KR20090021615A - Method for calculating driving voltage of optical modulator and driving method for optical modulating apparatus and optical modulating apparatus using it - Google Patents

Abstract

A method for calculating the driving voltage of optical modulator and a driving method for an optical modulating apparatus and an optical modulating apparatus using the same are provided to reduce the quantity of light error of the modulated photo generated according to the Hysteresis characteristic. The voltage-quantity of light property between the applied voltage and the light emission amount at the light modulator according to the polarization Hysteresis of the piezoelectric layer are measured. The voltage-quantity of light property shows up as the Hysteresis curve shaped having the other voltage value about the same light intensity. The voltage value corresponding to the target intensity of radiation of the diffracted light of two is extracted from the measured voltage-quantity of light property. One of two voltage values is calculated to the driving voltage about the target intensity of radiation.

Description

Method for calculating driving voltage of optical modulator, driving method of optical modulator, and optical modulator using same {Method for calculating driving voltage of optical modulator and driving method for optical modulating apparatus and optical modulating apparatus using it}

The present invention relates to a method for calculating a driving voltage of an optical modulator, a driving method of an optical modulator, and an optical modulator using the same. More specifically, the present invention relates to a hysteresis characteristic curve (polarization hysteresis curve) generated in a piezoelectric type optical modulator. The present invention relates to a driving voltage calculation method of an optical modulator using an average value of two voltage values corresponding to a light amount and using the same as a driving voltage (gradation voltage) of an optical modulator, a driving method of an optical modulation device, and an optical modulation device using the same.

The piezoelectric element is a micromachine that gives a driving force for generating displacement of an object (hereinafter, referred to as a displacement object) to induce a position change by using characteristics of a piezoelectric material that contracts or expands according to an applied driving voltage. to be. Piezoelectric devices are widely used in various MEMS devices, such as scanning microscopes, optical probes, optical modulators, and data storage devices.

Such a piezoelectric element exhibits a hysteresis characteristic such that the voltage-displacement relationship between the applied driving voltage and thus the displacement generated at the displacement object is shown in Fig. 1A. The hysteresis characteristic of the piezoelectric element is caused by a polarization hysteresis phenomenon related to the piezoelectric effect (ie, shrinkage or expansion due to polarization of the piezoelectric layer) in the piezoelectric element due to the application of a driving voltage. This will be described below with reference to FIGS. 1B and 1C with reference to FIG. 1A. Here, FIG. 1B is a diagram illustrating a stepped driving voltage applied to the piezoelectric element, and FIG. 1C is a displacement occurring in the displacement target according to the hysteresis characteristics of the piezoelectric element when the driving voltage shown in FIG. 1B is applied to the piezoelectric element. The figure which shows.

Referring to the hysteresis characteristic curve of the piezoelectric element shown in FIG. 1A, when the driving voltage is gradually increased and applied to the piezoelectric element, the position of the displacement target is changed along the first characteristic curve 11, and the driving voltage is applied to the piezoelectric element. In the case of gradually decreasing and applying, the position of the displacement object changes along the second characteristic curve 12. That is, due to the hysteresis characteristics (polarization hysteresis) of the piezoelectric element, the voltage-displacement relationship shows different characteristics with respect to the increase direction and the decrease direction of the driving voltage. For this reason, when the driving voltage having the stepped shape shown in FIG. 1B is applied, although the driving voltage of the same magnitude is applied to the piezoelectric element, the displacement occurring at the displacement target at that time is in the direction in which the driving voltage increases and decreases. There is a problem in that the displacement value is different depending on whether the direction. Referring to FIGS. 1B and 1C, even when the same voltage V ₂ is applied to the piezoelectric element, when the driving voltage increases from V ₁ to V ₂ , the displacement occurring in the displacement target is S ₂₁ , and when the driving voltage decreases from V _max to V ₂ , it can be seen that the displacement occurring in the displacement target is represented by S ₂₂ and has different values.

Therefore, according to the related art, even when the driving voltage of the same magnitude is applied, the displacement of the displacement target may have different displacement values due to the hysteresis characteristic problem of the piezoelectric element, and thus, various application elements utilizing the piezoelectric element and In a device (especially an optical modulator as in the present invention), there is a problem in that the accuracy and reliability of its operation cannot be determined.

Accordingly, the present invention solves the hysteresis problem in the piezoelectric optical modulator, and includes a display device using the piezoelectric optical modulator. A method, a method of driving an optical modulator, and an optical modulator using the same are provided.

In addition, the present invention provides a method for calculating a driving voltage of an optical modulator and a driving of an optical modulator capable of realizing a higher quality and higher definition image by greatly reducing the light quantity error of modulated light generated according to hysteresis characteristics in a piezoelectric optical modulator. A method and an optical modulation device using the same are provided.

Other objects of the present invention will be readily understood through the following description.

According to an aspect of the invention, the position change of the displacement target is induced by the contraction or expansion of the piezoelectric layer according to the driving voltage applied between the electrodes, and diffracted light diffracted incident light corresponding to the displacement induced on the displacement target A method of calculating a driving voltage of an optical modulator for outputting, the method comprising: (a) measuring a voltage-light quantity characteristic between an applied voltage and an output light quantity in the optical modulator according to the polarization history of the piezoelectric layer; (b) extracting two voltage values corresponding to a target light quantity of the diffracted light from the measured voltage-light quantity characteristic; And (c) calculating one voltage value between the extracted two voltage values as a driving voltage for the target amount of light.

Here, the voltage-light quantity characteristic is represented by a hysteresis curve having different voltage values for the same light quantity according to the direction in which the applied voltage increases and decreases due to the polarization history, and the 2 extracted in the step (b). Voltage values may be voltage values obtained corresponding to increasing and decreasing directions of the hysteresis curve with respect to the target amount of light.

Here, the one voltage value may be an arithmetic mean value of the extracted two voltage values.

The present invention may further include, after step (c), (d) storing the driving voltage calculated for the target amount of light.

According to another aspect of the invention, the position change of the displacement target is induced by the contraction or expansion of the piezoelectric layer according to the driving voltage applied between the electrodes, diffracted light diffracted incident light corresponding to the displacement induced on the displacement target A method of driving an optical modulator comprising an optical modulator for outputting and a driving unit for generating the driving voltage, the method comprising: (a) a voltage-light quantity between an applied voltage and an output light quantity in the optical modulator according to the polarization history of the piezoelectric layer; Generating one voltage value between two voltage values extracted corresponding to the target light amount of the diffracted light from the characteristic curve as a driving voltage for the target light amount; And (b) applying a driving voltage with respect to the target amount of light between the electrodes.

Here, the one voltage value may be an arithmetic mean value of the extracted two voltage values.

According to another aspect of the invention, the position change of the displacement target is induced by the contraction or expansion of the piezoelectric layer according to the driving voltage applied between the electrodes, diffracted light diffracted incident light corresponding to the displacement induced on the displacement target An optical modulator outputting the light; And a driving unit generating the driving voltage to be applied between the electrodes, wherein the driving unit includes a target light amount of the diffracted light from a voltage-light-quantity characteristic curve between an applied voltage and an output light amount in the optical modulator according to the polarization history of the piezoelectric layer. An optical modulation device may be provided that generates one voltage value between two voltage values extracted corresponding to the driving voltage for the target light amount.

Here, the one voltage value may be an arithmetic mean value of the extracted two voltage values.

The optical modulator driving method and the optical modulator using the same according to the present invention solve the hysteresis problem in the piezoelectric optical modulator, and include the display device using the piezoelectric optical modulator. There is an effect that can be trusted.

In addition, the present invention has the effect of realizing a higher-quality, high-definition image by greatly reducing the light amount error of the modulated light generated by the hysteresis characteristics of the piezoelectric optical modulator.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Prior to describing the optical modulator driving method and the optical modulator according to the embodiment of the present invention in detail, a piezoelectric optical modulator and an application example thereof are described with reference to FIGS. 2 to 9 to assist in understanding the optical modulator. The color display device will first be briefly described with reference to the contents related to the present invention.

2 is a perspective view schematically showing a structure of a piezoelectric optical modulator to which the driving method of the optical modulation device according to the present invention is applicable, and FIG. 3 is a piezoelectric method to which the driving method of the optical modulation device according to the present invention is applicable. FIG. 6 is a perspective view schematically showing another structure of the optical modulator, and FIG. 6 is a view for explaining a light modulation principle in the piezoelectric type optical modulator shown in FIG. 3.

2 and 3, the piezoelectric optical modulator includes a substrate 110, an insulating layer 120, a sacrificial layer 130, a ribbon layer 140, and a piezoelectric element 150. Here, a plurality of holes (140 (b) of FIG. 2 or 140 (d) of FIG. 3) are provided in the center portion of the ribbon layer 140 (hereinafter, referred to as a ribbon). In addition, an upper light reflection layer (140 (a) of FIG. 2 or 140 (c) of FIG. 3) is formed on a portion where no hole is formed in the ribbon, and a lower light reflection layer is formed on the insulating layer 120 corresponding to the position of the hole. (120 (a) of FIG. 2 or 120 (b) of FIG. 3) is formed.

In addition, the piezoelectric element 150 vertically moves the ribbon according to the degree of contraction or expansion of the piezoelectric layer 152 generated by the driving voltage applied between the two electrodes (ie, the lower electrode 151 and the upper electrode 153). It gives driving force to move. For example, when no driving voltage is applied to the piezoelectric element 150, the ribbon is in the original position as shown in FIG. 4 (ie, the position S _min from the insulating layer 120). When the driving voltage is applied, as shown in FIG. 5, the driving voltage is moved to a predetermined position corresponding to the applied voltage (ie, a position having a predetermined distance S ₁ from the insulating layer 120).

Hereinafter, the light modulation principle in the piezoelectric type optical modulator (that is, piezoelectric diffraction type optical modulator) will be described with reference to FIG. 6. 6 is a cross-sectional view showing the BB 'line of FIG. 7 to be described later as a reference line.

First, in FIG. 6A, when the wavelength of light incident on the light modulator is λ, the insulating layer 120 having the ribbon on which the upper light reflection layer 140 (a) is formed and the lower light reflection layer 120 (a) are formed. It is assumed that a first driving voltage is applied to the piezoelectric element 150 so that the interval between them becomes (2n) λ / 4 (n is a natural number). In this case, in the case of the zero-order diffracted light, the total path difference between the light reflected from the upper light reflecting layer 140 (a) and the light reflected from the lower light reflecting layer 120 (a) is equal to nλ. Luminance, and in the case of + 1st and -1st diffraction light, the brightness of light has a minimum brightness due to destructive interference.

In FIG. 6B, the distance between the ribbon on which the upper light reflection layer 140 (a) is formed and the insulating layer 120 on which the lower light reflection layer 120 (a) is formed is (2n + 1) λ / 4 (n It is assumed that the second driving voltage to be a natural number) is applied to the piezoelectric element 150. In this case, in the case of zero-order diffracted light, the total path difference between the light reflected from the upper light reflecting layer 140 (a) and the light reflected from the lower light reflecting layer 120 (a) is equal to (2n + 1) λ / 2 to cancel. The interference light has the minimum luminance, and in the case of the + 1st and -1st diffraction light, the brightness of the light has the maximum brightness due to constructive interference.

As described above, the piezoelectric type optical modulator reflects the reflected light using the result of the interference of the reflected light reflected by the upper light reflecting layer 140 (a) and the lower light reflecting layer 120 (a) according to the driving voltage applied to the piezoelectric element. Alternatively, the signal can be loaded on the light by adjusting the amount of diffracted light. 6 illustrates only the case where two driving voltages are applied such that the distance between the ribbon and the insulating layer 120 is (2n) λ / 4 or (2n + 1) λ / 4. It is apparent that various sizes of driving voltages can be applied to the piezoelectric elements, which can be driven at intervals that can control the intensity (ie, amount of light) of the diffracted light interfered by the diffraction. For example, in the piezoelectric type optical modulator described with reference to FIGS. 2 to 6, the light intensity value is divided into 0 to 255 steps for light modulation for each pixel (i.e., 1 pixel is divided into 8 bit image data). Assuming a case of expression), a driving voltage having a total of 256 distinct voltage values (that is, gray scale voltage values) may be used. In addition, in the present specification, a description will be given of a voltage control method for applying a voltage in driving a piezoelectric optical modulator, but the piezoelectric optical modulator may be driven by various driving methods and driving signals.

4 to 6 illustrate the optical modulator having a plurality of holes in the ribbon, the upper and lower driving force is applied to the ribbon to be displaced by contracting and expanding according to the driving voltage applied between the electrodes in order to realize the optical diffraction characteristics. If the piezoelectric type optical modulator including a piezoelectric element to generate it is obvious that the present invention can be applied without any limitation.

FIG. 7 is a plan view of an optical modulator array including the piezoelectric type optical modulator shown in FIG. 2, and FIG. 8 is a view schematically illustrating a configuration of a color display apparatus as an application example of the optical modulator array of FIG. 7. FIG. 8 is a diagram for describing a method of realizing an image of one frame projected on a screen according to the color display device of FIG. 8. Hereinafter, a color display apparatus will be described as an application example of the piezoelectric type optical modulator array of FIG. 8 with reference to FIGS. 7 and 9.

The color display device of FIG. 8 includes a three-color light source 210, an illumination optical system 220, an optical modulator array 230, a driver 235, a relay optical system 240, a scanner 250, a projection optical system 260, and a screen. 270, an image control circuit 280. Here, the three-color light source 210, the illumination optical system 220, the relay optical system 240, and the projection optical system 260 are common components in a display device such as a projection device, and a detailed description thereof will be omitted.

The three-color light source 210 irradiates color light corresponding to a predetermined light source control signal 212, 214, or 216 transmitted from the image control circuit 280, which passes through the illumination optical system 220 and the light modulator array 230. Incident.

The optical modulator array 230 may be configured as shown in FIG. 7. That is, the optical modulator array 230 includes the first pixel (pixel # 1), the second pixel (pixel # 2), ... as shown in FIG. And m optical modulators 100-1, 100-2,..., And 100-m each responsible for one m-th pixel (pixel #m), thereby realizing a 1D image corresponding to a vertical scan line or a horizontal scan line. Light modulation is performed for. For example, an image implemented on a screen has a resolution of 640 (horizontal pixels) ㅧ 480 (vertical pixels) as shown in FIG. 9, and the optical modulator array 230 is used to implement a 1D image corresponding to a vertical scan line. Assuming the case of light modulation, the light modulator array 230 may be configured with a total of 480 light modulators corresponding to the number of vertical pixels.

At this time, each optical modulator constituting the optical modulator array 230 performs light modulation on the incident color light according to the light intensity information for each pixel constituting the vertical scanning line to generate diffracted light. Herein, the light intensity information is transmitted from the image control circuit 280 (see the light modulator control signal of FIG. 8), and the driving unit 235 transmits a driving voltage having a predetermined magnitude corresponding to the transmitted light intensity information of each light modulator. By applying to the piezoelectric elements included in each optical modulator, the optical modulator array 230 can perform optical modulation for realizing a 1D image.

The scanner 250 scans the modulated light (ie, diffracted light) transmitted from the optical modulator array 230 on the screen 270 according to the scanner control signal transmitted from the image control circuit 280. For example, the scanner 250 scans, in a horizontal direction, a one-dimensional image corresponding to each vertical scan line (first vertical scan line to nth vertical scan line) transmitted from the optical modulator array 230 as shown in FIG. 9. A two-dimensional image may be displayed on 280.

When the light modulation and scanning process of the color light is performed once for the red light, the green light, and the blue light, the color image of one frame may be displayed on the screen 280. Here, the total time for light modulation for red light, green light and blue light should be within 1 / (field frequency according to the television broadcasting method). In the present specification, a color image is implemented using red, green, and blue light, which are three primary colors of light, as an example. However, it is obvious that the color image may be realized by a combination of different color lights.

The field frequency according to the television broadcasting method means a minimum frequency at which a human cannot visually detect a break in the moving picture screen. As a color display apparatus, a television broadcasting method includes an NTSC (national television system committee) method, a PAL (phase alteration by line) method, and the like. The NTSC method converts the three primary color signals of red, green, and blue into one luminance signal (Y) and two color difference signals (I, Q), and then multiplexes and transmits them in a frequency bandwidth of 6 MHz. The PAL method complements the color transmission method, which is a disadvantage of the NTSC method. The NTSC system consists of 525 scan lines and 60 Hz field frequency. The PAL method consists of 625 scan lines and 50 Hz field frequency.

Therefore, according to the field frequency, each modulated light for the three primary colors of light, red light, green light, and blue light, is displayed on one screen within 1 / (field frequency, for example, 60 Hz for NTSC, 50 Hz for PAL). Once projected once, the human eye recognizes that a screen in which a full color image including red, green, and blue is simultaneously formed is formed. That is, a total of three subframes of red, green, and blue are displayed on one screen to realize a color image of one frame.

Hereinafter, the driving voltage calculation method, the driving method, and the optical modulation device in the piezoelectric optical modulator according to the present invention will be described in detail with reference to FIGS. 10 to 12.

Here, the optical modulation device according to an embodiment of the present invention is a piezoelectric layer according to the driving voltage applied between the electrodes (for example, the lower electrode 151 and the upper electrode 153 of FIGS. 2 to 5 described above). The piezoelectric optical modulator outputs diffraction light diffracted by incident light in response to the displacement induced by the contraction or expansion of (see identification number 152 of FIGS. 2 to 5) and the displacement induced on the displacement object. 2 to 5, and a driving unit (see identification number 235 of FIG. 8) for generating a driving voltage to be applied between electrodes. Therefore, in the following description, the piezoelectric element, the optical modulator, and the driving unit use the same identification numbers as those used in FIGS. 2 to 9.

FIG. 10 is a diagram illustrating voltage-light quantity characteristics between an applied voltage and an output light quantity in a piezoelectric optical modulator, and FIG. 11 is a calculation of a target light quantity used in a method of driving an optical modulator according to an exemplary embodiment of the present invention. It is a figure for demonstrating the light quantity error in a drive voltage.

10 and 11 show examples of characteristic curves showing voltage-light quantity characteristics between an applied voltage and an output light amount in a piezoelectric optical modulator. Here, the horizontal axis of the voltage-light-quantity characteristic curve represents the applied voltage, and the vertical axis represents the light quantity of the diffracted light accordingly.

That is, FIGS. 10 and 11 illustrate an insulating layer 120 (or more precisely, an insulating layer) changed according to a voltage applied to two electrodes (ie, the lower electrode 151 and the upper electrode 153) in a piezoelectric optical modulator. 120 shows the output characteristics of the amount of light (ie, output luminance) of diffracted light which is diffracted by incident light due to the separation distance between the lower light reflection layer formed on 120) and the ribbon to be displaced (more precisely, the upper light reflection layer formed on the ribbon). have.

In the piezoelectric optical modulator, the voltage-light quantity characteristic is similar to the polarization hysteresis curve illustrated in FIG. 1 in relation to the polarization phenomenon according to the applied voltage generated in the piezoelectric layer 152 described above. You can check it. This is a content that can be easily understood by those skilled in the art without a separate detailed description, a detailed description thereof will be omitted. This is because the luminance intensity (ie, the amount of light) of the diffracted light output from the optical modulator is determined by the separation interval between the ribbon and the insulating layer 120 that changes according to the applied voltage. That is, the displacement) indicates polarization hysteresis characteristics (ie, voltage-displacement characteristics) as illustrated in FIG. 1 according to the polarization of the piezoelectric layer 152.

That is, the voltage-light quantity characteristic of the piezoelectric type optical modulator is an increase curve according to the characteristic in the direction in which the applied voltage increases as shown in FIGS. 10 and 11 and the direction in which the applied voltage decreases. There are two forms of decay curves (see Ident. No. 60) depending on the characteristics of. As described above, it can be seen that the hysteresis curve has a general shape similar to the polarization hysteresis curve of the piezoelectric layer 152. Therefore, referring to the voltage-light-quantity characteristic curves of FIGS. 10 and 11, for the output light quantity having the same value, the applied voltage values corresponding thereto are each one by the increase curve 50 and the decrease curve 60. There is a dog. For example, in FIGS. 10 and 11, the applied voltage value corresponding to the magnitude (or intensity of output luminance) P ₄ of the output light quantity is V ₁ corresponding to the increase curve 50 and V corresponding to the decrease curve 60. ₂ is present. As a result, the voltage-light quantity characteristic of the piezoelectric type optical modulator has a curved shape corresponding to the polarization hysteresis characteristic of the piezoelectric layer 152, so that different voltage values (ie, V ₁ and V ₂ ) are applied between the electrodes. This means that the amount of diffracted light output from the optical modulator will have the same value (ie, P ₄ ).

According to the voltage-light-quantity characteristic described above, the following problems are encountered in applying the driving voltage to the optical modulator. That is, in order to accurately generate the diffracted light having the actual target amount of light, the voltage value corresponding to each of the light modulators is separately considered when the applied voltage increases or decreases according to the voltage-light quantity characteristics. There is a problem that should be used as the driving voltage. However, the method of applying the driving voltage to the optical modulator in consideration of the increase direction and the decrease direction of the applied voltage in this way complicates the design of the driving unit, thereby causing a problem that the manufacturing cost of the optical modulator increases. . In conclusion, considering the design, configuration, and cost of the optical modulation device, it is preferable to apply any one of the voltage values as the actual driving voltage for realizing the target light quantity value, and to increase the curve 50 in the voltage-light intensity characteristic curve. In the case of selecting any one of the voltage values (that is, V ₁ or V ₂ ) corresponding to any one of the curves and / or the reduction curve 60, there is a problem in that a large light quantity error occurs based on the target light quantity. This will be described in detail below with reference to FIG. 11.

For example, assume a case in which V ₂ , which is a voltage value corresponding to the reduction curve 60, is selected from the voltage-light-quantity characteristic curves as a driving voltage for implementing the target light quantity P ₄ in FIG. 11. In this case, when the applied voltage applied to the optical modulator is in the decreasing direction, the output light quantity of the diffracted light output from the optical modulator according to the reduction curve 60 can accurately realize P ₄ , which is a target light quantity value originally intended. On the contrary, on the contrary, assuming that the applied voltage applied to the optical modulator is in the increasing direction, according to the increase curve 50, the target light amount of the diffracted light is much lower than the target light amount P ₄ , which is contrary to the original intention. values (see the identification code _K P in Fig. 11) is given. At this time, the amount of light error is generated by ΔP ₀ as shown in FIG. Therefore, in the above-described assumption, when the applied voltage is in the increasing direction, the luminance of the diffracted light output from the optical modulator does not have the intended target value. It causes a problem that a distorted color image due to an unintended color having a difference is realized.

In order to solve the above problems, the optical modulation device driving method and the optical modulation device using the same according to an embodiment of the present invention adopts the following driving method.

That is, the driving method of the optical modulation device according to an embodiment of the present invention is extracted from the increase curve 50 and the reduction curve 60 corresponding to the output light amount of the target diffraction light from the voltage-light intensity characteristic curve in the optical modulator, respectively. The arithmetic mean value of the two voltage values to be calculated as a driving voltage for the target light amount is applied to the optical modulator (more precisely two electrodes).

This will be described with reference to FIG. 11 as an example. In FIG. 11, arithmetic expressions of a voltage value V ₁ corresponding to an increase curve 50 and a voltage value V ₂ corresponding to a decrease curve 60 are shown as driving voltages for implementing the target light amount P ₄ in FIG. 11. Assume that the average V _mean (that is, V _mean = {V ₁ + V ₂ } / 2) is selected. When the arithmetic mean value V _mean is selected as the driving voltage for the target light amount P ₄ , the actual target light amount P ₄ cannot be realized regardless of whether the applied voltage is in the increasing direction or the decreasing direction. However, the light quantity error between the target light quantity and the actual output light quantity when the target light quantity P ₄ is referred to can be reduced. That is, when V _mean is applied as the driving voltage for the target light amount P ₄ , the light amount error when the applied voltage applied to the optical modulator is in the increasing direction occurs by ΔP ₁ , and the applied voltage applied to the optical modulator decreases. The light quantity error when in the direction occurs by ΔP ₂ . That is, when the driving method according to the embodiment of the present invention is used, the light quantity error occurs when the applied voltage in the voltage-light-quantity characteristic curve is in the increasing direction or the decreasing direction compared to the target light quantity. The light quantity error (ΔP ₁ or ΔP _{2 in} the case of FIG. 11) is a light quantity error when one of the voltage values corresponding to the increase curve 50 or the decrease curve 60 is used as a driving voltage according to a conventional method. In the case of 11, it is reduced by about half compared to ΔP ₀ ) (see Equation 1 below).

Therefore, according to the driving method of the optical modulation device according to an embodiment of the present invention, the arithmetic mean value of two voltage values corresponding to the target light quantity extracted from the voltage-light quantity characteristic curve is applied as the driving voltage for the target light quantity. Although the diffracted light having the output light amount having a slight error from the intended actual target light amount is generated and output from the optical modulator, the light amount error can be reduced by about half as compared with the conventional method. Therefore, assuming that the driving method of the optical modulation device of the present invention is applied to a color display device, a very accurate color image to be expressed according to the amount of diffracted light is not realized, but the error is much reduced as compared with the prior art. There is an advantage of realizing a color image having a vivid, closer image quality and color closer to the target color.

Hereinafter, a driving voltage calculation method applied to the driving method of the optical modulation device according to the present invention will be described with reference to the flowchart of FIG. 12.

12 is a flowchart illustrating a driving voltage calculation method of an optical modulator according to an embodiment of the present invention.

Referring to step S110 of FIG. 12, first, a voltage-light quantity characteristic between an applied voltage and an output light quantity is measured in an optical modulator. Through this step, the voltage-light-quantity characteristic curves as shown in FIGS. 10 and 11 generated according to the polarization history of the piezoelectric layer 152 in the fabricated optical modulator can be obtained. That is, in this step, a predetermined rated voltage is applied to each of the electrodes of the optical modulator in the direction of increasing and decreasing, respectively, and the output light of the diffracted light (i.e., the luminance intensity of the diffracted light) is measured. The voltage-light intensity characteristic curve (or the corresponding voltage-light intensity characteristic table) indicated by the modulator is obtained.

Referring to step S120 of FIG. 12, two voltage values corresponding to the target amount of diffracted light are extracted from the voltage-light quantity characteristic of the optical modulator measured through the previous step. That is, as described above with reference to FIGS. 10 and 11, through this step, each voltage corresponding to the increase curve 50 and the decrease curve 60 in the voltage-light intensity characteristic curve, respectively, corresponding to any desired target amount of light. The value will be extracted.

Referring to step S130 of FIG. 12, an arithmetic mean value of two voltage values extracted corresponding to the target light quantity from the voltage-light intensity characteristic curve is calculated as the driving voltage for the target light quantity. That is, the driving voltage calculation method of the optical modulator according to an embodiment of the present invention drives the replacement voltage value corresponding to the arithmetic mean value of two voltage values extracted corresponding to the target light quantity from the voltage-light intensity characteristic curve for the target light quantity. It is used as a voltage. As described above, by using the substitute voltage corresponding to the arithmetic mean as the driving voltage for the target light amount, the light amount error generated as compared with the conventional method can be reduced by about half.

However, in the method of calculating the driving voltage of the optical modulator and the driving method of the optical modulator according to an embodiment of the present invention, the target voltage is a target of an alternative voltage corresponding to an arithmetic mean value of two voltage values extracted from the voltage-light intensity characteristic curve. Although a description has been made mainly on the case of using as a driving voltage for the light quantity, in addition to the arithmetic mean value, an alternative voltage corresponding to one voltage value (for example, geometric mean value, etc.) between the two voltage values is a driving voltage for the target light quantity. It is also possible to use it as an example, and in this case, it will be easily understood by those skilled in the art through the above description that the light quantity error is reduced as compared with the conventional method.

The alternative voltage value calculated as the driving voltage for the target light amount through this step may be a separate storage device (for example, a storage device for storing the replacement voltage may be provided inside or separately of the image control circuit 280 of FIG. 8). It can be stored in the) and then used to drive the optical modulator (see step S140 of Figure 12).

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be readily understood that modifications and variations are possible.

1A is a diagram illustrating hysteresis characteristics in displacements generated at displacement objects according to driving voltages applied to piezoelectric elements.

1B is a diagram illustrating a stepped voltage as an example of a driving voltage applied to a piezoelectric element.

FIG. 1C is a view showing a displacement occurring in a displacement target according to the hysteresis characteristics of the piezoelectric element when the driving voltage shown in FIG. 1B is applied to the piezoelectric element.

Figure 2 is a perspective view schematically showing one structure of a piezoelectric optical modulator to which the driving method of the optical modulator according to the present invention is applicable.

3 is a perspective view schematically showing another structure of a piezoelectric light modulator to which a method of driving an optical modulator according to the present invention is applicable.

4 is a diagram illustrating a position of a ribbon when no driving voltage is applied to the piezoelectric optical modulator shown in FIG. 3.

FIG. 5 is a diagram illustrating a position of a ribbon when a driving voltage is applied to the piezoelectric optical modulator shown in FIG. 3.

6 is a view for explaining a light modulation principle in the piezoelectric optical modulator shown in FIG.

7 is a plan view of an optical modulator array including the piezoelectric optical modulator shown in FIG.

FIG. 8 is a view schematically illustrating a configuration of a color display device as an application example of the optical modulator array of FIG. 7.

FIG. 9 is a diagram for describing a method of realizing an image of one frame projected on a screen according to the color display device of FIG. 8; FIG.

10 is a diagram showing voltage-light quantity characteristics between an applied voltage and an output light quantity in a piezoelectric optical modulator.

FIG. 11 is a view for explaining a light amount error in a calculated driving voltage with respect to a target light amount used in a method of driving an optical modulator according to an embodiment of the present invention; FIG.

12 is a flowchart illustrating a driving voltage calculation method of an optical modulator according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

150 piezoelectric element 151 lower electrode

152: piezoelectric layer 153: upper electrode

230: optical modulator array 235: drive unit

Claims (8)

Position change of the displacement target is induced by contraction or expansion of the piezoelectric layer according to the driving voltage applied between electrodes, and the driving voltage of the optical modulator outputs diffracted light diffracted incident light corresponding to the displacement induced on the displacement target. In the method, (a) measuring a voltage-light quantity characteristic between an applied voltage and an output light amount in the optical modulator according to the polarization history of the piezoelectric layer; (b) extracting two voltage values corresponding to a target light quantity of the diffracted light from the measured voltage-light quantity characteristic; And (c) calculating one voltage value between the extracted two voltage values as a driving voltage for the target amount of light; Driving voltage calculation method of the optical modulator comprising a. The method of claim 1, The voltage-light quantity characteristic is in the form of a hysteresis curve having different voltage values for the same light quantity depending on the direction in which the applied voltage increases and decreases due to the polarization history, and the two voltages extracted in step (b). And a value is a voltage value obtained corresponding to the increase direction and the decrease direction of the hysteresis curve with respect to the target amount of light, respectively. The method of claim 1, And said one voltage value is an arithmetic mean value of said two extracted voltage values. The method of claim 1, After step (c), and (d) storing the driving voltage calculated for the target amount of light. Position change of the displacement target is induced by the contraction or expansion of the piezoelectric layer according to the driving voltage applied between the electrodes, and the optical modulator for outputting diffracted light diffracted incident light corresponding to the displacement induced in the displacement target and the driving voltage In the method for driving an optical modulator comprising a drive unit for generating a; (a) The target voltage value between two voltage values extracted corresponding to the target light amount of the diffracted light from the voltage-light-quantity characteristic curve between the applied voltage in the optical modulator and the output light amount according to the polarization history of the piezoelectric layer. Generating a driving voltage for the amount of light; And (b) applying a driving voltage for the target amount of light between the electrodes; Method of driving an optical modulator comprising a. The method of claim 5, And said one voltage value is an arithmetic mean value of said two extracted voltage values. An optical modulator for inducing a change in position of the displacement target by contraction or expansion of the piezoelectric layer according to a driving voltage applied between electrodes, and outputting diffracted light diffracted by incident light corresponding to the displacement induced in the displacement target; And A driving unit generating the driving voltage to be applied between the electrodes, The driving unit targets one voltage value between two voltage values extracted corresponding to a target light amount of the diffracted light from a voltage-light quantity characteristic curve between an applied voltage and an output light amount in the optical modulator according to the polarization history of the piezoelectric layer. An optical modulator, characterized in that generated by the driving voltage for the amount of light. The method of claim 7, wherein And said one voltage value is an arithmetic mean value of said two extracted voltage values.

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