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Special Issue "Microlenses"

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A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (31 May 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Hongrui Jiang (Website)

Department of Electrical and Computer Engineering, University of Wisconsin - Madison, 3440 Engineering Hall, 1415 Engineering Drive, Madison, WI 53706, USA
Phone: 001-608/265-9418
Fax: +1 608 262 1267
Interests: microsensors and microactuators; microfabrication technology; optical MEMS; bioMEMS; lab on chips; microfluidics; biomimetics and bioinspiration

Special Issue Information

Dear Colleagues,

The study and application of microscale lenses and lens arrays enjoys a long history. Advances in microfabrication technologies in the past few decades have enabled the design and fabrication of microlenses and microlens arrays through many different approaches. In recent years, there has been notably a host of exciting developments in the microlenses and microlens arrays, including tunable-focus ones, those fabricated on non-planar substrates and surfaces, and microlens arrays mimicking natural compound eyes, to name just a few. The developments in microlenses and microlens arrays have found profound applications in many engineering and biomedical fields, including but not limited to optical coherence tomography (OCT), endoscopy, photolithography, 3-dimensional imaging, optical communications, and lab on chips. This Special Issue aims to highlight the state of the art in the development of microlenses and microlens arrays; examples being fabrication technologies and optical characterizations. It also focuses on their applications when implemented in microoptical systems.

Prof. Dr. Hongrui Jiang
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs).

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Keywords

  • microlens
  • microlens array
  • tunable-focus microlens
  • variable-focus microlens
  • liquid microlens
  • optofluidics
  • artificial compound eye
  • microcamera
  • micro imaging system
  • microoptics
  • electrowetting
  • dielectrophoresis
  • liquid crystal
  • optical characterization
  • optical aberration
  • fill factor
  • focal length
  • polymer
  • optical MEMS
  • microscopy
  • photolithography
  • flexible substrate

Published Papers (11 papers)

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Editorial

Jump to: Research, Review

Open AccessEditorial Special Issue on Microlenses
Micromachines 2014, 5(4), 1342-1343; doi:10.3390/mi5041342
Received: 4 December 2014 / Accepted: 5 December 2014 / Published: 8 December 2014
PDF Full-text (189 KB) | HTML Full-text | XML Full-text
Abstract
The study and application of microscale lenses and lens arrays have been actively researched in recent years; new approaches in the fabrication of microlenses and microlens arrays have emerged. Also, novel applications of these microlenses and microlens arrays have been demonstrated. In [...] Read more.
The study and application of microscale lenses and lens arrays have been actively researched in recent years; new approaches in the fabrication of microlenses and microlens arrays have emerged. Also, novel applications of these microlenses and microlens arrays have been demonstrated. In an effort to disseminate the current advances in this specialized field of microlenses and microlens arrays, and to encourage discussion on the future research directions while stimulating research interests in this area, a Special Issue of Micromachines has been dedicated to “Microlenses”. [...] Full article
(This article belongs to the Special Issue Microlenses) Print Edition available

Research

Jump to: Editorial, Review

Open AccessArticle Simulation Study on Polarization-Independent Microlens Arrays Utilizing Blue Phase Liquid Crystals with Spatially-Distributed Kerr Constants
Micromachines 2014, 5(4), 859-867; doi:10.3390/mi5040859
Received: 23 June 2014 / Revised: 3 September 2014 / Accepted: 28 September 2014 / Published: 3 October 2014
Cited by 1 | PDF Full-text (1326 KB) | HTML Full-text | XML Full-text
Abstract
Polarization independent liquid crystal (LC) microlens arrays based on controlling the spatial distribution of the Kerr constants of blue phase LC are simulated. Each sub-lens with a parabolic distribution of Kerr constants results in a parabolic phase profile when a homogeneous electric [...] Read more.
Polarization independent liquid crystal (LC) microlens arrays based on controlling the spatial distribution of the Kerr constants of blue phase LC are simulated. Each sub-lens with a parabolic distribution of Kerr constants results in a parabolic phase profile when a homogeneous electric field is applied. We evaluate the phase distribution under different applied voltages, and the focusing properties of the microlens arrays are simulated. We also calculate polarization dependency of the microlenses arrays at oblique incidence of light. The impact of this study is to provide polarizer-free, electrically tunable focusing microlens arrays with simple electrode design based on the Kerr effect. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Open AccessArticle An Optofluidic Lens Array Microchip for High Resolution Stereo Microscopy
Micromachines 2014, 5(3), 607-621; doi:10.3390/mi5030607
Received: 9 June 2014 / Revised: 10 August 2014 / Accepted: 20 August 2014 / Published: 28 August 2014
Cited by 1 | PDF Full-text (11155 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report the development of an add-on, chip-based, optical module—termed the Microfluidic-based Oil-immersion Lenses (μOIL) chip—which transforms any stereo microscope into a high-resolution, large field of view imaging platform. The μOIL chip consists of an array of ball mini-lenses that are assembled [...] Read more.
We report the development of an add-on, chip-based, optical module—termed the Microfluidic-based Oil-immersion Lenses (μOIL) chip—which transforms any stereo microscope into a high-resolution, large field of view imaging platform. The μOIL chip consists of an array of ball mini-lenses that are assembled onto a microfluidic silicon chip. The mini-lenses are made out of high refractive index material (sapphire) and they are half immersed in oil. Those two key features enable submicron resolution and a maximum numerical aperture of ~1.2. The μOIL chip is reusable and easy to operate as it can be placed directly on top of any biological sample. It improves the resolution of a stereo microscope by an order of magnitude without compromising the field of view; therefore, we believe it could become a versatile tool for use in various research studies and clinical applications. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessArticle Adaptive Liquid Lens Actuated by Droplet Movement
Micromachines 2014, 5(3), 496-504; doi:10.3390/mi5030496
Received: 5 June 2014 / Revised: 22 July 2014 / Accepted: 29 July 2014 / Published: 4 August 2014
Cited by 3 | PDF Full-text (16561 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate) substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide) sheets stick on the bottom substrate. One PMMA sheet with a [...] Read more.
In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate) substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide) sheets stick on the bottom substrate. One PMMA sheet with a light hole is inserted in the middle of the device. A conductive droplet is placed on the substrate and touches the PMMA sheet to form a small closed reservoir. The reservoir is filled with another immiscible non-conductive liquid. The non-conductive liquid can form a smooth concave interface with the light hole. When the device is applied with voltage, the droplet stretches towards the reservoir. The volume of the reservoir reduces, changing the curvature of the interface. The device can thus achieve the function of an adaptive lens. Our experiments show that the focal length can be varied from −10 to −159 mm as the applied voltage changes from 0 to 65 V. The response time of the liquid lens is ~75 ms. The proposed device has potential applications in many fields such as information displays, imaging systems, and laser scanning systems. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Open AccessArticle CO2 Laser Manufacturing of Miniaturised Lenses for Lab-on-a-Chip Systems
Micromachines 2014, 5(3), 457-471; doi:10.3390/mi5030457
Received: 30 May 2014 / Revised: 11 July 2014 / Accepted: 15 July 2014 / Published: 21 July 2014
Cited by 1 | PDF Full-text (2356 KB) | HTML Full-text | XML Full-text
Abstract
This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and [...] Read more.
This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and for lens diameters of more than 3 mm. Experimental characterisation of the lens focal lengths shows good correlation with theory. The plano-convex lenses have been successfully embedded into capillary microfluidic systems alongside planar microlenses, allowing for a significant reduction of ancillary optics without a loss of detection sensitivity when performing fluorescence measurements. Such technology provides a significant step forward towards the portability of fluorescence- or luminescence-based systems for biological/chemical analysis. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessArticle Fabrication and Characterization of Flexible Electrowetting on Dielectrics (EWOD) Microlens
Micromachines 2014, 5(3), 432-441; doi:10.3390/mi5030432
Received: 19 May 2014 / Revised: 16 June 2014 / Accepted: 16 June 2014 / Published: 4 July 2014
Cited by 6 | PDF Full-text (572 KB) | HTML Full-text | XML Full-text
Abstract
We present a flexible variable-focus converging microlens actuated by electrowetting on dielectric (EWOD). The microlens is made of two immiscible liquids and a soft polymer, polydimethylsiloxane (PDMS). Parylene intermediate layer is used to produce robust flexible electrode on PDMS. A low-temperature PDMS-compatible [...] Read more.
We present a flexible variable-focus converging microlens actuated by electrowetting on dielectric (EWOD). The microlens is made of two immiscible liquids and a soft polymer, polydimethylsiloxane (PDMS). Parylene intermediate layer is used to produce robust flexible electrode on PDMS. A low-temperature PDMS-compatible fabrication process has been developed to reduce the stress on the lens structure. The lens has been demonstrated to be able to conform to curved surfaces smoothly. The focal length of the microlens is 29–38 mm on a flat surface, and 31–41 mm on a curved surface, varying with the voltage applied. The resolving power of the microlens is 25.39 line pairs per mm by a 1951 United States Air Force (USAF) resolution chart and the lens aberrations are measured by a Shack-Hartmann wavefront sensor. The focal length behavior on a curved surface is discussed and for the current lens demonstrated the focal length is slightly longer on the curved surface as a result of the effect of the curved PDMS substrate. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Open AccessArticle Bio-Inspired Wide-Angle Broad-Spectrum Cylindrical Lens Based on Reflections from Micro-Mirror Array on a Cylindrical Elastomeric Membrane
Micromachines 2014, 5(2), 373-384; doi:10.3390/mi5020373
Received: 11 May 2014 / Revised: 10 June 2014 / Accepted: 10 June 2014 / Published: 20 June 2014
Cited by 2 | PDF Full-text (2047 KB) | HTML Full-text | XML Full-text
Abstract
We present a wide-angle, broad-spectrum cylindrical lens based on reflections from an array of three-dimensional, high-aspect-ratio micro-mirrors fabricated on a cylindrical elastomeric substrate, functionally inspired by natural reflecting superposition compound eyes. Our device can perform one-dimensional focusing and beam-shaping comparable to conventional [...] Read more.
We present a wide-angle, broad-spectrum cylindrical lens based on reflections from an array of three-dimensional, high-aspect-ratio micro-mirrors fabricated on a cylindrical elastomeric substrate, functionally inspired by natural reflecting superposition compound eyes. Our device can perform one-dimensional focusing and beam-shaping comparable to conventional refraction-based cylindrical lenses, while avoiding chromatic aberration. The focal length of our cylindrical lens is 1.035 mm, suitable for micro-optical systems. Moreover, it demonstrates a wide field of view of 152° without distortion, as well as modest spherical aberrations. Our work could be applied to diverse applications including laser diode collimation, barcode scanning, holography, digital projection display, microlens arrays, and optical microscopy. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessArticle Wafer-Level Hybrid Integration of Complex Micro-Optical Modules
Micromachines 2014, 5(2), 325-340; doi:10.3390/mi5020325
Received: 31 March 2014 / Revised: 21 May 2014 / Accepted: 27 May 2014 / Published: 5 June 2014
Cited by 5 | PDF Full-text (1048 KB) | HTML Full-text | XML Full-text
Abstract
A series of technological steps concentrating around photolithography and UV polymer on glass replication in a mask-aligner that allow for the cost-effective generation of rather complex micro-optical systems on the wafer level are discussed. In this approach, optical functional surfaces are aligned [...] Read more.
A series of technological steps concentrating around photolithography and UV polymer on glass replication in a mask-aligner that allow for the cost-effective generation of rather complex micro-optical systems on the wafer level are discussed. In this approach, optical functional surfaces are aligned to each other and stacked on top of each other at a desired axial distance. They can consist of lenses, achromatic doublets, regular or chirped lens arrays, diffractive elements, apertures, filter structures, reflecting layers, polarizers, etc. The suitability of the separated modules in certain imaging and non-imaging applications will be shown. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Figures

Open AccessArticle Fabrication of Polydimethylsiloxane Microlenses Utilizing Hydrogel Shrinkage and a Single Molding Step
Micromachines 2014, 5(2), 275-288; doi:10.3390/mi5020275
Received: 9 April 2014 / Revised: 9 May 2014 / Accepted: 14 May 2014 / Published: 21 May 2014
Cited by 3 | PDF Full-text (359 KB) | HTML Full-text | XML Full-text
Abstract
We report on polydimethlysiloxane (PDMS) microlenses and microlens arrays on flat and curved substrates fabricated via a relatively simple process combining liquid-phase photopolymerization and a single molding step. The mold for the formation of the PDMS lenses is fabricated by photopolymerizing a [...] Read more.
We report on polydimethlysiloxane (PDMS) microlenses and microlens arrays on flat and curved substrates fabricated via a relatively simple process combining liquid-phase photopolymerization and a single molding step. The mold for the formation of the PDMS lenses is fabricated by photopolymerizing a polyacrylamide (PAAm) pre-hydrogel. The shrinkage of PAAm after its polymerization forms concave lenses. The lenses are then transferred to PDMS by a single step molding to form PDMS microlens array on a flat substrate. The PAAm concave lenses are also transferred to PDMS and another flexible polymer, Solaris, to realize artificial compound eyes. The resultant microlenses and microlens arrays possess good uniformity and optical properties. The focal length of the lenses is inversely proportional to the shrinkage time. The microlens mold can also be rehydrated to change the focal length of the ultimate PDMS microlenses. The spherical aberration is 2.85 μm and the surface roughness is on the order of 204 nm. The microlenses can resolve 10.10 line pairs per mm (lp/mm) and have an f-number range between f/2.9 and f/56.5. For the compound eye, the field of view is 113°. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Review

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Open AccessReview Fast-Response Liquid Crystal Microlens
Micromachines 2014, 5(2), 300-324; doi:10.3390/mi5020300
Received: 4 May 2014 / Revised: 23 May 2014 / Accepted: 27 May 2014 / Published: 3 June 2014
Cited by 11 | PDF Full-text (2242 KB) | HTML Full-text | XML Full-text | Correction
Abstract
Electrically tunable liquid crystal microlenses have attracted strong research attention due to their advantages of tunable focusing, voltage actuation, low power consumption, simple fabrication, compact structure, and good stability. They are expected to be essential optical devices with widespread applications. However, the [...] Read more.
Electrically tunable liquid crystal microlenses have attracted strong research attention due to their advantages of tunable focusing, voltage actuation, low power consumption, simple fabrication, compact structure, and good stability. They are expected to be essential optical devices with widespread applications. However, the slow response time of nematic liquid crystal (LC) microlenses has been a significant technical barrier to practical applications and commercialization. LC/polymer composites, consisting of LC and monomer, are an important extension of pure LC systems, which offer more flexibility and much richer functionality than LC alone. Due to the anchoring effect of a polymer network, microlenses, based on LC/polymer composites, have relatively fast response time in comparison with pure nematic LC microlenses. In addition, polymer-stabilized blue phase liquid crystal (PS-BPLC) based on Kerr effect is emerging as a promising candidate for new photonics application. The major attractions of PS-BPLC are submillisecond response time and no need for surface alignment layer. In this paper, we review two types of fast-response microlenses based on LC/polymer composites: polymer dispersed/stabilized nematic LC and polymer-stabilized blue phase LC. Their basic operating principles are introduced and recent progress is reviewed by examples from recent literature. Finally, the major challenges and future perspectives are discussed. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessReview The Five Ws (and one H) of Super-Hydrophobic Surfaces in Medicine
Micromachines 2014, 5(2), 239-262; doi:10.3390/mi5020239
Received: 26 January 2014 / Revised: 8 April 2014 / Accepted: 22 April 2014 / Published: 5 May 2014
Cited by 5 | PDF Full-text (5856 KB) | HTML Full-text | XML Full-text
Abstract
Super-hydrophobic surfaces (SHSs) are bio-inspired, artificial microfabricated interfaces, in which a pattern of cylindrical micropillars is modified to incorporate details at the nanoscale. For those systems, the integration of different scales translates into superior properties, including the ability of manipulating biological solutions. [...] Read more.
Super-hydrophobic surfaces (SHSs) are bio-inspired, artificial microfabricated interfaces, in which a pattern of cylindrical micropillars is modified to incorporate details at the nanoscale. For those systems, the integration of different scales translates into superior properties, including the ability of manipulating biological solutions. The five Ws, five Ws and one H or the six Ws (6W), are questions, whose answers are considered basic in information-gathering. They constitute a formula for getting the complete story on a subject. According to the principle of the six Ws, a report can only be considered complete if it answers these questions starting with an interrogative word: who, why, what, where, when, how. Each question should have a factual answer. In what follows, SHSs and some of the most promising applications thereof are reviewed following the scheme of the 6W. We will show how these surfaces can be integrated into bio-photonic devices for the identification and detection of a single molecule. We will describe how SHSs and nanoporous silicon matrices can be combined to yield devices with the capability of harvesting small molecules, where the cut-off size can be adequately controlled. We will describe how this concept is utilized for obtaining a direct TEM image of a DNA molecule. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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