Full color laser projection display is realized on the large screen using a krypton-argon laser (white laser) as a light source, and acousto-optic devices as light modulators. The main wavelengths of red, green and blue color are 647, 515, and 488 nm separated by dichroic mirrors which are designed to obtain the best performance for the s-polarized beam with the 45 degree incident angle. The separated beams are modulated by three acousto-optic modulators driven by rf drivers which has energy level of 1 watt at 144 MHz and recombined by dichroic mirrors again. Acousto-optic modulators (AOM) are fabricated to satisfy high diffraction efficiency over 80% and fast rising time less than 50 ns at the video bandwidth of 5 MHz. The recombined three beams (RGB) are scanned by polygonal mirrors for horizontal lines and a galvanometer for vertical lines. The photodiode detection for monitoring of rotary polygonal mirrors is adopted in this system for the compensation of the tolerance in the mechanical scanning to prevent the image joggling in the horizontal direction. The laser projection display system described in this paper is expected to apply HDTV from the exploitation of the acousto- optic modulator with the video bandwidth of 30 MHz.
With the continuing development of laser-display-technology, a new possibility for the production high level image projection is forwarded and with it the beginning of a new era in television: TV picture formats previously thought impossible, the sharpness, color intensity and unsurpassed resolution of which make the dream of home cinema a reality. The key to this experience is visible laser light in red, green and blue, projected on a screen with the aid of horizontal and vertical deflection units. In this paper, a primarily horizontal deflection system in the form of a rotating polygonal scanner is described. The design of this scanner assembly combines a double spherical air bearing with an integrated polygonal mirror for deflection and a high torque inside drive for quickly reaching high rotation. The Fraunhofer Institute of Applied Optics and Precision Engineering (IOF Jena) develops, from conception to assembled prototype, new self-acting precision bearing systems. This new scanner solution developed out of IOF's previous developments resulting in the first ever sealed, minimal-maintenance, self- acting bearing.
Projection display is one of the fastest growing markets of the display industry. Light-modulating systems are fast approaching technical, physical, and cost limitations. Amongst light-emissive systems only laser display offers sharp focus, color brilliance, and high resolution on a large screen. This paper delineates a large-screen laser display operating at 2XNTSC/PAL, and HDTV. The light engine is described, and the design and manufacturing of the high-performance polygonal scanning system is discussed.
The inertial stability of a uniquely balanced optical scanner is analyzed and reported. A scanner having two symmetric pairs of facets is balanced additionally to inertial stress, and is shown to exhibit significantly reduced dynamic deformation and scanned beam aberration. Evaluation of an aluminum scanner rotating at the high speed of 30,000 rpm reveals a developed focal spot astigmatic oblateness of less than 4%.
The usual xerographic polygon raster output scanner (ROS) design is a set of compromises among speed, image quality, reliability and cost. The design solution presented here pushes the ROS print speed and quality boundaries well beyond the desktop printer while keeping cost low. A dual diode laser source is used to simultaneously write two high resolution, high contrast scan lines that are offset in the cross-scan plane in an underfilled polygon embodiment. The benefits of a dual diode laser design are the high print rate with a low motor polygon assembly (MPA) speed; each beam power is half of that required of a single source; and the electronic data transfer rates are reduced by a factor of two. As the number of sources increases clearly so do these benefits. Reliable and cost effective MPA speeds are limited to less than 30,000 rpm. Multiple diode laser sources impose additional design constraints over single laser sources. The demanding image quality specifications of single laser ROS designs such as spot size and shape, wobble, bow and scan linearity must be achieved while managing new, multiple laser characteristics such as line separation and differential bow. Appropriate compromises of individual image quality parameters must always be made in order to achieve a system design that meets all of the image quality specifications over a reasonable depth of focus.
Holographic-based scanning systems have been used for years in the high resolution prepress markets where monochromatic lasers are generally utilized. However, until recently, due to the dispersive properties of holographic optical elements (HOEs), along with the high cost associated with recording 'master' HOEs, holographic scanners have not been able to penetrate major scanning markets such as the laser printer and digital copier markets, low to mid-range imagesetter markets, and the non-contact inspection scanner market. Each of these markets has developed cost effective laser diode based solutions using conventional scanning approaches such as polygon/f-theta lens combinations. In order to penetrate these markets, holographic-based systems must exhibit low cost and immunity to wavelength shifts associated with laser diodes. This paper describes recent developments in the design of holographic scanners in which multiple HOEs, each possessing optical power, are used in conjunction with one curved mirror to passively correct focal plane position errors and spot size changes caused by the wavelength instability of laser diodes. This paper also describes recent advancements in low cost production of high quality HOEs and curved mirrors. Together these developments allow holographic scanners to be economically competitive alternatives to conventional devices in every segment of the laser scanning industry.
This presentation is intended to provide a general overview of optical scanning from an optical designer's point of view. The level and content of this discussion is intended to be somewhat basic in nature, in the belief that newcomers to the field may benefit from this more elementary level of review. Hopefully it will provide a good springboard for the more specific and advanced papers in this session. A substantial portion of this presentation is contained in the viewgraphs that attempt to summarize key points.
The demands for increased throughput, pixel density, and format size in the laser beam imaging field continue to challenge opto-mechanical scanning products and the electronics that drive them. The polygon line scanner has superior scan rate and scan efficiency among candidate mechanical scanners but, historically, has had inferior cross- scan and in-scan accuracy. To date, due to cost considerations, these limitations have excluded the polygon scanner from practical use in high resolution, flat field, large format commercial applications. This paper illustrates the tradeoffs among the three most common mechanical scanners; single reflection rotary scanner, resonant galvanometric scanner, and polygon scanner. The purpose of this discussion is to illustrate that the polygon scanner holds the best promise of advancing the state-of-art in reasonable cost, large format, high resolution, flat field imaging once the problems of cross-scan and in-scan errors are reconciled in the design of the system. Also introduced is a polygon scanning system that fulfills the requirements of an advanced flat field, large format line imaging platform.
Light emitting diode (LED) printbars are finding wider use as imaging devices in digital copiers and printers. The key to their acceptance in high quality printers requires tight control of the image plane irradiance profile. As a first step in understanding the imaging capabilities of an LED printbar a measurement system was developed to characterize the radiometric performance of the printhead from a slit scan of the image plane. From this scan of the image profile, statistics on the pixel to pixel irradiance, pixel to pixel placement, and pixel to pixel image size and shape are developed for an entire LED printhead.
Two categories of optical beam steering micro-electro- mechanical systems (MEMS) were investigated: variable blaze gratings (VBGs) and linear optical phased arrays. All devices were surface micromachined using the multi-user MEMS processes (MUMPs). VBGs use an adjustable blaze angle to direct the majority of reflected light into a selectable diffraction order. Diffraction efficiencies greater than 50% were demonstrated. Linear optical phased arrays use a single row of piston micromirrors to create a far-field pattern with a steerable main lobe along one axis. All devices were constructed of polysilicon and gold and were actuated with electrostatic force. Electrostatic actuation provides high speed operation at a very low drive power. These optical beam steering devices discussed in this work are less optically efficient than a single pivoting mirror, but they require no post-fabrication assembly and can handle large beam diameters. Also, the low individual mass of the elements in surface micromachined VBGs and optical phased arrays yield faster system response times than a single macroscale pivoting mirror.
A solid-state broad band beam deflector is described. This non-mechanical system steers spatially coherent broad band light to a common location in the far field. The components include a liquid crystal grating and achromatic Fourier transformer. The liquid crystal grating employs a polarization modulation scheme which produces a wavelength independent phase shift. The achromatic Fourier transformer eliminates grating dispersion. The modulation theory for the liquid crystal grating is introduced. Observations of the far field patterns for white light illumination of a binary liquid crystal grating and the design for the achromatic Fourier transformer are presented. Future research, including mid- infrared implementation is discussed.
A novel type of electro-optic diffractive element is presented which can satisfy the requirements for a high space-time bandwidth deflector while providing for two-dimensional random access beam steering control. The basic device consists of a multichannel array of phase modulators fabricated using Lanthanum-modified lead zirconate titanate (PLZT) operating as a programmable diffractive optical element. Two-dimensional deflection control can be readily obtained by crossing two one-dimensional arrays. This device is useful for wavelengths in the visible to mid-IR range and is based on PLZT ceramic materials which can be readily mass-produced. It possesses the versatility and multifunctionality of liquid crystal based optical phased array systems while allowing for very fast switching speeds with good thermal stability. We present a brief comparison of this novel deflector with other scanning technologies and outline the benefits and trade-offs of the PLZT-based device. Experiments on 16- and 32-channel arrays with full wave voltages less than 400 volts demonstrate continuous lateral beam steering control of a HeNe laser beam. We also demonstrate full deflection control with a minimum number of control lines using a modified deflector arrangement. And we present measurements showing sub- microsecond switching speeds from such PLZT-based phase modulators. Mature versions of this type of scanner will find use in a wide variety of applications including 2-D and 3-D laser displays, laser communications, and LIDAR systems.
This paper reports on micromachined polysilicon scanning and rotating micromirrors and the development of a CMOS drive system. The micromirrors described in this research were developed at the Air Force Institute of Technology and fabricated using the DARPA-sponsored multi-user MEMS processes (MUMPs). The scanning micromirror is connected to the substrate using micro-hinges. This allows the mirror plate to rotate off the substrate surface and lock into a support mechanism. The angle between the scanning mirror and the substrate is modulated by driving the mirror with a thermal actuator array through a range of 20 degrees. For the rotating mirror, the mirror plate is attached to the substrate by three floating substrate hinges connected to a rotating base. Actuator arrays are also used to position the rotating mirror. A computer controlled electrical interface was developed which automates the positioning of both the scanning and rotating mirrors. The low operating voltages of the micromirror positioning mechanism makes the use of CMOS technology attractive; and the development of a digital interface allows for flexible operation of the devices. These designs are well suited for micro-optical applications such as optical scanners, corner cube reflectors, and optical couplers where electrical positioning of a mirror is desired.
Optical phased array technology has the potential to dramatically reduce the cost of pointing, tracking, beam stabilization, focusing, and beam fanouts. Optical phased array technology will also be able to provide an adaptive technology that allows internal optical system design 'reprogramming' as well as the traditional beam clean up functions. Flexible optical systems that can be reprogrammed will allow easier upgrade to include new technology or new requirements, a critical need for long life aircraft in a rapidly progressing and changing world. The vision for a final aperture is a simple flat surface similar to a flat panel display that provides random access rapid beam steering and other beam deflection functions. The vision for intermediate optical elements is one of reprogrammability to adapt to future requirements and technology developments. Three major approaches are considered to provide the physical implementation of optical phased array capability. They are liquid crystal writable grating technology, deformable micro- mirrors, and lenslet arrays.
Today diffractive elements are routinely designed and fabricated that diffract laser beams into hundreds of spots with diffraction efficiencies in excess of 90%. Thus it is easy to imagine that an electrically addressed phase-only spatial light modulator (SLM) could be used for the simultaneous and independent scanning of multiple spots in arbitrary directions. As opposed to single spot scanning, each spot would be present for the entire frame time of the modulator, thereby increasing dwell time over raster-based scanners. Key to actually achieving arbitrary scanning operations at real-time rates is the issue of specifying the electrical control values to the SLM. The control values are not obvious because arbitrary complex modulation is needed to produce arbitrary diffraction patterns. Calculation of the control values using global optimization (as is used to design diffractive optics) is too slow. Group oriented encoding procedures are fast but the use of groups to represent individual complex values reduces the resolution of the scanner correspondingly. The recently developed method referred to as pseudorandom encoding can be computed in real- time and does not sacrifice resolution. This statistically based encoding procedure is reviewed with emphasis on its performance and suitability for applications requiring multispot beam steering.
We have devised a nonmechanical beam-scanning system to subdivide a large field of regard into smaller fields of view and then to image these individual fields of view with high resolution. Selection of the individual fields of view is performed by spatially multiplexing the fields of view through an optical relay system onto a single camera. Selection of a particular field of view is accomplished by a series of ferroelectric liquid-crystal half-wave plates. We designed our beam-scanning system to cover a 3 degree multiplied by 12 degree field of regard in the mid-infrared waveband, and we built a proof-of-concept prototype to verify system performance. The prototype is a scalable building block that can be used to fabricate a two-dimensional system to scan a large field of regard at high resolution, low power, and high speed. We also describe how such a beam-scanning system can be combined with galvanometer-driven mirrors to produce a hybrid system that incorporates the advantages of both types of systems and minimizes the drawbacks of either system for very large fields of regard.
The objective of the design of the multibeam laser scanning system is to produce cost effective, high reliability, yet versatile system. This modulated and accurately calibrated multibeam design has a minimum jitter to produce high speed, high quality and low cost laser system.
A multi-point dynamic displacement probe was developed for measuring dynamic displacement and deformation. This method uses an acousto-optic deflector (AOD) as a diffractive scanner to allow the laser beam to scan a self-focusing microlens array (SMLA), and then uses the resulting focused spot to scan the diffuse surface. The focus information contained in the laser beam reflected from the diffuse surface is then transformed into the variations in shape of spot for detection. Due to the very high scanning speed of the AOD, the relative position of many points, and thus the dynamic deformation, can be measured in near real-time. This paper describes the method's principles, accuracy, and error sources.
Since 1988, Image Automation has marketed a float glass inspection system using a novel retro-reflective laser scanning system. The (patented) instrument scans a laser beam by use of a polygon through the glass onto a retro-reflective screen, and collects the retro-reflected light off the polygon, such that a stationary image of the moving spot on the screen is produced. The spot image is then analyzed for optical effects introduced by defects within the glass, which typically distort and attenuate the scanned laser beam, by use of suitable detectors. The inspection system processing provides output of defect size, shape and severity, to the factory network for use in rejection or sorting of glass plates to the end customer. This paper briefly describes the principles of operation, the system architecture, and limitations to sensitivity and measurement repeatability. New instruments based on the retro-reflective scanning method have recently been developed. The principles and implementation are described. They include: (1) Simultaneous detection of defects within the glass and defects in a mirror coating on the glass surface using polarized light. (2) A novel distortion detector for very dark glass. (3) Measurement of optical quality (flatness/refractive homogeneity) of the glass using a position sensitive detector.
The present paper introduces new electro-optical sensing technology for electronic blackboard and related passive stereo measurement applications. The electronic blackboard enables real-time digitization of hand-written and hand-drawn information using a totally passive writing surface and writing instrument. Two resonant laser scanners sweep out a plane, the angular position of the two beams (at the instants that the beams are interrupted by the laser beams of a hand- held stylus such as a felt tip marker) are detected. These data are used to digitize coordinates along hand-drawn lines with high precision (approximately 1 part in 25,000) and digitization rates (approximately 160 Hz). The data input surface dimensions vary from small to large (permitting digitization on wall-sized writing surfaces as large as 2 meters by 6 meters) thus enabling a new family of applications. In particular, we discuss a novel application of this laser digitizing system to the automation of class or conference room presentations, and the authors describe a newly developed multimedia podium for classroom presentations. Other applications exist in emerging multi-media systems, manufacturing and robotics, large area digitizing for the drafting market, and automated note taking for the education market.
The use of filmless laser scanner (FLS) for medical imaging can provide many benefits including improved diagnostic quality, better user interface and time and operating cost efficiency. From the beginning radiography has depended on silver-halide film for recording and displaying images. The use of phosphor as x-ray to light converter has intrigued scientists and engineers for many years and phosphors are used in many forms in a variety of applications. The acceptance of digital imaging in the medical field has triggered an increased interest in an improved and new imaging sensors for x-ray which generated new products. Phosphor plates and CCD are among the most popular sensors currently used commercially. This development is based on the use of phosphor plate which have been found to be far superior in performance and cost-effectiveness than competitive media. The laser scanner is integrated with a computerized workstation which provides image control, display and analysis as well as archiving and communication of x-ray images for the dental industry.
A non-contact body measurement system (BMS) is under development for use in making made-to-measure apparel, and for other applications related to body measurement. The BMS design is discussed which consists of six stationary structured-light projectors and six CCD cameras utilizing a phase-shifting technique. The solution for calculating three-dimensional surface points of a human body from the camera images is described. A statistical error analysis is summarized for the phase measurement error due to image noise. The phase errors due to image and pattern quantizations are analyzed. the effect of phase measurement error upon the three-dimensional point solution is shown in terms of the system parameter values. An operating development implementation of the BMS is described and pictured. Contour plots of test subjects taken with this system, showing digitized three-dimensional surface segments, are presented and discussed.
Holographic scanning systems have been used for years in point-of-sale bar code scanners and other low resolution applications. These simple scanning systems could not successfully provide the accuracy and precision required to measure, inspect and control the production of today's high tech optical fibers, medical extrusions and electrical cables. A new class of instruments for the precision measurement of industrial processes has been created by the development of systems with a unique combination of holographic optical elements that can compensate for the wavelength drift in laser diodes, the application of proprietary post-processing algorithms, and the advancements in replication methods to fabricate low cost holographic scanning discs. These systems have improved upon the performance of traditional polygon mirror scanners. This paper presents the optical configuration and design features that have been incorporated into a holographic scanning inspection system that provides higher productivity, increased product quality and lower production costs for many manufacturers.
One approach to the design of a non-contact, automated system able to measure in three axes is based on triangulation. A system comprised of a CCD sensor and laser source oriented to each other in a triangulation configuration will provide range information. Taking this arrangement and scanning it with the use of a rotating polygonal mirror over a moving conveyor allows for three axis measurement. There are many considerations and parameters that must be taken into account when such a system is designed. The most critical parameter is the triangulation angle which has direct effects on resolution, working distance, and the size of the completed unit. A method is presented to design a system that will measure the length, width and height of a moving object. The genal approach is covered and the major parameters to be decided upon are explained.
Recently developed undersea imaging systems are cable of providing three-dimensional surface maps of the image space using a scanning laser configuration. Triangulation methods, whereby the scene is viewed from a separate location, provide depth information, while instantaneous position of the laser scanning elements are used to estimate the lateral position in object space. A specially developed detector provides an approximate position for the apparent landing spot of the laser beam for each scan angle, which in turn, is used to compute an estimated range value in real time. Several prototype systems constructed using these techniques are in a testing phase. One system reported here is designed to scan a 10 by 10 degree field-of-view with a 10 milliwatt laser at distances from 20 to 40 centimeters with a resolution of less than 1 millimeter.
Invasion by cells with malignant or transformed phenotypes precedes destruction of adjacent tissue and fatal cell metastasis. State-of-the-art confocal laser scanning technology facilitates both in vitro and in vivo research into cell invasion and metastasis. In particular, studies performed with living cells yield more precise information than those with fixed cells, giving new insight into cell invasion and metastasis. We have tested a variety of vital florescent dyes and fluorogenic protease substrates in our studies of invasion of cartilage by transformed synoviocytes or osteosarcoma cells. The fluorescent dyes tested include Calcein acetoxy methyl-FITC (Calcein), Hoechst 33342 (Hoechst), CellTracker, DiI, DiO, DiD, and ethidium bromide (EB). The fluorogenic protease substrate used Meoxysuccinyl-Gly-Pro-Leu-Gly-Pro-AFC (MOS-GPLGP-AFC) for detection of collagenase activity. We found that Calcein-FITC labeling permitted the clearest direct observation of the penetration of transformed synoviocytes and osteosarcoma cells into cartilage. Even better results were obtained when chondrocyte nuclei were counter-stained with Hoechst 33342. During the invasion process, collagenase activity was observed around the synoviocyte in the cartilage matrix labeled with the fluorogenic collagenase substrate. We concluded that of the vital fluorescent dyes tested, a combined application of Calcein-FITC, Hoechst 23223, and MOS- GPLGP-AFC is most appropriate for the study of the cell invasion process.
This paper reports design and characterization testing of thermally actuated piston micromirror arrays. The micromirrors were fabricated in the DARPA-sponsored MUMPs polysilicon surface micromachining process. The power averaging characteristic of thermal actuation is exploited in a novel line addressing scheme which reduces wiring for an n2 array to 2n wires. Mirror deflections were measured with a microscope laser interferometer system equipped with a vacuum chamber. Data presented includes device uniformity, frequency response, and deflection versus drive power for varied ambient pressure. Initial test results confirm that thermally actuated piston micromirrors offer several advantages over more common electrostatic designs. Thermally actuated micromirrors offer greater deflections at drive voltages compatible with CMOS circuitry. Measured thermal piston micromirror deflection versus drive voltage is nonlinear, but does not exhibit the 'snap through instability' characteristic of electrostatic devices. Operation of thermally actuated devices in rarefied ambient significantly decreases power dissipation. For a given deflection range, the power reduction facilitated by vacuum operation makes large arrays feasible. Frequency response of thermally actuated devices is limited by the ability of the device to dissipate heat, but operation at 1 kHz rates is feasible.
Two key problems for designing laser scanning confocal microscopy (LSCM)are : 1 ) how to design a nice laser focusing system for getting the small focusing spot for iliminating object;2)how to design excellent microscopiel imaging systen for getting the poinat image which has high contrast .These problems decide the resoluion of LSCM. This paper anslysed the optical character of LSCM by Fourier theory and dicussed the effective confocal spot will depend the optics used, the aberration of optical system, and the size of pinhole Key words: laser,scanning system, confocal microscope, Fourier analyes,resolution
The new formula that was used to develop the free-form-surface is more advantageous in regard to spot size and linearity than usual aspherical and troidal lens systems. However, the free form surface is much more complicated, compared to the usual optical system. Now, we would like to express the advantage of the free-form-surface design. We had to improve the nano CADCAM and compensation systems for the fabrication of injection molded plastic optics. In the future we plant to design a new optical system, now that the development of the one-piece f-theta lens has been completed. We describe the free-form optics now.
The advances in the digital data processing and in design and manufacturing of high-performance single-facet scanning devices have made large scan-angle, high-speed/high-resolution digital imaging on cylindrical surfaces possible. Single facet deflectors operating at high speeds in open air tend to be noisy (70+ dBA at 30,000 rpm), collect contaminants (hence requiring frequent cleaning), and require high power to overcome the windage (hence high heat dissipation). For converging laser beam systems, flat and cylindrical window enclosures cannot be used as they induce astigmatism. A spherical window enclosure introduces power and spherical aberration. However, when a spherical window enclosure is used with a spherical lens before the deflector, power and spherical aberration can be eliminated.
A multiple channel optical modulator provides a means of parallel information processing and enables fast laser printing. We have studied a multiple channel optical modulator utilizing total internal reflection (TIR) and the electro- optical properties of LiTaO3 crystals. We characterized the multichannel TIR modulator by illuminating it separately with a source of a single mode coherent radiation (a Ti:Sapphire laser), and with a source of multimode radiation (a laser diode). The best contrast ratio (on/off intensity ratio) is 100:1, and a contrast ratio of 20:1 is achieved at a driving voltage as low as 60 V. No significant cross-talk has been observed at a modulation frequency of 10 Hz. We found that the response of the modulator is very strongly influenced by the spatial coherence of the illumination source. We also found the presence of a photorefractive effect induced by the high power density of the impinging light beam. This photorefractive effect is not permanent, and can be recovered if the laser illumination is removed for a period of time.