JPS6119019B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical polarizer suitable for use as a scanner in various optical scanning devices.

Conventionally, mechanical deflection methods using polygon mirrors, galvano mirrors, etc. have been often used to deflect light. These methods are superior in terms of energy efficiency and deflection angle compared to deflection methods that use crystals such as electro-optic crystals and acousto-optic crystals.
It is still used in many devices. However, these methods have a much slower deflection speed than those using crystals, and cannot be used in recording devices and display devices that require high-speed image scanning. In terms of deflection speed, polygon mirrors are generally superior to galvanometer mirrors, but even with polygon mirrors, the maximum possible deflection speed is about 10,000 to 20,000 rpm.

One of the reasons for this speed limit is the destruction of the mirror. That is, when a polygon mirror is rotated at a high speed and its speed is increased, the internal stress acting on the mirror itself due to rotational centrifugal force gradually increases, eventually causing the mirror to break. One way to prevent this mirror from breaking as much as possible and make it possible to rotate at high speed is to use a strong metal or other material for the mirror, which is less likely to break due to increased internal stress. .

Another possibility is to select a light material with a low specific gravity. This is because internal stress based on centrifugal force is proportional to the weight of the material, so the lighter the material chosen, the smaller the internal stress will be at the same rotation speed.

However, the above two means are generally contradictory, and the reality is that the stronger the material, the heavier it is.

Also, an optical scanning system using a polygon mirror, that is, a parallel beam is incident on the polygon mirror and deflected,
In an optical system that performs scanning by focusing this image on the surface to be scanned using an f-theta lens, the direct meridian d of the beam incident on the polygon mirror and the diameter δ of the imaging spot of the beam on the surface to be scanned are There is a relationship between them as shown in equation (1) below.

δ=ελf/d...(1) ε: Constant determined by the intensity distribution of the incident beam λ: Wavelength of the light source used f: Focal length of the f-θ lens For example, ε=2.44, λ=0.6328μ, f =
Calculate the required diameter d of the incident beam using the above formula (1) when the scanning surface is scanned with an imaging spot of δ = 100μ by inputting a circular beam with a uniform intensity distribution into the polygon mirror with a diameter of 300mm. Then d=4.63
mm. In other words, the thickness of the polygon mirror used needs to be at least as thick as the incident beam diameter d (=4.63 mm) mentioned above, and for this reason, the mirror inevitably has a large volume and weight, which hinders speeding up. It is also a major factor. Furthermore, polygon mirrors have a major problem of tilting errors between mirrors.

Examples of deflectors that solve the above problems with polygon mirrors include Appl, Opt, Vol6, No9,
A holographic deflector was proposed in 1531 ('67). In this technique, as shown in FIG. 1, a hologram plate 101 on which a point image is recorded is rotated about a rotation axis 102, thereby deflecting an incident light beam 103. A light beam 103 incident on the hologram plate 101 is diffracted by the hologram to become scanning light beams 104 ₁ and 104 ₂ , which further reproduce rotating point images 105 ₁ and 105 ₂ .
The locus of movement of these point images becomes a circular locus 105.

A curved surface 106 that includes this locus 105 within its surface
Or, when the movement of the point images 105 ₁ and 105 ₂ is observed on the plane 107, it becomes a straight line scan within the curved surface 106, and an arc scan 105' within the plane 107 as shown in FIG.

In image recording or display using an optical deflector, such curved surface scanning or circular arc scanning is generally not preferred, and straight line scanning within a plane is preferred.

The present invention also pertains to holographic deflectors, but it is an object of the present invention to improve the conventional holographic deflectors so that they can perform planar linear scanning.

In addition, by taking advantage of the features of the holographic deflector,
This solves the problem of tilting errors between mirrors, which is the biggest problem with conventional polygon mirrors.

A further object of the present invention is to obtain a deflector that can be mass-produced using embossing technology.

The present invention provides an optical waveguide, a means for rotating the optical waveguide around a rotation axis substantially perpendicular to the waveguide surface, and a grating arranged on a circumference around the rotation axis of the waveguide, each of which has a grating. and a plurality of diffraction gratings arranged in different directions, and a light beam irradiated onto a part of the optical waveguide is diffracted by one of the diffraction gratings and propagates through the waveguide, and is then propagated from the end face of the waveguide. Emits,
An optical deflector configured to deflect the emitted light as the optical waveguide rotates.

In other words, the present invention suppresses air resistance and internal stress by rotating a lightweight and thin optical waveguide around a rotation axis perpendicular to the waveguide surface, and has a configuration that can withstand high-speed rotation. By arranging a plurality of diffraction gratings around the rotation axis on the circumference for introducing a light beam into the surface, high-speed planar linear scanning is possible.

3 to 6 show a first embodiment of the present invention, in which 10 is a hologram, which is composed of a grating section (Grating diffraction grating) 11 and a waveguide section 12. FIG. When the light beam 13 that has been emitted from the light source 2 and collimated by the collimating optical system 3 enters the grating 11, it is diffracted and its path is bent, leading to the waveguide 1.
2 and reaches the end face 14 of the hologram plate. Outgoing light 15 from end face 14 is hologram 10
The beam is deflected by rotating around the axis 16, and an image is formed on the surface of the member to be scanned 19 by the imaging lens 17 (FIG. 6), thereby scanning the surface to be scanned.

FIG. 5 shows a diffraction phenomenon caused by the grating 11, and the grating 11 is a blazed grating. That is, it is manufactured so that energy is concentrated in the +1st order or higher order direction of diffraction from the pitch p of the grating 11 and the inclination α of the grating 11. Therefore, highly efficient energy conversion can be performed. For gratings with such surface shapes, a master mold is created using methods such as machining, photo etching, and ion etching, and then mass-produced as a replica (rePlica) using a mold. Therefore, when produced in large quantities, the cost per unit becomes considerably low. Epoxy material is used as a replica material.
Acrylic material etc. can be used.

Diffraction efficiency of approximately 80% has been obtained using this pre-grained grating, but it is possible to further increase the efficiency.

Furthermore, if the replica method is not used, a photoresist material is suitable for the hologram 10.

The light beam 13 whose direction has been changed by the grating section 11 travels within the waveguide section 12 as a waveguide for lower-order modes when the thickness t (Fig. 5) of the waveguide section 12 is several microns. In the case of mm, the light travels by total internal reflection.

Therefore, the base material 18 supporting the hologram 10
must be made of a material having a refractive index lower than that of the constituent material of the hologram 10. The base material 18 can be made of such a material to hold the hologram 10, but if the base material 18 is to be rotated at high speed and used, it is better to make the base material 18 metal. However, in this case, it is necessary to provide an optical thin film layer with a low refractive index between the metal base material 18 and the hologram 10.
The thin film layer may also serve as an adhesive for bonding the hologram 10 to the metal base material 18.

Further, a plased diffraction grating 11 may be provided on the lower surface of the waveguide 12 as shown in FIG. In this case, since the diffraction grating 11 is used as a reflective type,
It is better to apply a reflective film 26 such as Al on the surface of the diffraction grating 11 and the waveguide surface. This waveguide is the base 18
is glued to.

Further, a hologram of a volume type diffraction grating can be used instead of a plased type diffraction grating.

That is, the present invention rotates an optical waveguide 12 having a diffraction grating structure 11 to deflect a light beam 13, and can deflect light with high energy efficiency.
As such, the thickness may be from several μ to several 100 μ, and the thickness that satisfies the beam diameter (diameter) required for the front and rear polygon mirrors is no longer required.

However, the base material 18 is necessary to prevent deformation of the hologram 10 during rotation. However, although its thickness varies depending on the overall diameter, it only needs to be a few millimeters (even in the case of polygon mirrors, metal fittings to hold the polygons are required). The thickness of the optical deflector as a whole is also overwhelmingly thin and lightweight. The hologram 10 constructed as described above is arranged in a polygonal shape (an octahedron in the example in FIG. 3) around the axis 16, and is constructed as a single optical deflector 1 as a whole. Assuming that the above arrangement is an N-hedron, the resulting light deflection angle (full angle) β is β=2π/N (rad) (2).

FIG. 6 shows an example in which such an optical deflector 1 is used in an image scanning device. That is, the output deflected light 15 from the optical deflector 1 is directed to the photosensitive drum 19 by the lens 17.
Tie spot 20 on top. Driven by the motor 21, the optical deflector 1 rotates around the shaft 16 to perform scanning in the main scanning direction, and the photosensitive drum (scanned member) 1
9 performs scanning in the sub-scanning direction, and a two-dimensional image is formed on the surface of the drum 19.

The lens 17 is of an anamorphic type that includes a cylindrical lens inside. That is, since the gratings 11 of the hologram 10 are a group of parallel straight lines in this embodiment, the emitted light 15 from the optical deflector 1 is
In the scanning plane of the deflected beam, that is, in the plane perpendicular to the axis 16, it is parallel light (FIG. 3). However, in the direction perpendicular to the scanning plane, the incident light beam 13 is compressed and becomes a diverging light whose secondary light source is the end face 14 of the hologram 10 (FIG. 4).

Therefore, the imaging optical system must form an image of the emitted light 15 linearly onto the surface of the scanned member 19 as a circular spot 20. Such an optical system can be easily obtained by designing an anamorphic optical system that has different powers in the scanning plane and in the direction perpendicular thereto.

Furthermore, with respect to a plane perpendicular to the scanning plane, the emitted light 15 uses the end face 14 of the hologram 10 as a secondary light source, as described above, and is moved by the rotation of the deflector, so that it moves not in a plane but in a circle. Therefore, in this direction, it is necessary to correct the aberration for the finite object point and at the same time to correct the curvature of field so that the scanning is flat on the image plane. However, this can be easily obtained by controlling the Petzval sum of third-order aberration theory.

In this way, the holographic deflector 1 of the present invention enables parallel linear scanning.

Furthermore, as described above, the exit end surface 14 of the hologram deflector 1 and the scanning line 22 on the surface of the scanned member 19 have an imaging relationship in the vertical direction of the deflector 1, so that the pitches of the gratings 11 of each hologram 10 are different from each other. Even if there is a slight difference, it only affects the vertical direction deviation of the emitted light 15, but does not cause the imaged circular spot 20 to move in the direction perpendicular to the scanning line 22.

Therefore, in the hologram deflector of the present invention,
As long as the planarity of the waveguide portion 12 of the hologram 10 is maintained, the deviation between each scanning line that occurs in conventional deflectors (polygon, hologram deflectors) does not occur.

The thickness t of the waveguide section 12 is the scanning point image 20 to be obtained.
It is determined by the size δ _y of the anamorphic lens 17 and the vertical magnification m _y of the anamorphic lens 17, and is given by t=δ _y /m _y (3). For example, when δ _y =100 μm and m _y =5, t=20 μm.

Further, the lateral size δ _x of the point image 20 is determined by the lateral diameter d _x of the incident light beam 13 and the lateral focal length f _x of the anamorphic lens 17, and δ _x = ελf _x /d _x ... ...(4) ε: Constant determined by the beam intensity distribution λ: Wavelength of the light source used From equations (3) and (4) above, the conditions for the shape of the point image 20 to be circular are as follows: The horizontal direction of the incident light beam 13 The diameter d _x =ελf _x /tm _y ...(5).

For example, f _x = 300 mm, λ = 0.6328 μm, tm _y = 100
When μm and ε=2.44, d _x =4.63 mm.

In the embodiments shown in FIGS. 3 to 6, the parallel grating 11 is used as the diffraction grating structure, so the exit end face 1
4, a parallel light beam 15 (FIG. 3) was emitted within the scanning plane. In contrast, the second
In the hologram 10 of the embodiment, the diffraction grating lines 11' are curve group grating lines, and in this case, the diffracted light propagating within the waveguide 12 of the hologram 10 toward the exit end face 14 is reflected at the exit end face 14. imaged,
This is used as a secondary point light source 2' and is emitted as a diverging light beam 15'. Therefore, the imaging lens 17' in this case only needs to form an image of the secondary point light source 2' on the surface of the scanned member, and the above-mentioned anamorphic optical system is no longer necessary, and an ordinary spherical lens may be used. However, since the secondary light source 2' to be scanned draws a circular locus centered on the axis 16, it is necessary to correct the field curvature in the same way as in the above case in order to perform a plane scan on the surface of the scanned member. be. Note that the shape of the deflector 1 in this second embodiment is preferably circular as shown in the illustrated example.

The shape of the diffraction grating 11' having the converging function is a concentric arc pattern centered on the exit end face 14 of the hologram 10, and the pitch thereof is constant. Further, even when the grating lines 11' are made into a plased grating as shown in FIG. 5, the plased angle α may be constant. However, such a diffraction grating with arcuate grating lines 11' having a constant pitch and a constant prestressed angle does not have an imaging effect in the direction perpendicular to the diffraction grating plane. However, since the waveguide section 12 is thin in this vertical direction, the light beam is confined therein, resulting in a compressed shape.

A hologram created by interference between a spherical wave and a plane wave can also be used as a diffraction grating that also has a convergence effect in the vertical direction. The grid lines in this case are off-axis Fresnel zone plates (Fresnelzone
plate). When using a hologram, a volume type hologram is preferable in terms of efficiency.

FIG. 10 shows a cross section of a volume type hologram 10. The volume type is a layer 11'' that has a different refractive index in the thickness direction of the emulsion layer (e.g. dichromated gelatin).
1'', the incident light 13 is reflected when it satisfies the Bragg condition.This type cannot be mass-produced using a replica method compared to the previously mentioned plazed type grid lines 11 and 11', but it is possible to do so by using appropriate equipment. This can be done at low cost by coating the base layer with a sensitive material (such as a photopolymer) in advance, creating gratings using laser interferometry, and then performing a development process.

11 and 12 show a third embodiment, in which a geometry lens 23 is formed in the waveguide 12 of the hologram 10 to obtain a convergence spot, and the shape of the blazed grating 11 is a straight line.・Even pitch and constant angle of inclination are sufficient.
This grating 11 is easier to manufacture than the concentric grating 11'. The astringent action is carried out by a geometries cleanse 23. The geometry lens 23 is formed by pressing a steel ball against the waveguide 12 to form a concave mold, and has the function of converging parallel light incident on the waveguide 12 to a single point.

13 to 15 show a fourth embodiment in which the optical deflector 1 is combined into a sheet-like deflector, which takes full advantage of the ability to reduce the thickness, which is a feature of the optical deflector of the present invention, and the hologram 10. It is made of flexible material and maintains flatness through high-speed rotation. In this embodiment, the drive system can be particularly simplified.

As shown in FIGS. 14 and 15, the hologram 10 of this embodiment has a convergence type grating 11' of 10μ to
Flexible substrate 24 with a thickness of about 100μ
made on top. The flexible material is preferably one with a small elongation, such as polyethylene glycol terephthalate (trade name: Mylar).

One way to form hologram 10 is to form substrate 2
It is obtained by applying photoresist to the surface of 4, recording two-beam interference fringes on it, and developing it. In addition, when manufacturing in large quantities, the epoxy replica method (for details, see Optical Engineering, vol. 15,
No.5, P435 (1976)) can also be made. In this embodiment, the substrate 24 itself can be used as the waveguide 12, so there is no need to make the waveguide using materials with two types of refractive indexes, high and low, as in the previous embodiment.

This hologram sheet 10 is attached to a rotating shaft 16 and rotated at high speed by a motor 21. A back plate 25 is provided below the hologram sheet 10, and a manifold (ventilation hole) 25' is opened near the center of this plate 25. When the hologram sheet 10 is rotated by the motor 21, air is sucked from the manifold 25', flows between the hologram sheet 10 and the plate 25, and maintains the hologram sheet 10 in a flat state in balance with atmospheric pressure (dashed line in FIG. 13). A scanned secondary light source is obtained from the outer peripheral end surface of the hologram sheet 10.

In this embodiment, the weight of the rotating member 10 can be significantly reduced, the load on the motor 21 can be reduced, and the accuracy of perpendicularity between the rotating shaft 16 and the rotating member 10 can be greatly relaxed, resulting in a significant cost reduction. become.

In each of the above embodiments, when the light source 2 is a semiconductor laser, the emitted light beams 15 and 15' have different orientation angles depending on the direction with respect to the stripe, but when implementing the present invention, the direction in which the orientation angle is narrower (stripe direction) is It is better to match the radiation direction from the rotating shaft 16. This is because when guiding light to the waveguide 12, the smaller the beam diameter _dy in the waveguide direction, the less multiple diffraction occurs at the diffraction grating portion, and the less energy loss occurs during introduction.

In the examples of FIGS. 3 to 6, as described above, the emitted light 15 from the optical deflector 1 normally passes through the optical waveguide end face 14 as shown in FIG. 4 in the direction perpendicular to the scanning plane.
Since this is a diverging light with a secondary light source of 17th
Diffracted light 1 diffracted by a diffraction grating 11 as shown in the figure
The thickness t of the optical waveguide 12 is appropriately increased so that the number of repetitions of reflection during the time when the optical waveguide 3 reaches the optical waveguide end face 14 while being reflected within the optical waveguide 12 is appropriately increased (or the thickness t is increased by increasing the thickness t of the scanning member 19 The diffracted light 1
Since the light beams 3 propagate within the optical waveguide 12 and reach the end face 14 while maintaining their mutual parallelism, the light 15 emitted from the end face 14 is emitted as a substantially parallel light beam even in the direction perpendicular to the scanning plane. Therefore, the imaging optical system in this case does not need to be an anamorphic optical system as described above, but may be an ordinary spherical lens. Further, by making the end surface 14 of the optical waveguide 12 a surface cut off obliquely as shown in the figure, the direction of the emitted light 15 can be made substantially parallel to the scanning plane.

As is clear from the above explanation, the present invention is directed to the optical waveguide film 1.
2 has a diffraction grating structure 11, which guides the light beam 13 to the waveguide film 12, and rotates the optical waveguide film to deflect the light flux emitted from the end face 14 of the waveguide film 12. (1) The deflector can be made thinner and the load on the drive system can be reduced.

(2) Unlike conventional hologram deflectors, linear scanning within a plane is possible.

(3) Large quantities can be produced using the replica method and costs can be significantly reduced.

(4) It essentially does not have the surface tilt error that conventional polygon mirror scanners have, and can perform highly accurate scanning.

(5) Even sheet-like holograms can be scanned stably, allowing for significant cost reductions.

[Brief explanation of the drawing]

1 and 2 illustrate a conventional holographic deflector. FIG. 1 is a perspective view, FIG. 2 is a point image movement locus diagram, and FIGS.
3 is a perspective view, FIG. 4 is a sectional view, FIG. 5 is an enlarged sectional view, FIG. 6 is a perspective view of a scanned member being scanned, and FIGS. 9th
The figure shows the second embodiment, and FIG. 7 is a slope view;
8 is a plan view, FIG. 9 is a sectional view, FIG. 10 is an enlarged sectional view of the volume type hologram plate, 11th,
12 shows a third embodiment, FIG. 11 is a sectional view, FIG. 12 is a plan view, and FIGS. 13 to 15 are a fourth embodiment, in which FIG. 13 is a sectional view,
FIG. 14 is a sectional view of only the hologram plate, and FIG. 15 is a plan view of the hologram plate. Figure 16 is the fifth
FIG. 17 is an enlarged sectional view of a modified example of the illustrated example, and FIG. 17 is an enlarged sectional view of another modified example. 10 is a hologram plate, 11, 11', 11'' are diffraction gratings (gratings), 12 is an optical waveguide, 1
6 is a rotating shaft, 13 is incident light, 15 and 15' are output lights, 17 and 17' are imaging optical systems, 19 is a member to be scanned, and 20 is an imaging spot.

Claims (1)

[Scope of Claims] 1. an optical waveguide, a means for rotating the optical waveguide around a rotational axis substantially perpendicular to the waveguide surface, and a means for rotating the optical waveguide around a rotational axis substantially perpendicular to the waveguide surface; ,
It has a plurality of diffraction gratings each having a different arrangement direction of the gratings, and a light beam irradiated onto a part of the optical waveguide is diffracted by one of the diffraction gratings and propagates within the waveguide. An optical deflector configured to emit light from an end face and deflect the emitted light as the optical waveguide rotates. 2. The optical deflector according to claim 1, wherein the diffraction grating comprises grating lines of a group of curves so as to have a light focusing function. 3. The optical deflector according to claim 1, wherein the diffraction grating is a blazed diffraction grating of equal pitch and equal tilt angle. 4. The optical deflector according to claim 1, wherein the diffraction grating is a blazed diffraction grating having concentric arcs of equal pitch and equal inclination. 5. The optical deflector according to claim 1, wherein the optical waveguide is made of a thin flexible material.