Tile-shaped collimator array

Abstract

A tiled collimator array is disclosed. The tiled collimator array comprises a plurality of end caps, each connected to an optical fiber at its rear end, wherein the end caps are selected from hexagonal end caps and square end caps, and include an adhesive for bonding the end caps together, and the end caps are stacked in a compact structure.

Description

Technical Field

[0001] This application is a PCT patent application claiming the benefit of priority of Israeli Patent Application No. 301657, filed on March 26, 2023. The content of the above application is hereby incorporated by reference in its entirety as if fully set forth herein.

[0002] The present invention generally relates to a collimator array. More specifically, the present invention relates to a tiled collimator array.

Background Art

[0003] High-power laser beams are typically achieved by combining a plurality of collimated small-diameter laser beams. In order to effectively combine them, all the beams need to be aligned in a compact structure. This alignment must be maintained throughout the life of the high-power laser, taking into account retention during temperature changes and vibrations.

[0004] In high-power laser sources, the power density in the fiber core becomes extremely high. Therefore, the exit end of the fiber (to the free-space environment) needs to be processed to avoid melting. Thus, an end cap is attached to the end of the optical fiber. The end cap is a glass block having a diameter much larger than that of the fiber, and the fiber end is joined thereto. As a result, the laser spot diameter at the output becomes significantly large, thereby greatly reducing the power density to a value safe for long-term laser operation.

[0005] One of the known techniques for achieving coherent beam combination is known as a tiled aperture, in which a number of collimated beams are aligned to generate the desired wavefront amplitude and phase.

[0006] To obtain proper performance, the collimators need to be aligned with high precision and stability in the micrometer range.

[0007] To overcome the aforementioned drawbacks, attempts have been made to manufacture monolithic collimators, which are created by joining multiple fibers into a single glass block. One of the main drawbacks of such glass structures is that the manufacturing process is not trivial, which can result in very low yields of such products or damage to some of the fiber joints.

[0008] Therefore, there is a need for a tiled collimator array for high-power lasers that minimizes retention during temperature changes and vibrations while keeping the fiber array and end caps aligned. [Overview of the project]

[0009] Some aspects of the present invention relate to a plurality of end caps, each connected to an optical fiber at its rear end, wherein the end caps comprise an end cap selected from hexagonal end caps and square end caps, and an adhesive for bonding the end caps together, and the end caps are stacked in a compact structure, and are directed toward a tiled collimator array.

[0010] In some embodiments, the adhesive is selected from transparent adhesives and optical adhesives. In some embodiments, the thickness of the adhesive is between 0.0001 and 0.1 of the diameter of the inscribed circle of the end cap cross-section. In some embodiments, the optical fiber is joined to the rear end such that the optical axis of the fiber coincides with the optical axis of the end cap.

[0011] In some embodiments, each end cap is provided with a front lens at a second end. In some embodiments, the tiled collimator array further comprises a diffractive optical element (DOE) located in front of the front lens on the optical axis of the tiled collimator array. In some embodiments, the length of the end cap is equal to or shorter than the focal length of the lens.

[0012] In some embodiments, all optical fibers are aligned with the same polarization. In some embodiments, the length of each end cap is determined based on the wavelength, the numerical aperture (NA) of the fiber, and the desired beam diameter. In some embodiments, the diameter of the circumscribed circle of each end cap is determined based on the desired beam diameter and the internal reflectivity within the end cap. In some embodiments, the diameter of the optical fiber core is between 5 and 50 μm. In some embodiments, the side facets of each end cap are coated with an anti-reflective coating.

[0013] The main parts considered to be the present invention are specifically pointed out and explicitly asserted in the concluding section of this specification. However, the present invention, both in terms of its configuration and operation, as well as its objectives, features, and advantages, can be best understood by referring to the following detailed description when viewed together with the accompanying drawings. [Brief explanation of the drawing]

[0014] [Figure 1A] This is an example of a perspective view of a tiled collimator array according to some embodiments of the present invention. [Figure 1B] This is an example of a cross-sectional view of a tile-shaped collimator array according to some embodiments of the present invention. [Figure 1C] This is an example of an end cap connected to an optical fiber according to some embodiments of the present invention. [Figure 1D] This is an example of another end cap connected to an optical fiber according to some embodiments of the present invention. [Figure 1E] This is an example of reflected light returning from the lens surface to the end cap according to some embodiments of the present invention. [Figure 2A] This is an example of a perspective view of a tile-shaped collimator array equipped with hexagonal end caps, according to some embodiments of the present invention. [Figure 2B]This is an example of a perspective view of a tile-shaped collimator array equipped with hexagonal end caps, according to some embodiments of the present invention. [Figure 3] This is an example of a perspective view of a tile-shaped collimator array with square end caps, according to some embodiments of the present invention. [Modes for carrying out the invention]

[0015] For the sake of simplicity and clarity, please understand that the elements shown in the diagrams are not necessarily drawn to scale. For example, the dimensions of some elements may be emphasized relative to others for clarity. Furthermore, reference numbers may be repeated between diagrams to indicate corresponding or similar elements where deemed appropriate.

[0016] Those skilled in the art will understand that the present invention can be embodied in other specific forms without departing from its spirit or essential features. Therefore, the above embodiments should be considered illustrative in all respects and not limiting the invention as described herein. Thus, the scope of the invention is indicated not by the above description but by the appended claims, and all modifications that fall within the meaning and scope of equivalence of the claims are intended to be incorporated into the invention.

[0017] Some aspects of the present invention are directed toward tiled collimator arrays for high-power lasers (e.g., lasers with power greater than 1 kW). High-power lasers with collimation of multiple aligned laser beams require a special structure. Such a structure may include an array of end caps, each connected to an optical fiber, and an adhesive for bonding the end caps together. The end caps are designed to achieve a power density of several MW / cm². 2 From at least two orders of magnitude (for example, three orders of magnitude or more), for example, several kW / cm² 2 It is designed to reduce it to a certain extent.

[0018] During operation, internal reflections within the end cap can cause movement due to thermal expansion of the adhesive and / or surrounding mechanisms by transmitting light to the surrounding mechanisms, resulting in heat that raises the temperature of the adhesive on the end cap surface. Also, heating of the end cap can occur due to heat absorption by the adhesive. Reflections from other optical elements (e.g., collimation lenses) also heat the end cap and its surroundings.

[0019] Thus, the array of end caps is selected from hexagonal end caps, square end caps, triangular end caps, rhombic end caps, etc. adhesively bonded to each other in a compact array. As will be understood by those skilled in the art, end caps having other polygonal cross-sections are also within the scope of the present invention.

[0020] In some embodiments, to minimize reflections, the adhesive can be selected to be a transparent optical adhesive.

[0021] Reference is now made to FIGS. 1A and 1B, which are examples of perspective and cross-sectional views of a tiled collimator array according to some embodiments of the present invention. The tiled collimator array 100 may include a plurality of end caps 50 each connected to a fiber optic 40 at a rear end 51, and the end caps 50 are selected from hexagonal end caps (as illustrated) and square end caps (illustrated and discussed with respect to FIG. 3) in these embodiments. In some embodiments, the end caps 50 are stacked in a compact structure, such as the honeycomb structure illustrated in FIGS. 1A and 1B, and are bonded by an adhesive 60.

[0022] As those skilled in the art should understand, the honeycomb arrays illustrated in Figures 1A and 1B, the box-shaped arrays illustrated in Figures 2A and 2B, and the array illustrated in Figure 3 are merely illustrative examples, and the present invention is not limited to these specific examples. Any compact array of end caps having hexagonal or square or any other polygonal cross-section is within the scope of the present invention.

[0023] Furthermore, the present invention is not limited to the inclusion of a specific number of end caps in each array, and the number of end caps may be any number greater than 2, for example, 5, 10, 15, 20, 30, 40, 50, 100, 125, 150, 175, 200, 300, 400, 500, and any number in between.

[0024] In some embodiments, the rear end 51 of the end cap 50 may be a plane perpendicular to the longitudinal direction / optical axis 55 of the end cap 50, as illustrated in Figures 1B and 1D. In some embodiments, the perpendicularity may vary between 0 and 0.5. In some embodiments, the optical fiber 40 is joined to the rear end 51 such that the optical axis of the fiber 40 (also 55) is aligned with the optical axis 55 of the end cap 50, or at least parallel to the optical axis 55. To achieve such parallelism, the optical fiber may be joined such that its optical axis is perpendicular to the plane of the rear end 51.

[0025] In some embodiments, all optical fibers 40 are aligned with the same polarization. For example, one side 54 of the end cap 50 is marked to indicate the polarization of the fiber. Thus, all end caps 50 need to be bonded so that all markers are oriented in the same direction and that uniform polarization of the fibers in the array is ensured.

[0026] In some embodiments, each end cap 50 may include a front lens 52 at the front end 53 of the end cap 50, as illustrated in Figures 1A and 1C, which illustrate hexagonal end caps with lenses. In some embodiments, the optical profile of each lens 52 may be determined to form a Gaussian beam. In some embodiments, the optical profile of each lens 52 may be determined to form a desired profile (e.g., a supergaussian beam, a top-hat beam, etc.) at the output surface of the system. In some embodiments, the lens 52 may be a spherical lens or an aspherical lens, for example, in a supergaussian beam.

[0027] In some embodiments, the length "L" may be determined such that the front facets 53 / 52 of the end cap are less susceptible to contamination by reducing the power density.

[0028] In some embodiments, each end cap 50 may include a flat front end 53 substantially perpendicular to the optical axis of the end cap 50, as illustrated in Figures 1A and 1D, which illustrate end caps having a flat front end. As illustrated in Figure 1D, the light 11 reflected back from the flat surface 53 diverges on the surface of the rear end 51.

[0029] In some embodiments, the length "L" of each end cap 50 is determined, for example, using Equation 1, based on the wavelength, the numerical aperture (NA) of the fiber 40, and the desired beam diameter D.

number

[0030] In some embodiments, NA is directly proportional to the wavelength of the beam and inversely proportional to the core diameter of the fiber 40.

[0031] In some embodiments, the diameter of the circumscribed circle of each end cap (e.g., a hexagonal end cap, a square end cap, or an end cap having any other arbitrary polygonal cross-section) is determined based on the desired beam diameter and the internal reflectance within the end cap.

[0032] The length "L" is optimized so that a uniform collimated beam 15 with maximum energy is formed from the surface 25 of the DOE (diffractive optical element) 20, without overlap or gaps between the collimated beams 10.

[0033] Herein, reference is made to Figure 1E, which shows the reflected light returning from the lens surface to the end cap according to some embodiments of the present invention. In some embodiments, the focal length f of lens 52 lens When the length of the end cap 50 is equal to the length L of the end cap, the light reflected back from the lens 52 will be scattered, as illustrated. Therefore, the diameter of the reflected beam is wider than the diameter of the beam incident from the fiber 40 into the encamp 50. Thus, no damage occurs at all to the fiber / end cap interface.

[0034] Lens 52 focal length f lens This can be determined using equations 2a and 2b. f lens =ROC lens / Δn (2a) f lens =2·ROC lens (2b)

[0035] At this time,

number

[0036] In some embodiments, the focal length of lens 52 may be determined based on a determined length "L". In some embodiments, the length of the end cap is approximately the same as, but slightly shorter than, the focal length of lens 52, in order to prevent the reflected light from focusing onto the fiber.

[0037] In some embodiments, the dimensions of the end cap 50 are determined to minimize heat accumulation due to thermal effects, such as reflection and the propagation of light from one end cap to an adjacent end cap via the side faces 54 of the end cap. Light 11 may be guided to exit the end cap 50 from the rear end 51. In some embodiments, the side facets 54 of each end cap 50 are coated with an anti-reflective coating to prevent light from passing between adjacent end caps. Some non-limiting examples of the anti-reflective coating may include nanostructure formation, monolayer ion deposition, volatilization, and the like.

[0038] In some embodiments, the optical fiber 40 may be made of optical glass. In some embodiments, the core diameter of the optical fiber 40 is between 5 and 50 μm, for example between 5 and 20 μm, 10 and 30 μm, 10 and 40 μm, 20 and 50 μm, and any value or range in between.

[0039] In some embodiments, the adhesive 60 used to bond the end caps 50 together may be selected from transparent adhesives, optical adhesives, transparent optical adhesives, and the like.

[0040] In some embodiments, the material of the adhesive 60 may be further selected to have a (post-curing) thermal coefficient as close as possible to that of the end cap 50. The thermal coefficient is selected to minimize the formation of thermal stress on the end cap 50. Thus, the thermal coefficient (CTE) of the adhesive material may be between 0.1 and 200 [ppm°C] (and any value in between), and the light absorption at the required wavelength is less than 5 ppm.

[0041] In some embodiments, the thickness of the adhesive 60 is between 0.0001 and 0.1 of the diameter of the inscribed circle of the end cap cross-section. For example, the thickness of the adhesive 60 is between 0.0001 and 0.0005, 0.0005 and 0.001, 0.001 and 0.005, 0.005 and 0.01, 0.01 and 0.05, 0.05 and 0.1, and any value or range between them.

[0042] In some embodiments, the adhesive 60 may cover at least 50% of the surface between each of the two sides 45 that are joined together. For example, the adhesive 60 may cover at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or 100%, and any value or range in between.

[0043] In some embodiments, the adhesive 60 may further contain small spherical particles of uniform diameter that can be added to ensure the formation of a uniform thickness of the adhesive 60. The diameter of the small spherical particles may vary between 0.0001 and 0.1 of the diameter of the inscribed circle of the end cap cross section. In some embodiments, the small spherical particles may include glass, fused silica, alumina, or any other ceramic material.

[0044] Referencing Figures 2A and 2B, which illustrate perspective views of two tiled collimator arrays equipped with hexagonal end caps according to some embodiments of the present invention, is provided here. The tiled collimator array 200 or 250 may include substantially the same hexagonal end caps 50, optical fibers 40, and adhesive 60 as the tiled collimator array 100. In some embodiments, the hexagonal end caps 50 of the collimator array 200 or 250 may include or not include a front lens. In the non-limiting example of Figure 2A, the tiled collimator array 200 may include a plurality of hexagonal end caps 50 stacked in a three-layer compact structure. In the non-limiting example of Figure 2B, the tiled collimator array 250 may include a plurality of hexagonal end caps 50 stacked in a substantially rectangular compact structure.

[0045] Herein, reference is made to Figure 3, which is an example of a perspective view of a tiled collimator array having square end caps according to some embodiments of the present invention. The tiled collimator array 300 may include a plurality of square end caps 150, each connected to an optical fiber 40 at its rear end 151, and an adhesive 60 for bonding the end caps 150 together.

[0046] In some embodiments, the rear end 151 of the end cap 150 may be a plane perpendicular to the longitudinal axis of the end cap 150. In some embodiments, the degree of perpendicularity may vary between 0 and 0.5. In some embodiments, the optical fiber 40 is joined to the rear end 151 such that the optical axis of the fiber 40 coincides with the optical axis of the end cap 150, or at least is parallel to the optical axis. To achieve such parallelism, the optical fiber 40 may be joined such that its optical axis is perpendicular to the plan of the rear end 151.

[0047] In some embodiments, each end cap 150 may include a front lens (not illustrated) at its front end 153. In some embodiments, the front lens may be substantially the same as the front lens 52 of the end cap 50.

[0048] In some embodiments, the length "L" of the end cap 150 can be determined in the same manner as the determination of the length "L" of the end cap 50 discussed above.

[0049] In some embodiments, the diameter of the circumscribed circle of each end cap 150 is determined based on the desired beam diameter and internal reflection within the end cap.

[0050] In some embodiments, the dimensions of the end cap 150 are determined to minimize heat buildup due to thermal effects, such as reflection and the propagation of light from one end cap to an adjacent end cap across the sides of the end caps.

[0051] In some embodiments, the tiled collimator arrays 100, 200, 250, or 300 may include or be optically connected to additional optical components. For example, the additional optical components may include a diffractive optical element (DOE) 20, as illustrated in Figure 1B, located in front of the front lens 52 on the optical axis of the tiled collimator array. In some embodiments, the DOE may include a wavefront shaping element having a surface 25 configured to collimate the beam 10 to form a beam 15 in a plane 25 adjacent to the arrays 100, 200, 250, or 300. In some embodiments, the additional optical components may include spherical and non-spherical surfaces (e.g., lenses), optical wedges, and the like.

[0052] Unless explicitly stated otherwise, the embodiments described herein are not limited to any particular order or sequence. Furthermore, all formulas described herein are intended merely as examples, and other or different formulas may be used. Also, some of the described method embodiments or elements thereof may occur or be performed at the same time.

[0053] While certain features of the present invention have been illustrated and described herein, a number of modifications, substitutions, alterations, and equivalents can be devised by those skilled in the art. It is understood that the appended claims are intended to encompass all such modifications and alterations as being true to the spirit of the invention.

[0054] Various embodiments have been presented. Each of these embodiments may, of course, include features of other embodiments presented, and embodiments not specifically described may include various features described herein.

Claims

1. A tiled collimator array, A plurality of end caps connected to the optical fiber at the rear end, wherein the end caps are selected from hexagonal end caps and square end caps, An adhesive for bonding the end caps together, A tile-shaped collimator array comprising, The aforementioned end caps are stacked in a compact structure, forming a tile-like collimator array.

2. The tile-shaped collimator array according to claim 1, wherein the adhesive is selected from a transparent adhesive and an optical adhesive.

3. The tile-shaped collimator array according to claim 1 or claim 2, wherein the thickness of the adhesive is between 0.0001 and 0.1 of the diameter of the inscribed circle of the cross-section of the end cap.

4. The tiled collimator array according to claim 3, wherein the optical fiber is joined to the rear end such that the optical axis of the fiber coincides with the optical axis of the end cap.

5. The tiled collimator array according to any one of claims 1 to 4, wherein each end cap is provided with a front lens at a second end.

6. The tiled collimator array according to claim 5, further comprising a diffractive optical element (DOE) located in front of the front lens on the optical axis of the tiled collimator array.

7. The tiled collimator array according to claim 5 or 6, wherein the length of the end cap is equal to or shorter than the focal length of the lens.

8. The tiled collimator array according to any one of claims 1 to 7, wherein all of the optical fibers are aligned with the same polarization.

9. The tiled collimator array according to any one of claims 1 to 8, wherein the length of each end cap is determined based on the wavelength, the numerical aperture (NA) of the fiber, and the desired beam diameter.

10. The tiled collimator array according to any one of claims 1 to 9, wherein the diameter of the circumscribed circle of each end cap is determined based on the desired beam diameter and the internal reflectance within the end cap.

11. The tiled collimator array according to any one of claims 1 to 10, wherein the diameter of the optical fiber core is between 5 and 50 μm.

12. The tiled collimator array according to any one of claims 1 to 11, wherein the side facets of each end cap are coated with an anti-reflective coating.

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