Film Optical Waveguides Research Articles

MgTiO3 thin films prepared by metalorganic solution deposition and their properties

We have proposed the application of metatitanate MgTiO3 thin films for optical and microwave devices. MgTiO3 thin films have been prepared by metalorganic solution deposition. MgTiO3 thin films were grown on a-plane Al2O3 substrate for optical device applications and on platinized Si for microwave applications. Epitaxial MgTiO3 thin films were obtained on the a-plane Al2O3 substrate. These MgTiO3 thin films grown on Al2O3 have fine features in surface microstructures. The grain size of MgTiO3 thin films crystallized at a temperature of 700°C is less than 70 nm and increased with the crystallization temperature. MgTiO3 thin films grown on Al2O3 are transparent in the visible and have a sharp absorption edge at the wavelength of 270 nm. This transparency with fine microstructures, i.e. smooth surface and small grain size, of MgTiO3 thin films suggests the feasibility of MgTiO3 thin films for optical waveguides or as the buffer layer of multilayer integrated optic devices. MgTiO3 thin films made on Pt electrodes were highly 110 oriented and their surface morphology was also very fine. The dielectric constant and dielectric loss of MgTiO3 thin films were 21 and 2% at 100 kHz, respectively.

Superconducting and electro-optical thin films prepared by pulsed laser deposition technique

The pulsed laser deposition (PLD) technique is an excellent method to prepare single crystalline complex oxide thin films. We have successfully grown films for the use in HTS SQUID-devices as well as for thin film optical waveguides. The Josephson junction used in the HTS SQUIDs is formed by a step edge type grain boundary junction. The step preparation is a very critical process in the SQUID preparation to achieve reproducible low 1/f noise devices. We have established a new ion beam etching process to achieve clean and steep edges in LaAlO3(100) substrates. The 1/f noise of SQUIDs prepared with the new method is drastically reduced. In the process of developing thin film electro-optical waveguide modulators we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO3 thin films. These films are grown on MgO(100), MgAl2O4(100), SrTiO3(100) and MgO buffered Al2O3(11̄02) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C), X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The dielectric constant, the ferroelectric hysteresis loop and the transition temperature (ferroelectric to paraelectric state) of the BaTiO3 thin films are measured.

Optimization of plasma-deposited silicon oxinitride films for optical channel waveguides

In view of applications of SiO x N y thin films in MOEMS technology, a study of the optomechanical characteristics of the PECVD deposited material are investigated. To optimize the quality of SiO x N y layers we establish the relationship between the chemical properties, optical performances, micromechanical stress, and growth parameters of deposited films. To use the SiO x N y thin film for the core layer of a strip-loaded waveguide, we propose preparation conditions of SiO x N y that offer a low-loss optical waveguide with well-controlled refractive index, based on a low-internal stress multilayer structure.

Study of optical waveguide of barium sodium niobate films on potassium titanyl phosphate

Barium sodium niobate (BSN) optical waveguide films were grown on potassium titanyl phosphate (KTP) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray pole spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the as-grown BSN films are epitaxially smooth, fine-particled and show small constituent deviation. Both m lines of the waveguided TE and TM modes were recorded. Lattice match between the BSN(110) and both the KTP(001) and KTP(100) planes is examined with mismatch less than 3%. Effective refractive indices as a function of incident wavelength and order of the waveguided modes are studied. A phase matching relationship of k(1)−2k(0)=0 is established between the first-order and fundamental modes in the BSN/KTP waveguided system. Effective thicknesses for TE and TM modes were obtained to be equal to 0.76 and 0.72 μm, respectively, larger than the thickness of the as-grown BSN film of 0.60 μm. A constituent ratio of Ba:Na:Nb in the BSN film measured was equal to 2:0.82:5.14, slightly deviating from the stoichiometric ratio of 2:1:5, which is attributed to higher relative asymptotic velocity for Nb species and higher evaporation pressure for Na species. Finally, the main factors affecting quality of the as-grown BSN films are also discussed.

Inductively Coupled Plasma-Enhanced Chemical Vapor Deposition of SiO2 and GeO2–SiO2 Films for Optical Waveguides Using Tetraethylorthosilicate and Tetramethylgermanium

SiO2 and GeO2–SiO2 films have been deposited by employing inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) from tetraethylorthosilicate (TEOS) and oxygen discharge using tetramethylgermanium (TMGe) as a dopant. A pure SiO2 film deposited with TEOS:O2 at a flow rate ratio of 17% and an operating pressure of 5 Pa showed a low wet-etching rate of 114 nm/min approaching that of a thermally grown oxide. Ge doped SiO2 films were deposited at various TMGe flow rates, and it was found that Ge was incorporated into the film as a replacement for Si. The refractive index of the film is in proportion to the Ge content in the film. Fourier transform infrared (FTIR) analysis confirmed that there were few O–H and C–H defects in the films. Optical waveguides were fabricated using ICP-CVD and reactive ion etching (RIE). A propagation loss of 0.027 dB/cm at 1.55 µm was achieved for the optical waveguide by using GeO2–SiO2 film as the core layer.

BaTiO3 Waveguides on MgO Buffered-Sapphire Single Crystals

AbstractWithin our program to develop ferroelectric thin film optical waveguides, we have studied the growth of epitaxial waveguides BaTiO3 on r-plane sapphire substrates with a MgO buffer layer. The films were prepared by pulsed laser deposition (PLD). Their structural properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) in random and channeling (RBS-c) configuration and atomic force microscopy (AFM). They displayed good crystalline quality, characterized by an RBS-c minimum yield of about 4–6%, a full width at half maximum (FWHM) of the XRD rocking curve measurement of the BaTiO3(200) reflection of 0.32° and a rms roughness of 1.2 nm in a film of ∼ 1.0 μm thickness. The epitaxial relationship was found to be BaTiO3(100) // MgO(100) // A12O3(1102). The refractive index, the birefringence and the optical losses have been measured.

From Ferroelectrics to Polymers - Perspectives for Thin Film Optical Waveguides and Devices

AbstractPresently commercial optical fiber links experience an explosive growth. On the other hand, the integration of optical functions on a single substrate (“Integrated Optical Device”) is still mostly limited to the R & D-laboratories. Only Mach-Zehnder modulators, made from ferroelectric crystals, have found commercial applications so far. The development phase of the integrated optical devices, based on bulk crystalline LiNbO3, is now covering a time span of nearly 30 years. In comparison, the development of the thin film growth of optical oxide ferroelectrics or of tailored optical polymers is just a few years old and we are still at the beginning of the learning curve.

Polymeric optical waveguide films for short-distance optical interconnects

We describe three different applications of polymeric waveguide films as short-distance optical interconnects. We fabricated the waveguide films, which were 6.5 cm long and mounted in MT-compatible (MTC) connectors by passive alignment, for MM fiber systems with a 50-/spl mu/m diameter graded index (GI) core. The average insertion loss of these devices was approximately 0.6 dB at 0.85-/spl mu/m wavelength. We also fabricated waveguide films with a 350 mirror and an MTC connector for use as 90/spl deg/ out-of-plane optical deflectors, and they exhibited an insertion loss of 1 dB. Two silica planar waveguides for single-mode (SM) fiber systems were also connected by a polymeric waveguide film. Low insertion losses were obtained in both MM and SM films designed to be employed as bending waveguides. This reveals their good potential for use as practical short-distance optical interconnects.

Packaging for a 40-channel parallel optical interconnection module with an over-25-Gbit/s throughput

NTT is currently working on developing a high-throughput interconnection module that is both compact and cost effective. The technology being developed is called parallel inter-board optical interconnection technology, or ParaBIT. The ParaBIT module that has been developed is the first step; it is a front-end module with 40 channels, a throughput of over 25 Gbit/s, and a transmission distance of over 100 m along multimode fibers. One major feature of this module is the use of vertical-cavity surface-emitting laser (VCSEL) arrays as very cost-effective light sources. These arrays enable the same packaging structure to be used for both the transmitter and receiver. To achieve super-multichannel performance, high-density multiport bare-fiber (BF) connectors were developed for the module's optical interface. Unlike conventional optical connectors, these BF connectors do not need a ferrule or spring. This ensures physical contact with an excellent insertion loss (less than 0.1 dB per channel). A polymeric optical waveguide film with a 45/spl deg/ mirror for coupling to the VCSEL and photo-diode (PD) arrays by passive optical alignment was also developed. To facilitate coupling between the VCSEL/PD array chips and the waveguide, a packaging technique was developed to align and die bond the optical array chips on a substrate. This technique is called transferred multichip bonding (TMB); it can be used to mount optical array chips on a substrate with a positioning error of only several micrometers. These packaging techniques enabled ultra-parallel interconnections to be achieved in prototype ParaBIT modules.

Singular perturbation theory of a thin film surface-polariton polarizer for a planar optical waveguide

An on-line polarizer of the order of a millimeter in length is designed by locating a thin metal film suitably close and parallel to a dielectric film waveguide. The polarizer transmits the transverse electric guided mode of the dielectric film with negligible insertion loss. As a consequence of the phase-matched wave interaction between the surface polariton supported by the metal film and the transverse magnetic guided mode of the dielectric film, the transverse magnetic guided mode is severely attenuated resulting in a high extinction coefficient. A singular perturbation theory using multiple space scales is developed for the analysis of this thin film surface polariton polarizer for a planar dielectric film optical waveguide and illustrative numerical results are presented. The sensitivity of the performance of the polarizer to small changes in the various physical parameters is examined.

Polymeric optical waveguides for optical interconnections

Free-standing polymeric optical waveguide films with 45° mirrors and MT connectors (mechanically transferable spacing connectors) were fabricated by spin-coating, photolithography and reactive ion etching. The spin-coated films had sufficient thickness controllability and surface smoothness for them to be used to fabricate multimode waveguides with a low loss of less than 0.02 dB/cm at 0.83 μm using deuterated-polymethylmethacrylate for the core and UV-cured resin for the cladding. For application to optical interconnections, a 45° mirror was formed in the waveguide by using a 90° V-shaped diamond blade, and the mirror loss was 0.3–0.7 dB depending on the measurement conditions. Free-standing polymeric waveguide films were mounted in an MT-compatible connector made of Pyrex glass by using UV curable resin. The insertion loss was about 1 dB which was sufficiently low for practical use.

ポリマー光導波路フィルムの表面状態の評価

Polymeric optical waveguide films have been developed with a view to optical interconnection module applications. Three fabrication processes are employed: (1) spin coating to form thick films, (2) reactive ion etching (RIE) to form core ridges, and (3) cutting with a diamond saw to form 45° mirrors. We evaluated the surface roughness of the fabricated films, core-ridges and mirrors using an atomic force microscope (AFM) and a scanning electron microscope (SEM), and discuss them in relation to the optical characteristics. Spin coating provides a uniform film with a roughness of less than 3nm. The etched surfaces of the core ridges fabricated by RIE have a roughness of less than 0.3μm, which suggests that this roughness causes the loss of the curved waveguide. The diamond saw cutting process generated a roughness of 50nm over the whole surface with occasional projections several hundred nanometers high, suggesting that this roughness causes the mirror loss.We confirmed that it is possible to fabricate polymer optical waveguide films with sufficient levels of performance for use in optical interconnection modules.

Synthesis and Characterization of Highly Oriented Sol-Gel (Pb, La) TiO3 Thin Film Optical Waveguides

The preparation and the optical characteristics of highly oriented PLT thin films are investigated. PLT films fabricated on MgO(100) and c-plane sapphire substrates have highly grown in (100) and (111) orientations, respectively. PLT films with high La content have a near cubic structure and weak anisotropy of refractive indices. The optical propagation losses of PLT films decrease as the La content of the films increases due to a complex interaction of surface roughness reduction and a reduction in the anisotropy refractive index. However, optical scattering in thicker sol-gel PLT thin film waveguides occurs by the internal scattering mechanism from the defects and the interfaces rather than by the surface scattering mechanism.

Polymeric optical waveguide films with 45°mirrors formed with a 90° V-shaped diamond blade

A novel method for forming high quality 45° mirrors in polymeric waveguides is described. Singlemode and multimode polymeric waveguide films with 45° mirrors were fabricated by cutting the waveguide with a 90° V-shaped diamond blade. The mirror losses were as low as 0.1 dB for the singlemode and 0.3 dB for the multimode waveguides.

Fluorinated Polyimides for Optical Applications.

Fluorinated polyimides are synthesized for optical application. They have good thermal stability, low water absorption, high optical transparency in visible and near-infraredregions, and refravtive index controllability. Film optical waveguide is fabricated using the fluorinated co-polyimides. This optical waveguide has single-mode and low optical loss of less than 0.3 dB/cm at the telecommunication wavelength of 1.3μm. This waveguide has high thermal and environmental stability.

PZT Electro-Optic Waveguide Devices Fabricated by Solid-Phase Epitaxy

ABSTRACTHigh quality epitaxial PZT optical waveguides have been grown by solid-phase epitaxy based on metal alkoxide solution process. Optical propagation loss was 4 dB/cm in epitaxial PZT thin film optical waveguides grown on SrTiO3 substrates. Epitaxial PZT optical waveguides were grown on Nb doped conductive SrTiO3 substrates, since considerable reduction in drive voltage will be expected when top electrode / optical waveguide / conductive substrate structures are realized. Propagation loss was relatively large, as compared with the structure using non-dope insulative substrates. Preliminary electrooptic deflection devices were fabricated by preparing prism electrodes on the surface of the PZT optical waveguides. Efficient deflection/switching of coupled laser beam in the PZT optical waveguides as large as 26 mrad was observed by applying 70 volts between prism electrode and Nb doped SrTiO3 substrates.

Excimer laser ablation of Ba 2NaNb 5O 15 optical waveguide films on MgO(001) substrates

Polycrystalline Ba 2NaNb 5O 15 (BNN) optical waveguide films were grown on MgO (001) substrates by excimer laser ablation for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were applied to characterize the as-grown BNN film, which showed that single-phase nearly stoichiometric BNN films, with flat surface and uniform thickness were obtained. The favorable optical waveguide properties were evaluated by m-line observation and measurement of the propagation loss of the He-Ne laser beam confined in the waveguide film of TE and TM mode.

Quasioptics of second-order Bragg interaction in a thin film optical waveguide

For the transverse magnetic mode, the second-order Bragg interaction of the guided and the radiated waves is considered for a thin film dielectric waveguide with a corrugated film–cover interface. A set of four canonical equations for the deexcitation and the excitation of the guided waves are derived by employing a quasioptical technique. The governing equations are applied for the treatment of a surface-emitting distributed feedback laser. Some design criteria are obtained for optimizing the performance of the laser. When these design criteria are used, the laser characteristics are insensitive to small changes in the physical parameters about their designed values. Numerical results are presented to illustrate the performance of the laser. The shape of the surface relief grating is found to play a vital role in determining the gain threshold and the gain margin of the laser.

Lattice matching, phase matching, and constituent consistency of optical waveguide Ba2NaNb5O15 films on KTiOPO4

Optical waveguide films of barium sodium niobate (BSN) grown on potassium titanyl phosphate (KTP) substrate by pulsed laser deposition (PLD) with a lattice geometry BSN(110)//KTP(001) were studied. A small lattice mismatch of 2.9% under such geometry was obtained, and excellent parallelism is established between the as-grown BSN(110) film and the KTP(001) substrate. Effective refractive index and effective thickness of the BSN films caused by Goos–Hanchen shifts are examined. A phase matching relation of k(1)–2k(0)=0 is obtained from the dispersion curves of effective refractive index of the BSN films versus incident wavelength for various orders of the guided wave modes (m=0, 1, 2, 3, and 4). The measured constituent ratio 2.0:0.82:5.14 of Ba:Na:Nb in the BSN film deviates slightly from the stoichiometric ratio 2:1:5, which is due to longer flight time and a comparatively higher evaporation pressure for sodium.

Direct observation of defect-diminished fatty acid monolayers and their optical applications

The aggregation structure of fatty acid monolayers on the water surface have been classified with respect to thermal ( T sp , T αc , T m ) and chemical (the degree of ionic dissociation of hydrophilic group) factors. In the case of amphiphiles with a non-ionic hydrophilic group, at T sp below T m , the monolayer is in a crystalline phase which is designated “the crystalline monolayer”. The crystalline monolayer is further classified into “the fusing-oriented crystalline monolayer” and “the randomly assembled crystalline monolayer” at T sp below and above T αc , respectively. At T sp above T m , the monolayer is in an amorphous phase which is designated “the amorphous monolayer”. In the case of amphiphiles with an ionic hydrophilic group, at T sp below T m , amphiphile molecules form “the compressing crystallized monolayer”, and T sp above T m , the monolayer is not crystallized by compression. Molecular-resolution images of molecules in the monolayers were successfully observed with an atomic force microscope (AFM) for the first time. A high mechanical stability of the monolayer is inevitably required for the non-destructive AFM observation of the fatty acid monolayer. For the preparation of the mechanically stable monolayer, the continuous compression method up to a low surface pressure and the multi-step creep method were used. Further, the Langmuir-Blodgett (LB) films with a homogeneous surface morphology could be constructed by the mechanically stable monolayers, and the morphological homogeneity was necessary for the construction of low-propagation loss LB film optical waveguides.