All-optical Components Research Articles

Hosting exceptional point in all-lossy dual-core optical fiber and its exotic chiral light dynamics

Exploration of exceptional points (EPs) and associated unique features in gain-loss assisted optical systems to develop future all optical devices have been a great interest in recent years. However, incorporation and adjustment of gain distribution in a system is quite challenging. Here, we design a fabrication feasible dual-core optical fiber where only the customized transverse loss profile controls the interaction between two coupled modes and results in hosting an EP. Parametric encirclement of the identified EP and corresponding chirality-driven asymmetric mode conversion phenomenon between the supported modes have been reported. The proposed structure features ease of fabrication using state-of-the-art techniques with possible applications in all-optical components for communication and all fiber photonic devices.

Exceptional-point-induced asymmetric mode conversion in a dual-core optical fiber segment

The engineering of exceptional points (EPs) in open optical systems has lately attracted much attention for developing future all-optical devices. However, investigation of the fascinating features of EPs in fiber geometries is lacking. We design a fabrication feasible dual-core optical fiber segment, where non-Hermiticity in terms of a symmetric customized gain-loss profile is introduced to modulate the interaction between two corresponding coupled modes toward hosting a dynamical EP encirclement scheme in the gain-loss parameter space. An asymmetric conversion process between two supported modes is reported by exploiting the chirality of the encountered EP. The proposed scheme can lead to an advanced platform to design mode-manipulative all-optical components in communication and all-fiber photonic devices.

Three-photon-induced free-carrier absorption in Ga-doped ZnO.

Ga-doped ZnO (Ga:ZnO) possesses many advantages due to the unique atomic structure and intriguing physical and chemical properties of Ga, but its optical nonlinear characteristics are rarely studied, so it is difficult to expand its application in the fields of optoelectronics and all-optical components. Here, we examine the optical nonlinearity of Ga:ZnO with the help of a theoretical quantitative model of three-photon-absorption (3PA)-induced free carrier absorption (FCA) and free carrier refraction (FCR). 3PA-induced FCA was examined and distinguished successfully from 3PA through z-scan measurements. Experimental results prove that Ga:ZnO exhibits strong nonlinear absorption at a wavelength of 800 nm. The FCA cross section and 3PA coefficient are σα=3×10-17 cm2 and β3=2.5×10-4 cm3/GW2, respectively, and the optical limiting related to FCA was also experimentally examined. This study of the optical nonlinear properties of Ga:ZnO may provide a strategy for applying this material in the fields of optoelectronics and photonic devices.

Simultaneous detection of atmospheric HONO and NO<sub>2</sub> utilising an IBBCEAS system based on an iterative algorithm

Abstract. We present an improved incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) system based on an iterative retrieval algorithm for the simultaneous detection of atmospheric nitrous acid (HONO) and nitrogen dioxide (NO2). The conventional IBBCEAS retrieval algorithm depends on the absolute change in the light intensity, which requires high light source stability and the stable transmission of the light intensity of all optical components. The new algorithm has an iterative module to obtain the effective absorption optical path length, and the concentrations of HONO and NO2 are then determined by differential optical absorption spectroscopy (DOAS) retrieval; thus, the method is insensitive to the fluctuation in the absolute light intensity. The robustness of the system is verified by simulating the influence of the relative change in the light intensity on the spectral retrieval results. The effect of nitrogen purging in front of the cavity mirrors on shortening the actual cavity length was measured and corrected using NO2 gas samples. Allan deviation analysis was conducted to determine the system stability, and it indicated that the detection limits (2σ) of HONO and NO2 are 0.08 and 0.14 ppbv at an integration time of 60 s respectively. Furthermore, Kalman filtering was used to improve the measurement precision of the system. The measurement precision at an integration time of 3 s can be improved 4.5-fold by applying Kalman filtering, which is equivalent to the measurement precision at an integration time of 60 s without applying Kalman filtering. The atmospheric HONO and NO2 concentrations were observed by the IBBCEAS system based on an iterative algorithm and were compared with values measured by conventional IBBCEAS.

Effects of self- and cross-phase modulation on the spontaneous symmetry breaking of light in ring resonators

We describe spontaneous symmetry breaking in the powers of two optical modes coupled into a ring resonator, using a pair of coupled Lorentzian equations, featuring tunable self- and cross-phase modulation terms. We investigate a wide variety of nonlinear materials by changing the ratio of the self- and cross-phase interaction coefficients. Static and dynamic effects range from the number and stability of stationary states to the onset and nature of oscillations. Minimal conditions to observe symmetry breaking are provided in terms of the ratio of the self-/cross-phase coefficients, detuning, and input power. Different ratios of the nonlinear coefficients also influence the dynamical regime, where they can induce or suppress bifurcations and oscillations. A generalised description on this kind is useful for the development of all-optical components, such as isolators and oscillators, constructed from a wide variety of optical media in ring resonators.

Toward All-Optical Layered Encryption: A Feasibility Analysis of Optical Stream Cipher

We study whether the layered encryption and, thus, anonymity of communication can be implemented all-optically, granting ultra-high speed communication and processing. To this end, we evaluate the feasibility of the state-of-the-art all-optical components, including optical linear feedback shift register (oLFSR) and optical XOR (oXOR), for implementing an all-optical stream cipher (oSC). Just like the function of key expansion in today's electronic ciphers, we use pRNGs and oLFSRs to expand short bit sequences of the secret key, thus enabling the transmission and en-/decryption at line rate; oXOR is used for the actual all-optical encryption. Using the principles of information-theoretical entropic security, we evaluate the key uncertainty (entropy and equivocation) and, thus, the computational complexity of various guessing attacks. We also analyze the maximum length of optical key stream and show that oSC can be designed as secure as in today's systems while operating all-optically at higher line rates.

Nanosystems, Edge Computing, and the Next Generation Computing Systems.

It is widely recognized that nanoscience and nanotechnology and their subfields, such as nanophotonics, nanoelectronics, and nanomechanics, have had a tremendous impact on recent advances in sensing, imaging, and communication, with notable developments, including novel transistors and processor architectures. For example, in addition to being supremely fast, optical and photonic components and devices are capable of operating across multiple orders of magnitude length, power, and spectral scales, encompassing the range from macroscopic device sizes and kW energies to atomic domains and single-photon energies. The extreme versatility of the associated electromagnetic phenomena and applications, both classical and quantum, are therefore highly appealing to the rapidly evolving computing and communication realms, where innovations in both hardware and software are necessary to meet the growing speed and memory requirements. Development of all-optical components, photonic chips, interconnects, and processors will bring the speed of light, photon coherence properties, field confinement and enhancement, information-carrying capacity, and the broad spectrum of light into the high-performance computing, the internet of things, and industries related to cloud, fog, and recently edge computing. Conversely, owing to their extraordinary properties, 0D, 1D, and 2D materials are being explored as a physical basis for the next generation of logic components and processors. Carbon nanotubes, for example, have been recently used to create a new processor beyond proof of principle. These developments, in conjunction with neuromorphic and quantum computing, are envisioned to maintain the growth of computing power beyond the projected plateau for silicon technology. We survey the qualitative figures of merit of technologies of current interest for the next generation computing with an emphasis on edge computing.

A study of the behaviour of copper in different types of silicate glasses implanted with Cu+ and O+ ions

Glasses containing copper are promising photonic materials for lasing devices and all-optical components. It has already been shown that the oxidation state of the implants depends on many factors. This paper is going to report on one of them, i.e. the influence of the composition of a silicate glass matrix on the behaviour of the implanted Cu ions before and after a subsequent implantation of oxygen ions.Three types of silicate glasses having a different extent of cross-linking were implanted with copper ions with an energy of 330keV and a fluence 1×1016ionscm−2. Then the glasses were implanted with oxygen ions with an energy of 110keV into the same depth as the already implanted Cu ions. The concentration depth profiles of Cu in the glasses were studied by Rutherford Backscattering Spectrometry. After the implantation, the samples were characterised by optical absorption and photoluminescence spectroscopy. The samples were annealed in ambient atmosphere for 1h at 600°C, which is near the transformation temperature of those glasses. The effect of annealing on the distribution of the implants and on the absorption and emission spectra of the as-implanted glasses will be discussed as well.

The formation of silver metal nanoparticles by ion implantation in silicate glasses

It has been shown that glasses containing silver metal nanoparticles are promising photonics materials for the fabrication of all-optical components. The resulting optical properties of the nanocomposite glasses depend on the composition and structure of the glass, as well as on the type of metal ion implanted and the experimental procedures involved. The main aim of this article was to study the influence of the conditions of the ion implantation and the composition of the glass on the formation of metal nanoparticles in such glasses.Four various types of silicate glasses were implanted with Ag+ ions with different energy (330keV, 1.2MeV and 1.7MeV), with the fluence being kept constant (1×1016ionscm−2). The as-implanted samples were annealed at 600°C for 1h. The samples were characterised in terms of: the nucleation of metal nanoparticles (linear optical absorption), the migration of silver through the glass matrix during the implantation and post-implantation annealing (Rutherford backscattering spectroscopy), and the oxidation state of silver (photoluminescence in the visible region).

Optical computing circuits, devices and systems

Information forms the basis of modern technology. To meet the ever-increasing demand for information, means have to be devised for a more efficient and better-equipped technology to intelligibly process data. Advances in photonics have made their impact on each of the four key applications in information processing, i.e., acquisition, transmission, storage and processing of information. The inherent advantages of ultrahigh bandwidth, high speed and low-loss transmission has already established fiber-optics as the backbone of communication technology. However, the optics to electronics inter-conversion at the transmitter and receiver ends severely limits both the speed and bit rate of lightwave communication systems. As the trend towards still faster and higher capacity systems continues, it has become increasingly necessary to perform more and more signal-processing operations in the optical domain itself, i.e., with all-optical components and devices that possess a high bandwidth and can perform parallel processing functions to eliminate the electronic bottleneck.

Control and Management Issues in All-Optical Networks

As more intelligence and control mechanisms are added into optical networks, the need for the deployment of a reliable and secure management system using efficient control techniques has become increasingly relevant. While some of available control and management methods are applicable to different types of network architectures, many of them are not adequate for all-optical networks. These emerging transparent optical networks have particularly unique features and requirements in terms of security and quality of service thus requiring a much more targeted approach in terms of network management. In particular, the peculiar behavior of all-optical components and architectures bring forth a new set of challenges for network security. In this article, we briefly overview security and management issues that arise in all-optical networks. We then discuss the key management functions that are responsible for ensuring the secure and continued functioning of the network. Consequently, we present a framework for the realization of an appropriate management system that can meet the challenges posed by all-optical networks .

Control Mechanism for All-Optical Components

In this article, we give a brief overview of security and management issues that arise in all-optical networks (AONs). Then we present an outline of the multiple attack localization and identification (MALI) algorithm that can participate in some of the tasks for fault management in AONs. Consequently, we discuss a hardware-based control unit that can be embedded in AON nodes to accelerate the performance of the MALI algorithm. We conclude the article with a discussion concerning the applicability and implementation of this device in AON management systems.

Storing light in optical fibers using sound waves

Increasing traffic on the Internet demands faster optical transmission networks. Future high-speed communication networks may rely largely on all-optical components that are intrinsically faster than their electronic counterparts. To achieve such networks, however, one needs to overcome a number of obstacles that exist at levels from devices to systems. For example, the lack of all-optical memory for storing optical data remains a bottleneck in modern optical information networks.1 There has been substantial progress in addressing this problem using spatial-spectral holography in systems that operate at cryogenic temperatures2 or stored light based on electromagnetically induced transparency, where optical information is impressed upon internal degrees of freedom of an ensemble of atoms or ions.3 Both of these methods, however, are limited to operating at the resonance wavelength of the ions or atoms used. These limitations have recently been partially overcome using a dynamically controlled resonator in which a single optical pulse was stored for ∼100ps.4 We recently presented a different approach: a simple storedlight approach5 in which optical pulse information is transferred onto a slowly moving hypersonic wave (∼1/40,000 of the light speed) in an optical fiber and converted back at a later time through stimulated Brillouin scattering (SBS) as illustrated in Figure 1. In the storage process, optical data pulses (of carrier frequency ν0) interact with a counterpropagating short intense ‘write’ pulse (of carrier frequency ν0 + νB, where νB is the Brillouin frequency shift of the fiber). The optical data pulses become depleted as energy is shifted to a hypersonic wave in the fiber. In the retrieval process, a short intense ‘read’ pulse at the same frequency as the ‘write’ pulse depletes the acoustic wave and releases the data back to the original optical frequency, thereby generating a replica of the incident data pulses. This stored-light approach has advantages such as room-temperature Figure 1. Stimulated Brillouin scattering allows data storage in an optical fiber. In the storage process, (a) optical data pulses interact with a ‘write’ pulse . (b) The optical data pulses become depleted as the information shifts to an acoustic wave in the fiber. To retrieve the data, (c) a ‘read’ pulse depletes the acoustic wave, (d) generating a replica of the original data pulses.5

All-optical injection of ballistic electrical currents in unbiased silicon

Silicon has been the dominant material in electronics since the invention of the integrated transistor. In contrast, silicon’s indirect bandgap and vanishing second-order optical nonlinearity limit its applications in optoelectronics1. Although all-optical components such as Raman lasers2, parametric amplifiers3 and electro-optic modulators4,5 have recently been reported, control over charge motion in silicon has only ever been achieved electronically. Here, we report all-optical generation of ultrafast ballistic electrical currents in clean, unbiased, bulk silicon at room temperature. This current injection, which provides new insights into optical processes in silicon, results from quantum interference between one- and two-photon absorption pathways across the indirect bandgap despite phonon participation and the multi-valley conduction band. The transient currents induced by 150 fs pulses are detected via the emitted THz radiation. The efficiency of this third-order optical process is surprisingly large for fundamental wavelengths in the 1,420–1,800 nm range.

Electronic equalization of 10Gbit/s upstream signals for asynchronous-modulation and chromatic-dispersion compensation in a high-speed centralized supercontinuum broadband-light-source WDM-PON

We propose maximum likelihood sequence estimation (MLSE) for upstream signal detection in a high-speed centralized supercontinuum broadband-light-source (SC-BLS) wavelength-division-multiplexing passive optical network (WDM-PON). Upstream pulse carriers are produced by a SC-BLS at the central office (CO), modulated by 10Gbit/s upstream data at optical network units (ONUs), and finally detected by MLSE at the CO. MLSE effectively compensates the impairments from (1) asynchronous modulation of upstream pulse carriers at ONUs; and (2) chromatic dispersion (CD) in the fibers. Compared to the conventional method using alignment monitors at ONUs for upstream modulation synchronization and all-optical components for CD compensation, the proposed method features significant cost saving, lower power requirement for upstream signals, and lower operation complexity for ONUs in the SC-BLS WDM-PON.

All-optical switching technologies for protection applications

One of the key issues when designing an optical transport network is how to ensure survivability in the event of a network failure. With the increased penetration of dynamic DWDM networks the demand for new, reliable, and flexible protection schemes at the optical layer rises. Furthermore, over the last several years, enormous advances have been made in optical component technologies. As a result, all-optical components, such as the optical switch, now offer additional functionalities. This article examines the applicability of new and legacy all-optical switching technologies to serve as building blocks for different protection applications.

Delay analysis of all-optical packet-switching ring and bus communications networks

We study the delay performance of all-optical packet communication networks configured as ring and bus topologies employing crossconnect switches (or wavelength routers). Under a cross-connect network implementation, a packet experiences no (or minimal) internal queueing delays. Thus, the network can be implemented by high speed all-optical components. We further assume a packet-switched network operation, such as that using a slotted ring or bus access methods. We also derive the delay performance for networks under a store-and-forward network operation. We show these implementations to yield very close average end-to-end packet queueing delay performance. We note that a cross-connect network operation can yield a somewhat higher queueing delay variance levels. However, the mean end-to-end queueing delay for all traffic flows are the same for a cross-connect network operation (under equal nodal traffic loading), while that in a store-and-forward network increases as the path length increases. Similar delay performance results are obtained for bus networks.

SEROS - A SELF-ROUTING OPTICAL ATM SWITCH

A fault-tolerant high-performance SElf-Routing 2 × 2 Optical ATM Switch (SEROS) is proposed. The switch is designed using all-optical components which allows the exploitation of spatial parallelism. SEROS can be used with any multistage interconnection network such as Omega, Banyan, Shuffle or Benes. For the purpose of this study, SEROS has been incorporated into a generic self-routing multistage interconnection network that uses 2 × 2 switches and is not fault tolerant. Reliability analysis is carried out and the results are compared with two major fault-tolerant networks. They show that without redundant switches, better network survivability is achieved. All the switches in the network are 2 × 2, making it easier to mass produce.