Experimental investigation of millimeter wave Gunn oscillator circuits in circular waveguides

Millimeter wave Gunn oscillator circuits using circular waveguides for 33–50 GHz and 75–110 GHz frequency bands are described. These oscillators are simpler to construct at millimeter wavelengths compared to the conventional rectangular waveguide circuits. The effect of various circuit parameters on the oscillator frequency and output power has been experimentally studied. The CW power and mechanical tuning range obtained from the circular waveguide Gunn oscillators are found to be comparable and sometimes even better than those obtained with conventional rectangular waveguide circuits using the same Gunn device.     

Electroluminescence performance of organic light-emitting devices with KCl inside hole transport layer

A new multilayer organic light-emitting device (OLED) is fabricated by inserting kalium chloride (KCl) thin layer (1 nm) into hole transport layer (HTL). It has the configuration of ITO/NPB(15 nm)/KCl(1 nm)/NPB(25 nm)/Alq₃(60 nm)/KCl(1 nm)/Al. The electroluminescence (EL) result shows that the performance of the novel device has obviously improvement compared with the normal structure (ITO/NPB(40 nm)/Alq₃(60 nm)/KCl(1 nm)/Al). The EL and efficiency are about 1.4 and 1.3 times than that of conventional device. The suggested mechanism is that the KCl layer in N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1,1′-biphenyl-4,4′-diamine (NPB) can block the holes of NPB and then balance the holes and electrons. The better recombination of holes and electrons is beneficial to the enhancing properties of OLED.     

Enhancing properties of organic light-emitting diodes with LiF inside the hole transport layer

A new device has been made by inserting thin LiF layer in N,N′-diphenyl-N,N′-bis(1-napthyl–phenyl)-1, 1′-biphenyl-4,4′-diamine (NPB), which has a configuration of ITO/NPB(20 nm)/LiF(0.5 nm)/NPB(20 nm)/Alq₃(60 nm)/LiF(0.5 nm)/Al. Compared with normal device, the device inserted LiF layer inside NPB (HTL) can improve its performance. The luminance and efficiency is about 1.4 and 1.3 folds high of the conventional structure, respectively. The suggestion mechanism is that the LiF in the NPB layer can block holes of NPB, and balance the holes and electrons. Consequently, there are more excitons formed to boost the diode’s luminance and efficiency. And it may offer some valuable references for OLED’s structure.     

Monolithic integration technology between microlens arrays and infrared charge coupled devices

In this paper, we develop an integration technology between Si microlens and 256(H)×256(V) element PtSi Schottky-barrier infrared charge coupled device (IR-CCD) to improve the optical responsivity of CCD sensor. The refractive microlenses with the pixel size of approximately 28×28 μm² is directly fabricated on the backside of CCD substrate to focus the incident irradiation onto the active area. For the integration device the fill factor is improved by a factor of 2.1. As a result, the IR-CCD image sensors operating at 77 K indicate an approximate 0.06–0.4 increase in relative optical responsivity in the spectral range of from 1 to 5 μm. CCD imaging quality with microlens has been improved comparing to that without microlens to a great extent.     

Design of a neutron polarizer using polarizing super mirrors for the TOF-SANS instrument at the J-PARC

Small-angle neutron scattering technique using polarized neutrons is powerful for studying structures in the range between nm and μm of magnetic materials. In addition, they have been used for the incident beam of focusing-geometry SANS instruments using a magnetic neutron lens, where a high polarization degree of about 99.9% is necessary because the imperfectness of the neutron polarization increases the background level. We are going to install such a magnetic focusing system on the new time-of-flight SANS (TOF-SANS) instrument at the J-PARC so as to make q_min smaller than 10⁻³ Å⁻¹ and improve the resolution of the conventional TOF-SANS at low q. As a polarizing device of the instrument, two V-shaped polarizing super mirrors arranged in crossed geometry to enhance the polarization degree has been considered. In this paper, we present the concept and the detailed design of this device and its performance estimated by Monte Carlo simulations.     

An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

In this paper, we design an ultra-short 1 × 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 μm, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device.     

Basic Study on Imaging Interferometer using Long Gradient-Index Lenses for Optical Coherence Tomography

An imaging interferometer with two long gradient-index (GRIN) lenses and a charge coupled device (CCD) sensor array is proposed and studied for application to an optical coherence tomography system that can observe the subsurface structure of internal organs through a small hole in the body. An image of lines 11 μm wide was obtained using the phase-shifting method and a test pattern as a sample. The lateral resolution obtained was 22 μm. The axial resolution was also measured and found to be 19.4 μm by measuring the coherence function. The dynamic range was about 60 dB, based on the RF spectrum of the beat signal. A sectional image of a 10-yen Japanese coin was measured as a rough surface sample.     

Infrared photography in liquid films by thermocapillary convection

A thermal imaging system using a liquid-liquid interface has been studied, which utilizes the extreme temperature sensitivity of surface tension (Marangoni Effect). Theoretical considerations for the design and the operating conditions of the device are given. The experimental results using a detection by polarization interferometer indicate that the limitations on such a device are primarily due to the finite film thickness of the upper solution (on the order of 50–80 m). This system was able to image 1°C with a limiting resolution of ten lines pair per millimeter.     

Quantum-dot superluminescent diode: A proposal for an ultra-wide output spectrum

We propose a novel superluminescent diode (SLD) with a quantum dot (QD) active layer, which should give a wider output spectrum than a conventional quantum well SLD. The device makes use of inhomogeneous broadness of gain spectrum resulting from size inhomogeneity of self-assembled quantum dots grown by Stranski– Krastanow mode. Taking a design made out in the In_xGa_1-xAs/GaAs system for example, the spectrum characteristics of the device are simulated realistically, 100–200 nm full width of half maximum of output spectrum can be obtained. The dependence of the output spectrum on In composition, size distribution and injection current of the dots active region is also elaborated.     

A preliminary study of the distribution of plankton using hologrammetry

The distribution and dynamics of particles in the aquatic environment play an important role in the modelling of bio-geochemical processes. Previous work on the measurement of such particles, which vary in size from tens of micrometres (individual cells) to several centimetres (aggregates such as ‘marine snow’), has mainly used electronic counting or conventional photography coupled with image analysis. Here we report on an initial study of the use of holographic mensuration, otherwise known as hologrammetry, for the enumeration, sizing and spatial distribution determination of plankton. We present results on imaging plankton in water tanks using both in-line and off-axis pulsed-laser holography. In this work, we have recorded in-line holograms in a volume of 2400 cm³ of water with a resolution of better than 20 μm and off-axis holograms in a volume of 36000 cm³ with a resolution of 140 μm. In both cases, identifiable images of plankton were obtained and precise spatial coordinates determined from the in-line holograms.     

Bichromatic two-photon photoemission spectroscopy of image potential states on Ag(100)

Bichromatic two-photon photoemission spectroscopy (Bi2PPES) leads to an increased signal-to-noise ratio compared to conventional two-photon photoemission spectroscopy and therefore allows the observation of the first four image potential states as well as a lineshape analysis with improved accuracy on Ag(100). The n=2 image state with a measured linewidth of 37 meV FWHM is the narrowest unoccupied structure measured on any solid surface so far. The intrinsic linewidths of the first two image states were determined as 21±4 meV and 5±5 meV, respectively, in reasonable agreement with theoretical calculations. Disordered adsorption of oxygen on Ag(100) leads to a linewidth broadening of the first and — to a lesser extent — of the second image potential state. A quantitative analysis of the broadening suggests that the underlying mechanism is lifetime shortening due to scattering of the image state electrons by the adsorbate atoms.     

P-I-N Tuned hybrid device

Conclusions Thus, described device allows to control ultra high frequencies amplitude in wave propagation direction in the range from –3,5 dB to –43 dB. This device may be used as controlled filter with fixed controlling current values; as a variable attenuator with fluent current changing; and as a switcher with extreme controlling current value. The device has profitable weight-size parameters. Described device has two important advantages, namely higher attenuation level and a simple construction as compared with previously known one.     

Effect of image fiber on the speckle fringe pattern in image fiber-guided DSPI endoscopy

The effect of using an image fiber on the speckle fringe visibility in an endoscopic DSPI is analyzed here. An endoscope system was designed and developed, using image fiber as the speckle pattern image conduit, to work in the out-of-plane speckle interferometric configuration and experiments were carried out using a curved phantom tissue specimen as the test target. Experimental results obtained using the developed system are compared with that obtained using conventional DSPI system. To obtain a relative and quantitative comparison of the quality of the fringes obtained employing the two methods, an evaluation method that can give a quantified ‘score’ is proposed here.     

Oropharyngeal pH Monitoring for the Detection of Liquid and Aerosolized Supraesophageal Gastric Reflux

The association between gastroesophageal reflux disease (GERD) and extraesophageal symptoms is poorly understood and difficult to document. pH monitoring in this group of patients has resulted in conflicting data due to lack of diagnostic sensitivity. Recently, a new sensitive pH device for detection of liquid and aerosolized droplets in the oropharynx (The Dx–pH Measurement System [Dx–pH]) has become available. Our hypothesis is that we will be able to improve our ability to identify and understand this group of patients with this device. The aim of this preliminary observation study was to compare the results of this new device to the standard esophageal and pharyngeal pH probes in a small group of patients with extraesophageal symptoms. Patients with suspected extraesophageal GER symptoms underwent traditional 24-hour esophago-pharyngeal pH monitoring (24pH) simultaneous with Dx–pH monitoring in the oropharynx. Tracings were reviewed for comparison and correlation between the two probes, with an event in the Dx–pH Probe being defined as a rapid drop >3 standard deviation from baseline. Fifteen patients (10 females, 5 males) with mean age of 57.5 years (range, 25–75) were studied. The predominant chief complaint included 12/15 chronic cough, 2/15 asthma; and 1/15 throat clearing. All Dx–pH events were preceded and associated with distal esophageal pH drops in a progressive ante grade manner. Ten patients had 1–13 abnormal oropharyngeal pH events as measured by Dx–pH monitoring with a total of 48 events. The median pH of reflux events had a statistically significant increase from 3.1 at the distal esophageal probe to 5.2 at the pharynx and 5.6 at the oropharynx, the latter being 80% higher than the distal esophageal probe (P < 0.001). The percentage of acid events decreased in a cephalad manner from 66.7% at distal esophagus to 25% at the pharynx and only 6.25% at the oropharyngeal Dx–pH Probe, with the remaining events being weakly acidic. Dx–pH Probe is a new sensitive oropharyngeal pH device whose values correlate well with the gold-standard 24-hour pH device, and appears to accurately detect pH events that begin at the distal esophagus and travel upward to the oropharynx. This device suggests that supraesophageal events manifest themselves as rapid pH drops (>10%), which are likely not to be identified using the standard criteria of pH <4 due to the gradient of increasing pH from the lower esophagus to the oropharynx.     

Realization of an advanced nozzle concept for compact chemical oxygen iodine laser

Conventional supersonic chemical oxygen–iodine lasers (SCOIL) are not only low-pressure systems, with cavity pressure of 2–3 Torr and Mach number of approximately 1.5, but also are high-throughput systems with a typical laser power per unit evacuation capacity of nearly 1 J/l, thus demanding high capacity vacuum systems which mainly determine the compactness of the system. These conventional nozzle-based systems usually require a minimum of a two-stage ejector system for realization of atmospheric pressure recovery in a SCOIL. Typically for a 500 W class SCOIL, a first stage requires a motive gas flow (air) of 120 gm/s to entrain a laser gas flow of 3 g/s and is capable of achieving the pressure recovery in the range of 60–80 Torr. On the other hand, the second stage ejector requires 4.5 kg/s of motive gas (air) to achieve atmospheric pressure recovery. An advanced nozzle, also known as ejector nozzle, suitable for a 500 W-class SCOIL employing an active medium flow of nearly 12 g/s, has been developed and used instead of a conventional slit nozzle. The nozzle has been tested in both cold as well as hot run conditions of SCOIL, achieving a typical cavity pressure of nearly 10 Torr, stagnation pressure of approximately 85 Torr and a cavity Mach number of 2.5. The present study details the gas dynamic aspects of this ejector nozzle and highlights its potential as a SCOIL pressure recovery device. This nozzle in conjunction with a diffuser is capable of achieving pressure recovery equivalent to a more cumbersome first stage of the pressure recovery system used in the case of a conventional slit nozzle-based system. Thus, use of this nozzle in place of a conventional slit nozzle can achieve atmospheric discharge using a single stage ejector system, thereby making the pressure recovery system quite compact.     

Continuous-Wave Magnetic Resonance Imaging of Short T2 Materials

There is growing interest in the use of magnetic resonance imaging (MRI) to examine solid materials where the restricted motion of the probed spins leads to broad lines and short T₂ values, rendering many interesting systems invisible to conventional 2DFT pulsed imaging methods. In EPR T₂ seldom exceeds 0.1 μs and continuous-wave methods are adopted for spectroscopy and imaging. In this paper we demonstrate the use of continuous-wave MRI to obtain 2-dimensional images of short T₂ samples. The prototype system can image samples up to 50 mm in diameter by 60 mm long and has been used to image polymers and water penetration in porous media. Typical acquisition times range between 10 and 40 min. Resolution of 1 to 2 mm has been achieved for samples with T₂ values ranging from 38 to 750 μs. There is the possibility of producing image contrast that is determined by the material properties of the sample.     

Stability of charged impurities in a coupled single electron transistor and antidot system

We have fabricated devices on GaAs/AlGaAs heterostructures, containing two-dimensional electron gases, that consist of three point contacts surrounding an etched antidot with an Al/AlO_x/Al single electron transistor. The single electron transistor measurement shows rearrangement of neighboring charged impurities with a characteristic stability time scale of 20 s in one device and greater than 1 h in a second device. We also measured the resistance of the point contact–antidot constriction versus magnetic field. In a device with a 20 s stability time, we see a high noise level and poor reproducibility. In a device with a long stability time, much greater than 1 h, we are able to see reproducible features including Aharonov–Bohm oscillations.     

A Time-Symmetric Formulation of Quantum Entanglement

I numerically simulate and compare the entanglement of two quanta using the conventional formulation of quantum mechanics and a time-symmetric formulation that has no collapse postulate. The experimental predictions of the two formulations are identical, but the entanglement predictions are significantly different. The time-symmetric formulation reveals an experimentally testable discrepancy in the original quantum analysis of the Hanbury Brown–Twiss experiment, suggests solutions to some parts of the nonlocality and measurement problems, fixes known time asymmetries in the conventional formulation, and answers Bell’s question “How do you convert an ’and’ into an ’or’?”     

A simple wavemeter with crossed dispersion

A simple wavemeter has been developed by crossing the dispersions of a conventional monochromator and a Fabry-Perot interferometer. The interference pattern is scanned by a linear image sensor and processed by a microcomputer to determine the wavelength of cw laser sources with a better than 0.02 Å accuracy even when the sources have more than one spectral peak.     

Characteristics of 980/1550 nm WDM coupler based on planar curved waveguides

A wavelength division multiplexer (WDM) for 980/1550 nm based on planar curved waveguide coupler (CWC) is proposed. Compared with conventional parallel straight waveguide coupler (SWC), this structure has more flexibility with two variable parameters of bending radius R and minimum edge-to-edge spacing d₀, which are the two main parameters for the splitting ratio of coupler and decrease the complexity of device design and fabrication. Based on coupled mode theory (CMT) and waveguide theory, R and d₀ of the WDM CWC are designed to be R=13.28 m and d₀=4.39 μm. The contrast ratio (CR) and insertion loss (IL) for 980 and 1550 nm are CR₁=24.62 dB, CR₂=24.56 dB and IL₁=0.014 dB, IL₂=0.015 dB, respectively. The 3D beam propagation method (BPM) is used to verify the validity of the design result. The influence of R and d₀ variations on the device performance is analyzed. For CR>20 dB, the variation ranges of R and d₀ should be within −0.10 to +0.44 m and −0.05 to +0.02 μm, respectively.