It is estimated that 5%–14% of cancer patients will develop symptomatic metastatic epidural spinal cord compression (ie, spinal metastasis) during the course of their disease, which can lead to devastating complicati...
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The optimum femtosecond laser direct writing of Bragg gratings on silica optical waveguides has been investigated. The silica waveguide has a 6.5 x 6.5 mu m(2) cross-sectional profile with a 20-mu m-thick silicon diox...
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The optimum femtosecond laser direct writing of Bragg gratings on silica optical waveguides has been investigated. The silica waveguide has a 6.5 x 6.5 mu m(2) cross-sectional profile with a 20-mu m-thick silicon dioxide cladding layer. Compared with conventional grating inscribed on fiber platforms, the silica planar waveguide circuit can realize a stable performance as well as a high-efficiency coupling with the fiber. A thin waveguide cladding layer also facilitates laser focusing with an improved spherical aberration. Different from the circular fiber core matching with the Gaussian beam profile, a 1030-nm, 400-fs, and 190-nJ laser is optimized to focus on the top surface of the square silica waveguide, and the 3rd-order Bragg gratings are inscribed successfully. A 1.5-mm long uniform Bragg gratings structure with a reflectivity of 90% at a 1548.36-nm wavelength can be obtained. Cascaded Bragg gratings with different periods are also inscribed in the planar waveguide. Different reflection wavelengths can be realized, which shows great potential for wavelength multiplexing-related applications such as optical communications or sensing.
Non-Hermitian systems have recently attracted broad interest and exhibited intriguing physical phenomena, including the non-Hermitian skin effect, which have been widely studied in various fermionic and bosonic system...
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Non-Hermitian systems have recently attracted broad interest and exhibited intriguing physical phenomena, including the non-Hermitian skin effect, which have been widely studied in various fermionic and bosonic systems. Here we propose a non-Hermitian atom-waveguide system composed of a tilted one-dimensional atomic array coupled with two identical waveguides with opposite chiralities. Such system creates an effective lattice model including nonreciprocal long-range hoppings through the chiral-waveguide photon-mediated interactions. We find the excitations of the collective atomic states concentrate in the middle interface associated with subradiant modes, while, on the contrary, superradiant modes exhibit extended features. Such a unique feature in our proposed system is linked to the non-Hermitian skin effect. Simulation results present a subradiant funneling effect, with robustness against small atomic position disorders. Our work underpins the fundamental comprehension towards the non-Hermitian skin effect in open quantum systems and also provides prospective paths to study non-Hermitian systems in the area of quantum optics.
Self-imaging of waves is an intriguing and spectacular effect. The phenomenon was first observed for light in 1836 by Henry Fox Talbot and to this day is the subject of research in many areas of physics, for various t...
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Self-imaging of waves is an intriguing and spectacular effect. The phenomenon was first observed for light in 1836 by Henry Fox Talbot and to this day is the subject of research in many areas of physics, for various types of waves and in terms of different applications. This article is a Talbot-effect study for spin waves (SWs) in systems composed of a thin, ferromagnetic waveguide with a series of single-mode sources of SWs flowing into it. The proposed systems are studied with the use of micromagnetic simulations, and the SW self-imaging dependencies on many parameters are examined. We formulated conditions required for the formation of self-images and suitable for experimental realization. The results of the research form the basis for the further development of self-imaging-based magnonic devices.
We characterize laser-written waveguides in silicon versus the inscription parameters such as scanning speed and pulse energy. The analysis is carried out at different wavelengths and polarization states. Finally, the...
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ISBN:
(纸本)9781957171258
We characterize laser-written waveguides in silicon versus the inscription parameters such as scanning speed and pulse energy. The analysis is carried out at different wavelengths and polarization states. Finally, the silicon sample is annealed to investigate the possible mechanism that leads to positive refractive index changes.
We present lithography and argon plasma etching of lithium niobate on insulator (LNOI) rib waveguides using reflowed photoresist etch masks and 405 nm photolithography. Melting the photoresist at temperatures greatly ...
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We present lithography and argon plasma etching of lithium niobate on insulator (LNOI) rib waveguides using reflowed photoresist etch masks and 405 nm photolithography. Melting the photoresist at temperatures greatly exceeding its glass transition temperature while minimizing feature distortion through photoresist adhesion control reduces sidewall surface roughness and allows the photoresist to be used both as the pattern mask and the hard etch mask. Waveguide sidewall surfaces exhibiting sub-nm root mean square roughness are fabricated. Dependence of sidewall roughness and angle on feature width, and propagation loss on thermal annealing of the fabricated devices is characterized. Measured quality factors on fabricated microresonators exceed one million. LNOI rib waveguides and resonators with low propagation loss increase nonlinear optical conversion efficiencies and are useful for efficient electro-optic modulation. Photolithography compatible fabrication of low loss LNOI photonic integrated circuits facilitates scalable commercialization.
We have developed a recurrent neural network that efficiently simulates the unidirectional pulse propagation equation. The model is validated via predicting complex nonlinear interactions in a periodically poled nanop...
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ISBN:
(纸本)9781957171258
We have developed a recurrent neural network that efficiently simulates the unidirectional pulse propagation equation. The model is validated via predicting complex nonlinear interactions in a periodically poled nanophotonic LiNbO 3 waveguide.
To achieve ultrahigh-density nanoplasmonic integrated circuits, low-loss conventional dielectric waveguides (CDWs) are used to transfer light into and out of the metal-dielectric-metal (MDM) plasmonic waveguides. We s...
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To achieve ultrahigh-density nanoplasmonic integrated circuits, low-loss conventional dielectric waveguides (CDWs) are used to transfer light into and out of the metal-dielectric-metal (MDM) plasmonic waveguides. We show that sandwiching the MDM plasmonic waveguide between two CDWs forms a Fabry-Perot cavity-like structure, which causes oscillations in the transmission coupling efficiency (TCE) into the output CDW as the length of the MDM waveguide is increased. Three types of compact air-gap couplers (AGCs) were used at the interface between those two types of waveguides to enhance the coupling efficiency between them. Our simulation results indicate that tapering CDW before it is connected to AGC not only enhances TCE into the output CDW by 9% over a wide spectrum range but also reduces the need for high-precision fabrication techniques to align AGC at the interface. Moreover, we achieved a TCE into the output CDW of 77% optimized for the optical communications wavelength of 1550 nm when the length of the MDM plasmonic waveguide is 600 nm. In addition, we showed that our proposed design has large fabrication tolerance by investigating the change in its spectrum response as various parameters of the design dimensions differ from that of the targeted optimum dimensions. We found that increasing the dimensions of AGC reduces the width of the spectrum, whereas increasing the width of CDW with its tapered part shifts the spectrum to the right by 100 nm per 40 nm increase in the width. We also found that increasing the refractive index of the MDM plasmonic waveguide with AGC controls the cutoff wavelength, in which TCE is almost zero at wavelengths shorter than the cutoff wavelength, and consequently provides a unique advantage in using our proposed design in sensing applications. (C) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)
Integrated silicon nitride $(\text{SiN}_{\mathrm{x}})$ waveguides and microresonators are extensively studied for nonlinear demonstrations, including parametric amplification, optical parametric oscillation and supe...
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ISBN:
(纸本)9798350345995
Integrated silicon nitride $(\text{SiN}_{\mathrm{x}})$ waveguides and microresonators are extensively studied for nonlinear demonstrations, including parametric amplification, optical parametric oscillation and supercontinuum generation, since $\text{SiN}_{\mathrm{x}}$ is a mature, versatile and efficient platform for third-order nonlinearity. Recently, its lack of second-order nonlinearity $(\chi^{(2)})$ has been overcome with all-optical poling (AOP) [1], relying on multiphoton absorption interference of optical fields to inscribe a $\chi^{(2)}$ through coherent photogalvanic effect (PGE) [2]. As such a self-organized quasi-phase matching (QPM) grating for second-harmonic generation (SHG) can be spontaneously obtained by solely launching a pump light in a waveguide, or in a seeded fashion by also injecting the pump SH which reduces the time and power requirements and increases the achievable efficiencies [2]. While the existence of trap states in $\text{SiN}_{\mathrm{x}}$ makes it possible to unlock the coherent PGE, measurements on trap locations indicate that traps in stochiometric $\text{SiN}_{\mathrm{x}}$ are 1.4 eV deep [3]. As such previous demonstrations were focused on pumping at 1550 nm (SH with 1.6 eV energy) [1] and 1064 nm (SH with 2.3 eV energy) [4] for stochiometric $\text{SiN}_{\mathrm{x}}(\text{Si}_{3}\mathrm{N}_{4})$ . However, the depth of the traps is a limitation for AOP for longer wavelengths. In this work, we demonstrate all-optical inscription of QPM gratings in the 2000 nm region leveraging silicon-rich $\text{SiN}_{\mathrm{x}}$ waveguides.
Virtually every molecule can uniquely be identified by a series of characteristic mid-infrared (IR) absorption lines, thus commonly referred to as the molecule's spectral fingerprint. A-priori unknown substances c...
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ISBN:
(纸本)9798350345995
Virtually every molecule can uniquely be identified by a series of characteristic mid-infrared (IR) absorption lines, thus commonly referred to as the molecule's spectral fingerprint. A-priori unknown substances can therefore be detected with exceptional high selectivity by measuring a sample's response to illumination with broadband mid-infrared light [1]. Consequently, potential applications of mid-IR spectroscopy are vast and are ranging from airport security screening and non-invasive breath analysis to medical imaging and the detection of chemical warfare agents and toxic industrial chemicals, to only name a few. However, the main roadblock for the widespread adoption of this powerful technique is the current lack of integrated miniaturised components that are needed to realise field-deployable mid-IR spectral fingerprinting systems.
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