Efficient Optical Transmission Research Articles

Hydroelectric Plant Safety: Real-Time Monitoring Utilizing Fiber-Optic Sensors.

In the context of hydroelectric plants, this article emphasizes the imperative of robust monitoring strategies. The utilization of fiber-optic sensors (FOSs) emerges as a promising approach due to their efficient optical transmission, minimal signal attenuation, and resistance to electromagnetic interference. These optical sensors have demonstrated success in diverse structures, including bridges and nuclear plants, especially in challenging environments. This article culminates with the depiction of the development of an array of sensors featuring Fiber Bragg Gratings (FBGs). This array is designed to measure deformation and temperature in protective grids surrounding the turbines at the Santo Antônio Hydroelectric Plant. Implemented in a real-world scenario, the device identifies deformation peaks, indicative of water flow obstructions, thereby contributing significantly to the safety and operational efficiency of the plant.

Fabrication of Quasi-Sinusoidal Surface Relief Optical Transmission Gratings in Pyrex and IOG Glasses by Implantation with Oxygen and Nitrogen Ion Microbeams of the 5-6 MeV Energy Range.

A method for the fabrication of high diffraction efficiency optical transmission gratings with quasi-sinusoidal profile in glasses by microbeams of medium-mass ions of 5-6 MeV energy was devised and demonstrated. Gratings with a 30 μm grating constant have been manufactured and characterized by interference microscopy and microprofilometry. The obtained surface profiles of the gratings were found to be quasi-sinusoidal with up to 265 nm amplitude. Measured highest first-order diffraction efficiencies were around 26% in both Pyrex and IOG glasses. Such gratings could serve as coupling elements in integrated optics and photonic integrated circuits.

Optimizing Spatial Channel Networks (SCNs) in Hierarchical Optical Cross-Connect (HOXC) architectures: Impact of wavelength switching granularity on performance

The increasing demand for network bandwidth highlights the critical need to enhance optical transmission systems. Utilizing the entire C-band for a single optical channel(OCh) eliminates the requirement for wavelength switching, prompting the emergence of spatial channel networks (SCNs). SCNs transform the optical layer into hierarchical spatial division multiplexing (SDM) and wavelength division multiplexing (WDM) layers through the implementation of hierarchical optical cross-connects (HOXCs). A HOXC comprises a spatial channel cross-connect (SXC) for spatial bypass switching and multiple wavelength cross-connects (WXCs) for wavelength channel switching, ensuring efficient optical transmission. Therefore, the design of the HOXC plays a pivotal role in determining both the device cost and network performance in SCNs. This study investigates the impact of wavelength switching granularity on core-selective switch (CSS)-based HOXC architectures. We propose an adaptive dynamic Routing, Spatial Channel, and Spectrum Assignment (RSCSA) algorithm to solve routing and resource allocation problems in SCNs. By examining SCN designs with varying wavelength switching granularities, we assess the overall network deployment cost, considering both network throughput and spectrum resource utilization. Our findings indicate that adjusting the granularity of wavelength switching in SCNs can significantly affect device costs and performance, highlighting the importance of identifying an optimal SCN design that strikes a balance between these factors. These insights offer valuable guidance for the practical planning and management of future SCN deployments.

Broadband and highly efficient asymmetric optical transmission through periodic Si cylinder arrays on the dielectric substrates

Asymmetric optical transmission is widely used in various fields due to the manipulation of light direction. This work theoretically investigates highly efficient and polarization-independent asymmetric optical transmission in the broadband wavelength through the periodic Si cylinder arrays on the dielectric substrates. The simulated results show that the maximum asymmetric optical transmission can reach 0.894, with high forward transmission of 0.898 and nearly zero backward transmission of 0.004 at the wavelength of 540 nm. The structure also exhibits excellent light-trapping characteristics with low energy loss and anti-reflection. The formation of asymmetric optical transmission comes from the diffraction which contributes differently to the transmission under forward and backward illuminations. Furthermore, asymmetric optical transmission in the structure is insensitive to the refractive index of the dielectric substrate and the height of the Si cylinder, and the wavelength position of the maximum asymmetric optical transmission is only sensitive to the height of the Si cylinder. This work proposes a multifunctional nanostructure and provides guidelines for designing practical devices that utilize asymmetric optical transmission.

Efficient LED-Array Optical Wireless Power Transmission System for Portable Power Supply and Its Compact Modularization

Optical wireless power transmission (OWPT) has been a promising solution for remote power supply, eliminating the need for power cables or batteries. In this paper, we propose a light emitting diode (LED) array based OWPT system with improved transmission efficiency and compact system dimension. In this experiment, the proposed four-LED-array collimation scheme achieved a lens system efficiency as high as 70%, while obtaining an electrical power of 0.8 W from a 50 × 50 mm2 GaAs solar cell at 1 m. The emitting side with the lens system was integrated into a 120 × 114 × 61 mm3 portable device by 3D printing. In addition, the thermal performance of the integrated module and the effective surface irradiance at the receiving side were analyzed in detail. The proposed system exhibits high efficiency and portability, with the advantageous potential to temporarily power remote devices.

Constellation Shaped 3D HQAM-DPSK Modulation for Single Wavelength Multi-Dimensional Optical Transmission

A novel concept for single wavelength high spectral-efficient multi-dimensional optical transmission with geometric and probabilistic constellation shaping and bit mapping technique is presented in this study. We propose a simultaneous Hexagonal RF-Quadrature Amplitude Modulation – Differential Phase Shift Keying(HQAM-DPSK) optical modulation for spectral efficient optical transmission. In order to mitigate signal distortion by inter-dimensional interference between intensity and phase, constellation shaping technique is applied to multi-dimensional optical transmission scheme. The validity of the proposed scheme is demonstrated by optical fiber transmission simulation.

Theory of Dronized Laser Source for Next Generation of Optical Wireless Power Transmission

A theory of dronized laser resonator source which can be applied effectively to achieve an efficient remote wireless optical power transmission (WOPT) for the next 6G mobile communications, internet of things (IoT) devices, and continuous flying unmanned aerial vehicles (UAV) is proposed. The proposed laser resonator composes mainly of mirrors and a gain element that can be carried individually by drones to form a relatively long cavity. The airborne components can be assembled according to a specified formation flight of drones to configure a flying laser cavity that exposes its output towards the corresponding target. The stability of the proposed device is theoretically analyzed in terms of main important intracavity parameters, such as length, g-geometrical parameters, and radius of curvature of mirrors. Accordingly, the performance of the confocal symmetric laser resonator is determined in terms of mode size, beam waist size, and beam divergence angle of the fundamental mode in presence of refractive power variation. Simulation results have shown that a stable operation over a wide range of refractive power of confocal long laser resonator can be obtained when the value of curvature of mirror approaches resonator length. In addition, an acceptable fundamental mode size at gain element and mirrors is obtained with an expected efficient gain medium excitation and low diffraction loss.

Feedforward neural network-based chaos encryption method for polarization division multiplexing optical OFDM/OQAM system

Optical orthogonal frequency division multiplexing offset quadrature amplitude modulation （O-OFDM/OQAM), as a technique that has a great potential to provide high spectral efficiency optical transmission in physical layer for future communication systems, faces challenges in data transmission security like malicious eavesdropping. In this letter, a novel twice encryption method based on chaotic mapping and feedforward neural network (FNN) is proposed to achieve the capability of anti-eavesdropping and security enhancement for polarization division multiplexing (PDM) O-OFDM/OQAM system. In the proposed method, the symbols in an OFDM/OQAM block are first used for symbol substitution by the chaotic sequences generated by Lorenz mapping and then permutated by chaotic scrambling vectors generated by FNN. The simulation results show that the FNN-based chaos encryption (FNNCE) method can strengthen the security of data transmission and realize the large key space simultaneously, and without apparent bit error rate (BER) deterioration in comparison with the original system.

Highly Sensitive Photoelectric Detection and Imaging Enhanced by the Pyro-Phototronic Effect Based on a Photoinduced Dynamic Schottky Effect in 4H-SiC.

Silicon carbide (SiC), one of the third-generation semiconductor materials with excellent electrical and optoelectronic properties, is ideal for high light-sensing performance. Here, a self-powered SiC ultraviolet (UV) photodetector (PD) is constructed with wider applicability and higher commercialization potential. The great performance of the PD is realized by a remarkable photoinduced dynamic Schottky effect derived from the symbiotic modulation of Schottky and Ohmic contact. Using the pyro-phototronic effect that exists in the N-doped 4H-SiC single crystal PDs, a fast pyroelectric response time of 0.27 s is achieved, which is almost ten times shorter than that obtained from the steady-state signal under UV illumination. The maximal transient photoresponsivity reaches 9.12 nA mW-1 , which is ≈20% higher than the conventional photoelectric signal. Moreover, different regions of the 4H-SiC centimeter-scale chip output distinct signals under UV illumination, demonstrating efficient optical imaging and information transmission capabilities of this device. This work not only reveals the fundamental optoelectronic physics lying in this vital third-generation semiconductor, but also sheds light on its potential photosensing applications for large-scale commercialization.

Integrated 1 × 3 MEMS silicon nitride photonics switch.

We present a 1 × 3 optical switch based on a translational microelectromechanical system (MEMS) platform with integrated silicon nitride (SiN) photonic waveguides. The fabricated devices demonstrate efficient optical signal transmission between fixed and suspended movable waveguides. We report a minimum average insertion loss of 4.64 dB and a maximum average insertion loss of 5.83 dB in different switching positions over a wavelength range of 1530 nm to 1580 nm. The unique gap closing mechanism reduces the average insertion loss across two air gaps by a maximum of 7.89 dB. The optical switch was fabricated using a custom microfabrication process developed by AEPONYX Inc. This microfabrication process integrates SiN waveguides with silicon-on-insulator based MEMS devices with minimal stress related deformation of the MEMS platform.

Efficient optical duobinary transmission for high-speed next generation passive optical networks

Efficient optical duobinary transmission for high-speed next generation passive optical networks

Modeling and spectral analysis of high speed optical fiber communication with orthogonal frequency division multiplexing

Abstract Optical communication has emerged as the best solution to high-speed transmission systems due to its higher bandwidth and higher data rates. The higher data rates with simple transmitter and receiver modeling are one of the best solutions to design the spectrally efficient high-speed optical transmission system using different modulation techniques. In the recent past, optical communication networks have been specifically designed and optimized to support different communication standards increasing the capabilities of optic fiber, integrated waveguides, and related optical fiber hardware, and signal conditioning circuits. So, this research paper presents a study, modeling, simulation, and analysis of optical performance under different transmission systems which are considered in a practical high-speed design using orthogonal frequency division multiplexing (OFDM). This can be done by using both coherent detection OFDM and direct detection OFDM to minimize dispersion effects in optical communication because OFDM is basic for modern technology to increase the data rate and increase the requirement of bandwidth in broadband services. Many optical fiber problems, such as chromatic dispersion (CD) and polarization mode dispersion (PMD) are solved using OFDM. The performance analyses made in this work by using different parameters such as bit error rate (BER), optical signal-to-noise ratio (OSNR), quality (Q) factor at different distance transmission by using different quadrature modulation such as 4-QAM, 16-QAM, 32-QAM, and 64-QAM to maintain the OSNR value, spectral efficiency, and the required data rates. The simulated results have shown that the coherent detection OFDM and direct detection OFDM with considered QAM provides the best value of BER and quality of the signal at a specific distance.

Simulation of the Effect of Relative Refractive Index for Light Transmission Through Double Cladding Step Index Optical Fibre

This work establishes computational analysis of relative refractive index property for light transmission via fiber optics using MATLAB simulation. Optical fiber is a dielectric wave guide which transmits signal with a low attenuation and dispersion at higher bandwidth or data rate. Recent advances in fiber optics introduced a largely new dimension into optical technology with the effect of improving transmission through the application of cladding system. Cladding in fiber communication is importantly applied to ease light transmission in the fiber-core interface by total internal reflection at the boundary between two light propagation region of a typical fiber. Optical fiber communication is a well recognized aspect of optical light transmission where clad fibers of different refractive indices recount for a measurable Numerical aperture and Acceptance angle in fiber networking and communication technology. This has lead to the efficient and effective optical transmission due to the adequate emergence and utilization of optical properties and parameters in optical fiber applications. A double cladding was set for the fiber and a maximum relative refractive index of 2.000% is obtained for an acceptance angle and numerical aperture range of 59°-64° and 0.859-0.900 respectively. This implies fast light transmission, high bandwidth and small bending sensitivity for fiber networking with applications in medicine and telecommunication compared to single cladding fiber.

Highly efficient asymmetric optical transmission based on the gradient metasurface and subwavelength grating

In this paper, an asymmetric transmission device by combining the gradient metasurface and the subwavelength grating is proposed and investigated numerically. The gradient metasurface produces a transmitted wave with a certain angle upon normal incidence. The subwavelength grating can block light under the condition of normal incidence, although it can transmit light with an angle realized by the gradient metasurface. All materials employed in the proposed device are dielectric. The asymmetric transmission device exhibits high working efficiency and possesses a high-contrast ratio up to 41 dB. Our results are beneficial in designing devices with high-performance asymmetric optical transmission.

Photonic crystal with 2-fold rotational symmetry for highly efficient asymmetric transmission

Here we demonstrate a photonic crystal heterostructure with 2-fold rotational symmetry elliptical shape lattice for highly efficient optical asymmetric transmission based on the self-collimation effect. The forward transmitted light can be collimated along the propagation direction and efficiently coupled out of the structure. Thus, the high forward transmittance up to 0.661 and 0.581 at the telecommunication wavelength of 1550 nm for TE and TM polarized modes can be achieved by this design. The 2-fold rotational symmetry allows further optimizing the structure by tuning the angle between the major axis of the ellipse and the Γ-X direction, and found that high forward transmittance can be achieved when the major axis of the ellipse is along the Γ-X direction.

Practical Innovations Enabling Scalable Optical Transmission Networks: Real-World Trials and Experiences of Advanced Technologies in Field Deployed Optical Networks

We introduce and expand on key high speed optical innovations that enable scalable and efficient optical transmission networks; technologies such as advanced modulation formats including Probabilistic Constellation Shaping (PCS), flexible grid and optical superchannels as well as emerging high speed Ethernet client technology. We describe and show examples of our recent industry leading technology trials giving real-world experiences of leading edge technologies in field deployed network environments. We focus on a recent successful trial of real-time 2 × 200G PCS DP-16QAM superchannel transporting 400 GbE over a 727 km live flexible grid link, achieving high spectral efficiency of 5.33 bit/s/Hz. We also show that 200G PCS DP-16QAM has significantly enhanced performance over the conventional DP-16QAM, achieving a distance of 1454 km. These industry leading trials give network operators crucial understanding of the performance, maturity and operational viability of emerging high speed technologies, and therefore confidence that they are fit for purpose and will allow network operators to scale their networks gracefully to meet increasing bandwidth demands.

Ball Lens Embedded Through-Package Via To Enable Backside Coupling Between Silicon Photonics Interposer and Board-Level Interconnects

Development of an efficient and densely integrated optical coupling interface for silicon photonics based board-level optical interconnects is one of the key challenges in the domain of 2.5D/3D electro-optic integration. Enabling high-speed on-chip electro-optic conversion and efficient optical transmission across package/board-level short-reach interconnections can help overcome the limitations of a conventional electrical I/O in terms of bandwidth density and power consumption in a high-performance computing environment. In this context, we have demonstrated a novel optical coupling interface to integrate silicon photonics with board-level optical interconnects. We show that by integrating a ball lens in a via drilled in an organic package substrate, the optical beam diffracted from a downward directionality grating on a photonics chip can be coupled to a board-level polymer multimode waveguide with a good alignment tolerance. A key result from the experiment was a 14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m chip-to-package 1-dB lateral alignment tolerance for coupling into a polymer waveguide with a cross-section of 20 × 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^2$</tex-math></inline-formula> . An in-depth analysis of loss distribution across several interfaces was done and a −3.4 dB coupling efficiency was measured between the optical interface comprising of output grating, ball lens and polymer waveguide. Furthermore, it is shown that an efficiency better than −2 dB can be achieved by tweaking few parameters in the coupling interface. The fabrication of the optical interfaces and related measurements are reported and verified with simulation results.

On Performance Limits for Spectrally Efficient Optical Transmission Techniques in Short-Haul Metro/Access Links

The demand for transmitting optical signals with high spectral efficiency (SE) by exploiting cost-effective systems and techniques is raising an increasing interest in the area of wide or metro area networks (WAN/MAN). Recently, many different solutions, e.g., amplitude modulation formats, direct-detection schemes, line coding, and simple signal processing techniques have been investigated for wavelength division multiplexing (WDM) short haul optical links, where coherent systems turn out to be economically unfavourable. In this article the Time-Frequency Packing technique, already successfully proposed for long-haul coherent optical links, is extended to direct-detection systems, based on pulse amplitude modulation (PAM) and differential phase-shift keying (DPSK), with the purpose of trading between detection complexity and SE, and of providing performance limits for advanced digital signal processing (DSP) at the receive side.

Overhead-optimization of pilot-based digital signal processing for flexible high spectral efficiency transmission.

We present a low-complexity fully pilot-based digital signal processing (DSP) chain designed for high spectral efficiency optical transmission systems. We study the performance of the individual pilot algorithms in simulations before demonstrating transmission of a 51×24 Gbaud PM-64QAM superchannel over distances reaching 1000 km. We present an overhead optimization technique using the system achievable information rate to find the optimal balance between increased performance and throughput reduction from adding additional DSP pilots. Using the optimal overhead of 2.4%, we report 9.3 (8.3) bits/s/Hz spectral efficiency, or equivalently 11.9 (10.6) Tb/s superchannel throughput, after 480 (960) km of transmission over 80 km spans with EDFA-only amplification. Moreover, we show that the optimum overhead depends only weakly on transmission distance, concluding that back-to-back optimization is sufficient for all studied distances. Our results show that pilot-based DSP combined with overhead optimization can increase the robustness and performance of systems using advanced modulation formats while still maintaining state-of-the-art spectral efficiency and multi-Tb/s throughput.

Highly efficient asymmetric optical transmission by unbalanced excitation of surface evanescent waves in a single—layer dielectric gradient metasurface

Asymmetric optical transmission has recently been demonstrated using Lorentz‒reciprocal devices with patterned photonic structures of linear materials by breaking spatial inversion symmetry. However, it is a huge challenge to fabricate such devices due to their sophisticated multilayer configurations. In this letter, we show that a simple single‒layer dielectric gradient metasurface (GM) enables high-efficiency asymmetric optical transmission under the oblique incidence. The underlying mechanism is ascribed to the unbalanced excitation of surface evanescent waves for forward and backward light. Our results provide strategies for creating compact, integrated and high performance asymmetric optical transmission devices.