Liquid crystals beyond displays chemistry physics and applications

LIQUID CRYSTALS BEYOND DISPLAYS LIQUID CRYSTALS BEYOND DISPLAYS CHEMISTRY, PHYSICS, AND APPLICATIONS Edited by Quan Li Liquid Crystal Institute Kent, OH Copyright Ó 2012 by John Wiley & Sons, Inc All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River 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Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002 Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic formats For more information about Wiley products, visit our web site at www.wiley.com Library of Congress Cataloging-in-Publication Data: Liquid crystals beyond displays : chemistry, physics, and applications / edited by Quan Li, Liquid Crystal Institute, Kent, OH pages cm Includes bibliographical references and index ISBN 978-1-118-07861-7 Liquid crystals–Research Optoelectronic devices–Research I Li, Quan, 1965- editor of compilation QC173.4.L55L55 2012 530.40 29–dc23 2011052325 Printed in the United States of America 10 CONTENTS Preface vii Contributors ix Liquid Crystal Lasers Hideo Takezoe Self-Organized Semiconducting Discotic Liquid Crystals for Optoelectronic Applications 29 Chenming Xue and Quan Li Magnetic Liquid Crystals 83 Rui Tamura, Yoshiaki Uchida, and Katsuaki Suzuki Ferroelectric Liquid Crystals for Nonlinear Optical Applications 111 Yongqiang Zhang and Jesus Etxebarria Photo-Stimulated Phase Transformations in Liquid Crystals and Their Non-Display Applications 157 C V Yelamaggad, S Krishna Prasad, and Quan Li Light-Driven Chiral Molecular Switches or Motors in Liquid Crystal Media 213 Yan Wang and Quan Li Liquid Crystal-Functionalized Nano- and Microfibers Produced by Electrospinning 251 Jan P F Lagerwall Functional Liquid Crystalline Block Copolymers: Order Meets Self-Assembled Nanostructures 285 Xia Tong and Yue Zhao Semiconducting Applications of Polymerizable Liquid Crystals 303 Mary O’Neill and Stephen M Kelly v vi CONTENTS 10 Liquid Crystals of Carbon Nanotubes and Carbon Nanotubes in Liquid Crystals 341 Giusy Scalia 11 Liquid Crystals in Metamaterials 379 Augustine M Urbas and Dean P Brown 12 Ferroelectric Colloids in Liquid Crystals 403 Yuriy Reznikov 13 Fact or Fiction: Cybotactic Groups in the Nematic Phase of Bent Core Mesogens 427 Bharat R Acharya and Satyendra Kumar 14 Lyotropic Chromonic Liquid Crystals: Emerging Applications 449 Heung-Shik Park and Oleg D Lavrentovich 15 Liquid Crystal-Based Chemical Sensors 485 Jacob T Hunter and Nicholas L Abbott 16 Polymer Stabilized Cholesteric Liquid Crystal for Switchable Windows 505 Deng-Ke Yang 17 Liquid Crystals for Nanophotonics 525 Timothy D Wilkinson and R Rajesekharan Index 569 PREFACE Liquid crystals (LCs) were discovered more than 100 years ago, however the renaissance of research and development activities during the last quarter of 20th century led to the successful commercialization of LC devices for information displays Currently the global market of LC displays (LCDs) stands more than $100 billion annually Though the LCDs ubiquitous in our daily life seem mature, there is still considerable interest in the development of 3D-displays using LCs Nevertheless parallel to this development, nowadays there is an unprecedented growth of interest for non-display applications of LCs during the 1st decade of 21st century Consequently the research and development of LCs are moving rapidly beyond displays and evolving into entirely new scientific frontiers, opening broad avenues for versatile applications such as lasers, photovoltaics, light-emitting diodes, field effect transistors, nonlinear optics, biosensors, switchable windows, and nanophotonics These fields, which gain extensive attentions of physicists, chemists, engineers, and biologists, are of a most engaging and challenging area of contemporary research, covering organic chemistry, materials science, bioscience, polymer science, chemical engineering, material engineering, electrical engineering, photonics, optoelectronics, nanotechnology, and renewable energy This book does not intend to exhaustively cover the field of LCs beyond displays, as it is extremely difficult to so within a single book Instead, the book focuses on the recent developments of most fascinating and rapidly evolving areas related to the theme The chapters span the following topics: LC lasers (Chapter 1), self-organized semiconducting discotic LCs (Chapter 2), magnetic LCs (Chapter 3), ferroelectric LCs for nonlinear optical applications (Chapter 4), photo-stimulated phase transformations in LCs (Chapter 5), light-driven chiral molecular switches or motors in LC media (Chapter 6), LC functionalized nano- and microfibers produced by electrospinning (Chapter 7), functional LC block copolymers (Chapter 8), semiconducting applications of polymerizable LCs (Chapter 9), LCs of carbon nanotubes and carbon nanotubes in LCs (Chapter 10), LCs in metamaterials (Chapter 11), ferroelectric colloids in LCs (Chapter 12), cybotactic groups in the nematic phase of bent core mesogens (Chapter 13), lyotropic chromonic LCs: emerging applications (Chapter 14), LC-based chemical sensors (Chapter 15), LCs for switchable windows (Chapter 16), and LCs for nanophotonics (Chapter 17) In each chapter, the state-ofthe-art along with future potentials in the respective fields has been discussed and highlighted by the leading experts I hope this book is not only to introduce fundamental knowledge, illustrative examples, and successful applications beyond displays, but also to stimulate more vii viii PREFACE interest for further development in this realm of research, wishing the interdisciplinary actions of physicists, chemists, engineers, and biologists can bring grateful values to push the LCs research forward in the 21st century For graduate students, researchers, and scientists from other fields who want to get involved in LCs, this book is anticipated to serve as a beginners’ guide For established researchers, this book is expected to provide insights into knowledge beyond their expertise I sincerely hope this book can generate interest to readers and help researchers to spark creative ideas I would like to express my gratitude to Jonathan Rose at John Wiley & Sons, Inc for inviting us to bring this exciting field of research to a wide audience, and to all our distinguished contributors for their dedicated efforts Also I am indebted to my wife Changshu, my sons Daniel and Songqiao for their great support and encouragement QUAN LI KENT, OHIO August 2011 CONTRIBUTORS Nicholas L Abbott, Department of Chemical and Biological Engineering, University of Wisconsin, Madison, WI, USA Bharat R Acharya, Platypus Technologies, Madison, WI, USA Dean P Brown, Materials and Manufacturing Directorate, Air Force Research Laboratory WPAFB, OH, USA Jes us Etxebarria, Department of Condensed Matter Physics, University of the Basque Country, Bilbao, Spain Jacob T Hunter, Department of Chemical and Biological Engineering, University of Wisconsin, Madison, WI, USA Stephen M Kelly, Department of Physics and Chemistry, University of Hull, UK Satyendra Kumar, Department of Physics, Kent State University, Kent, OH, USA Jan P F Lagerwall, Graduate School of Convergence Science and Technology, Seoul National University, Gyeonggi-do, Korea Oleg D Lavrentovich, Liquid Crystal Institute, Kent State University, Kent, OH, USA Quan Li, Liquid Crystal Institute, Kent State University, Kent, OH, USA Mary O’Neill, Department of Physics and Chemistry, University of Hull, UK Heung-Shik Park, Liquid Crystal Institute, Kent State University, Kent, OH, USA S Krishna Prasad, Center for Soft Matter Research, Bangalore, India R Rajesekharan, Electrical Engineering Division, University of Cambridge, Cambridge, UK Yuriy Reznikov, Institute of Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine Giusy Scalia, Department of Nanoscience and Technology, Seoul National University, Gyeonggi-do, Korea Katsuaki Suzuki, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan ix x CONTRIBUTORS Rui Tamura, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan Hideo Takezoe, Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo, Japan Xia Tong, Department of Chemistry, University of Sherbrooke, Que´bec, Canada Yoshiaki Uchida, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan Augustine M Urbas, Materials and Manufacturing Directorate, Air Force Research Laboratory WPAFB, OH, USA Yan Wang, Liquid Crystal Institute, Kent State University, Kent, OH, USA Timothy D Wilkinson, Electrical Engineering Division, University of Cambridge, Cambridge, UK Chenming Xue, Liquid Crystal Institute, Kent State University, Kent, OH, USA Deng-Ke Yang, Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH, USA C V Yelamaggad, Center for Soft Matter Research, Bangalore, India Yongqiang Zhang, Micron Technology, Inc., Longmont, CO, USA Yue Zhao, Department of Chemistry, University of Sherbrooke, Que´bec, Canada FIGURE 1.21 Helical structure in a CLC microdroplet Image of microdroplet in a lasing condition is also shown [76] FIGURE 2.20 Top: Synchrotron XRD patterns from homeotropic monodomain of material 35 (a) and the blend of 35 (b) with PC61BM in an 8-mm-thick glass cell Bottom: Calculated geometric dimensions of porphyrin 35 and 3D ChemDraw spacing-filling model of fullerene derivative PC61BM and the schematic representations of homeotropically aligned architecture of the blend of 35 and PC61BM Reproduced with permission from ref 110 Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications, Edited by Quan Li Ó 2012 John Wiley & Sons, Inc Published 2012 by John Wiley & Sons, Inc 550 LIQUID CRYSTALS FOR NANOPHOTONICS 10 µm –5 (a) Unwrapped Phase (Radians) –10 –15 10 20 30 40 50 60 –5 (b) –10 –15 –20 10 20 30 40 50 60 –4 –6 (c) –8 –10 10 20 30 Pixel 40 50 60 FIGURE 17.29 Unwrapped phase of a single lenlet and interference fringes from the nanophotonic device (four lenslets) at 0.98 Vrms (a) 1.1 Vrms and (b) 2.5 Vrms parabolic at voltages below Vrms with phase modulation of 3p–4.2p The phase modulation decreased with the distortion in phase profile as the voltage increased Light intensity and focal length variation of the device at each nanotube group site (lenslet) were studied to understand the imaging characteristics of the device These parameters are also needed for making suitable applications using the device In order to study the light intensity profile from each lenslet, the device was fixed in a polarized microscope where the objective was focused on to the top of each nanotube position The image of the device was recorded on a CCD at different voltages The light focusing effect at different voltages is shown in Figure 17.30(a)–(f) The nanotubes distort the planar orientation of the LC around the nanotube which results in a graded refractive index profile At Vrms, the light focusing was not uniform for all the lenslets because the LC distortion was different for each nanotube position as shown in Figure 17.30(a) The focusing started improving as the voltage increased from Vrms The light focusing at 0.75 Vrms is shown in Figure 17.30(b) The focusing of light became most uniform at around 1.1 Vrms and light intensity increased at each lenslet position as shown in Figure 17.30(c) The focusing effect reduced with further increase in the applied voltage This can be seen in the images at 1.8 Vrms and Vrms, as shown in Figures 17.30(d) and (e), respectively As the voltage increased above Vrms, the light intensity at each lenslet position started decreasing and finely disappeared at higher voltages as shown in Figure 17.30(f) Figure 17.31 shows one-dimensional (1D) cross section of the intensity profile across five lenslets at 0, 1.1, 2.2, and Vrms It was clear that at Vrms the light intensity was more at the nanotube positions compared to that remaining in the area of the device But the light intensity between each of the nanotube groups was not uniform and hence created an TRANSPARENT NANOPHOTONIC DEVICE 551 FIGURE 17.30 The nanophotonic lens array focusing the light at (a) Vrms, (b) 0.75 Vrms, (c) 1.1 Vrms, (d) 1.8 Vrms, (e) Vrms, and (f) Vrms aberrated lens array When the voltage was 1.1 Vrms, the light intensity was maximum at these nanotube positions with a wider profile The light intensity was also smooth and uniform between the nanotube groups The device acted as a lens array with least aberration at around 1.1 Vrms Further increase in the voltage distorted the light intensity profile and there was no proper lensing above 1.8 Vrms The focal length of each lenslet was calculated using the Eqs (17.3) and (17.4) The focal length varied with respect to the applied voltage as shown in Figure 17.32 Further increase in the voltage distorted the orientation of the LC molecules in the device and hence no focusing was observed The nanophotonic device was, however, 552 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.31 The 1D light intensity profile across six lenslets at (a) Vrms, (b) 1.1 Vrms, (c) 1.5 Vrms, and (d) Vrms acting like a voltage reconfigurable lens array at lower voltages The focal length variation was due to the change in phase profile with respect to the applied voltage The focal length varied from 10 mm (0 Vrms) to 36 mm (2.2 Vrms) and hence the lens array became more concave in nature with increased applied voltage The lensing nature of the lens arrays disappeared after Vrms because the LC molecules aligned randomly at higher electric fields The focal length variation was slightly better for the transparent sample because the light was incident normal to the device surface 40 35 A 30 25 20 15 10 0 Voltage (Vrms) FIGURE 17.32 Focal length variation of one lenslet with respect to applied voltage Region ‘A’ represents the useful region for imaging NANOPHOTONIC COMPOUND EYE-BASED 3D VISION SENSOR 553 and there was no double pass of light through each micro lenslet as in the case of the reflective device Only the transparent device can be used for imaging applications because of the easy integration with rest of the optical components and lower distortion in the image The light intensity variation across the lenslet in the device and focal length variation with respect to the applied field was calculated to find the useful range for imaging applications Though the focal length varied from 10 mm to 36 mm, the useful region for imaging was found to be from 10 mm to 14 mm which corresponds to the voltage range 0–1.8 Vrms There were distorted interference fringes above 1.84 Vrms and hence the focal length variation From the light intensity studies it was clear that the light focusing ability of the device considerably decreased from 1.8 Vrms upwards This was due to the fact that as the voltage increased above 1.8 Vrms, the alignment of LC molecules got distorted and further increased in the voltage forced the molecules at each nanotube site to align homeotropically Figure 13.32 shows the focal length verses voltage graph where the region ‘A’ is most useful for imaging The focal length varied until Vrms because the interference fringes were present up till this voltage The number of fringes decreased as the voltage increased above 1.8 Vrms 17.12 NANOPHOTONIC COMPOUND EYE-BASED 3D VISION SENSOR Large vertabrates like humans have large single aperture eyes The eyes are optimized to provide high resolution, large field of view, focusing ability, color detection, and a very large dynamic range to see both in the bright sunshine and in the dark night Small invertebrates on the other hand cannot afford large single heavy aperture eyes that consume a lot of metabolic energy They have instead compound eyes, where the image capturing is distributed amongst a matrix of small eye sensors Miniaturized imaging systems based on artificial compound-eye vision have been examined experimentally by several groups [22, 23] Little attention has been paid to the optical imaging system compared to the comparatively large effort in the electronics, and the burden of the extraordinarily complex image processing This has prevented the realization of a fully functional, miniaturized high-resolution compact camera Their optical performance has also been limited by inadequate fabrication and assembly technologies for the individual components This chapter presents the development of a nanophotonic 3D sensor system for high resolution 2D imaging, and 3D video by overcoming the diffraction barrier The key component for achieving this goal is the imaging optics itself We have developed a novel nanophotonic micro-lens array as discussed in Chapter suitable for a compound eye based high-resolution imaging sensor We apply integral imaging to enable 3D video/display in the sensor to give advantages such as continuous view points, full parallax, no convergence-accommodation conflict and no need for any special glass to evoke the 3D image Integral imaging is based on integral photography, which was proposed by Lippmann [24] Integral imaging is a 3D image display technique that produces 554 LIQUID CRYSTALS FOR NANOPHOTONICS true 3D images The advantages of integral imaging compared to other 3D image systems include continuous view points, full parallax, no convergence accommodation conflict and no special viewing glasses are required to see the 3D image [25–28] It is an auto stereoscopic technique where the 3D object is sampled by a micro-lens array or a pinhole Each micro lenslet picks up a particular perspective of the object which is called an elemental image Reconstruction of a 3D image of the object from 2D elemental images is a reverse of the pickup process The 3D image is reconstructed from all the elemental images using a lens array Figure 17.33 shows the block diagram of the camera and display stage The camera stage is the capture stage The captured image is transmitted as electrical signals and converted back into optical signal in the display stage The integral imaging system can be divided into camera stage (pick up stage) and display stage (3D image reconstruction stage) Figure 17.34 shows the principle of the pickup method by a camera The 3D object is sampled by a micro-lens array An inverted real image (for a convex lens array) of the object is created by each micro lenslet behind the micro-lens array The image formed by each lenslet is called the elemental image Each elemental image is formed from a different perspective of the object Then all the elemental images are recorded on a CCD camera We define the following parameters, WL is the width of the lens array, WS is the width of the pickup device, fC is the focal length of the camera lens in front of CCD to demagnify all the elemental images down to the size of the CCD, and ZMC is the distance between the lens array and the camera lens [27] WL WS ZMC fC 17:5ị WL ẳ WM N and WS ẳ NMPC 17:6ị Also WM is the pitch of the microlenses, N is the number of micro lenslets, M is the number of pixels in the elemental image, and PC is the pitch of the pickup device It is clear from the above equations that the number of pixels in the pickup device is the product of the number of micro lenses and pixels in the elemental image The resolution of the reconstructed 3D image is given by the number of micro lenses The number of pixels per elemental image is related to the viewing zone, or the resolution, of the reconstructed 3D image It has been experimentally observed that at least ten pixels per elemental image in the vertical and horizontal directions are required for minimum clarity in the reconstructed 3D image Capture Transmission Signal Conversion Display FIGURE 17.33 Block diagram of camera (pick up) and display stage OPTICAL RECONSTRUCTION TECHNIQUE 555 FIGURE 17.34 Block diagram of the camera stage The 3D image can be reconstructed from the elemental images by two methods, namely computational reconstruction or optical reconstruction Computational reconstruction uses pixel mapping techniques to get 3D/2D image In optical reconstruction, the reconstruction is done using a LCD and lens array in real time, and is useful for 3D video and microscopy Real time or computational 2D reconstruction of the image from the elemental images is used for compound eyebased imaging systems Integral imaging technique provides a 3D image from the elemental images and that aspect is explored further in this chapter 17.13 OPTICAL RECONSTRUCTION TECHNIQUE In the optical reconstruction stage, the set of elemental images is displayed on a LCD in front of a second lens array [28, 29] The light rays from these elemental images then go through the lens array, reconstructing the image of the object at the same position as the object as shown in Figure 17.35 Note that although all the elemental images are imaged by the corresponding lenslet into the same plane or the reference image plane, the 3D scene is reconstructed in the image space by the intersection of the ray bundles emanating from each of the lenslets This method allows viewers to observe a reconstructed 3D image in real time floating in air Here also the resolution of the reconstructed 3D image is given by the number of lenslets in the lens array The viewing angle and the depth of the reproduced 3D images depend on the focal length of the convex lenses The viewing angle F is expressed as [28] F ¼ tanÀ1  P 2g  ð17:7Þ where P is the pitch of the elemental image and g is the distance between the principle plane and elemental images on the LCD The main resolution limitation of this 3D imaging sensor lies in the resolution of the micro-lens array Miniaturization strategies that have been applied with great success to electronics cannot be simply transferred to optical imaging systems We have started to exploit nanophotonics and integral imaging technologies to 556 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.35 Schematic diagram of the proposed 3D vision sensor – imaging lens, – nanophotonic lens array, – pinhole array (optional), – CMOS/CCD sensor, – control electronics, – LCD, – pixel mapping/image processing, – large lens array, – out put 3D image, 10 – output: 2D image (compound eye sensor) overcome these issues In the designed sensor, the above mentioned problems of imaging optics, resolution, and miniaturization issues of the sensor system are addressed by introducing the transparent nanophotonic lens array, where each lenslet radius is of the order of mm which is much smaller compared to any commercially available fixed lens array and the focal length is voltage reconfigurable Applications of this type sensor are mainly in miniaturized 3D camera, 3D microscopy, and endoscopy Figure 13.35 shows the general architecture of the sensor The sensor head (camera stage) has an imaging lens (convex lens) The imaging lens is used to demagnify the image of a far away object to a suitable scale The voltage dependant lenses also give us an option to get real and virtual 3D image capture by changing the focal length Without this lens the operating distance of the sensor is limited to millimeters and field of view is very small When multiple objects are present at a large distance, without this imaging lens only nearby objects get clarity in the image plane and other images will be out of focus The 3D images near the lens array for reproduction have a higher resolution than those farther away from the lens array These problems can be solved by incorporating a suitable imaging lens The imaging lens focuses the image in front (for real 3D) or behind (for virtual 3D) of the nanophotonic micro-lens array to generate many elemental images The elemental images are recorded on a high resolution CCD/CMOS recording device The display stage has a high-resolution LCD where all the elemental images recorded by the CCD are displayed The large lens array to reconstruct the 3D image was fabricated from crossed lenticular sheet with 10 lines per in inch (10 LPI) In the lenticular lens array, two lenticular sheets (10 LPI acrylic sheets with refractive index 1.49) were crossed at right angles The lens side of the two lenticular sheets was contacted together in this scheme Since the focal length of the lens is determined only by the lens side, the two lens arrays have the same focal length when crossed at OPTICAL RECONSTRUCTION TECHNIQUE 557 right angle The fabricated lens array is shown in Figure 13.36 The light focusing capability of the lens array was studied using a white light source The lens array focused light in the back focal plane as shown in Figure 17.36 The focal length of the array was experimentally measured at 3.9 mm from the center of the lens array Calibration of the 3D vision sensor was performed using a standard micro-lens array (suss micro-optics, circular lenses, quadratic grid: lens pitch 110 mm, ROC 0.817 mm, numerical aperture 0.03, size 15 mm  15 mm  0.9 mm) in the camera FIGURE 17.36 Left, lens array fabricated from two lenticular sheets having pitch 2.5 mm; right, light focused by the lenticular lens array 558 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.37 The 3D vision sensor camera stage developed (See the color version of this figure in Color Plates section.) stage to fix system parameters Figure 17.37 shows the 3D vision sensor camera stage developed for calibrating the system parameters including the display stage and the lens array fabricated with two lenticular sheets The sensor consists of capture lens (imaging lens) to demagnify the image of a far away object to a suitable scale followed by the standard micro-lens array to sample the image and CCD with a convex lens to record the elemental images We used a very high resolution CMOS color camera (EO-10012C 1=2 inch CMOS Color GigE) to record the elemental images with pixel resolution 3840  2748 and pixel size 1.67  1.67 mm in the camera stage The 3D display stage for the sensor was fabricated using the crossed lenticular lens array and silicon graphics 1600SW, 17 in LCD monitor as shown in Figure 13.38 The dot pitch of the display was 0.23 mm for high resolution The separation between the display and the lens array was adjustable for improving the quality of the 3D image reconstructed The size of the lens array was 15  15 cm Computationally simulated elemental images of the number 3D was used to calibrate [29] the display as shown in Figure 17.38 The inverted version of the image was used in experiment All the elemental images were displayed on the display and the lenticular lens array was kept mm away (the distance measured from centre of the lens array to the display) Figure 17.39 shows the reconstructed 3D image in the display from two different angles (top view and bottom view) The ‘D’ moved with respect to the ‘3’ in top and bottom view This shows that there was a full parallax in the reconstructed 3D image Each elemental images was displayed using 10  10 pixels on the LCD and each elemental was covered by a single lenslet of size 2.5 mm on the lenticular lens array This experiment helped to fix the distance between the lenticular lens array and the display stage 17.14 IMAGING USING THE NANOPHOTONIC LENS ARRAY The imaging characteristics of the nanophotonic lens array were studied for calibration US air force (USAF) test pattern was used an object A transmission microscope with a CCD camera was used to capture the images from the nanophotonic device at different voltages The number (100 mm) in the USAF pattern was used for imaging IMAGING USING THE NANOPHOTONIC LENS ARRAY 559 FIGURE 17.38 Fabricated 3D display stage using crossed lenticular lens array and silicon graphics 1600 SW, 17 in LCD monitor, the elemental images of 3&D [29] The images formed from the nanophotonic lens array was not clear at zero volts because of the less ordered alignment of the LC molecules around the nanotubes and hence created a non uniform gradient refractive index profile This matched the interference experiments where fringes were observed at zero volts as discussed in 560 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.39 The reconstructed 3D image in the developed 3D display from all the elemental images viewed from top and bottom (See the color version of this figure in Color Plates section.) Section 17.8 The images became very clear at 1.1 Vrms and started disappearing with increase in the applied voltage The performance exactly matched with the focal length study Figure 17.40 shows the image formed from the nanophotonic lens array at different voltages The focal length variation and the phase profile with respect to the applied voltage of the nanophotonic lens array were as discussed previously The focal length increased with respect to the applied voltage and hence the concave nature increased The behavior of the lens array at Vrms and close to Vrms was not clear from the IMAGING USING THE NANOPHOTONIC LENS ARRAY 561 FIGURE 17.40 Object used and captured elemental images from the nanophotonic lens array at different voltages (a) object, (b) images at Vrms, (c) images at 0.75 Vrms, (d) images at 1.1 Vrms, (e) images at 1.8 Vrms, (f) images at 2.2 Vrms, and (g) images at 3.5 Vrms previous results The image formation at various distances from the nanophotonic lens array was used to find the behavior of the lens array at Vrms Figure 17.41 shows the images captured of the object ‘3’ at different images planes In Figure 17.41(b), the image plane was 10 mm away from the plane at Figure 17.41(a) It was clear from the images that the image size reduced with distance as well as the fact that the images were non-inverted and hence both planes were before the focal plane When the distance increased by another 30 mm from the previous plane, the focal plane was reached as shown in Figure 17.42 When the distance increased by 562 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.41 The images formed at two different focal planes (b) the focal plane is 10 mm away from the image focal plane (a) another 41 mm from the focal plane, the inverted images appeared and hence the image plane was after the focal plane as shown in Figure 17.43(a) With a further increase in distance of mm, the image size increased as shown in Figure 17.43(b) Hence the refractive index profile created a distorted convex lens at Vrms and the convex nature reduced (concave nature increased) with respect to the applied voltage In some part of the lens array, the convex nature slightly increased at very lower voltages just after Vrms and then concave nature increased with further increase in voltage The nanophotonic lens array is useful for imaging just before the concave nature increases This is because when the concave nature increases, there is more distortion in the refractive index profile The optimum voltage for the imaging was around 1.1 Vrms 17.15 CONCLUSIONS AND DISCUSSION In this chapter we have presented a nanophotonic device based on a hybrid combination of multi-wall carbon nanotubes and LCs The carbon nanotube CONCLUSIONS AND DISCUSSION 563 FIGURE 17.42 An image plane near to the focal plane electrode arrays were grown on silicon substrate (reflective device) and on quartz (transparent device) by plasma enhanced chemical vapor deposition after employing e-beam lithography and covered with nematic LC The multi-wall carbon nanotubes act as individual electrode sites that spawn an electric-field profile, dictating the refractive index profile within the LC and hence creating a series of graded index profiles, which form various photonic elements The device was analyzed under an optical microscope and it was found that photonic element was formed at each nanotube site and the photonic elements switched with respect to the applied voltage This has led to the conclusion that micro/nano regions in the device interact with light The phase profile from micro region in the device was recovered using an interference set-up attached with an optical microscope Each nanotube site acted like a lenslet The phase profile was more or less parabolic at lower voltages and hence acted like a voltage reconfigurable nanophotonic lens array The effect of nanotube electrode geometry in the phase profile and the lenslet diameter has been studied using electric field simulation followed by fabricating the devices with one, three, four, and five nanotube groups The four nanotube group was found to be optimum for lens array applications and one nanotube for display applications However, a larger number of nanotubes per group could be used for increasing the lenslet diameter A transparent nanophotonic device was also discussed where the nanotube electrodes were grown on a quartz substrate The device is suitable for lens array applications because of the easy alignment with other optical components and there was no double pass of light through the device The electrode geometry used had six nanotubes per group in a hexagonal pattern The phase profile and focal length were calculated and found that the device acted as nanophotonic lens array at lower voltages The light focusing was also studied at different voltages to understand the focusing properties of the device The light intensity profile at each lenslet was smooth and maximum at a lower voltage and at the same voltage the phase profile was 564 LIQUID CRYSTALS FOR NANOPHOTONICS FIGURE 17.43 The images formed at two different focal planes (b) the focal plane is mm away from the image focal plane (a) parabolic like The useful voltage range of the device for imaging application was obtained from the studies of phase profile, phase aberrations, intensity profile, and focal length variation Electro-optic characteristics, such as transmission voltage characteristic, response time and the contrast ratio of the device were studied to optimize the device performance for different applications These analyses showed that the device finds application as a nanophotonic lens array, reconfigurable hologram, and grating at lower voltages in addition to the suitability of the device for display application at higher voltages This chapter also presented a 3D vision sensor realized using the nanophotonic lens array The imaging characteristic of the lens array was studied using USAF test pattern at different voltages The useful voltage range for imaging obtained from the imaging experiments were matched with previously obtained voltage range from the intensity profile An insect eye-based imaging system was developed first where each nanophotonic lenslet captured a particular perspective of an object called the elemental image The number of elemental images was equal to number of lenslets One pixel from each elemental image was extracted to get a 2D image of the object as in the case of compound eye imaging system of an insect This imaging system was then extended using integral imaging techniques to realize a 3D vision sensor ... Cataloging-in-Publication Data: Liquid crystals beyond displays : chemistry, physics, and applications / edited by Quan Li, Liquid Crystal Institute, Kent, OH pages cm Includes bibliographical references and index.. .LIQUID CRYSTALS BEYOND DISPLAYS CHEMISTRY, PHYSICS, AND APPLICATIONS Edited by Quan Li Liquid Crystal Institute Kent, OH Copyright Ó 2012 by... Semiconducting Applications of Polymerizable Liquid Crystals 303 Mary O’Neill and Stephen M Kelly v vi CONTENTS 10 Liquid Crystals of Carbon Nanotubes and Carbon Nanotubes in Liquid Crystals 341