Low Loss Coefficient Research Articles

Controlling Morphology and Chain Aggregation in Semiconducting Conjugated Polymers: The Role of Solvent on Optical Gain in MEH-PPV

We report the results of a detailed investigation that addresses the influence of polymer morphology and chain aggregation, as controlled by the chemical nature of the solvent, on the optical gain properties of the conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV). Using the variable stripe length technique in the picosecond regime, we have extensively studied the optical gain performance of asymmetric planar waveguides formed with thin MEH-PPV films spin-cast from concentrated chlorobenzene (CB) and tetrahydrofuran (THF) solutions onto thermally oxidized silicon substrates. CB and THF solvents were chosen based on their known ability to promote and effectively limit aggregate formation, respectively. Very large net gain coefficients are demonstrated, reaching values of 330 and 365 cm(-1), respectively, when optically pumping the waveguides with a maximum energy density of 85 μJ/cm(2). Our results clearly demonstrate that polymer morphology, and hence, the chain conformation dependence of the degree of aggregation in the films as controlled by the solvent, has minimal impact on the net gain. Moreover, the waveguides exhibit low loss coefficients of 10-20 cm(-1) at the ASE wavelength. These results question the importance of polymer morphology and aggregate formation in polymer-based optical devices operating at high excitation densities in the stimulated emission regime as would be characteristic of lasers and optical amplifiers.

Microwave Dielectric Properties of LiF- and CaTiO3-Added MgO with Low Dielectric Loss and Near-Zero Temperature Coefficient of Resonant Frequency for Low-Temperature Cofired-Ceramic

The influences of LiF and CaTiO3 addition on the microwave dielectric properties of MgO ceramics were investigated in this study. The LiF was effective in reducing the sintering temperature of MgO without a detrimental effect on the quality factor (Q·f). The 0.05 mol LiF-added MgO ceramics were sintered at a temperature of 950 °C which resulted in dielectric constant (εr) and Q·f values of 9.6 and 215,000 GHz, respectively, though the temperature coefficient of resonant frequency (TCf) had a large negative value of -63.5 ppm/°C. In order to achieve near-zero TCf values, (0.95-x)MgO–xCaTiO3–0.05LiF ceramics were also investigated and the formation of a secondary phase in MgO–CaTiO3–LiF ceramics was not observed in the X-ray powder diffraction profiles. Although the Q·f values of the ceramics were lowered by CaTiO3 addition, a near-zero TCf was obtained at x = 0.05 (TCf= -3.2 ppm/°C). The εr and Q·f values of the 0.90MgO–0.05CaTiO3–0.05LiF (x = 0.05) ceramic were 12.7 and 93,500 GHz, respectively. From these results, it is considered that CaTiO3-added (0.95-x)MgO–xCaTiO3–0.05LiF ceramics are appropriate candidates as high-Q low-temperature cofired-ceramics (LTCCs).

Microwave Dielectric Properties of LiF- and CaTiO3-Added MgO with Low Dielectric Loss and Near-Zero Temperature Coefficient of Resonant Frequency for Low-Temperature Cofired-Ceramic

Microwave Dielectric Properties of LiF- and CaTiO3-Added MgO with Low Dielectric Loss and Near-Zero Temperature Coefficient of Resonant Frequency for Low-Temperature Cofired-Ceramic

Limits to Maximum Absorption Length in Waveguide Photodiodes

The maximum photocurrent, power dissipation, and linearity of waveguide photodiodes are limited by the length over which the input optical power is absorbed. This absorption length is determined by the absorption coefficient of the absorbing layer material (αo), the optical confinement factor (Γ), and the excess loss coefficient (αi). In this paper, we analyze the fundamental limits to maximizing the absorption length and demonstrate a new waveguide photodiode structure that approaches these limits. The new structure is referred to as a slab-coupled optical waveguide photodiode (SCOWPD) and is realized in the InGaAsP/InP material system. Assuming 100% coupling efficiency, the SCOWPD has an ultralow optical confinement factor and a low excess loss coefficient, both calculated from measurements, of Γ = 0.069% and αi = 1.65 cm-1, respectively. This results in a 1/e absorption length of 2.1 mm. The SCOWPD exhibits an external responsivity of 0.8 A/W and a maximum photocurrent of 250 mA at a wavelength of 1.55 μm.

Thermoplastic Wire Drawing from Bulk Metallic Glass

ABSTRACTThe low loss coefficient and high elastic energy storage of amorphous metals may provide novel opportunities in the design of stringed musical instruments. To produce prototypes for metallic glass music wire, bulk metallic glass pre-forms were reheated into the supercooled liquid region and stretched into wires. Investigations of these wires’ geometrical, mechanical, and physical properties are reported. The process is relatively simple and could be practical for producing continuous wire. A theoretical analysis shows the importance of the interaction between heating power input, radiative and convective cooling, and area reduction in determining the wire’s final properties.

A theoretical model of firm heterogeneity, FDI, and optimal technology strategy

This study uses Melitz's (2003) model of heterogeneous firms as the basis and expands it to analyze the optimal technology strategies of multinational firms. Analytical results demonstrate that the firms with the lowest productivity will either exit or not enter the market. The firms with the second-lowest productivity will adopt low technology both domestically and abroad. The firms with a comparatively high productivity will adopt high technology in at least one location. A higher efficiency loss coefficient stemming from adoption of high technology abroad will lead to adoption of high technology domestically; a low loss coefficient will lead to adoption of high technology abroad. Finally, the firms with the highest productivity will adopt high technology in both domestic and foreign markets. In addition, it is more likely for a firm to adopt the high technology in the foreign market when theforeign market size is enormous, which could result in the loss of domestic technology competitiveness.

Optimization of Interface Transmission between Integrated Solid Core and Optofluidic Waveguides

Optofluidic waveguides have been integrated with solid core waveguides on silicon using an antiresonant reflecting optical waveguide (ARROW) design. Interface transmission between solid and liquid core waveguides is one of the most important factors for overall optical throughput. The optimization of interface transmission by adjusting the thickness of top waveguide cladding layers was demonstrated experimentally and theoretically. The measured coupling efficiency increases from 18% to 67% and the overall throughput was improved <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$17\times$</tex></formula> due to improved mode matching while liquid core waveguides maintain a low average loss coefficient. <?Pub _bookmark="" Command="[Quick Mark]"?>

Ba0.68Sr0.32TiO3/Ba0.68Sr0.32TiO3 + Mn composite with low loss and high pyroelectric coefficient

AbstractPure barium strontium titanate (BST) and 10 mol% Mn(NO)3 doped BST were combined in a three‐dimensional structure, and the dielectric and pyroelectric properties of the ceramics were investigated. Compared with conventional doped ceramics, samples with the three‐dimensional structure exhibited excellent properties. When Mn was added in this special structure, the dielectric loss was depressed dramatically. However, the dielectric constant peak depression effect caused by the dopants was weakened simultaneously. This phenomenon was nontraditional but conducive to the improvement of pyroelectric properties of BST as dielectric bolometer. The dielectric loss, pyroelectric coefficient, and flgure‐of‐merit of three‐dimensional structural specimens could be 0.5%, 9500 µC/m2 K, and 18.0 × 10−5 Pa−0.5, respectively. All these properties were better than samples prepared by conventional doping method. The improvement of pyroelectric property is beneficial for the development of infrared detectors.

Improving the emission efficiency of periodic plasmonic structures for lasing applications

We report on a two dimensional plasmonic structure that utilizes an Ag film for the generation of surface plasmons and a layer of the organic semiconductor tri(8-hydroxyquinoline) aluminum (Alq 3) doped with the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4 H-pyran (DCM) as an active medium. The dispersion diagram of this structure exhibits a plasmonic bandgap in the dye emission wavelength range. At the flat band-edge, the group velocity tends to zero, so that the density of surface plasmon modes is high. This may yield a lasing action. However, the device suffers from the energy dissipation due to metal absorption and unwanted radiation. We examine how some of them may be overcome. Firstly, we propose the use of long range surface plasmons (LRSPs) characterized by a low loss coefficient. To this end, we investigate theoretically and experimentally the best conditions for the excitation of these modes. A strong emission is observed compared to that from a planar structure. These modes provide a high performance–an enhancement factor of 3–when the dye thickness is about 100 nm, a value consistent with the numerical findings. We further demonstrate that the use of a spacer layer significantly increases the emission efficiency. Finally, we suggest a specific design for the laser structure for minimal radiation loss.

Broadly tunable deep blue laser based on a star-shaped oligofluorene truxene

We report amplified spontaneous emission (ASE) and optically pumped deep-blue-emitting distributed feedback (DFB) lasers based on a star-shaped oligofluorene truxene molecule. A low ASE threshold of 2.1 kW/cm 2 at 439 nm was achieved. The material exhibits a high net gain of 38 cm −1 and also low optical loss coefficient of 3.5 cm −1. Second-order DFB lasers show tuning of the emission wavelength from 422 to 473 nm, and a minimum threshold density of 515 W/cm 2. This is the broadest tuning range (51 nm) reported for organic deep-blue/blue lasing materials.

Grounding and the influence of the total pressure losses in ducted wind turbines

AbstractDucted wind turbines are known to exceed the Betz limit for the power that may be extracted from free currents per unit cross‐sectional area of their rotors. The present study points to another advantage: the fact that the turbine rotor (and the associated subassemblies) need not be lifted up on the air and rotated to align with the wind. They can function just as effectively by installing them on the ground and sucking air inside it. The analysis evaluates the efficiency of a ducted wind turbine plant, exhausting into the wake of a bluff body, under both ideal and realistic component performance. The results indicate that there exists a strong need to develop diffusers with a very low loss coefficient (e.g. by employing suction or transpiration techniques). Under such conditions and by employing the above exhaust assist techniques, the ducted wind turbine concept may deliver efficiencies more than an order of magnitude larger than those of the conventional plants. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Amplified spontaneous emission in optically pumped neat films of a polyfluorene derivative

We report the emissive properties of a fluorene-based polymer, PF-1SOR, in planar asymmetric waveguides under optical pumping. A laser beam homogenizer setup was applied to achieve the flat-top intensity profile of the excitation light. Amplification of deep blue light via stimulated emission (SE) occurred at an energy threshold of 11 μJ cm −2 and the amplified spontaneous emission (ASE) peak could be tuned from 411 to 423 nm. A net gain coefficient of 19.8 cm −1 was obtained by means of the modified variable stripe length (VSL) method. The PF-1SOR thin films delivered a remarkably low loss coefficient of 1.5 cm −1, among the lowest ever reported for a single component polymer waveguide.

Design of ultra wideband microstrip 180 degree phase shifter

AbstractA Ultra Wideband microstrip 180 degree phase shifter is presented. It is obtained by a novel design of Microstrip‐to‐Coplanar Waveguide (CPW)‐to‐Microstrip transition. Via holes are used to transfer the current from the top to the bottom substrate layer and vice versa. The presented phase shifter is operating in a wide bandwidth between 5.5 and 17.2 GHz, with low insertion loss and reflection coefficients. This phase shifter can be used in phased arrays and power combiners. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1841–1844, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23487

Stimulated Brillouin Scattering in a Single-Mode Tellurite Fiber for Amplification, Lasing, and Slow Light Generation

In this paper, Brillouin gain performances of tellurite fiber are investigated for photonics applications. We demonstrate stimulated Brillouin amplification and lasing and the simulated performance of slow light generation in a single-mode tellurite fiber. A Brillouin gain of 29 dB is achieved in a 100-m tellurite fiber with a pump power of 10 mW at 1550 nm. A peak value of Brillouin gain coefficients of 1.6989 X 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> m/W is measured on the base of gain characteristics. An all-fiber Brillouin laser with the maximum unsaturated power of 54.6 mW at 1550 nm and a slope efficiency of 38.2% is achieved from a 200-m tellurite fiber by employing a ring cavity. Furthermore, widely tunable (~27 nm) Brillouin comb laser with 26 lines spaced at 7.97 GHz is obtained from the ring laser cavity including an erbium-doped fiber amplifier (EDFA). A simple theoretical model based on laser threshold theory successfully explains the properties of Brillouin comb lasers. Stimulated Brillouin scattering (SBS)-induced time delay per unit power and per unit length is also calculated using the measured data of Brillouin gain coefficients. A peak value of 0.09246 ns/mW/m and a time delay slope efficiency of 1.75 ns/dB are obtained for this tellurite fiber. Potential performance of a tellurite fiber for slow light generation is clarified on the base of Brillouin gain characteristic. Our results show that tellurite fiber is a promising gain medium for Brillouin fiber amplifiers, lasers, and slow light generation due to its low background loss and large Brillouin gain coefficient.

Materials for violin bows

Abstract The bow quality determines the ease with which an experienced violinist can produce a high-quality sound. Factors influencing its playability are partly structural (shape, point of balance) and partly material dependent (mass, stiffness, mechanical damping). Pernambuco, a tropical wood, most revered for high-quality violin bows is practically extinct in the wild. Measuring the properties of pernambuco and thirteen alternative materials by a resonant bar technique and mechanical spectroscopy in both the vacuum- and the air-dry states and comparing their performance objectively using property charts and performance indices reveals that bow-grade pernambuco has a high bending stiffness per unit mass, a high speed of sound parallel to the wood grain, and an exceptionally low loss coefficient at room temperature, and that, on purely mechanical grounds, materials exist that could make as good violin bows as pernambuco. The consequences of the use of such alternatives for bow design are described.

Very low amplified spontaneous emission threshold and electroluminescence characteristics of 1,1′-diphenyl substituted fluorene derivatives

A blue amplified spontaneous emission with a very low threshold was observed in novel fluorene derivatives doped into a 4,4′-bis-(N-carbazole)-biphenyl (CBP) host. With 6wt%-2,7-bis[4′-(N,N-diphenylamino)-1,1′-biphenyl-4-yl]-9,9-bis(1,1′-biphenyl-4-yl)-9H-fluorene (BDF2) or 2,7-bis[1,1′-biphenyl-4-yl]-9,9-bis(1,1′-biphenyl-4-yl)-9-H-fluorene (BBF) as a dopant, high photoluminescence quantum efficiencies of 90%±1% and 78%±2% with extremely low amplified spontaneous emission thresholds of 0.15±0.05μJ/cm2 (300W/cm2) and 0.17±0.04μJ/cm2 (340W/cm2) were obtained. We also observed a high gain coefficient (38cm−1) and a low loss coefficient (6cm−1) in a 6wt%-BDF2:CBP thin film optical-waveguide. Furthermore, an organic light emitting diode with BDF2 as an emitter demonstrated a high external quantum efficiency (ηext) of 4.5%±0.1%. In addition, electroluminescence from an organic field-effect transistor with BDF2 as an active material was also observed with a maximum ηext of 0.02%.

Low loss GaN at 1550nm

We report absorption loss coefficients at 1550nm of free-standing GaN grown by hydride vapor phase epitaxy. We measured propagation loss values at numerous locations of the facets and observed an average of 2.41dB∕cm and 1.85dB∕cm for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively, in the low loss region of the sample. The minimum loss values in the sample were found to be 0.82dB∕cm (TE) and 0.61dB∕cm (TM). The ability to achieve such low propagation loss coefficients in GaN opens up the possibility of using this material in a variety of integrated optics and nonlinear optics applications.

Amplified spontaneous emission from fluorene-based copolymer wave guides

Amplified spontaneous emission (ASE) from optically pumped thin film wave guides of a fluorene-based copolymer, poly(2,7-(9,9-di- n-octylfluorene)-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB), which has a high hole mobility and a low ionization potential in comparison with those of fluorene-based copolymers, has been observed. The net gain spectra and the loss coefficient of TFB wave guides are measured as gain media for use in solid-state organic lasers. A maximum net gain of 15.5 cm −1 and a low loss coefficient of 12.1 cm −1 are obtained at the ASE wavelength of 459 nm.

Fluorene-based conjugated polymer optical gain media

We report a detailed investigation of the optical gain properties of a series of semiconducting polyfluorenes with photoluminescence emission spectra that span the entire visible spectrum. Stimulated emission was demonstrated at low pump pulse energies (⩾0.1 μJ for 10 ns, 10 Hz pulses) in the blue, green and red parts of the spectrum via amplified spontaneous emission (ASE) measurements on asymmetric slab waveguides. These structures exhibit large net gains g⩽74 cm−1, and corresponding gain cross-sections σ⩾7×10−16 cm2, together with very low loss coefficients, α⩾3.2 cm−1. The spectral location of the maximum waveguide amplification can be widely tuned (Δλ⩾30 nm) by controlling the allowed propagating modes or by blending the active emitter with a second larger optical gap polyfluorene. Our results confirm that fluorene-based polymers are attractive gain media for use in highly tuneable solid-state polymer lasers and amplifiers.

Semiconducting polyfluorenes as materials for solid-state polymer lasers across the visible spectrum

We report a detailed study of the gain properties of three polyfluorenes: poly(9,9-dioctylfluorene- co-9,9-di(4-methoxyphenyl)fluorene (F8DP), poly(9,9-dioctylfluorene- co-benzothiadiazole) (F8BT), and a Dow proprietary copolymer, Dow Red F. The emission spectra of these conjugated polymers span the full visible spectrum from 400 to 800 nm. We observe amplified spontaneous emission (ASE) with peak wavelengths at 452, 576 and 685 nm for F8DP, F8BT and Red F, respectively. Low stimulated emission thresholds in the region of 0.1–0.45 μJ per pulse are demonstrated for planar asymmetric waveguides. Variable stripe length gain measurements at the peak ASE wavelengths show large net gains up to 66 cm −1. Very low loss coefficients, in the range of 3.2–14.8 cm −1, were also found.