Electrical Equalization Research Articles

The electro-thermal equalization behaviors of battery modules with immersion cooling

The electrical and thermal characteristics of Li-ion batteries (LIBs) are closely related and need to be further investigated. Especially for the promising immersion cooling LIBs, the interaction between battery performance and immersion thermal management system still needs to be clearly illustrated. This research aims to reveal the electro-thermal equalization behaviors of LIB modules with immersion cooling. An electro-thermal test platform was established for a series-connected LIB module. Besides the experimental research on the thermal control capability, the electro-thermal equalization behaviors of the LIB module with different cooling methods are also investigated at steady and dynamic operations. Results show that the electrical inconsistency between the LIBs with different cooling schemes intensifies at the end of discharge, and the voltage deviation (δU,t) increases quickly at high rates. However, immersion cooling can mitigate this behavior effectively. As the immersion height ratio varies from 0 to 1, the δU,t at the end of the 2C discharge declines from 17.1% to 4.3%, then rises to 7.9%. From a general viewpoint, the indicators, including the equalization rates of the voltage, average temperature, and temperature difference, are defined further to assess the electro-thermal equalization behaviors of the module. According to the estimation, the equalization capacities are static flow > forced flow > air cooling for all indicators. Static flow immersion cooling demonstrates superiority in thermal and electrical equalization, while forced flow immersion cooling is still necessary at high discharge rates for reducing thermal recovery time and temperature rise.

Cost-Effective C-Band 50-Gb/s PON Implemented by Using a 2-Bit DAC and Linear Electrical Equalizer

We propose and demonstrate a cost-effective C-band 50-Gb/s downstream 4-ary pulse amplitude modulation passive optical network system implementable by using a 2-bit digital-to-analog converter and a linear electrical equalizer. The waveform distortions induced by band-limitation of opto-electronic devices and fiber chromatic dispersion are compensated by using an electrical and optical pre-equalizers realized by a high-pass filter (HPF) and a dispersion-compensation module (DCM), respectively. To facilitate easy operation and management of the system, the amounts of pre-equalization are all fixed regardless of transmission distance up to 20 km. At the receiver, a linear feed-forward equalizer is employed to compensate for the remaining waveform distortions adaptively to transmission distance. Also, a semiconductor optical amplifier (SOA) is used as an optical pre-amplifier to increase the power budget. We determine the system parameters through experiment to maximize the power budget of the system. The experimental results show that the proposed system is capable of securing the power budget of 29.2 dB.

Electrical Equalization Analysis of PAM-4 Transmission in Short-Reach Optical Systems

Inclusive and intensive performance analysis of electrical equalizers in a short-reach optical system using four-level pulse amplitude modulation (PAM-4) is presented in this paper. Two equalizers are used—a feedforward equalizer and decision feedback equalizer using the least mean square algorithm. The sensitivity to cut-off frequency for the transmitter and receiver filters, fiber length and number of equalizers taps in the means of the bit error rate vs. optical input power are shown. The analysis reveals the considerable impact of the filters’ bandwidth, particularly in the receiver, on the equalizer performance. These results and their reasons are analyzed and broadly discussed.

Wideband QAM-over-SMF/turbulent FSO downlinks in a PON architecture for ubiquitous connectivity

We propose and investigate for the first time a seamless millimeter-wave (mmW) radio-over-fiber (RoF) and radio-over-free-space optics (FSO)-based downlink for use in a passive optical network architecture using 4-, 16- and 64-quadrature amplitude modulation (QAM) for broadband wireless access (BWA) networks. The proposed system is implemented in both experiment and simulation to realize continuous and ubiquitous coverage in urban and rural areas. We outline, a proof-of-concept demonstration of 4-, 16- and 64-QAMs at data rates of 34, 67 and 100 Mb/s, respectively transmitted over a 15 km standard single-mode fiber (SMF), which is then optically up-converted to 25 GHz for transmission over a 10 km of SMF and a 2 m of FSO channel under a non-uniform turbulent condition. We show the measured error vector magnitude (EVM) values of 13, 9.2 and 7.3% for 4-, 16- and 64-QAM, respectively, which are below the corresponding standard EVM requirements and therefore confirm the practicality of the proposed hybrid system. Depending on the data rates, each modulation can be adaptively configured. We report a simulation of a 10 Gb/s 4- and 64-QAM hybrid RoF-FSO downlink under an extended non-uniform turbulence regime to verify the feasibility of the proposed scheme for use in practical applications. By implementing the decision-directed carrier phase recovery and linear electrical equalization, EVMs can be efficiently reduced below the required limits. We further evaluate the proposed system performance in terms of the bit error rates, constellation diagrams, received optical and mmW powers. Using state-of-the-art K-band power amplifiers and conical horn antennas, the maximum wireless transmission distance is estimated to be about 135 m for use in the last-mile BWA networks.

Spiral-Phased Laguerre-Gaussian Modes Generation in SWDM over Few Mode Fiber based on Electrical Equalization

Space division multiplexing, in conjunction with wavelength division multiplexing, is a powerful mechanism that increases spatial channels significantly in a single optical fiber. Spiral Phased-Laguerre-Gaussian (SP-LG) modes indicate that they effectively reduce mode coupling, thereby increasing the channel response and performance positively. However, mode-coupling influence optical fiber system leads to inter-symbol interference (ISI) between the channels and reduces both capacity and distance. In this paper, we apply the SP-LG modes in a space wavelength division multiplexing over a few-mode fiber system. The results demonstrate significant improvements in reducing channels effects and ISI. The performance evaluations are based on the bit-error-rate (BER), eye diagram and spectrum analyzer.

C-band 56-Gb/s PAM4 transmission over 80-km SSMF with electrical equalization at receiver.

In this paper, a memory polynomial equalizer combined with decision feedback equalizer (MPE-DFE) is proposed to eliminate channel distortions for intensity modulation and direct detection (IM/DD) systems. Compared with traditional feedforward equalizer and decision feedback equalizer (FFE-DFE), the proposed MPE-DFE introduces extra square terms and cubic terms to jointly equalize chromatic dispersion and nonlinear distortions. We demonstrated a C-band 56-Gb/s four-level pulse-amplitude modulation (PAM4) system over 80-km standard single mode fiber (SSMF) transmission. Experimental results show that the proposed MPE-DFE achieved up to 6.2 dB higher SNR than traditional FFE-DFE. Moreover, the achieved bit error ratio (BER) with MPE-DFE reaches 3.1 × 10-3, which is below 7% feedforward error correction (FEC) threshold of 3.8 × 10-3. To the best of our knowledge, we achieved a record transmission distance for C-band 56-Gb/s PAM4 signal with only electrical equalization at the receiver.

Mitigation of dispersion and turbulence in a hybrid optical fibre and free-space optics link using electronic equalisation

Transmission of a 25 Gbps non-return to zero signal over a hybrid link of 20 km standard single-mode fibre and 500 m free-space optics under weak-to-moderate turbulence regimes is demonstrated via simulation to provide a practical solution for the last-mile access networks. Even though there are several complex mitigating methods to reduce the waveform distortions caused by both the fibre chromatic dispersion and atmospheric turbulence, we provide and discuss a simple approach using an electrical equalizer at the receiver. The simulation results demonstrate that, the proposed equalization technique offer about an order of magnitude improvement in the bit error rate at the received optical power of -20 dB m and a receiver sensitivity gain of 1.5 dB at the 7% forward error correction limit.

Compensation of Mode Crosstalk in MDM System Using Digital Optical Phase Conjugation

We propose to utilize the digital optical phase conjugation (D-OPC) technique for the compensation of mode crosstalk in the mode-division-multiplexed (MDM) transmission system. To realize the D-OPC technique, we send the CW light from the receiver side, measure its wavefront at the transmitter side, and then, transmit the phase-conjugated signal to the receiver. By using this technique, we demonstrate the transmission of four LP modes, each carrying 10-Gb/s ON–OFF keying signals, over a 100-m long few-mode fiber link. These signals are detected by using direct-detection receivers with no electrical equalizer. The results show that, by applying the proposed D-OPC technique, we can achieve the bit-error rate of < 10−3 for all four modes.

Mitigation of Nonlinear Effects with Volterra and Wiener Hammerstein Electrical Equalizer in LDPC Coded Coherent Optical OFDM System

Mitigation of Nonlinear Effects with Volterra and Wiener Hammerstein Electrical Equalizer in LDPC Coded Coherent Optical OFDM System

Comparison of Different Wavelength Propagations over Few-Mode Fiber based on Space Division Multiplexing in Conjunction with Electrical Equalization

Comparison of Different Wavelength Propagations over Few-Mode Fiber based on Space Division Multiplexing in Conjunction with Electrical Equalization

Mitigation of Non-linear Impairments in Optical Fast-OFDM using Wiener-Hammerstein Electrical Equalizer

Mitigation of Non-linear Impairments in Optical Fast-OFDM using Wiener-Hammerstein Electrical Equalizer

C-band real-time 400/300 Gb/s OOK bidirectional interconnection over 20 km multicore fibers

We experimentally demonstrate a real-time quasi-full-duplex 400G/300G optical interconnection over 20 km multicore fibers (MCFs), using 10G-class transponders operated in the C-band. Optical delay interferometer (ODI)-based optical frequency equalization is applied to mitigate chirp and dispersion induced impairments, so that the tolerance to inter-symbol interference (ISI) can be enhanced, thus enabling 4×25 Gb/s on-off keying (OOK) transmission per core over severely limited bandwidth channels. Real-time bit error ratio (BER) performances of the bidirectional 400 Gb/s transmission are measured without using extra digital signal processing (DSP) or electrical equalization, which ensures low complexity and less power consumption.

Transmission of 28-Gb/s Duobinary and PAM-4 Signals Using DML for Optical Access Network

We explore the possibility of utilizing 1.55- $\mu \text{m}$ directly modulated lasers (DMLs) for optical access networks operating at 28 Gb/s per wavelength. For this purpose, we attempt to maximize the power budgets of 28-Gb/s duobinary and four-level pulse amplitude modulation (PAM-4) signals generated from a DML without using optical amplifiers or optical dispersion compensation modules. For experimental investigation, we set the bias current of the DML far above the threshold current, optimize the extinction ratio of the signals, and utilize the electrical equalization at the receiver. The experimental results show that we can secure power margins of 9.6 and 10 dB after transmission over 40-km long standard single-mode fiber for the duobinary and PAM-4 signals, respectively.

Effects of Electrical and Optical Equalizations in 28-Gb/s RSOA-Based WDM PON

We experimentally investigate the roles of electrical and optical equalizers in the 28-Gb/s wavelength-division-multiplexed passive optical network implemented by using reflective semiconductor optical amplifiers (RSOAs) and direct-detection receivers. For the generation of 28-Gb/s signal, we directly modulate an RSOA in the polar return-to-zero (RZ) ${N}$ -ary pulse-amplitude-modulation (PAM) format. The results show that the optical equalization is capable of compensating the waveform distortions caused by both the bandwidth-limitation of RSOA and fiber’s chromatic dispersion without deteriorating the signal-to-noise ratio (SNR). On the other hand, the electrical equalization is effective for the compensation of the bandwidth-limitation of RSOA only at the cost of SNR. The results also show that the electrical equalization is helpful to compensate for the remaining waveform distortions after the optical equalization. By using both equalizers, we demonstrate the transmission of the 28-Gb/s signals in polar RZ-PAM- ${N}$ formats ( ${N} =2$ , 3, and 4) over 20 km of standard single-mode fiber.

Transmission of 51.56-Gb/s OOK signal using 1.55-μm directly modulated laser and duobinary electrical equalizer.

We demonstrate the transmission of 51.56-Gb/s on-off keying (OOK) signals generated by using a 1.55-μm directly modulated laser (DML) over 15-km long standard single-mode fiber. In this experiment, a duobinary electrical equalizer based on a finite-impulse-response filter is used at the receiver to increase the dispersion-limited transmission distance. We evaluate the performances of the 51.56-Gb/s OOK signals with respect to the transmission distance by using the frequency response analysis of the proposed system. This result is used to explain why it is effective to utilize the duobinary equalization (instead of binary equalization) for increasing the transmission distance.

25-Gb/s OOK Transmission Using 1.5-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu{\rm m}$&lt;/tex-math&gt; &lt;/inline-formula&gt; 10G-Class VCSEL for Optical Access Network

We explore the possibility of transmitting 25-Gb/s on–off keying (OOK) signals generated by using a 1.5- μ m 10G-class vertical-cavity surface-emitting laser (VCSEL) over standard single-mode fiber (SSMF) for optical access applications. A transistor-outline-can packaged VCSEL having a 3-dB modulation bandwidth of 7 GHz is utilized to transmit the 25-Gb/s signals. We experimentally investigate the transmission performances of OOK signals obtained from two different transmitter schemes: with and without a delay interferometer (DI) at the output of the directly modulated VCSEL. In order to maximize the transmission distance without using bulky and lossy dispersion compensation modules, we optimize the extinction ratio of the signals and apply the electrical equalization at the receiver. Also optimized is the free-spectral range (FSR) of the DI when it is utilized. The experimental results show that we can successfully transmit the 25-Gb/s OOK signals over 33- and 45-km long SSMF with and without the DI, respectively. The use of DI not only alleviates the band limitation of the VCSEL but also significantly improves the receiver sensitivity of the 25-Gb/s OOK signal up to 30 km. Moreover, a larger power budget is achieved for transmission distances shorter than 25 km when a DI having an FSR of 25 GHz is utilized at the output of the VCSEL.

25-Gb/s TDM Optical Link Using EMLs for Mobile Fronthaul Network of LTE-A System

We propose and demonstrate a common public radio interface (CPRI)-compliant 25.2923-Gb/s mobile fronthaul network for long term evolution-advanced (LTE-A) systems. In order to meet the CPRI specifications and the stringent latency requirement of the LTE-A fronthaul network cost-effectively, we use the synchronous time-division-multiplexing, forward-error correction, and electrical equalization techniques. To enhance the cost-effectiveness, we also use an electroabsorption-modulated laser and exploit the possibility of using simple modulation formats such as the ON–OFF keying, electrical duobinary, and four-level pulse amplitude modulation. The performance of the proposed network is evaluated experimentally in terms of the tolerances to fiber dispersion and optical reflection.

Transmission Performance of OOK and 4-PAM Signals Using Directly Modulated 1.5-μm VCSEL for Optical Access Network

We evaluate the possibility of realizing optical access networks using 1.5-μm vertical-cavity surface-emitting lasers (VCSELs) in the on-off keying (OOK) and four-level pulse amplitude modulation (4-PAM) formats. In order to maximize the power budget of the networks, we optimize the extinction ratio of the 10.7- and 21.4-Gb/s signals and exploit the electrical equalization at the receiver. The experimental comparison made at 10.7 Gb/s shows that the OOK format vastly outperforms the 4-PAM format in terms of tolerance to chromatic dispersion. For example, we achieve the 80-km transmission of the OOK signal over standard single-mode fiber (SSMF), but the maximum reach is halved when the 4-PAM signal is employed. Nevertheless, the 4-PAM format is still an effective way to double the data rate of the VCSEL links in optical access networks. We successfully transmit the 21.4-Gb/s 4-PAM signal generated by using the 1.5-μm VCSEL over 18-km long SSMF.

20-Gb/s Polar RZ 4-PAM Transmission Over 20-km SSMF Using RSOA and Direct Detection

We demonstrate 20-Gb/s upstream transmission in the wavelength-division-multiplexed passive optical network based on reflective semiconductor optical amplifiers (RSOAs) and direct-detection receivers by using the polar return-to-zero (RZ) four-level pulse amplitude modulation (4-PAM) format. In order to compensate for the limited modulation bandwidth of the RSOA, an optical delay interferometer is used together with an electrical equalizer at the receiver. We successfully transmit the 20-Gb/s polar RZ 4-PAM signal over the 20-km long loopback link without using optical dispersion compensator. We also show that the proposed polar RZ 4-PAM format provides superior performances to the conventional RZ 4-PAM format due to the up-down symmetry of its waveform.

Nyquist 4-ary pulse amplitude modulation scheme based on electrical Nyquist pulse shaping and fiber Bragg grating filter

Intensity modulation and direct detection signal are sensitive to power fading and nonlinear intersymbol interference (ISI) induced by modulator chirp, fiber dispersion, and square-law photo-detection. We propose and experimentally demonstrate a Nyquist 4-ary pulse amplitude modulation and direct detection scheme relying on pulse-shaping with an electrical filter and optical equalization with a vestigial-sideband (VSB) filter in the transmitter. The power fading could be eliminated by using the VSB filter. Compared with conventional 4-ary pulse amplitude modulation, the Nyquist signal has a stronger resistance to nonlinear ISI.