KR20050023335A - Bipolar operation of light-modulating array - Google Patents

Abstract

One disclosed embodiment includes a method for bipolar operation of a light-modulated array. The method includes driving 602 the photo-modulation elements of the array at a first polarity, switching the polarity from the first polarity to a second polarity 604, driving the photo-modulation elements of the array at a second polarity. A step 606, a step 608 of switching the polarity from the second polarity to the first polarity, and repeating the above steps. Another disclosed embodiment includes an apparatus using a light-modulated array. The apparatus includes a first lookup table 702 for storing data for operating the elements of the light-modulation array in a first electrode mode, and data for operating the elements of the light-modulation array in a second polarity mode. A second lookup table 704 is included. The apparatus also includes a drive system 708 for driving the elements of the light-modulated array. The drive system is coupled to both the first and second lookup tables.

Description

BIPOLAR OPERATION OF LIGHT-MODULATING ARRAY}

The present invention relates generally to optical systems. In particular, the present invention relates to optical systems used in projection displays or communication systems.

The two-dimensional projection image can be formed by using one or more linear arrays of light-modulating elements. The light-modulating element may comprise, for example, a GRATING LIGHT VALVE (GLV) element. In such display systems, the linear array modulates the incident light rays to display the pixels along a column (or alternatively a row) of the two-dimensional (2D) image. Scanning systems have been used to move columns across the screen such that each light-modulating element can produce a row of 2D images. In this way, the entire 2D image is displayed.

The array of light-modulating elements can also be applied to communication systems. For example, the array can be used as an optical micro-electromechanical system (MEMS) for optical networks.

Publications describing the GLV device and its application include, in February 1997, D.M. Bloom's "The Grating Light Valve: Revolutionizing Display Technology"; D.T. of Silicon Light Machines, Sunny Valley, California, an article in the May 19, 1998 Information Display Society, Anaheim, California. Am and R.W. Corrigan, "Grating Light Valve Technology: Update and Novel Application"; "Optical Performance of the Grating Light Valve Technology" by David T. Am and Robert W. Corrigan of Silicon Light Machines, a 1999 paper on optical western-electronic imaging; R.W., an article in the Information Display Society of San Jose, California, May 18, 1999. Corrigan, D.T. Am, P.A. Alliocin, B. Stacker, D.A. Rehoti, K.P. Gross and B.R. Lange's "Calibration of a Scanned Linear Grating Light Valve Projection System"; R.W. of Silicon Light Machines, a paper presented on November 20, 1999, at the 141st SMPTE Technology Conference and Exhibition in New York City, NY. Corrigan, B.R. Lang, D.A. Rehoti and P.A. "An Alternative Architecture for High Performance Display" by Aliosin; "Breakthrough MEMS Compnent Technology for Optical Networks" by Robert Corrigan, Randy Cook and Oliver Pabot, 2001, Silicon Light Machines-Grating Light Valve Technology Brief; And US Pat. No. 6,215,579, entitled "Method and Apparatus for Modulating an Incident Light Beam for Forming a Two-Dimensional Image," published by Silicon Light Machines. Each of the above publications is incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing an operating state of reflection and diffraction of a grating light valve (GLV) element. The left side of the figure shows the reflection (dark) state, while the right side of the figure shows the diffraction (bright) state.

In the example shown in FIG. 1, the substrate may comprise a silicon substrate on which oxide (eg, 5000 angstroms thick) is covered with silicon and tungsten (eg, 1000 angstroms thick) is covered by the oxide. Reflective members are placed on tungsten with an air gap in between. For example, three pairs of reflective members (ie six members) are shown. Reflective members include, for example, reflective ribbons comprising nitride (eg, about 1000 Angstroms thick) nitride having a reflective layer of aluminum (eg, about 500 Angstroms thick) on top. Incident light is reflected on the reflective members. The incident light ray may be perpendicular to the plane of the substrate.

In the reflective or dark state (left), all the reflective members are in the same plane and the incident light is reflected from the surfaces of the members. This reflection state can be called a dark state because it can be used to generate dark spots (dark pixels) in a projection display system. Such dark pixels can be produced by blocking light that is reflected back in the same path as incident light.

In the diffractive or bright state (right), the alternative member of the reflective member is refracted downward. This results in diffraction of the incident light in the angular direction with the path of the incident light. This reflection state can be called a bright state because it can be used to generate bright spots (bright pixels) in a projection display system. Such bright pixels can be created because each reflected light is not blocked. As will be explained further below, the optical response of the element depends on the amount of downward deflection of the alternative members.

2 illustrates a GLV element comprising a pair of fixed ribbons and movable ribbons. As shown in FIG. 2, the GLV element may comprise a pair of reflective ribbons, each pair having one fixed ribbon and one movable ribbon.

3 is a diagram showing the refraction of the reflective members for the GLV element in the diffraction state. The GLV element includes a plurality of reflective members. Reflective members include alternate bias members 04 and active member 306. In the described example, the GLV element includes three pairs of reflective members (ie six members).

In the diffractive state, the reflective members are controllably arranged in an alternate configuration at two heights from the common electrode 308, the bias members 304 are at a first height, and the active (movable) members 306 are It is at the second height. The bias members 304 may be fixed ribbons. The active members 306 may be movable ribbons drawn by the application of a voltage. Voltage may be applied to the common electrode 308. As shown in FIG. 3, the incident ray 310 impinges the element at right angles to the grating plane 308. Diffracted light 312 is away from the element.

The difference between the first height and the second height is the refraction distance It can be defined as. refraction The amount of may change by application of different voltages to adjust the amount of incident light reflected from the element. When it is close to zero, the element is almost fully reflected. this /4( Is the wavelength of the incident light), the element is almost at its maximum diffraction state.

4 is a graph showing the nonlinear electron-light response for the GLV element. The graph shows light intensity versus voltage (in any unit). The higher the voltage, the more displacement of the element Becomes bigger. Depending on the voltage applied to the active members, the light intensity changes. Most of the time, the higher the voltage applied, the higher the light intensity (this relationship is reversed for sufficiently high voltages, where the downward slope of the graph on the far right appears as the light intensity decreases for higher voltages).

5 is a top view illustrating a projection display system 500 using a light-modulated array. System 500 includes one or more light sources 502, one or more arrays 504 of light-modulating elements, light scanner 506, and screen 508. 5 is for illustration and not necessarily accurate in scale or angle.

Light source 502 may comprise one or more laser light sources. Three laser light sources of different colors can be used in the color display system. Light-modulated array 504 may comprise an array of GLV elements (also referred to as GLV “pixels”) described above. Each light source 502 may illuminate the light-modulated array 504. Each element of the array 504 modulates light incidence on that element to adjust the amount of light diffracted therefrom. Light diffracted from the elements of array 504 is transmitted to optical scanner 506.

The light scanner 506 is used to move a column (or row) of light across the screen 508. Various types of scanners 506 may be used. For example, galvanometer-based scanners, resonant scanners, polygon scanners, rotating prisms or other types of scanners may be used. A drive signal is applied to the scanner to control (“drive”) the movement of the column (or row) of light. For example, a sawtooth drive signal may be used to achieve a sequential scan of heat across the screen (eg from left to right).

One disadvantage of using GLV and other MEMS techniques involves changes in device performance as a function of time. Whether used in displays or communication systems, the response function of GLV elements and other MEMS devices has been observed to change over time. Such time-dependent changes can lead to unpredictable behavior, limiting applications for GLV elements and other MEMS devices.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows the reflection and diffraction operating states of a conventional grating light valve (GLV) element.

2 illustrates a typical GLV element comprising a pair of fixed ribbons and movable ribbons.

3 shows the refraction of the reflective members for a typical GLV element in the reflective state.

4 is a graph showing nonlinear electron-light response for a typical GLV element.

5 is a top view illustrating a projection display system using a light-modulated array.

6 is a flow chart illustrating a method for bipolar operation of a light-modulated array in accordance with an embodiment of the present invention.

FIG. 7 illustrates an apparatus for bipolar operation of a light-modulated array in accordance with one embodiment of the present invention. FIG.

8A illustrates a first lookup table of a first polarity in accordance with one embodiment of the present invention.

8B illustrates a second lookup table of second polarity in accordance with one embodiment of the present invention.

The use of the same reference label in different drawings represents the same or similar component. Unless otherwise known, the drawings are not designed to scale.

One embodiment of the invention includes a method for bipolar operation of a light-modulated array. The method includes driving a photo-modulation element of the array at a first polarity, switching a polarity from the first polarity to a second polarity, driving a photo-modulation element of the array at a second polarity, a second polarity. Switching the polarity to the first polarity at and repeating the above steps.

Another embodiment of the invention includes an apparatus using a light-modulated array. The apparatus comprises a first search table for storing data for operating the elements of the light-modulation array in a first polarity mode, and a second search for storing data for operating the elements of the light-modulation array in a second polarity mode. Include a table. The apparatus also includes a drive system for driving the elements of the light-modulated array. The drive system is coupled to both the first and second lookup tables.

These and other features of the present invention will become fully apparent upon reading the entirety of the present specification, including the accompanying drawings and claims, by those skilled in the art.

One cause of the time-dependent performance of GVL technology is related to the charging of light-modulating elements. As the element operates, it can be filled onto nitride based reflective members. This charging disadvantageously results in a change in performance over time. The present invention provides a method and apparatus for overcoming such adverse charging. The invention is particularly applicable to GVL elements, but also to other MEMS devices. The present invention may result in lower time-dependent behavior of such devices and may be used in both display systems and communication systems.

6 is a flowchart illustrating a method 600 for bipolar operation of a light-modulated array, in accordance with an embodiment of the present invention. As shown, the method 600 includes four steps 602, 604, 606, and 608.

In a first step 602, elements of the array are driven at a first polarity. The first polarity refers to the applied potential at which the voltage driving the active element is generally more positive than the voltage of the bias element and the common electrode. The first polarity corresponds, for example, to a positive voltage applied to the active element, while the bias element and the common electrode are grounded (0 volts). As another example, the first polarity corresponds to a lower negative voltage applied to the active element, while the bias element and the common electrode are retained at the more negative electrode level.

For each element, the voltage applied to obtain the required intensity level can be determined by using the first lookup table (LUT). An example of such a first LUT is described below with respect to FIG. 8A.

In a second step 604, the device switches from operation of the first polarity mode to operation of the second polarity mode. Switching of the polarity can be accomplished by switching from using the first LUT to using the second LUT.

In a third step 606, the elements of the array are driven at the second polarity. The second polarity refers to the applied potential, at which the voltage driving the active element is generally negative than the voltage of the bias element and the common electrode. The second polarity corresponds, for example, to a negative voltage applied to the active element, while the bias element and the common electrode are grounded (0 volts). As another example, the second polarity corresponds to a lower positive voltage applied to the active element, while the bias element and the common electrode are retained at the more positive electrode level.

For each element, the voltage applied to obtain the required intensity level can be determined by using a second lookup table (LUT). An example of such a second LUT is described below with respect to FIG. 8B.

In a fourth step 608, the device switches back from the second polarity mode of operation to the first polarity mode of operation. This switching of polarity can be accomplished by switching from using the second LUT to using the first LUT.

By switching the polarity as described above, the electric field in the elements of the array is reversed. The inverse of the electric field advantageously reduces the charge on the element because the charge is dissipated over time.

FIG. 7 illustrates an apparatus 700 for bipolar operation of a light-modulated array in accordance with an embodiment of the present invention. Apparatus 700 includes a first lookup table (LUT) 702, a second LUT 704, a multiplexer (MUX) 706, a drive system 708, and a light-modulated array 710.

The first LUT 702 provides data for use during operation of the first polarity mode, and the second LUT 704 provides data for use during operation of the second polarity mode. Examples of first and second LUTs are described below with respect to FIGS. 8A and 8B, respectively. LUTs 702 and 704 may be implemented in memory structures. In one embodiment, the LUT may be implemented in a semiconductor memory that provides quick access to the data stored therein.

MUX 706 provides a selection of either the first LUT 702 or the second LUT 704. In the first polarity mode, the MUX 706 provides the drive system 708 with access to data from the first LUT 702. In the second polarity mode, the MUX 706 provides the drive system 708 with access to data from the second LUT 704. In one embodiment, the MUX 706 may be controlled by controlling the signal from the drive system 708. The control signal may simply be a bit signal such that the first LUT 702 is selected when the bit is high and the second LUT 704 is selected (and vice versa) when the bit is low. Can be.

The drive system 708 finds a drive voltage corresponding to the intensity required for each element of the light-modulated array 710. Drive system 708 applies a lookup voltage to the appropriate element of array 710 to achieve the required intensity from that element.

In an alternative embodiment of the invention, both the first LUT 702 and the second LUT 704 may be implemented as a combined LUT. Such a combined LUT may have data for both the first polarity mode and the second polarity mode in a single table. Such a combined LUT requires a separate field to distinguish the data for the first polarity mode from the data for the second polarity mode.

FIG. 8A is a diagram illustrating information in a first lookup table (LUT) 800 of a first polarity, in accordance with an embodiment of the invention. The first LUT 800 includes three data fields, an element identifier (ID) 802; Required strength 804; And drive voltage level 806.

In this example, there are 1024 elements in the light-modulation array. Accordingly, element ID 802 shown in FIG. 8A ranges from 1 to 1024. Of course, there may be various numbers of elements in the light-modulation array, and thus the number of element IDs 802 will vary.

This example shows the required light intensity 804 ranging from 0 to 255. This corresponds to 256 intensity levels. 256 different levels can be distinguished using 8-bit information. Of course, various numbers of intensity levels are available in different systems, and thus the number of intensity 804 required will vary.

The value for the drive voltage level 806 of FIG. 8A is shown for illustration. The drive level is shown to vary between about 0 volts (0V) and about +14 volts (13.8V in the figure). For elements comprising a grating light valve element, a greater voltage difference is needed at lower intensities and a smaller voltage difference at higher intensities. This is seen from the intensity versus voltage curve of FIG.

The drive voltage level 806 in the first LUT 800 may be determined by a calibration procedure. The calibration procedure can be performed periodically. As a result of the calibration, for each element 802 of the array, a suitable positive drive level 806 will be determined that achieves each desired intensity 804. This calibration result is stored in the first LUT 800.

8B is a diagram illustrating information in a second lookup table 850 of a second polarity, according to an embodiment of the invention. The second LUT 850 includes three data fields (element ID 802) identical to the first LUT 800; Required intensity 804; And drive voltage level 806}. Also, in the second LUT 850, the data for the element ID and the data for the required intensity level are the same as in the first LUT 800. This is because the identification of elements in the light-modulation array 710 does not change with the polarity mode, and the required light intensity does not change with the polarity mode.

However, the drive voltage level 806 in the second LUT 850 is different from the drive voltage level in the first LUT 800. The value for the drive voltage level 806 shown in FIG. 8B is for illustration. The drive level is shown to vary between about 0 volts (0 V) and about -13 volts (-13.1 V in the figure). In one embodiment, the second LUT 850 may actually store a positive value that is converted to a negative voltage level when the system is in the second (negative) polarity mode.

The drive voltage level 806 in the second LUT 850 may also be determined by periodic calibration. As a result of the calibration, for each element 802 of the array, a negative drive level 806 suitable to achieve each desired intensity 804 will be determined. This calibration is stored in the second LUT 850.

The following describes one specific implementation for LUTs 800 and 850. In this implementation, the tables are combined into a single LUT so that information about the first polarity and the second polarity is in different parts of the combined LUT. In this particular implementation, the number of elements is 1088. Since 1088 is larger than 1024, 11 bits are required to address each element. This particular implementation can also specify 1024 different drive strengths using 10 address bits. Thus, the combined LUT addresses the storage location within the LUT using 21 address bits per polarity. Each storage location may include 10 bits for output. In this particular implementation, eight maximum validities of ten output bits can be used to specify 256 different drive levels. The remaining two bits effectively interpolate between drive levels by using dithering. In this case, each image frame can be refreshed four times. Thus, two bits can be used to dither between the first level and the next level during frame refresh. For example, if both bits are both zero, the first level may be displayed four times. If two bits are 0 and 1, the first level can be displayed three times and the next level once. If two bits are 1 and 0, the first level can be displayed twice, and the next level twice. Finally, if the two bits are both 1, the first level may be displayed once and the next level three times. Of course, other specific implementations of LUT addressing and output may be used.

In this specification, numerous specific details are provided, such as examples of apparatus, process parameters, data, process steps, and structures, to provide a thorough understanding of embodiments of the present invention. However, one of ordinary skill in the art will understand that the present invention may be practiced without one or more of these specific details. In other instances, well known details are not shown or described in order to avoid obscure aspects of the invention.

While certain embodiments of the invention have been provided, these embodiments are for illustrative purposes, and are not intended to be limiting. Many additional embodiments will be apparent to those of ordinary skill in the art upon reading this specification. Accordingly, the invention is limited only by the following claims.

Claims (20)

A method for bipolar operation of a light-modulated array, Driving light-modulating elements of the array at a first polarity; Switching polarity from the first polarity to a second polarity; Driving light-modulating elements of the array at the second polarity; And Switching polarity from the second polarity to the first polarity How to include. The method of claim 1, Repeating the preceding steps. The method of claim 2, Driving the light-modulation element at the first polarity includes reading a drive level from a first lookup table of drive levels corresponding to light intensity, and driving the light-modulation element at the second polarity. And reading the drive level from a second lookup table of drive levels corresponding to the light intensity. The method of claim 3, Switching the polarity from the first polarity to the second polarity includes switching from using the first lookup table to using the second lookup table, wherein the first polarity from the second polarity is used. Switching polarity to polarity comprises switching from using the second lookup table to using the first lookup table. The method of claim 1, Charging on the light-modulating element is reduced by bipolar operation of the light-modulating array. The method of claim 1, The photo-modulation array comprises a micro electromechanical system (MEMS). The method of claim 1, The element of the light-modulation array comprises a grating light valve type element. The method of claim 6, The MEMS is used to convert an optical signal in an optical network. The method of claim 6, The MEMS is used in a projection display system. An apparatus for bipolar operation of a light-modulated array, A first look-up table storing data for operating the elements of the light-modulated array in a first polarity mode; A second lookup table for storing data for operating the elements of the photo-modulation array in a second polarity mode; And And a drive system for driving the elements of the light-modulated array, wherein the drive system is coupled to both the first lookup table and the second lookup table. The method of claim 10, And the drive system is configured to access data from the first lookup table in the first polarity mode and to access data from the second lookup table in the second polarity mode. The method of claim 11, And the drive system switches back and forth between the first polarity mode and the second polarity mode. The method of claim 10, The charging on the light-modulating element is reduced by bipolar operation of the light-modulating array. The method of claim 10, The photo-modulation array comprises a micro electromechanical system (MEMS). The method of claim 10, And the elements of the light-modulation array comprise grating light valve type elements. The method of claim 14, The MEMS device is used to convert an optical signal in an optical network. The method of claim 14, The MEMS device is used in a projection display system. In a system using a light-modulated array, Means for driving light-modulating elements of the array at a first polarity; Means for switching polarity from said first polarity to a second polarity; Means for driving light-modulating elements of the array at the second polarity; And Means for switching polarity from the second polarity to the first polarity System comprising. The method of claim 18, Means for repeating the preceding step. The method of claim 19, Driving the light-modulating element at the first polarity comprises reading a drive level from a first lookup table of drive levels corresponding to light intensity, Driving the light-modulating element at the second polarity includes reading a drive level from a second lookup table of drive levels corresponding to light intensity, Switching polarity from the first polarity to the second polarity comprises switching from using the first lookup table to using the second lookup table, Switching polarity from the second polarity to the first polarity comprises switching from using the second lookup table to using the first lookup table.