Hasil untuk "Applied optics. Photonics"

Janpeter Hirsch, Simon Kubitza, Max Schiemangk et al.

We present a robust and compact micro-integrated, frequency-tunable, optical frequency reference module developed to improve the long-term frequency stability of lasers in quantum technology and satellite laser communication applications. The module is based on a volume holographic Bragg grating (VHBG) and features a multi-level temperature stabilization concept, packaged into a sealed housing with dimensions of <inline-formula><tex-math notation="LaTeX">$96\,\times \,96\,\times \,35\,\text{mm}^{3}$</tex-math></inline-formula>. The module has a frequency tuning range of more than <inline-formula><tex-math notation="LaTeX">$\text{65}\,\text{GHz}$</tex-math></inline-formula> with a near-linear behavior. We demonstrate short-term frequency stabilities between <inline-formula><tex-math notation="LaTeX">$2 \times 10^{5}\,\text{Hz}^{2}/\text{Hz}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$4 \times 10^{7}\,\text{Hz}^{2}/\text{Hz}$</tex-math></inline-formula> in the Fourier frequency range from <inline-formula><tex-math notation="LaTeX">$\text{20}\,\text{Hz}$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$\text{200}\,\text{kHz}$</tex-math></inline-formula>, and a minimum overlapping Allan deviation of <inline-formula><tex-math notation="LaTeX">$\sigma (\tau =1000\,s) = 1.7 \times 10^{-10}$</tex-math></inline-formula>, and <inline-formula><tex-math notation="LaTeX">$1.5 \times 10^{-9}$</tex-math></inline-formula> over 24<inline-formula><tex-math notation="LaTeX">$\,$</tex-math></inline-formula>h. The module can also be operated as a wavemeter and spectrometer, yielding residuals below <inline-formula><tex-math notation="LaTeX">$\text{0.33}\,\text{GHz}$</tex-math></inline-formula> with second-order polynomial regression calibration, and reliably measuring frequency noise PSDs of lasers whose noise exceeds that of the reference module.

Mikhail I. Skvortsov, Kseniya V. Kolosova, Alexander V. Dostovalov et al.

A high-resolution temperature sensor using the beat frequency measurement between the modes of two DFB fiber lasers is presented. The laser cavities are formed by the femtosecond inscription technique in a highly Er/Yb co-doped phosphosilicate fiber with low optical losses and compact design. The experimental results show a sensitivity of 1 GHz/°C, leading to a temperature resolution of 0.02 °C restricted by the thermistor used in the experiment. The maximum possible resolution determined by the laser linewidth is estimated as 2 × 10⁻⁶ °C. The operation of such a sensor at high temperatures (≈750 °C) with the possibility of further temperature increase is demonstrated. The combination of high resolution and broad temperature range makes the sensor attractive for various applications, especially in high-temperature monitoring.

J. Goswami, V. Senpakapriya, C. Goswami et al.

Agriculture faces unprecedented challenges due to the increasing frequency and severity of natural disasters and extreme weather events. Agriculture sector needs resilience to support food production and livelihoods because it is susceptible to cyclones, floods, droughts, soil erosion, pests, and disease outbreaks. Geospatial technology plays a significant role in disaster management for agriculture, offering tools for preparedness, response, and recovery. This study explores the role of geospatial technology in early warning systems and risk assessment for different types of natural disasters that impact agriculture activity. Sustainable farming practices that are essential for resilience include crop diversity, climate-resilience varieties, and adaptation strategies. Capacity building and training are vital for effective geospatial technology utilization, especially in developing countries like India, where infrastructure and technology access may be limited. Tailored capacity-building programs are essential, emphasizing climate-smart practices, sustainable land management, and post-disaster recovery strategies. Access to financial services and insurance schemes enhances resilience by helping farmers cope with losses and recover from disasters. In order to improve resilience and sustainability in agriculture, geospatial decision support systems make it possible to evaluate alternative planning, optimise resource allocation, and implement adaptive management.

Ayaka Mori, Kyohei Yamashita, Eiji Tokunaga

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David Benton, Yiming Li, Antonin Billaud et al.

Multi-plane light converters (MPLC) are a means of deconstructing a wavefront into constituent modes that are focused at specific spatial locations, and the reverse—that specific inputs result in controlled modal output. We have used a pair of MPLCs with 21 Hermite–Gaussian modes to represent a free-space optical connection. The effects of strong atmospheric turbulence (C_n² = 10⁻¹³ m^−2/3) are emulated using a micromirror array producing a time sequence of aberrating frames. The modal crosstalk between transmitter and receiver modes induced by the turbulence is presented by measuring the intensity in receiver channels for the same turbulence. Six receiver modes are used for optical communication channels with a rate of 137 Gbits/s displaying the benefits of single input multiple output (SIMO) operation for overcoming the deleterious effects of turbulence.

Jesús E. Gómez-Correa, Brian Vohnsen, Barbara K. Pierścionek et al.

The field of visual and physiological optics is undergoing continuous significant advancements, driven by a deeper understanding of the human visual system and the development of cutting-edge optical technologies. This Roadmap, authored by leading experts, delves into critical areas such as corneal biomechanical properties, keratoconus, and advancements in corneal imaging and elastography. It explores the intricate structure-function relationship within the eye lens, offering new perspectives through lens models and ray tracing techniques. The document also covers advancements in retinal imaging, highlighting the current state and future directions, and the role of adaptive optics in evaluating retinal structure and function in both healthy and diseased eyes. Furthermore, it addresses the modelling of ocular surfaces using different mathematical functions and examines the factors affecting peripheral image quality in the human eye, emphasizing the importance of these aspects in visual performance. Additional topics include schematic and functional models of the human eye, the impact of optical and chromatic aberrations, and the design of contact, and intraocular lenses. Finally, the Roadmap addresses the intersection of neurosciences with vision health, presenting a comprehensive overview of current research and future trends aimed at improving visual health and optical performance. Ultimately, this Roadmap aims to serve as a valuable resource for ophthalmologists, optometrists, vision scientists, and engineers dedicated to advancing the field of visual and physiological optics.

Xinyue Niu, Qilin Wu, Bin Wang et al.

Photoconductive semiconductors operating in linear mode can be used for adaptive high-power microwave (HPM) generators by modulating incident light. This paper presents the design scheme and preliminary test results of a narrowband kW class adaptive photonic microwave generator by employing a wide-bandgap semi-insulating 6H-SiC photoconductive semiconductor and a burst-mode laser. The experimental scheme of the generator is described along with the circuit simulation of the radio frequency generator. The laser operated at a wavelength of 532 nm with a pulse width of 100 ns and a repetition rate of 100 Hz. The laser modulates the frequencies of the generated microwave, and preliminary tests are conducted in the frequency range of 0.8&#x2013;1.2 GHz. The maximum output microwave power of the designed scheme reaches up to 2.6 kW when the bias voltage is 10 kV. The results confirm that this method can be used for high-power frequency-adjustable microwave signal generation. The microwave source system presented in this paper has continuously adjustable frequency and flexible waveform control.

Rahul Kumar Gangwar, Sneha Kumari, Akhilesh Kumar Pathak et al.

The current generation is witnessing a huge interest in optical waveguides due to their salient features: they are of low cost, immune to electromagnetic interference, easy to multiplex, have a compact size, etc. These features of optical fibers make them a useful tool for various sensing applications including in medicine, automotives, biotechnology, food quality control, aerospace, physical and chemical monitoring. Among all the reported applications, optical waveguides have been widely exploited to measure the physical and chemical variations in the surrounding environment. Optical fiber-based temperature sensors have played a crucial role in this decade to detect high fever and tackle COVID-19-like pandemics. Recognizing the major developments in the field of optical fibers, this article provides recent progress in temperature sensors utilizing several sensing configurations including conventional fiber, photonic crystal fiber, and Bragg grating fibers. Additionally, this article also highlights the advantages, limitations, and future possibilities in this area.

Kaili Sun, Hui Jiang, D. Bykov et al.

Qing-An Huang

Parity (P)-Time (T) symmetry is the concept of quantum mechanics and has been extended to classical systems because of the mathematical equivalence between the Schrödinger equation and the classical wave equation. PT-symmetric systems are invariant under the joint parity and time reversal operation. They have two distinguished regimes: an exact PT-symmetric regime with real eigenvalues and a broken PT-symmetric regime with complex-conjugate eigenvalues. An exceptional point (EP) at which the eigenvalues and corresponding eigenvectors simultaneously coalesce separates the exact regime from the broken regime. Systems at the EPs exhibit a strong response to a small perturbation. Therefore, EPs-based sensors have recently received significant attention in optics and photonics, acoustics, and electronics. Our group has applied PT-symmetry to MEMS (Microelectromchanical Systems) design, leading to enhanced sensing of micromachined silicon resonators and piezoelectric resonators, respectively. This article presents the preliminary results of PT-symmetric MEMS.

Ronja Köthemann, Christian Golla, Hong Qu et al.

We study the influence of gold nanoantennas on the photoluminescence signal of silicon nanocrystals. Unlike bulk silicon, which only exhibits low photoluminescence at room temperature due to its indirect band gap, silicon nanocrystals have the advantage of producing strong and size-dependent photoluminescence. Here, we place gold nanoantennas on a layered system in which silicon nanocrystals are integrated. The nanoantennas are embedded in the layered system by subsequent overgrowth. We find that the photoluminescence signal can be manipulated ranging from attenuation to enhancement. Moreover, we investigate the impact of grating coupling and the number of antennas per antenna array on the amplification of the photoluminescence signal.

Joseph E. Golec, Shreya Sutariya, Rebecca Jackson et al.

We present the design, fabrication, and measured performance of metamaterial Anti-Reflection Cuttings (ARCs) for large-format alumina filters operating over more than an octave of bandwidth to be deployed on the Simons Observatory (SO). The ARC consists of sub-wavelength features diced into the optic's surface using a custom dicing saw with near-micron accuracy. The designs achieve percent-level control over reflections at angles of incidence up to 20$^\circ$. The ARCs were demonstrated on four 42 cm diameter filters covering the 75-170 GHz band and a 50 mm diameter prototype covering the 200-300 GHz band. The reflection and transmission of these samples were measured using a broadband coherent source that covers frequencies from 20 GHz to 1.2 THz. These measurements demonstrate percent-level control over reflectance across the targeted pass-bands and a rapid reduction in transmission as the wavelength approaches the length scale of the metamaterial structure where scattering dominates the optical response. The latter behavior enables the use of the metamaterial ARC as a scattering filter in this limit.

M. Negri, L. Francaviglia, D. Kaplan et al.

MoS2 micro-pyramids have demonstrated interesting properties in the fields of photonics and non-linear optics. In this work, we show the excitonic absorption and cathodoluminescence (CL) emission of MoS2 micro-pyramids grown by chemical vapor deposition (CVD) on SiO2 substrates. The excitonic absorption was obtained at room and cryogenic temperatures by taking advantage of the cathodoluminescence emission of the SiO2 substrate. We detected the CL emission related to defect intra-gap states, localized at the pyramid edges and with an enhanced intensity at the pyramid basal vertices. The photoluminescence and absorption analysis provided the Stokes shift of both the A and B excitons in the MoS2 pyramids. This analysis provides new insights into the optical functionality of MoS2 pyramids. This method can be applied to other 3D structures within the 2D materials family.

T. Griffiths, S. Woodbury, A. Brooks et al.

Abstract Two innovative hot cell Laser-Induced Breakdown Spectroscopy (LIBS) instruments, designed and built by Applied Photonics Limited, are set to be deployed for the purpose of material characterisation in a high radiation environment. One LIBS instrument uses a ‘through wall’ optical periscope, where the laser and optical spectrograph are located outside of the hot cell. The second instrument uses a remote probe located within the hot cell, containing a compact Nd:YAG (neodymium-doped yttrium aluminium garnet) passively Q-switched laser and plasma light collection optics. The design of both LIBS instruments means that some optical components (e.g. prisms, lenses, fibre optic cables and, in the case of the in-cell remote probe, a Nd:YAG laser head custom-designed and manufactured by Applied Photonics Ltd) will be exposed to high levels of gamma radiation. This entails that these components must be suitably reliable and gamma radiation resistant to last the duration of the planned work. In this article, we report on the results of a limited study on the effect of gamma irradiation (5 kGy, 25 kGy and 50 kGy absorbed dose using a cobalt-60 gamma source) on the optical properties of BK7 (Crown glass) and Ultra-Violet Fused Silica (UVFS) lenses, both with and without high-energy V-coat anti-reflection coating, and UVFS fibre optic cables. The effect of gamma irradiation on the pulsed laser beam energy output of three passively Q-switched Nd:YAG laser heads was also evaluated. The performance of each of the laser heads was tested before and after gamma irradiation by using an energy meter to measure the laser energy output of each of the three laser heads. The optical transmission properties of the components used for plasma light collection and transmission (i.e. lenses, fibre-optics) were tested using a deuterium-halogen lamp in combination with an optical spectrometer. In this limited study, we found that the BK7 lenses were clearly affected by the gamma radiation in that they became light to dark brown in appearance with increasing gamma irradiation whereas the UVFS optics (coated and uncoated) appeared visually, at least, to be unaffected. The optical transmission tests showed that the BK7 lenses became increasingly opaque to UV-VIS wavelengths with increasing gamma irradiation whereas the UVFS lenses and prisms were not so affected. The high-energy V-coat anti-reflection coatings appeared also to be unaffected by the gamma irradiation levels used in this study, at least within the limits of this investigation. However, the UVFS fibre-optic cables did show a reduction in transmission of UV light with increasing gamma irradiation.

A. Madsen, R. Eriksen, J. Glückstad

Computer Generated Holography (CGH) promises unprecedented capabilities for a variety of applications in Optics and Photonics. However, one of the biggest challenges for CGHs is the fundamental tradeoff between algorithm runtime and achieved reconstruction fidelity and efficiency while maintaining light projections at real-time frame rates. In addition, the light projection quality achieved by most CGH-modalities are rather low due to the mismatch between the optical wave propagation of the applied Spatial Light Modulator (SLM) and its simulated model. A promising new avenue of CGH, neural holography, utilizes machine learning models in the generation of single and multi plane holograms. Neural network generated holograms have the distinct advantage that inference is performed in constant time without the need for iterative calculations of the phase SLM pattern. This allows the networks to generate holograms 3-500 times faster than traditional iterative algorithms, which enables the applications dependent on real-time holography. State-of-the-art implementations of neural holography [1, 2] furthermore achieve higher accuracy than traditional iterative algorithm, when compared to target images. Applications of these SLM-encoded CGHs include all areas where a fast and parallel one- or two-photon light excitation is needed such as in Laser Material Processing, Additive Manufacturing and 3D printing, Neurophotonics and Optogenetics, Laser Image Projection and many more.

Fen Xiao, Mingxing Lv, Xinwan Li

Brillouin scattering-based distributed optical fiber sensors have been successfully employed in various applications in recent decades, because of benefits such as small size, light weight, electromagnetic immunity, and continuous monitoring of temperature and strain. However, the data processing requirements for the Brillouin Gain Spectrum (BGS) restrict further improvement of monitoring performance and limit the application of real-time measurements. Studies using Feedforward Neural Network (FNN) to measure Brillouin Frequency Shift (BFS) have been performed in recent years to validate the possibility of improving measurement performance. In this work, a novel FNN that is 3 times faster than previous FNNs is proposed to improve BFS measurement performance. More specifically, after the original Brillouin Gain Spectrum (BGS) is preprocessed by Principal Component Analysis (PCA), the data are fed into the Feedforward Neural Network (FNN) to predict BFS.

Xuanxi Li, Manman Ding, Jun Wang et al.

We report on high power, single-frequency operation of a compact Tm:Y₂O₃ ceramic laser in 2&#x00A0;&#x03BC;m spectral region employing a volume Bragg grating in a simple linear resonator to serve simultaneously as a resonator mirror and mode selector. The home developed laser quality Tm:Y₂O₃ ceramic sample has a Tm doped concentration of 2 at.&#x0025; and pumped with a fiber coupled 793&#x00A0;nm laser diode. Up to 1.5 W of CW single frequency output power at 2014.9&#x00A0;nm has been generated, corresponding to a slope efficiency of 37.9&#x0025; with respect to absorbed pump power. M² factor of the output beam was measured to be &#x223C;1.03.

Stefano Longhi

The Maryland model was introduced more than 30 years ago as an integrable model of localization by aperiodic order. Even though quite popular and rich of fascinating mathematical properties, this model has so far remained quite artificial, as compared to other models displaying dynamical localization like the periodically-kicked quantum rotator or the Aubry-Andre$^{\prime}$ model. Here we suggest that light propagation in a polygonal optical waveguide lattice provides a photonic realization of the Maryland model and enables to observe a main prediction of this model, namely fragility of wave localization in the commensurate potential limit.

Jung-Ping Liu, Chau-Jern Cheng, Y. Hayasaki et al.

This feature issue of Applied Optics is dedicated to the international meeting of Information Photonics 2020 (IP'20), which was held September 11-12, 2020, in Taipei, Taiwan. IP'20 covered a broad range of topics, including advanced display techniques, optical computing, and optical storage. This feature issue, however, limits topics to unconventional imaging techniques, such as digital holography, artificial-intelligence associated imaging, compressive imaging, and single-pixel imaging.