Photonics

15 pages, 4723 KiB

Open AccessArticle

A Modified Regular Perturbation Model for the Single-Span Fiber Transmission Using Learnable Methods

by Shuhong He, Zhongya Li, Sizhe Xing, An Yan, Yingjun Zhou, Jianyang Shi, Chao Shen, Ziwei Li, Zhixue He, Wei Chen, Nan Chi and Junwen Zhang

Photonics 2024, 11(12), 1178; https://doi.org/10.3390/photonics11121178 (registering DOI) - 14 Dec 2024

Abstract

In fiber optic communication systems, the dispersion and nonlinear interaction of optical signals are critical to modeling fiber optic communication, and the regular perturbation (RP) model is a simplified modeling method composed of parallel branches, which has obvious advantages in deep learning backpropagation. [...] Read more.

In fiber optic communication systems, the dispersion and nonlinear interaction of optical signals are critical to modeling fiber optic communication, and the regular perturbation (RP) model is a simplified modeling method composed of parallel branches, which has obvious advantages in deep learning backpropagation. In this paper, we propose a simplified single-mode fiber signal transmission model based on the RP model, which significantly improves the fitting accuracy of the model for dispersion and nonlinear interactions at the same complexity by adding trainable parameters to the standard RP model. We explain in the paper that this improvement is applicable to dual-polarization systems and still effective under the conditions of large launch power, without dispersion management, and containing amplified spontaneous emission (ASE) noise. The model uses the standard split-step Fourier method (SSFM) to generate labels and updates parameters through gradient descent method. When transmitting a dual-polarization signal with a launch power of 13 dBm, the modified regular perturbation (MRP) model proposed in the paper can reduce the fitting errors by more than 75% compared to the standard RP model after transmitting through a 120 km standard single-mode fiber. Full article

(This article belongs to the Special Issue Machine Learning Applied to Optical Communication Systems)

► Show Figures

Figure 1

10 pages, 5839 KiB

Open AccessCommunication

Broadband Thermo-Optic Photonic Switch for TE and TM Modes with Adiabatic Design

by Babak Hashemi, Maurizio Casalino, Teresa Crisci, Mohamed Mammeri and Francesco G. Della Corte

Photonics 2024, 11(12), 1177; https://doi.org/10.3390/photonics11121177 (registering DOI) - 14 Dec 2024

Abstract

Optical power switches are essential components in fiber optic communication systems, requiring minimal losses, a broad operating wavelength range, and high tolerance to fabrication errors for optimal performance. Adiabatic optical power switches inherently meet these criteria and are well suited for manufacturing processes [...] Read more.

Optical power switches are essential components in fiber optic communication systems, requiring minimal losses, a broad operating wavelength range, and high tolerance to fabrication errors for optimal performance. Adiabatic optical power switches inherently meet these criteria and are well suited for manufacturing processes which support large-scale production at low costs. This paper presents the design and simulation of an adiabatic switch with a flat response in the whole 1525–1625 nm wavelength range (C band and L band) for both TE and TM polarizations. The switch is based on the thermo-optic effect induced by local variations in temperature. The impacts of the design parameters, such as the device length and dissipated heat, are analyzed. The simulation results indicate that the switch achieved high efficiency and low insertion losses, highlighting the potential of adiabatic switches for reliable and scalable integration into advanced optical circuits. Full article

(This article belongs to the Special Issue Photonics: 10th Anniversary)

► Show Figures

Figure 1

15 pages, 12696 KiB

Open AccessArticle

Coherence Properties of a Supercontinuum Generated by Cascade Raman Processes in a Hollow-Core Fiber Filled with a Mixture of Deuterium and Hydrogen

by Yury Yatsenko, Andrey Pryamikov and Alexey Gladyshev

Photonics 2024, 11(12), 1176; https://doi.org/10.3390/photonics11121176 (registering DOI) - 14 Dec 2024

Abstract

Here, we report a numerical study of supercontinuum generation in an antiresonant optical fiber with a hollow core filled with a mixture of deuterium (D₂) and hydrogen (H₂). For 1 ps pulses at a wavelength of 1.03 μm with [...] Read more.

Here, we report a numerical study of supercontinuum generation in an antiresonant optical fiber with a hollow core filled with a mixture of deuterium (D₂) and hydrogen (H₂). For 1 ps pulses at a wavelength of 1.03 μm with different chirp values, we demonstrate a possibility of obtaining a mid-IR coherent supercontinuum with a spectral width of 2300 nm, initiated by cascade processes at resonance frequencies of vibrational and rotational levels of D₂ and H₂. We show that an increase in the chirped pulse duration to 25 ps while maintaining the energy and spectral width allows increasing the quantum conversion efficiency in the mid-IR from 10 to 50% and expanding the range of optimal fiber lengths at which a high degree of supercontinuum coherence is achieved. Full article

(This article belongs to the Special Issue Cutting-Edge Developments in Fiber Laser)

► Show Figures

Figure 1

21 pages, 12036 KiB

Open AccessArticle

Erbium-Doped Fibers Designed for Random Single-Frequency Lasers Operating in the Extended L-Band

by Denis Lipatov, Alexey Abramov, Alexey Lobanov, Denis Burmistrov, Sergei Popov, Dmitry Ryakhovsky, Yuriy Chamorovskiy, Alexey Bazakutsa, Liudmila Iskhakova, Olga Egorova and Andrey Rybaltovsky

Photonics 2024, 11(12), 1175; https://doi.org/10.3390/photonics11121175 - 13 Dec 2024

Abstract

The paper presents the results of developing Er-doped optical fibers for creating random single-frequency lasers in the wavelength range of 1570–1610 nm. The possibility of broadening the luminescence band of Er³⁺ ions in silicate glasses in the long-wavelength region of the spectrum [...] Read more.

The paper presents the results of developing Er-doped optical fibers for creating random single-frequency lasers in the wavelength range of 1570–1610 nm. The possibility of broadening the luminescence band of Er³⁺ ions in silicate glasses in the long-wavelength region of the spectrum by introducing a high concentration of P₂O₅, as well as by additional doping with Sb₂O₃, is investigated. It is found that both approaches do not improve the dynamics of luminescence decay in the L-band. In addition, Er₂O₃-GeO₂-Al₂O₃-SiO₂ and Er₂O₃-GeO₂-Al₂O₃-Р₂О₅-SiO₂ glasses were studied as the core material for L-band optical fibers. The developed fibers exhibited high photosensitivity and a high gain of 5 and 7.2 dB/m, respectively. In these fibers, homogeneous arrays of extended weakly reflecting Bragg gratings were recorded directly during the fiber drawing process. Samples of arrays 5 m long and with a narrow reflection maximum at ~1590 nm were used as the base for laser resonators. Narrow-band random laser generation in the wavelength region of 1590 nm was recorded for the first time. At a temperature of 295 K, the laser mode was strictly continuous wave and stable in terms of output power. The maximal power exceeded 16 mW with an efficiency of 16%. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

15 pages, 10080 KiB

Open AccessTutorial

Spatial Ensemble Mapping for Coded Aperture Imaging—A Tutorial

by Narmada Joshi, Agnes Pristy Ignatius Xavier, Shivasubramanian Gopinath, Vipin Tiwari and Vijayakumar Anand

Photonics 2024, 11(12), 1174; https://doi.org/10.3390/photonics11121174 - 13 Dec 2024

Abstract

Coded aperture imaging (CAI) is a well-established computational imaging technique consisting of two steps, namely the optical recording of an object using a coded mask, followed by a computational reconstruction using a computational algorithm using a pre-recorded point spread function (PSF). In this [...] Read more.

Coded aperture imaging (CAI) is a well-established computational imaging technique consisting of two steps, namely the optical recording of an object using a coded mask, followed by a computational reconstruction using a computational algorithm using a pre-recorded point spread function (PSF). In this tutorial, we introduce a simple yet elegant technique called spatial ensemble mapping (SEM) for CAI that allows us to tune the axial resolution post-recording from a single camera shot recorded using an image sensor. The theory, simulation studies, and proof-of-concept experimental studies of SEM-CAI are presented. We believe that the developed approach will benefit microscopy, holography, and smartphone imaging systems. Full article

(This article belongs to the Special Issue Optical Imaging Innovations and Applications)

► Show Figures

Figure 1

12 pages, 20525 KiB

Open AccessCommunication

Performance Analysis of Chirped Graded Photonic Crystal Resonator for Biosensing Applications

by Jasmine Saini, Ajay Kumar and Amit Kumar Goyal

Photonics 2024, 11(12), 1173; https://doi.org/10.3390/photonics11121173 - 13 Dec 2024

Abstract

In this manuscript, a chirped graded photonic crystal (PhC) resonator structure is optimized for biosensing applications. The proposed structure comprises a bilayer PhC with an aqueous defect layer, where the thickness grading within the material is introduced, considering alpha (

α

) as [...] Read more.

In this manuscript, a chirped graded photonic crystal (PhC) resonator structure is optimized for biosensing applications. The proposed structure comprises a bilayer PhC with an aqueous defect layer, where the thickness grading within the material is introduced, considering alpha (

α

) as a grading parameter. The device performance is analytically evaluated using the finite element method (FEM). The impact of

α

, the resonator thickness, and the incidence angle on the device performance is analyzed. Further, the device’s ability to be used as a biosensor is evaluated, considering cholesterol as an analyte. The analytical results demonstrate an average sensitivity of 410 nm/RIU, a quality factor of 0.91 ×

10^{3}

, and a figure of merit (FOM) of 2.47 ×

10^{2}

{RIU}^{- 1}

, showing 88.5% and 43% improvements in sensitivity and FOM compared to recently reported devices. The device’s superior sensing performance makes it suitable for medical and commercial applications, while the use of thickness grading addresses fabrication limitations, offering a robust framework for advanced photonic device design. Full article

(This article belongs to the Section Optical Interaction Science)

► Show Figures

Figure 1

19 pages, 9326 KiB

Open AccessArticle

U-Net Driven High-Resolution Complex Field Information Prediction in Single-Shot Four-Step Phase-Shifted Digital Holography Using Polarization Camera

by Askari Mehdi, Yongjun Lim, Kwan-Jung Oh and Jae-Hyeung Park

Photonics 2024, 11(12), 1172; https://doi.org/10.3390/photonics11121172 - 12 Dec 2024

Abstract

We present a novel high-resolution complex field extraction technique utilizing U-Net-based architecture to effectively overcome the inherent resolution limitations of polarization cameras with micro-polarized arrays. Our method extracts high-resolution complex field information, achieving a resolution comparable to that of the original polarization camera. [...] Read more.

We present a novel high-resolution complex field extraction technique utilizing U-Net-based architecture to effectively overcome the inherent resolution limitations of polarization cameras with micro-polarized arrays. Our method extracts high-resolution complex field information, achieving a resolution comparable to that of the original polarization camera. Utilizing the parallel phase-shifting digital holography technique, we extracted high-resolution complex field information from four high-resolution phase-shifted interference patterns predicted by our network directly at the hologram plane. Extracting the object’s complex field directly at the hologram plane rather than the object’s plane, our method eliminates the dependency on numerical propagation during dataset acquisition, enabling reconstruction of objects at various depths without DC and conjugate noise. By training the network with real-valued interference patterns and using only a single pair of low- and high-resolution input and ground truth interference patterns, we simplify computational complexity and improve efficiency. Our simulations demonstrate the network’s robustness to variations in random phase distributions and transverse shifts in the input patterns. The effectiveness of the proposed method is demonstrated through numerical simulations, showing an average improvement of over 4 dB in peak-signal-to-noise ratio and 25% in intensity normalized cross-correlation metrics for object reconstruction quality. Full article

(This article belongs to the Special Issue Holographic Information Processing)

► Show Figures

Figure 1

16 pages, 1254 KiB

Open AccessArticle

The Optimization Guidance of Hollow Antiresonant Fibers Based on Various Optimization Methods

by Lina Guo, Biyou Jiang, Zhiyu Chang, Yu Li, Xueqin Sun, Sukai Wang, Ping Chen, Deqing Niu and Zihan Liu

Photonics 2024, 11(12), 1171; https://doi.org/10.3390/photonics11121171 (registering DOI) - 12 Dec 2024

Abstract

This paper employs five different general-purpose optimization methods to perform parameter optimization on single-layer hollow antiresonant fibers. It provides guidance on the establishment of hyperparameters for various optimization methods, with the aim of further defining and standardizing the necessary conditions and convergence criteria [...] Read more.

This paper employs five different general-purpose optimization methods to perform parameter optimization on single-layer hollow antiresonant fibers. It provides guidance on the establishment of hyperparameters for various optimization methods, with the aim of further defining and standardizing the necessary conditions and convergence criteria for applying optimization algorithms to specialty optical fibers. Through numerical experiments, the study ultimately obtains the converged optimal performance and the range of optimized parameter guidance for single-layer, double-layer, and triple-layer antiresonant fibers with different topological structures. Full article

(This article belongs to the Special Issue Recent Advances in Hollow-Core Fiber Optics: Design, Fabrication, and Applications)

► Show Figures

Figure 1

12 pages, 16440 KiB

Open AccessCommunication

Resolution Enhancement of Geometric Phase Self-Interference Incoherent Digital Holography Using Synthetic Aperture

by Youngrok Kim, KiHong Choi, Keehoon Hong and Sung-Wook Min

Photonics 2024, 11(12), 1170; https://doi.org/10.3390/photonics11121170 - 12 Dec 2024

Abstract

Incoherent digital holography is a promising solution for acquiring three-dimensional information in the form of interference without a laser. Self-interference is the principal phenomenon of incoherent holography which splits the incident light wave into two waves and interferes with each one. The characteristics [...] Read more.

Incoherent digital holography is a promising solution for acquiring three-dimensional information in the form of interference without a laser. Self-interference is the principal phenomenon of incoherent holography which splits the incident light wave into two waves and interferes with each one. The characteristics of incoherent holograms are defined by the optical configuration of wavefront dividing units. In this paper, we propose the synthetic aperture method to achieve super-resolution of geometric phase lens-based self-interference incoherent digital holography. We analyze the resolution of incoherent holograms acquired from geometric phase lenses and experimentally demonstrate the resolution enhancement via the synthetic-aperture method. Moreover, the sparse synthetic-aperture method is proposed to ensure effective data capturing and the numerical optimization method is also proposed to fill the gap between the empty space of sparsely acquired holograms. Full article

(This article belongs to the Special Issue Optical Imaging Innovations and Applications)

► Show Figures

Figure 1

19 pages, 2520 KiB

Open AccessArticle

Super Broad Non-Hermitian Line Shape from Out-of-Phase and In-Phase Photon-Phonon Dressing in Eu³⁺: NaYF₄ and Eu³⁺: BiPO₄

by Muhammad Kashif Majeed, Muhammad Usman, Iqbal Hussain, Usman Javed, Muhammad Qasim Khan, Faisal Nadeem, Faisal Munir, Huanrong Fan, Yin Cai and Yanpeng Zhang

Photonics 2024, 11(12), 1169; https://doi.org/10.3390/photonics11121169 - 12 Dec 2024

Abstract

We report super broad non-Hermitian line shape from out-of-phase and in-phase photon-phonon dressing (quantization) in Eu³⁺: NaYF₄ and Eu³⁺: BiPO₄ nanocrystals. The line shape is controlled by changing time gate position, time gate width, power, temperature, sample, [...] Read more.

We report super broad non-Hermitian line shape from out-of-phase and in-phase photon-phonon dressing (quantization) in Eu³⁺: NaYF₄ and Eu³⁺: BiPO₄ nanocrystals. The line shape is controlled by changing time gate position, time gate width, power, temperature, sample, photomultiplier tubes, and laser. We observed that the fluorescence (FL) line-shape contrasts are 69.23% for Eu³⁺: BiPO₄ and 43.75% for Eu³⁺: NaYF₄, owing to the stronger out-of-phase photon-phonon dressing (destructive quantization). Moreover, we observed that the spontaneous four-wave mixing (SFWM) line shape was approximately three times wider at 300 K than at 77 K for the [(12:1)-phase] Eu³⁺: NaYF₄ due to more high-frequency in-phase phonon dressing (strong constructive quantization). Furthermore, we showed that the noise line-shape width remains unchanged for Eu³⁺: BiPO₄ (16 nm) and Eu³⁺: NaYF₄ (12 nm) due to out-of-phase and in-phase photon-phonon dressing balance. Such results have potential applications in multi-channel band stop filter. Full article

► Show Figures

Figure 1

12 pages, 2268 KiB

Open AccessArticle

An Ultrafast Optical Imaging System with Anamorphic Transformation Based on STEAM Structure

by Guoqing Wang, Yuan Zhou, Rui Min, Fang Zhao, E Du, Xingquan Li, Cong Qiu, Dongrui Xiao and Chao Wang

Photonics 2024, 11(12), 1168; https://doi.org/10.3390/photonics11121168 - 12 Dec 2024

Abstract

The time-stretch (TS) imaging system is one type of ultrafast optical imaging system that enables imaging with an unprecedented imaging speed of tens of hundreds of megahertz. The TS imaging achieves linear one-to-one mapping between wavelength and time using a temporal dispersive medium. [...] Read more.

The time-stretch (TS) imaging system is one type of ultrafast optical imaging system that enables imaging with an unprecedented imaging speed of tens of hundreds of megahertz. The TS imaging achieves linear one-to-one mapping between wavelength and time using a temporal dispersive medium. However, the data issue of high throughput and the fixed resolution in TS imaging limits its wide applications. In this paper, we propose an ultrafast optical imaging system with anamorphic transformation (AT) based on the STEAM structure, which has the benefit of data compression and changing group delay-related resolution. AT is obtained by the usage of chirped fiber Bragg grating (CFBG) with a nonlinear group delay profile. A state-of-the-art experimental demonstration shows that more acquired data are employed to describe the dense information region and the group delay-related resolution is improved by 58% using our proposed ultrafast optical imaging system without reducing the line scanning speed of 50 MHz. The proposal could increase the group delay-related resolution of the target image without adding extra data acquisition or changing the system setup, which has great potential in ultrafast optical imaging systems. Furthermore, the AT in our proposal could also be applied to data compression algorithms to mitigate the data issue in ultrafast optical imaging systems. Full article

► Show Figures

Figure 1

9 pages, 13511 KiB

Open AccessCommunication

Polarization-Independent Focusing Vortex Beam Generation Based on Ultra-Thin Spiral Diffractive Lens on Fiber End-Facet

by Luping Wu, Zhiyong Bai, Rui Liu, Yuji Wang, Jian Yu, Jianjun Ran, Zikai Chen, Zilun Luo, Changrui Liao, Ying Wang, Jun He, George Y. Chen and Yiping Wang

Photonics 2024, 11(12), 1167; https://doi.org/10.3390/photonics11121167 - 11 Dec 2024

Abstract

An ultra-thin spiral diffractive lens (SDL) was fabricated by using focused ion beam milling on a fiber end-facet coated with a 100 nm thick Au film. Focusing vortex beams (FVBs) were successfully excited by the SDLs due to the coherent superposition of diffracted [...] Read more.

An ultra-thin spiral diffractive lens (SDL) was fabricated by using focused ion beam milling on a fiber end-facet coated with a 100 nm thick Au film. Focusing vortex beams (FVBs) were successfully excited by the SDLs due to the coherent superposition of diffracted waves and their azimuth dependence of the phase accumulated from the spiral aperture to the beam axis. The polarization and phase characteristics of the FVBs were experimentally investigated. Results show that the input beams with various polarization states were converted to FVBs, whose polarization states were the same as those of the input beams. Furthermore, the focal length of the SDL and the in-tensity and phase distribution at the focus spot of the FVBs were numerically simulated by the FDTD method in the ultra-wide near-infrared waveband from 1300 nm to 1800 nm. The focal length was tuned from 21.8 μm to 14.7 μm, the intensity profiles exhibited a doughnut-like shape, and the vortex phase was converted throughout the broadband range. The devices are expected to be candidates for widespread applications including optical communications, optical imaging, and optical tweezers. Full article

► Show Figures

Figure 1

11 pages, 1398 KiB

Open AccessCommunication

Conversion of Arbitrary Three-Dimensional Polarization States to Regular States via Spin Cancellation

by José J. Gil

Photonics 2024, 11(12), 1166; https://doi.org/10.3390/photonics11121166 - 11 Dec 2024

Abstract

The present work is motivated by the necessity of handling and controlling three-dimensional polarization states, whose appropriate preparation has increasing interest in areas like nanotechnologies, quantum computing and near-field phenomena. By virtue of the so-called characteristic decomposition, any polarization state of light can [...] Read more.

The present work is motivated by the necessity of handling and controlling three-dimensional polarization states, whose appropriate preparation has increasing interest in areas like nanotechnologies, quantum computing and near-field phenomena. By virtue of the so-called characteristic decomposition, any polarization state of light can be represented as an incoherent superposition of a pure state, a fully unpolarized state and a discriminating state. The discriminating component has nonzero spin in general, in which case the state is said to be nonregular. A simple procedure to transform an arbitrary nonregular state to a regular one through its incoherent composition with a pure state is described, resulting in a state that lacks a discriminating component. In addition, a method to suppress the spin vector of any given polarization state through its incoherent combination with a circularly polarized pure state is presented. Both approaches allow for the configuration of polarization states with simple features. Full article

► Show Figures

Figure 1

11 pages, 4652 KiB

Open AccessArticle

Improving 795 nm Single-Frequency Laser’s Frequency Stability by Means of the Bright-State Spectroscopy with Rubidium Vapor Cell

by Junye Zhao, Yongbiao Yang, Lulu Zhang, Yang Li and Junmin Wang

Photonics 2024, 11(12), 1165; https://doi.org/10.3390/photonics11121165 - 11 Dec 2024

Abstract

The utilization of atomic or molecular spectroscopy for frequency locking of single-frequency laser to improve laser frequency stability plays an important role in the experimental investigation of optically pumped atomic magnetometers, atomic clocks, laser cooling and trapping of atoms, etc. We have experimentally [...] Read more.

The utilization of atomic or molecular spectroscopy for frequency locking of single-frequency laser to improve laser frequency stability plays an important role in the experimental investigation of optically pumped atomic magnetometers, atomic clocks, laser cooling and trapping of atoms, etc. We have experimentally demonstrated a technique for frequency stabilization of a single-frequency laser employing the bright state spectroscopy (BSS) with a rubidium atomic vapor cell. By utilizing the counter-propagating dual-frequency 795 nm laser beams with mutually orthogonal linear polarization and a frequency difference of 6.834 GHz, which is equal to the hyperfine splitting of rubidium-87 ground state 5

S_{1 / 2}

, an absorption-enhanced signal with narrow linewidth at the center of Doppler-broadened transmission spectroscopy is observed when continuous scanning the laser frequency over rubidium-87 D1 transition. This is the so-called BSS. Amplitude of the absorption-enhanced signal in the BSS is much larger compared with the conventional saturation absorption spectroscopy (SAS). The relationship between linewidth and amplitude of the BSS signal and laser beam intensity has been investigated. This high-contrast absorption-enhanced BSS signal has been employed for the laser frequency stabilization. The experimental results show that the frequency stability is

4.4 \times 10^{- 11}

with an integration time of 40 s, near one order of magnitude better than that for using the SAS. Full article

► Show Figures

Figure 1

24 pages, 12348 KiB

Open AccessReview

Advances in Soliton Crystal Microcombs

by Zhihui Liu, Haoran Zhang, Yuhang Song, Xiaotian Zhu, Caitlin E. Murray, Yunping Bai, Mengxi Tan, Sai T. Chu, David J. Moss, Xingyuan Xu and Kun Xu

Photonics 2024, 11(12), 1164; https://doi.org/10.3390/photonics11121164 - 11 Dec 2024

Abstract

Soliton crystal microcombs, as a new type of Kerr frequency comb, offer advantages such as higher energy conversion efficiency and a simpler generation mechanism compared to those of traditional soliton microcombs. They have a wide range of applications in fields like microwave photonics, [...] Read more.

Soliton crystal microcombs, as a new type of Kerr frequency comb, offer advantages such as higher energy conversion efficiency and a simpler generation mechanism compared to those of traditional soliton microcombs. They have a wide range of applications in fields like microwave photonics, ultra-high-speed optical communication, and photonic neural networks. In this review, we discuss the recent developments regarding soliton crystal microcombs and analyze the advantages and disadvantages of generating soliton crystal microcombs utilizing different mechanisms. First, we briefly introduce the numerical model of optical frequency combs. Then, we introduce the generation schemes for soliton crystal microcombs based on various mechanisms, such as utilizing an avoided mode crossing, harmonic modulation, bi-chromatic pumping, and the use of saturable absorbers. Finally, we discuss the progress of research on soliton crystal microcombs in the fields of microwave photonics, optical communication, and photonic neural networks. We also discuss the challenges and perspectives regarding soliton crystal microcombs. Full article

(This article belongs to the Section Optoelectronics and Optical Materials)

► Show Figures

Figure 1

9 pages, 2649 KiB

Open AccessArticle

Photonic Generation of Multiband and Multi-Format Chirped Microwave Waveforms Based on an Optoelectronic Oscillator

by Jinfeng Du, Fangping Li, Huiyun Tang, Zexuan Kong, Ming Li and Wei Li

Photonics 2024, 11(12), 1163; https://doi.org/10.3390/photonics11121163 - 11 Dec 2024

Abstract

We propose and demonstrate a microwave photonic system to generate multiband and multi-format microwave waveforms based on an actively mode-locked optoelectronic oscillator (AML-OEO) using a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). In the proposed system, the upper DDMZM is injected by two baseband single-chirped [...] Read more.

We propose and demonstrate a microwave photonic system to generate multiband and multi-format microwave waveforms based on an actively mode-locked optoelectronic oscillator (AML-OEO) using a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). In the proposed system, the upper DDMZM is injected by two baseband single-chirped signals, and the lower DDMZM is biased to realize single-sideband (SSB) modulation using a 90° hybrid coupler. The lower DDMZM is also used to construct an AML-OEO loop, which outputs microwave frequency comb signals. By setting the phase difference in the applied two single-chirped signals, multiband up-, down-, and dual-chirped microwave signals are successfully generated. Furthermore, the tunability of the system can be realized by adjusting the frequency and power of the injection signal in the AML-OEO loop, the passband of the electrical filter, and the chirp rate of the single-chirped signal. The proposed scheme is theoretically analyzed and experimentally verified. Full article

(This article belongs to the Special Issue Optoelectronic Oscillators (OEO): Principles and Applications)

► Show Figures

Figure 1

24 pages, 6573 KiB

Open AccessArticle

Performance Analysis of Parallel Free-Space Optical/Radio Frequency Transmissions in Satellite–Aerial–Ground Integrated Network with Power Allocation

by Xin Li, Yongjun Li, Shanghong Zhao, Xinkang Song and Jianjia Li

Photonics 2024, 11(12), 1162; https://doi.org/10.3390/photonics11121162 - 9 Dec 2024

Abstract

Satellite–aerial–ground integrated networks (SAGINs) combined with hybrid free-space optical (FSO) and radio frequency (RF) transmissions have shown great potential in improving service throughput and reliability. The coverage mismatch and rate limitation of traditional hybrid FSO/RF design have restricted its development. In this paper, [...] Read more.

Satellite–aerial–ground integrated networks (SAGINs) combined with hybrid free-space optical (FSO) and radio frequency (RF) transmissions have shown great potential in improving service throughput and reliability. The coverage mismatch and rate limitation of traditional hybrid FSO/RF design have restricted its development. In this paper, we investigate the performance of parallel FSO/RF transmissions in SAGIN, taking into account the effect of weather conditions and the quality of service (QoS) of ground users. A three-hop relay system is proposed, where the FSO and RF links jointly provide services to ground users in remote areas. Specifically, considering the limited transmit power of the relay node, we have studied the optimal power allocation between parallel FSO and RF links to further improve system energy efficiency. The performance of the proposed system is evaluated in terms of capacity outage probability, weighted average bit-error rate (BER), and energy efficiency. Moreover, asymptotic capacity outage probability is also derived to obtain more engineering insights. Finally, numerical results show that the energy efficiency of the proposed parallel scheme improves by 30.9% compared to only the FSO scheme at a total transmit power of 15 dBW. Full article

(This article belongs to the Special Issue Challenges and Opportunities in Optical Wireless Communications for beyond Fifth and Sixth Generations Networks)

► Show Figures

Figure 1

17 pages, 7298 KiB

Open AccessArticle

Temperature-Dependent Raman Scattering and Correlative Investigation of AlN Crystals Prepared Using a Physical Vapor Transport (PVT) Method

by Zhe Chuan Feng, Manika Tun Nafisa, Yao Liu, Li Zhang, Yingming Wang, Xiaorong Xia, Ze Tao, Chuanwei Zhang, Jeffrey Yiin, Benjamin Klein and Ian Ferguson

Photonics 2024, 11(12), 1161; https://doi.org/10.3390/photonics11121161 - 9 Dec 2024

Abstract

Ultrawide bandgap (UWBG) AlN c- and m-face crystals have been prepared using the physical vapor transport (PVT) method and studied penetratively using temperature-dependent (TD) Raman scattering (RS) measurements under both visible (457 nm) and DUV (266 nm) excitations in 80–870 K, plus correlative [...] Read more.

Ultrawide bandgap (UWBG) AlN c- and m-face crystals have been prepared using the physical vapor transport (PVT) method and studied penetratively using temperature-dependent (TD) Raman scattering (RS) measurements under both visible (457 nm) and DUV (266 nm) excitations in 80–870 K, plus correlative atomic force microscopy (AFM) and variable-angle (VA) spectroscopic ellipsometry (SE). VASE identified their band gap energy as 6.2 eV, indicating excellent AlN characteristics and revealing Urbach energy levels of about 85 meV. Raman analyses revealed the residual tensile stress. TDRS shows that the E₂(high) phonon lifetime decayed gradually in the 80–600 K range. Temperature has the greater influence on the stress of m-face grown AlN crystal. The influence of low temperature on the E₂(high) phonon lifetime of m-plane AlN crystal is greater than that of the high-temperature region. By way of the LO-phonon and plasma coupling (LOPC), simulations of A₁(LO) modes and carrier concentrations along different faces and depths in AlN crystals are determined. These unique and significant findings provide useful references for the AlN crystal growth and deepen our understanding on the UWBG AlN materials. Full article

(This article belongs to the Special Issue Research, Development and Application of Raman Scattering Technology)

► Show Figures

Figure 1

13 pages, 16111 KiB

Open AccessArticle

Simple Design of Polarization-Selective Tunable Triple Terahertz Absorber Based on Graphene Rectangular Ring Resonator

by Jiang Wang, Haixia Zhu, Bo Ni, Minhao Zhou, Chengtao Feng, Haibin Ni and Jianhua Chang

Photonics 2024, 11(12), 1160; https://doi.org/10.3390/photonics11121160 - 9 Dec 2024

Abstract

In this paper, a simple design of a polarization-selective tunable triple terahertz absorber based on a graphene rectangular ring resonator was proposed and studied. The absorber structure consists of a graphene rectangular ring resonant array on the top, SiO₂ dielectric layer in [...] Read more.

In this paper, a simple design of a polarization-selective tunable triple terahertz absorber based on a graphene rectangular ring resonator was proposed and studied. The absorber structure consists of a graphene rectangular ring resonant array on the top, SiO₂ dielectric layer in the middle and gold at the bottom. The calculated results show that the absorber can achieve high-efficiency triple-band absorption under both x and y polarization incident light. When x-polarized light is incident, three distinctive absorption peaks at 2.73, 5.70 and 11.19 THz with absorption rates of 96.7%, 98.5% and 96.5% are achieved. When y-polarized light is incident, three additional absorption peaks at 2.29, 7.55 and 9.98 THz can be obtained with absorption rates of 96.3%, 90.3% and 97.4%, respectively. Moreover, the absorption wavelength of the absorber can be tuned by adjusting the chemical potential of the graphene. Owing to the high efficiency of triple-band absorption in different polarization states, the absorber has broad application prospects in terahertz polarization imaging, sensing and detection. Full article

(This article belongs to the Section New Applications Enabled by Photonics Technologies and Systems)

► Show Figures

Figure 1

Journal Description

Photonics

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Further Information

Guidelines

MDPI Initiatives

Follow MDPI