Optical device arrays with optimized image resolution

[0002] The present invention relates to the field of optical devices. More particularly, the present invention relates to tiling a plurality of arrays of optical devices configured for imaging with higher resolution than provided by a single array.

[0003] Print and display resolution has become a critical parameter in the design of imaging systems. From paper print, photo print and display, industries are demanding higher and higher resolutions for a wide range of imaging applications. Besides the higher resolution, there is also a demand for reproducing images with minimal artifacts, distortions and/or other defects.

[0004] One solution for the demand of high fidelity and high resolution print and display imaging has been to use imaging systems capable of generating images with a greater number of smaller pixels. In certain applications, pixels are configured as a linear, or substantially linear, arrays of pixels for generating an image line on a display unit or print medium.

[0005] Optical MEM (micro-electro-mechanical) devices are useful in imaging technologies. Examples of optical MEM devices that can be used in imaging technologies are disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, all issued to Bloom et al., the contents of which are hereby incorporated by reference.

[0006] Briefly, optical MEM devices described in the above referenced patents have one or more sets of movable ribbons that comprise a support layer and a reflective top-layer. The support layer is preferably a silicon nitride layer and the reflective top-layer is preferably an aluminum layer. The ribbons are coupled to a substrate at opposite ends of the ribbons, whereby center portions of the ribbons (active portions) move up and down to modulate an incident light source. Imaging with the aforementioned optical MEM devices offers the capability of generating high contrast, high resolution images efficiently within a compact circuit package. In certain applications, each pixel within an image is formed with three or more sets of ribbon pairs.

[0007] What is desired is a method of making an array of optical MEM devices for imaging which is capable of generating image lines with high resolution while minimizing artifacts, distortions, and/or other defects.

[0008] Embodiments of the invention are directed to optical devices, arrays of optical devices and related methods. In accordance with the embodiments of the invention, an optical device preferably comprises an array of addressable optical MEM devices having ribbon pairs for modulating a light source. The array of ribbon pairs are grouped into a center group and end groups. The center group has sets of ribbon pairs, such as three ribbon pairs per set, that are collectively addressed to image pixels. The end groups have fractional sets of ribbon pairs, such as one pair of ribbons per set, that are addressed to image sub-pixels. The optical MEM device preferably comprises bond pads corresponding to each set and fractional set of ribbon pairs for coupling to a driver circuit. It will be apparent to those of ordinary skill in the art that optical devices other than MEM devices can be used including arrays of liquid crystal display (LCD) pixels. In such a case, a sub-pixel of an LCD would be formed of a separately addressable LCD device which is reduced in size relative to an LCD pixel. The present invention can be implemented using an LCD formed using any conventional LCD technology.

[0009] The ribbons are preferably elongated ribbons formed from silicon-based materials, such as silicon-nitride, silicon-oxide and combinations thereof. The ribbons preferably have layers of reflective material, such as aluminum, for reflecting light from the top surfaces of the ribbons. The ribbons can have any dimension suitable for the applications at hand, but preferably have lengths in a range of about 50 to about 500 microns and widths in a range of about 4.0 to about 40 microns and are capable of modulating light having at least one wavelength in a range of about 300 to about 3000 nanometers.

[0010] An apparatus, in accordance with embodiments of the invention, comprises one or more linear arrays of optical MEM devices for generating pixels in an image line. The array comprises a first row of optical MEM devices and a second row of optical MEM devices that are tiled in a staggered configuration with respect to the first row, such that end groups of ribbons, as described above, form overlap regions for generating pixels in the image line. In accordance with further embodiments, the apparatus comprises a third row of optical MEM devices staggered relative to the first row and/or second row. In yet further embodiments, the apparatus comprises a display means, such as a screen or a monitor for displaying image lines and/or a print means for printing image lines onto a suitable print medium.

[0011] In accordance with the method of the invention, optical MEM devices configured for generating pixels and end sub-pixels are tiled (arranged) in an array, with the ends forming overlap regions, as described above. A test image is generated from the array and selected end sub-pixels, or sub-pixels and pixels, are disabled or suppressed to optimize the image quality and/or tailor the image quality for the intended application. Preferably, selected sub-pixels are disabled to remove artifacts and defects and to maximize pixel density of the image line corresponding to the overlap regions.

[0012] FIG. 1 illustrates a schematic top-view of optical MEM devices tiled in an end-to-end configuration.

[0013] FIG. 2 illustrates a schematic top-view of optical MEM devices tiled in a staggered configuration and forming an overlap region.

[0014] FIG. 3 illustrates artifacts that can occur in an array of optical MEM devices tiled in a staggered configuration, as shown in FIG. 2.

[0015] FIG. 4 illustrates a schematic top-view of optical MEM devices tiled in a staggered configuration with center pixels and end sub-pixels, in accordance with the invention.

[0016] FIG. 5 illustrates a schematic top-view of a overlap region modified in accordance with the invention.

[0017] FIG. 6 illustrates a schematic top-view of a overlap region modified in accordance with alternative embodiments of invention.

[0018] FIG. 7 illustrates a schematic top-view of an overlap region modified in accordance with further embodiments of the invention.

[0019] FIG. 8 illustrates a schematic top-view of an array of optical MEM devices tiled in accordance with the invention.

[0020] In a preferred embodiment of the present invention, optical MEM devices are used to modulate one or more wavelengths of light. The optical MEM device preferably comprises an array of ribbon structures to modulate light, such as those disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, and referenced previously. However, any number of different optical devices or light modulator devices, such as LCD-based light modulators, which can be tiled and fractionated in the manner described below are considered to be within the scope of the invention. It will be apparent to those of ordinary skill in the art that optical devices other than MEM devices can be used including LCD arrays. Where the invention is implemented using LCD technology, an LCD pixel is formed of a pixel sized LCD device. The size of the pixel could be that of a display or of a size that is optically manipulated to form a pixel. A sub-pixel of an LCD would be formed of a separately addressable LCD device which is reduced in size relative to an LCD pixel. The reduction in size of an LCD sub-pixel is relative to the degree of variability required for tiling according the specific implementation. The present invention can be implemented using an LCD formed using any conventional LCD technology. While the following discussion is made relative to the preferred optical MEM device, it will be apparent after reading this disclosure that other light modulators can be substituted.

[0021] An array of optical MEM devices can be fabricated on a single chip. However, the circuit requirements to minimize the number of bonding pads in such an integrated process is both costly and complex. Alternatively, an array of optical MEM devices can be tiled, or arranged, on a wafer or substrate that is configured to support and secure the optical MEM devices. The optical MEM devices are preferably tiled in a high density configuration to maximize the pixel density of an image line generated therefrom. Unfortunately, there are limitations to tiling processes and there are manufacturing tolerances associated with the fabrication of the optical MEM devices themselves, which can both lead of imaging artifacts and defects, as described below.

[0022] FIG. 1 schematic top-view of optical MEM devices 100A and 100B tiled in an end-to-end configuration is to generate an image line. Each block within each optical MEM device 100A and 100B schematically represents a pixel. However, it is understood that each block can represent multiple ribbon pairs that are collectively addressed to image a pixel on the image line.

[0023] Still referring to FIG. 1, one shortcoming with placing optical MEM devices 100A and 100B in the end-to-end configuration 10 is that pixels 11 do not extend to the edge of each of the optical MEM devices 100A and 100B, because support structures (not shown) and bonding pads (not shown) occupy the outside area surrounding the optical MEM devices 100A and 100B. Accordingly, a pixel, or pixels are not generated on the image line corresponding to the interface or overlap region 40 resulting in a visible defect (typically a stripe oriented along the scan axis).

[0024] FIG. 2 illustrates a schematic top-view optical MEM devices 100A and 100B tiled in a staggered configuration 20 and forming an overlap region 40 for generating an image line. Because the optical MEM devices 100A and 100B are placed in an offset, or staggered configuration, pixels 10 overlap in the overlap region 40.

[0025] With the configuration 20 schematically shown in FIG. 2, the overlap region 40 corresponds to the width of a single pixel. Generally, each pixel in this configuration is designed to image a unique location on the image line to maximize the image fidelity and minimize artifacts and distortions. To achieve this condition, one of the pixels 11A or 11B can be disabled or suppressed to avoid having more than one pixel imaged on the image line; a condition which could cause a distortion in the image line. Unfortunately, tiling processes have tolerances that are on the order of a hundred microns or higher. Since the width of a pixel is on the order of a few microns, or less, the ideal alignment of a single end pixel, such as shown in FIG. 2, can not be consistently be achieved.

[0026] FIG. 3 schematically shows a pixel alignment which can result from tiling the optical MEM devices 100A and 100B in a staggered configuration 13 using current tiling methods. The pixels 11B and 12B both overlap with portions of pixel 11A. Under these circumstances, the pixel 11B can be disabled to avoid multiple pixels imaging the identical location of the image line. However, pixel 12B and pixel 11A both remain active to avoid a blank region on the image line, a distortion of the image line which is unacceptable for high resolution imaging applications.

[0027] FIG. 4 illustrates a schematic top-view of optical MEM device 200A and 200B tiled in a staggered configuration 210, in accordance with the invention. For simplicity purposes, only two optical MEM devices are shown. However, arrays comprising any number of staggered optical MEM devices are considered to be within the scope of the invention. Each of the optical MEM devices 200A and 200B includes a plurality of ribbon pairs. Preferably, the ribbon pairs are arranged as a linear array, or substantially linear array for generating pixels on an image line. The optical MEM devices 200A and 200B preferably have an equal numbers of pixels and/or ribbons, or alternatively have different numbers of pixels and/or ribbons. The preferred number of pixels in each of the optical MEM devices 200A and 200B is determined by the intended application and the desired resolution.

[0028] Still referring to FIG. 4, the optical MEM devices 200A and 200B include central groups 213 of center pixels 214, and end groups 217 of end pixels 215A, 215B, 216A and 216B. The optical MEM devices 200A and 200B are arranged in a staggered configuration such that end pixels 215A and 216B are at opposite ends of the array 210 and the end pixels 215B and 216A at least partially overlap in the overlap region 250. The end pixels 215A, 215B, 216A and 216B are divided into sub-pixels 218, each comprising one or more ribbon pairs. The sub-pixels 218 are configured to be individually addressed to optimize the image generated in the overlap region 250 of the array configuration 210, as explained below. Accordingly, the optical MEM devices 200A and 200B require bonding pads for each center pixel 214 and each sub-pixel 218, wherein individually controlled driver signals can be applied to selected ribbon corresponding to each center pixel 214 and each sub-pixel 218.

[0029] FIG. 4 illustrates the end pixels 215A, 215B, 216A and 216B being divided into three sub-pixels 218. However, the end pixels 215A, 215B, 216A and 216B can be divided into any number sub-pixels depending on the application at hand and the desired resolution. Preferably, however, the end-pixels 215A, 215B, 216A and 216B are divided into fractional sub-pixels, wherein a selected number of sub pixels represent one center pixel 214.

[0030] As illustrated in FIG. 4, the optical MEM devices 200A and 200B are tiled into the array configuration 210 with an overlap region 250 which is dependent on manufacturing processes and tolerances. Accordingly, the overlap region 250 will vary from array to array and between adjacent optical MEM devices in an extended array configuration 250, such as shown in FIG. 8. As described below, sub-pixels 218 and pixels can be selectively controlled and/or suppressed to minimize artifacts and defects of the image line

[0031] While FIG. 4 shows a single overlap region 250 the invention is particularly useful for optimizing the image quality generated from an extended linear array of densely tiled optical MEM devices, wherein the optical MEM devices are tiled in staggered rows. Also, the principles and applications of the invention can be readily extended larger two dimensional arrays of optical MEM devices.

[0032] Embodiments of the invention allow for optical MEM device arrays capable of generating high resolution image lines and which can be tailored to the specific imaging demands of a specific application. High resolution staggered arrays of optical MEM devices can generate image lines with resolution that approaches the sum of the resolutions afforded by each of the optical MEM devices 200A and 200B. For example, if each of the optical MEM devices 200A and 200B image 1000 pixels, the array 210 can image nearly 2000 pixels. In accordance with embodiments of the invention, variations in the overlap regions between optical MEM device tiled in staggered rows are compensated, adjusted or modified by selectively disabling selected sub-pixels and/or sub-pixels and pixels to minimize artifacts and defects in the overlap regions. Further, by selectively operating pixels and/or suppressing sub-pixels 218 and/or center pixels 214, the image quality can be optimized, as described below.

[0033] With a staggered array of optical MEM devices, selective pixel and/or sub-pixel addressing can be used to compensate for a distribution of pixels generated from an extended array 230 of an optical MEM device tiled in a first row and a second row, such as shown in FIG. 8. Selective addressing of pixels and/or sub-pixels can be done, for example, with selective timing adjustments of driver signals applied to the ribbons. Alternately, or in addition to timing adjustments of driver signals, optics can be used to correct for the fact that a single image line is being generated from two or more rows in the optical array. For example, a first optical system can be implemented for imaging pixels from the first row while a second optical system can be implemented for imaging pixels from the second row, wherein each optical system makes the necessary optical changes to compensate for pixels being generated from two or more rows in the extended optical array 230.

[0034] FIG. 5 illustrates an overlap region 250A after the overlap region has been arrangement modified to improve the image quality. Here, the overlap region 250A includes a first end pixel 216C and a second end pixel 215D. The driver signals to the sub-pixels 218C are suppressed so that these sub-pixels 218C do not contribute the image formed in the overlap region 250A, while the sub-pixels 218A and 218B remain active. There will still be distortion in the overlap region 250A due to the fraction of the sub-pixel 245A generated by both the sub-pixel 218A and the sub-pixel 218B. However, the distortion in the overlap region 250A is minimized relative to the distortions that can result from the configuration 13 shown in FIG. 3.

[0035] FIG. 6 illustrates a schematic top-view of an overlap region 250B modified in accordance with an alternative embodiment of the invention. In this example, the overlap region 250B comprises two end pixels 216D from the device 200E and two end-pixels 215E from the device 200F. Driver signals are suppressed to the sub-pixels 218E, such that the sub-pixels 218F do not contribute to the image formed by the overlap region 250B. There will be distortion in the overlap lap region 250B due to the fraction of the sub-pixel 245B generated by both the sub pixel 218D and the sub-pixel 218E. However, the distorting in the overlap region 245B is minimized relative the distortions that can result from configuration 13 shown in FIG. 3.

[0036] FIG. 7 illustrates a schematic top-view of an overlap region 250C modified in accordance with further embodiments of the invention. In this example, the overlap region 250C comprises two end pixels 216E from the device 200G and two end-pixels 215F from the device 200H. The overlap region 250C also includes a portion of a center pixel 222A from the device 200G. To optimize the image formed by the overlap region 250C, the driver signals to all of the sub-pixels 218G are disabled, such that the sub-pixels 218G do not contribute to the image formed by the overlap region 250C. Again, there is some distortion in the overlap region 250C due to the fraction of the image 245C generated by both the sub-pixel 218H and the center pixel 222A. However, the distorting in the overlap region 250C is minimized relative the distortions that can result from the configuration 13 shown in FIG. 3.

[0037] The selection of which driver signal to suppress and/or which pixels and sub-pixels to suppress can be judiciously made using any number of methods including physical inspection of a test image generated by an array. Other methods include computer enhanced methods, whereby images generated by a first row of optical MEM devices, a second row of optical MEM devices and the array of optical MEM devices comprising the first and the second rows, are captured and analyzed to identify the location of defects. Any number of image analysis methods and image manipulation techniques as applied to staggered array of optical MEM devices, are considered to be within the scope of the invention.

[0038] FIG. 8 illustrates a schematic top-view of an array of optical MEM devices 200I, 200J, 200K, 200L and 200M that are tiled in a staggered configuration 230 for generating an image line, in accordance with the invention. Each of the optical MEM devices 200L 200J, 200K, 200L and 200M comprise a liner arrangement of ribbon structures elongated in a direction that is substantially perpendicular to the length L of the array 230. The optical MEM devices 200I, 200J, 200K, 200L and 200M overlap to form the overlap regions 261, 263, 265 and 267. The overlap regions 261, 263, 265 and 267 comprise end pixels device into sub-pixels and/or center pixels, as described above. The array configuration 230 can be extend to have any number of optical MEM devices suitable for the application at hand.

[0039] An imaging apparatus in accordance with embodiments of the invention comprises a light source for generating light having one or more wavelengths in a range of about 300 to about 3000 nanometers and suitable optics for generated image lines from the array of optical MEM devices. The imaging apparatus can also include a display unit, such a monitor and screen for displaying the image lines generated from the array of optical MEM devices. In yet further embodiments, an imaging apparatus comprises printer for printing image lines generated from the array of optical MEM devices onto a suitable print medium. The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles, the construction and the operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications may be made in the embodiments chosen for illustration without departing from the spirit and scope of the invention. In particular, eliminating the sub-pixels which are not part of an overlap region and which are located at opposite ends of an array of optical MEM devices is within the scope of the present invention. Further, tiling arrays of optical MEM devices in more than two rows is also contemplated.