We report on a compact, broadband, 2 x 2 adiabatic 3 dB coupler using sub-wavelength gratings (SWGs) for silicon-on-insulator waveguides. In our device, two SWG waveguides that support two transverse electric modes an...
详细信息
We report on a compact, broadband, 2 x 2 adiabatic 3 dB coupler using sub-wavelength gratings (SWGs) for silicon-on-insulator waveguides. In our device, two SWG waveguides that support two transverse electric modes and have tapered waveguide widths were used to achieve an adiabatic mode evolution of the two-waveguide system for broadband 3 dB power splitting. We present results for a SWG adiabatic 3 dB coupler that has an overall coupler length of 50 mu m and achieves broadband power splitting over a 130 nm wavelength range with an imbalance of no greater than +/- 0.3 dB and with low excess losses of less than 0.5 dB. (C) 2016 Optical Society of America
We consider the twisted waveguide Omega(theta), i.e. the domain obtained by the rotation of the bounded cross section omega subset of R-2 of the straight tube Omega := omega x R at angle theta which depends on the var...
详细信息
We consider the twisted waveguide Omega(theta), i.e. the domain obtained by the rotation of the bounded cross section omega subset of R-2 of the straight tube Omega := omega x R at angle theta which depends on the variable along the axis of Omega. We study the spectral properties of the Dirichlet Laplacian in Omega(theta), unitarily equivalent under the diffeomorphism Omega(theta) -> Omega to the operator H-theta', self-adjoint in L-2(Omega). We assume that theta' = beta - is an element of where beta is a 2 pi-periodic function, and is an element of decays at infinity. Then in the spectrum sigma(H-beta) of the unperturbed operator H-beta there is a semi-bounded gap (-infinity,epsilon(+)(0)), and, possibly, a number of bounded gaps (epsilon(-)(j),epsilon(+)(j)). Since is an element of decays at infinity, the essential spectra of H-beta and H beta-is an element of, coincide. We investigate the asymptotic behaviour of the discrete spectrum of H beta-is an element of near an arbitrary fixed spectral edge epsilon(+/-)(j). We establish necessary and quite close sufficient conditions which guarantee the finiteness of sigma(disc)(H beta-is an element of) in a neighbourhood of epsilon(+/-)(j). In the case where the necessary conditions are violated, we obtain the main asymptotic term of the corresponding eigenvalue counting function. The effective Hamiltonian which governs the the asymptotics of sigma(disc)(H beta-is an element of) near epsilon(+/-)(j) could be represented as a finite orthogonal sum of operators of the form -mu d(2)/dx(2) - eta is an element of, self-adjoint in L-2 (R);here, mu > 0 is a constant related to the so-called effective mass, while eta is 2 pi-periodic function depending on beta and omega.
In this paper, we give the expression and the asymptotic behaviour of the physical solution of a time harmonic wave equation set in a periodic waveguide. This enables us to define a radiation condition and show well-p...
详细信息
In this paper, we give the expression and the asymptotic behaviour of the physical solution of a time harmonic wave equation set in a periodic waveguide. This enables us to define a radiation condition and show well-posedness of the Helmholtz equation set in a periodic waveguide.
We describe wave decay rates associated to embedded resonances and spectral thresholds for waveguides and manifolds with infinite cylindrical ends. We show that if the cut-off resolvent is polynomially bounded at high...
详细信息
We identify the dynamical drivers of systematic changes in persistent quasi-stationary states (regimes) of the Southern Hemisphere troposphere and their secular trends. We apply a purely data-driven approach, whereby ...
详细信息
We identify the dynamical drivers of systematic changes in persistent quasi-stationary states (regimes) of the Southern Hemisphere troposphere and their secular trends. We apply a purely data-driven approach, whereby a multiscale approximation to nonstationary dynamical processes is achieved through optimal sequences of locally stationary fast vector autoregressive factor processes, to examine a high resolution atmospheric reanalysis over the period encompassing 1958-2013. This approach identifies regimes and their secular trends in terms of the predictability of the flow and is Granger causal. A comprehensive set of diagnostics on both isentropic and isobaric surfaces is employed to examine teleconnections over the full hemisphere and for a set of regional domains. Composite states for the hemisphere obtained from nonstationary nonparametric cluster analysis reveal patterns consistent with a circumglobal wave 3 (polar)-wave 5 (subtropical) pattern, while regional composites reveal the Pacific South American pattern and blocking modes. The respective roles of potential vorticity sources, stationary Rossby waves and baroclinic instability on the dynamics of these circulation modes are shown to be reflected by the seasonal variations of the waveguides, where Rossby wave sources and baroclinic disturbances are largely contained within the waveguides and with little direct evidence of sustained remote tropical influences on persistent synoptic features. Warm surface temperature anomalies are strongly connected with regions of upper level divergence and anticyclonic Rossby wave sources. The persistent states identified reveal significant variability on interannual to decadal time scales with large secular trends identified in all sectors apart from a region close to South America.
Tunable diode laser absorption spectroscopy (TDLAS) is an excellent analytical technique for gas sensing applications. In situ sensing of relevant hydrocarbon gases is of substantial interest for a variety of in-field...
详细信息
Tunable diode laser absorption spectroscopy (TDLAS) is an excellent analytical technique for gas sensing applications. In situ sensing of relevant hydrocarbon gases is of substantial interest for a variety of in-field scenarios including environmental monitoring and process analysis, ideally providing accurate, molecule specific, and rapid information with minimal sampling requirements. Substrate-integrated hollow waveguides (iHWGs) have demonstrated superior properties for gas sensing applications owing to minimal sample volumes required while simultaneously serving as efficient photon conduits. Interband cascade lasers (ICLs) are recently emerging as mid-infrared light sources operating at room temperature, with low power consumption, and providing excellent potential for integration. Thereby, portable and handheld mid-infrared sensing devices are facilitated. Methane (CH4) is among the most frequently occurring, and thus, highly relevant hydrocarbons requiring in situ emission monitoring by taking advantage of its distinct molecular absorption around 3 mu m. Here, an efficient combination of iHWGs with ICLs is presented providing a methane sensor calibrated in the range of 100 to 2000 ppm(v) with a limit of detection at 38 ppmv at the current stage of development. Furthermore, a measurement precision of 0.62 ppb(v) during only 1 s of averaging time has been demonstrated, thereby rendering this sensor concept useful for in-line and on-site emission monitoring and process control applications.
There has recently been great interest in chiral waveguides, where the polarisation of the forwards and backwards propagating light fields are oppositely circular at certain positions in space (C-points) [1]. This res...
详细信息
ISBN:
(纸本)9781509067374
There has recently been great interest in chiral waveguides, where the polarisation of the forwards and backwards propagating light fields are oppositely circular at certain positions in space (C-points) [1]. This results in new phenomena, such as the one way emission of light from spin-transitions in quantum dots (QDs) or atoms (simulation, fig. b). The emitted photon's direction is determined by the spin state of the emitter.
We present a mathematical theory of time-harmonic wave propagation and reection in a two-dimensional random acoustic waveguide with sound soft boundary and turning points. The boundary has small uctuations on the scal...
详细信息
We correct typographical errors in four equations showing the integral forms of the equations of motion and the corresponding perturbative approximation. Subsequently presented derivations, results, and conclusions re...
详细信息
We correct typographical errors in four equations showing the integral forms of the equations of motion and the corresponding perturbative approximation. Subsequently presented derivations, results, and conclusions remain unchanged. (C) 2017 Optical Society of America
This paper reports on the fabrication details and performance of chalcogenide waveguides consisted of a ridge geometry 2.2-2.6μm wide on a silica substrate with different film thickness (550-950nm) and etching depth ...
详细信息
ISBN:
(纸本)9781509067374
This paper reports on the fabrication details and performance of chalcogenide waveguides consisted of a ridge geometry 2.2-2.6μm wide on a silica substrate with different film thickness (550-950nm) and etching depth (30-50%). A silica cladding layer was also used to improve acoustic confinement compared to previous designs using polymer claddings. Spiral waveguides formed on a 2cm wide chip, with up to 24cm long spirals used in the experiments. The propagation loss of these waveguides were around 0.2dB/cm. Highest on-chip SBS gain of up to 47dB in this As 2 S 3 waveguide platform is reported. This extremely high level of SBS gain means that much better applications can be realized.
暂无评论