All-optical Communication Networks Research Articles

1 × 2 broadband polarization-independent beam splitter based on air annular photonic crystal designed by a particle swarm optimization algorithm

We propose a 1×2 broadband polarization-independent beam splitter based on air annular photonic crystals. The inner and outer radii of the air annular photonic crystals at the V-shaped waveguide side and corners can influence the transmittance and broadband performance. To improve the design efficiency and transmittance of the broadband splitter, particle swarm optimization was used to reverse-design the splitter. The performance of the designed splitter was studied, and the results show that the designed splitter has a wide bandwidth range of 1530–1565 nm. It exhibits a minimum transmittance of 84% and an average transmittance of 87.8% for TE polarization and a minimum transmittance of 81% and an average transmittance of 83% for TM polarization. The response times for both polarizations are below 0.7 ps. This device has promising applications in all-optical communication networks and photonic high-density integration.

Numerical simulation of an in-fiber broadband plasmonic polarization filter using photonic crystal fiber with dual elliptical gold layers

The demand for advanced and compact photonic filters is increasing in today's optical communication systems. This work introduces a new all-fiber broadband polarization filter using photonic crystal fiber with dual elliptical gold layers. The filtering performance is evaluated and analyzed by the finite element method. The simulation results demonstrate that the two elliptical gold layers can effectively induce a significant change in the energy of x-polarized light, leading to a great difference between the two polarized lights. By selecting reasonable structural parameters of the proposed PCF, the 1 mm-long in-fiber filter has a maximum extinction ratio of -108.90 dB, a low insertion loss of 0.64 dB around 1.31 µm and an ultra-broad bandwidth of 1020 nm, covering two common communication windows of 1.31 µm and 1.55 µm. Additionally, the filtering experimental scheme is discussed. This filter is expected to drive the advancement of optical integrated chips and all-optical communication networks.

High-efficiency all-optical switching based on broadband coherent perfect absorption in an atom-cavity system

We propose an ultrahigh-efficiency and broadband all-optical switching scheme based on coherent perfect absorption (CPA) in linear and nonlinear excitation regimes in a cavity quantum electrodynamics (CQED) system. Two separate atomic transitions are excited simultaneously by two signal fields coupled from two ends of an optical cavity under the collective strong coupling condition. Three polariton eigenstates are produced which can be tuned freely by varying system parameters. The output field intensities of multiple channels are zero when the CPA criterion is satisfied. However, destructive quantum interference can be induced by a free-space weak control laser when it is tuned to be resonant to the polariton state. As a consequence, the CQED system acts as a coherent perfect light absorber/transmitter as the control field is turned on/off the polariton resonances. In particular, the proposed scheme may be used to realize broadband multi-throw all-optical switching in the nonlinear excitation regime. The proposed scheme is useful for constructing all-optical routing, all-optical communication networks and various all-optical logic elements.

Controllable optical bistability in a Fabry–Pérot cavity with a nonlinear three-dimensional Dirac semimetal

Optical bistability (OB) is capable of rapidly and reversibly transforming a parameter of an optical signal from one state to another, and homologous nonlinear optical bistable devices are core components of high-speed all-optical communication and all-optical networks. In this paper, we theoretically investigated the controllable OB from a Fabry–Pérot (FP) cavity with a nonlinear three-dimensional Dirac semimetal (3D DSM) in the terahertz band. The OB stems from the third-order nonlinear bulk conductivity of the 3D DSM and the resonance mode has a positive effect on the generation of OB. This FP cavity structure is able to tune the OB because the transmittance and the reflectance can be modulated by the Fermi energy of the 3D DSM. We believe that this FP cavity configuration could provide a reference concept for realizing tunable bistable devices.

Photonic crystal broadband y-shaped 1 × 2 beam splitter inversely designed by genetic algorithm

A novel two-dimensional photonic crystal broadband Y-shaped 1 × 2 beam splitter is proposed. Broadband performance of the 1 × 2 beam splitter can be greatly improved by optimizing the z-axis offset of the dielectric rods adjacent to the input and output waveguides, and the offset along the V-shaped oblique waveguide of the dielectric rods at the junction area. To enhance the optimization efficiency and achieve excellent splitting performance of the 1 × 2 beam splitter, the genetic algorithm is applied to inversely design the above offsets of the 1 × 2 beam splitter. The results show that, in the bandwidth range of 1515 to 1587 nm, the highest and lowest transmittance of the 1 × 2 beam splitter are 99.6% and 97.9%, respectively, the additional loss is <0.1 dB, and the uniformity tends to 0 dB. Finally, the tolerance analysis of the 1 × 2 beam splitter is carried out. When the deviation of each variable reaches ±10 nm, the total transmittance of the 1 × 2 beam splitter in the bandwidth range of 1515 to 1587 nm is still higher than 95.2%, with the additional loss <0.22 dB. Due to the virtues of broad operating bandwidth, high transmittance, good uniformity, and strong robustness, the proposed 1 × 2 beam splitter will have great application prospects in the field of photonic integrated circuits, all-optical communication network, and so on.

1 × 5 broadband photonic crystal power splitter designed by the Powell algorithm.

We propose a novel, to the best of our knowledge, 1×5 broadband power splitter based on the photonic crystal. The Powell algorithm is used to reverse-design the proposed broadband power splitter. The results show that the transmittance of each output port of the broadband photonic crystal power splitter can be adjusted by changing the radii and offsets of the dielectric rods at the junction area of each waveguide. According to the target splitting ratio, the reverse design of the structural parameters using the Powell algorithm significantly improves the optimization efficiency and splitting performance of the broadband power splitter. The designed power splitters have a wide working bandwidth of 1525-1565 nm, a flexible and designable power splitting ratio, excellent splitting performance, and a compact size, which have great application prospects in all-optical communication networks, high-density photon integration, and other fields.

Wave mixing efficiency in InAs/GaAs semiconductor quantum dot optical amplifiers and lasers

The nonlinear features of both semiconductor optical amplifiers (SOAs) and semiconductor lasers, which are made from the same InAs/GaAs quantum dot (QD) wafers, are investigated in detail. By employing pump-probe driven four-wave mixing as an experimental tool, the wave conversion process shows notably different profiles for the two types of devices. Due to the contributions of ultrafast, sub-picosecond mechanisms, such as carrier heating and spectral hole burning, the pump-probe frequency can be easily tuned to the THz range. SOAs generally benefit more from sub-picosecond carrier dynamics, hence exhibiting a higher conversion efficiency (CE) in the THz range, compared to their laser diode counterparts. The discrepancy even exceeds 10 dB. In addition, laser experiments yield some differences from the amplifier ones, hence leading to a higher nonlinear CE at small detuning ranges. These results strongly improve our insight into the fundamental nonlinear properties of InAs/GaAs QD material, and contribute to the conception of novel devices for future on-chip applications in all-optical communication networks, such as signal wavelength conversion, mode-locking, and optical frequency comb generation.

Free-space optical delay line using space-time wave packets

An optical buffer featuring a large delay-bandwidth-product—a critical component for future all-optical communications networks—remains elusive. Central to its realization is a controllable inline optical delay line, previously accomplished via engineered dispersion in optical materials or photonic structures constrained by a low delay-bandwidth product. Here we show that space-time wave packets whose group velocity is continuously tunable in free space provide a versatile platform for constructing inline optical delay lines. By spatio-temporal spectral-phase-modulation, wave packets in the same or in different spectral windows that initially overlap in space and time subsequently separate by multiple pulse widths upon free propagation by virtue of their different group velocities. Delay-bandwidth products of ~100 for pulses of width ~1 ps are observed, with no fundamental limit on the system bandwidth.

Photonic crystal add–drop filter: a review on principles and applications

Add–drop filter (ADF) is a key component in optical integrated circuits that can be used in all-optical communication networks and wavelength division multiplexing (WDM) systems. The quality factor, coupling efficiency, transmission efficiency and coupling length are important parameters in add–drop filters. Photonic crystal (PC) optical devices have become popular among researchers because their structure is suitable to embed into optical circuits. This paper covers a comprehensive review of the principle structure of ADF, coupled mode theory (CMT), types and recent applications in WDMs, accelerometer and bio/chemical sensors. Although there are some different categories of photonic crystal ring resonator-based ADF in general, all of them can be divided into photonic to two class of non-circular and circular. This article is reported a comprehensive study about ADF and improvement of these ADF.

Orbital angular momentum multiplexed deterministic all-optical quantum teleportation

Quantum teleportation is one of the most essential protocol in quantum information. In addition to increasing the scale of teleportation distance, improving its information transmission capacity is also vital importance for its practical applications. Recently, the orbital angular momentum (OAM) of light has attracted wide attention as an important degree of freedom for realizing multiplexing to increase information transmission capacity. Here we show that by utilizing the OAM multiplexed continuous variable entanglement, 9 OAM multiplexed channels of parallel all-optical quantum teleportation can be deterministically established in experiment. More importantly, our parallel all-optical quantum teleportation scheme can teleport OAM-superposition-mode coded coherent state, which demonstrates the teleportation of more than one optical mode with fidelity beating the classical limit and thus ensures the increase of information transmission capacity. Our results open the avenue for deterministically implementing parallel quantum communication protocols and provide a promising paradigm for constructing high-capacity all-optical quantum communication networks.

Ultra-low loss electro-optical polymer modulator based on D-shaped few-mode fiber using improved M-Z structure

Abstract An electro-optical polymer optical fiber modulator based on D-shaped few-mode fiber is proposed and optimized. In the D-shaped few-mode fiber, the electro-optic polymer coated on the few-mode fiber influences the refractive index of LP01 mode and LP02 mode, while LP01 mode is more sensitive. According to that, the mode field distribution has been analyzed and the varying properties of D-shaped FMF covered with electro-optic polymer has been discussed. Its simple cascade and axial alignment design enhances the stability of all-fiber modulators. Using improved M-Z structure with advanced operating point, the electro-optic modulator achieves an insertion loss of less than 2 dB with a modulation depth of 22 dB at 1550 nm. And the length of modulator is 25.69 mm. Moreover, the Vpi is 2.7 V and the optical bandwidth is 6.9 nm, which make the modulator have low power consumption and can be used in next-generation all-optical communication networks.

Terahertz routing with graphene magnetic metamaterials

Terahertz wireless communication has emerged as a fast-growing research area. Routing, which is designed to control the propagation of terahertz wave, is of great importance for building the terahertz all-optical communication network. Metamaterials provide a good method for manipulating the terahertz wave, which can be used to realize the wave router. To steer the input wave in different directions, for example negative refraction angle, some structures have been proposed, such as stacked structures and nanowire arrays. However, in these metamaterials, the incident wave is generally limited to transverse magnetic polarization. Here, a new terahertz routing method for transverse electric wave is put forward with using graphene magnetic metamaterials. Theoretical analysis is performed to show that this metamaterial has negative components not only in effective permittivity tensor but also in effective permeability tensor. Routing is realized by topological transitions between different dispersion regimes in this metamaterial. Our finding provides a new candidate for signal routing of terahertz wave.

Ultrafast passive all-optical full function logic gates on micro-silicon-on-insulator waveguide chip

Ultrafast passive all-optical full-function logic gates (FLOGs), such as AND, NOT, XOR, XNOR, and OR gates, are studied and designed. FLOGs can be realized only by changing the state of input ports in a designed micro-Sagnac waveguide ring unit. The whole chip is internally passive with unified off-chip source fabricated on a silicon-on-insulator substrate. The transmission performance of FLOGs waveguide ring and integrated chip unit are investigated by both the finite-difference time-domain method and beam propagation method. The research shows that FLOGs have the advantages of low power (μW) consuming, multifunctional, and high transmission rate. The simulated device cascades are indicated that the FLOG structure can be well cascaded, which may be used to form the neural network element. There will be potential applications in all-optical communication networks and large-scale integration circuits in the future.

Bidirectional all-optical switches based on highly nonlinear optical fibers

All-optical switches have become one of the research focuses of nonlinear optics due to their fast switching speed. They have been applied in such fields as ultrafast optics, all-optical communication and all-optical networks. In this paper, based on symbolic computation, bidirectional all-optical switches are presented using analytic two-soliton solutions. Various types of soliton interactions are analyzed through choosing the different parameters of high-order dispersion and nonlinearity. Results indicate that bidirectional all-optical switches can be effectively achieved using highly nonlinear optical fibers.

On-chip passive three-port circuit of all-optical ordered-route transmission.

On-chip photonic circuits of different specific functions are highly desirable and becoming significant demands in all-optical communication network. Especially, the function to control the transmission directions of the optical signals in integrated circuits is a fundamental research. Previous schemes, such as on-chip optical circulators, are mostly realized by Faraday effect which suffers from material incompatibilities between semiconductors and magneto-optical materials. Achieving highly functional circuits in which light circulates in a particular direction with satisfied performances are still difficult in pure silicon photonics platform. Here, we propose and experimentally demonstrate a three-port passive device supporting optical ordered-route transmission based on silicon thermo-optic effect for the first time. By injecting strong power from only one port, the light could transmit through the three ports in a strict order (1→2, 2→3, 3→1) while be blocked in the opposite order (1→3, 3→2, 2→1). The blocking extinction ratios and operation bandwidths have been investigated in this paper. Moreover, with compact size, economic fabrication process and great extensibility, this proposed photonic integrated circuit is competitive to be applied in on-chip all-optical information processing systems, such as path priority selector.

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s.

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of −7 dB on transmission has shown very promising applicability to all-optical communication networks.

Ultralow-light-level all-optical transistor in rubidium vapor

An all-optical transistor (AOT) is a device in which one light beam can efficiently manipulate another. It is the foundational component of an all-optical communication network. An AOT that can operate at ultralow light levels is especially attractive for its potential application in the quantum information field. Here, we demonstrate an AOT driven by a weak light beam with an energy density of 2.5 × 10−5 photons/(λ2/2π) (corresponding to 6 yJ/(λ2/2π) and about 800 total photons) using the double-Λ four-wave mixing process in hot rubidium vapor. This makes it a promising candidate for ultralow-light-level optical communication and quantum information science.

All-optical random number generation using highly nonlinear fibers by numerical simulation

A new scheme of all-optical random number generation based on the nonlinear effects in highly nonlinear fibers (HNLF) is proposed. The scheme is comprised of ultra-wide band chaotic entropy source, all-optical sampler, all-optical comparator and all-optical exclusive-or (XOR), which are mainly realized by four-wave mixing (FWM) and cross-phase modulation (XPM) in highly nonlinear fibers. And we achieve 10Gbit/s random numbers through numerically simulating all the processes. The entire operations are completed in the all-optical domain, which may overcome the bottleneck problem of electronic devices, and apply directly in high-speed all-optical communication network.

Investigation of the Thermal Sensitive Spectral Response of Chalcogenide Fiber Bragg Grating

This contribution presents numerical studies of the nonlinear fiber Bragg grating (FBG). The proposed model corresponds well to chalcogenide FBG as a considerable tool for optical switching. The spectral response of this device is discussed theoretically. Simulations based on the nonlinear coupled mode theory are used for investigating the relationships between the spectral transmission of nonlinear chalcogenide FBG and the grating parameters. The influence of the temperature dependence of FBG is numerically investigated. Numerical results show that the ambient temperature has an influence on the spectral response of FBG. The results are indications for applications in optical switches for all-optical communication networks and this can be important for wavelength division multiplexing optical networks.

Numerical Studies of Optical Bistability of Absorptive Type

Theoretical analysis is presented to search for the purely absorptive optical bistability in a Fabry-Perot cavity filled with a saturable absorber. A simple model of singlet absorption is used on numerically solving the relationships between the input and output light fields. The proposed model corresponds well to organic compounds considered as novel optical materials with third-order optical nonlinearities. The effects of saturable absorber parameters on the output light characteristics are studied and purely absorptive optical bistabilities are shown numerically to search for bistable behaviour. The simulated results are indications for promising applications in optical switches for all-optical communication networks.