Time Division Multiplexing Technique Research Articles

1.5 μm polarization coherent lidar incorporating time-division multiplexing.

Atmospheric depolarization ratio and wind velocity are measured simultaneously by a single versatile coherent Doppler lidar (CDL). Backscattering components at parallel and perpendicular polarization states are obtained by using a single balanced detector, adopting time-division multiplexing technique. Thus systematic error induced by the non-uniform response of different detectors in traditional lidars is avoided. The operation mode of the instrument can be switched from polarization CDL to traditional CDL by the user depending on atmospheric conditions and desired performance. As demonstrated, the perpendicular component of the backscattering, usually wasted, not only can be used to retrieve the ADR, but also can be used to improve the carrier to noise ratio in wind detection. In the traditional mode, given a tolerance of 0.5 m/s precision, a detection range of 6 km is achieved by using a 300 ns laser pulse with energy of 100 μJ, where the temporal and spatial resolution of 2 s and 60 m, respectively. Continuous wind detection of the atmospheric boundary layer over 26 hours is presented to demonstrate the robustness and stability of the system. Dynamic evolution and wind structure are recorded.

Optimization of the Microwave Properties of the Kinetic-Inductance Bolometer (KIBO)

Silicon nitride membrane based cryogenic bolometers exhibit high sensitivity and enable ultra-sensitive detector applications. Multi-pixel instruments were already introduced as devices for submillimeter-wave imaging. Nevertheless, the numbers of pixels are limited by the readout process which is typically a time-division multiplexing or code-division multiplexing technique. To overcome this challenge, a replacement of the transition-edge sensor as thermometer by a lumped-element resonance circuit seems to be a promising solution. Therefore, one can benefit from the intrinsic capability of frequency-division multiplexing that allows the readout of large detector arrays simultaneously and in real-time. The number of pixels is then limited by the available readout bandwidth and the quality factors of each individual resonance circuit. We successfully demonstrated, based on our feasibility study, the principal operation of such a device, what we call kinetic-inductance bolometer (KIBO). But the overall performance of the achievable noise-equivalent power (NEP) was limited by implementation and operation temperature of KIBO. Therefore, improved KIBO designs were developed and fabricated with niobium thin-film technology. In this paper, we describe the improvement procedure and estimate the expected NEP value.

Brillouin optical time domain reflectometry for fast detection of dynamic strain incorporating double-edge technique

For the first time, to the best of our knowledge, a direct detection Brillouin optical time-domain reflectometry (BOTDR) is demonstrated for fast distributed dynamic strain sensing incorporating double-edge technique, time-division multiplexing technique and upconversion technique. In order to guarantee the robust stability of the system, the double-edge technique is implemented by using a convert single-channel FPI and a fiber-coupled upconversion single-photon detector, incorporating a time-division multiplexing method. The upconversion single-photon detector is adopted to upconvert the backscattering photons from 1548.1nm to 863nm, which is subsequently detected by a Silicon avalanche photodiode (Si-APD). In the experiment, dynamic strain disturbance up to 1.9mε over 1.5km of a polarization maintaining fiber is detected at a sampling rate of 30Hz. An accuracy of ±30με and spatial resolution of 0.6m are realized.

A Wireless and Passive Online Temperature Monitoring System for GIS Based on Surface-Acoustic-Wave Sensor

A novel temperature monitoring system for gas-insulated switchgears (GISs) based on surface-acoustic-wave (SAW) sensing is proposed in this paper. Compared with the existing systems, this system has several unique advantages, such as being wireless, passive, and at a proper cost with continuous monitoring. First, an accurate SAW temperature sensor is designed for the GIS conductor, where epoxy encapsulating and loop antennas are adopted in the SAW sensor to prohibit the potential partial discharge of the sensor itself. After that, a multifunctional reader antenna is developed, which can measure the conductor temperature and partial discharge by the time-division multiplexing technique. Experiments are carried out to examine the accuracy and response speed of the SAW sensors, and the results indicate that the uncertainty of the contact temperature measurement is smaller than 10 $^{\circ}$ C. Moreover, the insulation level and anti-interference ability are demonstrated based on experiments carried out on a 126-kV GIS. At last, temperature monitoring performance of the developed system is investigated by changing the current in the 126-kV GIS conductor. The experiment results prove that the developed system can meet the requirement of temperature monitoring in GIS.

Study of buffer storage in video channelization

In this paper, we propose a model for estimating the buffer storage for continuous delivery of video data. For this, the physical channel is divided into logical channels and the videos running on the video server into segments. The video segments are transmitted through logical channels using the time-division multiplexing (TDM) technique. Switching between two consecutive video segments in a logical channel creates some delay during which no data is transmitted and that delay, called jitter delay, is of random nature. In this work, jitter delay is incorporated while estimating the buffer storage. The buffer storage is a random variable and its probability density function is derived. This study is important for applications related to on-demand services such as cable TV, news-on-demand, movie-ondemand, audio-on-demand, etc.

Time division multiplexed orbital angular momentum access system

We propose and experimentally demonstrate time division multiplexed orbital angular momentum (OAM) access system to increase transmission capacity and spectral efficiency. In this system, data carried on different time tributaries share the same OAM mode. Multiple time division multiplexed OAM modes are multiplexed to realize two-dimensional (time dimension and OAM dimension) multiplexing. Therefore, the capacity and spectral efficiency of the access system will increase. The orthogonality between optical time division multiplexing (OTDM) and OAM techniques is also verified in our experiment. In a proof-of-concept experiment, 2×5-Gbps return-to-zero signal over OAM mode +4 is transmitted and investigated. The bit error ratio performance after transmission in this system can be smaller than 1×10−9. Results show that the proposed time division multiplexed OAM access system is suitable for future broadband access network.

Combined Optical and Electrical Spectrum Shaping for High-Baud-Rate Nyquist-WDM Transceivers

We discuss the benefits and limitations of optical time-division multiplexing (OTDM) techniques based on the optical generation of a periodic train of sinc pulses for wavelength-division multiplexing (WDM) transmission at high baud rates. It is shown how the modulated OTDM spectrum bandwidth is related to the optical comb parameters and the pulse shaping of the modulating waveforms in the electrical domain. Such dependence may result in broadening of the modulated spectra, which can degrade the performance of Nyquist-WDM systems due to interchannel crosstalk penalties. However, it is shown and experimentally demonstrated that the same technique of optical pulse train generation can be allied with digital pulse shaping to improve the confinement of the modulated spectrum toward the Nyquist limit independently of the number of OTDM tributaries used. To investigate the benefits of the proposed approach, we demonstrate the first WDM Nyquist-OTDM signal generation based on the periodic train of sinc pulses and electrical spectrum shaping. Straight line transmission of five 112.5-Gbd Nyquist-OTDM dual-polarization quadrature phase-shift keying (QPSK) channels is demonstrated over a dispersion uncompensated link up to 640 km, with full-field coherent detection at the receiver. It is shown that such a design strategy effectively improves the spectral confinement of the modulated OTDM signal, providing a minimum intercarrier crosstalk penalty of 1.5 dB in baud-rate-spaced Nyquist-WDM systems.

Capacity of Wavelength and Time Division Multiplexing for Quasi-Distributed Measurement Using Fiber Bragg Gratings

In this paper, an analysis of the use of wavelength and time division multiplexing techniques for quasi-distributed measurement in uniform fiber Bragg gratings is presented. To date, publications have concentrated on the determination of the maximum number of fiber Bragg gratings on one optical fiber using wavelength and time division multiplexing. In this paper, these techniques will be extended to determine the spectral width of wavelength division multiplexing in terms of the spectral width of the light emitting diode, the spectral width of the Bragg gratings, the measurement ranges of the individual sensors, and the guard band between two adjacent Bragg gratings. For time division multiplexing, a description of the time and power conditions are given. In particular the reflected power, first order crosstalk and chromatic dispersion have been considered. Finally, these relationships were applied to verify a design in a simulation using OptiSystem software.

Multi-Phase Convex Lens Array for Directional Backlights to Improve Luminance Distribution of Autostereoscopic Display

SUMMARY We realize homogenous luminance of the directional backlight for the time-division multiplexing autostereoscopic display using a convex lens array with the elemental lenses whose phase of placement in each row differs from one another. The validity of the proposed optical With the recent advances of LCD technologies, LCD panels that attain short response time have been developed, which has enabled commercialization of 3D LCD TV sets. The ad- vanced LCD technologies with high refresh rates can also be applied to autostereoscopic displays with high resolutions. Most of the conventional autostereoscopic display sys- tems are based either on parallax barrier technology or on lenticular lens technology, both of which display stereo- scopic images with lower resolutions than those of the dis- play panels. Time-division multiplexing technique with a fast response panel has enabled presentation of a stereo- scopic image with the same resolution as that of the display panel.

Distributed Quantum Packet Transmission in Non-maximally Entangled Relay System

A novel distributed quantum packet transmission scheme is proposed with teleportation in the non-maximally entangled relay channel. Quantum signals are encoded as quantum signal packets and transmitted from the source to the destination with assistance of the relay. The TDM (Time Division Multiplexing) technique is applied in order to improve the efficiency of quantum communications. The security depends on the security of signal particles and an upper bound of attackers’ intercepting quantum information under their strongest collective attacks is derived. The communication efficiency can be improved to four times of the traditional schemes, and the timesaving percentage may approach to 75 %. It has a wide application in quantum networks as well.

A Novel Interrogation System for Large Scale Sensing Network With Identical Ultra-Weak Fiber Bragg Gratings

A novel interrogation system for large scale sensing network with identical ultra-weak fiber Bragg gratings (FBG) is proposed, theoretically analyzed and experimentally studied. Based on time-division multiplexing (TDM) technique, two semiconductor optical amplifiers are introduced to the interrogation system to achieve fast and flexible demodulation. A simulation depending on the formula of reflected pulse spectra, derived by analyzing the source of disturbance along the optical path, is processed for evaluating the performance theoretically. Experiment was demonstrated on an 843 serial FBGs sensor network, with a peak reflectivity of -40 to -45 dB and a spatial resolution of 2 m along a single optical fiber by launching a 50 kHz scanning frequency with 20 ns effective pulse width to the system. Due to the low crosstalk, it is possible to integrate several thousands of FBG sensors in a single optical fiber.

Integrated real-time monitoring system for strain/temperature distribution based on simultaneous wavelength and time division multiplexing technique

Based on the combination of wavelength- and time-division multiplexing technique, a novel fiber Bragg grating (FBG) sensor multiplexing system is proposed, which can be used for monitoring the two-dimensional strain and temperature field distribution in large structures. The FBG sensing unit is encoded simultaneously in both wavelength and time domains. Using the semiconductor optical amplifier (SOA) resonant cavity technology, a large capacity multiplexing technology with mixed time-division and wave-division multiplexing (TDM+WDM) is presented. The sensor array contains many groups with each group composed of many sensors. The group is addressed by TDM mode and each sensor of the groups is accessed by WDM mode. Therefore, the total multiplexing capacity is multiplication of TDM and WDM. In theory, more than 1000 sensors can be multiplexed on one single fiber. The feasibility of the scheme was experimentally demonstrated through a sensor system with a two dimensional FBG sensing network with 5×5 sensors arrays. In addition, the strain/temperature distribution in an aluminum plate was measured at real time under different loading/heating by using above FBG sensing network.

Highly accelerated acquisition and homogeneous image reconstruction with rotating RF coil array at 7 T—A phantom based study

Parallel imaging (PI) is widely used for imaging acceleration by means of coil spatial sensitivities associated with phased array coils (PACs). By employing a time-division multiplexing technique, a single-channel rotating radiofrequency coil (RRFC) provides an alternative method to reduce scan time. Strategically combining these two concepts could provide enhanced acceleration and efficiency. In this work, the imaging acceleration ability and homogeneous image reconstruction strategy of 4-element rotating radiofrequency coil array (RRFCA) was numerically investigated and experimental validated at 7T with a homogeneous phantom. Each coil of RRFCA was capable of acquiring a large number of sensitivity profiles, leading to a better acceleration performance illustrated by the improved geometry-maps that have lower maximum values and more uniform distributions compared to 4- and 8-element stationary arrays. A reconstruction algorithm, rotating SENSitivity Encoding (rotating SENSE), was proposed to provide image reconstruction. Additionally, by optimally choosing the angular sampling positions and transmit profiles under the rotating scheme, phantom images could be faithfully reconstructed. The results indicate that, the proposed technique is able to provide homogeneous reconstructions with overall higher and more uniform signal-to-noise ratio (SNR) distributions at high reduction factors. It is hoped that, by employing the high imaging acceleration and homogeneous imaging reconstruction ability of RRFCA, the proposed method will facilitate human imaging for ultra high field MRI.

Transmission Performance Investigation of RF Signal in RoF-DAS Over WDM-PON With Bandpass-Sampling and Optical TDM

The radio over fiber (RoF)-distributed antenna system (DAS) over a wavelength division multiplexing-passive optical network (WDM-PON) with multiple input multiple output (MIMO) employing bandpass-sampling and optical time division multiplexing (TDM) techniques has been proposed to realize next generation broadband wireless access with higher throughput and its preliminary feasibility has been confirmed. To investigate the performance of bandpass-sampled and time domain multiplexed optical signals, and enhance the transmission performance in the wireless link of the RoF-DAS over WDM-PON, we perform two-tone signal transmission experiments with 2.4 GHz band radio frequency (RF) signals and analyze the RF carrier power, third-order intermodulation distortion (IMD) power and noise power. The analysis results confirmed that the nonlinearity of the proposed system is mainly caused by a lithium niobate-Mach-Zehnder modulator (LN-MZM) as with the other RoF systems and that the dominant noise components are the signal-spontaneous beat noise arising from the amplified spontaneous emission (ASE) of two erbium doped fiber amplifiers (EDFAs) and the signal-signal beat noise caused by the interference between the optical TDM pulses. The latter is the specific noise component in the proposed system. In addition, we clarify the principle of the signal-signal beat noise generation and report that the signal-spontaneous beat noise can be reduced by the gain optimization of the two EDFAs.

Design of DC Power Line Communication System Using Time-Division Multiplexing

This work investigates a power line communication (PLC) in a DC power management system comprising master-slave control networks. Microcontroller-based master and slave units are designed with serial ports for communication with a controller and a transmission port to couple the signal to modems at both ends. However, coupling data signals to power line through modulation interfacing circuits is a challenging task. In this work, we used time-division multiplexing (TDM) technique to divide into two timings, Powering Time and Communication Time, on the DC power line and can reduce the complexity of the master-slave network and noise effect on the power line.

New Trends of Transmission Capacity Evaluation of Submarine Fiber Cable systems with Different Ultra-High Multiplexing, Amplification and Propagation Techniques

This paper has presented the new trends of the performance evaluation of submarine fiber cable system with different ultra-high multiplexing and propagation techniques over a wide range of the affecting parameters. We have taken into account the ultimate optical transmission of 10,000 channels huge submarine cables under different depth conditions. Two amplification techniques are considered (the engagement of Raman and Erbium-doped fiber amplifiers). The double impact of both temperature and pressure is investigated through the defined depth penalty. Three transmission time division multiplexing techniques are studied, namely soliton, nonlinear and maximum time division multiplexing. Also, two multiplexing methods are considered in the design of ultra-wide wavelength division multiplexing (UW-WDM) (10,000 optical channels) and ultra-wide space division multiplexing UW-SDM (400 fiber links). Based on experimental data, both the deep ocean water temperature and pressure are tailored as functions of the water depth. The product of the transmitted bit rate and the repeater spacing is processed over wide ranges of the affecting parameters, where both the repeater spacing and the transmitted soliton bit rate are in positive correlations with the total number of links.

An integrated optical 3D electric field sensing system based on time-division multiplexing

A new integrated optical three-dimensional (3D) electric field (E-field) sensing system is shown in this paper. In the system, the method of tuning laser’s wavelength is used for controlling the working point of the integrated optical E-field sensor to keep it always in linear working area. The sensing system contains three independent E-field sensors, and the tuning of their working points and the sensing of electric signal are completed by adopting time-division multiplexing (TDM) technique. Then, the theoretical analysis and simulation of the working mechanism of the E-field sensing system are done in this paper. The results show that the bandwidth of electric signal is directly related with the tuning time of working point, and also determines the working rate of the controlling system.

一种三维物体相息图的迭代计算方法

A novel method for computing kinoform of 3D object based on traditional iterative Fourier transform algorithm is described.The method divides three-dimensional object into many object planes by tomographic technique and treat every object plane as a target image,then iterative computation is carried out between one input plane(kinoform) and several output planes(reconstruction images).A space phase factor is added into iterative process to represent depth characters of 3D object.The experimental result shows that this algorithm computational and convergent velocity is fast.At last,the influences of object planes number and distance to reconstruction quality of kinoform are analyzed,and time-division multiplexing technique is used to reconstruct several object planes based on spatial light modulator.

A SDM-TDM-Based Circuit-Switched Router for On-Chip Networks

This article proposes a circuit-switched router that combines Spatial Division Multiplexing (SDM) and Time Division Multiplexing (TDM) in order to increase path diversity in the router while sharing channels among multiple connections. In this way, the probability of establishing paths through the network is increased, thereby significantly reducing contention in the network. Furthermore, Quality of Service (QoS) is easily guaranteed. The proposed router was synthesized on an Stratix III 3SL340F FPGA device. A 4 × 4 2D Mesh SDM-TDM Network-on-Chip (NoC) was built with the proposed router and synthesized on the 3SL340F FPGA device. The 4 × 4 2D Mesh SDM-TDM NoC was used to build on an FPGA device, a Multiprocessor System-on-Chip (MPSoC) platform consisted of 16 Nios II/f processors, 16 20-KB On-chip Memories, and 16 Network Interfaces. Synthesis results of the MPSoC platform show that the proposed router architecture can be used to built large practicable MPSoC platforms with the proposed NoC architecture with a reasonable hardware overhead and appreciable clock frequency. Simulation results show that combining SDM and TDM techniques in a router allows the highest probability of establishing paths through the network.

Recent four-wave mixing suppression methods

This paper reviews various techniques that have been proposed by many researchers to reduce the effect of four-wave mixing (FWM). A review was suggested to investigate the recent method of each technique and to compare their benefits and limitations in a wavelength division multiplexing (WDM) system. A FWM is defined as an undesirable nonlinear effect that gives significantly degraded system performance, and is expected to become the major drawback for optical communication systems. Among all the suppression techniques, there are six categories that are reviewed in this paper to suppress the effect of FWM and improve the overall system performance, which are: analysis of the individual and combined effects of high dispersion on FWM; using a hybrid WDM and time division multiplexing technique; using optic code division multiple access, using a short fiber optical parametric amplifier; using ultra-low unequal channel spacing, and finally, using a return-to-zero frequency shift-keying modulation format. The reduction techniques of FWM effect were compared according to the benefits and weaknesses of each technique in the application of WDM communication systems.