Time Division Multiplexing System Research Articles

Optical fiber sensor with a bi-cavity ring-down differential technology for robot-finger distributed systems

Contemporary intelligent robots typically necessitate the implementation of a distributed sensing network system within their digits to execute a range of intricate tasks collaboratively. In this investigation, we have introduced a novel fiber sensor founded on an enhanced fiber-loop ring-down spectral technology. This sensor employs double differential ring-down cavities to mitigate prevalent sources of interference, such as temperature and humidity. Consequently, it exhibits a robust linear response with remarkable sensitivity, quantified at 105.2 ns/N for force measurement and 53.2 ns/mm for displacement measurement, as validated by experimental outcomes. Furthermore, the sensor boasts a compact and diminutive sensing structure that can be effortlessly integrated into the robotic finger casing. Of utmost significance, it facilitates a cost-effective time-division multiplexing system for distributed measurements. Considering these distinctive advantages, this sensor lends itself to the establishment of a practical robot-finger distributed network system, characterized by superior performance attributes, encompassing high precision (up to 19 μm for contact detection and 0.0095 N for grasping and other manipulations), relatively modest expenses, and versatile applicability across a broad spectrum of scenarios, in stark contrast to the presently prevalent systems. In light of these noteworthy merits, the developed sensor exhibits tremendous potential for integration into robotics applications.

Paper] Reduction of Crosstalk in Time-Division Multiplexing Parallax Barrier with Low Power Consumption

This paper proposes a method to reduce stereoscopic crosstalk in time-division multiplexing parallax barrier system with reduced power consumption, where a fine slit pattern is generated by projecting LED striped light bars through a lenticular lens. When LEDs and a lenticular lens are used to generate a slit pattern, crosstalk level becomes higher than that of the system using a pair of LCD panels because the LED backlight does not fully synchronize with the update of image in the LCD panel. To overcome this problem, the lighting time of LED light bars is shortened, which enables reduction of crosstalk without lowering the ratio of luminance to power consumption.

Solving Ambiguity in Target Detection for BPSK-Based MIMO FMCW Radar System

In a binary phase shift keying (BPSK)-based multiple-input and multiple-output (MIMO) frequency-modulated continuous wave (FMCW) radar system, real and ghost targets are detected simultaneously, causing ambiguity in target detection. In this paper, we define the targets that are inevitably generated by the BPSK modulation as ghost targets and propose a method for suppressing them. The proposed ghost target suppression method consists of two main steps. First, at the receiving end, a received signal is demodulated using a specific code orthogonal to binary codes used to modulate transmitted signals. With the orthogonality between the codes, only ghost targets remain in the demodulated received signal. Then, by subtracting the demodulated signal including the ghost targets from the initially received signal, only the information of the actual targets can be restored. We verify the performance of the proposed method through simulations and actual signal measurements. In addition, the target estimation performance of the proposed method is compared with that of the time-division multiplexing MIMO FMCW radar system.

Dual-Wavelength Differential Detection of FBGs Using a Frequency-Scanning Pulsed Laser

The dual-wavelength differential detection of fiber Bragg gratings is reported. A directly modulated distributed-feedback laser array is used as a frequency-scanning pulsed light source. Trains of four 100-ns pulses with a frequency drift of 6.5 GHz and the same intensity are generated. Interrogating two serially connected Bragg gratings using the pulse trains, we show the selectivity of the high-sensitivity measurement and the wide measurement range, and the possibility of expansion to time-division multiplexing systems with a simple setup.

Integrated Hybrid Sub-Aperture Beamforming and Time-Division Multiplexing for Massive Readout in Ultrasound Imaging.

This paper demonstrates hybrid sub-aperture beamforming (SAB) with time-division multiplexing (TDM) for massive interconnect reduction in ultrasound imaging systems. A single-chip front-end system prototype has been fabricated in 180-nm HV BCD technology that combines 5×1 SAB with 8×1 TDM to efficiently reduce the number of receive signal interconnects by a factor of 40. The system includes on-chip high-voltage (HV) pulsers capable of generating unipolar pulses up to 70 V in transmit (TX) mode. The receiver (RX) chain consists of a T/R switch, a variable-gain low-noise amplifier (VG-LNA) with 4-step gain control (15-32 dB) for time-gain compensation followed by a programmable switched-capacitor analog delay-and-sum beamformer. The proof-of-concept prototype operates at a 200-MHz clock frequency and the SAB provides 32-step fine delays with a maximum delay of 310 ns corresponding to better than λ/20 delay quantization at 5 MHz. With these specifications, the SAB is capable of beam steering from 0 ° to 45 ° for a 5-element subarray with 150-micron pitch ( λ/2), providing a near-ideal phased array imaging performance. The sub-aperture beamformer is followed by the TDM system where each of the 8 channels is sampled at a rate of 25 MS/s after an anti-aliasing bandpass filter. The full functionality of the prototype chip is validated through electrical and acoustic measurements on a 1-D capacitive micromachined ultrasonic transducer (CMUT) array designed for intracardiac echocardiography (ICE).

Micro-X Sounding Rocket Payload Re-flight Progress

Micro-X is an X-ray sounding rocket payload that had its first flight on July 22, 2018. The goals of the first flight were to operate a transition edge sensor (TES) X-ray microcalorimeter array in space and take a high-resolution spectrum of the Cassiopeia A supernova remnant. The first flight was considered a partial success. The array and its time-division multiplexing readout system were successfully operated in space, but due to a failure in the attitude control system, no time on-target was acquired. A re-flight has been scheduled for summer 2022. Since the first flight, modifications have been made to the detector systems to improve noise and reduce the susceptibility to magnetic fields. The three-stage SQUID circuit, NIST MUX06a, has been replaced by a two-stage SQUID circuit, NIST MUX18b. The initial laboratory results for the new detector system will be presented in this paper.

Generation of cylindrical vector beams in a linear cavity mode-locked fiber laser based on nonlinear multimode interference.

In this paper, a linear cavity mode-locked pulsed fiber laser generating cylindrical vector beams (CVBs) is proposed and demonstrated based on a nonlinear multimode interference. A homemade long-period fiber grating with a broad bandwidth of 121 nm is used as a mode converter inside the cavity. The saturable absorber was formed by single-mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure. By controlling the pump power, the operation states are switchable among continuous-wave, Q-switched mode-locked (QML), and mode-locked regimes. The repetition rate of the QML CVB pulse envelope varies from 57.4 kHz to 102.7 kHz at the pump range of 118 to 285 mW. When increasing pump power to 380 mW, mode-locked CVB pulse repetition rate of 3.592 MHz, and pulse duration of 4.62 ns are achieved. In addition, the maximum single-pulse envelope energy can reach 510 nJ, and 142 mW average-power CVBs with a slope efficiency of as high as 20.2% can be obtained. Moreover, azimuthally and radially polarized beams can be obtained with mode purity over 95% in different operating regimes. The proposed fiber laser has a simple structure, and the operation is controllable in both temporal and spatial domains, which presents a flexible pulsed CVB source for application of laser processing, time or mode division multiplexing system, and spatiotemporal nonlinear optics.

Reduction of power consumption for autostereoscopic display based on time-division multiplexing parallax barrier

In this paper, we propose a time-division multiplexing parallax barrier system with reduced power consumption by using a lenticular lens to generate active barrier slits. In the conventional study, the ratio of luminance to power consumption is low because of the usage of two LCD panels with limited transmittance. In the proposed system, a fine slit pattern is generated by projecting LED striped light through a lenticular lens, where active change of slit pattern is realized by changing the positions of LED emission. We measure and confirm reduction of power consumption in the proposed method. We also compare the effects of time division on crosstalk in the conventional and the proposed methods.

High precise time division multiplex UV pulse waveform measurement system for high power laser facility

In high power laser facility, the waveform measurement of UV pulse injected to target is very important for power balanced control and experiment result analysis. A time division multiplex UV frequency modulation pulse waveform measurement system based on fiber bundle and lens array is built for a high precise measurement result as well as low construction and maintaining cost. The system can remarkably improve coupling efficiency inject to fiber contribution to the aperture splicing sampling technology and a 50μm multi-mode UV fiber specially developed with 9.2GHz bandwidth@60m transmission. A “four-in-one” time division multiplex measurement system is built for laser facility and the practical experiment indicated that the system can realize precise waveform measurement within good economy and anti-interference performance.

Recording Strategies for High Channel Count, Densely Spaced Microelectrode Arrays.

Neuroscience research into how complex brain functions are implemented at an extra-cellular level requires in vivo neural recording interfaces, including microelectrodes and read-out circuitry, with increased observability and spatial resolution. The trend in neural recording interfaces toward employing high-channel-count probes or 2D microelectrodes arrays with densely spaced recording sites for recording large neuronal populations makes it harder to save on resources. The low-noise, low-power requirement specifications of the analog front-end usually requires large silicon occupation, making the problem even more challenging. One common approach to alleviating this consumption area burden relies on time-division multiplexing techniques in which read-out electronics are shared, either partially or totally, between channels while preserving the spatial and temporal resolution of the recordings. In this approach, shared elements have to operate over a shorter time slot per channel and active area is thus traded off against larger operating frequencies and signal bandwidths. As a result, power consumption is only mildly affected, although other performance metrics such as in-band noise or crosstalk may be degraded, particularly if the whole read-out circuit is multiplexed at the analog front-end input. In this article, we review the different implementation alternatives reported for time-division multiplexing neural recording systems, analyze their advantages and drawbacks, and suggest strategies for improving performance.

Application of TDM and FDM methods in TDLAS based multi-gas detection

Multi-gas tunable diode laser absorption spectroscopy (TDLAS) system based on time division multiplexing (TDM) demodulation technology which combine with frequency division multiplexing (FDM) technology is proposed, called F-TDM (frequency- time division multiplexing) system. In addition, traditional TDM technology and FDM technology are introduced to analyze and compare their performance. As for the performance of F-TDM system, multi-gas detection of CH4 and C2H2 has been accomplished with minimum detection limits of 10.24 ppmv for CH4 at 1653.72 nm and 0.763 ppmv for C2H2 at 1532.83 nm respectively. The relationships (CH4: R-square = 0.9989; C2H2: R-square = 0.9995) between gas concentration and second harmonic signal amplitude are proved as a good linear response. It is consistent with the data obtained by traditional TDM and FDM demodulation methods, indicating that the F-TDM system is feasible. By comparison, it is known that different methods have their advantages in different applications. The TDM system uses less equipment and is the most cost-effective. The system based on FDM technology is the most time-saving. The F-TDM system is a compromise method that combines the advantages of both and has no obvious disadvantage at the detection limit.

Design of Simulation for Time-Division Multiplexing Digital Optimal Frequency Band Transmission System

This paper designs a simulation experiment model of the overall structure of time-division multiplexing digital optimal frequency band transmission system based on MATLAB simulation platform. The parameters of each module in the simulation model are set. The working process and performance of the time-division multiplexing digital optimal band transmission system are simulated. The simulation results show that the digital optimal band transmission system achieves the best transmission receiving conditions and performance, and the designed time-division multiplexing optimal digital band transmission simulation system achieves its functions. The research in this paper will help to improve the level of digital communication technology and to understand the structure of time-division multiplexing digital optimal band transmission system.

Proposal for optical TDM system for digital payload in next generation high throughput satellites

The digital payload for next generation high throughput communication satellites is expected to reduce the operators’ CAPEX and OPEX. Photonic technologies, which have a great affinity with digital signals, have been studied in order to increase the data throughput and reduce the mass of the satellites. Here, we propose an optical time division multiplexing system for routing the signals in the digital channelizer and have conducted a feasibility study on the transmission efficiency. This system has the potential to reduce the cost, mass, and power consumption, and to improve reliability by cleaning up the switches used for routing the signals within the satellites.

A Predictive Control Algorithm for Time-Division-Multiplexed Readout of TES Microcalorimeters

Time division multiplexing (TDM) uses a digital flux-locked loop (DFLL) to linearize each first-stage SQUID amplifier. Presently, the dynamic range of our TDM systems is limited by the use of a proportional-integral controller to maintain the DFLL. In this paper, we use simulations to assess the improvements possible with a predictive control algorithm that anticipates rapid changes in transition-edge sensor current during the rising edge of an X-ray pulse. We calculate that the predictive control algorithm can improve our TDM architecture’s dynamic range by 35%. This significant increase in multiplexing capabilities could be used to read out higher-energy X-rays, reduce readout noise, increase multiplexing factors, or reduce SQUID power output.

First Operation of TES Microcalorimeters in Space with the Micro-X Sounding Rocket

Micro-X is a sounding rocket-borne instrument that uses a microcalorimeter array to perform high-resolution X-ray spectroscopy. This instrument flew for the first time on July 22nd, 2018 from the White Sands Missile Range, USA. This flight marks the first successful operation of a Transition-Edge Sensor array and its time division multiplexing read-out system in space. This launch was dedicated to the observation of the supernova remnant Cassiopeia A. A failure in the attitude control system prevented the rocket from pointing and led to no time on target. The on-board calibration source provided X-rays in flight, and it is used to compare detector performance during pre-flight integration, flight, and after the successful post-flight recovery. This calibration data demonstrates the capabilities of the detector in a space environment as well as its potential for future flights.

FWM Mitigation in DWDM Optical Networks

In this paper, three optical communication systems have been proposed to mitigate Four Wave Mixing (FWM). Three techniques are used, namely; low input power with high gain amplifier, a collective Optical Time Division Multiplexing (OTDM) and Dense Wavelength Division Multiplexing (DWDM) system, and the use of alternative circular polarization. The first technique involves reduction in input power to -20 dBm and then amplifying it 40 dB before demultiplexing. The second technique divides the input signal into four time slots and then combine them with a power combiner. In the third technique, the polarization of light coming from input channels is changed after modulation into right and left handed circular polarization. Exhaustive sets of simulations are performaed using Optisys. The performance analysis includes Q-factor, Optical Signal to Noise Ratio (OSNR), received optical power, minmum Bit Error Rate (BER) and eye diagram.

Microwave Multiplexing on the Keck Array

We describe an on-sky demonstration of a microwave-multiplexing readout system in one of the receivers of the Keck Array, a polarimetry experiment observing the cosmic microwave background at the South Pole. During the austral summer of 2018-2019, we replaced the time-division multiplexing readout system with microwave-multiplexing components including superconducting microwave resonators coupled to radio-frequency superconducting quantum interference devices at the sub-Kelvin focal plane, coaxial-cable plumbing and amplification between room temperature and the cold stages, and a SLAC Microresonator Radio Frequency system for the warm electronics. In the range 5-6 GHz, a single coaxial cable reads out 528 channels. The readout system is coupled to transition-edge sensors, which are in turn coupled to 150-GHz slot-dipole phased-array antennas. Observations began in April 2019, and we report here on an initial characterization of the system performance.

Time-division multiplex auto-impedance matching system for high-intensity focused ultrasound

Time-division multiplex auto-impedance matching system for high-intensity focused ultrasound

Eavesdropping and countermeasures for backflash side channel in fiber polarization-coded quantum key distribution

Nowadays, the practical security of quantum key distribution (QKD) is the biggest challenge. In practical implementation, the security of a practical system strongly depends on its device implementation, and device defects will create security holes. The information leakage from a receiving unit due to secondary photon emission (backflash) is caused by a single-photon detector in the avalanche process. Now studies have shown that the backflash will leak the information about time and polarization and the eavesdropping behavior will not generate additional error rate in the communication process. An eavesdropping scheme obtaining time information by using backflash is proposed. Targeting this security hole for backflash leaking polarization information, an eavesdropping scheme for obtaining polarization information by using backflash is proposed in free-space QKD; however, it has not been reported in fiber QKD. In this study, the eavesdropping scheme and countermeasures for obtaining information by using backflash in fiber polarization-coded QKD is proposed. Since the polarization state of the fiber polarization-coded QKD system is easy to change, the scheme is proposed based on the time-division multiplexing polarization compensation fiber polarization-coded QKD system. In theory, the eavesdropper in this scheme obtaining the key information by using the backflash is theoretically deduced, and corrects the polarization change of the backflash by time-division multiplexing polarization compensation method, thus obtaining the accurate polarization information. The probability of backflash in the fiber polarization-coded QKD is measured to be 0.05, and the information leakage in the proposed eavesdropping scheme is quantified. The lower limit of the information obtained by the eavesdropper is 2.5 × 10<sup>–4</sup>. Due to the fact that the polarization compensation process increases invalid information in actual operation, the information obtained by the eavesdropper will be further reduced, thus obtaining the lower limit of information leakage. The results show that the backflash leaks a small amount of key information in a time-multiplexed polarization-compensated fiber polarization-coded QKD system. The wavelength characteristics of the backflash can be utilized to take corresponding defense methods. Backflash has a wide spectral range, and the count of backflash has a peak wavelength. So, tunable filters and isolators can be used to reduce backflash leakage, thereby reducing the information leakage.

RETRACTED: Study of a novel distributed vibration sensing system based on weak fiber Bragg gratings

A novel vibration sensing system based on distributed weak fiber Bragg gratings is demonstrated to overcome the drawbacks of the conventional methods used in optical fiber sensing networking, such as insufficient quantity of multiplexed fiber Bragg gratings in wavelength-division multiplexing systems and low signal intensity in conventional time-division multiplexing systems. By mixing wavelength-division multiplexing technology and time-division multiplexing technology, the physical parameters of the fiber Bragg grating locations can be measured, but the distributed measurement along the whole optical fiber cannot be realized. The proposed novel sensing system detects the vibration events along the optical fiber link according to the signal’s intensity interference variation caused by the reflected signals with the adjacent weak fiber Bragg gratings. The position of the vibration events can be accurately determined by using time-division multiplexing technology. The experimental results verify that this novel system is more convenient for realizing vibration detection and demodulation along the whole optical fiber than before, and the system locating accuracy can be up to 20.5 m, with the capability of detecting various signals with 0.2 V of the driven signals as the bottom limit of voltage and a frequency range from 3 to 1000 Hz.