Browsing by Subject "Prism coupling"

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Open Access
Plasma enhanced chemical vapor deposition of low-loss as-grown germanosilicate layers for optical waveguides
(SPIE, 2004) Ay, Feridun; Agan, S.; Aydınlı, Atilla
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.
Open Access
Silicon based dielectrics : growth, characterization, and applications in integrated optics
(2005) Ay, Feridun
In recent years, growing attention has been paid to silicon based dielectrics, such as silicon oxynitrides, silicon nitrides, and semiconductor doped silicon oxides, all combined under the name silica on silicon technology. This attention has been motivated mainly due to their excellent optical properties such as well controlled refractive index and high transparency over a wide range of wavelength. In accordance with the main goal of this study that relied on the utilization of silicon based dielectrics and their optimization for applications in integrated optics, an emphasis was given to optimize the compositional and optical properties of these materials. A detailed quantitative compositional analysis using Fourier transform infrared spectroscopy resulted in identification of the germanosilicate dielectrics as the most promising candidates for use in integrated optics. The first reported systematic study of propagation losses for different-index planar waveguides by using prism coupling method was correlated with the compositional analysis. This study had an important outcome for planar waveguides fabricated with germanosilicate core layers resulting in the lowest propagation loss values reported so far for as deposited CVD-grown films at λ=1.55 µm, eliminating the need for costly and cumbersome annealing process. An improvement of the prism coupling technique led to a new approach for elasto-optic characterization of thin polymer films. This completely new method allows one to determine the optical anisotropy and out-of-plane mechanical properties and to correlate both in order to obtain the elasto-optical properties of thin polymer films, for the first time. Of interest as potential electro-optic material, we have concentrated on thermally poled germanosilicate films deposited on fused-silica substrates by PECVD. As a result of an optimization study, we demonstrated a record peak nonlinear coefficient of ∼1.6 pm/V, approximately twice as strong as the highest reliable value reported in a thermally poled fused silica glass. Finally, we have demonstrated several applications of this technology in the field of integrated optics. Since optical waveguides constitute the building blocks of many integrated optical devices, we had first concentrated on design and optimization of waveguides employing germanosilicates as the core layers. The final step of our work concentrated on design and implementation of microring resonator devices based on germanosilicate layers.
Open Access
Silicon oxynitride layers for applications in optical waveguides
(2000-09) Ay, Feridun
Silicon oxynitride layers, aimed to serve as the core material for optical waveguides operating at l.55µm, v.-ere grown by a PECVD technique using SiH4, N20, and NH3 as precursor gases. The films were deposited at 350 °c, 13.56 MHz RF frequency, and 1 Torr pressure by varying the flow rates of N20 and l\"H3 gases. The resulting refractirn indices of the layers varied between 1.47 and 2.0. The compositional properties of the layers were analyzed by FTIR and ATR infrared spectroscopy techniques. A special attention was given to the N-H bond stretching absorption at 3300-3400 cm-1, since its first overtone is known to be the main cause of the optical absorption at l.55µm. An annealing study was performed in order to reduce or eliminate this bonding type. For the annealed samples the corresponding concentration was strongly reduced as verified by FTIR transmittance and ATR 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. lts absorption and insertion loss values were determined by butt-coupling method, resulting in low loss waveguides.