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Elements of Integrated Optics

#A-340.2


The Elements of Integrated Optics on Ferroelectric Films Created by Sol-Gel Method

Tech Area / Field

  • PHY-SSP/Solid State Physics/Physics
  • MAT-COM/Composites/Materials

Status
3 Approved without Funding

Registration date
09.04.2001

Leading Institute
Institute for Physical Research, Armenia, Ashtarak-2

Collaborators

  • Stanford University / SLAC / Center for Materials Research, USA, CA, Stanford\nPennsylvania State University / Materials Research Institute, USA, PA, University Park\nThe University of Electro-Communications, Japan, Tokyo\nDepartment of the Navy / Naval Research Laboratory, USA, DC, Washington\nAll Optical Networks, Inc., USA, CA, San Diego\nTeraBurst Networks Co, USA, CA, Sunnyvale

Project summary

Systems of information transfer and processing are now the main consumers of integrated optical devices. The intensive development of laser communication systems demands new approaches for the production of multielement integrated optical devices, which stems from the need for an increase in the degree of integration, speed of information transfer and processing, and also a decrease in cost. The elements of integrated optics, prepared on single crystal ferroelectric thin films, and possessing an entire complex of very important and interesting optical-electrical and physical properties, are the most prospective for telecommunication systems.
A key stage in the production of integrated optics devices is the formation of microtopography on crystalline films.
There are now a variety of methods for production of topographical patterns on crystalline films. They are generally comprised of two separate steps: obtaining thin film and creation of topographical pattern. The majority of these traditional methods are based on obtaining patterned films, using photoresist, photolithography with further chemical etching to form the pattern on the crystalline thin film.
The technology of photolithography is widely used in the microelectronics industry and is significantly less used in integral optics and photonics. The adjustment of this technology for integral optics and photonics is a difficult task, since, besides problems of creating a topographical picture, which is conventional for electronics, the Project supposes the development of methods for selected space exposure of films, modeling their properties in terms of various parameters. In addition to thickness, these parameters include impurity presence, polarization, refractive index, conductivity, etc.
Photoenhanced CVD, usually with laser sources, or photochemical deposition methods provide direct lithographic patterning methods. However, this method has limitations, since precursors for the CVD method must be volatile complexes and they must fit a very narrow range of volatility (temperature and stability) reactivity. Hence, the range of complexes is quite restrictive.
Modified sol-gel technology, including photosensitive gel, is one of the newest and most prospective technologies for obtaining integrated optics devices.

Project A-340 supposes the development of this technology for creation of a topographical pattern at the stage of amorphous (precursor) gel with consequent firing and crystallization. Such an approach, compared with existing technology of the creation of integrated optics elements, will allow the technology to be simplified and will create new schemes and devices for integrated optics, which are not possible using conventional methods.

The proposed method of production of films of metals, their oxides, and of other metal compositions by a modified (photosensitive) sol-gel method involves the synthesis of a photo-reactive complex of metal. The metal complex undergoes change under the influence of light of a suitable wavelength. A pattern can be obtained on an amorphous (precursor) film by exposition of the selected part of the film. After etching an unirradiated part of a film the subsequent crystallization yields a crystalline film with the necessary topographical pattern.
Thus, the suggested method includes the following basic steps:
deposition of an amorphous film of a metal complex on a substrate;
exposition of selected areas of the film by radiation, preferably UV, to cause the metal complex to undergo a photochemical reaction;
etching (dissolution) of an unirradiated area of a film;
crystallization of the patterned film.

Use of a modified sol-gel method for deriving integrated optics devices is especially important for those materials, upon which patterned films are very complicated to obtain using traditional methods because of their special properties (for example, with lithium niobate and lithium tantalate films, which are very difficult to etch using a mask, because the etching velocity strongly depends on crystallographic orientation).
It is proposed that the following integrated optics elements be obtained using modified sol-gel technology with photosensitive gel:
linear and curvilinear channel waveguides;
directional couplers located in vertical or horizontal planes.

The above elements could become the basis for making new integrated optics devices. Obtaining these integrated optics elements and devices is supposed on the basis of crystalline ferroelectric films of the LiNbxTa1-xO3 system, where 0х1. The crystals of this system show high nonlinear and electro-optic characteristic. Moreover, the variation of composition will allow the control of electrical and crystallographic properties, which will essentially expand the area of their application.

The objective of the Project: Development of a method of production of integrated optical elements on the basis of LiNbxTa1-xO3 ferroelectric thin films by direct crystallization of a topographical pattern obtained by a modified (photosensitive) sol-gel method.


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