Browsing by Subject "Integrated optics"

Now showing 1 - 17 of 17

Open Access
Balancing gain narrowing with self phase modulation: 100-fs, 800-nJ from an all-fiber-integrated Yb amplifier
(IEEE, 2013) Pavlov, Ihor; Rybak, A.; Cenel, C.; İlday, F. Ömer
There is much progress in Yb-fiber oscillator-amplifier systems, which enable generation of high-repetition-rate, microjoule energies and sub-picosecond pulse widths [1,2]. Given the extremely large total gain factors to reach microjoules starting from nanojoules, which is often in the range of 40-60 dB, due to losses, and the impact of mismatched high-order dispersion as temporal stretching and compression of pulses by large factors (30-40 dB) need to be employed. As a result of these challenges, most of the Yb-fiber amplifiers have resulted in pulse durations of several 100 fs or longer. While pulse durations in this range are suited for some applications, there are many cases where 100-fs or shorter pulses in microjoule range are required. Gain narrowing can be effectively countered by self-phase modulation (SPM) [3] by limiting amplification factor in each stage of amplification and through careful optimization of SPM and inversion level along the gain fiber. The conceptual template is readily present in the evolution of the pulse inside the oscillator cavity, where gain factors are often in the 10-50 range per roundtrip. To the extend that the B-integral and the gain distribution along the amplifier can be kept identical to the oscillator by proper scaling of the chirped pulse width and fiber mode area, the original oscillator can be preserved in arbitrary number of amplification stages. Here, we demonstrate a highly fiber-integrated master-oscillator power-amplifier (MOPA) system, from which - 1 μJ pulses are extracted and externally compressed to 100 fs by arranging amplification in each stage as close as possible to the intra-cavity evolution. To our knowledge, these results are the shortest demonstrated from all-fiber-integrated amplifier at the microjoule level. © 2013 IEEE.
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.
Open Access
Computer aided analysis and simulation of complex passive integrated optical circuits
(1993) Önal, Gürkan
In this thesis, a method is developed for the analysis and simulation of arbitrary complex, single layer, rectilinear, passive optical interconnection circuits. The method considers dielectric waveguide type optical interconnections which can be beneficially employed at the chip-to-chip or backplane level of high performance computing circuits. In the method developed, a circuit is broken down into elementary blocks whose loss and coupling properties are known. Thus, the overall loss and noise for each connection can be calculated. A high speed algorithm based on this method has been imjjlemented. The high speed of the analysis system makes it suitable for incorporation in an iterative design system, which determines the minimum spacings I)etween the guides that result in acceptable crosstalk and noise levels.
Open Access
Computer-aided analysis and simulation of complex passive integrated optical circuits of arbitrary rectilinear topology
(SPIE, 1994-05) Önal, G.; Altintaş, A.; Özaktaş, Haldun M.
Optical interconnections can be beneficially employed at the chip-to-chip or backplane level of high-performance computing systems. One method of providing high speed and density interconnections among a large number of integrated circuit chips is with a passive integrated optics circuit. We have developed a method of breaking down arbitrarily complex rectilinear circuits into elementary blocks whose loss and coupling properties are known. Thus, the overall loss and noise for each connection can be calculated. A high-speed algorithm based on this method has been implemented. The high speed of our analysis system makes it suitable for incorporation in an iterative design system, which determines the minimum spacings between the guides and results in acceptable crosstalk and noise levels.
Open Access
Doping management for high-power fiber lasers: 100 W, few-picosecond pulse generation from an all-fiber-integrated amplifier
(Optical Society of America, 2012-07-16) Elahi, P.; Yilmaz, S.; Akçaalan, Ö.; Kalaycioğlu, H.; Öktem, B.; Şenel, Ç.; Ilday, F. Ö.; Eken, K.
Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100 W at 100 MHz with pulse energy of 1 μJ. The seed source is a passively mode-locked fiber oscillator operating in the all-normaldispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13 ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5 ps pulses with ∼200 kW peak power directly from fiber, without using external pulse compression.
Open Access
An elastomeric grating coupler
(IOP Institute of Physics, 2006) Kocabas, A.; Ay, F.; Dâna, A.; Aydınlı, Atilla
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. © 2006 IOP Publishing Ltd.
Open Access
Electro-optic modulation of InAs quantum dot waveguides
(Technische Universiteit Eindhoven, 2008) Akça, İmran. B.; Dâna, Aykutlu; Aydınlı, Atilla; Rossetti, M.; Li, L.; Fiore, A.; Dağlı, N.
The linear electro-optic properties in waveguides containing self-organized In As quantum dots were studied experimentally. Fabry-Perot measurements at 1515 nm on InAs/GaAs quantum dot structures yield a significantly enhanced linear electro-optic efficiency compared to bulk GaAs.
Open Access
Integrated asymmetric vertical coupler pressure sensors
(SPIE, 2004) Kıyat, İsa; Kocabaş, Aşkın; Akçağ, İmran; Aydınlı, Atilla
Design and analysis of a novel pressure sensor based on a silicon-on-insulator asymmetric integrated vertical coupler is presented. The coupler is composed of a single mode low index waveguide and a thin silicon slab. Wavelength selective optical modulation of asymmetric vertical coupler is examined in detail. Its potential for sensing applications is highlighted as an integrated optical pressure sensor which can be realized by standard silicon micro-fabrication. Sensitivity of transmission of such couplers on refractive index change of silicon slab ensures that they are good candidates for applications requiring high sensitivities.
Open Access
Integrated optical displacement sensors for scanning force microscopies
(2003) Kocabaş, Coşkun
In this thesis, we have studied the use of integrated optical waveguide devices acting as integrated displacement sensors on cantilevers for scanning probe microscopes. These displacement sensors include integrated optical waveguide devices such as Bragg gratings, ring resonators, race track resonators and waveguide Michelson interferometers fabricated on a cantilever to measure the displacement of the cantilever tip due to the forces between surface and the tip. The displacement of the cantilever tip is measured directly from the change of the transmission characteristics of the optical device. As the cantilever tip displaces, the stress on the cantilever surface changes the refractive index of the materials that make up the integrated optical device which cause variations in its optical transmission characteristics. We have also studied an optical waveguide grating coupler fabricated on the cantilever for the same purpose. In two different embodiments of this device, light is either coupled in or out of the waveguide via the waveguide grating coupler. The displacement of the cantilever alters the direction of the scattered light and measuring the power of the scattered light with a position sensitive detector allows for the detection of cantilever i tip displacement. The novel design proposed in this work provides very high displacement sensitivity of the order of 10−4˚A−1 .
Open Access
Low-power thermooptical tuning of SOI resonator switch
(IEEE, 2006) Kiyat, I.; Aydınlı, Atilla; Dagli, N.
A wavelength selective optical switch is developed based on a high-Q racetrack resonator making use of the large thermooptic coefficient of silicon. The racetrack resonator was fabricated using a silicon-on-insulator (SOI) single-mode rib waveguide. The resonator shows a high Q factor of 38 000 with spectral sidelobes of 11 dB down and can be thermooptically scanned over its full free-spectral range applying only 57 mW of electrical power. A low power of 17 mW is enough to tune the device from resonance to off-resonance state. The device functions as a wavelength selective optical switch with a 3-dB cutoff frequency of 210 kHz.
Open Access
Microjoule-energy, 1 MHz repetition rate pulses from all-fiber-integrated nonlinear chirped-pulse amplifier
(Optical Society of America, 2010-03-23) Kalaycioglu, H.; Oktem, B.; Şenel, Ç.; Paltani, P. P.; Ilday, F. Ö.
We demonstrate generation of pulses with up to 4 μJ energy at 1 MHz repetition rate through nonlinear chirped-pulse amplification in an entirely fiber-integrated amplifier, seeded by a fiber oscillator. The peak power and the estimated nonlinear phase shift of the amplified pulses are as much as 57 kW and 22π, respectively. The shortest compressed pulse duration of 140 fs is obtained for 3.1 μJ of uncompressed amplifier output energy at 18 π of nonlinear phase shift. At 4 μJ of energy, the nonlinear phase shift is 22 π and compression leads to 170-fs-long pulses. Numerical simulations are utilized to model the experiments and identify the limitations. Amplification is ultimately limited by the onset of Raman amplification of the longer edge of the spectrum with an uncompressible phase profile.
Open Access
Monolithic and hybrid silicon-on-insulator integrated optical devices
(2005) Kiyat, İsa
Silicon, the basic material of electronics industry is rediscovered nowadays for its potential use in photonics and integrated optics. The research activity in silicon integrated optics have been speeding up during the last decade and even attracting interest of leading industrial companies. As a contribution to this world wide effort, we have designed, fabricated and characterized a class of monolithic and hybrid silicon integrated optical devices. These devices were realized on high-quality silicon-on-insulator (SOI) wafers. Beam propagation method (BPM) based simulations and analytical calculations were employed for the design. We have demonstrated for the first time an SOI device that splits light into its TE and TM components. An SOI rib waveguide becomes birefringent as its size reduced. This idea is used to design and fabricate a directional coupler polarization splitter based on geometrical birefringence. The device uses 1 µm sized SOI waveguides. This compact device (only 110 µm in length) shows extinction ratios larger than 20 dB. SOI waveguides with the same geometry was used to realize a batch of single and double bus racetrack resonators having radii in the range of 20 to 500 µm. Design of these racetrack resonators are presented in detail. The bending loss and coupling factor calculations were performed using BPM. During the design and analysis of waveguide resonators, we proposed a novel displacement sensor that can be used for scanning probe microscopies. The sensor operates by means of monitoring the changes in transmission spectrum of a high finesse micro-ring resonator due to stress induced by displacement. Operation principles and sensitivity calculations are discussed in detail. SOI resonators with quality factors (Q) as high as 119000 have been achieved. This is the highest Q value for resonators based on SOI rib waveguides to date. Finesse values as large as 43 and modulation depths of 15 dB were observed. Free spectral ranges increased from 0.2 nm to 3.0 nm when radius was decreased from 500 to 20 µm. The thermo-optical tunability of these resonators were also studied. A high-Q racetrack resonator is used to develop a wavelength selective optical switch. The resonator was thermo-optically scanned over its full free spectral range applying only 57 mW of electrical power. A low power of 17 mW was enough to tune from resonance to off-resonance state. The device functioned as a wavelength selective optical switch with a 3 dB cutoff frequency of 210 kHz. We have also demonstrated wavelength add/drop filters using the same racetrack resonators with double bus. Asymmetric lateral coupling was used in order to get better filter characteristics. Filters with crosstalks as low as -10.0 dB and Q-factors of as high as 51000 were achieved. Finally, we introduce the use of a layer transfer method for SOI wafers. Such a layer transfer results in the possibility of using the back side of the silicon layer in SOI structure for further processing. With this method, previously fabricated SOI waveguides were transferred to form hybrid silicon-polymer waveguides. Benzocyclobutene (BCB) polymer was used as the bonding agent. The method is also applied to SOI M-Z interferometers to explore the possibilities of the technology. We additionally studied asymmetric vertical couplers (AVC) based on polymer and silicon waveguides and fabricated them using a hybrid technology.
Open Access
An optical microcantilever with integrated grating coupler
(IEEE, 2009-06) Olcum, Selim; Karademir, Ertuğrul; Taş. Vahdettin; Akça, İmran; Kocabaş, Aşkın; Atalar, Abdullah; Aydınlı, Aydınlı
In this paper, we have fabricated an optical cantilever with an integrated grating coupler. We have used an inexpensive and repeatable method for integrating the grating to the silicon cantilever with a microfabrication compatible process. The sensitivity of the method can be further increased by integrating the detection circuitry onto the cantilever substrate. We believe that this is a promising method for sensing applications which provide a simple yet sensitive measurement technique using microcantilevers.
Open Access
Polarization characteristics of compact SOI rib waveguide racetrack resonators
(IEEE, 2005) Kiyat, I.; Aydınlı, Atilla; Dagli, N.
We report on the development of compact optical racetrack resonators on silicon-on-insulator (SOI) rib waveguides. We make use of large-cross-section waveguides instead of photonic wire waveguides. We fabricated resonators with bending radii down to 20 μm and characterized for both transverse-electric and transverse-magnetic polarizations. Different polarization characteristics were analyzed and related to the modal shape of the SOI waveguide. These compact resonators show large free spectral ranges (3.0 nm), high finesse (19), and Q-factor (28 000) values.
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-on-insulator optical waveguides and waveguide devices
(2000) Kiyat, İsa
Silicon-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.
Open Access
Study of wet oxidized AlxGa1-xAs for integrated optics
(Institute of Electrical and Electronics Engineers, 1999) Bek, A.; Aydınlı, Atilla; Champlain, J. G.; Naone, R.; Dagli, N.
An investigation of wet oxidized AlxGa1-xAs layers in integrated optical applications is reported. Refractive index and thickness shrinkage of wet oxidized AlxGa1-xAs layers are measured using spectroscopic ellipsometry. A Cauchy fit to the refractive index is found in the wavelength range between 0.3 and 1.6 μm. The refractive index at 1.55 μm is found to be 1.66±0.01 with little dispersion around 1.55 μm. Very low loss single-mode waveguides with metal electrodes showing very low polarization dependence of loss coefficient are fabricated using wet oxidized AlxGa1-xAs layers as upper cladding. Optical polarization splitters are also designed and fabricated from the same type of waveguides taking advantage of increased birefringence. Designs utilizing wet oxidized AlxGa1-xAs are compared with conventional designs using only compound semiconductor heterostructures.