JP2000304949A - Light source unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light source unit having an effective countermeasure against deposition of dust on the exit end face of light by disposing a transparent plate to the exit end of light if an optical waveguide or optical fiber and forming a transparent electrically conductive film on the exit side of light of the transparent plate. SOLUTION: A transparent plate 3 is adhered with an adhesive 5 having a matched refractive index to the exit face 11a. A transparent electrically conductive film 4 is preliminarily formed on the exit side (air layer side) of the transparent plate 3. The conductive film consists of an electrically conductive material showing no significant decrease in the transmittance, and for example, an ITO(indium tin oxide) film or NESA (tin oxide SnO2 or NESA coating) film is used. The transparent electrically conductive film 4 is formed by vapor deposition or the like on the transparent plate 3. The transparent electrically conductive film 4 may be formed all over the exit side 3a of the transparent plate 3 or only in an area near the exit end 1b of a core 1. However, it is easier to from the film all over than to partly form the film, so that the transparent electrically conductive film 4 is preferably formed all of the exit side 3a of the transparent plate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a countermeasure against dust adhesion on a light emitting end face of an optical fiber or an optical waveguide.

[0002]

2. Description of the Related Art With the development and digitization of information networks in recent years, there has been a strong demand for faster laser beam printers. One of the means for increasing the speed of the laser beam printer is to increase the speed of rotation of the scanning polygon mirror. However, at present, when the number of rotations of the polygon mirror approaches 50,000, distortion of the polygon surface occurs due to centrifugal force, and it is said that there is a limit to further speeding up the rotation of the polygon mirror. Therefore, in order to further increase the drawing speed of the laser beam printer, the surface of the photoconductor is scanned with a plurality of laser beams.

[0003] Specifically, for example, Japanese Patent Application Laid-Open No. 10-2824.
No. 41, US Pat. No. 4,637,679, US Pat.
As described in US Pat. No. 47038, US Pat. No. 4,958,893, a configuration in which a plurality of laser beams are optically deflected to appropriate intervals and adjusted using a polarizing beam splitter, a half mirror, reflection of a prism surface, and the like. Has been proposed or adopted. However, these methods have the disadvantage that when the number of laser beams is large, alignment becomes difficult, the components become large and the cost becomes too high, and it is very difficult to achieve higher speeds than at present. .

Therefore, there is a demand for a method of forming a so-called multi light source in which a plurality of laser light sources are arranged at a fine pitch. The method is described in, for example, JP-A-54-73.
No. 28, a method using a so-called array laser having a plurality of laser diodes formed on a substrate as a plurality of laser light sources, a method using light emitted from an optical fiber as a secondary light source, and a method emitting light from an incident side There is a method using an optical waveguide in which the pitch on the side is narrowed.

However, in the method using an array laser, the pitch at which the laser diodes are arranged is set to a small value of 100 μm or less in order to bring a plurality of laser beam spots sufficiently close in consideration of the state of image formation on the photoreceptor surface. It is desirable that the interval is, but to form a laser diode on the substrate at such a small pitch,
This is difficult because the operation becomes unstable due to insufficient heat radiation. Therefore, it is considered that the other method using an optical fiber or an optical waveguide is effective.

In this case, in order to obtain a laser beam having an appropriate intensity and shape, it is important to treat the end face on the light emitting side by mirror finishing or the like. However, for example, mirror-polishing the end faces of the optical fibers and optical waveguides arranged in an array causes a reduction in work efficiency, and thus adversely affects productivity. In addition, when dust adheres to the light emission side end surface, the light emission efficiency is reduced and the shape of the laser beam is disturbed. Therefore, according to a paper by Kataoka et al., A configuration in which a glass plate is attached to the emission end of an optical fiber array with a resin or the like whose refractive index is matched by bonding is proposed.

The source of this paper is K. Kataoka, Y. Shib
ayama, M.Ohuchi, and S.Yokokawa “Laser printer optic
s withuse of slant scanning of multiple beams ”App
lied Optics Vol. 36, No. 25, p. 6294 (1997).

According to the configuration shown in FIG. 4 (c) of this paper, the distance from the light exit end to the air layer is increased by the thickness of the glass plate, so that the laser beam from the light exit end Is spread to some extent before reaching the end face of the glass plate, so that even if dust in the air adheres to the surface of the glass plate, the amount of light hardly decreases due to the influence.

Further, even when the optical fiber is susceptible to mechanical vibration, fluctuations in the laser emission power from the optical fiber can be suppressed by being fixed to the glass plate with a resin or the like. Further, the amount of light returning to the laser diode, which is the light source, is reduced. At this time, even if the end face of the optical fiber array or the optical waveguide on the light emission side is insufficiently polished and the flaw remains, the emission power is greatly reduced by matching the refractive index with a resin or the like. Can be prevented.

As described in JP-A-8-304602, CRTs and lenses are mainly used.
We apply anti-reflective coating by multilayer film on the surface,
A configuration is disclosed in which one of the layers is made of a transparent conductive film to release charges to the outside to eliminate the charge and reduce the adhesion of dust due to static electricity.

[0011]

However, the above Ka
With the configuration shown in the paper by taoka et al., it is possible to reduce the decrease in the amount of light due to dust adhesion, but it is not possible to reduce the dust itself adhering to the glass plate surface. In the configuration described in JP-A-8-304602, a transparent conductive film is provided as a third layer from the outside in order to obtain an antireflection effect. Therefore, since this cannot be provided in the outermost layer, the effect of static elimination becomes insufficient. The object of the present invention is a device such as an optical fiber or an optical waveguide, which has a small light emitting end area. Since these devices are more susceptible to the attachment of dust, a larger static elimination effect is required.

FIG. 4 is a diagram showing an example of the intensity distribution of a laser beam. The figure shows a so-called NFP (Near Field P)
attern) It is a beam shape measurement result by a measuring device, and shows an emission light profile from an optical fiber. Here, the beam intensity is represented by a contour line, and the length indicated by an arrow indicates 2.00 μm. FIG.
This is a measurement result after polishing the exit end of the optical fiber after lapping sheet polishing (particle size: several μm), and assumes a state in which dust does not adhere to the exit end surface. Also, FIG. 2B shows that the exit end of the optical fiber is about # 1000 (average particle size 14.
This is a measurement result after polishing at 5 to 18 μm), which is simulated by assuming a state where dust adheres to the emission end face.

When a laser beam is guided in an optical fiber in a single mode, the beam shape becomes almost circular in an ideal state where dust does not adhere to the exit end face as shown in FIG. The laser beam intensity distribution has a Gaussian distribution, and the peak position P is also substantially at the center. However, in the state where dust adheres to the exit end face as shown in FIG.
The laser beam intensity distribution is also separated from the Gaussian distribution, and the peak position P is also shifted. And
The beam intensity becomes weak overall.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an efficient light source unit having a simple structure and effectively taking measures against dust adhesion on a light emitting end face.

[0015]

According to the present invention, a transparent plate is provided at the light emitting end of an optical waveguide or an optical fiber, and a transparent conductive film is provided on the light emitting side of the transparent plate. The configuration of item 1 is adopted.

In addition, a measure is taken to release the electric charge on the transparent plate from the transparent conductive film to the outside.
The structure of claim 2 described above. This measure for releasing the charge to the outside indicates, for example, that the transparent conductive film is grounded.

Further, the transparent plate is bonded to the light emitting end by an adhesive whose refractive index is matched with the optical waveguide or the optical fiber. .

Further, the transparent conductive film has a configuration according to any one of claims 1 to 3, which is set so as to approximately satisfy the following theoretical formula. n ₁ d ₁ = 2 mλ / 4 where λ: wavelength of light to be used d ₁ : physical thickness of the transparent conductive film n ₁ : refractive index of the transparent conductive film m: integer (1, 2, 3,...) .

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an emission end configuration using an optical waveguide according to an embodiment of the present invention. FIG. 1 (a) is a plan view and FIG. 1 (b) is a side view. As shown in the figure, for example, four cores 1 provided in a clad 2 of an optical waveguide are located at positions where incident ends 1 a are separated from each other on a light (laser beam) incident surface 11 in the clad 2. It is provided in. Then, the light converges as the light travels through the clad 2, and the light emitting surfaces 11 a of the clad 2 are in a state where the respective light emitting ends 1 b of the core 1 are adjacent to each other.

The transparent plate 3 is adhered to the exit surface 11a with an adhesive 5 whose refractive index has been matched. Such an adhesive is a resin that matches the refractive index of the core layer that guides light, and includes an ultraviolet curable type, a thermosetting type, a two-component mixed type, and the like, but is not limited to these types. . On the emission side (air layer side) 3a of the transparent plate 3, a transparent conductive film 4 is provided.
Is provided in advance. This is based on ITO (Indium Tin O
It is a conductive material such as xide, indium tin oxide) or a nesa film (SnO ₂ , tin oxide, NESA Coating) without a significant decrease in transmittance. Means for providing such a transparent conductive film on a transparent plate include vapor deposition, sputtering, spray pyrolysis, and dip coating, but are not limited to these methods.

The transparent conductive film 4 may be provided on the entire surface of the transparent plate 3 on the emission side 3 a or on the emission end 1 of the core 1.
It may be provided only in a portion near b. However, since it is easier to provide the film over the entire surface than to provide the film partially, it is desirable to provide the transparent conductive film 4 over the entire emission side 3a of the transparent plate 3, and this is the case in the present embodiment. . Note that the emission light 6 (laser beam) is finally emitted from the emission surface 12 of the transparent conductive film 4.

The adhesion of dust due to static electricity occurs when dust in the air is positively or negatively charged, and is attracted to a dielectric having a charge of the opposite polarity. Therefore, in order to prevent the adhesion of dust due to static electricity, it is only necessary to cancel the charge of the dust by the charge of the opposite polarity or to prevent the charge of the dielectric. Therefore, in the present embodiment, as described above, the transparent conductive film 4 is provided on the surface of the transparent plate 3 which is a dielectric, and the ground wire 14 is connected to the transparent conductive film 4 as shown in FIG. , The electric charge is released to the outside by grounding to the ground E. Thereby, the electric potential on the surface of the transparent plate 3 can be maintained at 0, and charging can be prevented. Holding the potential at 0 can be easily performed by grounding as described above, but is not limited to this, and another method may be used.

FIG. 2 is a perspective view schematically showing a configuration using an optical fiber according to another embodiment of the present invention. In the figure, for example, three optical fibers 7 each have a laser diode 13 connected to its incident end 7a. The optical fibers 7 are fixed on the V-groove substrate 8, respectively, and the emission ends 7b thereof are bundled and housed and fixed in a plurality of V-grooves (not shown) on the V-groove substrate, respectively. The emitting end 7b is aligned with the end face 8a of the V-groove substrate 8, and the transparent plate 3 is adhered to these with an adhesive 5 whose refractive index is matched.

The adhesive here is a resin that matches the refractive index of the optical fiber that guides light. On the emission side (air layer side) 3a of the transparent plate 3, a transparent conductive film 4 is provided in advance. Although not shown, similarly to the above, a measure is taken here to release charges from the transparent conductive film 4 to the outside and keep the potential of the surface of the transparent plate 3 at 0 to prevent charging.
The laser beam emitted from the laser diode 13 enters the optical fiber 7 from the incident end 7a, passes therethrough, exits from the emission end 7b, and passes through the transparent plate 3 and the transparent conductive film 4.
After that, the light is finally emitted as the emission light 6.

FIG. 3 is a perspective view schematically showing another configuration using an optical fiber. In the figure, for example, four optical fibers 7 have laser diodes 13 connected to their incident ends 7a, respectively. Each of the optical fibers 7 has its emission end 7b bundled in an array with a jig or the like, and the transparent plate 3 is directly adhered to the optical fiber 7 with an adhesive 5 whose refractive index is matched. The adhesive here is a resin that matches the refractive index of the optical fiber that guides the light in the same manner as described above. On the emission side (air layer side) 3a of the transparent plate 3, a transparent conductive film 4 is provided in advance. Although not shown, similarly to the above, a measure is taken here to release charges from the transparent conductive film 4 to the outside and keep the potential of the surface of the transparent plate 3 at 0 to prevent charging.

In the transparent conductive film described so far, if the following theoretical formulas are set so as to be satisfied, theoretically,
The intensity of the reflected light can be minimized. n ₁ d ₁ = 2 mλ / 4 where λ: wavelength of light to be used d ₁ : physical thickness of the transparent conductive film n ₁ : refractive index of the transparent conductive film m: integer (1, 2, 3,...) .

For example, when the transparent conductive film 4 is composed of ITO having a refractive index of about 2, a recording light source (here, a laser diode 13) used in a laser beam printer.
Assuming that the wavelength of the laser light emitted from 780 nm,
The thickness of the transparent conductive film 4 may be approximately 1950 °. The number of the cores 1 or the optical fibers 7 is not limited to the number in the embodiment. Also, the transparent plate 3
May be glass, resin or other materials.

[0028]

As described above, according to the present invention,
With a simple configuration, it is possible to provide an efficient light source unit that effectively takes measures against dust adhesion on the light emitting end face.

In particular, according to the third aspect, even if the end face of the optical fiber or the optical waveguide on the light emission side is insufficiently polished and the flaw is left, it is possible to prevent the emission power from being greatly reduced. Can be.

According to the present invention, since the reflectance of the transparent conductive film takes a minimum value and becomes equal to that of the substrate, it is possible to minimize the influence of providing the transparent conductive film having a high refractive index. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an emission end configuration using an optical waveguide.

FIG. 2 is a perspective view schematically showing a configuration using an optical fiber.

FIG. 3 is a perspective view schematically showing another configuration using an optical fiber.

FIG. 4 is a diagram showing an example of an intensity distribution of a laser beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core 2 Cladding 3 Transparent plate 4 Transparent conductive film 5 Adhesive 6 Emission light 7 Optical fiber 8 V-groove substrate 13 Laser diode 14 Earth wire E Earth

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 6/12 B41J 3/00 D H04N 1/04 101 G02B 6/12 Z F term (Reference) 2C362 AA43 AA44 BA25 DA14 2H046 AA03 AA42 AA48 AB10 AD05 AZ04 2H047 KA03 KA15 MA05 RA04 2H050 AC86 AC90 5C072 AA03 BA05 BA20 CA06 DA08 DA21 DA23 DA30 HA02 HA06

Claims (4)

[Claims] 1. A light source unit comprising: a transparent plate provided on a light emitting end of an optical waveguide or an optical fiber; and a transparent conductive film provided on a light emitting side of the transparent plate. 2. The light source unit according to claim 1, wherein a measure is taken to release electric charges on the transparent plate from the transparent conductive film to the outside. 3. The light emitting end according to claim 1, wherein the transparent plate is bonded to the light emitting end by an adhesive whose refractive index is matched with the optical waveguide or the optical fiber.
The light source unit according to item 1. 4. The light source unit according to claim 1, wherein the transparent conductive film is set so that the following theoretical formula is approximately satisfied: n ₁ d ₁ = 2mλ / 4, where λ: wavelength of light used d ₁ : physical thickness of transparent conductive film n ₁ : refractive index of transparent conductive film m: integer (1, 2, 3,...)