Properties Of Optical Waveguides Research Articles

Low loss silica waveguides containing Si nanocrystals

AbstractWe study the optical and structural properties of rib-loaded waveguides working in the 600-900 nm spectral range. A Si nanocrystal-rich SiOx with Si excess nominally ranging from 10 to 20% forms the active region of the waveguide. Starting materials were fused silica wafers and 2 μm-thick SiO2 thermally grown onto Si substrate. Si nanocrystals were precipitated by annealing at 1100°C after quadruple Si ion implantation to high doses in a flat profile. The complete phase separation and formation of Si nanocrystals were monitored by means of optical tools, such as Raman, optical absorption and photoluminescence. Grain size distribution was obtained by electron microscopy. The actual Si excess content was obtained by X-ray photoelectron spectroscopy. The rib-loaded structure of the waveguide was fabricated by photolitographic and reactive ion etching processes, with patterned rib widths ranging from 1 to 8 μm. M-lines spectroscopy measurements provided a direct measurement of the refractive index and thickness of the active layers versus Si excess. When coupling a probe signal at 780 nm or 633 nm into the waveguide, an attenuation of at least 11 dB/cm was observed. These propagation losses have been attributed to Mie scattering, waveguide irregularities and direct absorption by the silicon nanocrystals.

UV-laser assisted Fabrication of integrated-optical Waveguides

By UV-laser-irradiation a controllable change of the refractive index of some polymers can be attained in the irradiated zone. The detailed UV-photon-induced process mechanisms have been investigated on the basis of PMMA employed as an UV-modifiable model polymer. By mask lithographic methods the UV-laser-assisted technology for the modification of the polymer optical properties enables the local increase of the refractive index and thus the fabrication of integrated-optical waveguiding elements in the surface of a planar polymer chip. These elements are relevant for the manufacturing of complex integrated-optical components. The optical and functional properties of the integrated-optical waveguides have been characterized.

Propagation loss in three-dimensional photonic crystal waveguides with imperfect confinement

Perfect confinement and efficient propagation of electromagnetic (EM) waves can be realized in waveguides created into a three-dimensional (3D) layer-by-layer photonic crystal that exhibits a complete band gap. However, the difficulty to build very thick 3D photonic crystals in the fundamental optical and infrared regimes by means of current lithography techniques will induce leakage of EM waves away from the waveguide through limited cladding layers. In order to assess the degradation of the optical properties of these photonic crystal waveguides, we build waveguides in a microwave-frequency 3D layer-by-layer photonic crystal and measure the leakage induced propagation loss. We find that this propagation loss exponentially decays with respect to the thickness of the cladding wall of the waveguide. The measurement results can scale to optical and infrared wavelengths and provide useful information for optimal design of photonic crystal structures in these regimes.

Erratum to “Compensating and equivalence properties of optical waveguides with a linear and sinusoidal variation of the core refractive index and core size along the propagation direction”

Microwave and Optical Technology LettersVolume 39, Issue 4 p. 348-348 Free Access Erratum to “Compensating and equivalence properties of optical waveguides with a linear and sinusoidal variation of the core refractive index and core size along the propagation direction” P. C. Pandey, P. C. Pandey Ajay Kumar Garg Engg. College, Ghaziabad, 27th Km stone Delhi, Hapur By Pass, Adhyatmik Nagar Ghaziabad–201009, U.P., IndiaSearch for more papers by this authorS. P. Ojha, S. P. Ojha Dept. of Applied Physics, I.T., BHU, Varanasi–221005, IndiaSearch for more papers by this author P. C. Pandey, P. C. Pandey Ajay Kumar Garg Engg. College, Ghaziabad, 27th Km stone Delhi, Hapur By Pass, Adhyatmik Nagar Ghaziabad–201009, U.P., IndiaSearch for more papers by this authorS. P. Ojha, S. P. Ojha Dept. of Applied Physics, I.T., BHU, Varanasi–221005, IndiaSearch for more papers by this author First published: 10 September 2003 https://doi.org/10.1002/mop.11212AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. REFERENCE 1 P.C. Pandey and S.P. Ojha, Compensating and equivalence properties of optical waveguides with a linear and sinusoidal variation of the core refractive index and core size along the propagation direction, Microwave Opt Technol Lett 28 (2001), 326– 328. Volume39, Issue420 November 2003Pages 348-348 ReferencesRelatedInformation

Optical gain, gain saturation, and waveguiding in group III‐nitride heterostructures

The optical gain and waveguiding properties of nitride heterostructures are essential prerequisites for device optimisation. We address the mechanism of optical gain using direct measurements of optical gain spectra and demonstrate the impact of polarisation fields. Limits to the optical gain are shown to be imposed by carrier escape and by gain saturation. Control of guided modes by waveguiding nitride structures differs from other materials due to their birefringence. Careful optimisation is therefore needed in order to obtain good far-field properties. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical waveguiding properties of lead titanate thin films grown on quartz by pulsed-laser deposition

Waveguiding thin films of lead titanate have been deposited on quartz substrate by pulsed-laser deposition. The quartz substrate temperature and the oxygen pressure in the ablation chamber were optimized in order to limit the formation of the pyrochlore phase in the film. The surface morphology observed by atomic force microscopy is characterized by a roughness in the range of 5–10 nm with only some droplets. The optical waveguiding performances were demonstrated by using the m-lines spectroscopy technique. The optical losses measured by a CCD camera were found to be less than 2 dB cm−1.

Amorphous Thin Films of Chiral Binaphthyls for Photonic Waveguides

The synthesis of chiral nonracemic materials and the polarization properties of chiral optical waveguides fabricated from them are presented. These materials are based on binaphthyl compounds designed to produce a glassy isotropic optically active material in a thin solid film form. Chiral‐core optical waveguides may find use as novel elements in integrated optic devices for photonics applications.

Effect of OH-group content on optical properties of silica core fiber waveguides during reactor irradiation

The transient optical loss (TOL) of silica core optical fiber waveguides of KU-1 grade (Russia, OH content 1000 ppm) and K-3 grade (Japan, OH content 10 ppm) have been measured during pulsed reactor irradiation (BARS-6 pulsed fission reactor (IPPE), pulse 80 μs, dose per pulse <5.5×10 12 n/cm 2 (9 Gy), dose rate <7×10 16 n/cm 2 s (1.1×10 5 Gy/s) in the visible range (fixed wavelengths 532 and 632 nm). Strong contribution from the light scattering induced by the irradiation in the silica fibers resulted in TOL. The light scattering is responsible for similarity of the spectral and temporal dependence of TOL of the optical fibers tested. The TOL of the unirradiated silica fibers is lower in the fiber with higher OH-group concentration (KU-1), whereas the difference in TOL of the KU-1 (high OH) and K-3 fiber (low OH) irradiated to a dose of ≈10 3 Gy is not so significant. The lower TOL of the KU-1 fiber is probably due to the effect of OH-groups on phase stability in the trap subsystem.

GROWTH AND CHARACTERIZATION OF C-ORIENTED LiNbO3 THIN FILMS ON Si (100) BY PLD

Lithium niobate ( LiNbO 3) thin film is an important material for optical waveguide. Recently, particular attention has been paid to the application of LiNbO 3 (LN) thin films. To develop and fabricate integrated optical devices, the growth of thin LN epitaxial films onto silicon substrate is of great importance and particularly attractive. In this paper, LN thin film was grown by pulsed laser deposition (PLD). Stoichiometric LN ceramic is used as a target. Amorphous SiO 2 buffer layer was coated on Si (100) wafer by in-situ themal oxidation before the deposition. The optimized condition of growing LN film on Si (100) by PLD is found: O 2 pressure 30 Pa, substrate temperature 600°C. Only (006) reflection of LN was observed besides the (002) reflection of silicon substrate from XRD pattern. The FWHM (~0.21°) of (006) reflection peak is much narrower than the value reported by Lee [1]. The results of XRD measurement indicate that the LN film was epitaxially grown along the c-axis. Transmission electron microcopy (TEM) patterns confirm that the film has superior crystalline quality. The optical waveguiding properties of the films were demonstrated by a prism coupler method. Fully c-oriented thin film could be grown on silicon substrate by PLD without the buffer layer and the induced electric field.

Poly(p-phenylenevinylene) derivatives: new promising materials for nonlinear all-optical waveguide switching

Several new derivatives of poly(p-phenylenevinylene) (PPV) are investigated regarding their linear and nonlinear optical material and waveguide properties, including their nonlinear photonic bandgap properties that are induced by photoablated periodic Bragg gratings. The new materials were prepared by means of the polycondensation route, which yields polymers with excellent solubilities and film-forming properties. Comparative data suggest that the new polycondensation-type MEH-PPV (completely soluble, strictly linear and fully conjugated), in particular, is the most promising polymer under investigation to fulfill the requirements for all-optical switching in planar waveguide photonic bandgap structures. UV-photobleaching techniques and photoablation in the UV, VIS, and near-infrared ranges at different pulse durations are investigated. Homogeneous submicrometer gratings that serve as Bragg reflectors have been fabricated in MEH-PPV thin films by application of these methods. The great potential of this type of materials for nonlinear all-optical switching applications that arises from their unique optical properties and their patterning behavior is discussed in detail. Numerical simulations of a switching device based on gap-soliton formation in a nonlinear periodic waveguide structure with the newly obtained material data have been carried out. We show that one can expect photonic bandgap all-optical switching in MEH-PPV planar waveguides. Device performance considering different grating parameters is discussed.

Optical properties of waveguides fabricated in fused silica by femtosecond laser pulses.

With tightly focused femtosecond laser pulses, waveguides are fabricated in fused silica. The guiding and attenuation properties of these waveguides at wavelengths of 514 nm and 1.5 microm are studied. We demonstrate that by changing only the writing speed, waveguides with a controllable mode number can be produced.

Sol-gel fabrication and properties of optical channel waveguides and gratings made from composites of titania and organically modified silane

Optical waveguide thin films have been prepared from composites of TiO 2 and organically modified silane (ormosil) at low temperature by the sol-gel technique, using γ-glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as precursors. Atomic force microscopy and ellipsometry have been used to characterize the morphologies and properties of the waveguide thin films deposited on compound-semiconductor and silicon substrates. These results indicated that a dense and porosity-free waveguide film could be obtained at 100°C. The refractive index of the film could be varied from 1.44 to 1.55 at 633 nm by varying the titanium content. It was experimentally demonstrated that a channel waveguide and grating structures could easily be fabricated for these composite thin films by etching and embossing. It was found that this method is specifically useful for the fabrication of diffractive grating and optical planar waveguides on sol-gel-derived glass films coated on temperature-sensitive substrates such as III-V compound semiconductors. By this means, channel waveguides have been fabricated using laser writing and reactive ion etching or wet etching, and gratings with a period of 1.102 μm and depth of 57.2 nm have also been obtained by embossing.

AlGaAs-based two-dimensional photonic crystal slab with defect waveguides for planar lightwave circuit applications

An AlGaAs-based near-infrared 2-D photonic crystal (PC) with an air-bridge structure featuring defect waveguides has been developed. For the sample without defect waveguides, measurements of the optical transmission characteristics in the wavelength range from 850 nm to 1100 nm showed a deep attenuation due to a bandgap with 30-35 dB attenuation and transmittance of nearly 100% for the guided modes. Optical propagation properties of defect waveguides were obtained by two methods: measurements of transmission spectra and plan-view observations of the optical beam trace along the waveguide with an infrared-vidicon camera. 3-D finite-difference time-domain simulations for the band structure and transmission spectra in the air-bridge slab with and without defect waveguides have revealed the appearance of four defect propagation modes specific to the defect waveguide, between two slab modes for the defect-free photonic crystal slab. These defect modes were experimentally identified in the measured transmission spectra.

Molecular Azo Glasses as Grating Couplers and Resonators for Optical Devices

Multifunctional molecular glasses are versatile tools for organic optoelectronics. Their optical waveguide properties are of increasing interest. By using photopatterned molecular azo glass gratings, optical waves within multilayer devices can be controlled, optically excited, and brought to resonance.

Analysis of fundamental property of 2D photonic crystal optical waveguide with various medium conditions by condensed node spatial network

AbstractPhotonic crystals have a stopband characteristic (photonic bandgap: PBG) in which the light in a specific wavelength band is strongly attenuated. This structure is expected to exhibit the possibility of fine‐structure devices with sharp bends on the order of a wavelength that cannot be realized by weakly guided waves such as those in an optical fiber and a slab waveguide. However, significant difficulties are expected for their design and fabrication. Therefore, understanding and prediction by simulation are indispensable. To date, many analyses have been carried out by the FDTD method and the BPM method. In particular, for the fabrication of functional optical‐circuit devices, it is necessary to carry out a global analysis of the photonic crystal optical waveguide, including dielectric materials with dispersion and nonlinear effects. In this paper, the fundamental properties of photonic crystal optical waveguides containing various media are analyzed by means of the special feature of treating the medium condition in the condensed node spatial network method. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(5): 10–20, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10018

LiNbO/sub 3/ optical waveguides formed in a new proton source

Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r/sub 33/=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided.

Structural and optical properties of LiNbO3 thin films grown by pulsed laser deposition

We report the deposition of good quality, highly textured LiNbO 3 thin films on sapphire substrates using the pulsed laser deposition technique. Thin films composition and structure have been determined using Rutherford Backscattering Spectroscopy (RBS) and X-Ray Diffraction (XRD) experiments. The influence of deposition parameters such as substrate temperature and oxygen pressure on the structure of the films has been studied. To improve surface smoothness of the film, an off-axis geometry has been used. The substrate surface lies in the plane defined by the plasma plume. The optical waveguiding properties of the as-obtained films have been demonstrated by m-line measurements of transverse-magnetic and transverse-electric modes at 633 nm.

Porous silica materials as low- k dielectrics for electronic and optical interconnects

The need to decrease signal delay and cross-talk in interconnects within integrated circuits is becoming increasingly important as device dimensions shrink. Electrical connections require lower resistivity metals and lower dielectric constant insulating films to meet future goals. Even these materials may not provide for sufficient signal bandwidth, and so optical interconnections are also envisioned. Porous materials offer the opportunity to fabricate scaleable dielectric constant materials for both electrical and optical interconnections. At Rensselaer, we have been working on projects using porous silica materials (xerogels) as low- k dielectrics for electrical interconnections and as low refractive index ‘cladding’ materials for optical interconnections. This paper focuses on the relationship between the porosity of the material and its optical, electrical, interfacial and mechanical properties. We find porosity has profound effects on the adhesion and stability of thin metal or dielectric films deposited on porous materials. In some instances, such as copper, porosity actually enhances the stability of the film. In others, such as silicon dioxide or tantalum, small changes in porosity lead to buckling or delamination of the film. The interfacial properties also affect the diffusion of metals into these films. The leakage current of copper into porous silica films is an order of magnitude or more less than that through solid SiO 2. This may be the result of surface passivation processes used to make the materials hydrophobic. The elastic modulus of the films varies as a power law with density in accordance with the prediction for open-cell foam materials. Finally, the optical properties of waveguides formed using porous silica claddings are discussed. Core/cladding refractive index differences of 0.6 or more are possible for compact optical waveguide interconnects. Low refractive index, space-filling porous materials may also find uses in photonic crystal applications.

Influence of low-temperature buffer layers on the optical waveguiding properties of AlxGa1−xN alloys

The influence of buffer layers on the optical waveguide properties of nitride related semiconductors films grown on sapphire by metalorganic vapor phase epitaxy has been investigated. Using the prism coupling technique, we measured the ordinary (nTE) and extraordinary (nTM) refractive indices of AlxGa1−xN/AlN and AlxGa1−xN/GaN heterostructures, where AlN, GaN are low temperature buffer layers. We investigated the relationship between the refractive indices of AlxGa1−xN alloys and the Al content (x) at a wavelength of 632.8 nm: nTE=2.3240–0.33x. This investigation demonstrates optical waveguiding in gallium nitride materials. It is shown that the indices of thick AlxGa1−xN films are independent of the buffer layer (AlN, GaN). However, the optical propagation losses are highly sensitive to the crystalline quality of the layers, particularly to the density of dislocations in the film. The best optical result of 1.2 dB/cm is obtained when the GaN buffer layer was employed, in comparison to 1.8 dB/cm with the AlN buffer layer. We interpret these results in relation with the transmission electron microscopy analysis.

Four layer polymeric mode polarization filter for integrated optics

We report on our systematic study of fabrication and characterization of four-layer polymer waveguides. Various optical properties (such as refractive index, birefringence, and propagation loss) of polycarbonate and polystyrene waveguides are presented. The thin film structure consisting of glass/polycarbonate/polystyrene/air has been used for demonstrating polarization filter action because the two polymers are quite different with respect to their optical anisotropy. Modal electric field plots for both TE and TM are generated to support the observed behavior. It is also observed that the four-layer lightguide exhibits relatively low loss values compared to the monolayer configuration.