JP4340551B2 - Light source unit, optical writing unit, and image forming apparatus - Google Patents

Description

  The present invention relates to a light source unit, an optical writing unit, and an image forming apparatus.

  Conventionally, an electrophotographic process is used to write write data on the surface of the photoconductor by turning on / off the light by an optical writing unit to form an electrostatic latent image, and an image is formed on the recording paper by processes such as development, transfer, and fixing. An image forming apparatus for forming is known. For example, if the optical writing unit system of this image forming apparatus is a laser, it is called a laser printer, if it is an LED element system, it is called an LED printer, and if it is a liquid crystal shutter, it is called a liquid crystal printer. Are also provided as digital copiers and digital facsimile machines.

  Each of these methods will be described. That is, as an optical writing unit used in an exposure unit of an image forming apparatus, a light beam emitted from a light source such as a semiconductor laser is optically scanned by an optical deflector (polygon scanner), and is scanned on an image carrier by a scanning imaging lens. An optical scanning method for forming a light spot on the surface, and a solid-state optical writing method for forming a light spot on an image carrier by an imaging element array using a light beam emitted from a light emitting element array such as an LED array or an organic EL array, This is known as a digital writing method.

  In recent years, there has been a strong demand for downsizing digital image output devices such as digital copying machines, printers, and digital facsimiles. For this reason, in the optical scanning type optical writing unit, the optical path length becomes long and the optical writing unit itself becomes large, whereas in the solid optical writing type optical writing unit, the optical path length must be very small. The optical writing unit can be configured in a compact manner.

  The solid writing type optical writing unit includes a light emitting element array in which a plurality of light emitting elements are arranged in a line, and an imaging optical system for imaging light emitted from the light emitting elements on an image plane. . FIG. 9 shows a configuration of the rod lens array, and FIG. 10 shows an optical writing unit in which an LED array is combined. That is, the rod lens array 15 is arranged on the LED array 10 in which the LEDs 12 and the drive drivers 13 are arranged on the substrate 11 so as to collect the light from the LEDs 12 on the imaging surface 16.

  As a light emitting element array of the solid writing type optical writing unit, an LED array in which light emitting diodes (LEDs) are arranged at a predetermined pitch as light emitting elements is used. 11 and 12 are schematic views. The LED array 10 includes an LED array chip in which several hundreds of LEDs 12 are arranged on the same substrate 11 at a predetermined interval, and a plurality of IC chips that control light emission of the LEDs 12. As shown in FIG. 12, the rod lens array 15 includes a rod lens 15a, a side plate 15b, and an opaque member 15c. Each LED array chip is arranged so that the interval between the LEDs 12 at the adjacent chip ends is equal to a predetermined interval in the LED array chip. For example, when the writing density is 1200 dpi, if the LEDs are arranged at an interval of about 21.2 μm on the LED array chip and 256 LEDs are arranged on the LED array chip, the LED array chip is about 55. Thus, an LED array satisfying the writing width A4 length (297 mm) can be formed.

  In addition to light emitting element arrays using LEDs, EL arrays using organic EL or the like as light emitting elements, and LD arrays using semiconductor lasers as light emitting elements are also known as light emitting element arrays.

  A rod lens array in which rod lenses having a refractive index distribution are bundled is known as an imaging optical system of a solid-state optical writing type optical writing unit. As shown in FIG. 12, the rod lens array generally has a configuration in which rod lenses are bundled in a two-row staggered arrangement, and the periphery thereof is held by a side plate. In addition, an opaque member is filled between the rod lenses and cured to suppress flare light leaking between the rod lenses.

  Further, there is a roof prism lens array as an imaging optical system of a solid optical writing system other than the rod lens array. As shown in FIG. 13, the roof prism lens array includes a first lens array unit and a second lens array unit in which a plurality of lens surfaces are arranged in a line in the arrangement direction, and a middle of the first and second lens arrays. Although not shown in the figure, a roof prism portion 21 in which a plurality of roof prism lenses are arranged in a line in the arrangement direction is integrally provided via a rib 22, and an arbitrary lens center of the first lens array portion is provided. The arbitrary prism ridgeline of the roof prism array portion and the arbitrary lens center of the second lens array portion are arranged in the same orthogonal direction plane orthogonal to the arrangement direction. Since the roof prism lens array 20 can be formed integrally, there is no step of bundling rod lenses like the rod lens array, and it is an imaging optical system that does not adversely affect the image due to the tilting of the rod lens. In FIG. 13, reference numeral 23 denotes an incident surface, and reference numeral 24 denotes an outgoing surface.

  Each imaging optical system receives emanating light from a single light source with a plurality of rod lenses and lens surfaces, emanates from opposing surfaces, and collects them again at a single point on the image surface. It is an optical system.

  By the way, in recent years, it has been desired to increase the speed of digital copying machines, digital printers, etc., and it is necessary to improve the light emission quantity of the optical writing unit. The amount of emitted light can be improved by increasing the current injected into each light emitting element. However, the amount of emitted light does not increase so much because the power consumption increases or the amount of heat generated increases. Is concerned. Therefore, as a method for increasing the amount of light without increasing the injection current, a first method using a brighter imaging optical system and an auxiliary optical system for increasing the amount of light that can be used by the imaging optical system are added. There are two possible methods, the second method.

  When an imaging optical system brighter than the current imaging optical system is used as in the first method, the conjugate length (distance from the light emitting element to the image carrier) of the imaging optical system is shortened. This makes the layout of the optical writing unit and the image carrier difficult. In addition, even if it can be brightened without shortening the conjugate length, it captures light with a high angle of view, so that the beam spot diameter on the image plane due to defocus position shift (position shift in the optical axis direction) The variation becomes large. For these reasons, it is currently difficult to use a bright imaging optical system.

  In the second method, by forming a microlens on the light emitting element while maintaining the conventional imaging optical system, the light emitted from the light emitting element can be collected and the amount of light that can be used by the imaging optical system can be increased. (For example, refer to Patent Document 1). With this method, since the conventional imaging optical system can be used, there is no problem in the layout described above, and the microlens itself hardly contributes to the imaging action. There is little effect on variation.

  In addition, a microlens is integrally formed to increase the height of the microlens surface (for example, see Patent Document 2).

JP 2002-164579 A JP-A-11-170605

  However, since the microlens disclosed in Patent Document 1 is a formation method based on the surface tension of a material to be a microlens, the lens has a spherical shape. Therefore, when trying to make the height of the microlens higher than the bottom surface of the microlens, a swelled portion is formed between the apex of the microlens and the light emitting surface. At this time, there is no problem when the size of the light emitting surface is sufficiently small and the space between the light emitting elements is wide, but in the opposite case, there is a problem that adjacent microlenses stick to each other. The problem that it cannot be made higher than the radius occurs. Certainly, if the area of the light emitting surface of the light emitting element is reduced, it is possible to form such a microlens. However, if the light emitting surface is reduced, the current density increases at the same current. Decrease in the amount of light emission due to increase or destruction due to overcurrent becomes a problem, and eventually it must be used as a dark light emitting surface.

  Further, the microlens according to Patent Document 2 does not have the above-mentioned problem, but originally, only the light that has passed through the microlens immediately above the light emitting surface should be guided to a position where it should be condensed. Since the lenses are integrally formed, it is not possible to completely prevent extra light that has passed through another microlens that is not compatible from entering the light collection target position.

  The present invention has been made in view of the above, and provides a microlens that effectively improves brightness and suppresses the generation of unnecessary light even when the area of a light emitting element is large to some extent. Is the first purpose.

  It is a second object of the present invention to provide a solid-state optical writing unit that requires high-density and high-speed optical writing, or a small and high-speed image forming apparatus that performs high-density image formation.

In order to solve the above-described problems and achieve the object, the invention according to claim 1 is a microlens for condensing emitted light from the light emitting elements at a predetermined position on a light emitting element array in which a plurality of light emitting elements are arranged. Is a light source unit directly formed on each of the light emitting elements, and in the first region at the center of the lens including the lens apex of the microlens, the curvature of the lens surface is substantially equal to the curvature near the lens apex, In the second region around the first region, the curvature of the lens surface is different from the curvature in the vicinity of the lens apex, and in the second region, the direction from the lens apex to the light emitting element is defined as upward with respect to the lens apex. the said height of the lens surface of the micro lens becomes higher toward the outer periphery from the lens apex than the height approximated by the curvature of the lens near the vertex, the top of the microlens The diameter of the bottom surface of the distance between the micro lens to the light emitting surface of the light emitting element from is equal to or equal.

  According to the first aspect of the invention, the height of the lens surface of the macro lens formed on the light emitting element becomes higher as it goes from the lens apex to the outer circumference than the height approximated by the curvature near the lens apex. By adopting the shape, even when the light emitting surface of the light emitting element has an area and the light emitting elements are arranged at an arbitrary interval, the bottom surface of the microlens is also formed in the intermediate portion from the apex to the outer periphery of the microlens. It becomes a shape that there is no thicker part, it is possible to increase the height of the micro lens, and by suppressing the generation of unnecessary light to the adjacent part by making each micro lens independent It becomes possible.

The invention according to claim 2 is characterized in that the size of the first region is equal to or greater than the size of the light emitting surface of the light emitting element .

According to the second aspect of the present invention, in the first aspect, by making the size of the first region equal to or greater than the size of the light emitting surface of the light emitting element, it is possible to make it brighter than using a spherical microlens. It becomes possible.

  The invention according to claim 3 is characterized in that the bottom surface of the microlens is formed so as to cover at least the light emitting surface of the light emitting element.

  According to the invention of claim 3, in claim 1, by forming the bottom surface of the microlens so as to cover at least the light emitting surface of the light emitting element, the light of the light emitting element can be used effectively. Become.

  The invention according to claim 4 is characterized in that the bottom surface of the microlens has a shape substantially similar to the light emitting surface of the light emitting element.

  According to the invention of claim 4, in claim 1, the bottom surface of the microlens has a shape substantially similar to the light-emitting surface of the light-emitting element, so that the light-emitting element is arranged even when the light-emitting elements are arranged. The emitted light can be used effectively.

  The invention according to claim 5 is characterized in that the light emitting element is a surface emitting type light emitting diode in which the emitted light has a light emitting pattern having a Lambertian distribution.

  According to the invention of claim 5, the aspherical microlens described above is effectively used in claim 1 by using a light emitting element of a surface emitting type light emitting diode whose emitted light has a light emitting pattern of Lambert distribution. It becomes possible to use.

  The invention according to claim 6 is characterized in that the microlens is formed of a transparent photoresist material.

  According to the sixth aspect of the present invention, by using a transparent photoresist material in the first aspect, it is possible to form a desired aspherical microlens by an existing process.

  The invention according to claim 7 is characterized in that the light source unit according to any one of claims 1 to 6 is used.

  According to the seventh aspect of the present invention, the light source unit according to any one of the first to sixth aspects is configured by the optical writing unit, whereby high-speed writing with high writing density can be realized.

  The invention according to claim 8 uses the optical writing unit according to claim 7.

  According to the eighth aspect of the present invention, by mounting the optical writing unit according to the seventh aspect on an image forming apparatus, a small-sized, high-speed and high recording density image forming apparatus is realized.

  In the light source unit according to the present invention (claim 1), the height of the lens surface of the macro lens formed on the light emitting element becomes higher as it goes from the lens apex to the outer circumference than the height approximated by the curvature in the vicinity of the lens apex. By adopting an aspherical shape, even when the light emitting surface of the light emitting element has an area and the light emitting elements are arranged at an arbitrary interval, the microlens is also formed in the middle part from the apex to the outer periphery of the microlens. Since the shape does not have a portion that is thicker than the bottom of the microlens, the height of the microlens can be easily increased, and by making each microlens independent, the generation of unnecessary light in adjacent portions is suppressed. There is an effect that can be done.

In addition, the light source unit according to the present invention (Claim 2) is more preferable than using a spherical microlens in Claim 1 by making the size of the first region equal to or greater than the size of the light emitting surface of the light emitting element. There is an effect that it can be brightened .

  According to a light source unit of the present invention (Claim 3), the bottom surface of the microlens is formed so as to cover at least the light-emitting surface of the light-emitting element. There is an effect that can be.

  Further, the light source unit according to the present invention (Claim 4) is the light source unit according to Claim 1, in which the bottom surface of the microlens has a shape substantially similar to the light emitting surface of the light emitting element, so that even when the light emitting elements are arranged, the light source unit emits light. There is an effect that light emitted from the element can be used effectively.

  A light source unit according to the present invention (Claim 5) is the light source unit according to Claim 1, wherein the light emitting element of the surface-emitting light emitting diode in which the emitted light has a light emission pattern of Lambert distribution is used. There is an effect that the lens can be used effectively.

  Moreover, the light source unit according to the present invention (Claim 6) can easily form a desired aspherical microlens by an existing process by using a transparent photoresist material according to Claim 1. There is an effect.

  Moreover, since the optical writing unit according to the present invention (Claim 7) comprises the light source unit according to any one of Claims 1 to 6 as an optical writing unit, writing at high speed and high writing density is possible. An optical writing unit that can be performed is provided.

  An image forming apparatus according to the present invention (claim 8) is provided with the optical writing unit according to claim 7 in the image forming apparatus, and therefore provides a small, high-speed and high recording density image forming apparatus. There is an effect that can be.

  Exemplary embodiments of a light source unit, an optical writing unit, and an image forming apparatus according to the present invention are explained in detail below with reference to the accompanying drawings.

  The present invention forms an aspherical microlens that effectively narrows the divergence angle of the emitted light with respect to a light emitting element array in which light emitting elements having an area are arranged at arbitrary intervals to ensure effective brightness, In addition, a light source unit that suppresses generation of unnecessary light is realized, and is mounted on the optical writing unit and the image forming apparatus. This will be described in detail below.

(First embodiment)
The configuration of the light source unit according to the first embodiment of the present invention is shown in FIGS. FIG. 1 is a cross-sectional view in the direction in which the light emitting elements are arranged, and FIG. 2 is an explanatory view showing the shape of the microlens and the light emitting elements. As shown in the drawing, a light emitting element (LED) 102 is disposed on a substrate 101, and an independent aspherical microlens 103 is formed on the light emitting element (LED) 102. That is, the aspherical microlens 103 of the present invention is an independent microlens that is not connected to an adjacent microlens. Further, as shown in FIG. 2, the shape of the microlens is expressed by using the height h ′ (d) from the apex of the microlens, and the height h ( When compared with d), h ′ (d) is an aspherical microlens that becomes higher than h (d) from the apex of the microlens toward the outer periphery. Incidentally, Mt in FIG. 2 is a lens surface having a curvature near the apex of the microlens.

  By forming and using such an aspheric microlens 103 in the light emitting element 102, even if the light emitting surface of the light emitting element has an area and the light emitting elements are arranged at an arbitrary interval, Even in the middle part from the apex to the outer periphery, there is no part that is thicker than the bottom surface of the microlens, so it is easy to increase the height of the microlens and the adjacent microlens is independent Therefore, there is almost no possibility that unnecessary light is generated.

  Next, the relationship between the shape and brightness of the aspherical microlens 103 will be described below. The distance d is approximately equal to the height h (d) of the lens surface that approximates the shape of the aspherical microlens 103 by the curvature near the vertex of the microlens and the height h ′ (d) of the lens surface of the aspherical microlens 103. (This distance is defined as L), and the relationship of brightness improvement with respect to L was calculated using a commercially available simulation tool. The result is shown in the graph of FIG.

The calculation conditions are as follows: the light emitting element is a square having a width D = 10 μm, the shape of the bottom surface of the microlens is a circle having a diameter W = 19 μm, the height H from the top of the microlens to the light emitting surface is H = 19 μm, and the vicinity of the top of the microlens. A radius of curvature R = 9.5 μm, a refractive index N of the microlens N = 1.52, and the vertical axis represents a surface light source with a Lambert distribution similar to that of the LED, with the light emitting element having a uniform light intensity in the surface. When 10,000 light rays are randomly extracted from the surface, the amount of light taken into a 2 mm square light receiving portion at a position of about 2.7 mm is calculated, and an aspherical microlens is not used. The ratio divided by the calculated value. The horizontal axis is L (here, the maximum value of d that satisfies h ′ (d) −h (d) <0.1 μm). Note that h ′ (d) [μm] was obtained by the following equation. In this equation, c is a curvature (1 / R [μm]), and C _2n is an aspheric coefficient.

  Also, the solid line in FIG. 3 is the calculation result when a spherical microlens with a radius of curvature of 9.5 μm is placed at a height H = 19 μm (dotted line microlens in FIG. 1). As can be seen from FIG. 3, it can be seen that by making L twice as large as the light-emitting surface size D of the light-emitting element, the brightness can be made higher than when the spherical microlens is used. In other words, if the range of the lens surface approximated by the curvature near the apex of the microlens is made larger than the size of the light emitting element, it becomes possible to make it brighter than the conventional spherical microlens.

  FIG. 4 shows the calculation result of the brightness of an aspherical microlens with L = 7 μm by shaking H. The vertical axis is the same as above. From the graph of FIG. 4, it can be seen that the brightness effect obtained by using the aspherical microlens 103 can be maximized when the height H is about the same as the diameter of the microlens. Although this relationship varies somewhat depending on the size of the light emitting surface, it can be said that it is desirable that the height of the aspherical microlens 103 be approximately the same as the diameter of the microlens. Although the present aspherical microlens 103 is expressed by the above formula, it need not be expressed by this formula, and may be any one that expresses the same aspherical shape.

  Such an aspherical microlens 103 can be formed by using a photoresist material.

  As a manufacturing method, a transparent photoresist material that is exposed to light having an arbitrary wavelength (a wavelength different from the emission wavelength of the LED) is applied to the surface of the LED array. As a coating method, a substrate in a wafer state before being cut out as an LED array chip before being cut out is placed on a rotating stage, and the solution is dropped while rotating the substrate at an arbitrary number of rotations. A spin coating method in which the solution is cured by applying a heat treatment after uniform coating, a spray coating method in which the solution is sprayed on the substrate 101 by spraying or the like, and then the solution is cured by applying a heat treatment. It is possible by a known method.

  Next, the photoresist material coated as described above is exposed at an arbitrary wavelength to produce a microlens. Here, when making an aspherical microlens, a gradation mask whose light transmittance gradually changes according to the shape of the aspherical microlens 103 is used. As a method for producing a gradation mask, a method is known in which a large number of fine opening patterns are provided in a chromium mask, the size of the opening pattern is changed, and the light transmittance is gradually changed so as to become denser.

  In the present invention, the photoresist material may be either negative or positive. If it is a negative resist material, the microlens can be formed by irradiating light using a gradation mask that forms the desired aspherical microlens shape only on the part where the microlens is to be formed, and performing dry etching. On the contrary, if a positive resist material is used, a gradation mask in which the light transmittance is gradually lowered so that the portion where the microlens is not formed can be irradiated with light as it is, and the portion where the microlens is to be formed corresponds to the aspherical microlens 103. It is possible to form the aspherical microlens 103 in the same manner.

(Second Embodiment)
In the first embodiment, the bottom surface of the microlens is described as a circle as shown in FIG. However, as the writing density of the LED array is improved, the pitch of the LEDs is becoming narrower, and accordingly, if the size of the LED 102 is reduced, it becomes darker because it becomes darker. The pitch of the LED 102 and the width of the LED 102 do not change so much. Therefore, when the area of the bottom surface of the microlens 104 is circular, the light emitting surface of the LED array having a high writing density cannot be sufficiently covered. If the bottom surface of the microlens 104 does not sufficiently cover the light emitting surface of the LED, the amount of light that does not pass through the microlens 104 increases. In order to brighten, it is necessary that the bottom surface of the microlens 104 sufficiently covers the light emitting surface.

  Therefore, as shown in FIG. 6, by making the bottom surface of the microlens 105 substantially similar to the shape of the light emitting surface, even when the size of the light emitting surface approaches the arrangement pitch of the LEDs 102, they can be arranged at the same pitch as the LED 102. It becomes easy.

(Third embodiment)
The third embodiment shown in FIG. 7 is an optical writing unit 100 in which the light source unit 110 and the imaging element array 111 are combined. The imaging element array is a SELFOC lens array (SLA) sold by Nippon Sheet Glass Co., Ltd. The SELFOC lens array is a rod lens array (see FIGS. 9 and 10) in which rod lenses that are cylindrical and have a refractive index that gradually decreases from the center are arranged in a row and are arranged in a plurality of rows. is there.

  The self-lens array is an optical system in which each rod lens is an erecting equal magnification system, light emitted from one light emitting element is incident on each rod lens, and light emitted from the rod lens is collected again at one point. It is. In addition, although there are several types of Selfoc lens arrays, light having an emission angle of about 12 ° to 20 ° can be captured. However, when the light emitting element has a light emission pattern close to a Lambertian distribution such as an LED, most of the emitted light cannot be used. For example, even if a Selfoc lens array that can capture up to 20 ° is used, the amount of emitted light Only about 5% can be used.

  Therefore, by using the light source unit 110 provided with the aspherical microlens 103 in each light emitting element of the present invention, the divergence angle can be made smaller than the Lambert distribution emitted from the light source unit 110, and therefore, the SELFOC lens array. It is possible to easily increase the amount of light that can be used.

(Fourth embodiment)
In the fourth embodiment, the optical writing unit 100 of the third embodiment is applied to the image forming apparatus shown in FIG. This image forming apparatus (optical printer) has an image forming system according to an electrophotographic process, and particularly includes the above-described optical writing unit 100 as an exposure optical system (writing optical system). When printing output is performed, light corresponding to print data is irradiated by the optical writing unit 100 onto the photoconductor 120 charged in advance by the charging unit 121 to form an electrostatic latent image of the print image. This electrostatic latent image is converted into a toner image by the developing unit 122. In parallel with this, the transfer unit 123 resumes conveyance so that the recording paper fed from the paper feeding unit (not shown) and waiting on the registration roller 126 is transferred to the toner image at a predetermined position. The image is transferred, fixed by the action of heat and pressure by the fixing unit 127, and discharged. Thereafter, the residual toner on the photoconductor 120 is removed by the cleaning unit 124, and the residual charge is removed by the charge eliminating unit 125 to return to the initial state and prepare for the next printing.

  As described above, the photosensitive member 120 (image carrier) forms a latent image in accordance with the amount of light of the optical writing unit 100. Therefore, the optical writing unit 100 of the present invention is brighter than the conventional optical writing unit. Therefore, the light emission time required for forming the latent image can be shortened. That is, since the rotational speed of the photoconductor 120 can be increased, a higher-speed image forming apparatus (such as an optical printer, a digital copying machine, or a digital facsimile apparatus) can be provided. Or, if it is used for an image forming apparatus having sufficient brightness equivalent to that of the conventional optical writing unit, even if the current injected into the light source unit of the present invention is reduced, the brightness equivalent to that of the conventional optical writing unit is obtained. Is advantageous for energy saving.

  As described above, the light source unit, optical writing unit, and image forming apparatus according to the present invention are useful for digital copying machines, digital facsimile apparatuses, non-impact printers, and the like. It is suitable for an apparatus that requires a writing density and requires a small writing optical system.

It is sectional drawing which shows the structure of the light source unit concerning embodiment of this invention. It is explanatory drawing which shows the shape of the aspherical microlens of the light source unit in FIG. It is a graph which shows the relationship between L and brightness of a spherical microlens and the aspherical microlens of this invention. It is a graph which shows the relationship between H of the aspherical microlens concerning this invention, and brightness. It is explanatory drawing which shows the relationship between a light emitting element and an aspherical micro lens (a bottom face is circular). It is explanatory drawing which shows the relationship between a light emitting element and an aspherical micro lens (a bottom face is substantially similar to a light emission surface). It is sectional drawing which shows the structure of the optical writing unit concerning embodiment of this invention. It is explanatory drawing which shows the structure of the image forming apparatus carrying the optical writing unit concerning embodiment of this invention. It is explanatory drawing which shows the structure of the light emitting element and imaging element in the past. It is sectional drawing which shows the structure of the conventional optical writing unit. It is explanatory drawing which shows the structure of the conventional LED array. It is sectional drawing which shows the structure of the rod array lens in the past. It is explanatory drawing which shows the structure of the conventional roof prism lens array.

Explanation of symbols

100 Optical Writing Unit 101 Substrate 102 Light Emitting Element (LED)
103, 104, 105 Aspherical microlens 110 LED array 111 Rod lens array

Claims (8)

A light source unit in which a microlens for condensing emitted light from the light emitting element at a predetermined position is directly formed on each light emitting element in a light emitting element array in which a plurality of light emitting elements are arranged,
In the first region at the center of the lens including the lens apex of the microlens, the curvature of the lens surface is substantially equal to the curvature near the lens apex,
In the second region around the first region, the curvature of the lens surface is different from the curvature near the lens apex,
In the second region, the height of the lens surface of the microlens with the lens vertex as a reference and the direction from the lens vertex to the light emitting element upward is higher than the height approximated by the curvature near the lens vertex. It gets higher as you go to
A light source unit, wherein said that the distance from the vertex of the microlens to the light emitting surface of the light emitting element and the bottom surface of a diameter of the microlens is equal. The light source unit according to claim 1, wherein a size of the first region is equal to or greater than a size of a light emitting surface of the light emitting element .   The light source unit according to claim 1, wherein a bottom surface of the microlens is formed so as to cover at least a light emitting surface of the light emitting element.   The light source unit according to claim 1, wherein a bottom surface of the microlens has a shape substantially similar to a light emitting surface of the light emitting element.   2. The light source unit according to claim 1, wherein the light emitting element is a surface emitting type light emitting diode in which emitted light has a light emitting pattern having a Lambertian distribution.   The light source unit according to claim 1, wherein the microlens is formed of a transparent photoresist material.   An optical writing unit using the light source unit according to claim 1.   An image forming apparatus using the optical writing unit according to claim 7.

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