Jarmila Müllerová

On wavelength blocking for XG-PON coexistence with GPON and WDM-PON networks

Reference optical configuration for coexistence of 10-Gigabit-capable passive optical networks (XG-PON) with Gigabit passive optical networks (GPON) according to ITU-T G.987.1 standard recommends the usage of specific wavelength blocking filters (WBF). In this contribution, WBFs are designed to separate wavelength bands allocated for XG-PON downstream and upstream signals. The WBFs are proposed to guarantee high filter contrast factors achieved by steep transmission curves in the vicinity of cut-on/cut-off wavelengths of the specific allocated wavelength bands and facilitate migration from legacy GPON to XG-PON. Their deployment protects the allocated wavelength bands from the undesirable interference of GPON with XG-PONs. Wavelength blocking for future wavelength-division-multiplexed PONs is discussed too.

Super-separation thin film filtering for coexistence-type colorless WDM-PON networks

Two wavelength blocking filters (WBF) are designed to separate wavelength regions allocated for the Gigabit passive optical network (GPON) downstream and upstream signals. The designed WBFs guarantee high filter contrast factors achieved by steep transmission curves in the vicinity of cut-on/cut-off wavelengths of 1290 nm / 1330 nm and 1480 nm / 1500 nm. FBFs have pass passbands of less than ∼5 dB ripple and reject wavelengths outside the widths of the passband at ∼32 dB. The deployment of both WBFs could not only prevent the allocated wavelength bands from the undesirable interference with the future next-generations PON such as XG-PON, but it could also vacate wavelength space for future WDM or additional services re-allocation.

Properties of semiconductor surfaces covered with very thin insulating overlayers prepared by impacts of low-energy particles

This paper deals with the formation of very thin insulating layers on crystalline (GaAs) and amorphous semiconductors (a-Si:H and a-SiGe:H) prepared by the impacts of particles of a very low energy. Plasma, ion beams and plasma immersion ion implantation (PIII) as the sources of impacting particles were used and compared. The last technique was applied successfully for the first time in the case of amorphous silicon-based semiconductors. More diagnostics techniques were used for the investigation of the transformation of the semiconductor surface properties. In the a-Si:H based MOS structures prepared by PIII technology, only two groups of defects 0.82 and 1.25 eV (D(z) and D(e), respectively) were found. We suppose that the PIII technology using the implantation at the sample voltage of ca. -1000V causes the formation of a-Si:H layers with missing group of D(h) states. The only decisive parameter determining the formation of two groups of states is the negative potential of the sample during the implantation. In aSiGe:H based MOS structures, three distributions could be prepared by a bias annealing procedure: 0.47, 0.58 and 0.95 eV corresponding to p-type (D(h)) intrinsic (D(z)) and n-type (D(e)) distributions, respectively.

Numerical studies on wavelength-selective all-optical switching using optical bistability in nonlinear chalcogenide FBGs

In this paper, temporal and spectral characteristics of uniform nonlinear fiber Bragg gratings (FBG) are investigated in detail using numerical solutions of nonlinear coupled mode equations. The acquired data are considered in terms of using nonlinear FBGs as wavelength converters and all-optical on-off switches in WDM optical networks. The numerical experiments are focused on transmission properties of FBGs based on nonlinear chalcogenide glasses which are suitable candidates due to their strong third-order optical nonlinearities.

Wavelength protection within coexistence of current and next-generation PON networks

Future development of broad-band access technologies expects increasing bandwidth demands under dynamic growth of FTTH across the world. Coexistence of current and next-generation PONs applying colorless ONUs sharing the same ODN infrastructure has been one of the most discussed issues nowadays especially for technical and commercial implications. This paper deals with some protective measures that can be easily deployed to avoid interferences between signals allocated to specific wavelength bands of current and next-generation PONs. There are several possibilities discussed how to separate and filter optical signals using wavelength blocking filters for GPON, XG-PON and other PON technologies to coexist.

Influence of deposition temperature on amorphous structure of PECVD deposited a-Si:H thin films

The effect of deposition temperature on the structural and optical properties of amorphous hydrogenated silicon (a-Si:H) thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane diluted with hydrogen was under study. The series of thin films deposited at the deposition temperatures of 50–200°C were inspected by XRD, Raman spectroscopy and UV Vis spectrophotometry. All samples were found to be amorphous with no presence of the crystalline phase. Ordered silicon hydride regions were proved by XRD. Raman measurement analysis substantiated the results received from XRD showing that with increasing deposition temperature silicon-silicon bond-angle fluctuation decreases. The optical characterization based on transmittance spectra in the visible region presented that the refractive index exhibits upward trend with increasing deposition temperature, which can be caused by the densification of the amorphous network. We found out that the scale factor of the Tauc plot increases with the deposition temperature. This behaviour can be attributed to the increasing ordering of silicon hydride regions. The Tauc band gap energy, the iso-absorption value their difference were not particularly influenced by the deposition temperature. Improvements of the microstructure of the Si amorphous network have been deduced from the analysis.

Microstructure related optical characterization of technologically relevant hydrogenated silicon thin films

We report results obtained from measurements of UV Vis, FTIR and Raman spectra carried out on a series of silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from silane diluted with hydrogen. Spectral refractive indices, extinction coefficients, optical band gap energies, hydrogen content, the microstructure factor, and grain size were determined as a function of the hydrogen dilution. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (µc-Si:H). With increasing dilution Si:H films become mixed-phase materials with changing volume fractions of crystalline and amorphous phases and voids. The optical band gap energies were determined from transmittance spectra. The grain size was determined from Raman spectra and the contribution of small and large grains was detected.

Numerical modeling of all optical self switching in chalcogenide fibre Bragg grating

We study numerically nonlinear behavior of nonlinear chalcogenide fiber Bragg gratings. We consider more types of gratings with different apodization profile and compare their performance in all-optical processing. The nonlinear coupled mode equations were solved numerically to obtain the transmission characteristics. As numerical method is used optimized split step method. We demonstrate the bistable behavior and also time and spectral properties of these gratings. The results show advantages and disadvantages of apodized gratings in several respects of all-optical processing.

Study of microstructural and optical properties of a-Si:H thin films

Undoped amorphous silicon thin films pasivated by hydrogen (a-Si:H) are important for a number of industrial and research applications, especially for optoelectronics, photovoltaics, optical communications, senzorics, laser technology and so on. We experimentally studied properties of the a-Si:H thin films prepared by the plasma-enhanced chemical vapour deposition (PECVD) method. Sample microstructure properties and the effect of the microstructure on optical properties of the a-Si:H thin films deposited by PECVD on glass were analysed. The spectral refractive index, extinction coefficient, and surface morphology were analysed for the series of a-Si:H samples prepared in different technological conditions from H diluted silane plasma. Surface morphology of studied samples was described by the atomic force microscopy (AFM) method. Optical properties of a-Si:H thin films were analysed by numerical optimization of the microstructural and dispersion model of optical parameters relative to the experimental spectral reflectance. The results show that at dilution between 20 and 30 the transition between amorphous and polycrystalline phase occurs. The sample becomes a mixture of amorphous and polycrystalline phase with nano-sized grains and voids with decreasing hydrogen concentration.

Optical properties of zinc titanate perovskite prepared by reactive RF sputtering

Abstract In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of ZnTiO3 perovskite thin films deposited on glass by reactive magnetron co-sputtering. The members of the series differ by the titanium content that was revealed as an origin of the changes not only in structure but also in dispersive optical properties. Low porosity has been discovered and calculated using the Bruggeman effective medium approximation. An apparent blue-shift of the optical band gap energies with increasing titanium content was observed. The observed band gap engineering is a good prospective for eg optoelectronic and photocatalytic applications of ZnTiO3.