JPH01252941A - Optical scanner - Google Patents

Abstract

PURPOSE:To form a lens optical system at a low cost and to reduce the cost thereof by separating the plural light beams which are emitted from an optical waveguide and is different in wavelengths to separate optical paths by utilizing the wavelength dispersibility of a diffraction grating for light emission. CONSTITUTION:The respective color light beams guided collectively as one beam within one light guide are emitted at the different emission angles to the outside of the optical waveguide by utilizing the wavelength dispersibility of the diffraction grating and the light beams separated from each other in the space on the outside of the optical waveguide are subjected to aberration correction by the simple correction lens optical system for monochromatic light. Namely, scanning imaging lenses 22R, 22G, 22B are disposed in the optical paths of the respective light beams 13R'', 13G'', 13B''. The lenses 22R, 22G, 22B are ftheta lenses combined with slender lenses constituting a part of spherical lenses and are so constituted that the chromatic aberration correction and the curvature of field correction of the light beam on a photosensitive material 23 can be executed according to the wavelengths of the respective beams 13R'', 13G'', 13B''. The entire part of the lens optical system is thereby inexpensively formed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical scanning device, and more particularly, to an optical scanning device, which uses a surface acoustic wave to diffract and deflect light beams of different wavelengths guided in an optical waveguide. The present invention relates to an optical scanning device that emits a light beam out of an optical waveguide to scan a photosensitive material or the like.

(Prior Art) For example, mechanical optical deflectors such as galvanometer mirrors and polygon mirrors and EOD (electro-optic optical deflectors) have been used as optical deflection devices for deflecting light beams in optical scanning recording devices, optical scanning reading devices, etc. AOD (acousto-optic optical deflector) is widely used. However, mechanical optical deflectors have problems such as poor durability and tend to be bulky.On the other hand, EOD and AOD do not have a large optical deflection angle, so the beam optical path becomes long, and optical scanning recording devices etc. There is a problem in that it leads to an increase in size.

Recently, as a light deflection device that solves the above-mentioned problems,
Optical deflection devices using optical waveguides are attracting attention. This optical deflection device uses an optical waveguide formed from a material that allows surface acoustic waves to propagate, and a surface acoustic wave whose frequency changes continuously as it travels in the direction intersecting the optical beam guided within this optical waveguide. A means for generating a surface acoustic wave in the optical waveguide (for example, composed of a pair of crossed comb-shaped electrodes), and a drive circuit that drives the surface acoustic wave generating means to generate a surface acoustic wave whose frequency continuously changes. It is something that you have. In this optical deflection device, the light beam guided in the optical waveguide undergoes Bragg diffraction due to acousto-optic interaction with the surface acoustic wave, and this diffraction angle changes depending on the surface acoustic wave frequency, so the surface acoustic wave By varying the frequency as described above, the light beam can be continuously deflected within the optical waveguide.

This optical deflection device has excellent durability and vibration resistance, is easy to adjust, has high light utilization efficiency, is capable of precision scanning, and is formed to be compact to a certain extent. Further, such a light deflecting device is described in detail in, for example, Japanese Patent Laid-Open No. 62-77761.

(Problems to be Solved by the Invention) By the way, in order to configure an optical scanning recording device that can record color images using the optical deflection device made of the above optical waveguide, it is necessary to use a plurality of colors (generally R, G, 83 colors). ) may be used, but if this is done, the recording apparatus will become larger. Therefore, in order to miniaturize the recording device, it is preferable to make light beams of a plurality of colors enter one optical waveguide and to deflect these light beams together within the optical waveguide.

However, in order to take the light beams deflected in this way out of the optical waveguide and scan them onto a photosensitive material, it is necessary to correct chromatic aberrations, etc. of each light beam for practical purposes.
As mentioned above, when each color light beam is deflected together and emitted out of the optical waveguide, the optimum aberration correction (chromatic aberration correction or field curvature correction A complicated and expensive correcting lens optical system is required to perform the following steps (e.g.), and the recording apparatus becomes expensive.

Therefore, the present invention deflects each color light beam using an optical deflection device consisting of an optical waveguide as described above, easily and effectively corrects the aberrations of the deflected light beam, and then scans the light beam onto a photosensitive material, etc. The object of the present invention is to provide an optical scanning device that can perform the following steps.

(Means and Effects for Solving the Problems) The optical scanning device of the present invention uses wavelength dispersion of a diffraction grating (grating coupler) to guide each color light beam in one optical waveguide. The light beams are emitted from the optical waveguide at different exit angles using the optical waveguide, and the aberrations of each of the separated light beams in the space outside the optical waveguide are corrected using a simple correction lens optical system for monochromatic light. This is a characteristic feature.

That is, more specifically, the optical scanning device of the present invention includes an optical waveguide formed of a material capable of propagating surface acoustic waves as described above, and n light beams having different wavelengths entering the optical waveguide. (2≦n) light sources, and a plurality of surface acoustic wave generation means for generating surface acoustic waves that cause Bragg diffraction of the guided light, and a drive circuit for driving the surface acoustic wave generation means. , The surface of the optical waveguide is equipped with one diffraction grating that outputs the guided lights of n different wavelengths out of the optical waveguide at mutually different emission angles, and the n lights of different wavelengths emitted from the optical waveguide. The optical system is characterized in that a monochromatic light correcting lens optical system for correcting aberrations according to the wavelength of each light beam is disposed in each of the optical paths of the beams.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

1 and 2 show an optical scanning device 0 according to an embodiment of the present invention. This optical scanning device 10, together with the photosensitive material transport means 30 and the modulation circuit 40, constitutes a color image recording device. The optical scanning device 10 includes a slab-shaped optical waveguide 11 formed on a transparent substrate 16 and three pairs of interdigitated electrodes provided at the side ends of the optical waveguide 11.
(hereinafter referred to as IDT) 15R, 15G
, 15B, and a linear diffraction grating (Llnear) for light incidence provided spaced apart from each other on the surface of this optical waveguide 11
crattng coupler (hereinafter referred to as LGC) 20, light emitting LGC 21, and the above IDT 15
R.

IDT that applies alternating voltage to 15G and 15B respectively
It has drive circuits 17R, 17G, and 17B. Each of these drive circuits 17R, 17G, and 17B is
It consists of a high frequency amplifier and a sweeper that continuously changes the frequency of the alternating voltage. Further, one end surface 16a (the end surface on the opposite side to the photosensitive material transfer means 30) and the end surface 18b on the opposite side of the substrate 16 are cut obliquely with respect to the optical waveguide 11, and serve as a light input end surface and a light output end surface, respectively. has been done.

In this embodiment, as an example, the substrate 16 is made of LiNbO.
The optical waveguide 11 is formed by using three wafers and providing a Ti diffusion film on the surface of the wafer. Note that substrate 1
As the material 6, a crystalline substrate made of sapphire, Si, etc. may also be used. Furthermore, the optical waveguide 11 is not limited to the above-mentioned Ti diffusion, but can also be formed by sputtering, vapor depositing, or the like other materials on the substrate 16. Regarding optical waveguides, for example, Tamil (T, Ta51r)
“Integrated Obtics” (ed.)
rated 0pt1cs)” (Topics in Applied Physics (Topics 1n Ap
plied Physlcs) Volume 7) Sprlnger-Verlag
Published (1975), affiliation: Haruna, Suhara co-authors “Optical Integrated Circuits J
There are detailed descriptions in published works such as Ohmsha (1985).
In the present invention, any of these known optical waveguides can be used as the optical waveguide 11. However, this optical waveguide 11 is formed from a material such as the above-mentioned Ti diffusion film that allows surface acoustic waves to be propagated, which will be described later. Further, the optical waveguide may have a laminated structure of two or more layers.

Three light sources 18R are located at positions facing the substrate end surface lea.
, 18G, and 18B are provided. These light sources L8
R, LAG, 18B are, for example, semiconductor lasers, LEDs
red (R) and green (
G), a light beam 13R with a wavelength in the blue (B) region.

It is arranged to emit 13G and 13B. These light beams 13R, 13G, and 13B are made into parallel beams by collimator lenses 25R, 25G, and 25B, respectively, and then irradiated onto the LGC 20, diffracted by the LGC 20, and incident on the optical waveguide II. propagates in the direction of arrow A in waveguide mode.

When recording an image, the photosensitive material 23 is set on a transport means 30 such as an endless belt. And light? R18R, 18G, 18B are light source drive circuits 19R,
19G and 19B produce light beams 13R and 13G, respectively.
Driven to inject 13B, along with ID
T15R, 15G, and 15B have an IDT drive circuit 17R.
, 17G, and 17B, an alternating voltage whose frequency changes continuously is applied. Note that the light source drive circuit 19R.

19G and 19B are modulation circuits 4 that receive image signals Sr, Sg, and Sb carrying red, green, and blue image information, respectively;
0, and the image signals Sr, Sg.

Each light source 18R, 18G, so as to change the light output according to sb (that is, change the intensity of the light beam, or the number of pulses and pulse width when emitting the light beam in a pulsed manner).
18B.

By applying the voltage as described above to the IDTs 15R, 15G, and 15B, surface acoustic waves 12R, 12G, and 12B propagate on the surface of the optical waveguide it. IDT15
R, 15G, 15B are each surface acoustic wave +2R, 12G
, 12B is guided light (parallel beam) 13R' , 1
3G' and 13B' are arranged so as to travel in a direction intersecting with the optical paths of 13B'. Therefore, the guided light 13R',
13G', 13B' are surface acoustic waves 12R, 12G
, 1.2B, and at this time, the guided lights 13R', 13G', 13B' undergo Bragg diffraction due to acousto-optic interaction with the surface acoustic waves 12R, 12G, 12B, respectively.

Bragg diffraction of guided light by surface acoustic waves has been known for some time, but will be briefly explained here. The traveling direction of the surface acoustic wave 12 propagating through the optical waveguide 11 and the guided light 1
If the angle (Bragg angle) formed by the 3° traveling direction is θ, then the deflection angle (diffraction angle) δ of the guided light 13′ due to acousto-optic interaction with the surface acoustic wave 12 is δ−2θ. The wavelength and effective refractive index of the guided light 13' are λ and Ne,
The wavelength, frequency, and speed of the surface acoustic wave 12 are A and f, respectively.
Sv, 2θ-25in-1(λ/(2Ne・Δ
)) λ/(Nc-A) part·f/(Ne-v), and 2θ, that is, δ is approximately proportional to the frequency f of the surface acoustic wave 12. As described above, the drive circuits 17R and 17G.

17B applies an alternating voltage whose frequency changes continuously to IDTs 15R, 15G, and 15B, respectively.
The frequencies of the surface acoustic waves 12R, 12G, and 12B change continuously, and the deflection angle δ changes continuously. Therefore, these guided lights HR', 13G'.

As shown by arrow C, 13B' is diffracted and deflected so that the diffraction angle changes continuously. The guided light beams 13R', 13G', and i3B' deflected in this way are LGC2
1, the light is diffracted and emitted from the optical waveguide 11 to the substrate 16 side, and emitted to the outside of the substrate from the substrate end surface 16b.

As is clear from the above equation, the guided light 13R'.

Since the deflection angle δ of 13G', 13B' changes depending on the wavelength λ, the surface acoustic waves 12R, 12G, 12B
The frequencies of are set to be different from each other, so that
Guided light beams 13R', 13G', 13B' after diffraction
are arranged to take almost the same optical path.

Red, green, and blue light beams 13 emitted from LGC 21
R″, 13G″, and 13B′ have different emission angles φ1. It emits at φ2° and φ3 (see Figure 2). This output angle φ is the waveguide light 13R
', 13G' or 138° wavelength is λ, the refractive index of the substrate 16 with respect to it is n□ (λ), the effective refractive index of the optical waveguide 11 is Ne (λ), and the pitch of the LGC 21 is A. . In this way, three color light beams 13R', 13G
", 13B" output angle φ1. φ2. Since φ3 is different,
These light beams travel along different optical paths in the space outside the optical waveguide it. Each light beam +3R''.

Scanning and imaging lenses 22R, 22G, and 22B are arranged in the optical paths of 13G' and 13B', respectively. These scanning imaging lenses 22R, 22G, and 22B are each
It is an fθ lens that is made up of a combination of elongated lenses that form part of a spherical lens, and each has a light beam of 13R” and 130
It is designed to be able to correct chromatic aberration and correct curvature of field of the light beam on the photosensitive material 23 according to the wavelength of ", 13B". In this way, each scanning imaging lens 22
If R, 22G, and 22B are correction lenses for monochromatic light,
Each lens can be formed relatively inexpensively, so one lens optical system can produce three color light beams 13R", 130", 1
Compared to the case where the above-mentioned correction is performed on all 3B'', the entire lens optical system can be formed at a lower cost.

The light beams 13R", 13G", and 13B" are focused by scanning imaging lenses 22R, 22G, and 22B into a small beam spot at a common position, and scan the photosensitive material 23 in the direction of arrow X (main scanning). At the same time, the photosensitive material 23 is transferred by the transfer means 30 in the direction of the arrow y, which is substantially perpendicular to the main scanning direction, and sub-scanning is performed, so that the photosensitive material 23 is exposed to the light beams 3R'' and 13G''.
, 13B'. As mentioned above, these light beams l:lR', 13G-,13
B'' is modulated based on the image signals Sr, Sg, Sb, so these image signals Sr, Sg are displayed on the photosensitive material 123.
, Sb are responsible for recording the color image.

Image signals for one main scanning line Sr, Sg, Sb
In order to synchronize the main scanning of the light beams 13R'', 13G', and 13B'' with the image signals Sr and Sg.

The blanking signal St included in sb may be used as a trigger signal to control the timing of voltage application to the IDTs 15R, 15G, and 15B. Also, this blanking,
By controlling the drive timing of the transfer means 30 using the signal St, the main scanning and sub-scanning can be synchronized.

In the embodiment described above, the three scanning imaging lenses 22R, 22C; It may be provided separately from the scanning imaging lens, and only one relatively large scanning imaging lens may be used for the three light beams. Further, the above-mentioned correction lens optical system may be composed of a spherical lens or, for example, a hologram lens. Even in such a case, if each of the three hologram lenses is used as a correction lens for monochromatic light, one complex hologram lens can be used to produce three-color light beams 13R'' and 13G''.

13B", the correction lens optical system can be formed more easily and inexpensively than in the case where chromatic aberration correction etc. are performed for each.

Furthermore, only one common drive circuit may be provided for driving the IDTs 15R, 15G, and 15B. Moreover, each waveguide light 13R', 13G'.

By providing a plurality of IDTs for each of 13B', it is also possible to cause each guided light to undergo Bragg diffraction a plurality of times, thereby widening the deflection angle range.

Further, although the above embodiment is formed to scan a light beam of three colors on a photosensitive material, the optical scanning device of the present invention is configured to scan a light beam of two colors or four or more colors. Of course, it is also possible to configure.

(Effects of the Invention) As explained in detail above, in the optical scanning device of the present invention, the wavelengths emitted from the optical waveguide are different by utilizing the wavelength dispersion of the light output diffraction grating provided on the surface of the optical waveguide. A plurality of light beams are separated into separate optical paths, so that a simple correction lens optical system for monochromatic light can be applied to each light beam.

Therefore, in the optical scanning device of the present invention, the correction lens optical system is inexpensive compared to a device that performs corrections such as chromatic aberration correction using one complicated correction lens optical system for multiple light beams with different wavelengths. The cost can be reduced by the amount that can be formed, and it is also smaller and cheaper to form than an optical scanning device that is equipped with an optical deflection device and a correction lens optical system for each of multiple light beams with different wavelengths. Become what you can.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are a perspective view and a side view, respectively, showing an optical scanning device according to an embodiment of the present invention. IO... Optical scanning device 11... Optical waveguide 12
R, 12G, 12B...Surface acoustic wave 13R, 13G,
13B... Light beams 13R', 13G',
13B'... Waveguide light 13R', 13G", 13B
″...Light beams 15R, 15G, 15B...IDT 1B... emitted from the optical waveguide
Boards 17R, 17G, 17B... IDT drive circuit 18
R, 18G, IgB...Light sources 19R, 19G, 19B...Light source drive circuit 20...
Light input LGC21...Light output LGC22R, 22
G, 22B...Scanning imaging lens 23...Photosensitive material
30...Photosensitive material transfer means 40...Modulation circuit

Claims (1)

[Scope of Claims] An optical waveguide formed of a material through which surface acoustic waves can propagate; n light sources (2≦n) that make light beams of different wavelengths enter the optical waveguide; and the optical waveguide. a plurality of surface acoustic wave generating means for generating, in the optical waveguide, surface acoustic waves that propagate in a direction intersecting the optical path of the guided light beams of n different wavelengths and cause each guided light beam to Bragg diffract; a driving circuit that drives each of the surface acoustic wave generating means to generate a surface acoustic wave whose frequency changes continuously; Emit light out of the optical waveguide at the exit angle 1
a diffraction grating, and n monochromatic light correction lens optical systems each disposed in the optical path of the n light beams having different wavelengths emitted from the optical waveguide and performing aberration correction according to the wavelength of each light beam. An optical scanning device consisting of.