The main challenge in developing a LED-based projection system is to meet the brightness requirements of the market. Therefore a balanced combination of optical, electrical and thermal parameters must be reached to achieve these performance and cost targets. This paper describes the system design methodology for a digital micromirror display (DMD) based optical engine using LEDs as the light source, starting at the basic physical and geometrical parameters of the DMD and other optical elements through characterization of the LEDs to optimizing the system performance by determining optimal driving conditions. LEDs have a luminous flux density which is just at the threshold of acceptance in projection systems and thus only a fully optimized optical system with a matched set of LEDs can be used. This work resulted in two projection engines, one for a compact pocket projector and the other for a rear projection television, both of which are currently in commercialization.
We have built a mini-projector with LED light sources that is sufficiently small for portable applications. The projector has a three-panel architecture with transmissive LCD micro-displays in order to combine a high lumen output with a low cost price. The volume of the light engine is 100 cc.
In our contribution we present a solution to an important question in the design of a LED-based illumination engine for projection systems: the collimation of the LED light. We tested the principle in the modification of a common device in non-imaging optics, the compound Parabolic Concentrator. This CPC-like achieves a collection of 72% (ideal reflective coating presumed). This CPC-like was tailored by numerically solving an differential equation. This approach has some serious drawbacks. For a compact collection device with high collimation, an other approach is required. A more elegant design strategy will rely fully on geometrical principles. The result of our work is a compound collection lens that achieves a collection efficiency of 87%, assuming an ideal reflective coating and neglecting Fresnel losses. We study the performance of this device in detail. Further enhancements are suggested.
LED based projectors have numerous advantages compared to traditional projectors: they are more compact, exhibit a larger color gamut and a longer lifetime, the supply voltage is lower, the absence of ultra violet, infrared radiation and mercury vapour, etc. Furthermore LED's can switch on and off very rapidly (possibility to pulse them) and they have a high dimming ratio that can be used to improve the contrast. However, there is also an important disadvantage: the optical power per unit of etendue (luminance) of an LED is significantly lower than that of e.g. an UHP-lamp. Because of this and the etendue limitation of the projector (small light valve, f-number projection lens), the projected flux on the screen will not be high. Despite this shortcoming, LED's are still very interesting for low power applications because of their superior properties. However we have to collect the available light flux optimally and combine multiple LED's with high luminance within the available system etendue. In this paper we have studied collection optics that collect the LED flux with high optical efficiency and collimation and reshape the spot in a uniform illuminated rectangle with the sizes of the micro display. We have designed 'Gradually Tapered Light Pipes', 'Elliptical Reflectors' and 'Parabolic Reflectors'. Furthermore we have combined many of these LED/collector combinations to get a high luminance illumination engine for LED based projectors.
Illumination systems with lens array integrators for LED-based projection systems are thoroughly investigated. The aim is to develop compact and efficient projection systems with a high image-quality. Different possible illumination configurations for single-panel LCOS projection architectures, are critically evaluated with the use of advanced optical simulations. LED-light collectors which are to be used in combination with the lenslet integrators are also investigated.
This paper gives an overview of the requirements for, and current state-of-the-art of, CCD and CMOS imagers for use in digital still photography. Four market segments will be reviewed: mobile imaging, consumer "point-and-shoot cameras", consumer digital SLR cameras and high-end professional camera systems. The paper will also present some challenges and innovations with respect to packaging, testing, and system integration.
The visual revolution triggered by the commercial application of digital image capturing devices generates the need for new miniaturized and cheap optical imaging systems and cameras. However, in imaging we can observe only a permanent miniaturization of elements but always similar optical principles are applied which are known to the optical designers for many decades. With the newly gained spectrum of technological capabilities it is the time to ask: Which vision principle should be used at which level of miniaturization and which technology has to be applied in order to achieve the perfectly adapted imaging system? In this paper we present an overview of two insect inspired artificial compound eye concepts for compact vision systems fabricated by lithographic technologies, one classical miniaturized objective and its wafer-scale fabrication and the use of variable focal length liquid lenses for miniaturized autofocus- and zoom objectives without moving parts.
This paper gives an overview of featuring possibilities in CCD imagers. By careful manipulation of charge packets in CCD imagers, a CCD can often be read out in different modes by simply modifying the applied pulse patterns. Since featuring is done in the charge domain and not in the voltage domain, it offers the best possible performance with respect to noise, dynamic range and signal-to-noise ratio.
Our new type of camera module has a four-lens-array and an imaging sensor. The imaging sensor is divided to four regions, and these four regions are aligned in one-to-one correspondence with the four lenses. Four color filters are placed over the four imaging regions. First region has a blue filter, second has a red, and the other two have green filters, and two regions with green filters are aligned diagonally. Diffraction gratings are formed on aspheric surfaces of the four lenses, and MTF characteristics of these lenses are improved. The four images taken through the different lenses have parallax, but these parallaxes can be calculated by comparison of the two green images. Pixel shifts of blue, red and green images are realized by rotating the four-lens-array slightly with respect to the imaging sensor. After correcting the parallaxes, the green image, the parallax-corrected blue image and the parallax-corrected red image are composed to generate the resultant color image with high resolution. Distances between objects and the four-lens-array are detected by use of the above parallaxes, and measurement error is less than 2.5% for near objects. With above configuration and functions, our camera module has realized smaller height, higher image resolution and distance-detection capability, and will be applied for cellular phones and automobile vehicles.
One of the fastest growing markets in consumer markets today are camera phones. During past few years total volume has been growing fast and today millions of mobile phones with camera will be sold. At the same time resolution and functionality of the cameras has been growing from CIF towards DSC level. From camera point of view the mobile world is an extremely challenging field. Cameras should have good image quality but in small size. They also need to be reliable and their construction should be suitable for mass manufacturing. All components of the imaging chain should be well optimized in this environment. Image quality and usability are the most important parameters to user. The current trend of adding more megapixels to cameras and at the same time using smaller pixels is affecting both. On the other hand reliability and miniaturization are key drivers for product development as well as the cost. In optimized solution all
parameters are in balance but the process of finding the right trade-offs is not an easy task. In this paper trade-offs related to optics and their effects to image quality and usability of cameras are discussed. Key development areas from mobile phone camera point of view are also listed.
This paper presents a non conventional optical imaging system providing two very important features. The first one is related to new way of obtaining optical zooming, i.e. a super resolved imaging at the center of the field of view and yet allowing seeing the remaining of the original field of view with the original resolution. This operation resembles optical zooming while the zoomed and the non zoomed images are obtained simultaneously. This is
obtained by taking a single snap shot and using a single imaging lens. The technique utilizes a special static/still coding element and a post processing algorithmic, without any mechanical movements or/and increase of the focal length of the lens module. The second feature is related to extended depth of focus, i.e. axially super resolved imaging where the depth of focus is extended using a binary phase and non diffractive optical mask attached to the entrance pupil of the lens module. The increase in the depth of focus is obtained by all-optical means.
There is a great demand today for ever-smaller low-cost zoom lenses for digital cameras. To meet this demand, we have been realizing some compact zoom lenses by using plastic lens elements. Nowadays, plastic lens elements produced by injection molding are widely used in zoom lenses for digital cameras because of their suitability for volume production and ease of forming aspherical surfaces. Although using plastic lens elements in digital camera zoom lenses has its advantages mentioned above, there are some difficulties to be overcome for using plastic lens elements, such as an elevated sensitivity to the temperature change and the non existence of high-refraction materials. In this paper, we show some examples of commercialized digital camera zoom lens optical designs employing plastic lens elements such as a) retractable 3x zoom lens for digital still cameras and, b) 3x zoom lens using a right angle prism for digital still cameras and c) 25x zoom lens for digital camcorders in which benefits of plastic lens elements are effectively exploited and drawbacks of the material are well overcome.
This paper gives an outline of the coverage of the Standard Mobile Imaging Architecture (SMIA) standard and its adoption by the mobile phone industry for camera phone applications. The different elements of the standard, including functionality, interface, package options, and characterization will be described in brief. The paper then moves on to describe in detail image sensor characterization using the SMIA standard. The overall test method, and coverage will be reviewed along with the detail of the individual tests, highlighting the depth of detail of the SMIA characterization documentation. Both electrical and optical tests are reviewed with some emphasis on the colour accuracy test. Throughout this paper where required, the example of a typical CMOS camera module will be used to illustrate the method of parameter extraction. Finally, the paper examines some of the exceptions to and possible weaknesses of the current SMIA characterization standard and considers future possible revisions of the standard. This includes both refinements of and improvements in the existing test coverage and extension of the standard into areas it does not cover today, for example the definition of test requirements for auto-focus and optical zoom modules.
Advances in design, materials and production technology for micro-optical components have led to strong growth in their use in today's consumer products. In particular, micro-optical components produced by replication technologies such as UV embossing can now withstand the severe processing and environmental requirements of the consumer
electronics industry, including lead-free IR reflow and thermal shock. With their small size and low weight, as well as the possibility of optical function not achievable by conventional optics, micro-optical components and systems are finding applications in a wide variety of products. In the field of multimedia, novel designs and new production techniques are enabling applications in key areas such as illumination and display. The extreme compactness of micro-optical components, with typical thickness under 1 mm and footprints of only some millimeters square, makes them a natural candidate for consumer products such as mobile
phones, pocket projectors and displays. Advances in UV embossing technology, enabling micro-optics to be mounted over various light sources in a variety of different ways, also allow extremely compact opto-electronic modules to be realized at highly competitive prices. In this paper we summarize recent technology developments and describe a number of multimedia applications utilizing state-of-the-art micro-optics.
In this paper we describe the design of a lenticular based 2D/3D display for mobile applications. This display combines look-around capability with good 3D resolution. In order to allow high resolution datagraphic applications we have developed a concept based on actively switched lenses. A very noticeable problem for such displays is the occurrence of dark bands. We will show that, despite slanting the lenticular and defocusing the lens, banding becomes unacceptable when the display is viewed from an angle. As a solution, we introduce fractional viewing systems to reduce the banding intensity by almost two orders of magnitude. The resulting 3D display can be viewed from any horizontal direction without banding.
We discuss residual lens effects in multi-view switchable auto-stereoscopic lenticular-based 2D/3D displays. With the introduction of a switchable lenticular, it is possible to switch between a 2D mode and a 3D mode. The 2D mode displays conventional content, whereas the 3D mode provides the sensation of depth to the viewer. The uniformity of a display in the 2D mode is quantified by the
quality parameter modulation depth. In order to reduce the modulation depth in the 2D mode, birefringent lens plates are investigated analytically and numerically, by ray tracing. We can conclude
that the modulation depth in the 2D mode can be substantially decreased by using birefringent lens plates with a perfect index match between lens material and lens plate. Birefringent lens plates do not disturb the 3D performance of a switchable 2D/3D display.
The biggest challenges in multimedia technologies are connecting with createing fully interactive virtual reality (VR) systems. This requires generating numerically or even better gathering real data about static or dynamic 3D objects and scenes and delivering them to virtual reality environment.
Application of the structure light measurement system based on digital light projection supported by special data coding and processing technology allow to record 3D data with significantly higher accuracy of reconstructed shape and simplified data manipulation process.
In the paper the general concept of virtual reality system supported by data gathered by means of structure light projection is presented. The methodology of conversion of cloud of measurement points (x,y,z,R,G,B) into virtual reality environment is described. The methodology of real time visualization of variable in time 3D object based on its coding by means of specially formed contours and their B-spline approximation is presented. The applicability of the methodology has been shown at the case of real object monitoring. The total processing path was successfully tested.
The proliferation of digital information is leading to a wide range of applications which make it desirable to display data easily in many locations, all changeable and updateable. The difficulty in achieving such ubiquitous displays is the cost of signage, the cost of installation, and the software and systems to control the information being sent to each of these signs. In this paper we will talk about a networked system of such signs which are made from gyricon electronic paper. Gyricon electronic paper is a reflective, bistable display which can be made in large web sheets at a reasonable price. Since it does not require a backlight nor does it require power to refresh the display image, such technology is ideal for making signs which can be run on batteries with extremely long battery life, often not needing replacement for years. The display also has a very broad illumination scattering profile which makes it readily viewable from any angle. The basic operating mechanism of the display, its manufacturing technique, and achieved performance will be described, along with the description of a networked solution using many such signs controlled with system software to identify speakers and meetings in conference rooms, hospitality suites, or classrooms in universities. Systems will also be shown which are adapted to retail pricing signage and others which can be used for large format outdoor billboards.
Particularly for miniature camera modules, manufactured in high volumes, characterization and measurement approaches are needed that provide information on camera key properties efficiently. An integrated measurement system named has been developed that uses images taken on specifically designed test chart targets, which are then automatically analysed by software. The chart combines target elements for measurement of optoelectronic conversion function, resolution, noise, uniformity, distortion and colour reproduction. The software applies machine vision to recognize the various target elements from the images, and to register analysis locations properly. The actual analysis methods conform with existing standards. The software includes graphical user interface, and in addition to the automatic analysis, also user-defined analysis can be flexibly done. The software supports modifications in the chart layout, batch analysis of images and storing the results in spreadsheet report format.
We describe the design of a light-guide that is part of a sensor which continuously measures the "quality" of Cold Cathode Fluorescent Lamp (CCFL) backlights. This sensor gives information to the electronic system that compensates the screens degradations. The light-guide should fulfill several conditions. First of all the acceptance angle of the light-guide should be in accordance with a predefined value, this for reasons of calibration. Secondly the energy-loss inside the light-guide should be minimal. This is indispensable especially when using the light-guide for color screens. In this case the flux density on the photodiodes surface is much lower in comparison with monochromatic screens due to the color filters which are present. Finally we want the light-guide to be low-cost and we have to make sure that the design could easily be built inside a screen. For the optical design of this light-guide we used both sequential and non-sequential ray-tracing software. We started our simulations with an L-shaped light-guide profile. The dimensions of this guide were chosen in such a way that the element easily fits into a standard screen. To make sure that the sensor only captures light within the desired acceptance angle we proposed a system using a lens on top of this light-guide. In this paper we describe the design and simulation results of this L-shaped light-guide with extra lens. After making some final changes to the design to reduce the influence of environmental stray light, we ended up with a light-guide which fulfilled most of the predefined specifications.
A novel cone-shaped lens cap for High Brightness Light Emitting Diodes (HB-LEDs) is proposed for improving brightness and high uniformity of the direct LED Backlight Units (BLUs) for large area LCD-TVs. Combining the designed lens cap with red, green and blue (RGB) chips on a Metal Core Printed Circuit Board (MCPCB), the LED module with the proposed cap is able to provide a compact white light source with unique features such as instant color variability and lower power usage, etc  . The cone shape of the proposed lens cap is designed to emit only a small portion of light upward along the optical axis of the lens, while most of the light rays to the sides, providing a uniform luminance distribution and the high brightness on the backlight. In addition, a small, local square reflective box is designed and coupled to enclose the proposed LED module  , the inner surfaces of which are attached with reflective films to increase the level of light mixing in the larger, global reflector box. With the structure of the LED module well designed, the placement of the LED modules in the BLU is next optimized via the method of optimization algorithm (OA). In the process of OA executions, the locations of the LED modules are the design factors to be optimized with chosen enclosure dimensions and number of LEDs to maximize brightness and uniformity of the entire BLU. Moreover, in the OA process, the software TRACEPRO is utilized to compute brightness and uniformity of the BLU with certain combination of the aforementioned design and control parameters considered. With the theoretically-optimized placement of the LED modules in hand, experiments based on a realistic BLU built in the laboratory are conducted to verify the performance of the proposed LED module and associated optimized locations. The results indeed identify the attributes of the BLU, which make it possible to achieve excellent backlight performance using a direct illumination approach from the light source of "Cone-Shaped Lens Cap of LEDs".
The feasibility of optical wireless communication link using high-brightness illumination light-emitting diodes (LEDs) is reported. The eye patterns of single-color red, green, and blue LEDs are measured and compared. For the blue LED, the 3 dB bandwidth is measured. An optical transmitter module incorporates seven LEDs as a basic
building block for planar light and a packaged silicon photodiode is used as a receiver. From the experimental demonstration with the 7-LED transmitter and a receiver, it is shown that the optical wireless communication link using high-brightness illumination LEDs can perform 10 Mb/s data transmission without any optimized optical filter to enhance optical gain.
LED-optics for homogeneous illumination of rectangular areas - as required for reading lamps or lighting of imagers - employ a primary optics which acts as collimator and a secondary optics for beam shaping, homogenization and relaying the light onto the illuminated plane. Efficient primary optics are realized by concentrators which are either simple reflecting or combined refractivereflective
devices. Different design algorithms based on the modelling of the concentrators by Bezier splines were developed: A modification of the edge-ray principle allows the formulation of the merit function in geometrical terms (for instance the divergence after collimator), while a more general algorithm with direct Powell optimization allows for combined optimization criteria like efficiency and homogeneity in near- and/or farfield. Concentrator prototypes were realized by direct diamond-turning into PMMA. Telecentric, homogeneous illumination of rectangular areas is achieved by a subsequent secondary optics with tandem lens array integrators. We describe design rules for array integrator optics derived from a simple ABCD-matrix formalism. Based on these rules, sequential real raytracing is used for the actual optics system design and analysis of
aberrations, which deteriorate homogeneity and useful system transmission. We realized miniaturized array integrators with monolithic tandem microlens arrays, which remarkably reduce overall system length compared to light-pipe approaches. Double-sided cylindrical microlens arrays with large fill-factor over 99%, realized by polymer-on-glass replication of reflow lenses, relax system assembly by shifting critical adjustment steps into element manufacturing.
Nowadays the processing power of mobile phones, Smart phones and PDA is increasing, as well as the transmission bandwidth. Nevertheless there is still the need to reduce the content and the need of processing the data. Proposals and solutions for dynamic reduction of the transmitted content will be discussed. For that, device specific properties will be taken into account, aiming at reducing the need of processing power at the client side to display the 3D Virtual Reality data. Therefore, well known technologies like data compression are combined with new approaches to achieve the goal of adaptive content transmission. For device dependant reduction of processing power the data has to be pre-processed at the server side or the server itself has to take over functionality of weak mobile devices.
A colour-separating backlight can be made by using a surface-relief grating as an outcoupling structure on top of a lightguide. By combining such a structure with a birefringent layer, a polarised colour-separating backlight can be realised. We discuss experiments and simulations on a prototype of such backlight structures, as well as directions how to optimise them. First optimised samples of gratings made by laser-interference lithography show promising results.