JP2000182764A - El device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an end luminescence type EL device having remarkably narrower spectral band width of luminescent wavelength compared with the conventional EL(electroluminescence) element, capable of applying to optical communication in addition to a display device, and emitting light having different wave lengths. SOLUTION: An end luminescence type EL device 1000 has an organic luminescent layer 40; a pair of electrode layers 30, 50 (50a, 50b) for applying an electric field to the organic luminescent layer 40; and a light guide channel for transmitting light generated in the organic luminescent layer 40 to the end. The light guide channel has a core layer 20 for mainly transmitting light and clad layers 10, 60 having smaller index of refraction than the core layer 20. The core layer 20 is made of a layer different from the organic luminescent layer 40. A diffraction grating 100 is formed between the core layer 20 and the clad layer 10. The diffraction grating 100 has two diffraction gratings 100a and 100b having different resonance wave lengths, and emits light having two different wave lengths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using EL (electroluminescence).

[0002]

2. Description of the Related Art For example, a semiconductor laser is used as a light source used in an optical communication system. A semiconductor laser is preferable because it has excellent wavelength selectivity and can emit a single-mode light, but requires many times of crystal growth and is not easy to fabricate.
Further, the semiconductor laser has a drawback that the light emitting material is limited and light of various wavelengths cannot be emitted.

Further, the conventional EL light emitting device has a wide spectral width of an emission wavelength and is applied to some uses such as a display body, but is used for an application requiring light with a narrow spectral width such as optical communication. Was unsuitable.

An object of the present invention is to provide a light emitting wavelength spectrum width that is much narrower than that of a conventional EL light emitting element, has directivity, can be applied not only to a display, but also to optical communication and the like. An object of the present invention is to provide an EL device capable of emitting light of a wavelength.

[0005]

An EL device according to the present invention has a light emitting layer capable of emitting light by electroluminescence, at least one pair of electrode layers for applying an electric field to the light emitting layer, and a light emitting layer formed in the light emitting layer. An optical waveguide for propagating light, wherein a diffraction grating is formed in the optical waveguide, the diffraction grating comprises a plurality of diffraction gratings having different optical lengths of the pitch, and a plurality of diffraction gratings corresponding to each diffraction grating. Light having different resonance wavelengths can be emitted.

According to this EL device, electrons and holes are injected into the light emitting layer from at least one pair of electrode layers, that is, a cathode and an anode, and the electrons and holes are recombined in the light emitting layer to form a molecule. Light is generated when returns to the ground state from the excited state. Light generated in the light emitting layer resonates by a diffraction grating formed in any layer of the optical waveguide, and has wavelength selectivity and directivity. Since a plurality of diffraction gratings having different pitch optical lengths are formed in the light propagation direction, a plurality of light beams corresponding to the resonance wavelength of each diffraction grating can be emitted. The diffraction grating means a grating in which two types of regions having different refractive indexes are alternately and periodically arranged.

The plurality of diffraction gratings have the following configuration (1)
To (3).

(1) The plurality of diffraction gratings are each made of the same material and have different pitch lengths.

(2) The plurality of diffraction gratings are made of different materials and have the same pitch length.

(3) The plurality of diffraction gratings are made of different materials and have different pitch lengths.

Furthermore, it is preferable that the electrode layers are formed so as to form pairs corresponding to the number of diffraction gratings, and that the electrode layers can be independently controlled corresponding to each of the plurality of diffraction gratings.

Preferably, the diffraction grating is a distributed feedback type or a distributed Bragg reflection type diffraction grating. As described above, by forming a distributed feedback type or a distributed Bragg type diffraction grating, light having wavelength selectivity, a narrow emission spectrum width, and directivity can be obtained.
In these diffraction gratings, the optical length and depth of the pitch of the diffraction grating are set according to the wavelength of the emitted light.

Further, the diffraction grating of the distributed feedback type has a wavelength of λ /
By using a four-phase shift structure or a gain-coupling type structure, emitted light can be made to have a single mode. Here, λ represents the wavelength of light in the optical waveguide.

In particular, it is a desirable common configuration in the EL device according to the present invention that the diffraction grating is of a distributed feedback type and further has a λ / 4 phase shift structure or a gain coupling type structure. The diffraction grating only needs to be able to achieve the function of the above-described diffraction grating, and its formation region may be any layer constituting the optical waveguide.

The light emitting layer preferably contains an organic light emitting material as a light emitting material. By using an organic light emitting material, for example, a material selection range is wider than when a semiconductor material or an inorganic material is used, and light of various wavelengths can be emitted.

Such an EL device can take, for example, the following embodiments (a) and (b).

(A) In the EL device according to the first aspect, the optical waveguide includes a core layer through which light mainly propagates, and a cladding layer having a lower refractive index than the core layer. It is characterized in that it is formed by a layer different from the light emitting layer.

Preferably, the core layer is made of a material having a higher refractive index than the light emitting layer. When the refractive index has such a relationship, light generated in the light emitting layer can be efficiently introduced into the core layer.

For example, when the light emitting layer is made of an organic material, the core layer includes not only a layer for only light propagation but also a hole transport layer, an electron transport layer, and a transparent electrode layer. It can also serve as one. Further, the clad layer may be a layer having a smaller refractive index than the core layer. For example, when the light emitting layer is made of an organic material, not only a layer only for confining light but also an electrode layer, It can also serve as a substrate, a hole transport layer, an electron transport layer, and the like.

(B) In the EL device according to a second aspect, the optical waveguide includes a core layer through which light is mainly propagated, and a clad layer having a smaller refractive index than the core layer. It is characterized in that it includes the light emitting layer.

The core layer may further include at least one of a hole transport layer, an electron transport layer, and a transparent electrode layer, for example, when the light emitting layer is made of an organic material. Further, the clad layer may be a layer having a smaller refractive index than the core layer. For example, when the light emitting layer is made of an organic material, not only a layer only for confining light but also an electrode layer, It can also serve as a substrate, a hole transport layer, an electron transport layer, and the like.

In the first and second aspects, the diffraction grating in the optical waveguide is provided in any one of the core layer, the cladding layer, and an interface region between the cladding layer and a layer such as the core layer which is in contact with the cladding layer. Can also be formed by the above-described configurations (1) to (3).

The EL device of the present invention can be easily manufactured by a film forming method which is considerably simpler than a semiconductor laser, has a much narrower spectral width of an emission wavelength than a conventional EL light emitting device, and has a directivity. And can be applied not only to display bodies but also to optical communication and the like.

Next, some of the materials that can be used for each part of the EL device according to the present invention will be described. These materials are only a part of known materials, and it is a matter of course that materials other than those exemplified can be selected.

(Light Emitting Layer) The material of the light emitting layer is selected from known compounds in order to obtain light emission of a predetermined wavelength. The material of the light emitting layer may be either an organic compound or an inorganic compound, but is preferably an organic compound from the viewpoint of abundant types and film-forming properties.

As such an organic compound, for example,
Aromatic diamine derivatives (TPD), oxydiazole derivatives (PBD), oxydiazole dimers (OXD) disclosed in JP-A-10-153967
-8), distilylylene derivative (DSA), beryllium-benzoquinolinol complex (Bebq), triphenylamine derivative (MTDATA), rubrene, quinacridone, triazole derivative, polyphenylene, polyalkylfluorene, polyalkylthiophene, azomethine zinc complex, Porphyrin zinc complex, benzoxazole zinc complex, phenanthroline europium complex and the like can be used.

More specifically, examples of the material for the organic light emitting layer include those described in JP-A-63-70257 and JP-A-63-1758.
No. 60, JP-A-2-135361, 2-1.
JP-A-35359, JP-A-3-152184, JP-A-8-248276 and JP-A-10-1539
Known materials such as those described in JP-A-67 can be used. These compounds may be used alone or as a mixture of two or more.

As inorganic compounds, ZnS: Mn (red region), ZnS: TbOF (green region), SrS: C
u, SrS: Ag, SrS: Ce (blue region), and the like.

(Optical Waveguide) The optical waveguide includes a core layer and a cladding layer having a smaller refractive index than the core layer. Known inorganic and organic materials can be used for the core layer and the clad layer.

Representative inorganic materials include, for example,
As disclosed in JP-A-5-273427, Ti
O_Two, TiO_Two-SiO_TwoMixture, ZnO, Nb_TwoO_Five, S
i_ThreeN _Four, Ta_TwoO_Five, HfO_TwoOr ZrO_TwoFor example
Can be

As typical organic materials, known resins such as various thermoplastic resins, thermosetting resins, and photocurable resins can be used. These resins are appropriately selected in consideration of a method of forming a layer and the like. For example, by using a resin that can be cured by at least one of heat and light, a general-purpose exposure apparatus, a baking furnace, a hot plate, or the like can be used.

As such a substance, for example, there is an ultraviolet curable resin disclosed in Japanese Patent Application No. 10-279439 filed by the present applicant. Acrylic resin is suitable as the UV-curable resin. By using various commercially available resins and photosensitizers, it is possible to obtain an ultraviolet-curable acrylic resin which is excellent in transparency and can be cured by a short-term treatment.

Specific examples of the basic constitution of the ultraviolet-curable acrylic resin include a prepolymer, an oligomer and a monomer.

As the prepolymer or oligomer,
For example, acrylates such as epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, and spiroacetal acrylates; methacrylates such as epoxy methacrylates, urethane methacrylates, polyester methacrylates, and polyether methacrylates; Is available.

Examples of the monomer include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-vinyl-2-pyrrolidone, carbitol acrylate, tetrahydrofurfuryl acrylate, isovol Monofunctional monomers such as nyl acrylate, dicyclopentenyl acrylate, and 1,3-butanediol acrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate,
Bifunctional monomers such as neopentyl glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol diacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
Polyfunctional monomers such as pentaerythritol triacrylate and dipentaerythritol hexaacrylate can be used.

In the above, an inorganic material or an organic material considering only the propagation or confinement of light has been exemplified. As described above, the core layer or the clad layer may include a light emitting layer, a hole transport layer, an electron transport layer, and an electrode layer. When at least one of the layers functions as a core layer or a cladding layer, the material forming these layers can also be adopted as the material forming the optical waveguide.

(Hole transporting layer) The material of the hole transporting layer provided as necessary may be a material used as a hole injecting material of a known photoconductive material or an organic E material.
It can be selected from known materials used for the hole injection layer of the L device. The material of the hole transport layer has a function of injecting holes or blocking electrons, and may be an organic substance or an inorganic substance. As a specific example, see, for example,
No. 48276 can be exemplified.

(Electron Transporting Layer) The material of the electron transporting layer provided as necessary may have a function of transmitting electrons injected from the cathode to the light emitting layer. You can choose. Specific examples thereof include those disclosed in JP-A-8-248276.

(Electrode Layer) As the cathode, an electron-injecting metal, an alloy electrically conductive compound or a mixture thereof having a small work function (for example, 4 eV or less) can be used.
Examples of such an electrode material include, for example, JP-A-8-248.
No. 276 can be used.

As the anode, a metal, an alloy, an electrically conductive compound or a mixture thereof having a large work function (for example, 4 eV or more) can be used. When an optically transparent material is used for the anode, CuI, ITO, SnO
₂ , conductive transparent materials such as ZnO can be used,
When transparency is not required, a metal such as gold can be used.

In the present invention, the method of forming the diffraction grating is not particularly limited, and a known method can be used. Representative examples are shown below.

Lithography Method A positive or negative resist is exposed and developed with ultraviolet rays or X-rays to pattern the resist layer.
Create a diffraction grating. As a patterning technique using a resist such as polymethyl methacrylate or a novolak resin, there are, for example, JP-A-6-224115 and JP-A-7-20637.

A technique for patterning polyimide by photolithography is disclosed in, for example,
181689 and 1-222141. Furthermore, as a technique for forming a diffraction grating of polymethyl methacrylate or titanium oxide on a glass substrate by using laser ablation, there is, for example, Japanese Patent Application Laid-Open No. 10-59743.

Method of Forming Refractive Index Distribution by Light Irradiation Light of a wavelength causing a change in the refractive index is applied to the optical waveguide (core layer) of the optical waveguide, and a portion having a different refractive index is periodically applied to the optical waveguide. To form a diffraction grating. As such a method, it is particularly preferable to form a layer of a polymer or a polymer precursor, partially polymerize the layer by light irradiation or the like, and periodically form regions having different refractive indexes to form a diffraction grating. . Examples of this type of technology include, for example, JP-A-9-31238 and JP-A-9-17890.
No. 1, No. 8-15506, No. 5-29720
No. 2, No. 5-32523, No. 5-39480
JP, JP-A-9-211728, JP-A-10-2670
No. 2, No. 10-8300, and No. 2-51
No. 101 publication.

Method by stamping Hot stamping using a thermoplastic resin (Japanese Unexamined Patent Publication No.
No. 201907), stamping using an ultraviolet curable resin (Japanese Patent Application No. 10-279439), stamping using an electron beam curable resin (Japanese Unexamined Patent Publication No. 7-235075).
A diffraction grating is formed by stamping as described in Japanese Unexamined Patent Publication (Kokai) No. H11-209686.

Etching Method The thin film is selectively removed and patterned by lithography and etching techniques to form a diffraction grating.

Method by Capillary A material constituting a diffraction grating is selectively applied directly to a substrate by a capillary to form a diffraction grating. Publications that disclose capillary technology include, for example,
36337 and JP-A-8-160239.

The method of forming the diffraction grating has been described above. In short, the diffraction grating only needs to be composed of two regions having different refractive indices, and two regions having different refractive indices are formed. It can be formed by a method, a method of forming two regions having different refractive indexes by partially modifying a kind of material, or the like.

Each layer of the EL device can be formed by a known method. For example, a suitable film forming method is selected for the light emitting layer depending on its material, and specific examples include a vapor deposition method, a spin coating method, an LB method, and an ink jet method.

[0050]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows an edge-emitting EL device (hereinafter referred to as "organic E") according to this embodiment.
FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a diffraction diagram taken along the line BB of FIG. It is sectional drawing which shows a grating | lattice.

In the organic EL device 1000, a first cladding layer 10, a core layer 20, an anode 30, an organic light emitting layer 40, a cathode 50, and a second cladding layer 60 are laminated in this order. In the organic EL device 1000, the refractive index of the first clad layer 10 and the second clad layer 60 is such that light having a refractive index between the first clad layer 10 and the second clad layer 60 can be transmitted. Is set smaller than the refractive index of each layer to be formed.

In the present embodiment, a plurality of diffraction gratings 100 (two in the illustrated example) are formed in the boundary region between the first cladding layer 10 and the core layer 20. Diffraction grating 100
As shown in FIGS. 2 and 3, a first diffraction grating 100a and a second diffraction grating 100b are provided side by side in the light propagation direction. The refractive index of the first cladding layer 10 is n
1. Assuming that the refractive index of the core layer 20 is n2, a relationship of n1 <n2 holds. When the optical length of the pitch P1 of the first diffraction grating 100a is L1, and the optical length of the pitch P2 of the second diffraction grating 100b is L2, a relationship of L1> L2 is established. That is, in this example, the resonance wavelength is changed by changing the optical length of the pitch between the two diffraction gratings. The optical length of the pitch has the following relationship with the width d of the unevenness of the diffraction grating and the refractive index n.

L1 = n1 · d2 + n2 · d1 L2 = n1 · d4 + n2 · d3 where n1: refractive index of the core layer 20 n2: refractive index of the first cladding layer 10 d1: convex portion of the first diffraction grating 100a D2: the width of the concave portion of the first diffraction grating 100a d3: the width of the convex portion of the second diffraction grating 100b d4: the width of the concave portion of the second diffraction grating 100b The first diffraction grating 100a and the second diffraction Lattice 100b
And λ1 and λ, respectively.
If 2 (λ1 and λ2 are different), the following equation is established.

L1 = λ1 / 2 · (2m ₁ +1) L2 = λ2 · 2 (2m ₂ +1) Here, m ₁ and m ₂ are integers of 0 or more.

The diffraction grating 100 (100a, 100b)
Is preferably a distributed feedback diffraction grating. By forming the distributed feedback type diffraction grating in this manner, light can resonate in the optical waveguide, and light having excellent wavelength selectivity and a narrow emission spectrum width can be obtained. Further, although not shown, the diffraction grating 100 preferably has a λ / 4 phase shift structure or a gain coupling type structure. By having the λ / 4 phase shift structure or the gain-coupling type structure as described above, the emitted light can be made into a single mode.

In the electrode layer for applying an electric field to the organic light emitting layer 40, at least one of an anode and a cathode is separated in order to apply electric fields having different intensities to the organic light emitting layer 40 corresponding to the resonance wavelength. It is desirable. In this example,
As shown in FIG. 1, the anode 30 is formed as a common electrode, and the cathode is separated into a first cathode 50a and a second cathode 50b by an insulating layer 52. These things are
The same applies to other embodiments.

The anode 30 is made of a conductive material transparent to the light, since the light generated in the organic light emitting layer 40 is introduced into the core layer 20. As the material of such a transparent electrode, the above-mentioned materials can be used. Further, in order for light generated in the organic light emitting layer 40 to be efficiently introduced into the core layer 20, it is desirable that the refractive index of the core layer 20 is larger than the refractive index of the organic light emitting layer 40.

As shown in FIG. 1, an organic EL device 1000 has a first coating layer 1 having a low reflectance on one end face.
10, and a second coating layer 120 having high reflectivity is formed on the other end face. These coating layers 110 and 120 are, for example, generally semiconductor D
For example, a dielectric multilayer mirror used for an FB laser can be used.

Next, the operation and operation of the organic EL device 1000 will be described.

An anode 30 and first and second cathodes 50a,
When a predetermined voltage is applied to the organic light emitting layer 40 and the anode 30, holes are injected from the cathodes 50 a and 50 b respectively. In the organic light emitting layer 40, the electrons and holes are recombined to generate excitons, and when the excitons are deactivated, light such as fluorescence or phosphorescence is generated. Part of the light generated in the organic light emitting layer 40 is reflected by the cathodes 50a, 50b or the second cladding layer 60, and part of the light is introduced into the core layer 20 via the anode 30 made of a transparent conductive layer. Is done. The light introduced into the core layer 20 is distributed-propagation-type propagated by the first diffraction grating 100a and the second diffraction grating 100b, propagates through the core layer 20 toward the end face, and has low reflection. The light is emitted from the first coating layer 110 having the same ratio. At this time, the light of wavelength λ1 resonated by the first diffraction grating 100a and the light of wavelength λ2 resonated by the second diffraction grating 100b are
Emitted independently. That is, it is possible to independently drive and control the organic light emitting layers corresponding to the respective diffraction gratings, and to independently emit light having different resonance wavelengths from the regions corresponding to the respective diffraction gratings.

The outgoing light is transmitted to the diffraction gratings 100a and 100a.
Since the light is emitted after being distributed and fed back by 00b, it has wavelength selectivity, a narrow emission spectrum width, and excellent directivity. Further, by making each of the diffraction gratings 100a and 100b have a λ / 4 phase shift structure or a gain coupling type structure, the emitted light can be made to have a single mode.

(Modification of Diffraction Grating) FIG.
00 shows a modified example. In this example, the pitch (P3) of the diffraction grating is set to the same length, and the optical length of the pitch is changed by changing the refractive index. By thus making the physical shape (pitch) of the diffraction grating uniform, the manufacturing process is simplified. Such a diffraction grating is particularly effective when formed by an inkjet method. For example, in the first diffraction grating 100a, the refractive index n1
And n2, and the second diffraction grating 100b uses materials with refractive indices n1 and n3.

The optical length of the pitch is the width d of the unevenness of the diffraction grating.
And the refractive index n have the following relationship.

L3 = n1 · d2 + n2 · d1 L4 = n2 · d1 + n3 · d2 where n1: refractive index of the core layer 20 of the first diffraction grating 100a n2: refractive index of the first cladding layer 10 n3: second D1: Refractive index of core layer 20 of first diffraction grating 100b: first and second diffraction gratings 100a and 100
The width d2 of the protrusion of b: the first and second diffraction gratings 100a and 100
The width of the concave portion b The first diffraction grating 100a and the second diffraction grating 100b
And λ3 and λ, respectively.
4 (λ3 and λ4 are different), the following equation is established.

L3 = λ3 / 2 · (2m ₁ +1) L4 = λ4 / 2 · (2m ₂ +1) Here, m ₁ and m ₂ are integers of 0 or more.

Although not shown, the optical length of the pitch can be changed by appropriately changing both the pitch and the refractive index of the diffraction grating. Further, the diffraction grating is not limited to the illustrated rectangular shape, but may take various forms such as a sine wave shape.

The diffraction grating is not limited to the first embodiment, but can be applied to other embodiments described below.

The following embodiments are some examples showing the form of the layer structure of the organic EL device of the present invention, and the layer structure can take many forms depending on the position where the diffraction grating is formed.

(Second Embodiment) FIG. 5 is a sectional view schematically showing an organic EL device 2000 according to a second embodiment. The organic EL device 2000 according to the first embodiment is different from the organic EL device 2000 in that the organic EL device 2000 has a hole transport layer and an electron transport layer.
Different from the L device 1000. In FIG. 5, the illustration of the coating layer on the end face is omitted.

The organic EL device 2000 includes a first clad layer 10, an anode 30, a hole transport layer 70, an organic light emitting layer 4
0, the electron transport layer 80, the cathode 50, and the second cladding layer 60 are stacked in this order. The organic EL device 2000 includes the first clad layer 10 and the second
Is set to be smaller than the refractive index of each light-transmitting layer existing between the first cladding layer 10 and the second cladding layer 60.

In the present embodiment, the hole transport layer 7
0 has a feature in that it also functions as the core layer 20 in the first embodiment. That is, the hole transport layer 7
Numeral 0 is composed of upper and lower layers, and a lower layer 72 and an upper layer 74 form a diffraction grating 100 (one diffraction grating 100a is shown in FIG. 5) along the light propagation direction.

Further, in order for the light generated in the organic light emitting layer 40 to be efficiently introduced into the hole transport layer 70, it is desirable that the refractive index of the hole transport layer 70 is larger than the refractive index of the organic light emitting layer 40.

The diffraction grating 100 is preferably a distributed feedback type diffraction grating. By forming a distributed feedback diffraction grating in this manner, light having excellent wavelength selectivity, a narrow emission spectrum width, and directivity can be obtained. Further, although not shown, the diffraction grating 100 has a λ /
It is preferable to have a four phase shift structure or a gain coupling type structure. By having the λ / 4 phase shift structure or the gain-coupling type structure as described above, the emitted light can be made into a single mode.

In the organic EL device 2000, similarly to the first embodiment, although not shown, a first coating layer having a low reflectance is formed on one end surface, and a high reflection layer is formed on the other end surface. A second percentage of the coating layer is formed. For these coating layers, for example, a dielectric multilayer mirror generally used in a semiconductor DFB laser can be used.

Next, the operation and action of the organic EL device 2000 will be described.

When a predetermined voltage is applied to the anode 30 and the cathode 50, electrons enter the organic light emitting layer 40 from the cathode 50 via the electron transport layer 80 and from the anode 30 via the hole transport layer 70. Holes are injected into the organic light emitting layer 40. In the organic light emitting layer 40, the electrons and holes are recombined to generate excitons, and when the excitons are deactivated, light such as fluorescence or phosphorescence is generated. A part of the light generated in the organic light emitting layer 40 is reflected by the cathode 50 or the second cladding layer 60 and a part is introduced into the hole transport layer 70 as it is. The light introduced into the hole transport layer 70 is distributed-propagation-type propagated by the diffraction grating 100, propagates through the hole transport layer 70 toward the end face thereof, and from the first coating layer having a low reflectance. Emit. The emitted light is distributed and fed back in the hole transport layer 70 by the diffraction grating 100 and is emitted. Therefore, the emitted light has wavelength selectivity, a narrow emission spectrum width, and excellent directivity. Furthermore, by making the diffraction grating 100 a λ / 4 phase shift structure or a gain-coupling type structure, the emitted light can be made into a single mode. Where λ is
Indicates the wavelength of light in the optical waveguide layer. Then, the light of wavelength λ1 resonated by the first diffraction grating 100a and the light of wavelength λ2 resonated by the second diffraction grating (not shown) are emitted independently.

In this embodiment, an example in which the diffraction grating 100 is provided on the hole transport layer 70 has been described. However, a diffraction grating can be provided on the electron transport layer side instead of the hole transport layer. Further, it is not always necessary to provide both the hole transport layer and the electron transport layer, and only one of the transport layers may be provided. This is the same in other embodiments.

(Third Embodiment) FIG. 6 is a sectional view schematically showing an organic EL device 3000 according to the present embodiment. This example is different from the first and second embodiments in that a diffraction grating is provided in the organic light emitting layer.

In the organic EL device 3000, a hole transport layer 70 and an electron transport layer 80 are formed with the organic light emitting layer 40 interposed therebetween. Specifically, organic EL
In the device 3000, a first clad layer 10, an anode 30, a hole transport layer 70, an organic light emitting layer 40, an electron transport layer 80, a cathode 50, and a second clad layer 60 are laminated in this order. In this organic EL device 3000, the refractive index of the first clad layer 10 and the second
Is set to be smaller than the refractive index of the light transmitting layer existing between the second clad layer 10 and the second clad layer 60.

In this embodiment, the organic light emitting layer 40 functions as a core layer through which light propagates. The diffraction grating 100 (100a) is formed between the organic light emitting layer 40 and the electron transport layer 80. Considering the confinement of light in the organic light emitting layer 40, the refractive index of the organic light emitting layer 40,
It is desirable that the refractive indexes of the hole transport layer 70 and the electron transport layer 80 be different.

The diffraction grating 100 is preferably a distributed feedback type diffraction grating. By forming a distributed feedback diffraction grating in this manner, light having excellent wavelength selectivity, a narrow emission spectrum, and good directivity can be obtained. Further, although not shown, the diffraction grating 100 preferably has a λ / 4 phase shift structure or a gain coupling type structure. By having the λ / 4 phase shift structure or the gain-coupling type structure as described above, the emitted light can be made into a single mode.

In the organic EL device 3000, although not shown, a first coating layer having a low reflectance is formed on one end face, and a second coating layer having a high reflectance is formed on the other end face. ing. For these coating layers, for example, a dielectric multilayer mirror generally used in a semiconductor DFB laser can be used.

Next, the operation and action of the organic EL device 3000 will be described.

By applying a predetermined voltage to the anode 30 and the cathode 50, electrons are emitted from the cathode 50 via the electron transport layer 80, holes are emitted from the anode 30 via the hole transport layer 70, and It is injected into 40. In the organic light emitting layer 40, the electrons and holes are recombined to generate excitons, and when the excitons are deactivated, light such as fluorescence or phosphorescence is generated. The light generated in the organic light emitting layer 40 is distributed and propagated by the diffraction grating 100, propagates through the organic light emitting layer 40 and the electron transport layer 80 toward the end face, and has a low reflectance of the first coating. Light is emitted from the layer. This outgoing light is reflected by the diffraction grating 100
As a result, the light is distributed and returned by the organic light emitting layer 40 and emitted, so that it has wavelength selectivity, a narrow emission spectrum width, and excellent directivity. Further, by making the diffraction grating 100 a λ / 4 phase shift structure or a gain coupling type structure,
The emitted light can be made into a single mode. here,
λ represents the wavelength of light in the optical waveguide layer. Then, light of wavelength λ1 resonated by the first diffraction grating 100a,
Wavelength λ resonated by a second diffraction grating (not shown)
And two lights are emitted independently.

According to the organic EL device 3000, the light generated in the organic light emitting layer 40 propagates through the organic light emitting layer 40 as it is. Is made.

(Fourth Embodiment) FIG. 7 is a sectional view schematically showing an organic EL device 4000 according to the present embodiment. The organic EL device 4000 is different from the above-described organic EL device in having a distributed Bragg reflection type diffraction grating.

The organic EL device 4000 includes the clad layer 1
0, the anode 30, the hole transport layer 70, the organic light emitting layer 40, and the cathode 50 are stacked in this order. In this organic EL device 4000, the cladding layer 10 has a refractive index of
The refractive index is set smaller than the refractive index of the other layer that transmits light.

The diffraction grating 100 is formed in a boundary region between the hole transport layer 70 and the air layer 90, and forms a distributed Bragg diffraction grating having a so-called air gap.
In this case, depending on the selection range of the material of the hole transport layer,
The difference between the refractive indices of the two media constituting the diffraction grating can be increased, and a diffraction grating that is efficient with respect to a desired light wavelength can be formed. Then, a concave portion 42 is formed in a part of the surface of the hole transport layer 70, and the organic light emitting layer 40 is formed in the concave portion 42. On the organic light emitting layer 40, a cathode 50 is formed. This organic EL device 4000
In, the hole transport layer 70 and the air layer 90 function as a core layer for transmitting light.

As described above, the distributed Bragg type diffraction grating 10
By forming 0, light resonates, and light with excellent wavelength selectivity and directivity can be obtained.

In the organic EL device 4000, although not shown, a first coating layer having a low reflectivity is formed on one end face, and a second coating layer having a high reflectivity is formed on the other end face. ing. For these coating layers, for example, a dielectric multilayer mirror generally used in a semiconductor DFB laser can be used.

Next, the operation and action of the organic EL device 4000 will be described.

When a predetermined voltage is applied to the anode 30 and the cathode 50, electrons are injected from the cathode 50, and holes are injected from the anode 30 via the hole transport layer 70 into the organic light emitting layer 40, respectively. In the organic light emitting layer 40, the electrons and holes are recombined to generate excitons, and when the excitons are deactivated, light such as fluorescence or phosphorescence is generated.

In the present embodiment, since the diffraction grating 100 of the distributed Bragg reflection type is provided, the organic light emitting layer 40
Are reflected by the diffraction gratings on both sides of the organic light emitting layer 40 and resonate. Therefore, the light generated in the organic light emitting layer 40 resonates more efficiently, propagates in the hole transport layer 70 and the air layer 90 toward the end face, and is emitted from the first coating layer having a low reflectance. The emitted light is resonated and emitted by the distributed Bragg reflection type diffraction grating 100, so that it is not only excellent in wavelength selectivity and directivity but also emitted with high efficiency.

Although the diffraction grating 100 is formed on the hole transport layer 70 in the illustrated example, an electron transport layer may be provided instead of the hole transport layer, and a diffraction grating may be provided on the electron transport layer. Further, instead of the hole transport layer or the electron transport layer, the core layer can be formed of another material having low light absorption. Further, in the illustrated example, the gap of the diffraction grating is constituted by an air gap, but the diffraction grating may be constituted by a layer formed of another material instead of the air layer 90.
Further, in addition to the organic light emitting layer, at least one of the hole transport layer and the electron transport layer may be filled in the recess 42 in which the organic light emitting layer 40 is embedded.

In the example shown, the diffraction grating 100 is connected to the anode 30.
Although formed by the upper hole transport layer 70 and the air layer 90, for example, a distributed Bragg reflection type diffraction grating using two media having different refractive indexes (for example, a clad layer and an air layer) under the anode 30 Can also be formed.

In the above embodiment, an organic EL device capable of obtaining two emitted lights having different wavelengths has been described. However, the present invention is not limited to this, and an organic EL device capable of obtaining three or more different resonance wavelengths is provided. Also applicable to Further, in the present invention, the cladding layer may not be formed when the confinement of light in the waveguide layer by the electrode layer made of metal or the like is sufficient.

Further, in the above embodiment, the case where the organic light emitting layer is used as the light emitting layer has been described, but a light emitting layer made of an inorganic material may be used instead of the organic light emitting layer.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an organic EL device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the organic EL device shown in FIG. 1 along line AA.

FIG. 3 is a plan view schematically showing the organic EL device shown in FIG. 2 along line BB.

FIG. 4 is a sectional view schematically showing a modification of the diffraction grating of the present invention.

FIG. 5 is a sectional view schematically showing an organic EL device according to a second embodiment of the present invention.

FIG. 6 is a sectional view schematically showing an organic EL device according to a third embodiment of the present invention.

FIG. 7 is a sectional view schematically showing an organic EL device according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 First clad layer 20 Core layer 30 Anode 40 Organic light emitting layer 50 (50a, 50b) Cathode 60 Second clad layer 70 Hole transport layer 80 Electron transport layer 100 (100a, 100b) Diffraction grating 110, 120 Coating layer

Claims (13)

[Claims] 1. A light emitting layer capable of emitting light by electroluminescence, at least a pair of electrode layers for applying an electric field to the light emitting layer, and an optical waveguide for propagating light generated in the light emitting layer. A diffraction grating formed in the optical waveguide, the diffraction grating being composed of a plurality of diffraction gratings having different optical lengths of a pitch, and being capable of emitting light having a plurality of different resonance wavelengths corresponding to each diffraction grating; . 2. The EL device according to claim 1, wherein the diffraction grating is a distributed feedback diffraction grating. 3. The EL device according to claim 2, wherein the diffraction grating has a λ / 4 phase shift structure. 4. The EL device according to claim 2, wherein the diffraction grating has a gain coupling type structure. 5. The EL device according to claim 1, wherein the diffraction grating is a distributed Bragg reflection type diffraction grating. 6. The EL according to claim 1, wherein the light emitting layer includes an organic light emitting material as a light emitting material.
apparatus. 7. The diffraction grating according to claim 1, wherein the plurality of diffraction gratings are each made of the same material,
EL devices having different pitch lengths. 8. The EL device according to claim 1, wherein the plurality of diffraction gratings are made of different materials and have the same pitch length. 9. The EL device according to claim 1, wherein each of the plurality of diffraction gratings is made of a different material and has a different pitch length. 10. The optical waveguide according to claim 1, wherein the optical waveguide includes a core layer through which light is mainly propagated, and a clad layer having a lower refractive index than the core layer. An EL device comprising a layer different from the light emitting layer. 11. The light emitting device according to claim 10, wherein the core layer has a higher refractive index than the light emitting layer.
L device. 12. The optical waveguide according to claim 1, wherein the optical waveguide includes a core layer through which light mainly propagates, and a clad layer having a smaller refractive index than the core layer. An EL device comprising a layer including the light emitting layer. 13. The EL device according to claim 1, wherein the electrode layer can be independently controlled corresponding to each of the plurality of diffraction gratings.