Electro-optic Switch Research Articles

薄膜电极重频电光开关的热管理

薄膜电极重频电光开关的热管理

薄膜电极重频电光开关的热管理

薄膜电极重频电光开关的热管理

Electro-optical switching of liquid crystals sandwiched between ion-beam-spurted graphene quantum dots-doped PEDOT:PSS composite layers.

PSS composite layers were utilized to align liquid crystals (LCs) via an ion-beam (IB)-spurting pre-treatment process. LCs were homogeneously aligned between sandwiched GQDs/ PSS composite thin layers, and the alignment of LCs was found to be affected by both the quantity of doped GQDs and IB-spurting intensity. Competitive electro-optical switching properties and non-residual DC performance of the cell equipped with GQDs/ PSS composite alignment layers were obtained because of the enhanced field effect and charge transport induced by doped GQDs. Notably, using IB-spurted GQDs/ PSS layers as alignment layers for next generation high-performance liquid crystal display (LCD) is promising.

Fast response in TN liquid-crystal cells: effect of functionalised carbon nanotubes

ABSTRACTThe optical response time of a nematic liquid crystal (NLC) decreases due to incorporation of carbon nanotubes (CNTs) in the liquid-crystal host. Such reduction is believed to be due to an increase in the elastic constant of the nanotube-doped LC system. In this paper, we present the effect on optical response due to doping an NLC with octadecylamine functionalised single-walled carbon nanotubes (ODA-SWCNT) in a twisted alignment mode. The electro-optic switching amplitude of ODA-SWCNT nanocomposites of NLC decreases compared to pure NLC. A fast response time is observed with an increase in the concentration of ODA-SWCNT in NLC host. Additionally, optical response of pure NLC in a twisted nematic (TN) cell fabricated using mixtures of polyimide (PI) and ODA-SWCNT as an alignment layer is investigated. The optical response time decreased by ~75% in a TN cell fabricated with a mixture of PI and ODA-SWCNT compared to that of a TN cell prepared using a pure PI alignment layer. The presence of ODA-SWCNT in the alignment layer enhances the surface anchoring of the NLC molecules leading to an increase in the elastic constant and a decrease in the optical response time of NLC.

Electro-optic switching in metamaterial by liquid crystal.

Electro-optic switching of reflection and refraction is experimentally demonstrated in metasurface liquid crystal cell. Negative metasurface is fabricated by focused-ion-beam milling, and twisted nematic cells are constructed with complementary double-split ring resonator and V-shape slot antenna metasurface. By application of an external voltage, electro-optic switchings are achieved in reflection and refraction. It has a strong implication for applications in spatial light modulation and wavelength division multiplexer/demultiplexer in a near-IR spectral range.

Photoluminescence as a Probe of the Electrical Charge Dependence of Gold Nanoparticles.

Electro-optical switching can be achieved by changing the optical absorption of metal nanoparticles by adding or removing electrical charge, corresponding to increased, respectively, decreased electron density. In this work a different approach is taken by changing the photoluminescence properties as a function of electrical charge on gold nanoparticles. Whereas larger gold nanoparticles (diameter d = 5 and 10 nm), exhibiting a plasmon resonance peak in the absorption spectrum, were used to measure changes of the optical absorption spectrum upon electrical charging, for smaller gold nanoparticles (d = 2 and 5 nm) electrical charging was observed via changes of the photoluminescence. Increase and decrease in photoluminescence was observed at positive and negative applied potentials, respectively. The relation between changes of optical absorption and photoluminescence for the 5 nm particles by electrical charging provides information on the influence of the charge state on the electronic properties and therefore the optical transition probability. The reported observation that not only the optical absorption, but also the photoluminescence is affected by alteration of the electrical charge onto gold nanoparticles may open a new way towards electro-optical switching and bio-sensing.

$4\times 4$ Silicon Optical Switches Based on Double-Ring-Assisted Mach–Zehnder Interferometers

We present the experimental demonstration of a $4\times 4$ silicon electro-optic (EO) switch fabric based on a Benes architecture. Double-ring-assisted Mach–Zehnder interferometers (DR-MZIs) are utilized as the basic switch elements. Silicon resistive microheaters and p-i-n diodes are embedded in both of the microrings of the DR-MZIs for low-loss thermo-optic (TO) phase correction and high-speed switching operation, respectively. The TO tuning power dissipated to align all resonances is 22.37 mW. The maximum EO tuning power required to switch all DR-MZIs is only 1.38 mW. The average on-chip insertion loss is in the range of 4–5.8 dB for all switching states. The transmission spectrum measurement shows that the device can perform switching in a $\sim 35$ -GHz spectral window with the worst crosstalk being −18.4 dB.

Design of a Compact High-Performance Electro-Optic Plasmonic Switch

Here, we report a compact high-performance electro-optic (E-O) plasmonic switch constructed in a directional coupler like structure, including a plasmonic waveguide and an optical waveguide, and operated around the telecommunication wavelength of 1500 nm. An organic crystal, 4-dimethyl-amino-N-methyl-4-stilbazolium tosylate, is adopted to serve as both the E-O material of the switch and the dielectric in the plasmonic waveguide. The variation of phase matching between the two waveguides is achieved by applying a voltage as low as 22.5 V on the E-O material, so that the optical wave can be switched between the two output ports. Simulation analysis using finite-element method was employed for the design of the E-O plasmonic switch. For the optimized dimensions, a transmittance up to 66% and an extinction ratio nearly 10 dB are achieved.

A water dissolution method for removing micro-waviness caused by SPDT process on KDP crystals

Single crystals of potassium dihydrogen phosphate (KDP) are an irreplaceable optical material in laser-induced inertial confinement fusion (ICF), where they are used as electro-optic switches and for laser-frequency conversion. The KDP lenses used in ICF applications must be pristine, high quality, and have a surface roughness of less than 3 nm. Currently, single-point diamond turning (SPDT) is the primary method for performing ultra-precision machining on KDP crystals. However, after the SPDT process, the crystal surface exhibits micro-waviness and subsurface damage, both of which have adverse effects on the optical performance of the KDP elements, especially the laser-induced damage threshold. In this study, a new method of micro-dissolution polishing was developed, which is based on the solubility of KDP crystals in water, to achieve controllable material removal. A material removal function was formulated to describe the material removal in terms of both the path and parameters used to polish the SPDT-machined samples with a small polishing tool. An experimental study showed that this method is able to reduce the surface micro-waviness and surface roughness (from 6.205 to 2.107 nm) significantly. The method is also applicable to the polishing of other water-soluble materials.

Two-step switching in dual-frequency nematic liquid crystal mixtures

The so-called dual-frequency nematic mixtures are very promising components for applications in fast operating devices. Compared with classical nematics, they exhibit positive or negative anisotropy of the electric permittivity depending on the applied frequencies of an external electric field. Owing to this property, an overall switching process from planar to homeotropic orientations, and vice versa, can be shortened by using the electric field with two different frequencies. Electro-optical switching characteristics of transmission versus time as a function of applied voltage were obtained for two different dual-frequency mixtures in twisted nematic cells. For one of the investigated mixtures, unusual decrease in the light transmission at switching from the homeotropic to planar orientation at threshold voltage was observed. The switching process apparently occurs in two steps. The mechanism of the two-step switching at twisted dual-frequency nematic structures was discussed. The explanation of the switching mechanism takes into account the influence of the electric field with different frequencies on molecules with transverse and longitudinal dipole moments. Moreover, molecular structure of compounds constituting the mixtures was analyzed. Additionally, response times of the switching driven with low and high frequency pulses were shown. This work helps to understand the molecular interaction and electro-optical switching in the dual-frequency nematic liquid crystals.

Electro-optical switch based on continuous metasurface embedded in Si substrate

Switchable metasurfaces with fast responses and high efficiency are highly desirable in various applications. In this paper, we propose and analyze a novel electro-optical switch based on continuous metasurface embedded in Si substrate. The simulative results indicate that the embedded and continuous metasurface structure is able to increase the interaction volume between the metal antennas and the surrounding substrate, hence enhances the tuning effect when changing the refractive index of Si by an injection current, resulting in fully switching between anomalous and normal reflections, and achieving a high extinction ratio even under a smaller refractive index variation.

Strictly non-blocking 4×4 silicon electro–optic switch matrix**Project supported by the National Basic Research Program of China (Grant No. 2011CB301701), the National High Technology Research and Development Program of China (Grant Nos. 2013AA014402, 2012AA012202, and 2015AA016904), and the National Natural Science Foundation of China (Grant Nos. 61275065 and 61107048).

The first path-independent insertion-loss (PILOSS) strictly non-blocking 4×4 silicon electro–optic switch matrix is reported. The footprint of this switch matrix is only 4.6 mm×1.0 mm. Using single-arm modulation, the crosstalk measured in this test is –13 dB∼ –27 dB. And a maximum crosstalk deterioration of 6dB caused by two-path interference is also found.

Pitch-Length Independent Threshold Voltage of Polymer/Cholesteric Liquid Crystal Nano-Composites

Polymer/cholesteric liquid crystal (ChLC) nano-composites consisting of mesogenic monomers and LCs have nano-sized LC domains dispersed in an anisotropic polymer matrix. They exhibit characteristics not observed in conventional ChLCs, such as sub-millisecond and “deformation-free” electro-optic tuning of the selective reflection band; however, their driving voltage is high compared to conventional ChLCs, and is an issue that needs to be solved for the practical use. Here, we investigate the helical pitch dependence of threshold voltage in polymer/ChLC nano-composites. Five samples with different helical pitches were prepared and their electro-optic characteristics were compared before and after photopolymerization. Although the threshold voltage of the unpolymerized samples were inversely proportional to its helical pitch, the threshold voltage of the polymerized samples showed no dependence on the helical pitch. These results are explained to be a consequence of the driving mechanism of the polymer/ChLC nano-composite, in which electro-optic switching is achieved as a consequence of the nano-confined LC molecules reorienting along the electric field, instead of the helical structure becoming unwound. The threshold voltage is independent of pitch length because the pore sizes are similar in all samples.

Investigation on an ultra-compact Mach–Zehnder interferometer electro-optic switch using poled-polymer/silicon slot waveguide

By using poled-polymer/silicon slot waveguides in the active region and employing the Pockels effect of the poled-polymer, we propose a kind of Mach–Zehnder interferometer (MZI) electro-optic (EO) switch operated at 1550 nm. Dependencies of switching characteristics versus the slot waveguide parameters are investigated, including EO overlap integral, power ratio confined in the slot, and voltage-length product. Given the dimension of the silicon strip of 190 × 300 nm, as the slot width varies within 50–100 nm, the switching voltage can be as low as 1.0 V with only 0.17–0.35 mm active region length, and the whole device length is only about 770–950 μm. For the switch with 50 nm slot width, the insertion loss is about 4.42 dB under both operation states, and the crosstalk under cross-state and that under bar-state are about −48.2 and −65.3 dB, respectively. An impressive advantage of this switching structure lies that the voltage-length product (0.17–0.35 V mm) is at least 19–40 times smaller than that of the traditional polymer MZI EO switch (6.69 V mm). Compared with our previously reported two kinds of MZI or microring resonator assisted MZI EO switches, this switch does exhibit some superior characteristics, including low switching voltage, compact device size and small wavelength dependency, due to the use of slot waveguides in the MZI EO region.

Ultra-compact electro-optical switches based on long-range air-hole assisted subwavelength waveguides

An ultra-compact electro-optical (EO) switch based on long-range air-hole assisted subwavelength waveguides with a high extinction ratio, low insertion loss, and high operation speed is proposed and investigated, both analytically and numerically. The switching characteristic of the EO switch also is addressed at three different resonant wavelengths. A modulation depth of 26.8 dB and a small active region of 1.04 μm2 at the wavelength of 1.597 μm can be achieved. Such an active TE-mode device based on subwavelength waveguides provides a promising approach for highly effective EO switches, and is beneficial for high-density photonic integration.

A Mach-Zehnder interferometer electro-optic switch with ultralow voltage-length product using poled-polymer/silicon slot waveguide

By using poled-polymer/silicon slot waveguides in the active region and the Pockels effect of the poled-polymer, we propose a kind of Mach-Zehnder interferometer (MZI) electro-optic (EO) switch operated at 1 550 nm. Structural parameters are optimized for realizing normal switching function. Dependencies of switching characteristics on the slot waveguide parameters are investigated. For the silicon strip with dimension of 170 nm×300 nm, as the slot width varies from 50 nm to 100 nm, the switching voltage can be as low as 1.0 V with active region length of only 0.17–0.35 mm, and the length of the whole device is only about 770–950 μm. The voltage-length product of this switching structure is only 0.17–0.35 V·mm, and it is at least 19–40 times smaller than that of the traditional polymer MZI EO switch, which is 6.69 V·mm. Compared with our previously reported MZI EO switches, this switch exhibits some superior characteristics, including low switching voltage, compact device size and small wavelength dependency.

Comparison of electro-optical switching between polymer-stabilised cubic and amorphous blue phases

We prepared polymer-stabilised cubic and amorphous blue phase liquid crystals consisting of the same materials at different UV-curing temperatures using photopolymerisation. Then we investigated the effects of polymer stabilisation on their physical properties. The UV-curing temperature does not affect phase stabilisation of the polymer-stabilised amorphous BPIII (PS-BPIII). Temperatures of the PS-BPIII were found to be extended to more than 50 K. However, a critical temperature exists in the polymer stabilisation process for the PS-cubic BP. Although no substantial difference in response speed was found between the polymer-stabilised cubic and amorphous structures, larger hysteresis and higher residual birefringence were observed in the PS-cubic BP than in the PS-BPIII. Amorphous BPIII with an amorphous network of disclination lines has no critical temperature for the polymer stabilisation and realises a high-performance display.

Electro-optical phase-change 2 × 2 switching using three- and four-waveguide directional couplers.

Theoretical modeling and numerical simulation have been performed at λ=2100 nm on silicon-on-insulator channel-waveguide directional couplers in which the outer two Si waveguides are passive and the central waveguide(s) are electro-optical (EO) "islands." The EO channel(s) utilize a 10 nm layer of Ge2Sb2Te5 phase-change-material sited at midlevel of a doped Si channel. A voltage-driven phase change produces a large change in the effective index of the TE(o) and TM(o) modes, thereby inducing crossbar 2×2 switching. A mode-matching method is employed to estimate EO switching performance in the limit of strong interguide coupling. Low-loss switching is predicted for cross-to-bar and bar-to-cross coupling lengths. These "self-holding" switches had active lengths of 500-1000 μm, which are shorter than those in couplers relying upon free-carrier injection. The four-waveguide devices had lower cross talk but higher loss than the three-waveguide devices. For the crystalline phase we sometimes used an active length that was smaller than that for the amorphous phase.

Effective Electro-Optical Modulation with High Extinction Ratio by a Graphene-Silicon Microring Resonator.

Graphene opens up for novel optoelectronic applications thanks to its high carrier mobility, ultralarge absorption bandwidth, and extremely fast material response. In particular, the opportunity to control optoelectronic properties through tuning of the Fermi level enables electro-optical modulation, optical-optical switching, and other optoelectronics applications. However, achieving a high modulation depth remains a challenge because of the modest graphene-light interaction in the graphene-silicon devices, typically, utilizing only a monolayer or few layers of graphene. Here, we comprehensively study the interaction between graphene and a microring resonator, and its influence on the optical modulation depth. We demonstrate graphene-silicon microring devices showing a high modulation depth of 12.5 dB with a relatively low bias voltage of 8.8 V. On-off electro-optical switching with an extinction ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with a 4 V peak-to-peak voltage.

Design and fabrication of DR1/PC-based electro-optic switch

A Mach–Zehnder interferometer (MZI) electro-optic (E-O) switch based on a guest–host material DR1/PC was designed and fabricated. The optical properties and long-term stability of the material were studied. By optimizing the concentration of DR1, the DR1/PC material exhibited an E-O coefficient of 12.8 pm/V at 1310 nm. The characteristic parameters of the waveguide were calculated, and the fabrication process was strictly controlled. The MZI switch on-off time was found to be about 50 ns. The extinction ratio was measured to be about 13.4 dB. At room temperature, the switch could keep operating for at least 150 days.