Non-return Zero Research Articles

Optimizing 20 Gbps of ground-to-satellite free-space optical communication in low earth orbit with hybrid wavelength-mode division multiplexing

High-speed free-space optical (FSO) communication has emerged as a promising technology for low earth orbit (LEO) region in the last decade. In this paper, we simulate 20 Gbps simplex ground-to-satellite with various wavelengths and transmitter beam pointing error of 0.1 to 2.5 urad. The C-band wavelength is chosen, and a non-return-zero (NRZ) pulse generator with 16 channels hybrid wavelength-mode division multiplexing (WDM-MDM) technique employing Hermite-Gaussian (HG) modes is used to vary the pointing error. The effect of beam pointing error and receiver aperture diameter was discussed in this paper. A transmitter beam pointing error of 2.5 urad can work appropriately at distances of 1000 km and 1500 km, with a BER value of 1.41 × 10−6 and 3.56 × 10−5, respectively. Based on the receiver aperture diameter of 100 cm, it successfully achieves a BER value of 2.4 × 10−8 at the LEO region and a clear eye diagram.

Design and performance of WDM system for high-speed optical communication on different modulation formats

Abstract In this paper, the performance analysis of the WDM (wavelength division multiplexing) system on the optical fiber transmission link is proposed. High data transmission is possible by implementing a WDM optical communication system using different modulation formats. Firstly, the WDM optical communication system is designed on an Optiwave simulation tool and distortion in the optical fiber by “eye pattern analysis” is analyzed. Secondly, the optical SNR of the proposed WDM optical communication system is studied. Further, the bit-error rate (BER) plot is studied and optimization techniques are applied to enhance the proposed system for long-haul communication. Furthermore, the BER plots are analyzed by varying the length of the fiber and applying different coding techniques like NRZ (non-return zero), RZ (return to zero), QAM (quadrature amplitude modulation) etc. using the Optiwave simulation tool. The results obtained in the Optiwave simulation tool are validated by theoretical implementation in the MATLAB tool.

Asymmetric hybrid full-duplex POF-based VLC transmission links

This paper presents an asymmetric full-duplex solution based on visible light communications (VLC) for indoor wired and wireless hybrid signal transmission. The signal is distributed by a polymer optical fiber (POF) link and passively radiated. The proposed system includes two VLC links: a low-speed downlink and a high-speed uplink using an image sensor (IS) and photodiode detection (PD) based receivers. PD-based system communication performance is evaluated by means of error vector magnitude (EVM) for different modulation orders quadrature phase shift keying (QPSK), 16- and 64-quadrature amplitude modulation (QAM), while the IS-based system is characterized in terms of the success of reception (SoR). High-speed data transmission up to 160 Mbps with a 16-QAM modulation scheme and low-speed data transmission up to 500 bps with 98.6% of SoR using a non-return zero on–off keying (NRZ-OOK) scheme over a 1.5 m optical wireless link are demonstrated. Finally, simulations of the wireless channel are performed to evaluate the misalignment tolerance of the system; and, to estimate the uplink performance at longer distances.

Design and Performance Analysis of DWDM-PON

This paper presents on the design and analysis of Dense Wavelength Division Multiplexing Passive Optical Network (DWDM-PON) which is the upcoming trend technology nowadays to transmit up to 40 Gbps data. Various modulation techniques such as Non-Return Zero (NRZ), Return-Zero (RZ) and duo binary coding are simulated in this DWDM-PON. Using OptiSystem software, DWDM-PON is designed and simulated for 32 channels with spacing of 100 GHz and bit rate of 10 Gbps. An Erbium Doped Fiber Amplifier (EDFA) and Dispersion - Compensating Fiber (DCF) is deployed in the DWDM design. It is found that duo binary modulation technique gives the best performance with minimum BER of 2.66x10-19. From the simulation result, it also found that the proposed DWDM PON design is suitable to be deployed for current network.

Lateral-Zigzag PN Junction Enabled High-Efficiency Silicon Micro-Ring Modulator Working at 100Gb/s

We propose and demonstrate a novel lateral-zigzag PN junction for silicon modulator working in C and O bands. The designed PN junction exhibits characteristics of large bandwidth, high modulation efficiency, and easy fabrication. For demonstration, it is embedded in a 220 nm silicon rib waveguide on a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thick buried oxide layer to form a micro-ring modulator. The measured 3 dB electro-optic bandwidth of the fabricated modulator is 42 GHz while the resistor-capacitor (RC) bandwidth is measured and calculated to be 174 GHz. Clear and open eye diagrams are obtained for 50 Gb/s non-return zero (NRZ) and 100 Gb/s four-level pulse amplitude modulation (PAM4) signals. The modulation power consumption is only 14 fj/bit.

A 56-Gb/s Reconfigurable Silicon-Photonics Transmitter Using High-Swing Distributed Driver and 2-Tap In-Segment Feed-Forward Equalizer in 65-nm CMOS

This article presents a reconfigurable silicon- photonics transmitter (TX) for short-reach optical interconnects. The proposed hybrid-integrated TX combines a 65-nm CMOS driver with a 180-nm SOI-CMOS silicon-photonic Mach-Zehnder Modulator (MZM). The driver integrated with in- segment fractional-UI spaced feed-forward equalizer (FFE) is proposed to support the non-return-zero (NRZ) signaling, electrical- and optical-domain 4-level pulse-amplitude modulation (PAM-4) signaling. The driver employs a reconfigurable distributed topology to achieve high swing, wide bandwidth and flexible operation. The MZM is driven differentially in a push-pull configuration for high modulation efficiency. Measurement results show that the proposed TX operates up to 50-Gb/s NRZ data rate with 4-Vppd swing and 1.92-ps RMS jitter. In the optical PAM-4 mode, it reaches 56-Gb/s data rate and achieves &#x003E;5-dB extinction ratio (ER) at the cost of 10.9-pJ/bit power efficiency.

Design and analysis of optimized CORDIC based GMSK system on FPGA platform

The Gaussian minimum shift keying (GMSK) is one of the best suited digital modulation schemes in the global system for mobile communication (GSM) because of its constant envelop and spectral efficiency characteristics. Most of the conventional GMSK approaches failed to balance the digital modulation with efficient usage of spectrum. In this article, the hardware architecture of the optimized CORDIC-based GMSK system is designed, which includes GMSK Modulation with the channel and GMSK Demodulation. The modulation consists of non-return zero (NRZ) encoder, an integrator followed by Gaussian filtering and frequency modulation (FM). The GMSK demodulation consists of FM demodulator, followed by differentiation and NRZ decoder. The FM Modulation and demodulation use the optimized CORDIC model for an In-phase (I) and quadrature (Q) phase generation. The optimized CORDIC is designed by using quadrant mapping and pipelined structure to improve the hardware and computational complexity in GMSK systems. The GMSK system is designed on the Xilinx platform and implemented on Artix-7 and Spartan-3EFPGA. The hardware constraints like area, power, and timing utilization are summarized. The comparison of the optimized CORDIC model with similar CORDIC approaches is tabulated with improvements.

Analysis of 2 × 10 Gbps MDM enabled inter satellite optical wireless communication under the impact of pointing errors

Technological advancement in Optical Wireless Communication has led the race to harvest such a novel technique which is capable of providing higher data rates and at the same time lower power consumptions. To provide more cost effective solution and immunity to various losses, the use of mode division multiplexing (MDM) technique is proposed. In this work, 2 independent channel each having unique mode is used to carry non return zero (NRZ) encoded data of 10 Gbps each on inter-satellite optical wireless communication (Is-OWC) network. The impact of pointing errors is also studied in this work. The result are presented in form of BER and Eye Diagrams.

Assessment of Rz and Nrz Coders In Free Space Multiplexing System with Reduced Attenuation Effect and Increased Q Factor

Free space optical communication (FSO) is the key technology for connecting systems by means of air as a medium. However signal will lose its strength due to atmospheric losses like rain, fog and other external environmental factors. Wavelength division multiplexing (WDM) approaches are used nowadays which improves signal strength at the receiver. For a perfect communication to happen, the attenuation has to be reduced as much as possible. In this paper, Quality factor (Q) and Bit error rate (BER) of the signal are analysed by simulation models. The line encoding techniques Non- Return-Zero (NRZ) and Return- Zero (RZ) methods were evaluated. The maximum achievable distance is 5kms for power of 40dbm.

Manchester encoder component for data processing IoT environment

Line encoding is crucial especially in data communication which part of internet of things environment. Line encoding doing encode raw bit stream and applying some rules before transmitting to transmission medium. Some example of encoding technique is: non-return zero encoding (NRZ), return-zero encoding, and Manchester encoding. Manchester coding technique have advantages compared to NRZ and RZ coding. Manchester coding can recognize bit interval and will have no problem to encode long same bit stream. Manchester encoder commonly built using logical XOR gate, with clock and bit stream as input and output of XOR gate will determined as encoded signal. The common design has a weakness since the clock is use in operation, and the output will be separate into two parallel bit stream. Common design also has spike glitch in some transitions. In this work, the new design of Manchester encoder using FPGA device is proposed to overcome common design problems and suitable to be implemented in IoT environment.

Analysis and Reduction of Crosstalk in Hybrid TWDM System using Transmitter Line Coding Diversity

Objectives: Optical fibres are becoming the backbone of communication network due to its huge data carrying capacities. But there are many losses in the data transfer such as crosstalk which can reduce the data carrying capacity of an optical fibre network. Methods: This paper presents a crosstalk immune transmitter diversity hybrid modulation for wavelength division passive optical network, with the incorporation of Differential Phase Shift Keying (DPSK) format for downstream and Non Return-Zero (NRZ) for upstream. Findings: The network becomes less prone to nonlinearities and enables the system to support 6144/512 users. Data rate of system has been achieved for 120 Gbps downstream as each wavelength carry 10 Gbps and total 80 Gbps for upstream. An acceptable Bit Error Rate (BER) range i.e. 10-9 has been attained for a significant distance of 110 Km for both directions. The results have been attained without any dispersion compensation and costly modules only using Erbium Doped Fiber Amplifier (EDFA) for downstream. A semiconductor optical amplifier is placed to re modulate data streams. Also comparison is being done by using same transmitter and hybrid transmitters. It is observed that Differential Phase Shift Keying (DPSK) for one direction Non Return-Zero (NRZ) for upstream provide better results. Applications: This model can significantly reduce the crosstalk over an optical fibre network during the transmission of data in upstream and downstream by achieving 80Gbps and 10Gbps respectively

Simulation Analysis of 240gbps Hybrid OTDM System over Symmetrical Pulse Reshaping Module

Objective: Optical fibers are the fastest way to transmit the data or information from one place to another without any loss of data. Optical fibers are evolving since their invention, and hence number of researchers is currently working on its evolution Findings: This paper proposed a new approach in Optical Time Division Multiplexing (OTDM) at 240Gbps by incorporating using three different approaches. Different approaches consisting of transmission employing Return- Zero (RZ) transmitter for all time delayed signals, Non Return-Zero (NRZ) for signal and finally hybrid configuration Return-Zero to Non Return-Zero (RZ-NRZ). Hybrid technique is carried out to reduce crosstalk and interference among time multiplexed channels. Methods: The variety of experiments has been carried out under the controlled simulation environment with the help of optic system results reveal that very less crosstalk found in hybrid configuration. Proposed system is designed in such a way that it is capable to support 240gbps Optical Time Division Multiplexing (OTDM) over 180 km with acceptable bit error rate. Applications: The proposed technique is based on hybrid model and hence easily able to meet the huge demand for higher capacity and larger bandwidth, this system is able to provide high speed transmission.

Experimental demonstration of a 10BASE‐T Ethernet visible light communications system using white phosphor light‐emitting diodes

In this study, a compact design of a highly efficient, and a high luminosity light-emitting diode (LED)-based visible light communications system is presented, which is capable of providing standard room illumination levels and also wide-coverage Ethernet 10BASE-T optical wireless downlink communications over a distance of 2.3 m using commercial white light phosphor LEDs. The measured signal-to-noise ratio of the designed Ethernet system is >45 dB, thus allowing error-free communications with both on-off keying non-return zero and differential Manchester-coded modulation schemes at 10 Mbps. The uplink has been provided via a wireless infra-red link. A comparative study of a point-to-point wired local area network (LAN) and the optical wireless link confirms no discernible differences between them. The design of the transmitter is also shown to be scalable, with the frequency response for driving 25 LEDs being almost the same as driving a single LED. LED driving units are designed to match with the Ethernet sockets (RJ45) that conform to the existing LAN infrastructures (building and portable devices).

Experimental Demonstration of 50-Mb/s Visible Light Communications Using 4&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\,\times\,$ &lt;/tex-math&gt;&lt;/inline-formula&gt;4 MIMO

This letter reports the experimental demonstration of an indoor visible light nonimaging multiple-input multiple-output system with an aggregate error free bit rate of 50 Mb/s over a distance of 2 m. The system uses four independent white LED transmitters, each transmitting 12.5 Mb/s of data in the ON-OFF keying nonreturn zero format, and four independent nonimaging optical receivers. The performance of four detection methods ranging from the basic channel inversion to the more advanced space time techniques is compared experimentally. The results gathered demonstrate that the simplest technique is capable of the same bit error rate as the most complex scheme. The system also provides full illumination with a mean level of 350 Lux satisfying the ISO lighting standards for home and office environments.

160-Gb/s NRZ-DQPSK optical transmission system employing QC-LDPC code

A quasi-cyclic low-density parity check (QC-LDPC) code is constructed by an improved stability of the shortest cycle algorithm for 160-Gb/s non-return zero differential quadrature phase shift keying (NRZ-DQPSK) optical transmission system with the fiber-based optical parametric amplifier (FOPA). The QC-LDPC code with stability of the shortest cycle reduces the bit error ratio (BER) to 10-14 and restrains the error floor effectively.

FFT based Acquisition Techniques of GPS L2C Signals

The modernization of the GPS lead to the launch of additional GPS signal, L2C second civilian GPS signal to become available in full constellation. L2C signals have longer ranging codes which leads to larger search space and increase in computational complexity. L2C signals makes use of two PRN sequences CM (Civil Moderate) and CL (Civil Long) of 20ms and 1.5sec long. In this paper a code generator is designed for generating the CM and CL sequences, and two local replica codes NRZ (Non Return Zero) and RZ (Return Zero) Codes are designed. The code phase and carrier Doppler are estimated based on the various FFT (Fast Fourier Transform) based acquisition techniques.

12.5 Gb/s carrier-injection silicon Mach—Zehnder optical modulator

We demonstrate a 12.5 Gb/s carrier-injection silicon Mach—Zehnder optical modulator. Under a nonreturn-zero (NRZ) pre-emphasized electrical drive signal with voltage swing of 6.3 V and forward bias of 0.7 V, the eye is clearly opened with an extinction ratio of 8.4 dB. The device exhibits high modulation efficiency, with a figure of merit VπL of 0.036 V·mm.

Theoretical investigation of phase-based all-optical logic gates based on AlGaAs microring resonators

We propose and numerically verify a phase-based all-optical logic gates (AND, OR, XOR, NOT, NAND, NOR and XNOR, i.e. all seven basic logic gates) operation scheme based on cascaded AlGaAs microring resonators. The logic function realization is supported by the signal light phase change and extraction, the phase control in this scheme depending on cross phase modulation (XPM) in the AlGaAs microring. By inputting a non-return zero (NRZ) intensity signal as pump light, the probe light (continuous-wave, CW) will experience different phase shift and then a phase-based logical function can be obtained in this process. By choosing different pump power level, reference phase and the output port of a Mach–Zehnder interferometer (MZI), all seven basic logic operations can be realized by using the same device. The modulation depth, bandwidth and minimum power requirement of this scheme have also been discussed in detail.

Theoretical investigation of phase-based all-optical NOT, XOR and XNOR logic gates based on AlGaAs microring resonators

We propose and numerically verify a phase-based all-optical logic gate (NOT, XOR and XNOR) operation scheme based on cascaded AlGaAs microring resonators. Phase control in this scheme depends on cross-phase modulation in the AlGaAs microring. The realization of NOT logic depends on the π phase shift of light transmission, and this π phase shift can be naturally obtained in microring resonators in the under-coupled state. Inputting a non-return zero intensity signal as pump light, the probe light (continuous wave) will experience a different phase shift and a phase-based logical function can be realized in this process. The bandwidth and the minimum power requirement of this scheme are also discussed in detail.

Investigation of data-format-transparent multiwavelength all-optical clock recovery using a single FP-SOA

Multiwavelength clock recovery (CR) is desired to perform all-optical parallel processing, which has potential application in optical communication systems that use WDM technology. Fabry–Pérot semiconductor optical amplifier (FP–SOA) can perform the similar filter function as passive FP filter, and can simultaneously provide gain for oscillation pulses in the cavity; it is essentially an active filter. We experimentally demonstrated simultaneous multiwavelength all-optical CR from input 36.47-Gb/s pseudo-return-zero (PRZ) data and non-return-zero (NRZ) data using a single multi-quantum-well (MQW) FP-SOA with facets reflectivity of 30%. The presented multiwavelength CR scheme is also suitable for PSK signals. Dual-channel CR from input two channels 36.47-Gb/s 2 23−1 NRZ-DPSK data located at different wavelength is experimentally demonstrated. This scheme is transparent for data formats, which is very important for next generation optical networks.