ALMA Band 10 tertiary optics

The ALMA Band 10 (787–950 GHz) receiver is a dual-polarization heterodyne system based on NbTiN superconducting technology. The coupling of energy from the secondary mirror of the ALMA Cassegrain antenna to the Superconductor–Insulator–Superconductor (SIS) mixers used for down-conversion is achieved by a frequency-independent optical system composed of two elliptical mirrors to focus and redirect the incoming radiation, a wire-grid to separate orthogonal linear polarizations and two corrugated horns, one for each polarization and SIS mixer. In this paper, we present the ALMA Band 10 tertiary optics design and evaluate its performance by quasi-optical techniques, Physical Optics simulations and measurements. Detailed results of secondary aperture efficiency and beam-squint are provided. The characterization procedure described in this paper can be used for any optical system at around 1 THz.     

Theoretical analysis and test for off-axis Cassegrain optical antenna

By detailed analysis of Cassegrain optical antenna with inclined optical axis, the receiving antenna power and the curve of power attenuation are obtained for different deflection angles. Three-dimensional images which describe the power distribution of the receive laser beam have been obtained. The coupling efficiency of antenna system is obtained from specific experiment. If the deflection angle is less than 0.1519 rad, the coupling efficiency is beyond 80%. In this case, the optical antenna system can be viewed as in alignment approximately. This research will provide a theoretical base and broad application for achieving precise alignment of optical axis in the field of optical communications and three-dimensional laser radar images.     

Simulative investigation on the impact of laser-spectral width in single-tone radio-over-fiber transmission system using optical single side-band technique

In this paper, we analyzed the impact of laser-spectral width incorporating dual-electrode Mach–Zehnder modulator (DEMZM) in single-tone radio-over-fiber (RoF) transmission system by simulation setup. It is shown that an improvement in the measurement of received radio frequency (RF) power is achieved by reducing the laser line width from 100 MHz to 100 kHz, which further improves the BER rate and optical link by transmitting the information with low power. The results are calculated for 20 and 50 km optical single sideband (OSSB)–RoF transmission system by varying the chirp from 0 to −3 as it requires less bandwidth than optical dual sideband (ODSB)–RoF system and is tolerable for power degradation due to a chromatic fiber-dispersion, through a standard single-mode fiber (SSMF) carried by a continuous wave (CW) laser at 1550 nm of laser-spectral width varying from 100 MHz to 100 kHz with CW power of 10 mW that modulates a single RF channel of 20 GHz. Further, deployment of such lasers with OSSB scheme helps the telecom industry to reduce the designing cost of RoF communication systems.     

Microstructural characterization and optical polarization of glass with needle-like micro–nano silver oriented arrangement

Homogeneous glasses in the Na₂O–B₂O₃–Al₂O₃–SiO₂ system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 °C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.     

Three-dimensional diffuse optical imaging of hand joints: System description and phantom studies

In this paper we describe a three-dimensional (3D) continuous wave (CW) diffuse optical tomography (DOT) system and present 3D volumetric reconstruction studies using this DOT system with simple phantom models that simulate hand joints. The CCD-based DOT system consists of 64×64 source/detector fiber optic channels, which are arranged in four layers, forming a cylindrical fiber optic/tissue interface. Phantom experiments are used to evaluate system performance with respective to axial spatial resolution, optical contrast and target position for detection of osteoarthritis where cartilage is the primary target region of interest. These phantom studies suggest that we are able to quantitatively resolve a 2 mm thick “cartilage” and qualitatively resolve a 1 mm thick “cartilage” using our 3D reconstruction approach. Our results also show that optical contrast of 3:1–7:1 between the “disease cartilage” and normal cartilage can be quantitatively recovered. Finally, the target position along axial direction on image reconstruction is studied. All the images are obtained using our 3D finite-element-based reconstruction algorithm.     

Characterization of Submillimeter Wave Absorbers from 200–600 GHz

This paper presents measurements of both specular and non-specular scattering from several submillimeter wave absorber materials designed for antenna testing and from low-cost carpet materials. The frequency range is 200–600 GHz in specular scattering, and 300–400 GHz in non-specular scattering measurements. The constructed bistatic test bench allows testing of the full continuous angular range of 0°–90°. The measurement results show large differences in performance of different materials. It is shown that reflectivities below –50 dB over limited angular ranges are possible with a correct alignment of the material. Also, low-cost carpet materials have lower than –15 dB reflectivities in most angles, and may be useful in non-critical parts of the antenna test range. The results can be used to optimise the absorber placement inside an antenna range, concerning both best performance and lowest cost.     

Investigation of plasmonics resonance infrared bowtie metal antenna

An approximate resonance wavelength equation that varies with metal antenna structure size is developed to design a bowtie gold metal antenna working at near-infrared (IR) wavelength. Bowtie antenna structures with resonance wavelength of 1.06 μm, 1.55 μm and 10.6 μm are designed based on this equation. A finite-difference time domain (FDTD) algorithm with total field scattered field (TFSF) source simulation shows the resonance wavelength of the designed structures being precisely in agreement with the expected wavelengths from the equation. Planar integration of the metal bowtie antennas is discussed as well. Gold nanohole bowtie antenna arrays are fabricated and the near-field optical transmission properties of the nanohole array are investigated with a near-field scanning optical microscope (NSOM). Our experimental results verify the near-field optical transmission performance and further demonstrate that they are in agreement with the theoretical calculation results. The high enhancement efficiency and integration of the metal bowtie antennas open the possibility of a wide application in IR optoelectronics detection and imaging.     

10 Gb/s optical carrier distributed network with W-band (0.1 THz) short-reach wireless communication system

Millimeter-wave (mm-wave) operated in W-band (75 GHz–0.11 THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10 Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1 THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10 Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10 Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20 km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed.     

A Low Noise 100 GHz Sideband-Separating Receiver

We have built a 100 GHz sideband-separating receiver. The receiver, a breadboard for the band 3 cartridges for ALMA, achieves a SSB noise temperature of 6hf/k with a 4–8 GHz IF. We show that it is possible to meet the ALMA specifications. The design of the receiver is reviewed and the relationships between the receiver noise temperature and properties of the components used in the receiver are discussed.     

The microstructure, optical, and electrical properties of sol–gel-derived Sc-doped and Al–Sc co-doped ZnO thin films

Transparent conductive ZnO:Al–Sc (1:0.5, 1:1, 1:1.5 at.% Al–Sc) thin films were prepared on glass substrates by sol–gel method. The microstructure, optical, and electrical properties of ZnO:Sc and ZnO:Al–Sc films were investigated. Results show that Sc-doping alone obviously decreases grain size and degrades the crystallinity; there is an amorphous phase on the surface of ZnO grains; the transmittance spectra fluctuate dramatically with a large absorption valley at about 430–600 nm. However, Al–Sc co-doping can stabilize grain size and improve the microstructure; an average visible transmittance of above 73% is obtained with no large absorption valley; the amorphous phase does not appear. The optical band gaps of ZnO:Sc and ZnO:Al–Sc films (3.30–3.32 eV) are blue-shifted relative to pure ZnO film (3.30 eV). Hall effects show that the lowest resistivity of 2.941 × 10⁻² Ω cm and the maximum Hall mobility of 24.04 cm²/V s are obtained for ZnO:Al–Sc films while ZnO:Sc films do not exhibit any electrical conductivity. Moreover, there is an optimum atomic ratio with Al to Sc of 1:0.5–1 at.%. Although the resistivities are increased compared with that of ZnO:Al film, the Hall mobilities are raised by one order of magnitude.     

DWDM VSB modulation-format optical transmission: Effects of optical filtering and electrical equalization

The transmission of 40 Gb/s wavelength multiplexed channels under vestigial single side band modulation format is transmitted over long haul optically amplified fiber systems. Bit-error-rate (BER) of 10⁻¹² or better can be achieved across all channels. Optical filters are designed with asymmetric roll-off bands. Simulations of the transmission performance, BER versus receiver sensitivity are demonstrated with wavelength channel spacing of 20–40 GHz. An optical filter, whose passband is 28 GHz and 20 dB cut-off band, performs best for 40 Gb/s bit rate due to optimum filtering and minimum noise contribution. Furthermore the single-sideband property of VSB format can assist linear equalization by electronic processing. The transmission performance is accurately evaluated based on the eye opening using a fast statistical method based on an equivalent Gaussian probability density distribution (pdf) which is derived from multiple peaks pdf of distorted eye diagram.     

The Virgo interferometric gravitational antenna

The interferometric gravitational wave detectors represent the ultimate evolution of the classical Michelson interferometer. In order to measure the signal produced by the passage of a gravitational wave, they aim to reach unprecedent sensitivities in measuring the relative displacements of the mirrors. One of them, the 3-km-long Virgo gravitational wave antenna, which will be particularly sensitive in the low-frequency range (10–100 Hz), is presently in its commissioning phase. In this paper the various techniques developed in order to reach its target extreme performance are outlined.     

Structural and optical properties of In0.5Ga0.5As/GaAs quantum dots in an In0.1Ga0.9As well using repeated depositions of InAs/GaAs short-period superlattices for the application of optical communication

We report structural and optical properties of In_0.5Ga_0.5As/GaAs quantum dots (QDs) in a 100 Å-thick In_0.1Ga_0.9As well grown by repeated depositions of InAs/GaAs short-period superlattices with atomic force microscope, transmission electron microscope (TEM) and photoluminescence (PL) measurement. The QDs in an InGaAs well grown at 510 °C were studied as a function of n repeated deposition of 1 monolayer thick InAs and 1 monolayer thick GaAs for n=5–10. The heights, widths and densities of dots are in the range of 6–22.0 nm, 40–85 nm, and 1.6–1.1×10¹⁰/cm², respectively, as n changes from 5 to 10 with strong alignment along [1 −1 0] direction. Flat and pan-cake-like shape of the QDs in a well is found in TEM images. The bottoms of the QDs are located lower than the center of the InGaAs well. This reveals that there was intermixing—interdiffusion—of group III materials between the InGaAs QD and the InGaAs well during growth. All reported dots show strong 300 K-PL spectrum, and 1.276 μm (FWHM: 32.3 meV) of 300 K-PL peak was obtained in case of 7 periods of the QDs in a well, which is useful for the application to optical communications.     

Real-time measurement of glucose concentration and average refractive index using a laser interferometer

This study presents a non-destructive, highly precise optical metrology system for measuring the average refractive index of a liquid solution such that its glucose concentration can be derived. The metrology system is employed to measure the average refractive indices of samples with known glucose concentrations ranging from 0 to 200 g/l. By applying a regressional analysis technique to the experimental results, an analytical expression is derived to describe the relationship between the refractive index and the glucose concentration. An excellent agreement is observed between the experimentally determined values of the glucose concentration and the analytically derived results. For an assumed laser interferometer resolution of 1 nm, the measurement resolution of the proposed metrology system is found to be at least F=0.05 g/l, which is significantly better than that of F=2 g/l obtained using the polarimetric glucose sensor presented by Lo and Yu [A polarimetric glucose sensor using a liquid-crystal polarization modulator driven by a sinusoidal signal. Opt Commun, 2006; 259: 40–8].     

Appearances of internal micro bubbling, multiple micro explosions, multiple micro jets and micro diffusion flames around an abruptly heated micro plastic-resin particle

Heating, gasifying and burning processes of a micro plastic-resin particle, which has a diameter of about 200 μm and is suddenly exposed to a hot oxidizing atmosphere, are observed and optically processed by combining a micro schlieren system with a high-speed CCD video camera. The following three devised approaches are introduced: the use of an oxidizing combustion gas downstream of a spark-ignited propane–air lean premixed flame as a sudden heat source, the use of a spherically reformed micro particle on a fine tungsten wire of 5 μm diameter, and the use of a simultaneous direct and schlieren optical system. The first technique realizes slow heating and enables a micro resin particle to undergo the same circumstances as those experienced by plastic-resin particles in the plastic-resin powder combustion. The second approach improves the accuracy and reproducibility of image processing, whereas the third optical system gives simultaneous pictures of the transparent visible image and the schlieren image around a micro resin particle of one heating process. The results show that there exists intense multiple internal bubbling, multiple micro explosions, multiple micro jets and micro diffusion flames, and that their existence exerts strong influences on gasification characteristics of a micro resin particle and results in a high burning rate constant.     

Threshold reduction of a pulsed narrow-band β-Ba2BO4 optical parametric oscillator in a grazing–incidence configuration by injection of amplified spontaneous emission

Threshold reduction of a nanosecond, narrowband β-barium borate optical parametric oscillator by injection of amplified spontaneous emission (ASE) from a dye laser is described. The BBO-OPO uses a grazing–incidence–grating cavity and pumped at 355 nm by a single-mode Nd : YAG laser. A threshold reduction of 33% has been achieved over a tuning range of 20 nm using this technique.     

Neural estimator to determine alpha parameter in terms of quantum-well number

The value of the α (Alpha) parameter, which is also called Linewidth enhancement factor, is particularly important in optical communication systems. This paper presents a new approach based on artificial neural networks (ANNs) to determine the α parameter for different number of quantum-wells (QWs). ANNs are trained in different structures with the use of five learning algorithms to obtain better performance and faster error convergence. The Levenberg–Marquardt (LM) algorithm, which has a quadratic speed of convergence, gives the best result among other learning algorithms used in the analysis. Both the training and the test results are in very good agreement with the experimental results reported elsewhere.     

Reinvestigation of the (4, 20) band of the O2 second negative system

High resolution absorption spectra of the (4, 20) band in the second negative system (A²Π_u–X²Π_g) of O₂⁺ cation were measured and analyzed in the range of 11 900–12 300 cm^–1 via optical heterodyne velocity modulation spectroscopy. Precise molecular constants of the levels involved were obtained by a nonlinear least-squares fitting procedure combining with our previous spectra of the (4, 19) and (6, 20) bands.     

Effect of cadmium addition on the optical constants of thermally evaporated amorphous Se–S–Cd thin films

Se₇₅S_25−xCd_x is a promising ternary material, which has received considerable attention due to its applications in the fabrication of various solid state devices. These have distinct advantages, large packing density, mass replication, fast data rate, high signal-to-noise ratio and high immunity to defects. Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on Se₇₅S_25−xCd_x (where x = 0, 2, 4, 6 and 8) thin films of thickness 3000 Å as a function of photon energy in the wave length range 400–1000 nm. It has been found that the optical band gap and extinction coefficient increases while the value refractive index decreases on incorporation of cadmium in Se–S system. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. Due to the large absorption coefficient and compositional dependence of reflectance, these materials may be suitable for optical disk material.     

Compact wideband implantable antenna for biomedical applications

Wideband miniaturized antenna along with high gain is much needed for biomedical implantable applications. Square patch with loop structure of 51.2 mm³ (8 mm × 8 mm × 0.8 mm) volume is printed on RT Duroid 5880 (ε_r = 2.2) low permittivity substrate. Parametric study is conducted to optimize the antenna structure. Tissue model is used to take the simulation results and Body Equivalent Solution is used for measuring the antenna performance. Good radiation performance is confirmed by obtaining a gain of −16.7 dBi at 2.45 GHz and a low SAR value of 35.03 W/kg over 10g tissue with input power 1W is obtained. Proposed antenna gives a 64.9% measured wide impedance bandwidth. This study reveals that simple antenna structure can provide good performance when it is placed in complicated environment.