[Optical properties of one-dimensional metallodielectric photonic crystals].
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The optical characteristics of one-dimensional metallodielectric photonic crystals (MDPC), constructed by inserting metal aluminum layers of certain thickness into the Si/SiO2 system, were studied theoretically with the transfer matrix method. The results show that the reflection efficiency can be enhanced considerably after the introduction of metallic layers, e. g. the rejection level of each period increased from 7.2 dB([Si(46 nm)/SiO2 (120 nm)]5) to 20 dB ([Si(46 nm)/SiO2 (60 nm)/Al (10 nm)/SiO2 (60 nm)]5). In addition, high omnidirectional reflection band with broader width can be obtained, e. g. bandwidth of 550 nm can be offered with [Si(46 nm)/SiO2 (60 nm)/Al (30 nm)/SiO2 (60 nm)]5. Rules of how the absorption, thickness and position of the metal layers affect the optical characteristics of the MDPC are also discussed. These MDPC structures may be used as compact-size, low-loss and broad-band optical reflectors.Keywords:
Reflection
Transfer-matrix method (optics)
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Rare earth-activated 1-D photonic crystals were fabricated by RF-sputtering technique. The cavity is constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten pairs of SiO2/TiO2 layers. Scanning electron microscopy is employed to put in evidence the quality of the sample, the homogeneities of the layers thickness and the good adhesion among them. Near infrared transmittance and variable angle reflectance spectra confirm the presence of a stop band from 1500 nm to 2000 nm with a cavity resonance centered at 1749 nm at 0° and a quality factor of 890. The influence of the cavity on the ⁴I₁₃/₂ -->⁴I₁₅/₂ emission band of Er3+ ion is also demonstrated.
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Since thin-film silicon solar cells have limited optical absorption, we explore the effect of a nanostructured back reflector to recycle the unabsorbed light. As a back reflector we investigate a 3D photonic band gap crystal made from silicon that is readily integrated with the thin films. We numerically obtain the optical properties by solving the 3D time-harmonic Maxwell equations using the finite-element method, and model silicon with experimentally determined optical constants. The absorption enhancement relevant for photovoltaics is obtained by weighting the absorption spectra with the AM 1.5 standard solar spectrum. We study thin films either thicker ($L_{Si} = 2400$ nm) or much thinner ($L_{Si} = 80$ nm) than the wavelength of light. At $L_{Si} = 2400$ nm, the 3D photonic band gap crystal enhances the spectrally averaged ($\lambda = 680$ nm to $880$ nm) silicon absorption by $2.22$x (s-pol.) to $2.45$x (p-pol.), which exceeds the enhancement of a perfect metal back reflector ($1.47$ to $1.56$x). The absorption is enhanced by the (i) broadband angle and polarization-independent reflectivity in the 3D photonic band gap, and (ii) the excitation of many guided modes in the film by the crystal's surface diffraction leading to enhanced path lengths. At $L_{Si} = 80$ nm, the photonic crystal back reflector yields a striking average absorption enhancement of $9.15$x, much more than $0.83$x for a perfect metal, which is due to a remarkable guided mode confined within the combined thickness of the thin film and the photonic crystal's Bragg attenuation length. The broad bandwidth of the 3D photonic band gap leads to the back reflector's Bragg attenuation length being much shorter than the silicon absorption length. Consequently, light is confined inside the thin film and the absorption enhancements are not due to the additional thickness of the photonic crystal back reflector.
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SiO2 three-dimensional photonic crystals were deposited through colloidal crystal method.The crystal structure properties and spectral characteristics were studied by scanning electron microscopy(SEM)and the spectrophotometer,respectively.The influences of different factors such as particle concentrationr,eaction temperature on the photonic band gap were investigated in detail.The results show that the reflection intensity increased with the increase of SiO2 particle concentration until it reached maximum at the concentration of 1.92%.A further increase in SiO2 concentration resulted a decrease in the reflection intensitya,narrower photonic band gap and blue shift in the photonic band gap position.When the temperature was raiseda,n increase of the reflection intensity and blue shift for the photonic band gap position were observedr,espectively.
Reflection
Yablonovite
Blueshift
Colloidal crystal
Crystal (programming language)
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High quality colloidal photonic crystals made from polystyrene spheres with diameter 240 nm are fabricated by the vertical deposition method. The scanning electron microscopy (SEM) and the transmittance spectrum are used to characterize the properties of the photonic crystal. The SEM images show that there are few lattice defects. The transmittance of the photonic crystal is above 75% in the pass band at 700 nm and is lower than 5% at the centre of the band gap, respectively. It is found that proper concentration is a very important factor to fabricate the photonic crystal when the diameter of the spheres is lower than 300 nm.
Colloidal crystal
Polystyrene
Yablonovite
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The size influence of silica microspheres on the photonic band gap (PBG) of three-dimensional face-centered-cubic (fcc) photonic crystals (PCs) is studied by means of colloidal photonic crystals, which are self-assembled by the vertical deposition technique. Monodispersed SiO 2 microspheres with a diameter of 220–320 nm are synthesized using tetraethylorthosilicate (TEOS) as a precursor material. We find that the PBG of the PCs shifts from 450 nm to 680 nm with silica spheres increasing from 220 to 320 nm. In addition, the PBG moves to higher photon energy when the samples are annealed in a temperature range of 200–700°C. The large shift results from the decrease in refraction index of silica due to moisture evaporation.
Colloidal crystal
Deposition
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Photoluminescence (PL) modulation realized by one-dimensional photonic band gap structures.Microcavity was designed to confine electromagnetic field and control light transfer by the idea of doped photonic crystal,and fabricated by alternating the composition of a-SiN_x in PECVD system.It is observed the wide emission band width 208 nm is strongly narrowed to 11 nm,and a two order enhancement of PL peak intensity.The linewidth and quality factor of a-SiN_x photonic crystal microcavity is 11 nm and 69,respectively.A cavity mode at 710 nm is observed in transmittance spectra,which further verifies the cavity effects.
Laser linewidth
Modulation (music)
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The authors report on one-dimensional dielectric photonic crystals activated by Er3+ ion and fabricated by rf-sputtering deposition. The cavity was constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of six pairs of SiO2∕TiO2 layers. Near infrared transmittance spectra evidence the presence of a stop band from 1350to1850nm and a cavity resonance centered at 1537nm. Intensity enhancement and narrowing of the I13∕24→I15∕24 emission band of Er3+ ion, due to the cavity effect, were observed. A cavity quality factor of 171 was achieved.
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Nanoporous
Transfer-matrix method (optics)
Reflection
Pulsed Laser Deposition
Deposition
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