Several 3-D multilayer silicon photonics platforms have been proposed to provide densely integrated structures for complex integrated circuits. Amongst these platforms, great interest has been given to the inclusion o...
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ISBN:
(纸本)9781510601369
Several 3-D multilayer silicon photonics platforms have been proposed to provide densely integrated structures for complex integrated circuits. Amongst these platforms, great interest has been given to the inclusion of silicon nitride layers to achieve low propagation losses due to their capacity of providing tight optical confinement with low scattering losses in a wide spectral range. However, none of the proposed platforms have demonstrated the integration of active devices. The problem is that typically low loss silicon nitride layers have been fabricated with LPCVD which involves high processing temperatures (>1000 C-O) that affect metallisation and doping processes that are sensitive to temperatures above 400 C-O. As a result, we have investigated ammonia-free PECVD and HWCVD processes to obtain high quality silicon nitride films with reduced hydrogen content at low temperatures. Several deposition recipes were defined through a design of experiments methodology in which different combinations of deposition parameters were tested to optimise the quality and the losses of the deposited layers. The physical, chemical and optical properties of the deposited materials were characterised using different techniques including ellipsometry, SEM, FTIR, AFM and the waveguide loss cut-back method. Silicon nitride layers with hydrogen content between 10-20%, losses below 10dB/cm and high material quality were obtained with the ammonia-free recipe. Similarly, it was demonstrated that HWCVD has the potential to fabricate waveguides with low losses due to its capacity of yielding hydrogen contents <10% and roughness <1.5nm.
A low loss transmission line is one of key elements for realization of sub THz band collective Thomson scattering (CTS) diagnostics in large fusion devices. This paper reports transmission tests of corrugated waveguid...
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ISBN:
(纸本)9781467384858
A low loss transmission line is one of key elements for realization of sub THz band collective Thomson scattering (CTS) diagnostics in large fusion devices. This paper reports transmission tests of corrugated waveguides with 300 GHz band gyrotron power. Two types of corrugated waveguide are considered. One is 1.25 inch corrugated waveguide. The other is 3.5 inch corrugated waveguide already installed in the Large Helical Device (LHD) for electron heating with lower frequency gyrotrons. At first, transmission test with existing 1.25 inch waveguides was carried out. This waveguide is not optimized for 300 GHz band and substantial attenuation along waveguides was observed. A theoretical analysis explaining the large attenuation is performed.
waveguides with arbitrary cross-section and periodic loading are analyzed using an eigenmode projection technique. The analysis procedure is based on expanding the fields of the given structure in terms of the solenoi...
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ISBN:
(纸本)9781509006984
waveguides with arbitrary cross-section and periodic loading are analyzed using an eigenmode projection technique. The analysis procedure is based on expanding the fields of the given structure in terms of the solenoidal and irrotational eigenmodes of a canonical waveguide with cross-section enclosing that of the original waveguide. Floquet harmonics are incorporated in the canonical eigenmodes to account for the periodicity. Results obtained using the proposed approach and other techniques are compared and show excellent agreement. The proposed approach has many advantages, namely that the problem reduces to a simple eigenvalue problem and the field distribution is directly given as weighted expansion of the canonical eigenmodes.
We designed and fabricated a two-guiding-layer AlGaAs/GaAs chip. It consists of a lower layer facilitating end-fire coupling and an upper layer for high contrast waveguides, and a vertical spot size converter (SSC) to...
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ISBN:
(纸本)9781509019069
We designed and fabricated a two-guiding-layer AlGaAs/GaAs chip. It consists of a lower layer facilitating end-fire coupling and an upper layer for high contrast waveguides, and a vertical spot size converter (SSC) to connect the two layers. We measured a conversion efficiency of 91%.
A SOI pedestal waveguide can greatly reduce the material absorption induced loss at the Mid-IR wavelengths range. We propose using the second-order TE mode to reduce the propagation loss of the waveguide by > 7 tim...
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ISBN:
(纸本)9781509019038
A SOI pedestal waveguide can greatly reduce the material absorption induced loss at the Mid-IR wavelengths range. We propose using the second-order TE mode to reduce the propagation loss of the waveguide by > 7 times compared to the fundamental TE mode.
Gyroelectric n and p type's waveguides were usually investigated using differential Maxwell's equations, coupled mode and partial area methods, coherent approaching, least square methods. Computation time of o...
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ISBN:
(纸本)9781509044733
Gyroelectric n and p type's waveguides were usually investigated using differential Maxwell's equations, coupled mode and partial area methods, coherent approaching, least square methods. Computation time of one particular model of this type of waveguide might take quite a long time and even to a couple of days using one of these analytical methods. The whole investigation may require a lot of time in the first stage of research until the right model of waveguide will be found. The artificial neural networks were adjusted for the investigation of gyroelectric n GaAs waveguides. Multilayer perceptron network was selected during investigation. Advantages of artificial neural networks comparing with analytical methods are presented in this paper. The investigation showed that difference between results, obtained using analytical methods, and results, obtained by using artificial neural networks, do not differ by more than 12%. On the other hand prediction using artificial neural networks is performed about 2000 times faster than using traditional methods.
We present the use of ferntosecond laser ablation for the removal of monolayer grapheme from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from t...
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ISBN:
(纸本)9781510601369
We present the use of ferntosecond laser ablation for the removal of monolayer grapheme from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to he 0.132 dB/mu m.
In this study, phononic crystals are employed to elastic waveguide transducers for controlling its beam patterns. When signals from the transducer array are inputted to a homogeneous waveguide, they are distorted as p...
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ISBN:
(纸本)9781467398978
In this study, phononic crystals are employed to elastic waveguide transducers for controlling its beam patterns. When signals from the transducer array are inputted to a homogeneous waveguide, they are distorted as propagating due to generation of multiple wave modes and wave dispersion. For this reason, it is difficult to apply transducer array to manipulate the beam pattern of waveguide transducers. Here, the self-collimation of phononic crystals is applied to guide an input signal in the waveguide, maintaining the phase difference between active elements at the exit of the waveguide. To achieve this, the lattice parameters of phononic crystals are carefully chosen to exhibit the self-collimation effect at the operating frequency of the waveguide transducer and the beam steering through the proposed waveguide is demonstrated by numerical simulations.
Power scaling analysis based on the model by Dawson et al. [1,2] for circular core fibers has been applied to estimating power scaling of crystalline fiber waveguides (CFWs) with RE3+ doped single crystalline or ceram...
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ISBN:
(纸本)9781628419795
Power scaling analysis based on the model by Dawson et al. [1,2] for circular core fibers has been applied to estimating power scaling of crystalline fiber waveguides (CFWs) with RE3+ doped single crystalline or ceramic YAG (RE=rare earth: Yb, Er, Tm and Ho). Power scaling limits include stimulated Brillouin scattering, thermal lensing effect, and limits to coupling of pump light into CFWs. The CFW designs we have considered consist, in general, of a square doped RE3+:YAG core, an inner cladding of either undoped or laser-inactive-ion-doped YAG and an outer cladding of sapphire. The presented data have been developed for the structures fabricated using the Adhesive-Free Bonding (AFB (R)) technique, but the results should be essentially independent of fabrication technique, assuming perfect core/inner cladding/outer cladding interfaces. Hard power scaling limits exist for a specific CFW design and are strongly based on the physical constants of the material and its spectroscopic specifics. For example, power scaling limit was determined as similar to 16 kW for 2.5% ceramic Yb:YAG/YAG (core material/inner cladding material) at fiber length of 1.7 m and core diameter of 69 mu m. Considering the present manufacturing limit for CFW length to be, e.g., 0.5 m, the actual maximum output power will be limited to similar to 4.4 kW for a Yb:YAG/YAG CFW. Power limit estimates have also been computed for Er3+, Tm3+ and Ho3+ doped core based CFWs.
We developed a general method for direct and fully integrated generation of photon pairs in counter-propagating spatially entangled Bell-states using parametric down-conversion in photonic crystal slab waveguides with...
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ISBN:
(纸本)9781943580118
We developed a general method for direct and fully integrated generation of photon pairs in counter-propagating spatially entangled Bell-states using parametric down-conversion in photonic crystal slab waveguides without the need for periodic poling.
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