Variable magnification infinite focal telescope element

Abstract

The apparatus includes a transmissive optical substrate configured to receive a plurality of laser beams propagating along respective parallel beam axes at respective initial beam displacements relative to an optical axis of the transmissive optical substrate, and configured to produce a laser output beam having reduced displacements, the transmissive optical substrate including first and second surfaces with respective first and second curvatures defined to increase output beam magnification and to nonlinearly increase output beam displacement from the optical axis for linearly increasing input beam displacement from the optical axis.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 62 / 886,912, filed Aug. 14, 2019. This application also claims the benefit of U.S. Provisional Application No. 62 / 886,907, entitled "HIGH BRIGHTNESS FIBER COUPLED DIODE LASERS WITH CIRCULARIZED BEAMS," filed Aug. 14, 2019. These applications are incorporated herein by reference.

[0002] This application is related to U.S. Application No. 15 / 435,117, filed February 16, 2017 (and issued as US 10,261,261), which is incorporated herein by reference.

[0003] (Field) The field is the combination of an afocal telescope and a laser diode beam. [Background technology]

[0004] There is a great demand for fiber-coupled, high power, high brightness diode lasers for applications such as fiber laser pumping and material processing. In existing fiber-coupled laser diode package devices, multiple single emitter diode lasers are stacked in the fast axis to emit individual beams, achieving power scaling and brightness improvement. However, additional improvements to brightness are desirable for at least the applications mentioned above. Summary of the Invention [Means for solving the problem]

[0005] The apparatus and method involve an afocal telescope element that can be used to impart variable magnification to an exiting diode laser beam based on the incident diode laser beam position.

[0006] According to an aspect of the disclosed technology, an apparatus includes a transmissive optical substrate configured to receive a plurality of laser beams propagating along respective parallel beam axes at respective initial beam displacements relative to an optical axis of the transmissive optical substrate and configured to produce a laser output beam having reduced displacement, the transmissive optical substrate including a first surface and a second surface with respective first and second curvatures defined to increase output beam magnification for increasing input beam displacement from the optical axis. In some embodiments, the first and second curvatures are defined to non-linearly increase output beam displacement from the optical axis for linearly increasing input displacement from the optical axis. In any of the aforementioned embodiments, at least one of the first and second curvatures is hyperbolic. In any of the aforementioned embodiments, the second curvature is hyperbolic concave. In any of the preceding embodiments, the first curvature is parabolic convex. In any of the aforementioned embodiments, the first and second curvatures are aspheric. In any of the aforementioned embodiments, the initial beam displacement corresponds to a displacement along a common fast axis of the laser beams. In some embodiments, the first curvature and the second curvature are configured to circularize the ensemble image space and the NA space of the laser output beams at the ensemble combining plane by elongating the image at the ensemble combining plane along the common fast axis for laser output beams having smaller input beam displacements relative to the optical axis and shortening the image at the ensemble combining plane along the common fast axis for laser output beams having larger input beam displacements relative to the optical axis. In any of the aforementioned embodiments, the transmissive optical substrate is a cylindrical meniscus lens. In some embodiments, the cylindrical meniscus lens includes a reference surface extending parallel to the optical axis and a cylindrical axis associated with the first surface and the second surface. In any of the aforementioned embodiments, the first curvature and the second curvature define a variable curvature ratio between the parallel input beam position and the transmitted output beam position associated with an increased output beam magnification.Any of the preceding embodiments may further include an objective lens configured to receive the laser output beams from the transmissive optical substrate and focus the multiple laser output beams at the ensemble combining plane, and an optical fiber including an end face configured to receive the laser output beams at the ensemble combining plane, the transmissive optical substrate configured to circularize an ensemble image space and an NA space of the laser output beams at the ensemble combining plane based on the increasing output beam magnification and the nonlinearly increasing output beam displacement. In any of the preceding embodiments, the output beam magnification is less than for each of the laser beams received within the input aperture of the transmissive optical substrate. In any of the preceding embodiments, the transmissive optical substrate comprises a cylindrical fast axis telescope. In any of the preceding embodiments, the transmissive optical substrate comprises a slow axis telescope. In any of the preceding embodiments, the transmissive optical substrate comprises a combined fast axis telescope and a slow axis telescope. The apparatus may include a laser diode package including the transmissive optical substrate of any of the preceding embodiments. The method may include fabricating the transmissive optical substrate of any of the preceding embodiments.

[0007] The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description which proceeds with reference to the accompanying drawings. The present specification also provides, for example, the following items: (Item 1) An apparatus comprising: A transmissive optical substrate configured to receive a plurality of laser beams propagating along respective parallel beam axes at respective initial beam displacements relative to an optical axis of the transmissive optical substrate, the transmissive optical substrate being configured to produce a laser output beam having reduced displacements, the transmissive optical substrate including a first surface and a second surface with respective first and second curvatures defined to increase output beam magnification for increasing input beam displacements from the optical axis. An apparatus comprising: (Item 2) 2. The apparatus of claim 1, wherein the first and second curvatures are defined to non-linearly increase output beam displacement from the optical axis for a linear increase in input displacement from the optical axis. (Item 3) Item 2. The apparatus of item 1, wherein at least one of the first curvature and the second curvature is a hyperbola. (Item 4) Item 2. The apparatus of item 1, wherein the second curvature is hyperbolic concave. (Item 5) Item 2. The apparatus of item 1, wherein the first curvature is a parabolic convex surface. (Item 6) Item 2. The apparatus of item 1, wherein the first curvature and the second curvature are aspheric. (Item 7) 2. The apparatus of claim 1, wherein the initial beam displacement corresponds to a displacement along a common fast axis of the laser beams. (Item 8) 8. The apparatus of claim 7, wherein the first and second curvatures are configured to circularize an ensemble image space and an NA space of the laser output beams at the ensemble combining plane by elongating an image at the ensemble combining plane along the common fast axis for laser diode beams having a smaller input beam displacement relative to the optical axis and shortening an image at the ensemble combining plane along the common fast axis for laser diode beams having a larger input beam displacement relative to the optical axis. (Item 9) Item 2. The apparatus of item 1, wherein the transmissive optical substrate is a cylindrical meniscus lens. (Item 10) 10. The apparatus of claim 9, wherein the cylindrical meniscus lens includes a reference surface extending parallel to the optical axis and a cylindrical axis associated with the first and second surfaces. (Item 11) 2. The apparatus of claim 1, wherein the first curvature and the second curvature define a variable curvature ratio between a parallel input beam position and a transmitted output beam position associated with the increased output beam magnification. (Item 12) an objective lens configured to receive the laser output beam from the transmissive optical substrate and to focus the laser output beam at an ensemble combining plane; an optical fiber, the optical fiber including an end face configured to receive the laser output beam at the ensemble combining plane; Further equipped with 3. The apparatus of claim 2, wherein the transmissive optical substrate is configured to circularize an ensemble image space and an NA space of the laser output beam at the ensemble combining plane based on the increasing output beam magnification and the nonlinearly increasing output beam displacement. (Item 13) 2. The apparatus of claim 1, wherein the output beam magnification is less than for each of the laser beams received within an input aperture of the transmissive optical substrate. (Item 14) Item 1 , the apparatus comprising: a cylindrical fast axis telescope; (Item 15) Item 1 , the apparatus comprising: a transmissive optical substrate comprising a slow axis telescope. (Item 16) Item 1 , the apparatus of item 1 , wherein the transmissive optical substrate comprises a combined fast axis telescope and a slow axis telescope. (Item 17) A laser diode package comprising an apparatus according to any one of items 1-16. (Item 18) 17. A method comprising making a transmissive optical substrate according to any of items 1-16. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a side schematic diagram and ray trace of an exemplary variable afocal telescope. [Diagram 2] FIG. 2 is a graph of magnification versus aperture height for the variable afocal telescope embodiment shown in FIG. 1 and for a non-variable afocal telescope that may be used in a laser diode package. [Figure 3A]FIG. 3A is a modeled image of a laser diode beam spot focused at the fiber input face using a variable afocal telescope. [Figure 3B] FIG. 3B is a modeled image of a laser diode beam spot focused at the fiber input face using a non-variable afocal telescope (or no telescope). [Figure 4A] FIG. 4A shows side and end views of an exemplary fast axis telescope. [Figure 4B] FIG. 4B is the SAG equation and associated coefficients for the example fast axis telescope of FIG. 4A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Detailed Description) As discussed above, laser diode packages typically couple laser diode beams emitted from rectangular diode facets into circular fibers. This leads to unused space and angular laser nature associated with laser diode ensembles that are optically and physically arranged for fiber coupling at an ensemble coupling plane (such as the fiber input face). There are significant problems associated with the high aspect ratio of the rectangular portion of the laser diode, both in physical space and in angular space, and the mismatch with the circular space of the fiber. Although the circular space of the fiber can be filled more completely by varying the laser diode chip geometry or varying the FAC lens for different laser diodes, such approaches are typically not cost-effective.

[0010] By using one or more of the variable afocal telescope embodiments described herein, channel-specific optics or layouts can be reduced or avoided by providing variable magnification of the collimated beam. When applied to a laser diode package to angularly and spatially circularize its aggregated beam, individual diode channels can receive specific different magnifications based on, for example, their specific NA spatial juxtaposition or arrangement. This varying magnification varies their vertical physical dimensions at the focal point, which can allow for a higher net compression of the aggregated beam space, for example, so that additional laser channels can be added within the same NA of the fiber input.

[0011] A monolithic telescope optic typically provides a single magnification ratio associated with different, but constant, surfaces of curvature. Alternatively, the surfaces are made aspheric to reduce spherical aberration across the effective aperture. In some embodiments herein, variable magnification is provided with a variable afocal telescope, which can allow for up to 22% increase in output brightness (i.e., radiance) in various laser diode package embodiments. For example, a fiber-coupled laser diode package that uses 18 single-emitter laser diodes to generate beams and optics to couple the beams into a 0.15 NA 105 μm output fiber can instead use 22 single-emitter laser diodes of the same type to generate beams and optics (including a variable afocal telescope) to couple the beams into the same 0.15 NA 105 μm output fiber.

[0012] FIG. 1 illustrates the physical form factor and surface geometry for an exemplary afocal telescope 100. The afocal telescope 100 includes a transmissive optical substrate 101 having a first surface 102, which is convex, and a second surface 104, which is concave, each having a respective curvature defined therefor. The transmissive optical substrate 101 can have portions made of different materials or with different materials, including glass, plastic, fused silica, transparent crystalline or amorphous materials. The curvatures for the first and second surfaces 102, 104 can be symmetric across the optical axis 106 of the afocal telescope 100 in the plane of FIG. 1. In an exemplary embodiment, the afocal telescope 100 is a one-piece cylindrical meniscus lens, with cylindricity associated with a lack of rotational symmetry about the optical axis 106 (such as with a spherical lens) rather than the constant curvature of a cylinder. In additional examples, separate lens elements spaced apart from one another can be used to form a non-integral lens, or separate lens elements can be joined together to form an integral lens having multiple elements. One or both of the first and second surfaces 102, 104 can have a hyperbolic shape. As shown, the first surface 102 has a parabolic shape and the second surface 104 has a hyperbolic shape. The shapes can define a higher curvature pair (magnification) near the center (e.g., closer to the optical axis 106) and a more gradual curvature near the edge of the aperture of the afocal telescope 100. In further examples, the afocal telescope can be configured to provide a variable slow axis magnification, or can have a complex shape configured to provide both variable fast axis and slow axis magnification.

[0013] FIG. 1 also shows multiple input beam axes 108a-108k that are parallel to each other and to the optical axis 106. Each of the input beam axes 108a-108k can be associated with a laser diode beam that is collimated in both the fast axis dimension and the slow axis dimension. With adjacently arranged parallel input beam axes 108a-108k, the afocal telescope 100 is configured as a fast axis telescope such that the common fast axes of the laser diode beams extend approximately perpendicular (e.g., upward and downward) to the optical axis 106 in the plane of FIG. 1. Following the ray trace, the laser diode beam propagates through the substrate 101, becomes compressed, and propagates along output beam axes 110a-110k, with the distance between the two outer output beam axes 110a, 110k being shorter than the distance between the two outer input beam axes 108a, 108k.

[0014] As shown, the input beam axes 108-108k have a displacement from one another and form a uniform spacing. In an exemplary embodiment, based on the selected curvatures of the first and second surfaces 102, 104, the compressed output beam axes 110a-110k are not uniformly spaced. Instead, as the displacement distance from the optical axis 106 increases, adjacent output beam axes are increasingly displaced from one another, such that the displacement between output beam axes 110e, 110f is less than the displacement between output beam axes 110d, 110e, which is less than the displacement between output beam axes 110c, 110d, which is less than the displacement between output beam axes 110b, 110c, which is less than the displacement between output beam axes 110a, 110b, etc. Thus, linear input spacing can produce variable output spacing, such that a linear increase in input beam displacement from the optical axis 106 (e.g., uniform spacing) produces a non-linear increase in output beam displacement (e.g., non-uniform spacing). Based on the curvature symmetry across the optical axis 106, a similar effect is achieved below the optical axis 106 in FIG. 1, such that the displacement between output beam axes 110g, 110h is less than the displacement between output beam axes 110h, 110i, which is less than the displacement between output beam axes 110i, 110j, which is less than the displacement between output beam axes 110j, 110k, etc.

[0015] In an exemplary embodiment, for laser diode beams propagating along input beam axes 108a-108k with a common cross-sectional shape (e.g., each having the same area and aspect ratio), the afocal telescope 100 introduces a variable magnification for the laser diode beams propagating along output beam axes 110a-110k that depends on the displacement distance of the respective input beam axes 108a-108k from the optical axis 106. For example, referring to FIG. 2, a variable magnification can be produced and plotted along a magnification line 200 such that for increasing distance from the optical axis 106, the magnification increases for the transmitted laser diode beams. For comparison, a magnification line 202 shows the flat magnification of an afocal telescope that does not provide variable magnification. Thus, the laser diode beams propagating along the input beam axes 108a, 108k are compressed in the fast axis direction by a smaller amount than the laser diode beams propagating along the input beam axes 108f, 108g. Reduced compression for laser diode beams propagating along input beam axes 108a, 108k produces a smaller spot size in the fast axis direction in physical space at the subsequent coupling plane (such as an optical fiber) after propagation through the objective lens. In contrast, increased compression for laser diode beams propagating along input beam axes 108f, 108g produces a larger spot size in the fast axis direction in physical space at the subsequent coupling plane after propagation through the objective lens. By separately selecting the slow axis magnification, laser diode beams propagating along input beam axes 108f, 108g can have a larger fast axis image size at the coupling plane and a smaller slow axis image size at the coupling plane, and laser diode beams propagating along input beam axes 108a, 108k can have a smaller fast axis image size at the coupling plane and a larger slow axis image size at the coupling plane. The resulting ensemble or coherent beam image in physical space is shown in Figure 3 A. The different aspect ratios for the different laser diode beams are imaged onto the fiber, producing a circularized ensemble image in physical space.3B shows an example of ensemble beam imaging where the beams do not propagate through an afocal telescope providing variable magnification, resulting in a square shaped image as each beam images a common overlapping area. By introducing variable spacing and variable magnification between the output beam axes 110a-110k using the afocal telescope 100, additional laser diode beams can be focused at the combination plane to improve the combined brightness.

[0016] FIG 4A shows another embodiment of an afocal telescope 400 configured to provide variable magnification, and FIG 4B includes the SAG equations and suitable coefficients for surfaces S1, S2. The coefficients generally define surface S1 as a parabola or ellipse with k close to -1, and surface S2 as a hyperboloid with k<-1. As shown, the afocal telescope 400 includes a flat reference surface 402 that can be used to align the afocal telescope 400 with respect to the base of the laser diode package housing to improve alignment with multiple laser diode beams directed through the interior of the laser diode package.

[0017] General considerations

[0018] As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "includes" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0019] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, both alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and devices are not limited to any specific aspect or feature or combination thereof, and the disclosed systems, methods, and devices do not claim that any one or more specific advantages exist or problems are solved. Any theory of operation is intended to facilitate explanation, but the disclosed systems, methods, and devices are not limited to such theory of operation.

[0020] Although operations of some of the disclosed methods have been described in a particular sequential order for convenient presentation, it should be understood that this mode of description encompasses rearrangements unless a particular ordering is required by specific wording described below. For example, operations described sequentially may in some cases be rearranged or performed simultaneously. Also, for simplicity, the accompanying figures may not show the various ways in which the disclosed systems, methods, and apparatuses may be used in conjunction with other systems, methods, and apparatuses. In addition, the description sometimes uses terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms vary depending on the implementation and are readily discernible by one of ordinary skill in the art.

[0021] In some examples, values, procedures, or devices are referred to as "lowest," "best," "minimum," or the like. It should be understood that such descriptions are intended to indicate that choices may be made between many functional alternatives used, and that such choices are not necessarily better, less, or otherwise preferred than other choices. Examples are described with reference to directions indicated as "upper," "lower," "upper," "lower," and the like. These terms are used for convenient description and do not imply any particular spatial orientation.

[0022] Any theories of operation, scientific principles, or other theoretical explanations presented herein with reference to the devices or methods of the present disclosure are provided for the purpose of better understanding and are not intended to limit the scope, and the devices and methods within the appended claims are not limited to those devices and methods that function in a manner described by such theories of operation.

[0023] In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely representative examples and should not be taken as limiting the scope of the present disclosure. The alternatives specifically mentioned in these sections are merely exemplary and do not constitute all possible alternatives to the embodiments described herein. For example, the various components of the systems described herein may be combined in function and use. We therefore claim all that comes within the scope of the appended claims.

Claims

1. An apparatus comprising: a transmissive optical substrate configured to receive a plurality of laser beams propagating along respective parallel beam axes at respective initial beam displacements relative to an optical axis of the transmissive optical substrate, the transmissive optical substrate being configured to produce a laser output beam having reduced displacement, the transmissive optical substrate including first and second surfaces with respective first and second curvatures configured to increase an output beam magnification of the laser output beam as beam displacement of an input beam increases. Equipped with At least one of the first curvature and the second curvature is a hyperbola.

2. 2. The apparatus of claim 1, wherein the first and second curvatures are defined to provide a non-linear increasing output beam displacement from the optical axis for a linear increasing input displacement from the optical axis.

3. The apparatus of claim 1 , wherein the second curvature is hyperbolic concave.

4. The apparatus of claim 1 , wherein the first curvature is a parabolic convex surface.

5. The apparatus of claim 1 , wherein at least one of the first curvature and the second curvature is aspheric.

6. The apparatus of claim 1 , wherein the initial beam displacement corresponds to a displacement along a common fast axis of the laser beams.

7. 7. The apparatus of claim 6, wherein the first and second curvatures are configured to circularize an ensemble image space and an NA space of the laser output beams at the ensemble combining plane by elongating an image at the ensemble combining plane along the common fast axis for laser diode beams having smaller input beam displacements relative to the optical axis and shortening an image at the ensemble combining plane along the common fast axis for laser diode beams having larger input beam displacements relative to the optical axis.

8. The apparatus of claim 1 , wherein the transmissive optical substrate is a cylindrical meniscus lens.

9. The apparatus of claim 8 , wherein the cylindrical meniscus lens includes a reference surface extending parallel to the optical axis and a cylindrical axis associated with the first and second surfaces.

10. 2. The apparatus of claim 1, wherein the first curvature and the second curvature define a variable curvature ratio between a parallel input beam position and a transmitted output beam position associated with the increased output beam magnification.

11. an objective lens configured to receive the laser output beam from the transmissive optical substrate and to focus the laser output beam at an ensemble combining plane; an optical fiber, the optical fiber including an end face configured to receive the laser output beam at the ensemble combining plane; Further equipped with 3. The apparatus of claim 2, wherein the transmissive optical substrate is configured to circularize an ensemble image space and an NA space of the laser output beams at the ensemble combining plane based on the increasing output beam magnification and the nonlinearly increasing output beam displacement.

12. The apparatus of claim 1 , wherein the output beam magnification is less than for each of the laser beams received within an input aperture of the transmissive optical substrate.

13. The apparatus of claim 1 , wherein the transmissive optical substrate comprises a cylindrical fast axis telescope.

14. The apparatus of claim 1 , wherein the transmissive optical substrate comprises a slow axis telescope.

15. The apparatus of claim 1 , wherein the transmissive optical substrate comprises a combined fast axis telescope and a slow axis telescope.

16. A laser diode package comprising a device according to any one of claims 1 to 15.

17. A method comprising making a transmissive optical substrate according to any of claims 1 to 15.

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