as their combined power. When this type of combiner is used within the laser cavity, the polarizing combiner cube can also serve as a strong polarization selecting element so as to allow only photons of the appropriate polarization to be amplified.
An “output coupler” element, which is shared by the output beam bundles of the combiner cube, can consist of a piece of flat optical material such as glass, with a partially-transparent reflective coating on one side to form the optical resonator for the combined beam bundle. This same surface can also accommodate other devices such as a micro-lens array or a micro-mirror array whose individual elements are matched to each laser beam in the bundle. The flat optical material of the output coupler could also be made of a frequency-doubling crystal with a partially-transparent reflective coating on the far side of the crystal to make the crystal intra-cavity. Micro-lens arrays on the output coupler are used in favor of micro-concave-mirror arrays because micro-lenses will re-collimate each beam in the bundle, which facilitates an output coupler coating on a simple flat surface rather than on the micro-concave-reflectors. While the use of a glass substrate for the output coupling element is adequate, using a substrate comprised of a frequency-doubling crystal can provide a new capability for creating other wavelengths.
The combiner cube and output coupler described above are further illustrated in
A combination of pellicle combiners and polarizing element combiners can also be used to combine laser beam bundles from more than two laser array chips. The distribution of the laser arrays among two or more laser chips facilitates the distribution of heat and the supply of current to each device as opposed to constraining the combined heat and electrical power to one chip. This combination is further illustrated in
Hence, while a number of embodiments have been illustrated and described herein, along with several alternatives and combinations of various elements, for use in geo-reinforcing, it is to be understood that the embodiments described herein are not limited to the embodiments shown and can have a multitude of additional uses and applications. Accordingly, the embodiments should not be limited to just the particular descriptions, variations and drawing figures contained in this specification, which merely illustrate a preferred embodiment and several alternative embodiments.
This is a non-provisional application that takes priority from provisional application Ser. No. 61/345,513, filed 17 May 2010, which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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61345513 | May 2010 | US |