JPH1098591A - Color image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color image reader in which occurrence of a fog on a face of a light receiving means resulting from a deviation in an image forming position depending on difference of refracted lights of each degree is prevented and a color image is read with high accuracy by three color lights, R (red), green (G) and blue (B). SOLUTION: A color image is formed on a light receiving means 4 where a plurality of line sensors are arranged on the same board face via a color decomposition means 3 consisting of a linear brazed diffraction grating that separates an incident luminous flux via an image forming optical system 2 into a plurality of color lights, the color image and the light receiving means 4 are scanned relatively to allow the light receiving means 4 to read the color image. In this case, a diffracting optical element 71 that has a unidirectional diffraction and an inverse color dispersion characteristic is placed to an optical path between the color decomposition means 3 and the light receiving means 4 so that a fog on the face of the light receiving section 4 caused by difference from the wavelength of each color light separated by the reflection linear brazed diffraction grating is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reading apparatus, and more particularly, to a plurality (three) of color separation means composed of a reflection type one-dimensional blazed diffraction grating having an appropriately set grating pitch.
By using light receiving means provided with a line sensor (light receiving element) of the same type on the same substrate surface and a diffractive optical element having reverse chromatic dispersion characteristics, the light receiving element surface due to the deviation of the reflection diffraction angle due to the difference in the incident angle The present invention relates to a color image reading apparatus suitable for, for example, a color scanner, a color facsimile, etc., which can prevent color blur and can read color image information on a document surface with high accuracy.

[0002]

2. Description of the Related Art Conventionally, color image information on a document surface is imaged on a line sensor (CCD) surface via an optical system, and color image information is converted using an output signal from the line sensor at this time. Various digital reading devices have been proposed.

For example, FIG. 16 is a schematic view of a main part of an optical system of a conventional color image reading apparatus. In the figure, when a light beam from a color image on the document surface 11 is condensed by an imaging lens 19 and formed on a line sensor surface, which will be described later, the light beam is, for example, red (R) and green through a 3P prism 20. After color separation into three colors (G) and blue (B), the light is guided on the respective line sensors 21, 22, 23. The color images formed on the respective line sensors 21, 22, and 23 are line-scanned in the sub-scanning direction, and reading is performed for each color light.

FIG. 17 is a schematic view of a main part of an optical system of a conventional color image reading apparatus. In the figure, when a light beam from a color image on the document surface 11 is condensed by the imaging lens 29 and formed on a line sensor surface described later, a wavelength selective transmission film having dichroism is added to the light beam. The light is split into three light beams corresponding to three colors via two beam splitters 30 and 31 for color separation.

[0005] A color image based on the three color lights is formed on a so-called monolithic three-line sensor 32 in which three line sensors are provided on the same substrate surface. Thus, the color image is line-scanned in the sub-scanning direction, and reading is performed for each color light.

FIG. 18 is an explanatory view of the monolithic three-line sensor 32 shown in FIG. 17. The monolithic three-line sensor 32 includes three line sensors (CCD) 25, 26, and 27 parallel to each other as shown in FIG. Are arranged at a finite distance on the same substrate surface so that a color filter (not shown) based on each color light is provided on the surface of the line sensors 25, 26 and 27.

The distances S1 and S2 between the line sensors 25, 26 and 27 are generally manufactured to be, for example, about 0.1 to 0.2 mm due to various manufacturing conditions. Are, for example, 7 μm × 7 μm,
It is set to about 10 μm × 10 μm.

[0008]

The color image reading apparatus shown in FIG. 16 requires three independent line sensors, requires high precision, and requires a 3P prism which is difficult to manufacture. The whole becomes complicated and expensive. In addition, it is necessary to perform matching adjustment between the imaged light beam and each line sensor three times independently, and there is a problem that assembly adjustment is troublesome.

In the color image reading apparatus shown in FIG. 17, when the plate thickness of the beam splitters 30 and 31 is x, the distance between each line of the line sensor is 2√2x.
If the distance between the lines of the line sensor, which is preferable for manufacturing, is about 0.1 to 0.2 mm, the plate thickness x of the beam splitters 30 and 31 is about 35 to 70 μm.

In general, it is very difficult to construct a beam splitter having such a small thickness and good optical flatness, and if a beam splitter having such a thickness is used, an image is formed on a line sensor surface. There is a problem that the optical performance of a color image is reduced.

On the other hand, as shown in FIG.
The distances S1 and S2 between the other two lines 25 and 27 relative to the center line 26 of the line sensor are generally equidistant in the opposite directions, respectively, and an integer of the pixel size W2 in the sub-scanning direction (see FIG. 18). It is set to double. This is for the following reasons.

That is, as shown in FIG. 19, when reading a color image with the above-described monolithic three-line sensor using only the normal imaging optical system 45, the three line sensors 25, 26, and 27 simultaneously read the color image. The reading positions on the document surface 11 that can be read are three different positions 2 as shown in FIG.
5 ', 26', 27 '.

For this reason, the signal components of the three colors (R, G, B) at an arbitrary position on the document surface 11 cannot be read at the same time. Come up.

To this end, the distances S1 and S2 between the lines of the three-line sensor are set so as to be an integral multiple of the pixel size W2, and a redundant line memory corresponding thereto is provided. By delaying each of the G and R signals (signal components based on the G and R color lights) with respect to the color light based signal components, a composite signal component of three colors can be obtained relatively easily.

Therefore, as described above, the distances S1 and S2 between the other two line sensors 25 and 27 with respect to the center line sensor 26 of the three line sensors are set to be an integral multiple of the pixel size W2 in the sub-scanning direction. It is.

However, in the above-described color image reading apparatus, the use of the redundant line memory corresponding to the distance between the lines of the three-line sensor requires the provision of a plurality of expensive line memories, which is costly. There are problems such as being extremely disadvantageous, and the whole apparatus becoming complicated.

According to the present invention, when a color image is read using a reflection type one-dimensional blazed diffraction grating as a color separation means and a color image is read by a monolithic three-line sensor as a light receiving means, the reflection type one-dimensional blazed diffraction grating and the monolithic light source are used. By disposing a diffractive optical element having the inverse chromatic dispersion characteristic in the optical path between the three-line sensor, blurring (deviation of the imaging position) on the light receiving element surface in the cross-sectional direction of the grating pitch of ± 1st-order diffracted light is generated. Is effectively prevented, for example, R,
It is an object of the present invention to provide a color image reading device capable of digitally reading a color image with high precision using three color lights of G and B.

[0018]

The color image reading apparatus according to the present invention comprises: (1) a color separation comprising a reflection type one-dimensional blazed diffraction grating for separating an incident light beam into a plurality of color lights by an image forming optical system; When a plurality of line sensors are imaged on the light receiving means surface arranged on the same substrate surface through the means, and the color image is read by the light receiving means by relatively scanning the color image and the light receiving means. A diffractive optical element having an inverse chromatic dispersion characteristic and having a diffractive action in one direction having an inverse chromatic dispersion characteristic in an optical path between the color separating means and the light receiving means, and each color light separated by the reflection type one-dimensional blazed diffraction grating. Is characterized in that the blur on the light receiving means surface caused by the difference in wavelength is corrected.

In particular, (1-1) the plurality of line sensors are arranged so as to be parallel to each other, the imaging optical system is constituted by an emission type telecentric system, and the color separation means converts the incident light beam. Color separation into three color lights in a direction orthogonal to the arrangement direction of the pixels of the line sensor;
(1-2) The diffractive optical element has a negative diffractive effect on a fundamental wavelength, and (1-3) the diffractive optical element has a positive diffractive effect on a fundamental wavelength. And (1-4)
The fundamental wavelength is a wavelength of the 0th-order diffracted light that is separated and reflected and diffracted by the reflection type one-dimensional blazed diffraction grating, and (1-5) a grating pitch of the reflection type one-dimensional blazed diffraction grating (1-6) the thickness of the reflection type one-dimensional blazed diffraction grating is set from the center of the optical axis of the imaging optical system to the periphery. (1-7) The diffractive optical element is arranged at a position where each color light separated by the reflective one-dimensional blazed diffraction grating is spatially separated. And so on.

[0020]

1A and 1B are a plan view (main scanning section) and a side view (sub-scanning section) of a main part of a first embodiment of the present invention, respectively.

FIG. 2 is a partial explanatory view showing an optical path of a light beam after passing through the imaging optical system shown in FIG. 1, FIG.
(B) is an enlarged explanatory view of a part of the reflection type one-dimensional blazed diffraction grating shown in FIG. 2.

In FIG. 1, reference numeral 1 denotes a document surface on which a color image is formed. Reference numeral 2 denotes an imaging optical system, which in the present embodiment is configured to be a so-called emission type telecentric system in which a principal ray on the emission side is emitted in parallel with the optical axis. An image is formed on a light receiving means (monolithic three-line sensor) surface via a reflective one-dimensional blazed diffraction grating.

Reference numeral 3 denotes a color separating means, which is constituted by a reflection type one-dimensional blazed diffraction grating (hereinafter also referred to as "one-dimensional blazed diffraction grating"), and which makes the incident light beam orthogonal to the arrangement direction of the pixels of the line sensor. The light is decomposed in the direction into predetermined color lights, for example, three primary color lights of R (red), G (green), and B (blue) and reflected and diffracted. In the present embodiment, R color light is obtained as + 1st order diffracted light, G color light is obtained as 0th order diffracted light, and B color light is obtained as −1st order diffracted light.

Reference numeral 71 denotes a transmission-type diffractive optical element having a chromatic dispersion characteristic opposite to that of a normal glass material, which is composed of an optical element described later, and which emits each color light (each color) separated by the one-dimensional blazed diffraction grating 3. It is arranged in a region (position) where spatially separated diffracted light) is spatially separated and near the light receiving means. The diffractive optical element 71 in the present embodiment has a negative diffractive action (divergence action) with respect to the fundamental wavelength (the wavelength of the 0th-order diffracted light separated and reflected and diffracted by the one-dimensional blazed diffraction grating 3). This prevents blurring on the light receiving element surface due to a shift in the imaging position due to the difference in the wavelength of each color light (diffracted light of each order) separated by the blazed diffraction grating 3.

Reference numeral 4 denotes light receiving means, which is a so-called monolithic three-line sensor (hereinafter, also referred to as "three-line sensor") in which three line sensors (CCD) 8, 9, and 10 are arranged on the same substrate surface so as to be parallel to each other. ). A color filter (not shown) based on each color light is provided on each of the line sensors 8, 9, and 10 as necessary. Different values are set corresponding to the color separation direction (sub-scanning direction).

In this embodiment, a color image on the document surface 1 is line-scanned by a scanning means including a mirror or the like (not shown), a light beam from the color image is condensed by an imaging optical system 2, and one-dimensional blazed diffraction is performed. After color separation into three color lights via the grating 3, respective color images are formed on the corresponding line sensors 8, 9 and 10 through the diffractive optical element 71. The light receiving means 4 digitally reads a color image based on each color light.

In this embodiment, the reflection type 1 for color separation is used.
As shown in FIG. 2, the one-dimensional blazed diffraction grating 3 converts the light reflected and diffracted by the one-dimensional blazed diffraction grating 3 into a negative beam.
The light is split into three directions of primary light 5, zero-order light 6, and + 1st-order light 7 and is focused on the line sensors 8, 9, and 10 as light beams of focused spherical waves by the imaging optical system 2. .

In the focused spherical wave, a cross section of the lattice pitch (FIG. 1)
2 (B), FIG. 2) (in the sub-scanning section), a light beam incident on the one-dimensional blazed diffraction grating 3 from above with respect to the optical axis (hereinafter referred to as “upper light beam”) and a one-dimensional blazed from the optical axis. The luminous flux incident on the diffraction grating 3 and the luminous flux incident on the one-dimensional blazed diffraction grating 3 from below with respect to the optical axis (hereinafter referred to as “lower luminous flux”) with respect to the optical axis are the one-dimensional blazed diffraction grating 3, respectively. Are different from each other.

For example, as shown in FIG. 2, when the incident angle of the upper light beam is θ ₁ , the incident angle of the light beam on the optical axis is θ ₀ , and the incident angle of the lower light beam is θ ₂ , θ ₁ > θ _0. Incident on the one-dimensional blazed diffraction grating 3 in a relationship of> θ ₂ .

Here, the reflection diffraction angle θ 'in the first-order diffraction in the reflection diffraction and the incident angle θ have a relationship represented by the following equation.

Sin θ′−sin θ = ± λ / P λ: wavelength, sign positive: + 1st order, sign negative: −1st order, P: grating pitch Therefore, from the above equation, the reflection diffraction angle θ ′ is θ ′ = sin ^{− 1} (± λ / P + sin θ)... (1)

The reflection diffraction angle θ 'is different in the above-mentioned sub-scan section. Therefore, when a one-dimensional blazed diffraction grating is arranged in a focused spherical wave by the imaging optical system, the blur corresponding to the deviation of the reflection diffraction angle θ ′ of the diffracted light of each order on the imaging plane (light receiving element surface). Will occur.

Here, a specific numerical example will be described. For example, the incident angle θ ₀ of the light beam on the optical axis is 45 °,
The convergence angle β of the focused spherical wave is 5.5 ° and the grating pitch P is 16
0 μm, the distance L ₀ from the one-dimensional blazed diffraction grating 3 along the optical axis to the light receiving element (three-line sensor) surface is 3
5.2 mm. In this case, for example, the wavelength λ ₊₁ = 606 nm in the _{+ 1st} order light, and the incident angle θ ₁ =
At 50.5 °, the reflection diffraction angle θ ′ _{1, + 1} = 50.8 °, and for the lower beam, the incident angle θ ₂ = 39.5 °, and the reflection diffraction angle θ ′ _{1, + 1} = 39. 8 °. In the light beam on the optical axis, the incident angle θ ₀ = 45 ° and the reflection diffraction angle θ ′ _{0, + 1} = 4
5.3 °.

FIG. 4 shows an optical path of the three reflected diffracted light beams toward the surface of the three-line sensor 4. FIG. 4 shows an optical path diagram in which the ± 1st-order light and the 0th-order reflected and diffracted light travel toward the three-line sensor 4 surface.

As can be seen from the figure, both the upper and lower light beams have a type of aberration in this cross section.
The + 1st-order light is condensed (imaged) in front of the light receiving element surface of the three-line sensor 4, and at this time, approximately 75 μm blur occurs on the light receiving element surface due to geometrical optics.

Similarly, in the case of the -1st-order light having the wavelength λ _-1 = 471 nm, blurring occurs similarly to the above-mentioned + 1st-order light. That is, both the upper and lower light beams of the -1st order light are focused (imaged) behind the light receiving element surface of the three-line sensor 4, and at this time, the light beam is also geometrically optically reflected on the light receiving element surface.
8 μm blur occurs.

On the other hand, in the zero-order light, the reflection type one-dimensional blazed diffraction grating 3 simply acts as a mirror surface, so that there is no blur on the light receiving element surface generated by the ± first-order light.

It should be noted that the reflection type one-dimensional brake used in the above calculation was used.
The shape of the shifted diffraction grating 3 has a grating thickness d. ₁ = D_Two = D_Three = 7
49.5 nm, each step width W₁ = W_Two = W_Three = W_Four And
The periodic pitch P is

[0039]

(Equation 1) It is.

At this time, the efficiency peak wavelength λ in each order of diffracted light (color light) was obtained by the following equations. For ± primary light,

[0041]

(Equation 2) From (n, m) = (4,2), the wavelength λ ₊₁ is 606 nm,
The wavelength λ _-1 is 471 nm, and the wavelength λ ₀ is 530 nm for the zero-order light from 2d · cos θ ₀ = m · λ ₀ ... (2).

Although the above-mentioned blur amount was obtained based on the geometrical optical calculation, the results obtained by strictly performing a simulation by Kirchhoff diffraction and obtaining a point image intensity distribution are shown in FIGS. . As shown in each figure, the blur amount in both cases shows relatively good agreement.

Generally, in order to read color image information with high accuracy in a color image reading apparatus, the blur amount described above impairs the resolution in the sub-scanning direction at the time of reading and cannot be tolerated.

As is apparent from the example of the optical path diagram shown in FIG. 4, the + 1st-order light component, in this case red light having an efficiency peak wavelength of 606 nm, has a significant negative chromatic aberration with respect to the green light having the 0th-order light wavelength of 530 nm. , While -1
This is equivalent to showing a remarkable positive chromatic aberration in the next light component, in this case, blue light having an efficiency peak wavelength of 471 nm in the same comparison as described above.

In this embodiment, the transmission type diffractive optical element 71 is used to correct the blur on the surface of the three-line sensor 4 in the sub-scanning direction of the ± primary light, which is also referred to as chromatic aberration. In this embodiment, as is apparent from FIGS. 4 and 5 to 7, the image forming point of the + 1st-order light (λ = 606 nm) in the sub-scan section is −0.39 mm from the surface of the line sensor 10 shown in FIG. In this case, the image forming point in the −1st order light (λ = 471 nm) is +0.3 mm from the surface of the line sensor 8 shown in FIG.

However, if the focal length of a transmission type diffractive optical element which exerts a diffractive action in the sub-scanning section is f and the wavelength of a passing light beam is λ, it is known that the characteristic becomes f · λ = constant. I have. It exhibits the inverse chromatic dispersion characteristics of a normal refractive glass system. If this is applied to the present embodiment, f (606 nm) × 606 nm = f (471 nm) × 471 nm → f (606 nm) / f (471 nm) = 0.777 (3) On the other hand, f (606 nm) −f (471 nm) = 0.69 (mm) (4) From the above equations (3) and (4), f (471 nm) = − 3.09 (mm), f (606 nm) = −
2.40 (mm) Similarly, f (530 nm) = − 2.75 (mm) is obtained.

That is, f = −2.75 m at λ = 530 nm
By using the transmission type diffractive optical element 71 having a negative power (diffraction action) indicating m, it is possible to obtain 3
Blur on the surface of the line sensor 4 can be corrected.

In general, a diffractive optical element has a chromatic dispersion value of a glass material such as ordinary glass which is limited to a positive value of about 30 to 80, whereas the value is νd = −3.453.
It is also known to exhibit large chromatic dispersion. The following equation shows the refractive index dispersion with respect to the wavelength.

[0049]

(Equation 3) (N: refractive index, d, F, and C are the respective spectral wavelengths) The dispersion of the element substrate is assumed to be negligible with respect to the large negative dispersion of the diffractive optical element. If necessary, it can be implemented in an easy way to consider.

Next, features of the one-dimensional blazed diffraction grating of the present embodiment formed by a reflection type diffraction grating will be described in comparison with a transmission type one-dimensional blazed diffraction grating.

The transmission type one-dimensional boozed diffraction grating is Appl.
ied Optics, Vol. 17, No. 15, pp. 2273-2279 (1978.8.1
As disclosed in Japanese Patent Application Laid-Open No. H10-260, an incident light beam incident on the transmission type one-dimensional borated diffraction grating is transmitted and diffracted and separated mainly into three directions. 1 dimensional Burezudo diffraction grating of the transmission type, for example, when the blazed wavelength is lambda _0, the blazed wavelength lambda ₀ grating thickness d _i needed to the d _i = m · λ ₀ / a (n [lambda ₀ -1) Become.

Here, nλ ₀ is the refractive index of the medium, m and λ ₀ are the same values as in the above embodiment, and m = 2, λ ₀ = 53.
0 nm and the refractive index nλ ₀ = approximately 1.5, the grating thickness d _{i of the} transmission type one-dimensional borated diffraction grating
Requires d _i = 2120 nm.

On the other hand, in the case of the reflection type one-dimensional blazed diffraction grating of the present invention (the incident angle of the light beam on the optical axis is 45 °).
°) is a grating thickness d _i as described above is 749.5Nm.
Therefore, the grating thickness d _{i of the} transmission-type one-dimensional borated diffraction grating
Requiring even deeper level difference of about 3-fold compared to the grating thickness d _i of the one-dimensional Burezudo diffraction grating of the reflection type.

This is extremely difficult in fabricating a reflection type one-dimensional borated diffraction grating. For example, if the refractive index of the medium is increased, it is somewhat relaxed.
Generally, as a one-dimensional blazed diffraction grating, for example, a medium such as SiO ₂ having a refractive index of about n ₁ = 1.5 is often used in view of workability, cost, and the like.

Further, from the viewpoint of the space efficiency in the apparatus, the reflection type one-dimensional blazed diffraction grating also has an advantage that the whole apparatus can be easily made compact.

In this embodiment, the imaging optical system is configured to be an emission type telecentric system. This is for the following reasons.

That is, when the angle of incidence of each light beam on the one-dimensional blazed diffraction grating according to the angle of view in the main scanning section is not constant, the blazed wavelength λ ₀ changes according to the following equation.

[0058]

(Equation 4) Specifically, when the incident angle α ′ in the main scanning plane according to the angle of view is set to 20 ° and a normal imaging optical system that is not a telecentric system and a reflection type one-dimensional blazed diffraction grating are used,
The blazed wavelength λ ₀ shifts by about 30 nm.

In order to prevent the shift of the blazed wavelength λ ₀ , in the present embodiment, the image forming optical system is constituted by an emission type telecentric system, and the main component of each angle of view of the light emitted from the image forming optical system. Light rays are always incident perpendicularly in the main scanning section.

Next, a second embodiment of the present invention will be described.

In the first embodiment, as shown in FIG. 3, the light beam enters the reflection type one-dimensional blazed diffraction grating from the upper left to the upper right step grating, and is reflected and diffracted upward and to the right. In this embodiment, a light beam is incident in the opposite direction, that is, from the upper right, and is reflected and diffracted to the upper left. In such a case ±
The blurring of the first-order diffracted light on the three-line sensor surface is reversed. That is, the luminous flux 7 in FIG. 4 corresponds to the −1st-order light (blue light), and the luminous flux 5 corresponds to the + 1st-order light (red light).

Accordingly, as the so-called chromatic aberration, the +1 order light has a positive value and the -1 order light has a negative value. The diffractive optical element for correcting this is f (606 nm) -f (407 nm) =-0.69 (mm). Based on the above-mentioned equations (3) and (4), f (530 nm)
= 2.15 (mm), f (471 nm) = 3.09 (mm), f (60
6 nm) = 2.40 (mm), which is a diffractive optical element having a positive power (diffraction effect).

As described above, in the present embodiment, λ =
By using a diffractive optical element having a positive diffraction function (convergence function) of f = 2.15 mm at 530 nm, the same effect as in the first embodiment is obtained.

FIGS. 8A and 8B show typical cross sections of the transmission type diffractive optical elements described in the first and second embodiments. The element is a well-known manufacturing method using a mask and etching used in semiconductor manufacturing, or a replica thereof,
Alternatively, it is processed and manufactured by cutting or the like.

FIGS. 8A and 8B show a typical diffraction type Fresnel element. For example, as shown in FIG. 9, each of the sawtooth-shaped cross-sections has a step-like lattice cross-section quantized. B
Needless to say, the effect does not change even if the OE (Binary Optics Element) structure is used. 8 and 9, reference numerals 71, 72, and 73 denote diffractive optical elements, respectively, and h denotes a grating thickness.

FIG. 10 is a schematic view of a main part of an optical system according to Embodiment 3 of the present invention. In the present embodiment, the reflection type one-dimensional blazed diffraction grating 40 as the color separation means is formed of a cylindrical shape, so that the imaging optical system is formed of a normal optical system (not a telecentric system).

The light beam incident at the angle of view α is
It is assumed that the light is emitted at an emission side at an angle α ′. At this time, as shown in FIG.
It is assumed that a two-dimensional blazed diffraction grating is used. Then, the distance when the light flux reflected and diffracted therefrom enters one of the line sensors 4 of the light receiving means 4 is L ₀ on the axis and L ₁ off the axis of the emission angle α ′. Where L ₁ = L ₀ / c
osα ′ (in FIGS. 10 and 11, the optical path is expanded as shown by a broken line. In a normal optical system, α ≒ α ′). Therefore, each emission angle α ′ between the one-dimensional blazed diffraction grating 40 and the light receiving element surface.
Is different on-axis (α ′ = 0) and off-axis (α ≠ 0) and is not constant.

Here, the incident angle θ of each light beam on the reflection type one-dimensional blazed diffraction grating 40 and the position (separation distance) Z on the light receiving element surface in the sub-scanning direction have the following relationship.

Z = L · tan {sin ⁻¹ (± λ / P + sin θ) −θ} (6) Sign positive: +1 order, sign negative: −1 order, L: L ₀ or L ₁ As shown in the above equation (6), the position Z is not constant due to each incident angle α 'on the light receiving element surface, that is, a light beam of a constant wavelength is correctly formed on each line sensor surface arranged in parallel with a straight line. Not imaged.

Therefore, in the present embodiment, in order to solve the above-mentioned problem, as shown in FIG. 10, the reflection type one-dimensional blazed diffraction grating 40 is formed by the existence of the emission angle α ′ in the main scanning section (finite angle of view). The formed substrate has a cylindrical surface centered on the exit pupil of the imaging optical system, and the exit chief ray corresponding to each angle of view is always perpendicularly incident on the diffraction grating 40. Thereby, the shift of the blazed wavelength due to the incident angle dependence in the cross section is effectively prevented.

On the other hand, after being reflected and diffracted by the diffraction grating 40, the optical path length reaching the light receiving element surface of the three-line sensor 4 is L ₀ = g−R on the axis (α ′ = 0) and off-axis (α ′). ≠ 0) and L
₁ ′ = g / cosα′-R, and both are not constant, and the reflected diffracted light does not form an image correctly on the light receiving element surface of each line sensor with the same contents as in the above equation (6).

In order to eliminate this, the grating pitch of the reflection type one-dimensional blazed diffraction grating is shifted from on-axis to off-axis (from the center to the periphery) symmetrically in the main scanning section with respect to the optical axis as shown in FIG. Each is set so as to increase as it moves (P → P ′ in FIG. 12). As a result, the first-order diffraction angle is changed, and as a result, an image is formed on four line sensors (light receiving elements) that are arranged in a straight line in parallel from the axis to the axis.

As described above, in this embodiment, the reflection type 1
The shape of the dimensional blazed diffraction grating 40 is constituted by a cylindrical shape, and the arrangement of the grating pitch is appropriately set as described above. As a result, even if the imaging optical system is composed of a normal optical system, spectral separation is correctly performed, and color image information is read with high accuracy for each color light.

FIG. 13 is a schematic view of a main part of the light receiving means 50 according to the fourth embodiment of the present invention. In the third embodiment described above, the substrate of the reflection type one-dimensional blazed diffraction grating 40 has a cylindrical surface in the main scanning section. However, in the present embodiment, the center line 52 of the monolithic three-line sensor 50 as the light receiving means is conversely sandwiched. Two line sensors 51, 5 on both sides
3 is removed from the parallel configuration to provide a configuration as shown in FIG. As a result, the diffraction grating substrate remains a flat plate, and the shift in the Z direction according to the equation (6) is absorbed by the position shift of each pixel of the light receiving section of the line sensor.

On the other hand, regarding the shift of the blazed wavelength depending on the incident angle α ′ caused by making the substrate of the one-dimensional blazed diffraction grating a flat plate, as shown in FIG. The problem is solved by continuously increasing the lattice thickness at the same ratio in each stage from the on-axis to the off-axis (from the center to the periphery).

[0076] Specifically when using a one-dimensional blazed diffraction grating of the first embodiment described above and will be described as a numerical example, 'angle of incidence α of the grating thickness d _i in = 20 °' = 0 ° angle of incidence α For a lattice thickness d ₁ = 749.5 nm at
By increasing the thickness to ₁ = 797.6 nm, the blazed wavelength λ ₀ = 530 nm is kept constant.

FIG. 15 is an explanatory view of a reflection type one-dimensional blazed diffraction grating 70 as color separation means according to the fifth embodiment of the present invention.

In this embodiment, the reflection type one-dimensional blazed diffraction grating 70 is constituted by a three-dimensional structure, and the grating pitch P of the one-dimensional blazed diffraction grating gradually increases from the center of the optical axis toward the peripheral portion in the main scanning section direction. (Pc → Pe), and a diffractive optical element is arranged in the optical path between the color separation means and the light receiving means as in the first embodiment. As a result, deviation of the diffraction image forming position on the line sensor surface is prevented, and blurring of the ± 1st-order diffracted light in the sub-scanning section direction is suppressed.

Further, in this embodiment, similarly to Embodiment 4 described above, the grid thickness is continuously increased from on-axis to off-axis (from the center to the periphery) (hc → he). The shift of the blazed wavelength due to the angle α 'is effectively prevented.

By using the reflection type one-dimensional blazed diffraction grating 70 having a three-dimensional structure formed on a flat substrate as described above, a color image reading apparatus can be constructed without using a telecentric system as an imaging optical system. ing.

In the above embodiment, the change of the grating pitch and the grating thickness on the grating surface is assumed to be continuous. However, the change is not limited to this change, and the change may be divided into a plurality of steps. Even if it gives, the same effect as the above-mentioned embodiment can be obtained.

[0082]

According to the present invention, when a color image is read by a light receiving means comprising a monolithic three-line sensor via a reflective one-dimensional blazed diffraction grating as a color separating means as described above, the reflective one-dimensional blazed diffraction is performed. By disposing a transmissive diffractive optical element in the optical path between the grating and the monolithic three-line sensor, a focused spherical wave, which is a light beam emitted from the imaging optical system, enters the reflective one-dimensional blazed diffraction grating. In this case, blurring on the monolithic three-line sensor surface in the sub-scanning direction of the ± 1st-order diffracted light due to the shift of the reflection diffraction angle due to the difference in the incident angle of each light beam on the grating surface within the sub-scanning cross section It is possible to achieve a color image reading apparatus capable of effectively removing the deviation and reading a color image with high accuracy.

In addition, by forming the reflection type one-dimensional blazed diffraction grating with a three-dimensional structure, it is possible to use a normal optical system which is a compensation system without using a telecentric optical system as an imaging optical system. A color image reading device that can be achieved can be achieved.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view of a main part of a first embodiment of the present invention.

FIG. 2 is a partial explanatory view showing an optical path of a light beam after passing through an imaging optical system in FIG. 1;

FIG. 3 is an enlarged explanatory view of a part of the reflection type one-dimensional blazed diffraction grating shown in FIG. 2;

FIG. 4 is an optical path diagram showing an optical path of reflected and diffracted light of each order light going to a three-line sensor.

FIG. 5 is a conventional diffraction pattern diagram for + 1st-order light.

FIG. 6 is a conventional diffraction pattern diagram for zero-order light.

FIG. 7 is a conventional diffraction pattern diagram of −1st order light.

8A is a sectional view of a principal part of a diffractive optical element according to a first embodiment of the present invention, and FIG. 8B is a sectional view of a principal part of a diffractive optical element according to a second embodiment of the present invention.

FIG. 9 shows a diffractive optical element (BOE) according to an embodiment of the present invention.
Main part sectional view of

FIG. 10 is a schematic diagram of a main part of a third embodiment of the present invention.

FIG. 11 is a schematic diagram of a main part for comparing and describing the configuration of the present invention.

FIG. 12 is an explanatory diagram of a one-dimensional blazed diffraction grating according to a third embodiment of the present invention.

FIG. 13 is a schematic diagram of a main part of a light receiving unit according to a fourth embodiment of the present invention.

FIG. 14 is an explanatory diagram of a one-dimensional blazed diffraction grating according to a fourth embodiment of the present invention.

FIG. 15 is an explanatory diagram of a one-dimensional blazed diffraction grating according to a fifth embodiment of the present invention.

FIG. 16 is a schematic diagram of a main part of an optical system of a conventional color image reading apparatus.

FIG. 17 is a schematic view of a main part of an optical system of a conventional color image reading apparatus.

FIG. 18 is an explanatory diagram of a monolithic three-line sensor.

FIG. 19 is a schematic view of a main part of an optical system of a conventional color image reading apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Original surface 2 Imaging optical system 3, 40, 60 Color separation means (reflective one-dimensional blazed diffraction grating) 4, 50 Light receiving means (monolithic three-line sensor) 5, 6, 7 Reflected diffracted light 8, 9, 10 lines Sensors 51, 52, 53 Line sensor 70 Color separation means (reflective one-dimensional blazed diffraction grating) 71, 72, 73 Diffractive optical element

Claims (8)

[Claims] 1. A plurality of line sensors are arranged on the same substrate surface through a color separation means comprising a reflection type one-dimensional blazed diffraction grating for color-separating a color image into a plurality of color lights by an imaging optical system. An image is formed on a light receiving means surface, and when the color image is read by the light receiving means by relatively scanning the color image and the light receiving means, an optical path between the color separation means and the light receiving means is provided. A diffractive optical element having a diffractive action in one direction having an inverse chromatic dispersion characteristic is provided, and a blur on the light receiving means surface caused by a difference in the wavelength of each color light color-separated by the reflective one-dimensional blazed diffraction grating is corrected. A color image reading device. 2. The plurality of line sensors are arranged so as to be parallel to each other, the imaging optical system is constituted by an emission type telecentric system, and the color separation means converts an incident light beam to the line sensor. 2. The color image reading apparatus according to claim 1, wherein the color image is separated into three color lights in a direction orthogonal to the arrangement direction of the pixels. 3. The color image reading apparatus according to claim 1, wherein said diffractive optical element has a negative diffraction effect with respect to a fundamental wavelength. 4. The color image reading apparatus according to claim 1, wherein said diffractive optical element has a positive diffraction effect with respect to a fundamental wavelength. 5. The color image reading apparatus according to claim 3, wherein the fundamental wavelength is a wavelength of a 0th-order diffracted light that is separated and reflected and diffracted by the reflection type one-dimensional blazed diffraction grating. 6. The color image according to claim 1, wherein a grating pitch of said reflection type one-dimensional blazed diffraction grating is set so as to increase gradually from a center of an optical axis of said imaging optical system to a periphery thereof. Reader. 7. The color image according to claim 1, wherein the thickness of the reflection type one-dimensional blazed diffraction grating is set so as to gradually increase from the center of the optical axis of the imaging optical system to the periphery. Reader. 8. A color image reading apparatus according to claim 1, wherein said diffractive optical element is arranged at a position where each color light separated by said reflection type one-dimensional blazed diffraction grating is spatially separated. apparatus.