Patent Publication Number: US-2021181518-A1

Title: Light source module

Description:
TECHNICAL FIELD 
     One aspect of the present disclosure relates to a light source module. 
     BACKGROUND 
     There is known a light source module including a light source, an optical fiber that guides light output from the light source, and vibration means that vibrates the optical fiber (for example, refer to Japanese Unexamined Patent Publication No. 2003-156698). In the light source module, the vibration means vibrates the optical fiber so that speckle noise in output light is reduced. 
     SUMMARY 
     Technical Problem 
     An object of one aspect of the present disclosure is to provide a light source module that can improve spatial homogeneity of output light. 
     Solution to Problem 
     According to one aspect of the present disclosure, there is provided a light source module including: a light source; an optical fiber that guides light output from the light source; a pair of holding members that holds both ends of a first portion of the optical fiber such that the first portion extends linearly; a first vibrator that vibrates the first portion along a first direction intersecting an extending direction of the first portion; and a second vibrator that vibrates the first portion along a second direction intersecting the extending direction and differing from the first direction. 
     In the light source module, both ends of the first portion are held by the pair of holding members, so that the first portion of the optical fiber extends linearly. The first vibrator vibrates the first portion along the first direction intersecting the extending direction of the first portion, and the second vibrator vibrates the first portion along the second direction that intersects the extending direction of the first portion and differs from the first direction. As in the light source module disclosed in Japanese Unexamined Patent Publication No. 2003-156698, when the optical fiber vibrates only along one direction, vibration (standing wave) dependent on the natural frequency of the optical fiber occurs. In contrast, in the light source module, since the first portion having a linear shape vibrates along the first direction and the second direction which differ from each other, such a standing wave can be suppressed from occurring, and spatial homogeneity of the output light can be improved. 
     A second portion of the optical fiber may be bent such that stress is applied to the second portion. In this case, the light can be irregularly reflected in the second portion, and the spatial homogeneity of the output light can be further improved. 
     A second portion of the optical fiber may be wound at least once. In this case, the light can be irregularly reflected in the second portion, and the spatial homogeneity of the output light can be much further improved. 
     The second portion may be located downstream of the first portion in a guiding direction of the light by the optical fiber. In this case, the spatial homogeneity of the output light can be much further improved. 
     The light source module may further include a holder that holds an output end of the optical fiber. The optical fiber may include a third portion located downstream of the second portion in the guiding direction. The holder may include a cylindrical member having flexibility. The third portion may be disposed inside the cylindrical member. In this case, the cylindrical member inside which the third portion is disposed can be moved (bent), so that the output end of the optical fiber is pointed toward a desired direction. In addition, when the cylindrical member is moved, since the second portion which is bent serves as play, unnecessary stress can be suppressed from being applied to the optical fiber. 
     At least one of the first vibrator and the second vibrator may include a plate-shaped member, and a vibration body fixed to the plate-shaped member to vibrate the plate-shaped member. The first portion of the optical fiber may be fixed to the plate-shaped member. In this case, the plate-shaped member and the vibration body can be used to vibrate the first portion of the optical fiber. 
     The first vibrator may include a first plate-shaped member extending perpendicular to the first direction, and a first vibration body fixed to the first plate-shaped member to vibrate the first plate-shaped member. The second vibrator may include a second plate-shaped member extending perpendicular to the second direction, and a second vibration body fixed to the second plate-shaped member to vibrate the second plate-shaped member. The first portion of the optical fiber may be fixed to each of the first plate-shaped member and the second plate-shaped member. In this case, the first portion of the optical fiber can vibrate independently along the first direction and the second direction. 
     The light source may be a quantum cascade laser. In this case, spatially homogeneous light in a mid-infrared range can be output as output light from the light source module. 
     The light source module may further include a compressor that applies compression force to a compression portion that is a part of the optical fiber. The compression portion may be compressed in at least one direction intersecting an extending direction of the compression portion by the compression force. In this case, spatially homogeneous ring-shaped light can be output. 
     The compression portion may be a part other than the first portion in the optical fiber. In this case, the compression force can be avoided from disturbing the vibration of the first portion, and the spatial homogeneity of the output light can be secured. 
     The compressor may be formed of one of the pair of holding members. In this case, the configuration can be simplified. 
     The compressor may be configured to change a magnitude of the compression force. In this case, the compression force can be changed to adjust the shape, the intensity, or the like of the output light. 
     The light source module may further include a housing that accommodates the light source, the optical fiber, the pair of holding members, the first vibrator, and the second vibrator. The compression portion may be a part of the optical fiber, the part being located outside the housing. In this case, the compression force can be easily applied to the compression portion. 
     The compression portion may be compressed along a single direction intersecting the extending direction of the compression portion or may be compressed over an entire periphery. In either case, spatially homogeneous ring-shaped light can be output. 
     Advantageous Effects of Invention 
     One aspect of the present disclosure can provide the light source module that can improve spatial homogeneity of output light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a light source module according to an embodiment. 
         FIG. 2  is a view illustrating a first vibrator. 
         FIG. 3  is a view illustrating a second vibrator. 
         FIGS. 4A to 4D  are pictures showing the shapes of output light at an output end of an optical fiber. 
         FIGS. 5A to 5D  are graphs showing the shapes of output light at the output end of the optical fiber. 
         FIG. 6  is a view illustrating a light source module according to a modification example. 
         FIG. 7  is a view illustrating a mode where an optical fiber is compressed by a compressor. 
         FIGS. 8A to 8C  are pictures showing the shapes of output light at an output end of the optical fiber. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the drawings. Incidentally, in the following description, the same reference signs are used for the same or equivalent components and duplicated descriptions will be omitted. 
     As illustrated in  FIG. 1 , a light source module  1  includes a light source  2 , an optical fiber  3 , a pair of holding members  4 , a first vibrator  5 , a second vibrator  6 , a housing  7 , and a holder  8 . The housing  7  is formed in, for example, a box shape, and accommodates the light source  2 , the optical fiber  3 , the pair of holding members  4 , the first vibrator  5 , and the second vibrator  6 . In the light source module  1 , light L 1  output from the light source  2  is guided to be output from an end portion of the optical fiber  3  to the outside as output light L 2  by the optical fiber  3 . The light source module  1  is used to process a resin material, for example. 
     The light source  2  is, for example, a quantum cascade laser. In this case, the light L 1  output from the light source  2  is a laser beam in a mid-infrared range having a wavelength of approximately 4 μm to 15 μm. The light source  2  may be a Sb-based or Pb-based semiconductor laser diode, an interband cascade laser, a solid-state laser of which the wavelength is variable by optical parametric oscillator, or the like. 
     The optical fiber  3  is a multimode fiber. The optical fiber  3  is, for example, a plastic hollow fiber, and the inner surface of the optical fiber  3  is coated with a metal such as silver. In this case, the reflectance on the inner surface of the fiber can be brought close to 100%, and the transmission efficiency can be improved. 
     A connector  11  is provided at an input end of the optical fiber  3 , and the optical fiber  3  is fixed to an adapter  12  via the connector  11 . The light L 1  output from the light source  2  is input to the adapter  12  via a collimating lens  13  and a condensing lens  14  to be incident into the optical fiber  3 . 
     A connector  15  is provided at an output end of the optical fiber  3 , and the optical fiber  3  is fixed to an adapter  16  via the connector  15 . The output light L 2  is output from the optical fiber  3  to the outside of the light source module  1  via the adapter  16 . The output end of the optical fiber  3  is held by the holder  8 . The holder  8  will be described later in detail. 
     The optical fiber  3  includes a first portion  31 , a second portion  32 , and a third portion  33 . The first portion  31  is one portion in a longitudinal direction of the optical fiber  3 , the second portion  32  is another portion in the longitudinal direction, and the third portion  33  is further another portion in the longitudinal direction. The second portion  32  is located downstream of the first portion  31  (on a side opposite to the light source  2 ) in a guiding direction of the light L 1  by the optical fiber  3 . The third portion  33  is located downstream of the second portion  32  in the guiding direction. 
     Both ends of the first portion  31  are held by the pair of holding members  4 . Therefore, the first portion  31  extends linearly along an extending direction A. In other words, the pair of holding members  4  hold both ends of the first portion  31  such that the first portion  31  extends linearly. Each of the holding members  4  is, for example, a jig that can fix the optical fiber  3  by clamping. The jigs are fixed to, for example, a fixing surface such as a bottom surface of the housing  7 . 
     The first vibrator  5  is disposed between the pair of holding members  4  to vibrate (displace) the first portion  31  along a first direction D 1  intersecting the extending direction A. In this example, the first direction D 1  is perpendicular to the extending direction A, and is a vertical direction. 
     The second vibrator  6  is disposed between the pair of holding members  4  to vibrate (displace) the first portion  31  along a second direction D 2  that intersects the extending direction A and differs from the first direction D 1 . In this example, the second direction D 2  is perpendicular to the extending direction A and the first direction D 1 , and is a horizontal direction. The second vibrator  6  is located downstream of the first vibrator  5  in the guiding direction of the light L 1  by the optical fiber  3 . 
     As illustrated in  FIG. 2 , the first vibrator  5  includes a plate-shaped member (first plate-shaped member)  51 , an vibration body (first vibration body)  52 , and a column (support portion)  53 . The plate-shaped member  51  is formed in a plate shape by metal, for example. The plate-shaped member  51  extends along the second direction D 2  (direction perpendicular to the extending direction A and the first direction D 1 ). The thickness of the plate-shaped member  51  is, for example, approximately 0.2 mm The metal material forming the plate-shaped member  51  is, for example, phosphor bronze. In this case, the durability of the plate-shaped member  51  can be improved. 
     The first portion  31  of the optical fiber  3  is fixed to a distal portion of the plate-shaped member  51  with a restraint member  54 . Specifically, for example, in a state where the first portion  31  is interposed between the restraint member  54  and the plate-shaped member  51 , the restraint member  54  is fastened to the plate-shaped member  51  with fastening members  54   a  such as screws, so that the first portion  31  is fixed to the plate-shaped member  51 . A proximal portion of the plate-shaped member  51  is fixed to, for example, a distal portion of the column  53  with fastening members  53   a  such as screws. A proximal portion of the column  53  is fixed to, for example, a fixing surface such as the bottom surface of the housing  7 . 
     The vibration body  52  is, for example, a coin-shaped (columnar) eccentric motor. In the eccentric motor, a weight having an asymmetric shape is fixed to a rotary shaft, and vibration is generated as the rotary shaft rotates. The vibration body  52  is fixed to the plate-shaped member  51  with a fixing member  52   a.  The vibration of the vibration body  52  is transmitted to the first portion  31  of the optical fiber  3  via the plate-shaped member  51 , so that the first portion  31  vibrates along the first direction D 1 . 
     As an example, the ratio of a distance R 1  from the center of the vibration body  52  to a proximal end of the plate-shaped member  51  to a distance R 2  from the center of the vibration body  52  to the center of the optical fiber  3 , namely, R 1 :R 2  is 5:2. In this case, since the vibration body  52  is disposed close to the optical fiber  3  in the plate-shaped member  51  (closer to the optical fiber  3  than to the center of the plate-shaped member  51 ), the vibration of the vibration body  52  can be efficiently transmitted to the optical fiber  3 . In addition, since the distance between the vibration body  52  and the optical fiber  3  can be secured, the restraint member  54  can be suppressed from being damaged. 
     The vibration frequency of vibration of the first portion  31  induced by the first vibrator  5  is, for example, approximately 100 Hz to 1 kHz. When the vibration frequency is 100 Hz or more, the effect of improving spatial homogeneity of the output light L 2  which will be described later is effective. When the vibration frequency is 1 kHz or less, the restraint member  54  can be suppressed from being damaged. 
     As illustrated in  FIG. 3 , the second vibrator  6  includes a plate-shaped member (second plate-shaped member)  61 , an vibration body (second vibration body)  62 , and a support portion  63 . The plate-shaped member  61  is formed in, for example, a metal plate shape. The plate-shaped member  61  extends along the first direction D 1  (direction perpendicular to the extending direction A and the second direction D 2 ). The thickness of the plate-shaped member  61  is, for example, approximately 0.2 mm. The metal material forming the plate-shaped member  61  is, for example, phosphor bronze. In this case, the durability of the plate-shaped member  61  can be improved. 
     The first portion  31  of the optical fiber  3  is fixed to a distal portion of the plate-shaped member  61  with a restraint member  64 . Specifically, for example, in a state where the first portion  31  is interposed between the restraint member  64  and the plate-shaped member  61 , the restraint member  64  is fastened to the plate-shaped member  61  with fastening members  64   a  such as screws, so that the first portion  31  is fixed to the plate-shaped member  61 . A proximal portion of the plate-shaped member  61  is fixed to, for example, the support portion  63  with fastening members  63   a  such as screws. The support portion  63  is fixed to, for example, a fixing surface such as the bottom surface of the housing  7 . 
     The vibration body  62  is, for example, a coin-shaped (columnar) eccentric motor. In the eccentric motor, a weight having an asymmetric shape is fixed to a rotary shaft, and vibration is generated as the rotary shaft rotates. The vibration body  62  is fixed to the plate-shaped member  61  with a fixing member  62   a.  The vibration of the vibration body  62  is transmitted to the first portion  31  of the optical fiber  3  via the plate-shaped member  61 , so that the first portion  31  vibrates along the second direction D 2 . 
     As an example, the ratio of a distance R 3  from the center of the vibration body  62  to a proximal end of the plate-shaped member  61  to a distance R 4  from the center of the vibration body  62  to the center of the optical fiber  3 , namely, R 3 :R 4  is 5:2. In this case, since the vibration body  62  is disposed close to the optical fiber  3  in the plate-shaped member  61  (closer to the optical fiber  3  than to the center of the plate-shaped member  61 ), the vibration of the vibration body  62  can be efficiently transmitted to the optical fiber  3 . In addition, since the distance between the vibration body  62  and the optical fiber  3  can be secured, the restraint member  64  can be suppressed from being damaged. 
     The vibration of the first portion  31  induced by the second vibrator  6  is not synchronized (unsynchronized) with the vibration of the first portion  31  induced by the first vibrator  5 . Therefore, vibration is randomly (irregularly) applied to the first portion  31  along the first direction D 1  and the second direction D 2  which differ from each other. The vibration frequency of vibration of the first portion  31  induced by the second vibrator  6  is, for example, approximately 100 Hz to 1 kHz. When the vibration frequency is 100 Hz or more, the effect of improving spatial homogeneity of the output light L 2  which will be described later is effective. When the vibration frequency is 1 kHz or less, the restraint member  64  can be suppressed from being damaged. 
     As illustrated in  FIG. 1 , the second portion  32  of the optical fiber  3  includes a winding portion  32   a  that is formed by winding the optical fiber  3  once. The winding portion  32   a  has, for example, a circular shape when viewed in the first direction D 1 . The second portion  32  is bent so as to form the winding portion  32   a,  so that bending stress is applied to the winding portion  32   a.  In other words, the second portion  32  is bent such that stress is applied to the winding portion  32   a.    
     Stress is applied to the winding portion  32   a  to the extent that the transmission efficiency of the optical fiber  3  is not impaired. The diameter of the winding portion  32   a  is, for example, approximately 2 to 4 times the minimum bending radius of the optical fiber  3 . As one example, when the diameter of the core of a hollow fiber forming the optical fiber  3  is 1,500 μm and the minimum bending radius is 5 cm, the diameter of the winding portion  32   a  may be 15 cm. Therefore, a mode concentrated in the core can be suppressed from leaking to a cladding mode to cause loss. 
     As illustrated in  FIG. 1 , the holder  8  includes a cylindrical member  81  and an irradiation unit  82 . The irradiation unit  82  includes a collimating lens  84  and a housing  85  that accommodates the collimating lens  84 . The cylindrical member  81  has flexibility and is formed in a cylindrical shape. The cylindrical member  81  is fixed to the housing  7 . More specifically, an insertion hole  7   a  is formed in the housing  7 , and a fixing member  83  having an annular shape is fixed to the insertion hole  7   a.  A proximal portion  81   a  of the cylindrical member  81  is connected to the housing  7  via the fixing member  83 . A distal portion  81   b  of the cylindrical member  81  is connected to the housing  85  of the irradiation unit  82 . The optical fiber  3  is inserted into the insertion hole  7   a,  and the third portion  33  of the optical fiber  3  is disposed inside the cylindrical member  81 . 
     The housing  85  of the irradiation unit  82  accommodates the collimating lens  84  and the connector  15  and the adapter  16  which are provided at the output end of the optical fiber  3 . In addition, the housing  85  is provided with an emission window  86  from which the output light L 2  is to be emitted. The output light L 2  emitted from the optical fiber  3  is guided to be output from the emission window  86  to the outside by the collimating lens  84 . In the holder  8 , the irradiation unit  82  is movable due to the flexibility of the cylindrical member  81 , and the cylindrical member  81  inside which the third portion  33  is disposed is moved (bent), so that the output end of the optical fiber  3  can be pointed toward a desired direction. Namely, the flexible irradiation of the output light L 2  is feasible. 
     [Functions and Effects] 
       FIGS. 4A to 4D  and  FIGS. 5A to 5D  show the shapes of the output light L 2  at the output end of the optical fiber  3 , which are acquired in different test conditions. In a first example shown in  FIGS. 4A and 5A , the first vibrator  5  and the second vibrator  6  did not vibrate the optical fiber  3 . In a second example shown in  FIGS. 4B and 5B , only one of the first vibrator  5  and the second vibrator  6  vibrated the optical fiber  3 . In a third example illustrated in  FIGS. 4C and 5C  and a fourth example shown in  FIGS. 4D and 5D , both of the first vibrator  5  and the second vibrator  6  vibrated the optical fiber  3 . In the first to third examples, the winding portion  32   a  was not formed in the second portion  32  of the optical fiber  3 . In the fourth example, the winding portion  32   a  was formed in the second portion  32  of the optical fiber  3 . 
     From the comparison of results of the first to third examples, it is found that when the first vibrator  5  and the second vibrator  6  vibrate the optical fiber  3 , spatial homogeneity of the output light L 2  is improved. Namely, it is found that in  FIGS. 4A and 5A , the output light L 2  is spatially inhomogeniously distributed, whereas in  FIGS. 4C and 5C , the output light L 2  is concentrated in a hollow core mode to have a shape close to a unimodal Gaussian beam shape. In addition, it is found that in  FIGS. 4C and 5C , the spatial homogeneity of the output light L 2  is improved than in  FIGS. 4B and 5B . It is considered that the reason is that in the second example, since the optical fiber  3  vibrates only along one direction, vibration (standing wave) dependent on the natural frequency of the optical fiber  3  occurs. 
     In addition, it is found that in  FIGS. 4D and 5D , the spatial homogeneity of the output light L 2  is further improved than in  FIGS. 4C and 5C . As shown in  FIGS. 4D and 5D , in the fourth example, the output light L 2  had a top hat shape. The top hat shape of the output light L 2  is useful for application to perforating, welding, or the like in resin processing. 
     As described above, in the light source module  1 , both ends of the first portion  31  are held by the pair of holding members  4 , so that the first portion  31  of the optical fiber  3  extends linearly. The first vibrator  5  vibrates the first portion  31  along the first direction D 1  intersecting the extending direction A of the first portion  31 , and the second vibrator  6  vibrates the first portion  31  along the second direction D 2  that intersects the extending direction A of the first portion  31  and differs from the first direction D 1 . When the optical fiber  3  vibrates only along one direction, vibration (standing wave) dependent on the natural frequency of the optical fiber  3  occurs, which is a concern. In contrast, in the light source module  1 , since the first portion  31  having a linear shape vibrates along the first direction D 1  and the second direction D 2  which differ from each other, such a standing wave can be suppressed from occurring, and the spatial homogeneity of the output light L 2  can be improved. 
     The case where “the first portion  31  extends linearly” is meant to include a case where the first portion  31  extends linearly with an allowable degree of deflection. For example, when the diameter (inner diameter) of the optical fiber  3  is 1,500 μm, the allowable amount of deflection is approximately 1 mm Namely, the allowable amount of deflection is smaller than the diameter of the optical fiber  3 . Alternatively, the allowable amount of deflection is 1% or less of the distance between the pair of holding members  4  along the extending direction A of the optical fiber  3 . Namely, when the distance between the pair of holding members  4  is 10 cm, the allowable amount of deflection is 1 mm or less. 
     The second portion  32  of the optical fiber  3  is bent such that stress is applied to the second portion  32 . Therefore, light can be irregularly reflected in the second portion  32 , and the spatial homogeneity of the output light L 2  can be further improved. As a result, as described above, the output light L 2  can be formed in a top hat shape. Since the output light L 2  has a top hat shape, when the light source module  1  is applied to resin processing, efficient and precise processing can be realized. In addition, in the light source module  1 , the output light L 2  can be formed in a top hat shape without using a complicated optical system where a lens, a space light modulator, and the like are assembled, and thus the configuration of the light source module  1  can be simplified. 
     The second portion  32  of the optical fiber  3  is wound once. Therefore, light can be irregularly reflected in the second portion  32 , and the spatial homogeneity of the output light L 2  can be much further improved. 
     The second portion  32  is located downstream of the first portion  31  in the guiding direction of light by the optical fiber  3 . Therefore, the spatial homogeneity of the output light L 2  can be much further improved. Namely, by applying stress to the second portion  32  after the first vibrator  5  and the second vibrator  6  apply vibration to the first portion  31  to form light in a unimodal beam shape, the output light L 2  can be formed in a top hat shape. 
     The holder  8  includes the cylindrical member  81  having flexibility, and the third portion  33  of the optical fiber  3  is disposed inside the cylindrical member  81 . Therefore, the cylindrical member  81  inside which the third portion  33  is disposed can be moved (bent), so that the output end of the optical fiber  3  is pointed toward a desired direction. In addition, when the cylindrical member  81  is moved, since the second portion  32  which is bent serves as play, unnecessary stress can be suppressed from being applied to the optical fiber  3 . 
     The first vibrator  5  and the second vibrator  6  include the plate-shaped members  51  and  61 , and the vibration bodies  52  and  62  that are fixed to the plate-shaped members  51  and  61  to vibrate the plate-shaped members  51  and  61 , and the first portion  31  of the optical fiber  3  is fixed to the plate-shaped members  51  and  61 . Therefore, the plate-shaped members  51  and  61  and the vibration bodies  52  and  62  can be used to vibrate the first portion  31  of the optical fiber  3 . In addition, the first portion  31  of the optical fiber  3  can vibrate independently along the first direction D 1  and the second direction D 2 . Namely, the vibration induced by the first vibrator  5  and the vibration induced by the second vibrator  6  can be suppressed from being mixed together, and the vibration induced by the first vibrator  5  and the vibration induced by the second vibrator  6  can be reliably independent from each other. 
     The light source  2  is a quantum cascade laser. Therefore, spatially homogeneous light in a mid-infrared range can be output as the output light L 2  from the light source module  1 . 
     The present disclosure is not limited to the above embodiment. For example, the material and the shape of each configuration are not limited to the material and the shape described above, and various materials and shapes can be adopted. The second portion  32  may be bent to form an angle or bent in a zigzag shape to apply stress to the second portion  32  of the optical fiber  3 . The second portion  32  may be located upstream of the first portion  31  in the guiding direction of light by the optical fiber  3 . The second portion  32  may be wound two or more times. A plane on which the winding portion  32   a  is disposed is not limited, and for example, the winding portion  32   a  may have a circular shape when viewed in the second direction D 2 . The optical fiber  3  may be bundled in a portion of the winding portion  32   a,  in which the optical fiber  3  overlaps itself, by a holding member. In this case, the holding member  4  of the pair of holding members  4 , which is located on a second portion  32  side, may be omitted. 
     In addition to the first vibrator  5  and the second vibrator  6 , a third vibrator may be provided. The third vibrator may vibrate the first portion  31  of the optical fiber  3 , for example, along a third direction that intersects the extending direction and differs from the first direction D 1  and the second direction D 2 . The first direction D 1  may be a direction intersecting the extending direction A, and may not be necessarily perpendicular to the extending direction A. However, if the first direction D 1  is perpendicular to the extending direction A, the optical fiber  3  can be suppressed from extending or contracting when the first portion  31  vibrates along the first direction D 1 . This also applies to the second direction D 2 . The case where “the first portion  31  vibrates along the first direction D 1  perpendicular to the extending direction A” also includes a case where a direction where vibration is applied to the first portion  31  is slightly deviated from the first direction D 1 , for example, due to an error or the like in position where each member is disposed. This also applies to the second direction D 2 . 
     A light source module  1 A according to a modification example will be described with reference to  FIG. 6 . In the light source module  1 A, one of the pair of holding members  4  is formed as a compressor  9 . More specifically, the compressor  9  is formed of the holding member  4  of the pair of holding members  4 , which is located downstream in the guiding direction. 
     The compressor  9  is, for example, a fixing jig, and applies compression force to a compression portion  34  of the optical fiber  3 . As illustrated in  FIG. 7 , the compression portion  34  is compressed along the first direction D 1  by the compression force. In this example, the compression portion  34  is compressed only along a single direction (first direction D 1 ) intersecting the extending direction A of the compression portion  34 . The compression portion  34  is a part of the optical fiber  3 , and is a boundary portion between the first portion  31  and the second portion  32  of the optical fiber  3 . The compression portion  34  can be regarded as a part of the second portion  32  (namely, a part other than the first portion  31 ). In the light source module  1 A, the winding portion  32   a  is not provided in the second portion  32  of the optical fiber  3 , and the second portion  32  extends linearly. 
     Similar to the above embodiment, the light source module  1 A according to a modification example can also improve the spatial homogeneity of the output light L 2 . In addition, the compression portion  34  of the optical fiber  3  is compressed by the compressor  9 , so that spatially homogeneous ring-shaped light can be output. This point will be further described with reference to  FIGS. 8A to 8C . 
     In the examples shown in  FIGS. 8A to 8C , both of the first vibrator  5  and the second vibrator  6  vibrated the first portion  31  of the optical fiber  3 , and the compression portion  34  of the optical fiber  3  was compressed by the compressor  9 . The winding portion  32   a  was not formed in the second portion  32  of the optical fiber  3 . The magnitude of the compression force that the compressor  9  applied to the compression portion  34  of the optical fiber  3  was increased in order of  FIGS. 8A, 8B, and 8C . Namely, the compression force in  FIG. 8C  is larger than the compression force in  FIG. 8B , and the compression force in  FIG. 8B  is larger than the compression force in  FIG. 8A . 
     From  FIGS. 8A to 8C , it is found that the optical fiber  3  is compressed by the compressor  9  and thus spatially homogeneous ring-shaped light can be output. In addition, from comparison between  FIGS. 8B and 8C , it is found that the larger the compression force is, the larger an opening formed at the center of the output light is. Such ring-shaped light can not only be applied to processing but also be used in, for example, a local excitation light source in a stimulated emission depletion (STED) microscope or the like. When the magnitude of the compression force is determined, for example, the compression force is changed while the shape and the intensity of the output light are monitored, and thus the magnitude of a proper compression force can be determined such that spatially homogeneous ring-shaped light is output. 
     In addition, in the light source module  1 A, the compression portion  34  is a part other than the first portion  31  in the optical fiber  3 . Therefore, the compression force of the compressor  9  can be avoided from disturbing the vibration of the first portion  31 , and the spatial homogeneity of the output light can be secured. 
     As another modification example, in the light source module  1 A, the compressor  9  may be configured to be able to change the magnitude of the compression force. For example, the compressor  9  may be configured to include a screw mechanism and to be able to change the magnitude of the compression force according to the amount of fastening of a screw. When the magnitude of the compression force is changeable, the compression force can be changed to adjust the shape, the intensity, or the like of the output light. 
     As another modification example, in the light source module  1 A, the compression portion  34  may be a part of the optical fiber  3 , which is located outside the housing  7 . In the example of  FIG. 6 , a part of the third portion  33  of the optical fiber  3  is located outside the housing  7 . The compressor  9  may be provided to apply compression force to the part of the third portion  33 . Namely, the compression portion  34  may be a part of the third portion  33 . When the compression portion  34  is a part of the optical fiber  3 , which is located outside the housing  7 , compression force can be easily applied to the compression portion  34 . Particularly, when the compressor  9  is configured to be able to change the magnitude of the compression force, the configuration where the compression portion  34  is a part of the optical fiber  3 , which is located outside the housing  7 , is advantageous in that the adjustment of the compression force of the compressor  9  can be facilitated. 
     As another modification example, in the light source module  1 A, the compression portion  34  may be compressed over the entire periphery. For example, the compressor  9  may be formed of a jig that compresses the compression portion  34  in all circumferential direction. Even in this case, spatially homogeneous ring-shaped light can be output. 
     As another modification example, in the light source module  1 A, the winding portion  32   a  may be provided in the second portion  32  of the optical fiber  3 . The optical fiber  3  may be bundled in a portion of the winding portion  32   a,  in which the optical fiber  3  overlaps itself, by a holding member, and the holding member may be formed as a compressor. In this case, the holding member  4  (compressor  9 ) of the pair of holding members  4 , which is located on the second portion  32  side, may be omitted. In other words, the compressor  9  may be provided separately from the pair of holding members  4  to compress the second portion  32  of the optical fiber  3 . In the light source module  1 A, the compressor  9  may be formed of the holding member  4  of the pair of holding members  4 , which is located upstream in the guiding direction.