JP2015179657A - Light emitting element and light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting device of a new configuration with directivity.SOLUTION: A light emitting element 100 comprises a laminar light emitting body 110 that emits light of wavelength λ by receiving excitation light, and a periodic structure 120 of a dielectric formed on the surface of the light emitting body 110. When a refractive index of the light emitting body 110 is nand the period of the periodic structure 120 is p, mλ/n<p<mλ (m represents an integer of 1 or more) is satisfied.

Description

  The present application relates to a light emitting device having directivity.

  Optical devices such as lighting, displays, and projectors are required to emit light in a necessary direction in many applications. For example, in lighting, a device for ensuring directivity using an optical system such as a reflector or a lens and illuminating a necessary place has been devised. Similarly, an optical system such as a reflector or a lens that controls the direction of light so that the display can be viewed with a certain viewing angle centered on the front, and the projector displays an image appropriately on the screen. Is used. For example, Patent Document 1 discloses an illumination system that secures directivity using a light distribution plate and an auxiliary reflector.

JP 2010-231941 A

  Since phosphors used in incandescent bulbs, fluorescent lamps, LED lighting, etc. emit light isotropically, an optical system such as a reflector or lens is generally required to emit light only in a specific direction. It is. However, when an optical system such as a reflector or a lens is arranged, it is necessary to enlarge a device or an instrument in order to secure the space.

  An LED that emits monochromatic light or a white LED that has been devised in the arrangement of phosphors can realize light emission having a certain degree of directivity, for example, light that spreads only about several tens of degrees. However, in applications where higher directivity is required, such as projectors and illumination, optical systems such as reflectors and lenses are still necessary.

  On the other hand, if a laser is used, extremely high directivity can be obtained. However, since laser light has high coherence, when it enters the human eye, it may damage the retina and impair visual acuity. Further, when an object is irradiated with laser light, speckles are generated on the irradiated surface, and there is a possibility that a person may feel uncomfortable when the person sees the object.

（ｍは１以上の整数）を満足する。 In order to solve the above problems, a light-emitting element according to one embodiment of the present invention includes a layered light-emitting body configured to emit light having a wavelength λ in response to excitation light, and the light-emitting element formed on the surface of the light-emitting body A dielectric periodic structure, where n _wav is the refractive index of the light emitter, and p is the period of the periodic structure,

(M is an integer of 1 or more).

  According to one embodiment of the present invention, a light-emitting device having directivity with a simple configuration can be realized.

It is a perspective view which shows the structure of the light emitting element in a certain embodiment. It is a fragmentary sectional view of the light emitting element shown to FIG. 1A. It is a perspective view which shows the structure of the light emitting element in other embodiment. It is a fragmentary sectional view of the light emitting element shown to FIG. 1C. It is a figure which shows the result of having calculated the intensity | strength of the light radiate | emitted in a front direction by changing the light emission wavelength and the height of a periodic structure, respectively. It is the graph which illustrated the conditions of m = 1 and m = 3 in Formula (10). It is a figure which shows the result of having calculated the intensity | strength of the light output to a front direction by changing the light emission wavelength and the thickness t of a waveguide. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 238 nm. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 539 nm. It is a figure which shows the result of having calculated the electric field distribution of the mode guided to x direction when thickness t = 300nm. It is a figure which shows the result calculated about the case where the polarization of light is TE mode which has an electric field component perpendicular | vertical to ay direction on the same conditions as the calculation of FIG. It is a top view which shows the example of a two-dimensional periodic structure. It is a figure which shows the result of having performed the calculation similar to FIG. 2 regarding 2D periodic structure. It is a figure which shows the result of having calculated the intensity | strength of the light output to a front direction by changing the light emission wavelength and the refractive index of a periodic structure. It is a figure which shows the result at the time of setting the film thickness of a waveguide to 1000 nm on the conditions similar to FIG. It is a figure which shows the result of having calculated the intensity | strength of the light which changes the light emission wavelength and the height of a periodic structure, and outputs it to a front direction. It is a figure which shows the calculation result when the refractive index of a periodic structure is set to _np = 2.0 on the conditions similar to FIG. It is a figure which shows the result of having performed the calculation similar to the calculation shown in FIG. 9, assuming that the polarization of light is a TE mode having an electric field component perpendicular to the y direction. It is a figure which shows the result at the time of changing the refractive index _{nwav of a} waveguide to 1.5 on the conditions similar to the calculation shown in FIG. It is a figure which shows the calculation result at the time of providing the waveguide and periodic structure of the same conditions as the calculation shown in FIG. 2 on the transparent substrate whose refractive index is 1.5. It is a graph which illustrated the conditions of Formula (13). It is a figure which shows the structural example of the light-emitting device 200 provided with the light emitting element 100 shown to FIG. 1A and 1B and the light source 180 which makes excitation light inject into the light-emitting body 110. FIG. It is a figure for demonstrating the structure which radiate | emits light efficiently by couple | bonding excitation light with waveguide mode. (A) shows a one-dimensional periodic structure having a period px in the x direction, (b) shows a two-dimensional periodic structure having a period px in the x direction and a period py in the y direction, and (c) shows a part of (a). The wavelength dependence of the absorptance to the waveguide mode of light in the configuration is shown, and (d) shows the wavelength dependence of the absorptance to the waveguide mode of light in the configuration of (b). It is a figure which shows an example of a two-dimensional periodic structure. It is a figure which shows the other example of a two-dimensional periodic structure. It is a figure which shows the modification which formed the periodic structure on the transparent substrate. It is a figure which shows the other modification which formed the periodic structure on the transparent substrate. FIG. 19B is a diagram illustrating a result of calculating the intensity of light output in the front direction by changing the emission wavelength and the period of the periodic structure in the configuration of FIG. 19A. It is a figure which shows the structure which mixed several powdery light emitting element. It is a top view which shows the example which arranged the several periodic structure from which a period differs on a waveguide two-dimensionally. It is a figure which shows an example of the light emitting element which has the structure where the several light emitting body 110 in which the uneven structure was formed on the surface was laminated | stacked. FIG. 5 is a cross-sectional view illustrating a configuration example in which a protective layer 150 is provided between a light emitter 110 and a periodic structure 120. It is a figure which shows the example which formed the periodic structure 120 by processing only a part of light-emitting body 110. FIG. It is a perspective view which shows typically an example of a slab type | mold waveguide.

  The outline | summary of embodiment of this indication is as follows.

（ｍは１以上の整数）を満足する。 (1) A light-emitting element according to one embodiment of the present disclosure includes a layered light-emitting body configured to receive excitation light and emit light having a wavelength λ, and a periodic structure of a dielectric formed on a surface of the light-emitting body When the refractive index of the light emitter is n _wav and the period of the periodic structure is p,

(M is an integer of 1 or more).

（ｍは１以上の整数）を満足する。 (2) A light-emitting element according to another aspect of the present disclosure includes a light-transmitting substrate and a layered light-emitting element formed on the light-transmitting substrate and configured to emit light having a wavelength λ upon receiving excitation light. And a periodic structure of a dielectric formed on the surface of the light emitter, the refractive index of the translucent substrate is n _s , the refractive index of the light emitter is n _wav , and the period of the periodic structure is When p is

(M is an integer of 1 or more).

  (3) In one embodiment, the thickness of the light emitter is designed so that a waveguide mode for light having a wavelength λ is formed inside the light emitter.

  (4) In one embodiment, m = 1.

  (5) In one embodiment, when the periodic structure is a first periodic structure, the light emitter is formed on a side opposite to a side on which the first periodic structure is formed, and the first structure A second periodic structure having the same period as the periodic structure is further provided.

  (6) In one embodiment, the dielectric is the same material as the light emitter.

  (7) In one embodiment, the refractive index of the dielectric is smaller than the refractive index of the light emitter.

  (8) In one embodiment, the periodic structure has a height of 150 nm or less.

  (9) In an embodiment, when the light emitter is a first light emitter and the periodic structure is a first periodic structure, the light emitter is formed on the opposite side of the first light emitter via the light-transmitting substrate. And a second light emitter configured to emit light of wavelength λ2, and a second periodic structure formed on the surface of the second light emitter.

（ｍは１以上の整数）を満足する。 (10) In an embodiment, when the wavelength λ2 and the wavelength λ are different, the refractive index of the second light emitter is n _wav2 , and the period of the second periodic structure is p ₂ ,

(M is an integer of 1 or more).

  (11) In one embodiment, the periodic structure has a structure in which a plurality of regions having different periods are two-dimensionally arranged.

  (12) In one embodiment, the periodic structure is a one-dimensional periodic structure.

  (13) In one embodiment, the periodic structure is a two-dimensional periodic structure.

  (14) In one embodiment, the periodic structure is a two-dimensional periodic structure having a plurality of periodic components.

  (15) In one embodiment, the light emitter includes a phosphor.

  (16) In one embodiment, the light emitter includes quantum dots.

  (17) A light-emitting device according to another aspect of the present disclosure includes any one of the light-emitting elements described above and a light source that causes excitation light to enter the light-emitting body so as to generate light having a wavelength λ from the light-emitting body. And comprising.

を満足するように設定されている。 (18) In one embodiment, the periodic structure has a periodic component having a period p in a first direction, and a period having a period p _ex different from the period p in a second direction different from the first direction. A two-dimensional periodic structure having components, where the wavelength of the excitation light is λ _ex , and the medium having the highest refractive index excluding the periodic structure among the media in contact with the light emitter is n _out. p _ex is

Is set to satisfy.

[1. Knowledge underlying this disclosure]
Before describing specific embodiments of the present disclosure, first, knowledge that is the basis of the present disclosure will be described. As described above, phosphors used in incandescent bulbs, fluorescent lamps, LED lighting, and the like emit isotropically, so an optical system such as a reflector or a lens is required to illuminate a specific direction with light. . However, if the light emitter itself emits light with directivity, the optical system as described above is not necessary, so that the size of the device or instrument can be greatly reduced. Based on such an idea, the inventor of the present application examined the configuration of the light emitter in detail in order to obtain directional light emission.

The inventor of the present application first considered that the light emission itself has a specific directionality so that the light from the light emitter is biased in a specific direction. The light emission rate Γ, which is an index characterizing light emission, is expressed by the following formula (1) according to Fermi's golden rule.

In equation (1), r is a position vector, λ is the wavelength of light, d is a dipole vector, E is an electric field vector, and ρ is a density of states. In many materials except some crystalline materials, the dipole vector d has a random orientation. In addition, when the size of the light emitter is sufficiently larger than the wavelength of light, the magnitude of the electric field E is almost constant regardless of the direction. Therefore, in most cases, the value of <(d · E (r))> ² does not depend on the direction. That is, the light emission rate Γ is constant regardless of the direction. For this reason, in most cases, the light emitter emits isotropically.

  On the other hand, in order to obtain anisotropic light emission from the formula (1), it is necessary to devise either the dipole vector d aligned in a specific direction or the electric field E enhanced only in a specific direction. is there. There is a possibility that directional light emission can be realized by any of these devices. In the present disclosure, a configuration for enhancing the electric field E only in a specific direction is examined, and a detailed analysis result will be described below.

[2. Configuration to strengthen only the electric field in a specific direction]
The inventor of the present application first focused on a slab type waveguide as a simple configuration for strengthening only an electric field in a specific direction. The slab type waveguide is a waveguide in which a light guiding portion has a flat plate structure. FIG. 25 is a perspective view schematically showing an example of a slab type waveguide. When the refractive index of the waveguide portion 110 is higher than the refractive index of the transparent substrate 140 supporting the waveguide, there is a mode of light propagating in the waveguide. If such a slab-type waveguide is formed of a phosphor material, the electric field of light generated from the light emitting point largely overlaps with the electric field of the guided mode, so that most of the light generated from the light emitting point is guided to the guided mode. Can be combined. Furthermore, by reducing the thickness of the slab waveguide, it is possible to create a situation where only a small number of waveguide modes exist.

式（２）におけるｍは整数であり、回折の次数を表す。 The inventor of the present application has conceived that light is coupled to a waveguide mode in a specific angular direction by forming a periodic structure on the surface of a waveguide (light emitter) where such a waveguide mode exists. FIG. 1A is a perspective view schematically showing an example of a light emitting device 100 having such a waveguide 110 and a periodic structure 120. In this example, the periodic structure 120 is a one-dimensional periodic structure in which a plurality of stripe-shaped convex portions each extending in the y direction are arranged at equal intervals in the x direction. FIG. 1B is a cross-sectional view of the light emitting device 100 taken along a plane parallel to the xz plane. When the periodic structure 120 having the period p is provided so as to be in contact with the waveguide 110, the waveguide mode having the wave number k _wav in the in-plane direction is converted into propagating light outside the waveguide, and the wave number k _out is expressed by the following equation: (2).

M in Formula (2) is an integer and represents the order of diffraction.

これらの式において、λ₀は光の波長、ｎ_wavは導波路の屈折率、ｎ_outは出射側の媒質の屈折率、θ_outは光が導波路外の基板または空気に出射するときの出射角度である。式（２）〜（４）から、出射角度θ_outは、以下の式（５）で表すことができる。

式（５）より、ｎ_wavｓｉｎθ_wav＝ｍλ₀／ｐが成立するとき、θ_out＝０となり、導波路の面に垂直な方向（正面）に光を出射させることができることがわかる。 Here, for the sake of simplicity, it is assumed that the light guided in the waveguide approximately is a light beam propagating at an angle θ _wav , and the following equations (3) and (4) hold.

In these equations, λ ₀ is the wavelength of light, n _wav is the refractive index of the waveguide, n _out is the refractive index of the medium on the output side, and θ _out is the output when the light is output to the substrate or air outside the waveguide. Is an angle. From the equations (2) to (4), the emission angle θ _out can be expressed by the following equation (5).

From equation (5), it can be seen that when n _wav sin θ _wav = mλ ₀ / p is satisfied, θ _out = 0, and light can be emitted in a direction (front) perpendicular to the plane of the waveguide.

  Based on the principle as described above, it is possible to emit strong light in that direction by coupling light emission to a specific waveguide mode and converting it into light having a specific emission angle using a periodic structure. it is conceivable that.

In order to realize the above situation, there are some constraints. First, since the waveguide mode must exist, it is necessary that the light propagating in the waveguide is totally reflected. The condition for this is expressed by the following formula (6).

In order to diffract this waveguide mode by the periodic structure and emit light outside the waveguide, it is necessary to satisfy −1 <sin θ _out <1 in Equation (5). Therefore, it is necessary to satisfy the following formula (7).

On the other hand, considering the equation (6), it can be seen that the following equation (8) should be satisfied.

Further, in order to make the direction of the light emitted from the waveguide 110 the front direction (θ _out = 0), it can be seen from the equation (5) that the following equation (9) is necessary.

From formula (9) and formula (6), it can be seen that the necessary condition is the following formula (10).

When the periodic structure as shown in FIGS. 1A and 1B is provided, the first-order diffracted light with m = 1 should be designed mainly because the high-order diffraction efficiency with m = 2 or higher is low. . For this reason, in the periodic structure in the present embodiment, m = 1 and the period p is determined so as to satisfy the following expression (11) obtained by modifying expression (10).

As shown in FIG. 1A and FIG. 1B, when the waveguide (light emitter) 110 is not in contact with the transparent substrate, n _out is the refractive index of air (about 1.0). ) Should be determined so as to satisfy the above.

On the other hand, a structure in which the light emitter 110 and the periodic structure 120 are formed on the transparent substrate 140 as illustrated in FIGS. 1C and 1D may be employed. In this case, determined from the refractive index n _s of the transparent substrate 140 is larger than the refractive index of air, the following equation was n _out = n _s in equation (11) the period p to satisfy (13) do it.

In equations (12) and (13), it is assumed that m = 1 in equation (10), but m ≧ 2 may be satisfied. That is, when both surfaces of the light emitting element 100 are in contact with the air layer as shown in FIGS. 1A and 1B, the period p is set so that m is an integer of 1 or more and the following expression (14) is satisfied. It only has to be done.

Similarly, as shown in FIGS. 1C and 1D, when the light emitting element 100 is formed on the transparent substrate 140, the period p may be set so as to satisfy the following expression (15). .

  By determining the period p of the periodic structure so as to satisfy the above inequality, light generated from the light emitter 110 can be emitted in the front direction, and thus a light emitting device having directivity can be realized.

[3. Verification by calculation]
[3-1. Period, wavelength dependence]
The inventor of the present application has verified by optical analysis whether light can be emitted in a specific direction as described above. The optical analysis was carried out by calculation using the Cybernet DiffractMOD. The film thickness of the waveguide is 1 μm, the refractive index of the waveguide is n _wav = 1.8, the height of the periodic structure is 50 nm, the refractive index of the periodic structure is 1.5, and the emission wavelength and the height of the periodic structure are respectively set. FIG. 2 shows the result of calculating the intensity of the electric field of the light emitted in the front direction. As shown in FIG. 1A, the calculation model was calculated with a uniform one-dimensional periodic structure in the y direction, and the polarization of light was a TM mode having an electric field component parallel to the y direction. In this calculation, for the sake of simplicity, the electric field distribution when light is incident from the front of the light emitting element was obtained by electromagnetic field analysis. Actually, since the light is emitted to the outside due to the waveguide mode of the light generated by the excitation light given from the external light source, the actual process is the reverse process of this calculation. From the results of FIG. 2, it can be seen that an intensity peak exists at a certain combination of wavelength and period.

  In the above calculation, the cross section of the periodic structure is assumed to be rectangular as shown in FIG. 1B. In a structure with a rectangular cross section, only odd-order diffracted light is generated, and even-order diffracted light is not generated. In order to confirm this, a graph illustrating the conditions of m = 1 and m = 3 in equation (10) is shown in FIG. Comparing FIG. 2 with FIG. 3, it can be seen that the peak positions in FIG. 2 exist at locations corresponding to m = 1 and m = 3 as expected. The reason why m = 1 is stronger is that the diffraction efficiency of the first-order diffracted light is higher than that of the third-order or higher-order diffracted light. The reason why the peak of m = 2 does not exist is that the diffraction efficiency in the periodic structure is low.

  In the region corresponding to each of m = 1 and m = 3 shown in FIG. 3, it can be confirmed that there are a plurality of lines in FIG. This is considered to be because there are a plurality of waveguide modes.

[3-2. Thickness dependence]
FIG. 4 is a front view in which the refractive index of the waveguide is n _wav = 1.8, the period of the periodic structure is 400 nm, the height is 50 nm, the refractive index is 1.5, and the emission wavelength and the waveguide thickness t are changed. It is a figure which shows the result of having calculated the intensity | strength of the electric field of the light output to a direction. It can be seen that the light intensity reaches a peak when the thickness t of the waveguide is a specific value.

  FIG. 5A and FIG. 5B show the results of calculating the electric field distribution of the mode guided in the x direction when the wavelength where the peak exists in FIG. 4 is 600 nm and the thickness is t = 238 nm and 539 nm. For comparison, FIG. 5C shows the result of the same calculation performed when t = 300 nm where no peak exists. The calculation model was assumed to be a one-dimensional periodic structure uniform in the y direction, as described above. In each figure, the black region indicates that the electric field strength is high, and the white region indicates that the electric field strength is low. In the case of t = 238 nm and 539 nm, there is a high electric field intensity distribution, whereas in the case of t = 300 nm, the electric field intensity is low overall. This is because when t = 238 nm and 539 nm, a waveguide mode exists and light is strongly confined. Further, comparing the case of t = 238 nm and the case of t = 539 nm, it can be seen that the number of nodes (white portions) of the electric field in the z direction is different by one. This is an effect due to the difference in the order of the waveguide mode by one. Furthermore, it can be seen that in the electric field distribution of t = 238 nm and 539 nm, an antinode of the electric field always exists at the center position of each convex portion of the periodic structure 120. That is, it can be seen that a guided mode is obtained according to the arrangement of the periodic structure 120.

[3-3. Polarization dependence]
Next, in order to confirm the polarization dependence, calculation was performed for the case where the polarization of light is a TE mode having an electric field component perpendicular to the y direction under the same conditions as those in FIG. The result of this calculation is shown in FIG. Compared to the TM mode (FIG. 2), the peak position is slightly changed, but the peak position is within the region shown in FIG. Therefore, it was confirmed that the configuration of this embodiment is effective for both TM mode and TE mode polarization.

[3-4.2 Two-dimensional periodic structure]
Furthermore, the effect by a two-dimensional periodic structure was examined. FIG. 7A is a plan view showing a part of a two-dimensional periodic structure 120 ′ in which concave and convex portions are arranged in both the x and y directions. The black area in the figure indicates a convex portion, and the white area indicates a concave portion. In such a two-dimensional periodic structure, it is necessary to consider diffraction in both the x and y directions. Diffraction only in the x direction or only in the y direction is the same as in the one-dimensional case, but there is also diffraction in a direction having both x and y components (oblique 45 ° direction). Different results can be expected. FIG. 7B shows the result of calculation regarding such a two-dimensional periodic structure. The calculation conditions other than the periodic structure are the same as the conditions in FIG. As shown in FIG. 7B, in addition to the peak position shown in FIG. 2, a peak position coinciding with the peak position in the TE mode shown in FIG. 6 was also observed. This result indicates that, due to the two-dimensional periodic structure, the TM mode waveguide mode is also converted into the TE mode by diffraction and output. In addition, regarding the two-dimensional periodic structure, it is necessary to consider diffraction that satisfies the first-order diffraction conditions simultaneously in both the x direction and the y direction. Such diffracted light is emitted in the direction of an angle corresponding to a period that is √2 times the period p. Therefore, in addition to the peak in the case of the one-dimensional periodic structure, it is considered that a peak is generated for a period that is √2 times the period p. In FIG. 7B, such a peak can also be confirmed.

  The two-dimensional periodic structure is not limited to a square lattice structure having the same period in the x direction and the y direction as shown in FIG. 7A, and may be a structure having different periods in the x direction and the y direction. Further, other lattice structures such as a triangular lattice and a hexagonal lattice may be used.

  As described above, according to the present embodiment, the characteristic guided mode light formed by the periodic structure and the waveguide can be selectively emitted only in the front direction using the diffraction phenomenon by the periodic structure. It could be confirmed. With such a configuration, a waveguide is made of a luminescent material, and the luminescent material is excited with excitation light such as ultraviolet light or blue light, whereby directional light emission can be obtained.

[4. Examination of periodic structure and waveguide configuration]
Next, the effect when various conditions such as the structure of the periodic structure and the waveguide and the refractive index are changed will be described.

[4-1. Refractive index of periodic structure]
First, the refractive index of the periodic structure was examined. The film thickness of the waveguide is 200 nm, the refractive index of the waveguide is n _wav = 1.8, the periodic structure is a one-dimensional periodic structure uniform in the y direction as shown in FIG. 1A, the height is 50 nm, and the period is 400 nm. The calculation was performed assuming that the polarization of light is a TM mode having an electric field component parallel to the y direction. FIG. 8 shows the result of calculating the intensity of light output in the front direction by changing the emission wavelength and the refractive index of the periodic structure. Further, FIG. 9 shows the result when the thickness of the waveguide is 1000 nm under the same conditions. First, focusing on the thickness of the waveguide, the light intensity with respect to the change in the refractive index of the periodic structure is more peak when the thickness is 1000 nm (FIG. 9) than when the thickness is 200 nm (FIG. 8). It can be seen that the shift of the wavelength (peak wavelength) is small. This is because as the film thickness is smaller, the waveguide mode is more susceptible to changes in the effective refractive index of the waveguide due to changes in the refractive index of the periodic structure. That is, the higher the refractive index of the periodic structure, the higher the effective refractive index, and the corresponding peak wavelength shifts to the longer wavelength side. This effect becomes more pronounced as the film thickness decreases. Next, paying attention to the change in the peak with respect to the change in the refractive index of the periodic structure, it can be seen that the higher the refractive index, the wider the peak and the lower the intensity. This is because the higher the refractive index of the periodic structure, the higher the rate at which guided mode light is emitted to the outside, so that the effect of confining the light decreases, that is, the Q value decreases. In order to keep the peak intensity high, it is only necessary to use a waveguide mode that has a high light confinement effect, that is, a high Q value, so that light is appropriately emitted to the outside. In order to realize this, it is understood that it is not desirable to use a material having a refractive index that is too large compared to the refractive index of the waveguide for the periodic structure. Therefore, in order to increase the peak intensity and Q value to some extent, the refractive index of the dielectric constituting the periodic structure may be made smaller than the refractive index of the light emitting material constituting the waveguide.

[4-2. Periodic structure height]
Next, the height of the periodic structure was examined. The film thickness of the waveguide is 1000 nm, the refractive index of the waveguide is n _wav = 1.8, the periodic structure is a uniform one-dimensional periodic structure in the y direction as shown in FIG. 1A, and the refractive index is n _p = 1.5, The calculation was performed on the assumption that the period was 400 nm and the polarization of light was a TM mode having an electric field component parallel to the y direction. FIG. 10 shows the result of calculating the intensity of light output in the front direction by changing the emission wavelength and the height of the periodic structure. FIG. 11 shows the calculation result when the refractive index of the periodic structure is n _p = 2.0 under the same conditions. In the result shown in FIG. 10, the peak intensity and the Q value (peak line width) do not change at a certain height or higher, whereas in the result shown in FIG. It turns out that intensity | strength and Q value are falling. This is because, when the refractive index n _{wav of the} waveguide is higher than the refractive index n _{p of the} periodic structure (FIG. 10), the light is totally reflected, so that only the portion where the electric field of the waveguide mode oozes out (evanescent). This is due to the interaction with the periodic structure. When the height of the periodic structure is sufficiently large, the influence of the interaction between the evanescent part of the electric field and the periodic structure is constant even if the height changes further. On the other hand, when the refractive index n _{wav of the} waveguide is lower than the refractive index n _{p of the} periodic structure (FIG. 11), the light reaches the surface of the periodic structure without being totally reflected. The bigger it is, the more affected. As can be seen from FIG. 11, it is sufficient that the height is about 100 nm, and the peak intensity and the Q value are lowered in the region exceeding 150 nm. Therefore, in order to increase the peak intensity and Q value to some extent, the height of the periodic structure may be set to 150 nm or less.

[4-3. Polarization direction]
Next, the polarization direction was examined. FIG. 12 shows the result of calculation assuming that the polarization of light is a TE mode having an electric field component perpendicular to the y direction under the same conditions as those shown in FIG. In the TE mode, the leakage of the electric field in the waveguide mode is larger than that in the TM mode, so that it is easily affected by the periodic structure. Therefore, in the region where the refractive index n _p of the periodic structure is larger than the refractive index n _{wav of the} waveguide, the peak intensity and the Q value are significantly decreased as compared with the TM mode.

[4-4. Refractive index of waveguide]
Next, the refractive index of the waveguide was examined. FIG. 13 shows the result when the refractive index n _{wav of the} waveguide is changed to 1.5 under the same conditions as the calculation shown in FIG. It can be seen that the same effect as in FIG. 9 is obtained even when the refractive index n _{wav of the} waveguide is 1.5. However, it can be seen that light having a wavelength of 600 nm or more is not emitted in the front direction. This is because λ ₀ <n _wav × p / m = 1.5 × 400 nm / 1 = 600 nm from Equation (10).

  From the above analysis, if the refractive index of the periodic structure is smaller than the refractive index of the waveguide, or if the refractive index of the periodic structure is equal to or higher than the refractive index of the waveguide, the height is reduced to 150 nm or less. It can be seen that the peak intensity and the Q value can be increased.

[5. Modified example]
Hereinafter, modifications of the present embodiment will be described.

[5-1. Configuration with substrate]
As described above, the light emitting element may have a structure in which the waveguide 110 and the periodic structure 120 are formed on the transparent substrate 140 as shown in FIGS. 1C and 1D. In order to manufacture such a light emitting device 100a, first, a method of forming a thin film with a light emitting material constituting the waveguide 110 on the transparent substrate 140 and forming the periodic structure 120 thereon may be considered. In this arrangement, the waveguide 110 and the periodic structure 120, in order to have a function of emitting light in a specific direction, it is necessary to pay attention to the refractive index n _s of the transparent substrate 140. When the transparent substrate 140 is provided so as to be in contact with the waveguide 110, it is necessary to set the period p so as to satisfy Expression (15) where the refractive index n _out of the output medium in Expression (10) is n _s .

In order to confirm this, calculation was performed when the waveguide 110 and the periodic structure 120 having the same conditions as those shown in FIG. 2 were provided on the transparent substrate 140 having a refractive index of 1.5. The result of this calculation is shown in FIG. As in the result of FIG. 2, it can be confirmed that a peak of light intensity appears in a specific period for each wavelength, but it can be seen that the range of the period in which the peak appears is different from the result of FIG. In contrast, shows the condition of the expression condition of (10) was n _out = n _s equation (15) in FIG. 15. In FIG. 14, it can be seen that the peak of the light intensity appears in the region corresponding to the range shown in FIG.

  Therefore, in the light emitting element 100a in which the waveguide 110 and the periodic structure 120 are provided on the transparent substrate 140, an effect can be obtained in the range of the period p that satisfies the expression (15), and the period p that satisfies the expression (13). A particularly remarkable effect is obtained in the range.

[5-2. Light emitting device having excitation light source]
FIG. 16 is a diagram illustrating a configuration example of a light emitting device 200 including the light emitting element 100 illustrated in FIGS. 1A and 1B and a light source 180 that causes excitation light to enter the light emitter 110. As described above, in the configuration of the present disclosure, light emission having directivity can be obtained by exciting a light emitter made of a light emitter material with excitation light such as ultraviolet light or blue light. By providing the light source 180 configured to emit such excitation light, the light emitting device 200 having directivity can be realized. The wavelength of the excitation light emitted from the light source 180 is typically a wavelength in the ultraviolet or blue region, but is not limited thereto, and is appropriately determined according to the light emitting material constituting the light emitter 110. In FIG. 16, the light source 180 is drawn so that the excitation light is incident from the side surface of the light emitter 110. However, the present invention is not limited to such an example. It may be incident.

There is also a method for efficiently emitting light by coupling excitation light to a waveguide mode. FIG. 17 is a diagram for explaining such a method. In this example, it is assumed that the layered light emitter 110 and the periodic structure 120 are formed on the transparent substrate 140 as in the configuration shown in FIGS. 1C and 1D. First, as shown in FIG. 17A, the period p _x in the x direction is determined to enhance the emission, and then, as shown in FIG. 17B, the excitation light is coupled to the waveguide mode. determining the period p _y in the y direction. The period p _x is determined so as to satisfy the condition in which p is replaced with p _x in Equation (10). On the other hand, in the period _py , m is an integer of 1 or more, the wavelength of the excitation light is λ _ex , and the medium having the highest refractive index excluding the periodic structure 120 among the media in contact with the light emitter 110 is n _out . It is determined so as to satisfy the following expression (16).

Here, n _out is n _s of the transparent substrate 140 in the example of FIG. 17, but in the configuration in which the transparent substrate 140 is not provided as in FIG. 16, it is the refractive index of air (about 1.0).

In particular, if m = 1 and the period py is determined so as to satisfy the following expression (17), the effect of converting the excitation light into the waveguide mode can be further enhanced.

Thus, by setting the period py so as to satisfy the condition of the expression (16) (particularly the condition of the expression (17)), the excitation light can be converted into the waveguide mode. As a result, light can be efficiently absorbed by the thin film of the illuminant 110, and light having the wavelength _λex can also be emitted to the outside.

FIGS. 17C and 17D are diagrams showing the results of calculating the ratio of light absorption for each wavelength when light is incident on the structure shown in FIGS. 17A and 17B, respectively. It is. In this calculation, p _x = 365 nm, and p _y = 265 nm, about 600nm and emission wavelength lambda of the light emitter 110, about 450nm wavelength lambda _ex of the exciting light, the extinction coefficient of the light emitter 110 is 0.003 . As shown in FIG. 17 (d), high absorptance is shown not only for light generated from the light emitter 110 but also for light of about 450 nm which is excitation light. This is because the incident light is effectively converted into the waveguide mode, so that the proportion absorbed by the light emitter can be increased. In addition, the absorptance is increased with respect to the emission wavelength of about 600 nm. This is because, if light having a wavelength of about 600 nm is incident on this structure, it is effectively converted into the waveguide mode as well. It is converted. Therefore, if light having a wavelength of about 600 nm is generated, the reverse process occurs, and the waveguide mode is effectively converted into propagating light.

  As described above, the periodic structure 120 illustrated in FIG. 17B is a two-dimensional periodic structure having structures (periodic components) having different periods in the x direction and the y direction, respectively. Thus, by using a two-dimensional periodic structure having a plurality of periodic components, it is possible to increase the emission intensity while increasing the excitation efficiency. In FIGS. 17C and 17D, the excitation light is incident from the substrate side, but the same effect can be obtained even if it is incident from the periodic structure side.

  Furthermore, as a two-dimensional periodic structure having a plurality of periodic components, a configuration as shown in FIG. 18A or 18B may be adopted. A configuration in which a plurality of convex portions having a hexagonal planar shape are periodically arranged as shown in FIG. 18A, and a configuration in which a plurality of convex portions having a triangular planar shape are periodically arranged as shown in FIG. 18B By doing so, a plurality of main axes (in the example of the figure, axes 1 to 3) that can be regarded as periods can be determined. For this reason, a different period can be assigned to each axial direction. Each of these periods may be set to increase the directivity of light having a plurality of wavelengths, or may be set to efficiently absorb the excitation light. In any case, each cycle is set so as to satisfy the condition corresponding to the equation (10).

[5-3. Periodic structure on transparent substrate]
As shown in FIGS. 19A and 19B, the periodic structure 120a may be formed on the transparent substrate 140, and the light emitter 110 may be provided thereon. In the configuration example of FIG. 19A, as a result of the light emitter 110 being formed so as to follow the periodic structure 120a made of irregularities on the substrate 140, the periodic structure 120b having the same period is also formed on the surface of the light emitter 110. On the other hand, in the configuration example of FIG. 19B, the surface of the light emitter 110 is processed to be flat. Also in these configuration examples, directional light emission can be realized by setting the period p of the periodic structure 120a so as to satisfy Expression (15).

In order to verify this effect, the intensity of light output in the front direction was calculated by changing the emission wavelength and the period of the periodic structure in the configuration of FIG. 19A. Here, the film thickness of the light emitter 110 is 1000 nm, the refractive index of the light emitter 110 is n _wav = 1.8, the periodic structure 120a is a uniform one-dimensional periodic structure in the y direction, the height is 50 nm, and the refractive index is n _p. = 1.5, the period was 400 nm, and the polarization of the light was a TM mode having an electric field component parallel to the y direction. The result of this calculation is shown in FIG. 19C. Also in this calculation, a peak of light intensity was observed at a period satisfying the condition of Expression (15).

[5-4. Powder]
According to the above embodiment, light emission of an arbitrary wavelength can be emphasized by adjusting the period of the periodic structure and the film thickness of the waveguide. For example, if a light emitting material that emits light in a wide band is used as shown in FIGS. 1A and 1B, only light having a certain wavelength can be emphasized. Therefore, the structure of the light emitter as shown in FIGS. 1A and 1B may be powdered and used as a phosphor. Further, a light emitter as shown in FIGS. 1A and 1B may be used by being embedded in a resin or glass.

  1A and 1B, since only a specific wavelength can be emitted in a specific direction, it is difficult to realize light emission such as white having a spectrum in a wide wavelength range. Therefore, as shown in FIG. 20, by using a mixture of a plurality of powdered light emitting elements 100 having different conditions such as the period of the periodic structure and the film thickness of the waveguide, a light emitting device having a spectrum in a wide wavelength region is obtained. realizable. In this case, the size of each light emitting element 100 in one direction is, for example, about several μm to several mm, and may include, for example, a one-dimensional or two-dimensional periodic structure of several cycles to several hundred cycles.

[5-5. Arrange structures with different periods]
FIG. 21 is a plan view showing an example in which a plurality of periodic structures having different periods are two-dimensionally arranged on a waveguide (light emitter). In this example, three types of periodic structures 120a, 120b, and 120c are arranged without a gap. For example, the periodic structures 120a, 120b, and 120c have a period set so as to emit light in the red, green, and blue wavelength ranges to the front. Thus, a directional light emitter having a spectrum in a wide wavelength region can be realized by arranging a plurality of structures with different periods on the waveguide. The configuration of the plurality of periodic structures is not limited to the above, and may be set arbitrarily.

[5-6. Laminated structure]
FIG. 22 shows an example of a light-emitting element having a structure in which a plurality of light-emitting bodies 110 having an uneven structure formed on the surface are stacked. A transparent substrate 140 is provided between the plurality of light emitters 110, and the uneven structure formed on the surface of the light emitter 110 of each layer corresponds to the periodic structure. In the example shown in FIG. 22, the three-layer periodic structures having different periods are formed, and the periods are set so as to emit light in the red, blue, and green wavelength ranges to the front. Further, the material of the light emitter 110 of each layer is selected so as to emit light of a color corresponding to the period of each periodic structure. Thus, a light emitter having a spectrum in a wide wavelength range can also be realized by laminating a plurality of periodic structures having different periods.

  Note that the number of layers and the configurations of the light emitters 110 and the periodic structures in each layer are not limited to those described above, and may be arbitrarily set. For example, in the two-layer configuration, the first light emitter and the second light emitter are formed to face each other with the light-transmitting substrate interposed therebetween, and the first and second light emitters are respectively formed on the surfaces of the first and second light emitters. And the 2nd periodic structure will be formed. In this case, the first light emitter and the first periodic structure pair and the second light emitter and the second periodic structure pair need only satisfy the conditions corresponding to Expression (15). . Similarly, in the configuration of three layers or more, it is only necessary to satisfy the condition corresponding to the formula (15) for the light emitter and the periodic structure in each layer. The positional relationship between the light emitter and the periodic structure may be reversed from that shown in FIG. In the example shown in FIG. 22, the period of each layer is different, but they may all be the same period. In that case, the spectrum cannot be widened, but the emission intensity can be increased.

[5-7. Configuration with protective layer]
FIG. 23 is a cross-sectional view illustrating a configuration example in which a protective layer 150 is provided between the light emitter 110 and the periodic structure 120. As described above, the protective layer 150 for protecting the light-emitting body 150 may be provided. However, when the refractive index of the protective layer 150 is lower than the refractive index of the light emitter 110, the electric field of light oozes out only about half the wavelength inside the protective layer 150. Therefore, when the protective layer 150 is thicker than the wavelength, light does not reach the periodic structure 120, and thus a function of emitting light in a specific direction cannot be obtained. When the refractive index of the protective layer 150 is equal to or higher than the refractive index of the light emitter 110, the light reaches the inside of the protective layer 150, and thus the protective layer 150 is not limited in thickness. However, even in that case, it is desirable that the protective layer 150 is thin because a larger light output can be obtained by forming most of the material of the waveguide portion with the light emitter 110.

[6. Material and Manufacturing Method]
If the waveguide and the periodic structure are made of a material that satisfies the above conditions, directional light emission can be realized. A light emitting material is used for the waveguide, but any material can be used for the periodic structure. However, if the light absorptivity of the medium forming the waveguide or the periodic structure is high, the effect of confining light is reduced, and the peak intensity and the Q value are reduced. Therefore, a medium having a relatively low light absorption can be used as a medium for forming the waveguide and the periodic structure.

As the material of the periodic structure, for example, a dielectric having low light absorption can be used. Examples of the material of the periodic structure include, for example, MgF (magnesium fluoride), LiF (lithium fluoride), CaF ₂ (calcium fluoride), SiO ₂ (quartz), glass, resin, MgO (magnesium oxide), ITO (indium tin oxide), TiO2 (titanium oxide), SiN (silicon nitride), Ta ₂ O ₅ (tantalum pentoxide), ZrO ₂ (zirconia), ZnSe (zinc selenide), and the like ZnS (zinc sulfide) . However, when the refractive index of the periodic structure is lower than the refractive index of the light emitter as described above, MgF, LiF, CaF ₂ , SiO ₂ , glass, and resin having a refractive index of about 1.3 to 1.5 are preferable. Can be used.

Examples of the light emitting material include phosphors, quantum dots, and other dyes. In general, a phosphor using an inorganic material as a host tends to have a high refractive index. Examples of phosphors emitting blue light include M ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca), BaMgAl ₁₀ O ₁₇ : Eu ²⁺ , M ₃ MgSi ₂ O ₈ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), M ₅ SiO ₄ Cl ₆ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) Can be used. Examples of phosphors emitting green light include M ₂ MgSi ₂ O ₇ : Eu ²⁺ (M = at least one selected from Ba, Sr and Ca), SrSi ₅ AlO ₂ N ₇ : Eu ²⁺ , SrSi _2. O ₂ N ₂ : Eu ²⁺ , BaAl ₂ O ₄ : Eu ²⁺ , BaZrSi ₃ O ₉ : Eu ²⁺ , M ₂ SiO ₄ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) BaSi ₃ O ₄ N ₂ : Eu ²⁺ Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu ²⁺ , Ca ₃ SiO ₄ Cl ₂ : Eu ²⁺ , CaSi _{12-(m + n)} Al _{(m + n ) ) O n n 16-n:} Ce 3+, β-SiAlON: Eu 2+ can be used. Examples of phosphors emitting red light include CaAlSiN ₃ : Eu ²⁺ , SrAlSi ₄ O ₇ : Eu ²⁺ , M ₂ Si ₅ N ₈ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca). Species), MSiN ₂ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), MSi ₂ O ₂ N ₂ : Yb ²⁺ (at least one selected from M = Sr and Ca), Y ₂ O ₂ S: Eu ³⁺ , Sm ³⁺ , La ₂ O ₂ S: Eu ³⁺ , Sm ³⁺ , CaWO ₄ : Li ¹⁺ , Eu ³⁺ , Sm ³⁺ , M ₂ SiS ₄ : Eu ²⁺ (At least one selected from M = Ba, Sr and Ca), M ₃ SiO ₅ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) can be used. Examples of phosphors that emit yellow light include Y ₃ Al ₅ O ₁₂ : Ce ³⁺ , CaSi ₂ O ₂ N ₂ : Eu ²⁺ , Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , and CaSc ₂ O _4. : Ce ³⁺ , α-SiAlON: Eu ²⁺ , MSi ₂ O ₂ N ₂ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca), M ₇ (SiO ₃ ) ₆ Cl ₂ : Eu ²⁺ (at least one selected from M = Ba, Sr and Ca) can be used.

  For the quantum dots, for example, materials such as CdS, CdSe, core / shell CdSe / ZnS, and alloy type CdSSe / ZnS can be used, and various emission wavelengths can be obtained depending on the material.

The transparent substrate 140 shown in FIGS. 1C and 1D is made of a light-transmitting material lower than the refractive index of the waveguide 110. Examples of such materials include MgF (magnesium fluoride), LiF (lithium fluoride), CaF ₂ (calcium fluoride), SiO ₂ (quartz), glass, and resin.

  Then, an example of a manufacturing method is demonstrated.

  As a method for realizing the configuration shown in FIGS. 1C and 1D, for example, a thin film of the light emitter 110 is formed on the transparent substrate 140 by a process such as vapor deposition, sputtering, and coating, and then a dielectric is formed. There is a method of forming the periodic structure 120 by patterning by a method such as photolithography. Instead of the above method, the periodic structure 120 may be formed by nanoimprinting. In addition, as shown in FIG. 24, the periodic structure 120 may be formed by processing only a part of the light emitter 110. In that case, the periodic structure 120 is formed of the same material as the light emitter 110.

  1A and 1B can be realized by, for example, manufacturing the light emitting element 100a shown in FIGS. 1C and 1D and then removing the waveguide 110 and the periodic structure 120 from the substrate 140. .

  In the configuration shown in FIG. 19A, for example, the periodic structure 120a is formed on the transparent substrate 140 by a method such as a semiconductor process or nanoimprint, and then the material constituting the light emitter 110 is formed thereon by a method such as vapor deposition or sputtering. This is possible. Alternatively, the structure shown in FIG. 19A can be realized by embedding the concave portion of the periodic structure 120a with the light emitter 110 using a method such as coating.

  In addition, said manufacturing method is an example and the light emitting element of this indication is not limited to said manufacturing method.

  According to the light emitting element of the present disclosure, since a light emitting device having directivity can be realized, the light emitting device can be applied to an optical device such as an illumination, a display, and a projector.

100, 100a Light-emitting element 110 Light emitter (waveguide)
120, 120 ′, 120a, 120b, 120c Periodic structure 140 Transparent substrate 150 Protective layer 180 Light source 200 Light emitting device

Claims (18)

A layered light emitter configured to emit light of wavelength λ in response to excitation light;
A periodic structure of a dielectric formed on the surface of the light emitter;
With
When the refractive index of the light emitter is n _wav and the period of the periodic structure is p,

A light-emitting element satisfying (m is an integer of 1 or more). A translucent substrate;
A layered light emitter formed on the translucent substrate and configured to emit light of wavelength λ upon receiving excitation light;
A periodic structure of a dielectric formed on the surface of the light emitter;
With
When the refractive index of the translucent substrate is n _s , the refractive index of the light emitter is n _wav , and the period of the periodic structure is p,

A light-emitting element satisfying (m is an integer of 1 or more).   3. The light emitting device according to claim 1, wherein a thickness of the light emitter is designed so that a waveguide mode for light having a wavelength λ is formed inside the light emitter.   The light emitting device according to claim 1, wherein m = 1. When the periodic structure is the first periodic structure,
The light emitter further includes a second periodic structure formed on a side opposite to the side on which the first periodic structure is formed and having the same period as the first periodic structure. 5. The light emitting device according to any one of 4.   The light emitting device according to claim 1, wherein the dielectric is the same material as the light emitter.   The light emitting element according to claim 1, wherein a refractive index of the dielectric is smaller than a refractive index of the light emitter.   The light emitting device according to claim 1, wherein a height of the periodic structure is 150 nm or less. When the light emitter is a first light emitter and the periodic structure is a first periodic structure,
A second light emitter formed on the opposite side of the first light emitter through the translucent substrate and configured to emit light of wavelength λ2,
A second periodic structure formed on the surface of the second light emitter;
The light emitting device according to claim 2, further comprising: Wavelength λ2 and wavelength λ are different,
When the refractive index of the second light emitter is n _wav2 and the period of the second periodic structure is p ₂ ,

The light emitting device according to claim 9, wherein m is an integer of 1 or more.   The light emitting device according to any one of claims 1 to 10, wherein the periodic structure has a structure in which a plurality of regions having different periods are two-dimensionally arranged.   The light emitting device according to claim 1, wherein the periodic structure is a one-dimensional periodic structure.   The light emitting device according to claim 1, wherein the periodic structure is a two-dimensional periodic structure.   The light emitting device according to claim 1, wherein the periodic structure is a two-dimensional periodic structure having a plurality of periodic components.   The light emitting device according to claim 1, wherein the light emitter includes a phosphor.   The light emitting element according to claim 1, wherein the light emitter includes quantum dots. The light emitting device according to any one of claims 1 to 16,
A light source that makes excitation light incident on the light emitter so as to generate light of wavelength λ from the light emitter;
A light emitting device comprising: The periodic structure is a two-dimensional periodic structure having a periodic component having a period p in a first direction and having a periodic component having a period p _ex different from the period p in a second direction different from the first direction. Yes,
When the wavelength of the excitation light is λ _ex and the refractive index of the medium having the highest refractive index excluding the periodic structure among the media in contact with the light emitter is n _out , the period p _ex is

The light emitting device according to claim 17, which is set to satisfy

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