LIGHT SOURCE ASSEMBLY

Abstract

A light source assembly having N outputs is disclosed. The assembly comprising: a light source arrangement arranged for supplying light to M inputs, where M an N independently of each other are integers and where M2 and MN; at least one optical couplers, each having at least one input arm and a plurality of output arms; and an integer number, P, of mode scramblers;

The light source arrangement may comprise a broadband light source and a multimode coupler configured for receiving one or more light beams from the light source arrangement, wherein the one or more light beams being derived from the broadband light source and wherein a mode scrambler is arranged for mode scrambling one of said light beams before it enters the multimode coupler.

Claims

1. A light source assembly having N outputs, where N is an integer, the assembly comprising: a light source arrangement arranged for supplying light to M inputs, where M is an integer and where M 2 and M N; a plurality of optical couplers each having at least one input arm and a plurality of output arms; and an integer number, P, of mode scramblers; and wherein the plurality of optical couplers is arranged to divide the light supplied to the M inputs to the N outputs, where each of the N outputs includes light supplied to each of the M inputs; and wherein for at least one of the M inputs there is a respective mode scrambler of the P mode scramblers in the optical communication path between the light source and the at least one of the M inputs, and wherein at least one mode scrambler of the P mode scramblers is arranged in an optical communication path between an output arm of one optical coupler of the plurality of optical couplers and an input arm of a different optical coupler of the plurality of optical couplers, preferably where M>2 and M<N.

2. The light source assembly of claim 1, wherein for a plurality of the M inputs there is a respective mode scrambler of the P mode scramblers in the optical communication path between the light source arrangement and the respective M inputs, preferably for at least two and/or for all of the M inputs there is a respective mode scrambler of the P mode scramblers in the optical communication path between the light source assembly and the respective M inputs.

3. The light source assembly of claim 1 or claim 2, wherein the M inputs are input arms of a first coupler of the optical couplers and wherein M preferably is from 2 to 10, such as from 2 to 4.

4. The light source assembly of claim 3, wherein an output arm of the first coupler is in optical communication via an optical communication path with an input arm of a second line coupler of the optical couplers, preferably said optical communication path is the optical communication path comprising said at least one mode scrambler.

5. The light source assembly of claim 3, wherein each of two or more output arms of the first coupler is in optical communication via an optical communication path with an input arm of a second line coupler of the optical couplers, preferably each of said optical communication paths comprises a respective mode scrambler of the P mode scramblers.

6. The light source assembly of claim 4 or claim 5, wherein an output arm of at least one of the second line couplers is in optical communication via an optical communication path with an input arm of a third line coupler of the optical couplers, preferably said optical communication path is an optical communication path comprising a respective mode scrambler of the P mode scramblers.

7. The light source assembly of claim 6, wherein each of two or more output arms of the second line coupler(s) is in optical communication via an optical communication path with an input arm of a third line coupler of the optical couplers, preferably each of said optical communication paths comprises a respective mode scrambler of the P mode scramblers.

8. The light source assembly of claim 6 or claim 7, wherein said plurality of couplers comprises a number of further line couplers, such as at least one third line coupler, such as at least one fourth line coupler, such as at least one fifth line coupler, preferably respective mode scramblers of the P mode scramblers are in respective optical communication paths between a lower numbered line coupler and a higher numbered line coupler.

9. The light source assembly of any one of the preceding claims, wherein the arms of the optical couplers are fiber arms, said optical couplers preferably being fused fiber coupler(s) or AB multimode combiner(s).

10. The light source assembly of any one of the preceding claims, wherein the couplers are independently of each other selected from couplers with m input arms and n output arms, wherein m is 1, 2, 3, 4, 5, 6 or 7 and n is 2, 3, 4, 5, 6 or 7.

11. The light source assembly of any one of the preceding claims, wherein the couplers comprises at least one 22 coupler, optionally all of the remaining couplers are 1n couplers and n is 2, 3, 4, 5 or 6, preferably 2.

12. The light source assembly of any one of the preceding claims, wherein each of one or more of the couplers, such as all of the couplers, is (are) arranged for dividing the input light substantially uniformly with respect to light intensity between its output arms.

13. The light source assembly of any one of the preceding claims, wherein each of one or more of the couplers are multimode couplers comprising multimode arms.

14. The light source assembly of any one of the preceding claims, wherein N is at least 4, such as from 5 to 40, such as from 6 to 32, such as from 8 to 16, such as 2 times M.

15. The light source assembly of any one of the preceding claims, wherein MP<N, preferably P is at least 2, such as at least 3, preferably P is up to the total number of input arms.

16. The light source assembly of any one of the preceding claims, wherein the P mode scramblers are selected from step a Step-Graded-Step mode scrambler and a Step Index with Bends mode scrambler.

17. The light source assembly of any one of the preceding claims, wherein the light source arrangement comprises a light source selected from a fiber laser, a LED, a solid-state laser, a semiconductor laser or any combinations thereof, said light source arrangement optionally comprises two or more lasers.

18. A light source assembly comprising a light source arrangement comprising a broadband light source and a multimode coupler configured for receiving one or more light beams from the light source arrangement, wherein the one or more light beams are derived from the broadband light source and wherein a mode scrambler is arranged for mode scrambling one of said light beams before it enters the multimode coupler.

19. The light source assembly of claim 18, wherein the multimode coupler is a multimode fused coupler comprising at least two input arms and at least two output arms.

20. The light source assembly of claim 18 or claim 19, wherein at least one of the light beams being derived from the broadband light source being delivered by free space coupling from the light source arrangement to the multimode coupler or to the mode scrambler.

21. The light source assembly of claim 18 or claim 19, wherein at least one of the light beams derived from the broadband light source is delivered from the light source arrangement to the multimode coupler or to the mode scrambler at least partly by fiber coupling.

22. The light source assembly of any one of claims 18-21, wherein the mode scrambler comprises a mode scrambling component, such as a non-fiber based mode scrambling component.

23. The light source assembly of any one of claims 18-21, wherein the mode scrambler comprises a fiber mode scrambler, said fiber mode scrambler optionally being arranged a or forming part of a multimode fiber optically connected to an input arm of said multimode coupler.

24. The light source assembly of any one of claims 18-23, wherein said light source arrangement comprises a wavelength filter for filtering light from the broadband light source to provide a filtered light beam of the one or more light beams derived from the broadband light source, said scrambler being configured for receiving and scrambling said filtered light beam prior to entering the multimode coupler.

25. The light source assembly of any one of the preceding claims 18-24, wherein said light source arrangement comprises an additional light source arranged for supplying a further light beam to said multimode coupler, said additional light source being a single mode light source or a multimode light source, said light source assembly preferably comprises a mode scrambler configured for mode scrambling said further light beam prior to entering the multimode coupler.

26. The light source assembly of any one of the preceding claims 18-25, wherein said light source arrangement is configured for filtering light from the broadband light source to provide two or more filtered light beams of the one or more light beams derived from the broadband light source, preferably mode scramblers are arranged for mode scrambling said respective filtered light beams before they enter the multimode coupler.

27. The light source assembly of any one of the preceding claims 18-26, wherein said broadband light source is configured for generating a broadband light spanning over at least 100 nm, such as over at least 500 nm, such as over at least 800 nm, preferably said broadband light source is a supercontinuum light source.

28. The light source assembly of any one of the preceding claims 18-27, wherein said broadband light source comprises a single mode light source or a few moded light source with up to 20 guided modes per polarization direction, such as up to 10 guided modes per polarization direction determined at the peak wavelength of the first filtered light beam.

29. The light source assembly of any one of the preceding claims 24-28, wherein said wavelength filter is preferably wavelength tunable, and is preferably configured for filtering off two or more wavelength ranges from an input light beam from the broadband light source, said wavelength filter preferably being an acousto-optic tunable filter.

30. The light source assembly of any one of the preceding claims 18-29, wherein said light source arrangement comprises two wavelength filters arranged for filtering off two or more wavelength ranges from an input light beam from the broadband light source, said light source arrangement preferably comprises a beam splitter arranged for splitting the input light beam from the broadband light source in two beam portions, the wavelength filters being arranged for filtering said respective beam portions.

31. The light source assembly of any one of the preceding claims 18-30, wherein said multimode coupler comprises a 50/50 coupler, said coupler preferably being a graded index coupler, or a step index coupler, preferably having cores of at least about 100 m, such as at least about 200 m.

32. The light source assembly of any one of the preceding claims 18-31, wherein said scrambler(s) is/are configured for increasing the number of excited modes in the one or more light beams derived from the broadband light source, preferably said derived and scrambled light beam(s) supplied to said coupler comprises more than 100 modes, such than more than 150 modes.

33. The light source assembly of any one of the preceding claims 18-32, wherein each of the one or more light beams derived from the broadband light source and scrambled in the mode scrambler has a first beam M.sup.2 factor prior to being scrambled in the scrambler and a second beam M.sup.2 factor after being scrambled, wherein the second beam M.sup.2 factor is larger than the first beam M.sup.2 factor, such as at least about 10% larger, such as at least about 50% larger, such as at least about 100% larger or even at least 500% larger.

34. The light source assembly of any one of the preceding claims 18-33, wherein said one or more light beams derived from the broadband light source light beam has/have a bandwidth of up to about 50 nm, such as up to about 20 nm, such as up to about 10 nm, such as up to about 5 nm.

35. The light source assembly of any one of the preceding claims 19-34, wherein the light beam from at least one of the output arms of the multimode coupler is guided to a further coupler for being split into two or more sub-beams.

36. The light source assembly of any one of the preceding claims 18-35, wherein the multimode coupler comprises a pair of output arms, and wherein the light source assembly further comprises at least two further multimode couplers, each having a pair of input arms and a pair of output arms, one arm of the pair of input arms of each of two of such further multimode coupler being in optical communication with respective output arms of the multimode coupler.

37. The light source assembly of any one of the preceding claims 18-36, wherein the light source assembly is as defined in any one of claims 1-17.

Description

[0097] The figures are schematic and are not drawn to scale and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

[0098] FIG. 1a is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises one single light source.

[0099] FIG. 1b is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises two light sources.

[0100] FIG. 1c is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises a supercontinuum light source.

[0101] FIG. 1d is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises a supercontinuum light source and a wavelength filter.

[0102] FIG. 1e is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises a supercontinuum light source and two wavelength filters.

[0103] FIG. 2a is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises a second line coupler.

[0104] FIG. 2b is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises two second line couplers.

[0105] FIG. 3 is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises second line and third line couplers.

[0106] FIG. 4 is a schematic illustration of an embodiment of a light source assembly where the light source arrangement comprises second line, third line and fourth line couplers.

[0107] FIG. 5 is a schematic illustration of an embodiment of a light source assembly where the second line couplers differ from the other couplers of the light source assembly.

[0108] FIG. 6 is a schematic illustration of an embodiment of a light source assembly, which is a variation of the light source assembly of FIG. 3.

[0109] FIG. 7 is a schematic illustration of an embodiment of a light source assembly configured for supplying light at spatially discrete sites for illumination and/or sensing purpose.

[0110] FIG. 8 is a schematic illustration of an embodiment of a light source assembly configured for supplying light at a high number of spatially discrete sites for illumination and/or sensing purpose.

[0111] FIG. 9a show the splitting ratio of a standard 12 splitter and standard deviation thereof.

[0112] FIG. 9b show the splitting ratio of a first coupler of an embodiment of the light source assembly and standard deviation thereof.

[0113] The light source assembly shown in FIG. 1a comprises a light source arrangement 1 a multimode coupler 2 and two mode scramblers 3.

[0114] The multimode coupler 2 comprises two input arms 4 and two output arms 5. The mode scramblers 3 are arranged in the optical path between the light source arrangement 1 and the optical arms 4, at the respective input arms 4. The light source arrangement 1 comprises a single light source (not shown) and at least one splitter (not shown) for splitting the light of the light source to deliver two light beams to the respective input arms 4 of the multimode coupler 2. As illustrated, the light beams delivered from the light source arrangement 1 may be delivered fully or partly by fiber 6 to the multimode coupler 2 via the respective mode scramblers 3. In an alternative embodiment one or both of the mode scramblers 3 may be located before, i.e. optically upstream of the fiber 6.

[0115] The light source assembly shown in FIG. 1b comprises a light source arrangement, a multimode coupler 12 and a mode scrambler 13.

[0116] The multimode coupler 12 comprises two input arms 14 and two output arms 15. The mode scrambler is arranged at one of the input arms 4 whereas no mode scrambler is arranged at the other of the input arms 14.

[0117] The light source arrangement comprises a first section 11a with a first light source and a second section 11b with a second light source. The first light source arrangement section 11a is configured for delivering a light beam to the multimode coupler 12 via the input arm comprising the mode scrambler 13.

[0118] The second light source arrangement section 11b is configured for delivering a light beam to the multimode coupler 12 via the input arm without a mode scrambler. The first light source may be a single mode or a few moded light source, which when scrambled may increase in M.sup.2 value, as well as increase in the number of modes. Advantageously the second light source is configured for delivering a multimode light beam. Preferably, with a higher number of modes, such as 8 or higher. When the light beams are coupled in the multimode coupler 2 the combined light may have a high number of modes for ensuring an even split of light to the output arms 15. As illustrated the light beams delivered from the light source arrangement may be delivered fully or partly by fiber 16 to the multimode coupler 12. In a variation thereof the mode scramblers 13 may be located before, i.e. optically upstream of, the fiber 16.

[0119] The light source assembly shown in FIG. 1c comprises a light source arrangement 21, a multimode coupler 22 and a mode scrambler 23.

[0120] The multimode coupler 22 comprises one input arm 24 and two output arms 5. The mode scrambler is arranged at the input arm 24. The light source arrangement 21 comprises a supercontinuum light source and is arranged for delivering a light beam at least partly via fiber 26 to the input arm 24 of the multimode coupler 22. It should be understood that the supercontinuum light source in a variation thereof may be any broadband source.

[0121] The light source assembly shown in FIG. 1d differs from the light source assembly of FIG. 1c in that the light source arrangement 21a further comprises a wavelength filter 27, e.g. an AOTF. The AOTF is arranged to receive the light beam from the supercontinuum light source via fiber and/or via free space, for wavelength filtering the received light beam and for delivering the derived light beam to the input arm 24 of the multimode coupler 22 via the mode scrambler 23. The derived beam may be delivered by fiber or by free space.

[0122] The light source assembly shown in FIG. 1e comprises a light source arrangement 31, a multimode coupler 32 and two mode scramblers 33.

[0123] The multimode coupler 32 comprises two input arms 34 and two output arms 35. The mode scramblers 33 are arranged at the respective input arms 34.

[0124] The light source arrangement 31 comprises a supercontinuum light source, a splitter 38 and two wavelength filters 37 e.g. AOTFs. The splitter 38 is arranged to split the light from the supercontinuum system in two portions, which may be equal or different. The light beam from the supercontinuum light source may be transmitted via free space to the splitter 38. Each of the AOTFs is arranged to receive one respective portion of light from the splitter and to wavelength filter the received portion of light. The light portions from the splitter 38 may be transmitted via free space to the respective AOTF. The wavelength filtered portions of light are supplied via fibers 36 to the respective arms 34 of the multimode coupler 32 via the respective mode scramblers 33. The AOTF may be configured to filter off corresponding wavelength of light or the AOTF may be configured to be independently tunable. Thereby for example, two different range of wavelengths may be combined in the combiner 32 and split into output portions having substantially equal intensity in the output arms 35.

[0125] The light source arrangements 111a/11b may comprise one or more supercontinuum light sources.

[0126] The light source assembly shown in FIG. 2a comprises a light source arrangement 41, a first multimode coupler 42, a second line multimode coupler 42a and two mode scramblers 43.

[0127] The first multimode coupler 42 comprises two input arms 44 and two output arms 45. The second line multimode coupler 42a comprises one input arm 44a and two output arms 45a.

[0128] The light source arrangement may be any of the light source arrangement disclosed above configured for delivering two light beams, one for each of the two input arms 44 of the first multimode coupler 42. One of the light beams of the light source arrangement 41 may be delivered by free space and/or by fiber to a first arm of the first multimode coupler 42 via one of the scramblers 43. The other one of the light beams of the light source arrangement 41 may be delivered by free space and/or by fiber to a second arm of the first multimode coupler 42 without passing any scrambler, or alternatively, may also include a scrambler.

[0129] One of the output arms 45 of the first multimode coupler 42 is in optical communication via an optical communication pathhere illustrated by a fiber couplingwith the input arm 44a of the second line multimode coupler 42a and the second of the scramblers 43 is arranged in the optical communication path.

[0130] The output light portion at the one of the output arms 45 of the first multimode coupler 42 not in optical connection with any second line coupler has an intensity, which is about twice the intensity of the each of the output beams of the respective output arms 45a of the second line multimode coupler 42a. The light source assembly shown in FIG. 2b is a variation of the light source assembly of FIG. 2a and differs therefrom in that it comprises further scramblers 33 and a further second line coupler 42a. Thus in the embodiment of FIG. 2a a scrambler 43 is arranged at each of the light path from the light source arrangement 41 to the respective input arms 44 to the first multimode coupler 42 and further each of the output arms 45 of the first multimode coupler 42 is in optical communication via an optical communication pathhere illustrated by a fiber couplingwith the input arm 44a of the respective second line multimode couplers 42a and the scramblers 43 are arranged in each of the optical communication paths. The second line multimode couplers 42a are advantageously equal. Thereby the output light portions of each output arm 45a of each second line multimode coupler 44a have substantially equal intensity and may be divided further if desired.

[0131] The light source assembly shown in FIG. 3 comprises a light source arrangement 51, a first multimode coupler 52, two second line multimode couplers 52a, four third line multimode couplers 52b and a plurality of mode scramblers, one arranged in each light path to an input arm of the respective couplers 52, 52a, 52b. In the shown embodiment the first multimode coupler 52 is a 22 coupler and each of the second line and third line couplers 52a, 52b are 12 couplers. It should be understood that each of the couplers 52, 52a, 52b in variations of the embodiment may have a different number of input and/or output arms. Generally, it is desired that second and higher line couplers have one single input arm.

[0132] The light source arrangement 51 may be any of the light source arrangement disclosed above configured for delivering 2 light beams, one for each of the input arms of the first multimode coupler 52. The light may be delivered from the light source 51 to the input arms of the first multimode coupler 52 by fiber and/or via free space.

[0133] Each of the second line couplers is arranged for receiving light from an output arm of the first coupler 52 and for delivering light to two third line couplers. By the embodiment of FIG. 3 N outputs 55b may deliver output light portions of substantially equal intensity wherein N is 8.

[0134] The light source assembly of FIG. 4 is a variation of the light source assembly of FIG. 3 and differs therefrom in that the light source assembly further comprises 8 fourth line multimode couplers 52c each with one input arm and two output arms and where each fourth line multimode coupler 52c is in optical communication via an optical communication pathhere illustrated by a fiber couplingto receive light from an output arm of a third line coupler 52b and wherein a scrambler 53 is arranged in each of the optical communication paths between the third line couplers 52b and the fourth line couplers.

[0135] By the embodiment of FIG. 4 N outputs 55c may deliver output light portions of substantially equal intensity wherein N is 16.

[0136] The light source assembly shown in FIG. 5 comprises a light source arrangement 61, a first multimode coupler 62, two second line multimode couplers 62a, six third line multimode couplers 62b, twelve fourth line multimode couplers 62c and a plurality of mode scramblers 63 one arranged in each light path to an input arm of the respective couplers 62, 62a, 62b, 62c. In the shown embodiment the first multimode coupler 62 is a 22 coupler the two second line coupler are 23 couplers and each of the third line and fourth line couplers 62b, 62c are 12 couplers.

[0137] The light source arrangement 61 may be any of the light source arrangement disclosed above configured for delivering 2 light beams, one for each of the input arms of the first multimode coupler 62. The light may be delivered from the light source 61 to the input arms of the first multimode coupler 62 by fiber and/or via free space.

[0138] Each of the second line couplers 62a is arranged for receiving light from an output arm of the first coupler 62 and for delivering light to the respective input arms of three of the third line couplers 62b. Each third line coupler 62b is arranged for receiving light from an output arm of a second line coupler 62a and for delivering light to the respective input arms of two of the fourth line couplers 62c.

[0139] By the embodiment of FIG. 5 N outputs 65c may deliver output light portions of substantially equal intensity wherein N is 24.

[0140] The light source assembly shown in FIG. 6 is a variation of the embodiment of FIG. 3 and differs therefrom in that the light source arrangement 51a comprises a first and a second light source 59a, 59b and a first and a second filter 57a, 57b arranged for filtering the light of respectively the first and the second light source 59a, 59b. The first and the second light source 59a, 59b may be equal or different e.g. at least one of them may be a broadband light source. The first and the second filter 57a, 57b may be substantially the same or different and preferably include at least one tunable wavelength filter.

[0141] FIG. 7 shows a light source assembly comprising, a first multimode coupler 72, two second line multimode couplers 72a, four third line multimode couplers 72b and a plurality of mode scramblers 73, one mode scrambler 73 arranged in each light path to an input arm of the respective couplers 72, 72a, 72b. A light source arrangement (not shown) is arranged to supply light to each of the input arms of the first multimode coupler 72.

[0142] The light source assembly has M inputs provided by the input arms of the first multimode coupler 72, so here M is 2. The light source assembly has N outputs provided by the output arms 75b of the third line multimode couplers 72b, so here N is 8.

[0143] The light source assembly is arranged for illumination and sensing of pellets 76b in sensing chambers 76. Each of the N outputs delivers an output light portion of essentially equal intensity. The respective output light portion of the N outputs may be supplied at the spatially discreetly arranged sensing chambers 76 for projecting illuminating beams 76a towards the pellets 76b for sensing one or more characteristics of the pellets, such as color, content, structure and etc.

[0144] A light sensor, such as a camera 77 is arranged in each sensing chamber 76 to image light reflected from the pellets 76b and the image data from the respective light sensors 77 are transmitted via wires 78 to a data analyzer 79. The light system may e.g. be arranged for supplying illumination for hyperspectral sensing as described in the PhD thesis by Otto Abildgaard Broadband optical characterization of material properties. DTU Compute PHD-2014; No. 334, DOI: 10.11581/DTU:00000009.

[0145] In an embodiment the pellets comprise pills and the detector system is arranged for detecting if the coating on the pills fulfills one or more quality parameters. The sensing chamber 76 may comprise a pill coater.

[0146] FIG. 8 shows a light source assembly comprising, a first multimode coupler 82, two second line multimode couplers 82a, four third line multimode couplers 82b, eight fourth line multimode couplers 82c and a plurality of mode scramblers 83, one mode scrambler 83 arranged in each light path to an input arm of the respective couplers 82, 82a, 82b, 82c. A not shown light source arrangement is arranged to supply light to each of the input arms of the first multimode coupler 82.

[0147] The light source assembly has M inputs provided by the input arms of the first multimode coupler 82, so here M is 2. The light source assembly has N outputs provided by the output arms 85c of the fourth line multimode couplers 82c, so here N is 16.

[0148] With reference to the above discussed figures and embodiments, it is noted that one or more, including all, of the output arms 5 (FIG. 1a), output arms 25 (FIGS. 1b-1d), output arms 35 (FIG. 1e), output arms 45a (FIGS. 2a, 2b), output arms 55b (FIGS. 3, 6), output arms 55c (FIG. 4), output arms 65c (FIG. 5), output arm 75b (FIG. 7) and output arms 87 (FIG. 8) may be in optical communication with a mode scrambler, e.g., with a mode scrambler that receives light from the optical arm, such as by be positioned at the output of the optical arm.

[0149] The light source assembly is arranged for illumination for supplying light at spatially discrete sites for illumination, e.g. for vehicle lights. Each of the N outputs delivers an output light portion of essentially equal intensity. The respective output light portion of the N outputs may be supplied at the spatially discreetly arranged lights 87 which may e.g. include left headlight, right head light, left rear light and etc.

[0150] The left-hand side of FIG. 9a shows the splitting ratio as a function of wavelength of a standard 12 splitter. Four runs of light were supplied to the splitter and the output light power of one of the output arms as well as the average (mean) was plotted. As seen, the variation between the runs and mean is quite substantial which is a clear indication of a high speckle pattern formation. The right-hand side of FIG. 9a shows the standard deviation as a function of wavelength and confirms that there is a high degree of speckle patter formation.

[0151] The left-hand side of FIG. 9b shows the splitting ration as a function of wavelength of a first coupler of an embodiment of the light source assembly. Four runs of light were supplied to the splitter and the output light power of one of the output arms as well as the average (mean) was plotted. As seen, the variation between the runs and mean is very small, which is a clear indication of a very low speckle pattern formation. The right side of FIG. 9b shows the standard deviation as a function of wavelength and confirms that there is a very low degree of speckle pattern formation.