Digital Optical Transmission Research Articles

Research on high-speed digital optical signal jitter measurement technology based on clock recovery algorithm using eye diagram opening area

With the rapid development of information technology, high-speed digital optical signal transmission technology has become the core of modern communication networks. However, the increase in transmission rates brings challenges such as noise, distortion, and interference, which affect the accuracy of clock recovery. To address these issues, this study proposes a clock recovery algorithm based on the eye diagram opening area to improve the accuracy and efficiency of high-speed digital optical signal jitter measurement. The proposed method extracts clock information from the signal using the opening area and curvature characteristics of the eye diagram for jitter measurement. Experimental results demonstrate that the clock recovery algorithm based on the eye diagram opening area can stably reconstruct the signal eye diagram and obtain jitter parameters under different optical power conditions. At optical powers of −7.2 dBm, −12.2 dBm, and −17.2 dBm, the Q-factors were 8.8, 7.6, and 4.3, respectively, and the RMS jitter values were 12.2 ps, 13.4 ps, and 21.2 ps, respectively. At optical powers of −2.3 dBm, 0.1 dBm, 2.4 dBm, 4.6 dBm, and 6.0 dBm, the Q-factors were 9.1, 9.3, 9.5, 9.7, and 10.0, respectively, and the average jitter values were 8.9 ps, 8.5 ps, 8.0 ps, 7.5 ps, and 7.0 ps. These results indicate that the proposed algorithm performs excellently under low optical power conditions and maintains high recovery accuracy even when jitter increases at higher optical powers. The clock recovery algorithm based on the eye diagram opening area significantly improves the accuracy and stability of high-speed digital optical signal jitter measurement, enriches the theoretical research of clock recovery algorithms, and shows significant advantages in improving signal transmission quality, reducing bit error rate, and enhancing communication link reliability. The research outcomes provide key technical support for the optimization of modern high-speed optical communication systems.

Evaluation Fiber Optic Communication Network Performance through Manchester Code

There has been, and will continue to be, discussion over how to monitor wireline communications with increased data rates. In order to meet bandwidth requirements while keeping complexity at an acceptable level, engineers have dealt with many data formats over the years. Manchester encoding is a popular choice among the current solutions for various applications. Another benefit in high-speed input-output lines when the power budget is limited is the Manchester coding transceiver, which can be realized in a reasonably simple fashion. For inexpensive digital data optical transmission, the Manchester data format can be utilised as a modulation mechanism. The performance of the related transceivers under different conditions can be estimated by doing a comprehensive analysis of the Manchester data format and comparing it with other line coding types. System developed and fine-tuned for performance and feasibility evaluation. We used Opti system 2014 to test the system.

A review of wireless-photonic systems: Design methodologies and topologies, constraints, challenges, and innovations in electronics and photonics

Photonic networks form the backbone for data communications. In particular, in current and future wireless communication systems, photonic networks are becoming increasingly popular for data distribution between the central office and the remote antenna units at base stations. As wireless-photonic systems become in increasing demand, low-cost implementation of such systems will be desirable. This paper describes how integrated photonics and electronics, on silicon, can be used to design such systems. Various building blocks of such silicon-photonics systems are reviewed. The emphasis is on a 60GHz wireless system which could be suitable for the emerging 5th-generation (5G) cellular networks. The implementation discussed here uses digital baseband optical transmission as opposed to the radio-over-fibre approach.

Digital time-resolved optical measurement of discharge currents in long air gaps

Shortcomings in the dynamic range and the frequency bandwidth of current diagnostic methods mean that measurement of the time-resolved discharge current in a long air gap discharge is still a serious problem. This work presents data from a novel discharge current sensor that takes the parameters required to determine the accuracy of the current measurement into account. The design of a coaxial current sensor with ±0.7% accuracy and a bandwidth of 75 MHz is presented. A digital optical fiber transmission system with a bandwidth that exceeds 100 MHz is used to transmit the signal. To demonstrate the efficiency of the whole system, experiments using a rod-plane discharge geometry with 2 m and 4 m air gap lengths are performed to analyze the measured current data in comparison with that taken from synchronized high-speed photographs. The results demonstrate that the investigated experimental set-up improves substantially the understanding of the fundamental mechanisms of long air gap discharges.

The Effect of Sputtering Power on the Properties of Zr-Ga Co-Doped ZnO Films by DC Magnetron Sputtering

Zr-Ga co-doped ZnO transparent conductive films were prepared on glass substrates by DC magnetron sputtering at room temperature. The influence of sputtering power on the structural, electrical and optical properties of Zr-Ga co-doped ZnO films was investgated by X-ray diffraction, scanning electron microscopy (SEM), digital four-point probe and optical transmission spectroscopy. The lowest resistivity of the Zr-Ga co-doped ZnO films is 3.02×10-4Ω﹒cm and the average transmittance of the films is over 90% in the visible range. The obtained optical band gap of these films is much larger than of pure ZnO (3.34 eV).

Electrothermal-Chemical Gun Chamber Pressure Measurement System Based on Digital Optical Fiber Transmission

There were problems of strong electromagnetic interfere (EMI) and floating of ground potential when the electrothermal-chemical gun (ETCG) was launched. EMI seriously affected the chamber pressure measurement, and affected the accurateness of data and the security of apparatus. The chamber pressure testing technology was put forward which adopted the field testing technique with digital storage and the digital optical fiber transmission technique. The on-site storage pressure gauge and multilayer electromagnetic shielding structure was designed. Test data real-time transmission and remote reappear are realized by using high speed digital optical transceiver module and optical fiber. This testing technology effectively solved the EMI problem, improved the reliability and safety of chamber pressure measurement. The test data provide a basis for research of interior ballistic properties of ETCG. This testing technology can be widely applied to the parameters measurement with strong electromagnetic interfere.

Coherent DWDM technology for high speed optical communications

The introduction of coherent digital optical transmission enables a new generation of high speed optical data transport and fiber impairment mitigation. An initial implementation of 40 Gb/s coherent systems using Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) is already being installed in carrier networks. New systems running at 100 Gb/s DP-QPSK data rate are in development and early technology lab and field trial phase. Significant investment in the 100 Gb/s ecosystem (optical components, ASICs, transponders and systems) bodes well for commercial application in 2012 and beyond. Following in the footsteps of other telecommunications fields such as wireless and DSL, we can expect coherent optical transmission to evolve from QPSK to higher order modulations schemes such as Mary PSK and/or QAM. This will be an interesting area of research in coming years and poses significant challenges in terms of electro-optic, DSP, ADC/DAC design and fiber nonlinearity mitigation to reach practical implementation ready for real network deployments.

Method for the measurement of rotor voltage and current of power generator

A method to measure rotor voltage and current in power generator is described in this study. The system is based on analogue to digital conversion and optical fibre transmission principle. The voltage and current signals from the semiconductor controlled rectifier (SCR) bridge of the power generator are conditioned to proper amplitude for the A/D converter's (ADC) input and then the digital signal from the ADC is transmitted to the local module through optical fibre. The power consumption of the circuitry in the remote module is about 50 mW and the power efficiency of the optically powered supply at the high-voltage side is about 76%. The uncertainty of the electronic instrument transducer (EIT) developed in this study is estimated to be less than 1.1% in ratio and the delay time of the step response is less than 7 ms.

Polarization recovery for Polarization Shift Keying transmission based on analysis of torsion and curvature of three dimensional curve segments

A solution to the problem of recovering and tracking the signal configuration at the receiver side for digital optical transmission systems employing the modulation of polarization (POLSK) is proposed. The tracking algorithm for signal configuration is based on analysis of torsion and curvature of three dimensional curve segments. Impact of polarization effects on presented method is investigated. The only impairments considered in this paper are: frequency-independent birefringence and one lumped PDL element. The numerical simulations and experiments shows that the presented method is resistant to change of fiber optics birefringence; and is sensitive to depolarization effect and state of polarization location fluctuations which are equal or faster than the data rate.

Low-cost, signed online chromatic dispersion detection scheme applied to a 2×10 Gb/s RZ-DQPSK optical transmission system

Chromatic dispersion (CD) in single-mode optical fibres limits the maximum transmission distance of digital optical transmission systems at 10 and 40 Gb/s. It can be eliminated by a tunable CD compensator, provided that the residual dispersion is detected, including its sign. A low-cost hardware implementation of a signed online CD detection scheme is reported. It is based on synchronous detection of frequency modulation (FM)-induced arrival time modulations in the clock recovery phase locked loop (PLL) of a 2 x 10 Gb/s return-to-zero differential quadrature phase shift keying (RZ-DQPSK) optical receiver. The RZ-DQPSK transmitter laser is modulated by a synthesised 4.732 MHz sinusoidal signal. This results in ≃1% (rms) intensity modulation and an optical FM with ≃105 MHz (rms) deviation. Low-cost components were used to build a synchronous detector for the arrival time signal that yields the fibre CD, including its sign. The total measurement interval is ≃84 μs. The sign of the CD is detected within a range of ±700 ps/nm. This range is limited by the locking range of the clock recovery PLL. The CD measurement readout is fairly linear over the range ±360 ps/nm.

A [formula omitted] optical link for a fast and reliable data readout and acquisition

We report on a digital optical transmission system with a data rate of 2.488 Gbit/ s . A novel parallel coding and synchronization concept has been introduced which offers a 16-times reduced operating frequency for the concerned circuit parts. The performance of the chosen 3b4b-block coder is discussed by an evaluation of the frequency characteristics of the coded pulse train and a comparison to other standard coding concepts. A simple simulation model of the complete optical path enables the prediction of basic system characteristics in the time domain for a large range of operating parameters. The receiver provides the transmitted data to a user-defined bus or to the industrial VMEbus. Reliability studies have shown a system's bit error rate below 10 −13.

Linear optical modulation in a serially cascaded electroabsorption modulator

ABSTRACT: An all-optical linearization scheme in a serially cascadedEAM using different deri ati e signs of the transfer function of an EAMis proposed. Both the IMD3 and IMD5 supressions are obtained at thesame dc bias oltage, and 15 dB of SFDR enhancement is achie ed innarrowband operation. 2000 John Wiley & Sons, Inc. MicrowaveOpt Technol Lett 27: 447 450, 2000. Key words: electroabsorption modulator; linearity; intermodulationproducts; SFDR; analog optical link I. INTRODUCTION The optical transmission of analog radio-frequency RF sig-Ž.nals has wide applications, including wireless communicationssystems, cable television applications, and antenna remoting.External optical modulation becomes important for the low-loss transmission of a millimeter-wave band and RF signalover a fiber link due to its high-frequency response andlow-chirp characteristic. For external modulation, a Ti-dif-fused LiNbO Mach 3 Zehnder interferometer modulatorŽ. Ž .MZM and an electroabsorption modulator EAM aremainly used for digital optical transmission. An EAM takesadvantage of the low driving voltage, small size, monolithicintegration capability with other optical components, andbroad bandwidth compared to an MZM. But an EAM has acomplicated nonlinear transfer function. So an intermodula-tion distortion IMD product and a harmonic distortionŽ.product in subcarrier multiplexing SCM transmission ofŽ.analog radio-frequency signals are generated, and the analogoptical link performance is degraded. Thus, nonlinear prod-

Asynchronous digital optical regeneration and networks

This paper outlines the concept of the asynchronous digital optical network, which is aimed to combine the advantages, and overcome the drawbacks, of existing approaches to photonic networking. The network is based on digital optical transmission and processing, which offers the prospect of almost infinite scalability. Optical transmission throughout the network is in burst mode, using a standard digital optical signal format. The main defining feature of the asynchronous network is that the network nodes (in which the optical processing and routing take place) do not share global synchronization at the bit level. Instead, the nodes each operate with independent bit-level clocks. This approach removes the architectural constraints found in synchronous networks. An essential component of the network is the asynchronous digital optical regenerator. Various design and performance aspects of this new type of regenerator are analyzed.

Polarization recovery in optical polarization shift-keying systems

For the first time, a solution to the problem of recovering and tracking the signal constellation at the receiver side for binary and octonary digital optical transmission systems employing the modulation of polarization (POLSK) is proposed and analyzed. The effect of two recovery algorithms on the system performance is evaluated in terms of power penalty induced at P(e)=10/sup -9/, acquisition and tracking speed, and hardware complexity. The results show that very small penalties are obtainable in practical situations by properly designing the recovery algorithms.

On the simulation of digital optical links with EDFA's: an accurate method for estimating BER through Gaussian approximation

A new method for the semi-analytical estimation of the bit-error rate (BER) of digital optical systems is presented. It is based on system simulation and accurately considers the performance degradation caused by waveform distortion. The method profits from the simplicity of Gaussian approximation for noise statistics, though explicitly accounting for intersymbol interference (ISI) effects in noise during the BER estimation. Optically preamplified and avalanche photodiodes (APD) receivers are considered, for which signal-dependent noise components are dominant. The system parameters influence on receiver sensitivity is studied. A digital optical transmission link with a single in-line erbium-doped fiber amplifier (EDFA) and with an EDFA chain is then analyzed. The influence of the EDFA chain characteristics on system performance is investigated: amplifier gain, noise figure and spacing are considered. The tradeoffs between EDFA parameters and system optimization are addressed.

Optical PSK homodyne system using a switched residual carrier for phase synchronisation

In this new concept for a digital optical homodyne transmission system, phase synchronisation of the receiver's local oscillator relies on an additional low-key phase modulation at the clock frequency. The front-end uses a 180° hybrid and is AC coupled.

Operation of digital optical transmission system with minimal degradation due to polarisation mode dispersion

The probability of BER degradation above 10/sup -9/ is evaluated theoretically as the quality parameter for examining the robustness of an optical transmission system incorporating an EDFA to fibre polarisation mode distortion (PMD). Provided that there is an existing power margin, a significantly reduced sensitivity to PMD is achieved by detuning the decision level of the optical receiver from the optimum for zero PMD. >

Distributed amplifier signal shaping strategy for multigigabit digital optical transmission

A novel technique is presented for using the distributed amplifier (DA) as an active pulse shaping/filtering network by effectively constructing a transversal filter. This technique is versatile, and judicious selection of the effective stage delays and gains allows a variety of filtering functions to be implemented. The capability of the technique is illustrated with reference to a GaAs MMIC design for 10 Gbit/s.

Two-dimensional plasma-electron temperature measurements

A system to measure the two-dimensional cold-electron temperature profile in a magnetic confinement laboratory plasma is described. Using a digital storage CCD camera, image intensifier, and optical transmission filters, a two-dimensional helium-line emission-ratio measurement shows plasma features which are not possible to resolve using only a single detector or an array of detectors. The system is especially useful for nonaxisymmetric magnetic geometries, where the three-dimensional equilibria make interpretation of more standard measurements difficult. Other two-dimensional plasma-profile measurements including density and ionization source measurements are also possible using the system.

Decision-point steering in optical fibre communication systems: theory

In a digital optical transmission system, the decision threshold, the sampling instant and the gain of the avalanche photodiode need to be maintained at their optimum values in order to maintain a minimum bit error ratio. In the paper the authors consider in detail the theory of steering these three parameters while pseudoerror monitoring is used to monitor the system performance, and they show that this decision-point steering can allow the optical link to maintain its performance under system variations, thus allowing a reduction in the system power margin that needs to be allocated.