Delay Modulation Research Articles

10 Gbit/s Delay Modulation Using a Directly Modulated DFB Laser for a TWDM PON With Converged Services [Invited

A 10 Gbit/s transmission with delay modulation is demonstrated using directly modulated lasers for time- and wavelength-division-multiplexed passive optical networks (TWDM PONs), and error-free performance is achieved over 20 km standard single-mode fiber with a small dispersion penalty. Delay modulation can also mitigate the crosstalk from the TWDM PON downstream signals to the coexisting RF video signal because of its small power spectral density at low frequencies. The carrier-to-crosstalk ratio of the RF video signal is improved by about 10 dB using delay modulation, instead of nonreturn-to-zero (NRZ) modulation, for 10 Gbit/s downstream transmissions in a TWDM PON. Furthermore, using low-pass-filtered 2.5 Gbit/s NRZ modulation and bandpass-filtered 10 Gbit/s delay modulation, dual-rate transmission is demonstrated for converged services in a TWDM PON. Experimental results exhibit 37.7 and 25.7 dB power budgets, respectively, for simultaneous 2.5 and 10 Gbit/s transmissions over 20 km standard single-mode fiber.

Improving the resolution in proton-detected through-space heteronuclear multiple quantum correlation NMR spectroscopy

Connectivities and proximities between protons and low-gamma nuclei can be probed in solid-state NMR spectroscopy using two-dimensional (2D) proton-detected heteronuclear correlation, through Heteronuclear Multiple Quantum Correlation (HMQC) pulse sequence. The indirect detection via protons dramatically enhances the sensitivity. However, the spectra are often broadened along the indirect F1 dimension by the decay of heteronuclear multiple-quantum coherences under the strong 1H–1H dipolar couplings. This work presents a systematic comparison of the performances of various decoupling schemes during the indirect t1 evolution period of dipolar-mediated HMQC (D-HMQC) experiment. We demonstrate that 1H–1H dipolar decoupling sequences during t1, such as symmetry-based schemes, phase-modulated Lee–Goldburg (PMLG) and Decoupling Using Mind-Boggling Optimization (DUMBO), provide better resolution than continuous wave 1H irradiation. We also report that high resolution requires the preservation of 1H isotropic chemical shifts during the decoupling sequences. When observing indirectly broad spectra presenting numerous spinning sidebands, the D-HMQC sequence must be fully rotor-synchronized owing to the rotor-synchronized indirect sampling and dipolar recoupling sequence employed. In this case, we propose a solution to reduce artefact sidebands caused by the modulation of window delays before and after the decoupling application during the t1 period. Moreover, we show that 1H–1H dipolar decoupling sequence using Smooth Amplitude Modulation (SAM) minimizes the t1-noise. The performances of the various decoupling schemes are assessed via numerical simulations and compared to 2D 1H–{13C} D-HMQC experiments on [U–13C]–L-histidine⋅HCl⋅H2O at various magnetic fields and Magic Angle spinning (MAS) frequencies. Great resolution and sensitivity enhancements resulting from decoupling during t1 period enable the detection of heteronuclear correlation between aliphatic protons and ammonium 14N sites in L-histidine⋅HCl⋅H2O.

A 13.56-mbps pulse delay modulation based transceiver for simultaneous near-field data and power transmission.

A fully-integrated near-field wireless transceiver has been presented for simultaneous data and power transmission across inductive links, which operates based on pulse delay modulation (PDM) technique. PDM is a low-power carrier-less modulation scheme that offers wide bandwidth along with robustness against strong power carrier interference, which makes it suitable for implantable neuroprosthetic devices, such as retinal implants. To transmit each bit, a pattern of narrow pulses are generated at the same frequency of the power carrier across the transmitter (Tx) data coil with specific time delays to initiate decaying ringing across the tuned receiver (Rx) data coil. This ringing shifts the zero-crossing times of the undesired power carrier interference on the Rx data coil, resulting in a phase shift between the signals across Rx power and data coils, from which the data bit stream can be recovered. A PDM transceiver prototype was fabricated in a 0.35- μm standard CMOS process, occupying 1.6 mm(2). The transceiver achieved a measured 13.56 Mbps data rate with a raw bit error rate (BER) of 4.3×10(-7) at 10 mm distance between figure-8 data coils, despite a signal-to-interference ratio (SIR) of -18.5 dB across the Rx data coil. At the same time, a class-D power amplifier, operating at 13.56 MHz, delivered 42 mW of regulated power across a separate pair of high-Q power coils, aligned with the data coils. The PDM data Tx and Rx power consumptions were 960 pJ/bit and 162 pJ/bit, respectively, at 1.8 V supply voltage.

A spin light emitting diode incorporating ability of electrical helicity switching

Fabrication and optical characteristics of a spin light-emitting-diode (spin-LED) having dual spin-injection electrodes with anti-parallel magnetization configuration are reported. Alternating a current between the two electrodes using a computer-driven current source has led us to the observation of helicity switching of circular polarization at the frequency of 1 kHz. Neither external magnetic fields nor optical delay modulators were used. Sending dc-currents to both electrodes with appropriate ratio has resulted in continuous variation of circular polarization between the two opposite helicity, including the null polarization. These results suggest that the tested spin-LED has the feasibility of a monolithic light source whose circular polarization can be switched or continuously tuned all electrically.

TDC Implementation Based on Internal Delay Module of FPGA

Currently the time to digital converter (TDC) integrated in FPGA performs time-to-digital conversion in the carry chain mode and inter-slot offset is caused to be severe by internal wiring in the FPGA. Based on the carry chain interpolation method, this paper proposes the method for using a delay module in FPGA to achieve accurate signal delay. By calculating the phase difference of multi-clock signal between two latch sampling points, the interval between two sampling points was obtained. Experimental results indicate a measurement accuracy of 78ps or 52ps can be reached by precisely collecting time through the delay module in FPGA. Compared to the carry chain interpolation method, this method is significantly advantageous in small inter-slot offset, stable performance and convenient design and can meet the requirement for time measurement or requirement by laser interferometer with a nm-level accuracy in nuclear physics.

Group delay modulation for pulse position coding based on periodically coupled C-sections

Chipless radio frequency identification (RFID) is an emerging research area nowadays. The recent development in this area proves its efficiency to compete with low cost identification systems like barcodes in the upcoming years. Chipless RFID encodes data using different kinds of spectral signature produced from some planar images as in the case of barcodes, the difference here is those images are made with conductive materials. Among the different ways of information encoding, a powerful way of encoding is time domain approach. This paper incorporates a tag using group delay encoding. The proposed chipless tag is composed of commensurate cascaded transmission line sections coupled at alternative ends (also known as C-sections). It consists of single group of C-sections. However, in order to increase the coding capacity, the proposed tag can allow multi-frequencies also. In addition to this, the tag is also compatible with commercial ultra wide band radar. The proposed tag is validated experimentally. It exhibits a good reading range of 1.2 m.

Hybrid Photonic True-Time Delay Modules for Quasi-Continuous Steering of 2-D Phased-Array Antennas

Hybrid photonic true-time delay modules for phased-array antennas are designed and demonstrated. Continuously tunable true-time delay network based on highly dispersive photonic bandgap fiber (up to 2135 ps/nm/km at 1570 nm), combined with a programmable true-time delay network utilizing optical waveguide delay line and optical switches, provides the antenna with quasi-continuous steering ability. Far-field patterns are simulated and measured to confirm the squint-free beam steering.

Ole Rømer's method still on the stage: the study of two bound eclipsing binaries in quintuple system V994 Her

More than three hundred years ago, Ole Romer measured the speed of light only by observing the periodic shifting of the observed eclipse arrival times of Jupiter's moons arising from the varying Earth-Jupiter distance. The same method of measuring the periodic modulation of delays is still used in astrophysics. The ideal laboratories for this effect are eclipsing binaries. The unique system V994 Her consists of two eclipsing binaries orbiting each other. However, until now it was not certain whether these are gravitationally bound and what their orbital period is. We show that the system is in fact quintuple and the two eclipsing binaries are orbiting each other with period about 6.3 years. This analysis was made only from studying the periodic modulation of the two periods, when during the periastron passage one binary has an apparently shorter period, while the other one longer, exactly as required by a theory. Additionally, it was found that both inner eclipsing pairs orbit with slightly eccentric orbits undergoing a slow apsidal motions with a period of the order of centuries.

ALL-OPTICAL DELAY MODULE USING CASCADED POLYMER ALL-PASS-FILTER RING RESONATORS

An APF (All-Pass Filter) delay module in which eight single-ring resonators are serially cascaded is designed and fabricated. The polymer waveguide used for the realization of the APF delay module is a buried structure whose core width and height are 1.5m. The core and cladding index are 1.51 and 1.378, respectively, which corresponds to the relative index difierence of 8%. In order to use a thermo-optic efiect of polymer materials, electrodes are evaporated above the ring resonator to provide heating currents. The time delay is measured to be about 50ps when 2 rings are in resonance, and about 105ps and 150ps, respectively, when 4 and 6 rings of APF are in resonance, respectively. When all of 8 rings are in resonance, the delay is measured to be about 200ps.

Synchronized operation by field programmable gate array based signal controller for the Thomson scattering diagnostic system in KSTAR

The Thomson scattering diagnostic system is successfully installed in the Korea Superconducting Tokamak Advanced Research (KSTAR) facility. We got the electron temperature and electron density data for the first time in 2011, 4th campaign using a field programmable gate array (FPGA) based signal control board. It operates as a signal generator, a detector, a controller, and a time measuring device. This board produces two configurable trigger pulses to operate Nd:YAG laser system and receives a laser beam detection signal from a photodiode detector. It allows a trigger pulse to be delivered to a time delay module to make a scattered signal measurement, measuring an asynchronous time value between the KSTAR timing board and the laser system injection signal. All functions are controlled by the embedded processor running on operating system within a single FPGA. It provides Ethernet communication interface and is configured with standard middleware to integrate with KSTAR. This controller has operated for two experimental campaigns including commissioning and performed the reconfiguration of logic designs to accommodate varying experimental situation without hardware rebuilding.

LLRF and timing system for the SCSS test accelerator at SPring-8

The 250MeV SCSS test accelerator as an extreme-ultra violet (EUV) laser source has been built at SPring-8. The accelerator comprises a 500kV thermionic gun, a velocity bunching system using multi-sub-harmonic bunchers (SHB) in an injector and a magnetic bunch compressor using a chicane of 4 bending magnets, a 5712MHz main accelerator to accelerate an electron beam up to 250MeV, and undulators to radiate the EUV laser. These bunch compression processes make short bunched electrons with a 300A peak current and a 300fs pulse width. The pulse width and peak current of an electron beam, which strongly affect the pulse width and intensity of the laser light, are mainly decided by the pulse compression ratio of the velocity bunching and the magnetic bunch compressing processes. The compression ratio is also determined due to an energy chirp along the beam bunch generated by an off-crest rf field at the SHB and cavities before the chicane. To constantly keep the beam pulse-width conducted by rf and timing signals, which are temporally controlled within subpicoseconds of the designed value, the low-level rf and timing system of the test accelerator has been developed. The system comprises a very low-noise and temporally stable reference signal source, in-phase and quadrature (IQ) modulators and demodulators, as well as VME type 12 bits analog-to-digital and digital-to-analog converter modules to manipulate an rf phase and amplitude by IQ functions for the cavity. We achieved that the SSB noise of the 5712MHz reference signal source was less than −120dBc/Hz at 1kHz offset from the reference frequency; the phase setting and detecting resolution of the IQ-modulators and demodulators were within +/−0.5° at 5712MHz. A master trigger VME module and a trigger delay VME module were also developed to activate the components of the test accelerator. The time jitter of the delay module was less than 0.7ps, sufficient for our present requirement. As a result, a beam energy variation of 0.06% was achieved and a time jitter of 46fs between the acceleration rf signal and the beam was realized.

Mass ratio from Doppler beaming and Rømer delay versus ellipsoidal modulation in the Kepler data of KOI-74★

We present a light curve analysis and radial velocity study of KOI-74, an eclipsing A star + white dwarf binary with a 5.2 day orbit. Aside from new spectroscopy covering the orbit of the system, we used 212 days of publicly available Kepler observations and present the first complete light curve fitting to these data, modelling the eclipses and transits, ellipsoidal modulation, reflection, and Doppler beaming. Markov Chain Monte Carlo simulations are used to determine the system parameters and uncertainty estimates. Our results are in agreement with earlier studies, except that we find an inclination of 87.0 \pm 0.4\degree, which is significantly lower than the previously published value. We find that the mass ratio derived from the radial velocity amplitude (q=0.104 \pm 0.004) disagrees with that derived from the ellipsoidal modulation (q=0.052 \pm 0.004} assuming corotation). This was found before, but with our smaller inclination, the discrepancy is even larger than previously reported. Accounting for the rapid rotation of the A-star is found to increase the discrepancy even further by lowering the mass ratio to q=0.047 \pm 0.004. These results indicate that one has to be extremely careful in using the amplitude of an ellipsoidal modulation signal in a close binary to determine the mass ratio, when a proof of corotation is not firmly established. The radial velocities that can be inferred from the detected Doppler beaming in the light curve are found to be in agreement with our spectroscopic radial velocity determination. We also report the first measurement of R{\o}mer delay in a light curve of a compact binary. This delay amounts to -56 \pm 17 s and is consistent with the mass ratio derived from the radial velocity amplitude. The firm establishment of this mass ratio at q=0.104 \pm 0.004 leaves little doubt that the companion of KOI-74 is a low mass white dwarf.

Backward influence of the interference signal from the sensors of physical quantities on the radiation intensity spectrum of a low-coherent source

We consider specific features of optical-circuit operation in the presence of radiation which is returned to the source after having passed an optical path exceeding the initial coherence length of the reference wave when, as was previously assumed, the delay modulation should not influence the oscillation mode. However, experiments with the Michelson and Sagnac fiber interferometers showed that intensity modulation of the interference signal and, therefore, intensity modulation of the source radiation related to the active-medium nonlinearity appear when the interfering waves with the phase-difference modulation return. The revealed effect leads to distortion of a signal at the interferometer output irrespectively of the delay time and can be removed by placing an optical isolator at the source output.

Stability Analysis of Machining with Spindle Speed Variation

In this paper the chatter stability of turning and full-immersion milling operations with spindle speed variation is studied. We present a method to calculate the stability lobes in the limit of very low and very high frequencies of the delay modulation. These approximations help to classify the results of numerically exact methods, as for example semi-discretization or multi-frequency approaches. For slowly time-varying delay, the position of the stability lobes is understandable from a simple connection between the lobes for constant and time-varying delay. Furthermore, this method can be used to estimate the efficiency of an application of spindle speed variation and helps to find optimal parameters for it.

Phase drift cancellation of remote radio frequency transfer using an optoelectronic delay-locked loop

In this Letter, we propose a phase drift cancellation method for remote radio frequency transfer. Phase fluctuation along the transmission fiber, which is induced by temperature and pressure changes, is measured and compensated by a heterodyne optoelectronic delay-locked loop. The control loop consists of a heterodyne optoelectronic phase detector, a microwave delay module, and the loop filter. We demonstrate the concept by transmitting a 10 GHz microwave frequency over 50 km single-mode fiber, with subpicosecond jitters measured at the remote end.

UCTM: A user friendly configurable trigger, scaler and delay module for nuclear and particle physics

A configurable trigger scaler and delay NIM module has been designed to equip nuclear physics experiments and lab teaching classes. It is configurable through a Graphical User Interface (GUI) and provides a large number of possible trigger conditions without any Hardware Description Language (HDL) required knowledge. The design, performances and typical applications are presented.

Enhancing signal detection and completely eliminating scattering using quasi-phase-cycling in 2D IR experiments

We demonstrate how quasi-phase-cycling achieved by sub-cycle delay modulation can be used to replace optical chopping in a box-CARS 2D IR experiment in order to enhance the signal size, and, at the same time, completely eliminate any scattering contamination. Two optical devices are described that can be used for this purpose, a wobbling Brewster window and a photoelastic modulator. They are simple to construct, easy to incorporate into any existing 2D IR setup, and have attractive features such as a high optical throughput and a fast modulation frequency needed to phase cycle on a shot-to-shot basis.

Instantaneous Microwave Frequency Measurement Using Programmable Differential Group Delay (DGD) Modules

We propose and experimentally demonstrate a photonic approach for the measurement of microwave frequencies with adjustable measurement range and resolution. After an unknown microwave signal is modulated onto an optical carrier by a Mach-Zehnder modulator (MZM), the optical output of the MZM is sent to two programmable differential group delay (DGD) modules to introduce different microwave power fading effects, respectively. When the microwave powers of the two channels are measured with two photodetectors separately, a fixed relationship between the microwave power ratio and the microwave frequency is established. The frequency measurement range and resolution can be tuned by electrically varying the DGD values. Frequency measurement with good accuracy for the microwave signals is experimentally realized. When the input power of a continuous-wave microwave signal is within the range of 15 to 3 dBm, the measured errors remain within 0.04 GHz for a measurement range of 4.5-6.5 GHz.

Photonic Beamformer Receiver With Multiple Beam Capabilities

A multiple-beam photonic beamforming receiver is proposed and demonstrated. The architecture is based on a large port-count demultiplexer and fast tunable lasers to achieve a passive design, with independent beam steering for multiple beam operation. A single true time delay module with four independent beams is experimentally demonstrated, showing extremely smooth RF response in the -band, fast switching capabilities, and negligible crosstalk.

Pseudo-Random Binary Sequence Selection for Delay and Add Direct Sequence Spread Spectrum Modulation Scheme

Recently, correlation delay shift keying (CDSK) has been proposed as a modulation scheme for noncoherent detection which inherits the advantages of conventional spread-spectrum communications using a chaotic reference signal. The CDSK modulation scheme transmits the sum of a chaotic reference signal with its delayed modulated version. In this paper, we consider the utilisation of pseudo-random binary sequences (PRBS) instead of chaotic reference signals. This new modulation scheme is defined as the delay and add direct sequence (DADS) modulation scheme. DADS offers some interesting properties compared to CDSK, mainly the possibility to select some PRBS which improves the BER performance. To this end, a new criterion for PRBS selection is proposed. Theoretical analysis and simulation results show that the BER performance of CDSK is comparable to DADS with arbitrary PRBS, however the DADS performance can be improved by 3 dB with PRBS selection.