The simulation model presented yields the properties of ion-exchanged waveguides in glass in a very close approximation. The manufacturing process is a double thermal ion exchange in the glass BGG31, which was developed especially for the sodium/silver ion exchange. The resulting waveguides have several advantages compared to waveguides in other materials, for example, a low birefringence and low intrinsic losses; due to the flexibility of the process, the mode field can be matched to different types of fibers.
Fabrication of buried single-mode glass waveguides by ion exchange through the ionic barrier is studied. In this process, an unmasked potassium ion exchange is first performed to form an ionic barrier. The purpose here is to reduce sodium concentration near the surface (not to make a waveguide). The waveguides are formed in the second step of the process by masked silver ion exchange through this leaky ionic barrier. The calculated waveguide index profiles and both calculated and measured mode profiles are presented.
The use of e-beam direct write lithography for the microfabrication of OEICs is demonstrated. Special design tools were developed for waveguide structures to enhance CAD and lithographic performance. Besides high resolution applications (e.g., gratings), e-beam lithography was used for three-dimensional resist shaping in order to develop waveguide tapers.
A laser beam writing system for the fabrication of micro-optical elements as relief structures in photoresist is described. Using a computer controlled precision xy stage and a modulated, focused laser beam, a wide range of surface relief microstructures has been produced, with typical periods of 10 - 100 micrometers and a maximum relief amplitude of about 5 micrometers . Examples include microlens arrays, kinoforms and other phase structures for applications in optical computing, optical interconnects and micro-optical systems in general.
Nd:MgO:LiNbO3 combines the laser capabilities of rare-earth doped crystals and the non- linear and electro-optic properties of a well-known material in integrated optics. In this paper the basic characteristics of such a material are reviewed with respect to the goal of fabricating integrated optic lasers and amplifiers.
The LIGA process which is based on deep-etch lithography in combination with high-precision electroforming and moulding processes is a particularly promising method for the fabrication of three-dimensional microstructures. Some interesting applications can be seen in the field of integrated optics. Passive waveguide structures can be fabricated by deep-etch synchrotron radiation lithography of multilayer resist systems. Using this technique, multimode strip waveguides with a PMMA core and a P (TFPMA/MMA) cladding as well as a planar grating spectrograph have been realized. The attenuation of 0.18 dB/cm measured at a wavelength of 850 nm can be reduced, especially in the near IR-region, by the use of deuterated PMMA as a core material. For plastic fiber LAN applications, moulding processes for the replication of passive multimode waveguide components like Y-couplers or star couplers are under investigation. The advantages of the LIGA process--unrestricted design in the cross-sectional shape and a small surface roughness in the range of 10 - 20 nm--are of special interest for these developments. For coupling fibers to integrated-optical chips, structures of a coupling array have been fabricated. The fibers are guided by exactly positioned stop faces and then precisely located and prefixed by integrated spring elements. The main advantages are as follows: the thermal expansion coefficient of the array can be matched to the optical chip material, the use of spring elements for prefixing simplifies the handling, and adhesives and the connected problems can be avoided.
The general goal of integration is to provide enhanced stability and compactness in the construction of complex systems. In the present situation the term 'Integrated Optics' usually denotes two-dimensional planar integration in thin films allowing only the propagation of zero-dimensional optical signals in wave guides. One of the main potentials of optics arises from the fact that the wavefield is three—dimensional, allowing to interconnect a large number of information channels through space with high bandwidth and without crosstalk. An earlier approach to an integrated three-dimensional structure utilized diffractive-reflective components fabricated in dichromated gelatine to connect arrays of optical devices through free space /1/. Diffractive elements by holographic techniques or by etching in glass substrates /2,3/ are one possibility to fabricate three-dimensional integrated optical systems. Diffractive elements however, due to the requirement of constructive interference, are very sensitive to thermal expansion and to wavelenght changes. An alternate concept for 3D-integrating regularly structured digital optical systems based on reflective and refractive components has recently been proposed
For high-precision dimensional measurement, the use of an optical interferometer is often a suitable method. A Michelson interferometer is interesting because of its simple construction. However, to detect the direction of a movement the interferometer has to be modified. Two solutions are possible: first, a double Michelson interferometer made using integrated optics technology on silicon is presented; second, a homodyne modulation and demodulation technique for a single Michelson interferometer on silicon is presented. An analysis of the performance of the both solutions is described. The interferometer developed is very small and low in price compared to the present technology. Many applications of this interferometer are possible; the measurement of displacement, force, and refractive index are presented as examples.
Optical sensor applications will make use of passive integrated optics in two different types of functions. On one hand, an integrated optic circuit can perform one or a group of optical signal preprocessing functions on the signal of an optical fiber sensor. On the other hand, an integrated waveguide can also be the transducer, or part of it, converting a physical or chemical quantity into an optically measurable quantity. This paper describes a few significant examples belonging to these two types of functions.
A compact optical system for coupling high-power laser radiation (Nd:YAG) to optical fibers is described. Graded-index optics (GRIN rod) have been used because of their characteristics, such as small dimensions, plane and parallel faces with focus near the exit face, which make them suitable for fiber components. A special coupling unit to connect the microlens with the fiber has been designed, thus obtaining a very compact and stable element. The insertion of a conventional lens at the laser exit has been provided to obtain a better coupling efficiency and to increase misalignment tolerances of the GRIN rod-fiber component. A theoretical approach and an analysis by means of an optical design program, together with details on experimental characterization of the coupling systems with a low-power laser (He-Ne) and high-power laser (Nd:YAG), are reported.
The self-oscillation phenomenon of all-fiber optically addressed silicon microresonators may be one of the best ways to realize the practical implementation of all-fiber optically addressed silicon microresonator sensors. In this paper, the detailed theoretical analysis of the self- oscillation phenomenon is presented. The full conditions for achieving stable self-oscillation are discussed. Some feasible ways for improving the self-oscillation are suggested.
The transfer matrix method is employed to analyze the propagation of leaky waves within planar multiple quantum well (MQW) waveguides implemented in the GaAs/AlGaAs material system and formed on GaAs substrates. The analysis provides an accurate picture of attenuation of both TE and TM polarized waves at the operational wavelength of 1.15 micrometers . Particular attention has been drawn to the variation of the loss coefficient as a function of parameters of the AlGaAs buffer layer separating the MQW core and the high index GaAs substrate.
In several industrial environments it can be necessary to utilize control devices connected to alarm systems for the monitoring of temperature variations, for example, those related to the occurrence of fires. In particular situations, such as in the presence of either electromagnetic interference or explosive substances, the use of a fiber optic device to control the increase of heat can be extremely convenient. This work is concerned with two micro-optic temperature switches based on bimetallic strip temperature behavior. The first type is constituted by two faced fibers: one fiber is connected with a LED source and is placed on a bimetallic strip; the other receives the light coming from the first one. The second device consists of only one fiber terminated with a GRIN microlens: light coming from the lens is reflected by a mirrored GRIN lens placed on a bimetallic strip and is then collected by the same fiber. A temperature variation causes a strip bending and, consequently, an intensity modulation of the transmitted radiation. Such devices are an improvement over traditional thermal microswitches; in fact, in the proposed configurations, the off condition is characterized by a reduction in, instead of an interruption of, the signal. It is thus possible to check for possible failures in operation (i.e., breaks in the fiber), as well as monitor the temperature. The second device is particularly suitable to be miniaturized and so it appropriate for realizing multiple-microswitch systems.
The evanescent field coupling from a single-mode optical fiber, side polished close to the core, to a high index (> core index), multimode, planar waveguide overlay has been investigated as a means of realizing in-line components such as modulators, wavelength filters, and sensors without interruption of the fiber. Such structures offer considerable advantages in terms of fiber-to-device interfacing and ruggedization over other component technologies such as integrated, bulk, or micro optics. The results reported here confirm the technical feasibility of manufacturing rugged, low loss, all solid state devices of this nature, and the measured or projected performances are realistic in terms of application requirements.
By analyzing the complex values of the electromagnetic fields along surface relief gratings for TE polarization, the diffractive properties of surface relief micro-structures are discussed. The edges and walls of the grooves are found to have significant effects on the surface fields for wavelength-size grooves. The dependence of these effects upon several factors, including the complex refractive index of the material, incident angle and the depth of the grooves, is examined. An oscillating property of the surface field amplitude at the bottom of the grooves against the depth is discovered and discussed. The far field intensity is also found to be closely related to the depth of the grooves.
The applicability of the transverse interferometric method and the refracted near-field technique to characterize gradient index lenses is investigated. The main features of these methods are illustrated, and preliminary experimental results are reported for both of them.
Deep-etch x-ray lithography allows the fabrication of micro-optical components with critical lateral dimensions of a few micrometers and structural heights up to several hundred micrometers. Using interferometric methods, the structural tolerances of the side walls of fabricated microstructures are shown to be about 0.3 micrometers per 300 micrometers of structural height. A parallel HeNe laser beam is easily passed through several microprisms, which is evidence for the high precision achievable in positioning micro-optical components on a baseplate. Focussing a light beam by cylinder lenses is also possible. The free two- dimensional shape and the high precision achievable in positioning allow fabrication of micro- optical components with integrated fiber fixing grooves in which multi-mode fibers are precisely positioned. Simple fiber connectors, e.g., fiber forks or Y-couplers, can be achieved. By using a light-guiding resist system, divergence losses can be diminished.
A new method of film structure in situ monitoring is proposed for MBE (molecular beam epitaxy) and MOCVD technologies. It is based on the analysis of second harmonic (SH) radiation induced in a growing film irradiated by a laser beam. SH intensity measurement versus angle of polarization plane of the incident light and versus film thickness provides the in situ information about film crystal quality, presence of polycrystal component, and crystallographic axes orientation. This method can be complementary to the well-known technique of fast electron diffraction (RHEED) and is supposed to be especially suitable for research groups since it allows a correlation between technological and crystallographic parameters to be quickly determined.
This paper describes two optical measurements on single picture elements of liquid crystal television displays. The first measurement is olthe transmission voltage characteristics, and the second is olthe colour of the mosaic colour elements.
Distributed Optical-Fibre Sensing (DOFS) is a technique which utilizes the very special properties of the optical fibre to make simultaneous measurements of both the spatial and temporal behaviour of a measurand field [1,2. As such, it provides an extra dimension in the measurement process, leading to finer monitoring and control, and to a new level of understanding, especially in regard to the behaviour of large structures. Thus we may expect to measure spatial distributions with a resolution 0.1 - im over a distance lOOm, to an accuracy '-1%. The advantages of optical fibres for general measurement functions are well known: they rely on the insulating, dielectric, passivity of the medium, allied to the sensitivity of its optical propagation properties to xternal influences, over a broad range. DOFS takes advantage of two additional properties of the fibre: its one-dimensional nature, and its mechanical flexibility. With the aid of these, it becomes possible, in principle, to determine the value of a wanted measurand continuously as a function of position, along the length of a suitably-configured fibre, with arbitrarily large spatial resolution; the normal temporal variation is determined simultaneously, from the time-dependence of the signal. Such a facility as this offers many attractive possibilities for industrial and research application. The value of having access to the spatial/temporal behaviour of strain and temperature in, for example, large, critical structures such as dams, aircraft, space-craft, bridges, multi-storey buildings, electrical generators, boilers, chemical pressure vessels etc., are clear, from the points of view both of safety monitoring, and of improved understanding of behaviour under anomalous conditions. The flexibility of the fibre makes it relatively easy to install over the chosen measurement path and thus allows, unlike many other sensor systems, retrospective fitting. Furthermore, again in contradistinction to other sensor arrangements, DOFS offers a facility which is unique: there are no conventional techniques for acquiring the same information. This paper will summarize the principles of DOFS, will give examples of systems which have been studied, and give some indication as to what is in store for the future.
The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially electronic, optical, and electro-optical properties. They also operate int he 30 - 80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach- Zehnder-type YBa2Cu3O7-y-on LiNbO3 optical modulator is introduced. The second, more futuristic, approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high- frequency modulators, ultrafast-pulse generators, and sensitive photodetectors, are presented.