Optical multiplex system

Abstract

Optical multiplexing system (100; 400) comprising: - a light source (1; 201; 301) having a plurality of light emitting elements (11) of surface emitting lasers; - an optical path changing element (2; 402) configured to change and concentrate the optical paths of the laser light beams emitted by the light emitting elements; and - a light condensing element (4; 204; 304) including a plurality of lens portions (40; 240; 340) arranged to correspond to the respective optical paths of the laser light beams changed by the optical path changing element, and configured to condense the laser light beams through the lens portions (40; 240; 340) to form a multiplexed beam; wherein the light condensing element (4; 204; 304) is arranged at a position where the outermost diameters of adjacent laser light beams emerging from the optical path changing element (2) are in contact with each other; wherein the size of each of the lens regions (40; 240; 340) included in the light condensing element (4; 204; 304) is determined such that the size is equal to an outermost diameter of each of the laser light beams entering the lens regions (40; 240; 340); wherein the laser light beams emerge from the light condensing element (4; 204; 304) such that the outermost diameters of the adjacent laser light beams are in contact with each other; wherein the light-concentrating element is a lens arrangement (4; 204; 304) with the lens regions (40; 240; 340); and where for each of the lens areas (40; 240; 340) the curvature of the lens surface on the side of the light collecting point of the lens region (40; 240; 340) varies depending on the distance between the optical axis of the lens region and the optical axis of the optical multiplexing system, or the surface vertex of the lens surface on the side of the light collecting point of the lens region (40; 240; 340) varies in position in the direction along the optical axis of the optical multiplexing system depending on the distance between the optical axis of the lens region (40; 240; 340) and the optical axis of the optical multiplexing system.

Description

TECHNICAL FIELD

[0001] The present invention relates to an optical multiplexing system. STATE OF THE ART

[0002] An optical multiplexing system is known for achieving high laser power. The optical multiplexing system is configured to combine a plurality of laser light beams emitted from a light source into a single multiplexed beam and couple the multiplexed beam to a light guide or other transmission medium (see, for example, Patent Document 1).

[0003] Patent Document 1 describes an optical power combining system configured to combine laser light beams emitted from M×N light sources to a single light receiving device using a coupling device. The coupling device of the optical power combining system includes a collimating optical element, an anamorphic optical element, and a light-collecting optical element. The anamorphic optical element is arranged such that the magnification in the direction of the array of M elements is greater than the magnification in the direction of the array of N elements.

[0004] Patent Document 2 describes a method and apparatus for a filterless parallel WDM multiplexer. The filterless multiplexer comprises two or more lens planes that allow light to be directed into a series of waveguides. The filterless multiplexer can have either refractive or diffractive lenses.

[0005] Patent Document 3 describes an optical multiplexing device and a projector. The optical multiplexing device includes: a light source section that uses light source units to emit collimated beams; a first lens section that converges the collimated beams entering at different incident angles from each other to define converging positions; and a second lens section that has focal points corresponding to the converging positions, respectively. The first and second lens sections form a reduction optical system, and an optical axis of the second lens section, which is directed to the corresponding focal point at one of the converging positions, extends along another optical axis of the second lens position, which is directed to the corresponding focal point at another of the converging positions.

[0006] Patent Document 4 describes a laser module equipped with: a plurality of laser elements, each emitting optical beams; a collimating optical system that collimates the thus emitted optical beams; and a light-collecting optical system that collects the thus collimated optical beams. The laser elements are surface-emitting photonic crystal lasers (PCSELs). The laser elements are arranged in a hexagonal lattice on a plane of a base. STATE OF THE ART Patent document 1: JP 2005 - 114 977 A Patent document 2: US 2004 / 0 218 854 A1 Patent document 3: US 2012 / 0 236 212 A1 Patent document 4: WO 2016 / 129 323 A1 BRIEF DESCRIPTION OF THE INVENTION Problems to be solved by the invention

[0007] However, in the optical power combining system according to Patent Document 1, the optical element reduces the beam diameters of the laser light beams. Therefore, for each laser light beam, both the beam diameter and the beam pitch are reduced in the same proportion.

[0008] In the optical power combining system according to Patent Document 1, the beam pitch is not relatively reduced. That is, the relationship between the beam diameter and the beam pitch is not changed. Therefore, in the multiplexed beam, the beam occupancy in the total beam diameter is not changed. This makes it difficult to reduce the light gathering angle and also improve the light gathering property.

[0009] The present invention has been conceived in view of these problems and has the object of providing an optical multiplexing system capable of forming a multiplexed beam with a high light gathering property. Means to solve the problems

[0010] To solve the above-mentioned problems, according to the present invention, there is provided an optical multiplexing system according to claim 1. Advantageous embodiments are set out in dependent claims 2 to 12. Effect of the invention

[0011] With the optical multiplexing system of the present invention, it is possible to form a multiplexed beam with a high light gathering property. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an arrangement of an optical multiplexing system according to a first embodiment; Fig. Fig. 2 shows a light source in the first embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 3 shows a lens arrangement in the first embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 4 shows a light source in a second embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 5 shows a lens arrangement in the second embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 6 shows a light source in a third embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 7 shows a lens arrangement in the third embodiment, viewed from the direction of the optical axis A of the optical multiplexing system; Fig. 8 shows an arrangement of an optical multiplexing system according to a fourth embodiment; Fig. 9 shows how laser light beams that have passed through the lens array are collected in a case where the lens array has an inappropriate shape in the first embodiment; Fig. 10 shows a first example of a suitable shape of the lens arrangement in the first embodiment, and Fig. 11 shows a second example of a suitable shape of the lens arrangement in the first embodiment. Description of the embodiments

[0012] Hereinafter, details of embodiments of an optical multiplexing system disclosed in the present application will be described with reference to the accompanying drawings. However, it should be noted that the embodiments described below are merely examples, and the present invention is not limited to these embodiments.

[0013] In the following embodiments, an optical multiplexing system is described in particular, which is constructed to collect or condense a plurality of laser light beams emitted from a light source into a multiplexed beam. Light collection properties of an optical multiplex system

[0014] In an optical multiplexing system, laser light beams emitted by light-emitting elements contained in a light source are multiplexed to form a high-power multiplexed beam. In this case, as described above, it is important that the multiplexed beam has a high light gathering property.

[0015] A beam parameter product (BPP) is an index for evaluating the light gathering performance of a beam. BPP is defined as the product of a beam radius and a light gathering angle, or a product of a beam radius and a divergence angle. As can be seen from this definition, when the beam radius is constant, decreasing the light gathering angle is effective for increasing the light gathering performance.

[0016] The same applies when multiplexing multiple laser beams. When multiple laser beams are spatially condensed to form a multiplexed beam with high light gathering properties, the laser beams are condensed in such a way that the distances between adjacent laser beams are reduced. This allows the beam coverage in the multiplexed beam to be increased. In particular, when the distances between neighboring laser beams are zero, the multiplexed beam can exhibit the highest beam coverage in terms of beam diameter. That is, the outermost diameters of the neighboring laser beams are in contact with each other.

[0017] In other words, by increasing the beam coverage in the beam diameter of the multiplexed beam, the light gathering angle of the multiplexed beam can be reduced. Thus, a multiplexed beam with high light gathering properties can be obtained. Embodiment 1 Configuration of an optical multiplexing system 100

[0018] Fig. 1 shows an arrangement of an optical multiplexing system 100 according to a first embodiment of the present invention. Fig. 1 shows a cross section with an optical axis A of the optical multiplexing system 100. Referring to Fig. 1, the overall structure of the optical multiplexing system 100 is now described.

[0019] The optical multiplexing system 100 includes a light source 1, a lens 2, and a lens array 4. The optical multiplexing system 100 may include a light guide 5. The light source 1 includes a plurality of light-emitting elements 11. The lens 2 is an example of an optical path changing element. The lens array 4 is an example of a light converging element. The light guide 5 is an example of a transmission device.

[0020] The light source 1 includes the light-emitting elements 11, which are two-dimensional photonic crystal surface-emitting lasers. In the first embodiment, the light-emitting elements 11 are arranged on a surface 31 of a heat sink 3. In this case, the surface 31 is a single surface. Furthermore, the light-emitting elements 11 are arranged so that they are aligned in directions parallel to the optical axis A. In this way, the heat sink 3 counteracts heating of the light-emitting elements 11.

[0021] Fig. 2 shows the light source 1 with the light emitting elements 11 in the view from the direction of the optical axis A of Fig. 1. In the first embodiment, the light source 1 includes 19 light-emitting elements 11. Further, the 19 light-emitting elements 11 are arranged at intervals in a hexagonal lattice pattern. However, the number of the light-emitting elements 11 and an arrangement form thereof are not limited to those described above.

[0022] As in Fig. As shown in Figure 1, the optical axis Ae of each light-emitting element 11 is perpendicular to the surface 31. Therefore, the light-emitting elements 11 emit laser light beams in a direction perpendicular to the surface 31. The optical axes Ae of the light-emitting elements 11 are parallel to each other. Furthermore, the optical axes Ae of the light-emitting elements 11 are parallel to the optical axis A of the optical multiplexing system 100.

[0023] The laser light beams emitted by light source 1 enter lens 2. Lens 2 has a light-collecting function. Lens 2 is arranged perpendicular to the optical axis A of optical multiplexing system 100. That is, the optical axis Ad of lens 2 is parallel to the optical axis A of optical multiplexing system 100.

[0024] The lens 2 changes the propagation directions of the laser light beams emitted from the light source 1. That is, the lens 2 changes the optical paths of the laser light beams emitted from the light source 1. Specifically, the lens 2 changes the propagation directions of the laser light beams emitted from the light source 1 toward a center 50 of an incident surface 51 of the light guide 5. In this way, when the lens assembly 4 to be described later is omitted, the optical paths of the laser light beams are concentrated on the center 50 of the incident surface 51 of the light guide 5 after passing through the lens 2.

[0025] The laser light beams, whose optical paths have been changed by the lens 2, enter the lens array 4. The lens array 4 is arranged so that it is perpendicular to the optical axis A of the optical multiplexing system 100. The lens array 4 includes a plurality of lens regions 40 arranged in the same plane ( Fig. 3).

[0026] The plurality of light-emitting elements 11 of the light source 1 and the plurality of lens regions 40 of the lens array 4 have a one-to-one correspondence. The lens regions 40 of the lens array 4 are arranged at positions corresponding to the respective optical paths of the laser light beams whose optical paths have been changed by the lens 2.

[0027] Fig. 3 shows the lens arrangement 4 in the view from the direction of the optical axis A of Fig. 1. In the first embodiment, the light source 1 includes 19 light-emitting elements 11. Therefore, the lens array 4 also includes 19 lens regions 40. Each lens region 40 has a light-collecting function. Furthermore, the lens regions 40 are arranged so that they are adjacent to each other on the same plane. The effective area of the lens array 4 is smaller than the light-emitting area of the light source 1.

[0028] As in Fig. 1, the laser light beams entering the respective lens regions 40 of the lens arrangement 4 pass through the lens arrangement 4, being condensed into a multiplexed beam on the incident surface 51 of the light guide 5.

[0029] The optical fiber 5 is a transmission optical fiber. The optical fiber 5 transmits the multiplexed beam. That is, the optical fiber 5 couples and transmits the collected laser light beam. Furthermore, in the first embodiment, the optical fiber 5 is a multimode optical fiber. In the multimode optical fiber, the light is split into multiple modes to propagate in the core.

[0030] A multimode optical fiber is available in a step-index type and a graded-index type. The step-index type corresponds to an optical fiber with a uniform core refractive index. The graded-index type corresponds to an optical fiber with a uniformly distributed core refractive index. The specification of the optical fiber 5 can be selected accordingly, taking into account the properties and the number of light-emitting elements 11. Two-dimensional photonic crystal surface emitting laser

[0031] The following describes the two-dimensional photonic crystal surface-emitting lasers used in the first embodiment. The two-dimensional photonic crystal surface-emitting laser is a surface-emitting type semiconductor laser in which a periodic structure with approximately one oscillation wavelength is provided near the active layer. This periodic structure is referred to as a "photonic crystal structure."

[0032] Generally, a semiconductor laser can achieve higher power by increasing its light-emitting area. However, a practical vertical-cavity surface-emitting laser (VCL) has the problem that the light-gathering property decreases as the light-emitting area is increased. Therefore, the VCL cannot simultaneously achieve high power and high light-gathering property.

[0033] In contrast, the two-dimensional photonic crystal surface-emitting laser is capable of maintaining its light-gathering properties in principle even when the light-emitting area is increased. Therefore, high power and high light-gathering properties can be expected from a two-dimensional photonic crystal surface-emitting laser as a laser light source.

[0034] Typical features of the two-dimensional photonic crystal surface-emitting laser include the size of the light emission area, which is several hundred µm in diameter. Furthermore, the beam quality is around M 2 -value of about 1 to about 5. For example, if the oscillation wavelength is 940 nm, the size of the light emission area is 300 µm in diameter and the beam quality is 2 in the M 2-value, the divergence angle of the emitted beam is approximately 0.5 degrees at full angle. The two-dimensional photonic crystal surface-emitting laser has a large light emission area and good beam quality, so that an emission beam with a high straight-line property can be obtained. The phrase "good beam quality" means that the M 2 -value is small.

[0035] Furthermore, in the two-dimensional photonic crystal surface-emitting laser, for example, if the size of the light-emitting region is increased to a diameter of 1 mm, it is expected that a power of the 10 W class can be obtained. Therefore, the two-dimensional photonic crystal surface-emitting laser can be a laser light source with high power and high light gathering property. Arrangement interval of the light-emitting elements

[0036] To operate the semiconductor laser satisfactorily at high power, it is important to take measures to combat heat generation. In a semiconductor laser, 40% to 60% of the input power is converted into heat. As the power increases, heat generation increases further. Therefore, the light-emitting elements of the high-power semiconductor laser are preferably mounted on a cooling structure that includes a base or heat sink.

[0037] In the cooling structure, the heat generated by the light-emitting elements is transferred, dissipated, and radiated. As the heat generated increases, the cooling structure is enlarged. When using a two-dimensional photonic crystal surface-emitting laser to achieve a power of 10 W, it can be calculated that the arrangement interval of the light-emitting elements 11 for heat radiation must be approximately several mm.

[0038] Furthermore, the two-dimensional photonic crystal surface-emitting laser is constructed such that an electrode structure for power supply is provided around a light-emitting surface. If the electrode is made of a metal that does not transmit light, the adjacent light-emitting elements 11 must be arranged so that they do not block the laser light beam at this location.

[0039] For the above-mentioned reason, in the arrangement of the light-emitting elements 11 of the two-dimensional photonic surface-emitting lasers, it is necessary that the light-emitting elements 11 be arranged so that they are close to each other, while ensuring the required distances between the adjacent light-emitting elements 11. In other words, the light-emitting elements 11 must be arranged at intervals. As described above with reference to Fig. 2, the light emitting elements 11 are arranged at intervals in the first embodiment. Operation of the optical multiplex system 100

[0040] Next, the operation of the optical multiplexing system 100 according to the first embodiment will be described. As shown in Fig. As shown in Figure 2, the optical multiplexing system 100 collects the plurality of laser light beams emitted from the light-emitting elements 11 arranged at intervals to thereby form the multiplexed beam. In this case, the light collecting property of the multiplexed beam is improved by increasing the beam coverage in the diameter of the multiplexed beam.

[0041] First, the reference numerals used in the optical multiplexing system 100 are described. Fig. 1. The focal length of lens 2 is designated F2. Furthermore, although Fig. 1 not shown, the focal length of the lens arrangement 4 is designated F4.

[0042] The distance from each light-emitting element 11 of the light source 1 to the lens 2 is denoted by L1. The distance from the lens 2 to the lens array 4 is denoted by L2. The distance required to collect the laser light beams that have passed through the lens array 4 is denoted by L3.

[0043] The diameter of each laser light beam entering the lens array 4 is denoted by W2. The diameter of the laser light beam corresponds to a beam diameter. The size of each lens region 40 of the lens array 4 is denoted by D4. D4 is, for example, a diameter of each lens region 40. The arrangement interval of the light-emitting elements 11 arranged on the surface 31 of the heat sink 3 is denoted by P.

[0044] Furthermore, although in Fig. 1 not shown, a central light beam of each of the 19 laser light beams emitted from the 19 light emitting elements 11, with A n The suffix n is n = 1, 2, ..., N. N is the number of light-emitting elements 11, which in the first embodiment is N = 19. The center light beam refers to a center line passing through the center of the beam diameter in the laser light beam.

[0045] In the first embodiment and the second to fourth embodiments to be described later, the beam diameter of each laser light beam is defined as a diameter such that the encompassed power of the light intensity distribution is 86.5%. Furthermore, the "laser light beam" herein means light with the beam diameter thus defined. In this case, the outermost diameter of the laser light beam refers to a diameter at which the encompassed power of the light intensity distribution is 86.5%. The beam diameter of the multiplexed beam is defined similarly.

[0046] Next, the operation of the optical multiplexing system 100 will be described. The light-emitting elements 11 emit laser light beams parallel to the optical axis A of the optical multiplexing system 100. The laser light beams enter the lens 2 perpendicularly. That is, the laser light beams emitted by the light-emitting elements 11 are parallel to the optical axis Ad of the lens 2. In this case, the light-emitting elements 11 are two-dimensional photonic crystal surface-emitting lasers.

[0047] The directions of the middle light rays A n of the laser light rays that have entered the lens 2 are changed before the laser light rays exit the lens 2. Specifically, the middle light rays A nof the laser light rays emerging from the lens 2 are condensed to a point which is located at a distance F2 from the lens 2. This means that the middle light rays A n the laser light rays are collected at the position which is away from the lens 2 by the distance F2.

[0048] In the first embodiment, the incident surface 51 of the light guide 5 is arranged at the position away from the lens 2 by the distance F2. Therefore, in the absence of the lens arrangement 4, the average light rays A n the laser light beams emerging from the lens 2 are condensed in the center 50 of the incident surface 51 of the light guide 5.

[0049] Furthermore, in the laser light beams emerging from the lens 2, the adjacent laser light beams approach each other along their path. Then, at the position away from the lens 2 by the distance L2, the outermost diameters of the adjacent laser light beams are in contact with each other.

[0050] The lens array 4 is arranged at a position spaced apart by the distance L2 from the lens 2. In other words, the lens array 4 is arranged at a position where the outermost diameters of the adjacent laser light beams exiting the lens 2 are in contact with each other. The laser light beams then enter the corresponding lens regions 40 of the lens array 4.

[0051] In the lens array 4, the 19 lens regions 40 are integrally molded. When the lens array 4 is manufactured by integral molding, a support structure between the lens regions 40 is not required. Furthermore, an ineffective region that does not have a lens effect can be reduced or eliminated.

[0052] In the first embodiment, the size D4 of each lens region 40 of the lens array 4 is set to be equal to the beam diameter W2 of the incident laser light beam. Therefore, the adjacent laser light beams that have entered the lens array 4 exit the lens array 4 with their outermost diameters in contact with each other.

[0053] Furthermore, each middle light ray A n of the laser light beams through the center of the corresponding lens area 40 in the lens arrangement 4. Thus, each central light beam A nof the laser light rays just inside the lens arrangement 4. The middle light rays A n the laser light beams that have passed through the lens areas 40 of the lens arrangement 4 are collected at a focal point position of the lens arrangement 4.

[0054] Furthermore, each laser light beam enters the corresponding lens region 40 of the lens array 4. Each laser light beam enters only the corresponding lens region 40 of the lens array 4. Therefore, each laser light beam passes through the lens array 4 in such a way that its energy loss is minimized. The laser light beams that have passed through the lens array 4 are condensed into the multiplexed beam at the center 50 of the incident surface 51 of the light guide 5. Their energy is concentrated at the center 50 of the incident surface 51 of the light guide 5.

[0055] In the first embodiment, the conditions of the optical multiplexing system 100 are set so that the sum of the distances L2 and L3 is equal to the focal length F2.

[0056] The conditions of the optical multiplexing system 100 are set depending on the characteristics of the light source 1 and the desired characteristics of the multiplexed beam. The "characteristics of the light source 1 and the multiplexed beam" include, for example, the number of light-emitting elements to be multiplexed, the beam quality, the beam diameter, and the oscillation wavelength.

[0057] Once these values have been determined, the beam diameters W2 of the laser light beams entering the lens array 4 can be calculated. In this way, the size D2 of the lens regions 40 in the lens array 4 and the arrangement interval P of the light-emitting elements 11 can be determined.

[0058] In the optical multiplexing system 100 described above, the laser light beams emitted by the light-emitting elements 11 are converged at a single point, thereby forming a multiplexed beam. At the point where the laser light beams are converged into a single point, each laser light beam forms a smallest point.

[0059] In the first embodiment, the 19 light-collecting spots of the 19 laser light beams emitted by the 19 light-emitting elements 11 overlap at one point. That is, the light-collecting spots of the laser light beams overlap each other. Here, the energies of the laser light beams emitted by the 19 light-emitting elements 11 are concentrated at one point with little loss.

[0060] Furthermore, after passing through the lens array 4, the laser light beams exit such that the outermost diameters of the adjacent laser light beams are in contact with each other. This allows the beam coverage in the beam diameter of the multiplexed beam to be increased. That is, the light gathering property of the multiplexed beam can be enhanced.

[0061] If an actual lens with an appropriate thickness is used, the mean light rays A n The laser light beams entering the lens at an angle are slightly offset parallel between the front and back of the lens. This situation can be counteracted by adjusting the arrangement pitch P of the light-emitting elements 11 on the heat sink 3.

[0062] By adjusting the arrangement interval P of the light emitting elements 11, the central light beam A nThe laser light beams are condensed at an assumed position after passing through the lens array 4. In this case, the assumed position is the center 50 on the incident surface 51 of the light guide 5. After adjusting the arrangement interval P of the light-emitting elements 11, the arrangement interval P is uneven across all the light-emitting elements 11. However, this arrangement does not pose a problem.

[0063] In the above description, the "beam diameter" is defined as a width such that the encompassed power of the light intensity distribution is 86.5%. However, the definition of the beam diameter is not limited to this. The beam diameter can be defined depending on the required light utilization efficiency or beam quality of the multiplexed beam.

[0064] Furthermore, not every lens area 40 in the lens arrangement 4 has to be circular, as in Fig. 3. For example, each lens region 40 may be formed into a hexagonal shape with a circular lens region. For example, each lens region 40 may be formed into a hexagonal shape inscribed with a circular lens. Further, a partial side of the hexagonal shape may have an arc shape. Coupling to the optical fiber

[0065] The light guide 5 is arranged such that the center 50 of its incident surface 51 coincides with the position where the laser light beams emitted by the light-emitting elements 11 are condensed at one point to form the multiplexed beam. The center 50 of the incident surface 51 of the light guide 5 corresponds to the position where the laser light beams emitted by the light-emitting elements 11 are condensed to form the multiplexed beam.

[0066] In the light guide 5, the light-collecting spot diameter of the laser light beam and the core diameter of the light guide have a corresponding relationship, as described below. The light-collecting spot diameter of the laser light beam is the beam diameter of the multiplexed beam. Furthermore, in the light guide 5, the NA during light condensation of the optical multiplexing system 100 and the allowable NA of the light guide 5 have a corresponding relationship, as described below. "NA" refers to the numerical aperture.

[0067] Preferably, the core diameter of the optical fiber 5 ensures a coupling efficiency of 90% to 99.5%, based on the total power of the multiplexed beam.

[0068] When a large core diameter is selected, the beam coupling efficiency at the incident surface 51 of the optical fiber 5 is close to 100%. However, the laser light beam entering the optical fiber 5 is reflected at the interface between the core and the cladding during propagation within the fiber or optical fiber 5. Therefore, the laser light beam is scattered to a cross section perpendicular to the transmission direction. This reduces the light gathering property of the laser light beam.

[0069] Conversely, if a smaller core diameter is selected, the energy loss of the laser light beam propagating within the light guide 5 increases. Furthermore, the laser light beam that has not entered the core of the light guide 5 is radiated toward or around the cladding. As a result, the laser light beam that has not entered the core of the light guide 5 causes heating or burning in the vicinity of the incident surface 51.

[0070] Furthermore, it is preferable that the allowable NA of the optical fiber 5 be 1.2 to 3 times the NA when collecting the multiplexed beam. If the allowable NA of the optical fiber 5 is too large, coupling into a higher-order mode is likely to occur, depending on the installation state of the optical fiber 5, for example. Therefore, the light collection property when transmitting the laser light beam is deteriorated.

[0071] If the allowable NA of the optical fiber is equal to or smaller than the NA when collecting the multiplexed beam, energy losses will occur during coupling or transmission of the laser light beam. As a result, damage to the optical fiber 5 or damage to surrounding components may occur due to a light leakage area.

[0072] In this way, the laser light beams are efficiently coupled to the light guide 5. The laser light beams then propagate within the light guide 5, thus suppressing any reduction in beam quality. A multiplexed beam with high power and high light gathering properties is output from an exit surface of the light guide 5.

[0073] When the number of light-emitting elements 11 is from about 2 to about 20, it is preferable to use a large-mode area optical fiber as the optical fiber 5. A large-mode area optical fiber is a type of multimode optical fiber. The large-mode area optical fiber has a large core diameter of several tens of µm and a small allowable NA of about 0.15 or less. The large-mode area optical fiber allows transmission only in a low-order mode. While the multiplexed beam is transmitted in the optical fiber, coupling to a high-order mode is suppressed. This allows the light gathering property of the output laser light beam to be kept high. Specific numerical examples

[0074] Next, specific numerical examples in the optical multiplexing system 100 according to the first embodiment will be described. Numerical Example 1

[0075] Table 1 shows a first embodiment of the optical multiplexing system 100. The light emitting elements 11 of the light source 1 are arranged in a hexagonal lattice shape. Table 1 Symbol Wert W0 1 mm M 2 2 N 19 P 1,6 mm F4 3,3 mm F2 60 mm L1 2 mm L2 57 mm L3 2,7 mm D4 0,15 mm

[0076] In Table 1, the beam diameter of each light-emitting element 11 of the light source 1 is represented by W0. The beam quality is represented by M 2 The number of light-emitting elements 11 is represented by N.

[0077] In the case of the specification according to Table 1, the characteristics of the optical multiplexing system 100 are as follows. The size of the light collection spot is approximately 48 µm in diameter. The NA with light collection is approximately 0.13. The characteristics of the light guide 5 are exemplary as follows. The core diameter of the light guide 5 is approximately 50 µm in diameter. The allowable NA of the light guide is NA = 0.16. Numerical example 2

[0078] Table 2 shows a second example of the specification of the optical multiplexing system 100. The light emitting elements 11 of the light source 1 are arranged in a hexagonal lattice shape. Table 2 Symbol Wert W0 0,2 mm M 2 1,5 N 19 P 0,7 mm F4 5,5 mm F2 35 mm L1 2 mm L2 28,5 mm L3 6,4 mm D4 0,26 mm

[0079] In the case of the specification according to Table 2, the characteristics of the optical multiplexing system 100 are as follows. The size of the light collection spot is approximately 44 µm in diameter. The NA with light collection is approximately 0.1. The characteristics of the light guide 5 are exemplary as follows. The core diameter of the light guide 5 is approximately 50 µm in diameter. The allowable NA of the light guide is NA = 0.12. Effects of the first embodiment

[0080] As described above, the optical multiplexing system 100 according to the first embodiment of the present invention includes a light source, an optical path changing element, and a light condensing element. The light source includes a plurality of light-emitting elements. The light-emitting elements are two-dimensional photonic crystal surface-emitting lasers.

[0081] The optical path changing element is configured to change the optical paths of the laser light beams emitted by the light-emitting elements and to converge or condense them. The light converging element is configured to converge the laser light beams emerging from the optical path changing element into a multiplexed beam through a plurality of lens sections.

[0082] With the above features, the optical multiplexing system 100 according to the first embodiment of the present invention is an optical multiplexing system with a high light gathering property. Furthermore, the optical multiplexing system 100 is a high-performance optical multiplexing system.

[0083] Furthermore, the light condensing element is arranged at a position where the outermost diameters of adjacent laser light beams emerging from the optical path changing element are in contact with each other. This further enhances the light condensing property of the multiplexed beam.

[0084] Furthermore, the size of each of the lens regions included in the light condensing element is determined so that the size is equal to the beam diameter of each of the laser light beams entering the lens regions. Furthermore, the laser light beams exit the light condensing element with their outermost diameters in contact with each other. This further enhances the light gathering property of the multiplexed beam.

[0085] Furthermore, a lens is used as an optical path modification element. This allows the optical path of the laser light beams to be modified with high precision using simple means.

[0086] Furthermore, a lens array is used as a light-concentrating element. This minimizes the ineffective area between the lens sections, allowing the laser light beams to be brought closer together. This can increase the light-collecting capacity of the multiplexed beam.

[0087] Furthermore, the light-emitting elements are arranged in a hexagonal lattice pattern. Furthermore, the light-emitting elements are arranged as densely as possible. Therefore, the laser light beams enter the optical path change element as a multiplexed beam, ensuring that the laser light beams are as close to each other as possible.

[0088] In this way, a multiplexed beam with high light gathering properties can also be easily achieved. The term "dense" generally refers to a crowded and tightly packed state.

[0089] Furthermore, a fiber with a large mode area is used as the optical fiber. This allows the light gathering properties of the laser beam emitted by the fiber to be maintained at a high level. Embodiment 2Arrangement with square grid shape

[0090] Fig. Fig. 4 shows an arrangement of light emitting elements 11 included in a light source 201 in an optical multiplexing system according to a second embodiment of the present invention. Fig. 5 shows an arrangement of lens regions 240 in a lens arrangement 204 in the second embodiment.

[0091] In the second embodiment, the light source 201 includes 16 light-emitting elements 11. The 16 light-emitting elements 11 are arranged in a square lattice pattern on the surface 31 of the heat sink 3. For example, the surface 31 is a single surface.

[0092] The beam coverage achieved by the arrangement with the square grid shape in the second embodiment is lower than the beam coverage achieved by the arrangement with the hexagonal grid shape in the first embodiment. However, if Fig. 4 and Fig. 5 of the second embodiment, the beam occupancy in Fig. 5 compared to Fig. 4 increased. Therefore, in the second embodiment, when the arrangement having the hexagonal lattice shape cannot be adopted as the arrangement of the light emitting elements 11 due to various limitations such as the performance of a device used when arranging the light emitting elements 11, the electrode structure of the light source 1, or the required number of light emitting elements 11, the beam occupancy can be increased to some extent to increase the light collecting property of the multiplexed beam. Embodiment 3Arc-shaped arrangement

[0093] Fig. Fig. 6 shows an arrangement of light emitting elements 11 included in a light source 301 in an optical multiplexing system according to a third embodiment of the present invention. Fig. 7 shows an arrangement of lens regions 340 in a lens arrangement 304 in the third embodiment.

[0094] In the third embodiment, the light source 301 includes ten light-emitting elements 11. The ten light-emitting elements 11 are arranged in a (circular) circumference at equal angles on the surface 31 of the heat sink 3. The surface 31 is, for example, a single surface.

[0095] The beam coverage obtained by the arrangement with the circumference at equal angles in the third embodiment is lower than the beam coverage obtained by the arrangement with the hexagonal lattice shape in the first embodiment. However, if Fig. 6 and Fig. 7 of the third embodiment, the beam occupancy in Fig. 7 compared to Fig. 6 increased.

[0096] Therefore, in the third embodiment, when the arrangement having the hexagonal lattice shape cannot be adopted as the arrangement of the light-emitting elements 11 due to various limitations such as the performance of a device used when arranging the light-emitting elements 11, the electrode structure of the light source 1, or the required number of light-emitting elements 11, the beam occupancy can be increased to some extent to increase the light gathering property of the multiplexed beam. Embodiment 4Polyhedral prism

[0097] Fig. 8 shows a cross section along a plane containing the optical axis A in an optical multiplexing system 400 according to a fourth embodiment of the present invention.

[0098] The optical multiplexing system 400 includes the light source 1, a polyhedral prism 402, and the lens array 4. The optical multiplexing system 400 may include the light guide 5.

[0099] In the fourth embodiment, the polyhedral prism 402 is used instead of the lens array 2 of the first embodiment. Other components of the multiplexing optical system 400 are identical or similar to those of the multiplexing optical system 100. Therefore, the same or similar components as those of the multiplexing optical system 100 are denoted by the same reference numerals, and their descriptions are omitted.

[0100] The distance from each light emitting element 11 of the light source 1 to the polyhedral prism 402 is denoted by L 401 Furthermore, the distance from the polyhedral prism 402 to the lens arrangement 4 is denoted by L 402 Furthermore, the distance from the lens arrangement 4 to the incident surface 51 of the light guide 5 is denoted by L403 designated.

[0101] The polyhedral prism 402 is arranged between the light source 1 and the lens array 4. The polyhedral prism 402 has prism surfaces Pn corresponding to the respective light-emitting elements 11. The suffix n is n = 1, 2, 3, ..., N. N is the number of light-emitting elements 11. Furthermore, the suffix n also corresponds to the suffix n of the central light beam An. That is, the suffix n of the prism surfaces P n is identical to the suffix n of the center light beam A n .

[0102] The polyhedral prism 402 has an incident surface 421 and an exit surface 422. The incident surface 421 of the polyhedral prism 402 is a flat surface perpendicular to the optical axis A of the optical multiplexing system 400. The exit surface 422 of the polyhedral prism 402 includes the prism surfaces P n . The prism surfaces P nare surfaces corresponding to the respective N light emitting elements 11, and they are aligned differently to each other.

[0103] In this case, the inclinations of the prism surfaces P1 to P n with respect to the optical axis A so that the mean light rays A n of the laser light beams emitted by the light-emitting elements 11 on the optical axis A at a focal length F 402 of the polyhedral prism 402. The position on the optical axis A at the focal length F 402 from the polyhedral prism 402 corresponds to a light collection position. In the fourth embodiment, the light collection position corresponds to the center 50 of the incident surface 51 of the light guide 5.

[0104] The laser light beams emitted by the light-emitting elements 11 enter perpendicularly into the incident surface 421 of the polyhedral prism 402. The laser light beams that have entered the polyhedral prism 402 exit the corresponding prism surfaces P n out of.

[0105] The laser light beams emerging from the polyhedral prism 402 move toward the above-mentioned light collection position. If the lens arrangement 4 is missing, the central light beams A n the laser light beams emerging from the polyhedral prism 402 are condensed in the center 50 of the incident surface 51 of the light guide 5.

[0106] In the laser light beams emerging from the polyhedral prism 402, the neighboring laser light beams approach each other on their path. At the position spaced apart by the distance L 402 from the polyhedral prism 402, the outermost diameters of the neighboring laser light beams then touch each other.

[0107] The lens arrangement 4 is arranged at the position which is spaced apart by the distance L 402 from the polyhedral prism 402. In other words, the lens array 4 is arranged at a position where the outermost diameters of the adjacent laser light beams exiting the polyhedral prism 402 are in contact with each other. Then, the laser light beams enter the corresponding lens regions 40 of the lens array 4.

[0108] Each laser light beam passes through the lens array 4 in such a way that its energy loss is minimized. The laser light beams that have passed through the lens array 4 are condensed into the multiplexed beam at the center 50 of the incident surface 51 of the light guide 5. Their energy is concentrated at the center 50 of the incident surface 51 of the light guide 5.

[0109] In the fourth embodiment, the conditions of the optical multiplexing system 400 are set such that the sum of the distances L 402 and L 403 equal to the focal length F 402 The conditions of the optical multiplexing system 400 are as follows: the focal length F 402 , the focal length F 404 the lens arrangement 4, the distance L 401 , the distance L 402 and the distance L 403 .

[0110] The conditions of the optical multiplexing system 400 are determined depending on the characteristics of the light source 1 and the desired characteristics of the multiplexed beam. As described above, a multiplexed beam with a high light gathering property can be obtained, similar to the first embodiment.

[0111] The incident surface 421 of the polyhedral prism 402 is not limited to a flat surface. For example, the incident surface may be a polyhedron.

[0112] Furthermore, the optical path changing element in the present invention is a lens 2 in the first to third embodiments and a polyhedral prism 402 in the fourth embodiment. However, the optical path changing element is not limited to these two elements. For example, a diffractive optical element can be used as the optical path changing element. By using the diffractive optical element, the thickness of the optical path changing element can be reduced.

[0113] In the above-mentioned embodiments, in some cases, a term indicating a positional relationship between elements, such as "parallel" or "perpendicular," or a term indicating a shape of an element is used, but these terms are intended to include ranges that take into account manufacturing tolerances, assembly variations, and the like. Therefore, when a positional relationship between elements or a shape of an element is described in the claims, the claims are intended to include the ranges taking into account manufacturing tolerances, assembly variations, and the like. Method for designing the shape of the lens array

[0114] Finally, a method for designing the shape of the lens array 4 in the above-mentioned first embodiment will be described. In the first embodiment, in order to enhance the light gathering property of the multiplexed beam, it is necessary to design the shape of the lens array 4 and the shapes of the lens surfaces of the lens regions 40 included in the lens array 4. The design method described below can be similarly applied to the second to fourth embodiments.

[0115] Fig. Fig. 9 illustrates how the laser light beams that have passed through the lens array 4 are condensed in the case where the lens array 4 has an inappropriate shape in the first embodiment. Fig. 9, in the lens regions 40 included in the lens array 4, the lens region 40R1 arranged on the optical axis A and the lens regions 40R2 and 40R3 arranged outside the optical axis A all have the same shape and lie in the same plane.

[0116] In Fig. 9, the laser light beam that has passed through the lens region 40 R1 arranged on the optical axis A forms a smallest point on the incident surface 51 of the light guide 5. In contrast, the laser light beams that have passed through the lens regions 40 R2 and 40 R3 arranged away from the optical axis A form smallest spots before arriving at the incident surface 51. In addition, the laser light beams do not intersect at a point, but are shifted.

[0117] If the laser light beam enters the lens region 40 at an angle to the optical axis of the lens region 40, aberrations such as field curvature, astigmatism, or coma (asymmetry error) may occur. In the optical multiplexing system with aberrations, the light gathering spot is disadvantageously enlarged. This increases the beam diameter at the incident surface 51 of the light guide 5, thus reducing the light gathering property of the multiplexed beam.

[0118] As a method for correcting these aberrations, methods that combine a plurality of lenses or form a lens surface into an aspherical surface are known. However, in an arrangement using a lens array, a method of using a plurality of lenses to correct the aberrations is not suitable for the following reasons. The lens array is an expensive optical element, and the relative positions of the plurality of lens arrays must be adjusted with high precision. Of the above-mentioned aberrations, curvature of field is known to be an aberration that cannot be corrected by a lens array.

[0119] In this case, it is useful to use a lens array to adjust the light gathering positions of the laser light beams that have passed through the lens sections, thereby obtaining a multiplexed beam with high light gathering properties. The shape of the lens array refers to the shapes of the two surfaces and the thickness of each lens section, as well as the relative positions of the lens sections within the lens array. To ensure that all lens sections have the same magnification, the lens sections must also have the same focal lengths. Suitable form of lens arrangement: First example

[0120] Fig. 10 shows a first example of a suitable shape of the lens arrangement 4 in the first embodiment.

[0121] In Fig. 10, the optical axes of the lens regions 40 of the lens arrangement 4 are parallel to the optical axis A of the optical multiplexing system 100.

[0122] In each lens region 40, at least one lens surface (in this case, a lens surface on the light source side) is an aspherical surface and corrects aberrations other than field curvature. In particular, the lens regions 40R2 and 40R3 arranged in front of the optical axis A suppress astigmatism and coma. When both surfaces of each lens region 40 are formed as aspherical surfaces, the aberrations can be better corrected.

[0123] In Fig. 10, the lens surfaces on the light source side of the lens areas 40R1, 40R2 and 40R3 are each labeled S1 R1 , S1 R2 and S1 R3 Furthermore, lens surfaces on the light collecting point side of the lens areas 40R1, 40R2 and 40R3 are designated S2 R1 , S2 R2 or S2 R3 designated.

[0124] Furthermore, the curvatures of the lens surfaces S1 R1 , S1 R2and S1 R3 on the side of the light source with C 1R1 , C 1R2 or C 1R3 Furthermore, the curvatures of the lens surfaces S2 R1 , S2 R2 and S2 R3 on the side of the light collection point with C 2R1 , C 2R2 or C 2R3 designated.

[0125] Here, the curvatures C 2R1 , C 2R2 and C 2R3 designed to satisfy the following relation. C2R1 <C2R2<C2R3

[0126] In general, for each lens area 40, the curvature of the lens surface on the light gathering point side is designed to increase with increasing distance between the optical axis of the lens area and the optical axis A of the optical multiplexing system 100.

[0127] When the curvature of the lens surface on the light-collecting point side is increased, a long back focus can be achieved in the case of a constant focal length. When the lens array 4 is configured as described above, the distance from the lens surface on the light-collecting point side to the light-collecting position is increased when the lens region 40 is separated from the optical axis A of the multiplexing optical system 100.

[0128] That is, the farther the lens section 40 is from the optical axis A of the multiplexing optical system 100, the greater the curvature of the lens surface on the light-collecting point side, so that the extension of the flange focal distance and the forward tilt caused by the field curvature can cancel each other out at the light-collecting position. As a result, the laser light beams that have passed through the lens sections 40 form tiny spots at the same position.

[0129] In the case described above, the front focus is reduced. However, in the first embodiment, the distance L2 is several to ten times the distance L3. Therefore, such a tiny change in the front focus distance caused by the field curvature has only a small effect.

[0130] By designing the shape of the lens array 4 as described above, aberrations can be corrected to obtain satisfactory light-collecting spots, and the positions where the smallest spots are formed can be aligned. This can enhance the light-collecting property of the multiplexed beam. Suitable form of lens arrangement: Second example

[0131] Fig. 11 shows a second example of a suitable shape of the lens arrangement 4 in the first embodiment.

[0132] In Fig.11, the optical axes of the lens regions 40 of the lens array 4 are parallel to the optical axis A of the multiplexing optical system 100. Furthermore, the lens regions 40 have the same shape. That is, in the lens regions 40, all lens surfaces on the light source side have the same shape, and all lens surfaces on the light converging point side also have the same shape.

[0133] In each lens region 40, at least one lens surface (in this case, the lens surface on the light source side) is an aspherical surface and corrects aberrations other than field curvature.

[0134] Furthermore, for each of the lens regions 40R1, 40R2, and 40R3, the lens region protrudes more toward the light-converging point side because the lens region is positioned closer to the peripheral edge of the lens array 4. That is, the lens region protrudes toward the light-converging point side in the order of the lens regions 40R1, 40R2, and 40R3. That is, the farther the optical axis of the lens region is from the optical axis A of the multiplexing optical system 100, the further the lens region is shifted toward the light-converging point side along the optical axis A of the multiplexing optical system 100.

[0135] In other words, for each lens region 40, as the distance between the optical axis of the lens region 40 and the optical axis A of the multiplexing optical system 100 is increased, the surface vertex of the lens surface on the light-collecting point side of the lens region 40 is positioned closer to the light-collecting point side. In this way, the forward tilt of the image plane caused by the field curvature is corrected.

[0136] When the lens portion 40 protrudes more toward the light-collecting point side, since the lens portion 40 is closer to the peripheral edge, the distance between the lens portion 40 and the lens 2 is slightly reduced. However, similar to the case of the above-mentioned first example, this arrangement has only a small effect.

[0137] By designing the shape of the lens array 4 as described above, aberrations can be corrected to obtain satisfactory light-collecting spots, and the positions where the smallest spots are formed can be aligned. This can enhance the light-collecting property of the multiplexed beam. List of reference symbols 100, 400 optical multiplex system 1, 201, 301 light source 11 Light emitting element 2 Lens (optical path change element) 402 Polyhedral prism (optical path changer) 4, 204, 304 lens arrangement (light condensing element) 40, 240, 340 lens range 5 light guides 51 Incident surface

Claims

[1] Optical multiplexing system (100; 400) comprising: - a light source (1; 201; 301) having a plurality of light emitting elements (11) of surface emitting lasers; - an optical path changing element (2; 402) configured to change and concentrate the optical paths of the laser light beams emitted by the light emitting elements; and - a light condensing element (4; 204; 304) including a plurality of lens portions (40; 240; 340) arranged to correspond to the respective optical paths of the laser light beams changed by the optical path changing element, and configured to condense the laser light beams through the lens portions (40; 240; 340) to form a multiplexed beam; wherein the light condensing element (4; 204; 304) is arranged at a position where the outermost diameters of adjacent laser light beams emerging from the optical path changing element (2) are in contact with each other; wherein the size of each of the lens regions (40; 240; 340) included in the light condensing element (4; 204; 304) is determined such that the size is equal to an outermost diameter of each of the laser light beams entering the lens regions (40; 240; 340); wherein the laser light beams emerge from the light condensing element (4; 204; 304) such that the outermost diameters of the adjacent laser light beams are in contact with each other; wherein the light-concentrating element is a lens arrangement (4; 204; 304) with the lens regions (40; 240; 340); and where for each of the lens areas (40; 240; 340) the curvature of the lens surface on the side of the light collecting point of the lens region (40; 240; 340) varies depending on the distance between the optical axis of the lens region and the optical axis of the optical multiplexing system, or the surface vertex of the lens surface on the side of the light collecting point of the lens region (40; 240; 340) varies in position in the direction along the optical axis of the optical multiplexing system depending on the distance between the optical axis of the lens region (40; 240; 340) and the optical axis of the optical multiplexing system. [2] An optical multiplexing system according to claim 1, wherein the optical axes of the light emitting elements (11) are parallel to each other. [3] An optical multiplexing system according to claim 1 or 2, wherein the light emitting elements (11) are arranged on a single surface (31). [4] An optical multiplexing system according to any one of claims 1 to 3, wherein the light condensing element (4; 204; 304) condenses the laser light beams at a predetermined point through the lens portions (40; 240; 340). [5] An optical multiplexing system according to claim 1, wherein said optical path changing element is a lens (2) disposed between said light source (1) and said light condensing element (4). [6] An optical multiplexing system according to claim 1, wherein said optical path changing element (402) is a polyhedral prism disposed between said light source and said light condensing element (4). [7] An optical multiplexing system according to claim 1, wherein said optical path changing element (402) is a diffractive optical element disposed between said light source and said light condensing element. [8] An optical multiplexing system according to claim 1, wherein in the lens regions (40; 240; 340), the optical axis of each lens region is parallel to the optical axis of the optical multiplexing system. [9] An optical multiplexing system according to claim 1 or 8, wherein for each of the lens regions (40; 240; 340), at least one lens surface of the lens region (40; 240; 340) is an aspherical surface. [10] An optical multiplexing system according to any one of claims 1 to 9, wherein the light emitting elements (11) are arranged in a hexagonal lattice shape. [11] Optical multiplexing system according to one of claims 1 to 10, wherein the optical multiplexing system further comprises a light guide (5) configured to transmit the multiplexed beam formed by the light condensing element (4) and entering the light guide (5) from an incident surface (51), where the light guide is a large-mode-area light guide. [12] An optical multiplexing system according to any one of claims 1 to 11, wherein the surface-emitting lasers are two-dimensional photonic crystal surface-emitting lasers.

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