Power Fading Research Articles

Recurrent Neural Networks and Recurrent Optical Spectrum Slicers as Equalizers in High Symbol Rate Optical Transmission Systems

The transition to the edge-cloud era makes ultra-high data rate signals indispensable for covering the immense and increasing traffic demands created. This ecosystem also seeks for power efficient optical modules that will deliver this enormous data load. Optical communication systems and their continuous evolution have responded to the upward trend of capacity needs in all different network ecosystems, scaling from short-reach links serving data center, fiber-to-the-home and 5G/B5G services to metro and long-haul transoceanic cables. Kerr induced non-linearities at long haul and dispersion induced power fading at short reach remain intractable problems that vastly affect high symbol rate systems. So, they must be addressed in a power efficient way in order to cope with the ever-increasing traffic requirements. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we review our recent work in machine learning and neuromorphic processing in the optical domain for the mitigation of transmission impairments at very high symbol rates. Post-detection techniques based on bidirectional recurrent neural networks for non-linearity compensation and neuromorphic recurrent optical spectrum slicers for power fading mitigation and self-coherent detection emerge as promising solutions for mid-term deployment in long-haul and short-reach communication systems respectively. The current work provides new results in both fields focusing on multi-channel detection in the coherent long-haul domain and on a cost/consumption/performance assessment of neuromorphic photonic processing based on recurrent spectrum slicing in comparison to the state-of-the-art. A thorough analysis of other state-of-the-art techniques in both domains is also provided revealing the merits and shortcomings of recurrent neural networks and neuromorphic photonic processing in high-speed optical communication systems.

Performance metrics for the comparison of lithium ion cell aging experiments

The increasing use of lithium-ion cells in large-scale, long-term applications drives a need for design methods that considers aging and accurate state of health estimation. A common approach is to rely on an empirical or semi-empirical aging model fit to experimental data to estimate the evolution of capacity and power fade. Because aging data are costly to collect, pack designers either use Design of Experiment (DOE) techniques to define a set of efficient tests, or use existing aging data to calibrate aging models. Given the increasing quantity of available aging data, the question arises: how can experimental aging campaigns be quickly compared? However, a methodology for the comparison of sets of aging experiments is not discussed in the literature. As a result, pack designers usually rely on intuition to select between multiple aging studies proposed by DOE techniques or in the literature. This work proposes metrics to quantitatively capture the alignment between a set of aging experiments and a target application. These metrics allow pack designers to quickly compare many sets of aging experiments to evaluate those which have tested conditions relevant to the application. Case studies are presented to illustrate the application of these metrics using aging campaign data from the literature. To validate these metrics, this work examines the relationship between these metric values and aging model validation error for calendar aging data for 18650 NMC battery cells. It is demonstrated that greater metric values correspond to reduced model error for an empirical capacity fade model.

Monolithically Integrated O-Band Coherent ROSA Featuring 2D Grating Couplers for Self-Homodyne Intra Data Center Links

In this work, we present an O-band dual-polarization coherent receiver optical sub-assembly (cROSA), monolithically integrated in a 0.25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m BiCMOS technology. The receiver features 248 nm deep ultra violet compatible 2-dimensional grating couplers (2D-GRCs), and an adaptive polarization controller, suitable for mitigation of local oscillator induced power fading in self-homodyne transmission systems. The cROSA is evaluated in system experiments at 64 GBd quadrature-phase shift-keying. Experimental results are related to grating coupler induced polarization crosstalk through Monte-Carlo simulations. Second generation 2D-GRCs are proposed.

Photonic-assisted generation of joint radar and communication signals with immunity to power fading

In this paper, a photonic-assisted generation of joint radar and communication signals with immunity to power fading is proposed based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator. Two dual-drive Mach–Zehnder modulators (DD-MZMs) named DD-MZM1 and DD-MZM2 are respectively located on the upper and lower arms of the DP-BPSK modulator. In DD-MZM1, an intermediate frequency communication signal is single sideband (SSB) modulated on the optical carrier. At one radio frequency (RF) port of DD-MZM2, a split parabolic waveform signal is phase-modulated on the optical carrier to generate SSB radar signal, and the other RF port is used to phase modulate local oscillator signal. By simply adjusting a polarization controller, radar or communication signal can be respectively generated at different frequency band after balanced photoelectric conversion. Experiments are carried out to verify the feasibility of the scheme. Radar signals with bandwidths of 500 MHz and 1 GHz are generated. The error vector magnitude of the generated 16-QAM signal with a baud rate of 100 Msym/s is 5.42%. The frequency tunability and the immunity to power fading are also verified. The proposed method has a simple and compact structure and meets the requirement of long-distance transmission, which has potential applications in emerging intelligence scenarios.

Feedback-based fault-tolerant and health-adaptive optimal charging of batteries

The key technology barriers that hinder the growth of Electric Vehicles (EVs) are long charging time, the shorter life-time of EV batteries, and battery safety. Specifically, EV charging protocols have significant effects on battery lifetime and safety. If not charged properly, the battery could end up with shorter life, and more importantly, improper charging can cause battery faults leading to catastrophic failures. To overcome these barriers, we propose a closed-loop feedback based approach, that enables real-time optimal fast charging protocol adaptation to battery health and possess active diagnostic capabilities in the sense that, during charging, it detects real-time faults and takes corrective action to mitigate such fault effects. We utilize battery electrical–thermal model, explicit battery capacity and power fade aging models, and thermal fault model to capture battery behavior. In conjunction with the models, we adopt linear quadratic optimal control techniques to realize the feedback-based control algorithm. Simulation studies are presented to illustrate the effectiveness of the proposed scheme.

Photonic generation of dual-band dual-chirp waveforms with anti-dispersion transmission.

A photonic approach for generating dual-band dual-chirp waveforms with the capability of anti-dispersion transmission is proposed. In this approach, an integrated dual-drive dual-parallel Mach-Zehnder modulator (DD-DPMZM) is adopted to realize single-sideband modulation of a RF input and double-sideband modulation of baseband signal-chirped RF signals. By properly presetting the central frequencies of the RF input and the bias voltages of DD-DPMZM, dual-band dual-chirp waveforms with anti-dispersion transmission can be achieved after photoelectronic conversion. A complete theoretical analysis of the operation principle is presented. Full experimental verification of the generation and anti-dispersion transmission of dual-chirp waveforms centered at 2.5 and 7.5GHz as well as 2 and 6GHz over two dispersion compensating modules with dispersion values equivalent to 120km or 100km standard single-mode fiber is successfully carried out. The proposed system features a simple architecture, excellent reconfigurability, and immunity to dispersion-induced power fading, which are highly desired in distributed multi-band radar networks with optical-fiber-based transmission.

Receive-diversity-aided power-fading compensation for C-band IM/DD OFDM systems.

A receive-diversity-aided power-fading compensation (RDA-PFC) scheme is proposed and demonstrated to eliminate the chromatic dispersion (CD)-induced power fading for C-band double-sideband (DSB) intensity modulation and direct detection (IM/DD) orthogonal frequency division multiplexing (OFDM) systems. By combining the responses before and after a dispersive element using a maximal-ratio combining (MRC) algorithm, the CD-induced power fading dips within the signal bandwidth of around 50 GHz can be effectively compensated for, which results in an up to 17.6-dB signal-to-noise ratio (SNR) improvement for the fading subcarriers after transmission over 10 km of standard single-mode fiber (SSMF). Using the 16 quadrature amplitude modulation (QAM) format, a diversity receiver with the proposed RDA-PFC scheme can support 170.6-Gbit/s OFDM signal transmission over a 10-km SSMF and reduces the bit error rate (BER) by more than an order of magnitude compared with a conventional receiver. Moreover, 208.1-Gbit/s adaptive bit and power loading OFDM signal transmission over a 10-km SSMF is realized by the proposed RDA-PFC scheme, which improves the capacity by 15.3% compared with the case without RDA-PFC at a BER of 3.8 × 10-3. The proposed RDA-PFC scheme shows great potential in CD-induced power-fading compensation for high-speed IM/DD OFDM systems.

Tailoring electrolyte solvation to push the capacity limit of layered oxide cathodes via polarized ferroelectric polymers

The critical challenges for full lithium utilization in nickel-rich lithium transition metal oxide cathodes are the capacity loss and power fading, which stem from irreversibly structural transition and unstable cathode-electrolyte interface upon excessive delithiation at high charge voltages. Here we discover a novel electrochemical phenomenon that the local solvation structure of the electrolyte can be regulated by well-polarized ferroelectric polymer and demonstrate its potential in pushing the capacity limit of Ni-rich lithium layered oxide cathodes without sacrificing their structural integrity. This polarized configuration in the ferroelectric polyvinylidene fluoride (PVDF) coating tailors the local solvation structure by repelling the electrolyte anions and promoting the aggregation of lithium-ions at the cathode-electrolyte interface, which significantly boost the (de)lithiation kinetics, redox reversibility and structural integrity of the cathodes. The LiNi0.8Co0.1Mn0.1O2 cathode with polarized PVDF displays an exceptionally high capacity of 232 mAh g−1 with a high initial Coulombic efficiency of 92.5%, and the NCM811/graphite pouch cell with polarized-PVDF/PP separator shows a higher capacity retention rate of 88.6% after 200 cycles at 55 °C.

On the Exact Closed-Form ABEP Analysis of Downlink NOMA Over mmWave TWDP Fading

This paper presents the performance analysis of two users’ downlink non-orthogonal multiple access (NOMA) over a millimeter-wave two-wave with diffuse power (TWDP) fading model for successive interference cancellation errors. The new closed-form expressions of average bit error probability (ABEP) for both users are derived for quadrature phase-shift-keying and binary phase-shift-keying modulation pairs. Further, the asymptotic ABEP expressions are derived to provide better insights into the performance analysis. The diversity order of each user is also derived with the aid of asymptotic ABEP expression. The obtained expressions over TWDP fading channels are generalized ABEP expressions as it also shows ABEP expressions for both Rician and Rayleigh fading channels as special cases. Simulation results support the correctness of each analytical ABEP expression.

Photonic Generation of Switchable Multiformat Chirp Signals With Immunity to Power Fading

In this article, a photonic approach for the generation of switchable multiformat chirp signals with immunity to power fading by simply adjusting the bias voltages of a dual-polarization binary phase-shift keying (DP-BPSK) modulator is proposed. A parabolic waveform signal with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> times split is employed to increase the time bandwidth product (TBWP) of the generated chirp signal by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> times. A proof-of-concept experiment is established to verify the feasibility of the proposed scheme. Major characteristics of the signal are verified, such as format switching capability, frequency tunability, immunity to power fading, and pulse compression performance. The relationship between unwanted frequency components and the amplitude of the split parabolic waveform signal is analyzed by simulation. The maximum bandwidth of the generated chirp signal is also given.

Critical Comparison of Li-Ion Aging Models for Second Life Battery Applications

Lithium-ion batteries (LIBs) from electrified vehicles (EVs) that have reached the automotive end of life (EoL) may provide a low-cost, highly available energy storage solution for grid-connected systems, such as peak shaving and ancillary services. There are several issues related to the integration of second life batteries (SLBs) in power systems, such as the variability of the pack design and cell chemistry, in-field assessments of the state of health (SoH), and estimations of the expected lifetimes of SLBs in different power system applications. Model-based approaches are commonly used in the automotive industry for estimating/predicting the capacity and power fade trajectories of LIBs during their life. However, a large variety of models are available with different fidelities, complexities, and computational costs. The accuracy of these estimations is critical for the derivation of business models for SLB applications. This paper presents a qualitative and quantitative assessment of the performance of two well-accepted, state-of-the-art aging models, initially developed for automotive applications and here applied to different SLB applications to predict both the capacity and power fade. These models are evaluated with respect to several performance metrics, such as fidelity of estimation and capability of extrapolation outside the calibration data range. The considered models are classified as semi-empirical physics-based and empirical models, respectively. Three different SLB power profiles, bulk energy for DC fast charge stations and two frequency regulation profiles, are considered, corresponding to different ranges of the SoC, C-rates, and battery temperatures, with the aim of exciting different aging mechanisms. The numerical results provide insight for the selection of aging models for SLB applications based on their performances and limitations.

Two-Way 5G NR Fiber-Wireless Systems Using Single-Carrier Optical Modulation for Downstream and Phase Modulation Scheme for Upstream

Fifth-generation (5G) millimeter-wave (MMW)/sub-THz signals over a two-way fiber-wireless system using single-carrier optical modulation for downstream and phase modulation (PM) scheme for upstream are proposed and implemented for the first time. Compared to multi-carrier optical modulation, using single-carrier optical modulation in downlink is attractive because it can suppress RF power fading due to fiber dispersion and interference caused by optical beating from multiple carriers. Furthermore, compared to intensity modulation scheme, using PM scheme with remotely injection-locked distributed feedback laser diode in uplink is attractive because it enables high robustness to noise and distortion. Through 40-km single-mode fiber, 500-m free-space optical, and 2-m/1-m/0.5-m (downstream)/4-m (upstream) RF wireless cascaded-medium, 5G new radio (NR) MMW/sub-THz signals are transported with low bit error rates and clear constellations in downlink/uplink performance. Such a newly-built two-way 5G NR fiber-wireless system shows promise to perform 5G NR evolution in MMW and sub-THz frequencies, which has significant impacts on fiber-wireless integration.

Experimental research of precoding techniques in a DML-based MB-OFDM UWBoF system

In this paper, an intensity-modulated direct-detection (IM/DD) multiband orthogonal-frequency-division-multiplexing ultra-wideband over fiber (MB-OFDM UWBoF) transmission system using a low-cost directly modulated laser (DML) is analyzed and experimentally verified. Precoding techniques and inter-symbol frequency-domain averaging (ISFA) algorithm are used in this experiment. Precoding techniques are used to suppress the noise introduced by DML and the power fading due to the imperfect frequency response of optoelectronic devices and frequency selective fading. Orthogonal Circular Matrix Transform (OCT) precoding and Discrete Fourier Transform (DFT) precoding were compared when the ISFA algorithm was used. In this scheme, for a single-mode fiber (SMF) link at a distance of 20 km, the 64 Quadrature amplitude modulation (QAM) mapped MB-OFDM UWBoF system using OCT precoding with ISFA and DFT precoding with ISFA scheme can improve the sensitivity of the optical receiver by 0.4 dBm and 0.284 dBm, respectively, compared to no precoding with ISFA at a BER of 3.8e-3. The minimum BER of the 64QAM mapped MB-OFDM UWBoF system scheme with OCT precoding and ISFA scheme is 2.56e-5, which achieves two orders of magnitude improvement compared to the BER threshold of the 7% hard-decision forward error correction (HD-FEC, 3.8e-3).

Improved Weighted Volterra DFE for C-Band 100-Gbit/s PAM-4 Transmission Over 60-km SSMF

To cope with the nonlinear distortions and the chromatic dispersion (CD) induced power fading in double-side band (DSB) intensity modulation and direct detection (IM/DD) transmission systems, high-performance Volterra decision-feedback equalizers (VDFEs) are widely applied. However, similar as linear DFE, the VDFEs suffer from error propagation in the case of wrong decisions. In this letter, to reduce the error propagation probability of VDFEs, we propose and experimentally demonstrate a diagonally-pruned improved weighted VDFE (DP-IWVDFE) in a C-band 4-level pulse amplitude modulation (PAM-4) transmission system. By replacing the hard-decision output by the soft-decision feedback symbol based on a compressed sigmoid nonlinear function in DP-IWVDFE, the error propagation probability can be significantly reduced, which lowers the bit error ratio (BER) by a factor of around two as compared to the DP-VDFE. Besides, 100-Gbit/s PAM-4 transmission over 60-km standard single-mode fiber (SSMF) using DP-IWVDFE is realized with the achieved BER below 3.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{-3}$ </tex-math></inline-formula> , achieving around 3.8-dB, 1.5-dB, and 1-dB improvements of the receiver sensitivity over the polynomial DFE (PDFE), improved weighted PDFE (IWPDFE), and DP-VDFE, respectively.

Electronic dispersion compensation and functional link neural network equalization for IM/DD links

Short-reach fiber optical links employing intensity modulation (IM) at the transmitter (Tx) and direct detection (DD) at the receiver (Rx), suffer from linear and nonlinear sources of impairments due to the interaction of chromatic dispersion (CD) with DD. In this article, joint electronic dispersion compensation (EDC) at the Tx, using two distinct Gerchberg–Saxton(GS) based approaches, and at the Rx, using a functional link neural network (FLNN) equalizer is demonstrated for IM/DD transmission. The first Tx approach utilizes the modified iterative GS algorithm, which partially mitigate linear and nonlinear sources of inter-symbol interference (ISI). The second Tx pre-EDC approach only pre-compensates for the linear power fading effect through implementing a GS based finite impulse response (FIR) filter. At the Rx, a T/2-spaced or T-spaced adaptive post-feed forward equalizer (FFE) is employed to fully compensate residual chromatic dispersion prior to attempting nonlinear equalization. Furthermore, a Volterra nonlinear equalizer (VNLE) is introduced to benchmark the performance and complexity of the FLNN, Subsequently, either a FLNN or a VNLE are utilized for nonlinear system identification and subsequent post-equalization mitigating uncompensated nonlinear sources of ISI. The FLNN nonlinear taps resulting from the functional expansion block are optimized using the recursive least square (RLS) algorithm. The Tx-FIR and Rx-FLNN enable 112 Gbit/s non-return to zero (NRZ) on–off keying (OOK) transmission over 20 km of single mode fiber (SMF) and 112 Gbit/s 4-level pulse-amplitude modulation (PAM-4) transmission over 10 km of SMF. It is shown that the use of Tx pre-EDC reduces the complexity of the required equalization at the Rx. In addition, the FLNN was found to offer a 74% reduction in computational complexity relative to the third-order VNLE.

Reconfigurable microwave photonic mixer for hybrid macro-micro cellular systems.

Microwave photonic mixing can realize the frequency conversion of microwave signals in the optical domain, breaking through the bandwidth bottleneck and electromagnetic interference problems of traditional microwave mixing methods. In the background of the hybrid macro-micro cellular system, a wideband, large dynamic range and reconfigurable microwave photonic mixer is proposed, theoretically analyzed and experimentally demonstrated in this paper. By adjusting the modulator bias voltages and matching the proper digital domain operations, a microwave photonic mixer with reconfigurable functions including single-ended dispersion immune mixing, I/Q frequency down-conversion, image rejection mixing, and double-balanced mixing are realized, respectively. Meanwhile, optimizing the electrical attenuator using convex optimization can suppress the third-order intermodulation distortion (IMD3), maximize the conversion gain, and finally improve the spur-free dynamic range (SFDR). Experimental results show that the proposed scheme can be operated with a frequency from 5 to 20 GHz, and the SFDR can achieve 118.3 dB·Hz4/5. Over the whole frequency range, I/Q frequency down-conversion can be well conducted with an amplitude imbalance below 0.7 dB and a phase imbalance below ±0.7°. After an I/Q imbalance compensation algorithm, the image rejection ratio of over 60 dB is produced. The power fading caused by fiber dispersion is also compensated successfully. For a vector signal with 16 quadrature amplitude modulation, the best error vector magnitude (EVM) reaches 3.4%.

Broadband and linearized photonic time-stretch analog-to-digital converter based on a compact dual-polarization modulator.

A broadband linearization scheme for a photonic time-stretch (PTS) analog-to-digital converter (ADC) is proposed based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator with complementary parallel single-sideband (SSB) modulation. In this system, two stretched radio frequency signals, corresponding to the two orthogonal polarizations of the DP-BPSK modulator, are complementary, which can realize differential operation to eliminate the second-order harmonic distortion and pulse envelope distortion. Meanwhile, SSB modulation is used to avoid dispersion-induced power fading. Theoretical analysis and simulation results show that the proposed scheme can effectively improve the linear performance of PTS ADC, even considering the polarization-dependent delay deviation and amplitude offset.

Analysis and Demonstration of Low-Complexity Joint Optical-Electrical Feedforward Equalization (OE-FFE) For Dispersion-Limited High-Speed IM/DD Transmission

High-speed intensity-modulation direct-detection (IM/DD) fiber optical transmission system is of great interest to the applications of datacenter interconnects (DCI) as well as edge/access networks. However, when the fiber reach is beyond 40 km such as ER or ZR, the power fading induced by chromatic dispersion (CD) in C-band, S-band and even edge-wavelengths of O-band becomes a severe issue with the ever-increasing signal data rate. In this work, we focus on an ultra-low complexity joint optical-electrical feedforward equalization (OE-FFE) scheme to mitigate the CD distortion. We establish a comprehensive theory to jointly model the IM/DD channel, optical circuit and the digital equalizer, which offers analytical bit-error ratio (BER) expressions of pulse amplitude modulation (PAM)-2 and PAM4 formats and guides co-optimization of optical and electrical parts. As proofs of concept, we experimentally demonstrate C-band 60 Gb/s PAM2 over 85.8 km single-mode fiber (SMF) and up to 112 Gb/s PAM4 over 50 km or 61.3 km SMF, enabled by OE-FFE with only a 1-tap optical delay line and lean digital equalizers. For 112 Gb/s PAM4 over 50 km, BER satisfying 7% hard-decision FEC limit is achieved using a symbol-spaced simplified polynomial FFE with only 39 multiplications per PAM-4 symbol. For 60 Gb/s PAM-2, we achieved 85.8 km transmission with symbol-spaced 25-tap linear FFE and KP4 FEC-compliant BER. In addition, investigations on the parameters of the optical delay line are also carried out. The analytical and experimental results show the great potential of proposed OE-FFE approach for CD-constrained beyond-100G/λ ER and beyond-50G/λ ZR IM/DD systems.

Stable and Widely Tunable Optoelectronic Oscillator Using a Cascade Microwave Photonic Filter

A widely tunable optoelectronic oscillator (OEO) with stable output based on a cascade microwave photonic filter (MPF) is proposed and demonstrated. The cascade MPF is implemented by a combination of a finite impulse response (FIR) filter based on shifted dispersion-induced power fading and an infinite impulse response (IIR) filter based on a double-parallel recirculating delay lines (DP-RDLs). Through adjusting the time delay difference between the upper and lower connecting arms of the dual-input Mach-Zehnder modulator within FIR filter, the center frequency of cascade MPF is changed and the oscillation frequency of the OEO can be tuned. The theoretical analysis and verified experiment of the proposed OEO is performed. Tunable oscillation signals from 6.1 to 11.98 GHz with an average step size of 490 MHz are generated. Due to the introduce of the IIR filter, the stable performance of the OEO is obtained, where the maximum frequency drift at 7.48 GHz is observed to be 1.817 kHz over 1 hour. The phase noise of the structure is also investigated

Photonic Generation of Background-Free Phase-Coded Microwave Pulses with Elimination of Power Fading

We report a novel photonic scheme to generate background-free phase-coded microwave pulses with elimination of power fading by cascading a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM is driven by a radio frequency (RF) signal to generate two first-order optical sidebands with an orthogonal polarization state, while the PolM is driven by a three-level electrical coding signal. By properly adjusting the polarization state, a series of background-free frequency-doubled phase-coded microwave pulses can be generated after optical-to-electrical conversion. Benefiting from the carrier-suppressed single-sideband (CS-SSB) modulation, the proposed signal generator can suppress the chromatic-dispersion-induced power-fading effect, which has excellent potential for long-distance fiber transmission. In addition, the system can directly generate phase-coded microwave signals in pulse mode by truncating continuous wave (CW) microwave signals. Moreover, the microwave signal generator has wideband tunability since no optical filter is involved in our scheme. The proposed method was theoretically analyzed and experimentally verified. Phase-coded microwave pulses centered at 14 GHz and 19.2 GHz with a bit rate of 0.5 Gb/s were successfully generated.