Passive Optical Components Research Articles

Concurrent Direct Inter-ONU and Upstream Communications in IMDD PONs Incorporating P2MP Flexible Optical Transceivers and Advanced Passive Remote Nodes

Driven by a large number of emerging diversified services, in the 5G and beyond era, concurrent direct inter-ONU and upstream communications inside a PON-based mobile access network are highly desirable to provide dynamic, ultra-dense, and fast ONU-to-ONU (without involving an OLT) and ONU-to-OLT connections. To cost-effectively deliver highly dynamic and low latency direct inter-ONU communications, this paper proposes and experimentally demonstrates novel concurrent direct inter-ONU and upstream communications in an upstream 27 km, >62.47 Gbit/s IMDD PON. For supporting inter-ONU communications between a large number of ONUs, an advanced passive remote node is also proposed. Based on different passive optical components, this remote node can be implemented using two approaches, which can, respectively, reduce the inter-ONU signal power losses by >12.2 dB and >16.6 dB (for 128 ONUs) in comparison with existing inter-ONU communication techniques’ remote nodes. In each ONU and OLT, a single pair of cascaded IFFT/FFT-based point-to-multipoint (P2MP) flexible optical transceivers are employed to simultaneously and dynamically establish multiple ONU-to-ONU and ONU-to-OLT communications according to actual users’ requirements. Experimental results show that the proposed network has excellent robustness against various transmission system impairments, including chromatic dispersion, the Rayleigh and Brillouin backscattering effects, and the channel interference effects. For each ONU, dynamic channel allocation can be made without compromising its overall performance.

Tailoring Space-Time Nonlocality for Event-Based Image Processing Metasurfaces.

Analog computation with passive optical components can enhance processing speeds and reduce power consumption, recently attracting renewed interest thanks to the opportunities enabled by metasurfaces. Basic image processing tasks, such as spatial differentiation, have been recently demonstrated based on engineered nonlocalities in metasurfaces, but next-generation computational schemes require more advanced capabilities. Here, by simultaneously tailoring the nonlocal electromagnetic response of a metasurface in space and time, we demonstrate a passive ultrathin silicon-based device that performs mixed spatiotemporal differentiation of input images, realizing event-based edge detection. The metasurface performs spatial differentiation only when the input image is evolving in time, resulting in spatiotemporal image processing on subpicosecond timescales. Moreover, the metasurface design can be tailored to selectively enhance objects moving at desired speeds. Our results point towards fully passive processing of spatiotemporal signals, for highly compact neuromorphic cameras.

Optical response and temperature shielding coatings using tri-layer structure composed of titania/silica/titania

The fabrication of metamaterials with inspiration from nature paved the door for the creation of revolutionary passive and active devices. Butterfly wings are one of them, and their multilayered structure motivated nanotechnologists, physicists, and other optoelectronic and photonic engineers to develop photonic crystals, dielectric reflectors, and Bragg reflectors for use in visible light communication, solar cells, and other photonic and optoelectronic applications. We report the sol–gel spin coating of a dielectric reflector on the glass substrate, an optical passive component consisting of titania and silica thin films for infrared radiation reflection. Individual thin films of titania and silica on glass substrates were studied using an x-ray diffractometer, which indicated anatase of titania and the amorphous nature of silica at a Bragg angle of 25° with a sharp and wide peak, respectively. The multilayer structure of titania/silica/titania was further investigated using Fourier transform infrared spectroscopy, which revealed the presence of Ti–O–Ti and Si–O–Si vibrational bonds at wavenumbers 546 and 973 cm−1, respectively, as well as the presence of Ti–O–Si vibrational bond at 1100 cm−1. The thickness of the multilayer titania/silica/titania was measured using a cross-sectional field emission scanning electron microscope (FESEM) and found to be 160/240/160 nm, respectively. Finally, reflection investigation on the multilayer structure using ultraviolet–visible–near-infrared spectroscopy validated the reflection of the infrared spectrum area by around 70% and showed to be beneficial for temperature shielding applications on glass furnishings.

Terahertz focusing blazed diffractive optical elements for frequency demultiplexing

This study presents the novel optical passive components for spatial frequency division demultiplexing of terahertz (THz) radiation. Four different diffractive optical elements (DOEs) were designed as the combination of phase kinoform lenses and phase blazed diffraction gratings. The designed structures were verified in numerical simulations and they showed the promising results. Subsequently, they were manufactured using fused deposition modeling (FDM) 3D printing technology from highly transparent cyclic olefin copolymer (COC). The manufactured structures were examined in the experimental setup. The results matched numerical simulations. Thus, eight frequencies in the range from 150 GHz to 220 GHz every 10 GHz were spatially separated. The novel design solution guaranteed 63% higher relative efficiency compared to the reference DOE. The presented study can be suitable as the application for 6G technology telecommunication systems as the spatial frequency division demultiplexing component for the THz radiation band.

A simple fiber optic sensing system based on dual Sagnac interferometer for disturbance location detection

In this paper, a simple sensing system for disturbance location detection is presented. The system utilizes a dual loop Sagnac interferometer, where one of the loops is substantially longer than the other. Both Sagnac loops share a common section of a sensing fiber which is exposed to the sensing field of interest, while a pulse modulated low coherence light source is used for proposed system excitation. Dual loop configuration introduces different propagation delays among pulses launched into the both loops of Sagnac interferometer which allows their temporal separation at the system output. Furthermore, different propagation delays among these split pulses within both Sagnac loops leads also to different phase delays among interfering pulses at the loops output when the sensing fiber is exposed to a time varying disturbance. By measuring the ratio of the pulses amplitudes obtained at system output, the precise location of time varying disturbance can be determined. The entire sensing loop is made of passive optical components which allows for simple remote operation of the proposed system. A very simple signal processing is required to extract the position of the disturbance.

Topological polarisation states

Polarisation states are described by spin expectation values, known as Stokes parameters, the trajectories of which in a rotationally symmetric system form a sphere named after Poincaré. Here, we show that the trajectories of broken rotational symmetric systems can exhibit distinct topological structures in polarisation states. We use a phase-shifter to form a polarisation circle(S1), which interferes with the original input due to the phase change of the output state upon rotation. By rotating the circle using a rotator, the trajectories become a polarisation torus(S1×S1), which was experimentally confirmed in a simple setup using passive optical components together with the Mach–Zehnder interferometer. We also discuss the realisations of other topological features, such as a Möbius strip, a trefoil knot, Hopf links, and topological Dirac bosons, with a bulk-edge correspondence.

Enhancing the stimulated emission of polarization-entangled photons using passive optical components

Bright sources of polarization-entangled photon pairs are essential components for quantum information technologies. In general, it is necessary to introduce a resonator that combines active optical components such as an electric optical modulator to enhance the stimulated emission of polarization-entangled photons. It is technically difficult to perform the time series operation to output the stimulated entangled photons in the resonator by synchronizing laser pulses. In this paper, we propose a scheme to scale up the stimulated emission of polarization-entangled photon pairs using a resonator with only passive optical components. We show the theoretical aspects of the scheme and also perform a proof-of-principle experimental demonstration of the scheme in a double-pass configuration.

Coherent feedback in optomechanical systems in the sideband-unresolved regime

Preparing macroscopic mechanical resonators close to their motional quantum groundstate and generating entanglement with light offers great opportunities in studying fundamental physics and in developing a new generation of quantum applications. Here we propose an experimentally interesting scheme, which is particularly well suited for systems in the sideband-unresolved regime, based on coherent feedback with linear, passive optical components to achieve groundstate cooling and photon-phonon entanglement generation with optomechanical devices. We find that, by introducing an additional passive element – either a narrow linewidth cavity or a mirror with a delay line – an optomechanical system in the deeply sideband-unresolved regime will exhibit dynamics similar to one that is sideband-resolved. With this new approach, the experimental realization of groundstate cooling and optomechanical entanglement is well within reach of current integrated state-of-the-art high-Q mechanical resonators.

A simulator of optical coherent-state evolution in quantum key distribution systems

Quantum key distribution (QKD) is believed to represent a viable solution to achieve theoretically unconditionally secure key generation. However, the available optical systems for experimental QKD, based on photon transmission, are flawed by non-idealities that ultimately limit the achievable performance. Classical simulation of the optical hardware employed in these systems may take on a determining role in engineering future QKD networks. In this article, attempts for developing a QKD simulator based on low-computational-cost models of the employed hardware are presented. In particular, the simulation infrastructure targets polarization-based QKD setups with faint laser sources, whose behaviour can be described by semiclassical coherent states and Mean Photon Number (MPN) per beam. The effects of passive optical components on the photonic qubit evolution are described by Jones matrices, whose coefficients, for some commercial devices, are stored in an ad-hoc library. Realistic eavesdropping attacks and non-idealities, such as optical losses, fibre attenuation, polarization misalignment and limited efficiency of single-photon detectors, are also taken into account. The infrastructure allows the user to describe the desired QKD configuration and it provides in output the MPN at the receiver and two fiducial performance parameters: Quantum Bit Error Rate (QBER) and secure key rate. The comparison of the simulation results with experimental data in the state-of-the-art literature highlights that this work is a step forward towards the definition of compact models for the hardware-dependent simulation of quantum-assisted communication networks.

Analytical design of fiber-optic FM/PM demodulator

Abstract In this paper, the concept of a novel optical FM/PM demodulator which can be designed from low-cost passive optical components and can have peak-to-peak bandwidth in the GHz region has been described. The bandwidth can be increased by reducing the single mode fiber length incorporated in the design, which is followed by a corresponding fall in frequency sensitivity of the device. The bandwidth and frequency sensitivity can be traded-off keeping their product a constant. The crossover wavelength can be tuned by changing the length of the optical delay line and the length of the single mode fiber (SMF). The Figure of Merit (FOM) of the demodulator, defined as the bandwidth sensitivity product, has a value of π which is greater than that of a passive hybrid Tee microwave discriminator and those of Mach-Zehnder interferometer-based designs. Calculated third harmonic distortion (3HD) of the demodulated optical FM signal increases with the increase in FM index and with the increase in SMF length for a given modulation frequency. Typical 3HD for the device with SMF length of 1 cm is calculated to be −39.9 dB for FM index = 2 and a modulation frequency of 400 MHz.

Collision-free distributed MAC protocol for passive optical intra-rack data center networks

In this paper, we present a distributed medium access control (MAC) protocol and a network architecture suitable for optical intra-rack data center networks (DCNs). The intra-rack communication is performed using passive optical components, over four data wavelength division multiplexing (WDM) channels of either 40 or 100 Gbps each, keeping low power consumption. On the other hand, the inter-rack communication is performed over a separate network through upper layer routers. In this study, we focus only on the intra-rack communication. We introduce an intra-rack DCN (IR-DCN) architecture that works in the optical domain, and two IR-DCN configurations with different total nominal capacity: 160 and 400 Gbps, respectively. Also, we propose a synchronous pre-transmission coordination fair access intra-rack MAC (intra-MAC) protocol taking into account the traffic characteristics and priority classes within existing DCNs. The proposed intra-MAC protocol totally eliminates packet collisions, achieving high performance. Particularly, it reaches high bandwidth utilization even under heavy loads: 90% and 87.5% for the two IR-DCN configurations of 160 and 400 Gbps total capacity, respectively. Also, it achieves low mean end-to-end (e2e) packet delay, lower than 0.25 and 0.12 ms, respectively, providing a reliable solution for time-sensitive DCN traffic. Specifically, simulation results demonstrate that the highest priority traffic experiences e2e delay lower than 1.9 and 1.1 µs, respectively, which is sufficient for the service of the strictest delay requirements of time-sensitive cloud applications. The intra-MAC protocol is decentralized, without the need for a network controller, providing high flexibility. Our IR-DCN proposal is studied in comparison to other currently dominant intra-rack/cluster DCNs, and it achieves from 6% to 57% higher throughput and from 20% to 99% lower e2e delay at high loads. Comparatively, it is on average 80% and 68% more energy and cost efficient, respectively.

Fault-tolerant [formula omitted] control for optical parametric oscillators with pumping fluctuations

Optical Parametric Oscillators (OPOs) have wide applications in quantum optics for generating squeezed states and developing advanced technologies. When the phase or/and the amplitude of the pumping field for an OPO have fluctuations due to fault signals, time-varying uncertainties will be introduced in the dynamic parameters of the system. In this paper, we investigate how to design a fault-tolerant H∞ controller for an OPO with a disturbance input and time-varying uncertainties, which can achieve the required H∞ performance of the quantum system. We apply robust H∞ control theory to a quantum system, and design a passive controller and an active controller based on the solutions to two Riccati equations. The passive controller has a simple structure and is easy to be implemented by using only passive optical components, while the active quantum controller may achieve improved performance. The control performance of the proposed two controllers and one controller that was designed without consideration of system uncertainties is compared by numerical simulations in a specific OPO, and the results show that the designed controllers work effectively for fluctuations in both the phase and amplitude of the pumping field.

Chip integrated photonics for ion based quantum computing

Ion traps are a promising platform for the realisation of high-performance quantum computers. To enable the future scalability of these systems, integrated photonic solutions for guiding and manipulating the laser light at chip level are a major step. Such passive optical components offer the great advantage of providing beam radii in the μm range at the location of the ions without increasing the number of bulk optics. Different wavelengths, from UV to NIR, as well as laser beam properties, such as angle or polarisation, are required for different cooling and readout processes of ions. We present simulation results for different optical photonic components, such as grating outcouplers or waveguide splitters and their applications on ion trap chips. Furthermore, we will introduce the experimental setup for the optical characterisation of the fabricated structures.

Passive Ground‐Based Optical Techniques for Monitoring the On‐Orbit ICESat‐2 Altimeter Geolocation and Footprint Diameter

AbstractCorner cube retro‐reflectors (CCRs), passive optical components, are used to independently evaluate the geolocation accuracy and effective laser footprint diameter of NASA's laser altimetry mission, ICESat‐2, at two specific study sites: White Sands Missile Range in New Mexico and along a segment of the 88°S line of latitude in Antarctica. The CCR methodology provides ICESat‐2 the ability to monitor these altimeter performance metrics throughout the mission lifetime as an indicator of the health of the instrument and the quality of the observations for science applications. The results using this technique reveal a mean geolocation accuracy of the ICESat‐2 measurements of 3.5 m ± 2.1 m, meeting the mission requirement of 6.5 m. For those instances where multiple CCRs are illuminated, the mean effective laser footprint diameter is 10.9 m ± 1.2 m, with the variability assumed to be due to the influence of atmospheric conditions, but warrants further investigation.

An Effective Evaluation of Wavelength Scheduling for Various WDM-PON Network Designs with Traffic Protection Provision

Recently, metropolitan and access communication networks have markedly developed by utilizing a variety of technologies. Their bearer communication infrastructures will be mostly exploiting the optical transmission medium where wavelength division multiplexing techniques will play an important role. This contribution discusses the symmetric sharing of common optical network resources in wavelength and time domains. Wavelength-Division Multiplexed Passive Optical Networks (WDM-PON) attract considerable attention regarding the next generation of optical metropolitan and access networks. The main purpose of this contribution is presented by the analysis of possible scheduling of wavelengths for our novel hybrid network topologies considered for WDM-PON networks. This contribution briefly deploys adequate Dynamic Wavelength Allocation (DWA) algorithms for selected WDM-PON network designs with the provision of traffic protection when only passive optical components in remote nodes are utilized. The main part of this study is focused on the use of wavelength scheduling methods for selected WDM-PON network designs. For evaluation of offline and online wavelength scheduling for novel hybrid network topologies, a simulation model realized in the Matlab programming environment allows to analyze interactions between various metropolitan and access parts in the Optical Distribution Network (ODN) related to advanced WDM-PON network designs. Finally, wavelength scheduling methods are compared from a viewpoint of utilization in advanced WDM-PON networks designs.

Poincaré Rotator for Vortexed Photons

A Poincaré sphere is a powerful prescription to describe a polarized state of coherent photons, oscillating along certain directions. The polarized state is described by a vector in the sphere, and various passive optical components, such as polarization plates and quartz rotators are able to rotate the vectorial state by changing the phase and the amplitude among two orthogonal basis states. The polarization is originated from spin of photons, and recently, significant attentions have been made for optical Orbital Angular Momentum (OAM) as another fundamental degree of freedom for photons. The beam shape of photons with OAM is a vortex with a topological charge at the core, and the state of vortexed photons can be described by a hyper-Poincaré sphere. Here, we propose a compact Poincaré rotator, which controls a vortexed state of photons in a silicon photonic platform, based on Finite-Difference Time-Domain (FDTD) simulations. A ring-shaped gear is evanescently coupled to two silicon photonic waveguides, which convert optical momentum to OAM with both left and right vortexed states. By controlling the relative phase and the amplitude of two traveling waves in input ports, we can control the vortexed states in the hyper-Poincaré sphere for photons out of the gear. The impact of the geometrical Pancharatnam-Berry-Guoy's phase and the conservation law of spin and OAM for vortexed photons out of the gear are discussed.

Visible and Near-IR Nano-Optical Components and Systems in CMOS

Integration of complex optical systems operating in the visible and near-IR range, realized in a CMOS fabrication process with an absolutely ‘no change’ approach, can have a transformative impact in enabling a new class of miniaturized, low-cost, smart optical sensors and imagers for emerging applications. While ‘silicon photonics’ has demonstrated the path towards such advancements in the IR regime, the field of VIS/NIR integrated optics has seen less progress. Therefore, while currently ultra high-density and higher performance image sensors are commonplace in CMOS, all passive optical components (such as lenses, filters, gratings, collimators) that typically constitute a high-performance sensing or imaging system, are typically non-integrated, bulky and expensive, severely limiting their application potential in the space of connected sensors. Here, we present an approach to utilize the embedded copper-based metal interconnect layers in modern CMOS processes with sub-wavelength feature sizes to realize multi-functional nano-optical structures and components. Based on our prior works, we illustrate this electronic-photonic co-design approach exploiting metal/light interactions and integrated electronics in the 400nm-900 nm wavelengths with three design examples. Realized in 65-nm CMOS, these demonstrate for the first time: fully integrated multiplied fluorescence based biosensors with integrated filters, optical spectrometer, and CMOS optical physically unclonable function (PUF). These examples cover a range of optical processing elements in silicon, from deep sub-wavelength nano-optics to diffractive structures. We will demonstrate that when co-designed with embedded photo-detection and signal processing circuitry, this approach can foster millimeter-scale, intelligent optical sensors for a wide range of emerging applications in healthcare, diagnostics, smart sensing, food, air quality, environment monitoring and others.

Synchronous Imaging of Multiple Slices Using Higher-Order Bessel Beams and a Spherical Lens

Higher-order Bessel-like optical beams can be created through off-axis coupling of light into a multimode fiber. Thanks to the aberration that is inherent in spherical surfaces, through directing the Bessel-like beam comprising multiple concentric rings onto a low-cost lens, we created multiple foci at different depths. Moreover, scanning of the optical fiber with a piezoelectric actuator in the lateral direction, we were able to acquire data from different targets located at different planes. After coupling back into the fiber, the reflected portions of light from different targets could be spatially differentiated and directed to different photo-detection units. The proposed architecture is particularly appealing for laser scanning endoscopy applications, as it does not require additional passive or active optical components for generating Bessel beams (axicons or spatial light modulators), therefore offering both miniaturized realization and high optical transmission. We've further demonstrated the tunability of foci separation via altering fiber-coupling conditions with tilt and translation stages. Overall, the proposed scanning method has paved the way for addressing multiple slices at single lateral scan, thus offering improved speed for imaging or ablation applications.

PCOI: Packet Classification‐Based Optical Interconnect for Data Centre Networks

To support cloud services, Data Centre Networks (DCNs) are constructed to have many servers and network devices, thus increasing the routing complexity and energy consumption of the DCN. The introduction of optical technology in DCNs gives several benefits related to routing control and energy efficiency. This paper presents a novel Packet Classification based Optical interconnect (PCOI) architecture for DCN which simplifies the routing process by classifying the packet at the sender rack and reduces energy consumption by utilizing the passive optical components. This architecture brings some key benefits to optical interconnects in DCNs which include (i) routing simplicity, (ii) reduced energy consumption, (iii) scalability to large port count, (iv) packet loss avoidance, and (v) all-to-one communication support. The packets are classified based on destination rack and are arranged in the input queues. This paper presents the input and output queuing analysis of the PCOI architecture in terms of mathematical analysis, the TCP simulation in NS2, and the physical layer analysis by conducting simulation in OptiSystem. The packet loss in the PCOI has been avoided by adopting the input and output queuing model. The output queue of PCOI architecture represents an M/D/32 queue. The simulation results show that PCOI achieved a significant improvement in terms of throughput and low end-to-end delay. The eye-diagram results show that a good quality optical signal is received at the output, showing a very low Bit Error Rate (BER).

Tunable optical loss and multi-band photodetection based on tin doped CdS nanowire

Abstract Inorganic semiconductor nanowires is the fundamental connector in on-chip nano-photonic circuitry systems. The optical loss during light propagation as the key parameter influence its performance as waveguide. So accurate determination of optical loss is imperative for the optical information communication between different active and passive optical components. In this work, pumping power dependent optical loss along the tin doped CdS nanowires were investigated. By calculating the out-coupling photoluminescence intensity from one end of a nanowire with respect to the propagation length, the attenuation coefficient of the near band edge emission changed from 0.097 μm−1 to 0.061 μm−1 with the laser power increases. Similarly, with the increasing of excitation power, the attenuation coefficient of the defects related emission can be tuned from 0.098 μm−1 to 0.067 μm−1. In addition, the activation energy is determined to be 34.29 meV by the low temperature photoluminescence experiment, demonstrating the main carriers decay channel is exciton recombination at room temperature (T = 300 K). Therefore, the individual tin doped CdS nanowire photodetector is fabricated and systematically testing. Under a low illumination intensity (142 μW/cm2@405 nm), the detector exhibit a high responsivity of 51.2 A/W, together with the gain of 313.3. Furthermore, the nanowire detector shows stable photos-witching and multi-band response characteristic. Based on the tunable optical loss and broad spectrum response property, the tin doped CdS nanowires used as waveguide or active material can be electively applied in integrated nanophotonic and optoelectronic systems.