JPH06289440A - Optical scanner - Google Patents

Abstract

PURPOSE:To provide the optical scanner of an electrooptical deflection type having high efficiency and photoresolving power. CONSTITUTION:The refractive indices of a double refractive optical material 2a and optical material 2b are both equaled and the periodic structure of a diffraction grating 2 is not sensed when the incident light on an optical waveguide 1 is propagated as, for example, a polarization mode (a), This light advances rectilinearly in the optical waveguide 1 without being diffracted. The polarization mode is changed from (a) to (b) by an electrooptical effect when an electric field is generated in the optical waveguide 1 by impressing a prescribed voltage to an electrode group 3. Consequently, the double refractive optical material 2a and the optical material 2b have eventually the refractive indices different with the polarization mode (b) and the light senses the periodic structure of the diffraction grating 2 and is immediately diffracted so as to be bent in the progression direction. Then, the light scanning is executed by changing over the position where the voltage of the electrode group 3 is impressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device for switching a traveling path of a light beam emitted in one direction such as a laser beam into a plurality of directions, for example, an image reading device (scanner), a recording device (laser). Beam printers), surface inspection devices, display devices, and other optical scanning devices.

[0002]

BACKGROUND OF THE INVENTION Conventionally, as the above optical scanning device,
When classified by focusing on the switching means in the scanning direction, they are roughly classified into a mechanical scanning device and a non-mechanical scanning device. As a mechanical scanning device, for example, a scanning device using a polygon mirror, a galvanometer, a hologram scanner, or the like is known. Such a mechanical scanning device literally causes a beam of light to move by a mechanical movement such as rotation or vibration. To scan,
The scanning speed is significantly limited. Further, it is difficult to stop the light beam at an arbitrary position during scanning or perform optical scanning in an arbitrary manner. As such a device, for example, one disclosed in Japanese Patent Laid-Open No. 62-1212937 is known. Therefore, in order to eliminate the disadvantages of these mechanical scanning devices, non-mechanical scanning devices have been proposed. For example,
An acousto-optic deflector, a piezo scanner, a thermo-optic deflector, an electro-optic deflector, etc. FIG. 5A shows an example of an acousto-optic deflector, which is realized on a Ti-diffused LiNbO ₃ waveguide. The ultrasonic wave emitted from the transducer traverses the waveguide and creates periodic density variation of the refractive index. This causes Bragg diffraction, which diffracts or deflects the waveguide. When the frequency of ultrasonic waves is changed, the pitch (wavelength) of density changes, and the deflection direction changes. An optical scanning device using such an acousto-optic deflector has not been put to practical use because of its small deflection angle and insufficient deflection resolution. Moreover, the piezo scanner is not practical because the deflection angle is small. Further, the thermo-optic deflector uses the thermo-optic effect in which the refractive index changes with temperature changes, and has the drawback that the scanning speed is slow because heat is used. The electro-optical deflector is a deflector that utilizes the change in the refractive index (electro-optic effect) of the ferroelectric substance due to the electric field, and FIG. 5B is an improved example thereof. FIG. 5B shows LiNbO.
_{This is} an example realized using a ₃ (LN) waveguide, and uses the principle of the Fresnel zone plate. That is, even-numbered zones are provided with LN crystal waveguides, which are focused at point P when no voltage is applied, but the phase of light passing through the waveguides of each channel is controlled by applying a voltage. Therefore, it can be focused on an arbitrary point Q. Although this element has advantages such as a higher scanning speed and a condensing function than the above-described deflection element, it has a drawback in that efficiency and deflection resolution are low. Therefore, it is an object of the present invention to provide an optical scanning device which improves the efficiency and the deflection resolution in the above-mentioned waveguide type electro-optical deflector.

[0003]

[Means for Solving the Problems] To achieve the above object
In addition, the present invention provides multiple traveling paths of rays emitted in one direction.
In an optical scanning device that switches to several paths, the electro-optical effect
It is composed of a fruit-bearing material and has two different rays.
Depending on the presence or absence of electric field
An optical waveguide member whose polarization mode changes between a and b;
Adjacent to the optical waveguide member, for the above polarization modes a and b
Refractive index n₁, N ₂First having
Optical material and the above refractive index n₁, N₂If different, above bias
The above refractive index n for the optical modes a and b₁, N₂Which of
Is almost equal to ₁, N₂When is almost equal
Different refractive index n for the above polarization modes a and b₃, N
_Four(However, n₃Or n_FourIs n₁, N₂Is approximately equal to)
And the second optical material, which is
The diffraction grating and the electric
A predetermined voltage is applied to the field-generating electrode group and each electrode of the electrode group.
Selectively apply an electric field to change the polarization mode
and a control circuit for switching between a and b.
It is configured as a characteristic optical scanning device.

[0004]

For example, when the light incident on the optical waveguide member is propagated as the polarization mode a, the refractive index n of the first optical material is
_{(1) Since} the refractive indices n ₃ of the second optical materials are both equal or close to each other, the periodic structure of the diffraction grating is not felt, and the light travels straight in the optical waveguide member without being diffracted. When a predetermined voltage is applied to the electrode group to generate an electric field, the polarization mode is switched from a to b. As a result, the polarization mode b
On the other hand, the refractive index n ₂ of the first optical material and the refractive index n ₄ of the second optical material have different values, and light is diffracted immediately by feeling the periodic structure of the diffraction grating, and the traveling direction is bent.
Therefore, optical scanning becomes possible by switching the position to which the voltage of the electrode group is applied by the control circuit. In this case, the first optical material or the second optical material is a so-called birefringent optical material. Both the first and second optical materials are birefringent optical materials, and the degree of change in the refractive index of either the first or second optical material between the polarization modes a and b is the other optical material. The periodic structure of the diffraction grating may be felt depending on the presence or absence of an electric field as a value that is small with respect to the degree of change in the refractive index. Furthermore, contrary to the above case,
The polarization mode may be switched from b to a by applying an electric field.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples of embodying the present invention and are not intended to limit the technical scope of the present invention. 1 is a diagram showing a concept of an optical scanning device according to an embodiment of the present invention, FIG. 2 is a diagram showing an optical scanning operation in the optical scanning device, and FIG. 3 is a diffraction grating of the optical scanning device. FIG. 4 is a diagram showing a shape example, and FIG. 4 is a diagram showing a schematic configuration of an optical scanning device according to another embodiment of the present invention. FIG. 1 shows the structure of a LiNbO ₃ waveguide type optical scanning device according to an embodiment of the present invention, and the manufacturing procedure of the device is shown below in order to further clarify the structure. (1) First, a slab type optical waveguide 1 capable of propagating light rays in two different polarization modes a and b to the substrate 5 is formed on the upper surface of the X plate LiNbO ₃ substrate 5 by the Ti diffusion method. (2) A resist is coated on the optical waveguide 1, and a band-shaped diffraction grating 2 pattern is formed by a photolithography method with a straight line substantially orthogonal to the light propagation direction (Y-axis direction) in one polarization mode. . Using this as a mask, dry etching is performed to form irregularities on the surface layer of the optical waveguide 1 at a pitch Λg. This convex portion is used as the birefringent optical material 2a (first optical material) forming the diffraction grating 2. That is, in this embodiment, the same material is used for the birefringent optical material 2a and the optical waveguide 1. (3) Niobate (Nb _{1 + x} O
_3-X ) is filled by a sputtering method or the like. This corresponds to the optical material 2b (second optical material). In general, Nb _{1 + X} O _3−x deposited by sputtering becomes polycrystalline and its refractive index does not change depending on the polarization mode. However, the stoichiometric ratio x in this case is such that the refractive index _ng is T
_It is set so as to match the ordinary refractive index n _o of the substrate 5 (LiNbO ₃ ) by _i diffusion.

Table 1 below shows the relationship between each polarization mode and the refractive index of each optical material in the diffraction grating 2 formed as described above.

[Table 1] That is, the diffraction grating 2 has a different refractive index (2.29, for the mode a (TM mode) polarized in the X-axis direction and the mode b (TE mode) polarized in the Z-axis direction in the figure).
2.20) having a birefringent optical material 2a and a refractive index of 2.29 of the birefringent optical material 2a in the TM mode.
And the refractive index is equal in each mode (2.
29, 2.29) and the optical material 2b are alternately arranged in the Y-axis direction. (4) Subsequently, the diffraction grating 2 formed as described above
A buffer layer 6 is formed by depositing SiO ₂ on the upper surface of the substrate by sputtering. (5) On the upper surface of the buffer layer 6, band-shaped electrodes 3a substantially orthogonal to the light propagation direction are arranged at a pitch Λm / 2 to form an electrode group 3 for generating an electric field. (6) Of the electrode group 3, for example, each even-numbered electrode 3a
Is grounded, and a predetermined voltage V is applied to each odd-numbered electrode 3a.
Switch 4a capable of selectively switching application of voltage and ground
To form the voltage control circuit 4. In the above configuration, the switch 4a is switched to change the odd-numbered electrodes 3
By applying a predetermined voltage V to a, an electric field is generated in the electrode group 3 and the polarization mode is switched from TM to TE. In this case, the odd-numbered and even-numbered electrodes 3a may be connected in reverse.

Next, the operation of the optical scanning device configured as described above when the light is propagated in the optical waveguide 1 in the TM mode, for example, will be described. (A) When no voltage is applied to the electrode group 3 (see FIG. 2A). The birefringent optical materials 2a and 2b forming the diffraction grating 2 have the same refractive index of 2.29 in the TM mode, and the periodic structure in the diffraction grating 2 is not sensed. Therefore, the light goes straight inside the waveguide 1 without being diffracted. In the optical scanning device, as described above, the optical waveguide 1 and the optical material 2b are the same material, and the light travels straight inside the diffraction grating 2 without being diffracted. (B) When voltage is applied to the electrode group 3 (see FIG. 2B). When the switch 4a is switched to apply a predetermined voltage to the electrode group 3, an electric field shown by an electric force line 7 in the figure is generated. When an electric field is generated, the TM mode is switched to the TE mode due to the electro-optic effect. As a result, the birefringent optical material 2a and the optical material 2b have different refractive indices (2.20, 2.29) for the TE mode, and the light is diffracted by feeling the periodic structure of the diffraction grating 2 and the substrate 5 The light is emitted to the side at an angle θ. At this time, the pitch Λm of the electrode group 3 for switching the polarization mode most efficiently is given by Λm = λ / | N _TE −N _TM | Here, λ is the light wavelength, and N _TE and N _TM are the effective refractive index in the waveguide 1 in the TE mode and the TM mode, respectively. In this embodiment, the optical waveguide 1 is made of the same material as the birefringent optical material 2a, so that the respective values are equal to the birefringent optical material 2a. Furthermore, at this time,
The angle θ is given by the following equation. n _g · sin θ = N _TE + q · λ / Λg Here, n _g is the refractive index of the substrate 5, q is the order of diffraction, and is a negative integer. Therefore, from the above equation, in order to emit the q = −1 next-order diffracted light at θ = 45 °, Λg = 0.37 μm. By arranging a plurality of the voltage control circuits 4 as described above in parallel in the light propagation direction of the optical scanning device and sequentially switching the voltage application to each electrode group 3 at high speed, the light emission position is moved. Thus, optical scanning can be performed at high speed.

Next, it will be shown below that the apparatus of this embodiment can perform optical scanning with a high resolution and a high extinction ratio, that is, in a state in which the reduction of the emission intensity is extremely small. Regarding the resolution The resolution is determined by the pitch Λm of the electrode group 3. In the device of this embodiment, the light wavelength is λ = 0.633 μm, and the waveguide 1
As described above, since the effective refractive index of N is equal to that of the birefringent optical material 2a and N _TE = 2.20 and N _TM = 2.29, the above formula shows that Λm = 7 μm is a high resolution value. can get. In this embodiment, by providing the switch 4a capable of switching between voltage application and grounding for all the electrodes 3a of the electrode group 3, it is possible to perform scanning with a higher resolution of Λm / 2. Extinction ratio In the above diffraction grating 2, when a difference occurs between the refractive index n _g of the optical material 2 b and the refractive index n _o of the birefringent optical material 2 a due to a manufacturing error of the optical material 2 b, etc.
It is considered that the extinction ratio is deteriorated due to the diffraction by
Therefore, the setting accuracy of the refractive index _ng of the optical material 2b will be considered. Generally, the diffraction efficiency is approximately proportional to the square of the refractive index difference Δn between the two types of materials that form the diffraction grating. In the case of the TE mode in this embodiment, Δn = 2.29−
2.20 = 0.09, the general diffraction efficiency in the TM mode Taken together considered smaller than the diffraction efficiency of the TE mode and the refractive index n _O of the refractive index n _g 0.01 accuracy
It becomes clear that a high extinction ratio can be obtained relatively easily by making the difference of 100: 1 or more possible.

Other examples will be described below. (1) Regarding the shape of the diffraction grating In the above-mentioned embodiment, the birefringent optical material 2a and the optical material 2 are used.
The diffraction grating 2 is configured by alternately arranging b and b in the shape of a straight line substantially orthogonal to the light propagation direction. The diffraction grating 2 is formed in a curved band shape in plan view to collect the emitted light. Good. Further, in order to emit the light from the side surface of the waveguide, the diffraction grating 2 '(see FIG. 3) may be formed in the shape of a straight line inclined with respect to the light propagation direction. (2) Material of Diffraction Grating As the material of the optical material 2b in the above embodiment, Nb is used.
LiNbO ₃ may be used instead of _{1 + X} O _3-X . Table 2 shows the relationship of the refractive index of the diffraction grating in this case.

[Table 2] Further, in the diffraction grating 2 in the above-described embodiment, light propagates inside itself. For example, as shown in Table 3 below, as the birefringent optical material 2a ′, TiO ₂ and optical material 2b ′ are used.
As ₂ Se which is a kind of chalcogenide type glass
_In a diffraction grating 2 ″ (see FIG. 4) constructed using ₃ ,
No light propagates inside it. In the above structure, the optical waveguide 1 and the birefringent optical material 2a ′ are different in material, and the light propagating inside the optical waveguide 1 and leaking to the surface side thereof is operated by the diffraction grating 2 ″. Be diffracted.

[Table 3]

Further, in the diffraction grating according to the present invention, an optical material having no birefringence is used as the first optical material, and an optical material having birefringence is used as the second optical material. It may be configured with. Furthermore, it may be made of an optical material having birefringence together with the first and second optical materials. In this case, it is necessary to set the refractive index of one of the optical materials for different polarization modes so that the degree of change is smaller than that of the other optical material. (3) Shape of Optical Waveguide Although the optical waveguide 1 is a slab type in the above-mentioned embodiment, a channel type optical waveguide (three-dimensional optical waveguide) may be used. (4) Regarding Material of Optical Waveguide In the above-mentioned embodiment, the Ti diffusion type waveguide formed on the substrate 5 of the X plate LiNbO ₃ was used, but the Ti diffusion type waveguide formed on the Z plate LiNbO ₃ substrate is used. It is also possible to use. Further, other electro-optic crystal such as lithium tantalate (LiTaO ₃ ) may be used.

[0011]

As described above, the present invention is an optical scanning device that switches the traveling path of a light beam emitted in one direction into a plurality of paths. An optical waveguide member that is capable of propagating in two polarization modes a and b and whose polarization mode changes between a and b depending on the presence or absence of an electric field;
The first optical material having different or substantially equal refractive indexes n ₁ and n ₂ with respect to the polarization modes a and b, and the refractive index n
_{When 1} and n ₂ are different from each other, the polarization modes a and b are substantially equal to _{one of} the refractive indices n ₁ and n ₂ , and when the bending indices n ₁ and n ₂ are substantially equal, the polarization modes a and b are selected. On the other hand, different refractive indices n ₃ and n ₄ (where n ₃ or n ₄ is n
_And a second optical material having substantially the same number ₁ and n ₂ ) are alternately arranged in the propagation direction of the light beam, and an electric field generating electrode group provided opposite to the diffraction grating. An optical scanning device comprising: a control circuit for selectively applying a predetermined voltage to each electrode of the electrode group to generate an electric field and switching the polarization mode between a and b. , It has the following excellent effects. 1) High-speed scanning: In the present invention, since the electro-optical effect capable of high-speed response is utilized, high-speed optical scanning is possible by high-speed switching of electrodes to which a voltage is applied. Random scanning can also be performed by selecting the electrode application position. 2) High resolution: Scanning with high resolution is possible by finely dividing the electrode group. 3) High efficiency: Since the diffraction grating having the periodic structure in the light propagation direction is formed by the first and second optical materials, the interaction length can be long and the light utilization efficiency is high. 4) High extinction ratio: A high extinction ratio can be easily obtained because the difference in diffraction efficiency due to so-called birefringence is utilized.

[Brief description of drawings]

FIG. 1 is a diagram showing a concept of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of the optical scanning.

FIG. 3 is a diagram showing a shape example of a diffraction grating of the optical scanning device.

FIG. 4 is a diagram showing a schematic configuration of an optical scanning device according to another embodiment of the present invention.

FIG. 5 is a conceptual diagram of a conventional optical scanning device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical waveguide 2, 2 ', 2 "... Diffraction grating 2a, 2a' ... Birefringent optical material 2b, 2b '... Optical material 3 ... Electrode group 3a ... Electrode 4 ... Voltage control circuit 4a ... Switch 5 ... Substrate 6 … Buffer layer

Claims (1)

[Claims] 1. An optical scanning device for switching a traveling path of a light beam emitted in one direction into a plurality of paths, which is made of a material having an electro-optical effect and can propagate the light beam in two different polarization modes a and b. And an optical waveguide member whose polarization mode changes between a and b depending on the presence or absence of an electric field, and a refractive index n ₁ or n that is provided adjacent to the optical waveguide member and is different or substantially equal to the polarization modes a and b. If the first optical material having a ₂ and the refractive indexes n _1, n ₂ are different the polarization mode a, substantially equal to the one of the refractive indexes n _1, n ₂ with respect to b, and the bending modulus n _1, When n ₂ is substantially equal, different refractive indexes n ₃ for the polarization modes a and b,
and a second diffraction grating having n ₄ (where n ₃ or n ₄ is substantially equal to n ₁ and n ₂ ) alternately arranged in the propagation direction of the light beam, and facing the diffraction grating. It is provided with an electric field generating electrode group provided and a control circuit for selectively applying a predetermined voltage to each electrode of the electrode group to generate an electric field and switching the polarization mode between a and b. An optical scanning device characterized by the above.