Q-factor Values Research Articles

Performance characterization of a closed-loop chaotic communication system including fiber transmission in dispersion shifted fibers

The transmission performance of an all-optical closed-loop chaotic communication system is numerically studied, assuming various span lengths of dispersion shifted fiber between transmitter and receiver. Calculation of the mean synchronization error and Q-factor values obtained from the corresponding eye diagrams has been carried out for two encoding methods (chaotic modulation and chaos shift keying) and two repetition rates (2.4 and 5 Gbps). It is shown that transmission impairments including chromatic dispersion, fiber nonlinearity, fiber losses, and amplified spontaneous emission noise of the inline amplifiers degrade significantly the synchronization quality especially when high-bit-rate message encoding is applied. The influence of key system parameters such as launched optical power, amplifier spacing, positive or negative dispersion, etc., to the transmission performance has been investigated. Acceptable system performance can be achieved for approximately 200 km at 2.4 Gbps.

Transparent Monitoring of Rise Time Using Asynchronous Amplitude Histograms in Optical Transmission Systems

This paper describes the analysis, simulations, and proof-of-principle experiment on transparent monitoring of relative rise time using asynchronously sampled amplitude histograms in optical transmission systems. The method described is based on the count in a selected amplitude window between the mark and space levels. The method is evaluated under various amplitude windows and Q-factor values and is compared with synchronously sampled eye-diagram-based measurements. The results demonstrate that the 40-60% amplitude window is generally suitable for system rise-time monitoring purposes without clock information.

Performance of Open-Loop All-Optical Chaotic Communication Systems Under Strong Injection Condition

A numerical investigation of the performance of an open-loop optical chaotic communication system for the isochronous synchronization solution has been carried out, under strong optical injection conditions achieved using antireflective coating at the input facet of the receiver laser in combination with an optical erbium-doped fiber amplifier (EDFA). Different message encoding techniques have been considered and tested at multigigabit rates and for different levels of optical injection to the receiver. The effects induced by the amplified spontaneous emission (ASE) noise of the EDFA to the performance of the chaotic communication system have also been studied. The performance of all the examined encryption methods for the 1 Gb/s bit-rate messages was quite satisfactory and was characterized by Q-factor values that exceeded 10, after synchronizing in the strong injection regime. For higher message bit rates, the Q-factor values for all methods decrease considerably due to the residual frequency components of the chaotic carrier that are now more significant in the message spectral region. The effect of the amplifier's ASE noise to the system's performance was deteriorated as long as the EDFA chaotic input was kept in relatively high power levels.

Optical fiber microcoil resonators

The optical microfiber coil resonator with self-coupling turns is suggested and investigated theoretically. This type of a microresonator has a three-dimensional geometry and complements the well-known Fabry-Perot (one-dimensional geometry, standing wave) and ring (two-dimensional geometry, traveling wave) types of microresonators. The coupled wave equations for the light propagation along the adiabatically bent coiled microfiber are derived. The particular cases of a microcoil having two and three turns are considered. The effect of microfiber radius variation on the value of Q-factor of resonances is studied.

Flat coil-based tunnel diode oscillator enabling to detect the real shape of the superconductive transition curve and capable of imaging the properties of HTSC films with high spatial resolution

Owing to a pick-up coil's flat design, relatively low MHz-range operation frequency, and six orders relative resolution a flat coil-based tunnel diode oscillator has advantages, compared to all other methods. They become crucial in studies with thin high-Tc superconductivity (HTSC) materials (with small signals), especially at the start of the Cooper pairs’ formation. Due to this the superconductivity precursor ‘paramagnetic’ effect was detected recently in YBaCuO films at N/S transition. It precedes Meissner ejection and specifies details of the shape of the transition curve. We discuss the influence of the currents on this effect, and the relationship between the quality of the material and the shape of the effect. A new imaging device has also been created based on this test method (using a focused He–Ne laser beam as a probing signal), capable of imaging the properties of HTSC films with ∼3μm spatial resolution. The method is based on detection of the inductance and Q-factor value changes of a single-layer flat coil, placed at the face of the sample. This leads to frequency and/or amplitude changes of the stable oscillator. The test device enabled 2D-mapping of the grain structure of a bridge-shaped YBaCuO film. Basically, the method is capable of imaging 2D-current distribution in thin HTS with sub-μm spatial-resolution, using non-bolometric response. However, the achieved resolution ∼3μm of a bolometric nature (in a given device with 3.5mm-size coil) by no means is limited by the abilities of the method, but mainly, it depends on how narrowly it is possible to focus the probing beam, while the own resolution of a present flat coil-based technique is better than 0.1μm, and can be improved essentially by reducing the coil size.

Performance characterization of high-bit-rate optical chaotic communication systems in a back-to-back configuration

A comparative study of three data-encoding techniques in optical chaotic communication systems is reported. The chaotic carrier is generated by a semiconductor laser subjected to optical feedback and the data are encoded on it by chaotic modulation (CM), chaotic masking (CMS), or chaotic shift keying (CSK) methods. In all cases, the receiver-which is directly connected to the transmitter-consists of a semiconductor laser similar to that of the transmitter subjected to the same optical feedback. The performance of this back to back configuration is numerically tested by calculating the Q-factor of the eye diagram of the received data for different bit rates from 1 to 20 Gb/s. The CM scheme appears to have the best performance relative to the CMS and CSK scheme, before and after filtering the residual high-frequency oscillations remaining due to nonperfect synchronization between the transmitter and receiver. Moreover, in all encoding methods, a decrease in the Q-factor is observed when the repetition bit-rate of the encoding message increases. In order to achieve as high Q-factor values as possible, a well-synchronized chaotic master-slave system is required.

A Study to Determine an Effective Ground-Shield Structure for a Silicon On-Chip Spiral Inductor

This paper describes a study to improve the quality factor (Q-factor) of a silicon-on-chip spiral inductor by determining the most appropriate shape and structure of inductor wires and a ground shield. Electro-magnetic field simulation is carried out under the condition that the spiral inductor is formed on a P-substrate with an electric conductivity of 10 [Ω -1 m -1 ] in assuming the use of a conventional CMOS process. After assessing the simulation results, we propose a new, ring-type structure for the wires and a comb-shaped ground shield that is placed under the inductor wires only. This comb-like shape reduces the stray capacitance between the shield and the inductor wires. As the Q-factor value of a spiral inductor depends on the distance between the ground shield and the inductor wires, as well as on the resistivity of the ground shield material, those influences are also clarified. As a result, we obtain 15% to 23% increases in the Q-factor values in the frequency range of 2 to 3.5 GHz for a 7 nH inductor. We also identify a material possessing the appropriate resistivity to serve as a ground shield.

Miniaturized, highly sensitive single-chip multichannel quartz-crystal microbalance

A miniaturized highly sensitive single-chip multichannel quartz-crystal microbalance prepared by deep reactive ion etching is presented. In the present work, quartz resonators in a single-chip with the diameters in the range 0.05–1.0 mm and thicknesses in the range 18–82 μm were fabricated. The conductance measurements carried out on the resonators showed that the Q factor is inversely proportional to resonator thickness. The Q-factor value as high as ∼30 000 has been observed in case of a 94 MHz resonator whose diameter is 1 mm and the thickness 17.8 μm. The Q factor of a resonator of very small diameter (0.1 mm) reached the value 5700.

Peculiarities of the magnetic phase diagram in small-size untwinned YBa 2Cu 3O y crystal constructed by highly sensitive OFC-magnetometer

We applied OFC-magnetometer (open-flat coil-based tunnel diode oscillator) to study fine peculiarities of vortex flow and magnetic phase (MP) transitions between different phases of the vortex-matter in a high quality YBa 2Cu 3O y crystal. The method is based on a detection of the inductance and Q-factor value changes of a single-layer flat coil, which is placed at a face of flat sample. These finally lead to frequency and/or amplitude changes of the oscillator. Simultaneous frequency and amplitude tests enabled to construct the vortex MP-diagram for untwinned YBa 2Cu 3O y crystal with (0.25×0.6) mm 2 area and ∼50 μm-thick in the temperature range of 65 K to T c and the field of 0–12 T. In outlines, the plotted diagram is similar to the one defined by several other methods such as SQUID and cantilever magnetometers, etc. for the same crystal. However, our technique revealed clear separation of the lines on a diagram below the upper critical point H ucp i.e., no kink point was observed in our method. The amplitude tests revealed also some new lines on a diagram below the lower critical point H lcp (close to T c). The obtained results may help us to understand the behavior of the vortex-mater and its dynamics in HTS materials. The problem how to improve resolution of the method for very small-size HTS objects is also discussed.

Precise measurements of the Q factor of dielectric resonators in the transmission mode-accounting for noise, crosstalk, delay of uncalibrated lines, coupling loss, and coupling reactance

Accurate measurements of the unloaded Q/sub 0/ factor of microwave resonators are necessary in many microwave applications. The most accurate values of Q/sub 0/ can be obtained by Q-circle fits from multifrequency S-parameter data. Practical measurement systems cause S-parameters of the resonators to be distorted from the circular ideal shape, rotated, and shifted from the origin resulting in errors in the Q-factor values. A novel Q-factor measurement method has been developed based on equations derived for resonators working in the transmission mode and fractional linear circle-fitting techniques. The transmission-mode Q-factor (TMQF) technique removes measurement effects of noise, noncalibrated measurement cables, connectors, coupling structures, crosstalk between the coupling loops, and impedance mismatch from the measurement data. The TMQF is especially useful in cryogenic measurements of high-temperature superconducting thin films and dielectrics since these measurements are typically done in the transmission mode and contain cables and connectors that are difficult to calibrate. The accuracy of the TMQF is better than 1% for practical measurement ranges and the method is applicable to a wide range of coupling. The range of Q factors measurable is from 10/sup 3/ up to 10/sup 7/.

Microstructural Characterization of Sintered Ba(Mg ⅓ Ta ⅔)O3 Materials by Transmission Electron Microscopy and Convergent Beam Electron Diffraction

AbstractDevelopment of high performance dielectric materials is required to facilitate the trend towards miniaturization of microwave communications circuits. A novel two-step sintering process has been found that enhances the value of (Q-factor) (frequency) (QF)product of Ba(Mg ⅓ Ta ⅔)O3 (BMT). Detailed examination of samples densified in this way gives not only details of the grain size, defect content and state of order of the ordered perovskite grains but also reveals the presence of a number of previously unreported phases. These new phases have been examined by TEM using energy dispersive X-ray analysis to give them approximate chemical composition and convergent beam electron diffraction to determine their crystallography. Large unit cells are found which are evidently related to compounds studied previously in the x 3 BaMnO - system. The results will be discussed in relation to the enhanced performance of the materials.

The possibility of detection of small absorption in HTS thin films by means of the highly sensitive OFC magnetometer

We have essentially widened the capabilities of the open-flat coil-based tunnel diode oscillator technique (OFC magnetometer) for simultaneous tests of magnetic penetration depth, λ, of rf magnetic field and for detection of small changes of absorption inside the thin plate-like HTS materials. The updated method is based on simultaneous detection of the inductance and Q-factor value changes of the unusual flat (single-layer open-faced geometry) coil-based MHz-range resonator, which finally leads to the resonant frequency and amplitude changes of the oscillator. Our technique enables detecting the changes ∼10 −12 H of HTS film's magnetic inductance (the changes ∼1–3 Å of λ). It detects also the changes ∼10 −9 W of testing field's power absorption by the film, originated from the variation of its internal flux distribution (due to vortex flow during the suppression of superconductivity by external magnetic field). It can operate in wide ranges of temperature and magnetic field and measure in wide dynamic ranges of the testing parameters. We present the test results of the 0.2 μm thick and a few millimeter in diameter disk- and ring-shaped YBaCuO films illustrating wide capabilities of the updated OFC magnetometer to study weakly expressed peculiarities of superconductive state related, in particular, with the insignificantly small absorption at vortex motion.

The origin of Λ-doubling effect for the B 1∏ and D 1∏ states of NaK

The origin of Λ-doubling effect (q factors) for the regularly perturbed NaK B 1∏ and D 1∏ states has been investigated by means of ab initio many-body multipartitioning perturbation theory calculation of the electronic L-uncoupling matrix elements between the examined ∏1 and five lowest ∑+1 states for both Na3923K and Na4123K isotopomers. The hypothesis of pure precession was found to be valid for the B 1∏–A 1∑+ and D 1∏–C 1∑+ pairs of the interacted states, while the unique perturber approximation works properly for the D 1∏ state and completely breaks down for the B 1∏ state. The theoretical rovibronic q-factor values estimated for both states by means of the approximate sum rule agree well with their experimental counterparts and demonstrate high sensitivity to vibrational and rotational quantum numbers.

Measurement of the Parameters of the Dielectric Windows of the Linear Collider TESLA Cavities

A setup for measuring the permittivity and the loss parameter of ceramic samples is described. The setup operation is based on a conventional method for measuring changes in the frequency and Q-factor values of cavities caused by insertion of experimental samples into the cavity. Cylindrical ceramic samples with the permittivity e = 8–10 and loss parameter tan δ = (2–4) × 10–4 were studied. A cylindrical E010 cavity with a cutoff waveguide attached to one of the faces of the cavity was selected, because it provided sufficient accuracy of measurement and could be effectively used for testing series of samples of various sizes and shapes at a fixed frequency of 1300 MHz. It was shown that the permittivity of various samples could be determined with an accuracy of 1.5%, whereas the loss parameter could be determined with an accuracy of 7%.

New type detectors of particles and radiation based on HTSC materials

We developed an open-flat coil preparation technology allowing to make coils with high Q-factor values. It permits to develop a new measuring device based on a tunnel diode oscillator with such nontraditional open-flat coil. Such devices are very sensitive to the small changes of distances between the metallic planes and the coil's flat surface. The resolution is about (3-4) /spl Aring/. It permits to study small changes of the magnetic penetration depth in HTSC with the same resolution. New method allow to detect the S/N transitions of both the spherical shape single tin (Sn) grains with diameters up-to (2-3) /spl mu/m and 0.5 /spl mu/m thick and 4 /spl mu/m/spl times/5 /spl mu/m YBCO films. Such high resolution permits to use such devices in various areas of science and technology. Particularly, they may be used for the creation of a new detectors of particles and radiation based on HTSC materials. The basic principles and few designs of new detectors are presented suitable for various applications. The sensitivities achieved are: about 10/sup -11/ W/cm/sup 2/ for the visible spectrum radiation; about 0.1 mOe/cm/sup 2/ for the magnetic fields, and 0.1 /spl mu/A/cm/sup 2/ for the currents in HTSC films. Possible directions of the further improvement of the devices' features and also improvement of detectors' parameters are also suggested.

Optimized calibration curve for size exclusion chromatography applied to poly(vinyl chloride)

The problem of using a polystyrene-standard-based calibration curve for other polymers has been overcome by developing an algorithm based on the concept of parameter estimation and optimization. The algorithm modifies the regression coefficients of the polystyrene-standard-based calibration curve by interactively using the chromatographic output and the absolute number-average molecular weight of the experimental polymer. Analytical expressions have been derived for calculating the directional derivatives, which ensure rapid convergence of the objective function. The algorithm, applied to commercial poly(vinyl chloride), offered a number-average molecular weight of 32037 whereas that measured by membrane osmometry is 32 000. The polymer characterization parameters calculated from the optimized calibration curve closely matched those obtained from the universal calibration curve and Q-factor values. The algorithm needs no narrow standard of the experimental polymer, and holds for homopolymers, copolymers and polymer blends. It can be easily incorporated into commercial size exclusion chromatography data-reduction software packages.

Gyrator implementation from commercially available transimpedance operational amplifiers

A new configuration for a gyrator which is implemented from two commercially available transimpedance operational amplifiers (opamps) and uses only three passive components is described. A filter exhibiting simultaneously two transfer functions, bandpass and highpass (or lowpass), has been implemented from this gyrator. It is characterised by a Qfactor value which is adjustable from a passive component, without modifying coo. Experimental results which confirm the theoretical analysis are given and discussed. They have been obtained using the AD 844 AN transimpedance opamp from Analog Devices.

The determination of deep level concentrations in high resistivity semiconductors by DLTS, with special reference to germanium

When studying trapping centres in ultra-high-purity, quasi-intrinsic semiconductors by deep level transient spectroscopy (DLTS), considerable errors may be introduced in applying the original small theory. In the present work expressions are presented, which allow a more accurate determination of deep level concentrations with DLTS in the case of: (i) high relative trap concentrations rT (0<tT<or=1); (ii) the application of filling pulses covering only part of the depletion region; (iii) high resistivity material, giving rise to appreciable values of the diode Q-factor, as is the case for high-purity germanium (HP-Ge) in particular. A general trap concentration formula is proposed, which is suitable for routine calculations of rT in high resistivity material. It is furthermore shown that under certain conditions, a C-V analysis of HP-Ge diodes leads to the correct value of the net ionised impurity density. This way of obtaining the residual shallow level density, as compared to Hall measurements, is discussed.

Fast risetime InP oscillators employing cavity stabilisation and pulsed priming techniques

A high-peak-power short-pulse-length J-band (10-20 GHz) oscillator using high-efficiency InP devices is described. The circuit techniques employed enable simultaneous satisfaction of the conflicting requirements of a well defined fast RF risetime and extremely good frequency stability during the pulse. Incoherent phase-priming and cavity stabilisation techniques are described.A theoretical treatment is given on the problem of cavity stabilisation techniques for chirp suppression in pulsed oscillators using resonant structures coupled into the output transmission line. For a given pulse length, there exists an optimum value of cavity Q-factor to obtain maximum chirp reduction for minimum insertion loss. The design of this cavity is discussed in detail and some implications on device design and processing techniques to minimise transient thermal impedance are outlined.

Design of filters with prescribed time response and Chebyshev stopband attenuation

This paper presents a new class of low pass filters with Chebyshev stopband attenuation which are intended for pulse applications and characterized by very small values of the dominant polo Q-factor, Their transfer functions are obtained by computational optimization in the time domain of either step response or impulse response under the constraint of double or higher-order multiplicity of the dominant pair of poles. The comparison with Schüssler filters, which are known for their excellent rise-time-overshoot characteristics, reveals that the new filters yield superior frequency and time domain characteristics and yet they have much smaller values of the dominant pole Q-factor. The pole locations and other important frequency and time-domain parameters are tabulated for optimum step response and for optimum impulse response for n = 5, 6, 7, 8 and several values of the maximum tolerable overshoot.