JP2540870B2 - Optical scanner - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanner for scanning a beam of light,
In particular, it relates to an optical scanner using an optical switch.

[Conventional technology]

For example, in an image output device such as a laser printer, it is necessary to use an optical scanner and scan the photoconductor with a modulated laser beam to form an electrostatic latent image on the photoconductor.

As an optical scanner, for example, one using a rotary polygon mirror is known. In this optical scanner using a rotary polygon mirror, a beam from a light source such as a semiconductor laser is applied to the rotary polygon mirror, and the beam reflected by the rotary polygon mirror is focused on a photoconductor through an fθ lens to perform exposure scanning. Is going. Further, there is one in which a resonance mirror is used instead of the rotary polygon mirror, but basically the same.

[Problems to be Solved by the Invention] However, in an optical scanner using such a rotating polygon mirror, a resonant mirror, etc., there is a mechanical moving part, so there is a limit to the speedup and the reliability is low. . Also,
There is a problem that not only noise is generated due to rotation or vibration of the rotary polygon mirror, the resonance mirror, etc., but also disturbance of the scanning position such as jitter and wobble occurs.

In addition, there is a problem that the optical path of the beam from the light source to the photoconductor is long and optical elements such as various lenses are arranged in this optical path, so that the apparatus becomes complicated and large.

In order to solve these problems, it is possible to use, for example, an ultrasonic optical deflector utilizing the acousto-optic effect.

However, this ultrasonic optical deflector has a small deflection angle,
Further, it is difficult to continuously change the deflection angle. Further, a lens is required to form the beam emitted from the ultrasonic optical deflector on the image plane, but since the deflected beam has a wide swing width, a lens having a large diameter is required. Further, since the beam scans other than the center as well, there is a problem that the aberration increases and the resolution decreases at both ends of the scan, and the light is not completely taken into the lens, resulting in poor efficiency.

The present invention has been devised to solve the above-mentioned problems, and an object thereof is to reduce the size and efficiency of a high-speed and high-resolution optical scatter.

[Means for solving problems]

In order to achieve the above-mentioned object, the optical scanner of the present invention forms a plurality of optical waveguides on a substrate so that the optical axes of the emitted lights intersect at one point, and the incident light is directed to any of the plurality of optical waveguides. It is characterized in that an optical switch for selectively advancing is provided on the substrate, and a lens member for converging the respective emitted lights on an image plane is arranged at a point where the respective emitted lights intersect.

A geodesic lens can be used as the lens member. Further, this geodesic lens can be formed on a common substrate together with the optical waveguide.

[Action]

According to the present invention, the incident light is switched to the plurality of optical waveguides by the optical switch, and the emitted light from each optical waveguide passes through the lens member and is focused at different positions on the image plane for scanning. . At this time, the plurality of optical waveguides are formed so that the optical axes of the emitted light intersect at one point, and since the lens member is arranged at this intersection, the emitted light always passes through the center of the lens member regardless of the scanning position. To do. Therefore, the emitted light is not affected by the aberration of the lens member.

When a geodesic lens is used as the lens member, most of the incident light is taken in by the geodesic lens, so that the efficiency is improved and no aberration occurs.

〔Example〕

Hereinafter, features of the present invention will be specifically described based on embodiments with reference to the drawings.

FIG. 2 shows a schematic configuration of an example of an optical switch used in the optical scanner according to the present invention. 2 (a) is a plan view of the optical switch, FIG. 2 (b) is a front view thereof, and FIG. 2 (c) is a side view thereof.

In the figure, reference numeral 1 denotes a substrate having a refractive index n ₁ , and this substrate 1
An optical waveguide 2 on the incident side and optical waveguides 31 and 32 on the outgoing side branched from the optical waveguide 2 are formed on one surface. In FIG. 2 (c), the optical waveguide 31 is provided for reference.
Is indicated by a broken line. Refractive index n of these optical waveguides 31, 32
₂ is slightly higher than the refractive index n ₁ of the substrate 1.

Further, the electrode portion 4 is provided at the branched portion of the optical waveguides 31 and 32. The electrode portion 4 is provided with a pair of parallel electrodes 4a and 4b diagonally crossing over the optical waveguide 32. Then, one electrode 4a is grounded and the other electrode 4b is connected to the voltage terminal 4c. By turning on / off the voltage to the voltage terminal 4c, transmission and total reflection in the electrode portion 4 are controlled and the optical path is switched, as described later. The refractive index of the electrode portion 4 portion of the optical waveguide 32 is n ₃ .

Further, the optical waveguide 31 is bent in the direction of the optical waveguide 32 in the middle of the optical path, and the reflecting member 5 having a refractive index n ₄ is provided at this bent portion. The refractive index n ₄ of this reflecting material 5 is set to the lowest of the above-mentioned refractive indexes, and
The light traveling from 2a and reflected by the electrode portion 4 is totally reflected by the reflector 5 and travels to the waveguide emission end 31a with almost no loss.

All or at least the electrode portion 4 part of the material of the substrate 1, the optical waveguides 2, 31, 32, and the reflection material 5 described above is made of a material having an electro-optical effect.

For example, the substrate 1 is made of transparent glass-like LiNbO _3, and the optical waveguides 2, 31, 32 can be formed by a Ti diffusion method in which Ti is diffused in the substrate 1. In addition to the Ti diffusion method, an external diffusion method, a LiTaO ₃ crystal growth method, an ion exchange method, or the like can be used. In addition, the substrate 1 is LiTaO ₃
It is possible to form an optical waveguide by a Cu electric field diffusion method or diffusion of Nb, LiNbO ₃ or the like.
An optical waveguide can be formed by sputtering TaO ₃ and then sputtering PLZT. Further, the electrodes 4a and 4b can be formed by printing gold or silver paste or the like on the optical waveguide 32 and baking the paste.

Next, the operation of the optical switch shown in FIG. 2 will be described.

The light incident from the waveguide entrance end 2a travels in the optical waveguide 2 and reaches the electrode portion 4. Considering the case where a voltage is applied to the electrode section 4, the material of the waveguide is LiNb as described above.
By using a material having a large electro-optical effect such as O ₃ , the refractive index of only this portion changes. For example, 5-10
The change Δn in the refractive index with the voltage V is 2 to 5 × 10 ⁻³ . In this case, if the refractive index is lowered by 0.1, for example, total reflection occurs even at an incident angle of 80 ° C. or less. Therefore, the incident light is switched to the waveguide exit end 31a side or 32a side depending on the presence or absence of the applied voltage to the electrode portion 4. That is, when the refractive index n ₃ of the electrode portion 4 is equal to the refractive index n ₂ of the optical waveguide 32, light travels to the waveguide emission end 32a, and when the refractive index n ₃ is lower than the refractive index n ₂ ,
The light is totally reflected by the electrode portion 4 and proceeds to the waveguide emission end 31a.

FIG. 3 shows an optical switch array in which, for example, four optical switches described above are arranged in an array to switch five optical paths. The number of optical paths can be increased if necessary.

In the configuration shown in FIG. 3, the four electrode parts 41 to 44 are arranged in a straight line along the optical axis of the optical waveguide 2 on the incident side.
Is provided and the optical path is branched into five, and reflectors 51 to 55 are provided in the respective branched optical paths. The optical waveguides 31 to 35 on the emitting side are arranged so that their optical axes coincide with each other at a point 6.

FIG. 1 shows an example of an optical scanner of an embodiment of the present invention using the optical switch array shown in FIG.

In the configuration shown in FIG. 1, the optical switch array and the geodesic lens are integrally formed. That is, a point 6 where the optical axes of the optical waveguides 31 to 35 (see FIG. 3) on the emission side of the optical switch array intersect, that is, a geodesic lens 7 centered on the intersection of the emission optical axes is arranged, and the waveguide emission end 31a. Output light 8 from ~ 35a
The image is formed on the top. At this time, the optical switch and the geodesic lens 7 described in FIG. 3 can be formed on the common substrate 1.

Here, the geodesic lens 7 will be briefly described. As shown in FIG. 4, the optical waveguide 1 is formed on the substrate 101.
In addition to forming 02, a recess 103 having a predetermined curved surface is formed on the surface on the optical waveguide 102 side. Then, the light beam 104 propagating through the optical waveguide 102 is imaged at a point 105. For details of this geodesic lens 7, refer to "Journal of the Optical Society o
f America ”, vol.69 (1979), p1248, the geodesic lens 7 has the curved surface so that light incident from any direction passes through the shortest distance and converges to the image forming point. Is designed. A ray passing through the center shows the same image forming performance for a ray incident from any angle, so that it has a property that aberration does not become large at both ends unlike an ordinary optical lens. There is.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

Incident light from the waveguide entrance end 2a is selectively branched by the electrode portions 41 to 44 as in the embodiment shown in FIG. The branched light is reflected by the reflecting materials 51 to 55 that cause total reflection due to the low refractive index, and the light from the reflecting materials 51 to 55 is
It is radiated from the waveguide emission ends 31a to 35a (see FIG. 3) arranged toward the center of the geodesic lens 7. The emitted light travels in the waveguide 20 while spreading only in the scanning plane, and enters the geodesic lens 7. At this time, all the light emitted is incident on the geodesic lens 7, that is, by arranging the optical waveguides 31 to 35 (see FIG. 3) toward the center of the geodesic lens 7, the amount of light is efficiently used. can do.

Here, by optimizing the positions of the waveguide emission ends 31a to 35a (see FIG. 3) in the optical axis direction, the emission light 8 from the geodesic lens 7 is uniformly and linearly reflected on the image plane 9. It is illuminated as a spot.

Therefore, by sequentially switching the voltage applied to the electrode parts 41 to 44, the transmission and total reflection in the electrode parts 41 to 44 are controlled, and the light from the waveguide emission ends 31a to 35a is sequentially irradiated onto the image plane 9. Then, the image plane 9 can be scanned. For example,
When a voltage that causes total reflection at the electrode portion 41 is applied, the incident light is reflected by the electrode portion 41 and the reflective material 51 to become emitted light 8a, and when a voltage that passes through all the electrode portions 41 to 44 is applied, Incident light is reflected by the reflector 55 to become emitted light 8b. At this time, since the optical waveguides 31 to 35 are arranged toward the center of the geodesic lens 7, the light from the waveguide exits 31a to 35a always passes through the center of the geodesic lens 7.
Therefore, the aberration due to the lens is eliminated. Further, the light emitted from the optical waveguides 32 to 35 (see FIG. 3) is taken into the geodesic lens 7 in the same manner at both the center and both ends, so that both ends do not become dark.

FIG. 5 shows another embodiment of the optical scanner. The fifth
FIG. 5A is a plan view of the optical scanner seen from a direction orthogonal to the scanning plane, and FIG. 5B is a side view of FIG. 5A seen from a direction parallel to the scanning plane. . In addition, in FIG. 5B, the illustration of the electrode portion is omitted.

In this embodiment, the unidirectional gradient index lens 10 having a refractive index distribution only in the direction orthogonal to the scanning plane is used for the optical scanner shown in FIG. It is fixed and provided integrally. The emitted light 8 from the geodesic lens 7 is focused on the image plane 9 via the unidirectional gradient index lens 10. In the example shown in FIG. 5, the optical waveguide 20 is formed on the entire upper surface of the geodesic lens 7 portion.

Next, the operation of the embodiment shown in FIG. 5 will be described. However, the operation up to the geodesic lens 7 is the same as in the embodiment shown in FIG.

The light emitted from the geodesic lens 7 enters the unidirectional gradient index lens 10 while being focused in the scanning direction, as shown in FIG. 5 (a). Regarding the direction of the scan plane,
As in FIG. 1, the geodesic lens 7 focuses the light on the image plane 9, and in the direction orthogonal to the scanning, it is first released from the waveguide 20 and begins to spread by diffraction, but the unidirectional gradient index lens 10 Due to the focusing action, it is focused on the image plane 9 as shown in FIG. 5 (b). At this time, since there is no focusing effect of the unidirectional gradient index lens 10 in the scanning direction, only the focusing action of the geodesic lens 7 is acting, and both directions are imaged on the image plane 9 independently of each other. It Therefore, geodesic lens 7
By selecting the magnification of each of the unidirectional gradient index lens 10, the aspect ratio of the imaged light spot or the eccentricity of the ellipse can be arbitrarily set.

FIG. 6 shows the light quantity distribution of the light spots irradiated on the image plane 9, and this light quantity distribution is determined by the optical waveguide mode of the waveguide emission ends 31a to 35a. In the figure, the horizontal axis is the optical axis center.
The position x from X ₀ and the vertical axis represent the light intensity P.

For example, in the case of a high-order guided mode such as HE _21, the light amount distribution has a bimodal characteristic as shown in FIG. 6 (b), and when this scanner is used for an optical printer, the resolution is Is not desirable. Therefore, by setting the guided mode to the single mode HE ₁₁ , the light amount distribution has a single-peak characteristic as shown in FIG. 6 (a), and this problem is solved. As is well known, the waveguide mode is made into a single mode by selecting a waveguide cross-sectional shape, or a waveguide having a relationship between a core and a clad and a member around the waveguide, such as the waveguide 2 in the case of FIG. This can be realized by selecting the refractive index of the substrate 1, 31 and 32.

FIG. 7 shows still another embodiment, in which each electrode portion 4 is arranged on a curved line, and incident light is totally reflected when a voltage is applied to each electrode portion 4 and slightly refracted when a non-voltage is applied. The curved shape and the arrangement of the electrode portions 4 are selected for the angle.
With this, without using a reflecting material for bending the optical path,
The optical axis of the light emitted from the waveguide can have one intersection 6. In this case, since the reflecting material is unnecessary, there is an effect that the loss due to the reflecting material is eliminated.

8 to 10 show still another embodiment, in which
This is an example in which the geodesic lens 7 of the embodiment shown in the figure is replaced with a normal optical lens.

FIG. 8 shows a spherical lens 11 instead of the geodesic lens 7.
It is a top view of the Example which used.

9A and 9B, instead of the geodesic lens 7, two cylindrical lenses 12 and 13 orthogonal to each other are shown.
3A and 3B are a plan view and a side view of an embodiment using the.

Further, FIG. 10 shows an example in which the geodesic lens 7 is replaced with a gradient index lens 14.

Also in the embodiment shown in FIGS. 8 to 10 described above,
It is possible to converge the light in the scanning direction and the direction orthogonal to the scanning direction, but in either case, it is necessary to reduce the aberration of focusing in the scanning direction.

Next, an example of a method of manufacturing an optical switch using LiNbO ₃ as a substrate and forming an optical waveguide by Ti diffusion will be described below.

(1) Clean the LiNbO ₃ substrate.

(2) The surface of the substrate is coated with Ti.

(3) A resist pattern is formed on a portion to be an optical waveguide.

(4) Remove Ti other than the resist pattern by etching.

(5) Ti diffusion is performed. For example, thermal diffusion is performed for several hours to several tens of hours at 900 to 1100 ° C., which is below the Curie temperature, in air, in O ₂ , or in an atmosphere of argon and H ₂ O (steam).

(6) The electrode pattern is formed by printing a conductive paste or the like and firing.

(7) End face processing such as cutting, polishing, and cleavage is performed on the substrate.

By each of the above processes, an optical waveguide can be formed on the LiNbO ₃ substrate by Ti diffusion.

As described above, in each embodiment, an optical switch for switching the optical path of incident light to a plurality of outgoing optical paths is provided, and the optical axis of the outgoing optical path switched by the optical switch is set to 1.
Let it intersect at a point, and provide a lens member at this point,
The point where the optical axes of the outgoing optical paths intersect is made to coincide with the center of the lens member. Therefore, the emitted light is irradiated onto the image surface without loss, and the efficiency can be improved. In particular, when a geodesic lens is used as the lens member, the light amount can be made more uniform and the aberration can be reduced.

Further, as shown in FIGS. 1 and 5, the optical switch and the geodesic lens are integrally configured, so that the optical scanner can be downsized and can be adjusted.

Furthermore, in this embodiment, since there is no possible part such as a rotating mirror and a vibrating mirror for scanning light, the reliability is high and there is no noise. In addition, since the exit end of the waveguide is fixed, it is possible to reduce jitter such as when using a mechanical scanning system.
There is no disturbance in scanning position such as wobble.

Further, a desired light spot can be formed on the image plane by setting the shape, pitch, and position in the optical axis direction of the waveguide emission ends.

In the above-mentioned embodiments, the electro-optical effect is used for switching light, but the invention is not limited to this.
It is also possible to use other types of switches. For example, the acousto-optic effect can be used. Specifically, an optical deflector using surface acoustic waves can be used. In this case, ZnO can be sputtered on the Al ₂ O ₃ substrate to form an optical waveguide.

Further, the optical switch and the optical waveguide are made of, for example, a GaAlAs-based material, and a current is injected from the electrode portion 4 shown in FIG. 2 to cause a change in the refractive index to increase the energy gap of the waveguide. By preventing light absorption, it is possible to configure an optical scanner in which a GaAlAs semiconductor laser is integrally formed in the waveguide entrance end 2a.

Furthermore, for example, on the surface of the substrate where the optical waveguide is formed,
By fixing a prism made of Ti and irradiating the prism with a beam from a semiconductor laser, the beam of the laser can be made incident on the optical waveguide through the prism. Alternatively, an optical fiber may be used to enter the laser beam of the optical waveguide.

〔The invention's effect〕

As described above, in the present invention, the output optical axes of the plurality of selectively switched optical waveguides are concentrated at one point, and the lens member is arranged so that the centers thereof coincide with this point. As a result, the light from each optical waveguide passes through the center of the lens member with the least aberration, regardless of the scanning position, and high resolution can be obtained. In addition, almost all the light emitted from each optical waveguide is captured by the lens member, so that the image surface is irradiated without loss, and the efficiency can be improved. Further, in the present invention, since the optical waveguide and the optical switch are formed on the common substrate and scanning is performed without providing a movable portion, the optical scanner can be downsized and speeded up.

[Brief description of drawings]

FIG. 1 is a plan view of an optical scanner according to an embodiment of the present invention, and FIGS. 2 (a), (b), and (c) are plan views, front views, and side views showing an optical switch used in the optical scanner. 3 is a view showing an optical switch array, FIG. 4 is a perspective view for explaining a geodesic lens, and FIGS. 5 (a) and 5 (b) are a plan view and a side view of an optical scanner using a unidirectional refractive index lens. FIGS. 6 (a) and 6 (b) are graphs showing light intensity distributions in single mode and multimode, FIG. 7 is a plan view of an optical switch in which electrode parts are arranged on a curved line, and FIG. 8 is A plan view of an embodiment using a spherical lens, FIG. 9 (a),
(B) is a plan view and a side view of an embodiment using two cylindrical lenses, and FIG. 10 is a plan view of an embodiment using a gradient index lens. 1: Substrate, 2, 31 to 35: Optical waveguide 2a: Waveguide entrance end, 31a to 35a: Waveguide exit end 4,41 to 44: Electrode part, 4a, 4b: Electrode 5: Reflector, 6: Emitted light Axes 7: Geodesic lens, 8: Emitted light 9: Image plane

Claims (3)

(57) [Claims] 1. An optical switch, wherein a plurality of optical waveguides are formed on a substrate so that the optical axes of respective emitted lights intersect at one point, and the incident light is selectively advanced to any one of the plurality of optical waveguides. An optical scanner characterized in that a lens member provided on a substrate and converging the respective emitted lights on an image plane is arranged at a point where the respective emitted lights intersect. 2. The optical scanner according to claim 1, wherein the lens member is a geodesic lens. 3. The optical scanner according to claim 2, wherein the plurality of optical waveguides and the geodesic lens are formed in common on the substrate.