Patent Description:
Focal length is generally adjusted by mechanically changing the position of the lens assembly including a plurality of lenses.

There are cases where the lens assembly is mechanically moved, such as the case of observing an object moving at high speed. The adjustment speed of the focal length may be delayed, for example, with respect to the moving speed of the object. As described above, in the case of adjusting the focus by mechanically moving the lens assembly, the speed (speediness) of focusing has a limit.

Such previously known configurations are derivable from <CIT> and <NPL>. Further prior art is found in <CIT> that describes an optical element assembly in line with the preamble of the main claim.

The following is an explanation of an optical element assembly <NUM> with reference to drawings. The drawings are schematic or conceptual ones.

The problem to be solved by the present embodiment is to provide an optical element assembly, an optical imaging device, and an optical processing device capable of adjusting a focal position at higher speed.

The present invention is defined by the optical element assembly according to claim <NUM>, the optical imaging device according to claim <NUM>, and/or the optical processing device according to claim <NUM>.

The following is an explanation of the first embodiment with reference to <FIG>.

As illustrated in <FIG>, the optical element assembly <NUM> according to the present embodiment includes a rod <NUM>, a mirror <NUM>, and a light emitting element <NUM>.

The rod <NUM> is formed of a transparent material and in a columnar shape having a first end <NUM> and a second end <NUM>. The shape of the rod <NUM> is not limited to the columnar shape. The rod <NUM> is formed symmetrically with respect to the central axis C. The first end <NUM> and the second end <NUM> are formed as surfaces orthogonal to the central axis C.

The rod <NUM> has a diameter of several millimeters to tens of millimeters. The rod <NUM> has a length of several millimeters to tens of millimeters. The shape and/or the size of the rod <NUM> can be properly set.

The rod <NUM> transmits light of first wavelength region and absorbs light of second wavelength region. As a material of the rod <NUM>, for example, a glass material having infrared absorbency is used. A proper material is selected as the material of the rod <NUM> depending on the selection of a light beam B1 of the first wavelength region that the user wants to transmit through the rod <NUM>, and the selection of a light beam B2 of the second wavelength region that the user wants to absorb with the rod <NUM>.

In the present embodiment, the wavelength of the first wavelength region is shorter than the wavelength of the second wavelength region. The first wavelength region is, for example, <NUM> falling within wavelength range (<NUM> to <NUM>) of visible light. The second wavelength region is, for example, <NUM> falling within wavelength range (<NUM> to <NUM>) of infrared rays. The first wavelength region and the second wavelength region are mere examples, and can be properly set. For this reason, the rod <NUM> has infrared absorbency. In some wavelengths to be used, the wavelength of the first wavelength region is longer than the wavelength of the second wavelength region.

Because the rod <NUM> is symmetrical with respect to the central axis C, heat is uniformly radiated outward in the radial direction from the central axis C of the rod <NUM>.

The mirror <NUM> is disposed on a side of the first end <NUM> of the rod <NUM>. The mirror <NUM> crosses the central axis C. The mirror <NUM> is inclined by, for example, <NUM>° with respect to the central axis C of the rod <NUM>.

In the present embodiment, the mirror <NUM> transmits first light beam B1 including the first wavelength region, such as visible light, and reflects second light beam B2 including the second wavelength region, such as infrared rays. For example, the mirror <NUM> is a dichroic mirror. The mirror <NUM> may be a cube-type dichroic mirror <NUM> illustrated in <FIG>.

The light emitting element <NUM> is capable of emitting the second light beam B2 of the second wavelength region. The light emitting element <NUM> is capable of switching ON/OFF states. The light emitting element <NUM> emits light in the ON state, and applies the light to the mirror <NUM>.

As the light emitting element <NUM>, for example, a LED or a laser diode (LD) is used. When a laser diode is used as the light emitting element <NUM>, the light beam thereof approximates to a Gaussian beam. For this reason, when a laser diode is used as the light emitting element <NUM>, a lens <NUM> and a light beam intensity adjusting element <NUM> can be omitted.

A lens <NUM> is preferably disposed between the infrared light emitting element <NUM> and the mirror <NUM>. The lens <NUM> shapes, for example, the light beam from the light emitting element <NUM> into parallel light or the like.

A light beam intensity adjusting element <NUM> is preferably disposed between the lens <NUM> and the mirror <NUM>. The light beam intensity adjusting element <NUM> adjusts the beam profile of the second light beam B2 from the light emitting element <NUM>. As illustrated in <FIG>, the light beam intensity adjusting element <NUM> provides the transmittance of the second light beam B2 with distribution. The distribution has circular polar coordinates (r, θ) with respect to the X-Y coordinates. The second light beam B2 emitted from the light emitting element <NUM> has an axial-symmetrical beam profile directly after passing through the light beam intensity adjusting element <NUM>.

In this state, when the intensity of a cross section of the light beam is I, the beam profile is expressed as follows, as a function of r. <MAT> Expression (<NUM>) is based on the supposition that an axial-symmetrical beam, such as a Gaussian beam, is made incident on the mirror <NUM> as the second light beam B2, but a beam that is not axial-symmetrical may be made incident on the mirror <NUM>.

A tubular heat radiator <NUM> is provided around the external circumference of the rod <NUM>. The heat radiator <NUM> has a cylindrical body. A wall portion of the heat radiator <NUM> is preferably solid. The whole length of the heat radiator <NUM> is substantially the same as the whole length of the rod <NUM>. The heat radiator <NUM> is formed of a material having higher heat conductivity than that of the rod <NUM>. The heat radiator <NUM> is preferably formed of a metal material with good heat conductivity, such as copper and aluminum alloy.

The heat radiator <NUM> is formed of the material with good heat conductivity and in the cylindrical body. In addition, a Peltier element used for various types of cooling devices may be used instead of the cylindrical body.

The following is an explanation of operations of the optical element assembly <NUM> according to the present embodiment.

When the light emitting element <NUM> emits light, the second light beam B2 emitted from the light emitting element <NUM> becomes parallel light through the lens <NUM>. The parallel light passes through the light beam intensity adjusting element <NUM>. The second light beam B2 transmitted through the light beam intensity adjusting element <NUM> has a beam profile based on Expression (<NUM>). An example of the beam profile based on Expression (<NUM>) is a Gaussian beam.

The second light beam B2 adjusted to have a beam profile based on Expression (<NUM>) is reflected with the mirror <NUM>. The second light beam B2 adjusted to have a beam profile based on Expression (<NUM>) is made incident on the first end <NUM> of the rod <NUM>. In this state, the mirror <NUM> is in an adjusted position such that the second light beam B2 adjusted to be axial-symmetrical is made incident on a position in which the central axis of the second light beam B2 agrees with, or substantially agrees with, the central axis C of the rod <NUM>.

The rod <NUM> absorbs light of the second wavelength region of the second light beam B2 at proper rate, between the first end <NUM> and the second end <NUM>. The temperature of the rod <NUM> increases when the second light beam B2 is made incident thereon and the rod <NUM> absorbs the second light beam B2. The rod <NUM> generates refractive index distribution in accordance with temperature increase. Specifically, the refractive index of the rod <NUM> changes when the second light beam B2 is made incident thereon and the rod <NUM> absorbs the second light beam B2.

In this state, the central axis of the axial-symmetrical second light beam B2 agrees with, or substantially agrees with, the central axis C of the rod <NUM>. For this reason, the refractive index of the rod <NUM> changes outward in the radial direction from the central axis C. When the temperature increase ΔT in a proper position of the rod <NUM> is sufficiently small, such as ten to twenty, the refractive index distribution of the rod <NUM> linearly changes. The refractive index distribution of the rod <NUM> has a profile similar to Expression (<NUM>). When n0 is the refractive index of the rod <NUM> when the temperature distribution between the central axis C and the external circumferential surface of the rod <NUM> is fixed, that is, when the rod <NUM> has no temperature gradient, the change quantity Δn of the refractive index of the rod <NUM> after temperature increase is as follows.

The mirror <NUM> transmits the first light beam B1 from a region opposed to the first end <NUM> of the rod <NUM>, and the first light beam B1 is made incident on the first end <NUM> of the rod <NUM>. In this operation, the following light beam equation can be used. <MAT> Using the equation (<NUM>) described above enables calculation of a locus of the first light beam (visible light) B1 from the region opposed to the first end <NUM> of the rod <NUM>.

As described above, by making the second light beam B2 of the second wavelength region incident on the rod <NUM> and causing temperature change in the rod <NUM>, the refractive index of the rod <NUM> can be changed toward the outside in the radial direction with respect to the central axis C of the rod <NUM>. For this reason, the first light beam B1 opposed to the first end <NUM> of the rod <NUM>, transmitted through the mirror <NUM>, and passing between the first end <NUM> and the second end <NUM> of the rod <NUM> is curved (deflected) in accordance with the refractive index. Accordingly, when the second light beam B2 of the second wavelength region is made incident on the rod <NUM> and temperature change is caused in the rod <NUM>, the rod <NUM> can be used as a lens.

Part (A) to Part (C) in <FIG> illustrate states in which the refractive index of the rod <NUM> changes without mechanically moving the rod <NUM>, the mirror <NUM>, the light emitting element <NUM>, the lens <NUM>, or the light beam intensity adjusting element <NUM>.

Part (A) in <FIG> illustrates a state in which no second light beam B2 is made incident on the rod <NUM> from the light emitting element <NUM>, and no temperature distribution occurs in the rod <NUM> outward in the radial direction from the central axis C. In this case, the rod <NUM> does not function as a lens, and the first light beam B1 passing through the rod <NUM> is not focused, or focused at infinity. As described above, when the temperature distribution of the rod <NUM> is fixed in the radial direction from the central axis C, the refractive index of the rod <NUM> is fixed.

Part (B) in <FIG> illustrates a state in which the second light beam B2 is made incident on the first end <NUM> of the rod <NUM> from the light emitting element <NUM>, and temperature distribution is generated in the rod <NUM> outward in the radial direction from the central axis C. For example, by emission of the second light beam B2 from the light emitting element <NUM>, the refractive index of the rod <NUM> is instantly changed, and the locus of the first light beam B1 is instantly changed. In this case, the temperature is highest at the central axis C of the rod <NUM>, and the temperature decreases toward the outside in the radial direction from the central axis C. When the temperature distribution of the rod <NUM> changes, the refractive index of the rod <NUM> changes in accordance with the temperature distribution. In this state, the refractive index in the position along the central axis C is larger than the refractive index in an outside position in the radial direction with respect to the central axis C. The rod <NUM> in this state becomes equal to, for example, a GRIN lens. Light has a property of being deflected toward a direction with higher refractive index. For this reason, the first light beam B1 from the region opposed to the first end <NUM> of the rod <NUM> is focused, for example, in a position Fb at a proper distance Db from the second end <NUM> of the rod <NUM>.

Part (C) in <FIG> illustrates a state in which the second light beam B2 is made incident on the first end <NUM> of the rod <NUM> from the light emitting element <NUM>, and temperature distribution is generated in the rod <NUM> outward in the radial direction from the central axis C. In this case, the temperature decreases toward the outside in the radial direction from the central axis C of the rod <NUM>. In addition, the example illustrated in part (C) in <FIG> has a higher temperature gradient toward the outside in the radial direction from the central axis C than that in the example illustrated in part (B) in <FIG>. In this state, the first light beam B1 from the region opposed to the first end <NUM> of the rod <NUM> is focused in a position Fc at a proper distance Dc from the second end <NUM> of the rod <NUM>. The position Fc is closer to the second end <NUM> of the rod <NUM> than the position illustrated in part (B) of <FIG> is.

As described above, the focal position Fb of the example illustrated in part (B) of <FIG> is longer than the focal position Fc of the example illustrated in part (C) of <FIG> by a length L (= distance Db - distance Dc). In this case, the example illustrated in part (C) in <FIG> enables observation of the subject in a position closer to the first end <NUM> of the rod <NUM> than that in the example illustrated in part (B) in <FIG>.

In the present embodiment, the heat radiator <NUM> is disposed around the external circumference of the rod <NUM>. When the rod <NUM> absorbs the second light beam B2, the heat radiator <NUM> absorbs heat in the rod <NUM>, and radiates the heat outward in the radial direction. As the heat radiation quantity with the heat radiator <NUM> increases, temperature change (temperature gradient) between the central axis C of the rod <NUM> and the external circumferential surface of the rod <NUM> increases by adjustment of the light quantity (light beam intensity) of the second light beam with respect to the rod <NUM>.

In the state where the second light beam B2 is made incident on the first end <NUM> of the rod <NUM> from the light emitting element <NUM>, the heat radiator <NUM> adjusts the temperature gradient ranging from the central axis C of the rod <NUM> toward the outside in the radial direction. With this structure, the heat radiator <NUM> enables easy control of the refractive index of the rod <NUM> when the second light beam <NUM> is absorbed into the rod <NUM>.

The optical element assembly <NUM> is capable of changing the focal position F along the central axis C. With this structure, the optical element assembly <NUM> according to the present embodiment enables transmission of a signal, for example, to a distant place at high speed. In addition, this structure enables change of the refractive index of the rod <NUM> at high speed without requiring any mechanical element components, such as a galvanometer mirror. Accordingly, this structure enables change of the light beam direction of the first light beam B1 by making the second light beam B2 of the second wavelength region incident on the central axis C of the rod <NUM> from the light emitting element <NUM>.

With the structure described above, the image formation optical system of the optical element assembly <NUM> according to the present embodiment is capable of changing the focus position seamlessly at high speed. Accordingly, the present embodiment provides an optical element assembly capable of adjusting the focal position at higher speed.

The present embodiment illustrates the example of forming the rod <NUM> in a circular columnar shape. The rod <NUM> may be pillars of various shapes, such as an elliptic columnar shape and a rectangular prism shape. In the case of using a rod <NUM> having no circular columnar shape, such as a rod <NUM> of a rectangular prism shape, the temperature distribution around the external circumference of the rod <NUM> may become non-uniform with respect to the central axis C. In this case, the refractive index can be adjusted by adjusting the heat radiator <NUM> to make the temperature distribution with respect to the central axis C uniform.

A second embodiment will now be explained with reference to <FIG>. The present embodiment is a modification of the first embodiment, the members explained in the first embodiment or members having the same functions as those of the members explained I the first embodiment are denoted with the same reference numerals as much as possible, and a detailed explanation thereof is omitted.

As illustrated in <FIG>, an optical element assembly <NUM> according to the present embodiment includes a rod <NUM>, a mirror 24a, and a light emitting element <NUM>. The lens <NUM> and the light beam intensity adjusting element <NUM> are omitted herein, but the lens <NUM> and the light beam intensity adjusting element <NUM> may be arranged between the light emitting element <NUM> and the mirror 24a.

The mirror 24a is disposed on a side of the first end <NUM> of the rod <NUM>. The mirror 24a crosses the central axis C. The mirror 24a is disposed in a state of <NUM>° with respect to the first end <NUM> of the rod <NUM>. The mirror 24a reflects light of the first wavelength region and transmits light of the second wavelength region, unlike the mirror <NUM> explained in the first embodiment.

The light emitting element <NUM> emits light of the second wavelength region. The light emitting element <NUM> is disposed in a position, for example, opposed to the first end <NUM>. The light emitted from the light emitting element <NUM> is emitted toward the mirror 24a.

Disposition of the mirror 24a with respect to the rod <NUM> can be properly set. When the mirror 24a is rotated around the central axis C while the mirror 24a maintains the state of <NUM>° with respect to the first end <NUM>, an image of a region of <NUM>° in a direction orthogonal to the central axis C is emitted from the second end <NUM> through the first end <NUM> of the rod <NUM>.

Accordingly, the optical element assembly <NUM> according to the present embodiment is capable of transmitting an image of a proper position, as well as an image of a position opposed to the first end <NUM> of the rod <NUM>, through the rod <NUM> from the second end of the rod <NUM> to a position opposed to the second end <NUM> of the rod <NUM>.

As explained above, the optical element assembly <NUM> according to the first and the second embodiment includes the transparent rod <NUM>, the mirror <NUM> or 24a, and the light emitting element <NUM>. The rod <NUM> transmits light of the first wavelength region made incident on the first end <NUM>, emits the light from the second end <NUM>, and absorbs light of the second wavelength region falling out of the first wavelength region. The mirror <NUM> or 24a is disposed on a side of the first end <NUM> of the rod <NUM>, transmits one of the light of the first wavelength region and the light of the second wavelength region, reflects the other. The light of the first wavelength region and the second wavelength region is made incident on the first end <NUM> of the rod <NUM>. The light emitting element <NUM> emits light of the second wavelength region. The light of the second wavelength region is made incident on the first end <NUM> of the rod <NUM> through the mirror <NUM> or 24a.

The first and the second embodiments provide the optical element assembly <NUM> capable of adjusting the focal position at higher speed.

The following is an explanation of an optical imaging device <NUM> including the optical element assembly <NUM> according to the first embodiment and the second embodiment with reference to <FIG>. The explanation will be made using the optical element assembly <NUM> explained in the first embodiment, but the optical element assembly <NUM> explained in the second embodiment may be used.

As illustrated in <FIG>, the optical imaging device <NUM> according to the present example includes the optical element assembly <NUM> and an image sensor <NUM>.

The image sensor <NUM> is disposed on a side of the second end <NUM> of the rod <NUM>. The image sensor <NUM> is capable of imaging an image transmitted through the mirror <NUM> and the rod <NUM> along the central axis C of the rod <NUM>.

In the present example, the change quantity Δn of the refractive index of the rod after temperature increase is set to satisfy, for example, <MAT>.

According to the present example, an image formation imaging optical system (optical imaging device <NUM>) is acquired by combining the optical element assembly <NUM> with the image sensor <NUM>.

The focus position of a first light beam B1 of the first wavelength region with the rod <NUM> can be set variable by changing the intensity of a second light beam B2 of the second wavelength region made incident on the first end <NUM> of the rod <NUM> from the light emitting element <NUM>, or adjusting the heat radiator <NUM> to generate temperature distribution.

The refractive index of the optical element assembly <NUM> increases by increasing the gradient of the refractive index from the central axis C toward the outside in the radial direction, and the refractive index decreases by decreasing the gradient of the refractive index.

As described above, the example (C) in <FIG> enables observation of the subject in the position closer to the first end <NUM> of the rod <NUM> than that in the example (B) in <FIG>. The optical element assembly <NUM> enables acquisition of an image of a desired distance from the first end <NUM> of the rod <NUM>, from a position close to the first end <NUM> of the rod <NUM> to a distant position (infinity), without mechanically moving the rod <NUM>. Specifically, the optical imaging device <NUM> according to the present embodiment enables acquisition of an image of a wide focal length, such as close-up photography and distant-view photography, by adjustment at higher speed without mechanical mechanism.

The following is an explanation of the optical imaging device <NUM> including the optical element assembly <NUM> according to the first embodiment with reference to <FIG>. The present example is a modification of the first example.

As illustrated in <FIG>, the mirror <NUM> is disposed in a position opposed to the first end <NUM> of the rod <NUM>. In addition, a mirror <NUM> is disposed on the central axis C of the rod <NUM>. The mirror <NUM> is positioned between the mirror <NUM> and the first end <NUM> of the rod <NUM>.

The mirror <NUM> reflects the light of the first wavelength region, and the reflected light is made incident on the first end <NUM> of the rod <NUM> through the mirror <NUM>.

With this structure, the imaging device <NUM> is capable of imaging an image of a proper position, as well as an image on the central axis C, with the image sensor <NUM>.

As illustrated in <FIG>, a mirror cube <NUM> is used instead of the mirror <NUM>. The mirror cube <NUM> is a type of the mirror <NUM>.

The mirror cube <NUM> can be directly attached to the first end <NUM> of the rod <NUM>. The mirror cube <NUM> is hard to be affected by air pressure and/or water pressure. For this reason, the mirror cube <NUM> has higher adaptavility to environments. For this reason, the optical element assembly <NUM> and the imaging device <NUM> including the optical element assembly <NUM> according to the present example can be used even in the water and/or the space.

The image sensor <NUM> can also be directly attached to the second end <NUM> of the rod <NUM>. Accordingly, the optical element assembly <NUM> according to the present modification enables achievement of an all-solid lens. the optical element assembly <NUM> according to the present example is solid and robust against oscillation.

The following is an explanation of an optical processing device <NUM> including the optical element assembly <NUM> according to the first embodiment and the second embodiment described above with reference to <FIG> and <FIG>. The explanation will be made using the optical element assembly <NUM> explained in the first embodiment, but the optical element assembly <NUM> explained in the second embodiment may be used.

As illustrated in <FIG>, the optical processing device <NUM> according to the present example includes the optical element assembly <NUM> and a laser light source (light emitter of the first wavelength region) <NUM> to emit the light of the first wavelength region.

The laser light source <NUM> emits laser light having proper power density enabling laser processing, as the light of the first wavelength region. The laser light source <NUM> is configured to enter the laser light to the first end <NUM> of the rod <NUM> via the mirror <NUM>, and emit the laser light from the second end <NUM> of the rod <NUM>.

Proper laser is used as the laser light source <NUM>. Examples of the proper laser include UV laser (excimer laser), green laser, CO2 laser, YAG laser, YVO laser, and fiber laser.

As an example, the wavelength region of infrared light is <NUM> to <NUM> (<NUM>). In the wavelength region, the wavelength region of near-infrared light is <NUM> to <NUM>, as an example. The wavelength region of the middle infrared light is <NUM> to <NUM>, for example. The wavelength region of the far infrared light is <NUM> to <NUM> (<NUM>), for example.

The wavelength of the UV laser is, for example, <NUM>. The wavelength of the green laser is, for example, <NUM>. For this reason, the wavelength regions of the UV laser and the green laser fall out of the wavelength region of the infrared light.

The wavelength of the CO2 laser is, for example, <NUM>. The wavelength of the YAG laser and the YVO laser is, for example, <NUM>. The wavelength of the fiber laser is, for example, <NUM>. For this reason, the wavelength regions of the CO2 laser, the YAG laser, the YVO laser, and the fiber laser fall within the wavelength region of the infrared light.

The mirror <NUM> can be set to transmit the light (laser light) of the first wavelength region and reflect the light of the second wavelength region, even in the same infrared region (wavelength of <NUM> to <NUM>), by a publicly-known manufacturing technique. For this reason, when laser processing is performed using laser light of the wavelength region of the infrared light, such as CO2 laser, YAG laser, YVO laser, and fiber laser, the mirror <NUM> according to the present example transmits light (laser light) of the first wavelength region and reflects light of the second wavelength region in the infrared region.

The rod <NUM> is formed of a material transmitting laser of a proper wavelength region in the infrared region, such as CO2 laser, YAG laser, YVO laser, and fiber laser, without absorbing the laser. When the second wavelength region is, for example, <NUM> (near infrared region) as described above, the first wavelength region of the infrared region is, for example, <NUM> to <NUM>, and sufficiently longer than the second wavelength region. The second wavelength region is preferably a wavelength region falling widely out of the first wavelength region. For this reason, for example, a glass material having absorbency of infrared rays having a wavelength, such as <NUM>, is used as the material of the rod <NUM>. By contrast, for example, a glass material transmitting infrared rays having a wavelength, such as <NUM>, is used as the material of the rod <NUM> according to the present example.

As described above, the material of the rod <NUM> is selected according to selection of the light beam B2 of the second wavelength region to be absorbed and the light beam B1 of the first wavelength region to be transmitted.

As illustrated in <FIG>, the focal position of the light of the first wavelength region can be adjusted by adjusting the refractive index on the basis of the temperature distribution extending toward the outside in the radial direction from the central axis C of the rod <NUM> with the light of the second wavelength region. For this reason, the processing point P (see <FIG>) of laser processing is moved forward and backward along the central axis C by adjusting the refractive index of the rod <NUM>. Accordingly, the optical processing device <NUM> is capable of adjusting the focal position, for example, from a focal position P1 to a focal position P2 serving as a distant focal position, without mechanically moving the lens or the like. In addition, the optical processing device <NUM> is capable of adjusting the focal position from the distant focal position P2 to the close focal position P1. This structure enables easy execution of laser processing on, for example, a surface S having projections and depressions.

The present example enables achievement of the laser processing device (optical processing device) <NUM> capable of instantly adjusting the position of the processing point.

Claim 1:
An optical element assembly (<NUM>) comprising:
a transparent rod (<NUM>) including a first end (<NUM>) and a second end (<NUM>), the transparent rod (<NUM>) being configured to transmit light of first wavelength region made incident on the first end (<NUM>) and emit the light of the first wavelength region from the second end (<NUM>), and being configured to absorb light of a second wavelength region falling out of the first wavelength region;
a mirror (<NUM>, <NUM>) disposed on a side of the first end (<NUM>) of the rod (<NUM>), being configured to transmit one of the light of the first wavelength region and the light of the second wavelength region, reflect the other, and the light of the first wavelength region and the light of the second wavelength region being made incident on the first end (<NUM>) of the rod (<NUM>);
a light emitting element (<NUM>) configured to emit light of the second wavelength region, and the light of the second wavelength region being made incident on the first end (<NUM>) of the rod (<NUM>) in a direction of a central axis of the rod through the mirror (<NUM>, <NUM>), and
being characterized in that
the first wavelength region includes a wavelength region of visible light, and
the second wavelength region includes a wavelength region of infrared rays.