JPS627024A - Driving method for optical switch element - Google Patents

Abstract

PURPOSE:To provide a high speed optical switch element by applyinga voltage higher than a voltage applied to a selective scanning electrode to a selective electrode, and applying a voltage lower than the voltage of the selective scanning electrode to a non-selective signal electrode. CONSTITUTION:Rectifying elements 12 are arranged to interrupt the movement of electric charge on the scanning electrode 10 to constitute the scanning electrode 10. When switches 14, 14' are closed to select the electrode 10, electric potential V0 obtianed by dividing a voltage 2V0 by two resistors 11, 11' having the same capacity is generated in points C, C', ... and optical switches e1-en using ferrodielectric liquid crystal 13 are turned on and off in accordance with the potential of signal electrodes S1-Sn. When the switches 14, 14' are opened, the charge of the points C, C', ... on the electrode 10 can not be moved because of the existence of the elements 12 even if the potential of the electrodes S1-Sn is changed, so that the optical switches e1-en maintain the preceding states for a fixed period. The states of the optical switches can be maintained for a fixed period also by using high resistance.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a time-division driving method for optical switching elements.

In particular, the present invention relates to a method for driving an optical switch element suitable for printer heads and displays using ferroelectric liquid crystals.

[Background of the invention]

Ferroelectric liquid crystals, unlike conventional nematic liquid crystals, respond to DC voltage and have an extremely fast response speed of 1 ms or less. Optical switches that take advantage of this high-speed response are expected to be applied to high-speed printer heads and displays. At this time, the static drive method requires the same number of drivers as the number of optical switches, so in order to reduce the number of drivers, we proposed arranging the optical switches in a matrix with multiple scanning electrodes and signal electrodes and performing grid-split driving. is being done. One of them is the invention described in Japanese Patent Application Laid-Open No. 59-129837. This is characterized by reversing the polarity of the voltage applied to the optical switch at the intersection of the selected scanning electrode and the selected signal electrode, and the polarity of the voltage applied to the other optical switches.

However, in this driving method, all the optical switches on the unselected scanning electrodes are in a state of blocking light, and only the optical switches on the selected scanning electrodes operate effectively. Therefore, when this driving method is used for an optical printer head.

JP-A-59-193427 does not take into consideration the fact that as the number of time divisions increases, the opening time of each optical switch becomes shorter, and the effective irradiation energy becomes smaller, resulting in a slower printing speed. The method described in the publication proposes a time-division driving method for ferroelectric liquid crystals. This method utilizes the threshold of the driving voltage of the ferroelectric liquid crystal, but in order to develop the threshold, the thickness of the liquid crystal layer must be 1 μm.
It needs to be controlled back and forth and is not considered in terms of manufacturing technology.

[Purpose of the invention]

An object of the present invention is to provide an all-optical switch that effectively functions without causing crosstalk even for materials whose operating voltage does not have a clear threshold in a method for driving an optical switch element using a ferroelectric material. The object of the present invention is to provide a time-division driving method that allows

[Summary of the invention]

In general, a ferroelectric liquid crystal has two states depending on the polarity of the applied voltage, so by combining it with a polarizing plate, the blocking and transmission of light can be controlled by the polarity of the applied voltage. When optical switches using ferroelectric liquid crystals are arranged in a matrix and driven in a time-division manner, the optical switches on selected scanning electrodes are given information based on the polarity of the applied voltage, and are shaped to transmit light. After the MC becomes an ON state (hereinafter referred to as an ON state) or a cut-off state (hereinafter referred to as an OFF state), the state must be maintained for one frame in which the scan electrode is not selected.

As shown in FIG. 2, it has a structure in which a ferroelectric liquid crystal 20 is sandwiched between a pair of transparent electrodes 21.21', a glass substrate 22.22', and mutually orthogonal polarizing plates 23.23'. Transmits or blocks light from the light source 24. In the case of one isolated optical switch, as shown in the equivalent circuit of FIG. 3(a), the switch 31.31
Even if the optical switch 31, 31' is turned on or off by closing the switch 31, 31' and applying a DC voltage V to the ferroelectric liquid crystal 30, and then opening the switch 31, 31', the optical switch continues to maintain the previous state for a while. This property is shown in Figure 3(b)
There is no change even if a voltage V' is applied to one electrode as shown in FIG. This is because the resistance R inside is very large, and therefore the time constant CR, which is the product of the capacitance C of the liquid crystal, is sufficiently large.
In equivalent circuits other than FIG. 3, R is assumed to be infinite and is not shown.) This time constant corresponds to the state holding time.

One frame period T (<several ni) required when time-divisionally driving the liquid crystal in a printer head or display
It is clear that this characteristic can be used to time-divisionally drive a large number of optical switches.

During time-division driving, even if a scan electrode that does not select one is left open, all the optical switches on that scan electrode will have all electrodes on one side connected, and therefore, as shown in FIG.
), a plurality of signal electrodes S1. Optical switch all with ferroelectric liquid crystal sandwiched between S, S, and scanning electrode C
ame, the scanning electrode C has a potential v, and the signal electrode S
8 is given a potential of 2Vo, St is given a potential of 0, and the optical switch e
Consider the case where 1 is turned on and θ1 is turned off.

The charge distribution on each electrode is as shown in FIG. 4(a). Afterwards, when the scanning electrode C is opened as shown in FIG. 4(b), the signal electrode S1 has a potential of 0. If a potential of 2 V is applied to S3, the potential of the signal electrodes S, , S for the optical switch "tt e8" changes as shown in Fig. 4(b).
Charges move through the scanning electrode C as shown by the arrow. As a result, the charges on the signal electrodes S, , S, also change, resulting in a charge distribution as shown in FIG. 3(c). From this, it can be seen that the state of the optical switch 619a changes from ON to OFF and from OFF to ON, respectively.

Therefore, in order to prevent charge movement on the scanning electrode, which is the cause of the state change of the optical switch, a rectifying element 12 is arranged as shown in FIG. 1(a) to form the scanning electrode 10. Then, when selecting this scanning electrode (hereinafter referred to as scanning electrode AA'), by closing the switch 14.14', a voltage of 2V is applied to the points C9c', c', and c"'.
, is divided by two resistors 11 and 11' of the same size to generate a potential v6, and an optical switch e□ using a ferroelectric liquid crystal 13 is generated.

"ml e, e, are signal electrodes Si; 0th order switch 1 which turns on or off depending on the potential of
4. When 14' is open, the signal electrodes S,, S
Even if the potential of , c, c', c' on the scanning electrode is changed,
, c"' cannot move due to the rectifying element 12, and the optical switches e□, e1゜e3e, maintain their previous states for a certain period of time. This maintenance is necessary for printers and displays. Since the time is from several mg to several tens of ms, the rectifier used here does not need to be of high performance.It should be noted that potentials are applied to points C, C', C', and C"' by scanning electrodes AA'
Let us write it as the potential of .

Further, by using a high resistance, the speed of charge movement through the scanning electrode can be sufficiently slowed down, and the state of the optical switch can be maintained for a certain period of time. That is, as shown in FIG. 1(b), the optical switch e-work.

If the scanning electrode 15 of eseese is configured using a high resistance 16, by appropriately selecting the magnitude of this high resistance, the speed of the charges moving on the scanning electrode when the switch 17 is opened can be sufficiently slowed down. The maintenance time required in printers and displays, optical switches at
e e'aee.

It is possible to maintain this state.

[Embodiments of the invention]

As an example, we will explain an optical switch element for a printer head that has two scanning electrodes and uses ferroelectric liquid crystal.
Figures 5(a) and 5(b) show the structure of the scanning electrode used in this example.
), that is, a p shadow region 51.) is formed on the substrate 50 by vacuum evaporating silicon and then implanting boron ions.
By ion-implanting arsenic into 51', an n-shaded region 52°52' is formed, and a diode with a PN junction is formed with the structure shown in FIG. The structure includes an alignment film 54 and an alignment film 54. This scanning electrode substrate and a plurality of signal electrodes S1. s,
, S, to form an electrode as shown in FIG.
”it a4am, -t.

e2. In this embodiment, two scanning electrodes A, A1' and A, A,' are alternately selected, new information is given to the optical switch on the selected scanning electrode to turn it ON or OFF, and then the optical switch is turned ON or OFF. While the scan electrode is not selected and is electrically open, the optical switch is held in that state, and the optical switch on the scan electrode that is not selected is also allowed to function effectively.0 Potential of the selected scan electrode Let vo be 1
In order to drive the ferroelectric liquid crystal, the above-mentioned va is applied to the signal electrode.
It is necessary to apply a larger potential or a smaller 0 potential. Here, as an example, a potential of 2vll is applied to the selected signal electrode, and the optical switch located at the intersection with the selected scanning electrode is turned on.
In the N state, a potential of 0 is applied to unselected signal electrodes, and the optical switch located at the intersection with the selected scan electrode is turned off. An example of a circuit for controlling the potential of the scanning electrode to vo and an open state is shown in FIG. 7, where a resistor 70.
70' and 71°71' are resistors 11 and 11' in Figure 1.
Corresponds to 2vI.

Since they are intended to divide the pressure into 1/2, they must have the same size.

Based on the above configuration, v in FIG.

In FIG. 6, the potentials of scanning electrodes A, A,', A, A,', signal electrode S1. S, potential of optical switch “it”
! ! An example of a time chart of the voltage applied to the at eII e4 and the intensity of transmitted light B, L, B, . . . of the optical switch 611 aa is shown in FIG. 8. This time chart will be explained below.

At time 0-tl, by setting the potential of vl to 2V, scan electrodes A, A, ' are selected and given a potential v0, and unselected scan electrodes A, A, ' are opened. At the same time, the potential of the signal electrode S1 is set to 2V, and the signal electrode S
By setting the potential of 3 to O, the optical switch aie 6
Voltages V a and -V o are applied to =, respectively, to turn them ON and OFF, respectively.

The charge distribution state of 619 aa at this time is equal to "it 8." in FIG. 4(a).

At time 1L-1, by setting the potential of vi to 0, scan electrode A2' is selected and given potential v0, while scan electrode AiA,' is not selected and is left open. At this time, the optical switch EAT 64 is turned ON or OFF according to the potential applied to the signal electrodes S1 and S2.
However, the optical switch "it as" maintains the ON and OFF states, respectively, regardless of the potential of the signal electrode. This is because charge movement on the scanning electrodes as shown in FIG. 2(b) is blocked.

At subsequent times t3 to t, scanning electrodes A□A,' are selected in the same way as at times 0 to t, and signal electrodes S□
, S3, the optical switch ate_as changes to a new state. At this time, the optical switch aspe4 is activated at time t.
The state is maintained in the same manner as e1 to θ in 1 to t3.

Therefore, according to the driving method according to the present invention, even if the number of scanning electrodes in this embodiment is further increased, all optical switches can function effectively without causing crosstalk.

Furthermore, since the rectifying element used in this embodiment is used simply to prevent charge movement, it does not need to be a high-performance rectifying element, and can be formed by an inexpensive method, resulting in low cost.

Furthermore, in this embodiment, a diode is used to prevent charge movement on the scanning electrode side, but the diode shown in FIG. A similar effect can be obtained by arranging the high resistance 16 as shown.

〔Effect of the invention〕

As is clear from the above description, according to one aspect of the present invention, it is possible to time-divisionally drive an optical switch element using a ferroelectric material that does not exhibit a clear operating threshold voltage. The thickness of the ferroelectric material of the switch element is such that it can be manufactured economically using conventional technology, and the number of drivers can be reduced by one-time division driving. Since advanced performance is not required, a low-cost optical switch element can be provided.

Furthermore, in order to make the all-optical switch function effectively, it is possible to provide an optical switch element that takes advantage of the high-speed response characteristic of ferroelectric materials.

[Brief explanation of drawings]

Figure 1 (a) and (b) are equivalent circuit diagrams of scanning electrodes when the method for driving an optical switch element according to the present invention is implemented, and Figure 2 is a diagram showing the operating principle of an optical switch using ferroelectric liquid crystal. , Figure 3 is an equivalent circuit diagram explaining the state maintenance of an optical switch element using ferroelectric liquid crystal, Figure 4 is a diagram showing the charge distribution of the optical switch that changes depending on the potential of the scanning electrode, and Figure 5 is the diagram of this book. FIG. 6 is a diagram showing an example of the scanning electrode configuration when the method for driving an optical switch element according to the invention is implemented; FIG. 6 is a diagram showing an example of the electrode configuration when the method for driving an optical switch element according to the invention is implemented. , FIG. 7 is a diagram showing an embodiment of a circuit for controlling the potential of the scanning electrode when the method for driving an optical switch element according to the present invention is implemented, and FIG. FIG. 2 is a diagram showing potential and transmitted light intensity. 10・Scanning electrode, 11.11′・Resistors with equal size, 12・Rectifying element, 13・Ferroelectric liquid crystal, 14.1
4'・Switch, 15・Scanning electrode, 16・High resistance, 17・Switch, 20・Ferroelectric liquid crystal,
21.21'・Transparent electrode, 22.22'・Glass substrate,
23.23'・Polarizing plates perpendicular to each other, 24・Light source, 3
0・Equivalent circuit of ferroelectric liquid crystal, 31.31'・Switch, 50・Substrate, 51°51'・
A p-type semiconductor made of silicon doped with boron. 52.52'・N-type semiconductor in which silicon is doped with arsenic, 53.53'・Transparent electrode, 54.Alignment film, 70.70
'・Resistances that are equal in size to each other, 71°71'・Resistors that are equal in size to each other.

Claims (1)

[Scope of Claims] 1. In a method for driving an optical switch element in which an optical switch is formed in a matrix by sandwiching a ferroelectric material between scanning electrodes and a plurality of signal electrodes that intersect with each other, the plurality of scanning electrodes A voltage is applied only to a selected one of the plurality of signal electrodes, the other unselected scanning electrodes are electrically open or grounded through a high resistance, and the selected one of the plurality of signal electrodes is A method for driving an optical switching element, characterized in that a voltage higher than the voltage applied to a selected scan electrode is applied, and a voltage lower than the voltage applied to the selected scan electrode is applied to other unselected signal electrodes. 2. Each scanning electrode consists of the same number of independent transparent electrode parts as the signal electrodes, and rectifying elements are provided on both sides so as to sandwich the transparent electrode parts, so that when the scanning electrode is not selected, the selection 2. The method of driving an optical switch element according to claim 1, wherein the method is adapted to prevent charges from moving through scanning electrodes that are not connected to each other. 3. Each scanning electrode consists of the same number of independent transparent electrode parts as the signal electrodes, and high resistance is provided on both sides so as to sandwich the transparent electrode parts, so that when the scanning electrode is not selected, the selection 2. The method of driving an optical switching device according to claim 1, wherein the speed of charge movement through the scanning electrode is slowed down. 4. The method for driving an optical switch element according to claim 1, wherein the ferroelectric substance is a ferroelectric liquid crystal. 5. The method for driving an optical switch element according to claims 1 and 4, wherein the ferroelectric liquid crystal is a liquid crystal having a chiral smectic phase. 6. The method for driving an optical switch element according to claims 1 and 2, wherein the rectifying element is a PN junction element formed directly on a liquid crystal element glass substrate by a semiconductor process. .