Coherent Communication Research Articles

Towards optimal conversion efficiency of Brillouin random fiber lasers in a half-open linear cavity.

We proposed and demonstrated an unprecedented high-efficiency Brillouin random fiber laser (BRFL) by fiber length optimization in a half-open linear cavity. In terms of the trade-off between Brillouin gain saturation and weak distributed Rayleigh feedback strength, optimal laser efficiency associated to proper fiber length in a BRFL was theoretically predicted. As a proof-of-concept, a unidirectional-pumped BRFL with a half-open linear cavity was experimentally conducted, in which a fiber Bragg grating at one end of gain fiber served as a high-reflection mirror while Rayleigh scattering enabled distributed feedback for random lasing resonance. Results show that the optimal fiber length of ∼3.4 km in the BRFL offers sufficient Rayleigh scattered random feedback whilst alleviating the Brillouin gain saturation to a large extent. Consequently, an optimal laser efficiency of 77.0% in the BRFL was experimentally demonstrated, which reaches the state-of-the-art high record. Laser characteristics, including the linewidth, statistics and frequency jitter were also systematically investigated. It is believed that such efficient BRFL could provide a promising platform for inspiring new explorations of laser physics as well as potentials in long-haul coherent communication and fiber-optic sensing.

Spectral purification of single-frequency Stokes pulses in doubly resonant integrated diamond resonators

Pulsed spectrally pure light is required for applications in high-resolution spectroscopy, optical coherent communications, and quantum technologies. In this work, we report on the efficient generation of high peak power, single-frequency, and tunable nanosecond pulses utilizing stimulated scattering, with an increased spectral brightness by exploiting double resonances in an integrated diamond Raman resonator. The device is based on a miniature monolithic Fabry–Perot design pumped by a milliwatt-class average power Q-switched single-frequency pulsed laser at 532 nm. Our device was capable of enhancing the peak spectral brightness by greater than three times compared with conventional singly resonant diamond Raman lasers by tuning the effective resonator length at pump and Stokes wavelengths simultaneously. Our results facilitate the integration of pulsed and power scalable single frequency sources into hybrid photonic integrated platforms with a broad range of applications.

Coherent Communication Over Multi Mode Fibers for Intra-Datacenter Ultra-High Speed Links

Multimode fibers (MMFs) links using vertical cavity surface-emitting lasers (VCSELs) are still the solution of choice for today’s data center shorter distances thanks to their low cost and robustness. Currently, the market is moving towards 400G-capable systems using multiple lanes at 50 Gbps per lane, based on intensity modulation (IM) and direct detection (DD). A technology switch will probably be required to overcome the 100 Gbps per lane limit that will likely be the bottleneck of future IM-DD MMF-based links. In this manuscript we propose an intra-data center system based on coherent detection and MMF, analyzing experimentally and analytically the performance of polarization multiplexed coherent communication. We show that the advantages enabled by the coherent technology can be fully exploited in an MMF-based link when central launch is ensured. In particular, we study in detail the effect of lateral offsets introduced by the connectors at the interface between two MMF facets, in terms of net optical loss and signal-to-noise ratio (SNR) degradation. A statistical analysis is performed analytically exploiting a large database of OM3 and OM4 fibers modal delays and results are presented for various combinations of fiber length, type and number of MMF-to-MMF connections along the link. We show quantitative results on the maximum acceptable lateral offsets in the MMF connectors, highlighting that in practical conditions average offsets of up to 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m can be tolerable.

Analysis of the performance of a coherent SAC-OCDMA–OFDM–DWDM system using a flat optical frequency comb generator for multiservice networks

This research proposes the architecture of a SAC-OCDMA–OFDM–DWDM system using a flat optical frequency comb generator and coherent communication. Its aim is to create a new OCDMA communication system that is specifically intended for multiservice networks. The suggested architectural design is numerically simulated and analyzed using OptiSystem and MATLAB. To quantify the performance of the proposed system, SNR, EVM, and BER were used as metrics. Furthermore, a comparison between the two codes, EDW and RD, has been presented. Thus, it has been revealed that the RD code system has better performance in terms of robustness and number of users than the EDW code. Besides, by analyzing the BER for several symbol rates and comparing it to the pre-FEC threshold, the proposed system demonstrates its effectiveness against linear and nonlinear effects. The results also show that optical noise affects signal quality; the mathematical analysis used allowed us to determine the impact of noise on the number of potential active users.

R&D of a low-complexity OFDM acoustic communication payload for Micro-AUV in confined space

With small size, high flexibility, low cost, and deployment convenience, Micro-sized autonomous underwater vehicle (Micro-AUV) is capable of performing diverse underwater missions efficiently in confined underwater space, for the extensive purpose of rescue, sightseeing, pipeline engineering and so on. The underwater acoustic (UWA) communication technique provides an effective way to support this types of underwater mission for telemetry and remote control of Micro-AUV. However, while the adverse multipath caused by confined space poses significant challenge to the classic coherent acoustic communication schemes that need channel estimation and equalization processing, the employment of non-coherent communication scheme is generally limited by low data rate. By utilizing time-domain and frequency-domain differential modulation to suppress the influence of multipath, a low-complexity UWA communication payload is designed to provide an effective solution to make a tradeoff between data rate and implementation complexity. Based on a STM32 series processor, this paper introduced the software and hardware implementation of a time-frequency differential OFDM UWA communication payload for Micro-AUV and presented the performance evaluation of the system in confined underwater space. The experimental results achieved in a confined lake show that the proposed system has the potential of being used for Micro-AUV to achieve a data rate of 1.96 kbps at a distance of 200m with acceptable implementation overhead.

Air-gap Fabry-Pérot cavity filtered 30 nm broadband electro-optic frequency combs for high-order coherent communications.

Broadband electro-optic (EO) frequency combs, which have flexible and high repetition frequencies, are prospective light sources for dense-wavelength-division-multiplexed coherent optical communications. In most cases, nonlinear spectral broadening and amplification procedures are needed to achieve broadband and high-power EO frequency combs. This leads to a low optical carrier-to-noise ratio (OCNR) for comb lines, limiting the transmission capacity. Here, we propose to use an air-gap Fabry-Pérot (FP) cavity to improve the OCNR for all the comb lines covering a 30 nm broadband spectrum. A 12 dB OCNR (0.1 nm bandwidth) improvement is obtained experimentally via using an FP cavity with ∼790 MHz bandwidth. We apply a 150-channel filtered EO comb with 25 GHz channel spacing and load 20 GBaud signals on each comb line to demonstrate the effect of OCNR improvement. The 137/150 channels have a bit error rate below the threshold of soft-decision forward error correction when using the 128 quadrature amplitude modulation (QAM) format. However, none of these channels can support this modulation format without cavity filtering. We also investigate dispersion tolerance and the long-term stability when using an air-gap FP cavity, highlighting its advantages. Our results show a practical solution to boost the transmission capacity when applying broadband EO combs in optical communications.

A Low-Complexity Underwater Acoustic Coherent Communication System for Small AUV

While underwater acoustic (UWA) communication offers a practical way to establish a wireless link with underwater vehicles, designing a UWA communication system onboard a small autonomous underwater vehicle (AUV) still poses significant challenges. As the adoption of the low-complexity, robust noncoherent communication technology is limited by low bandwidth efficiency and a low data rate, coherent UWA communication requires Doppler mitigation and channel equalization measures to achieve a relatively high data rate in a moving state. Due to the strict constraints of a small-scale AUV in terms of resources and energy consumption, it is not appropriate to use high-complexity Doppler/multipath compensation technology from the prospect of system implementation. In this paper, an efficient and low-complexity UWA differential binary phase-shift keying (DBPSK) system onboard a small AUV is proposed by simplifying the Doppler and multipath compensation. Specifically, for Doppler, the delay of the adjacent DBPSK symbols is calculated according to the Doppler estimate to facilitate delay-tuning Doppler correction. For multipath, low-complexity LMS channel equalization is incorporated with error correction coding to enable multipath mitigation. With a simple structure and low computational complexity, the proposed scheme facilitates the practical hardware implementation and system integration in the small AUV platform. The numerical simulations are conducted to assess the validity of the proposed scheme under different channel conditions and the effectiveness of the proposed scheme is further verified by two UWA communication field tests, which are performed at a practical shallow water sea and lake, respectively.

Reasonable requests: echocardiography referral forms as a measure of coherent clinical communication

BackgroundWell performed clinical communication is a cornerstone of collaborative care in medicine but may be confounded by inconsistent intentions of the messenger and biased interpretation by the recipient. A comparison of the findings of electronic echocardiography reports with clinician-completed standardised request forms provided an opportunity to assess communication quality.AimThe study aimed to determine clinician aptitude to complete written echocardiography referral forms by assessing the completeness, appropriateness, accuracy, and coherency of the reported clinical findings, conclusions and requests made on the referral forms. The study explored factors that may influence the quality of communication through this referral medium.MethodsA retrospective cohort study was conducted on patients who underwent trans-thoracic echocardiography imaging at Cecilia Makiwane Hospital in East London over 26 months. Paper echocardiography request forms that recorded the requesting clinician’s findings on examination, the provisional clinical diagnosis, and the specific echocardiographic information sought, were compared with the actual findings on echocardiography.ResultsOf 613 request forms reviewed, 97 cases were excluded due to illegibility or because they lacked analysable information or requester details, leaving 516 forms suitable for study. No pathology was found on echocardiography in 31%. Of the murmurs expected from the echocardiography findings, only half were recorded on the request form (sensitivity and positive predictive value both 52%.). Only 35% of request forms that mentioned a mitral systolic murmur gave a working diagnosis of mitral regurgitation and only 38% of request forms that mentioned an aortic systolic murmur considered aortic stenosis. Clinically suspected cardiomyopathy (CMO) had a PPV of 43% and echocardiographic CMO was missed clinically in 41%. Apex beat displacement reported clinically was not associated with echocardiographic LV dilatation in 65% of cases. One-third (34%) of forms reporting murmurs did not request valve function assessment and 17% considering cardiomyopathy did not request left ventricular function assessment.ConclusionEchocardiography request forms highlight vulnerabilities in clinical communication. Specifically, important clinical features were missing and more concerningly, included when unlikely to be present. There was a lack of concordance between recorded clinical findings and postulated diagnoses. Clinicians sometimes appeared unclear about the value or appropriateness of the requested assistance. Greater emphasis on teaching examination and communication skills may foster safer and more efficient use of scarce resources.

On‐Chip High‐Speed Coherent Optical Signal Detection Based on Photonic Spin‐Hall Effect

AbstractThe use of coherent optical signal processing in long‐distance optical communication systems has dramatically increased data capacity enabling encoding of multiple‐bit information in the phase of a light beam. Direct detection of phase information of a high‐speed modulated light remains challenging and requires an external, local oscillator for referencing, which is expensive for short‐reach optical communications, for example, in data centers. The availability of less‐complex integrated photonics devices for coherent signal detection will alleviate this bottleneck. On the other hand, phase information of coherent, orthogonally polarized light beams can be extracted from their polarization states, and it is, therefore, possible to achieve phase measurements via fast polarization detection. Here, an on‐chip nanodisk device is demonstrated for high‐speed coherent optical signal detection enabled by spin–orbit coupling in Si‐photonics circuitry. In a coherent communication experiment with up to 32 GBaud rate, the high‐speed phase‐shift keying and quadrature amplitude modulation signals detected by a Si nanodisk based polarization measurements at multiple wavelengths in the C‐band are recovered with a bit error rate below the forward error correction threshold. The proposed on‐chip nanodisk device shows promise in high‐speed coherent optical communication applications where phase detection is required at low cost and small footprint.

Hardware Trojan Threats to Cache Coherence in Modern 2.5D Chiplet Systems

As industry moves toward chiplet-based designs, the insertion of hardware Trojans poses a significant threat to the security of these systems. These systems rely heavily on cache coherence for coherent data communication, making coherence an attractive target. Critically, unlike prior work, which focuses only on malicious packet modifications, a Trojan attack that exploits coherence can modify data in memory that was never touched and is not owned by the chiplet which contains the Trojan. Further, the Trojan need not even be physically between the victim and the memory controller to attack the victim's memory transactions. Here, we explore the fundamental attack vectors possible in chiplet-based systems and provide an example Trojan implementation capable of directly modifying victim data in memory. This work aims to highlight the need for developing mechanisms that can protect and secure the coherence scheme from these forms of attacks.

Practical Distributed Reception for Wireless Body Area Networks Using Supervised Learning

Medical applications have driven many areas of engineering to optimize diagnostic capabilities and convenience. In the near future, wireless body area networks (WBANs) are expected to have widespread impact in medicine. To achieve this impact, however, significant advances in research are needed to cope with the changes of the human body’s state, which make coherent communications difficult or even impossible. In this paper, we consider a realistic noncoherent WBAN system model where transmissions and receptions are conducted without any channel state information due to the fast-varying channels of the human body. Using distributed reception, we propose several symbol detection approaches where on-off keying (OOK) modulation is exploited, among which a supervised-learning-based approach is developed to overcome the noncoherent system issue. Through simulation results, we compare and verify the performance of the proposed techniques for noncoherent WBANs with OOK transmissions. We show that the well-defined detection techniques with a supervised-learning-based approach enable robust communications for noncoherent WBAN systems.

Microresonator frequency comb based high-speed transmission of intensity modulated direct detection data

Abstract Globally, the long-haul transmission of ultra-high bandwidth data is enabled through coherent communications. Driven by the rapid pace of growth in interconnectivity over the last decade, long-haul data transmission has reached capacities on the order of tens to hundreds of terabits per second, over fiber reaches which may span thousands of kilometers. Data center communications operate in regimes featuring shorter reaches and higher cost sensitivity. While integrated microresonator frequency combs are poised to revolutionize light sources used for high-speed data transmission over fiber, recent progress has focused largely on coherent detection schemes. Furthermore, though state-of-the-art intensity modulators are advancing in speed, it has not been demonstrated in the literature if microresonator-based comb lines can accommodate higher intensity modulated direction data (IMDD) line rates in tandem with these advancements. In this manuscript, we demonstrate the use of microresonator frequency combs pumped with a single laser for the transmission of high-speed IMDD data. We demonstrate error-free transmission of 30 Gbs−1 per comb non-return-to-zero data over fiber lengths of 6 km, as well as bit error rates under the forward error correction limit for propagation through 20 km of optical fiber. 60 Gbs−1 and 42 Gbs−1 pulse modulation amplitude 4 (PAM4) data modulated on each frequency comb line is further quantified to have a bit error rate under the forward error correction limit for fiber reaches of up to 6 km and 20 km respectively. The results showcase CMOS-compatible microresonator frequency comb modulated using IMDD formats as a promising technology for high-speed transmission in the data center transceiver industry.

Multiband Silicon Photonic ePIC Coherent Receiver for 64 GBd QPSK

Multiband coherent communication is being handled as a promising candidate to address the increasing demand for higher data rates and capacity. At the same time, coherent communication is expected to enter the data center domain in the near future. With coherent data links in both, data- and telecom, spanning multiple optical bands, novel approaches to coherent transceiver design and traffic engineering will become a necessity. In this work, we present a monolithically integrated silicon photonic coherent receiver for O- and C-band. The receiver features a 2 × 2 multi-mode interference coupler network as 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> hybrid optimized for 1430 nm (E-band). The total power consumption is 460 mW at a footprint of approximately 6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> , and an opto-electrical bandwidth of 33 GHz. 64 GBd operation is demonstrated in O- and C-band, which is competitive to the state-of-the-art for silicon photonic coherent receiver in the C-band, and the highest symbol rate to date for O-band coherent communication.

Characterization, Measurement and Specification of Device Imperfections in Optical Coherent Transceivers

Transceiver imperfections become the primary source of impairment as baud rate and modulation order grow in advanced optical coherent communications. Thus, transceiver imperfections, both linear and nonlinear, need to be appropriately characterized, measured, and specified. Treatments for linear imperfections are relatively mature. This study reviews the transceiver's linear imperfection modeling, characterization, and measurement technologies. In practical applications, in-field measurement using the transceiver and a few low speed additional devices is preferred. In the case of nonlinear imperfections, the situation is complex. One important task is to estimate the nonlinear system performance from the nonlinear characteristics of the devices. In this study, we attempt to establish a connection between them by examining different technologies. Although the orthogonal component has a good correlation with nonlinear system performance, its measurement is prohibitively complex. In the nonlinear noise to power ratio measurement, a certain frequency component of the input signal is notched, and the re-growth component at the notch frequency is measured at the nonlinear device output. The ratio between the re-growth component power and the output signal power is the noise to power ratio. While this method is easy to carry out, it does not correctly estimate nonlinear impairment in general. The reason for this is that the signal incurs different nonlinear responses in two conditions, i.e., with or without a notch. This method accurately estimates the nonlinear impairment in some special but useful cases, such as Gaussian input signals and nonlinear systems whose dominant nonlinear term is the even order term.

Brillouin Amplification for Enhanced Coherent Communication Applications

Brillouin amplification and its benefit for coherent communication applications with 64-QAM signals is evaluated. This utilizes the narrow gain bandwidth in the tens of megahertz range to enhance the carrier to noise ratio (CNR) of noisy spectral lines applied to either signal carriers at the transmitter before data modulation or pilot tones at the receiver for coherent detection. This expands on the projected capability of 30 dB gain enabling up to &approx;24 dB enhancement of CNR and the same reduction of the minimum tolerable pilot to signal power ratio (PSR) for maintaining the same performance than without in case of 48 Gb&#x002F;s 64-QAM signals. The limit being the narrowness of the Brillouin gain bandwidth (&approx;30 MHz). Here, the tolerance to larger Brillouin noise and its avoidance with reduced gain of &approx;25 dB permitting wider detuning from optimum of the pump frequency and its state of polarization with reduced power oscillations are shown. Extended analysis of carrier recovery for 48 Gb&#x002F;s 64-QAM signals also indicate a capable low PSR near &approx;&#x2212;40 dB for a bit error rate below the hard decision FEC threshold. This includes with 80 km link transmission and its induced nonlinear signal distortion. Overall, rather than an impediment, Brillouin amplification shows significant performance benefit for wide ranging conditions.

Electro-optic tuning of a single-frequency ultranarrow linewidth microdisk laser

Single-frequency ultranarrow linewidth on-chip microlasers with a fast wavelength tunability play a game-changing role in a broad spectrum of applications ranging from coherent communication, light detection and ranging, to metrology and sensing. Design and fabrication of such light sources remain a challenge due to the difficulties in making a laser cavity that has an ultrahigh optical quality (Q) factor and supports only a single lasing frequency simultaneously. Here, we demonstrate a unique single-frequency ultranarrow linewidth lasing mechanism on an erbium ion-doped lithium niobate (LN) microdisk through simultaneous excitation of high-Q polygon modes at both pump and laser wavelengths. As the polygon modes are sparse within the optical gain bandwidth compared with the whispering gallery mode counterpart, while their Q factors (above 10 million) are even higher due to the significantly reduced scattering on their propagation paths, single-frequency lasing with a linewidth as narrow as 322 Hz is observed. The measured linewidth is three orders of magnitude narrower than the previous record in on-chip LN microlasers. Finally, enabled by the strong linear electro-optic effect of LN, real-time electro-optical tuning of the microlaser with a high tuning efficiency of ∼50 pm / 100 V is demonstrated.

Thermal and driven noise in Brillouin lasers

Owing to their highly coherent emission and compact form factor, Brillouin lasers have been identified as a valuable asset for applications including portable atomic clocks, precision sensors, coherent microwave synthesis, and energy-efficient approaches to coherent communications. While the fundamental emission linewidth of these lasers can be very narrow, noise within dielectric materials leads to drift in the carrier frequency, posing vexing challenges for applications requiring ultrastable emission. A unified understanding of Brillouin laser performance may provide critical insights to reach new levels of frequency stability; however, existing noise models focus on only one or a few key noise sources, and do not capture the thermo-optic drift in the laser frequency produced by thermal fluctuations or absorbed power. Here, we develop a coupled-mode theory of Brillouin laser dynamics that accounts for dominant forms of noise in noncrystalline systems, capturing the salient features of the frequency and intensity noise for a variety of systems. As a result, theory and experiment can be directly compared to identify key sources of noise and the frequency bands they impact, revealing strategies to improve the performance of Brillouin lasers and pave the way for highly coherent sources of light on a chip.

Chatbots as Cognitive, Educational, Advisory &amp; Coaching Systems

Chatbots are software applications assimilating human communication with the aim to raise adherence and engagement between human-systems interaction. Text messaging-based conversational agents (CAs) make an interesting use of natural language processing and improve by learning, allowing coherent two-way communication with humans, either oral or written as well as real-time decision-making. Chatbots serve as means of learning and teaching, as virtual assistants and social companions. Machine learning algorithms embedded into Chatbots simulate human cognition, including cognitive learning, decision making and adaptation to the environment. Thus, the future of artificial intelligence in Chatbots lies in the development of a global, reliable and sustainable ecosystem of knowledge, skills and values by bringing together all interested stakeholders, such as scientists, consumers, businesses and the state. Such effective customized/personalized learning frameworks depend on sophisticated conversational flows based on user models, which cluster user preferences and attributes in combination with learning analytics to induce end users’ personal skills, knowledge mastery, learning ability as well as professional development.

Charismatic Leadership Style to Overcome Employee Resistance to the Management of Organizational Change Process

This study aims to clarify a theoretical model to explore how a charismatic leadership style can overcome employee resistance to the organizational change process. A qualitative method is used in a case study based on "Queen Alia International Airport" where a charismatic leadership style is observed in defending the organization's position in overcoming employee resistance against the chosen organizational change. The results suggest that charismatic leaders employ a set of coherent communication strategies in bringing up change in organizations and on the control of individuals and groups. Understanding the role of charismatic characteristics and features of leadership style gives us important insights into the role of the charismatic leader as well as his influence on his followers and their perceptions. Perhaps more importantly, it helps us understand how leaders can use, or at least take advantage of, organizational change processes and control of individuals and groups.

Lake experimentation of in-band full-duplex underwater acoustic communications

In-band full-duplex (IBFD) communications is a promising technique to achieve spectral-efficient communication in the underwater environment. Characteristics of self-interference and methods to suppress the self-interference are crucial to attaining IBFD acoustic communications. In this effort, we analyze the characteristic of the self-interference for the underwater acoustic channel through experimental measurements. Self-interference reduction using physical separation and digital cancellation is investigated under different transmitter-receiver geometries. An iterative IBFD receiver combining joint channel estimation, SI cancellation, and multichannel decision feedback equalizer is developed. The feasibility of coherent IBFD underwater acoustic communications was tested in a lake environment. The self-interference suppression methods and the receiver performance were evaluated using the experimental measurements. IBFD communications was demonstrated at 80 m. With 10 dB local self-interference source level reduction, IBFD communications was extended to the 170 m range. [Work supported by the National Science Foundation.]