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Compared with electrons, there is one distinct feature of photons, known as multiple physical dimensions. Frequency/wavelength, time, complex amplitude and polarization are typical physical dimensions of photons. Very recently, the spatial structure of photons, the only known physical dimension left, has attracted increasing interest in full access of photons worthy of exploration. Manipulating these physical dimensions of photons enables a diversity of light related applications such as trapping, sensing, metrology, microscopy, imaging, quantum information processing and optical communications. For instance, various multiplexing techniques such as wavelength-division multiplexing (WDM), time-division multiplexing (TDM) and polarization-division multiplexing (PDM) are widely used to increase the transmission capacity of optical communications. Moreover, advanced modulation formats such as m-ary phase-shift keying (m-PSK) and m-ary quadrature amplitude modulation (m-QAM) encoding multiple bits information into one symbol take full use of the complex amplitude physical dimension of lightwaves to increase the transmission capacity and spectral efficiency in coherent optical communications. Additionally, tailoring the spatial structure of lightwaves benefits the generation of various special light beams having inhomogeneous amplitude, phase and polarization distribution across the light beams. Generally, these special light beams can be called structured light, also known as tailored light, shaped light, sculpted light or custom light. There are several typical examples of structured light, such as Hermite-Gaussian (HG) light beams having spatially variant amplitude distribution, twisted light beams having spiral phase front and carrying orbital angular momentum (OAM), and vector light beams having spatially variant polarization distribution. Some other beams have both spatially variant amplitude and phase distribution, such as Laguerre-Gaussian (LG) and Bessel light beams. More complicated structured light may simultaneously have spatially variant amplitude, phase and polarization distribution. Even the space array light can be also considered as a general type of structured light accessing parallel spatial regions. Multi-core fiber (MCF), few-mode fiber (FMF) and multi-mode fiber (MMF) are typical fibers supporting structured light beams, i.e., different spatial mode sets of linearly polarized modes, OAM modes, eigenmodes. The space-division multiplexing (SDM) employing different spatial mode sets is considered to be the next frontier technique enabling continuous capacity scaling. Not only in optical communications, but also in other fields (such as optical trapping and manipulation), structured light has also played an increasingly important role. Recent years have witnessed the rapid development of light filed manipulation exploiting physical dimensions of photons. The trends and challenges are in-depth exploitation of each physical dimension and multi-dimensional light field manipulation.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.1–3
In this paper, we review our joint timing and frequency synchronization algorithms in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. We first present a timing estimation method by designing the pattern of the training symbol, whose timing metric has a sharp and clear peak, to ensure accurate timing offset (TO) estimation performance. Then we provide both data-aided (DA) and blind (BL) approaches to estimate the carrier frequency offset (CFO). For the DA algorithm, we utilize the same training symbol structure as the timing estimation does, while for the BL algorithm, we utilize the zero-subcarrier power (ZSP) to achieve full-range CFO estimation. Note that our joint timing and frequency synchronization approaches require only one OFDM symbol, which ensure not only the data transmission efficiency, but also the TO and CFO estimation performance. A modified BL ZSP algorithm is proposed to further improve the CFO estimation performance by taking the power average over a series of OFDM symbols. The effectiveness of the TO estimation algorithm, and both the DA and BL CFO estimation algorithms are verified and demonstrated in both simulations and experiments.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.4–14
In this paper, the recent progress on spectrally efficient single carrier (SC) 400G optical signal transmission was summarized. By using quadrature phase shift keying (QPSK), 16 quadrature amplitude modulation (16QAM) and 64QAM, we can realize transmission distance over 10000, 6000 and 3000 km, respectively, with large area fiber and all-Raman amplification. To improve the system performance and generate high-order QAM, advanced digital signal processing algorithms such as probabilistic shaping and look-up table pre-distortion are employed to improve the transmission performance.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.15–23
In this paper, we propose and demonstrate simultaneous phase regeneration of four different channels of QPSK signal based on phase sensitive amplification. The configuration can be divided into two parts. The first one uses four wave mixing in high nonlinear fiber (HNLF) to generate the corresponding three harmonic conjugates precisely at the frequency of the original signals. The other one uses optical combiner to realize coherent addition which is aimed at completely removing the interaction in phase regeneration stage. The simulation results suggest that this scheme can optimize signal constellation to a large extend especially in high noise environment. Besides, optical signal to noise ratio (OSNR) can improve more than 3 dB while the bit-error-rate (BER) reaches 10– 3 with a constant white noise and 15° phase noise.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.24–30
Multi-mode fiber (MMF) links are expected to greatly enhance capacity to cope with rapidly increasing data traffic in optical short-reach systems and networks. Recently, mode division multiplexing (MDM) over MMF has been proposed, in which different modes in MMF are utilized as spatial channels for data transmission. Stronglycoupled MDM techniques utilizing coherent detection and multiplex-input-multiplex-output (MIMO) digital signal processing (DSP) are complex and expensive for shortreach transmission. So the weakly-coupled approach by significantly suppressing mode coupling in the fiber and optical components has been proposed. In this way, the signals in each mode can be independently transmitted and received using conventional intensity modulation and direct detection (IM-DD). In this paper, we elaborate the key technologies to realize weakly-coupled MDM transmission over conventional MMF, including mode characteristic in MMF and weakly-coupled mode multiplexer/demultiplexer (MUX/DEMUX). We also present the upto-date experimental results for weakly-coupled MDM transmission over conventional OM3 MMF. We show that weakly-coupledMDMscheme is promising for high-speed optical interconnections and bandwidth upgrade of already-deployed MMF links.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.31–40
As one solution to implement the largecapacity space division multiplexing (SDM) transmission systems, the mode division multiplexing (MDM) has gained much attention recently. The vector mode (VM), which is the eigenmode of the optical fiber, has also been adopted to realize the optical communications including the transmission over free-space optical (FSO) and optical fiber links. Considering the concerns on the short-reach optical interconnects, the low cost and high integration technologies should be developed. Direct detection (DD) with higher-order modulation formats in combination of MDM technologies could offer an available trade-off in system performance and complexity. We review demonstrations of FSO and fiber high-speed data transmission based on the VM MDM (VMDM) technologies. The special VMs, cylindrical vector beams (CVB), have been generated by the q-plate (QP) and characterized accordingly. And then they were used to implement the VMDM transmission with direct-detection orthogonal frequency division multiplexing (DD-OFDM). These demonstrations show the potential of VMDM-DD-OFDM technology in the large-capacity short-reach transmission links.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.41–51
Optical vortices carrying orbital angular momentum (OAM) have attracted increasing interest in recent years. Optical vortices have seen a variety of emerging applications in optical manipulation, optical trapping, optical tweezers, optical vortex knots, imaging, microscopy, sensing, metrology, quantum information processing, and optical communications. In various optical vortices enabled applications, the generation of multiple optical vortices is of great importance. In this review article, we focus on the methods of multiple optical vortices generation and its applications. We review the methods for generating multiple optical vortices in three cases, i.e., 1-to-N collinear OAM modes, 1-to-N OAM mode array and N-to-N collinear OAM modes. Diverse applications of multiple OAM modes in optical communications and non-communication areas are presented. Future trends, perspectives and opportunities are also discussed.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.52–68
Optical vortices carrying orbital angular momentum (OAM) have attracted extensive attention in recent decades because of their interesting applications in optical trapping, optical machining, optical communication, quantum information, and optical microscopy. Intriguing effects induced by OAMs, such as angular momentum conversion, spin Hall effect of light (SHEL), and spin– orbital interaction, have also gained increasing interest. In this article, we provide an overview of the modulations of OAMs on the propagation dynamics of scalar and vector fields in free space. First, we introduce the evolution of canonical and noncanonical optical vortices and analyze the modulations by means of local spatial frequency. Second, we review the Pancharatnam–Berry (PB) phases arising from spin–orbital interaction and reveal the control of beam evolution referring to novel behavior such as spindependent splitting and polarization singularity conversion. Finally, we discuss the propagation and focusing properties of azimuthally broken vector vortex beams.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.69–87
Light with an optical orbital angular momentum (OAM) has attracted an increasing amount of interest and has found its way into many disciplines ranging from optical trapping, edge-enhanced microscopy, high-speed optical communication, and secure quantum teleportation to spin-orbital coupling. In a variety of OAM-involved applications, it is crucial to discern different OAM states with high fidelity. In the current paper, we review the latest research progress on OAM detection with micro- and nano-optical structures that are based on plasmonics, photonic integrated circuits (PICs), and liquid crystal devices. These innovative OAM sorters are promising to ultimately achieve the miniaturization and integration of high-fidelity OAM detectors and inspire numerous applications that harness the intriguing properties of the twisted light.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.88–96
An optical fiber serves as a versatile tool for optical trapping and manipulation owing to its many advantages over conventional optical tweezers, including ease of fabrication, compact configurations, flexible manipulation capabilities, ease of integration, and wide applicability. Here, we review recent progress in fiberbased optical trapping and manipulation, which includes mainly photothermal-based and optical-force-based trapping and manipulation. We focus on five topics in our review of progress in this area: massive photothermal trapping and manipulation, evanescent-field-based trapping and manipulation, dual-fiber tweezers for singlenanoparticle trapping and manipulation, single-fiber tweezers for single-particle trapping and manipulation, and single-fiber tweezers for multiple-particle/cell trapping and assembly.
PDF全文 Frontiers of Optoelectronics, 2019年第12卷第1期 pp.97–110
经新闻出书总署研讨，赞同Frontiers of Optoelectronics （《光电子前沿》）主办单位由高等教育出书社有限公司、华中科技大学变更为高等教育出书社有限公司、华中科技大学、我国光学学会，其间高等教育出书社有限公司为首要主办单位。（新出审字（2012）663号）