Patent Description:
A light source device including a solid-state light source and a light transmission fiber has been proposed in the art as a light-emitting device (see, for example, Patent Literature <NUM>). In the light source device, the light transmission fiber has a first end face and a second end face, and excitation light emitted from the solid-state light source is introduced into the fiber through the first end face thereof. The light transmission fiber includes a wavelength converting core, a light-guiding core, and a clad. The wavelength converting core contains a wavelength converting material that produces a population inversion state of electrons by absorbing the excitation light and that lets wavelength converted light, falling within the visible radiation range, emerge therefrom. The light-guiding core covers the peripheral surface of the wavelength converting core and transmits the wavelength converted light from the first end face toward the second end face. The clad covers the peripheral surface of the light-guiding core.

The light transmission fiber is configured to have stimulated emission produced by the wavelength converted light propagating through the light-guiding core and to let not only the excitation light, emitted from the solid-state light source, but also the wavelength converted light, amplified by the stimulated emission, emerge from the second end face.

It is difficult for a light-emitting device such as the light source device of Patent Literature <NUM> to increase the intensity of the wavelength converted light.

"<NPL>]" describes al three-stage L-band erbium-doped fiber amplifier using the forward ASE amplified spontaneous emission from the first section of the EDF erbium-doped fiber and the backward ASE from the third section of the EDF both serve as the secondary pump sources of energy to pump the second EDF.

<CIT> describes a feedback-based dynamic gain control technique for a WDM system employing multi-wavelength-pumped Raman fiber amplifiers RFAs, in which only one feedback or feed-forward signal is required for the control of multiple Raman pumps.

<CIT> describes a Raman system, a primary laser source emits laser light at an initial wavelength, and a seed source emits a multi-wavelength seed laser light. The seed wavelengths correspond to a respective Stokes orders of the primary laser light. The primary laser light and the seed laser light are combined and fed into a Raman gain medium. Stimulated Raman scattering SRS causes the primary laser light to be converted into laser light at a selected target wavelength. The seeding of the primary light source mediates the conversion process.

<CIT> describes a fiber laser device, a laser processing apparatus, and a laser processing method, wherein the fiber laser device includes: a first seed light source for emitting first pulse seed beams; a second seed light source for emitting second pulse seed beams having a wavelength different from that of the first pulse seed beams; an excitation light source for emitting an excitation light; and an optical fiber in which a rare-earth element added to a core absorbs the excitation light, and which emits first laser beams having first amplified beams in which the first pulse seed beams are amplified and second amplified beams in which the second pulse seed beams are amplified.

It is therefore an object of the present disclosure to provide a light-emitting device and optical fiber with the ability to increase the intensity of light having a different wavelength from excitation light.

This object is solved by a light-emitting device and an optical fiber having the features of the independent claims. Additional embodiments are defined in the dependent claims.

The drawings to be referred to in the following description of first to fourth embodiments and their variations are all schematic representations. Thus, the ratio of the dimensions (including thicknesses) of respective constituent elements illustrated on the drawings does not always reflect their actual dimensional ratio.

A light-emitting device <NUM> according to a first embodiment will now be described with reference to <FIG>.

The light-emitting device <NUM> makes excitation light P1 and seed light P2 incident on an optical fiber <NUM> to which a wavelength converting material is added. The excitation light P1 excites the wavelength converting material. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by the excitation light P1. To the optical fiber <NUM>, at least one wavelength converting material may be added. From the optical fiber <NUM>, light P4 including the excitation light P1 and the stimulated emission of light P3 emerges. <FIG> illustrates the principle of operation of the light-emitting device <NUM>. In the light-emitting device <NUM>, an electron e- in a ground state E0 (including a plurality of energy levels) of the wavelength converting material is excited to an excitation level E2 by the excitation light P1 that has been incident on the optical fiber <NUM>. Then, the electron e- at the excitation level E2 makes a transition to a metastable level E1, which is an energy level lower than the excitation level E2. Thereafter, the stimulated emission of light P3 is produced when the electron e- at the metastable level E1 is caused to make a transition to one of the highest ones of the plurality of energy levels (hereinafter referred to as a "first energy level") of the ground state E0 by the seed light P2, of which the wavelength corresponds to the difference in energy between the metastable level E1 and the first energy level, for example. In addition, a stimulated emission of light is also produced when the electron e- at the metastable level E1 is caused to make a transition to another energy level lower than the metastable level E1 (hereinafter referred to as a "second energy level") by the seed light, of which the wavelength corresponds to the difference in energy between the metastable level E1 and the second energy level.

The light-emitting device <NUM> may be used in, for example, light fixtures, lighting devices, lighting systems, projectors, printers, and light sources for endoscopes. The light-emitting device <NUM> is applicable to not only various types of devices, systems, and other equipment for dwelling houses but also various types of devices, systems, and other equipment for other types of facilities and numerous types of moving vehicles. Examples of moving vehicles to which the light-emitting device <NUM> is applicable include automobiles, bicycles, railway trains, aircrafts, watercrafts, and drones.

The light-emitting device <NUM> includes the optical fiber <NUM>, a first light source unit <NUM>, and a second light source unit <NUM> as shown in <FIG>. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes the seed light P2, which causes the stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by the excitation light P1 (hereinafter referred to as "external seed light P2"), incident on the light incident portion <NUM>.

The optical fiber <NUM> includes a core <NUM>, a clad <NUM>, and a coating portion <NUM> as shown in <FIG>. The clad <NUM> covers the outer peripheral surface of the core <NUM>. The coating portion <NUM> covers the outer peripheral surface of the clad <NUM>. A cross section, taken along a plane perpendicular to the optical axis, of the core <NUM> has a circular shape. The clad <NUM> is disposed coaxially with the core <NUM>.

The core <NUM> has a first end face <NUM> and a second end face <NUM>, which is located at the opposite longitudinal end of the core <NUM> from the first end face <NUM>. The core <NUM> includes a light-transmitting material and the wavelength converting material described above. The concentration of the wavelength converting material in the core <NUM> may or may not be uniform along the entire length of the core <NUM>. The refractive index of the core <NUM> may be substantially equal to the refractive index of the light-transmitting material that is a main component of the core <NUM>.

The light-transmitting material may be, for example, a fluoride, an oxide, or a nitride. The fluoride may be glass fluoride, for example. The oxide may be a silicon oxide or quartz, for example.

The wavelength converting material is a rare earth element. In this embodiment, the wavelength converting material contains an element selected from the group consisting of, for example, Pr, Tb, Ho, Dy, Er, Eu, Nd, and Mn. The wavelength converting material is contained as an ion of a rare earth element in the core <NUM>, e.g., contained as an ion of Pr (Pr<NUM>+) or an ion of Tb (Tb<NUM>+) in the core <NUM>. In this case, the wavelength converting material may be excited by either the excitation light P1 or the light produced by amplifying the spontaneous emission of light, emitted from the wavelength converting material, as internal seed light, i.e., an amplified spontaneous emission (ASE) of light. Through such excitation, the wavelength converting material emits not only an ASE unique to the element of the wavelength converting material but also a stimulated emission of light having the same wavelength as the external seed light P2, thus emitting them as the stimulated emission of light P3. The wavelengths of the ASE and the external seed light P2 are longer than the wavelength of the excitation light P1 (which may fall within the range from <NUM> to <NUM>, for example). The wavelength of the seed light P2 will be described later in the "(<NUM>) Second light source unit" section.

<FIG> is an exemplary energy level diagram of Pr<NUM>+ (as for <FIG>, see, for example, Document <NUM> [<NPL>)]). In <FIG>, the ordinate indicates the electron energy. The signs on the right of <FIG> indicate the electronic configuration according to Russell Saunders. Also, in <FIG>, each of the upward arrows indicates the absorption of excitation light and each of the downward arrows indicates a transition about the spontaneous emission of light or the stimulated emission of light. As can be seen from <FIG>, Pr<NUM>+ is a wavelength converting material (wavelength converting element) that may emit either an ASE or amplified seed light in the cyan to red range. The intensity of the stimulated emission of light depends on the respective intensities of the internal seed light (the spontaneous emission of light) and the external seed light. If the core <NUM> contains Pr<NUM>+ and Tb<NUM>+, then Tb<NUM>+ is excited by absorbing an ASE from Pr<NUM>+ and may produce an ASE having a wavelength unique to Tb<NUM>+.

The refractive index of the clad <NUM> is less than the refractive index of the core <NUM>. The clad <NUM> does not contain the wavelength converting material contained in the core <NUM>.

The coating portion <NUM> covers the outer peripheral surface of the clad <NUM>. The material of the coating portion <NUM> may be a resin, for example.

The optical fiber <NUM> includes the light incident portion <NUM>, the light emerging portion <NUM>, and the wavelength converting portion <NUM>.

The light incident portion <NUM> is a portion on which the excitation light P1 is incident and may include the first end face <NUM> of the core <NUM>, for example. The light emerging portion <NUM> includes the second end face <NUM> of the core <NUM>, through which light including the excitation light P1 and the stimulated emission of light P3 such as an ASE emerges.

The light incident portion <NUM> may include a reflection reducing portion for reducing the reflection of the excitation light P1 incident on the light incident portion <NUM> from outside of the optical fiber <NUM>. The reflection reducing portion may be, for example, an anti-reflection coating that covers the first end face <NUM> of the core <NUM>. The reflection reducing portion suitably includes a non-reflective coating with respect to light in a deep infrared range with a wavelength of <NUM> or more.

The light emerging portion <NUM> includes a reflection reducing portion <NUM> for reducing reflection of the excitation light P1 and the stimulated emission of light P3 including an ASE. The reflection reducing portion <NUM> is suitably made of a transparent material, of which the refractive index is substantially equal to that of the core <NUM>, for example. The reflection reducing portion <NUM> includes an end cap, for example. Providing the reflection reducing portion <NUM> for the light emerging portion <NUM> allows the optical fiber <NUM> to reduce an increase in the electric field strength due to reflection from the second end face <NUM> of the core <NUM> and also protect the second end face <NUM> of the core <NUM> from laser damage. In the light-emitting device <NUM>, if the second end face <NUM> of the core <NUM> is in contact with the air, a Fresnel reflection of a few % could be caused at the second end face <NUM>, thus possibly causing parasitic oscillation that makes it difficult to control the optical output. To reduce the Fresnel reflection, the optical fiber <NUM> suitably includes the reflection reducing portion <NUM> bonded to the second end face <NUM> of the core <NUM>. The material for the reflection reducing portion <NUM> may also be glass fluoride, silicon oxide, or quartz, for example. The light emerging portion <NUM> has a tilted surface <NUM> which is tilted by a predetermined angle (of <NUM> degrees, for example) with respect to a plane intersecting at right angles with the optical axis of the optical fiber <NUM>. This enables, even if there is a refractive index jump between the reflection reducing portion <NUM> and the core <NUM>, the light-emitting device <NUM> to reduce components of light reflected back from the boundary between the second end face <NUM> of the core <NUM> and the reflection reducing portion <NUM> to the first end face <NUM> (i.e., back reflected components) to -<NUM> dB or less, thus causing an increase in the efficiency of the light emerging from the light emerging portion <NUM>. The predetermined angle does not have to be <NUM> degrees. In this embodiment, the predetermined angle is suitably equal to or greater than <NUM> degrees, for example, more suitably equal to or greater than <NUM> degrees, and even more suitably equal to or greater than <NUM> degrees. Meanwhile, the predetermined angle is suitably equal to or less than <NUM> degrees, for example, more suitably equal to or less than <NUM> degrees, and even more suitably equal to or less than <NUM> degrees. When measured along the optical axis of the optical fiber <NUM>, the length of the end cap suitably falls within the range from <NUM> to <NUM>, for example. In this embodiment, the end cap is disposed over both the core <NUM> and the clad <NUM>. However, this is only an example and should not be construed as limiting. Rather, the end cap only needs to be disposed on the second end face <NUM> of the core <NUM>. The reflection reducing portion <NUM> does not have to be the end cap but may also be, for example, a microscopic surface unevenness (on the order of <NUM> or less) formed on the second end face <NUM> of the core <NUM>. In that case, the end cap may or may not be provided from the viewpoint of reflection reduction.

The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains the wavelength converting material. The wavelength converting material is excited by the excitation light P1 to emit light having a longer wavelength than the excitation light P1. The wavelength converting material is a material that may absorb the excitation light P1 and amplify, by stimulated emission, either the spontaneous emission of light or seed light having a longer wavelength than the excitation light P1. In this embodiment, the wavelength converting portion <NUM> is provided along the entire length of the core <NUM> between the light incident portion <NUM> and the light emerging portion <NUM>. However, this is only an example and should not be construed as limiting. Alternatively, the wavelength converting portion <NUM> may be provided for only a part of the core <NUM> between the light incident portion <NUM> and the light emerging portion <NUM>. That is to say, in this optical fiber <NUM>, the wavelength converting material may be added to either the entire core <NUM> or only a part of the core <NUM>, whichever is appropriate.

The core <NUM> may have a diameter falling within the range from <NUM> to <NUM>, for example. The optical fiber <NUM> may have a length falling within the range from <NUM> to <NUM>, for example. As for the length of the optical fiber <NUM>, the wavelength converting portion <NUM> suitably has a length equal to or greater than <NUM>, more suitably equal to or greater than <NUM>, and even more suitably equal to or greater than <NUM>. As for the length of the wavelength converting portion <NUM>, the lower the concentration of the wavelength converting material in the wavelength converting portion <NUM> is, the greater the length of the wavelength converting portion <NUM> suitably is. The optical fiber <NUM> may have a numerical aperture of <NUM>, for example.

The first light source unit <NUM> emits the excitation light P1 to excite the wavelength converting material contained in the wavelength converting portion <NUM> of the optical fiber <NUM>. The excitation light P1 emitted from the first light source unit <NUM> is incident on the light incident portion <NUM> of the optical fiber <NUM>.

The first light source unit <NUM> may include a laser light source <NUM>, for example. The laser light source <NUM> emits a laser beam. The first light source unit <NUM> makes the laser beam, emitted from the laser light source <NUM>, incident as the excitation light P1 on the light incident portion <NUM>. The laser light source <NUM> may be, for example, a semiconductor laser diode that emits a blue laser beam. In that case, the excitation light P1 may have a wavelength falling within the range from <NUM> to <NUM>, for example. The laser light source <NUM> does not have to be a semiconductor laser diode that emits a blue laser beam but may also be a light-emitting diode (LED) light source or another type of light source (such as a semiconductor laser diode that emits a violet laser beam).

The light coupling method for making the excitation light P1 incident on the light incident portion <NUM> of the optical fiber <NUM> may be fiber coupling using an optical fiber coupler or spatial coupling, whichever is appropriate.

In the light-emitting device <NUM> according to the first embodiment, the first light source unit <NUM> includes a grating <NUM> disposed between the laser light source <NUM> and the light incident portion <NUM> of the optical fiber <NUM>. The laser beam (excitation light P1) emitted from the laser light source <NUM> is diffracted by the grating <NUM> and then incident on the light incident portion <NUM>. The grating <NUM> may be a transmissive diffraction grating, for example. The material for the grating <NUM> may be, but does not have to be, quartz, for example.

The second light source unit <NUM> emits the seed light P2. The seed light P2 emitted from the second light source unit <NUM> is incident on the light incident portion <NUM> of the optical fiber <NUM>.

In the light-emitting device <NUM>, the second light source unit <NUM> makes a plurality of seed light rays P2, having mutually different wavelengths, incident on the light incident portion <NUM> of the optical fiber <NUM>. In this embodiment, the second light source unit <NUM> may include, for example, three seed light sources <NUM>, <NUM>, <NUM> that emit light rays with mutually different wavelengths. The seed light source <NUM> may be a semiconductor laser diode or an LED that emits a green light ray, for example. The seed light source <NUM> may be a semiconductor laser diode or an LED that emits an orange light ray, for example. The seed light source <NUM> may be a semiconductor laser diode or an LED that emits a red light ray, for example. If the wavelength converting material of the wavelength converting portion <NUM> includes Pr<NUM>+, then the wavelength of the green amplified light ray is suitably about <NUM>, for example, the wavelength of the orange amplified light ray is suitably about <NUM>, for example, and the wavelength of the red amplified light ray is suitably about <NUM>, for example (see <FIG>). The seed light sources <NUM>-<NUM> are light sources, each of which emits quasi-monochromatic light. As used herein, the "quasi-monochromatic light" refers to light falling within a narrow wavelength range (with a width of <NUM>, for example).

The second light source unit <NUM> makes the light ray emitted from the seed light source <NUM> incident as a seed light ray P2 (P21) on the light incident portion <NUM> of the optical fiber <NUM>. In addition, the second light source unit <NUM> also makes the light ray emitted from the seed light source <NUM> incident as a seed light ray P2 (P22) on the light incident portion <NUM> of the optical fiber <NUM>. Furthermore, the second light source unit <NUM> makes the light ray emitted from the seed light source <NUM> incident as a seed light ray P2 (P23) on the light incident portion <NUM> of the optical fiber <NUM>.

The second light source unit <NUM> shares the grating <NUM> in common with the first light source unit <NUM>. The light (seed light P2) emitted from the second light source unit <NUM> is diffracted by the grating <NUM> and then incident on the light incident portion <NUM>.

The light-emitting device <NUM> makes the first light source unit <NUM> emit the excitation light P1 and also makes the second light source unit <NUM> emit the seed light P2. Thus, in the light-emitting device <NUM>, the excitation light P1 and the seed light P2 are incident on the light incident portion <NUM> of the optical fiber <NUM>. Part of the excitation light P1 incident on the light incident portion <NUM> emerges from the light emerging portion <NUM>. In the light-emitting device <NUM>, the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM> is mixed light in which the excitation light P1, an ASE with a wavelength of about <NUM> and produced from the wavelength converting material, and the seed light P2 that has been amplified (i.e., the light having the same wavelength as the seed light P2) are mixed together. Four types of stimulated emissions of light P3 with mutually different wavelengths may be, for example, a cyan ray, a green ray, an orange ray, and a red ray. In that case, the mixed light may be white light, for example.

In the optical fiber <NUM>, stimulated emission is produced by the spontaneous emission of light and the seed light P2, and therefore, the excitation light P1 incident on the light incident portion <NUM> and the stimulated emission of light P3 amplified by stimulated emission emerge from the light emerging portion <NUM>. The mixed light emerging from the light emerging portion <NUM> of the optical fiber <NUM> is incoherent light. In the light-emitting device <NUM>, as the light incident through the light incident portion <NUM> of the optical fiber <NUM> comes closer toward the light emerging portion <NUM>, the stimulated emission of light P3 increases or decreases. In the light-emitting device <NUM>, the chromaticity, color temperature, color rendering performance, and other parameters of the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM> are determined by the respective wavelengths of the ASE and the seed light P2. Note that the operation of the light-emitting device <NUM> is different from the operation of a fiber laser that produces laser oscillation.

In the light-emitting device <NUM>, the wavelength converting material that serves as a heat source is distributed in the core <NUM> of the optical fiber <NUM>, and therefore, an increase in temperature may be reduced while the light-emitting device <NUM> is being used.

Optionally, the light-emitting device <NUM> may include a lens <NUM> disposed between the grating <NUM> and the light incident portion <NUM>. The lens <NUM> is provided to efficiently introduce the excitation light P1 and the seed light P2 into the light incident portion <NUM> of the optical fiber <NUM>.

Also, the light-emitting device <NUM> may further include a control member for controlling the intensity of each of the plurality of seed light rays P2. This allows the light-emitting device <NUM> to control the chromaticity of the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM>. In other words, the light-emitting device <NUM> may control the color of the emerging light.

The control member may be, for example, an optical member disposed between the plurality of seed light sources <NUM>-<NUM> of the second light source unit <NUM> and the optical fiber <NUM> and may include a plurality of wavelength filters. Each of the plurality of wavelength filters may be an optical element including an optical multi-layer film, for example.

The control member does not have to be an optical member including a plurality of wavelength filters but may also be, for example, a plurality of drivers provided one to one for the plurality of seed light sources <NUM>-<NUM> of the second light source unit <NUM> to drive the plurality of seed light sources <NUM>-<NUM>, respectively.

A light-emitting device <NUM> according to the first embodiment includes an optical fiber <NUM>, a first light source unit <NUM>, and a second light source unit <NUM>. The optical fiber <NUM> includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes seed light P2 incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. Thus, the light-emitting device <NUM> according to the first embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P3) having a different wavelength from the excitation light P1.

In addition, in the light-emitting device <NUM> according to the first embodiment, the wavelength converting portion <NUM> contains Pr<NUM>+ as the wavelength converting material. The wavelength converting material not only emits an ASE in cyan but also increases the respective intensities of stimulated emissions in green, orange, and red, because a plurality of seed light rays P2 with mutually different wavelengths are incident onto the light incident portion <NUM>. This allows the light-emitting device <NUM> according to the first embodiment to improve the color rendering performance of the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM>. Furthermore, in the light-emitting device <NUM> according to the first embodiment, the wavelength converting portion <NUM> contains Pr<NUM>+ and Tb<NUM>+ as wavelength converting materials, thus enabling further improving the color rendering performance of the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM>. At this time, Tb<NUM>+ absorbs the ASE in cyan from Pr<NUM>+, thus not only optimizing the ASE intensity in cyan but also producing an ASE in yellow green (with a wavelength of about <NUM>).

Furthermore, an optical fiber <NUM> according to the first embodiment includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light by stimulated emission to produce an amplified spontaneous emission of light. The excitation light P1 and seed light P2 are incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. Thus, the optical fiber <NUM> according to the first embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P3) having a different wavelength from the excitation light P1.

Next, a light-emitting device 1a according to a second embodiment will be described with reference to <FIG>. In the following description, any constituent element of the light-emitting device 1a according to this second embodiment, having the same function as a counterpart of the light-emitting device <NUM> of the first embodiment described above, will be designated by the same reference numeral as that counterpart's, and description thereof will be omitted herein.

The light-emitting device 1a according to the second embodiment includes neither the grating <NUM> nor the control member disposed between the plurality of (e.g., three in the example illustrated in <FIG>) seed light sources <NUM>-<NUM> of the second light source unit <NUM> and the optical fiber <NUM> of the light-emitting device <NUM> according to the first embodiment. The light-emitting device 1a according to the second embodiment includes a lens <NUM> disposed between the first light source unit <NUM> and the second light source unit <NUM> and the light incident portion <NUM>, which is a major difference from the light-emitting device <NUM> according to the first embodiment.

The first light source unit <NUM> and the second light source unit <NUM> are mounted on a single mount board <NUM>. The first light source unit <NUM> includes the laser light source <NUM>. The second light source unit <NUM> includes the plurality of seed light sources <NUM>-<NUM>.

The lens <NUM> may be, for example, a condenser lens for efficiently introducing, into the light incident portion <NUM> of the optical fiber <NUM>, the excitation light P1 emitted from the first light source unit <NUM> and the seed light P2 emitted from the second light source unit <NUM>.

In the light-emitting device 1a according to the second embodiment, the wavelength converting portion <NUM> also includes, as in the light-emitting device <NUM> of the first embodiment, the wavelength converting material that is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1 and that amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes the seed light P2 incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. This allows the light-emitting device 1a according to the second embodiment to increase the intensity of the light having a different wavelength from the excitation light P1 (i.e., the stimulated emission of light P3).

Optionally, the light-emitting device 1a according to the second embodiment may include, as a control member for controlling the respective intensities of the plurality of seed light rays P2 (P21), P2 (P22), P2 (P23), a plurality of drivers provided one to one for the plurality of seed light sources <NUM>-<NUM> of the second light source unit <NUM> to drive the plurality of seed light sources <NUM>-<NUM>, respectively.

Next, a light-emitting device 1b according to a third embodiment will be described with reference to <FIG>. In the following description, any constituent element of the light-emitting device 1b according to this third embodiment, having the same function as a counterpart of the light-emitting device <NUM> of the first embodiment described above, will be designated by the same reference numeral as that counterpart's, and description thereof will be omitted herein.

In the light-emitting device 1b according to the third embodiment, the first light source unit <NUM> and the second light source unit <NUM> each include a white light source <NUM> and a spectroscopic grating <NUM>.

The white light source <NUM> may be, for example, a white LED including a blue LED chip and a wavelength converting layer. The blue LED chip emits a blue light ray. The wavelength converting layer covers the blue LED chip. The wavelength converting layer includes particles of a wavelength converting material to be excited by the blue light ray emitted from the blue LED chip and emit a yellow light ray. The white light source <NUM> is mounted on a mount board <NUM>.

The spectroscopic grating <NUM> separates white light into, for example, the excitation light P1 (the blue light ray) and a plurality of (e.g., three in the example illustrated in <FIG>) seed light rays P21, P22, P23. The seed light ray P21 may be a green light ray, for example. The seed light ray P22 may be an orange light ray, for example. The seed light ray P23 may be a red light ray, for example. The grating <NUM> is a transmissive diffraction grating. The material for the grating <NUM> may be, but does not have to be, quartz, for example.

The light-emitting device 1b further includes a collimator lens <NUM>, a collimator lens 18A, a control member <NUM>, a collimator lens 18B, and a condenser lens <NUM>. The collimator lens <NUM> is disposed between the white light source <NUM> and the spectroscopic grating <NUM>. The collimator lenses 18A, 18B are arranged between the spectroscopic grating <NUM> and the grating <NUM>. The condenser lens <NUM> is disposed between the grating <NUM> and the light incident portion <NUM> of the optical fiber <NUM>.

The collimator lens <NUM> makes the white light emitted from the white light source <NUM> incident on the spectroscopic grating <NUM>.

The collimator lens 18A collimates the excitation light P1 and the plurality of seed light rays P21, P22, P23 that have come from the spectroscopic grating <NUM>.

The control member <NUM> controls the respective intensities of the plurality of seed light rays P21, P22, P23. The control member <NUM> may include, for example, a filter for controlling the transmission wavelength or a liquid crystal filter with the ability to control the transmittance.

The collimator lens 18B makes the excitation light P1 and the plurality of seed light rays P21, P22, P23 incident on the grating <NUM>.

The grating <NUM> diffracts the excitation light P1 and the plurality of seed light rays P21, P22, P23 that have been incident thereon.

The condenser lens <NUM> makes the excitation light P1 and the seed light rays P21, P22, P23, which have been transmitted through the grating <NUM>, incident on the light incident portion <NUM>.

In the light-emitting device 1b according to the third embodiment, the wavelength converting portion <NUM> also includes, as in the light-emitting device <NUM> of the first embodiment, the wavelength converting material. The wavelength converting material is excited by the excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1 and amplifies the spontaneous emission of light by stimulated emission to produce an amplified spontaneous emission of light. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes the seed light P2 incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. This allows the light-emitting device 1b according to the third embodiment to increase the intensity of the light having a different wavelength from the excitation light P1 (i.e., the stimulated emission of light P3).

Next, a light-emitting device 1c and an optical fiber 2c according to a fourth embodiment will be described with reference to <FIG>. In the following description, any constituent element of the light-emitting device 1c according to this fourth embodiment, having the same function as a counterpart of the light-emitting device <NUM> of the first embodiment described above, will be designated by the same reference numeral as that counterpart's, and description thereof will be omitted herein.

The light-emitting device 1c according to the fourth embodiment includes an optical fiber 2c instead of the optical fiber <NUM> of the light-emitting device <NUM> according to the first embodiment, which is a major difference from the light-emitting device <NUM> according to the first embodiment.

The optical fiber 2c further includes first optical fibers <NUM> and a second optical fiber <NUM>, which are coupled to the first end face <NUM> of the core <NUM>. Each of the first optical fibers <NUM> includes a core <NUM> to which no wavelength converting material is added. The second optical fiber <NUM> also includes a core <NUM> to which no wavelength converting material is added. The material for the core <NUM> may be the same as the main component of the core <NUM>, for example. The material for the core <NUM> may be the same as the main component of the core <NUM>, for example. The refractive index of the cores <NUM>, <NUM> is suitably the same as the refractive index of the core <NUM>.

In addition, in the optical fiber 2c according to the fourth embodiment, the light incident portion <NUM> includes first light incident portions <NUM> and a second light incident portion <NUM>. The excitation light P1 is incident on each of the first light incident portions <NUM>. The second light incident portion <NUM> is provided separately from the first light incident portions <NUM>. The seed light P2 is incident on the second light incident portion <NUM>. In this embodiment, a plurality of seed light rays P2 are incident on the second light incident portion <NUM>.

In the optical fiber 2c, each of the first light incident portions <NUM> is configured as the first optical fiber <NUM>, while the second light incident portion <NUM> is configured as the second optical fiber <NUM>. The optical fiber 2c includes a plurality of first light incident portions <NUM>. Thus, the light-emitting device 1c includes the plurality of first light incident portions <NUM>. The light-emitting device 1c includes a plurality of first light source units <NUM>. The plurality of first light source units <NUM> are arranged to correspond one to one to the plurality of first light incident portions <NUM>.

The optical fiber 2c according to the fourth embodiment, as well as the optical fiber <NUM> according to the first embodiment, includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light by stimulated emission to produce an amplified spontaneous emission of light. The excitation light P1 and seed light P2 are incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. Thus, the optical fiber 2c according to the fourth embodiment enables increasing the intensity of light (i.e., the stimulated emission of light P3) having a different wavelength from the excitation light P1.

In addition, the optical fiber 2c according to the fourth embodiment includes the first light incident portions <NUM> and the second light incident portion <NUM>, and therefore, makes it easier for the excitation light P1 and the seed light P2 to be incident on the light incident portion <NUM>.

Note that the first to fourth embodiments described above are only exemplary ones of various embodiments of the present disclosure and should not be construed as limiting. Rather, the first to fourth exemplary embodiments may be readily modified in various manners depending on a design choice or any other factor without departing from the scope of the present disclosure.

For example, in the optical fiber <NUM>, the number of the wavelength converting portion(s) <NUM> provided between the light incident portion <NUM> and the light emerging portion <NUM> does not have to be one but may also be multiple, for example. In the latter case, the plurality of wavelength converting portions <NUM> are arranged along the optical axis of the core <NUM>.

Also, the light emerging portion <NUM> does not have to have the tilted surface <NUM> which is tilted by a predetermined angle with respect to a plane intersecting at right angles with the optical axis of the optical fiber <NUM>. Alternatively, the second end face <NUM> of the core <NUM> may intersect at right angles with the optical axis of the optical fiber <NUM>.

Furthermore, the second light source unit <NUM> may be made up of a plurality of LEDs. In that case, the second light source unit <NUM> may include a photonic crystal having a super-lens effect between the plurality of LEDs and the light incident portion <NUM>, for example.

Furthermore, in the light-emitting devices <NUM>, 1a, 1c, the second light source unit <NUM> includes a plurality of seed light sources (e.g., three seed light sources <NUM>-<NUM>). However, this is only an example and should not be construed as limiting. Rather, the second light source unit <NUM> may include at least one seed light source.

Furthermore, the light-emitting device 1b includes the white light source <NUM>. Alternatively, the light-emitting device 1b may include, for example, an SC (super continuum) light source instead of the white light source <NUM>.

The first to fourth embodiments and their variations described above may be specific implementations of the following aspects of the present disclosure.

A light-emitting device <NUM>; 1a; 1b; 1c according to a first aspect includes an optical fiber <NUM>, a first light source unit <NUM>, and a second light source unit <NUM>. The optical fiber <NUM> includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes seed light P2 incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. A wavelength of the excitation light P1 falls within the range from <NUM> to <NUM>.

The light-emitting device <NUM>; 1a; 1b; 1c according to the first aspect enables increasing the intensity of light i.e., the stimulated emission of light P3 having a different wavelength from the excitation light P1.

In the light-emitting device <NUM>; 1a; 1b; 1c, the wavelength converting material contains Pr<NUM>+ and Tb<NUM>+.

This enables, when the wavelength converting material contains two or more elements, for example, excitation by an amplified spontaneous emission of light from at least one element to produce an amplified spontaneous emission of light at a different wavelength from another element.

In the light-emitting device <NUM>; 1a; 1b; 1c, a plurality of seed light rays P21, P22, P23, having mutually different wavelengths and forming the seed light P2, are incident on the light incident portion <NUM>.

Thus, the light-emitting device <NUM>; 1a; 1b; 1c enables light P4, including multiple stimulated emissions of light P3 corresponding one to one to the plurality of seed light rays P21, P22, P23, to emerge from the light emerging portion <NUM>.

The second light source unit <NUM> may include a plurality of light sources (seed light sources <NUM>, <NUM>, <NUM>) to emit the plurality of seed light rays P21, P22, P23, respectively.

Thus, the light-emitting device <NUM>; 1a; 1c enables mixed light (light P4), in which the excitation light P1 and a plurality of stimulated emissions of light P3 with mutually different wavelengths are mixed together, to emerge from the light emerging portion <NUM>.

The light-emitting device <NUM>; 1a; 1b; 1c may further include a control member <NUM> to control respective intensities of the plurality of seed light rays P21, P22, P23.

Thus, the light-emitting device <NUM>; 1a; 1b; 1c enables controlling the chromaticity of the light P4 emerging from the light emerging portion <NUM> of the optical fiber <NUM>.

A light-emitting device 1b according to a second aspect includes an optical fiber <NUM>, a first light source unit <NUM>, and a second light source unit <NUM>. The optical fiber <NUM> includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The first light source unit <NUM> makes the excitation light P1 incident on the light incident portion <NUM>. The second light source unit <NUM> makes seed light P2 incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. A plurality of seed light rays P21. P23 having mutually different wavelengths and forming the seed light (P2), are incident on the light incident portion (<NUM>). The first light source unit <NUM> and the second light source unit <NUM> each include: a white light source <NUM>; and a spectroscopic grating <NUM>. The spectroscopic grating <NUM> lets the excitation light P1 and the plurality of seed light rays P21, P22, P23 emerge therefrom by separating light emitted from the white light source <NUM> into multiple components of the light.

the light incident portion <NUM> may include a reflection reducing portion to reduce reflection of the excitation light P1 and the seed light P2.

Thus, reflection of the excitation light P1 and the seed light P2 is reduced when the excitation light P1 and the seed light P2 are incident on the light incident portion <NUM>, thus contributing to increasing the optical output of the light P4 emerging from the light emerging portion <NUM>.

The light emerging portion <NUM> may have a tilted surface <NUM> tilted by a predetermined angle with respect to a plane intersecting at right angles with an optical axis of the optical fiber <NUM>.

This contributes to increasing the optical output of the light P4 emerging from the light emerging portion <NUM>.

The light emerging portion <NUM> may include a reflection reducing portion <NUM> to reduce reflection of the excitation light P1 and the stimulated emission of light P3.

The first light source unit <NUM> may include a laser light source <NUM>.

This enables increasing the intensity of the excitation light P1.

An optical fiber <NUM>; 2c according to a third aspect includes a light incident portion <NUM>, a light emerging portion <NUM>, and a wavelength converting portion <NUM>. The wavelength converting portion <NUM> is provided between the light incident portion <NUM> and the light emerging portion <NUM>. The wavelength converting portion <NUM> contains a wavelength converting material. The wavelength converting material is excited by excitation light P1 to produce a spontaneous emission of light having a longer wavelength than the excitation light P1. The wavelength converting material also amplifies the spontaneous emission of light to produce an amplified spontaneous emission of light. The excitation light P1 and seed light P2 are incident on the light incident portion <NUM>. The seed light P2 causes a stimulated emission of light P3 to be produced from the wavelength converting material that has been excited by either the excitation light P1 or the amplified spontaneous emission of light. The wavelength converting material contains Pr<NUM>+ and Tb<NUM>+.

The optical fiber <NUM>; 2c according to the third aspect enables increasing the intensity of light i.e., the stimulated emission of light P3 having a different wavelength from the excitation light P1.

The light incident portion <NUM> may include a first light incident portion <NUM> and a second light incident portion <NUM>. On the first light incident portion <NUM>, the excitation light P1 is incident. The second light incident portion <NUM> is provided separately from the first light incident portion <NUM>. On the second light incident portion <NUM>, the seed light P2 is incident.

Claim 1:
A light-emitting device (<NUM>; 1a; 1c) comprising:
an optical fiber (<NUM>) including a light incident portion (<NUM>), a light emerging portion (<NUM>), and a wavelength converting portion (<NUM>), the wavelength converting portion (<NUM>) being provided between the light incident portion (<NUM>) and the light emerging portion (<NUM>) and containing a wavelength converting material, the wavelength converting material being able to be excited by excitation light (P1) to produce a spontaneous emission of light having a longer wavelength than the excitation light (P1), the wavelength converting material being suitable for amplifying the spontaneous emission of light to produce an amplified spontaneous emission of light (P3);
a first light source unit (<NUM>) configured to make the excitation light (P1) incident on the light incident portion (<NUM>); and
a second light source unit (<NUM>) configured to make seed light (P2) formed by a plurality of seed light rays (P21, P22, P23) incident on the light incident portion (<NUM>), the seed light (P2) being light for causing a stimulated emission of light (P3) to be produced from the wavelength converting material that has been excited by either the excitation light (P1) or the amplified spontaneous emission of light (P3), the plurality of seed light rays (P21, P22, P23), having mutually different wavelengths and forming the seed light (P2), being incident on the light incident portion (<NUM>), characterized in that
a wavelength of the excitation light (P1) falling within the range from <NUM> to <NUM>,
the wavelength converting material contains Pr<NUM>+ and Tb<NUM>+.