Generation Optical Communication Research Articles

Compact high extinction ratio high-order mode pass filter based on inverse-designed ultra-compact unidirectional mode converter

Mode division multiplexing (MDM) technology provides a pathway to enhance channel capacity beyond wavelength division multiplexing, positioning it as a pivotal advancement for next generation optical communications. Mode filters are essential for the low-loss transmission of specific modes and the reduction of modal crosstalk, thereby enhancing the feasibility of MDM systems. Although suppressing high-order mode is relatively straightforward, effectively blocking low-order modes poses a more intricate challenge. In this paper, we introduce a high-order mode pass strategy, effectively blocking low-order modes using the unidirectional mode converters. Specifically, a TE1 high-order mode pass filter (HOMPF) is demonstrated on a silicon-on-insulator platform, utilizing a unique inverse-designed ultra-compact unidirectional TE0-TE1 mode converter. Experimental results show the TE1-TE1 insertion loss of the HOMPF of below 1.0 dB and an average TE0-TE0 extinction ratio of 36.8 dB (42.1 dB for 2-cascaded HOMPF) within the C-band range of 1525-1565 nm. Additionally, the scalability of the HOMPF structure is explored, with simulations demonstrating a TE2 HOMPF. The proposed HOMPFs feature simplicity, compactness, low loss, and high extinction ratio, making them promising components for mode manipulation in MDM systems.

Impact of Scintillation Effect on Clear Weather and Fog Conditions using MDM-WDM Modulation Technique

The 5th generation optical wireless communication technologies have unique features of higher data rate, scalability in bandwidth, license free spectrum, cost effectiveness, easy deplorability and secured transmission. The role of free space optical (FSO) communication becomes important as the applications of next generation technologies are evolving in almost every sector. In this work, the performance of the terrestrial FSO MDM-WDM link has been investigated through a DP-QPSK modulation scheme at a data rate of 1000 Gbps. The link attenuation has been analysed with the help of Gamma- Gamma and Lognormal scintillation models considering clear weather and varying fog conditions. The link performance has been evaluated through SNR and received optical power for a varying distance of up-to 20 Km.

Low-Complexity Adaptive Background Compensation of Coherent Optical Transmitters

Next generation optical communications will demand coherent transceivers with data rates in the 1.6 Terabit-per-second range and beyond, requiring both high symbol rate and large constellations. In this scenario coherent systems become increasingly sensitive to transmitter imperfections such as In-phase/Quadrature time skew, amplitude and phase errors, bandwidth limitations and mismatches, etc. These impairments must be compensated to achieve satisfactory performance. In this work, we propose a novel and efficient technique for the precompensation of such impairments, requiring minimum additional hardware in current transmitter designs. This scheme is <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">adaptive</i> , as it readjusts itself to cope with time and environment dependent impairments, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">background</i> , as interruptions of normal operation are not required for the continuous recalibration of the system. Naturally, such <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-field</i> adaptation demands the real-time system identification of the coherent optical transmitter, which is performed from the sole information provided by a low bandwidth photodiode/analog-to-digital converter chain at the transmitter output. This fact represents a meaningful advance with respect to the usual channel estimation methods, which require the full bandwidth coherent demodulation of the optical output. A theoretical foundation for the proposed scheme is presented. Numerical simulations of a realistic coherent optical transmitter show excellent results for high symbol rate modulation formats.

High-speed multiwavelength InGaAs/InP quantum well nanowire array micro-LEDs for next generation optical communications

High-speed multiwavelength InGaAs/InP quantum well nanowire array micro-LEDs for next generation optical communications

Double exceptional points in grating coupled metal-insulator-metal heterostructure.

In this work we theoretically study the exceptional points and reflection spectra characteristics of a grating coupled metal-insulator-metal heterostructure, which is a non-Hermitian system. Our results show that by selecting suitable geometrical parameters with grating periodicity @150 nm, that satisfy zero reflection condition, double exceptional points appear in a mode bifurcation regime. Furthermore, the thickness of partition metal layer between two cavities plays an important role in controlling the reflection properties of the heterostructure. There is a clear mode splitting when the partition layer allows strong coupling between the two cavity modes. Conversely, in weak coupling regime the mode splitting becomes too close to be distinguished. Moreover, the vanishing of reflection leads to unidirectional reflectionless propagation, which is also known as unidirectional invisibility. With grating periodicity ≥400nm, the transmissions for forward and backward incident directions are no longer the same due to the generation of diffraction. High contrast ratio (≈1) between the two incident directions leads to asymmetric transmission. This work lays the basis for designing double exceptional points and asymmetric transmission in coupled non-Hermitian photonics system. The proposed heterostructure can be a good candidate for new generation optical communications, optical sensing, photo-detection, and nano-photonic devices.

Special Issue on Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications

Optical communication refers to the communication mode with optical signal as a carrier [...]

Graphene-enhanced polarization-insensitive all-optical wavelength conversion based on four-wave mixing.

All-optical wavelength conversion technology based on four-wave mixing (FWM) effect is a promising development need of the modern high-speed optical signal processing system. In this work, we report on the polarization insensitive four-wave mixing based on graphene for all optical wavelength conversion. To overcome the polarization sensitivity of FWM, a dual-pump configuration was proposed based on the combination of graphene and the optical fibers. Our experimental results illustrate that by using the dual pump configuration, the FWM-based wavelength conversion efficiency, can be enhanced by graphene with about 8 dB when the state of polarization of the two pumps are parallel. This proposed all-optical wavelength converter based on graphene may provide a new approach for the next generation optical communications and signal processing.

Photo thermal effect graphene detector featuring 105 Gbit s\u22121 NRZ and 120 Gbit s\u22121 PAM4 direct detection

One of the main challenges of next generation optical communication is to increase the available bandwidth while reducing the size, cost and power consumption of photonic integrated circuits. Graphene has been recently proposed to be integrated with silicon photonics to meet these goals because of its high mobility, fast carrier dynamics and ultra-broadband optical properties. We focus on graphene photodetectors for high speed datacom and telecom applications based on the photo-thermo-electric effect, allowing for direct optical power to voltage conversion, zero dark current, and ultra-fast operation. We report on a chemical vapour deposition graphene photodetector based on the photo-thermoelectric effect, integrated on a silicon waveguide, providing frequency response >65 GHz and optimized to be interfaced to a 50 Ω voltage amplifier for direct voltage amplification. We demonstrate a system test leading to direct detection of 105 Gbit s−1 non-return to zero and 120 Gbit s−1 4-level pulse amplitude modulation optical signals.

Next generation optical wireless communication: a comprehensive review

Abstract Next generation wireless networks are the need of the hour with reliable, high bandwidth, low Bit Error Rate (BER), high Signal to Noise Ratio (SNR), large network capacity, etc. for a paradigm shift to all optical networks from the prevailing conventional electro optic network due to the various benefits of optical links such as enormous bandwidth and extremely low losses. This paper presents a primitive overview of the foregoing technologies and then move on to encapsulating the contemporary techniques to enhance the system performance. For this, preceding limitation and their respective improvement measures from literature of fiber communication and its integration with the next generation networks mainly based upon Radio over Fiber (RoF), Fiber to the Home (FTTH) and Free Space Optics (FSO) are discussed. The advancement in the domain of optical wireless communication utilizing various methodologies is summarized. Finally, we conclude by incorporating various cost reduction methodologies developed which may further be explored to make next generation networks more promising.

Electrically Parallel Three-Element 980 nm VCSEL Arrays with Ternary and Binary Bottom DBR Mirror Layers.

To meet the performance goals of fifth generation (5G) and future sixth generation (6G) optical wireless communication (OWC) and sensing systems, we seek to develop low-cost, reliable, compact lasers capable of sourcing 5–20 Gb/s (ideally up to 100 Gb/s by the 2030s) infrared beams across free-space line-of-sight distances of meters to kilometers. Toward this end, we develop small arrays of electrically parallel vertical cavity surface emitting lasers (VCSELs) for possible future use in short-distance (tens of meters) free-space optical communication and sensing applications in, for example, homes, data centers, manufacturing spaces, and backhaul (pole-to-pole or pole-to-building) optical links. As a starting point, we design, grow by metal–organic vapor phase epitaxy, fabricate, test, and analyze 980 nm top-emitting triple VCSEL arrays. Via on-wafer high-frequency probe testing, our arrays exhibit record bandwidths of 20–25 GHz, optical output powers of 20–50 mW, and error-free data transmission at up to 40 Gb/s—all extremely well suited for the intended 5G short-reach OWC and sensing applications. We employ novel p-metal and top mesa inter-VCSEL connectors to form electrically parallel but optically uncoupled (to reduce speckle) arrays with performance exceeding that of single VCSELs with equal total emitting areas.

A review on fiber optic sensor used in electronics industry, internet of things, and new generation optical communications networks

حسگرهای فیبرنوری موجود در بازار برای اندازه‌گیری کمیت‌های فیزیکی در صنایع مختلف مانند میدان‌های الکتریکی و مغناطیسی، جریان الکتریکی، درجه حرارت، فشار، شتاب، جریان مایعات و گازها و اندازه‌گیری سطح مایعات به‌کار گرفته می‌شوند. امروزه به‌دلیل کاربردهای روزافزون حسگرهای فیبرنوری سازنده‌های بسیاری از ماشین آلات و سیستم‌های کنترل آمادگی خود را در به‌کارگیری این نوع حسگرها در فراورده‌های تولیدی اعلام کرده‌اند. در این مقاله، با توجه به اهمیت روزافزون حسگرهای نوری، به‌ویژه در شبکه‌های حسگر بی‌سیم، در اینترنت اشیا، و شبکه‌های فیبرنوری، این نوع حسگرها در طی دهه‌های گذشته تا به امروز مورد مطالعه گسترده‌ای قرار گرفته‌اند و با نظر به جنبه‌های فنی، ویژگی و کاربردهای آن‌ها مرور و گزارش شده است. نتیجه‌های این گزارش می‌توانند برای طرا‌ح‌های این حسگرها در صنایع مختلف و دانشجویان مقطع‌های کارشناسی، ارشد رشته‌های فیزیک و مهندسی مورد استفاده قرار گیرد.

A Semi-Supervised Machine Learning Approach Using K-Means Algorithm to Prevent Burst Header Packet Flooding Attack in Optical Burst Switching Network

Optical burst switching (OBS) network is a new generation optical communication technology. In an OBS network, an edge node first sends a control packet, called burst header packet (BHP) which reserves the necessary resources for the upcoming data burst (DB). Once the reservation is complete, the DB starts travelling to its destination through the reserved path. A notable attack on OBS network is BHP flooding attack where an edge node sends BHPs to reserve resources, but never actually sends the associated DB. As a result the reserved resources are wasted and when this happen in sufficiently large scale, a denial of service (DoS) may take place. In this study, we propose a semi-supervised machine learning approach using k-means algorithm, to detect malicious nodes in an OBS network. The proposed semi-supervised model was trained and validated with small amount data from a selected dataset. Experiments show that the model can classify the nodes into either behaving or not-behaving classes with 90% accuracy when trained with just 20% of data. When the nodes are classified into behaving, not-behaving and potentially not-behaving classes, the model shows 65.15% and 71.84% accuracy if trained with 20% and 30% of data respectively. Comparison with some notable works revealed that the proposed model outperforms them in many respects.

Vortex instability in turbulent free-space propagation

The spatial structuring of optical fields is integral within many next generation optical metrology and communication techniques. A verifiable physical model of the propagation of these optical fields in a turbulent environment is important for developing effective mitigation techniques for the modal degradation that occurs in a free-space link. We present a method to simulate this modal degradation that agrees with recently reported experimental findings. A 1.5 km free-space link is emulated by decomposing the optical turbulence that accumulates over a long distance link, into many, weakly perturbing steps of 10 m. This simulation shows that the high-order vortex at the centre of the helical phase profiles in modes that carry orbital angular momentum of are unstable and fracture into many vortices when they propagate over the link. This splitting presents issues for the application of turbulence mitigation techniques. The usefulness of pre-correction, post-correction, and complex field conjugation techniques are discussed.

Optical Frequency Comb synthesis for super channel based high-bandwidth data communication

Increasing demand for high bandwidth data communication requires development of innovative, reliable and scalable systems. Super-channels with Higher Order Modulation schemes will drive the next generation optical communication systems. The present work focusses on optical sources for such systems. Conventional implementations require hundreds of lasers and are not scalable; the proposed alternative is to develop and use an Optical Frequency Comb (a series of evenly spaced spectral components). Generating such a comb with precise spacing and stability is a challenge. This is addressed by system design using Electro-Optic Modulators and three lasers where we demonstrate a 24-line comb which is de-multiplexed to realize optical source for super channels. This is a scale up of number of carriers by a factor of 8.

Transmission of multi-dimensional signals for next generation optical communication systems

Over the past several decades, the data-carrying capacity of a single optical fiber have been increased significantly by fully exploring and optimizing physical dimensions of the light. Generally there are five major candidates of dimensions, including time, wavelength, polarization, space and quadrature (phase and amplitude). Multi-dimension, utilizing more than two dimensions of the light simultaneously, is one of the essential characteristics of next generation optical communication systems. We review recent advances in transmission of multi-dimensional signals, and highlight innovative ways of exploring the polarization dimension to further increase the capacity or spectral efficiency of a single optical fiber, a so-called pseudo-polarization-division-multiplexing (PPDM) technique. Related demonstrations include non-orthogonal PDM, PPDM of three and four states (PPDM-3 and PPDM-4). Brief discussions on trends of multi-dimensional signal transmission technologies are also presented.

Temperature Characteristics of Silicon-Polymer Hybrid Material Photonic Resonator

This paper presents temperature sensitivity analysis of a silicon-polymer hybrid photonic micro-ring resonator. Photonic micro-ring resonators have hailed for their potential used in the next generation optical communications. However, like any other optical devices, temperature fluctuations alter the functionality of the micro-ring resonator. Hence, this paper provides a proposal for solution to minimize the temperature sensitive effect on the resonance characteristics. The temperature sensitivity effect of the pure silicon micro-ring resonaltor has been investigated. It is shown that the pure silicon micro-ring resonator is very sensitive to temperature. We added a negative thermo-optic polymer material with the positive thermo-optic silicon material to investigate the efeect of temperature sensitivity. Simulation tool Lumerical solution has been used to simulate the ring resonator. A polymer material of LFR is used to analyze the temperature effects. The hybrid composition of silicon-polymer were as 30%-70%, 40%-60%, 50%-50% and 60%-40% to investigate the temperature effect. The simulation was carried out using a ring size of 5 um, 10 um, 15 um and 20 um. The results show that the temperature insensitive ring resonator is possible with a 42% LFR polymer mixwd with 58% silicon.

Frontier research of ultra-high-speed ultra-large-capacity and ultra-long-haul optical transmission

Ultra-high-speed, ultra-large-capacity and ultra-long-haul (3U) are the forever pursuit of optical communication. As a new mode of optical communication, 3U transmission can greatly promote next generation optical internet and broadband mobile communication network development and technological progress, therefore it has become the focus of international high-tech intellectual property competition ground. This paper introduces the scientific problems, key technologies and important achievements in 3U transmission research.

A Robust Adaptive Pre-Distortion Method for Optical Communication Transmitters

Present and next generation optical communication systems are constantly being developed to operate at higher baud rates and higher modulation formats. It then becomes inevitable to consider the various linear and nonlinear effects due to the imperfect components at the transmitter. State-of-the-art digital-to-analog converters, high bandwidth driver amplifiers, and dual-polarization (DP) Mach–Zehnder modulators are far from being ideal and present distortions in the form of bandwidth limitation, transmitter I/Q skew, and nonlinear effects. In this letter, we propose a new robust pre-distortion method to mitigate the undesirable linear and non-linear distortions of all electrical and optical transmitter components simultaneously. A step-by-step derivation and implementation of the algorithm are discussed and put forward. The performance of the algorithm is experimentally assessed across DP-4QAM, DP-8QAM, DP-16QAM, DP-32QAM, and DP-64QAM up to the signaling rates of 56 GBd. Significant improvements in the required optical signal-to-noise ratio at bit-error rate (BER) of $10^{-2}$ are demonstrated.

TEMPORAL SOLITON: GENERATION AND APPLICATIONS IN OPTICAL COMMUNICATIONS

In general, the temporal and spectral shape of a short optical soliton pulse does not change during propagation in a nonlinear medium due to the Kerr effect which balances the chromatic dispersion. Microring resonators (MRRs) can be used to generate chaotic signals. The smaller MRR is used to form the stopping and filtering system. The employed optical material was InGaAsP/InP, which is suitable for use in the practical devices and systems. The tuning and manipulation of the bandwidth of the soliton signals is recommended to control the output signals. The MRRs can be applied to produce ultra-short pulses, where the medium has a nonlinear condition, thus, using of soliton laser becomes an interesting subject. Therefore, an ultra-short pulse in the scope of pico and femtoseconds soliton pulses can be utilized for many applications in engineering communications. In order to obtain smaller bandwidth of the optical soliton pulses, we propose integrating series of MRRs. In this study, 5 fs soliton pulse could be generated using a series of five MRRs. The soliton signals experience less loss during the propagation, where they are more stable compared to normal conventional laser pulses. Using the series of MRRs connected to an add/drop system, shorter soliton bandwidth and highly multi soliton pulses can be obtained. Therefore, generation of ultra-short multi picosecond (1.2 and 1.3 ps), could be performed, where the radius of the add/drop system has been selected to 50 and 300 µm respectively.

Numerical Analysis of Orbital Angular Momentum based Next Generation Optical SDM Communications System

Numerical Analysis of Orbital Angular Momentum based Next Generation Optical SDM Communications System