Browsing by Subject "Optical loss"
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Item Open Access Comparative investigation og hydrogen bonding in silicon based PECVD grown dielectrics for optical(Elsevier, 2004-06) Ay, F.; Aydınlı, AtillaSilicon 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. (C) 2004 Elsevier B.V. All rights reserved.Item Open Access Low loss optical waveguides and polarization splitters with oxidized AlxGa1-xAs layers(Bilkent University, 1998) Bek, AlpanLow propagation loss waveguides, operating at 1.55 fim optical wavelength, are fabricated utilizing oxidized AhGai_a;As layers. MBE grown multilayer semiconductor heterostructures are characterized before and after oxidation by ellipsometric techniques. In fabrication of optical waveguides, reactive ion etching method is used extensively. Loss measurements are performed, involving a fiber input-coupled laser source setup using Fabry-Perot resonance technique. Propagation loss of an AlGaAs based multilayer rib waveguide with oxidized AhG ai_3,As top layer is observed to reduce from 6 dB/cm to as low as 1 clB/cm lor TM and from 3.7 dB/cm to as low as 0.6 dB/cm for TE polarizations in the presence of metal electrodes on top of the rib. These results arc compared with loss measurements on standard rib waveguides. Polarization splitters are also fabricated with the same material. Effect of the oxide layer on the polarization splitter’s coupling length for TE and TM polarizations are measured. Polarization extinction ratios as high as 12.4 dB are obtained. Polarization extinction ratios are also attempted to be controlled by the use of electro-optic effect in Al.x,.Gai_a;As system. Only AC fields are found to be effective.Item Open Access Plasma enhanced chemical vapor deposition of low-loss as-grown germanosilicate layers for optical waveguides(SPIE, 2004) Ay, Feridun; Agan, S.; Aydınlı, AtillaWe 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.Item Open Access Silicon-on-insulator optical waveguides and waveguide devices(Bilkent University, 2000) Kiyat, İsaSilicon-on-insulator(SOI) optical waveguides, directional couplers and some types of MMI couplers were designed, fabricated and characterized at a wavelength of 1.55 /im. Effective index method and the single mode condition for rib waveguide was used in design of optical waveguides. BPM simulations were extensively employed for all fabricated devices. Waveguides and the other devices were defined on SOI material by wet chemical etching in KOH solutions^ Fabricated devices were characterized on a standard fiber optic measurement setup with a DFB laser as its IR light source. In characterization of optical waveguides the single mode condition was verified and insertion loss was measured to be 12.2 dB for TE and 12.7 dB for TM polarized light as the best values. Furthermore, the propagation loss found to be 0.70 dB/cm for TE and 0.76 dB/cm for TM which is typical . Characterized directional couplers gave results completely consistent with their BPM simulations. 1x2, 2x2, 1x4 and 1x8 type MMI couplers were also found to gave expected behaviors. Splitting ratios as low as 0 dB and 0.55 dB was measured.