The present status of research on some photoinduced phenomena in organic thin films is outlined in relation light - sensitive recording media. Stress is laid on the photoinduced ablation, irreversible photochemical reactions, photochromic transformations, photoanisotropic processes, photoreffactive effects and reversible photochemical reactions in vacuum - deposited, polymeric and Langmuir - Blodgett (LB) films.
Metal doped polymers are used as holographic recording material in which the first step is the absorption of the light by the metallic center. The primary mechanism, in most cases an electron transfer in the excited state, is tentatively described for polymeric material doped with chromium(VI) and iron(III).
In this paper, we report the implementation of waveguide-based holograms for several on-going applied photonics research at the Microelectronics Research Center of the University of Texas, Austin. These include a wavelength division demultiplexer (WDDM), a nonblocking wavelength-selective crossbar, an IEEE protocol compatible optical backplane bus and true-time-delay lines for wide-band phased array antennae. The exclusive characteristics of waveguide holograms and the maturity of photopolymeric materials make the reported research findings highly attractive for system integration where device performance features and system reliability are pivotal.
The surface-normal configuration of both the WDDM and the wavelength-selective crossbar provides not only a much more rugged packaging due to the elimination of edge coupling but also an insertion compatibility with vertical cavity surface emitting laser integration. An eight channel wavelength division demultiplexing device with a center wavelength of 772 nm and a wavelength separation of 4 nm is demonstrated with channel to channel cross talk of less than -20 dB is experimentally confirmed in Section 2. A 3x3 crossbar with Δλ=10nm with a center wavelength of 765 nm is delineated in Section 3. An optical backplane bus containing nine memory/process boards with 72 interconnects is reported in section 4. A waveguide hologram based true-time-delay-line is presented in Section 5.
Ionizing radiation (light ions up to 200 keV and UV radiation with λ < 280 nm) is used to structure the surfaces of transparent polymers like Poly-(methyl-methacrylate) and related materials. Areas with an index increase up to 1% suitable for waveguiding are obtained.
Compaction of the irradiated areas leads to diffractive structures. Changes in the chemical structures of the irradiated samples are reported. The physical properties like mode spectra and attenuation were measured. Passive components with fibers coupled to the devices were fabricated.
Polymer waveguides may be fabricated by numerous methods. There is a large number of patterning techniques. Index matched guides may easily be fabricated by adjusting the thickness. Using polymer lightguides the change of the optical parameters is investigated where they occur, in the material directly. Measuring the anisotropy of different polymers the reversible in-diffusion of vapor molecules can be detected . Sensitivity curves can be established and the time constants yield information about the size, shape or polarity of the molecule. Combining plasmon- and leaky mode spectroscopy an absolute method of real and imaginary parts of the polymer film is obtained. Results for using Teflon AF(R) on Ag are presented. With the low index polymer Teflon AF(R) it is possible to make a new class of waveguides, the liquid core waveguides (LCW) with water as a core.
Photochemical hole burning in polymer systems are reviewed. Hie general concept of photochemical hole burning (PHB) is introduced and the types of photoreaction leading to PHB are outlined. Recent topics of PHB, namely, high-temperature hole burning, photon-gated hole burning, and possibility of applicating PHB to an optical device are presented. Single molecule spectroscopy and photon echo are briefly introduced.
The interaction of polymers and light as well as the production of polymers from photoinduced reactions is a vast subject area with numerous varied aspects. These areas include polymer formation from photopolymerizations, photocrosslinking reactions, and photodegradation reactions. This article will be restricted to reviewing the fundamental aspects of photopolymerizations as well as a summary of the current applications of photopolymerizations and other photochemical reactions in polymers.
Characteristics of plastic optical fibers (POF)s, i.e., handling ease because of their good ductility, splicing ease to each other and to light sources because of their large fiber diameter and high numerical aperture, processability, and high flexibility notwithstanding their larger fiber diameters, have attracted much attention. They are expected to be applied as a short distance optical signal transmission medium for certain kinds of computer-toterminal data links such as in office automation systems. Polymers for POF application should be as transparent as possible and therefore they should be low in scattering loss, and their refractive index should be controllable to fabricated fiber structures. In this paper, POF optical transparency, light scattering, optical bandwidth, and refractive index control are discussed in detail along with polymer loss limit
Photopolymer materials have been used for recording holograms since the late sixties.
A great variety of formulations and conditioning were developed with the object of meeting the requirements of specific applications in the fields of holography, information storage or optical elements.
The need for materials exhibiting a self-processing character aroused the creativity of many scientists who studied the details of the recording process in this original class of sensitive systems. In fact, the process of optical information storage that results from the coupling of the photochemically induced conversion of monomers, mass transport due to diffusion and grooving due to gradients of surface free energy can be made selfdeveloping by a proper choice of the physico chemical and photochemical parameters of the recording system.
Real-time, double exposure and time-averaged holographic interferometry, recording of image and computer generated holograms and chopped light recording are some of the typical applications of the self-developing materials.
A review of the current trends in microlithography is presented including the science and chemistry of this technology. The microelectronics technology has progressed with at an astounding rate during the past several decades which is in large measure due to advances in microlithography, which is the technology used to generate the high resolution circuit elements of today’s integrated circuits. Virtually all integrated circuits are made by photolithographic techniques that utilize 365-436 nm UV radiation. But as continued advances in device fabrication are trying the limits of conventional lithography, new strategies such as deep-UV, e-beam and x-ray are being increasingly required to provide the finer feature sizes of newer devices. This review examines the progress that has been made, especially in the last decade, in the development of new resist materials, as well as the chemistries and technologies that have emerged, in the quest to improve sensitivity, resolution, etching resistance, etc.
Organic molecules have been dispersed in polymers and used in 3D memory devices. The time resolved spectra of their transient species and kinetics of the photoinduced reaction have been studied by means of ultrafast time resolved absorption and emission spectroscopy. The reaction mechanism and rates have been determined and some photochromic materials have been used successfully to store and access information in 3D format.
Polymer materials have made a significant impact on optical storage technology. They played a key role in developing high information density and last access type memories with high read-out efficiency. Metal ion doped polymer materials, one of the important classes of recording materials, are classified as ‘Write-Once-Read-Many Self- Developing (WORM-SD) memories”. Holographic characterization of Cr(VI) and Fe(m) doped synthetic polymers are outlined with a brief description about the widely used dichromated gelatin. The mechanism of information storage on these materials has been followed by various elegant techniques. Volume transmission holograms, reflection holograms, computer generated holograms, waveguides, narrow band wavelength selective filters, holographic multiplexing, holographic imaging and space based photonic applications are some of the demonstrated applications with these materials.
Passive and dynamic polymer optical waveguide devices for implementation in optical communication networks are discussed. Different materials and fabrication technologies are compared with respect to their performance and potential applications.
From the beginning of holography, this new scientific understanding of the processing of optical information permitted to record and replay phase and amplitude of signals recorded on a photographic plates. With time, numerous authors did find in holographic technique, a way to fabricate optical systems which will replace conventional glass made optical elements. In this paper, an overview of the possibilities offered by holographic technique to make any kind of optical elements is presented. The review is brief, probably incomplete but it will give the important aspects and references to permit to the reader to find all required information into the open literature.