| US6452720B1 | 2002-09-17 | |||
| JPH09152639A | 1997-06-10 | |||
| US20070229939A1 | 2007-10-04 | |||
| US20030223670A1 | 2003-12-04 | |||
| US6600582B1 | 2003-07-29 |
| What is claimed is: 1. A laser system, comprising: a plurality of unpolarized laser sources having outputs in different spectral bands; and a beam combining assembly, disposed to receive and combine the outputs of the unpolarized laser sources, the assembly including: a polarization beam splitter dividing the collimated outputs into first and second polarized sets of beams; a first wavelength combining module positioned to wavelength combine the first polarized set of beams onto a first common beam line; a second wavelength combining module positioned to wavelength combine the second polarized set of beams onto a second common beam line; and a polarization beam combiner disposed in the first and second common beam lines and configured to combine the first and second polarized sets of beams onto an output beam on a combined beam path. 2. Any of the laser system of claim 1 or the assembly of claim 15, further comprising: a first polarization rotation module disposed between the polarization beam splitter and the first wavelength combining module to rotate the first set of beams, and a second polarization rotation module disposed between the second wavelength combining module and the polarization beam combiner to rotate the second common beam line. 3. The laser system of claim 2, wherein the polarization rotating modules are comprised of: a polarization rotator; or a set of staggered mirrors and corresponding parallel plates. 4. The laser system of claim 3, wherein the polarization rotator is a half-wave plate. 5. Any of the laser system or assembly of claim 2 or the system of claim 17, wherein the first and second wavelength combining modules are comprised of prisms, or gratings, or a plurality of filters having respective pass bands that correspond to the spectral bands of corresponding ones of the laser sources. 6. Any of the laser system or assembly of claim 5 or the system of claim 17, wherein the first wavelength combining module is comprised of a plurality of Fabry- Perot filters having respective pass bands that correspond to the spectral bands of corresponding ones of the laser sources. 7. Any of the laser system or assembly of claim 5 or the system of claim 17, wherein the second wavelength combining module is comprised of a plurality of Fabry-Perot filters having respective pass bands that correspond to the spectral bands of corresponding ones of the laser sources. 8. The laser system of claim 1, wherein at least one of the plurality of unpolarized laser sources includes a diode laser, including a line narrowing optic, and coupled to an optical fiber, wherein the unpolarized output of the optical fiber is the output of one of the unpolarized laser sources and a collimator aligned with output of the unpolarized laser source to provide a collimated output. 9. The laser system of claim 1, wherein the unpolarized laser sources in the plurality of unpolarized laser sources comprise heat sink mounted diode lasers, including respective line narrowing optics which are selective for wavelengths in the different spectral bands, the diode lasers being coupled to a plurality of optical fibers, wherein the unpolarized outputs of the optical fibers are the outputs of the unpolarized laser sources and a set of collimators aligned with respective outputs of the unpolarized laser sources to provide collimated outputs. 10. The laser system of claim 1, including a focusing optic in the combined beam path configured for coupling the output beam into an optical fiber. 11. A method to provide a combining a plurality of unpolarized laser beams in different spectral bands, comprising: providing a plurality of collimated unpolarized laser beams; dividing the collimated beams into first and second polarized sets of beams; using a first wavelength combining module to spatially combine the first polarized set of beams into a first combined polarized beam; using a second wavelength combining module to spatially combine the second polarized set of beams into a second combined polarized beam; and combining the first and second polarized beams onto a combined beam path. 12. The method of claim 1 1, further comprising the step of rotating the first polarized set of beams before wavelength combining and polarization rotating the second polarized beam after wavelength combining. 13. The method of claim 1 1 , including supplying at least one of the unpolarized laser beams using a line-narrowed diode laser coupled to an optical fiber, the output of the optical fiber being the unpolarized laser beam. 14. The method of claim 1 1 , including supplying at least some of the unpolarized laser beams using heat sink mounted, line-narrowed diode lasers in different spectral bands, coupled to respective optical fibers, the outputs of the optical fibers being the unpolarized laser beams. 15. An optical assembly, comprising: a polarization beam splitter configured to split a plurality of unpolarized laser beams, each beam having a different spectral band into a first set of beams having a first polarization state and a second set of beams having a second polarization state; a first wavelength combining module in functional communication with the polarization beam splitter and configured to combine the first set of beams having the first polarization state to form a first wavelength combined beam having the first polarization and combined spectral bands; a second wavelength combining module in functional communication with the polarization beam splitter and configured to combine the second set of beams having the second polarization state to form a second wavelength combined beam having the second polarization and combined spectral bands; and a polarization beam combiner in functional communication with each of the first and second wavelength combining modules and aligned to combine the first wavelength combined beam having the first polarization and the second wavelength combined beam having the second polarization into a single output beam. 16. The optical assembly of claim 2, wherein the first and second wavelength combining modules together consist essentially of a single wavelength combining module that is tuned to a single polarization direction. 17. An optical system providing a high brightness, high power laser diode output, comprising: a plurality of fiber coupled, line-narrowed laser diodes providing a plurality of unpolarized laser diode teams; a polarization beam splitter optically coupled to the unpolarized laser diode beams to split the plurality of unpolarizedj laser diode beams from the laser diode sources, each laser diode source having a different spectral band into a first set of beams having a first polarization state and a second set of beams having a second polarization state; a first polarization rotation module disposed between the polarization beam splitter and the first wavelength combining module to rotate the first set of beams, and a first wavelength combining module optically coupled to the polarization beam splitter to combine the first set of beams having the polarization rotated first polarization state to form a first wavelength combined beam having the polarization rotated first polarization state and combined spectra; a second wavelength combining module optically coupled to the polarization beam splitter to combine the second set of beams having the second polarization state to form a second wavelength combined beam having the second polarization state and combined spectra; and a second polarization rotation module disposed between the second wavelength combining module and the polarization beam combiner to rotate the second wavelength combined beam. a polarization beam combiner optically coupled to each of the first and second wavelength combining modules to combine the first wavelength combined beam having the polarization rotated first polarization state and the second wavelength combined beam having the polarization rotated second polarization state into a single output beam. 18. An optical system providing a high brightness, high power laser diode output, comprising: a plurality of fiber coupled, line-narrowed laser diodes providing a plurality of collimated unpolarized laser diode beams; a polarization beam splitter optically coupled to the collimated unpolarized laser diode beams to split the plurality of collimated unpolarized laser diode beams from the laser diode sources, each laser diode source having a different spectral band into a first set of beams having a first polarization state and a second set of beams having a second polarization state; a wavelength combining module optically coupled to the polarization beam splitter to combine each of the first and second set of beams having the first and second polarization state, respectively, to form first and second wavelength combined beams, respectively, having first and second polarization states, respectively, and combined spectra; a polarization beam combiner optically coupled to the wavelength combining module to combine the first wavelength combined beam having the first polarization state and the second wavelength combined beam having the second polarization state into a single output beam; a first polarization rotation module disposed between the polarization beam splitter and the wavelength combining module to rotate the first set of beams, and a second polarization rotation module disposed between the wavelength combining module and the polarization beam combiner to rotate the second wavelength combined beam. |
LASER OUTPUTS
BACKGROUND ART
Cross Reference to Related Applications
[1] This invention claims priority, under the Patent Cooperation Treaty and the Paris Convention, to the United States Non-Provisional Patent Application No.:
13/939,974 by Edmund L. Wolak, filed on July 11, 2013, which is incorporated by reference herein.
Technical Field
[2] The present invention relates to high brightness, high power laser diode systems. Industrial Applicability
[3] The present invention will be applicable in a variety of ways to a variety of industries. The invention may be used within fiber optic systems to provide improved systems using high power laser diodes. Description of Related Art
[4] In the field of high power laser diodes, certain applications are limited by the available brightness emitted by laser diodes. The available brightness may be limited by spatial and spectral brightness distributions.
[5] Spatial brightness is typically optical power divided by spatial angle (beam divergence) and focused spot size. It is desirable to have low divergence beams for many applications, including coupling the beams into fiber optics. Spectral brightness is the width of the spectral band of the beam In many applications it is desirable to produce beams with relatively narrow spectral bands, for controlled interaction with the target of the beam. In other applications, the wider spectral bands are acceptable.
[6] To reach high brightness levels, outputs of multiple laser diodes have been used. One technology for combining beams from multiple diode lasers is described in U.S. Patent No. RE40.173 titled "High Efficiency, High Power, Direct Diode Laser Systems and Methods Therefor" by Mark Zediker, et al. However, large arrays of laser diode sources needed to achieve high output powers for combined beams present practical issues with use of beam combiners of the prior art. For example, because of the need to mount such large arrays in configurations that allow for efficient delivery of power, effective cooling and for low cost manufacturing, blocks of fiber coupled, laser diodes have been developed. The fiber coupling however reduces beam quality, and therefore the efficiency of the beam combining technologies.
DISCLOSURE OF THE INVENTION
[7] High brightness, high power laser outputs can be developed using a technique of splitting, collimated outputs of multiple, line-narrowed laser sources, such as unpolarized outputs of fiber delivered beams from laser diodes, into two sets of polarized beams. The two sets of polarized, line-narrowed beams are combined using a first set of Fabry Perot filters configured for wavelength combining beams in polarization state of the first set onto a first common beam line, and a second set of Fabry Perot filters configured for separately wavelength combining beams in the polarization state of the second set onto a second common beam line. The wavelength combined beams on the first and second common beam lines can then be combined using a polarization combiner, which produces a collimated beam of high brightness, from an array of unpolarized sources.
[8] Other aspects and advantages of the present invention can be seen on review of the drawings, the detailed description and the claims, which follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[9] Fig. 1 illustrates a technique to spectrally narrow the output beam of a laser diode and using a Fabry-Perot filter to combine beams having different center frequencies.
[10] Fig. 2 depicts combining the outputs of three laser diodes each having a different center wavelength using Fabry-Perot filters.
[11 ] Fig. 3 is a simplified block diagram of an optical system wherein the outputs of multiple laser diodes are each polarization split into two polarization states, wavelength combining the same polarization state from the multiple laser diodes and using a polarization combining optical element to recombine the wavelength combined beams for the two polarizations states.
[12] Fig.4 depicts an alternate optical system mat achieves polarization splitting, wavelength combining of the outputs from multiple laser diodes and finally recombines the two polarization states into a single output beam having high brightness.
[13] Fig. 5 depicts an alternate arrangement of Figure 4 using fewer highly reflective mirrors and is more compact.
[14] Fig. 6 depicts an embodiment wherein one polarization state is rotated such that identical wavelength combining modules may be used for the two polarization states thus simplifying the design.
[15] Fig. 7 depicts an alternate embodiment to rotate one polarization state by reformatting the beams of one of the polarization states so mat identical wavelength combining modules may be used for the two polarization states.
MODE(S) FOR CARRYING OUT THE INVENTION
[16] A detailed description of embodiments of the present invention is provided with reference to the Figs 1-7. In the figures, optical elements are illustrated that are in functional communication (optically coupled) wherein the elements are positioned (location and/or orientation set as necessary) and/or coupled by other
devices/structures (fiber optic cables, etc.) in a manner that any output beam(s) from any preceding elements) (elements) in the upstream path of a beam) are properly received by such elements so that their intended function may be realized.
[17] Figure 1 illustrates spectrally combining beams from two laser diode sources using a Fabry-Perot filter 108. By correctly choosing a Bragg grating 106 to narrow the linewidth of a laser diode source 102 and the parameters of the Fabry-Perot filter
108, one can design filters such that at a given angle Θ 1 15, the spectrally narrowed output 1 10 of a laser diode source 102 passes through the Fabry-Perot filter 108 while all other wavelengths are reflected. A second laser diode beam 112 having a narrow linewidth with a different center wavelength and spectral shape 113 impinges Fabry- Perot filter 108 at the same angle Θ 1 15 but from the opposite side and is reflected by Fabry-Perot filter 108. The two beams are effectively combined in a single beam containing the spectrums of the two laser diode sources and occupying the same space (spatially combined).
[18] The lower portion of Figure 1 illustrates the property of a Fabry-Perot filter
108 transmitting the output spectrum of a first laser diode 111 while reflecting the spectrum of a second laser diode 113. Transmission passband 120 of the Fabry-Perot filter 108 allows the collimated and linewidth narrowed beam 110 having spectral shape 1 1 1 to be transmitted through filter 108. The spectrum of second laser diode
1 13 located outside the passband of Fabry-Perot filter 108 is reflected. The use of spectrally narrowed laser diodes and narrowband Fabry-Perot filters makes it possible to closely space different spectrum from multiple laser diodes using wavelength combining techniques. Using multiple laser diodes, each having an output in a different spectral band, and combining spectrums provides a higher brightness output.
[19] Figure 2 shows an example of wavelength and spatially combining the outputs of three laser diode sources. Specifically the light of laser diode source 1002, a second frequency narrowed laser diode of wavelength□ 2 passes through Fabry-Perot filter 210, and a first frequency narrowed laser diode source 1001 having wavelength □ 1 impinges on Fabry-Perot filter 210 from the opposite side of the filter such that on reflection it shares the same physical space as the beam from the first source 1002. As a result, the two beams are effectively combined. As the Fabry-Perot filter is broadly reflective, multiple wavelengths can be brought together in this manner. A third frequency narrowed laser diode source of wavelength □ 3 passes through Fabry- Perot filter 216 while the combined beam 214 of the first source 1002 and second source 1001 are reflected thus effectively combining the three beams into a single beam 215.
[20] To overcome problems of unpolarized light from a laser diode source, the source beams are split into two orthogonal polarization states before wavelength combining. Figure 3 is one embodiment illustrative of a technique to combine wavelength narrowed beams from multiple laser diodes to produce a high brightness output.
[21 ] Outputs of two sources, first laser diode source 1001 having a first spectral band and second laser diode source 1002 having a second spectral band, are split using polarization beam splitters 3021 and 3022. A first set of beams have a first polarization state, first beam 3031 from source 1001 and first beam 3032 from source
1002. First beam 3031 is directed towards a highly reflective mirror 3041 which redirects the first beam 3031 towards Fabry-Perot filter 3061 where it is reflected. Second beam 3032 is directed towards Fabry-Perot filter 3061 where it is transmitted through the filter 3061 and is effectively combined with first beam 3031. Combined beam 3 13 is then directed to highly reflective mirror 3042 where the combined beam 3 13 is redirected towards polarization beam combiner 3 10. Fabry-Perot filter 3062 comprises a first wavelength combining module.
[22] The second set of beams have a second polarization state, second beam 305 1 from source 1001 and second beam 3052 from source 1002. Second beam 3052 from source 1002 is directed towards highly reflective mirror 3043 which redirects the second beam 3052 towards Fabry-Perot filter 3062 where it is reflected. A prism 308 redirects second beam 3052 so it impinges on highly reflective mirror 3043 and is redirected at an angle such that the reflected second beam 3052 impinges on Fabry- Perot filter 3062 where second beam 3052 reflects at the correct angle to be combined with second beam 305 1. Second beam 305 1 from source 100 1 is directed towards Fabry-Perot filter 3062 through a set of prisms 308 which correct the angle of incidence so it is transmitted through the filter 3062. Second beam 3051 and second beam 30S2 are therefore effectively combined into a single combined beam 314. Fabry-Perot filter 3062 comprises a second wavelength combining module.
[23] Combined beam 3 14 is directed to highly reflective mirror 3044 where it is redirected towards polarization beam combiner 310. Polarization beam combiner is placed so mat the two combined beams, combined beam 313 and combined beam 314, each having a different polarization state are combined into a single output beam 320. This high brightness, high power laser diode output beam 320 can then be focused by lens 312 directly where it's needed or into a fiber 315 for transport to remote destination.
[24] The prisms 308 used to redirect the path of a given beam are included for illustrative purposes only and may or may not be needed in any given system depending on the arrangement of optical elements. To increase the output power and brightness level additional laser diode sources are added to the system. Each laser diode source added necessitates the addition of two Fabry-Perot filters, one for each polarization state. One Fabry-Perot filter for the first polarization state and highly reflective mirror goes in the first wavelength combining module and die second Fabry-Perot filter and second highly reflective mirror goes in the second wavelength combining module. The Fabry-Perot filters are designed to pass the spectrum of only one laser diode source and handle one polarization state.
[25] A second embodiment is illustrated in Figure 4 wherein the elements for two wavelength combining modules for the two polarization states are not co-planar, whereas in Figure 3 all the beams for both polarization states lie in the same plane. Also, the laser diode sources are shown schematically mounted in common on a heat sink 409, located remotely from the optical assembly. The optical fibers from the laser diode sources deliver unpolarized, line-narrowed outputs from the laser diode sources to the assembly. This configuration can support large numbers of laser diode sources, including 10, 20 or more, as suits a particular implementation, each of which can deliver an output beam in spectral band on the order on a nanometer in width, or less. This enables many sources closely spaced spectrally, to be used for a high power, and relatively narrow band combined output.
[26] Side view 400 depicts the output beam from a first laser diode source 4021 split into two beams having different polarization states. A first beam 4031 having a first polarization state is directed to a first plane 401 and a second beam 4032 having a second polarization state is directed to a second plane 405. [27 j Top view 420 shows three laser diode sources (4021 , 4022, and 4023), each having a different spectral band, and three beam splitters (4081, 4082, and 4083). Each laser diode source is collimated and split into two polarization states (as shown in side view 400) by a beam splitter. Fabry-Perot filters (4121 and 4122) located on the left hand side of the beam splitters handle wavelength combining of the three beams having the first polarization state and located in first plane 401 comprising a first wavelength combining module. Fabry-Perot filters (4123 and 4124) located on the right hand side of the beam splitters handle wavelength combining of the three beams having the second polarization state and located in second plane 405 comprising a second wavelength combining module. Wavelength combining for each polarization state is performed as described with respect to Figure 2.
[28] A more detailed description of side view 400 follows. The output of a first fiber coupled laser diode source 4021 is collimated by lens 404 before being directed to a polarization beam splitter 408 1. Polarization beam splitter 408 1 splits the collimated beam from the laser diode source 4021 into two orthogonal polarization states. First polarized beam 403 1 having a first polarization state is directed to highly reflective mirror 4101 where it is redirected to Fabry-Perot filter 4121 (see top view 420). Beam splitters 4081, 4082, and 4083, highly reflective mirrors 4101 and 4104, and Fabry-Perot filters 4121 and 4122 are located in the first plane 401. Fabry-Perot filters 4121 and 4124 comprise a first wavelength combining module.
[29] Second polarized beam 4032 having a second polarization state passes directly through beam splitter 4081 before being directed by highly reflective mirror 4102 towards highly reflective mirror 4103. Highly reflective mirror 4103 redirects second polarized beam 4032 towards Fabry-Perot filter 4123 (see top view 420). Highly reflective mirrors 4102, 4103 and 4105, and Fabry-Perot filters 4123 and 4124 are located in the second plane 405. Fabry-Perot filters 4123 and 4124 comprise a second wavelength combining module.
[30] Once the beams for each polarization state from all the laser diode sources have been wavelength combined the two polarization states must be recombined by polarization combiner 414. But first, one of the wavelength combined beams must be redirected to the same plane as the other wavelength combined beam. This is shown in insert 450 where combined beam 4131 having a first polarization state is direct by highly reflective mirror 4111 perpendicularly towards a second highly reflective mirror 41 12. Second highly reflective mirror 41 12 directs combined beam 4131 towards the polarization combiner 414 located in the second plane 405. The ellipse 407 denotes mat combined beam 4131 is directed in a direction perpendicular to the page.
[31] Highly reflective turning mirror 4108 redirects wavelength combined beam 4132 formed by Fabry-Perot filter 4 124 towards polarization combiner 414 such mat the wavelength combined beam 4131 having a first polarization state is polarization combined with wavelength combined beam 4132 having a second polarization state to form a single high brightness, high power output beam 417. High brightness, high power output beam 417 is then focused by lens 416 into a fiber 418. The fiber 418 may transport the light from output beam 417 to a remote position where it may be used for fiber laser pumping, solid state laser pumping, or cutting and welding using direct diode light. Alternatively, the high brightness, high power beam 417 may be directly focused onto a work piece such as two pieces of metal for laser welding.
[32] Figure S depicts an alternate arrangement combining three laser diode sources as shown in Figure 4 but occupying a small space and using fewer highly reflective turning mirrors. The laser diode sources are shown schematically mounted in common on a heat sink 409, located remotely from the optical assembly. The optical fibers from the laser diode sources deliver unpolarized, line-narrowed outputs from the laser diode sources to the assembly. The polarization beam splitters, Fabry-Perot filters, and the polarization beam combiner 414 operate as in Figure 4. Highly reflective mirrors 4101 and 4104 do double duty by replacing highly reflective mirrors 4103 and 4106 by redirecting both polarization states. Highly reflective mirror 4101 reflects both polarization states from laser diode source 402 1. Similarly, high reflective mirror 4104 reflects both polarization states of the beams from laser diode source 4022 mat have been wavelength combined with the respective polarized beams from laser diode source 4021. Highly reflective mirror 4109 redirects wavelength combined beam 4132 having the second polarization state to highly reflective mirror 4108. Highly reflective mirror 4108 then directs combined beam 4132 towards the polarization beam combiner 414 as it does in Figure 4. Highly reflective mirrors 41 1 1 and 41 12 redirect wavelength combined beam 4131 as described in Figure 4.
[33] In Figure 6 and 7 alternative embodiments are disclosed that simplify the design of the wavelength combining portion of the system. Two possible methods for rotating one the polarization states allows identical wavelength combining modules to be used for each polarization state.
[34] Fig. 6 depicts an embodiment wherein one polarization state is rotated using a polarization rotator such that identical wavelength combining modules may be used for the two polarization states thus simplifying the design. Input beams 602 from multiple laser sources are polarization split by a polarization splitter 604 into a set of beams having a first polarization state 606 and a set of beams having a second polarization state 608. A mirror 61 1 directs the set of beams having a first polarization state 606 to pass through a wavelength combining module 6121. The set of beams having a second polarization state 608 pass through a polarization rotating module consisting of a polarization rotator 6101 which rotates the polarization state of the set of beams having a second polarization state 608 to the same orientation as mat of the first polarization state. The polarization rotator may be a half wave plate or any other device that rotates the polarization state by 90 degrees. This allows an identical wavelength combining module 612 to wavelength combine the set of beams having a second polarization state 609. This simplifies the design of the system since only one wavelength combining module need be designed and manufactured to handle the two polarization states. After wavelength combining, the first combined beam 607 is directed to a second polarization rotator 610b to the appropriate orientation and then redirected by mirror 611 to a polarization combiner 615. The second combined beam 613 is directed to polarization combiner 615 to be polarization combined with the first combined beam 614. The polarization combined beam 616 may then be focused by a lens 618 into a fiber 620 for transport to a work object.
[35] Fig. 7 depicts an alternate embodiment to rotate one polarization state by reformatting the beams of one of the polarization states so that identical wavelength combining modules may be used for the two polarization states. The polarization reformatting module in this case consists of a set of staggered mirrors 710 and a set of path displacement elements 712. The input beams 702 from a multiple laser sources are polarization split by polarization splitter 704 into a first set of beams having a first polarization state 706 and a second set of beams having a second polarization state 708. The orientation of the two polarization states is depicted by double arrowhead lines. A set of staggered mirrors 710 are aligned such that a first staggered mirror 7101 redirects a first beam 7061 so that the first redirected beam 7141 has the same orientation as the first beam having the second polarization state 7081. The second beam having the first polarization state 706b is redirected by mirror 7102 to pass through a path displacement element 7121 such that the second redirected beam 7 142 now has the same orientation as the second beam having the second polarization state 7082. The path displacement element aligns the second redirected beam 7142 with the first redirected beam 7141 such that they are the same distance apart as the first beam having the second polarization state 7081 and the second beam having the second polarization state 7082. Each additional beam from the first set of beams having a first polarization state 706 is redirected by its corresponding staggered mirror 710 to a corresponding path displacement element 712. The result is a set of beams 714 having the same polarization orientation and alignment such that identical wavelength combining modules may be used to wavelength combine the two sets of beams. Once the two sets of beams are wavelength combined, one of the sets of beams must be polarization rotated or polarization reformatted using a second set of staggered mirror and path displacement elements before they can be polarization combined as described in Figure 6. Any combination of polarization rotators and polarization reformatting modules may be used to implement a system where identical wavelength combining modules may be used to wavelength combine the beams of the two polarization states.
[36] While the embodiments describe the wavelength combining modules with respect to Fabry-Perot filters as the wavelength combining elements other elements for wavelength combining are possible. Examples of other wavelength combining elements include prisms and gratings. Prisms refract beams having different wavelengths such that they are spatially combined. When prism combining is used, the wavelength combiner consists of a set of mounts that hold the collimated polarized wavelength stabilized beams with angle and position such that after passing through the prism the beams are spatially overlapped forming a common beam.
Specifically, the wavelength outputs will be chosen in ascending or descending order with slightly different angles impinging on the prism so as to allow the chromatic aberration quality of the prism (change of index with wavelength) to effect the beam combination.
[37] Gratings diffract beams having different wavelengths such that they are spatially combined. When grating combining is used, the wavelength combiner consists of a set of mounts that hold the collimated polarized wavelength stabilized beams in ascending or descending order in wavelength such that when the beams are directed at a common spot of the grating with slightly different incident angle the wavelength depended diffraction quality of the grating facilitates the spatial and wavelength overlap of the beams. Grating quality and design are chosen for either highly reflective operation or highly transmissive operation which may be an AR coated grating (which could be a volume holographic grating) fabricated from glass or other highly transmissive material such as fused silica.
[38] While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.