Optical waveguides – Optical fiber bundle – Imaging
Reexamination Certificate
1999-09-22
2002-04-16
Mack, Ricky (Department: 2873)
Optical waveguides
Optical fiber bundle
Imaging
C385S120000
Reexamination Certificate
active
06374024
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image sensor for use in hard-copy image reading devices such as facsimiles, scanners and so on and relates to a method of manufacturing the same image sensor.
Recently, there has been an increasing demand for further improved and miniaturized one-dimensional image sensors for converting image information into electric signals in conjunction with an increasing demand for image-reading apparatuses such as facsimiles and image scanners. Among the existing one-dimensional image sensors, there are two predominant types, one of which is a contract type optical image sensor using mirror and the other is a contact image sensor using a rod-lens array. A contract type image sensor using a micro-lens array and an optical waveguide array has been last developed.
FIG. 1
is illustrative of a system of a conventional contract type image sensor. Light from an LED array
1
striking a surface of an original
2
is reflected to a mirror
22
wherefrom it is further reflected several times between mirrors
22
. After this, the reflected light passes a lens
23
and forms an image on a light-receiving element array
5
. Thus, the image information can be obtained.
FIG. 2
is illustrative of a conventional contact type image sensor using a typical rod-lens array
24
. Light from an LED array
1
striking a surface of an original
2
is reflected and fall into a rod-lens array
24
through which it passes and forms an image on a light-receiving element array
5
. This device can be miniaturized owing to its simple construction.
FIG. 3
is illustrative of a contract type image sensor using a conventional micro-lens array
3
and optical waveguide array
25
. Light from an LED array striking a surface of an original
2
is reflected to a micro-lens array
3
including the specified number of equally spaced micro-lenses corresponding to respective pixels of a specified image format. The converged light passes the optical waveguide array
25
and forms an image on a light-receiving sensor array
5
. The device can be thus miniaturized. Furthermore, it is possible to precisely induce rays of light from the micro-lens array into the optical waveguide array
25
by matching numerical aperture NA of the micro-lens array
3
with that of the optical waveguide array
25
. This is disclosed in Japanese Laid-Open Patent Publication No. 9-37038.
The contract type image sensor of
FIG. 1
, however, necessarily contracts a whole image information to {fraction (1/10)} in size through a lens. Therefore, the sensor must have an elongated conjugate length. For example, a distance from an original document of B
4
in format size to a light-receiving element may be about 330 mm. An optical path is usually folded by mirrors
22
. However, the conjugate length of the device is above 70 mm. This makes it difficult to further reduce the size of the device.
The contact type image sensor using a rod-lens array
24
as shown in
FIG. 2
can have a considerably reduced distance between an original document and a light-receiving element by using a short-focusing lens since whole image information is formed in the same scale. The latest model has the document-to-element distance of about 10 mm. However, the device of this type has a very shallow depth of field of, e.g., 0.5 mm at which its MTF can be maintained at a level higher than 40% for the specification of 200 dots per inch. Application of a sensor having a shallow depth of field in a handy scanner or a flat head scanner may arise a problem that an uneven surface portion of a double spread page of a book or pasted slips cannot be read. To avoid this, a rod-lens having a small numeral aperture (NA) and a deep focal depth must be used. However, the use of such a rod-lens may elongate the conjugate length of the device. For example, a rod-lens array
24
having a depth of field of about 3 mm has a conjugate length of about 50 mm resulting in increasing the size of the device. In addition, the rod-lens array having a deep depth of field is expensive.
The compact type sensor may have a depth of field of 6 mm or more on the same conditions.
As described above, both types of sensors involve such a common problem that miniaturization of the device is always accompanied by shallowing a depth of field of the lens array while the use of the lens array having a deep depth of field necessarily increase the size of the device. In other words, these two factors are tradeoffs to each other.
There has been developed an image sensor (
FIG. 3
) having a micro-lens array and an optical waveguide array, which has a 20 mm distance between an original document (B
4
in size) and a light-receiving element. As disclosed in Japanese Laid-Open Patent Publication No. 9-37038, this image sensor is constructed in such a way that the micro-lens array
3
and the optical waveguide array
25
have the same numeric aperture and the image forming size of the former matches the core size of the latter. This feature can considerably reduce the crosstalk from neighboring elements of micro-lens array
3
and neighboring pixels. However, this arrangement may cause another problem that an image being in out-of-focus or as contacted in size due to a floating area of the original document may increase crosstalk and cause a considerable change in quantity of light due to the out-of-focus position of the image. In addition, this device causes an image information from the original to be contracted through the curved optical waveguide array and, therefore, may be necessarily increased in its general size as the number of image pixels increases. The device is more difficult to be miniaturized than the contact type sensor using a rod-lens array. It is also noted that elongation of the optical waveguide array is accompanied by increasing loss of light therein.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image sensor that includes an array of a specified pixel-corresponding quantity of micro-lenses arranged for forming an image of light reflected from an original document, an array of the specified pixel-corresponding quantity of optical fibers or waveguides arranged for transmitting an image formed by the micro-lens array as respective optical signals of pixels, and an array of light-receiving elements for receiving optical signals from the optical fiber or waveguide array and converting the signals into electric signals, wherein the optical fiber array or optical waveguide array has cores whose end-faces have each a size smaller than a size of an image formed by corresponding micro-lens and are located on the micro-lens-side from the image forming plane when the original document is placed at a given position. The construction of this image sensor is such that an image information of the original is transmitted pixel by pixel through pairs of micro-lens with an optical fiber or waveguide to respective light-receiving elements. This may reduce crosstalk due to floating of the original from the base level and contraction of its image through the micro-lens array if the image is formed in size larger than the core of the optical fiber or waveguide when the original document is placed at a given position. The image formed thus being in out of focus can be read at its center portion by the optic fiber array whose core-end-faces are located on the micro-lens side from the image-forming plane. This means that floating of the original may approach the image-forming plane to the core-end-faces of the optical fiber array, thereby the image becomes improved with a reduced variation of light quantity. As the result of the above-described effects, an image finally obtained through the light-receiving element array can have a deep depth of field.
Another object of the present invention is to provide an image sensor that includes an array of a specified pixel-corresponding quantity of micro-lenses arranged for forming an image of light reflected from an original document, an array of the specified pixel-corresponding quantit
Mack Ricky
Sharp Kabushiki Kaisha
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