(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(19) World Intellectual Property
`Organization
`International Bureau
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`(10) International Publication Number
`
`(43) International Publication Date
`WO 2013/088295 A1
`20 June 2013 (20.06.2013) WIPOI PCT
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`\Q
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`(74)
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`Agents: VAN EEUWIJK, Alexander Henricus Walterus
`el al.; High Tech Campus Building 44, NL-56 56 AE Eind-
`hoven (N L).
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`(51)
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`International Patent Classification:
`G023 6/00 (2006.01)
`G023 27/09 (2006.01)
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`(21)
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`International Application Number:
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`PCT/IB2012/056930
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`(31)
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`(22)
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`International Filing Date:
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`(25)
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`Filing Language:
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`(26)
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`Publication Language:
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`4 December 2012 (04.12.2012)
`
`English
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`English
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`(30)
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`(71)
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`(72)
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`Priority Data:
`61/570,475
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`14 December 2011 (14.12.2011)
`
`US
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`Applicant: KONINKLIJKE PHILIPS ELECTRONICS
`N.V. [NL/NL]; High Tech Campus 5, NL-5656 AE Eind-
`hoven (NL).
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`Inventors: TUKKER, Teunis Willem; c/o High Tech
`Campus Building 44, NL-5656 AE Eindhoven (NL).
`IJZERMAN. Willem Lubertus; c/o High Tech Campus
`Building 44, NL-5656 AE Eindhoven (NL). GOORDEN,
`Sebastianus Adrianus; c/o High Tech Campus Building
`44, NL-5656 AE Eindhoven (NL).
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`(84)
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`Designated States (unless otherwise indicated, for every
`kind ofnational protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY,
`BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM,
`DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
`HN, HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP,
`KR, KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD,
`ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI,
`NO, NZ, OM, PA, PE, PG, PH, PL, PT, QA, RO, RS, RU,
`RW, SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ,
`TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA,
`ZM, ZW.
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, SZ, TZ,
`UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV,
`MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM,
`TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW,
`ML, MR, NE, SN, TD, TG).
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`[Continued on nextpage]
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`(57) Abstract: An elongated optical ele—
`ment (100) arranged for homogenizing a
`bundle of light rays (1 10) is provided. A
`perimeter (120) of a lransversal cross-
`section (121) of the optical element is
`defined by at least two edges (122) of
`zero
`curvature
`and Vertices
`(123)
`between any two adjacent ends of the at
`least two edges, wherein at least one of
`the vertices is a segment with positive
`curvature, its length constituting at least
`1% and at most 90% of the length of the
`perimeter.
`
`(54) Title: OPTICAL ELEMENT AND METHOD FOR HOMOGENIZING LIGHT
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`Published:
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`— with international search report (Art. 21 (3))
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`WO 2013/088295
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`PCT/IB2012/056930
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`Optical element and method for homogenizing light
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`1
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`FIELD OF THE INVENTION
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`The present invention relates to an optical element and a method for
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`homogenizing a bundle of light rays.
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`BACKGROUND OF THE INVENTION
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`Numerous systems in various fields of industry require a provision of a beam
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`of light which is homogcncous (uniform) across thc span of thc light bcam, in terms of
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`properties such as a constant illuminance and/or colour. For example, in many medical
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`applications such as laser therapy, laser bio—stimulation, and photodynamic therapy, it is
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`highly desirable that the bundle of light rays has a homogeneous illuminance. As most light
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`sources, however, emit a light which is non—homogeneous, light filtering and/or devices for
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`light correction have been proposed to obtain the sought-for homogeneity of the light.
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`In a case where the light is generated by one or more light sources (e.g. LEDs
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`with different colours), a mixing of the light may be performed with the aim of rendering a
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`homogeneous light. The mixing of the light may be carried out by guiding the light from the
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`light source(s) through an optical guide. Embodiments of optical guides are solid mixing rods
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`(e.g. a glass/plastic fibre, rod, tube, or the like), utilizing the total internal reflection (TIR) at
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`the interfaces towards the surrounding medium (reflection back and forth), such that the light
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`reflected within the mixing rod has been mixed when exiting the mixing rod.
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`The structure of the mixing rod is of importance to obtain a preferred mixing
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`of the light, and various geometric structures of the mixing rods have been proposed for this
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`purpose. From practice, it is known that mixing rods having square cross—sections are
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`superior to circular ones, but that rods with hexagonal cross—sections are even better for the
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`purpose of obtaining a uniform light. Although hexagonal mixing rods are widely used
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`nowadays, this geometric shape does not provide an adequate homogeneity of the
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`illuminance at the exit face of the mixing rod. More specifically, the light rays are not
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`adequately mixed in the far field of the mixing rod since the mixing does not sufficiently alter
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`the angles of the light rays.
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`In view of this, there is a wish to provide an optical element which provides an
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`improved mixing of the light.
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`SUMMARY OF THE INVENTION
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`It is an object of the present invention to provide an optical element and a
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`method for homogenizing a bundle of light rays. This and other objects are achieved by an
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`optical element and a method having the features set forth in the independent claims.
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`Preferred embodiments are defined in the dependent claims.
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`Hence, according to a first aspect of the present invention, there is provided an
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`elongated optical element arranged for homogenizing a bundle of light rays. The perimeter of
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`a transversal cross-section of the optical element is defined by at least two edges of zero
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`curvature and vertices between any two adjacent ends of the edges. At least one of the
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`vertices is a segment with positive curvature, wherein its length constitutes at least 1% and at
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`most 90% of the length of the perimeter. Thus, the present invention is based on the idea of
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`providing an optical element having a transversal cross-section wherein the vertices between
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`the edges have positive curvature, i.e. wherein the vertices are outwardly curved/rounded. By
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`the term “zero curvature”, it is here meant that the edges of the transversal cross-section are
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`even/straight, i.e. not curved in the plane of the cross-section. Furthermore, by the term
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`“vertices”, it is here meant comers/angles between the edges of the transversal cross-section
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`of the optical element. By the term “positive curvature”, it is here meant that the at least one
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`vertex is rounded outwards from the perimeter (i.e. bulging convexly outwards). When light
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`rays are directed into the optical element and are reflected therein, the curved vertices of the
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`optical element lead to an improved mix of the light rays in the optical element, compared to
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`a mixing rod without rounded corners/vertices. The purposefully shaped/designed perimeter
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`of the optical element enhances the irregularity/chaos of the mixing of the light, and leads to
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`an increased homogeneity of the bundle of light rays when exiting the optical element.
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`According to a second aspect of the present invention, there is provided a
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`method for homogenizing a bundle of light rays. The method comprises the step of directing
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`a bundle of light rays towards an entry face of an elongated optical element. Furthermore, the
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`method comprises the step of mixing the bundle of light rays by means of the optical
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`element, wherein a perimeter of a transversal cross—section of the optical element is defined
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`by at least two edges of zero curvature and vertices between any two adjacent ends of the
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`edges. At least one of the vertices is a segment with positive curvature, wherein its length
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`constitutes at least 1% and at most 90% of the length of the perimeter. Furthermore, the
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`method comprises the step of extracting the bundle of light rays from the exit face of the
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`optical element.
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`The present invention is advantageous in that the elongated optical element
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`provides an improved mixing of a bundle of light rays, such that a more homogeneous light is
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`obtained after the bundle of light rays has passed through the optical element, compared to
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`existing mixing rods. More specifically, the edges and the vertices of the optical element,
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`wherein the vertices have positive curvature, provide an enhanced mixing of the light due to
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`an improved scattering/reflection of the light within the optical element. This is realized as
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`the perimeter of the optical element, comprising rounded/curved vertices, increases the
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`number of directions of the light ray reflection/scattering as the normal angle of the curved
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`vertices varies continuously. It will be appreciated that in an optical element with a
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`transversal cross-section comprising only straight edges, a ray direction can generally only
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`change by multiples of 27t/n, where n is the number of edges. In contrast, the optical element
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`of the present invention decreases the number of stable trajectories of the reflected light, i.e.
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`trajectories of the light ray reflections having a periodic propagation within the optical
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`element, and provides a more homogeneous light (i.e. even distribution of the light
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`components) at the exit face of the optical element with respect to one or more of e.g.
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`luminous intensity, colour point, wavelength spectrum, etc., compared to mixing rods in the
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`prior art.
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`The present invention is further advantageous in that the improved mixing of
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`the light is provided solely by the geometrical shape of the optical element. In other words,
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`the enhanced homogeneity of the light is obtained merely by the geometrical features of the
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`optical element, such that additional measures for the purpose of improving the mixing of the
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`light (e.g. a coating or other treatments of the inside of the optical element and/or a provision
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`of auxiliary elements to the optical element for the purpose of improving the reflectivity) may
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`be rendered superfluous. Consequently, the optical element of the present invention is easy to
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`manufacture, as the optical element may be produced merely from the material which has the
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`purpose of guiding and mixing the light (e. g. a transparent material comprising glass, plastic,
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`or the like), thereby omitting the need of other (auxiliary) materials. Moreover, as additional
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`treatments (e.g. inside coatings) may be refrained from, rendering the manufacture of the
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`optical element of the present invention relatively inexpensive. Since the element may be
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`manufactured from a single material, the optical element is easily recyclable.
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`Another advantage associated with the present invention is that the geometry
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`of the transversal cross—section of the optical element further provides an earlier homogeneity
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`of the bundle of light rays in a direction from the entry face to the exit face of the optical
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`element compared to known mixing rods. In other words, a bundle of light rays led into the
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`entry face of the optical element is quickly mixed along the elongated optical element due to
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`the optimized perimeter of the transversal cross-section according to the present invention.
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`The optical element of the present invention is able to achieve the task of mixing the initially
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`non-homogeneous bundle of light rays into a homogenized light earlier along its elongation
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`compared to mixing rods in the prior art. Hence, the optical element of the present invention
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`may have a relatively shorter length than other mixing rods in the prior art to fulfil this given
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`task. This is highly advantageous, as the present invention thereby provides an even lower
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`manufacture cost of the optical element, a lower weight, a more convenient handling and/or
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`transportation, and/or a simplified procedure if the optical element is to be mounted into an
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`optical system.
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`The elongated optical element is arranged for homogenizing a bundle of light
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`rays. In other words, the optical element is arranged to mix/homogenize a bundle of light rays
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`of one or more light sources, which light rays are directed into an entry face of the optical
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`element. After passing through the optical element, the bundle of light rays are mixed into a
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`homogeneous light at an exit face of the optical element.
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`The perimeter of a transversal cross-section of the optical element is partly
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`defined by at least two edges of zero curvature, i.e. even/straight edges (not curved). As the
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`perimeter (i.e. the boundary) of the transversal cross-section comprises at least two edges of
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`zero curvature, the cross-section is not circular.
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`Furthermore, the perimeter of the transversal cross-section of the optical
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`element is partly defined by vertices between any two adjacent ends of the at least two edges.
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`In other words, the perimeter is defined by the at least two edges and vertices between any
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`two adjacent ends of these edges. At least one of the vertices is a segment with positive
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`curvature, i.e. a segment outwardly rounded from the perimeter. Furthermore, it will be
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`appreciated that the positively curved vertex thereby differs from an angle with a sharp
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`corner having an undefined derivative.
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`At least one of the vertices, being a segment with positive curvature, has a
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`length constituting at least 1% and at most 90% of the length of the perimeter. In other
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`words, of the entire length of the perimeter, defined by the edges and the vertices between
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`any two adjacent ends of the edges, the length of the curved vertices represents 1790% of the
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`length of the perimeter.
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`Intervals defining suitable total vertex lengths may have one of the numbers 1,
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`2, 5, 10, 15, 20, 30, 40, 50% as lower endpoint and may independently have any one of the
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`numbers 90, 85, 80, 70, 60, 50, 40% as upper endpoint.
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`According to an embodiment of the present invention, the optical element may
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`be shaped as a cylinder. In other words, the optical element of the present embodiment has an
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`elongated shape, and has a transversal cross-section which is constant along the longitudinal
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`axis of the optical element. The cylinder-shaped optical element is advantageous in that it is
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`easily manufactured, e.g. by extrusion. Furthermore, the present embodiment is advantageous
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`in a case the length of the optical element needs to be changed. For example, if the optical
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`element is shortened, the cross-section of the exit face, as well as the cross-section between
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`the entry face and the exit face will still be the same. Hence, the length of the optical element
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`may be adapted more easily according to the required mixing of the light. Alternatively, the
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`optical element may have a frustoconical shape, wherein the entry face and the exit face have
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`different sizes. For example, the cross-section may decrease along the longitudinal axis of the
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`optical element, such that the exit face has a smaller area than the entry face.
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`According to an embodiment of the present invention, at least one of the
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`vertices may be a segment of a circular arc. In other words, the at least one vertex may be a
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`portion of the circumference of a circle. The present embodiment is advantageous in that the
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`vertex has a continuous and symmetric rounding which even further contributes to the mixing
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`of the light.
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`According to an embodiment of the present invention, the radius of the
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`circular arc may be equal to the length of at least one of the at least two edges. The present
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`embodiment is advantageous in that it decreases the number of stable trajectories of light ray
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`reflections within the transversal cross-section of the optical element, as can be verified by
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`numerical simulations. For example, if the cross—section of the optical element has a polygon
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`shape with an odd number of edges, only one stable trajectory exists between the segment of
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`the circular arc and the opposing edge having the same length as the radius of the circular arc.
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`Hence, the present embodiment will achieve to an even more improved mixing of the light.
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`According to an embodiment of the present invention, the radius of the
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`circular arc may be greater than the length of at least one of the at least two edges. An
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`advantage of the present embodiment is that it even further decreases the number of stable
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`trajectories of light ray reflections within the optical element. For example, if the transversal
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`cross—section of the optical element has a polygon shape with an odd number of edges, there
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`exists a unique trajectory between the segment of the circular arc and the opposing edge,
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`wherein the radius of the circular arc is greater than the opposing edge. Hence, the present
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`embodiment will achieve an even more improved mixing of the light.
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`According to an embodiment of the present invention, all of the at least two
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`edges may be of equal length and all of the vertices are of equal length. In other words, the
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`edges of the transversal cross-section of the optical element is equilateral, and the vertices
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`between any two adjacent ends of the edges are of equal length. The present embodiment is
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`advantageous in that the optical element provides an n-fold rotational symmetry (wherein n is
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`the number of edges). Consequently, an alignment of the optical element is facilitated, e.g.
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`when mounting the optical element in an optical system.
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`According to an embodiment of the present invention, the tangent of at least
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`one of the vertices and the tangent of any two adjacent ends of the edges may be equal at at
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`least one point of intersection between the at least one of the vertices and any two adjacent
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`ends. In other words, the vertex between two adjacent ends provides a smooth
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`rounding/connection/patching between the edges, wherein the tangent of any point on the
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`vertex is within the interval bounded by the tangents of the two adjacent ends and equal at the
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`points of intersection.
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`According to an embodiment of the present invention, the perimeter may
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`comprise six edges. In other words, the six edges constitute an hexagonal cross-section of the
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`optical element, further comprising rounded vertices between the edges. The present
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`embodiment is advantageous in that the mixing of the light by the optical element of the
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`present embodiment is superior to the mixing which is achieved by mixing rods in the prior
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`art having merely a hexagonal cross-section without rounded corners. This is realized as the
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`rounded vertices in the hexagonal cross-section of the present embodiment increases the
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`number of possible/distinct light ray reflections within the optical element. Furthermore, as
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`mixing rods with hexagonal cross—sections are known in the prior art, the present
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`embodiment is further advantageous in that the equipment for the manufacture of the mixing
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`rods from the prior art is easily modified for the manufacture of the optical element according
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`to the present embodiment, wherein the hexagonal cross—section filrther comprises rounded
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`vertices to provide an improved mixing of the light.
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`According to an embodiment of the present invention, the perimeter may be
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`defined by three edges wherein two edges are perpendicular and of equal length, the vertices
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`being three circular arcs of equal radius, and wherein the radius is equal to the length of one
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`of the two edges. In other words, the transversal cross—section of the optical element is
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`shaped as a right—angled triangle, having two perpendicular edges as catheti and one edge as
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`hypotenuse, but wherein the vertices are rounded such that no sharp comers exist. Further,
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`the vertices are circular arcs having the same radius, wherein the radius is equal to the length
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`of one of the two edges (catheti). As stable trajectories of light ray reflections are known to
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`exist in any transversal cross-section that has n-fold rotational symmetry (wherein n is an
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`integer), only one stable trajectory of light ray reflections is present in an optical element
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`having the perimeter as defined in the present embodiment. Hence, an advantage with the
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`present embodiment is that the homogeneity of the light at the exit face of the optical element
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`is even further increased.
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`According to an embodiment of the present invention, there is provided an
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`optical system for homogenizing a bundle of light rays, comprising an elongated optical
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`element as defined in any one of the preceding embodiments and at least one light source
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`arranged at a transversal entry face of the optical element, arranged for directing a bundle of
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`light rays towards the entry face. The optical system may comprise two or more light sources,
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`e.g., light sources emitting light with different properties which it is desired to mix into one
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`homogeneous bundle.
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`According to an embodiment of the present invention, the optical system
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`comprises a collimating means arranged at a transversal exit face of the optical element for
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`collimating the bundle of light rays exiting the optical element. By “collimating means” it is
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`here meant substantially any means for the purpose of collimating the light at the exit face of
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`the optical element into a beam of a required/desired shape, wherein examples of a
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`collimating means may be a lens, a Séller collimator or a TIR collimator.
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`Further objectives of, features of, and advantages with, the present invention
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`will become apparent when studying the following detailed disclosure, the drawings and the
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`appended claims. Those skilled in the art will realize that different features of the present
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`invention can be combined to create embodiments other than those described in the
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`following.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`These and other aspects of the present invention will now be described in more
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`detail, with reference to the appended drawings showing embodiment(s) of the invention.
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`Fig. 1 is a schematic illustration of an elongated optical element according to
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`an embodiment of the present invention;
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`Figs. Zaib are schematic illustrations of transversal cross—sections of optical
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`elements;
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`Figs. 3a-b are schematic illustrations of trajectories of light ray reflections;
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`Fig. 4 is a schematic illustration of a transversal cross-section of an elongated optical element
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`according to an embodiment of the present invention; and
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`Fig. 5 is a schematic illustration of an optical system according to an
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`embodiment of the present invention.
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`DETAILED DESCRIPTION OF THE EMBODIMENTS
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`In the following description, the present invention is described with reference
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`to an elongated optical element arranged for homogenizing a bundle of light rays.
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`Fig. 1 is a schematic illustration of an elongated optical element 100 according
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`to an embodiment of the present invention. The optical element 100, which may be made of a
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`transparent material like glass or plastic, is shaped as a cylinder and comprises an entry face
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`101 and an exit face 102. At operation, a bundle of light rays 110 is directed towards the
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`entry face 101, wherein the bundle of light rays 110 undergoes total internal reflection (TIR)
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`at the interfaces towards the surrounding medium. After being reflected within the optical
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`element 100, the bundle of light rays 1 10 exits the optical element 100 through the exit face
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`1 02.
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`The contour of the optical element 100 in Fig. 1 is designed such that the
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`perimeter 120 of a transversal cross-section 121 of the optical element 100 is defined by six
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`edges 122 of zero curvature and six vertices 123 between any two adjacent ends of the edges
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`122. In the present embodiment, the edges 122 are of equal length and the vertices 123 are of
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`equal length. The vertices 123 are segments with positive curvature (rounded segments),
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`wherein the lengths of the vertices 123 in Fig. 1 constitute 30—50% of the length of the
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`perimeter 120. When the bundle of light rays 110 is directed into the optical element 100, the
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`curved/rounded vertices 123 of the optical element 100 lead to an improved mix of the angles
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`and positions of the light rays in the optical element 100, compared to a mixing rod without
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`rounded comers/vertices. In three dimensions, the comers/vertices 123 may alternatively be
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`referred to as rounded ridges 123 extending longitudinally in the optical element 100. By
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`virtue of its geometry, the optical element 100 provides an increased homogeneity of the
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`bundle of light rays 110 when exiting the optical element 100 by the exit face 102.
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`Fig. 2a is a schematic illustration of a transversal cross—section 200 of a
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`mixing rod according to the prior art, wherein the cross—section 200 is hexagonal, comprising
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`six edges 201 and six comers 202. However, the geometric shape of the cross—section 200 as
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`disclosed does not provide the desired homogeneity of the illuminance at the exit face of the
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`mixing rod. More specifically, the light rays are not adequately mixed in the far field of the
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`mixing rod since the mixing does not sufficiently alter the angles of the light rays.
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`Fig. 2b is a schematic illustration of the transversal cross-section 121 of the
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`optical element 100 according to Fig. 1. Compared to the sharp corners 202 of the cross-
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`section 200 as shown in Fig. 2a, the vertices 123 of the optical element 100 are segments
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`with positive curvature. As a result, the cross section 121, comprising the vertices 123,
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`provides an improved mixing of a bundle of light rays directed into the optical element 100
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`compared to the use of an optical element with the cross-section 200.
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`Fig. 3a is a schematic illustration of trajectories of light ray reflections within
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`an exemplifying optical element 300. Here, the transversal cross-section 321 of the optical
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`element 300 comprises four straight edges 322 and four vertices 323 with positive curvature.
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`The four edges 322 of the cross-section 321 define an essentially quadratic shape, whereas
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`the curved/rounded vertices 323 smoothen the sharp comers of the square. Although the
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`cross-section 321 comprises rounded vertices 323, stable trajectories are still present in the
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`contour of the optical element 300. Three exemplifying trajectories are indicated in Fig. 3a as
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`330, 331 and 332. The first trajectory 330 is located between the base edge and the top edge
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`of the cross-section 321, as a light ray may be reflected back and forth between the parallel
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`base edge and top edge of the cross-section 321. Analogously, the second trajectory 331 is
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`located between the left edge and the right edge of the cross-section 321, as a light ray may
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`be reflected back and forth between the parallel left edge and right edge of the cross-section
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`321. Furthermore, the third trajectory 332 is located diagonally in the cross-section 321,
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`wherein the light ray is reflected from one edge to an adjacent edge by 90°, such that the
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`trajectory 332 encloses a rectangular shape by reflection from all four edges 322.
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`Fig. 3b is a schematic illustration of trajectories of light ray reflections within
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`an exemplifying optical element 350. Here, the transversal cross—section 371 of the optical
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`element 350 comprises three edges 372 and three vertices 373 with positive curvature. The
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`three edges 372 of the cross—section 371 define a triangular shape, whereas the
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`curved/rounded vertices 373 smoothen the sharp comers of the triangle. Analogously to
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`Fig. 3a, stable trajectories are still present in the contour of the optical element 350. An
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`exemplifying stable trajectory is indicated in Fig. 3b as 380, wherein the a light ray is
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`reflected from the three edges 372 such that the trajectory 380 achieves a pattern of triangles.
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`Fig. 4 shows a schematic illustrations of a transversal cross—section 421 of an
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`elongated optical element 400 according to an embodiment of the present invention. In this
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`embodiment, the transversal cross—section 421 of the optical element 400 comprises three
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`straight edges 422 and three vertices 423 with positive curvature. The three edges 422 of the
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`cross-section 421 provides the shape of a right-angled triangle, having two perpendicular
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`edges as catheti and one edge as hypotenuse, but wherein the vertices 423 are rounded such
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`that no sharp corners exist. Further, the vertices 423 are circular arcs having the same radius
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`R wherein the radius R is equal to the length L of one of the two edges (catheti). Compared to
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`transversal cross-sections having n-fold rotational symmetry (wherein n is an integer), e.g.
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`the cross-sections 321 and 371 as shown in Fig. 3a and Fig. 3b, respectively, the perimeter of
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`the optical element as defined in the present embodiment has only one stable trajectory 390
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`of light ray reflection. This trajectory 390 is located in Fig. 4 as a reflection between the
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`edge, which represents the hypotenuse of the cross-section 421, and its opposite vertex.
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`Hence, the present embodiment is advantageous in that the contour of the cross-section 421
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`provides a homogeneity of the light at the exit face of the optical element which is even
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`further increased.
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`Fig. 5 is a schematic illustration of an optical system 500 according to an
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`embodiment of the present invention. The optical system comprises an elongated optical
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`element 100 as described in any one of the preceding embodiments. Three light sources 510
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`are arranged at a transversal entry face 501 of the optical element 100, arranged for directing
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`a bundle of light rays 110 towards the entry face 501. The optical system 500 filrther
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`comprises a collimating means 511 arranged at a transversal exit face 502 of the optical
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`element 100 for collimating the bundle of light rays 110 exiting the optical element 100.
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`Even though the invention has been described with reference to specific
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`exemplifying embodiments thereof, many different alterations, modifications and the like
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`will become apparent to those skilled in the art after studying this description. The described
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`embodiments are therefore not intended to limit the scope of the invention, which is only
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`defined by the appended claims. For example, in Fig. 1, the relationship between the diameter
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`of the entry face 101 and the length of the elongated optical element 100 may be different
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`from that shown. For example, the optical element 100 may be thinner (longer) or thicker
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`(shorter) in relation to the entry face 101, such that the ratio between the length of the optical
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`element 100 and the entry face 101 becomes larger or smaller, respectively. Furthermore, in
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`Fig. 2b, the vertices 123 may constitute a greater or a smaller portion of the length of the
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`perimeter 120 than that shown. The light sources 510 as shown in Fig. 5 are shown as light
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`bulbs for an enhance understanding of the figure, and it will be appreciated that the light
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`sources 510 may alternatively be LEDs, as described earlier. It will also be appreciated that
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`the number of elements shown/described may vary. For example, the three light sources 510
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`in Fig. 5 may alternatively be any number of light sources.
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`CLAIMS:
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`1.
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`An elongated optical element (100) arranged for homogenizing a bundle of
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`light rays (110), wherein a perimeter (120) of a transversal cross—section (121) of said optical
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`element is defined by:
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`-
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`-
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`wherein
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`at least two edges (122) of zero curvature, and
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`vertices (123) between any two adjacent ends of said at least two edges,
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`-
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`at least one of the vertices is a segment with positive curvature, its length
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`constituting at least 1% and at most 90% of the length of said perimeter.
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`2.
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`The elongated optical element (100) as claimed in claim 1, wherein said
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`optical element is shaped as a cylinder.
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`3.
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`The elongated optical element (100) as claimed in claim 1, wherein at least
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`one of said vertices (123) is a segment of a circular arc.
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`4.
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`The elongated optical element (100) as claimed i