Integration Of Optical Components Research Articles

On the classification of discrete modes in lossy planar waveguides: the modal analysis revisited

In integrated-optical components such as integrated optical detectors or semiconductor light amplifiers, multilayer dielectric waveguiding structures occur in which some layers may be strongly lossy or may have gain. In such structures, the classification of the guided modes may become impossible. This paper reviews the modal analysis in which modes are only considered in connection with their possible excitation with a current line-source. Starting from the lossless situation, the analysis is extended to the lossy case and the details of the classification problem are investigated numerically. It was found that the validity of a unique classification is always limited. For that reason it is investigated, whether the classification problem might be due to the fact that in the time-harmonic formulation, the physical requirement of causality has been lost. To test this hypothesis, wave propagation is investigated along lossy waveguides in the timeLaplace-transform domain and using Lerch's causality theorem. It surprisingly turns out that in the time-Laplace-transform domain, the discrete part of the longitudinal spectrum does not exist, so that the test of the hypothesis is not conclusive. The classification problem of guided modes in strongly lossy waveguides is still an open problem.

Low cost monomode, integrated optics polymeric components with passive fibre-chip coupling

The results of a polymeric fabrication technology for low cost, monomode, integrated optics components suitable for passive fibre-chip coupling are presented. The waveguide substrates are moulded by reaction casting from microstructured nickel moulds comprising waveguide and fibre alignment structures as well. An excess loss figure of 6 dB at 1.3 /spl mu/m wavelength was measured for a 3 cm long waveguide between two passively coupled monomode fibres.

Active Silicon Integrated Optical Circuits

AbstractActive Silicon integrated Optical Circuits (ASOC™) is a technology based on single-mode rib waveguides formed on silicon-on-insulator that is being used to manufacture commercial integrated optics components. Silicon waveguides have excellent properties for many applications in the 1.3 and 1.55 micron telecommunications bands including relatively low loss. An important aspect of ASOC™ technology is the development of a set of waveguide-based elements that can be assembled into practical integrated optics devices. The fundamental waveguide elements include bends, couplers and fiber-waveguide interfaces, and additional elements include doped structures and waveguide gratings. Discrete lasers and photodetectors are also incorporated into ASOC™ technology to form hybrid devices. The technology is being used to manufacture devices for applications in telecomunications and optical sensing, the first major product being a two-wavelength single-fiber bi-directional optical transceiver.

Mode coupling analysis for the design of refractive ion exchange integrated optical components

Refractive integrated optical planar components such as prisms and lenses, consist of alternating regions of high- and low-index planar waveguides. Boundary transmission losses depend on the coupling efficiency between the fundamental modes in the two regions. Hence, a choice of appropriate parameters to achieve maximum coupling efficiency is an important design criterion of these components. We propose the use of the Ritz-Galerkin (RG) procedure to characterize the modal fields in planar graded index waveguides for obtaining coupling efficiency and, hence, the optimal design features. The procedure is "exact" and simple analytical expressions have been obtained for coupling efficiency. Further, coupling to higher order modes can also be obtained to estimate the background noise in component design when parameters deviate from the optimum. To confirm the convergence, results have been compared with the exact numerical procedure based on the multilayer staircase approximation. Various variational procedures limited to the fundamental mode coupling efficiency calculations are also summarized in this paper along with a discussion on their accuracies.

Light-induced refractive index changes in singlemode channel waveguides in KTiOPO 4

Light-induced changes of the effective refractive index in Rb ↔ K ion-exchanged singlemode channel waveguides in KTiOPO 4 have been investigated in the visible wavelength region dependent on time, guided optical mode intensity and temperature. A hypothesis for the explanation of the light-induced effects is suggested. Thermooptic and pyroelectric effects are discussed. The light-induced refractive index changes do not restrict the function of integrated-optic components in the visible.

Passive fiber optic bus using bidirectional integrated optic bus access couplers

The feasibility of a passive fiber optic bus that uses bidirectional integrated optics bus access couplers is studied. The number of bus nodes can be increased when an optimized asymmetric bus access coupler is used instead of a symmetric one. A modified Ag-Na ion exchange process provides the possibility of manufacturing integrated optics asymmetric couplers for the bus. The process is suitable for the processing of integrated optics components that combine deep multimode waveguides with different core sizes on a single substrate. An access coupler is designed, modeled, and processed. The coupler is optimized for seven nodes; the asymmetry of the coupler is 5 dB.

Beam-propagation in magnetooptic waveguides

The propagation of modes in magnetooptic waveguides distinguishes between the forward and the backward direction. This effect is applied to the realization of integrated optical isolators and circulators. The paper presents a finite-difference beam propagation simulation of such devices. Two different directions of the waveguide magnetization are considered. Finally, some consequences with respect to the practical realization of nonreciprocal integrated optical components are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hybrid optical integration technology

AbstractThe combination of hybrid integration technology with guided‐wave optical technology is expected to provide more functional optical devices with high performance, compactness, and high productivity.This paper reviews recent developments in the hybrid integration of optical and electronic components with a silica‐based planar lightwave circuit on silicon. First, edge‐hybrid, surface‐hybrid, and film‐hybrid integration technologies are described. Next, basic technical issues concerning optical component integration, electronic component integration, and packaging are discussed. Emphasis is placed on optical alignment, component fixing, mode‐field matching, and antireflection techniques in the optical component integration. Finally, examples of fabricated hybrid‐integrated optical devices are presented.

System integration of optical devices and analog CMOS amplifiers

Monolithic system integration of optical components, photodetectors, and analog transimpedance CMOS amplifiers is presented. An advanced SWAMI LOCOS technique, based on a submicron CMOS process is applied. Different optical devices including waveguides, beam splitters, interferometers and mirrors have been integrated using this technique. The optical system consists of a SiON layer deposited on 2-/spl mu/m oxide. The waveguides are made of structured SiO/sub 2/ layers on top of the SiON layer. Leaky wave or butt coupled photodiodes and phototransistors are used as light detectors. The photocurrents are amplified by low-noise CMOS transimpedance amplifiers with high sensitivity. They were designed for a large dynamic range of photocurrents together with short recovery times and low noise. Their reliability and yield were optimized with new CAD tools.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of an ultralinear pockels effect modulator: a successive approximation method based on Poincaré sphere analysis

A technique for synthesizing electro-optic light-intensity modulators with linear modulation characteristics is described. This technique is a quantitative-qualitative procedure based on the properties of the Poincaré sphere, and it can be applied for synthesizing many types of polarization devices with bulk, fiber, or integrated optics components. As an example, a three-stage monochromatic modulator showing a highly linear response is designed using this technique and compared with other modulators reported in the literature. It was found that in our design the manner in which the maximum electro-optically induced retardance, Γ(T), is chosen greatly influences the response of the device. A comparison between the Poincaré sphere and the impulse response methods for the synthesis of optical birefringent networks is given.

Characterization of graded-index planar waveguides and analysis of modal coupling for the design of integrated optical components produced by ion-exchange in glass and induced by Kerr effect

Abstract An experimental analysis of graded-index (GRIN) planar waveguides produced by ion exchange in soda-lime glass is presented. This study is based on a recent model describing nonlinear diffusion. Likewise the modal coupling between planar waveguides, produced in the same substrate, is analyzed in order to design efficient integrated optical components. Finally, waveguiding structures induced by Kerr effect in glass are proposed and analyzed.

Simulation and analysis of waveguide based optical integrated circuits

The employment of single-mode fiber technology, the potentials of coherent optical communication systems, and the novel sensor applications have emphasized the need for integrated optical components, such as couplers, modulators, switches, filters, etc., that are reliable, precise, wavelength selective, and even polarization selective. The design of optimized integrated optical components requires a detailed understanding of the various electromagnetic propagation characteristics of the structures defining the devices. Typical optical structures such as dielectric slab waveguides with junctions, rib waveguides, grating structures, and other dielectric waveguiding geometries could also be made from anisotropic materials, and their properties could be electro-optically altered. In addition to providing optimized design, an accurate method that can simulate the operation of the device allows ways of exploring new concepts. The main objective of this paper is to present the use of these simulation techniques. Three methods for the simulation of the propagation of light through dielectric guiding structures have been considered here. These methods are the finite-difference time-domain (FDTD) method, the coupled-mode theory (CMT) and the beam-propagation method (BPM). The time-explicit FDTD method has been demonstrated to be a very powerful tool in the analysis of arbitrary shaped structures, which may contain abrupt discontinuities in both the propagation and the transverse directions. However, solving an optically long structure by the FDTD method will require a large amount of computer resource. Although the CMT and the BPM are not recommended to analyze a structure with large discontinuities in the propagation direction, they can analyze a long structure very effectively if the transition in the propagation direction is adiabatic. Thus, an optically large (thousands of wavelengths long) structure with bends, junctions, discontinuities, and long guiding structures can be partitioned and solved by a combination of these three techniques. After a review of the various simulation methods for optical circuits, this article focuses on the formulation and the implementation of the FDTD method. Examples are presented on simulations of structures of current practical interest.

Low-optical-loss glass thin films

Low-optical-loss glass thin films have been prepared using sputtering and electron beam deposition methods. Results of film composition and optical property measurements are presented. Glass films have been prepared with optical loss values of 0.5 dB/cm. We discuss factors limiting the reduction in optical loss for sputtered and vapor-deposited films. These films can be easily patterned using standard photolithographic processes for fabrication of integrated optics components, such as grating couplers and planar lenses.

Silica waveguides on silicon and their application to integrated-optic components

A marriage of optical fibre fabrication technology and LSI microfabrication technology gave birth to fibre-matched silica waveguides on silicon: thick glass layers of high-silica-content glass are deposited on silicon by flame hydrolysis, a method originally developed for fibre preform fabrication. Silica channel waveguides are then formed by photolithographic pattern definition processes followed by reactive ion etching. This ‘high silica (HiS) technology’ offers the possibility of integrating a number of passive functions on a single silicon chip, as well as the possibility of the hybrid integration of both active and passive devices on silicon. This paper reviews the NTT HiS technology and its application to integrated-optic components such as optical beam splitters, optical switches, wavelength-division multi/demultiplexers and optical frequency-division multi/demultiplexers. The clear and simple waveguide structures produced by the HiS technology make it possible to design and fabricate these components with high precision and excellent reproducibility.

Effects of inhomogeneities on nonlinear integrated optics components

Calculations are presented showing how small index inhomogeneities, of a size likely to occur in real devices, limit the useful length of all-optical waveguide switches. The author derives scaling rules, showing the effects of device length and of the magnitude and correlation length of the inhomogeneities, and calculates the relative sensitivity of interferometers and directional couplers. The device lengths and index variations used in the calculations were typical of those expected in devices fabricated on planar substrates. Scaling indicates that similar effects will be seen with the greater lengths and smaller index inhomogeneities typical of all-fiber devices. Long all-fiber nonlinear couplers have been observed to behave in ways that can only be explained by index mismatches. Even short, i.e. 5 mm, couplers have been seen to deteriorate when the presence of light induces permanent index changes. >

Integrated Optics Some Aspects

Status of some key individual integrated optics components, their application in the field of telecommunications, integrated optoelectronic circuits, fibre optics sensors, optical interconnects and logic devices are highlighted in this paper. Possibilities of opto-opto processors in the computers field are also outlined.

Photoinduced conversion of radiation polarization in integrated optics components based on LiNbO/sub 3/

Two photoinduced effects in LiNbO/sub 3/ optical waveguides (unidirectional waveguide mode conversion from ordinary to extraordinary polarization and radiation coupling out of waveguides with polarization plane rotation) are discussed. The circular photovoltaic tensor component in LiNbO/sub 3/ is determined experimentally, and a photovoltaic mechanism to explain photoinduced radiation coupling out of waveguides is proposed. The impact of the effects discovered on the performance of phase modulators is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Integrated-optic devices on LiNbO3for optical communication

Integrated-optic components on LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> for fiber-optical communication systems are reviewed with respect to technology, fiber coupling, and device configurations. Typical devices for communication applications, such as modulators/switches, multiplexers, switch arrays, and heterodyne receiver chips rely on electrooptically controlled waveguide structures. Their operation mechanisms and performance characteristics are described to highlight the present status of development and of system applications.

Applications of chalcogenide glasses in integrated and fiber optics (review)

This review deals with applications of glassy chalcogenide semiconductors in fiber and integrated optics. The physicochemical properties of chalcogenide glasses are discussed in detail. It is shown that they are promising materials for fiber-optic communication lines operating in the near infrared and particularly in the middle infrared range. The problems of using the optical memory effect for some integrated-optics components, optical fibers, and waveguide holograms are considered. The optical strength of components made of glassy chalcogenide semiconductors is also discussed.

Integrated optics components and devices using periodic structures

The selected research activities on integrated optics components and devices using periodic structures are reviewed, with emphasis on the authors' works employing the electron-beam writing technique. The periodic structures include static gratings and dynamic ones produced through acoustooptic (AO) and electrooptic (EO) effects. They provide a variety of passive functions and effective means for guided-wave control. The review is made from the integration point of view, including the most recent results. First, the theoretical fundamentals are outlined and the electron-beam writing techniques, including the writing system, are discussed. Next, passive components (grating deflectors, filters, lenses, couplers, etc.) and elements for guided-wave controlling and detecting (AO and EO grating elements and photodetectors) are described. Then, integrated optic devices, i.e., wavelength demultiplexers, RF spectrum analyzers, optical disk pickup, etc., are presented. Finally, the possibility of future applications is discussed.