Single Sideband Transmission Research Articles

Spectrally efficient multi-service fiber-wireless access in low-cost direct-detection THz system at 300 GHz.

This Letter demonstrates a novel, to the best of knowledge, overlapping single-sideband (OSSB) transmission scheme for spectrally efficient multi-service fiber-wireless (FiWi) access in a low-cost direct-detection (DD) THz system. Utilizing the proposed OSSB scheme, user data from different services can share the same spectrum resource yet can be successfully demodulated via one cost-effective DD THz receiver in conjunction with the Kramers-Kronig (KK) based SSB field reconstruction and look-up table (LUT) enabled signal separation algorithms. A proof-of-principle experiment is conducted. Based on an IQ modulator and a single THz zero-bias diode (ZBD), two independent 10-GBd quadrature phase shift keying (QPSK) signals with an overlapped spectrum are successfully demodulated after 20-km fiber and up to 3-m wireless transmission at the 300-GHz band. To the best of our knowledge, this is the first demonstration of multi-service FiWi access with an OSSB format in a 300-GHz DD THz system.

Spectrally Efficient PDM-Twin-SSB Direct-Detection THz System Without Active Polarization Control

This Letter proposed a spectrally efficient polarization division multiplexed (PDM) twin single-sideband (twin-SSB) transmission scheme for direct-detection THz communication systems. The optical carrier of the twin-SSB is added at the optical THz converter, rather than being generated at the optical transmitter as in traditional SSB scheme. Hence the direct detection of each polarization branch of the PDM-twin-SSB signals at the THz receiver can be achieved, without active polarization control. Moreover, the SSB field recovery enabled by Kramers–Kronig algorithm can effectively eliminate the signal-to-signal beating interferences and contributes to better polarization de-multiplexing. The feasibility of the proposed scheme is verified with 5.75-GBd 16-quadrature amplitude modulation PDM-twin-SSB signals transmission over the 300-GHz direct-detection THz communication system by simulation. This scheme can not only significantly improve the spectral efficiency of direct-detection THz communication systems, but also effectively enhance the system’s operability and robustness.

Recent Advances in Coherent Optical Communications for Short-Reach: Phase Retrieval Methods

Short-reach transmission systems traditionally utilize intensity modulation (IM) at the transmitter and direct detection (DD) at the receiver due to their cost-effectiveness, small footprint, and low power consumption. However, with the exponential increase in bandwidth demand, coherent optical communication systems have become necessary for long-haul distances, requiring application-specific integrated circuits (ASIC) and advanced digital signal processing (DSP) algorithms coupled with high-speed digital-to-analog and analog-to-digital converters to achieve Tbit/s speeds. As coherent technology matures, it will eventually become feasible for short-reach transmission. In this context, self-coherent systems have emerged as an intermediary solution, offering advantages over traditional IM/DD systems. While comprehensive review studies exist on self-coherent transceivers, they do not cover recent advances in phase retrieval methods for short-reach optical communications. This review article highlights recent developments in cost-effective self-coherent detection for short-reach systems through comparing the benefits of single sideband (SSB) transmission and Kramers-Kronig detection to carrier-assisted phase retrieval, the Gerchberg-Saxton (GS) algorithm, and the transport of intensity equation (TIE) method.

Optical Single-Sideband Transmitters

Optical single-sideband (SSB) transmission technique fills the gap between intensity-modulation/direct-detection (IM/DD) and digital coherent transmission technologies. It provides a cost-effective solution to overcome the transmission distance limitation induced by fiber chromatic dispersion in IM/DD system at the expense of increased complexity of the transmitter (Tx) structure and receiver-side signal processing. This makes optical SSB system become a promising candidate for cost- and latency-sensitive datacenter interconnects. Previous research on optical SSB system mainly focused on improving the spectral efficiency and receiver sensitivity, whereas the increased complexity and cost of optical SSB Tx were overlooked. In this paper, we present a comprehensive review of the recent advances in the optical SSB Tx. First, we evaluate three conventional optical SSB Tx schemes based on optical filter, in-phase/quadrature modulator, and dual-drive Mach-Zehnder modulator. We then introduce the recently proposed optical SSB Tx schemes based on electro-absorption modulation lasers (EMLs), including the double-sided EML, two-segment EML, and the dually modulated EML. Compared with the conventional optical SSB Tx solutions, the EML-based schemes exhibit obvious friendliness to monolithic integration. Besides, we investigate the practical ways to add optical carrier with optical SSB signal and efficient implementation of the Hilbert transform, which are two practical issues in the optical SSB Tx. Finally, we explore the capability of monolithic integration of optical SSB Tx with state-of-the-art material platforms. Our comparison made among these schemes can provide a guideline for the selection of proper Tx scheme for specific optical SSB systems.

Experimental demonstration of single-span 100-km O-band 4×50-Gb/s CWDM direct-detection transmission.

We report on what is to the best of our knowledge the longest 50-Gb/s/λ O-band wavelength-division multiplexed (WDM) transmission. A pair of in-house built bismuth-doped fiber amplifiers (BDFAs) and the use of Kramers-Kronig detection-assisted single-sideband transmission are adopted to overcome the fiber loss and chromatic dispersion, respectively, in a reach-extended O-band coarse WDM (CWDM) system with a channel spacing of ∼10 nm. Through experiments on an amplified 4×50-Gb/s/λ direct-detection system based on booster and pre-amp BDFAs, we show the superior performance of single-sideband transmission in terms of both optical signal-to-noise ratio sensitivity and uniformity in performance amongst CWDM channels relative to double-sideband transmission after both 75-km and 100-km lengths of single-mode fiber. As a result, up to 100-km reach with comparable performance at all 50-Gb/s channels was achieved without the need for in-line optical amplification.

Modified low CSPR Kramer-Kronig receivers based on a signal-signal beat interference estimation.

Due to their simple structures and high robustness to fibre dispersion, single-sideband transmission systems using Kramer-Kronig (KK) receivers are an attractive solution for 80 km data centre interconnects. However, a major problem with KK receivers is that the optimal carrier signal power ratio (CSPR) needs to be large, due to the existence of signal-signal beat interference (SSBI), but this results in low receiver sensitivity. We propose two modified KK receivers that can estimate and eliminate SSBI and allow for signal detection when the CSPR is less than 0 dB. After transmission over an 80 km optical fibre, our modified KK receivers were able to increase the receiver sensitivity by 3 dB compared with a traditional KK receiver while the CSPR was reduced by 6 dB, and improvements of 1.16 and 1.60 dB in the OSNR were achieved with a reduction in the CSPR of 8 dB. Our improved KK receivers can greatly reduce the carrier power and CSPR necessary for the system, and thus reduce the cost of the system transmitter.

Optical Single Sideband Signal Reconstruction Based on Time-Domain Iteration

Due to its low cost, simple architecture and robustness to fiber dispersion, single sideband (SSB) transmission with direct detection (DD) system is an attractive solution for 80-km inter data center interconnects (DCIs). However, it will suffer performance penalty caused by the signal-to-signal beating interference (SSBI). Kramers-Kronig (KK) receiver has been extensively investigated for SSBI elimination by reconstructing the SSB signal. The nonlinear operations in KK algorithm require up-sampling to cope with spectral broadening, which results in high complexity for practical application. Optical signal phase retrieval method based on the minimum phase signal has also been investigated for SSB signal recovery, in which the SSB and DC-Value properties are iteratively imposed on the amplitude signal in frequency domain. In this paper, we propose a low complexity iterative algorithm for minimum phase signal recovery without up-sampling in time domain. Finite impulse response (FIR) filter is applied to iteratively generate the SSB signal and update the phase component. Based on the proposed scheme, the transmission of 30 GHz SSB 16-QAM discrete multitone (DMT) signal over 80 km single mode fiber (SMF) is successfully demonstrated with the bit error rate (BER) below the hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10−3. The experimental results show that, the BER performance of KK scheme with up-sampling factor of 2, frequency-domain iterative scheme and our proposed scheme is almost the same. However, compared with the KK scheme, the proposed method can save the numbers of adders and multipliers by the factors of 29 and 7, while the factors are 5.5 and 4 comparing to the frequency-domain iteration scheme.

Multichannel 16-QAM Single-Sideband Transmission and Kramers–Kronig Detection Using a Single QD-MLL as the Light Source

A 12-channel single-sideband transmission of 16-QAM signals at 18 GBd is experimentally demonstrated for the first time using a single quantum-dot mode-locked laser (QD-MLL) as the light source for both the modulated carriers and the continuous wave components. The Kramers–Kronig field reconstruction algorithm was used at the direct detection receiver for signal-signal beat interference cancellation. A total net data rate of >800 Gb/s is achieved over 78 km fiber of 1680 ps/nm accumulated chromatic dispersion with BER ≤ 2 × 10−3, which is lower than the threshold of hard-decision FEC with 7% overhead. Numerical simulations were also performed to assess the impact of noises from the laser source and the receiver front-end on the system performance.

Single Sideband Transmission Employing a 1-to-4 ADC Frontend and Parallel Digitization

Distributed data-centers have emerged as a key architecture for future optical networks. This architecture relies on power and cost-efficient high-speed fiber optical connections over distances up to 80 km which can be densely wavelength-division multiplexed (WDM) in the C-band. Recently, single-polarization single sideband (SSB) direct detection (DD) has been considered as an attractive transmission scheme for achieving data rates beyond 100 Gb/s per channel over 80 km. The advantages of SSB DD transmission includes the simple transceiver architecture and the capability of electronic dispersion compensation. However, the required digitizer's bandwidth in a single-polarization SSB transmission is around four times higher than in those of a conventional dual-polarization coherent detection system offering the same data rate. This critical issue prevents the practical implementation of high-speed SSB digital signal processing (DSP) in CMOS ASIC. To address this problem, we consider in this work a 112 GSa/s SiGe HBT BiCMOS ADC frontend. Using this ADC front-end, we experimentally demonstrate a WDM SSB DD transmission at a net data rate of 200 Gb/s per channel over 80 km while using only 14 GHz of digitizer's bandwidth which is comparable to those of a full-coherent counterpart.

High-speed SSB transmission with a silicon MZM and a soft combined artificial neural network-based equalization.

We experimentally demonstrate high-speed metro-scale optical transmission of a single sideband (SSB) 4-ary pulse amplitude modulation (PAM-4) signal based on a silicon photonic dual-drive Mach-Zehnder modulator (MZM). We propose a novel, to the best of our knowledge, artificial neural network (ANN) structure of soft combined ANN (SC-ANN) to compensate for both linear and nonlinear impairments of the signal. SC-ANN obtains the enhanced performance by averaging the outputs of conventional ANN with different sizes. With the help of the SC-ANN, we achieve a 320 km standard single-mode fiber (SSMF) transmission of 184 Gb/s (92Gbaud) PAM-4 with a bit-error rate (BER) below the 20% soft-decision forward error-correction (SD-FEC) threshold of ${2.4} \times {{10}^{ - 2}}$2.4×10-2, and the optical signal-to-noise ratio (OSNR) penalty is only 0.3 dB compared to the back-to-back (BTB) results.

Digital fronthaul link based on optimised digital radio over fibre system

The high optical bandwidth requirement in the mobile fronthaul link of the next generation cloud radio access network represents one of the major design constraints. In this study, a digital fronthaul link based on digital radio over fibre system that integrates the duobinary coding scheme with the optical single sideband (OSSB) transmission is proposed. This system reduces the spectral occupancy of the transmitted signals as well as the chromatic dispersion effects induced by fibre in both the electrical and optical domains. The OSSB signal is created by driving two cascaded optical modulators with a combination of a baseband digital signal and the Hilbert transform of that signal. The transmission performance of a digitised 16-quadrature amplitude modulation 16-QAM radio frequency signal with a bit rate of 1.25 Gb/s over a standard single mode fibre is investigated. The results show that the fronthaul transmission length can be extended by 75 and 16.6% relative to the case of transmitting the digitised signal using double sideband and single sideband (SSB) transmission formats, respectively. The power budget is improved by 10 dB compared to the SSB case with respect to the measured optical signal-to-noise ratio at 70 km fibre distance, while maintaining the EVM below the standardised values of the 3GPP.

Influence of EEPN and P2A noise with CD pre- and post-compensation in optical SSB transmission and Kramers-Kronig receiver system.

We present a comparative study of equalization-enhanced phase noise (EEPN) and phase to amplitude (P2A) noise with chromatic dispersion (CD) pre- and post-compensation in single side-band (SSB) transmission and direct-detection (DD) systems, respectively. We analyze the interplay of laser phase noise and fiber dispersion on an optical SSB Nyquist shaped four-level pulse amplitude modulation (PAM-4) signal in a Kramers-Kronig (KK) receiver. Our main results show that the EEPN in a DD-KK receiver dominates the system noise with the relaxed signal-to-noise ratio (SNR). The P2A noise in CD post-compensation scheme is relaxed due to the complex filed recovery with KK receiver. The numerical simulations are implemented to illustrate the interplay of laser linewidth and fiber dispersion in both CD pre- and post-compensation scenarios. Compared with CD pre-compensation, 3-dB reduction of power spectral density (PSD) of P2A noise at the peak is alleviated with CD post-compensation. The laser linewidth has ~1 MHz release with CD post-compensation for a 56-Gbaud PAM-4 signal over 100-km standard single-mode fiber (SSMF) transmission.

Beyond 100G Single Sideband PAM-4 Transmission With Silicon Dual-Drive MZM

We experimentally demonstrate beyond 100G single sideband (SSB) 4-ary pulse amplitude modulation (PAM-4) signal generation with a silicon dual-drive Mach-Zehnder modulator (DD-MZM) operating at C-band. With Kramers-Kronig detection, a 128-Gb/s PAM-4 signal is transmitted over 80-km standard single mode fiber (SSMF) with a bit error rate (BER) below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . In comparison, a 168-Gb/s PAM-4 signal is transmitted over 80-km SSMF with a BER below the 20% HD-FEC threshold of 1.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . A two-tap digital post filter and maximum likelihood sequence detection are applied to compensate for the limited system bandwidth. To the best of our knowledge, this letter reports the highest single-lane bitrate of 80-km SSB transmission with a DD-MZM and direct detection. It provides an attractive low-cost solution for inter-datacenter interconnection and metro-haul transmission.

Bidirectional single sideband transmission of Millimeter Waves over Fiber for 5G Mobile Networks

This study proposes, experimentally demonstrates, and simulates a network architecture for the transport of millimeter waves (MMW) based on Radio over Fiber (RoF) techniques for the transport of signals in the fronthaul segment of the next 5G generation mobile systems. Such approach exploits the benefits of bidirectional single-sideband modulation in order to generate an optical subcarrier for the downlink transmission and a second subcarrier for the transport of the uplink services, as well as the centralization of optical sources. The proposed architecture is evaluated based on the analyses of the Bit Error Rate (BER) performance and Error Vector Magnitude (EVM) in both downlink and uplink. Likewise, simulation modeling of the approach was conducted in order to evaluate the quality of the MMW signals at different frequencies available in the MMW spectrum. The results show a power penalty lower than 2 dB for a 1x1-12 BER and an EVM below 12% within a power margin of 6 dB, which demonstrates the feasibility of the approach.

Experimental comparison of direct detection Nyquist SSB transmission based on silicon dual-drive and IQ Mach-Zehnder modulators with electrical packaging.

We have designed and fabricated a silicon photonic in-phase-quadrature (IQ) modulator based on a nested dual-drive Mach-Zehnder structure incorporating electrical packaging. We have assessed its use for generating Nyquist-shaped single sideband (SSB) signals by operating it either as an IQ Mach-Zehnder modulator (IQ-MZM) or using just a single branch of the dual-drive Mach-Zehnder modulator (DD-MZM). The impact of electrical packaging on the modulator bandwidth is also analyzed. We demonstrate 40 Gb/s (10Gbaud) 16-ary quadrature amplitude modulation (16-QAM) Nyquist-shaped SSB transmission over 160 km standard single mode fiber (SSMF). Without using any chromatic dispersion compensation, the bit error rates (BERs) of 5.4 × 10-4 and 9.0 × 10-5 were measured for the DD-MZM and IQ-MZM, respectively, far below the 7% hard-decision forward error correction threshold. The performance difference between IQ-MZM and DD-MZM is most likely due to the non-ideal electrical packaging. Our work is the first experimental comparison between silicon IQ-MZM and silicon DD-MZM in generating SSB signals. We also demonstrate 50 Gb/s (12.5Gbaud) 16-QAM Nyquist-shaped SSB transmission over 320 km SSMF with a BER of 2.7 × 10-3. Both the silicon IQ-MZM and the DD-MZM show potential for optical transmission at metro scale and for data center interconnection.

Approaching Ideal Polyphase Filter Response in 65-nm CMOS

This work analyzes the effect of the most critical non-idealities on a passive polyphase filter implemented in a 65-nm CMOS technology, to attain single-sideband transmission in a 5 GHz Wi-Fi alike communication system. Non-idealities impact on this kind of passive complex filter have not been thoroughly analyzed in literature.

Power optimized OSSB modulation to support multi-band OFDM services along hybrid long-reach WDM-PONs

In this paper, optical single sideband (OSSB) transmission of multi-services based on orthogonal frequency division multiplexing (OFDM) with different signal constellations is investigated through numerical simulation, when the modulation efficiency obtained with a dual-electrode Mach–Zehnder modulator (DE-MZM) is optimized by biasing it below its quadrature point. Furthermore, in order to overcome the intermodulation distortion resulting from modulation efficiency optimization, it is demonstrated that driving each electrical signal with a different electrical power is an effective solution for the signals considered. As result of the optimization, successful delivery after 130km of a hybrid OSSB signal composed by a custom 16-quadrature amplitude modulation (QAM) OFDM gigabit Ethernet (GbE) signal, a 20MHz 64-QAM LTE signal and three independent OFDM-UWB channels of the first group of ECMA-386 is demonstrated, with negligible power penalty.

Comparison of Different Chromatic Dispersion Compensation Techniques in Radio over Fiber System

In this paper, we investigate the transmission of a 100 Gbit/s signal with 0.1THz carrier frequency using radio over fiber (RoF) for a fiber length of 50km. In our study, the impact of chromatic dispersion on the wireless signals transported through the fiber link and its mitigation using different dispersion compensation techniques are discussed. The techniques discussed here includes the optical single sideband transmission using dual electrode Mach Zehnder modulator, external filtering using FBG and compensation using chirped fiber grating. We also evaluated the performance of the three compensation techniques by plotting the eye diagram. The results clearly depict that compensation using chirped grating is the best among the three methods. The investigation is done on detailed simulative analysis using Optisystem.

Analog SC-FDE using SSB technique

In order to improve performance while keeping high spectrum efficiency of analog signal transmission, we recently proposed an analog single-carrier transmission with frequency-domain equalization (analog SC-FDE). In this paper, in order to improve the spectrum efficiency, analog SC-FDE using single sideband (SSB) technique is proposed. A theoretical analysis of normalized mean square error (NMSE) performance is carried out and confirmed by computer simulation. We show that analog SC-FDE using SSB technique achieves better NMSE performance than both conventional SSB transmission and analog SC-FDE while doubling spectrum efficiency of analog SC-FDE.

Application of phase-shifted fiber Bragg grating in single sideband transmission–based radio-over-fiber system

We propose a prototype for single-sideband (SSB) transmission based radio-over-fiber system by employing a phase-shifted fiber Bragg grating. The grating has different transmission spectrum characteristics with different phase-shift magnitudes. Then, it is used in a millimeter-wave (mm-wave) SSB modulation scheme. In the scheme, only one PS-FBG is used to realize the following functions: first, the conversion from optical dual-sideband to optical single-sideband with carrier reduction modulation can be easily achieved and second, the optical carrier-to-sideband ratio (OCSR) can be eliminated completely. In our work, the OCSR can be reduced from 33.95 dB to the optimum 0 dB and a 60 GHz mm-wave can be detected after photodiode.