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26 Nov 2012

Volume 101, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 221101 (2012); http://dx.doi.org/10.1063/1.4767646 (5 pages)

Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso
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Ultra-thin perfect absorber employing a tunable phase change material

Mikhail A. Kats, Deepika Sharma, Jiao Lin, Patrice Genevet, Romain Blanchard, Zheng Yang, M. Mumtaz Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso

Appl. Phys. Lett. 101, 221101 (2012); http://dx.doi.org/10.1063/1.4767646 (5 pages) | Cited 5 times

Online Publication Date: 26 November 2012

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We show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media. This design is implemented with an ultra-thin (∼λ/65) vanadium dioxide (VO2) layer on sapphire, temperature tuned in the vicinity of the VO2 insulator-to-metal phase transition, leading to 99.75% absorption at λ = 11.6 μm. The structural simplicity and large tuning range (from ∼80% to 0.25% in reflectivity) are promising for thermal emitters, modulators, and bolometers.
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78.66.Nk Insulators
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics

Photoacoustic spectrum analysis for microstructure characterization in biological tissue: A feasibility study

Guan Xu, Irfaan A. Dar, Chao Tao, Xiaojun Liu, Cheri X. Deng, and Xueding Wang

Appl. Phys. Lett. 101, 221102 (2012); http://dx.doi.org/10.1063/1.4768703 (5 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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This study investigates the feasibility of characterizing the microstructures within a biological tissue by analyzing the frequency spectrum of the photoacoustic signal from the tissue. Hypotheses are derived from theoretical analyses on the relationships between the dimensions/concentrations of the photoacoustic sources within the region-of-interest and the linear model fitted to the power spectra of photoacoustic signals. The hypotheses are validated, following the procedures of ultrasound spectrum analysis, by simulations and experiments with phantoms fabricated by embedding the polyethylene microspheres in porcine gelatin, indicating that photoacoustic spectrum analysis could be a potential tool for characterizing microstructures in biological samples.
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87.63.dh Ultrasonographic imaging
43.80.Qf Medical diagnosis with acoustics
87.63.L- Visual imaging
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Needle-like focus generation by radially polarized halo beams emitted by photonic-crystal ring-cavity laser

Kyoko Kitamura, Masaya Nishimoto, Kyosuke Sakai, and Susumu Noda

Appl. Phys. Lett. 101, 221103 (2012); http://dx.doi.org/10.1063/1.4767994 (4 pages)

Online Publication Date: 26 November 2012

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Focused fields that possess a small spot size and long depth of focus (DOF) are expected to lead to the further development of optical applications. Here, we develop a photonic-crystal ring-cavity laser that emits a beam with a radially polarized halo shape (rinner/router > 0.9). This beam has a needle-like focus with a spot size of less than 0.4λ and a depth of focus longer than 10 λ for a 0.9 numerical aperture objective lens. We evaluate the focusing properties of the emitted beam and demonstrate that it has a longer depth of focus than conventional beams.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Qs Photonic bandgap materials
42.25.Ja Polarization

High reflectance membrane-based distributed Bragg reflectors for GaN photonics

Danti Chen and Jung Han

Appl. Phys. Lett. 101, 221104 (2012); http://dx.doi.org/10.1063/1.4768806 (4 pages)

Online Publication Date: 26 November 2012

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Preparation of highly reflective distributed Bragg reflectors (DBRs) from III-nitrides is an important building block for cavity photonics. In this work, we report the fabrication of a membrane-based GaN/air-gap DBR for blue/green light emitting devices. The formation of membrane DBRs relies on a recently discovered electrochemical procedure in which selective etch is achieved by adjusting the conductivity rather than chemical composition, thus relieving greatly the burden in creating epitaxial DBRs. Micro-reflectance measurement shows over 98% peak reflectance and a wide stopband with only four pairs of GaN/air-gap layers. Micro-photoluminescence spectra of InGaN multiple quantum wells (MQWs) on DBRs show reduced linewidth and improved emission efficiency. After capping the MQWs on DBRs with silver, a significant linewidth narrowing indicates the modification of spontaneous emission due to the presence of a planar microcavity.
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85.60.Jb Light-emitting devices
42.55.Px Semiconductor lasers; laser diodes
42.79.-e Optical elements, devices, and systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Fiber-optic rotation of micro-scale structures enabled microfluidic actuation and self-scanning two-photon excitation

Bryan J. Black, Dijun Luo, and Samarendra K. Mohanty

Appl. Phys. Lett. 101, 221105 (2012); http://dx.doi.org/10.1063/1.4768232 (4 pages)

Online Publication Date: 26 November 2012

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Here, we report non-restricted, controlled fiber optic rotation of micro-motor, in counter-propagating fiber-optic beams having transverse-offset, for actuation of microfluidic flow. Ray-optics based simulations of the torque (and angular velocity) were conducted for different fiber transverse-offsets in order to determine optimal geometry for effective actuation. Further, self-scanning two-photon excitation of the fiber-optically rotated microscopic object is achieved by use of an ultrafast laser beam in one of the fiber arm.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.50.+d Electric motors
42.81.Wg Other fiber-optical devices
07.10.Cm Micromechanical devices and systems
07.60.Vg Fiber-optic instruments
07.07.Tw Servo and control equipment; robots

Ultra-thin silicon-on-insulator strip waveguides and mode couplers

Michael Gould, Andrew Pomerene, Craig Hill, Stewart Ocheltree, Yi Zhang, Tom Baehr-Jones, and Michael Hochberg

Appl. Phys. Lett. 101, 221106 (2012); http://dx.doi.org/10.1063/1.4768296 (3 pages)

Online Publication Date: 26 November 2012

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We demonstrate an ultra-thin silicon waveguide for wavelengths around 1.55 μm, and mode converters designed for transitions to and from standard 500 nm × 220 nm strip waveguides. The devices were fabricated in a CMOS-compatible process requiring two photolithography and etch steps. The ultra-thin waveguides exhibited losses of 2.01 ± 0.231 dB/cm, exhibited bend radii as small as 30 μm with losses of 0.05 ± 0.005 dB per bend, and exhibited coupling losses of 0.66 ± 0.014 dB to standard strip waveguides.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer

InP-based 2.8–3.5 μm resonant-cavity light emitting diodes based on type-II transitions in GaInAs/GaAsSb heterostructures

Christian Grasse, Peter Wiecha, Tobias Gruendl, Stephan Sprengel, Ralf Meyer, and Markus-Christian Amann

Appl. Phys. Lett. 101, 221107 (2012); http://dx.doi.org/10.1063/1.4768447 (4 pages)

Online Publication Date: 26 November 2012

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We present InP-based resonant-cavity light emitting diodes (LEDs), which are emitting at 2.8 μm, 3.3 μm, and 3.5 μm and were grown by metalorganic vapor phase epitaxy. This long wavelength electroluminescence is achieved by using highly strained GaInAs/GaAsSb type-II quantum wells. The performance of two different active region designs, superlattice (“SL”) and “W”-shaped quantum wells (“W”), is compared. Although continuous wave operation up to 80 °C could be proven, a spontaneous emission droop similar to nitride-based LEDs has been observed and is discussed.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Temperature and Bi-concentration dependence of the bandgap and spin-orbit splitting in InGaBiAs/InP semiconductors for mid-infrared applications

I. P. Marko, Z. Batool, K. Hild, S. R. Jin, N. Hossain, T. J. C. Hosea, J. P. Petropoulos, Y. Zhong, P. B. Dongmo, J. M. O. Zide, and S. J. Sweeney

Appl. Phys. Lett. 101, 221108 (2012); http://dx.doi.org/10.1063/1.4768532 (5 pages) | Cited 1 time

Online Publication Date: 26 November 2012

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Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ΔSO, respectively. The possibility of achieving ΔSO > Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure Eg(x, T) and ΔSO (x, T) in In0.53Ga0.47BixAs1−x/InP samples for 0 ≤ x ≤ 0.039 by various complementary optical spectroscopic techniques. While we find no clear evidence of a decreased dEg/dT (≈0.34 ± 0.06 meV/K in all samples) we find ΔSO > Eg for x > 3.3–4.3%. The predictions of a valence band anti-crossing model agree well with the measurements.
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71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Fiber-cavity-based optomechanical device

N. E. Flowers-Jacobs, S. W. Hoch, J. C. Sankey, A. Kashkanova, A. M. Jayich, C. Deutsch, J. Reichel, and J. G. E. Harris

Appl. Phys. Lett. 101, 221109 (2012); http://dx.doi.org/10.1063/1.4768779 (4 pages) | Cited 1 time

Online Publication Date: 27 November 2012

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We describe an optomechanical device consisting of a fiber-based optical cavity containing a silicon nitride membrane. In comparison with typical free-space cavities, the fiber-cavity's small mode size (10 μm waist, 80 μm length) allows the use of smaller, lighter membranes and increases the cavity-membrane linear coupling to 3 GHz/nm and the quadratic coupling to 20 GHz/nm2. This device is also intrinsically fiber-coupled and uses glass ferrules for passive alignment. These improvements will greatly simplify the use of optomechanical systems, particularly in cryogenic settings. At room temperature, we expect these devices to be able to detect the shot noise of radiation pressure.
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42.81.Wg Other fiber-optical devices
07.60.Vg Fiber-optic instruments

Mode coupling by plasmonic surface scatterers in thin-film silicon solar cells

M. van Lare, F. Lenzmann, M. A. Verschuuren, and A. Polman

Appl. Phys. Lett. 101, 221110 (2012); http://dx.doi.org/10.1063/1.4767997 (4 pages)

Online Publication Date: 27 November 2012

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We demonstrate effective mode coupling by light scattering from periodic Ag nanoparticle arrays printed onto a completed thin-film a-Si:H solar cell. Current-voltage measurements show a photocurrent enhancement of 10% compared to a flat reference cell with a standard antireflection coating. External quantum efficiency measurements for the nanopatterned cells show clear infrared photocurrent enhancement peaks, corresponding to coupling to discrete waveguide modes in the a-Si:H layer. The data are in good agreement with three-dimensional finite element simulations, which are used to further optimize the design. We show that broadband photocurrent enhancement can be obtained over the 450–750 nm spectral range.
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88.40.H- Solar cells (photovoltaics)
02.70.Dh Finite-element and Galerkin methods
72.40.+w Photoconduction and photovoltaic effects
79.60.-i Photoemission and photoelectron spectra
42.70.-a Optical materials

Compositional dependence of the absorption edge and dark currents in Ge1−x−ySixSny/Ge(100) photodetectors grown via ultra-low-temperature epitaxy of Ge4H10, Si4H10, and SnD4

R. T. Beeler, Chi Xu, D. J. Smith, G. Grzybowski, J. Menéndez, and J. Kouvetakis

Appl. Phys. Lett. 101, 221111 (2012); http://dx.doi.org/10.1063/1.4768217 (5 pages) | Cited 2 times

Online Publication Date: 27 November 2012

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Lattice-matched Ge1−x−ySixSny (x ≤ 0.2, y ≤ 0.05) alloys were deposited defect-free on Ge(001) substrates via low-temperature (330–290 °C) reactions of Ge4H10, Si4H10 and SnD4 hydrides, and used to fabricate pin photodetectors. The growth is carried out under gas-source molecular beam epitaxy conditions in a specially designed single-wafer reactor. Optical responsivity measurements reveal absorption edges between 0.88 eV and 0.98 eV, which are used to determine the compositional dependence of the direct band gap. A study of the I-V characteristics of the diodes shows that the dark current is very weakly correlated with the number of Si-Sn bonds in the alloy.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

An extremely low-noise heralded single-photon source: A breakthrough for quantum technologies

G. Brida, I. P. Degiovanni, M. Genovese, F. Piacentini, P. Traina, A. Della Frera, A. Tosi, A. Bahgat Shehata, C. Scarcella, A. Gulinatti, M. Ghioni, S. V. Polyakov, A. Migdall, and A. Giudice

Appl. Phys. Lett. 101, 221112 (2012); http://dx.doi.org/10.1063/1.4768288 (4 pages) | Cited 1 time

Online Publication Date: 27 November 2012

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Low noise single-photon sources are a critical element for quantum technologies. We present a heralded single-photon source with an extremely low level of residual background photons, by implementing low-jitter detectors and electronics and a fast custom-made pulse generator controlling an optical shutter (a LiNbO3 waveguide optical switch) on the output of the source. This source has a second-order autocorrelation g(2)(0) = 0.005(7), and an output noise factor (defined as the ratio of the number of noise photons to total photons at the source output channel) of 0.25(1)%. These are the best performance characteristics reported to date.
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42.50.-p Quantum optics
42.79.Gn Optical waveguides and couplers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Optical pulse generation in single section InAs/GaAs quantum dot edge emitting lasers under continuous wave operation

R. Rosales, K. Merghem, C. Calo, G. Bouwmans, I. Krestnikov, A. Martinez, and A. Ramdane

Appl. Phys. Lett. 101, 221113 (2012); http://dx.doi.org/10.1063/1.4768946 (3 pages)

Online Publication Date: 27 November 2012

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Observation of sub-picosecond pulses from a single section Fabry Perot InAs/GaAs edge emitting quantum dot (QD) based laser at 1.3 μm under continuous wave operation is reported. After group delay dispersion compensation, pulse durations as short as 770 fs in a 45 GHz repetition rate device have been measured, with 1.9 W of peak power and a narrow radio frequency spectrum of only a few kHz linewidth. The experiments show evidence of an unexplored mode locking regime in the InAs/GaAs quantum dot material system, which still needs theoretical modelling and further analysis.
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42.60.-v Laser optical systems: design and operation
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
68.65.Hb Quantum dots (patterned in quantum wells)
42.55.Px Semiconductor lasers; laser diodes

Gold substrate-induced single-mode lasing of GaN nanowires

Huiwen Xu, Jeremy B. Wright, Antonio Hurtado, Qiming Li, Ting-Shan Luk, Jeffrey J. Figiel, Karen Cross, Ganesh Balakrishnan, Luke F. Lester, Igal Brener, and George T. Wang

Appl. Phys. Lett. 101, 221114 (2012); http://dx.doi.org/10.1063/1.4768300 (4 pages)

Online Publication Date: 27 November 2012

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We demonstrate a method for mode-selection by coupling a GaN nanowire laser to an underlying gold substrate. Multimode lasing of GaN nanowires is converted to single-mode behavior following placement onto a gold film. A mode-dependent loss is generated by the absorbing substrate to suppress multiple transverse-mode operation with a concomitant increase in lasing threshold of only ∼13%. This method provides greater flexibility in realizing practical single-mode nanowire lasers and offers insight into the design of metal-contacted nanoscale optoelectronics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Absorption saturation in optically excited graphene

Torben Winzer, Andreas Knorr, Martin Mittendorff, Stephan Winnerl, Miao-Bin Lien, Dong Sun, Theodore B. Norris, Manfred Helm, and Ermin Malic

Appl. Phys. Lett. 101, 221115 (2012); http://dx.doi.org/10.1063/1.4768780 (4 pages) | Cited 3 times

Online Publication Date: 28 November 2012

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We investigate the saturation of the optical absorption in graphene induced by ultrafast optical pulses. Within a microscopic theory, we study the momentum-, angle-, and time-resolved interplay of anisotropic excitation, carrier-carrier, and carrier-phonon scattering, and its influence on the saturation of absorption and transmission. In agreement with performed experiments, we observe a linear regime for the intensity-dependence of the transmission at low pump fluences and a nonlinear saturation in the high excitation regime. Applying 10 fs-pulses, we obtain a saturation fluence of approximately 0.65 mJ/cm2. We demonstrate how the interplay of Pauli-blocking and intensity-dependent relaxation determines the saturation behavior.
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78.47.da Excited states
78.67.Wj Optical properties of graphene
81.05.ue Graphene

A superhigh-frequency optoelectromechanical system based on a slotted photonic crystal cavity

Xiankai Sun, Xufeng Zhang, Menno Poot, Chi Xiong, and Hong X. Tang

Appl. Phys. Lett. 101, 221116 (2012); http://dx.doi.org/10.1063/1.4769045 (5 pages) | Cited 2 times

Online Publication Date: 28 November 2012

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We develop an all-integrated optoelectromechanical system that operates in the superhigh frequency band. This system is based on an ultrahigh-Q slotted photonic crystal (PhC) nanocavity formed by two PhC membranes, one of which is patterned with electrode and capacitively driven. The strong simultaneous electromechanical and optomechanical interactions yield efficient electrical excitation and sensitive optical transduction of the bulk acoustic modes of the PhC membrane. These modes are identified up to a frequency of 4.20 GHz, with their mechanical Q factors ranging from 240 to 1730. Directly linking signals in microwave and optical domains, such optoelectromechanical systems will find applications in microwave photonics in addition to those that utilize the electromechanical and optomechanical interactions separately.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Jq Acousto-optical devices
43.38.Zp Acoustooptic and photoacoustic transducers
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.60.Bt Optoelectronic device characterization, design, and modeling

Guide-star-based computational adaptive optics for broadband interferometric tomography

Steven G. Adie, Nathan D. Shemonski, Benedikt W. Graf, Adeel Ahmad, P. Scott Carney, and Stephen A. Boppart

Appl. Phys. Lett. 101, 221117 (2012); http://dx.doi.org/10.1063/1.4768778 (5 pages) | Cited 1 time

Online Publication Date: 29 November 2012

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We present a method for the numerical correction of optical aberrations based on indirect sensing of the scattered wavefront from point-like scatterers (“guide stars”) within a three-dimensional broadband interferometric tomogram. This method enables the correction of high-order monochromatic and chromatic aberrations utilizing guide stars that are revealed after numerical compensation of defocus and low-order aberrations of the optical system. Guide-star-based aberration correction in a silicone phantom with sparse sub-resolution-sized scatterers demonstrates improvement of resolution and signal-to-noise ratio over a large isotome. Results in highly scattering muscle tissue showed improved resolution of fine structure over an extended volume. Guide-star-based computational adaptive optics expands upon the use of image metrics for numerically optimizing the aberration correction in broadband interferometric tomography, and is analogous to phase-conjugation and time-reversal methods for focusing in turbid media.
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42.30.Wb Image reconstruction; tomography
42.40.Kw Holographic interferometry; other holographic techniques
42.30.Va Image forming and processing
42.30.Lr Modulation and optical transfer functions
95.75.Qr Adaptive and segmented optics
42.30.Kq Fourier optics

Performance investigation of p-i-n ZnO-based thin film homojunction ultraviolet photodetectors

Tzu-Shun Lin and Ching-Ting Lee

Appl. Phys. Lett. 101, 221118 (2012); http://dx.doi.org/10.1063/1.4768786 (3 pages)

Online Publication Date: 29 November 2012

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The p-i-n ZnO-based ultraviolet (UV) photodetectors was deposited using the vapor cooling condensation system. The rejection ratio between the ultraviolet and the visible was 2.82 × 103 measured at a reverse bias of −1 V. The low-frequency noise, which was dominated by the flicker noise, exhibited the noise equivalent power of 1.70 × 10−12 W and the high detectivity of 5.53 × 1011 cm Hz1/2W−1 with the illumination wavelength of 360 nm at the reverse bias voltage of −1 V. The high performances were attributed to the low defects and interface states present in the p-i-n ZnO-based ultraviolet photodetectors prepared using the vapor cooling condensation system.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Td Noise processes and phenomena

Identification of quantum confined interband transitions in type-II InAs/GaSb superlattices using polarization sensitive photocurrent spectroscopy

Nutan Gautam, Ajit Barve, and Sanjay Krishna

Appl. Phys. Lett. 101, 221119 (2012); http://dx.doi.org/10.1063/1.4767358 (4 pages)

Online Publication Date: 29 November 2012

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We report on the use of polarization sensitive photocurrent spectroscopy for identifying the participating transitions in type-II InAs/GaSb strained layer superlattice system. Transverse electric and transverse magnetic photocurrents have been measured for both midwave infrared and longwave infrared superlattices, and prominent features have been analyzed to identify different interband transition energies and unambiguously predict the correct ordering of hole minibands. The interband transition energies have also been confirmed with theoretical simulations using empirical pseudopotential method. Order of the participating valence minibands has been determined as: heavy-hole1, light-hole1 and light-hole2, with increase in hole energy.
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73.21.Cd Superlattices
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
72.40.+w Photoconduction and photovoltaic effects
73.63.-b Electronic transport in nanoscale materials and structures
71.20.Nr Semiconductor compounds

Color filters for reflective display with wide viewing angle and high reflectivity based on metal dielectric multilayer

Deukseok Chung, Changgyun Shin, Byonggwon Song, Myonghoon Jung, Youngjun Yun, Sung Hyun Nam, Changho Noh, Jungwoo Kim, and Sangyoon Lee

Appl. Phys. Lett. 101, 221120 (2012); http://dx.doi.org/10.1063/1.4768298 (4 pages)

Online Publication Date: 29 November 2012

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We report high performance reflective color filters based on one-dimensional metal-dielectric multilayer. Wide viewing angle of ±50°, far beyond that with conventional all-dielectric multilayers, is achieved while maintaining approximately 100% peak reflectance and color reproducibility. Reflectance of 40% in white mode and color gamut of 47% to the United States National Television Systems Committee (NTSC) standard is demonstrated. The proposed color filter is integrated into 3.5-in. color reflective display and shows 30% increase in brightness than conventional dye color filters.
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07.07.Hj Display and recording equipment, oscilloscopes, TV cameras, etc.
42.79.Ci Filters, zone plates, and polarizers
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Tunable-focus liquid crystal Fresnel zone lens based on harmonic diffraction

Yimin Lou, Linsen Chen, Chinhua Wang, and Su Shen

Appl. Phys. Lett. 101, 221121 (2012); http://dx.doi.org/10.1063/1.4769090 (4 pages)

Online Publication Date: 29 November 2012

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We propose and demonstrate a tunable-focus liquid crystal Fresnel zone lens (TLCFZL) based on harmonic diffraction. The physical mechanism of the focus tuning is based on a multi-order diffraction process using a shallow surface relief type harmonic diffractive structure with uniform electrodes which results in significantly reduced fabrication complexity and excellent electro-optic performances. A rapid fabrication process including imprinting technique is studied, from which a high performance TLCFZL with three switchable focus lengths and high diffraction efficiency (about 70%) is fabricated. Focusing and imaging properties of the TFLCFZL are tested. The highest resolution of the lens reaches 22.6 lp/mm with low operating voltage of less than 7.2 Vrm and response time of ∼200 ms.
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42.79.Bh Lenses, prisms and mirrors
42.79.Kr Display devices, liquid-crystal devices
42.86.+b Optical workshop techniques
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