JP4479357B2 - Light emitting element with lens, light emitting element array with lens, self-scanning light emitting element array, writing head and optical printer - Google Patents

Description

  The present invention relates to a light emitting element with a lens, in particular, a light emitting element with a lens that contributes to an improvement in light utilization efficiency, and an imaging apparatus using the light emitting element with a lens.

  The optical system of the write head of the optical printer is designed to form an image of the light spot of each LED element constituting the LED array on a photosensitive drum by a lens array which is an imaging device. In many cases, a gradient index rod lens array is used as the lens array.

  FIG. 1 shows a typical configuration example of an LED array, a gradient index rod lens array, and a photosensitive drum used in a conventional optical printer. Reference numeral 10 denotes an LED, 12 denotes a rod lens array, and 14 denotes a photosensitive drum.

  While the effective aperture angle θ of the rod lens array 12 is 17 to 20 ° as a half angle, the LED 10 basically emits light with a Lambertian distribution, and the light utilization efficiency is extremely low. Of the light emitted from the LEDs emitting light with a Lambertian distribution, the amount of light transmitted to the photosensitive drum 14 via the rod lens array 12 is only about 3 to 5%. That is, there is a problem that 95 to 97% of the light emission amount of the LED cannot be used and the light use efficiency is low.

  In order to increase the light utilization efficiency, a microlens array is arranged immediately above the LED light emitting section, and the directivity of the LED light emission is narrowed as much as possible, thereby increasing the light incident on the aperture angle of the rod lens array. Can be considered. However, in general, as shown in FIG. 2, the light emitting portion of the LED array used in the optical printer has the electrode 20 protruding into the region of the light emitting portion 22 so as to block the vicinity of the center. As shown in FIG. 2, the shape of the region of the light emitting portion 22 is substantially U-shaped. When it is intended to narrow the directivity with a general microlens array 18 as shown in FIG. 3, it is desirable to use a light beam in the vicinity of the optical axis of the lens indicated by a broken line 24, but in the vicinity of the optical axis of the lens. Corresponds to the position of the electrode 20, and as a result, there is a problem that the light utilization efficiency cannot be sufficiently improved. In FIG. 3, reference numeral 16 denotes a light emitting element having a substantially U-shaped light emitting portion region.

  The LED array provided with the microlens array is described in the following Patent Documents 1, 2, and 3. However, these problems have not been studied, and thus are not related to the shape of the microlens.

The above problems apply not only to LEDs but also to other light emitting elements.
JP-A-9-109455 JP 2000-347317 A JP 2001-36144 A

  An object of the present invention is to improve the light use efficiency of a light emitting element array used in a so-called optical printer, in which an image of a light emitting portion of a light emitting element array is formed on a photosensitive drum using a lens array.

  Another object of the present invention is to provide a light-emitting element with a lens with improved light utilization efficiency.

  Still another object of the present invention is to provide a light emitting element array with a lens with improved light utilization efficiency.

  Still another object of the present invention is to provide an imaging apparatus having a light emitting element with lens or a light emitting element array with lens.

  Still another object of the present invention is to provide a writing head using such a lens-equipped light emitting element array or an imaging apparatus.

  Still another object of the present invention is to provide an optical printer having such a write head.

  The light emitting element with a lens of the present invention includes a light emitting element having a light emitting part region on a semiconductor substrate, an antireflection film covering the light emitting part region, and a lens provided on the surface of the antireflection film on the light emitting element. I have. The antireflection film is a single layer film, and its refractive index has an intermediate value between the refractive index of the light emitting portion region and the refractive index of the resin constituting the lens.

  If the lens is formed using a resin having a relatively large refractive index, the lens can be formed directly on the light emitting portion.

  The lens of the light-emitting element with a lens of the present invention is not a single spherical lens but a multiple spherical lens or a composite lens in which a plurality of spherical lenses and a cylindrical lens are combined.

  Such a compound lens is designed as follows.

  (1) A compound lens in which a part of a plurality of spherical lenses having the center of the lens located adjacent to a curve or a broken line connecting the maximum positions of light emission intensity of the light emitting element or adjacent to the line, or to the line It is a compound lens in which a part of a curved or polygonal cylindrical lens having an axis along the axis is adjacently arranged, or a compound lens in which a part of a spherical lens and a part of a cylindrical lens are combined.

(2) When the curve or broken line connecting the maximum positions of the light emission intensity of the light emitting element is substantially U-shaped, a part of the spherical lens is provided at each end of the substantially U-shaped three line segments or in the vicinity thereof. This is a compound lens in which a cylindrical lens is provided in a portion and these are arranged adjacent to each other.
Here, the substantially U-shape simply represents that a curve or a broken line connecting the maximum positions of the light emission intensity of the light-emitting element is substantially U-shaped as a whole.

  (3) In the case of a light emitting device similar to (2) above, a composite is provided in which a part of three spherical lenses whose centers are located in the vicinity of the middle position of three substantially U-shaped line segments are arranged adjacent to each other. It is a lens.

  Therefore, the lens-equipped light emitting device of the present invention is located on or adjacent to a line connecting a light emitting element having a light emitting part region and a maximum position of light emission intensity in the light emitting part region. In addition, a part of a plurality of spherical lenses in which the center of the lens is located are arranged adjacent to each other, or a part of a plurality of cylindrical lenses having an axis along the line is arranged adjacent to each other, or a part of the spherical lenses and the cylindrical lens A part of which is adjacently disposed.

  In the case where the line connecting the maximum positions of the light emission intensity in the light emitting part region is substantially U-shaped consisting of three line segments, the compound lens has four centers whose centers are located at or near both ends of each line segment. A part of the spherical lens and a part of three cylindrical lenses having an axis parallel to the line are arranged adjacent to each other in the middle of each line segment.

  Further, when the line connecting the maximum positions of the light emission intensity in the light emitting portion area is substantially U-shaped consisting of three line segments, the center of the compound lens is located near the middle position of each line segment. A part of two spherical lenses are arranged adjacent to each other.

  The present invention also relates to an imaging apparatus that forms an image on the imaging surface of the light emitting part region of the light emitting element via the light emitting pattern shape converting element and the imaging element. The shape is substantially U-shaped, and the shape of the image corresponding to the light emitting portion region formed on the imaging surface is substantially unimodal.

  The above-described compound lens can be used for the light emitting pattern shape conversion element.

  According to the light emitting element with a lens of the present invention, since the antireflection film is provided, the light transmittance is increased, and the light extraction efficiency is increased. In addition, by using a compound lens as the lens, it is possible to improve the utilization efficiency of light emitted with a Lambertian distribution. Moreover, according to the imaging apparatus using the light emitting element array with the lens array of the present invention, the emitted light can be effectively guided to the imaging element, and the light utilization efficiency can be greatly improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 4A, the light-emitting element with a lens of the present invention is provided with a compound lens 30 that is a light-emitting pattern conversion element on the light-emitting portion 22 of the substantially U-shaped LED.

  A polygonal line 32 is formed by connecting the maximum light emission intensity positions of the substantially U-shaped light emitting portion. A part of four spherical lenses whose centers are located at or near both ends of the three line segments of the broken line 32 are provided, and a part of three cylindrical lenses having axes parallel to the three line segments are provided at the middle part thereof. The compound lens 30 is formed by arranging them adjacent to each other.

  Epoxy or acrylic resins are used as materials for such compound lenses.

  FIG. 4B is a plan view showing the structure of the compound lens 30. In the figure, points 33, 34, 35, and 36 indicate the respective ends of the three line segments 32a, 32b, and 32c of the substantially U-shaped broken line 32 shown in FIG. The compound lens 30 is centered on a portion 43 of a spherical lens centered on a point 33, a portion 44 of a spherical lens centered on a point 34, a portion 45 of a spherical lens centered on a point 35, and a point 36. A portion 46 of a spherical lens. The compound lens 30 further includes a part of the cylindrical lens 48 having an axis parallel to the line segment 32a, a part of the cylindrical lens 50 having an axis parallel to the line segment 32b, and a cylindrical lens having an axis parallel to the line segment 32c. 52. A part of these four spherical lenses and a part of the three cylindrical lenses are arranged adjacent to each other as shown.

  FIG. 4B also shows an XX ′ line cross-sectional view and a YY ′ line cross-sectional view for understanding the shape of the compound lens.

  As described above, the compound lens 30 has a special shape in which each part of the substantially U-shaped light-emitting portion 22 is aligned with the center of the optical axis of the spherical lens or the axis of the cylindrical lens, and a part of the spherical lens is combined with the cylindrical lens. The lens.

  FIG. 5 shows an image forming apparatus using such a compound lens having a substantially U-shaped light emitting portion shape. The image forming apparatus includes a light emitting element 16, a light emitting pattern conversion element (compound lens) 30, and an image forming element (rod lens eye) 12.

  For each part of the substantially U-shaped light emitting part, each part of the compound lens can be used to refract the emitted light beam in the optical axis direction, that is, in the direction of the rod lens that is the imaging element. In addition, the directivity of Lambertian emission can be reduced.

  FIG. 6A shows a light amount distribution of a pixel image of an LED, which is a light spot, formed on the photosensitive drum 14 that is the imaging surface via the rod lens array 12 using the compound lens array 30 of the present embodiment. ). Compared to the light amount distribution without the compound lens (FIG. 6B), the low light amount portion at the center of the pixel disappears, and the distribution has a good substantially single peak shape. When the amount of light at this time was measured, it was 1.7 times as bright as the case without the compound lens.

  Further, by having the light pattern conversion element, the depth of focus becomes deep, and the alignment accuracy between the imaging element and the imaging surface can be relaxed.

  As described above, according to the example of the present invention, the light use efficiency improvement effect of the light emitting element with a lens of the present invention was confirmed. In addition, the light utilization efficiency and the mounting accuracy improvement effect of the imaging apparatus of the present invention were confirmed.

  In the compound lens of the present invention, for example, as shown in FIG. 7, a part of three spherical lenses each centered on a substantially U-shaped light-emitting portion 22 is like a “three-leaf clover”. The same effect can be obtained even if the shape is combined with any other shape.

  Such a compound lens is designed as follows. A polygonal line 32 is formed by connecting the maximum light emission intensity positions of the substantially U-shaped LED light emitting section. A part of three spherical lenses 63, 64, and 66 having centers 53, 54, and 56 positioned near the middle position of the three line segments of the broken line 32 are provided adjacent to each other.

  In general, the refractive index of the light emitting portion of the optical semiconductor element is 3.2 to 3.7, and in particular, the refractive index of the GaAs semiconductor of the LED used in the LED printer is 3.3 to 3.6. If the light emitted from the semiconductor is taken out into the air as it is, the light extraction efficiency is significantly reduced due to reflection at the interface with the air. Further, since the refractive index of the resin of the compound lens is generally smaller than the refractive index of the semiconductor, reflection occurs at the interface between the semiconductor and the resin.

  In the present invention, since the resin lens is provided for the purpose of increasing the light utilization efficiency, the effect is lost if the light extraction efficiency decreases due to reflection at the interface. Therefore, in consideration of the refractive index of the resin lens, it is necessary to provide means for preventing the light extraction efficiency from decreasing. In the present invention, in order to reduce reflection at the interface between the light emitting part and the resin lens, an antireflection film made of a transparent dielectric is provided on the surface of the light emitting part.

  FIG. 8 shows a cross section of an example of a light-emitting element with a lens provided with such an antireflection film.

  The LED is configured by growing an n-AlGaAs layer 91 and a p-AlGaAs layer 92 on a GaAs substrate 90 and forming a p-side electrode 93 and an n-side electrode 94. One layer of SiN film 95 having a refractive index of 1.8 to 2.1 was formed as an antireflection film on the light emitting portion surface of the LED, and a resin lens 96 was further formed.

  The refractive index of the AlGaAs light emitting part used in this example is 3.5 to 3.6, the refractive index of the SiN film is 1.8 to 2.1, and the refractive index of the resin lens is 1.47 to 1.7.

  When the refractive index of the AlGaAs light emitting part is 3.5 to 3.6, the thickness of the SiN film corresponding to the antireflection condition for the emission wavelength of 780 nm is 96 to 99 nm (or 470 to 490 nm). With the formation of this SiN film, a light transmittance of 93% or more was obtained. When the amount of light at this time was measured, the brightness was 2.2 times that obtained without the lens.

  In the above embodiment, the SiN film is used as the antireflection film, but the present invention is not limited to this. Any transparent material having a refractive index intermediate between the refractive index of the light emitting portion and the refractive index of the resin lens can be used. The antireflection film is not limited to a single layer film, and may be composed of a plurality of laminated films.

  In addition, if the lens is formed using a resin having a relatively large refractive index, the reflection on the semiconductor surface becomes smaller than when the light emitted from the light emitting portion is directly taken out into the air. Therefore, a lens can be directly formed on the light emitting portion without using an antireflection film.

  In the first embodiment, the case of the LED array as the light emitting element array has been described.

  In this example, a so-called “self-scanning light-emitting element array” was used as the light-emitting element array. Also in this case, the same light use efficiency improvement effect as above was confirmed.

  The self-scanning light-emitting element array uses a light-emitting thyristor having a pnpn structure as a component of the light-emitting element array, and is configured so that self-scanning of the light-emitting element can be realized. No. 2-14584, JP-A-2-92650, and JP-A-2-92651.

  Japanese Patent Laid-Open No. 2-263668 discloses a self-scanning light emitting element array having a structure in which a transfer element array is used as a shift unit and separated from a light emitting element array as a light emitting unit.

FIG. 9 shows an equivalent circuit diagram of a separation type self-scanning light emitting element array. This self-scanning light emitting element array is composed of transfer thyristors T ₁ , T ₂ , T ₃ ,... And write light emitting thyristors L ₁ , L ₂ , L ₃ ,. The configuration of the shift unit uses a diode connection. V _GK is a power supply (normally 5V), the gate electrode G ₁ of the transfer thyristor from the power supply line 72 via respective load resistor _{R L, G 2, G 3} , and is connected to .... Further, the gate electrodes G ₁ , G ₂ , G ₃ ,... Of the transfer thyristor are also connected to the gate electrode of the write light-emitting thyristor. The gate electrode of the transfer thyristor T ₁ is the start pulse phi _S is applied to the anode electrode of the transfer thyristor, transfer clock pulses φ1 alternately, .phi.2 is applied. These clock pulses are supplied via clock pulse lines 74 and 76. A writing signal φ _I is applied to the anode electrode of the writing light-emitting thyristor via a signal line 78.

  FIG. 10 shows a chip 80 of such a self-scanning light emitting element array. Bonding pads 82 are provided at both ends of the chip, and light emitting portions (substantially U-shaped) 84 of the light emitting thyristor are arranged linearly along the edge of the chip. The transfer thyristor array is not shown.

  The present invention can be applied to the light emitting thyristor array of the self-scanning light emitting element array as described above. FIG. 11 is a partially enlarged view of a light emitting thyristor array provided with a compound lens array. This enlarged portion corresponds to a portion surrounded by a dotted line in FIG. FIG. 12 shows a side view of FIG.

  From FIG. 11 and FIG. 12, it will be understood that an array of the compound lens 30 described in the first embodiment is provided on an array of light emitting portions 84 of a substantially U-shape of the light emitting thyristor.

It is a figure which shows the typical structural example of the LED array used for the conventional optical printer, a gradient index rod lens array, and a photosensitive drum. It is a figure which shows the shape of a light emission part area | region. It is a figure which shows the state of the light ray to the photosensitive drum at the time of using the conventional LED array with a lens. It is a figure which shows one Example of the light emitting element with a lens of this invention. It is a figure which shows an example of a structure of the imaging device of this invention. It is a figure which shows the light quantity distribution of the pixel image of LED formed on the photosensitive drum through the rod lens using the compound lens array. It is a figure which shows the other Example of the light emitting element with a lens of this invention. It is sectional drawing of the light emitting element with a lens in which the antireflection film was formed. It is a figure which shows the equivalent circuit of a self-scanning light emitting element array. It is a figure which shows the chip | tip of a self-scanning light emitting element array. It is a partially enlarged view of a light emitting thyristor array provided with a compound lens array. It is a side view of FIG.

Explanation of symbols

10 LED
12 Rod lens array 14 Photosensitive drum 18 Micro lens array 20 Electrode 22 Light emitting part 30 Compound lens 32 Polygonal line 43, 44, 45, 46 Part of spherical lens 48, 50, 52 Part of cylindrical lens 72 Power supply line 74, 76 Clock pulse line 78 Signal line 80 Chip 82 Bonding pad 84 Light emitting portion of light emitting thyristor 90 AlGaAs substrate 91 n-AlGaAs layer 92 p-AlGaAs layer 93 p-side electrode 94 n-side electrode 95 SiN film

Claims (10)

A light emitting element having a light emitting region on a semiconductor substrate;
A lens provided on the light emitting element,
The lens is
Both ends of three line segments that are broken lines connected to form a substantially U shape on the light emitting part region of the light emitting part region provided on the light emitting element and projectingly arranged to form a substantially U shape. A compound lens in which a part of four spherical lenses whose centers are located in the vicinity and a part of three cylindrical lenses having an axis parallel to the line segment are arranged adjacent to each other in the middle of each line segment .
Light emitting element with lens. The compound lens is made of resin, the lens with the light-emitting device according to claim 1. A light emitting element having a light emitting portion region;
Both ends of three line segments that are broken lines connected to form a substantially U shape on the light emitting part region of the light emitting part region provided on the light emitting element and projectingly arranged to form a substantially U shape. a portion of four spherical lenses centered near positioned in the intermediate portion of each line segment, a portion of three cylindrical lenses and a compound lens which is disposed adjacent with an axis parallel to the line segment,
A light-emitting element with a lens. The light-emitting element with a lens according to claim 3 , wherein the compound lens is made of resin. Lens attached light-emitting element array in which a lens-attached light-emitting element described plurality, linearly to claim 1-4. The light emitting element array with a lens according to claim 5 , wherein the light emitting element is a light emitting diode. The light emitting element array with a lens according to claim 5 , wherein the light emitting element is a light emitting thyristor. A self-scanning light-emitting element array comprising the lens-equipped light-emitting element array according to claim 7 . A writing head comprising the light emitting element array with a lens according to claim 5, 6 or 7 . An optical printer comprising the write head according to claim 9 .

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