Image forming apparatus and light emitting device
An image forming device comprises: an exposer having a plurality of light emitting devices, a light emitting device among the plurality of light emitting devices to transmit light toward a photosensitive drum; and a developer to develop an electrostatic latent image formed on a surface of the photosensitive drum by the light, wherein the light emitting device among the plurality of light emitting devices includes: a light emitting layer to generate the light; and a reflective layer to reflect at least a portion of the generated light. The reflective layer can include a plurality of sub-reflective layers, in which a thickness of a sub-reflective layer among the plurality of sub-reflective layers is different from a thickness of another sub-reflective layer among the plurality of sub-reflective layers, and/or a refractive index of a sub-reflective layer among the plurality of sub-reflective layers is different from a refractive index of another sub-reflective layer among the plurality of sub-reflective layers.
1. An image forming apparatus comprising:
an exposer having a plurality of light emitting devices, a light emitting device among the plurality of light emitting devices to transmit light toward a photosensitive drum; and
a developer to develop an electrostatic latent image formed on a surface of the photosensitive drum by the light,
wherein
the light emitting device among the plurality of light emitting devices includes:
a light emitting layer to generate the light having a central wavelength variable to:
a first wavelength,
a second wavelength different from the first wavelength, and
a third wavelength different from the first wavelength and the second wavelength; and
a reflective layer to reflect at least a portion of the generated light, and
the reflective layer includes a plurality of sub-reflective layers, wherein the plurality of sub-reflective layers includes three sub-reflective layers respectively having:
a first thickness and a first refractive index at a first ratio corresponding to the first wavelength,
a second thickness and a second refractive index at a second ratio corresponding to the second wavelength, and
a third thickness and a third refractive index at a third ratio corresponding to the third wavelength.
2. The image forming apparatus of claim 1 , wherein a sub-reflective layer of the plurality of sub-reflective layers is to reflect light ray having a wave length different from wavelengths of light rays to be reflected by other sub-reflective layers of the plurality of sub-reflective layers.
3. The image forming apparatus of claim 2 , wherein:
the plurality of sub-reflective layers include low refractive index layers and high refractive index layers; and
refractive indices of the low refractive index layers are lower than refractive indices of the high refractive index layers.
4. The image forming apparatus of claim 3 , wherein
a thickness of a low refractive index layer among the low refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another low refractive index layer among the low refractive index layers, and/or
a refractive index of a low refractive index layer among the low refractive index layers included in the plurality of sub-reflective layers is different from a refractive index of another low refractive index layer among the low refractive index layers.
5. The image forming apparatus of claim 3 , wherein
a thickness of a high refractive index layer among the high refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another high refractive index layer among the high refractive index layers, and/or
a refractive index of a high refractive index layer among the high refractive index layers included in the plurality of sub-reflective layers is different from a refractive index of another high refractive index layer among the high refractive index layers.
6. The image forming apparatus of claim 3 , wherein
a thickness of a low refractive index layer among the low refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another low refractive index layer among the low refractive index layers, and
a thickness of a high refractive index layer among the high refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another high refractive index layer among the high refractive index layers.
7. The image forming apparatus of claim 3 , wherein
a refractive index of a low refractive index layer among the low refractive index layers included in the plurality of sub-reflective layers is different from a refractive index of another low refractive index layer among the low refractive index layers, and
a refractive index of a high refractive index layer among the high refractive index layers included in the plurality of sub-reflective layers is different from a refractive index of another high refractive index layer among the high refractive index layers.
8. The image forming apparatus of claim 3 , wherein
the low refractive index layers are formed of aluminum-gallium-arsenic (AlGaAs) semiconductors having low refractive indices,
the high refractive index layers are formed of AlGaAs semiconductors having high refractive indices.
9. The image forming apparatus of claim 8 , wherein
a thickness of an AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices is different from a thickness of another AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices, and/or
an Al-mixing percentage of an AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices is different from an Al-mixing percentage of another AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices.
10. The image forming apparatus of claim 8 , wherein
a thickness of an AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices is different from a thickness of another AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices, and/or
an Al-mixing percentage of an AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices is different from an Al-mixing percentage of another AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices.
11. The image forming apparatus of claim 8 , wherein
a thickness of an AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices is different from a thickness of another AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices, and
a thickness of an AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices is different from a thickness of another AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices.
12. The image forming apparatus of claim 8 , wherein
an Al-mixing percentage of an AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices is different from an Al-mixing percentage of another AlGaAs semiconductor among the AlGaAs semiconductors having the low refractive indices, and
an Al-mixing percentage of an AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices is different from an Al-mixing percentage of another AlGaAs semiconductor among the AlGaAs semiconductors having the high refractive indices.
13. The image forming apparatus of claim 1 , wherein the reflective layer includes a first reflective layer including a plurality of first sub-reflective layers and a second reflective layer including a plurality of second sub-reflective layers.
14. The image forming apparatus of claim 13 , wherein:
each of the plurality of first sub-reflective layers includes a first low refractive index layer and a first high refractive index layer; and
each of the plurality of second sub-reflective layers includes a second low refractive index layer and a second high refractive index layer.
15. The image forming apparatus of claim 14 , wherein:
thicknesses and/or refractive indices of the first low refractive index layer and the second low refractive index layer are different from each other; and
thicknesses and/or refractive indices of the first high refractive index layer and the second high refractive index layer are different from each other.
16. The image forming apparatus of claim 1 , wherein
a thickness of at least one sub-reflective layer among the plurality of sub-reflective layers is different from a thickness of another sub-reflective layer among the plurality of sub-reflective layers, and/or
a refractive index of at least one sub-reflective layer among the plurality of sub-reflective layers is different from a refractive index of another sub-reflective layer among the plurality of sub-reflective layers.
17. An exposer for an image forming apparatus, comprising:
a plurality of light emitting devices, a light emitting device among the plurality of light emitting devices to transmit light toward a photosensitive drum of an image forming apparatus,
wherein the light emitting device among the plurality of light emitting devices includes:
a light emitting layer to generate the light having a central wavelength variable to:
a first wavelength,
a second wavelength different from the first wavelength, and
a third wavelength different from the first wavelength and the second wavelength; and
a reflective layer to reflect at least a portion of the generated light, and
the reflective layer includes a plurality of sub-reflective layers, wherein the plurality of sub-reflective layers includes three sub-reflective layers respectively having:
a first thickness and a first refractive index at a first ratio corresponding to the first wavelength,
a second thickness and a second refractive index at a second ratio corresponding to the second wavelength, and
a third thickness and a third refractive index at a third ratio corresponding to the third wavelength.
18. The exposer of claim 17 , wherein a sub-reflective layer of the plurality of sub-reflective layers is to reflect light ray having a wave length different from wavelengths of light rays to be reflected by other sub-reflective layers of the plurality of sub-reflective layers.
19. The exposer of claim 17 , wherein:
the plurality of sub-reflective layers include low refractive index layers and high refractive index layers;
refractive indices of the low refractive index layers are lower than refractive indices of the high refractive index layers; and
a thickness of a low refractive index layer among the low refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another low refractive index layer among the low refractive index layers.
20. The exposer of claim 19 , wherein
a thickness of at least one sub-reflective layer among the plurality of sub-reflective layers is different from a thickness of another sub-reflective layer among the plurality of sub-reflective layers, and/or
a thickness of a high refractive index layer among the high refractive index layers included in the plurality of sub-reflective layers is different from a thickness of another high refractive index layer among the high refractive index layers.