Illumination system with plural light sources and a freeform reflector

Abstract

An illumination system for illuminating an area of interest comprises a plurality of n individual light sources and a light guiding system comprising a reflective element arranged along an optical axis of the light guiding system. The reflective element has a freeform optical surface of the reflective element configured for guiding and combining radiation of at least two of said plurality of n individual light sources towards an output of said illumination system. The freeform optical surface of the reflective element is configured for guiding radiation of all of said plurality of n individual light sources towards the output pattern of said illumination system. The reflective element is or behaves as a monolithic optical element. The output of the illumination system has a curved or polygonal shape, the freeform optical surface of the reflective element being configured for reshaping the optical output of the plurality of n individual light sources towards the curved or polygonal shaped output of the illumination system.

Description

[0001] ILLUMINATION SOURCES

[0002] Technical field of the invention

[0003] The present invention relates to the field of optical illumination systems, and more specifically to illumination systems utilizing freeform optics.

[0004] Background of the invention

[0005] High-power fiber-coupled or pigtailed broadband multispectral illumination sources play a crucial role in various optical applications, including spectroscopy, medical imaging, and industrial inspection. These sources provide versatile illumination necessary for precise measurements and analyses across multiple wavelengths. Light-emitting diodes (LEDs) have become increasingly prominent in illumination optical designs due to their efficiency, compactness, and the ability to produce light at various wavelengths. Despite their advantages, there are limitations in the current availability and implementation of high-power, broadband, multispectral sources that are fiber-coupled or pigtailed. These sources are often expensive and bulky, which can restrict their use in applications where space and cost are critical factors. Additionally, they offer limited flexibility in tailoring the spectral properties to meet specific application requirements, which can be a significant drawback in fields that demand customization of the light spectrum.

[0006] Combining multiple LEDs to create a compact illumination beam suitable for input into an optical light guide or fiber presents significant challenges. One of the primary difficulties arises from the inherent emission properties of LEDs, particularly their light divergence angle. The wide divergence of LED emissions makes it challenging to efficiently couple the light into optical fibers or light guides without substantial losses. This inefficiency hampers the development of compact, high-efficiency illumination systems that can deliver the desired spectral characteristics.

[0007] Existing solutions for combining LED emissions often involve complex free-space optical systems. These systems typically use collimating lenses for each LED, followed by steering mirrors to direct the light towards a common target plane. While this method can merge emissions from multiple LEDs, it tends to be bulky and can suffer from alignment sensitivities. Moreover, the combination efficiency is often low, and the number of LEDs that can be effectively combined is limited, which restricts the achievable spectral flexibility and power output.Another approach involves coupling each LED into individual optical fibers, which are then combined using a fiber combiner. This method can be associated with high optical losses due to coupling inefficiencies and can be costly to implement, especially when dealing with a large number of LEDs. The cumulative losses can significantly reduce the overall system efficiency, making it less suitable for applications that require high power and efficiency.

[0008] Alternative high-power multispectral sources, such as plasma and supercontinuum sources, are available but come with their own set of limitations. These sources are typically expensive and have fixed spectral distributions, offering little to no flexibility in adjusting the output spectrum. This lack of tunability can be a significant limitation in applications where specific spectral profiles are necessary.

[0009] Current state-of-the-art LED multispectral sources generally incorporate free-space optics that first collimate the LED emissions, followed by multiple beam combiners or mirrors to merge the beams. However, these systems are often constrained by low combination efficiencies and limited scalability concerning the number of LEDs that can be integrated. The resultant systems can be bulky and may not provide the desired adaptability in spectral tuning or system configuration.

[0010] Therefore, there is a continuing need for advancements in illumination systems to address these challenges. Improvements that enable efficient combination of multiple LEDs into a compact, high-power, and spectrally flexible illumination beam would be beneficial. Such advancements could enhance the performance and applicability of optical systems across a wide range of fields by providing more efficient, adaptable, and cost-effective illumination solutions.

[0011] Summary of the invention

[0012] It is an object of embodiments of the present invention to provide a compact, efficient, and flexible illumination system capable of combining multiple light sources into a single output beam. This objective is accomplished by the aspects of the present invention.

[0013] In the first aspect, the present invention relates to an illumination system for illuminating an area of interest, the illumination system comprising a plurality of n individual light sources, and a light guiding system comprising a reflective element arranged along an optical axis of the light guiding system, and the reflective element having a freeform optical surface of the reflective element configured for guiding and combining radiation of at least two of said plurality of n individual light sources towards an output of said illumination system. This allows for obtaining a high intensityillumination system with a small optical diameter for devices with limited number of optical elements, in view of the available space. It also enables high collection efficiency of the radiation of the different individual light sources, resulting in a high intensity illumination system.

[0014] The plurality of n individual light sources comprises at least a first subset of light sources and a second subset of light sources. It is to be noted that a subset of light sources may exist of a single light source, or a larger number of light sources, but not all light sources in the illumination system.

[0015] According to the present invention, the non-spherical, freeform optical surface of the reflective element having at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the first subset of light sources and at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the second subset of light sources.

[0016] The freeform optical surface of the reflective element may have at least part of its surface lacking rotational symmetry.

[0017] The freeform optical surface of the reflective element may have at least part of its surface lacking translational symmetry.

[0018] Different local dedicated freeform optical surfaces may show different local surface changes tailored to their respective subset of light sources.

[0019] The part of the surface may correspond with the illumination area on the optical surface of the reflective element by at least one of the light sources.

[0020] In embodiments, the freeform optical surface of the reflective element may be configured for guiding radiation of all of said plurality of n individual light sources towards the output pattern of said illumination system. The output may correspond with the position where another device, such as a detector, is positioned. The detector may be a surface that needs to be illuminated directly, without the radiation being refracted through other optical elements, such as when considering UV illumination. The output may also correspond with the entrance of a light guide or an optical fiber that guides radiation to a targeted position.

[0021] In embodiments, the reflective element may be or behave as a monolithic optical element. Using a single reflective element reduces the amount of alignment required.

[0022] In embodiments, the output of the illumination system may have a curved shape, e.g. circular, or a polygonal shape, with the freeform optical surface of the reflective element being configured for reshaping the optical output of the plurality of n individual light sources towards the curved or polygonal shaped output of the illumination system. This solves a possible mismatch between an illumination system and an object, e.g. afiber optic incoupling facet, to which the radiation is guided, by allowing the mirror surface to be non-rotational symmetric while offering dedicated beam shaping properties for each of the individual sources.

[0023] In embodiments, the freeform optical surface of the reflective element may be not rotationally symmetrical with respect to the optical axis. Alternatively, in some embodiments, the light sources may be positioned such that the freeform optical surface of the reflective element is rotationally symmetrical with respect to the optical axis.

[0024] In embodiments, the freeform optical surface of the reflective element may be defined by a polynomial surface function having at least some terms in x and / or y coordinates having an order higher than 2, such as third, fourth, fifth, sixth order terms, etc. This allows for a better match of the illumination area with a rectangular shaped detection sensor or lightguide entrance facet. It also enables creating illumination according to a predetermined spectrum. The illumination system can be configured towards the required illumination beam, thus being an illumination beam shaping system. Beam shaping can be performed to optimize the design.

[0025] In embodiments, the illumination system may not comprise refractive optical elements. This provides a solution for obtaining intensity radiation system with small diameters, without the need for using more space or combining refracting and reflecting elements.

[0026] In embodiments, a length of the illumination system measured along the optical axis may be less than 100 mm. This stresses the compactness of the system.

[0027] In embodiments, the freeform optical surface of the reflective element may reallocate portions of a circular or elliptical optical field created by the individual light sources towards the illumination pattern of the illumination system. The freeform optical surface of the reflective element may be configured for reallocating portions of the individual output pattern of the light sources so that each light source matches the output illumination pattern of the illumination system. This provides a robust design where the illumination pattern is fully robust to the fall-out of sources.

[0028] In embodiments, the individual light sources may comprise a set of light sources positioned in a predetermined configuration with respect to the optical axis of the illumination system, such as a ring shape around the optical axis, square, or any other suitable configuration.

[0029] In embodiments, the individual light sources may comprise at least a first subset of light sources and a second subset of light sources, the light sources of the different subsets having at least one of a different divergence angle, footprint size, intensityand / or spectral composition. The first and second subsets may in some embodiments be arranged in concentric illumination rings.

[0030] In embodiments, the illumination beam created by the first subset of light sources may have the same beam shape as the illumination beam created by the second subset of light sources. This allows properties of the illumination system to be selected by selection of the different subsets, while maintaining the beam shape.

[0031] The illumination beam created by the first subset of light sources may be substantially different from the illumination beam created by the second subset of light sources, said difference being a difference in spectrum, intensity and / or beam shape. By selecting different subsets of individual light sources, the illumination beam can be tuned in spectrum, intensity and / or beam shape.

[0032] In some embodiments, the freeform optical surface comprises for each light source a dedicated local freeform optical surface.

[0033] It is an advantage of embodiments of the present invention that a high-intensity illumination system with a small optical diameter can be achieved, even in devices with limited space and a minimal number of optical elements.

[0034] It is an advantage of embodiments of the present invention that high collection efficiency from multiple individual light sources is possible, resulting in a powerful illumination system.

[0035] It is an advantage of embodiments of the present invention that light sources of various wavelengths can be combined, allowing for complete tuning of the illumination spectrum.

[0036] It is an advantage of embodiments of the present invention that an intense radiation system with a small diameter can be obtained without requiring additional space or combining refractive and reflective elements, thus conserving space.

[0037] It is an advantage of embodiments of the present invention that the use of a single reflective element reduces the amount of alignment needed.

[0038] It is an advantage of embodiments of the present invention that mismatches between the illumination system and the target object, such as detectors or lightguide entrance facets, are resolved.

[0039] It is an advantage of embodiments of the present invention that it provides a better match between the illumination area and devices like imaging lens systems or rectangular detection sensors.

[0040] It is an advantage of embodiments of the present invention that the illumination system allows for creating illumination with a predetermined spectrum.It is an advantage of embodiments of the present invention that the system can be configured to produce the required illumination beam, effectively serving as an illumination beam-shaping system.

[0041] It is an advantage of embodiments of the present invention that beam shaping can be performed to optimize the design for specific applications.

[0042] It is an advantage of embodiments of the present invention that high coupling efficiency surpassing the state of the art can be achieved.

[0043] It is an advantage of embodiments of the present invention that the design is robust regarding the number of LEDs used.

[0044] It is an advantage of embodiments of the present invention that the system is robust with respect to the emission angles of the LEDs.

[0045] It is an advantage of embodiments of the present invention that the design is independent of the LEDs' wavelengths, eliminating chromatic aberrations.

[0046] It is an advantage of embodiments of the present invention that it offers a tunable emission spectrum, enabling the creation of a light source with a specific spectrum by adjusting the output and spectral contributions of the LEDs.

[0047] It is an advantage of embodiments of the present invention that the spot size and intensity profile at the entrance of the lightguide can be adapted to suit the application.

[0048] It is an advantage of embodiments of the present invention that it provides a compact, miniaturized design.

[0049] It is an advantage of embodiments of the present invention that it is suitable for high-power applications and compatible with high-power LEDs.

[0050] It is an advantage of embodiments of the present invention that high-power light sources can be utilized.

[0051] It is an advantage of embodiments of the present invention that the design is flexible regarding the number of LEDs used and the wavelengths considered, making the output spectrum fully adjustable.

[0052] It is an advantage of embodiments of the present invention that by customizing the mirror's shape, the illumination pattern at the entrance facet of the light guide can be tailored to specific requirements.

[0053] It is an advantage of embodiments of the present invention that only a single freeform component is needed while achieving collection efficiencies greater than 50%.

[0054] It is an advantage of embodiments of the present invention that the design is suitable for both low and high-power applications.It is an advantage of embodiments of the present invention that it provides a generic concept enabling re-optimization toward different concentration areas and intensity profiles.

[0055] It is an advantage of embodiments of the present invention that multiple LEDs or lasers with the same or different wavelengths can be combined.

[0056] It is an advantage of embodiments of the present invention that the illumination pattern remains robust even if individual light sources fail.

[0057] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0058] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0059] Brief description of the drawings

[0060] Fig. 1 illustrates an exemplary illumination system using multiple light sources and a freeform optical reflective surface, according to an embodiment of the present invention.

[0061] FIG.2a to FIG. 9b illustrate respectively different designs for illumination systems according to embodiments of the present invention (FIG. 2a, FIG. 3a, FIG. 4a, FIG. 5a, FIG. 6a, FIG. 7a, FIG. 8a, FIG. 9a) and the corresponding output patterns for these illumination systems (FIG. 2b, FIG. 3b, FIG. 4b, FIG. 5b, FIG. 6b, FIG. 7b, FIG.

[0062] 8b, FIG. 9b).

[0063] FIG. 10a, 10b, 10c, 10d, 11a, 11b, and 12 illustrate a multi-LED design layout and the corresponding lighting intensity obtained, in an example according to an embodiment of the present invention.

[0064] FIG. 13 shows the construction of the proof of concept multi-LED design according to an example of an embodiment of the present invention.

[0065] In the different figures, the same reference signs refer to the same or analogous elements.Description of illustrative embodiments

[0066] The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0067] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0068] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term “comprising” therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. The word “comprising” according to the invention therefore also includes as one embodiment that no further components are present. Thus, the scope of the expression “a device comprising means A and B” should not be interpreted as being limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0069] Similarly, it is to be noticed that the term “coupled”, also used in the claims, should not be interpreted as being restricted to direct connections only. The terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression “a device A coupled to a device B” should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact, or that two or moreelements are not in direct contact with each other but yet still co-operate or interact with each other.

[0070] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0071] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0072] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0073] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0074] As used herein, and unless otherwise specified, the phrase "plurality of n individual light sources" refers to two or more discrete light-emitting devices, where "n" is an integer representing the total number of these devices in the system. The individual light sources may include, for example, one or multiple LEDs (Light EmittingDiodes), laser diodes, VCSELs (Vertical-Cavity Surface-Emitting Lasers), lasers, or a combination thereof.

[0075] As used herein, and unless otherwise specified, the term "light guiding system" refers to a component or assembly that directs and channels light from one or multiple sources toward a specific target or output. The light guiding system is based at least one component including freeform reflective optics. Advantageously, no refractive optics is used in the light guiding system.

[0076] As used herein, and unless otherwise specified, the term "freeform optical surface of the reflective element" refers to a non-spherical surface whose shape is specifically designed to manipulate and control light of at least two light sources in a precise manner so as to guide and combine radiation thereof towards an output of the illumination system. In embodiments according to the present invention, the freeform optical surface of the reflective element lacks translational symmetry, lacks rotational symmetry or lacks both translational and rotational symmetry.

[0077] The complexity of the mirror surface depends on the specifications of the considered light sources and their geometrical positioning. In the most generic case, the mirror will be fully freeform. However, in case the design is symmetrical, the freeform surface description may be simplified to an aspherical surface. Also, dependent on the particular case, it might be that locally the mirror surface is differing from a spherical surface and has no translational symmetry, rotational symmetry or no translational and no rotational symmetry, when considering the illumination area of a single light source, but when positioning the sources symmetrically around the optical axis, some symmetry when considering the full mirror will occur (since then the different local freeform parts are symmetrical with respect to each other).

[0078] In some embodiments, the freeform optical surface of the reflective element may differ from a spherical surface and may have no translational symmetry, rotational symmetry or no translational and no rotational symmetry over its full surface, e.g. when considering a combination of different light sources that have different emission patterns. In this case, the local surface that is illuminated by each of the LEDs will be different, enabling to shape the corresponding emission patterns optimally towards the detector surface I light guide. In case one considers a mix of light sources of which some have the same emission pattern, the full surface remains differing from a spherical surface and having no translational symmetry, rotational symmetry or no translational and no rotational symmetry, provided the sources are not positioned in a symmetric configuration.In some embodiments, the freeform optical surface of the reflective element may locally correspond with a spherical surface or may locally have translational, rotational or translational and rotational symmetry, in case the design contains some symmetry. One example thereof may be the case wherein the light sources emit circular symmetric light and need to illuminate a circular detector. The local surface description will be aspheric instead of freeform (the sources emit a circular symmetric pattern that can be maintained for the detector, thus bringing in symmetry to the system). The total mirror surface is then a combination of local aspheric surfaces, which end up to be freeform in case of a random positioning of the sources, but might also result in an aspheric surface in case of a rotationally symmetric mounting of the sources. In embodiments wherein the circular symmetric light emission of each of the sources needs to be shaped towards a non-symmetrical shape at the output, then again the surface will comprise local areas that are non-spherical and have no translational symmetry, no rotational symmetry or no translational and no rotational symmetry.

[0079] It is an advantage of the use of a reflective element having a freeform optical surface of the reflective element that it offers the largest degrees of freedom, which is required to optimize a general system comprising a combination of different light sources featuring different emission patterns that need to be beam-shaped towards a specific output irradiance, and which can be positioned in a non-symmetrical configuration. It is an advantage of embodiments of the present invention that in a system having rotational symmetry, within the emission properties of the sources, and within the geometrical positioning of the sources, the mirror surface may be a surface corresponding with an aspherical surface, since in this case less degrees of freeform are required. In this case, the mirror may be circular symmetric and can thus be described using an aspheric surface description. In the case the illumination system is symmetrical around the X axis and the Y axis, but the symmetry around X is different than around Y, the freeform surface might simplify to a biconic aspheric surface.

[0080] Some examples of freeform optical surface of the reflective element include those defined by polynomial surface functions with higher-order terms (orders higher than 2) in the x and / or y coordinates, allowing for customized beam shaping and redistribution of light from multiple sources. Nevertheless, embodiments are not limited thereto and the polynomial description is merely one way to express the shape of the optical surface of the reflective element. One exemplary alternative description of such a surface may be to define the surface using point clouds. As used herein, and unless otherwise specified, the term "radiation" and “illumination” refers to electromagnetic energyemitted by the light sources, including ultraviolet (UV) light, visible light, infrared (IR) light such as near-infrared light, or any combination thereof.

[0081] As used herein, and unless otherwise specified, the term "output of said illumination system" refers to the output pattern or shape of the beam at the point or area where the combined and guided light exits the illumination system or is coupled to another device or medium. Examples include matching of the illumination beam with an entrance facet of an optical fiber, waveguide or light guide, a detector surface that requires direct irradiation, or any targeted location where the illumination is needed.

[0082] As used herein, and unless otherwise specified, the term "curved shape" refers to an output illumination pattern that is continuous and smoothly contoured, such as circular or elliptical in geometry.

[0083] As used herein, and unless otherwise specified, the term "polygonal shape" refers to an output illumination pattern with straight edges and defined vertices, forming shapes like squares, rectangles, hexagons, or other multi-sided figures. An example of a polygonal shape output is a rectangular illumination pattern matching the entrance facet of a rectangular lightguide or the active area of a sensor array.

[0084] As used herein, and unless otherwise specified, the phrase "reshaping the optical output" refers to modifying the spatial distribution and geometry of the light emitted from the individual light sources to form a desired overall illumination pattern at the system's output. Examples include transforming multiple divergent beams from individual sources into a single beam with a specific shape, such as converting circular emission patterns into a rectangular or polygonal output pattern.

[0085] The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the technical teaching of the invention, the invention being limited only by the terms of the appended claims.

[0086] In a first aspect, the present invention relates to an illumination system for illuminating an area of interest. Such an illumination area of interest may be any targeted location where the illumination is needed, but may in particular embodiments be for example an entrance facet of an optical fiber, waveguide or light guide, or for example a detector surface. The illumination system comprises a plurality of individual light sources. The illumination system furthermore comprises a light guiding system comprising a reflective element arranged along an optical axis of the light guiding system and having a freeform optical surface of the reflective element that is configured for guiding and combining radiation of at least two of the light sources towards an outputof the illumination system. The freeform optical surface of the reflective element may be designed so that the output of the illumination system has a predetermined pattern, such as for example circular or rectangular pattern, a pattern with a particularly shaped central spot, etc.

[0087] The plurality of n individual light sources comprises at least a first subset of light sources and a second subset of light sources. It is to be noted that a subset of light sources may exist of a single light source, or a larger number of light sources, but not all light sources in the illumination system.

[0088] According to the present invention, the non-spherical, freeform optical surface of the reflective element having at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the first subset of light sources and at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the second subset of light sources. The local dedicated freeform optical surface may be obtained by local surface changes, specifically tailored to the particular subset of light sources.

[0089] By way of illustration, embodiments of the present invention not being limited thereto, a number of standard and optional features and advantages will now be discussed with reference to some exemplary embodiments.

[0090] FIG. 1 illustrates a general overview of an exemplary illumination system 100. The illumination system 100 comprises a plurality of n individual light sources 110a, 110b, 110c, .... The light sources 110a, 110b, 110c, ... can be any suitable light sources such as for example LEDs, lensed LEDS, lasers, VCSELS, lensed VCSELS or laser diodes. Different numbers of light sources may be used. Spectrally different light sources may be used. Different spatial configurations of the light sources may be used.i.e. the LEDs can be positioned in circle, square or any other geometrical distribution. Light sources featuring different emission angles may be used. Light sources with different divergence angles and / or different footprint sizes may be used. The light sources may be grouped in two or more groups and different groups may be used alternatively or in addition to each other to obtain different illumination conditions at the output of the illumination system. Such different illumination conditions may include different spectral output, different intensity, ....

[0091] FIG. 1 also illustrates a light guiding system 120. According to embodiments of the present invention, the light guiding system 120 comprises at least a reflective element 130 arranged along an optical axis of the light guiding system 120. The reflective element 130 has a freeform optical surface of the reflective element, i.e. the reflective surface has a freeform shape, that is configured for guiding and combining radiation of at least two of the light sources towards an output of the illumination system.The freeform optical surface of the reflective element thus may be designed so that the output of the illumination system has a predetermined output. The freeform optical surface of the reflective element may be as defined above and / or may be designed and manufactured using methods as described further below. In some examples this may be a predetermined shaped pattern, such as for example circular or rectangular pattern, a pattern with a particularly shaped central spot, a pattern with a particularly sized central spot, etc. Advantageously, the freeform optical surface of the reflective element 130 is part of a single monolithic optical reflective element, as this renders positioning the different components more easily during build up of the system. The freeform optical surface of the reflective element 130 advantageously guides and combines radiation of multiple light sources, advantageously of all light sources of the illumination system 100. Advantageously, the radiation of each individual light source 110a, 110b, 110c is guided towards the output 140 of the illumination system 100. This may be performed by reallocating the output of the individual light sources to the output 140 of the illumination system 100. This may include reshaping the output of the individual light sources to the shape of the output 140 of the illumination system 100.

[0092] In some embodiments, the light guiding system 120 may comprise the reflective element with the freeform optical surface. Nevertheless, in some embodiments, also additional optical components may be present in the light guiding system 120. Examples of such additional optical components may be one or more of spectral filters, additional reflective elements, polarizers, polarization controllers, lenses, diffractive optical elements, holographic optical elements, metasurfaces etc.

[0093] In some embodiments, the light guiding system 120 may be free of refractive optical elements, although embodiments are not limited thereto.

[0094] FIG. 1 also illustrates the output 140 of the illumination system 100. This output 140 may for example be an entrance facet of an optical fiber, waveguide or light guide, or for example a detector surface. It is an advantage of embodiments of the present invention that by using a freeform optical surface of the reflective element, the pattern at the output of the illumination system, e.g. at the entrance facet of the optical fiber, waveguide or light guide or at the detector surface can be optimally shaped to match those elements.

[0095] The design of the freeform optical surface of the reflective element 130 is based on optimized simulations. In one example, non-sequential ray tracing software is used to simulate, optimize and evaluate the design. In one embodiment, this includes optimisation using different algorithms, which may include damped least squares (DLS) and orthogonal descent (OD). The considered merit function for performing thissimulation in one example contains the targeted requirements on the illumination output (in terms of illumination uniformity, irradiance, illumination area). According to one embodiment, boundary conditions may be implemented during the design procedure, limiting the parameter space, and ensuring feasible parameters for subsequent manufacturing. As such, a design-for-manufacturing approach is followed. Following the design procedure, a tolerance analysis can be performed providing input for the manufacturing parameters and enabling to select the suitable manufacturing technology taking into account the required precision.

[0096] In one exemplary design method for the freeform optical surface of the reflective element 130, the following step-wise approach is used.

[0097] In a first step, simulation of the light sources emission pattern is performed. Extended source models taking into account the emission area and emission angle of the source, and particularly the emitted light intensity as function of the emission angle may be used.

[0098] In a second step, a start design is generated. The light sources are positioned in the preferred geometrical distribution (ring, square,...), taking into account the footprint size. A spherical mirror surface reflecting the light towards the output of the illumination system is implemented. The distance between the light sources and the reflective surface is set to minimize overlap between the illumination areas of the different light sources on the reflective surface. The radius of curvature of the reflecting surface is dependent on the distance between the reflective surface and the output of the illumination system. In one embodiment, this latter distance is minimized to maintain a compact design.

[0099] In a third step, the illumination output for the individual light sources is optimised. For each light source, its local illumination area on the reflective surface is optimized such that the reflected light is guided towards the required light distribution at the output of the illumination system. This optimization is in one embodiment performed by the addition of aspherical and polynomial terms to the initial spherical reflective surface. An iterative procedure is followed to optimize the local surface shape. It is to be noted that, whereas in the present example the freeform surface is mathematically represented by a polynomial equation, other representations also may be used.

[0100] In a fourth step, optimization of the combined design considering all light sources is performed. This includes a final optimization of the entire reflective surface shape, optimizing the combined design towards the required output light irradiance and shape when considering all combined light sources, and when considering particular subsets of light sources.Manufacturing of the reflective optical element having a freeform reflective surface may be performed using known manufacturing techniques, some of them being described below. Such a manufacturing technique may include an initial substrate preparation step, wherein a suitable material, such as a metal (e.g. aluminium, copper, electroless nickel-plated substrates), glass, ceramic, or polymer, is selected based on the intended application and thermal, mechanical, and optical properties required for the reflective element. The freeform surface is then generated using one or more precision fabrication techniques, including but not limited to ultra-precision diamond turning, computer numerical control (CNC) machining, high-precision grinding, or additive manufacturing methods such as direct metal laser sintering (DMLS) or stereolithography (SLA) followed by metallization. In embodiments utilizing subtractive machining, the freeform surface is shaped via multi-axis CNC milling or single-point diamond turning (SPDT) with nanometric precision, ensuring the desired curvature, slope variation, and optical path integrity. In embodiments employing additive manufacturing, the reflective element is fabricated using layer-by-layer deposition techniques, forming a near-net-shape freeform surface, which is subsequently subjected to precision grinding and polishing processes to reduce surface roughness to a level compatible with optical reflectivity requirements. Following the freeform shaping step, the surface further may undergo refinement through magnetorheological finishing (MRF), ion beam polishing, or chemical-mechanical planarization (CMP) to achieve the required surface smoothness, typically characterized by a root-mean-square (RMS) roughness of less than 10 nanometers. Once the desired freeform geometry and optical quality are attained, a reflective coating is applied to enhance the optical performance of the element. The reflective coating may be a metallic layer, such as aluminium, silver, or gold, deposited via physical vapor deposition (PVD), chemical vapor deposition or any other suitable deposition or coating technique. In certain embodiments, a protective overcoat, such as a magnesium fluoride (MgF2) or silicon dioxide (SiO2) layer, may be applied to improve environmental durability and resistance to oxidation. Alternatively to the precision fabrication techniques described above, the reflective element also may be made using replication techniques such as for example moulding.

[0101] By way of illustration, embodiments of the present invention not being limited thereto, a number of exemplary designs are now further illustrated, indicating different possibilities of illumination sources according to embodiments of the present invention. In FIG. 2a to FIG. 9b, a design of the illumination system with a plurality of light sourcesand a reflective element having a freeform optical reflective surface are shown, as well as the corresponding optical output pattern of the illumination system at the output thereof.

[0102] FIG. 2a shows a design of an illumination system using 6 light sources having a full divergence angle being less than 16°. The rectangles shown indicate the emission surfaces of each of the light sources used. The output coupling efficiency of the illumination system is 100% for a rectangular output with an area of 10 x 10 mm2. In the design, it is assumed that lensed LEDs, lasers, lensed VCSELS or laserdiodes are used. The resulting output pattern is shown in FIG. 2b, whereby the intensity is increasing from the edges of the output pattern towards the centre of the output pattern, and shows a squared high-intensity illumination area.. It is noted that the larger the divergence angles of the individual light sources will be, the smaller the coupling efficiency will become. The illumination output can further be influenced by controlling the freeform optical surface, e.g. by controlling aspherical, freeform terms of the surface description of the optical surface of the reflective element.

[0103] FIG. 3a illustrates an illumination system having the same light source distribution or configuration as the design shown for FIG. 2a, but wherein the output pattern is tuned towards an output with a circular hot spot by optimising the freeform optical surface. . It can be seen in the corresponding output pattern shown in FIG. 3b, that a more circular shaped central output spot can be obtained. The intensity is increasing from the edges of the output pattern towards the centre of the output pattern. The latter hence illustrates that by tuning the freeform optical surface of the reflective element, the shape of the output pattern can substantially be tuned.

[0104] FIG. 4a illustrates a design with a similar configuration as shown in the design of FIG. 2a, but wherein the light sources have an extended LED emission angle of 46°. It can be seen in the resulting output pattern shown in FIG. 4b that the increased emission angles result in a decreased efficiency, due to the changed etendue. In this example, the output pattern only features a collection efficiency of the light from the light sources of 52%. In FIG. 4b, the intensity is again increasing from the edges of the output pattern towards the centre of the output pattern.

[0105] FIG. 5a illustrates a design of an illumination system according to that shown for FIG. 4a, but wherein the number of light sources is increased. It can be seen that this can be performed without a decrease in the collection efficiency, since the output pattern still features a collection efficiency of the light from the light sources of 52%, as can be seen in FIG. 5b. Again, the intensity is increasing from the edges of the output pattern towards the centre of the output pattern.FIG. 6a illustrates a design of an illumination system using different LEDS having different emission angles (between 40 degrees and 56 degrees) as well as different footprint sizes. The rectangular shaped output is shown in FIG. 6b. Again, the intensity is increasing from the edges of the output pattern towards the centre of the output pattern.

[0106] FIG. 7a illustrates a design of an illumination system using different light sources featuring different wavelengths and different emission angles. Such a setup could for example be used for selecting a specific spectral output during use of the illumination source by selecting activation of a selected set of light sources in the configuration. This hence results in a spectrally tunable illumination system. The corresponding output is shown in FIG. 7b, wherein the intensity is increasing from the edges of the output pattern towards the centre of the output pattern.

[0107] FIG. 8a illustrates a design wherein the different light sources are arranged in two rings. The corresponding output is shown in FIG. 8b. 100% of the illumination is coupled to the 10 x 10 mm2output area, whereby 67% of the radiation is coupled in the central 5x5 mm2output area. The possibility of beam shaping is illustrated in FIG. 9a and FIG. 9b, whereby again light sources arranged in two rings are used and whereby a central circular hot spot is obtained. 100% if the illumination is coupled to the 10 x 10 mm2output area, whereby 54% of the radiation is coupled in the central 5x5 mm2output area. The intensity in the output pattern shown is increasing from the edges towards the centre.

[0108] Further, by way of illustration, an illustration of features and advantages of embodiments of the present invention is shown in the following example. The example shows a multi-LED optical design, combining and concentrating 20 LEDs. The example is based on two ring shaped sets of LEDs. It shows an optical design and the optimisation thereof, including the prototyping of the freeform mirror, the resulting proof-of-concept demonstrator and the implementation as a full assembly with cooling and light guide connection.

[0109] FIG. 10a and 10b illustrate an elevated side view and a side view of the combination of LEDs and mirror for the optical design of the example. FIG. 10c and 10d illustrate the light distribution at a detector position, as mapping and as cross-sectional intensity profile along an x direction and an y direction respectively, illustrating the good light spread and combination of the different LEDs.

[0110] FIG. 11a and FIG. 11b illustrate an intensity map at the position of the detector, in case only the first ring is used (FIG. 11a) and in case only the second ring is used (FIG. 11b).Fu rther, FIG. 12 illustrates both for the case where only the first ring of LEDs is used (upper part) and for the case where only the second ring of LEDs is used (lower part), the intensity profile in the x direction and in the y direction.

[0111] The coupling efficiency was evaluated and is given for different detector configurations in the below table.

[0112] "

[0113]

[0114] FIG. 13 shows the construction of the proof of concept system, wherein first the mirror is made as a preshape, then the submirrors for the specific lenses are created using diamond tooling, further the illuminating LEDS are mounted with respect to the mirror, followed by introduction of the cooling and light guide connection.

[0115] In conclusion, the freeform mirror shows successful combination and concentration of all LED emissions whereby the emission patterns of the LEDs show a good overlap. Further optimisation of the layout, the lightguide and the LEDs can be performed.

Claims

CLAIMS1. An illumination system (100) for illuminating an area of interest, the illumination system (100) comprising- a plurality of n individual light sources (110a, 110b, 110c, ...), and - a light guiding system (120) comprising a reflective element (130) arranged along an optical axis of the light guiding system (120) and the reflective element (130) having a non-spherical, freeform optical surface of the reflective element configured for guiding and combining radiation of at least two of said plurality of n individual light sources (110a, 110b, 110c,...) towards an output (140) of said illumination system (100),the plurality of n individual light sources (110a, 110b, 110c, ...) comprising at least a first subset of light sources and a second subset of light sources,the non-spherical, freeform optical surface of the reflective element having at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the first subset of light sources and at least a local dedicated freeform optical surface for allowing dedicated beam shaping for the second subset of light sources.

2. The illumination system (100) according to claim 1, wherein the freeform optical surface of the reflective element has at least part of its surface lacking rotational symmetry.

3. The illumination system (100) according to any of claims 1 or 2, wherein the freeform optical surface of the reflective element has at least part of its surface lacking translational symmetry.

4. The illumination system (100) according to any of claims 2 to 3, wherein different local dedicated freeform optical surfaces show different local surface changes tailored to their respective subset of light sources.

5. The illumination system (100) according to any of the previous claims, wherein the freeform optical surface of the reflective element is configured for guiding radiation of all of said plurality of n individual light sources (110a, 110b, 110c,...) towards the output (140) pattern of said illumination system (100).

6. The illumination system (100) according to any of the previous claims, wherein the reflective element (130) is or behaves as a monolithic optical element.

7. The illumination system (100) according to any of the previous claims, wherein the output (140) of the illumination system (100) has a curved shape, e.g. circular, or a polygonal shape, the freeform optical surface of the reflective element (130) being configured for reshaping the optical output of the plurality of n individual lightsources (110a, 110b, 110c,...) towards the curved shaped output (140), e.g. circular shaped output (140), or the polygonal shaped output (140) of the illumination system (100).

8. The illumination system (100) according to any of the previous claims, wherein the freeform optical surface of the reflective element (130) is defined by a polynomial surface function having at least some terms in x and / or y coordinates having an order higher than 2.

9. The illumination system (100) according to any of the previous claims, wherein the freeform optical surface of the reflective element (130) reallocates portions of a circular or elliptical optical field created by the individual light sources (110a, 110b, 110c, ...) towards the output (140) pattern of the illumination system (100).

10. The illumination system (100) according to claim 9, wherein the freeform optical surface of the reflective element (130) is configured for reallocating portions of the individual output pattern of the light sources (110a, 110b, 110c, ...) so that each light source matches the output (140) illumination pattern of the illumination system (100).

11. The illumination system (100) according to any of the previous claims, wherein the individual light sources (110a, 110b, 110c,...) comprise a set of light sources positioned in a predetermined configuration with respect to the optical axis of the illumination system (100.

12. The illumination system (100) according to any of the previous claims, wherein t light sources of different subsets having at least one of a different divergence angle, footprint size, intensity and / or spectral composition.

13. The illumination system (100) according to any of the previous claims, wherein the illumination beam created by the first subset of light sources has a substantially different spectrum than the illumination beam created by the second subset of light sources.

14. The illumination system (100) according to any of the previous claims, wherein the illumination beam created by the first subset of light sources has a substantially different output intensity than the illumination beam created by the second subset of light sources.

15. The illumination system (100) according to claim 12, wherein the freeform optical surface comprises for each light source a dedicated local freeform optical surface.

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