The technology for making glass integrated optical devices is reviewed. Modelling tools used for process and device performance optimization have been developed and are described. Also it is emphasized that mode power distribution measurements are a useful means of understanding the loss mechanisms.

Integrated optical components like directional couplers, Y-junctions, mirrors and polarizers have been realized to generate an integrated optical Michelson interferometer on silicon substrates. A good quality waveguide material with reasonable low attenuation (below 0.5 dB/cm at λ = 632.8 nm for filmwaveguides ) a uniformity better than 3% and an adjustable refractive index between 1.46 and 2 is the LPCVD deposited siliconoxinitride , which can be trimmed by thermal annealing (▵n up to 2%, ▵d = 2-10%). The basic geometry of the components is a strip loaded waveguide, which has been obtained by photolithography and plasma-etching. The losses of such waveguides due to surface scattering were about 1 dB/cm for monomode waveguiding at λ=632.8 nm.

In fiber-optics communications wavelength division multiplexing constitutes a means of increasing the information capacity of fibers. For application in a multimode fiber-optics transmission line a passive grating multiplexer / demultiplexer is being developed using the LIGA technique (German acronym for Lithographie, Galvanoformung, Abformung), which is a combination of deep-etch synchrotron radiation lithography, galvanoforming, and moulding. The optical configuration consists of a polymer slab waveguide, structured by X-ray lithography, with an integrated selffocusing, blazed reflection grating and an integrated fiber alignment support. Optimized blaze angles over the whole grating width, varying grating constants, and a free choice of the grating curvature with an accuracy of 0.5 μm can be realized for a grating. A grating design was worked out using Fermat's principle of geometric optics, including the light path function of a noncircular, cylindric grating with varying grating constants. For the 10 spectral channels (985 nm - 1300 nm, channel spacing 35 nm) coma and spherical aberration become negligible. In addition the focal conditions were examined by a ray trace procedure. The lateral dimensions of the device are about 2 cm x 1 cm. An X-ray mask for such a device was fabricated and first X-ray exposures of a polymethylmethacrylate (PMMA) resist served to examine the quality of the grating structure. Furthermore, a 125 μm thick 3-level X-ray resist with a PMMA core was fabricated and the structure accuracy after an X-ray exposure with a test pattern was examined.

Reliable and stable interferometric sensors will make use of highly birefringent fibers. Rugged and reasonably expensive systems must involve all-fibre components having prescribed polarization properties, one of which is a polarization maintaining fibre coupler. Such component is consistently achievable by means of a polishing technique which preserves most of the polarization features of the fibre. An extinction ratio of 20 dB is routinely achieved. A variable version has been developped in order to allow balancing and fine tuning of interferometric systems. It uses monolithic mechanical concepts which result in a very compact device with good temperature and mechanical stability.

An integrated optical Michelson interferometer in glass has been developed. Glass provides the advantage of having the same refractive index as fibers. Therefore, Fabry-Perot resonances due to Fresnel reflections are avoided at the fiber-chip connections. A symmetric coupler, which is the basic component in this Michelson configuration, was fabricated by a field assisted ion exchange of potassium in BK7 glass. The minimum interguide separation of the coupled arms was 7 um, and the waveguide width was 3 um for single-mode operation at 633 nm. Light of the single mode input fiber is devided by the symmetric coupler into two beams. One coupler arm, which works as the reference arm, is terminated by a mirror on the end-surface of the substrate. At the end of the other arm, which represents the sensing arm, a quarter pitch GRIN-lens with an antireflective coating collimates the outcoming light. A moving mirror mounted on a piezotranslator reflects the light into the GRIN-lens and the symmetric coupler recombines the sensing and the reference beam. A change in optical path length is converted to an intensity signal by the coupler. The distance between two peaks of the interference signal pattern corresponds to a displacement of half wavelength. Experimental measurements using 633 nm wavelength show that the amplitude remains constant within 10 %, scanning a distance of 25 mm between the GRIN-lense and the mirror. A resolution below 1/100 wavelength can be achieved by single sideband detection using integrated thermooptic phase modulators.

Low loss passive integrated optic interferometric sensors might successfully compete with optical fibre sensors in short path length applications such as distance measurement, force and perhaps also low performance rotation sensors. They are inherently polarization maintaining, stable, low cost and versatile. There is yet an important function which remains to be practically solved in integrated optics on passive substrates: the phaseshifting allowing a waveguide interferometer to delivering non degenerate optical power signals, ie, sine and cosine functions of the input optical phase difference. The proposed device achieving this function is a single process ion exchanged circuit on glass using a low mode number imaging waveguide caisson. The proposed configuration can be applied to all kinds of interferometers.

An original probe design for multimode optical fiber sensors, making use of a transducer, is presented. The probe is constituted by two facing quarter pitch graded-index (GRIN) microlenses which confine the transducer: the first GRIN is fixed to the fiber, while the other has a reflecting end face. The resultant micro-optical system works as a "nearly autofocusing cavity", which improves the coupling between the fiber and the transducer and shows a relatively low insertion loss.

A wavelength division multiplexer for multimode fibers is described which makes use of a 45° incidence dichroic filter as dispersive element and of GRIN rod lenses as collimating/ focusing optics. The device has been designed in two configurations: one constituted by a metallic cube with three lateral holes for lens ended fibers coupling and a slot in a diagonal plane for the insertion of the filter; the other one consisting of two glass prisms suitably designed between which the filter is interposed, while the GRIN lenses are directly cemented on the prism sides. Details on the two device assembling and characterization measurement are reported.

Increasing miniaturization is required in many domains of optical instrumentation, such as in the development of endoscopic devices. In combination with coherent metrology, especially holographic interferometry, a new class of minute instruments can be developed for high-resolving, non-contactive, non-destructive intra-cavity measurements. Three developments in micro-optics give main impulses to actual progress in holographic endoscopy: - micro-optical gradient-index imaging systems, - micro-optical (single-mode) imaging fiber bundles, and - electro-optical crystals as (micro-optical) holographic storage devices.

Aberration properties of planar microlens arrays, which are small lenslet arrays fabricated by an ion exchange technique, are described. The optical set-up of the measurement system. is designed to combine a Mach-Zehnder interferometer, a microscope imaging set-up and fringe scanning analysis to obtain precise measurements for microlenses. Many types of planar microlens have been measured, and the spherical aberration, coma in off-axis imaging etc., were evaluated. The experimental results indicate that the planar microlens can perform high quality imaging in a wide image field. Also, by using planar microlens arrays, multiple imaging optical systems in incoherent and coherent illumination are demonstrated.

A 2-axis compact microtranslator stage is describedl. It is part of a system including ultra-precision translation units and various controller options for digital programmable positioning or closed loop automatic alignment. Its design relies on a systematic application of flexure technology for guiding and transmission of movements, resulting in a considerable reduction of the adverse effects of backlash, friction and wear. A combination of monolithic planar elastic bodies allows for a translation in the xy plane with coupling between axes kept under 0.05 % over the entire 1000 x 1000 micron displacement range. The driving mechanism assembly consists of a prestressed bolt-screw pair acting on a rigid reduction lever with less than 0.03 % transmission non-linearity. All elementary displacement functions can be performed using dedicated microcontrollers for high performance DC motor position control with incremental angular encoders. The position within the entire xy field can thus be defined and maintained without additional electrical or optical feedback at 0.1 micron accuracy and 0.01 micron resolution. A description of the basic concepts, their implementation and the device performance is given, together with comments on the possibilities offered in this field.

The study and the development on an optical fibre sensor for the detection of pH is described. Phenol red, immobilized on XAD-2 microspheres, was used as pH indicator. Particular care was devoted in the planning and construction of the probe in order to obtain high sensitivity and good signal levels. The measuring apparatus is described as well as experimental results are reported.

An integrated optical refractive index sensor based on a Mach-Zehnder waveguide structure is demonstrated. The waveguides are fabricated by an ion-exchange technic in the BGG 21 glass from JOT, followed by end face preparation for fiber-chip coupling to get an all guided wave sensor system.

This work presents an updated digest of Multicore Optical Fibre (MOF) technology and applications. The digest bases mainly on our own technological experiments. Several technologies have been employed to manufacture multicore optical fibres. These are: multi-rod-in-tube (1) rod drilling (2), modified double crucible (3), multicrucible-zone diaphragm (MZD) (4) and mozaic-assembling (5). The following kinds of MOF have been pulled and tested: singlemode and multimode twin-core, double-core (with two different cores - so called hetero-core MOF), with cores arranged linearly and with cores axially symmetrical. Highly asymmetrical MOF are also subject of a separate part of this work. Basic parameters and waveguide properties of these MOF have been presented and debated. The pulled MOF have been used to manufacture several pieces of MOF microoptics like: single tapers, bi-tapers, multiple tapers, mixing-rods, attenuators, passive lossy insulators, unidirectional and nonreciprocal optical devices, directio-nal couplers, WDM muldex and a number of different fibreoptic sensors. The components have been used and tested in optical fibre information processing, telemetric and communication systems.

A tapered lenslike system with gain or losses is proposed for converting a gaussian laser beam into an uniform beam. The best foci of the lenslike system are determined: Best Front Focal Distance (BFFD) and Best Back Focal Distance (BBFD). The results are applied to a medium with quadratic gain profile to achieve uniform illumination controlling the gain parameter.

In many applications of micro optics, eg Fibre optic sensors or intergrated optics discrete components have to be assembled precisely and in an environmentally stable form. Several chemical companies have developed dental restorative materials which have many desirable features for optical assembly. ICI's Light Curing Resin family in particular is endowed with 1 Visible light cure - no hazards due to UV. 2 Rapid cure on command. Ideal for precision assembly. 3 Low shrinkage on cure. 4 Cure to 10 mm depth in one minute. 5 Cure through 4 mm of white alumina ceramic in one minute. 6 High refractive index for integrated optics applications. 7 Refractive index 1.52 for fibre splicing or lens assembly. 8 Wide range of viscosities for different assembly processes eg fibre bundle termination or laser Diode receptacles. 9 Low thermal expansion coefficent in reinforced grades. The paper will discuss how these properties are obtained and their uses in the exciting field of microptics assembly. Finally an interesting temperature sensor based upon a glass filed resin will be described to illustrate the range of properties which can be combined.

Integrated optical components in glass are commonly fabricated by thermal or field assisted ion exchange. We introduce the charge controlled, field assisted ion exchange. This process provides some advantages compared to thermal exchange. Exchange time is reduced remarkably, the waveguides can be buried and the index profile can be formed to a nearly circular cross section. A reproducible fabrication of optical waveguides is achieved by using the exchanged charge as the controlling process parameter. The ion current is integrated by a computer controlled unit which stops the process at a preset charge. The charge corresponds to the amount of exchanged ions and a reproducible process is available. It takes only several seconds to fabricate single mode waveguides in glasses like B-270 (Desalt) and BK-7 (Schott) at a temperature of 693 K and an applied field of 50 V/mm. Directional couplers are extremely sensitive to parameter deviations. They are used to control the reproducibility of the process. The measured variations of the coupling ratio were below 10 percent.

The production of low loss ion exchanged integrated optical components in glass usually requires buried waveguides, fabricated in a two step process. In addition, a strong sidediffusion of the ions is observed. Buried channel waveguides with negligible sidediffusion can be fabricated in a one step process by a suitable solid phase diffusion technique. We examined the field assisted solid phase ion exchange in glass to produce single- and multimode waveguides. Vapour deposited silverfilms could be structurized down to a linewidth of 2 μm, using common photoresist techniques. In order to achieve a homogeneous drift field during the diffusion process, the substrates were covered with a sodium nitrate melt. For applied drift fields of typically 150 V/mm (diffusion temperature: 588 K; diffusion time: 6 ... 15 min) the channel waveguides exhibited a negligible broadening even in the case of deep burial. Due to this fact an independent control of both lateral and vertical waveguide dimensions is possible, if the solution rate of silver for each type of glass is known. This allows the fabrication of waveguides by control of the silverstripe thickness and width with only small deviations. By this one-step-technique channel waveguides down to 4 μm nearfield diameter and an ellipticity of only 1.1 were buried 15 μm below the surface.

An integrated-optic Bragg-cell based on diffraction of light by a surface acoustic wave (SAW) was fabricated on glass with a piezoelectric ZnO-layer. The ZnO-film was deposited by RF-magnetron sputtering. To generate a SAW an interdigital electrode array is needed, which is positioned between the glass and the ZnO-film. Such a ZnO-transducer has been tested by the standard RF-measurment techniques for+ SAW filters. The optical waveguides were produced by thermal K -ion exchange in BK7-glass. A special waveguide structure with two intersecting waveguides was used. For increasing the interaction length in the crossing area the monomode waveguides were tapered adiabatically up to a width of 50μm. The diffraction efficiency of such a Bragg-cell in glass was measured to be about 4%-5% at an RF input power of 1W.

We present the details of a new fabrication technique for making planar waveguides in III-V semiconductors. Using this technique we made single mode totally planar waveguides in GaAs with measured propagation losses of 1.9 dB/cm.

Investigations of LiNbO3 waveguides using the non-standard Z-propagation are presented. Due to the isotropic refractive index of the bulk material and a small residual TE/TM modal birefringence, this orientation seems to be well suited for passive, polarization-insensitive devices with increased power handling capability. The measured wavelength response curves of BOA-type wavelength multiplexers, fabricated with Z-propagating waveguides on X-cut LiNb01, however, indicate the presence of increased waveguide birefringence. This results in an opposite shift of the sinusoidal TE/TM transmission curves of nearly 180°, which can not be verified by theoretical calculations (device simulation by the beam propagation method BPM ). The determination of the refractive index profile by m-line spectroscopy leads to gaussian profiles with polarization dependent 1/e-widths and maximum index increases An. BPM-simulations based on these profiles show results, which correspond well to the measurements.

The paper deals with the increase of refractive index of polyallyl diethylenglycol carbonate (CR 39) when irradiated by proton beams at 300 keV, with th the fluence range (5 10 13 - 5 10 15 protons cm -2). Such irradiations lead to refractive indexincreases which can reach 8%, depending on the fluence of the beam, the initial value being close to 1.493. As the irradiated samples become optical waveguides, integrated optic methods enable us to study the index variations; the effective index values were obtained by means of the m-lines method. These values were then used to calculate the index profil2 by inverse WKB method. An attenuation of about 2 db cm 14 was measured for an irradiation of 10 protons cm . It was also noted that the attenuation increases with the ion beam fluence. On the other hand, the number of guide modes depends on the beam fluence and the variation of effective index versus fluence is given. Many considerations lead to consider that the index variation is mainly due to energy transfer all along the proton path. This is in good agreement with the comparison of the stopping power curve as a function of depth penetration and that of the index profile.

K+-exchanged film and stripe waveguides have been fabricated. The diffusion time varied between one and 16 hours. m-line spectroscopy was used to characterize the waveguides. The refractive index profile of those waveguides is proportional to a concentration profile calculated under the assumption that the number of indiffused ions is limited by the glass network to a constant value at the surface. From those profiles derived n eff-values and near-fields compare well with the measurements in a wide range of strip widths and diffusion times. The waveguides can be described by four parameters: a constant ∆ N, the stripe width, the diffusion time and the diffusion coefficient.

On the basis of a fundamental description of a biological visual system and some psychological experimental results on image transformation in brain, a field theory of pattern identification is given. In this system the image in brain is postulated to be freely transformed into the standard one for pattern identification by the excitation of gauge field. Taking account of the idea of the image transformation, an optical-electronic recognition system is proposed as a model of biological visual perception. In the optical feature extracting part, the planar microlens array is used to form many images of an input pattern simultaneously, and from each image feature extraction is performed in parallel by the optical correlation with orthogonal spatial filters. The planar-lens array followed by spatial filters works as the hypercolumn structure in the first visual area in brain. In the recognition part, the extracted features are reorganized in the neural network such as "perception" or "neocognitron", giving rise to an image of input pattern. The reorganizing process corresponds to that in higher visual area in brain. For realizing the optical feature extracting part of the proposed system, some basic experiments on miniaturized matched spatial filter (MSF) are reported. In this system a graded index lens of small diameter 3.3 mm is used. The partial geometrical features of input pattern of the small size lx1 mm are shown to be extracted through the optical correlation with the miniaturized MSF.

Digital-phase gratings have groove-shapes in the form of a staircase with typically 4 phase levels. They have a large pitch in the order of 100 p.m, and a block of central diffraction orders is used for light splitting. Properties of such gratings for the appli-cation in wavelength-division-multiplexer are analysed, and experimental results are pre-sented. Reflection gratings are realized on flexible substrates so that one-dimensional concave gratings can be formed for focussing and imaging in "hybrid" planar multiplexers.

A Bragg-modulator on lithium niobate substrate (z-cut, y-cut) for x= 840 nm operated at 300 MHz has been fabricated. It is realized using two crossed tapered waveguides and an interdigital transducer to convert the high frequency electrical power to a surface acoustic wave (SAW). The monomode waveguide is tapered adiabatically into a width of 50 pm, which provides an interaction length of 3.2 mm. For reasons of low crosstalk the Bragg-angle is chosen to be θ B = 0.9°. Because of the need for the large acoustic aperture of 3.2 mm in some cases a special interdigital electrode transducer (ITD) for surface acoustic wave generation, the so called "dog leg" ITD is used. The deflected light intensity was measured to be up to 40% of the non-deflected intensity for y-cut and 15% for z-cut lithium niobate at an electrical power of 800 mW. The static optical crosstalk with coupled fiber is better than -32 dB.

The performance of optical grating filters, using ion-exchanged channel waveguides in glass covered with a dielectric grating quarter-wave resonator, is investigated theoretically and experimentally. For the transmission resonance peak of the filter a bandwidth of about 10 GHz has been obtained.