We apply discoveries in nanoscience towards applications relevant to health, environment, security, and connectedness. A materials fundamental to our research is the quantum dot. Each quantum dot is a particle of semiconductor only a few nanometers in diameter. These semiconductor nanoparticles confine electrons to within their characteristic wavelength. Thus, just as changing the length of a guitar string changes the frequency of sound produced, so too does changing the size of a quantum dot alter the frequency - hence energy - the electron can adopt. As a result, quantum dots are tunable matter (Fig. 2). We work with colloidal quantum dots, nanoparticles produced in, and processed from, solution. They can be coated onto nearly anything - a semiconductor substrate, a window, a wall, fabric. Compared to epitaxially-grown semiconductors used to make optical detectors, lasers, and modulators, they are cheap, safe to work with, and easy to produce. Much of our work with quantum dots involves infrared light - its measurement, production, modulation, and harnessing. While there exists an abundance of work in colloidal quantum dots active in the visible, there are fewer results in the infrared. The wavelengths between 1000 and 2000 nm are nonetheless of great practical importance: half of the sun's power reaching the earth lies in this wavelength range; 'biological windows' in which tissue is relatively transparent and does not emit background light (autofluorescence) exist in the infrared; fiber-optic networks operate at 1.3 and 1.5 um.

We report on the design, synthesis and optical properties of new two-photon absorbing multi-branched chromophores, based on a pyridine core. Measurements of TPA using the two-photon fluorescence method in the fs regime indicate that these chromophores exhibit two-photon absorptivity. The results indicate that a change of the substitution of the electron-acceptor core influences significantly the TPA cross sections. Moreover, upon protonation, the TPA properties are greatly enhanced in the 700-900 nm range. Thus, these molecules can serve as pH-sensitive TPA dyes. Preliminary results related to biological applications will be presented.

We report a large aperture laser beam attenuator by using electrically switchable gratings. This attenuator separates an incident beam into the transmitted and diffracted beams. The light intensities of both transmitted and diffracted beams can be adjusted through electro-optical effect. By carefully selecting the liquid crystals and polymer materials, we obtained a 25 dB dynamic range of attenuation with a 0.5 dB insertion loss and response time about 200 μs.

It has been shown recently, that organic nanofibers grown from para-hexaphenyl and from α-sexithiophene molecules can be used as a new type of nanoscopic waveguides. Their growth is due to a self-assembly process, thus large quantities of aligned nanofibers can be fabricated simultaneously. Because of the growth mechanism of the nanofibers, their widths and heights are limited to a few 100 nm and a few 10 nm, respectively. In this paper we show how this kind of control has been obtained via modification of the bare muscovite surface before organic molecule deposition. Introducing e.g. a thin layer of Au islands before nanofiber growth results in an up to 15-fold increase in height, whereas the mean width and the optical properties of the fibers remain almost unchanged. Au films of varying thickness lead to tailor-made height profiles along the fiber. Using atomic force microscopy the details of these Au/organic heterostructures are examined and the growth is compared to growth on untreated mica. By scratching the fibers with an AFM tip grating structures have been written into the fibers.

A new refractive index imaging media system is described, based on the photoinitiated isomerization of dewarbenzene derivatives in a solid polymer medium. The system can exhibit a refractive index contrast as high as 0.02, with low dimensional changes on recording. Furthermore, the medium is highly sensitive because the recording process is chemically amplified, that is, many product molecules are formed per photon absorbed. The change in refractive index occurs spontaneously under blue or UV irradiation; no subsequent processing is required. This system may find applications in holographic recording and for integrated optical devices. For example, many spatially overlapping holographic diffraction gratings were recorded (angular multiplexing) in the material in the same volume.

We demonstrate an widely electrically tunable long-period fiber grating with ultrathin first cladding and ferroelectric relaxor poly(vinylidene fluoride - trifluoroethylene - chlorofluoroethylene) terpolymer as the second cladding. Large Kerr effect is found in the terpolymer where a refractive index change of -2.6% can be induced under an electric field of 80MV/m. Simulations and experiments show that electrodes and the index matching between terpolymer and fiber have significant effect on the tuning range. An 18nm resonant wavelength shift is achieved by the terpolymer when electric field of 50MV/m is applied. On the other hand, over 100nm shift is observed by index matched terpolymer/PMMA blend as the temperature changes from 25^oC to 100^oC (temperature tuning). To realize this index matching condition, ZnS/terpolymer nanocomposite was developed which allowed the index of the composite to be varied over a large range while maintaining large electro-optical response. A simulation result predicts that large electrical tuning of the resonance band can be realized by the the index matched nanocomposite.

We present the preliminary experimental results on the measuring of third order optical nonlinearity in a 5HCB liquid crystal sample doped with methyl-red. These results are obtenided througth Z-scan tecnhique using a simple low power He-Ne laser in CW operation. We observe a great negative Kerr nonlinearity in the sample obtained in the regime temperature of nematic phase. For upper temperature, we observe a notable decreasing of the optical nonlinearity due to sample change to isotropic phase. In adition, we observe the presence of a nonlinear absorption contribution.

Suitable organic and polymeric based materials for electronic and photonic applications must possess the desired electromagnetic and optical properties to achieve optimal device performance in order to be more competitive with their inorganic counterparts. A new class of biopolymer, processed from purified marine-based deoxyribonucleic acid (DNA), has been investigated for use in both electronic and photonic applications and has demonstrated promise as an excellent dielectric and optical waveguide material. In this paper we present examples of devices using this new DNA-based biopolymer.

Marine-based deoxyribonucleic acid (DNA), purified from waste products of the Japanese fishing industry, has recently become a new material of interest in photonics applications. The water soluble DNA is precipitated with a surfactant complex, cetyltrimethl-ammonium chloride (CTMA), to form a water insoluble complex, DNA-CTMA, for application as a nonlinear optical material. It is possible to fabricate an all-DNA-CTMA waveguide by crosslinking the DNA-CTMA. Crosslinking causes the material to become resistant to its initial solvents upon curing; this allows a core layer of crosslinked DNA-CTMA-chromophore to be spin coated directly on top of a cladding layer of crosslinked DNA-CTMA. The chromophore dye provides for the electro-optic effect to be induced through contact poling. The chromophore also raises the index of refraction of the core layer above that of the cladding needed for waveguiding. Progress on the development of this all-DNA-CTMA electro-optic modulator is presented.

Optical switching properties based on the photochromism of spiropyran-doped DNA-lipid complex films have been studied. On-off switching of the incident light under the alternate excitation of UV- and visible light showed strong dependence of the intensity of the excitation light. We have obtained the switching times of around 200-300ms, but much faster response could be expected since the proportional tendency has not been saturated yet.

DNA and PPMA were doped with the laser dye sulforhodamine 640. Red emission was observed from both dye-doped DNA and PMMA upon photoexcitation. Photoluminescence (PL) emission was studied as a function of dye concentration. The maximum PL intensity of dye in DNA host material is at least 17 times higher than that in PMMA. The DNA host shows higher doping concentration without optical quenching than PMMA does.

Red/Blue emitting organic light emitting diodes (OLED) devices have been obtained using a Europium-doped organic emitting layer (NPB:Eu). The Eu-doped OLEDs emit in 2 color ranges: a broad blue (~420-500nm) band due to NPB emission and a narrow red peak at 620nm due to Eu emission. The red/blue devices achieve a brightness ~13x more intense than a similarly structured green (Alq₃) emitting OLED. These NPB:Eu emitting structures also reach a maximum efficiency of 0.2 cd/A at brightnesses above 100 cd/m².

The photoluminescence (PL) and amplified spontaneous emission (ASE) spectra of the conjugated polymer [2-methoxy-5-(2'- ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) is study under different conditions such as thin film and solution, solvent type and concentration. Experiments indicate that aggregation has a pronounced effect on the measured spectra of both the PL and the ASE. In solution form, the ASE emission bandwidth decreases with the increment on concentration as well as a red shift of the ASE peak. For the thin film samples, the ASE spectra show two emission bands corresponding to the emission of the inner and the outer polymer chains. These two emission bands were associated with the gas to crystal effect, previously reported for PL.

Ambipolar light-emitting field-effect transistors are fabricated with two different metals for the top-contact source and drain electrodes; a low-work-function metal defining the channel for the source electrode and a high-work-function metal defining the channel for the drain electrode. A thin film of polypropylene-co-1-butene on SiN_x is used as the gate dielectric on an n⁺⁺-Si wafer, which functioned as the substrate and the gate electrode. Transport data show ambipolar behavior. Recombination of electrons and holes results in a narrow zone of light emission within the channel. The location of the emission zone is controlled by the gate bias.

Displays based on polymer light emitting diodes are attractive due to their emissive nature, their wide viewing angles and the ability of electroluminescent conjugated polymers to be solution processable at room temperature and pressure. It is difficult, however, to deposit separate red, green and blue (RGB) pixels and to maximize performance by making the devices multi-layered. Here we present recent results on a semiconducting conjugated reactive-mesogen OLED material which is solution processable, can be potentially cured and patterned by photolithography and used in multi-layer devices. This material consists of a conjugated pentathiophene core with reactive endgroups. Spectroscopy, calorimetry and microscopy show that it forms crystalline, aggregate, liquid-crystalline and isotropic phases at a range of different temperatures. The material is deposited by spincoating from solution. Low density doping with a cationic photointiator and exposure to a specific UV wavelength to avoid damage to the conjugated core leads to cross-linking into an insoluble network. Current-voltage-luminousity and spectral measurements in standard OLED device structures show the effect of cross-linking on the transport and injection properties of the material. Quenching of fluorescence and electroluminescence is discussed. Insertion of lower-energy gap, fluorescent small molecules can potentially be used to tune the emission to any desired colour but material limitations to this technique due to dopant removal during the washing procedure were observed.

New architectural polymer photovoltaic cells approaching 5% power conversion efficiency have been fabricated using titanium oxide (TiO_x) as an optical spacer. Solar cells with a TiO_x layer (deposited by a sol-gel process) between the active layer and the electron collecting aluminum electrode exhibit approximately 50% enhancement in power conversion efficiency compared to similar devices without the optical spacer. The TiO_x layer increases the efficiency by modifying the spatial distribution of the light intensity inside the device, thereby creating more photogenerated charge carriers in the bulk heterojunction layer.

Polymers have a number of attributes that make them highly desirable for use in the design and fabrication of optical waveguide devices, such as modulators and directional couplers. They have relatively low (1.5-1.7) refractive indices, low (~4) dielectric constants at gigahertz frequencies, stable at high (150-190^oC) temperatures, resistivities that can be tailored by adding guest molecules and electro-optical responses via the addition of chromophore molecules. These materials are easily spin-coated on glass, quartz or silicon wafers to form optically conducting films that have low (1-2 dB/cm) optical loss at the near-IR communication wavelengths. In this paper we update resistivity, dielectric, electrooptic coefficient and waveguide loss characterization methods and improvements that we are using to provide the data needed to fabricate polymer waveguide devices and report new results for DNA-based polymers.

This paper describes the design of an optical to microwave converter. The physical effect used for the conversion is based on the non-linear behavior of an electro-optic polymer material. The microwave frequency is generated by the way of an optical waves mixing process, which means by the frequency difference of two optical waves propagating simultaneously inside an optical waveguide. If one of these optical waves is modulated by an informative signal, the microwave signal will infer the modulation. The converter is designed for working at the 1.55 μm optical telecommunication wavelength. The active waveguide is built with the crosslinked PMMA-DR1 electro-optic copolymer, and the cladding layers are made of NOA material. For the first characterizations there is no need of a master-slave configuration for the sources, and the two optical waves are produced by highly stable and fine tunable lasers. The microwave signal is collected on a strip line which characteristic impedance has to be adapted to the conversion process. Simulations have been conducted showing the feasibility of the method and by matching the velocities of the microwave signal and of the optical signal it is possible to create constructive microwave photonic mixing at more than 60 GHz. To achieve the conversion it is necessary to work with a traveling-wave configuration. Some special test devices have been built for the determination of the NOA material permittivity leading to a precise adjustment of the effective index of both optical and microwave waveguide. From all these measurements it has been possible to design completely the device, which is now under test.

A novel broadband E-field sensor based on electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated. A flat is made on the side of the optical fiber by polishing and an electro-optic polymer waveguide in the shape of a ring is placed on the polished flat. One side of the ring is directly above the core of the fiber and light is evanescently coupled between the fiber and the micro-ring. External electric fields change the index of refraction of the ring resonator and therefore its resonant wavelengths. The sensor is all dielectric without metal layers to distort the measured E-field. The resonance structure allows the sensor to potentially have much higher sensitivity than other electro-optic sensors based on interferometry or polarization modulation. Since electro-optic polymers have higher electro-optic coefficients, lower dielectric constants and faster electro-optic responses than inorganic crystals, higher sensitivity, lower invasiveness and higher bandwidth of E-field sensing can be expected. The sensor with EO polymer micro-ring directly coupled to side-polished fiber eliminates unreliable and possibly lossy fiber to waveguide butt coupling as well as the high propagation loss which comes from the long straight EO polymer waveguides. Unlike devices based on waveguide technology, a supporting substrate is not necessary in this device. This leads to sensors of small size and low disturbance to the measured electric field. In the proof-of-concept experiment, a sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system) using AJLS103 electro-optic polymer.

We reported the "birefringent crystal dopant method" in order to compensate the orientational birefringence of polymers for optical devices. In this method, a birefringent inorganic crystal which has rod-like shape is homogeneously doped into a polymer and it compensates the orientational birefringence of the polymer. Strontium carbonate (SrCO₃) was selected for this purpose because it has a large birefringence and a rod-like shape. SrCO₃ was synthesized and doped into a poly(MMA/BzMA=78/22 (wt/wt)) (78/22 polymer) film and a cycloolefin polymer film and the films were drawn above glass transition temperature (T_g). The orientational birefringence of the drawn film at a wavelength of 633 nm was compensated and reduced by doping with SrCO₃. Furthermore, we analyzed the transparency and thermostability of the films.

We fabricated original probes for the near-field scanning optical microscopy (NSOM) with polarization-preserving optical fibers, and succeed polarization observation in guide-collection-mode NSOM. The polarized guide-collection-mode NSOM technique revealed the polarized properties of propagation light within a polymeric optical waveguide by separating independent polarization components. Using the polarized NSOM technique, we characterized the influences of defects and weak stresses within the waveguide. For the characterization, we intentionally printed an indentation in the vicinity of the waveguide, then evaluated the resulting influences from the NSOM images taken around the indentation. When transverse magnetic (TM) polarized light enters a waveguide, the light intensity becomes greater on the near side of the indentation than on the far side, as measured by a linearly polarized component perpendicular to the direction of light propagation. Under the polarization conditions of incident light and collection, it is expected that only the polarization-independent component will be observed and the electric field therefore does not become large. However, if scattering phenomena are present, the electric field should have a non-zero value. The most likely origin of this scattering is microdefects in the polymer generated by the stress-strain field at the interface between the waveguide and the cladding region around the indentation. These microdefects, which are generally a disorder in molecular chains, cause Rayleigh scattering. Finally, it is important to keep in mind that the polarized guide-collection-mode NSOM technique is capable of detecting defects or weak stresses in the nanoscale range within an optical waveguide.

We have developed a dye-doping process into a polymer, termed the "vapor transportation method." This method enables us to prepare a favorable doped layer in the polymer, possessing both a uniform dye concentration and a smooth surface. As one of developments of the vapor transportation method, we expanded to preparation of the optical waveguide. In preparation of the waveguide, low-molecular weight compound (phenyl benzoate; PB) showing the higher refractive index was dispersed in a matrix polymer (poly (methyl methacrylate), PMMA) through a mask by the developed method. After dispersion, the mask was removed, and another PMMA plate was put on doped PMMA by vacuum press. A double-layered structure of the doped and non-doped regions was observed in the cross section, further, two regions described were transparent. It was confirmed that a beam incident on the edge of the doped region of the prepared sample emerged from the other edge, indicating that the doped regions acted as a core. The core radius (depth of the doped region) increased with treatment time and treatment temperature. Furthermore, refractive index of the core was controlled by treatment temperature. The fabricated waveguide showed the propagation loss of 0.47 dB/cm at 650 nm.

Electro-optic modulators based on polymer material are very promising devices because of the expected very high modulation rate and low cost fabrication process. These modulators are mainly based on Mach-Zehnder structure, but phase modulators associated to polarizer and analyzer can also be used. Until now there are no real devices commercially available. One of the problems concerns the temperature stability. Because of the optical power of the laser beam and the absorption of the polymer material used for the optical waveguide there is a slight temperature evolution of the modulator leading to a change in the bias point of the modulator and then to a slow drift of the bias point leading to a dissymmetry of the optical modulated signal. This evolution can be compensated by adding a small DC value to the voltage applied to the electrodes. A control loop has been designed and tested in order to stabilize the bias point of the modulator. This loop acts as a synchronous detection with a low frequency modulation at 500 Hz and a practical detection at 1 kHz. By this way it is in fact the first order derivative of the signal which is stabilized leading to the signal symmetry control. This low frequency signal can be added without any problem to the informative modulating signal. By using this control loop the modulator can be used for a very longer time than without it. Of course a temperature control of the modulator by a Peltier effect module should also be implemented for a better and complete stabilization.

In this study, four kinds of organic light-emitting diodes were developed using vacuum deposition technique. The typical multilayer structures of OLED are ITO / CuPc(200 Å) / α-NPD(600 Å) / Alq3(400 Å) : C545T(X%) / Alq3(200 Å) /LiF(10 Å) / Al(1000 Å) , X% is the doping consistence in Emitter Layer of OLED. The value is change from 1% to 4%. In this letter, the optical and electronic performance including brightness, efficiency, spectrum etc. was change with the doping consistence. When X% is 1%, the steady voltage of device start working is lower than other structures, only 2.5V. When X% is 3%, the brightness of the device was measured to be 10,500cd times m^-2 at the drive voltage 20V, CIE coordinates x=0.331, y=0.625 and maximum luminous efficiency 6.72 lm•W^-1 at 5 V. When X% is 4%, the green emission spectrum peak is 550nm, almost reach 555nm (standard green spectrum peak).