JPH02214372A - Color picture reader - Google Patents

Abstract

PURPOSE:To attain reduction in color slurring and compactness of the reader by arranging a linear blazed diffraction grating in an optical path between an image forming optical system and a sensor and varying the thickness of the diffraction grating in response to the incident picture angle. CONSTITUTION:A diffraction grating 2 comprising stepwise thickness parts d1 and d2 periodically in the direction Y is formed on a diffraction grating base 1a in a blazed diffraction grating 1. Then the thickness parts d1 and d2 are varied in the direction x as shown in the x-z cross section in figure. Then, the picture information light is led to a 3-color decomposition linear blazed diffraction grating 1 via an image forming optical system 9. Then the information light is separated into 3 colors of luminous flux in the so-called color reading and the image is formed on the sensor arrays 4-6 on the monolithic 3 line sensor 3. Since the grating thickness of the linear blazed diffraction grating is adjusted in response to the picture angle of an incident luminous flux in this way, no deviation of the information light having a picture angle in the wavelength distribution, that is, no color slurring takes place.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an apparatus for reading color images using a solid-state image pickup device, and in particular, a device for reading a color image using a solid-state image pickup device, in particular, a device for reading a color image from a subject through a one-dimensional blazed diffraction grating whose grating thickness is appropriately changed. The present invention relates to a color image reading device that guides light to a plurality of solid-state image sensor arrays.

[Prior Art] Conventionally, a device as shown in FIG. 9 has been known as a device that scans a subject such as a document in a line in the sub-scanning direction and reads the image in color with an array of solid-state image sensors (CCD sensors, etc.). . In the figure, information on a part of the document surface 18 illuminated by light from an illumination light source (not shown) is transmitted to a three-piece (3P) prism 20 via an imaging optical system 19.
After being separated into colors, three 1-line CCD sensors 21
．． 22 and 23 are imaged and read.

[Problem M to be solved by the invention] However, in this conventional example, three independent sensors are required, and the 3P prism 20 usually requires high precision in manufacturing, so the cost is high ( (Furthermore, it required three independent adjustments between the condensed light beam and each sensor 21, 22, and 23, making it difficult to manufacture.)

Therefore, it is possible to fabricate a sensor array in three lines parallel to each other over a finite distance on the same substrate, and form a monolithic three-line sensor with three lines on one element. This three-line sensor 24 is shown in FIG. 10. 0 shown in
In the figure, the distance Z1 between the three lines 25, 26, and 27. Due to various manufacturing conditions, Za is, for example, about 0.1 to 0.2 mm, and the widths a and b of each single element 28 are, for example, 7 μm×7
μm.

It is approximately 10 μm×10 μm.

FIG. 11 shows a known configuration of a color image reading device using such a monolithic three-line sensor as a light receiving element. In the figure, when reading the information on the document surface 18 by line scanning in the sub-scanning direction, light from the document surface 18 is passed through an imaging optical system 19 to which a selective transmission film having dichroism is added. Beam splitter for color separation-30, 31
After being decomposed and separated into 3 light beams of 3 colors, the monolithic 3
Corresponding sensor array 343 on line sensor 32
The light is focused at 5.36.

However, as shown in FIG.
, 31 is X, the distance between the arrays on the sensor 32 is 212x, and as mentioned above, the distance between the arrays (
212 It's not easy.

Further, color image reading devices having other configurations using such a monolithic three-line sensor are also known. In this configuration, an optical system using a blazed diffraction grating is provided as a color separation means that can be used for the above-mentioned monolithic three-line sensor.

However, in this configuration, only the light from one point on the subject is considered, and no consideration is given to so-called view angle characteristics due to the existence of a finite reading width on the subject plane in the main scanning direction.

Therefore, an object of the present invention is to solve the above problems (
An object of the present invention is to provide a color image reading device using a one-dimensional blazed diffraction grating having a special configuration.

[Summary of the Invention] In the color reading device according to the present invention, an angled light beam from an object is separated into a plurality of light beams each having different wavelength ranges through an imaging optical system and a one-dimensional blazed diffraction grating, The grating thickness of the one-dimensional blazed diffraction grating is configured to be imaged onto the corresponding sensor array on the sensor, and the grating thickness of the one-dimensional blazed diffraction grating is changed corresponding to the angle of view of the chief ray of light incident on the grating, thereby changing the color. The wavelength ranges of the three luminous fluxes to be resolved are substantially equal over the entire angle of view.

[Example] FIGS. 1 and 2 show a one-dimensional blazed diffraction grating 1 used in an embodiment of the present invention. This type of blazed diffraction grating is described in Applied Optics magazine,
Volume 17, No. 15, pages 2273-2279 (19
(August 1, 1978 issue).

The blazed diffraction grating 1 has a diffraction grating substrate la, I:
The diffraction grating 2 is periodically stepped in the direction (thickness d, and thickness d
(consisting of two parts) is formed. Then, the thickness d9 of the diffraction grating 2. d2 changes along the X direction, as shown in the xz section of FIGS. 1 and 2.

FIG. 3 shows a color reading optical system including the one-dimensional blazed diffraction grating 1. In the figure, image information on the document surface 8 is transmitted between the document surface 8 and the imaging optical system 9. The image information light is line-scanned in the sub-scanning direction by a mirror (not shown) or the like disposed in the image information system 9, and then guided to the one-dimensional blazed diffraction grating 1 for three-color separation via the imaging optical system 9. Here, the information light is the three colors (
For example, after being separated into RG and B light beams, images are formed on the respective sensor arrays 4, 5 and 6 on the monolithic 3-line sensor 3. The sensor surface of the three-line sensor 3 is arranged parallel to the line scanning direction (sub-scanning direction).

Now, in order to better understand the principle of the present invention, we will explain in detail what problems occur in the configuration of FIG. 3 when a one-dimensional blazed diffraction grating is a normal one.

In configuring an actual reading device, as shown in FIG. 3(a), a finite reading width W is required, and therefore an angle of view θ exists with respect to the imaging optical system 9. Therefore, in the main scanning cross-section, the light beam from a point off the optical axis of the imaging optical system 9 enters the imaging optical system 9 at an angle of θ, and its exit emerges as shown in FIG. In a normal optical system, the light exits from the pupil 10 at an angle of θ'.

When the principal ray of a luminous flux having such an angle of view is incident at an angle of θ' into a blazed diffraction grating 1' having a constant grating thickness d1 and dyo as shown in Figs. 5 and 6, , the actual optical path length within the grating 2' is different from that when the chief ray is perpendicularly incident 1
A problem arises in that the blaze wavelengths of the two are shifted.

This is because the following relationship exists between the blaze wavelength and the thickness d.

12λ (i=1.2) Here, Φ is the phase difference (rad), and n2 is the refractive index of the grating medium for light at the wavelength ahead.

That is, the wavelength range for obtaining the desired phase difference Φ for the diffracted light of a predetermined order is such that if the grating thickness d is constant as shown in FIG. This means that when reading image information on an l line with a width W, the wavelength distribution of the wavelength range of light captured by each sensor array shifts from on-axis to off-axis. This results in color misalignment.

For example, in the case of a blazed diffraction grating 1'' consisting of a two-stage stepped structure shown in FIGS. 5 and 6, dl = 3100n
m, d* = 6200 nm, n1 = 1.5, θ'
= On the axis of o, the first-order diffraction beam beam wavelength is 516.7n
m (Φ6=6π, Φ2=12π), but θ'
Off-axis at =20°, this wavelength becomes 4923 nm, which is a shift of about 24 nm.

Therefore, we will focus on the fact that, as can be seen from the above equation for the phase difference Φ, if the thickness dl of the diffraction grating is changed in accordance with the angle of view θ', the blaze wavelength can be made constant over the entire angle of view.

This is the idea of the present invention. For example, as mentioned above (, d
l = 3100 nm, d* = 6200 nm.

If nλ=1.5, Φ1=6π, Φ8 at θ'=o
= 12π, the blaze wavelength was 516.7 nm, but if d and d□ were determined so that the blaze wavelength would be this value even when θ' = 20'', dr = 3253,
7 nm.

da = 6507.4 nm.

Therefore, the grating thickness d+-di at the position where the principal ray of one view angle θ'=20'' passes through the diffraction grating 1 is set to the thickness as described above (so that the blaze wavelength is kept constant on-axis and off-axis). One-dimensional blazed diffraction grating 1 shown in Figures 1 and 2
In this way, the lattice thicknesses d+ and da change from on-axis to off-axis (to become thicker).

Next, consider another problem caused by the angle of view θ□θ′.

As shown in FIG. 4, the optical path length from the blazed diffraction grating 1 to the three-line sensor 3 is 10 for on-axis rays, but for off-axis rays at an incident angle θ, it exits from the exit pupil 10 at an exit angle θ'. Therefore, the distance is 1 l= l o /
COSθ′〉1° roar.

On the other hand, the diffraction angle α in the blazed diffraction grating l is the fifth
7, Psinα: E (P: lattice pitch, N: wavelength) From the above, the separation distance Z between the color separated lights on the sensor element surface shown in FIG. 143(b) and FIG.
is Z=to tanα on the axis, and Z=L+ off the axis.
tana=lo tana/cos θ' and 5The two do not match.In this way, the separation distance on the sensor element surface is different between on-axis and off-axis, and in a 3-line sensor where the sensor array spacing is constant, The three-color light beams will not be correctly imaged onto the corresponding sensor array 45.6 over the entire field of view.

For example, P=60um, N=540nm (green)
When the angle of view θ = 20 deg and 1o = 20 mm, the deviation of the separation distance between on-axis and off-axis is about 11.5 μm, and the above-mentioned element size is 7 μm × 7 μm% l
When compared with oum×10 μm, the center of image formation of the light beam is far away from the center of the sensor element.

The theory is that this deviation can be reduced by reducing the angle of view θ, but in order to make the device more compact, the angle of view θ cannot be reduced unnecessarily.

Therefore, for example, the lattice pitch P at Psinα=E
By changing on-axis and off-axis, the diffraction angle α of the first-order diffracted light is
3 on sensor array 4, 5, 6 of sensor 3.
To ensure that colored light beams form images correctly over the entire angle of view.

As mentioned above, the grating pitch P on the axis is P=60gm, λ
=540nm% io =20mm, θzakiθ
The grating pitch at the position where the chief ray of the luminous flux of '=20 deg is incident on the diffraction grating is P=63.85 am.

However, the one-dimensional blazed diffraction grating 1 of this embodiment has a grating thickness of d1 depending on the angle of view. Since dx is changed, if the grating pitch is also changed, the grating shape becomes two-dimensional and plural, making manufacturing considerably difficult.

Therefore, as shown in FIG.
To correct the deviation of the image formation position on the above axis, the 3-line sensor 3 is curved and the optical path length between the one-dimensional blazed diffraction grating l and the sensor 3 is kept constant over the entire angle of view. It is also possible to eliminate the deviation of the imaging position outside. In this way, information light having a wide angle of view can be well separated, separated, and imaged using the blazed diffraction grating 1, which has a relatively simple configuration, so it is possible to improve the productivity of the device and reduce costs. .

[Effects of the Invention] As explained above, in the present invention, since the grating thickness of the one-dimensional blazed diffraction grating is adjusted in accordance with the angle of view of the incident light beam, information light having an angle of view also has a wavelength distribution. A compact and inexpensive color image reading device is obtained by successfully color-separating, separating, and focusing images on corresponding sensor arrays without any misalignment or color misregistration.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a one-dimensional blazed diffraction grating used in one embodiment of the present invention, and FIGS. 3(a) and 3(b) are main scanning cross-sectional views of the reading optical system of this embodiment, 4 is a diagram explaining the optical path length between the blazed diffraction grating and one 3-line sensor, FIGS. 5 and 6 are diagrams explaining the function of the one-dimensional blazed diffraction grating, and FIG. 7 is a sub-scanning sectional view. A diagram explaining the separation distance by a blazed diffraction grating, FIG. 8 is a diagram showing a modification of the present invention, FIG. 9 is a diagram showing a conventional color image reading device, and FIG. 10 is a diagram showing a conventional monolithic 3-line sensor. 11 are diagrams showing other conventional color image reading devices.1...1-dimensional blazed diffraction grating, 2...Grating, 3...3 line sensor 4% 5.6...Sensor array 8...
Original, 9... Imaging optical system

Claims (1)

[Claims] A one-dimensional sensor array includes a plurality of line sensors arranged perpendicularly to the array direction on the same substrate with a plurality of lines separated by a finite distance, and an image of a subject onto the sensor. A color image reading device having an imaging optical system that forms an image, which separates light from a subject into a plurality of colors in a direction perpendicular to the array direction in an optical path between the imaging optical system and the sensor. A one-dimensional blazed diffraction grating is also arranged to guide this color-separated light to each corresponding sensor array,
Since the grating thickness of the blazed diffraction grating is changed in accordance with the angle of view at which the principal ray of light from the object is incident on the grating, an image without color shift of the light from the entire area of the object with the same blaze wavelength can be obtained. A color image reading device characterized in that an image is formed on each corresponding sensor array. 2. The color image reading device according to claim 1, wherein the grating pitch of the blazed diffraction grating is changed in accordance with the angle of view at which the principal ray of light from the object is incident on the grating. 3. The color image reading device according to claim 1, wherein the plural line sensor is curved so that the optical path length between the sensor and the blazed diffraction grating is equal over the entire angle of view.