We demonstrate a femtosecond Yb:fiber laser amplification system which delivers 97 W average output power at a repetition rate of 1.08 GHz using a rod-type photonic crystal fiber. The re-compressed output pulse is 233 fs. Numerical simulation was also conducted in agreement with our experimental results.
Spatiotemporal coupling is present when the electric fields of any pulsed beams fail to separate into a product of purely spatial and temporal factors, and it affects ultimately on the propagation of the light. Here we study the effect of spatiotemporal coupling on the Hanbury Brown and Twiss (HBT) effect for the first time, with the help of our recent developed method [Opt. Express28, 32077 (2020)10.1364/OE.405726], by assuming the Gaussian statistics of partially coherent spatiotemporal pulsed sources containing the intensity and correlation coupling effect between the spatial and temporal domain. The generalized results for the spatiotemporal coupling HBT effect are investigated and through a nontrivial two-dimensional case, we numerically illustrate the influence of the spatiotemporal coupling on the HBT effect. It observes that even a very tiny coupling effect will strongly change the HBT effect at longer distances. This work will be potentially useful for the study of the HBT effect (intensity-intensity correlations) with dynamic sources having spatiotemporal coupling in both optics and other branches of physics.
Enduring the rapidly growing demand for high data rates is the main challenge for the current network providers. Super passive optical network (Super-PON), a prominent next generation Ethernet PON (NG-EPON) candidate, can suffice this exponentially increasing data rate requirements. However, to appease such requirements, it employs many transceivers and increases the power-consumption of the network. In this work, we focus on reducing the carbon footprint of Super-PON and propose power-efficient dynamic bandwidth and wavelength allocation (DBWA) algorithms, namely best fit bin-packing sleep mode aware (BF-SMA) and updated BF-SMA (UBF-SMA). The proposed algorithms use SMA for bandwidth scheduling and different bin-packing techniques for wavelength allocation. In bin-packing, the number of available wavelengths and their efficient allocation is based on the network load. For restricting the number of available wavelengths, we can switch off the non-essential transceivers at the OLT, which also helps in maximizing the wavelength utilization and increasing the power efficiency. The simulation results show that in comparison to the state-of-the-art DBWA algorithms, the proposed algorithms improve the power efficiency and reduce the average delay of a Super-PON system. Furthermore, we use Jain’s fairness index to validate the fairness of the proposed DBWA algorithms.
Collimated ultraviolet (UV) light is generated via four-wave mixing (FWM) in cesium vapor by continuously tuning the wavelength of the pump laser. Terahertz (THz) Stokes light is generated by the stimulated Raman scattering (SRS) effect in the FWM process, and its frequency is adjustable. When exciting the cesium atom to a virtual level using different combinations of pump lasers (P1 and P2), the strength distribution of UV light is asymmetric, which can be explained through a phase-matching mechanism. Furthermore, the SRS effect and phase matching influence the FWM.
The dependencies of the polarization rotation on the probe ellipticity and the longitudinal magnetic field have been studied both experimentally and theoretically in a V type electromagnetically induced transparency for 87Rb vapour. The angle of rotation varies periodically with the change in the probe ellipticity and non-linearly with the variation of the magnetic field. We have observed that the plane of polarization is rotated maximum for linearly polarized light and have obtained angle of rotation 0.32 degrees 0.01 degrees for B = 0.036 +/- 0.001 mT while it was 0.0267 degrees +/- 0.0002 degrees without magnetic field. Thus our measurement becomes sensitive to the low magnetic field. A four-level system is considered and the corresponding density matrix equations have been solved analytically to explain these observations theoretically with the help of degenerate and non-degenerate magnetic sub-levels. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
We analyze the viewing angle of a holographic image reconstructed from the digital Fourier hologram with an enhanced numerical aperture (NA). The viewing angle of the reconstructed image depends on the NA of the digital hologram that is determined by a focal length of Fourier lens and hologram aperture size, which is irrespective of a location of imaging plane. The enhanced-NA digital hologram reconstructs the image with an angle larger than a diffraction angle of a hologram pixel. We also characterize the aliasing effect for this type of digital Fourier hologram, and find that the alias-free region exists even at a high numerical aperture. Numerical simulation and optical experiments are conducted to verify this interpretation of the viewing angle of holographic images.
Provoking high user acceptance in lighting can be a very challenging task and demands suitable tools for properly modelling and predicting the users’ perception of the lit environment. Recently, a new model formalism based on the perceptually relevant attributes of perceived brightness, visual clarity, and color preference has been introduced and successfully applied in some preliminary studies. However, a proof of the model’s applicability from a lighting practitioner’s point of view for realistic lighting scenarios and use-cases is still pending and should be performed as part of this work. For this purpose, results of two dedicated lighting condition rating experiments representing different lighting contexts are reported. It is shown that the model predictions for all three perceptual attributes exhibit excellent linear correlations with the respective subject mean ratings and, in all cases, correctly predict the test light sources’ rank order. These results clearly emphasize the applicability and practical relevance of the model and confirm the suitability of its multi-dimensional approach.
In this paper, we have presented a design and simulation of a graphene-coated surface plasmon resonance (SPR) based biosensor for targeting specific biological components. We have explicitly shown the detection of the hemoglobin level in blood samples and the glucose concentration level in urine samples by using the finite element method (FEM) based numerical simulation. In the blood component, the 0.001 refractive index increment causes a 6.1025 g/l hemoglobin (HB) level increment, which has been detected using this SPR based sensor with 200 deg/RIU angular sensitivity. Moreover, we have also detected the presence or absence of diabetes using the glucose concentration level in urine samples with this SPR sensor. Therefore, the novelty of this paper is detecting the blood hemoglobin level and glucose concentration levels in urine samples more accurately than the previously proposed whispering gallery mode (WGM) and photonic crystal nanocavity based optical sensors.
Optically controlled RF switches with a novel non-contact device architecture that achieves high performance in the millimeterwave-to-terahertz (mmW-THz) region are proposed and investigated through simulation. The significant change in conductivity in semiconductors caused by photogenerated carriers is used to develop RF switches having very high performance. By including a thin layer of insulator between the active semiconductor material and the metal contacts, the carrier concentration can be enhanced over that of conventional devices. For a prototype demonstration, G-band coplanar waveguide-based optical switches (using Si and Ge as active materials) with different contact geometries have been modeled and simulated. The proposed switches outperform both conventional solid-state switches and phase-change material-based switches in the switch figure-of-merit, and are promising for developing a novel class of tunable and reconfigurable mmW-THz circuits for advanced sensing, imaging, and communication.
Optical, charge carriers transport, quantum mechanics, magnetic, thermal, and plasmonic properties of the transition metal rhodium are considered. An extended Drude-Lorentz (DL) model is applied to describe the dielectric function (DF) of rhodium in a spectral range going from the mid-infrared (12.4 μm) to the vacuum ultraviolet (32 nm). The Drude term of the DF includes, as optimization parameters, the inverse of the high frequency dielectric constant, the volume plasma frequency and scattering frequency of the electrons, the scattering frequency of holes relative to that of electrons, the ratio between the effective masses of electrons and holes, the number of holes per atom relative to that of electrons, and the renormalized times between grain boundary scattering events for electrons and holes. The Lorentz contribution to the DF includes the number of conduction electrons per atom, the oscillator strengths, the resonance energies, and the Lorentzian widths. Values of the parameters involved in the DF are optimized by an acceptance-probability-controlled simulated annealing method that minimizes spectral differences between the real and imaginary parts of the DF values obtained from the literature and those evaluated from the DL parametric formulation, accounting for the presence of electrons and holes as charge carriers. Once an optimized spectral description of the DF of rhodium is obtained, a large set of charge-transport, magnetic, thermal, plasmonic, and quantum mechanics derived quantities are evaluated: mobilities, relaxation times, Fermi velocities, effective masses, electrical and thermal conductivities, heat capacity coefficients, Hall coefficient, diamagnetic and paramagnetic susceptibilities, effective number of Bohr magnetons, Fermi energies and corresponding densities of states, energy loss functions, effective number of charge carriers participating in conduction, and effective number of electrons involved in inter-band transitions.
In the 1990s, it was recognized that light beams carrying orbital angular momentum (OAM) have benefited applications ranging from optical manipulation to quantum information processing. In recent years, attention has been directed towards the opportunities for communication systems due to the inspiring application potential in both the optical and microwave fields. In this paper, a polarization-independent quadri-channel vortex beam generator based on transmissive metasurface is proposed that can achieve selectivity of polarization, 2-bit OAM modes and spatial distribution in the quadri-channel simultaneously. The transmissive metasurface consists of four metallic layers and three dielectric layers and is designed, fabricated, and experimentally demonstrated to generate multi-mode and dual-polarization OAM vortex beams at 10.0 GHz. Orthogonal polarization and 2-bit information are carried by OAM modes +1, −1 + 2 and −2 and a different phase gradient is superimposed at each channel to realize beam steering, ensuring the accuracy and integrity of the information. The simulation and experimental results verify that the vortex beams with different OAM modes in dual polarizations can be flexibly generated by using transmissive metasurfaces. The proposed method and metasurface pave a way to add extra channels to create an additional set of data carriers for space-division multiplexing (SDM).
For the emerging demands of three-dimensional (3D) profile measurement in daily life, a smartphone-based 3D profilometry based on structured light was presented in this paper. To measure 3D profiles within a large depth range, a method combing binary code and phase-shifting was employed. Applying anti-phase complementary binary code patterns successfully overcame the defocusing issue of both the camera and projector. It also helped reduce the influence of objects’ surface reflectivity and the phase unwrapping error. For a depth range of 1100 mm, an average height reconstruction error lower than 2 mm can be achieved with this system.
Quantum digital signature (QDS) has been proved to be secure in theory, but will inevitably be interfered by channel noise during the practice transmission of qubits. We propose two practical fault tolerant quantum digital signature protocols for the collective noises. For resisting the collective noises, a decoherence-free subspace (DFS) containing four logical qubits has been constructed, which improves the performance of QDS protocols in terms of communication fidelity. Moreover, we prove that the protocols are secure against forging and repudiation attacks, and further discuss the influence of different verification thresholds on the security and give a quantitative analysis.
This paper presents the mid-field model for an ultraviolet C light emitting diode (UVC LED) of wavelength around 275±5 nm by comparison of the 2-dimension (2-D) gray-level image captured from a mono-CMOS sensor and simulated irradiance pattern. Because of UVC light, we propose using a fluorescent film to absorb UVC light and re-emit visible light so that the 2-D image could be captured. The analysis and calibration to obtain accurate gray level of image are performed. Finally, we achieve the mid-field model with high accuracy. Furthermore, this model is also applied for dome lens design and then compares the performance with fabricated samples in measurement to expertise its validity.
Spatially and spectrally resolved imaging (S 2 imaging) is a technique that was developed as an alternative to beam quality (M 2 ) measurements to characterize the modal content of large mode area (LMA) fibers. While it is known that the success of S 2 imaging is highly dependent on the broadband source and the launch conditions into the fiber, the information resulting from this method is more limited than may appear at first glance. Experiments and numerical simulations are used to show that (a) the accuracy of the reconstructed LP 01 mode profile varies greatly depending on launch conditions, and (b) there are always errors in the reconstructed LP 11 mode profile. Not only do these findings reveal that the reconstructed mode areas cannot be accurately determined, but it also shows that the relative modal intensities can only be determined accurately under nearly perfect conditions of fundamental mode launch and propagation through the fiber. Despite these findings, the S 2 technique can still be used under nearly ideal launch and propagation conditions to identify the modes and their group delays, and accurately reconstruct only the fundamental mode.
We proposed a neural network model trained with a small amount of meniscus data (only 144 MR images) to improve the segmentation performance of CNNs, such as U-Net, by overcoming the challenges caused by surrounding tissues. We trained and tested the proposed model on 204 T2-weighted MR images of the knee from 181 patients. The trained model provided excellent segmentation performance for lateral menisci with a mean Dice similarity coefficient of 0.864 (range, 0.743-0.990; SD, ±0.077). The results were superior to those of contemporarily published meniscus segmentation methods based on CNNs.
Provoking high user acceptance in lighting can be a very challenging task and demands suitable tools for properly modelling and predicting the users' perception of the lit environment. Recently, a new model formalism based on the perceptually relevant attributes of perceived brightness, visual clarity, and color preference has been introduced and successfully applied in some preliminary studies. However, a proof of the model's applicability from a lighting practitioner's point of view for realistic lighting scenarios and use-cases is still pending and should be performed as part of this work. For this purpose, results of two dedicated lighting condition rating experiments representing different lighting contexts are reported. It is shown that the model predictions for all three perceptual attributes exhibit excellent linear correlations with the respective subject mean ratings and, in all cases, correctly predict the test light sources' rank order. These results clearly emphasize the applicability and practical relevance of the model and confirm the suitability of its multi-dimensional approach. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
We computationally study two-layer motheye nanostructures fabricated on MgAl2O4 spinel ceramic windows. We investigated the parameters of the structure, including height, width, and shape, in order to optimize its power transmission efficiency over a broad bandwidth. We found a two-layer motheye structure in which the cones of the upper structure have a concave shape that can theoretically achieve more than 99.8% transmission at normal incidence in the wavelength range between 0.4 μm and 5.0 μm.
