Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-06-11
2003-12-09
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S254000, C359S320000, C396S457000
Reexamination Certificate
active
06661555
ABSTRACT:
This application is based on application No. JP 2001-177813 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved light shutter device. More particularly, the present invention relates to a light shutter device including plural electrodes in an opposite structure provided on a substrate made of a material having an electro-optical effect and light modulation regions each sandwiched between electrodes.
2. Description of the Related Art
Heretofore, there have been used light shutter devices, each having plural light modulation regions provided on a substrate made of PLZT or LiNbO
3
, which are materials having an electro-optical effect, each including the substrates arranged in array, and on/off controlling light, in an external light modulator for use in large capacity optical communication, an optical path change-over switch in an optical time domain reflectometer or an optical signal generator for an optical printer.
To be detailed, as shown in
FIG. 5
, a voltage is applied between electrodes
32
and
33
of one pair provided on a PLZT substrate (a light shutter chip)
30
to thereby generate an electric field, to produce a birefringence in PLZT, to convert light incident on a light shutter element (a light modulation region)
31
, the light being transmitted through a polarizer
41
installed at the previous stage thereof, to 90 degree polarized light and to finally cause outgoing light to be transmitted through an analyzer
42
. On the other hand, in a case where no electric field is generated, light transmitted through the polarizer
41
is transmitted through the light shutter element
31
without being polarized, but intercepted by the analyzer
42
.
In such a light shutter element
31
, the maximum quantity of transmitted light can be obtained when incident light is converted to 90 degree polarized light, and an applied voltage at this time is called a half wavelength voltage.
In
FIG. 6
, there is shown an electrode pattern formed on a chip
30
adopted in a prior art light shutter device. On the chip
30
, there are formed a common electrode
32
grounded and individual electrodes
33
opposite it and light shutter elements
31
are formed between the electrodes
32
and
33
. The individual electrodes
33
are connected to bonding pads
33
b
through respective lead electrodes
33
a
, while the common electrode
32
is also connected to bonding pads
32
b
through respective lead electrodes
32
a.
In a case where this kind of a light shutter device is used in forming an image, a requirement arises for thousands of light shutter elements
31
in exposure across a length of the order of 30 cm in the main scan direction indicated by an arrow mark X. This requirement is difficult to realize with one chip
30
but instead, an array architecture is adopted in which chips
30
on each of which hundreds of elements
31
are formed are juxtaposed in parallel with each other along the arrow mark X direction. Moreover, the light shutter elements
31
are arranged in a double rowed, zigzag pattern and on/off controlled at prescribed timings in each row, thereby forming an image of one line on an exposed surface moving in the sub-scan direction indicated by an arrow mark Y.
Attention being focused on a group of light shutter elements
31
a,
31
b,
31
c
and
31
d,
variations in half wavelength voltage arise among the elements because of differences in position of the elements and shapes of electrodes around an element on a chip. That is, since the elements
31
a
and
31
d
are located at an end of a chip
30
, electric fields applied by the electrodes
32
and
33
tend to be confined, thereby strongly acting on the elements
31
a
and
31
d
as compared with electric fields of other elements
31
b
and
31
c
and so on. On the other hand, in comparison between the elements
31
b
and
31
c,
an electric field of an element is different according to whether a lead electrode
32
a
is located on the acute angle side or the obtuse angle side of an individual electrode
33
. A lead electrode
32
a
adjacent to the element
31
c
is located on the acute angle side of an individual electrode
33
; therefore, an electric field applied between the electrodes
32
and
33
leaks into the lead electrode
32
a
more than in the case of the element
31
b
located on the obtuse angle side of an individual electrode
33
, thereby weakening the electric field in the element
31
c
as compared with an electric field in the elements
31
b.
An influence of a lead electrode
32
a
is equally exerted on the elements
31
a
and
31
b.
In
FIG. 7
, there are shown relationships of a quantity of transmitted light versus an applied voltage of the respective light shutter elements
31
a,
31
b,
31
c
and
31
d.
Since each of the elements is driven by a prescribed voltage, variations in half wavelength voltage, as shown in the figure, result in differences in transmitted quantity, leading to variations in light quantity. For example, if a light shutter device is employed in recording of an image, uneven transmitted quantity is observed as unevenness in image density, resulting in degradation of an image quality.
OBJECTS AND SUMMARY
The present invention has been made in light of such circumstances and it is an object of the present invention to provide an improved light shutter device. That is, the object is to provide an improved light shutter including plural electrodes in an opposite structure provided on a substrate made of a material having an electro-optical effect and light modulation regions each sandwiched between electrodes. More particularly, it is an object of the present invention to provide a light shutter device capable of suppressing variations in quantity of transmitted light among light modulation regions regardless of differences in position of a light modulator element and pattern of electrodes around of a light modulator element on a substrate.
In order to achieve the object and other objects, a light shutter in an aspect of the present invention includes: a substrate made of a material having an electro-optical effect; and plural electrodes in an opposite structure provided on the substrate, wherein a region between electrodes of each pair on the substrate becomes a light modulation region and thereby the region serves as a light shutter, and a spacing between and/or a shape of electrodes in an opposite structure is made different according to an environment in which the light modulation region is placed, thereby almost equalizing half wavelength voltages of light modulation regions.
With such a construction adopted, variations in quantity of transmitted light among light modulation regions can be suppressed.
In another aspect, the environment is a position on the substrate of the light modulation region.
In still another aspect, the environment is a pattern of electrodes located around of the light modulation region.
In yet another aspect, the spacing between electrodes of a pair forming a light modulation region is narrower in an environment thereof having an electric field weaker in action, while being wider in an environment thereof having an electric field stronger in action.
In a further aspect, a wider spacing is set between electrodes of a pair forming a light modulation region located at an end of the substrate.
In a still further aspect, that the shape of electrodes is made different means that an areas of an electrode is made different.
In a yet further aspect, an electrode area of an electrode forming a light modulation region located at an end of the substrate is narrowed.
In another aspect, the light modulation regions are arranged zigzagging in 4 rows and a spacing between electrodes of a pair forming a light modulation region in the inner side of the 4 rows is narrower than in the outer side thereof.
A light shutter device instill another aspect includes a shielding layer having a window defining an aperture through which light is transm
Doi Isao
Hiromoto Yasuyuki
Masuda Tomohiko
Matsubara Ken
Epps Georgia
Hasan M.
McDermott & Will & Emery
Minolta Co. , Ltd.
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