Active liquid-crystal deflector and lens with Fresnel structure

SPIE OPTO, 2017, San Francisco, California, United StatesGiichi Shibuya, Shohei Yamano, Hiroyuki Yoshida, and Masanori Ozaki "Active liquid-crystal deflector and lens with Fresnel structure", Proc. SPIE 10125, Emerging Liquid Crystal Technologies XII, 101250V (15 February 2017). DOI: https://doi.org/10.1117/12.226111

Liquid crystal blazed grating beam deflector

A multiple-angle liquid crystal blazed grating beam deflector has been developed. It consists of a stack of liquid crystal blazed gratings where each layer can deflect incident light with very high efficiency into one of two different directions depending on the driving condition. Four steering angles (10.8 degrees, 7.2 degrees, 3.6 degrees, 0 degrees) with about 70% diffraction efficiency are demonstrated with 15 V. The device's working principle, design considerations, fabrication process, and characterization results are described

Liquid crystal blazed grating beam deflector

A multiple-angle liquid crystal blazed grating beam deflector has been developed. It consists of a stack of liquid crystal blazed gratings where each layer can deflect incident light with very high efficiency into one of two different directions depending on the driving condition. Four steering angles (10.8 degrees, 7.2 degrees, 3.6 degrees, 0 degrees) with about 70% diffraction efficiency are demonstrated with 15 V. The device's working principle, design considerations, fabrication process, and characterization results are described

Variable fiber-optic attenuator using optofluidics

Proposed is a Variable Fiber Optical Attenuator (VFOA) using an electronically controlled, variable focus liquid lens. The demonstrated experiment for the VFOA is shown for operation over the communication C-Band (1530nm- 1560nm)

Polarization independent VOA based on dielectrically stretched liquid crystal droplet

A polarization independent variable optical attenuator (VOA) based on a dielectrically stretched liquid crystal (LC) droplet is demonstrated. In the voltage-off state, the proposed VOA has the smallest attenuation. As voltage increases, the LC droplet is stretched by a dielectrophoretic force, which gradually deflects the beam leading to an increased attenuation. Such a VOA can cover the entire C-Band. At lambda = 1550 nm, the following results are obtained: dynamic range similar to 32 dB, insertion loss similar to 0.7 dB, polarization dependent loss similar to 0.3 dB, and response time similar to 20 ms

Liquid Crystal Optics For Communications, Signal Processing And 3-d Microscopic Imaging

This dissertation proposes, studies and experimentally demonstrates novel liquid crystal (LC) optics to solve challenging problems in RF and photonic signal processing, freespace and fiber optic communications and microscopic imaging. These include free-space optical scanners for military and optical wireless applications, variable fiber-optic attenuators for optical communications, photonic control techniques for phased array antennas and radar, and 3-D microscopic imaging. At the heart of the applications demonstrated in this thesis are LC devices that are non-pixelated and can be controlled either electrically or optically. Instead of the typical pixel-by-pixel control as is custom in LC devices, the phase profile across the aperture of these novel LC devices is varied through the use of high impedance layers. Due to the presence of the high impedance layer, there forms a voltage gradient across the aperture of such a device which results in a phase gradient across the LC layer which in turn is accumulated by the optical beam traversing through this LC device. The geometry of the electrical contacts that are used to apply the external voltage will define the nature of the phase gradient present across the optical beam. In order to steer a laser beam in one angular dimension, straight line electrical contacts are used to form a one dimensional phase gradient while an annular electrical contact results in a circularly symmetric phase profile across the optical beam making it suitable for focusing the optical beam. The geometry of the electrical contacts alone is not sufficient to form the linear and the quadratic phase profiles that are required to either deflect or focus an optical beam. Clever use of the phase response of a typical nematic liquid crystal (NLC) is made such that the linear response region is used for the angular beam deflection while the high voltage quadratic response region is used for focusing the beam. Employing an NLC deflector, a device that uses the linear angular deflection, laser beam steering is demonstrated in two orthogonal dimensions whereas an NLC lens is used to address the third dimension to complete a three dimensional (3-D) scanner. Such an NLC deflector was then used in a variable optical attenuator (VOA), whereby a laser beam coupled between two identical single mode fibers (SMF) was mis-aligned away from the output fiber causing the intensity of the output coupled light to decrease as a function of the angular deflection. Since the angular deflection is electrically controlled, hence the VOA operation is fairly simple and repeatable. An extension of this VOA for wavelength tunable operation is also shown in this dissertation. A LC spatial light modulator (SLM) that uses a photo-sensitive high impedance electrode whose impedance can be varied by controlling the light intensity incident on it, is used in a control system for a phased array antenna. Phase is controlled on the Write side of the SLM by controlling the intensity of the Write laser beam which then is accessed by the Read beam from the opposite side of this reflective SLM. Thus the phase of the Read beam is varied by controlling the intensity of the Write beam. A variable fiber-optic delay line is demonstrated in the thesis which uses wavelength sensitive and wavelength insensitive optics to get both analog as well as digital delays. It uses a chirped fiber Bragg grating (FBG), and a 1xN optical switch to achieve multiple time delays. The switch can be implemented using the 3-D optical scanner mentioned earlier. A technique is presented for ultra-low loss laser communication that uses a combination of strong and weak thin lens optics. As opposed to conventional laser communication systems, the Gaussian laser beam is prevented from diverging at the receiving station by using a weak thin lens that places the transmitted beam waist mid-way between a symmetrical transmitter-receiver link design thus saving prime optical power. LC device technology forms an excellent basis to realize such a large aperture weak lens. Using a 1-D array of LC deflectors, a broadband optical add-drop filter (OADF) is proposed for dense wavelength division multiplexing (DWDM) applications. By binary control of the drive signal to the individual LC deflectors in the array, any optical channel can be selectively dropped and added. For demonstration purposes, microelectromechanical systems (MEMS) digital micromirrors have been used to implement the OADF. Several key systems issues such as insertion loss, polarization dependent loss, wavelength resolution and response time are analyzed in detail for comparison with the LC deflector approach. A no-moving-parts axial scanning confocal microscope (ASCM) system is designed and demonstrated using a combination of a large diameter LC lens and a classical microscope objective lens. By electrically controlling the 5 mm diameter LC lens, the 633 nm wavelength focal spot is moved continuously over a 48 [micro]m range with measured 3-dB axial resolution of 3.1 [micro]m using a 0.65 numerical aperture (NA) micro-objective lens. The ASCM is successfully used to image an Indium Phosphide twin square optical waveguide sample with a 10.2 [micro]m waveguide pitch and 2.3 [micro]m height and width. Using fine analog electrical control of the LC lens, a super-fine sub-wavelength axial resolution of 270 nm is demonstrated. The proposed ASCM can be useful in various precision three dimensional imaging and profiling applications

Optical Fluid-based Photonic And Display Devices

Conventional solid-state photonic devices exhibit an ultra-high optical performance and durability, but minimal adaptability. Recently, optical fluid-based photonic and display devices are emerging. By dynamically manipulating the optical interface formed by liquids, the optical output can be reconfigured or adaptively tuned in real time. Such devices exhibit some unique characteristics that are not achievable in conventional solid-state photonic devices. Therefore, they open a gateway for new applications, such as image and signal processing, optical communication, sensing, and lab-on-a-chip, etc. Different operation principles of optical fluidbased photonic devices have been proposed, for instance fluidic pressure, electrochemistry, thermal effect, environmentally adaptive hydrogel, electro-wetting and dielectrophoresis. In this dissertation, several novel optical fluid-based photonic and display devices are demonstrated. Their working principles are described and electro-optic properties investigated. The first part involves photonic devices based on fluidic pressure. Here, we present a membrane-encapsulated liquid lens actuated by a photo-activated polymer. This approach paves a way to achieve non-mechanical driving and easy integration with other photonic devices. Next, we develop a mechanical-wetting lens for visible and short-wavelength infrared applications. Such a device concept can be extended to longer wavelength if proper liquids are employed. In the second part, we reveal some new photonic and display devices based on dielectrophoretic effects. We conceive a dielectric liquid microlens with well-shaped electrode for fixing the droplet position and lowering the operating voltage. To widen the dynamic range, we demonstrate an approach to enable focus tuning from negative to positive or vice versa in a single dielectric lens without any moving part. The possibility of fabricating microlens arrays iv with different aperture and density using a simple method is also proposed. Furthermore, the fundamental electro-optic characteristics of dielectric liquid droplets are studied from the aspects of operating voltage, frequency and droplet size. In addition to dielectric liquid lenses, we also demonstrate some new optical switches based on dielectrophoretic effect, e.g., optical switch based on voltage-stretchable liquid crystal droplet, variable aperture or position-shifting droplet. These devices work well in the visible and near infrared spectral ranges. We also extend this approach to display and show a polarizer-free and color filter-free display. Simple fabrication, low power consumption, polarization independence, relatively low operating voltage as well as reasonably fast switching time are their key features