Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-06-13
2003-07-01
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S010000, C385S122000, C372S045013, C257S079000
Reexamination Certificate
active
06587620
ABSTRACT:
Japanese Patent Application No. 2000-182135, filed Jun. 16, 2000, is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
The present invention relates to a surface-emitting device using electroluminescence.
BACKGROUND
An electroluminescence light-emitting element using electroluminescence has the problem that since the light is emitted isotropically and the directivity is poor, when viewed in a particular direction the light is of low strength, and light emission of high efficiency is not possible.
SUMMARY
The object of the present invention is the provision of a surface-emitting device capable of increasing the power of emitting light in a particular direction, and of making efficient use of the light.
The surface-emitting device of the present invention comprises a substrate and a light-emitting device section formed on the substrate, and emitting light in a direction intersecting the substrate,
wherein the light-emitting device section includes:
a light-emitting layer capable of emitting light by electroluminescence;
a pair of electrode layers for applying an electrical field to the light-emitting layer; and
a grating of at least second order.
According to the surface-emitting device of the present invention, from the pair of electrode layers, that is, the cathode and anode, electrons and holes respectively are injected into the light-emitting layer, these electrons and holes recombine in the light-emitting layer, and when the molecules return from the excited state to the ground state, light is generated. According to the surface-emitting device of the present invention, since a grating of at least second order is included, light generated by the emitting layer is controlled by the grating to be emitted in a direction intersecting the substrate.
Here, a grating of at least second order refers to a grating, for example, such that if the pitch in the periodic direction of the grating is (a+1) &lgr;/2n (“a” is a positive integer, “n” is the mean refractive index). In particular, in the case of a grating of second order (a−1), a surface-emitting device can be obtained in which light is emitted not only in the direction of extension of the substrate
10
(the X-direction in FIG.
1
), but in the film thickness direction of the substrate
10
(the Y-direction in FIG.
1
).
A grating refers to an optical element generally used to obtain a particular spectrum using the diffraction of light.
In this case, in the above-described surface-emitting device of the present invention, the grating may form a photonic band gap or a photonic band approximating to the photonic band gap. Here a photonic band approximating to a photonic band gap refers to a band formed when a complete photonic band gap is not formed. For example, when the grating is formed by alternating arrays of the first medium layers and second medium layers, the photonic band gap may not be completely formed in the case where the difference in refractive index between the first medium layer and second medium layer is small.
According to this construction, from the pair of electrode layers, that is, the cathode and anode, electrons and holes respectively are injected into the light-emitting layer, these electrons and holes recombine in the light-emitting layer, and when the molecules return from the excited state to the ground state, light is generated. That is to say, within the light-emitting layer, the recombination of these electrons and holes generates excitons, and on the deactivation of these excitons, light in the form of fluorescence, phosphorescence, or the like is generated. By means of this, light of an extremely narrow emission spectral range can be obtained with high efficiency, and restricted spontaneous emission.
As examples of a surface-emitting device including the above described grating may be cited the following first and second surface-emitting devices.
First Surface-emitting Device
In the first surface-emitting device according to the above-described surface-emitting device of the present invention, the grating may be formed so that an energy level of an emission spectrum of the light-emitting layer includes a band edge energy level included within a band formed by the grating.
According to the first surface-emitting device, a band with respect to light is formed by the grating. This band provides a high state density with a given band edge energy. Here, the grating is constructed so that in the light-emitting layer, the energy level of the spectrum of the emitted light includes this band edge energy level, and therefore, in the light emitting layer the light emission at this band edge energy level is more easily attained. By means of this, light including the wavelength corresponding to this band edge energy level, and of a narrow spectral band is emitted, and an element with a high efficiency can be obtained.
Second Surface-emitting Device
The second surface-emitting device may comprise a defect formed in a part of the grating, and so that the energy level arising from the defect is within a given emission spectrum. According to this construction, of the light generated in the light-emitting layer, only the light of the wavelength band corresponding to the energy level arising from the defect can be propagated within the grating. Therefore, by determining the energy level width arising from the defect, light with natural emission regulated in a given direction, with an extremely narrow emission spectral range, and with directivity can be obtained with a high yield.
In this case, the light-emitting layer can function as at least part of the grating. In this case, the light-emitting layer may function as at least part of the defect.
In the above-described first and second surface-emitting devices, for example, the following configuration are possible.
(1) The grating may be a distributed feedback type grating, or a distributed Bragg reflection type, and further, may have a gain coupled structure or a refractive index coupled structure.
(2) The grating may have a first medium layer and a second medium layer disposed periodically and being insulated, and may have a periodic refractive index distribution in at least one direction. For example, there may be periodicity in one direction, in given two directions (first and second directions), or in given three directions (first, second, and third directions).
In this case, the surface-emitting device may comprise a plurality of the first medium layers, the first medium layers may have a columnar shape, and be disposed in a grid, and the second medium layer may be disposed between the first medium layer. Further in this case, the grating may have a pitch in a periodic direction of (a+1) &lgr;/2n (“a” is a positive integer and “n” is the mean refractive index).
(3) Further, at one of a hole transport layer and an electron transport layer may be provided.
In this case, the grating may have a single medium formed by the hole transport layer or the electron transport layer.
(4) The light-emitting layer may function as at least part of the grating.
(5) On at least one of the electrode layers, a layer regulating propagation of the light may be provided.
In this case, the layer regulating the propagation of light may be a cladding layer or a dielectric multilayer film.
(6) The light-emitting layer may be formed in a different region from the grating.
(7) The light-emitting layer may include an organic light-emitting material as a light-emitting material. By using an organic light-emitting material, compared with the use of for example a semiconductor material or inorganic material, the range of material available for selection is wider, and it is possible for light of various wavelengths to be emitted.
The above-described surface-emitting device of the present invention may be used for a display.
Examples are given of some materials that may be used in parts of the surface-emitting device of the present invention. These materials are only some well-known materials, and materials other than those cited by way of example can of course be
Kaneko Takeo
Koyama Tomoko
Oliff & Berridg,e PLC
Palmer Phan T. H.
Seiko Epson Corporation
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