Channel Interferometer Research Articles

Interferometer direction‐finding system with time‐division multiplexing of spread spectrum signals

AbstractA single channel interferometer direction‐finding (DF) system is proposed in this article. The interferometer DF system adopts time‐division multiplexing to receive different antenna phase information, which can effectively eliminate the differences in time delay and channel gain due to different channels. In addition, the spread spectrum signal and integer ambiguity resolution algorithm are used to make the system suitable for low carrier‐to‐noise ratios (CNRs) and high‐frequency signals. The simulations show that the system can measure the angle with root mean square error accuracy at a CNR of 50 dB‐Hz.

A compact single channel interferometer to study vortex beam propagation through scattering layers

We propose and demonstrate a single channel interferometer that can be used to study how vortex beams propagate through a scatterer. The interferometer consists of a multifunctional diffractive optical element (MDOE) synthesized by the spatial random multiplexing of a Fresnel zone plate and a spiral Fresnel zone plate with different focal lengths. The MDOE generates two co-propagating beams, such that only the beam carrying orbital angular momentum is modulated by an annular stack of thin scatterers located at the focal plane of the Fresnel zone plate, while the other beam passes through the centre of the annulus without any modulation. The interference pattern is recorded at the focal plane of the spiral Fresnel zone plate. The scattering of vortex beams through stacks consisting of different number of thin scatterers was studied using the proposed optical setup. Conflicting results have been reported earlier on whether higher or lower charge beams suffer more deterioration. The proposed interferometer provides a relatively simple and compact means of experimentally studying propagation of vortex beams through scattering medium.

Construction of a meteor orbit calculation system for comprehensive meteor observation at Kochi University of Technology

The development of a Ham-band Radio meteor Observation (HRO) Interferometer (IF) at Kochi University of Technology began in 2003. Meteor orbit calculation system uses multi-site radio observation with global positioning system (GPS) timing combined with 5 channel (5 ch) interferometer. The HRO-IF utilizes forward-scattering of 53.750 MHz continuous radio waves transmitted from the Sabae station, realized in 2012. Since the last development, the observation data has been used to study the upper atmosphere from the meteor phenomenon. Here, we introduce the results of the 2015 Geminid meteor shower recorded by forward-scatter multi-site observations as a low-cost and low-power 24/7 continuous meteor observation system, as well as the concept of a comprehensive radio meteor orbit calculation system. As a result, 20 examples of Geminid meteor shower events with 3 levels of noise signal classification recorded in our observations. The predicted Geminid meteor shower speed is about 34 ± 8.86 km/s based on the average value of 12 meteor shower data group in the minimum noise signal category (class A).

Key Distribution using Dual Channel Technique for Ultimate Security

Background: A new approach for the implementation of Quantum Cryptography is proposed in this paper. Quantum Cryptography has practical weakness like lack of authentication, single photon generation and many real time implementation problems. This paper also explains how the drawback of BB84 protocol is eliminated by combining Classical Cryptography and Quantum techniques. Methods: We analyze the usage of Dual Channel Interferometer technique and thereby fusing Quantum techniques with classical technique. And their combination result in the feasibility of authentication, and hacker identification, thereby introducing a novel method of QKD transmission. A quantum digital authentication scheme based on hash function is proposed in this paper .The security of the quantum protocol lies on the existence of quantum one way function by fundamental quantum principle. The practical difficulties in quantum control and quantum computation made quantum protocol hard to implement. The lack of authentication made the quantum protocol vulnerable to hackers. Introducing two level quantum system authentications can be achieved with the help of hash function. To guarantee the authenticity, hash codes are split into two parts and exchange of code is made through two quantum channels. This scheme uses a programmable polarizer ensuring the quantum one way function and removing the practical difficulties of quantum control and quantum computation. The proposed scheme presents a novel method to construct secure quantum authentication for future communication. Result: Dual channel implementation helps in implementing authentication in quantum BB84 protocol. We combined the advantages of quantum techniques and classical techniques and tried to implement a novel technique to ensure secure communication. Application: People use the ATM for transactions such as cash withdrawal, money transfer and payment of electricity and telephone bills. ATM is the most convenient to access the accounts and funding transactions. Personal Identification Number (PIN) is an important aspect of the current ATM system in providing security and it is a commonly used method in protecting the transaction of one’s account.By implementing above technique ATM pin transfer can be successfully made.

Three-Dimensional Imaging by Self-Reference Single-Channel Digital Incoherent Holography.

Digital holography offers a reliable and fast method to image a three-dimensional scene from a single perspective. This article reviews recent developments of self-reference single-channel incoherent hologram recorders. Hologram recorders in which both interfering beams, commonly referred to as the signal and the reference beams, originate from the same observed objects are considered as self-reference systems. Moreover, the hologram recorders reviewed herein are configured in a setup of a single channel interferometer. This unique configuration is achieved through the use of one or more spatial light modulators.

Quantum shot noise in edge channels

AbstractCharge excitations under quantized magnetic field flow in one dimensional‐like strips along the edges of the sample. These excitations (quasiparticles) may behave independently (under weaker fields) or condense to an interacting chiral Luttinger liquid (under stronger fields). Adding a backscattering potential in the path of the quasiparticles, partitions them, hence inducing quantum shot noise that is proportional to their charge and is affected by their correlation. We summarize here our studies of the noise in edge states. At sufficiently low temperatures the correlations among the scattering events are strong, leading to highly non‐linear I –V characteristic and non‐classical shot noise. However, at finite temperatures and weak back scattering, quasiparticles backscatter independently, with noise proportional to e /3, e /5 and e /7 at filling factors 1/3, 2/5, and 3/7. Alternatively, at sufficiently strong backscattering induced bunching of e /3 quasiparticles takes place, with shot noise proportional to e. Diluting the impinging quasiparticles beam mimics an increased temperature, effectively weakening the correlation, rendering the quasiparticles scattering stochastic. Moreover, surprisingly, at finite temperatures (∼50 mK), highly dilute fractionally charged quasiparticle beams are found to traverse almost opaque barriers with no significant bunching. Bunching, however, takes place at lower temperatures. In the opposite case of very weak backscattering potential and at extremely low temperatures (∼9 mK), surprising bunching of quasiparticles takes place: e * = 2e /5 at filling factor 2/5 and e * close to 3e /7 at filling factor 3/7. Under the same conditions, as the temperature increases, (to 25–50 mK) bunching ceases and the scattered charge is again the familiar Laughlin's quasiparticles charge e/m. We show also the shot noise generated by an edge channel interferometer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design of multichannel laser interferometry for W7-X

An eight channel interferometer is developed for density feedback control and the continuous measurement of electron density profiles in the stellarator W7-X. An additional sightline is launched in the geometry of the Thomson scattering for cross calibration. Due to the W7-X coil geometry access is strongly restricted. This motivates the optimization of the sightline geometry and design studies for supplementary chords. In-vessel retroreflectors will be used and inserted in the first wall elements. To cope with associated mechanical vibrations and thermal drifts during the discharges with envisaged duration of 30min either two-color or second harmonic interferometry techniques must be applied. Optimum wavelengths are found to be about 10 and 5μm. A CO2∕CO interferometer (10μm∕5μm) will be tested and compared with an existing CO2∕HeNe test interferometer. A special difficulty of remotely operated diagnostics is the need of long transmission lines with a path length of about 60m required from the diagnostics location to the torus hall and back. Different arrangements will be compared.

Transport in the Laughlin quasiparticle interferometer: Evidence for topological protection in an anyonic qubit

We report experiments on temperature and Hall voltage bias dependence of the superperiodic conductance oscillations in the novel Laughlin quasiparticle interferometer, where quasiparticles of the 1/3 fractional quantum Hall fluid execute a closed path around an island of the 2/5 fluid. The amplitude of the oscillations fits well the quantum-coherent thermal dephasing dependence predicted for a two point-contact chiral edge channel interferometer in the full experimental temperature range 10.2<T<141 mK. The temperature dependence observed in the interferometer is clearly distinct from the behavior in single-particle resonant tunneling and Coulomb blockade devices. The 5h/e flux superperiod, originating in the anyonic statistical interaction of Laughlin quasiparticles, persists to a relatively high T~140 mK. This temperature is only an order of magnitude less than the 2/5 quantum Hall gap. Such protection of quantum logic by the topological order of fractional quantum Hall fluids is expected to facilitate fault-tolerant quantum computation with anyons.

Electron Temperature and Density Profile Measurements During Ion Cyclotron Resonance Heating of Hanbit Magnetic Mirror Device

The electron density and temperature profiles were measured in the central cell of Hanbit magnetic mirror device. The measured data were obtained during radio frequency (RF) discharges with frequencies of 3.5 and 3.75 MHz, and the RF heating power up to 200 kW under various experimental conditions. The radial electron density and temperature profiles were directly measured by a fast injection probe (FIP), and the axial and azimuthal ion saturation currents were measured from fixed array probes. The line integrated electron density was measured from a single channel interferometer and used as a reference signal for the FIP. The electron temperature measurements were carried out different diagnostic methods and compared with each other.

Characterization of fiber Bragg gratings by use of optical coherence-domain reflectometry

A method based on optical low coherence reflectometry for complete characterization of fiber Bragg gratings (FBG's) is presented. It is shown that the measured signal corresponds to the impulse response of the grating filter, and the measurement therefore yields all information about the device. Experiments have been carried out with a novel dual channel interferometer. The results are in excellent agreement with the theory, demonstrating the versatility of the method for characterization of fiber gratings.

A multichannel interferometer for electron density measurements in COMPASS

A compact seven channel interferometer has been designed and built to measure electron density profiles in the COMPASS (compact assembly) tokamak. Two far-infrared (FIR) laser cavities are optically pumped with a single continuous-wave CO2 laser, generating two similar beams at λ=433 μm with a small, tunable difference frequency (0.5–1.0 MHz). The COMPASS facility incorporates a complex set of poloidal field coils close to the vacuum vessel as well as a versatile set of close coupled ‘‘helical’’ resonant magnetic perturbation windings which severely restrict diagnostic access. As a result a novel approach to the optical circuit has been necessary. Wire grid polarizers are used to divide the laser power equally between channels and to overlay probing and local oscillator beams after the probe beams have made a double pass through the plasma. Gaussian beam-mode optics is used to minimize the size of the optical components.

CO2 laser interferometer array for Big Dee

A 12 channel interferometer array is planned for obtaining electron density profiles on Big Dee. Each channel consists of coaxial CO2 and HeNe laser beams. The reference beam is formed by splitting off half of the laser power at each wavelength by using acousto-optic modulators which introduce a 40-MHz frequency shift in the reference beam. The detected interference signals from room-temperature visible and IR detectors are mixed with the 40-MHz drive for the acousto-optic cells. The quadrature mixer signals result in phase information due to vibration and phase-velocity variation in the plasma. Simultaneous solution of the two equations describing the phase shift at the two wavelengths yields the phase shift due only to the plasma effects. The arithmetic operations will be performed digitally in real time by a dedicated microprocessor in each channel. The execution speed of the microprocessor is expected to be sufficient for measuring line integral density in the presence of vibrations of 1-mm amplitude at 1 Hz or 10-μm amplitude at 100 Hz. Phase resolution for each channel is 2π/64 and time between samples is 25 μs. Density profiles are derived from chordal line integral density data by computer tomography.

A 337?m density interferometer for the LT-4 tokamak

A 337 μm HCN laser and a single channel interferometer have been built for measurements of the line-average electron density in the LT-4 tokamak. The design of the system is conventional, using a rotating grating to produce continuous beat notes which are detected by pyroelectric detectors, but with considerable simplifications to reduce cost and complexity. With a beat frequency of 1 kHz the system has a response time of 0.5 ms and a detector-noise limited phase sensitivity of about π/20 (1/40th fringe). The resulting density sensitivity is 8×1011 cm−3 average, for a 20 cm pathlength, but is limited in practice by vibrations to 3×1012 cm−3 for the same pathlength. The system has operated reliably since May 1981.

Multiple Channel Interferometer for Metrology

A multiple channel interferometer was developed and used for the remote monitoring of the dynamic behavior of a large-diameter antenna experiencing simulated solar irradiance in a space simulation chamber. Reversible fringe-counting techniques were employed to measure changes in the distance between the equipment located outside the chamber and each of seven optical retroreflectors mounted on the face of the antenna. After the initial measurement program was completed, the equipment was modified to improve its performance.