Browsing by Subject "Birefringence"
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Item Open Access A Compact Silicon-on-insulator Polarization Splitter(IEEE, 2005) Kiyat, I.; Aydınlı, Atilla; Dagli, N.A compact directional coupler-based polarization splitter is designed and realized using silicon-on-insulator (SOI) waveguides. Even though silicon does not have any material birefringence, the high index contrast obtained in the SOI platform and reduced waveguide dimensions makes it possible to induce significant birefringence. Polarization splitting is achieved by making use of this geometry-induced birefringence. In this work, we demonstrate polarization splitting in devices as short as 120 gm. Even smaller devices can be made using submicron-thick Si waveguides.Item Open Access Femtosecond self-doubling optical parametric oscillator based on KTiOAsO4(IEEE, 2003) Kartaloğlu, T.; Aytür, O.We report a femtosecond intracavity-frequency-doubled optical parametric oscillator that employs a single KTiOAsO4 crystal for both parametric generation and frequency doubling. This device generates a yellow output beam at 575 nm with 39.4% power conversion efficiency when synchronously pumped by a femtosecond Ti:sapphire laser at a wavelength of 796 nm. An intracavity retarder is employed to alleviate temporal pulse overlap problems associated with group velocity mismatch inside the KTiOAsO4 crystal.Item Open Access Passive polarization filtering in negative curvature hollow-core fibers(SPIE - International Society for Optical Engineering, 2023-10-05) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, Mustafa; Yin, Shizhuo; Guo, RuyonA novel negative curvature hollow-core fiber (NCF) design is proposed capable of spectral and polarization filtering in the near-infrared region. The designed six-tube silica-based NCF contains nest elements in the form of suspended tubes radially anchored with a pole to the outer cladding in the vertical direction. In contrast, standard nested cladding elements without any suspension are used through the horizontal axis. This fiber configuration introduces an asymmetry in the core, which helps maintain the orthogonal X and Y polarization states in the fiber core. Pole anchors in vertically positioned tubes only give rise to the spectral filtering confinement loss profile for a vertically polarized state. Based on the geometrical optimization of the fiber, we achieved an improved birefringence on the order of 10-5 with filtered wavelength losses below 0.01 dB/km in the wavelength range of 1.4 µm to 1.7 µm. The operational bandwidth, polarization extinction ratio, filtered wavelengths, birefringence, and modulation depth loss can be tuned by optimizing the fiber parameters, including outer tube thickness, nest tube diameter, and pole dimensions. This proposed fiber design with selective transmission spectrums has untapped potential sensing capabilities in hollow-core negative curvature fibers. © 2023 SPIE. All rights reserved.Item Open Access Plane-wave dynamics of optical parametric oscillation with simultaneous sum-frequency generation(Institute of Electrical and Electronics Engineers, 1999-06) Dikmelik, Y.; Akgün, G.; Aytür, O.This paper presents a theoretical analysis of sum-frequency generating optical parametric oscillators where a single nonlinear crystal is used for both parametric generation and sum-frequency generation. In these devices, the parametric and sum-frequency generation processes are both phase matched for the same direction of propagation inside the crystal. Different polarization geometries for which this simultaneous phase-matching condition can potentially be satisfied are identified and categorized, for both birefringent and quasi-phase-matching methods. Plane-wave coupled-mode equations are presented for each of these categories. Solutions of these coupled mode equations and calculation of the single-pass saturated signal gain are outlined. Intracavity signal photon flux density calculations based on these solutions lead to stable steady-state upconversion, multistability, and chaos. The dependence of the photon conversion efficiency on various design parameters are investigated.Item Open Access Plane-wave dynamics of optical parametric oscillation with simultaneous sum-frequency generation(IEEE, 1998) Akgün, Gülbin; Dikmelik, Yamaç; Aytür, OrhanThe plane wave dynamics of a single-crystal upconversion optical parametric oscillators (OPO) with simultaneous sum-frequency generation (SFG) was studied. It was presumed that simultaneous phase-matching of the SFG and OPO processes were achieved by utilizing birefringent phase matching (BPM). Potential polarization geometries for collinear BPM led to four different sets of coupled mode equations depending on which field components were common to the two processes. The sets were designated as classes A through D. Classes A and D were efficient frequency upconverters. The performance of class A OPO's was limited by crystal properties whereas classes C and D was optimized by adjusting the polarization rotation angle.Item Open Access Polar Policryps diffractive structures generate cylindrical vector beams(American Institute of Physics Inc., 2015) Alj, D.; Paladugu, S.; Volpe, G.; Caputo, R.; Umeton, C.Local shaping of the polarization state of a light beam is appealing for a number of applications. This can be achieved by employing devices containing birefringent materials. In this article, we present one such enables converting a uniformly circularly polarized beam into a cylindrical vector beam (CVB). This device has been fabricated by exploiting the POLICRYPS (POlymer-LIquid CRYstals-Polymer-Slices) photocuring technique. It is a liquid-crystal-based optical diffraction grating featuring polar symmetry of the director alignment. We have characterized the resulting CVB profile and polarization for the cases of left and right circularly polarized incoming beams.Item Open Access Prism coupling technique investigation of elasto-optical properties of thin polymer films(American Institute of Physics, 2004) Ay, F.; Kocabas, A.; Kocabas, C.; Aydınlı, Atilla; Agan, S.The use of thin polymer films in optical planar integrated optical circuits is rapidly increasing. Much interest, therefore, has been devoted to characterizing the optical and mechanical properties of thin polymer films. This study focuses on measuring the elasto-optical properties of three different polymers; polystyrene, polymethyl-methacrylate, and benzocyclobutane. The out-of-plane elastic modulus, refractive index, film thickness, and birefringence of thin polymer films were determined by means of the prism coupling technique. The effect of the applied stress on the refractive index and birefringence of the films was investigated. Three-dimensional finite element method analysis was used so as to obtain the principal stresses for each polymer system, and combining them with the stress dependent refractive index measurements, the elasto-optic coefficients of the polymer films were determined. It was found that the applied stress in the out-of-plane direction of the thin films investigated leads to negative elasto-optic coefficients, as observed for all the three thin polymer films.Item Open Access A self-doubling optical parametric oscillator based on aperiodically-poled lithium niobate(IEEE, 2001) Kartaloǧlu, Tolga; Figen, Ziya Gürkan; Aytür, OrhanA self-doubling optical parametric oscillator (SDOPO) having one-dimensional aperiodic grating structure based on a LiNbO3 crystal was constructed. The structure was designed to quasi-phase-match both second harmonic generation (SHG) and optical parametric oscillation (OPO) processes. The grating structure contained in the LiNbO3 crystal was based on the construction of a function by summing up two cosine functions with arbitrary phase and amplitude.Item Open Access Silicon based dielectrics : growth, characterization, and applications in integrated optics(Bilkent University, 2005) Ay, FeridunIn 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.Item Open Access Stress effects in prism coupling measurements of thin polymer films(Springer, 2005) Agan, S.; Ay, F.; Kocabas, A.; Aydınlı, AtillaDue 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 μm. PMMA waveguide films were found not to be birefringent. In contrast, both BCB and PS films exhibit birefringence albeit of opposing signs.Item Open Access Sub-50 fs all-fiber Yb-doped laser with anomalous-dispersion photonic crystal fiber(IEEE, 2013) Zhang, Zewang; Cenel, C.; Hamid, R.; İlday, F. ÖmerAn intense research effort has been channelled into improving mode-locked Yb-fiber oscillators in recent years. Despite efforts in all-normal dispersion oscillators, dispersion management is evidently necessary to reach pulse durations below 50 fs. This is implemented most commonly with bulk optical components in Yb-doped fiber lasers. Increased robustness remains a valuable trait, for which all-fiber-integration is highly desirable. Photonic crystal fibers (PCF) with anomalous dispersion have small mode field diameters, enhancing nonlinear effects and usually are birefringent. The first mode-locked laser to incorporate a PCF was reported in 2002 [1]. However, mode-locking was not self-starting owing to the residual birefringence of the PCF Since then, a number of dispersion-managed Yb-doped fiber lasers using PCFs and all-fiber-integrated lasers have been reported. After 10 years, no all-fiber-integrated Yb-fiber laser has been demonstrated to support pulses below 60 fs [2]. © 2013 IEEE.