High-capacity Optical Communication Systems Research Articles

Minimization of dispersion and non-linear effects in WDM based long-haul high capacity optical communication systems

Abstract Chromatic dispersion and nonlinear impairments pose challenges in high-capacity optical transmission systems, leading to signal distortions, channel interference and diminished the transmission performances. This paper explores the utilization of dispersion compensating fibers (DCF) using different schemes to mitigate the dispersion that accumulates along the length of a fiber in a 16 × 10 Gbps high-capacity long haul WDM system over a range of 500 km. When different wavelengths of light pulses are transmitted through an optical fiber, they experience varying speeds due to the refractive index’s wavelength dependency. As a result, the light pulses become temporally spread out as they travel through the fiber, and this dispersion persists throughout the fiber’s length. Considering non-linear effects such as self-phase modulation (SPM) and cross-phase modulation (XPM), this paper analyze and compare the three compensation schemes of DCF in a 16 channel WDM system. Moreover the impact of non-linearities based on fiber length are also analyzed and compared. The results are evaluated by comparing metrics such as Q-factor, bit error rate (BER) and eye height. The analysis concludes that the symmetrical compensation scheme of DCF outperforms the pre- and post-compensation scheme. This finding suggests that the symmetrical compensation method offers a promising solution for high-capacity access networks, providing high spectral efficiency, cost-effectiveness, and improved flexibility.

Improved carrier phase recovery for high-capacity optical communication systems with high-order modulation formats

A modified Viterbi-Viterbi (MVV) carrier phase recovery (CPR) algorithm is comprehensively studied based on the quadrature phase-shift-keying (QPSK) partition scheme. By improving the QPSK partition scheme for the 16-ary quadrature amplitude modulation (16QAM), MVV algorithm is developed for the optical fiber communication systems with the modulation formats of dual-polarization 64-QAM (DP-64QAM) and DP-256QAM. Numerical simulations have been carried out in a 9-channel Nyquist-spaced 32-Gbaud optical transmission system for different modulation formats and the performance of MVV CPR with respect to pilot-aided (PA) CPR has been examined. Results show that MVV CPR can significantly mitigate the laser phase noise in the system using high-order modulation formats. Compared to PA CPR, MVV CPR performs better with the increase of the transmission distance, where the impact of equalization enhanced phase noise has to be taken into account. Furthermore, MVV has been compared with other CPR approaches in terms of the performance and the computational complexity.

Dual-Stage Double-Pass Extended L-Band Erbium-Doped Fiber Amplifier with Improved Gain Performance

Extended L-band erbium-doped fiber amplifiers (EDFAs) have attracted much attention in recent years despite their relatively low gain levels. In this paper, a dual-stage extended L-band EDFA with improved gain level is demonstrated by using an Er/Yb/P co-doped fiber-based double-pass structure assisted by a low noise pre-amplifier. High gain levels of up to 48.79 dB at 1566 nm and 20.05 dB at 1621.4 nm are achieved with saturated output power at 1605 nm of 20.58 dBm under a total pump power of only 400 mW. Bandwidths with the gain of more than 20 and 30 dB are reached up to 66 nm (1555.4–1621.4 nm) and 58.4 nm (1557.5–1615.9 nm), respectively. The noise figure benefited by using the low noise pre-amplifier is 5.40 ± 1.55 dB in the 1565–1610 nm range. The wide gain bandwidth, high gain level and relatively low pump power give it great potential for future high-capacity optical fiber communication systems.

Radio environment maps for indoor visible light communications aided by machine learning

VLC has been proposed as reliable high-capacity wireless optical communication system for indoor access networks. This technology comprises a high bandwidth unlicensed solution and has been suggested for ultra-reliable environments like hospitals. In this study, Machine Learning is used to investigate indoor wireless optical channels where ultra-reliable communications and signal coverage are required. Specifically, we assess the precision of different Decision Trees ML algorithms based on their mean absolute error metric in comparison to the anticipated simulated outcomes for optical channel estimation in various rooms that could be used in medical care. We demonstrate that Decision Trees models are capable of making fast and accurate predictions. It is shown that the Stack model is the most appropriate Decision Trees-based method, from the ones we studied, for predicting indoor VLC RSS values and constructing the corresponding REMs. These models are 300–65,000 times faster than traditional calculation methods, depending on the number of reflections bounces considered, and deliver accurate predictions, with less than 0.015 mean absolute percentage error, of the Radio Environment Map of a communication system that supports VLC. This is the first implementation of constructing optical REMs for Indoor VLC systems to the best knowledge of the authors.

Regrowth-free AlGaInAs MQW polarization controller integrated with a sidewall grating DFB laser

Polarization control is at the heart of high-capacity data optical communication systems, such as polarization-division multiplexers and Stokes vector modulation transmitters. Despite passive polarization control being mature, the realization of monolithically integrated polarization controllers and single longitudinal mode light sources, such as distributed-feedback (DFB) lasers, is of importance. In this research, we report an AlGaInAs multiple-quantum-well photonic integrated circuit device which can control the state of polarization of the output light source, consisting of a polarization mode converter (PMC), a differential phase shifter (DPS), and a sidewall grating DFB laser. We demonstrate an asymmetrical stepped-height ridge waveguide PMC to realize TE to TM polarization conversion and a symmetrical straight waveguide DPS to enable polarization rotation from approximately counterclockwise circular polarization to linear polarization. Based on the identical epitaxial layer scheme, all the PMC, DPS, and DFB lasers can be integrated monolithically using only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching. For the DFB-PMC device, a high TE to TM polarization conversion efficiency (98.4%) over a wide range of DFB injection currents is reported at 1555 nm wavelength. For the DFB-PMC-DPS device, a nearly 60° rotation of the Stokes vector on the Poincaré sphere was obtained with a range of bias voltage from 0 to −3.0 V at a laser drive current of 170 mA.

Miniaturized optical vortex mode demultiplexer: Principle, fabrication, and applications

Vortex beams have attracted extensive attention in recent decade due to the carried optical orbital angular momentum (OAM). Vortex beams carrying different OAM modes are orthogonal to each other, and thus have become highly promising in realizing high-capacity optical communication systems. This review is to introduce the fundamental principles of optical OAM mode demultiplexing, recent advances in the fabrication techniques and emerging applications in high-capacity optical communications. First, this review introduces the development history of the working principle of OAM mode demultiplexer. Subsequently, a variety of preparation techniques and emerging applications of OAM mode demultiplexing are discussed in detail. Finally, we provide an in-depth analysis and outlook for the future trends and prospects of the OAM mode demultiplexer.

High-order orbital angular momentum mode conversion based on a chiral long period fiber grating inscribed in a ring core fiber.

A chiral long period fiber grating (CLPFG) was designed according to the phase-matching condition and conservation law of angular momentum, and was inscribed in a ring core fiber (RCF). This CLPFG was used to directly excite the ±2nd- and ±3rd-order orbital angular momentum (OAM) modes. The coupling efficiency of the OAM mode is up to 98.7% and the insertion loss is within 0.5 dB. The uniformity of the annular mode intensity distribution, polarization characteristics, and the mode purity of coupled OAM modes were investigated in detail. Results show that the coupled high-order OAM modes possess a relative uniform annular intensity distribution, its mode purity is up to 93.2%, and the helical phase modulation is independent on the polarization state of incident light. These results indicate that the RCF-based CLPFG is an ideal OAM mode converter for future high-capacity optical fiber communication systems.

100 Hertz frame-rate switching three-dimensional orbital angular momentum multiplexing holography via cross convolution

The orbital angular momentum (OAM) of light has been implemented as an information carrier in OAM holography. Holographic information can be multiplexed in theoretical unbounded OAM channels, promoting the applications of optically addressable dynamic display and high-security optical encryption. However, the frame-rate of the dynamic extraction of the information reconstruction process in OAM holography is physically determined by the switching speed of the incident OAM states, which is currently below 30 Hz limited by refreshing rate of the phase-modulation spatial light modulator (SLM). Here, based on a cross convolution with the spatial frequency of the OAM-multiplexing hologram, the spatial frequencies of an elaborately-designed amplitude distribution, namely amplitude decoding key, has been adopted for the extraction of three-dimensional holographic information encoded in a specific OAM information channel. We experimentally demonstrated a dynamic extraction frame rate of 100 Hz from an OAM multiplexing hologram with 10 information channels indicated by individual OAM values from –50 to 50. The new concept of cross convolution theorem can even provide the potential of parallel reproduction and distribution of information encoded in many OAM channels at various positions which boosts the capacity of information processing far beyond the traditional decoding methods. Thus, our results provide a holographic paradigm for high-speed 3D information processing, paving an unprecedented way to achieve the high-capacity short-range optical communication system.

Extending the Detection Range of Optical Vortices by Dense Phase Stitching Algorithm

With the development of optical communication technology based on orbital angular momentum (OAM), more and more OAM modes are employed in communication systems, which puts forward higher requirements for the capacity of OAM state detection at the receiving end. In this work, we reported a scheme to measure and demultiplex OAM beams with topological charges from -32 to +32 by using a specially engineered two-dimensional 64-focus vortex demultiplexing array. The phase mask for generating this array was calculated by dense phase stitching algorithm which integrates four candidate phase masks that can generate four 16-focus arrays respectively. The first step of the algorithm is to extract sector phase areas from the four phase masks successively by using rotationally symmetric sector apertures whose total angular aperture is π/2. The second step of the algorithm is to form a stitched phase mask with the extracted sector phase areas. Consequently, the 64-focus vortex array can be generated by using the stitched phase mask, which is almost equivalent to generating four 16-focus arrays by four candidate phase masks simultaneously. Furthermore, by adjusting the number of sector apertures, the modal crosstalk in the OAM detection range can be greatly reduced. With the help of this scheme, both single OAM mode and multiplexing OAM modes in the range from -32 to +32 can be effectively measured. According to this scheme, simple devices can be arranged to achieve both low modal crosstalk and wide detection range of vortex beams, which can support the advanced high-capacity OAM-based optical communication systems.

Chip-based optical frequency combs for high-capacity optical communications

Abstract Current fibre optic communication systems owe their high-capacity abilities to the wavelength-division multiplexing (WDM) technique, which combines data channels running on different wavelengths, and most often requires many individual lasers. Optical frequency combs, with equally spaced coherent comb lines derived from a single source, have recently emerged as a potential substitute for parallel lasers in WDM systems. Benefits include the stable spacing and broadband phase coherence of the comb lines, enabling improved spectral efficiency of transmission systems, as well as potential energy savings in the WDM transmitters. In this paper, we discuss the requirements to a frequency comb for use in a high-capacity optical communication system in terms of optical linewidth, per comb line power and optical carrier-to-noise ratio, and look at the scaling of a comb source for ultra-high capacity systems. Then, we review the latest advances of various chip-based optical frequency comb generation schemes and their applications in optical communications, including mode-locked laser combs, spectral broadening of frequency combs, microresonator-based Kerr frequency combs and electro-optic frequency combs.

On-Chip Orbital Angular Momentum Sorting With a Surface Plasmon Polariton Lens

Orbital angular momentum (OAM) of light provides a new dimension to increase the communication capacity. The compact and miniaturized devices are preferred because of the advantages in reliability and easy integration. In this work, a quarter-ring-shaped phase-gradient metasurface (QR-PGM) is proposed to sort various propagating waves into fully separated waveguide channels according to their OAM states. The principle is based on focal spot shifting arising from the constructive interference of surface plasmon polaritons with azimuthal phase modulated by the vortex beam. A thorough analysis of the SPP focusing properties was also carried out, which suggests the superiority of quarter-circular arc in OAM sorting (compared with half-circular arc). Focusing efficiency of the QR-PGM reaches to 25%, owing to dense sampling of incident light and unidirectional excitation of SPPs. By coupling spots to waveguides, the wide band on-chip sorting was demonstrated. In the broad wavelength band from 1.3 to 1.6 μm, the extinction ratio of each waveguide port keeps above 3 dB. The proposed structure is compact, efficient, wavelength-division-multiplexing-compatible, and easy to integrate with other on-chip devices. It will be a promising element for high capacity optical communication systems.

Impact of Equalization-Enhanced Phase Noise on Digital Nonlinearity Compensation in High-Capacity Optical Communication Systems.

Equalization-enhanced phase noise (EEPN) can severely degrade the performance of long-haul optical fiber transmission systems. In this paper, the impact of EEPN in Nyquist-spaced dual-polarization quadrature phase shift keying (DP-QPSK), dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM), and DP-64QAM optical transmission systems is investigated considering the use of electrical dispersion compensation (EDC) and multi-channel digital backpropagation (MC-DBP). Our results demonstrate that full-field DBP (FF-DBP) is more susceptible to EEPN compared to single-channel and partial-bandwidth DBP. EEPN-induced distortions become more significant with the increase of the local oscillator (LO) laser linewidth, and this results in degradations in bit-error-rates (BERs), achievable information rates (AIRs), and AIR-distance products in optical communication systems. Transmission systems using higher-order modulation formats can enhance information rates and spectral efficiencies, but will be more seriously degraded by EEPN. It is found that degradations on AIRs, for the investigated FF-DBP schemes, in the DP-QPSK, the DP-16QAM, and the DP-64QAM systems are 0.07 Tbit/s, 0.11 Tbit/s, and 0.57 Tbit/s, respectively, due to the EEPN with an LO laser linewidth of 1 MHz. It is also seen that the selection of a higher-quality LO laser can significantly reduce the bandwidth requirement and the computational complexity in the MC-DBP.

Differential Gain Comparison of Optical Planar Amplifier on Silica Glasses Doped with Bi-Ge and Er, Yb Ions

The paper presents the measurement and calculation of the optical amplifier gain and the optimal length of the active optical amplifier waveguide doped with Bi-Ge radiation complexes compared to an optical amplifier with active doping with ions Er3+, Yb3+. At present are using optical amplifiers for the high-capacity optical communication systems in the narrow spectral region of 1530–1560 nm, determined by the gain bandwidth of erbium-doped fiber amplifiers (EDFA) or erbium-doped optical planar amplifiers (EDPA) realized as active planar waveguides in the optical integrated circuits technique. However, it is possible increase wavelength region up to 1610 nm, where optical losses of telecommunication fibers are less than 0.3 dB per km, if appropriate amplifiers are available. In this regard, the development of novel optical amplifiers operating in this spectral region have of great importance. The paper summarizes the results measurement of the attenuation and emission spectra for net gain spectra calculation of the new ion exchange Ag+ – Na+ optical Er3+ and Yb3+ doped active planar waveguides realized on silica glass substrates and parameters of novel optical amplifiers for extension of the bandwidth from 1530 to 1610 nm doped by bismuth – erbium ions.

Fiber Amplifiers and Fiber Lasers Based on Stimulated Raman Scattering: A Review.

Nowadays, in fiber optic communications the growing demand in terms of transmission capacity has been fulfilling the entire spectral band of the erbium-doped fiber amplifiers (EDFAs). This dramatic increase in bandwidth rules out the use of EDFAs, leaving fiber Raman amplifiers (FRAs) as the key devices for future amplification requirements. On the other hand, in the field of high-power fiber lasers, a very attractive option is provided by fiber Raman lasers (FRLs), due to their high output power, high efficiency and broad gain bandwidth, covering almost the entire near-infrared region. This paper reviews the challenges, achievements and perspectives of both fiber Raman amplifier and fiber Raman laser. They are enabling technologies for implementation of high-capacity optical communication systems and for the realization of high power fiber lasers, respectively.

Fully Passive User Localization for Beam-Steered High-Capacity Optical Wireless Communication System

By means of narrow infrared beams very high capacity wireless links can be set up to users individually, while also offering high privacy and high energy efficiency. Accurate device localization for steering the beams is required. This has been achieved within the 10 cm pico-cell resolution of a 2D beam-steered optical wireless communication system by applying a matrix of miniature corner-cube retro-reflectors. The localization process is self-calibrating, and does not need power-consuming elements at the receiver. In an indoor laboratory system setup, real-time transfer of multiple 10GbE high-definition video streams has been demonstrated.

Elliptical hollow-core optical fibers for polarization-maintaining few-mode guidance

Abstract We propose polarization-maintaining few-mode elliptical hollow-core optical fibers with simple triple-layer structure toward space-division-multiplexing based high-capacity optical communication systems. The proposed fibers include a central elliptical air hole, a concentric elliptical ring core and a circular cladding. The structure-dependent polarization-maintaining performance is comprehensively investigated via numerical simulations. With appropriate structural parameters, 10 distinct polarization-maintaining modes can be guided in this fiber. The effective refractive index differences (Δneff) between all adjacent modes are beyond 1.93 × 10−4 at 1550 nm, and the values are higher than 1.8 × 10−4 over 1510–1630 nm. The modal chromatic dispersions are analyzed subsequently. Furthermore, the number of guided polarization-maintaining modes can be expanded to 14 with modified structural parameters meanwhile keeping all Δneff values no less than 1.33 × 10−4 in range of 1510–1630 nm.

Theoretical investigation of optical modulators based on graphene-coated side- polished fiber.

The effective mode index (EMI) of a graphene-coated side-polished fiber (GSPF) is calculated numerically. Whereby, the influences of graphene atom layer number, residual radius of SPF, light frequency, scattering rate of graphene, and temperature on the EMI are investigated comprehensively. Two types of mechanisms for the electro-optical absorption modulation are found for such GSPF-based modulator. One mechanism is Pauli blocking effect (PBE) and the other is plasmonic attenuation effect (PAE). With the optimal design parameters, a PBE-based modulator is theoretically predicted to have a 0.0072 dB/μm modulation depth, 2.92 V driving voltage swing, 6.35 nJ/bit power consumption, and 56.2 THz optical modulation bandwidth. It is also predicted that a PAE-based modulator could have a 0.0056 dB/μm modulation depth, 0.6 V driving voltage swing, 0.27 nJ/bit power consumption, and 2.5 THz optical modulation bandwidth. By further optimization, the modulator performance such as the relatively high power consumption and the narrow operation bandwidth can be improved. Owing to their seamless connection to optical fiber networks, the GSPF-based modulators have great potential to be used in fast and high-capacity optical communication systems.

Analytical comparison of photonic crystal fibers for dispersion compensation with different structures using FDTD method

In new generation of optical communication networks, simultaneous transmission of several information channels has become possible over a single optical fiber. But dispersion and dispersion slope of optical fibers are important factors, which limit high capacity optical fiber communication systems to perform high speed transmission.

Review of Microwave Photonics Technique to Generate the Microwave Signal by Using Photonics Technology

AbstractMicrowave photonics system provides high bandwidth capabilities of fiber optic systems and also contains the ability to provide interconnect transmission properties, which are virtually independent of length. The low-loss wide bandwidth capability of optoelectronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. So, we can considered microwave photonics as the field that studies the interaction between microwave and optical waves for applications such as communications, radars, sensors and instrumentations. In this paper we have thoroughly reviewed the microwave generation techniques by using photonics technology.

Digital nonlinearity compensation in high-capacity optical communication systems considering signal spectral broadening effect

Nyquist-spaced transmission and digital signal processing have proved effective in maximising the spectral efficiency and reach of optical communication systems. In these systems, Kerr nonlinearity determines the performance limits, and leads to spectral broadening of the signals propagating in the fibre. Although digital nonlinearity compensation was validated to be promising for mitigating Kerr nonlinearities, the impact of spectral broadening on nonlinearity compensation has never been quantified. In this paper, the performance of multi-channel digital back-propagation (MC-DBP) for compensating fibre nonlinearities in Nyquist-spaced optical communication systems is investigated, when the effect of signal spectral broadening is considered. It is found that accounting for the spectral broadening effect is crucial for achieving the best performance of DBP in both single-channel and multi-channel communication systems, independent of modulation formats used. For multi-channel systems, the degradation of DBP performance due to neglecting the spectral broadening effect in the compensation is more significant for outer channels. Our work also quantified the minimum bandwidths of optical receivers and signal processing devices to ensure the optimal compensation of deterministic nonlinear distortions.