Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2001-02-09
2003-01-28
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S040000, C438S069000, C438S082000, C438S087000, C438S088000, C438S099000, C313S504000, C313S505000, C313S506000, C313S509000
Reexamination Certificate
active
06512250
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a light-emitting device using electroluminescence (EL).
BACKGROUND OF ART
Semiconductor lasers have been used as a light source for optical communications systems. Semiconductor lasers excel in wavelength selectivity and can emit light with a single mode. However, it is difficult to fabricate semiconductor lasers because many stages of crystal growth are required. Moreover, types of light-emitting materials used for semiconductor lasers are limited. Therefore, semiconductor lasers cannot emit light with various wavelengths.
Conventional EL light-emitting devices which emit light with a broad spectral width have been used in some applications such as for displays. However, EL light-emitting devices are unsuitable for applications related to optical communications and the like, in which light with a narrow spectral width is required.
An objective of the present invention is to provide a light-emitting device which can emit light with a remarkably narrow spectral width in comparison with conventional EL light-emitting devices and exhibiting directivity, and can be applied not only to displays but also optical communications and the like.
DISCLOSURE OF INVENTION
A first light-emitting device according to the present invention comprises a substrate and a light-emitting device section,
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 electric field to the light-emitting layer;
a light-transmitting section for transmitting light emitted from the light-emitting layer;
an insulation layer disposed between the electrode layers, having an opening formed in a part of the insulation layer, and functioning as a current concentrating layer for specifying a region through which current supplied to the light-emitting layer flows through a layer in the opening; and
a grating for light transmitting through the light-transmitting section.
According to this light-emitting device, electrons and holes are injected into the light-emitting layer respectively from the pair of electrode layers (cathode and anode). Light is emitted when the molecules return to the ground state from the excited state by the recombination of the electrons and holes in the light-emitting layer. The light emitted from the light-emitting layer has wavelength selectivity and directivity by the grating for light which is transmitted through the light-transmitting section, specifically, a grating in which two types of mediums having different refractive indices are arranged alternately and periodically.
The light-transmitting section is part of the light-emitting device section and supplies light obtained in the light-emitting layer of the light-emitting device section toward the waveguide section. The light-transmitting section has at least a grating section having a function of providing wavelength selectivity and a member (for example, one of the electrode layers) for connecting a core layer of the waveguide section with the grating.
According to this light-emitting device, since the insulation layer functions as a current concentrating layer in the light-emitting device section, the region where current is supplied to the light-emitting layer can be specified. Therefore, current intensity and current distribution can be controlled in the region from which it is desired to emit light, whereby light can be emitted with high emission efficiency. In the case where the insulation layer functions as cladding and the waveguide has a light-emitting layer as a core and an insulation layer as cladding, the waveguide mode of light transmitted to the waveguide section through the light-transmitting section can be controlled by specifying the opening of the insulation layer. Specifically, the waveguide mode of light transmitted through the light-emitting layer (core) can be set at a predetermined value by specifying the width of the region where light is confined (width of the opening perpendicular to the direction of light) using the insulation layer (cladding). The relation between the waveguide mode and the waveguide is generally represented by the following equation.
N
max+1
≧K
0
·a
·(
n
1
2
−n
2
2
)
½
/(&pgr;/2)
where
K
0
:2&pgr;/&lgr;
a: half width of core of waveguide
n
1
: refractive index of core of waveguide
n
2
: refractive index of cladding of waveguide
Nmax: maximum value of possible waveguide mode
Therefore, when the parameters of the above equation such as the refractive indices of the core and cladding have been specified, the width of the light-emitting layer (core) specified by the width of the opening of the current concentrating layer may be selected according to the desired waveguide mode. Specifically, the width (2
a
) of the light-emitting layer corresponding to the core at a desired waveguide mode can be calculated from the above equation by substituting the refractive indices of the light-emitting layer provided inside the current concentrating layer and the insulation layer (current concentrating layer) for the refractive indices of the core and cladding of the waveguide, respectively. The width of the core layer of the waveguide section to which light is supplied from the light-emitting device section is preferably calculated taking into consideration the resulting width of the light-emitting layer, calculated value obtained from the above equation based on the desired waveguide mode, and the like. Light with a desired mode can be transmitted from the light-emitting device section to the waveguide section with high combination efficiency by appropriately specifying the width of the light-emitting layer, width of the core layer, and the like. In addition, in the light-emitting device section, light-emitting layer in the current concentrating layer formed of the insulation layer may not uniformly emit light. Therefore, it is preferable to suitably adjust the designed values of each member such as the light-emitting layer, light-transmitting section, and waveguide section based on the width (2
a
) of the core (light-emitting layer) calculated from the above equation so that each member exhibits high combination efficiency.
The waveguide mode of the light-emitting device is preferably 0 to 1000. In particular, when used for communications, the waveguide mode is preferably about 0 to 10. Light with a predetermined waveguide mode can be efficiently obtained by specifying the waveguide mode of light in the light-emitting layer.
A second light-emitting device according to the present invention comprises a light-emitting device section and a waveguide section which transmits light emitted from the light-emitting device section, the light-emitting device section and the waveguide section being integrally formed on a 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 electric field to the light-emitting layer;
a light-transmitting section for transmitting light emitted from the light-emitting layer;
an insulation layer which is disposed to be in contact with the light-transmitting section and is capable of functioning as a cladding layer; and
a grating for light transmitting through the light-transmitting section, and
wherein the waveguide section includes:
a core layer integrally formed with at least part of the light-transmitting section; and
a cladding layer integrally formed with the insulation layer.
According to the second light-emitting device, light with superior wavelength selectivity and directivity can be emitted by the same principle as that of the first light-emitting device.
In the second light-emitting device, at least part of the light-transmitting section of the light-emitting device section and the core layer of the waveguide section are integrally formed. The insulation layer (cladding layer) of the light-emitting device section and the cladding layer of the waveguide section are integrally
Kaneko Takeo
Koyama Tomoko
Flynn Nathan J.
Forde Remmon R.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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