Single-mode optical waveguide devices with integrated fiber- alignment grooves have been fabricated by injection molding of structured substrates and by subsequent filling of the waveguide channels with higher refractive index polymer. The master forms of the microstructures have been micro-machined channels with higher refractive index polymers. The master forms of the microstructures have been micro-machined in silicon. A special injection molding tool has been developed to yield plastic substrate chips with high surface planarity and replicated microstructures with details in the submicron range. Hot embossing is a further technology applied for the fabrication of large area waveguide devices with integrated mirrors, mainly intended for optical backplane applications. The hot embossing tool is driven on an injection molding machine which is a more cost effective method than the acquisition of conventional hot embossing equipment. In this paper, the injection molding as well as the hot embossing tool will be described together with the process and the results in the field of passive components for optical telecommunications and datacommunications.
We present the results on fabrication of plastic integrated optical elements using molding, liquid jet delineation, and UV irradiation. Coupling gratings with a period of 620 mm-1 and a diffraction efficiency of 3.3 percent were molded in a preheated poly(methyl methacrylate) planar waveguide using master saw shaped grating. An experimental device is also described which uses computer controlled micro syringe to dispense polymer solution onto a moving substrate. This device consumes thousand times less material to produce integrated optical circuits than equivalent spin- casting equipment.We have made various structures such as Y- branches and Mach-Zehnder interferometers. All the structures demonstrated good performance. The same device was also equipped with a microscope-type UV illuminator for noncontact delineation of optical structures in polyimide films. The operation is based on the refractive index increase due to photo-oxidative decomposition of the material. The index difference 0.02 between exposed and unexposed regions is sufficient to define light guiding channels in polyimide without using liquid developing. UV radiation was also used to make graded-index polyimide waveguides. Their refractive index profile was successfully reconstructed by a specially developed calculation technique. All the techniques combined together give us the cost efficient tool for the fabrication of plastic integrated optics.
Photothermoplastics are shown to have a capacity to record the interference gratings or holograms with spatial frequencies ranging far away the self-rastering frequency. The frequencies is corresponding to the chaotic deformation shifts towards the low-frequency range with the increase of the recording temperature. The recorded holograms with various spatial frequency do not alter the absolute values of self-rastering. The temperature dependence of the square root of the diffraction efficiency shows a maximum at the flow point temperature of the thermoplastic used. As the temperature rises, the coefficient determining the relationship between the resonance frequency and thermoplastic layer thickness increases.
A blazed holographic optical element (HOE) has developed with injection molding technique. It is able to function as a beam splitter and aberration generator for focusing error detection of optical pick up head for optical storage system. The die was made by 4 axis controlled ultra precision cutting machine using single crystalline diamond cutting tool We carried out fabrication error estimation caused by cutting and injection, and derived adequate tolerance budget. The efficiency of HOE defined y the product of 0th and 1st order diffraction efficiency was measured by knife-edge method. We attained high efficiency of 15.5 percent which is close to theoretical limit. The efficiency is about 1.5 times as that of conventional non- blazed HOE.
After the successful development of micro-optical components today the first commercial applications are arising. This induces the necessity of adapted production technologies. Hot embossing and injection molding are two techniques to fabricate micro-optical components characterized by lateral structure details below 1 micrometers , structure heights up to one millimeter and aspect ratios between 20 and 100. Injection molding is famous for its short cycle times which makes this method well suited for mass production.Very delicate microstructures and multilayer components can be fabricated e.g. within the framework of the LIGA-process by hot embossing. Examples for micro-optical components fabricate by molding as well as process equipment will be discussed.
Plastic optical elements are used extensively for high- volume, low-quality, commercial applications. The advantages of plastic over glass elements include low weight, ease of modeling, high shock resistance, and low price in mass production. The use of plastic optical elements in military systems is limited by stringent environmental demands, and by the high image quality which is usually required. The disadvantages of plastic from this point of view are softness, low chemical resistance, thermal defaces, and inhomogeneity. Display systems are located in the same environment as the user. In an enclosed space, such as a vehicle, the requirements for environmental conditions can be greatly eased. In addition, visual optical systems may incorporate a focusing adjustment which can be controlled by the viewer. In combination with a limited temperature range, this solves the problem of thermal defaces. The resolution required in display systems is generally far from the diffraction limit, which reduces the significance of inhomogeneity. In addition, the eye pupil is usually smaller than the lens diameters, so that inhomogeneity only produces a local effect in the field of view. It would thus appear that plastic optical elements are a practical option for display systems, despite relatively severe environmental conditions.In this paper, the application of these considerations will be illustrated by a practical optical design for an airborne military display system incorporating plastic optical elements. The points of image quality and environmental requirements will be addressed.
We report the results of holographic and spectroscopic study of D2 dye doped PMMA and PS polymer compounds. The unusual non monotone relaxation dynamics observed in D2:PS compound shows the presence of unknown earlier excitation modes in this system.
We report on a new unique photochromic material which is based on a reversible formation - cleavage of a C-C bond. The bicyclic bindon derivative, 2 undergoes a photochemical and/or thermally induced ring opening to form the isomer 3. The form 3 presents a conjugated donor-acceptor system and exhibits a considerable second-order optical nonlinearity as found by the field induced SHG measurements. The photochromic conversion is also observed in the crystalline form indicated visually by a crystal red-to-green color change. We have studied the reversible ring opening - closure process in liquid and polymeric solutions. Optical and thermal switching and the NLO efficiency of these guest- host polymer are reported.
The operation of several singlemode erbium doped polymer waveguide amplifiers was demonstrated. Optical gain of 5 dB was achieved at two different signal laser wavelengths, using a 1.48 micrometers pump. The two polymer host in which gain was demonstrated were gelatin and polystyrene - both prepared in a waveguide structured with high doping levels.
Flexible PDLC-based devices having 'all-plastic'-made transparent electrodes were developed. Unlike the relatively non-flexible ITO-made electrodes, their polymer counterparts are mechanically flexible, allowing the fabrication of flexible devices. Other advantages of devices containing a conducting polymer are the reduction in operating energy consumption and the anticipated reduction in manufacturing costs. The electrooptical switching and imaging properties of devices having 'all-plastic' transparent electrodes were found to match those of their ITO-based counterparts. The optimal operation voltage in terms of switching rise times and optical transmittance shoed significant dependence on dimensional cell parameters, while the switching fall time was practically independent of these parameters.
Contactless embossing of microlenses (CEM) with LIGA molding tools is a new fabrication techniques for the production of refractive microlens arrays which combines high accuracy in the micrometer range, cost-effective production of the devices, and cost-effective high precision mounting concepts. The name refers to the fact that the surface of the microlenses has no contact with the embossing die during the shaping of the surface relief. A high precision matrix of holes made by LIGA microfabrication is pressed onto a thermoplastic sample which is heated. The material bulges into the openings of the molding tool due to the applied pressure and forms lens-like spherical structures. The embossing die touches the lens material only outside the lens area. High-speed microlenses with f/ < f/4 and diameters of the lens aperture between 30 micrometers and 500 micrometers have been fabricated in PMMA and PC. Excellent uniformity within the microlens arrays are achieved by using LIGA microfabricated embossing dies. In addition to the excellent optical performance of the microlenses, the CEM method assists hybrid integration in micro-opto-electro- mechanical systems by providing precise auxiliary structures for easy and cost-effective mounting and adjusting.
Various optical components using polarized optics have been developed for the optical data storage, imaging and display. For developing the high performance products with reduced cost, novel transparent plastics offering no birefringence are in demand. Birefringence-free acrylic copolymers that are based on the molecular design in which compensates the polarity of the macromolecule by using random copolymerization of the positive-birefringent monomers with the negative-birefringent monomers, have ben developed to meet the demand. These resins can offer the molded products having no birefringence even in the near-gate part because the birefringence based on the molecular orientation caused by molding process is compensated by the molecular structure. In addition, they offer high heat resistance or colorless transparency with low moisture absorption due to copolymers include the rigid and hydrophobic monomer components having cycloaliphatic hydrocarbon groups. Because of the above characteristics, it has just been applied to some precision-molded lenses for optical laser pick-ups and liquid crystalline projectors. It is fully able to meet the applications as optical laser pick-ups, liquid crystalline projectors, liquid crystalline displays, etc.
Using a drop-on-demand print head allows for PC-controlled production of various types of microlenses as well as lens arrays. The possibility to place microlenses on arbitrarily shaped substrates allows for novel optical elements like beam splitters or non-planar scattering discs. Another interesting possibility opened by pre-shaped substrates is the production of concave lenses, which are key elements for aberration correction in micro-optical systems.
We have developed industrial technique to produce plastic rod-lens and its linear array. The basic characteristics of the rod-lens was revealed. The optical resolution was 200dpi which was high enough to apply to G3-facsimile and monochromatic copy machine. 300dpi or 400dpi optical resolution is required for the application to G4-facsimile and image scanner of computer, LED printer and so on. Two approach to improve the optical resolution were proposed and discussed those method form the practical view point of durability in the linear rod-lens array. Finally the total characteristic of the plastic rod-lens were compared with that of glass material.
Hydrophilic photoactive plastic matrices are investigated by holographic and wave-guiding techniques. The photoactive matrices are based on acrylate type monomers, which are dissolved together with xanthine dyes and other additives in poly(vinylalcohol). Dry plastic coatings are obtained by casting the aqueous polymer solutions on glass substrates. Photo-recording occurs in real-time and in-situ, without any post-exposure processing. This paper first describes the recording and diffraction properties of thick asymmetric holographic volume gratings. Such holographic gratings exhibit very high diffraction efficiencies (DEs) approaching 80 percent into free space. Here, they are considered for coupling into and coupling out of wave-guide layers at 850 nm. Our investigations indicated good wave-guiding properties in both, unexposed and exposed photopolymer layers. Grating couplers exhibited angular and spectral bandwidths of about 0.15 degrees and of about 1 to 2 nm, respectively. Coupling DEs of over 50 and de-coupling DEs reaching 6 percent were determined. The large difference between coupling and de-coupling DEs are explained by the losses due to an increase in angular divergence as a result of diffraction and modal dispersion.
Recent results on waveguide device fabrication by replication of inorganic-organic copolymers (ORMOCERs) are presented. The use of optimized ORMOCER resins offers advantages over conventional organic polymers. The organic as well as inorganic crosslinking is responsible to high thermal and chemical stability and thus an improved stability of the waveguide devices. Fluorination of ORMOCER side chains reduces the NIR absorption to < 0.4 dB/cm at 1.55 micrometers and < 0.3 dB/cm at 1.3 micrometers . Furthermore, the synthesis of purely inorganically crosslinked CH-free ORMOCER is possible. The refractive index can be tuned so that highly fluorinated core material can be combined with low-cost unfluorinated cladding material. The influence of the sidewall roughness of replication tools on scattering losses is investigated, and methods to fabricate smooth original structures have been developed leading to an additional scattering loss < 0.1 dB/cm in single-mode strip waveguides even at visible wavelengths. Furthermore, an improved deforming behavior is achieved. UV-patterning by UV-induced crosslinking is a second waveguide fabrication method used in ORMOCER. Applications of ORMOCERs in thermo- optical switching nodes are discussed.
As an example for a new technology for the fabrication of passive components in polymers a 1:2 splitter has been made in PMMA bulk material. The geometrical structure of the waveguides has been preembossed by a Ni-shim together with precision grooves to hold the silica fibers. The waveguides have been formed by UV-exposure. The refractive index profile has been studied to optimize the depth of the grooves in order to fit the fiber core to the strip waveguide without any further alignment. Insertion loss of the component has been measured.
Samples of PMMA have ben modified by UV-radiation in order to generate a region of increased refractive index in a surface layer to act as an optical waveguide. The resulting refractive index profile was mathematically described by the use of error-functions. This profile was the base for the simulation of directional couplers by using a commercial BPM-program. A passive component was designed for spotting the wavelengths 1310 nm and 1540 nm into two different branches of the coupler. This splitter was generated in PMMA and function tests were performed. Also a coupler was realized which divided TE and TM polarized light into different waveguides. It was generated in PMMA by using different parameters for the UV-exposure.
This polymer films are known to interact with organic vapors via absorption or diffusion. In photosensitive polymers the surface properties as well as the free volume of the polymer may be changed by light exposure. In holographic gratings exposed and unexposed microregions are present next to each other. If both regions interact in a different way with the vapor molecules a change in the diffraction efficiency of the grating should occur as a function of the vapor concentration.For 2 different photopolymer systems we will investigate the use of holographic gratings for the optical vapor detection.
Working with silica the technique of anisotropic etching produces 'V'-shaped grooves which are suitable for fiber chip coupling.In this paper similar grooves are fabricated in PMMA using self developing excimer-laser etching in combination with a cylindric lens. The actually fabricated shape ranging from 'V' to 'U' is investigated by different technical means. The dimensions are determined as a function of the parameter number of pulses. A multi pulse technique implying a lateral displacement is investigated for the fine tuning of the pattern. Simulations using two finite difference methods allow the theoretical prediction of etched patterns.
Dichromated poly(acrylic acid) films with dimethyl formamide have been investigated as UV photosensitive recording medium for the fabrication of diffractive optical elements. Surface relief structures with large depth modulation have ben formed on these films. Relief depth of surface gratings as a function of exposure time and the spatial frequency of the gratings are presented. Atomic force microscopy 3D views of surface relief gratings are also presented.
In this paper, we investigate the application of precision plastic optics into a communication/computer sub-system, such as a hybrid computer motherboard. We believe that using optical waveguides for next-generation computer motherboards can provide a high performance alternative for present multi-layer printed circuit motherboards. In response to this demand, we suggest our novel concept of a hybrid motherboard based on an internal-fiber-coupling (IFC) wavelength-division-multiplexing (WDM) optical backplane. The IFC/WDM backplane provides dedicated Tx/Rx connections, and applies low-cost, high-performance components, including CD LDs, GRIN plastic fibers, molding housing, and nonimaging optics connectors. Preliminary motherboard parameters are: speed 100 MHz/100 m, or 1 GHz/10 m; fiber loss approximately 0.01 dB/m; almost zero fan-out/fan-in optical power loss, and eight standard wavelength channels. The proposed hybrid computer motherboard, based on innovative optical backplane technology, should solve low-speed, low-parallelism bottlenecks in present electric computer motherboards.
Using a rigorous differential theory of diffraction gratings, we have investigated the optical properties of some peculiar bandgap structures. We have dealt wit devices made of two stacks of equidistant rod gratings separated by a central planar defect which leads to the occurrence of a transmission peal inside the wavelength bandgap. We have studied how the stability of the effective bandgaps copes with fluctuations of various experimental parameters. For various bandgaps and polarizations in structures including a defect we have studied the resulting filter characteristics and its possibilities as optical switch when the defect is made of nonlinear materials. As long as plastics have convenient refractive indices, optical losses and nonlinearities, the devices we describe could be manufactured using such materials.
A method to produce polymer-based passive and active photonic bandgap devices for integrated optics is described. The aim of the method is to implement low-cost active and passive opto-electronic devices of high quality with a high degree of integration and high packing density. A structurable resist or polymer layer of high quality is placed onto an opto-electronic substrate. An etching mask and a high-grade anisotropical in-depth etching process are used to generate a structure which can be used as a photonic bandgap material. The permittivity of the structure is changed by filling the polymer structure with monomers by means of a vapor-phase or liquid-phase diffusion. Depending on the monomer type used for diffusion as well as on temperature and on interaction time, the optical properties of an optical element can be changed selectively. The method described will make possible an increase in the packing density of future integrated optics and low-cost production of large quantities alike.
Fluorinated polyimides (F-PI) have been specifically developed for optical waveguides; it features high optical transparency from visible to near-IR and god heat resistance. Buried optical waveguides fabricated from F-PI operate in a single mode. They also exhibit a low loss of less than 0.3 dB/cm at the wavelength of 1.3 micrometers , and are heat and moisture resistant: the increase in optical los is less than 5 percent after heating at 300 degrees C for 1h or after exposure to 85 percent relative humidity at 85 degrees C for 24h.
Gigabit-data transmission has been made possible by using a graded index type plastic optical fiber with dopants. However, there remains the problem of bandwidth which decreases due to dopant diffusion. Recently, two kinds of dopants with a very low diffusibility, triphenylphosphate and tricresylphosphate, have been found. On the other hand, for a step index type POF (SI-POF), quite a degree of improvement in its bandwidth can be achieved by reducing the numerical aperture (NA) of the POF so that a megabit-data transmissions made possible. This low NA-POF has enough reliability for practical use. Furthermore, we succeeded in developing a new type of broadband POF consisting of a multiphase polymer, with an excellent heat resistance and a bandwidth performance much broader than that of the low NA SI-POF.