JPH04237030A - Optical scanning device - Google Patents

Abstract

PURPOSE:To provide the small-sized optical scanning element which does not require movable parts, such as rotating mechanisms, is simple in constitution and is high in productivity. CONSTITUTION:The optical scanning element 10 is constituted of a Ti diffused waveguide 14 which is produced by dispersing Ti, etc., into a substrate 12 consisting of LiNbO3, etc., having an electrooptical effect and plural electrodes 16, which consist of Al, etc., and are formed on both sides thereof. A bent waveguide 20 is so produced that the refractive index decreases gradually in the propagation direction of light. The light 42 is no longer confined in the waveguide and is radiated to the outside of the bent waveguide 20 simply by impressing a low voltage to the electrodes 16 to slightly decrease the refractive index of the bent waveguide 20 in the part 40 where the refractive index is small. Then, the radiation direction of the light in the bent waveguide 20 is controlled by the magnitude of the voltage to be impressed to the electrodes 16.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical scanning element that irradiates light onto a photoreceptor drum in an optical printer and performs scanning exposure, or performs optical scanning in a barcode reader, etc., and more specifically, an optical waveguide. The present invention relates to an optical scanning element that performs optical scanning.

0002

2. Description of the Related Art Conventionally, an exposure device for exposing a photoreceptor drum such as a laser printer has, for example, a structure shown in FIG.
Semiconductor laser 101, collimator lens 102, polygon mirror 104, fθ lens 106, reflection mirror 108
It is composed of. Laser light emitted from the semiconductor laser 101 is turned into parallel light by the collimator lens 102, and is irradiated onto the rotating polygon mirror 104. Since the laser beam reflected by the polygon mirror 104 is deflected at a constant angular velocity, the laser beam is converted to move at a constant velocity by the fθ lens 106, and after being reflected by the total reflection mirror 108, it passes through the pre-charged photoreceptor. drum 110
Scan and expose the top. Since the exposed portion of the photoreceptor drum 110 loses charge due to photoconductivity, toner charged to the same polarity as the photoreceptor drum 110 is not repelled but adheres thereto. After transferring this toner to paper, printing is completed by fixing it by heating or the like.

0003

[Problems to be Solved by the Invention] However, in laser printers, the scanning optical system using polygon mirrors and lenses is complicated, making it difficult to adjust the optical axis, and requiring high processing precision, resulting in low productivity. There is a problem in that miniaturization is difficult because a mirror rotation mechanism is required.

The present invention has been made to solve the above-mentioned problems, and uses a curved waveguide which has an electro-optic effect and whose equivalent refractive index gradually decreases or changes with respect to the propagation direction of light. By using the present invention, it is an object to provide a compact optical scanning element that does not require a movable part such as a rotation mechanism, has a simple structure, and has high productivity.

[0005]

[Means for Solving the Problems] In order to achieve this object, the optical scanning element of the present invention includes a substrate, and is formed on the substrate or on the surface of the substrate, has an electro-optic effect, and has an electro-optic effect in the direction of propagation of light. It consists of a curved waveguide whose equivalent refractive index gradually decreases or changes, and an electrode that applies an electric field to the curved waveguide. In order to gradually decrease the equivalent refractive index in the light propagation direction, the waveguide width of the curved waveguide may be gradually decreased. Further, it may include an electrode that applies an electric field around the curved waveguide. Furthermore, the portion of the end surface of the substrate from which light is emitted to the outside may be made convex or other non-planar.

[0006]

[Operation] In the optical scanning element of the present invention having the above configuration, light emitted from a light source such as a semiconductor laser and guided into the curved waveguide propagates in the curved waveguide, but an electric field is applied to the curved waveguide by the electrode. By applying this voltage, the refractive index of the curved waveguide is reduced due to the electro-optic effect, so that the light is no longer confined within the waveguide and is radiated out of the waveguide. The equivalent refractive index of a curved waveguide gradually decreases in the direction of light propagation, and in parts where the equivalent refractive index is small, applying a small electric field can confine light with a slight decrease in the refractive index of the waveguide. light is emitted. on the other hand,
Light will not be emitted unless a large electric field is applied to a portion with a large equivalent refractive index and the refractive index of the waveguide is greatly reduced. Therefore, the position from which light is emitted can be controlled by the magnitude of the applied electric field. Furthermore, in a curved waveguide, if the light is emitted at a different position, the emitted direction is also different, so the emitted direction of the light can be controlled by an applied electric field, and optical scanning can be performed. Note that instead of changing the refractive index of the curved waveguide using an electric field, optical scanning can be similarly performed by changing the refractive index around the curved waveguide. Further, by processing the end face of the substrate from which light is emitted to the outside into a non-planar shape such as a convex shape, a function such as focusing the emitted light can be added.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings. An optical scanning element 10 to which the present invention is suitably applied includes, for example, as shown in FIG. Al formed
It is composed of a plurality of electrodes 16 consisting of, etc. Ti
The diffusion waveguide 14 includes a straight optical waveguide 18 and a curved waveguide 20.
It consists of The curved waveguide 20 is fabricated so that its refractive index gradually decreases in the light propagation direction. Further, a semiconductor laser 22 serving as a light source is attached to one end of the straight optical waveguide 18. Furthermore, the curved waveguide 20
A light absorbing material 23 is provided at the end.

A method of manufacturing such an optical scanning element 10 is shown in FIG.
Explain using. That is, as shown in FIG. 2(a), L
A photoresist 24 is applied onto a substrate 12 made of iNbO3 or the like by a spin coating method or the like. A mask 26 having a pattern of a predetermined waveguide shape is tightly attached thereon, and ultraviolet rays are irradiated for exposure. After exposure, when the photoresist 24 is developed, a portion irradiated with ultraviolet rays remains as shown in FIG. 2(b). A Ti thin film 28 is formed thereon by well-known thin film forming means such as sputtering and vacuum evaporation. At this time, T
The i-thin film 28 is manufactured so that its thickness gradually decreases in the direction of propagation of light. Such a film thickness distribution is, for example,
It can be manufactured by placing a mask at a position where the entire portion that will become the waveguide is shielded, and gradually removing this mask while depositing Ti on the portion that will become the waveguide. In other words, Ti is thick in the portion where the mask is removed early, and Ti is thin in the portion where the mask is removed late, so that a predetermined film thickness distribution is obtained. Thereafter, by removing the photoresist 24 with a solvent, the Ti thin film 28 can be processed into a predetermined waveguide shape as shown in FIG. 3(c). This board 12 is 10
When heated to about 00°C and thermally diffused for several hours, the Ti thin film 28 is diffused into LiNbO3, and the Ti thin film 28 is diffused into LiNbO3 as shown in FIG.
An i-diffusion waveguide 14 is formed. At this time, a portion where the Ti film is thick has a high refractive index, and a portion where the Ti film is thin has a low refractive index. Furthermore, as shown in FIG. 3(e), an Al thin film 30 that will become the electrode 16 is formed by a well-known thin film forming method such as sputtering or vacuum evaporation, and a photoresist 24 is applied thereon by a spin coating method or the like. Apply. A mask 32 having a pattern of a predetermined electrode shape is tightly attached thereon, and ultraviolet rays are irradiated for exposure. After exposure and development, only the portions of the photoresist 24 irradiated with ultraviolet rays remain as shown in FIG. 2(f). Here, after etching the portions of the Al thin film 30 to which the photoresist 24 is not attached using an etching solution such as acid or alkali or plasma etching, the remaining photoresist 24 is removed using a solvent or the like. The electrode 16 can be formed as shown in Figure (g).

The operation of the optical scanning element 10 of the present invention will be explained using FIGS. 3 and 4.

The LiNbO3 used for the substrate 12 is a Y-cut plate whose optical axis is parallel to the substrate surface, and when a voltage is applied to the electrode 16 as shown in FIG. 3, an electric field 36 approximately parallel to the substrate surface is applied to the waveguide 14. be done. Here, the applied voltage is E, Li
Assuming that the refractive indexes of NbO3 for ordinary light and extraordinary light are no and ne, and the electro-optic constant is γ33, the refractive index ng of the waveguide 14 for the TE mode, which is a waveguide mode in which the vibration direction of the electric field is parallel to the substrate surface, is LiNbO3. optical axis (
C axis) is perpendicular to the propagation direction of light, then ng=ne-(ne3γ33/2)E
(1), and the refractive index ng of the waveguide 14, that is, the curved waveguide 20, decreases in proportion to the electric field E. However, due to the bending of the waveguide, the optical axis (C
If the axis) deviates from the direction perpendicular to the light propagation direction, the change in ng becomes smaller, but this can be compensated for by increasing the electric field E.

In FIG. 4A, laser light emitted from a semiconductor laser 22 serving as a light source is guided to a straight waveguide 18 and further propagates through a curved waveguide 20. In FIG. here,
When a voltage is applied to electrode 16 to decrease the refractive index of curved waveguide 20 , light 38 is no longer confined within curved waveguide 20 and is emitted out of curved waveguide 20 . At this time, the curved waveguide 20 is formed so that its refractive index gradually decreases in the light propagation direction, and the smaller the refractive index, the weaker the confinement of light within the waveguide. Therefore, if a low voltage is applied to the electrode 16 in the portion 40 where the refractive index is small and the refractive index of the curved waveguide 20 is slightly decreased, the light 42 will no longer be confined within the waveguide and will be emitted outside the curved waveguide 20. be done. On the other hand, curved waveguide 2
Since light confinement is relatively strong in the portion 44 with a large refractive index of 0, a high voltage is applied to the electrode 16 in order to radiate the light 46 out of the curved waveguide 20.
It is necessary to increase the decrease in the refractive index. in this way,
Since the curved waveguide 20 is formed to have a small refractive index with respect to the light propagation direction, the light emission position in the curved waveguide 20 can be controlled by the magnitude of the voltage applied to the electrode 16. can. As shown in FIG. 4, since the direction of light emission differs depending on the position where the light is emitted, the light can be scanned by changing the voltage applied to the electrode 16 and changing the light emission position. The emitted lights 38, 42, 46 are transmitted to the photosensitive drum 5 by a lens 48.
The light is focused on 0 and exposed. For example, by applying a voltage having a waveform that changes as shown in FIG. 4(b) to the electrode 16, it is possible to scan from the bottom to the top in FIG. 4(a). Note that the light that is not emitted to the outside of the curved waveguide 20 is attenuated by a light absorbing material 23 that is provided at one end of the curved waveguide 20 and is made of a metal cladding such as Al.

Although one embodiment of the present invention has been described above in detail with reference to FIGS. 1 to 4, various other modifications can be made without departing from the spirit of the present invention. That is, the materials and shapes of the substrate, curved waveguide, and electrodes are not particularly limited. For example, there are no particular limitations on the magnitude of the refractive index of the curved waveguide 20 or the rate at which the refractive index changes. Further, the curvature of the curved waveguide 20 is not particularly limited, and furthermore, the curvature does not need to be constant. Further, a buffer layer made of SiO2 or the like may be provided between the substrate 12 and the electrode 16. As a result, the emitted light is transmitted to the electrode 16.
This can prevent attenuation. In addition, the electrode 16
The intervals between the two do not need to be constant. Further, the waveform of the voltage applied to the electrode 16 is not particularly limited.

Further, it is not necessary to change the refractive index itself of the curved waveguide, but it is sufficient that the equivalent refractive index that the light perceives as the refractive index of the entire waveguide changes with respect to the propagation direction of the light. For example, as shown in FIG. 5, the refractive index of the curved waveguide 52 may be constant, and the width of the waveguide may be gradually narrowed in the light propagation direction. The narrower the width of the waveguide, the smaller the equivalent refractive index of the waveguide, and the weaker the light confinement. Therefore, optical scanning can be performed in exactly the same manner as the optical scanning element shown in FIG. Note that the curved waveguide 52 does not need to be manufactured by Ti diffusion. That is, it is only necessary that one or both of the substrate and the curved waveguide be made of a material having an electro-optic effect, and LiTaO3 may be used for the substrate and LiNbO3 may be used for the curved waveguide. Furthermore, the substrate is made of glass, sapphire, etc., and the curved waveguide is made of PLZT,
A thin film such as ZnO may also be used. The waveguide shape at this time is a ridge-type waveguide in which a ridge 64 is formed by cutting a part of the thin film 62 formed on the substrate 60, as shown in FIG. A ridge-type waveguide with an asymmetrical ridge shape may also be used. That is, by making the ridge shape asymmetric and making the outer side 66 thicker than the inner side 68, the radiation efficiency to the outside of the waveguide is improved. Moreover, as shown in FIG. 6(c), a three-dimensional waveguide 6 is provided on the substrate 60
2 may be provided. In either case, the width of the ridge 64 or the waveguide 62 may be formed so as to gradually become narrower in the light propagation direction.

Furthermore, instead of applying an electric field to the curved waveguide 20 as shown in FIG.
A buffer layer 70 such as No. 2 may be provided, an electrode 72 may be formed thereon, and an electric field 76 may be applied to the outside 74 of the curved waveguide 20. At this time, the direction of the electric field is opposite to the direction shown in FIG. 3, and according to equation (1), the refractive index on the outside 74 of the curved waveguide 20 increases. Therefore, the light confinement in the curved waveguide 20 is weakened, and the light is radiated out of the waveguide.

Furthermore, the direction of the crystal axis of the crystal used for the substrate or waveguide is not limited, and for example, Y-cut LiNb
Z-cut LiNbO3 may be used instead of O3. In this case, as shown in FIG.
A buffer layer 70 such as O2 is provided, and electrodes 74 are formed on the top of the Ti diffusion waveguide 14 and on both sides thereof. The electric field 76 at this time is generated in a direction perpendicular to the substrate surface. Due to this electric field, the refractive index ng of the waveguide for the TM mode in which the vibration direction of the magnetic field is parallel to the substrate surface is also expressed by equation (1). Scanning can be performed. Here, since the change in the refractive index ng of the waveguide does not depend on the change in the propagation direction of light due to the bending of the waveguide, the voltage applied to the electrode 74 can be easily controlled.

[0016] Furthermore, in order to fabricate a curved waveguide, Li
The material that diffuses into NbO3 is also not limited. Also,
There are no particular limitations on the refractive index distribution of the diffusion waveguide either. For example, as shown in FIG. 9(a), the refractive index distribution of the diffusion waveguide 80 may be formed such that the region with a high refractive index spreads outward. In this case, light confinement to the outside of the waveguide becomes weaker, making it easier to control radiation. Furthermore, the buffer layer 70
may be provided, and an electric field having opposite directions may be applied between the inside and outside of the diffusion waveguide 80 using the electrode 82. As a result, the refractive index on the inside of the diffusion waveguide 80 decreases, and the refractive index on the outside increases, making it easier to emit light by applying an electric field. Further, as shown in FIG. 2B, a region 86 having a lower concentration of diffused substances than the region 84 may be provided around, particularly outside, a region 84 which has a high concentration of diffused substances such as Ti and serves as a waveguide. Furthermore, as shown in FIG. 2(c), a material such as MgO which lowers the refractive index of the substrate 12 may be diffused into the inner side 87 and outer side 88 of the region 84 which is a waveguide and has a high concentration of diffused substances such as Ti. . This strengthens the confinement of light within the waveguide and prevents the light from being emitted to the outside when a weak electric field is applied, making it effective for parts of the curved waveguide 20 with a large refractive index. be. That is, the shape of the curved waveguide 20 shown in FIG. 1 does not need to be constant, and the waveguides shown in FIGS. 9(a), (b), and (c) may be combined depending on the change in refractive index. good.

Furthermore, the curved waveguide 20 may be fabricated using well-known proton exchange instead of Ti diffusion. Since a large change in the surface refractive index can be realized by proton exchange, the radius of curvature of the curved waveguide 20 can be reduced overall, and the entire optical scanning element can be further miniaturized.

Furthermore, in the embodiment shown in FIG. 1, an electric field was applied to reduce the refractive index of the curved waveguide, but the direction in which the electric field is applied is not particularly limited. An electric field may be applied such that the rate increases. That is, the refractive index of the curved waveguide may be made small so that light is emitted when no electric field is applied, and when an electric field is applied, the refractive index increases and the light is confined. At this time, if a small electric field is applied to the portion of the curved waveguide where the refractive index is large, light can be confined. On the other hand, since light cannot be confined in a portion with a small refractive index unless a large electric field is applied, the light emission position can be controlled by the magnitude of the applied electric field.

Furthermore, the length, shape, etc. of the linear waveguide 18 in FIG. 1 are not limited. Further, the straight waveguide 18 is not necessarily required and may not be provided. At this time, the laser light may be made to directly enter the curved waveguide 20. Furthermore, the semiconductor laser 22, which is a light source, does not need to be directly coupled to the end face of the waveguide, but the laser light emitted from the semiconductor laser may be coupled to the straight waveguide 18 using an optical fiber as shown in FIG. 10(a). Good too. Alternatively, the laser beam emitted from the semiconductor laser 22 may be coupled to the linear waveguide 18 using an objective lens 92 as shown in FIG. 2(b).

Furthermore, the shape of the substrate 12 on which the curved waveguide 20 is formed is not particularly limited. For example, as shown in FIG. 11(a), the end surface 95 of the substrate 12 from which the radiation light is emitted may be processed into a convex shape. Thereby, light can be focused within a plane parallel to the substrate surface. The direction perpendicular to the substrate surface is focused using a cylindrical lens. Further, if the end surface 95 of the substrate 12 from which the radiation light is emitted is processed to have a convex shape also in the direction perpendicular to the substrate surface, the cylindrical lens becomes unnecessary. Alternatively, the end surface 95 of the substrate 12 from which the radiation light 94 is emitted may be processed into a concave shape, as shown in FIG. 2B. By combining with the convex lens 97, the scanning range can be enlarged.

Furthermore, as shown in FIG. 12(a), a slab waveguide 98 may be formed in a region around the curved waveguide 20 through which the emitted light propagates. As a result, since the emitted light also propagates through the slab waveguide 98, it propagates without spreading in the direction perpendicular to the substrate surface. In addition, as shown in FIG. 6(b), the substrate 60
A slab waveguide 62 is formed on the top, and a SiO2
A similar effect can be obtained even if a dielectric material 99 such as the like is loaded. At this time, the dielectric 99 may be manufactured in the shape of a curved waveguide.

[0022]

[Effect of the invention] As is clear from the detailed description above,
According to the present invention, an optical scanning element is constructed using a curved waveguide that has an electro-optic effect and the equivalent refractive index of the waveguide gradually changes with respect to the propagation direction of light. The structure is simple, productivity is high, and the size can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a top view showing the configuration of an optical scanning element according to the present invention.

FIGS. 2(a) to 2(g) are explanatory diagrams showing a method for manufacturing an optical scanning element.

FIG. 3 is a cross-sectional view showing a method of applying an electric field.

FIG. 4(a) is a top view illustrating the operation of the optical scanning element;
(b) is an explanatory diagram showing the waveform of an applied electric field.

FIG. 5 is a top view showing the configuration of an optical scanning element.

FIGS. 6(a) to 6(c) are explanatory diagrams showing the shape of a waveguide.

FIG. 7 is a cross-sectional view showing a method of applying an electric field.

FIG. 8 is a cross-sectional view showing a method of applying an electric field.

FIGS. 9(a) to 9(c) are cross-sectional views showing the shape of a diffusion waveguide.

FIGS. 10(a) and 10(b) are explanatory diagrams showing a method of light incidence.

FIGS. 11(a) and 11(b) are explanatory diagrams showing the shape of a substrate of an optical scanning element.

FIGS. 12(a) and 12(b) are cross-sectional views illustrating the shape of a waveguide.

FIG. 13 is an explanatory diagram showing a conventional scanning device.

[Explanation of symbols]

12 Board 14 Diffusion waveguide 16 Electrode 20, 52 Curved waveguide 72 Electrode 95　Board end surface

Claims (4)

[Claims] 1. A substrate, a curved waveguide formed on the substrate or on the surface of the substrate, which has an electro-optical effect and whose equivalent refractive index gradually decreases or changes with respect to the propagation direction of light, and the curved waveguide. An optical scanning element characterized by comprising an electrode that applies an electric field to a wave path. 2. The optical scanning element according to claim 1, wherein the waveguide width of the curved waveguide gradually decreases or changes in the light propagation direction. 3. The optical scanning element according to claim 1, further comprising an electrode for applying an electric field around the curved waveguide. 4. The optical scanning element according to claim 1, wherein a portion of the end face of the substrate from which light is emitted to the outside is non-planar.