Showing papers on "Optical communication published in 2014"
TL;DR: In this article, the authors demonstrate parity-time-symmetric optics on a chip at the 1,550-nm wavelength in two directly coupled high-Q silica-microtoroid resonators with balanced effective gain and loss.
Abstract: On-chip parity–time-symmetric optics is experimentally demonstrated at a wavelength of 1,550 nm in two directly coupled, high-Q silica microtoroid resonators with balanced effective gain and loss. Switchable optical isolation with a nonreciprocal isolation ratio between −8 dB and +8 dB is also shown. The findings will be useful for potential applications in optical isolators, on-chip light control and optical communications. Compound-photonic structures with gain and loss1 provide a powerful platform for testing various theoretical proposals on non-Hermitian parity–time-symmetric quantum mechanics2,3,4,5 and initiate new possibilities for shaping optical beams and pulses beyond conservative structures. Such structures can be designed as optical analogues of complex parity–time-symmetric potentials with real spectra. However, the beam dynamics can exhibit unique features distinct from conservative systems due to non-trivial wave interference and phase-transition effects. Here, we experimentally realize parity–time-symmetric optics on a chip at the 1,550 nm wavelength in two directly coupled high-Q silica-microtoroid resonators with balanced effective gain and loss. With this composite system, we further implement switchable optical isolation with a non-reciprocal isolation ratio from −8 dB to +8 dB, by breaking time-reversal symmetry with gain-saturated nonlinearity in a large parameter-tunable space. Of importance, our scheme opens a door towards synthesizing novel microscale photonic structures for potential applications in optical isolators, on-chip light control and optical communications.
943 citations
TL;DR: This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk, and presents the prospects for SDM in optical transmission and networking.
Abstract: Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.
621 citations
TL;DR: In this article, the authors demonstrate the viability of spatial multiplexing to reach a data rate of 5.1 Tbit/s−1/carrier−1 on a single wavelength over a single fiber, by employing few-mode multicore fiber, compact three-dimensional waveguide multiplexers and energy-efficient frequency-domain MIMO equalization.
Abstract: Single-mode fibres with low loss and a large transmission bandwidth are a key enabler for long-haul high-speed optical communication and form the backbone of our information-driven society. However, we are on the verge of reaching the fundamental limit of single-mode fibre transmission capacity. Therefore, a new means to increase the transmission capacity of optical fibre is essential to avoid a capacity crunch. Here, by employing few-mode multicore fibre, compact three-dimensional waveguide multiplexers and energy-efficient frequency-domain multiple-input multiple-output equalization, we demonstrate the viability of spatial multiplexing to reach a data rate of 5.1 Tbit s−1 carrier−1 (net 4 Tbit s−1 carrier−1) on a single wavelength over a single fibre. Furthermore, by combining this approach with wavelength division multiplexing with 50 wavelength carriers on a dense 50 GHz grid, a gross transmission throughput of 255 Tbit s−1 (net 200 Tbit s−1) over a 1 km fibre link is achieved. A few-mode, multicore fibre allows ultra-high-speed data transmission on a single wavelength of light.
426 citations
TL;DR: In this paper, a review of different techniques for the generation and processing of high-repetition-rate (>10GHz) optical frequency combs with technologies compatible with optical communication equipment is presented.
Abstract: The outstanding phase-noise performance of optical frequency combs has led to a revolution in optical synthesis and metrology, covering a myriad of applications, from molecular spectroscopy to laser ranging and optical communications However, the ideal characteristics of an optical frequency comb are application dependent In this review, the different techniques for the generation and processing of high-repetition-rate (>10GHz) optical frequency combs with technologies compatible with optical communication equipment are covered Particular emphasis is put on the benefits and prospects of this technology in the general field of radio-frequency photonics, including applications in high-performance microwave photonic filtering, ultra-broadband coherent communications, and radio-frequency arbitrary waveform generation
372 citations
TL;DR: An optical vehicle-to-vehicle (V2V) communication system based on an optical wireless communication technology using an LED transmitter and a camera receiver which employs a special CMOS image sensor, i.e, an optical communication image sensor (OCI).
Abstract: This paper introduces an optical vehicle-to-vehicle (V2V) communication system based on an optical wireless communication technology using an LED transmitter and a camera receiver, which employs a special CMOS image sensor, ie, an optical communication image sensor (OCI) The OCI has a “communication pixel (CPx)” that can promptly respond to light intensity variations and an output circuit of a “flag image” in which only high-intensity light sources, such as LEDs, have emerged The OCI that employs these two technologies provides capabilities for a 10-Mb/s optical signal reception and real-time LED detection to the camera receiver The optical V2V communication system consisting of the LED transmitters mounted on a leading vehicle and the camera receiver mounted on a following vehicle is constructed, and various experiments are conducted under real driving and outdoor lighting conditions Due to the LED detection method using the flag image, the camera receiver correctly detects LEDs, in real time, in challenging outdoor conditions Furthermore, between two vehicles, various vehicle internal data (such as speed) and image data (320 × 240, color) are transmitted successfully, and the 130-fps image data reception is achieved while driving outside
241 citations
TL;DR: In this paper, a q-plate-based mode (de)multiplexer for vector modes based on a liquid crystal technology referred to as a qplate is introduced, and four vector modes are used to increase the information capacity of free space optical communication via the method of optical communication referred as mode division multiplexing.
Abstract: Vector modes are spatial modes that have spatially inhomogeneous states of polarization, such as, radial and azimuthal polarization. They can produce smaller spot sizes and stronger longitudinal polarization components upon focusing. As a result, they are used for many applications, including optical trapping and nanoscale imaging. In this work, vector modes are used to increase the information capacity of free space optical communication via the method of optical communication referred to as mode division multiplexing. A mode (de)multiplexer for vector modes based on a liquid crystal technology referred to as a q-plate is introduced. As a proof of principle, using the mode (de)multiplexer four vector modes each carrying a 20 Gbit/s quadrature phase shift keying signal on a single wavelength channel (~1550nm), comprising an aggregate 80 Gbit/s, were transmitted ~1m over the lab table with <-16.4 dB (<2%) mode crosstalk. Bit error rates for all vector modes were measured at the forward error correction threshold with power penalties < 3.41dB.
239 citations
TL;DR: Simultaneous modulation of photocurrent and optical transmission has been achieved, which may lead to unprecedented optoelectronic applications.
Abstract: For optical communication, information is converted between optical and electrical signal domains at a high rate. The devices to achieve such a conversion are various types of electro-optical modulators and photodetectors. These two types of optoelectronic devices, equally important, require different materials and consequently it has been challenging to realize both using a single material combination, especially in a way that can be integrated on the ubiquitous silicon platform. Graphene, with its gapless band structure, stands out as a unique optoelectronic material that allows both photodetection and optical modulation. Here, we demonstrate a single graphene-based device that simultaneously provides both efficient optical modulation and photodetection. The graphene device is integrated on a silicon waveguide and is tunable with a gate made from another layer of graphene to achieve near-infrared photodetection responsivity of 57 mA/W and modulation depth of 64%. This novel multifunctional device may lead to many unprecedented optoelectronic applications.
182 citations
20 Dec 2014
TL;DR: In this article, the authors demonstrate simultaneous pre-and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system.
Abstract: As a recently explored property of light, orbital angular momentum (OAM) has potential in enabling multiplexing of multiple data-carrying beams, to increase the transmission capacity and spectral efficiency of a communication system. For the use of OAM multiplexing in free-space optical (FSO) communications, atmospheric turbulence presents a critical challenge. In this paper, we experimentally demonstrate simultaneous pre- and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system. Each beam carries a 100 Gbit/s signal, and propagates through an emulated atmospheric turbulence. A specifically designed AO system, which utilizes a Gaussian beam for wavefront sensing and correction, is built at one end of the bidirectional link. We show that this AO system can be used to not only post-compensate the received OAM beams, but also pre-compensate the outgoing OAM beams emitted from the same link end. Experimental results show that this compensation technique helps reduce the crosstalk onto adjacent modes by more than 12 dB, achieving bit error rates below the forward error correction limit of 1×10−3, for both directions of the link. The results of work might be helpful to future implementation of OAM multiplexing, in a high-capacity FSO bidirectional link affected by atmospheric turbulence.
175 citations
TL;DR: In this paper, a post-equalization circuit that contains two passive equalizers and one active equalizer was presented, which achieved a bandwidth of 151 MHz with a bit error ratio of 2×10-3.
Abstract: A research in extending bandwidth of the visible light communication (VLC) system that uses phosphorescent white LED has been reported in this letter. Slow response of the phosphorescent component limits the modulation bandwidth of white LED to the lower MHz range. In this letter, we present a post-equalization circuit that contains two passive equalizers and one active equalizer. With blue-filtering and the post-equalization circuit, a bandwidth of 151 MHz has been achieved in our VLC system, which allows OOK-NRZ data transmission up to 340 Mb/s. The VLC link operates at 43 cm using a single one Watt white LED, and the bit-error-ratio was below 2×10-3, which is within the forward error correction limit.
162 citations
TL;DR: It is demonstrated that it is possible to sustain higher data rates from the white light with ANN equalization than the blue component due to the high signal-to-noise ratio that is obtained from retaining the yellowish wavelengths.
Abstract: In this paper, we experimentally demonstrate for the first time an on off keying modulated visible light communications system achieving 170 Mb/s using an artificial neural network (ANN) based equalizer. Adaptive decision feedback (DF) and linear equalizers are also implemented and the system performances are measured using both real time (TI TMS320C6713 digital signal processing board) and offline (MATLAB) implementation of the equalizers. The performance of each equalizer is analyzed in this paper using a low bandwidth (4.5 MHz) light emitting diode (LED) as the transmitter and a large bandwidth (150 MHz) PIN photodetector as the receiver. The achievable data rates using the white spectrum are 170, 90, 40 and 20 Mb/s for ANN, DF, linear and unequalized topologies, respectively. Using a blue filter to isolate the fast blue component of the LED (at the cost of the power contribution of the yellowish wavelengths) is a popular method of improving the data rate. We further demonstrate that it is possible to sustain higher data rates from the white light with ANN equalization than the blue component due to the high signal-to-noise ratio that is obtained from retaining the yellowish wavelengths. Using the blue component we could achieve data rates of 150, 130, 90 and 70 Mb/s for the same equalizers, respectively.
154 citations
TL;DR: A new approach is introduced-the nonlinear inverse synthesis method-for digital signal processing based on encoding the information directly onto the nonlinear signal spectrum, providing an effective eigenvalue division multiplexing with no nonlinear channel cross talk.
Abstract: We scrutinize the concept of integrable nonlinear communication channels, resurrecting and extending the idea of eigenvalue communications in a novel context of nonsoliton coherent optical communications. Using the integrable nonlinear Schrodinger equation as a channel model, we introduce a new approach - the nonlinear inverse synthesis method - for digital signal processing based on encoding the information directly onto the nonlinear signal spectrum. The latter evolves trivially and linearly along the transmission line, thus, providing an effective eigenvalue division multiplexing with no nonlinear channel cross talk. The general approach is illustrated with a coherent optical orthogonal frequency division multiplexing transmission format. We show how the strategy based upon the inverse scattering transform method can be geared for the creation of new efficient coding and modulation standards for the nonlinear channel.
TL;DR: In this article, an analog pre-emphasis circuit based on NPN transistors and an active post-equalization circuit was proposed to enhance the 3-dB bandwidth of VLC link.
Abstract: In this paper, we first experimentally demonstrate a 550 Mbit/s real-time visible light communication (VLC) system based on nonreturn-to-zero on-off keying (NRZ-OOK) modulation of a commercial phosphorescent white light LED. The 3-dB modulation bandwidth of such devices is only a few megahertz. We proposed an analog pre-emphasis circuit based on NPN transistors and an active post-equalization circuit based on an amplifier to enhance the 3-dB bandwidth of VLC link. Utilizing our proposed pre-emphasis and post-equalization circuits, the 3-dB bandwidth of VLC link could be extended from 3 to 233 MHz with blue-filter, to the best of our knowledge, which is the highest ever achieved in VLC systems reported. The achieved data rate was 550 Mbit/s at the distance of 60 cm and the resultant bit-error-ratio (BER) was 2.6 × 10(-9). When the VLC link operated at 160 cm, the data rate was 480 Mbit/s with 2.3 × 10(-7) of BER. Our proposed VLC system is a good solution for high-speed low-complexity application.
TL;DR: In this paper, a dip-in direct-laser-writing optical lithography was used to fabricate three-dimensional polymeric functional devices on pre-fabricated planar optical chips containing Si3N4 waveguides as well as grating couplers made by standard electronbeam lithography.
Abstract: Integrated optical chips have already been established for application in optical communication. They also offer interesting future perspectives for integrated quantum optics on a chip. At present, however, they are mostly fabricated using essentially planar fabrication approaches like electron-beam lithography or UV optical lithography. Many further design options would arise if one had complete fabrication freedom in regard to the third dimension normal to the chip without having to give up the virtues and the know-how of existing planar fabrication technologies. As a step in this direction, we here use three-dimensional dip-in direct-laser-writing optical lithography to fabricate three-dimensional polymeric functional devices on pre-fabricated planar optical chips containing Si3N4 waveguides as well as grating couplers made by standard electron-beam lithography. The first example is a polymeric dielectric rectangular-shaped waveguide which is connected to Si3N4 waveguides and that is adiabatically twisted along its axis to achieve geometrical rotation of linear polarization on the chip. The rotator’s broadband performance at around 1550 nm wavelength is verified by polarization-dependent grating couplers. Such polarization rotation on the optical chip cannot easily be achieved by other means. The second example is a whispering-gallery-mode optical resonator connected to Si3N4 waveguides on the chip via polymeric waveguides. By mechanically connecting the latter to the disk, we can control the coupling to the resonator and, at the same time, guarantee mechanical stability of the three-dimensional architecture on the chip. Direct laser writing is a popular scheme for constructing three-dimensional integrated optical structures. Martin Schumann and co-workers from the Karlsruhe Institute of Technology and the Institute of Nanotechnology in Germany used two-photon polymerization to create three-dimensional polymer objects such as bridge waveguides, a twisted-waveguide polarization rotator and free-standing disk resonators. The structures, which would be difficult or impossible to construct using planar lithography, were successfully integrated with silicon optical chips featuring silicon nitride waveguides that guide light in the 1,550 nm telecommunications wavelength window. The researchers say that their approach could also be used to provide convenient access to three-dimensional photonic crystals. An advanced form of this approach that exploits higher resolutions would allow the construction of structures that are compatible with visible wavelengths.
TL;DR: It is shown experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.
Abstract: In this work we experimentally investigate the improved intra-channel fiber nonlinearity tolerance of digital subcarrier multiplexed (SCM) signals in a single-channel coherent optical transmission system. The digital signal processing (DSP) for the generation and reception of the SCM signals is described. We show experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold of 3.8 × 10−3 and by 8% in a 24 GBaud DP-16-QAM transmission with a BER threshold of 2 × 10−2. Moreover, we show by simulations that the improved performance of SCM signals is observed over a wide range of baud rates, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.
22 Dec 2014
TL;DR: An optical camera communication system utilizing the under-sampled phase shift ON-OFF keying modulation is proposed to support non-flickering visible light communication.
Abstract: In this paper, an optical camera communication system utilizing the under-sampled phase shift ON-OFF keying modulation is proposed to support non-flickering visible light communication. This system sends three types of light symbols through light emitting diode (LED) lamps, which are recorded by a camera. By employing a dual LED lamp with a designated mapping and framing method, the data rate can reach up to 3 times of the camera's frame rate. The experiment results show that the proposed camera communication system can achieve 150 bps error-free communications for a range up to 12 m.
TL;DR: In this paper, the generation, propagation, and detection of high-quality and coherently superimposed optical vortices, carrying two or more orbital angular momentum (OAM) states, is experimentally demonstrated using an optical arrangement based on spatial light modulators.
Abstract: The generation, propagation, and detection of high-quality and coherently superimposed optical vortices, carrying two or more orbital angular momentum (OAM) states, is experimentally demonstrated using an optical arrangement based on spatial light modulators. We compare our results with numerical simulations and show that, in the context of turbulence-free wireless optical communication (indoor or satellite), individual OAM state identification at the receiver of an OAM-modulated system can be achieved with good precision, to accommodate for high-dimensional OAM modulation architectures. We apply our results to the simulation of a communication system using low-density parity-check-coded modulation that considers optimal signal constellation design in a channel that includes OAM crosstalk induced by realistic (imperfect) detection.
26 Nov 2014
TL;DR: In this paper, a ground-to-ground free-space laser communications (FSO) is considered as an alternative to radio relay link line-of-sight (LOS) communication systems.
Abstract: FSO is a line-of-sight technology that uses lasers to provide optical bandwidth connections or FSO is an optical communication technique that propagate the light in free space means air, outer space, vacuum, or something similar to wirelessly transmit data for telecommunication and computer networking. Currently, FSO is capable of up to 2.5 Gbps [1] of data, voice and video communications through the air, allowing optical connectivity without requiring fiberoptic cable or securing spectrum licenses. Operate between the 780 – 1600 nm wavelengths bands and use O/E and E/O converters. FSO requires light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiberoptic cables; the only difference is the transmission media. Light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of the light. FSO communication is considered as an alternative to radio relay link line-of sight (LOS) communication systems. This chapter is concentrate on ground-to-ground free-space laser communications. FSO components are contain three stages: transmitter to send of optical radiation through the atmosphere obeys the Beer-Lamberts`s law, free space transmission channel where exist the turbulent eddies (cloud, rain, smoke, gases, temperature variations, fog and aerosol) and receiver to process the received signal. Typical links are between 300 m and 5 km, although longer distances can be deployed such as 8–11 km are possible depending
Patent•
12 Mar 2014
TL;DR: In this article, a non-invasive physiological patient sensor and a patient monitor capable of wireless communication with one another are discussed. But the authors focus on the optical communication path used to provide the communication path between the noninvasive sensor and the patient monitor.
Abstract: Embodiments of the disclosure include a noninvasive physiological patient sensor and a patient monitor capable of wireless communication with one another. An optical communication path can be used to provide the communication path between the noninvasive physiological patient sensor and the patient monitor. The path can be maintained by one or more light sources and detectors traditionally associated with noninvasive optical sensors or by one or more additional dedicated light sources and detectors.
TL;DR: A Monte Carlo numerical simulation for computing the received power for an underwater optical communication system is discussed and validated and power loss between receiver and transmitter is simulated.
Abstract: A Monte Carlo numerical simulation for computing the received power for an underwater optical communication system is discussed and validated. Power loss between receiver and transmitter is simulated for a variety of receiver aperture sizes and fields of view. Additionally, pointing-and-tracking losses are simulated.
TL;DR: In this paper, a 100-Gb/s MIMO visible laser light communication (VLLC) system employing vertical-cavity surface-emitting lasers with 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM) modulating signals is proposed and experimentally demonstrated.
Abstract: A 100-Gb/s multiple-input multiple-output (MIMO) visible laser light communication (VLLC) system employing vertical-cavity surface-emitting lasers with 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM) modulating signals is proposed and experimentally demonstrated. The transmission capacity of systems is significantly increased by space-division-multiplexing scheme. With the aid of low-noise amplifier and equalizer at the receiving site, good bit error rate performance and clear constellation map are obtained for each optical channel. A system of eight 16-QAM-OFDM channels over 5-m free-space links with a total data rate of 100 Gb/s (12.5 Gb/s/channel × 8 channels) is successfully achieved. Such a proposed MIMO VLLC system is shown to be a prominent one not only presents its convenience in free-space optical communication, but also reveals its potential for the real implementation.
01 Jan 2014
TL;DR: In this paper, the Stokes vector direct detection (SV-DD) algorithm was proposed to achieve photo-detection nonlinearity cancellation and phase diversity in SSMF transmission with 7.76 bit/s/Hz electrical spectrum efficiency.
Abstract: We propose the Stokes vector direct detection (SV-DD) algorithm to achieve photo-detection nonlinearity cancellation and phase diversity. A 160-Gb/s single-polarization modulated SV-DD signal is successfully received after 160-km SSMF transmission with 7.76-bit/s/Hz electrical spectrum efficiency. © 2014 OSA.
TL;DR: It is shown that in the DMT VLC system, the blue optical filter may be unnecessary, and even degrade the transmission performance (by reducing the optical signal-to-noise ratio (SNR)).
Abstract: Optical blue filter is usually regarded as a critical optical component for high speed phosphor-based white light emitting diode (LED) visible-light-communication (VLC). However, the optical blue filter plays different roles in VLC when using modulations of on-off keying (OOK) or discrete multi-tone (DMT). We show that in the DMT VLC system, the blue optical filter may be unnecessary, and even degrade the transmission performance (by reducing the optical signal-to-noise ratio (SNR)). Analyses and verifications by experiments are performed. To the best of our knowledge, this is the first time the function of blue filters in VLC is explicitly analyzed.
TL;DR: In this article, a real-time base-band orthogonal frequency division multiplexing (OFDM) transceiver with a simple symbol synchronization and channel estimation scheme is implemented on only one off-the-shelf commercial field programmable gate array (FPGA).
Abstract: A real-time base-band orthogonal frequency division multiplexing (OFDM) transceiver with a simple symbol synchronization and channel estimation scheme is implemented on only one off-the-shelf commercial field programmable gate array (FPGA). The real-time optical OFDM long-reach passive optical network (PON) system with direct detection over 100 km standard single-mode fiber (SSMF) employing a cost-effective directly modulated distributed feedback (DFB) laser has been successfully demonstrated experimentally. The experimental results show that the simplified symbol synchronization with low complexity and high accuracy is effective for long-reach optical OFDM transmission systems. After 100 km SSMF transmission, the power penalty at a bit-error rate of 1e-3 is only about 1.1 dB.
TL;DR: This article reports several examples of photonic-crystal nanocavity devices that exhibit record low consumption energy/power and indicates that current technology enables to integrate a large number of various wavelength-sized photonic devices with extremely low energy consumption, which will lead to fJ/bit-level optical communication in a chip.
TL;DR: In this paper, a scheme to realize an optical diode for photonic transport at the level of few photons is proposed, which consists of two spatially overlapping single-mode semiconductor microcavities coupled via nonlinearities.
Abstract: The semiconductor diode, which acts as an electrical rectifier and allows unidirectional electronic transports, is the key to information processing in integrated circuits. Analogously, an optical rectifier (or diode) working at specific target wavelengths has recently become a highly sought-after device in optical communication and signal processing. In this paper, we propose a scheme to realize an optical diode for photonic transport at the level of few photons. The system consists of two spatially overlapping single-mode semiconductor microcavities coupled via ${\ensuremath{\chi}}^{(2)}$ nonlinearities. The photon blockade is predicted to take place in this system. These photon blockade effects can be achieved by tuning the frequency of the input laser field (driving field). Based on those blockades, we analytically derive the one- and two-photon current in terms of a zero and a finite time-delayed two-order correlation function. The results suggest that the system can serve as a one- and two-photon quantum optical diode which allows transmission of photons in one direction much more efficiently than in the other.
Posted Content•
TL;DR: This work reports the first experimental realization of a quantum interface for a heralded single photon carrying OAM using a nonlinear crystal in an optical cavity and single-photon coherence is preserved during up-conversion as demonstrated.
Abstract: Light carrying orbital angular momentum (OAM) has great potential in enhancing the information channel capacity in both classical and quantum optical communications. Long distance optical communication requires the wavelengths of light are situated in the low-loss communication windows, but most quantum memories currently being developed for use in a quantum repeater work at different wavelengths, so a quantum interface to bridge the wavelength gap is necessary. So far, such an interface for OAM-carried light has not been realized yet. Here, we report the first experimental realization of a quantum interface for a heralded single photon carrying OAM using a nonlinear crystal in an optical cavity. The spatial structures of input and output photons exhibit strong similarity. More importantly, single-photon coherence is preserved during up-conversion as demonstrated.
TL;DR: In this article, the authors investigated the energy efficiency of optical OFDM-based networks and proposed a mixed integer linear programming model to minimize the total power consumption of rate and modulation adaptive OFDM networks.
Abstract: Orthogonal frequency-division multiplexing (OFDM) has been proposed as an enabling technique for elastic optical networks to support heterogeneous traffic demands by enabling rate and modulation adaptive bandwidth allocation. The authors investigate the energy efficiency of optical OFDM-based networks. A mixed integer linear programming model is developed to minimise the total power consumption of rate and modulation adaptive optical OFDM networks. Considering a symmetric traffic, the results show that optical OFDM-based networks can save up to 31% of the total network power consumption compared to conventional Internet protocol over wavelength division multiplexing (WDM) networks. Considering the power consumption of the optical layer, the optical OFDM-based network saves up to 55% of the optical layer power consumption. The results also show that under an asymmetric traffic scenario, where more traffic is destined to or originates from popular nodes, for example data centres, the power savings achieved by the optical OFDM-based networks are limited as the higher traffic demands to and from data centres reduce the bandwidth wastage associated with conventional WDM networks. Furthermore, the achievable power savings through data compression have been investigated, considering an optical OFDM-based network.
TL;DR: The receiver configuration for the multi-level signal in the Stokes space and the efficient DSP algorithm for demodulating such a signal are discussed and Simulation results demonstrate that 2, 4, 8, 16, and 32-ary signals in theStokes space have good bit-error rate (BER) characteristics.
Abstract: The Stokes vector of an optical signal does not depend on its absolute phase; therefore, we can construct the phase-insensitive optical communication system, using the Stokes vector as a modulation parameter. In such a system, multi-level optical signals can effectively be designed in the three-dimensional Stokes space and demodulated either by direct detection or by coherent detection, where low-complexity digital-signal processing (DSP) is employed. Although this system has the disadvantage that adaptive equalizers can hardly be implemented in the digital domain, it is still an attractive solution to large-capacity (≥ 100 Gbit/s) and medium-or short-reach (≤ 100 km) transmission. In this paper, we discuss the receiver configuration for the multi-level signal in the Stokes space and the efficient DSP algorithm for demodulating such a signal. Simulation results demonstrate that 2-, 4-, 8-, 16-, and 32-ary signals in the Stokes space have good bit-error rate (BER) characteristics. Especially, the 16-ary signal at the moderate symbol rate of 25 Gsymbol/s can reach the bit rate of 100 Gbit/s even by using direct detection.
TL;DR: The architecture of a single-chip dual-polarization QPSK/BPSK 50 Gigabits per second (Gb/s) DSP-based transceiver for coherent optical communications is presented and a novel low-latency parallel-processing carrier recovery implementation which is robust in the presence of laser phase noise and frequency jitter is proposed.
Abstract: The architecture of a single-chip dual-polarization QPSK/BPSK 50 Gigabits per second (Gb/s) DSP-based transceiver for coherent optical communications is presented. The receiver compensates the chromatic dispersion (CD) of more than 3,500 km of standard single-mode fiber using a frequency-domain equalizer. A time-domain four-dimensional MIMO transversal equalizer compensates up to 200 ps of differential group delay (DGD) and 8000 ps 2 of second-order polarization-mode dispersion (SOPMD). Other key DSP functions of the receiver include carrier and timing recovery, automatic gain control, channel diagnostics, etc. A novel low-latency parallel-processing carrier recovery implementation which is robust in the presence of laser phase noise and frequency jitter is proposed. The chip integrates the transmitter, receiver, framer and host interface functions and features a 4-channel 25 Gs/s 6-bit ADC with a figure of merit (FOM) of 0.4 pJ/conversion. Each ADC channel is based on an 8-way interleaved flash architecture. The DSP uses a 16-way parallel processing architecture. Extensive measurement results are presented which confirm the design targets. Measured optical signal-to-noise ratio (OSNR) penalty when compensating 200 ps DGD and 8000 ps 2 is 0.1 dB, while OSNR penalty when compensating 55 ns/nm CD (corresponding to 3,500 km of standard single-mode fiber) is 0.5 dB.
TL;DR: In this article, a digitally controlled LLC resonant dc-dc converter targeted to white LED luminaires in smart buildings is presented, which uses the LED array both for ambient lighting and for transmitting sensor data.
Abstract: This study presents a digitally controlled LLC resonant dc-dc converter targeted to white LED luminaires in smart buildings. The module uses the LED array both for ambient lighting and for transmitting sensor data. Visible light communication is implemented with minimal incremental cost, by operating the LLC converter in burst mode, without causing any visible disturbance. The converter operates with a regulated average LED current, while the burst pulse timing is controlled to minimize the current disturbance and reduce the output capacitance. Variable pulse position modulation is used to modulate the data, while supporting a range of dimming settings. A digital demodulation scheme that supports variable frequency transmission is demonstrated. The 80 W, 340-400 to 23 V converter prototype has an efficiency of 95.1%. The bit error rate of the complete system is fully characterized versus distance and angle.