An elastomeric grating coupler

We report on a novel nondestructive and reversible method for coupling free space light to planar optical waveguides. In this method, an elastomeric grating is used to produce an effective refractive index modulation on the surface of the optical waveguide. The external elastomeric grating binds to the surface of the waveguide with van der Waals forces and makes conformal contact without any applied pressure. As a demonstration of the feasibility of the approach, we use it to measure the refractive index of a silicon oxynitride film. This technique is nondestructive, reversible, low cost and can easily be applied to the characterization of optical materials for integrated optics

Turkish students' and teachers' attitudes toward the use of interactive whiteboards in EFL classrooms

This study explored the attitudes of students and teachers toward the use of interactive whiteboards (IWBs) in a foreign language teaching and learning context. The study also investigated possible factors affecting teachers' and students' attitudes toward IWB technology. Data were collected through questionnaires distributed to 458 students and 82 teachers in different institutions across Turkey, ranging from primary schools to universities. Questionnaire results revealed that both students and teachers have generally positive attitudes toward the use of IWBs in language instruction and are aware of the potential uses of this technology. The statistical analysis revealed that the more teachers use IWBs, the more they like this technology. It was also found that as the number of hours of IWB exposure increases, students' awareness of the distinctiveness of IWB technology increases. Suggestions are made for further research and for administrators considering whether or not to invest in IWBs. © 2010 Taylor & Francis

Plasma enhanced chemical vapor deposition of low loss as-grown germanosilicate layers for optical waveguides

We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguides. Plasma enhanced chemical vapor deposition (PECVD) technique was used to grow the films using silane, germane and nitrous oxide as precursor gases. Chemical composition was monitored by Fourier transform infrared (FTIR) spectroscopy. N-H bond concentration of the films decreased from 0.43 ×1022 cm -3 down to below 0.06x 1022 cm-3, by a factor of seven as the GeH4 flow rate increased from 0 to 70 seem. A simultaneous decrease of O-H related bonds was also observed by a factor of 10 in the same germane flow range. The measured TE loss rates at λ=632.8 nm were found to increase from are 0.20 ± 0.02 to 6.46 ± 0.04 dB/cm as the germane flow rate increased from 5 to 50 seem, respectively. In contrast, the propagation loss values for TE polarization at λ-1550 nm were found to decrease from 0.32 ± 0.03 down to 0.14 ± 0.06 dB/cm for the same samples leading to the lowest values reported so far in the literature, eliminating the need for high temperature annealing as is usually done for these materials to be used in waveguide devices

Optical transitions of Tm3+ ions for amplifiers: How the local structure works in (1 - Ex)TeO2 + (x)M (where M = LiCl, CdCl2, WO3) glass

Optical transitions of Tm3+ ions for amplifiers was presented. Stimulated emission cross-section at the peak wavelength of the emission bands was determined. It was concluded that Tm3+ doped binary tellurite glasses are promising materials for the infrared amplifiers

Light harvesting with Ge quantum dots embedded in SiO2or Si3N4

Germanium quantum dots (QDs) embedded in SiO2or in Si3N4have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850°C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2matrix, or in the 1-2 nm range in the Si3N4matrix, as measured by transmission electron microscopy. Thus, Si3N4matrix hosts Ge QDs at higher density and more closely spaced than SiO2matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4matrix in comparison with those in the SiO2host. Light absorption by Ge QDs is shown to be more effective in Si3N4matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices. © 2014 AIP Publishing LLC

Comparative investigation of hydrogen bonding in silicon based PECVD grown dielectrics for optical waveguides

Silicon oxide, silicon nitride and silicon oxynitride layers were grown by a PECVD technique. The resulting refractive indices of the layers varied between 1.47 and 1.93. The compositional properties of the layers were analyzed by FTIR and ATR infrared spectroscopy techniques. Comparative investigation of bonding structures for the three different layers was performed. Special attention was given to analyze N-H bond stretching absorption at 3300-3400 cm(-1). Quantitative results for hydrogen related bonding concentrations are presented based on IR analysis. An annealing study was performed in order to reduce or eliminate this bonding types. For the annealed samples the N-H bond concentration was strongly reduced as verified by FTIR transmittance and ATR spectroscopic methods. A correlation between the N-H concentration and absorption loss was verified for silicon oxynitride slab waveguides. Moreover, a single mode waveguide with silicon oxynitride core layer was fabricated. Its absorption and insertion loss values were determined by butt-coupling method, resulting in low loss waveguides

Stress effects in prism coupling measurements of thin polymer films

Due to the increasingly important role of some polymers in optical waveguide technologies, precise measurement of their optical properties has become important. Typically, prism coupling to slab waveguides made of materials of interest is used to measure the relevant optical parameters. However, such measurements are often complicated by the softness of the polymer films when stress is applied to the prism to couple light into the waveguides. In this work, we have investigated the optical properties of three different polymers, polystyrene (PS), polymethyl-methacrylate (PMMA), and benzocyclobutane (BCB). For the first time, the dependence of the refractive index, film thickness, and birefringence on applied stress in these thin polymer films was determined by means of the prism coupling technique. Both symmetric trapezoid shaped and right-angle prisms were used to couple the light into the waveguides. It was found that trapezoid shaped prism coupling gives better results in these thin polymer films. The refractive index of PMMA was found to be in the range of 1.4869 up to 1.4876 for both TE and TM polarizations under the applied force, which causes a small decrease in the film thickness of up to 0.06 mum. PMMA waveguide films were found not to be birefringent. In contrast, both BCB and PS films exhibit birefringence albeit of opposing signs

Influence of substrate temperature and bias voltage on the optical transmittance of TiN films

Titanium nitride (TiN) thin films were prepared by means of reactive DC sputtering on quartz and sapphire substrates. Structural, electrical and optical effects of deposition parameters such as thickness, substrate temperature, substrate bias voltage were studied. The effect of substrate temperature variations in the 100-300degreesC range and substrate bias voltage variations in the 0-200 V DC range for 45-180 nm thick TiN films were investigated. Temperature-ependent electrical resistivity in the 100-350K range and optical transmission in the 300-1500 nm range were measured for the samples. In addition, structural and morphological properties were studied by means of XRD and STM techniques. The smoothest surface and the lowest electrical resistivity was recorded for the optimal samples that were biased at about V-s= -120V DC. Unbiased films exhibited a narrow optical transmission window between 300 and 600 nm. However, the transmission became much greater with increasing bias voltage for the same substrate temperature. Furthermore, it was found that lower substrate temperatures produced optically more transparent films. Application of single layers of MgF2 antireflecting coating on optimally prepared TiN films helped increase the optical transmission in the visible region to more than 40% for 45 nm thick samples

Elasto-Optical Properties of Thin Polymer Films by Prism Coupling Technique

39th International School of Quantum Electronics: Microresonators as Building Blocks for VLSI Photonics -- 18 October 2003 through 25 October 2003 -- -- 122694Reliable measurement of stress dependent refractive index of thin polymer films has been achieved. The effect of the applied stress on the refractive index and birefringence of the films was investigated. The out-of-plane elastic moduli of the thin polymer films were deduced by using the same prism coupling setup. Three dimensional finite element method (FEM) analysis was used to obtain the principal stresses for each polymer film and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined, for the first time. © 2004 American Institute of Physics