Showing papers on "Optical communication published in 2021"
TL;DR: In this article, a high Q factor of 260 million was achieved in an electrically pumped integrated laser with a corresponding short-term linewidth of 12'Hz and the same configuration was shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms.
Abstract: Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with a high Q factor of over 260 million and finesse over 42,000 A five-orders-of-magnitude noise reduction in the pump laser is demonstrated, enabling a frequency noise of 02 Hz2 Hz−1 to be achieved in an electrically pumped integrated laser, with a corresponding short-term linewidth of 12 Hz Moreover, the same configuration is shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms The simultaneous realization of this high Q factor, highly coherent lasers and frequency combs using foundry-based technologies paves the way for volume manufacturing of a wide range of coherent optical systems Using CMOS-ready ultra-high-Q microresonators, a highly coherent electrically pumped integrated laser with frequency noise of 02 Hz2 Hz−1, corresponding to a short-term linewidth of 12 Hz, is demonstrated The device configuration is also found to relieve the dispersion requirements for microcomb generation that have limited certain nonlinear platforms
235 citations
TL;DR: An all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude.
Abstract: Spatial light modulators are essential optical elements in applications that require the ability to regulate the amplitude, phase and polarization of light, such as digital holography, optical communications and biomedical imaging. With the push towards miniaturization of optical components, static metasurfaces are used as competent alternatives. These evolved to active metasurfaces in which light-wavefront manipulation can be done in a time-dependent fashion. The active metasurfaces reported so far, however, still show incomplete phase modulation (below 360°). Here we present an all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude. The metasurface features 550 individually addressable nanoresonators in a 250 × 250 μm2 area with no micromechanical elements or liquid crystals. A key feature of our design is the presence of two independent control parameters (top and bottom gate voltages) in each nanoresonator, which are used to adjust the real and imaginary parts of the reflection coefficient independently. To demonstrate this array’s use in light detection and ranging, we performed a three-dimensional depth scan of an emulated street scene that consisted of a model car and a human figure up to a distance of 4.7 m. By controlling two voltage gates separately from one another, a spatial light modulator has been made that can continuously vary the phase of 360 degrees while independently adjusting the amplitude.
213 citations
20 May 2021
TL;DR: The thin-film LN platform inherits nearly all the material advantages from the legacy bulk LN devices and amplifies them with a smaller footprint, wider bandwidths, and lower power consumption.
Abstract: Electro-optic modulators (EOMs) convert signals from the electrical to the optical domain. They are at the heart of optical communication, microwave signal processing, sensing, and quantum technologies. Next-generation EOMs require high-density integration, low cost, and high performance simultaneously, which are difficult to achieve with established integrated photonics platforms. Thin-film lithium niobate (LN) has recently emerged as a strong contender owing to its high intrinsic electro-optic (EO) efficiency, industry-proven performance, robustness, and, importantly, the rapid development of scalable fabrication techniques. The thin-film LN platform inherits nearly all the material advantages from the legacy bulk LN devices and amplifies them with a smaller footprint, wider bandwidths, and lower power consumption. Since the first adoption of commercial thin-film LN wafers only a few years ago, the overall performance of thin-film LN modulators is already comparable with, if not exceeding, the performance of the best alternatives based on mature platforms such as silicon and indium phosphide, which have benefited from many decades of research and development. In this mini-review, we explain the principles and technical advances that have enabled state-of-the-art LN modulator demonstrations. We discuss several approaches, their advantages and challenges. We also outline the paths to follow if LN modulators are to improve further, and we provide a perspective on what we believe their performance could become in the future. Finally, as the integrated LN modulator is a key subcomponent of more complex photonic functionalities, we look forward to exciting opportunities for larger-scale LN EO circuits beyond single components.
130 citations
TL;DR: In this paper, a review describes challenges, advances, and perspectives on different aspects of the OAM-based optical communications, including (a) OAM generation/detection and (de) multiplexing, (b) classical free-space optical communication links, (c) fiber-based communication links and (d) quantum communication links.
Abstract: Structured light, especially beams carrying orbital angular momentum (OAM), has gained much interest due to its unique amplitude and phase structures. In terms of communication systems, multiple orthogonal OAM beams can be potentially utilized for increasing link capacity in different scenarios. This review describes challenges, advances, and perspectives on different aspects of the OAM-based optical communications, including (a) OAM generation/detection and (de)multiplexing, (b) classical free-space optical communication links, (c) fiber-based communication links, (d) quantum communication links, (e) OAM-based communications in different frequency ranges, (f) OAM-based communications using integrated devices, and (g) novel structured beams for communications.
102 citations
TL;DR: In this article, an analytical method with numerical results for the design of optical slab waveguides for optical communication system applications is developed and the effective index of the mode is studied against variations in the waveguide dimensions.
Abstract: This study develops an analytical method with numerical results for the design of optical slab waveguides for optical communication system applications. An optical slab waveguide structure made of silicon on silicon dioxide material is designed and analyzed. The effective index of the mode is studied against variations in the waveguide dimensions. Transmission and reflection coefficients are studied and compared to the wavelength and dimensions of the waveguide. Variations are sketched with the x-axis, in addition to the electric field intensity distribution and effective refractive index. Waveguide bending loss is also studied with waveguide thickness and length variations within three waveguide transmission windows of 850 nm, 1300 nm, and 1550 nm.
70 citations
TL;DR: A review of recent progress in structured light in turbulence, first with a tutorial style summary of the core concepts, before highlighting the present state of the art in the field, and with new experimental studies that reveal which types of structured light are best in turbulence.
Abstract: Optical communication is an integral part of the modern economy, having all but replaced electronic communication systems. Future growth in bandwidth appears to be on the horizon using structured light, encoding information into the spatial modes of light, and transmitting them down fibre and free-space, the latter crucial for addressing last mile and digitally disconnected communities. Unfortunately, patterns of light are easily distorted, and in the case of free-space optical communication, turbulence is a significant barrier. Here we review recent progress in structured light in turbulence, first with a tutorial style summary of the core concepts, before highlighting the present state-of-the-art in the field. We support our review with new experimental studies that reveal which types of structured light are best in turbulence, the behaviour of vector versus scalar light in turbulence, the trade-off of diversity and multiplexing, and how turbulence models can be exploited for enhanced optical signal processing protocols. This comprehensive treatise will be invaluable to the large communities interested in free-space optical communication with spatial modes of light.
65 citations
TL;DR: In this article, a low fiber-chip optical coupler based on thin-film lithium niobate on insulator (LNOI) is presented. But the coupler is not suitable for high optical power and temperature variation.
Abstract: Lithium niobate (LN) devices have been widely used in optical communication and nonlinear optics due to its attractive optical properties. The emergence of the thin-film lithium niobate on insulator (LNOI) improves performances of LN-based devices greatly. However, a high-efficient fiber-chip optical coupler is still necessary for the LNOI-based devices for practical applications. In this paper, we demonstrate a highly efficient and polarization-independent edge coupler based on LNOI. The coupler, fabricated by a standard semiconductor process, shows a low fiber-chip coupling loss of 0.54 dB/0.59 dB per facet at 1550 nm for TE/TM light, respectively, when coupled with an ultra-high numerical aperture fiber (UHNAF) of which the mode field diameter is about 3.2 μm. The coupling loss is lower than 1dB/facet for both TE and TM light in the wavelength range of 1527 nm to 1630 nm. A relatively large tolerance for optical misalignment is also proved, due to the coupler's large mode spot size up to 3.2 μm. The coupler shows a promising stability in high optical power and temperature variation.
59 citations
TL;DR: In this article, the simulative and analytical methods of bidirectional EDFA amplifiers in optical communication links in the optimum case were demonstrated, and the output power, max. Q factor and light signal/noise ratio variations were clarified with pump power variations at the Bidirectional amplification EDFA amplifier for the previous/proposed models at optimum EDFA length of 8m.
Abstract:
This study has demonstrated the simulative and analytical methods of bidirectional EDFA amplifiers in optical communication links in the optimum case. The output power, max. Q factor and light signal/noise ratio variations are clarified with pump power variations at the bidirectional amplification EDFA amplifier for the previous/proposed models at optimum EDFA length of 8 m. As well as the output power and max. Q factor variations with EDFA amplifier length variations are demonstrated at the bidirectional amplification EDFA amplifier for the previous/proposed models at various pump power levels. The optimum operation efficiency case is observed at 8 m EDFA amplifier length and 120 mW pumping power.
59 citations
TL;DR: This tutorial discusses the evolution of the technology deployed for optical interconnects and the trade-offs in the design of low complexity, low power DSP and implementation for direct detect and coherent, pluggable optical modules for data center applications.
Abstract: In this tutorial, we discuss the evolution of the technology deployed for optical interconnects and the trade-offs in the design of low complexity, low power DSP and implementation for direct detect and coherent, pluggable optical modules for data center applications. The design trade-offs include the choice of modulation format, baud rate, optical link design, forward error correction, signal shaping and dispersion compensation.
52 citations
TL;DR: The results highlight that the NN is able to mitigate not only part of the nonlinear impairments caused by optical fiber propagation but also imperfections resulting from using low-cost legacy transceiver components, such as digital-to-analog converter (DAC) and Mach-Zehnder modulator.
Abstract: Nonlinearity compensation is considered as a key enabler to increase channel transmission rates in the installed optical communication systems. Recently, data-driven approaches – motivated by modern machine learning techniques – have been proposed for optical communications in place of traditional model-based counterparts. In particular, the application of neural networks (NN) allows improving the performance of complex modern fiber-optic systems without relying on any a priori knowledge of their specific parameters. In this work, we introduce a novel design of complex-valued NN for optical systems and examine its performance in standard single mode fiber (SSMF) and large effective-area fiber (LEAF) links operating in relatively high nonlinear regime. First, we present a methodology to design a new type of NN based on the assumption that the channel model is more accurate in the nonlinear regime. Second, we implement a Bayesian optimizer to jointly adapt the size of the NN and its number of input taps depending on the different fiber properties and total length. Finally, the proposed NN is numerically and experimentally validated showing an improvement of 1.7 dB in the linear regime, 2.04 dB at the optimal optical power and 2.61 at the max available power on Q-factor when transmitting a WDM 30 × 200G DP-16QAM signal over a 612 km SSMF legacy link. The results highlight that the NN is able to mitigate not only part of the nonlinear impairments caused by optical fiber propagation but also imperfections resulting from using low-cost legacy transceiver components, such as digital-to-analog converter (DAC) and Mach-Zehnder modulator.
52 citations
TL;DR: In this paper, a vector-beam-based, turbulence-resilient communication protocol, namely spatial polarization differential phase shift keying (SPDPSK), is proposed to transmit high-dimensional information through a turbulent channel without the need of any adaptive optics for beam compensation.
Abstract: Free-space optical communication is a promising means to establish versatile, secure and high-bandwidth communication between mobile nodes for many critical applications. While the spatial modes of light offer a degree of freedom to increase the information capacity of an optical link, atmospheric turbulence can introduce severe distortion to the spatial modes and lead to data degradation. Here, we demonstrate experimentally a vector-beam-based, turbulence-resilient communication protocol, namely spatial polarization differential phase shift keying (SPDPSK), that can reliably transmit high-dimensional information through a turbulent channel without the need of any adaptive optics for beam compensation. In a proof-of-principle experiment with a controllable turbulence cell, we measure a channel capacity of 4.84 bits per pulse using 34 vector modes through a turbulent channel with a scintillation index of 1.09, and 4.02 bits per pulse using 18 vector modes through even stronger turbulence corresponding to a scintillation index of 1.54. Resistance to turbulence is an ongoing challenge for point-to-point freespace communications. Here the authors present a protocol for encoding a large amount of information in vector beams that are transmittable through a moderately strong turbulent channel without adaptive beam compensation.
TL;DR: In this paper, a variable-coefficient nonlinear Schrodinger equation that describes the optical soliton propagation in dispersion management fiber systems is studied, and two and three soliton solutions are obtained by using the Hirota bilinear method.
Abstract: In this paper, a variable-coefficient nonlinear Schrodinger equation that describes the optical soliton propagation in dispersion management fiber systems is studied. Two- and three-soliton solutions are obtained by using the Hirota bilinear method. Based on those solutions, the effects of related parameters on optical soliton propagation are discussed. By choosing different values of the third-order dispersion, the amplification of optical solitons can be realized. In addition, the interactions among the solitons can be reduced by setting a proper value of the group velocity dispersion. The results of this paper may be helpful to design optical amplifiers or to improve the quality of optical communications.
TL;DR: In this article, the authors proposed a novel optical encryption scheme for WDM fiber-optic communication systems, by utilizing the private chaotic phase scrambling, which can encrypt the entire network traffic.
Abstract: Protecting the security of optical network is a major worldwide challenge. The conventional schemes for securing communications are based on cryptography at the MAC layer and its higher layers, which are facing a great threat with the development of quantum computers. Optical encryption is a promising way for building security on the physical layer of optical communications. In this work, we propose a novel optical encryption scheme for wavelength division multiplexing (WDM) fiber-optic communication systems, by utilizing the private chaotic phase scrambling. Secure transmission of 50 Gbps signal over 50-km standard single-mode fiber is experimentally and numerically demonstrated. The results show that the WDM signal is efficiently encrypted into a noise-like signal, due to the spectral broadening effect of chaotic phase scrambling. Since the processes of encryption and decryption are totally implemented in the optical domain, the proposed scheme can encrypt the entire network traffic with low latency and high speed. Moreover, the proposed encryption scheme is compatible with the existing WDM optical networks, and only one pair of encryption and decryption devices is sufficient to encrypt all WDM channels, thus the scheme can be easily implemented at low hardware cost.
TL;DR: It is demonstrated that it is eminently suitable for intensity-modulation and direct-detection aided optical communication systems and characterize its design flexibility, and highlighted a suite of promising techniques capable of further improving the system performance, but require further research.
Abstract: Optical Orthogonal Frequency-Division Multiplexing (O-OFDM) is eminently suitable for mitigating the multi-path and chromatic dispersion in both Visible Light Communications (VLC) and Optical Fiber Communications. We commence our discourse by surveying the conception and historic evolution of O-OFDM designed for both VLC and optical fiber, culminating in the birth of its most flexible design alternative, namely Layered Asymmetrically Clipped Optical OFDM (LACO-OFDM). We demonstrate that it is eminently suitable for intensity-modulation and direct-detection aided optical communication systems and characterize its design flexibility. It is also shown that given its flexibility, it subsumes a wide range of optical OFDM schemes conceived over the past two decades or so. The LACO-OFDM transmitter and receiver designs strike a compelling compromise between the features of the popular Asymmetrically Clipped Optical OFDM (ACO-OFDM) and Direct-Current-biased Optical OFDM (DCO-OFDM). The pivotal role of forward error correction designs is also surveyed with the objective of striking a coding gain versus complexity trade-off. We conclude by highlighting a suite of promising techniques capable of further improving the system performance, but require further research. The take-away message of the paper crystallized in the associated design guidelines.
DOI•
01 Nov 2021TL;DR: In this article, a silicon photonic-electronic neural network was used to compensate for optical fiber nonlinearities and improve the quality of the signal in a 10,080 km submarine optical-fibre transmission system.
Abstract: In optical communication systems, fibre nonlinearity is the major obstacle in increasing the transmission capacity. Typically, digital signal processing techniques and hardware are used to deal with optical communication signals, but increasing speed and computational complexity create challenges for such approaches. Highly parallel, ultrafast neural networks using photonic devices have the potential to ease the requirements placed on digital signal processing circuits by processing the optical signals in the analogue domain. Here we report a silicon photonic–electronic neural network for solving fibre nonlinearity compensation in submarine optical-fibre transmission systems. Our approach uses a photonic neural network based on wavelength-division multiplexing built on a silicon photonic platform compatible with complementary metal–oxide–semiconductor technology. We show that the platform can be used to compensate for optical fibre nonlinearities and improve the quality factor of the signal in a 10,080 km submarine fibre communication system. The Q-factor improvement is comparable to that of a software-based neural network implemented on a workstation assisted with a 32-bit graphic processing unit. A neural network platform that incorporates photonic components can be used to predict optical fibre nonlinearities and improve the signal quality of submarine fibre communications.
TL;DR: In this paper, a general expression accounting for EEPN is presented based on Gaussian noise model to evaluate the performance of multi-channel optical communication systems using EDC and digital nonlinearity compensation (NLC).
Abstract: Equalization enhanced phase noise (EEPN) occurs due to the interplay between laser phase noise and electronic dispersion compensation (EDC) module. It degrades significantly the performance of uncompensated long-haul coherent optical fiber communication systems. In this work, a general expression accounting for EEPN is presented based on Gaussian noise model to evaluate the performance of multi-channel optical communication systems using EDC and digital nonlinearity compensation (NLC). The nonlinear interaction between the signal and the EEPN is analyzed. Numerical simulations are carried out in nonlinear Nyquist-spaced wavelength division multiplexing (WDM) coherent transmission systems. Significant performance degradation due to EEPN in the cases of EDC and NLC are observed, with and without the consideration of transceiver (TRx) noise. The validation of the analytical approach has been done via split-step Fourier simulations. The maximum transmission distance and the laser linewidth tolerance are also estimated to provide important insights into the impact of EEPN.
TL;DR: 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.
Abstract: 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. The fast carrier dynamics and ultra-broadband optical properties of graphene make it suitable for optical communications. Here, the authors demonstrate a photo-thermo-electric graphene photodetector integrated on a Si waveguide featuring 105 Gbit s−1 non-return to zero and 120 Gbit s−1 4-level pulse amplitude modulation direct detection.
TL;DR: In this paper, the authors report a peta-bit-per-second class transmission demonstration in multi-mode fibers, which is enabled by combining three key technologies: a wideband optical comb-based transmitter to generate highly spectral efficient 64-quadrature-amplitude modulated signals between 1528 nm and 1610 nm wavelength, a broadband mode-multiplexer, based on multi-plane light conversion, and a 15-mode multiuser with optimized transmission characteristics for wideband operation.
Abstract: Data rates in optical fiber networks have increased exponentially over the past decades and core-networks are expected to operate in the peta-bit-per-second regime by 2030. As current single-mode fiber-based transmission systems are reaching their capacity limits, space-division multiplexing has been investigated as a means to increase the per-fiber capacity. Of all space-division multiplexing fibers proposed to date, multi-mode fibers have the highest spatial channel density, as signals traveling in orthogonal fiber modes share the same fiber-core. By combining a high mode-count multi-mode fiber with wideband wavelength-division multiplexing, we report a peta-bit-per-second class transmission demonstration in multi-mode fibers. This was enabled by combining three key technologies: a wideband optical comb-based transmitter to generate highly spectral efficient 64-quadrature-amplitude modulated signals between 1528 nm and 1610 nm wavelength, a broadband mode-multiplexer, based on multi-plane light conversion, and a 15-mode multi-mode fiber with optimized transmission characteristics for wideband operation. Space division multiplexing solutions are one way to increase future fiber information capacity. Here, the authors show peta-bit/s transmission in a standard-diameter, multimode fiber enabled by combining several practical multiplexing technologies.
TL;DR: In this article, an optical comparator was designed and simulated based on photonic crystals and point and linear defects were also used in the proposed comparator, which can be used in today's optical telecommunication circuits.
Abstract: A comparator is one of the important combinational logic circuits. An optical comparator was designed and simulated based on photonic crystals. Point and linear defects were also used in the proposed optical comparator. The use of simple defect paths and the absence of ring resonators reduced the complexity of the structure. One of the characteristics of the proposed structure is that it has a very small size, which leads to the suitability of this comparator for optical integrated circuits. Another characteristic of this comparator is an increase in the optical power difference for the logical values “0” and “1,” which reduces the bit detection error in the output. This comparator is also designed to operate on the 1.55 µm wavelength, and it can be used in today’s optical telecommunication circuits.
TL;DR: In this paper, an actively tunable optical metadevice is proposed to realize multifunctional application by integrating self-assembly electrothermal actuator (ETA) and magnetic metamaterial.
Abstract: In this work, an actively tunable optical metadevice is proposed to realize multifunctional application by integrating self-assembly electrothermal actuator (ETA) and magnetic metamaterial The released frame of ETA can control the deformed height of the metamaterial plate and then provide high robustness By driving the external electromagnetic field, the metamaterial plate is actuated and rotated by a magnetic force to manipulate the incident electromagnetic response The transmission intensities of the metadevice can be gradually increased to characterize "on" and "off" states Along with the inputs of light source and magnetic field, the transmission results of the metadevice could provide the output of time-difference optical signal and then carry with digital information in the further optical logic operation Such an actuation method provides an ideal platform for actively tunable metamaterial with a large tilt angle and displacement MEMS-based metamaterial is a strategy to open an avenue for optical communication, 3D imaging, and optical logic switching applications
TL;DR: In this article, the authors introduce the digital twin (DT) technology to optical communication through interdisciplinary crossing and propose a DT framework suitable for optical communication, where the intelligent fault management model, flexible hardware configuration model, and dynamic transmission simulation model are established in the digital space with the help of deep learning algorithms to ensure the high-reliability operation and high-eficiency management of optical communication systems and networks.
Abstract: Optical communication is developing rapidly in the directions of hardware resource diversification, transmission system flexibility, and network function virtualization. Its proliferation poses a significant challenge to traditional optical communication management and control systems. Digital twin (DT), a technology that utilizes data, models, and algorithms and integrates multiple disciplines, acts as a bridge between the real and virtual worlds for comprehensive connectivity. In the digital space, virtual models are established dynamically to simulate and describe the states, behaviors, and rules of physical objects in the physical space. DT has been significantly developed and widely applied in the industrial and military fields. This study introduces the DT technology to optical communication through interdisciplinary crossing and proposes a DT framework suitable for optical communication. The intelligent fault management model, flexible hardware configuration model, and dynamic transmission simulation model are established in the digital space with the help of deep learning algorithms to ensure the high-reliability operation and high-ef-ficiency management of optical communication systems and networks.
TL;DR: In this paper, two uni-directionally coupled quantum cascade lasers operating in the chaotic regime were used for the extraction of the information that has been camouflaged in chaotic emission, and a proof-of-concept communication at a wavelength of 5.7 μm with message encryption at a bit rate of 0.5 Mbit/s was achieved.
Abstract: Mid-infrared free-space optical communication has a large potential for high speed communication due to its immunity to electromagnetic interference. However, data security against eavesdroppers is among the obstacles for private free-space communication. Here, we show that two uni-directionally coupled quantum cascade lasers operating in the chaotic regime and the synchronization between them allow for the extraction of the information that has been camouflaged in the chaotic emission. This building block represents a key tool to implement a high degree of privacy directly on the physical layer. We realize a proof-of-concept communication at a wavelength of 5.7 μm with a message encryption at a bit rate of 0.5 Mbit/s. Our demonstration of private free-space communication between a transmitter and receiver opens strategies for physical encryption and decryption of a digital message. Free-space communication in the mid-IR domain has many potential applications, but security is still challenging. Here, the authors use chaos synchronization in a QCL-based free-space link as a way to increase privacy of such transmissions.
TL;DR: In this article, a state-of-the-art OPD with a record response speed of 146.8 ns was demonstrated by employing tandem structure to simultaneously reduce both the carrier transit time and resistance-capacitance (RC) time constant of the device.
Abstract: Organic photodetectors (OPDs), which usually work as photodiodes, photoconductors, or phototransistors, have emerged as candidates for next-generation light sensing. However, low response speed caused by low carrier mobility and resistance-capacitance (RC) time constant, severely hinders the commercialization of OPDs. Herein, the authors demonstrate a state-of-the-art OPD with a record response speed of 146.8 ns by employing tandem structure to simultaneously reduce both the carrier transit time and RC time constant of the device, which is faster than that of previously reported OPDs as far as they know. Moreover, benefitting from the multi-level barrier enhancement and voltage division engendered by tandem structure, an ultralow noise current of 7.82 × 10-14 A Hz-1/2 is obtained, as well as a wide detection range in 300-1000 nm. In addition, the tandem OPDs are successfully integrated into the optical communication system as signal receivers, demonstrating the precise digital signal communication from visible to near-infrared light. It is believed that tandem OPDs have promising application potential in the wireless transmission system.
TL;DR: In this article, the fundamental bandwidth limits of LSCs as optical detectors in arbitrary free-space optical links, and establishes their equivalence with simple RC low-pass electrical circuits.
Abstract: Luminescent solar concentrators (LSCs) have recently emerged as a promising receiver technology in free-space optical communications due to their inherent ability to collect light from a wide field-of-view and concentrate it into small areas, thus leading to high optical gains. Several high-speed communication systems integrating LSCs in their detector blocks have already been demonstrated, with the majority of efforts so far being devoted to maximising the received optical power and the system's field-of-view. However, LSCs may pose a severe bottleneck on the bandwidth of such communication channels due to the comparably slow timescale of the fluorescence events involved, a situation further aggravated by the inherent reabsorption in these systems, and yet, an in-depth study into such dynamic effects remains absent in the field. To fill this gap, we have developed a comprehensive analytical solution that delineates the fundamental bandwidth limits of LSCs as optical detectors in arbitrary free-space optical links, and establishes their equivalence with simple RC low-pass electrical circuits. Furthermore, we demonstrate a time-domain Monte Carlo simulation platform, an indispensable tool in the multiparameter optimisation of LSC-based receiver systems. Our work offers vital insight into LSC system dynamic behaviour and paves the way to evaluate the technology for a wide range of applications, including visible light communications, high-speed video recording, and real-time biological imaging, to name a few.
TL;DR: This work demonstrates live evolution of both optical and thermal images for temporal communication in which time is the encoded information, based on a digital light cured polymeric phase change material for which the crystallization kinetics can be controlled in a pixelated manner.
Abstract: Switchable optical properties are essential for numerous technologies including communication, anticounterfeiting, camouflage, and imaging/sensing. Typically, the switching is enabled by applying external stimulation such as UV light for fluorescence detection. In contrast, ground squirrels utilize spontaneous live infrared emission for fencing off predators as a unique way of communication. Inspired by this, live evolution of both optical and thermal images for temporal communication in which time is the encoded information is demonstrated. This system is based on a digitally light-cured polymeric phase-change material for which the crystallization kinetics can be controlled in a pixelated manner. Consequently, live evolution in optical transparency during the crystallization process enables temporal optical communication. Additionally, by harnessing the dynamic evolution of the thermal enthalpy, multiple sets of time-specific information can be reversibly retrieved as self-evolving infrared thermal images. The versatility of this dual-mode temporal system expands the scope for secured communication, with potential implications for various other areas including optics, thermal regulation, and 3D/4D printing.
TL;DR: In this paper, a theoretical coupling model from the free-space optical communication link to a few-mode fiber is proposed based on a scale-adapted set of Laguerre-Gaussian modes.
Abstract: Few-mode fiber is a significant component of free-space optical communication at the receiver to obtain achievable high coupling efficiency. A theoretical coupling model from the free-space optical communication link to a few-mode fiber is proposed based on a scale-adapted set of Laguerre-Gaussian modes. It is found that the coupling efficiency of various modes behaves differently in the presence of atmospheric turbulence or random jitter. Based on this model, the optimal coupling geometry parameter is obtained to maximize the coupling efficiency of the selected mode of few-mode fiber. The communication performance with random jitter is investigated. It is shown that the few-mode fiber has better bit-error rate performance than single-mode fiber, especially in high signal-to-noise ratio regimes.
TL;DR: In this paper, a direct detection-based PAM-N wireless link was established by using commercialized optical and electrical components designed for the WR 3.4 frequency band (220-330 GHz).
Abstract: We investigate the feasibility of pulse amplitude modulation-N (PAM-N) signal transmission over a photonics-based cost-effective THz wireless link. A direct detection-based THz wireless link was established by using commercialized optical and electrical components designed for the WR 3.4 frequency band (220–330 GHz). At the THz signal transmitter, a uni-traveling carrier photodiode (UTC-PD) was used as a photomixer. The maximum output power of the UTC-PD was ∼47 μW when it was supplied with +17 dBm of optical power. At the THz signal receiver, the Schottky barrier diode was used as a diode detector; an offline digital signal processor (DSP) with a decision feedback equalizer was also used to mitigate the inter-symbol interference penalty. In the back-to-back configuration (i.e., antenna of Tx and Rx are placed at a distance of ∼1 cm), the driving condition of the optical modulator was optimized to obtain the best transmission performances of the PAM-N signal. A carrier frequency of 300 GHz is carefully selected considering the bit error rate (BER) dependency on the carrier frequency. After the optimization procedure, the BER performances were analyzed by varying the PAM order, baud rate, and wireless transmission distance. Finally, a 90 Gb/s PAM-8 signal is successfully transmitted over a wireless distance of 1.4 m, in which the measured BER is below the 20% soft-decision forward error correction threshold (2.0 × 10–2).
20 Oct 2021
TL;DR: In this article, the authors proposed a non-redundant array (NRA) concept to the OPA devices, which can realize high-resolution OPAs whose number of resolvable points scales quadratically with the number of antennas.
Abstract: Optical phased arrays (OPAs) are promising beam-steering devices for various applications such as light detection and ranging, optical projection, free-space optical communication, and optical switching. However, previously reported OPAs suffer from either an insufficient number of resolvable points, or complicated control requirements due to an extremely large number of phase shifters. To solve this issue, we introduce the non-redundant array (NRA) concept to the OPA devices. Based on this design, we can realize high-resolution OPAs whose number of resolvable points scales quadratically with the number of antennas N. In contrast, that of traditional OPAs scales only linearly with N. Thus, a significant reduction in the number of required phase shifters can be attained without sacrificing the number of resolvable points. We first investigate the impact of employing the NRA theoretically by considering the autocorrelation function of the array layout. We then develop a Costas-array-based silicon OPA and experimentally demonstrate 2D beam steering with ∼19,000 resolvable points using only 127 phase shifters. To the best of our knowledge, this corresponds to the largest number of resolvable points achieved by an OPA without sweeping the wavelength.
TL;DR: In this article, a pilot-assisted self-coherent detection approach is proposed to overcome the effect of atmospheric turbulence in free-space optical communications, where the data is recovered by mixing a Gaussian local oscillator with a received Gaussian data beam.
Abstract: In free-space optical communications that use both amplitude and phase data modulation (for example, in quadrature amplitude modulation (QAM)), the data are typically recovered by mixing a Gaussian local oscillator with a received Gaussian data beam. However, atmospheric turbulence can induce power coupling from the transmitted Gaussian mode to higher-order modes, resulting in a significantly degraded mixing efficiency and system performance. Here, we use a pilot-assisted self-coherent detection approach to overcome this problem. Specifically, we transmit both a Gaussian data beam and a frequency-offset Gaussian pilot tone beam such that both beams experience similar turbulence and modal coupling. Subsequently, a photodetector mixes all corresponding pairs of the beams’ modes. During mixing, a conjugate of the turbulence-induced modal coupling is generated and compensates the modal coupling experienced by the data, and thus the corresponding modes of the pilot and data mix efficiently. We demonstrate a 12 Gbit s−1 16-QAM polarization-multiplexed free-space optical link that is resistant to turbulence. A transmission scheme for free-space optical communications is shown to be highly robust against turbulence.