High Optical Modulation Research Articles

High-speed silicon microresonator modulators with high optical modulation amplitude (OMA) at input powers >10 mW.

A high-speed silicon photonic microdisc modulator is used with more than 10 mW optical power in the bus waveguide, extending the optical power handling regime used with compact silicon resonant modulators at 1550 nm. We present an experimental study of the wavelength tuning range and biasing path required to shift the resonant frequency to the optimal point versus on chip power. We measure the optical modulation amplitude (OMA) along different biasing trajectories of the microdisc under active modulation and demonstrate an OMA of 4.1 mW with 13.5 mW optical power in the bus waveguide at 20 Gbit/s non-return to zero (NRZ) data modulation.

Independent regulation of electrical properties of VO2 for low threshold voltage electro-optic switch applications

Vanadium dioxide has a unique insulator-metal phase transition characteristic near room temperature, meeting optical switches' requirements. However, due to its high resistance in the insulator state, the working voltage threshold of the VO2-based optical switch is also high. It is one of the obstacles for VO2-based optical switch applications. In this work, high-quality VO2 films were prepared by DC pulsed magnetron sputtering. By inserting a conductive ITO buffer layer, VO2 sheet resistance reduced about 2 orders, and the electrical phase change characteristics have almost disappeared. Still, the high optical modulation ability is hardly affected. The interesting results meet the requirements of a low threshold working voltage electro-optic switch. In the case of a 40 µm electrode gap size, the threshold voltage for VO2/ITO is only 1.4 V, which is much lower than 20 V of pure VO2 in the same condition, and the optical switch modulation depth at the wavelength of 1550 nm reaches 35%. For the switch with 5 µm electrode gap size, the threshold voltage is only 1.3 V, and the response times of "ON" and "OFF" are 0.24 ms and 2.1 ms, respectively. This result is valuable for the practical application of VO2-based optical switches.

High Dimensional Differential Optical Spatial Modulation with High Spectrum Efficiency

High Dimensional Differential Optical Spatial Modulation with High Spectrum Efficiency

Electrochromism in Nanoporous Tungsten Trioxide Films Prepared through Anodization and Thermal Oxidation

Nanoporous WO3 films were prepared via anodization and thermal oxidation from a sputtered dense W film on FTO glass at different anodization times producing WO3 films with different porosities. Moreover, an oxidation time of 1 h at 450 °C modified the crystallinity and optical transmittance in the nanoporous WO3 films. The crystallinity of the nanoporous WO3 films decreased as anodization time increased. The films’ electrochromic properties also improved considerably. Results showed that an anodization time of 12 min is optimal to synthesize nanoporous WO3 films with the best electrochromic properties and highest optical modulation.

High Modulation Efficiency and Dynamic Range Optical Single Sideband Modulation Without Gain Penalty in Nonlinear Distortion Suppression

The optical single sideband (OSSB) modulation with tunable optical carrier to sideband ratio (OCSR) is a promising and popular technique in wideband analog signal transmission and microwave signal processing, which can improve modulation efficiency and combat the fiber chromatic dispersion. However, in all reported schemes for achieving OSSB modulation with tunable OCSR, the spurious free dynamic ranges (SFDR) of the systems are all limited by the third-order intermodulation distortion (IMD3). In this paper, our object is to improve the SFDR and suppress the IMD3 in a novel OSSB modulation with tunable OCSR. The proposed system consists of a primary channel and a secondary channel. In primary channel, an OSSB modulation with tunable OCSR is implemented. In secondary channel, the optical carrier and first-order sidebands are perfectly cancelled out, which can suppress the IMD3 without gain penalty at the same received optical power. In this way, a large-SFDR OSSB modulation with tunable OCSR is realized. Experimental results exhibit that the IMD3 gets effective cancellations without gain penalty under unchanged total received power, and the output microwave signal power obtains about 11-dB improvement by optimizing the OCSR. A greatly increased SFDR of over 128 dBHz4/5 is achieved in the proposed system.

Preparation, investigation and application of nickel oxide thin films in flexible all-thin-film electrochromic devices: from material to device

In this study, the nickel oxide (NiOX) thin films were reactively sputtered at different working pressures in the oxide mode zone for application in flexible all-thin-film electrochromic devices (ATF-ECDs). The working pressure plays an important role on the various properties of the reactively sputtered NiOX thin film including the deposition rate, grain structure (microstructure), morphology, chemical composition, optical properties and electrochemical properties. The flexible ATF-ECDs with ≥2 Pa NiOX thin films perform high optical modulation and relatively fast response time during the electrochromic processes. The detailed electrochromic mechanism is discussed.

Complementary electrochromic devices based on acrylic substrates for smart window applications in aircrafts

Electrochromic devices (ECDs) fabricated using resin substrates are attracting considerable interest owing to their advantages of shape deformability and low weight. Acrylic substrates are used to fabricate aircraft windows because they are lighter and more impact-resistant than glass substrates. In this study, the wettability of an indium tin oxide (ITO) surface was enhanced using ultraviolet (UV) treatment prior to the spin-coating and deposition of Prussian blue (PB) and WO3 thin films, which were prepared using functional nanoparticle-dispersed inks on an ITO/acrylic substrate. The fabricated ECD was structured as acrylic/ITO/PB/K+-base gel electrolyte/WO3/ITO/acrylic, and was observed to exhibit excellent electrochromic performance. A high optical modulation and coloration efficiency of 76% and 112.99 cm2/C at a wavelength of 633 nm, respectively, and satisfactory cyclic durability over 1800 cycles were observed. The fabricated ECD possesses immense potential for application in various fields, especially in the field of smart windows for aircrafts.

3D conifer-like WO3 branched nanowire arrays electrode for boosting electrochromic-supercapacitor performance

Electrochromic-supercapacitors (ESCs) have shown great perspective in multifunctional smart devices due to their special function of monitoring the energy storage level by the visible color changes. However, the poor areal capacitance at high optical modulation(ΔT) and the inferior bifunctional lifespan hinder the practical application of ESCs. It is thus important to develop feasible ways to boost the optical-electrochemical properties and comprehend the corresponding inner mechanism. Inspired by nature’s conifer structure, herein, 3D hexagonal WO3 branched nanowire arrays/F-doped SnO2 (h-WO3 BNW/FTO) electrode have been successfully constructed via a single-step hydrothermal reaction followed by annealing process. Such biomimetic conifer-like structure is shaped by the separating crystal growth effect coupled with the specific topological structure of h-WO3. Benefiting from bionic structure, h-WO3 BNW/FTO electrode delivers a high areal specific capacity (0.0223 mAh cm−2) and large corresponding ΔT respond (80% ΔT at 650 nm) at 5 mV s−1, as well as outstanding optical-electrochemical cycle stability. Moreover, the aluminum storage mechanism during the optical-electrochemical process is affirmed using cyclic voltammetry and in-situ X-ray method. For practical application, the assembled ESC device based on the h-WO3 BNW/FTO electrode delivers a high 22.75 mF cm−2 areal specific capacitance, corresponding 45.81% ΔT (at 650 nm) and long-term bifunctional stability (over 90% bifunctional retention after 5000 cycles). Meanwhile, the visually monitoring capacity of the device is realized through the color changes. This study provides some insights into the biomimetic design for advanced bifunctional electrodes and the underlying mechanism affecting the electrochromic-charge storage performance.

Reversible Zn2+ Insertion in Tungsten Ion-Activated Titanium Dioxide Nanocrystals for Electrochromic Windows

HighlightsA reversible Zn2+ insertion in anatase TiO2 nanocrystals is reported for the first time.This is the first report regarding TiO2 for zinc-anode-based electrochromic devices, which will subsequently broaden its applications to zinc-ion electrochemical cells.A prototype device based on the TiO2 nanocrystals delivers a high optical modulation, fast response times, and robust electrochemical stability.

Controllable synthesis of hexagonal WO3 nanorod-cluster films with high electrochromic performance in NIR range

Hexagonal WO3 (h-WO3) nanorod-cluster films were controllably synthesized by a facile template-free hydrothermal technique. The pH value and the amount of urea in the precursor have critical influences on the crystal form and morphology of the WO3 film. The obtained uniform WO3 films feature a porous structure of clusters composed of h-WO3 nanorods with diameter of 6–10 nm and length of up to several hundred nanometers. Due to the novel microstructure and crystalline phase, the high electrochromic performance in NIR range with a high optical modulation of 46% in 1600 nm, fast switching speed (2.4 s for coloration and 3.6 s for bleaching), high coloration efficiency (106.1 cm2 C−1 in 1600 nm), and an excellent cycling stability (more than 96% charge capacity retained after 1000 cycles) was achieved.

Boosting charge-transfer kinetics and cyclic stability of complementary WO3–NiO electrochromic devices via SnOx interfacial layer

The effect of interfacial layer (SnO x ) on the performance of the complementary electrochromic devices (ECDs) was examined, revealing that the SnO x /WO 3 bilayer cathodes could enhance the electrochromic performance, such as a superior long-term cycling stability over 10,000 cycles, a high coloration efficiency of 101.61 cm 2 C −1 and a maximum transmittance modulation of 49.27%@633 nm. Moreover, compared with the single layer WO 3 , the SnO x /WO 3 bilayer exhibited improved electrochemical activities and reaction kinetics. The probable explanation is that the introduced interfacial layer can boost the double injection of ions and electrons, balance the transport of ions and electrons, and protect the electrode from degradation by serving as a buffer layer during coloration/bleaching cycles. These results further provide a valuable insight for improving the electrochromic properties of the films instead of relying on conventional methods such as nanostructural or compositional control. • The ECDs with the long-term stability and high optical modulation are obtained. • The cyclic stability of WO 3 –NiO ECDs is improved with SnO x interfacial layer. • Effect of SnO x interface on electrochemical performance of WO 3 is investigated. • The mechanism of charge-transfer kinetics of the active interface is clarified.

Flexible electrochromic fiber with rapid color switching and high optical modulation

Though flexible electrochromic devices have shown huge potential application in the fields of safety warning, display and smart windows, limited attention was paid on preparing flexible electrochromic fiber because of the difficulty in fabricating the multilayer electrochromic device structure in one-dimensional form. In this study, a flexible electrochromic nylon fiber based on Ag nanowires (NWs)/PEDOT:PSS/WO3 nanoparticles (NPs) (PEDOT:PSS = poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid) is successfully fabricated, delivering rapid color switching (2.5 and 9 s for bleaching and coloration) and high optical modulation (65.5% at 633 nm), and sustainable to repeated mechanical deformations. Ag NWs, PEDOT:PSS and WO3 NPs were dip-coated on the nylon fiber, resulting in an electrochromic fiber electrode with stable fiber resistance of 50–100 Ω/10 cm, which can withstand mechanical deformation against 300 times of bending cycles with bending radius of 0.5 cm, and sustain 30 times of tape-peeling. During the galvanostatic tests, the capacitance of the electrochromic electrode can maintain 70% of the initial value even after 5,000 times of charge-discharge cycles. Even in knotted shape, the fiber still shows excellent color contrast. This study provides a novel method to construct flexible electrochromic fiber and pave the way for the development of flexible optoelectronic devices, such as flexible and wearable displays.

Electrochromic property of tungsten trioxide films prepared by DC magnetron sputtering with oblique angle deposition and thermal oxidation

In this work, WO3 thin films were prepared in two steps: First, tungsten (W) films with thickness of 100-300 nm were deposited by DC magnetron sputtering with oblique angle deposition (OAD) technique at 0 and 85. Second, sputtered W films were annealed under air atmosphere at a temperature of 500℃ and different oxidation times for 1-3 h. The structure of WO3 thin films were examined by X-ray diffraction and field emission scanning electron microscope. In addition, the optical and electrochromic properties of the WO3 thin films were measured by a spectrophotometer before and after testing in potassium hydroxide electrolytes. The results showed that the OAD technique can enhance porosity and exert high oxidation in W films. The increase in film thickness and oxidation time indicated that the crystallinity of WO3 films increased. The condition of WO3 films for OAD at 85, thickness of 300 nm, and oxidation time of 1 h showed the best electrochromic property with the highest optical modulation and current density.

Bio-inspired electrochromic skin based on tungsten oxide

Some animals, such as the chameleon, have great capability of camouflage by changing their skin color to avoid detection. This outstanding property have inspired researchers to develop the ability of the materials and devices to mimic chameleon for applications in intelligent wearable and camouflage devices. Tungsten oxide (WO3), switching between blue and transparent, is widely studied due to its large optical modulation but it is difficult to obtain multicolor and flexibility. Here, we design a bio-inspired chameleon skin electrochromic device (ECD) assembled by inorganic electrochromic materials WO3, which can achieve the reversible color changes from yellow, light green to dark green according to subtractive color mixture theory. The flexible ECD exhibits a high optical reflectance modulation of 38.9% at voltage of ± 1.5 V in the wavelength range of 250–2500 nm. Fast response speed of 0.32 s for both coloring and bleaching process is obtained which can be attributed to the porous structure of the WO3 electrochromic layer. The ECD keeps excellent electrochromic performance even under bending conditions, indicating the great flexibility. The inorganic bio-inspired chameleon skin ECD opens new avenues for the design of intelligent and wearable devices.

Precise Optical Modulation and Its Application to Optoelectronic Device Measurement

Optoelectronic devices which play important roles in high-speed optical fiber networks can offer effective measurement methods for optoelectronic devices including optical modulators and photodetectors. Precise optical signal modulation is required for measurement applications. This paper focuses on high-speed and precise optical modulation devices and their application to device measurement. Optical modulators using electro-optic effect offers precise control of lightwaves for wideband signals. As examples, this paper describes frequency response measurement of photodetectors using high-precision amplitude modulation and wavelength domain measurement of optical filters using fast optical frequency sweep. Precise and high-speed modulation can be achieved by active trimming which compensates device structure imbalance due to fabrication error, where preciseness can be described by on-off extinction ratio. A Mach-Zehnder modulator with sub Mach-Zehnder interferometors can offer high extinction-ratio optical intensity modulation, which can be used for precise optoelectronic frequency response measurement. Precise modulation would be also useful for multi-level modulation schemes. To investigate impact of finite extinction ratio on optical modulation, duobinary modulation with small signal operation was demonstrated. For optical frequency domain analysis, single sideband modulation, which shifts optical frequency, can be used for generation of stimulus signals. Rapid measurement of optical filters was performed by using an optical sweeper consisting of an integrated Mach-Zehnder modulator for optical frequency control and an arbitrary waveform generator for generation of a source frequency chirp signal.

Self-Powered Rewritable Electrochromic Display based on WO3-x Film with Mechanochemically Synthesized MoO3-y Nanosheets.

Electrochromic displays with bistable color states provide a promising means toward transparent human-machine interfaces. However, the need for external power and the weak optical modulation in the visible light region of most electrochromic devices hinder their practical applications in displays. Here we prepare the MoO3-y/WO3-x films based on MoO3-y nanosheets, which show a dark blue color that matches the response of the eye and meets visual comfort standards compared to pure WO3-x film. By introducing the highly transparent Al3+ ion hydrogel layer, a convenient electrochromic device driven by the internal chemical potential has been designed. The device based on the MoO3-y /WO3-x film exhibits a high optical modulation in the whole visible light range and can operate at self-powered mode with fast response speed and excellent cycle stability. Moreover, we develop an ionic writing board based on the MoO3-y/WO3-x film to surmount the fixed display information issue in conventional electrochromic displays. The ionic writing board exhibits excellent visual display quality and realizes arbitrary writing with a self-powered characteristic. This work provides a simple mechanochemical synthesis procedure of MoO3-y nanosheets and an ingenious design of self-powered electrochromic devices, which will enable the development of next-generation high-performance electrochromic displays.

Long life all-solid-state electrochromic devices by annealing

Annealing temperature has a significant influence on the performances of the electrochromic films and devices, such as optical transmittance modulation, response time and cyclic stability. Although there are lots of reports on the effect of annealing temperature on the performance of monolayer, the relationship between annealing temperature and electrochromic devices (ECDs) is rarely studied. Here, all-solid-state ECDs glass/ITO/NiO/ZrO2/Li/WO3/ITO are prepared by evaporation method and annealed at different temperature from 200 °C to 400 °C. The results show that the cyclic stability of the ECDs has a strong association with the annealing temperature. The ECDs annealed at low temperature suffer from poor cyclic stability because of the irreversible insertion of Li ions in WO3 layer. The ECD annealed at 400 °C exhibits superior stability with high optical modulation of 50.2% even after 50000 cycles at wavelength of 400–1050 nm. The influence mechanism of annealing temperature on the ECDs is analyzed which has great value for practical application.

Reactively sputtered Ta2O5 solid electrolyte layers in all thin film electrochromic devices

The tantalum pentoxide (Ta2O5) thin films used as protonic conductive solid electrolyte layers (SELs) in all thin film electrochromic devices (ATF-ECDs) were widely investigated. The working pressure played a great role in the microstructure and proton transfer of the Ta2O5 thin films. The Ta2O5 thin films were deposited by direct current (DC) reactive magnetron sputtering at different working pressures and growth mechanism was studied. The optical properties, structural properties, chemical compositions, morphologies and protonic conductive properties of the Ta2O5 thin films were systematically investigated. Moreover, the electrochromic properties for corresponding ATF-ECDs with Ta2O5 SELs were studied as well. The ATF-ECD with a 2.0 Pa Ta2O5 SEL exhibited the best device performance with high optical modulation and fast switch speeds.

All-optical high-speed modulation of THz transmission through silicon core optical fibers.

High speed optical modulation of THz radiation is of interest for information processing and communications applications. In this paper infrared femtosecond pulses are used to generate free carriers that reduce the THz transmission of silicon based waveguides over a broad spectral range. Up to 96% modulation is observed from 0.5 to 7 THz in an optical fiber with a 210 µm diameter gold-doped silicon core. The observed carrier recombination time of 2.0 ± 0.2 ns makes this material suitable for high speed all-optical signal processing. These results show both enhanced modulation depth and reduced carrier lifetime when compared to the performance of a high resistivity float zone silicon rectangular guide with comparable cross sectional area.

The preparation and investigation of all thin film electrochromic devices based on reactively sputtered MoO3 thin films

Reactively sputtered molybdenum trioxide (MoO3) thin films were systematically investigated and employed as cathodic electrochromic layers in all thin film electrochromic devices (ATF-ECDs). The gas loop controller was employed for adjustment of inputted oxygen gas flux by monitoring the target voltage during reactive sputtering. The working pressure played a great role on the deposition rate, crystallite size, optical properties and the electrochromic properties of MoO3 and the applied ATF-ECDs (soda lime glass (SLG)/ITO/NiOX/Ta2O5/MoO3/ITO). A 4 Pa MoO3 based ATF-ECD achieved a high optical modulation (transmission @ 600 nm) of ~50% and a high coloration efficiency of 149.4 cm2/C.