The demand for high-speed and highly efficient optical communication techniques has been rapidly growing due to the ever-increasing volume of data traffic. As well as the digital coherent ...communication used for core and metro networks, intensity modulation and direct detection (IM-DD) are still promising schemes in intra/inter data centers thanks to their low latency, high reliability, and good cost performance. In this work, we study a microresonator-based frequency comb as a potential light source for future IM-DD optical systems where applications may include replacing individual stabilized lasers with a continuous laser driven microresonator. Regarding comb line powers and spectral intervals, we compare a modulation instability comb and a soliton microcomb and provide a quantitative analysis with regard to telecom applications. Our experimental demonstration achieved a forward error correction (FEC) free operation of bit-error rate (BER) <10
with a 1.45 Tbps capacity using a total of 145 lines over the entire C-band and revealed the possibility of soliton microcomb-based ultra-dense wavelength division multiplexing (WDM) with a simple, cost-effective IM-DD scheme, with a view to future practical use in data centers.
Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated ...for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.
We report on the direct observation of the phase locking of the attosecond pulse train (APT) via interferometric autocorrelation in the extreme ultraviolet region. APT is formed with Fourier ...synthesis of high-order harmonic fields of a femtosecond laser pulse. Time-of-flight mass spectra of N+, resulting from the Coulomb explosion of N2 absorbing two photons of APT, efficiently yield correlated signals of APT. The measured autocorrelation trace exhibits that the duration of the pulse should be only 1.3 periods of the extreme ultraviolet carrier frequency. A few interference fringes within the short pulse duration clearly show two types of symmetry, which ensure the phase locking between pulses in APT.
Spatio-time-resolved cathodoluminescence (STRCL), which uses a femtosecond-laser-driven pulsed photoelectron gun instead of the cw electron gun of spatially resolved cathodoluminescence (CL) combined ...with scanning electron microscopy (SEM), is introduced for probing local luminescence dynamics in quantum structures and nanostructures of wide-bandgap (WBG) semiconductors. As STRCL is based on SEM, multi-scale characterization of a structure with high spatial definition is possible, and the use of pulsed electron-beams allows the sub-picosecond excitation of any WBG semiconductor. By using our STRCL system, high-resolution near-band-edge CL imaging allowed the visualization of nonradiative recombination channels in a low dislocation density GaN substrate: the local CL decay curves of the sample at 300 K showed a nearly single-exponential lineshape, and the lifetimes were sensitively position-dependent. Free- and bound-exciton recombination dynamics with the energy transfer processes in GaN, AlN, and hexagonal BN, as well as local emission dynamics in Al0.68Ga0.32N quantum wells, were successfully investigated in the UV to deep UV wavelengths down to 200 nm.
NH4F is demonstrated to be a promising mineralizer for the acidic ammonothermal crystal growth of GaN. In comparison with other acidic mineralizers such as NH4Cl, NH4Br, and NH4I, NH4F behaves ...distinctively different. First, NH4F affords a negative temperature gradient for crystal growth of GaN in supercritical NH3 at a temperature range from 550 to 650 °C. Second, it enables GaN crystal growth in polar (c plane), semipolar, and nonpolar directions (a plane and m plane). Third, NH4F remarkably increases both the growth rate and quality of the GaN crystal. With the aid of NH4F, self-nucleation of GaN and bulk growth of hexagonal GaN crystals from the self-nucleated seed have been realized.
A strategy for increasing the square of an overlap integral of electron and hole wavefunctions (I2) in polar c-plane AlxGa1−xN multiple quantum wells (MQWs) is proposed. By applying quadratic ...modulation to AlN mole fractions along the c-axis, local bandgap energies and concentrations of immobile charges induced by polarization discontinuity are simultaneously controlled throughout the MQW structure, and optimized band profiles are eventually achieved. The I2 value can be substantially increased to 94% when the well width (Lw) is smaller than 4.0 nm. In addition, I2 greater than 80% is predicted even for thick MQWs with Lw of 10 nm.
Direct Microrolling Processing on a Silicon Wafer Aoki, Kanna; Ishiguro, Keita; Denokami, Masaki ...
Small (Weinheim an der Bergstrasse, Germany),
09/2017, Letnik:
13, Številka:
36
Journal Article
Recenzirano
Although, varieties of micro‐ to nanoscale fabrication technologies have been invented and refined for silicon (Si) processing because Si is the basic material of integrated circuits, the layouts are ...based on layer‐by‐layer approaches, making it difficult to realize three‐dimensional (3D) structures with complicated shapes normal to the planar surface (along the out‐of‐plane direction) of the wafers used. Here, a novel and direct Si‐processing technology that enables to bend thin layers of Si surfaces into various 3D curved structures at the micrometer scale is introduced. This bending is achieved by porosifying a Si wafer surface using anodic oxidation and then performing conventional photolithography patterning and wet etching. The porosity gradient in the depth direction gives rise to a stress‐internalized layer in which self‐rolling action is induced via subsequent patterning and wet etching. A subsequent oxidation process further enhances the curvature deformation, leading to the formation of tubes, for example. The rolling directions can be controlled by 2D patterning of the porous Si layer, which is explained well from a structural dynamics perspective. This technology has a wide range of capabilities for realizing 3D structures on Si substrates, enabling new design possibilities for Si‐based on‐chip devices.
A direct silicon‐processing technology that enables thin layers of silicon surfaces to be bent into various 3D curved structures at the micrometer scale is demonstrated. This bending is achieved by porosifying a silicon wafer surface using anodic oxidation and then performing conventional photolithography patterning and wet etching.
The effects of the chirp of the pump pulse in broadband terahertz (THz) pulse generation by optical rectification (OR) in GaP were systematically investigated. It was found that the pre-compensation ...for the dispersion of GaP is important for obtaining smooth and single-peaked THz spectra as well as high power-conversion efficiency. It was also found that an excessive amount of chirp leads to distortions in THz spectra, which can be quantitatively analyzed by using a simple model. Our results highlight the importance of accurate control over the chirp of the pump pulse for generating broadband THz pulses by OR.
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