JP2000323793A - Multibeam light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost by simplifying an optical system by realizing a constitution having a near field pattern whose mode diameters in the vertical direction are different from each other inside a projection surface of optical flux. SOLUTION: A laser diode 6 is connected to an incident end 3a of each fiber 3, and laser beam therefrom passes through the optical fiber 3, and is projected from a light projection end 2b through a core 2 inside an optical waveguide 1. The configuration of the optical projection end 2b is a rectangle when viewed from a front and a direction along a short side is a main scanning direction and a direction along a long side is a sub-scanning direction. In a multibeam light source, in this way, an optical waveguide is constructed to have a projection beam configuration (near field) whose mode diameter in a vertical direction is different from each other as a main scanning direction and a sub-scanning direction. Therefore, the cost can be reduced by simplifying an optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam light source based on an optical waveguide, and more particularly to a multi-beam light source based on an optical waveguide which is configured as a light source of a laser beam printer.

[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.

[0006]

However, when a multi-beam light source is used, for example, by using an optical waveguide provided with wiring having a very small pitch on the emission side, the size of the beam spot diameter on the surface to be scanned can be reduced. In order to perform the adjustment, an optical component such as a so-called beam expander that expands the light beam must be used, which increases the cost. The reason will be described below.

[0007] Since the intervals between the output beams of the optical waveguide as the multi-beam light source are extremely close, it is difficult to provide individual collimators for the individual output beams. Therefore, all beams are imaged on the surface to be scanned by the same optical system. In such a case,
It is extremely difficult to independently adjust the spot diameter and the spot interval on the surface to be scanned.

Here, in a laser scanning optical system using a polygon mirror, in the sub-scanning direction, the polygon mirror surface and the surface to be scanned are kept conjugate and the angular error in the sub-scanning direction between the respective polygon mirror surfaces is reduced. Compensated. Therefore, in the sub-scanning direction, a beam expander is formed before and after the polygon mirror surface, and the beam diameter in the sub-scanning direction can be controlled to some extent.

However, in the main scanning direction, the light beam passing through the collimator lens is directly incident on the scanning lens. Therefore, the focal length of the collimator lens and the F number directly determine the beam diameter on the surface to be scanned. Will be done. At this time, in order to control the beam diameter in the main scanning direction and, specifically, to reduce the beam diameter, it is necessary to first widen the light beam and then narrow it down with a scanning lens. It is necessary to separately insert the above-mentioned beam expander having the function of expanding the light flux, which causes an increase in cost.

The present invention has been made in view of the above problems, and has as its object to provide a multi-beam light source capable of simplifying an optical system and reducing costs.

[0011]

In order to achieve the above object, according to the present invention, a near-field pattern having different mode diameters in directions perpendicular to each other in a light emitting surface is provided.

[0012] Further, it has a configuration according to claim 1 which has optical paths having different diameters in directions perpendicular to each other.

[0013] Further, the light emitting device according to the first or second aspect has an optical path having different optical indices in directions perpendicular to each other.

Further, the light emitting portion of the light beam is made of a quartz-based material.

Further, the light emitting portion of the light beam is made of a polyimide resin.

Further, the structure of the light emitting portion is a buried optical waveguide.

Further, the structure of the light beam emitting portion is a rib optical waveguide according to any one of claims 1 to 3.

Further, the structure of the light beam emitting portion is a dielectric strip optical waveguide according to any one of claims 1 to 3.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view schematically showing a configuration of a multi-beam light source according to one embodiment of the present invention. As shown in the figure, in the multi-beam light source of the present embodiment, a plurality of cores 2 are formed in a film-shaped optical waveguide 1. A plurality of (four in this case) optical fibers 3 are fixedly arranged in a V-groove (not shown) on the V-groove substrate 4 and arranged in a single row. It is connected to the incident side 1a.

At this time, each light incident end 2a of the core 2 provided on the light incident side 1a is connected to the output end 3 of each optical fiber 3.
facing b. Then, a laser beam from each optical fiber 3 enters each light incident end 2a, passes through the core 2, and is emitted as a laser beam 5 from each light emitting end 2b provided on the light emitting side 1b.

Here, for example, the light incident side 1a of the optical waveguide 1
Core pitch (pitch between light incident ends 2a of core 2)
Is 127 μm, and the core pitch of the light emitting side 1 b (the pitch between the light emitting ends 2 b of the core 2) is 14 μm. The pitch on the incident side corresponds to the pitch between the optical fibers 3 on the optical fiber array 7, and the pitch on the emitting side is 600 d on the photosensitive member surface of the laser beam printer.
pi (spot interval about 42 μm)
The setting is made on the assumption that a three times magnification optical system is used.

FIG. 2 is a perspective view schematically showing the appearance of the multi-beam light source. Incident end 3 of each optical fiber 3
A laser diode 6 is connected to each of a, and a laser beam from each of the laser diodes 6 passes through the optical fiber 3 and is emitted from the light emitting end 2 b through the core 2 in the optical waveguide 1.

Here, as shown in FIG. 3, the shape of the light emitting end 2b is a rectangle when viewed from the front. Here, the direction of arrow A along the short side is along the main scanning direction and along the long side. The arrow B direction is the sub-scanning direction. In this manner, in the multi-beam light source of the present embodiment, within the exit surface of the optical waveguide, the main scanning direction and the sub-scanning direction
The optical waveguide has an emission beam shape (near field pattern) having different mode diameters in directions perpendicular to each other.

FIG. 4 is a longitudinal sectional view including the core 2 near the light exit side 1b of the optical waveguide 1. As shown in FIG. In the figure, it is assumed that the laser beam 5 emitted from the light emitting end 2b of the core 2 in the optical waveguide 1 is a so-called Gaussian beam with the width d of the core 2 as the beam diameter and the light emitting end 2b as the beam waist. Then, the following theoretical formula holds. θ = arctan (λ / πd) ≒ λ / πd (radian) where θ: beam divergence angle λ: beam wavelength.

According to the above equation, the divergence angle of the emitted beam from the optical waveguide can be set by adjusting the core diameter. By making this different between the main scanning direction and the sub-scanning direction, the optical system Can be simplified. Specifically, in a so-called waveguide-type multi-beam light source, if the divergence angle of the emission beam in the main scanning direction is designed to be widened in advance and the divergence angle in the sub-scanning direction is narrowed, It is not necessary to use a beam expander in the optical system, the existing optical system can be diverted, the number of optical points can be simplified, and the cost can be reduced.

Furthermore, in the above-described configuration, the laser beam is basically transmitted from the laser diode to the optical fiber, and from the optical fiber to the optical waveguide. However, a method of transmitting the laser beam by directly coupling the laser diode to the optical waveguide. You can also take. For example, a form in which several laser diodes are formed on one chip in the future and a laser beam is directly transmitted from the laser diode to the optical waveguide can be considered. In this case, by not only increasing the pitch of the light incident end of each core but also increasing the core diameter on the light incident side of the optical waveguide, direct incidence of the laser beam from the laser diode to the optical waveguide is facilitated.

On the other hand, on the exit side of the optical waveguide, the pitch of the light exit end of each core is small and the core diameter is also small regardless of the configuration of the entrance side. In this case, for example, if the shape of the light emitting end is a rectangle as shown in FIG. 3, the shape of the light incident end may be a square extending in the short side direction. At this time, it is necessary to take some measures such as making the core film thickness inclined from the light incident end to the light emitting end, or forming a funnel shape near the light incident end.

Hereinafter, a procedure for manufacturing a so-called three-dimensional optical waveguide in the multi-beam light source of the present invention will be described. Quartz, a polyimide resin, an epoxy resin, or the like is used as a material of the film forming the clad layer and the core layer of the optical waveguide. In the present embodiment, a quartz-based material is used as an example. First, TEOS is basically used as the material of the film.
(Tetra Ethyl Ortho Silicate: Si (OC ₂ H ₅ ) ₄ )
Are used to form SiO ₂ films by a low-temperature plasma CVD method. It is well known that doping SiO ₂ changes the refractive index.

For example, doping SiO ₂ with Ge increases the refractive index, and doping F decreases the refractive index. At this time, in accordance with (cladding layer / core layer / cladding layer) as the configuration of each layer of the optical waveguide, (SiO ₂ /
SiO _2: Ge / SiO ₂₎ doped with Ge to the core layer with increased refractive index as if, or (SiO _2:
A configuration is conceivable in which the cladding layer is doped with F to reduce the refractive index, as in F / SiO ₂ / SiO ₂ : F).
Here, a configuration in which F is doped will be described as an example.

FIG. 5 is a graph showing an example of how the refractive index changes with the doping amount of F. Here, the horizontal axis indicates the gas flow rate of C ₂ F ₆ at 0 ° C. and 1 atm (unit scc) during film formation.
m: standard cubic centimeter per minute), and the refractive index of SiO ₂ formed on the vertical axis is taken. However, the film forming conditions are: substrate temperature: 350 ° C., pressure: 0.6 Torr TEOS / O ₂ : 12/100 sccm RF: 300 w

Here, the substrate temperature refers to the temperature of a substrate on which a quartz substrate, which will be described later, is used when manufacturing an optical waveguide. TEOS / O ₂ is a flow rate of a mixture of these material gases and carrier gas. And R
F is high frequency power applied in the atmosphere. As shown in the figure, first, when the doping amount of F is 0, the refractive index is maintained at about 1.473, but the refractive index gradually increases as the flow rate of C ₂ F ₆ , that is, the doping amount of F increases. Decreased,
When the flow rate is 30 sccm, the refractive index is 1.44 or less. Therefore, by adjusting the flow rate of C ₂ F ₆ , that is, the doping amount of F, it is possible to form the cladding layer in which the refractive index is reduced to a predetermined value.

FIG. 6 is a schematic diagram showing an example of a specific process for manufacturing an optical waveguide in the multi-beam light source of the present invention. In the figure, the specific configuration of the optical waveguide is shown from the light emission side. Here, a quartz substrate 11 having the same thermal expansion coefficient as that of the quartz substrate 11 is used so that cracks and the like due to thermal stress do not occur in the optical waveguide. First, as shown in FIG.
To form This allows the F-doped SiO ₂ film, the C ₂ F
The ₆ were mixed TEOS at predetermined deposition conditions, about 15
It is formed to a thickness of μm.

Next, as shown in FIG. 3B, a core layer 13 is formed on the upper surface of the lower cladding layer 12a. This is the C ₂ F ₆ stops gas supply of TEOS containing, after evacuation of residual gas, a non-doped SiO ₂ film, C ₂ F ₆
About 5μ with TEOS not mixed
m. Further, as shown in FIG. 3C, an amorphous silicon film 14 is formed on the upper surface of the core layer 13 by a sputtering method so as to have a thickness of 0.6 μm.
Form. Then, as shown in FIG. 2D, a resist is applied on the upper surface of the amorphous silicon film 14, and is patterned by photolithography so as to have a core shape of the optical waveguide, thereby forming a resist 15.

In the state of (d), Reactive Ion Etching (RIE) using SF ₆ gas
By patterning the amorphous silicon film 14 and removing the resist 15 by ashing, the remaining portion becomes a mask 14a made of amorphous silicon as shown in FIG. Then, in the state of (e),
When the core layer 13 is patterned by RIE using CHF ₃ gas, the remaining portion becomes the core 13a as shown in FIG.

Further, in the state of FIG.
An upper clad layer 12b is formed on the upper surface of 2a so as to cover the core 13a. This is because the F-doped SiO ₂ film is formed under the same film forming conditions as the lower clad layer 12a described above for about 15 minutes.
It is formed to a thickness of μm. As a result, as shown in FIG. 1G, the lower clad layer 12a and the upper clad layer 12b are integrated, the clad 12 surrounding the core 13a is formed, and an optical waveguide is manufactured.

Incidentally, the configuration of the optical waveguide in the multi-beam light source according to the present invention may take various forms other than those described above, as shown below. First, FIG. 7 is a schematic diagram illustrating a configuration of a rib optical waveguide. Here, FIG. 1A is a perspective view showing the whole, and FIG.
FIG. 3 is a front view showing the periphery of the core from the light emission side. As shown in FIG. 1A, in this example, the core layer 1 is formed on the upper surface of the substrate 20.
3, and a plurality of (four in this example) strips are formed on the upper surface thereof as ribs 13b. Here, the function of the core is performed in units of each rib 13b.

The dimensions of each part around the core are, for example, as shown in FIG.
Is set to a thickness of 0.5 μm and a width of 6 μm. At this time,
The substrate 20 has a refractive index of 1.46, the core layer 13 and the rib 13
Assuming that b is 1.4673 and the upper part is air (1.0), the mode diameter at a wavelength of 780 nm of the beam passing through each rib 13b is, for example, 11.9 μm in the x direction in FIG.
The direction is 3.57 μm. The spread angle is, for example, 2.35 ° in the x direction and 9.16 ° in the y direction.

The core layer 13 and the ribs 13b have the same structure as that of FIG.
When glass is used as a material for the substrate, the refractive index of the substrate 20 is 1.53, and the refractive index of the core layer 13 and the rib 13b is 1.54 in the x direction.
Assuming that 784 and the y direction are 1.53608, the mode diameter is, for example, 10.51 μm in the x direction and 3.15 μm in the y direction. The spread angle is, for example, 2.64 ° in the x direction, y
The direction is 11.9 °. Thus, the same effect can be obtained even when an anisotropic material is used.

FIG. 8 is a schematic diagram showing the configuration of the embedded optical waveguide. Here, FIG. 1A is a perspective view showing the whole, and FIG. 1B is a front view showing the periphery of the core from the light emission side. As shown in FIG. 3A, in this example, a plurality of cores 13a (four in this case) are embedded in the substrate 20, and the upper surfaces of the cores 13a are made the same.

The dimensions of each part around the core are set to, for example, a thickness of 3 μm and a width of 6 μm of the core 13 a as shown in FIG. At this time, the refractive index of the substrate 20 was 1.46,
The core 13a has 1.4673 and the upper part is air (1.0)
Then, the wavelength 780 of the beam passing through each core 13a
The mode diameter in nm is, for example, 5.93 μm in the x direction in the figure.
3.27 μm in the m and y directions. The spread angle is, for example, 5.50 ° in the x direction and 8.71 ° in the y direction.

FIG. 9 is a schematic diagram showing the configuration of another embedded optical waveguide. Here, FIG. 1A is a perspective view showing the whole, and FIG. 1B is a front view showing the periphery of the core from the light emission side. As shown in FIG.
0, a plurality of cores 13a (four in this case) are embedded.

The dimensions of each part around the core are set to, for example, a thickness of 3 μm and a width of 6 μm of the core 13a as shown in FIG. At this time, the refractive index of the substrate 20 was 1.46,
Assuming that the core 13a is 1.4673, the mode diameter of the beam passing through each core 13a at a wavelength of 780 nm is, for example, 5.93 μm in the x direction and 3.85 μm in the y direction in the drawing. The spread angle is 5.52 ° in the x direction, for example.
It is 7.19 ° in the y direction.

FIG. 10 is a schematic diagram showing the configuration of a dielectric strip optical waveguide. Here, FIG. 1A is a perspective view showing the whole, and FIG. 1B is a front view showing the periphery of the core from the light emission side. As shown in FIG. 1A, the present embodiment has a structure in which a plurality of (here, four) cores 13a are provided on the upper surface of the substrate 20.

The dimensions of each part around the core are set to, for example, a thickness of 3 μm and a width of 6 μm of the core 13a as shown in FIG. At this time, the refractive index of the substrate 20 was 1.46,
The core 13a has 1.4673 and the upper part is air (1.0)
Then, the wavelength 780 of the beam passing through each core 13a
The mode diameter in nm is, for example, 4.75 μm in the x direction in the figure.
It is 3.31 μm in the m and y directions. The spread angle is, for example, 7.65 ° in the x direction and 8.40 ° in the y direction.

FIG. 11 is a schematic diagram showing another configuration of the optical waveguide from the light emitting side. FIG. 1A shows an optical waveguide loaded with a dielectric strip, in which a core layer 13 provided on an upper surface of a substrate 20 has a dielectric 16 provided in the center of the upper surface thereof.
, A predetermined portion at the center plays a role as a core. FIG. 2B shows a ridge-type optical waveguide, and a core layer 13 provided on the upper surface of the substrate 20.
Is a peak-shaped (ridge-shaped) dielectric 1 provided on the upper surface thereof.
By the function of 6, a predetermined portion at the center plays a role as a core. FIG. 3C shows a metal clad optical waveguide in which the core layer 13 provided on the upper surface of the substrate 20 has the metal clad 1 provided on the left and right surfaces thereof.
By the operation of 7, a predetermined portion in the center plays a role as a core.

Finally, FIG. 3D shows an electric field induced optical waveguide. A core layer 13 is provided on the upper surface of a substrate 20 shown in FIG. 1, an insulator 18 is provided on the upper surface, and an electrode 19 shown by oblique lines is attached to the center of the upper surface. When a voltage V ₀ is applied to the electrode 19, an electric field is induced between the electrode 19 and the substrate 20 on the earth side via the insulator 18 and the core layer 13. Among the core layer 13, is exposed portions in the electric field, increases by Δn than the original refractive index n _f, has a configuration which serves as a core at the core 13a.

The exit surface in the claims corresponds to the light exit side of the optical waveguide in the embodiment, and the optical path corresponds to the core of the optical waveguide.

[0048]

As described above, according to the present invention,
It is possible to provide a multi-beam light source capable of simplifying an optical system and reducing costs. Specifically, in a so-called waveguide-type multi-beam light source, if the divergence angle of the emission beam in the main scanning direction is designed to be widened in advance and the divergence angle in the sub-scanning direction is narrowed, Eliminates the need for beam expanders in the optics,
The existing optical system can be diverted, the number of optical points can be simplified, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a configuration of a multi-beam light source according to the present invention.

FIG. 2 is a perspective view schematically showing the appearance of a multi-beam light source according to the present invention.

FIG. 3 is a front view showing the shape of a light emitting end.

FIG. 4 is a vertical cross-sectional view including a core in the vicinity of a light emission side of the optical waveguide.

FIG. 5 is a graph showing an example of how the refractive index changes with the doping amount of F.

FIG. 6 is a schematic view showing an example of a specific manufacturing process of an optical waveguide.

FIG. 7 is a schematic diagram showing a configuration of a rib optical waveguide.

FIG. 8 is a schematic diagram showing a configuration of a buried optical waveguide.

FIG. 9 is a schematic diagram showing a configuration of another embedded optical waveguide.

FIG. 10 is a schematic diagram showing a configuration of a dielectric strip optical waveguide.

FIG. 11 is a schematic diagram showing another configuration of the optical waveguide from the light emission side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Core 3 Optical fiber 4 V-groove substrate 5 Laser beam 6 Laser diode 7 Optical fiber array

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Naoki Nishida, Inventor Naoki 2-3-1-3, Azuchicho, Chuo-ku, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Shinji Maruyama 2-chome, Azuchicho, Chuo-ku, Osaka-shi No. 13 Osaka International Building Minolta Co., Ltd. (72) Inventor Takashi Hatano 2-13-13 Azuchicho, Chuo-ku, Osaka City Osaka International Building Minolta Co., Ltd. F-term (reference) 2H045 BA22 BA43 CB68 2H047 KA04 KA05 KA15 MA05 PA24 PA28 RA01 RA04 TA31 TA36 2H076 AB05 AB06 AB07 AB52 EA04 5F073 AB25 AB28 BA07 EA18 EA29

Claims (8)

[Claims] 1. A multi-beam light source characterized by having near-field patterns having different mode diameters in directions perpendicular to each other on an exit surface of a light beam. 2. The multi-beam light source according to claim 1, wherein the multi-beam light source has optical paths having different diameters in directions perpendicular to each other. 3. The multi-beam light source according to claim 1, wherein the multi-beam light source has an optical path having different refractive indexes in directions perpendicular to each other. 4. The multi-beam light source according to claim 1, wherein the light beam emitting portion is made of a quartz-based material. 5. The multi-beam light source according to claim 1, wherein the light beam emitting portion is made of a polyimide resin. 6. The multi-beam light source according to claim 1, wherein the structure of the light emitting portion is a buried optical waveguide. 7. The multi-beam light source according to claim 1, wherein the structure of the light emitting portion is a rib optical waveguide. 8. The multi-beam light source according to claim 1, wherein the structure of the light emitting portion is a dielectric strip optical waveguide.