Gbps Signal Research Articles

Enhanced Performance Analysis of 120 Gbps Single‐Channel IQ Modulation Based PDM‐FSO Transmission System Using 64‐QAM Signals

ABSTRACTThe ever‐augmenting demand of data channel‐bandwidth by the end users has resulted in the exploration of new transmission techniques for wireless transmission networks. In this work, we have demonstrated the modeling of a single‐channel free space optics (FSO) transmission system by employing polarization‐division‐multiplexing (PDM) technique. Further, in‐phase‐quadrature modulation (IQM) has been used to increase the transmission efficiency of the system. To decrease the baud‐rate of the system, we have proposed the use of 64‐level quadrature amplitude modulation (QAM) signals. The net transmission rate of the system is 120 Gbps with a baud‐rate of 10 Gbps. Furthermore, the overcome the signal degradation of the 120 Gbps signal propagating through atmospheric channel, we have reported the use of advanced digital signal processing (DSP) algorithms. The system's performance is investigated for adverse external climate weather conditions and the results reported show reliable 120 Gbps data transmission along range between 870 m and 16.25 km with good performance of BER and EVM 7.5%.

Suppression of Simultaneous Switching Noise Using Embedded Capacitor Method in High-Speed Systems

Gbps signals are commonly used in modern high-speed IO designs. These systems require a high level of signal accuracy. However, these signals can cause current fluctuations at high frequencies due to parasitic inductance on the package and board, leading to significant changes in supply voltage. DDRX interfaces that transmit data up to 4.8 Gbps induce simultaneous switching noise (SSN) in the voltage regulator module (VRM). One of the adverse effects of SSN is timing jitter, also known as power supply-induced jitter. The amount of SSN is directly proportional to the number of signals on a parallel bus. Discrete capacitors may not be effective in reducing SSN impact when data is transmitted at high speeds. The current approach used to predict and evaluate errors in SSNs relies on the designer's expertise, which requires accurate estimates of packaging parasitic. In this paper, a practical approach to lessen SSN is presented through the use of embedded capacitors placed between planes and optimizing discrete capacitors by connecting them in a way that measures the impact of supply noise on the I/O transistor circuit performance at the DDRX interface. Two boards were designed, evaluated, and subsequently compared their results.

A Wavelength Tunable Multi-Section PIC as an Upstream Transmitter for TWDM Networks

In this paper, we demonstrate a novel multi-section directly modulated laser transmitter for upstream operation in the application of time wavelength division multiplexing (TWDM) architecture. The photonic integrated circuit (PIC) is fabricated using a regrowth-free process that favors simplified and fast manufacturing. The PIC is based on a master-slave configuration, with an addition of a variable optical attenuator (VOA) section between them, and a semiconductor optical amplifier (SOA) at the output. The VOA enables control of the optical injection from the master to the directly modulated slave laser improving the transmission performance. The integrated SOA section at the output is used to boost or turn off the optical output power of the transmitter, thereby enabling burst mode operation. Experimental results show that the PIC can be tuned to four wavelength channels on a 100 GHz frequency grid. We also demonstrate that each channel achieves error-free performance (bit error ratio < 10e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ), when modulated with 10 Gbps signal and transmitted over 25 km and 50 km fiber. The SOA-based output disable feature of the PIC delivers more than 60 dB attenuation.

A Decision Feedback Equalization Algorithm Based on Simplified Volterra Structure for PAM4 IM-DD Optical Communication Systems

A novel simplifying Volterra structure algorithm is proposed for an intensity modulation direct detection (IM-DD) optical fiber short distance communication system using the decision feedback equalization algorithm (DFE). Based on this algorithm, the signal damage for the four-level pulse amplitude modulation signal (PAM-4) is compensated, which is caused by device bandwidth limitation and dispersion during transmission. Experiments have been carried out using a 25 GHz Electro-absorption Modulated Laser (EML), showing that PAM-4 signals can transmit over 10 km in standard single-mode fiber (SSMF). The 112 Gbps and 128 Gbps signals can reach the error rate threshold of KP4-FEC (BER = 2 × 10−4) and HD-FEC (BER = 3.8 × 10−3), respectively. The simplified principle and process of the proposed Volterra-based equalization algorithm are presented. Experimental results show that the algorithm complexity is greatly reduced by 75%, which provides effective theoretical support for the commercial application of this algorithm.

A 40-Gbps fiber-FSO convergent transmission system employing OFCL-based WDM and external modulation technique

We have proposed and demonstrated a 40Gbps fiber-free space optics (FSO) convergent system based on external modulation and wavelength division multiplexing (WDM) technique. In this experiment, 4010×4 Gbps signal is successfully transmitted employing WDM scheme over 50 km single mode fiber plus 2.5 km FSO distance. Optical frequency comb lines (OFCL) are generated using a continuous wave laser diode, a radio frequency signal generator, a dual drive Mach Zehnder modulator, and an electrical attenuator. OFC lines, having a side mode suppression ratio (SMSR) value of ∼40 dB and flatness of ∼0.4 dB, are employed as broadband laser source in the presented convergent system. The performance of the fiber-FSO system is investigated theoretically for different weather conditions. Very low power penalty with low bit error rate (BER), clear eye diagrams, and standard Q-factor are achieved in the proposed system. The power penalty is restricted within 2.5 dB and 5.8 dB at a BER of 10−9 for 50 km SMF plus 2.5 km FSO distance in clear weather and 50-km SMF plus 0.4-km FSO distance in heavy fog condition respectively. Thus, the proposed WDM-convergent system is efficient enough for high data rate transmission along with low BER value of ∼10−9 and high Q-factor for different environmental scenarios.

Data-driven fiber model based on the deep neural network with multi-head attention mechanism.

In this paper, we put forward a data-driven fiber model based on the deep neural network with multi-head attention mechanism. This model, which predicts signal evolution through fiber transmission in optical fiber telecommunications, can have advantages in computation time without losing much accuracy compared with conventional split-step fourier method (SSFM). In contrast with other neural network based models, this model obtains a relatively good balance between prediction accuracy and distance generalization especially in cases where higher bit rate and more complicated modulation formats are adopted. By numerically demonstration, this model can have ability of predicting up to 16-QAM 160Gbps signals with any transmission distances ranging from 0 to 100 km under both circumstances of the signals without or with the noise.

Ring based hybrid FSO- fiber optic architecture utilizing same wavelengths for downstream and upstream transmission with FN/DN protection capability

This paper proposes a reliable hybrid 4 × 10 Gbps fiber optic-FSO based ring architecture. The proposed architecture aims to provide reliable and bandwidth-efficient transmission. The proposed architecture has a fault protection capability in presence of the link failure occurring at the feeder network (FN) and distribution network (DN) towards the central office (CO) and optical networking unit (ONU) respectively. To avail the benefits of free space optics (FSO), it is integrated with the optical fiber at the user end. The architecture transmits the data on the ring in only a clockwise direction for both downstream and upstream transmission and therefore enables the utilization of the same wavelengths without any interference. i.e. the proposed architecture improves the bandwidth utilization and needs only half of the spectrum. In the proposed architecture, four 10 Gbps signals are propagated through a 20 km single-mode fiber (SMF) and a 200 m length of free-space/optical fiber link for the downstream and upstream transmissions. We also compared the signal transmission performance of architecture in terms of bit error rate (BER) for different weather conditions of the FSO link at the user side. The architecture works well for the different weather conditions and can transmit data through the FSO link for upto 700 m and 200 m for clear and heavy rain weather conditions respectively. Protection against faults in the fiber links; improves the survivability and reliability of the network. The proposed architecture is useful in rural and urban hilly areas where signal transmission interrupts frequently due to various geographical challenges.

Design and Simulation of Physical Layer Security for Next Generation Intelligent Optical Networks

With the latest technological advancements and attractive features of next generation intelligent optical networks such as high bandwidth, low power consumption, and low transmission loss, etc., they have been considered as most viable solution to satisfy promptly growing bandwidth demands. However, main optical network components bring forth a set of security challenges and reliability issues, accompanied by new vulnerabilities within the network. This paper proposes a new design for an optical encryption and decryption method for enhancing optical network security using p–i–n photodiode which generates Pseudo Random Binary Sequence (PRBS) as a shot noise fluctuations and wavelength converter based design using Semiconductor Optical Amplifier based XOR gate which utilizes Cross-Phase Modulation. The system performance based on Bit Error Rate and Q factor are analyzed at different data rates for different link lengths up to 100 km using OptiSystem. It is observed that error free transmission with a BER of 10–12 is achieved a data rate of 10 Gbps for a link length of only 30 km for the system with PIN photodiode’s shot noise being used for PRBS sequence generation. However, wavelength conversion based system enables transmission of signal at 10Gbps signal up to a link length of 90 km.

High-speed silicon microring modulator at the 2 µm waveband with analysis and observation of optical bistability

Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with V π L of 0.85 V · cm . The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.

Suppression of Mode Partition Noise in FP Laser by Frequency Modulation Non-Coherent Detection

We propose a frequency modulation (FM) non-coherent detection (NCD) scheme, attempting to suppress the mode partition noise (MPN) in fiber-optic communication systems with the Fabry-Perot (FP) semiconductor laser as the light source. The system comprises a FM transmitter with a directly modulated FP laser and a semiconductor optical amplifier, standard single mode fiber, and a NCD receiver with an optical slope filter as the FM to intensity modulation (IM) signal convertor placed in front of a conventional photodetector. In this configuration, the MPN is converted into a random frequency deviation by the transmitter and is reduced by the slope filter after fiber transmission. The FM signal is therefore less noisy after being converted back into the IM signal. With optimized parameter selections, our simulation result shows that the FM-NCD system allows a direct transmission span of 40 km for the 10 Gbps signal at 1577 nm, and 120 km for the 25 Gbps signal at 1310 nm, respectively, as opposed to a span of only 3 km and 10 km achievable by a conventional FP laser driven IM direct detection (DD) system for the corresponding signals at the corresponding wavelengths. Remarkably, our simulation result also shows that the performance of the FM-NCD system even surpasses that of a directly modulated distributed feedback laser driven IM-DD system, in which the maximum span is around 15 km and 60 km for 10 Gbps and 25 Gbps signals at 1577 nm and 1310 nm, respectively.

Fibre optic parametric amplifier for high capacity burst-mode access networks.

We compare performance of a polarization insensitive fiber optic parametric amplifier (PI-FOPA), a commercial erbium doped fiber amplifier (EDFA) and a discrete Raman amplifier (DRA) in a 50 km long-reach optical access network transmitting bursts of 10 Gbps signal with traffic density ranged from 5% to 97%. We demonstrate that for the same power budget the PI-FOPA allows for transmission of bursty traffic with density up to 97% while DRA and EDFA are limited to 30% and 15%, respectively. Alternatively, we demonstrate PI-FOPA to allow for 3 dB and 5 dB higher power budget than the DRA and EDFA, respectively, for the worst case scenario of 75% traffic density.

Net 220 Gbps/λ IM/DD Transmssion in O-Band and C-Band With Silicon Photonic Traveling-Wave MZM

We present the design and characterization of O-band and C-band silicon photonic (SiP) traveling wave Mach-Zehnder modulators (TW-MZM) allowing 220 Gbps/λ net rate operation. The designed modulators show over 45 GHz 3-dB E-O bandwidth with a single-segment design. In the O-band, with simple linear feed forward equalization, we transmit net 203 (200) Gbps signal over 2 km (10 km) of single-mode fiber (SMF) below the hard-decision forward error correction (HD-FEC) BER threshold of 3.8 × 10−3. With the aid of nonlinear Volterra equalizer and one 2.3Vpp driving signal, we transmit net 225 (216) Gbps PAM8 signals assuming 20% overhead soft-decision FEC with a normalized general mutual information (NGMI) threshold of 0.8798 over 2 km (10 km) of SMF. The C-band design enables net 220 Gbps in B2B and net 215 Gbps over 500 m of SMF above the specified NGMI threshold. These results are the highest reported net rate for SiP MZM in an intensity modulation direct-detection (IM/DD) system, fabricated entirely in a commercial foundry.

On-Chip Selective Dual-Mode Switch for 2-μm Wavelength High-Speed Optical Interconnection

In this work, we designed and fabricated a dual-mode switch based on triple-waveguide couplers and two thermal phase shifters, and demonstrated the first silicon-integrated mode division multiplexing (MDM) switching network for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2-\mu \text{m}$ </tex-math></inline-formula> waveband. The proposed dual-mode switch shows < 2.6 dB insertion loss, <−20 dB inter-mode crosstalk at 1960 nm, with broadband operation over 100 nm. The experimental results of dynamic switching at 10 kHz presents 9.2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> rising time and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13.2-\mu \text{s}$ </tex-math></inline-formula> falling time, with switching power of 19.2 mW. High speed on-chip MDM routing of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 60$ </tex-math></inline-formula> Gbps signal was experimentally demonstrated using the proposed 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> MDM switching network, drawing the promising prospect for the future photonic integration and high-speed MDM networking at 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> waveband.

Physical Layer Encryption for WDM Optical Communication Systems Using Private Chaotic Phase Scrambling

Protecting the security of optical network is a major worldwide challenge. The conventional schemes for securing communications are based on cryptography at the MAC layer and its higher layers, which are facing a great threat with the development of quantum computers. Optical encryption is a promising way for building security on the physical layer of optical communications. In this work, we propose a novel optical encryption scheme for wavelength division multiplexing (WDM) fiber-optic communication systems, by utilizing the private chaotic phase scrambling. Secure transmission of 50 Gbps signal over 50-km standard single-mode fiber is experimentally and numerically demonstrated. The results show that the WDM signal is efficiently encrypted into a noise-like signal, due to the spectral broadening effect of chaotic phase scrambling. Since the processes of encryption and decryption are totally implemented in the optical domain, the proposed scheme can encrypt the entire network traffic with low latency and high speed. Moreover, the proposed encryption scheme is compatible with the existing WDM optical networks, and only one pair of encryption and decryption devices is sufficient to encrypt all WDM channels, thus the scheme can be easily implemented at low hardware cost.

Cascaded Microwave Photonic Filters for Side Mode Suppression in a Tunable Optoelectronic Oscillator applied to THz Signal Generation &amp; Transmission

We demonstrate experimentally an optoelectronic oscillator (OEO) in which high side-mode suppression is achieved by cascading a phase modulator-based single passband tunable microwave photonic (MWP) filter with an optoelectronic feedback loop-based infinite impulse response (IIR) MWP filter. The OEO provides an RF oscillation that can be tuned from 6.5 GHz to 17.8 GHz with a phase noise lower than -103 dBc/Hz. Experimental results show that inclusion of the IIR section leads to a 20 dB reduction of phase noise close to the carrier and an increase of 10 dB in side mode suppression, compared to the equivalent OEO without an IIR section. The OEO was used to drive an optical frequency comb generator to generate a THz signal at 242.6 GHz by optical heterodyning; inclusion of the IIR section increases suppression of the side modes neighboring the THz carrier. A radio over fiber link was then implemented at a 242.6 GHz carrier frequency, with transmission of a 24 Gbps signal over 40 km of fiber and a 30 cm wireless path at a bit error rate below the forward error correction limit. The proposed system may be applied to frequency reconfigurable THz links and radars.

1.28 and 5.12 Gbps multi-channel twinax cable receiver ASICs for the ATLAS Inner Tracker Pixel Detector upgrade

We present two prototypes of a gigabit transceiver ASIC, GBCR1 and GBCR2, both designed in a 65-nm CMOS technology for the ATLAS Inner Tracker Pixel Detector readout upgrade.The first prototype, GBCR1, has four upstream receiver channels and one downstream transmitter channel with pre-emphasis. Each upstream channel receives the data at 5.12 Gbps through a 5 m AWG34 Twinax cable from an ASIC driver located on the pixel module and restores the signal from the high frequency loss due to the low mass cable. The signal is retimed by a recovered clock before it is sent to the optical transmitter VTRx+. The downstream driver is designed to transmit the 2.56 Gbps signal from lpGBT to the electronics on the pixel module over the same cable. The peak–peak jitter (throughout the paper jitter is always peak–peak unless specified) of the restored signal is 35.4 ps at the output of GBCR1, and 138 ps for the downstream channel at the cable ends. GBCR1 consumes 318 mW and is tested.The second prototype, GBCR2, has seven upstream channels and two downstream channels. Each upstream channel works at 1.28 Gbps to recover the data directly from the RD53B ASIC through a 1 m custom FLEX cable followed by a 6 m AWG34 Twinax cable. The equalized signal of each upstream channel is retimed by an input 1.28 GHz phase programmable clock. Compared with the signal at the FLEX input, the additional jitter of the equalized signal is about 80 ps when the retiming logic is off. When the retiming logic is on, the jitter is 50 ps at GBCR2 output, assuming the 1.28 GHz retiming clock is from lpGBT. The downstream is designed to transmit the 160 Mbps signal from lpGBT through the same cable connection to RD53B and the jitter is about 157 ps at the cable ends. GBCR2 consumes about 150 mW when the retiming logic is off. This design was submitted in November 2019.

32 Gbps Data Transmission With 2D Beam-Steering Using a Silicon Optical Phased Array

We demonstrate optical wireless transmission with two-dimensional (2D) beam-steering using an optical phased array (OPA). The OPA consists of 64-elements of electro-optic p-i-n phase shifters and thermo-optic tunable n-i-n grating radiators, employed for 2D beam-steering in the transversal and longitudinal directions. The design of the transmitter and receiver device parameters allowed the error-free transmission of 32 Gbps data over a distance of 3 m. The beam-steering range covered 46.0°/10.2° in the transversal/longitudinal direction with a beam divergence of 0.7°/0.9°. When compared with a transmission over fiber, it was confirmed that free-space transmission through the OPA did not degrade the quality of the tens of Gbps signals.

Transmission Distance Extension of Directly Modulated Tunable V-cavity Laser Using AWG Wavelength Detuning

Directly modulated tunable lasers are highly desirable for constructing dense-wavelength division multiplexing (DWDM) access networks, owing to their advantages of low cost, compact size and low power consumption. However, the transmission distance for 10 Gbps is usually limited to about 10 km in the telecom C-band in standard single-mode fiber (SMF) due to wavelength chirp. Here we propose and demonstrate a simple technique for extending the transmission distance by detuning the wavelength of a tunable V-cavity laser with respect to DWDM multiplexers. Experiment results show that 10 Gbps signal can be transmitted error-free (BER<10−12) over 20 km SMF with a wavelength-detuning with respect to a Gaussian-type arrayed waveguide grating (AWG) without dispersion compensation. The power penalty is only 1 dB compared to the back-to-back transmission.

Opening up ROADMs: a filterless add/drop module for coherent-detection signals

We present an open design of a filterless add/drop reconfigurable optical add/drop multiplexer module with a NETCONF northbound interface. Compared to commercial offerings, the device design is openly documented and available for detailed inspection. Performance is evaluated with up to seven adjacent high-speed 100 Gbps signals on a 50 GHz frequency grid.

Techniques of impedance matching for minimal PCB channel loss at 40 GBPS signal transmission

PurposeThis paper aims to analyze the negative impact of surface mount (SMT) pad and imperfect via structure such as stub, pad, non-functional pad (NFP) and anti-pad on the signal integrity at 40 Gbps transmission on printed circuit board (PCB) due to impedance mismatch or discontinuity. The optimized modeling of via and SMT structures is performed to achieve minimal impedance mismatch and insertion loss less than 10 dB for six-inch full path transmission line between transmitter and receiver on PCB at Nyquist frequency 20 GHz.Design/methodology/approachThis work is split into two phases. The first phase involves optimization of via and SMT structures in three-dimensional electromagnetic (3DEM) simulation using Hyperlynx Via Wizard and Keysight EMPro software, respectively, followed by analysis of time domain reflectometry (TDR) and insertion loss (Sdd21). Whereas, in the second phase, full path hybrid mode simulation involving vias for signal layer transition, a 6-inch PCB channel and SMT pads is performed using Keysight ADS software to observe the TDR, Sdd21 and eye diagram at 40 Gbps transmission.FindingsImperfect via and SMT structures have a negative effect on signal reflection and attenuation. The optimized via and SMT minimizes the impedance mismatch by 81 per cent and insertion loss by 4.5 dB, ultimately enlarging the eye diagram opening to achieve minimal data loss at receiver with 40 Gbps transmission.Originality/valueThe results of original empirical research work on signal integrity analysis that optimizes the PCB channel design to achieve 40 Gbps signal transmission are presented in this study. It serves as a reference guide for high-speed PCB layout design.