All-optical Signal Processing Applications Research Articles

Fully integrated and broadband Si-rich silicon nitride wavelength converter based on Bragg scattering intermodal four-wave mixing

Intermodal four-wave mixing (FWM) processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide. This allows, in principle, to place signals in different spectral regions and satisfy the phase matching condition over considerably larger bandwidths compared to intramodal processes. However, the demonstrations reported so far have shown a limited bandwidth and suffered from the lack of on-chip components designed for broadband manipulation of different modes. We demonstrate here a silicon-rich silicon nitride wavelength converter based on Bragg scattering intermodal FWM, which integrates mode conversion, multiplexing and de-multiplexing functionalities on-chip. The system enables wavelength conversion between pump waves and a signal located in different telecommunication bands (separated by 60 nm) with a 3 dB bandwidth exceeding 70 nm, which represents, to our knowledge, the widest bandwidth ever achieved in an intermodal FWM-based system.

Light wave propagation and diffraction inhibition in three-dimensional photonic quasicrystal lattices

We have investigated the linear propagation of light wave in three-dimensional photonic quasicrystal lattices by numerical simulation. The diffraction characteristics of the light waves in the longitudinal non-modulated, in-phase modulated and out-of-phase modulated quasicrystal lattices have been compared and discussed. We have demonstrated the diffraction inhibition of light wave in three-dimensional photonic quasicrystals. Linear transverse light localization has been realized in the longitudinal out-of-phase modulated three-dimensional quasicrystal lattices by adjusting the structural parameters appropriately. Furthermore, the results also show that the longitudinal out-of-phase modulated photonic quasicrystals are easier to produce diffraction inhibition than the longitudinal out-of-phase modulated periodic lattices under low transverse refractive index contrast. Distortionless dot image transmission has numerically demonstrated in out-of-phase modulated photonic quasicrystals array. It provides a new way for distortion-free image transmission, which has promising applications in optical information transmission and all-optical signal processing.

Optical Bullets and Domain Walls with Cross Spatio-Dispersion and Having Kudryashov’s form of Self-Phase Modulation

In this paper, we investigate the retrieval of optical bullets and domain walls in a novel context, considering the interplay of cross spatio-dispersive effects and employing Kudryashov' s proposed form of self-phase modulation. The integration of these two key elements represents a significant advancement in the field of nonlinear optics, enabling the recovery of optical structures with enhanced precision and control. We propose an enhanced Kudryashov’s approach, which overcomes the limitations of conventional methods and facilitates the retrieval of optical bullets and domain walls even in the presence of cross spatio-dispersive effects. Kudryashov' s self-phase modulation mechanism has proven to be a powerful tool in controlling the nonlinear dynamics of optical systems, offering unique opportunities to manipulate light waves through phase variations induced by the medium' s response to intense optical fields. The results presented herein offer new insights into the intricate interplay between self-phase modulation and spatio-dispersive effects in nonlinear optical systems. Moreover, our findings provide a promising avenue for developing novel applications in ultrafast all-optical signal processing, such as the manipulation of light bullets for high-speed data transmission and storage. The enhanced retrieval and control of optical bullets and domain walls are expected to have a profound impact on the advancement of nonlinear optics and its practical implications.

An Integrated Pump-Controlled Variable Coupler Fabricated by Ultrafast Laser Writing.

The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er3+/Yb3+ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump's power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems.

A Review on Nonlinearity in Semiconductor optical Amplifer as Application in all Optical Signal Processing

The optical signal processing is the future of communication network. High speed all-optical packet routing is one of the essential applications of all-optical networks which is only possible with the development of all-optical logic technology. The development of optical logic elements and circuits are the steps in the growth of this technology and higher speed up to Tbit/sec can be achieved. The optical carrier frequency range 1013 to 1016 Hz provides enormous potential bandwidth with superior information carrying capacity over a long transmission distance. The need of higher capacity is continuing to encourage research in wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM) based transmission systems, which need optical demultiplexing and wavelength conversion technology. Therefore, for high-speed optical networks, it is required to develop the all-optical gates to avoid power consumption in opto-electronics conversion. All optical logic gates perform computing operations, storage and transmission of data using light also known as optical computing. Optical technology promises massive upgrades in the efficiency and speed of computers, aswell as significant shrinkage in their size and cost. The non-linear optical device to be used i.e. Semiconductor Optical Amplifier (SOA) has proved to be the promising for all optical functions like wavelength conversion, logic functions, signal representation in all optical domain. Its compact size, high gain, fast response, strong refractive index variation, easy to manufacture and integration, and power efficiency makes it most optimum device for optical signal processing. In this paper, the application of SOA in optical processing is thoroughly reviewed and orient towards the latest application in neural networks.

Pulsed Four-Wave Mixing at Telecom Wavelengths in Si3N4 Waveguides Locally Covered by Graphene.

Recently, the nonlinear optical response of graphene has been widely investigated, as has the integration of this 2D material onto dielectric waveguides so as to enhance the various nonlinear phenomena that underpin all-optical signal processing applications at telecom wavelengths. However, a great disparity continues to exist from these experimental reports, depending on the used conditions or the hybrid devices under test. Most importantly, hybrid graphene-based waveguides were tested under relatively low powers, and/or combined with waveguide materials that already exhibited a nonnegligible nonlinear contribution, thereby limiting the practical use of graphene for nonlinear applications. Here, we experimentally investigate the nonlinear response of Si3N4 waveguides that are locally covered by submillimeter-long graphene patches by means of pulsed degenerate four-wave mixing at telecom wavelength under 7 W peak powers. Our measurements and comparison with simulations allow us to estimate a local change of the nonlinearity sign as well as a moderate increase of the nonlinear waveguide parameter (γ∼-10 m-1W-1) provided by graphene. Our analysis also clarifies the tradeoff associated with the loss penalty and nonlinear benefit afforded by graphene patches integrated onto passive photonic circuits, thereby providing some guidelines for the design of hybrid integrated nonlinear devices, coated with graphene, or, more generally, any other 2D material.

Phase regeneration of 8PSK signal using phase-sensitive amplification based on an organic-Ge hybrid waveguide.

We numerically demonstrate the phase regeneration of eight-phase-shift keying (8PSK) in an organic-Ge hybrid waveguide with 10µm length. Through filling graphene oxide with a high Kerr coefficient and engineering of waveguide dimensions, an ultrahigh nonlinear coefficient with 5.86×106W-1m-1 is attained at 1550 nm. The phase regeneration of 8PSK signal is achieved by using phase-sensitive amplification of the dual-conjugated-pump degenerate four-wave mixing scheme. The error-vector magnitude (EVM), optical signal-to-noise ratio, as well as constellation diagrams of 8PSK signal are also used to evaluate the phase regeneration capacity quantitatively. A reduction of EVM from 39.25% to 1.34% for 8PSK signal is found. The results show great phase regeneration and noise-squeezing ability, which indicate that such a phase-sensitive amplifier of a waveguide can find critical promising applications in all-optical signal processing.

Intensity and phase encoding for realization of integrated Pauli X, Y and Z gates using 2D photonic crystal

Nano-scale all-optical logic gates systems are desirable for the all-optical computing and signal processing applications. All-optical Quantum computing offers excellent computational abilities and lossless operations. The Pauli X, Y and Z gates are vital quantum logic gates for all-optical systems. In this paper, the integrated all-optical Pauli X, Y, Z gate is realized using a square lattice 2D photonic crystal of silicon rods. The phase encoding and intensity encoding techniques have been used simultaneously for the integrated operation. Pauli X, Y, Z logic gate truth table has been verified at the operating wavelength of 1.55 µm.The system offers a linear operation, compact size, low power requirement, and high contrast ratio of 10.4 dB. The footprint of the proposed structure is about 70µm x 70µm and demonstrates a fast response time of 2 ps, bit rate of 0.25 Tbps, which makes it suitable for photonic integrated circuits (PICs).

Low-power all-optical switch based on a graphene-buried polymer waveguide Mach-Zehnder interferometer.

We propose a low-power all-optical switch based on the structure of a graphene-buried balanced Mach-Zehnder interferometer (MZI), where the signal light is switched between the two output ports of the MZI by the heat generated from graphene's absorption of the pump light. We use orthogonal polarizations for the pump and the signal light to maximize pump absorption and minimize graphene-induced signal loss. Our experimental device fabricated with polymer waveguides buried with 5-mm long graphene shows a pump absorption of 10.6 dB (at 980 nm) and a graphene-induced signal loss of 1.1 dB (at 1550 nm) and can switch the signal light with a pump power of 6.0 mW at an extinction ratio of 36 dB. The actual pump power absorbed by graphene for activating switching is estimated to be 2.2 mW. The rise and fall times of the switch are 1.0 and 2.7 ms, respectively. The switching characteristics are weakly sensitive to ambient temperature variations. Our device can be butt-coupled to single-mode fibers and could find applications in fiber-based and on-chip all-optical signal processing.

Polarization-Independent Large Third-Order-Nonlinearity of Orthogonal Nanoantennas Coupled to an Epsilon-Near-Zero Material.

The nonlinear optical response of common materials is limited by bandwidth and energy consumption, which impedes practical application in all-optical signal processing, light detection, harmonic generation, etc. Additionally, the nonlinear performance is typically sensitive to polarization. To circumvent this constraint, we propose that orthogonal nanoantennas coupled to Al-doped zinc oxide (AZO) epsilon-near-zero (ENZ) material show a broadband (~1000 nm bandwidth) large optical nonlinearity simultaneously for two orthogonal polarization states. The absolute maximum value of the nonlinear refractive index n2 is 7.65 cm2∙GW−1, which is 4 orders of magnitude larger than that of the bare AZO film and 7 orders of magnitude larger than that of silica. The coupled structure not only realizes polarization independence and strong nonlinearity, but also allows the sign of the nonlinear response to be flexibly tailored. It provides a promising platform for the realization of ultracompact, low-power, and highly nonlinear all-optical devices on the nanoscale.

Optical hysteresis shape transformation using linear polarization components

We provide a mathematical model to elucidate how a linear polarizer can be used to transform the shape of an optical-power hysteresis curve into the canonical counterclockwise (CCW) shape, clockwise (CW) shape, and upward-switching and downward-switching butterfly shapes. This transformation is possible for optical signals whose states of polarization also exhibit hysteresis. Critical to our model is a generalized Malus' law that accounts for elliptical input polarization as well as insertion loss, finite extinction ratio, and pass-axis orientation angle of the linear polarizer. The generalized Malus' law reveals that the transmittivity of the polarizer itself exhibits a bistable hysteresis curve, and this transmittivity acts on the input-power hysteresis curve to produce the variety of output-power shapes. Additionally, we model the optimization of the hysteresis contrast of the CCW and CW shapes, achieving 20 dB or more by using a polarization controller placed upstream of the polarizer. Modeling and experimental validation are carried out using a polarization-varying bistable signal generated by an anisotropic Fabry–Perot semiconductor optical amplifier, and the results are applicable to other nonlinear resonators and means of polarization-varying signal generation. This model can be used for the study, design, and optimization of a variety of sequential and combinational all-optical signal processing applications.

Design of Plasmonic NOT Logic Gate Based on Insulator – Metal – Insulator (IMI) waveguides

In this work, all-optical plasmonic NOT logic gate was proposed using Insulator-Metal-Insulator (IMI) plasmonic waveguides Technology. The proposed all-optical NOT gate is simulated and realized using COMSOL Multiphysics 5.3a software. Recently, plasmonic technology has attracted high attention due to its wide applications in all-optical signal processing. Due to its highly localization to metallic surfaces, surface plasmon (SP) may have huge applications in sub wavelength to guide the optical signal in the waveguides which results in overcoming the diffraction limit problem in conventional optics. The proposed IMI structure is consist of a dielectric waveguides plus metallic claddings, which guide the incident light strongly in the insulator region. Our design consists of symmetric nano-rings structures with two straight waveguides which based on IMI structure. The operation of all-optical NOT gate is realized by employing the constructive and destructive interface between the straight waveguides and the nano-rings structure waveguides. There are three ports in the proposed design, input, control and output ports. The activation of control port is always ON. By changing the structure dimensions, the materials, the phase of the applied optical signal to the input and control ports, the optical transmission at the output port is changed. In our proposed structure, the insulator dielectric material is glass and the metal material is silver. The calculated contrast ratio between (ON and OFF) output states is 3.16 (dB).

Manipulation of the dielectric properties of narrow-band gap material by an ultrashort laser pulse

The control of dielectric responses of narrow-band gap materials by an ultrashort laser pulse is investigated theoretically using time-dependent density functional theory, taking gallium phosphide as a concrete example. We demonstrate that, by using properly selected laser parameters an ultrashort laser pulse can induce reversible change of the electric and optical properties. The anisotropy of the transient permittivity of the material throughout the pulse duration can be enhanced so strongly that the dispersion of electromagnetic waves in the material becomes hyperbolic in some frequency interval with increasing laser energy. We describe the evolution of the transient permittivity throughout the duration of the laser pulse, pointing out to a fundamental possibility for applications of ultrafast all-optical signal processing and optical-field effect devices.

Phase-sensitive amplification of a QPSK signal using a dispersion engineered silicon-graphene oxide hybrid waveguide.

We numerically investigate phase-sensitive amplification of a quadrature phase shift keying (QPSK) signal in a 35 µm dispersion engineered silicon-graphene oxide hybrid waveguide. The four-wave mixing efficiency is effectively enhanced by exploiting the ultrahigh Kerr nonlinearity and low loss of graphene oxide in the ultrawide wavelength range. A new structure of dispersion flat silicon-graphene oxide hybrid waveguide is proposed and used to achieve the phase regeneration of a QPSK signal using a dual-conjugated-pump degenerate scheme. The phase-dependent gain and phase-to-phase transfer functions are calculated to analyze the properties of a phase-sensitive amplifier (PSA). The constellation diagrams of the QPSK signal and the error vector magnitude are used to assess the regeneration capacity. The simulation results show that the proposed PSA with a good phase noise squeezing capability has potential applications in all-optical signal processing.

Downstream hysteresis-shape control of a bistable optical signal created by an upstream nonlinear photonic resonator.

We experimentally demonstrate the control of the hysteresis shape of a bistable optical signal at a location downstream of the nonlinear photonic resonator within which the bistability is generated; this shape control mechanism is performed without any signal sent upstream to the bistable system. The downstream shape-control element consists of a fiber-optic polarization controller and linear polarizer in series, and the nonlinear resonator generates an optical signal whose bistable branches exhibit different states of power and polarization. The diversity of demonstrated hysteresis shapes include the canonical counter-clockwise (CCW) shape (S-shape), the clockwise (CW) shape (inverted S-shape), and butterfly shapes; since all shapes originate from the same bistable signal, all shapes exhibit the same switching input powers. Moreover, the shape-selection process enhances the bistable switching contrast to 20 and 21 dB for the CCW and CW shapes, respectively. The shape-selection technique is demonstrated using a Fabry-Pérot semiconductor optical amplifier, is applicable to other nonlinear photonic resonators, and provides flexibility to future combinational and sequential all-optical signal processing applications.

An all-optical 1× 2 Demultiplexer Using Kerr Nonlinear Nano-plasmonic Switches

In this paper, a novel surface plasmon polariton (SPP) based all-optical 1× 2 demultiplexer, which is based on a modified Y-branch structure and a controllable switching module, is presented. In the modified Y-branch structure, which acts as an ideal wide-band splitter, the width of the branches are chosen as one half the input waveguide. The switching module is constructed using two nano-plasmonic racetrack-shaped disk resonators which are side coupled to the branches of the Y-branch structure. It has been shown that using a pump light power, the transmissions of the input signal into the output ports can be controlled. The simulation results are based on the two dimensional finite-difference time-domain (2D FDTD) method. In the proposed device, the “on” state transmission coefficients and the extinction ratios (measured at the output ports), for the pump light source with the wavelength of 660 nm and the intensity of 1.75 MW/cm2, are about 0.74 and 28.75 dB, respectively. Furthermore, in this case, the switching times of the proposed device, measured at the port 1 and port 2, are about 100 fs and 180 fs, respectively. It is expected that the proposed device can find applications in all-optical signal processing.

Design of a dispersion-engineered broadband Ge11.5As24Se64.5-Si3N4 strip–slot hybrid waveguide with giant and flat dispersion over 350 nm for on-chip photonic networks

We propose a new strip–slot hybrid waveguide with extreme large and flat dispersion over broad wavelength range. The strong resonance coupling between the strip and slot modes has been employed to obtain a high dispersion at desired wavelength. The properties of dispersion are analyzed using the finite-difference time-domain method. All numerical simulation results reveal that for the optimized waveguide structure, a maximum dispersion of −1.54×106 ps nm−1 km−1 and dispersion full width at half-maximum of 2.5 nm at 1.55μm are obtained. By cascading the strip–slot hybrid waveguides with varied width and height, a large and flattened dispersion of −9.8×105 ps nm−1 km−1 covering 350 nm is achieved. Moreover, dispersion compensation of 100 Gbit/s return-to-zero on-off-keying optical-time-division-multiplexing signals after 50-km single mode fiber transmission, and after 7-km hollow-core photonic band-gap fiber transmission are demonstrated, separately. Such a waveguide will find widespread applications in on-chip all-optical signal processing.

All-optical signal processing in few-layer bismuthene coated microfiber: towards applications in optical fiber systems.

Two-dimensional (2D) bismuthene can find its wide potential applications due to its appealing optical and electronic properties. Especially, bismuthene exhibits layer-count dependent direct bandgaps and strong light-matter interaction, enabling its applications in all-optical signal processing area that can overcome the bottle-neck in existing electrical signal processing. However, light-bismuthene interaction based on main stream optical fiber systems and its application in all-optical signal processing is relatively less investigated. In this work, few-layer bismuthene, synthesized with facile solution processing method, is coated onto a piece of microfiber. The experimental results show that this device can operate as an optical Kerr switcher and a four-wave-mixing-based wavelength converter under different configuration. The results including wavelength applicability, information bandwidth, eye diagrams in combination with bit-error rate (BER) performance and stability measurements confirm its feasibility in optical fiber systems. To the best of our knowledge, it is first prototypic device reported in this work for bismuthene in all-optical signal processing optical fiber systems.

Influence of two-photon absorption and free-carrier effects on all-optical logic gates in silicon waveguides

We investigate the impact of two-photon absorption (TPA) and free-carrier effects on all-optical logic gates in silicon waveguides, in which the conversion efficiency is greatly reduced and the waveform is seriously distorted. A silicon–organic hybrid dual-slot waveguide without TPA is proposed for all-optical logic gates and could offer an extremely large nonlinear parameter higher than 1.4 × 107 W−1 km−1. The all-optical logic AND, OR, and XOR gates based on four-wave mixing in this waveguide are realized for 100 Gb s−1 data signals in the C-band. These results provide potential applications for all-optical signal processing in integrated optics, optical communications, and optical computation.

Dielectric properties of cubic boron nitride modulated by an ultrashort laser pulse

The transient dielectric responses of cubic boron nitride (cBN) modulated by an ultrashort laser pulse are introduced based on time-dependent density functional theory calculations. We theoretically investigate whether an ultrashort laser pulse is able to reversibly drive the electric and optical properties of cBN to change profoundly without damage. With easily tunable laser parameters, the cBN can even be switched by reversal of both elliptic and hyperbolic behaviors for a particular working frequency window. We describe the evolution of the transient dielectric function throughout the duration of the pulse, which can exhibit a reversible behavior driven by the instantaneous optical field for a purposely designed laser pulse, providing a fundamental possibility for applications of all-optical signal processing and optical-field-effect devices.