Sub-millisecond Switching Time Research Articles

A wide range room temperature antiferroelectric liquid crystal mixture with moderate spontaneous polarization and sub-millisecond switching time

A room-temperature antiferroelectric liquid crystal (AFLC) mixture has been prepared by doping two chiral fluorinated compounds into a four-component achiral phenyl pyrimidine-based host matrix. The suitability of the mixture for practical applications has been tested by optical polarizing microscopy, synchrotron X-ray diffraction, frequency-dependent dielectric, and electro-optic studies. The mixture possesses an antiferroelectric phase over a wide temperature range (nearly 82 °C) followed by a paraelectric phase for 13.7 °C. It is found to display very fast switching between 243 and 45 μs at the driving voltage of 3.2 V/μm in the SmC*A phase. At 20 °C, the mixture exhibits a moderately high spontaneous polarization (137 nC/cm2), low viscosity (1.01 Pa s) and fast switching (240μs). The formulated mixture is thus expected to be suitable for use in fast-response AFLC-based display devices.

Random access parallel microscopy.

We introduce a random-access parallel (RAP) imaging modality that uses a novel design inspired by a Newtonian telescope to image multiple spatially separated samples without moving parts or robotics. This scheme enables near-simultaneous image capture of multiple petri dishes and random-access imaging with sub-millisecond switching times at the full resolution of the camera. This enables the RAP system to capture long-duration records from different samples in parallel, which is not possible using conventional automated microscopes. The system is demonstrated by continuously imaging multiple cardiac monolayer and Caenorhabditis elegans preparations.

Directing light with liquid crystal metasurfaces

Liquid crystal metasurfaces self-assemble on polymer substrates regularly patterned by focused ion beam. Periodic deformations of nematic liquid crystal produce distinct colouring and strong diffraction. Applying AC voltage of 4 V across the liquid crystal layer straightens the nematic, suppresses diffraction and increases direct transmission within sub-millisecond switching times. Multi-parametric optimization of the metasurface design substantially enhances the efficiency of diffraction into a single particular channel.

Paper-like flexible optically isotropic liquid crystal film for tunable diffractive devices.

We have demonstrated a paper-like diffractive film in which nano-structured liquid crystal droplets are embedded in elastomeric monomer incorporated polymer matrix by polymerization induced phase-separation. The film with voltage-tunable phase grating exhibits an optically isotropic phase with high transparency and an effective chromatic diffraction for an incident white light with sub-millisecond switching time. In addition, the proposed diffractive film is exhibiting excellent chemical stability against organic and inorganic solvents. In this paper, the diffraction properties of test films depending on incident polarization direction, wavelength, and spatial dispersion are characterized. Easy processing and optically isotropic nature of the film imparts potential applications to flexible electro-optic devices that can be widely implemented in wearable photonics.

Dye-doped dual-frequency nematic cells as fast-switching polarization-independent shutters.

We present polarization-independent optical shutters with a sub-millisecond switching time. The approach utilizes dual-frequency nematics doped with a dichroic dye. Two nematic cells with orthogonal alignment are driven simultaneously by a low-frequency or high-frequency electric field to switch the shutter either into a transparent or a light-absorbing state. The switching speed is accelerated via special short pulses of high amplitude voltage. The approach can be used in a variety of electro-optical devices.

Monodomain Blue Phase Liquid Crystal Layers for Phase Modulation

Liquid crystal “Blue Phases” (BP) have evolved, in the last years, from a scientific curiosity to emerging materials for new photonic and display applications. They possess attractive features over standard nematic liquid crystals, like submillisecond switching times and polarization- independent optical response. However, BPs still present a number of technical issues that prevent their use in practical applications: their phases are only found in limited temperature ranges, thus requiring stabilization of the layers; stabilized BP layers are inhomogeneous and not uniformly oriented, which worsen the optical performance of the devices. It would be essential for practical uses to obtain perfectly aligned and oriented monodomain BP layers, where the alignment and orientation of the cubic lattice are organized in a single 3D structure. In this work we have obtained virtually perfect monodomain BP layers and used them in devices for polarization independent phase modulation. We demonstrate that, under applied voltage, well aligned and oriented layers generate smoother and higher values of the phase shift than inhomogeneous layers, while preserving polarization independency. All BP devices were successfully stabilized in BPI phase, maintaining the layer monodomain homogeneity at room temperature, covering the entire area of the devices with a unique BP phase.

A multi-plane optical see-through head mounted display design for augmented reality applications

Augmented reality (AR) display technology greatly enhances users' perception of and interaction with the real world by superimposing a computer-generated virtual scene on the real physical world. The main problem of the state-of-the-art 3D AR head-mounted displays (HMDs) is the accommodation-vergence conflict because the 2D images displayed by flat panel devices are at a fixed distance from the eyes. In this paper, we present a design for an optical see-through HMD utilizing multi-plane display technology for AR applications. This approach manages to provide correct depth information and solves the accommodation-vergence conflict problem. In our system, a projector projects slices of a 3D scene onto a stack of polymer-stabilized liquid crystal scattering shutters in time sequence to reconstruct the 3D scene. The polymer-stabilized liquid crystal shutters have sub-millisecond switching time that enables sufficient number of shutters to achieve high depth resolution. A proof-of-concept two-plane optical see-through HMD prototype is demonstrated. Our design can be made lightweight, compact, with high resolution, and large depth range from near the eye to infinity and thus holds great potential for fatigue-free AR HMDs.

Induction of a room temperature ferroelectric SmC* phase in binary mixtures with moderate spontaneous polarization and sub-millisecond switching time

Induction of room temperature SmC* phase in binary mixture.

Parallel Accumulation-Serial Fragmentation (PASEF): Multiplying Sequencing Speed and Sensitivity by Synchronized Scans in a Trapped Ion Mobility Device.

In liquid chromatography-mass spectrometry (LC-MS)-based proteomics, many precursors elute from the column simultaneously. In data-dependent analyses, these precursors are fragmented one at a time, whereas the others are discarded entirely. Here we employ trapped ion mobility spectrometry (TIMS) on an orthogonal quadrupole time-of-flight (QTOF) mass spectrometer to remove this limitation. In TIMS, all precursor ions are accumulated in parallel and released sequentially as a function of their ion mobility. Instead of selecting a single precursor mass with the quadrupole mass filter, we here implement synchronized scans in which the quadrupole is mass positioned with sub-millisecond switching times at the m/z values of appropriate precursors, such as those derived from a topN precursor list. We demonstrate serial selection and fragmentation of multiple precursors in single 50 ms TIMS scans. Parallel accumulation-serial fragmentation (PASEF) enables hundreds of MS/MS events per second at full sensitivity. Modeling the effect of such synchronized scans for shotgun proteomics, we estimate that about a 10-fold gain in sequencing speed should be achievable by PASEF without a decrease in sensitivity.

Polarization-independent phase modulation using a blue-phase liquid crystal over silicon device.

Liquid crystal over silicon (LCoS) spatial light modulator technology has become dominant in industries such as pico-projection, which require high-quality reflective microdisplays for intensity modulation of light. They are, however, restricted from being used in wider optical applications, such as computer-generated holography, adaptive optics, and optical correlation, due to their phase modulation ability. The main drawback of these devices is that their modulation is based on simple planar or twisted nematic liquid crystals, which are inherently slow mechanisms due to their viscoelastic properties. Their use is also limited due to fact that the phase modulation is dependent on the state of polarization of the illumination. In this paper, we demonstrate that a polymer-stabilized blue-phase liquid crystal can offer both phase modulation and high speed switching in a silicon backplane device which is independent of the input polarization state. The LCoS device shows continuous phase modulation of light with a submillisecond switching time and insensitivity to the input light polarization direction. This type of phase modulation opens up a whole new class of applications for LCoS technology.

A dual frequency addressed polymer stabilized pi‐cell liquid crystal device

Dual frequency addressing of nematic pi‐cell devices produces submillisecond switching times since the liquid crystal can be driven both parallel and perpendicular to the applied field and there is no kick‐back of the director during switching. The nucleation of the V state in devices containing dual frequency liquid crystal materials is much slower than that in conventional pi‐cells, however. Polymer stabilization of the V state eliminates the need for nucleation each time the device is used. In this paper we present a polymer stabilized pi‐cell containing a dual frequency liquid crystal material, and show that the presence of the polymer network significantly influences the switching of the device. Some optimization of the addressing scheme is required when switching the polymer stabilized device in order to avoid transient formation of the twisted state. Using this optimization, the switching time is under 3 ms across a wide range of addressing voltages. 1Now at: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, ML3 9PL.

High-Performance Stress-Induced Micromachined Optical Switch with Multiswitching Function Using Seesaw Structure

In this paper, we present a high-performance electrostatically actuated optical switch with a multiswitching function using stress-induced bending micromirrors and a seesaw structure. The use of a curved polysilicon seesaw structure and a torsional beam substantially lowers the electrostatic operating voltage of the optical switch and provides a multi-switching function. Large mirror deflection angles of 15° (with a mirror elevation of 310 µm) are obtained at a low operating voltage of 17 V. Furthermore, the device demonstrates a submillisecond switching time (<900 µs) and a low optical insertion loss (0.65 dB). The developed optical switch, which uses mirrors in an N ×N array, could redirect 4N optical inputs to 4N outputs. The compact nature of the optical multiswitch element renders it ideal for the construction of optical crossconnects (OXCs) with a large number of ports on a chip.

Optical projection display systems integrated with three-color-mixing waveguides and grating-light-valve devices

An integrated optical projection display technique utilizing three-color-mixing waveguides and grating-light-valve devices is demonstrated. This new projection display system comprises an optical lens, a microscanner, a grating light valve, and a 3x1 planar waveguide device. The planar waveguide device is fabricated using a SU-8 negative photoresist process, which is suitable material for rapid prototyping of integrated optical circuits. It works as a three-color-mixer and is successfully used for color image generation. The intensity of color for each pixel in the display picture is tuned by groups of movable ribbons comprising a grating light valve and image generating diffraction gratings. This study also demonstrates a surface-micromachined optical scanner using four stress-actuated polysilicon plates to raise a horizontal mirror. The electrostatically driven mirror can be used for scanning projection display applications. Experimental data show that the optical scanner has a mirror scanning angle up to +/-15(o) using an operating voltage of 25 V. A sub-millisecond switching time (<900 mus) and an optical insertion loss of 0.85 dB is achieved for multi-mode waveguides. The development of the proposed integrated optical system could be promising for an image generation system.

Projection display technique utilizing three-color-mixing waveguides and microscanning devices

An integrated-optical three-color-mixing projection display system is demonstrated. This projection display system comprises an optical lens, two microscanners, and a 3×1 planar waveguide device using a new combination of SU-8 and JSR photoresists, which are suitable materials for rapid prototyping of integrated optical circuits. The three-color-mixer fabricated by using a low-cost process has been successfully used for color image generation. This study also demonstrates a surface-micromachined optical scanner using two stress-induced polysilicon plates to raise a horizontal mirror. The electrostatically driven mirror could be used for scanning projection display applications. Experimental data show that the optical scanner has a mirror scanning angle up to 18/spl deg/ using a low operating voltage of 25 V, a submillisecond switching time (<600 μs) and optical insertion loss of 0.85 dB is achieved for multimode waveguides. The development of the proposed project display technology could be promising for integrated optics.

A High-Speed Low-Voltage Double-Switch Optical Crossconnect Using Stress-Induced Bending Micromirrors

A high-speed low-voltage double-switch electrostatically actuated optical crossconnect (OXC) is demonstrated using stress-induced bending micromirrors. A curved polysilicon seesaw structure substantially lowers the electrostatic operating voltage of the OXC and provides a double-switch option. Large mirror deflection angles of 13/spl deg/ (mirror elevation of 290 /spl mu/m high) and 5/spl deg/ (cantilever deflection of 90 /spl mu/m high), corresponding to low operating voltages of 25 and 18 V, could be obtained. A submillisecond switching time (<850 /spl mu/s), a low optical insertion loss (0.65 dB), and a small polarization-dependent loss (<0.08 dB) are achieved.

Self-aligned micromachining process for large-scale, free-space optical cross-connects

A new micromachining process for large-scale optical cross-connects is presented. It satisfies the high-accuracy optical alignment required for free-space optics. A self-aligned batch-process allowing the simultaneous fabrication of vertical mirrors and fiber guides is performed with only one-mask. This process is based on bulk micromachining of [100] silicon. A first demonstration is performed on a 2/spl times/2 elementary cell then, it is extended to the fabrication of larger mirror arrays. Promising performances such as insertion loss lower than 0.5 dB, sub-millisecond switching time (0.3 ms) and reliable operation (more than 20 million cycles) are demonstrated on a bypass switch. An improved fabrication process, leading to an increase of integration density is also presented. It is based on the combination of deep dry-etching and anisotropic wet-etching.

A high-speed low-voltage stress-induced micromachined 2 x 2 optical switch

A low-voltage electrostatically actuated 2/spl times/2 fiber optic switch is achieved using a stress-induced curved polysilicon actuator. The curved polysilicon beam substantially lowers the electrostatic operating voltage of the switch. Large mirror displacement (300 /spl mu/m) and low operating voltage (20 V) are obtained simultaneously. Sub-millisecond switching time (<600 /spl mu/s), low optical insertion loss (0.7 dB), and small polarization-dependent loss (0.09 dB) have been achieved.

Fast optical switching by a laser-manipulated microdroplet of liquid crystal

We demonstrate the feasibility of an all-optical liquid-crystal (LC) switch with submillisecond switching time. This switch is realized by optical manipulation of a three-dimensionally trapped microscopic nematic LC droplet using an “optical tweezers.” Transmission of a polarizer/LC droplet/analyzer system can be modulated at frequencies as high as 103 Hz, a faster response than that of a nematic LC demonstrated so far. The response corresponds to a submillisecond switching time when the LC droplet is rotated by an angle of π/4. The alignment of the LC droplet to the plane of the incident plane-polarized beam is also demonstrated.

Fast, low insertion-loss optical switch using lithographically defined electromagnetic microactuators and polymeric passive alignment structures

A micro-optoelectromechanical switch that combines microactuator technology developed via the Lithographie Galvanformung Abformung process with lithographically defined polymeric alignment elements is described. The multimode optical switch achieves submillisecond switching times, low insertion loss (&amp;lt;1 dB), low cross talk (&amp;lt;70 dB), low voltage (3 V), and wavelength independence.

Free-space micromachined optical switches with submillisecond switching time for large-scale optical crossconnects

Optical crossconnects with large port counts are fast becoming critical components for high-capacity optical transport networks. The free-space micromachined optical switches (FS-MOS) demonstrated in this letter represent a means of filling this network need by combining the advantages of free-space interconnection with the virtues of integrated optics. Featuring free-rotating hinged micromirrors, the switch overcomes the common drawback of mechanical-type switches, namely long switching time. Measurements have revealed switching times less than 700 μs, crosstalk less than -60 dB, extinction ratio greater than 60 dB, negligible polarization-dependent loss, and excellent bit-error-rate (BER) performance.