Thin Film Optical Devices Research Articles

From Ferroelectrics to Polymers - Perspectives for Thin Film Optical Waveguides and Devices

AbstractPresently commercial optical fiber links experience an explosive growth. On the other hand, the integration of optical functions on a single substrate (“Integrated Optical Device”) is still mostly limited to the R & D-laboratories. Only Mach-Zehnder modulators, made from ferroelectric crystals, have found commercial applications so far. The development phase of the integrated optical devices, based on bulk crystalline LiNbO3, is now covering a time span of nearly 30 years. In comparison, the development of the thin film growth of optical oxide ferroelectrics or of tailored optical polymers is just a few years old and we are still at the beginning of the learning curve.

Investigations on the structure of boron nitride films

Boron nitride films fabricated by ion beam assisted deposition (IBAD) have been analyzed using polarized infrared reflection spectroscopy (PIRR), generalized variable angle of incidence spectroscopic ellipsometry (gVASE), elastic recoil detection analysis (ERDA), and in situ ellipsometry during plasma etching. Hexagonal boron nitride (h-BN) films, with properties very similar to the interface material on top of which cubic boron nitride (c-BN) nucleates, have been prepared. PIRR and gVASE results show that these films are biaxially anisotropic. The h-BN basal planes are aligned to the surface normal and exhibit a preferential alignment parallel to the direction of the boron vapor stream. This behavior is unrelated to the substrate crystal orientation. The observed preferential alignment of the h-BN basal planes cannot be explained by compressive stress or ion beam induced processes. The biaxially anisotropic optical properties of these h-BN films can be employed to fabricate special optical thin film devices but require the application of generalized ellipsometry also for in situ measurements.

Modified complex method for constrained design and optimization of optical multilayer thin-film devices

A new computer design program based on the modified-complex method has been developed for constrained optimization and refinement of optical thin-film multilayer devices. This program is having a provision to include both limiting constraints as well as constraint equations. Constraints are suitably accommodated to generate designs which are practicable and withstand high laser power. Various rapid convergent processes like dynamic contraction and expansion of feasible vertices are incorporated for efficient scanning of the constraint parametric space. A broad band IR antireflection coating has been designed to test its relative efficiency with respect to other available methods. A wide varieties of highly useful multilayer devices have been successfully developed using this method.

Optical thin film devices

Thin film devices are applied to almost all modern scientific instruments, and these devices, especially optical thin film devices, play an essential role in the performances of the instruments, therefore, they are attracting more and more attention. Now there are numerous kinds of thin film devices and their applications are very diversified. The 300-page book, 'Thin Film Device and Applications,' by Prof. K. L. Chopra gives some general ideas, and my paper also outlines the designs, fabrication, and applications of some optical thin film devices made in my laboratory. Optical thin film devices have been greatly developed in the recent decades. Prof. A. Thelan has given a number of papers on the theory and techniques, Prof. H. A. Macleod's book, 'Thin Film Optical Filters,' has concisely concluded the important concepts of optical thin film devices, and Prof. J. A. Dobrowobski has proposed many successful designs for optical thin film devices. Recently, fully-automatic plants make it easier to produce thin film devices with various spectrum requirements, and some companies, such as Balzers, Leybold AG, Satis Vacuum AG, etc., have manufactured such kinds of coating plants for research or mass-production, and the successful example is the production of multilayer antireflection coatings with high stability and reproducibility. Therefore, it could be said that the design of optical thin film devices and coating plants is quite mature. However, we cannot expect that every problem has been solved, the R&D work still continues, the competition still continues, and new design concepts, new techniques, and new film materials are continually developed. Meanwhile, the high-price of fully-automatic coating plants makes unpopular, and automatic design of coating stacks is only the technique for optimizing the manual design according to the physical concepts and experience, in addition, not only the optical system, but also working environment should be taken into account when designing optical thin film devices. Therefore, chemical and mechanical, as well as optical properties of thin films and optical system, should be known. Following is the outline of design method and applications of optical thin film devices according to the classification of our factory, Shanghai Optical Instrument Factory.

Integrated optics and new wave phenomena in optical waveguides

Research in integrated optics has two goals: One is to apply thin-film technology to the formation of optical devices and circuits. The other is the integration of a large number of optical devices on a small substrate, so forming an optical circuit reminiscent of the integrated circuit in microelectronics. The result is a new breed of optical devices in the form of miniature optical waveguides. They include lasers, modulators, switches, detectors, prisms, lenses, and polarizers, and many of them have efficiencies better than their bulk counterparts. Simple integrated optical circuits have also been constructed, and rapidly advancing semiconductor technology indicates that monolithic integrated optical circuits can readily be developed using GaAs-related compounds. In this paper, we review the state-of-the-art of integrated optics and explore new wave phenomena in optical circuits. The specific topics to be discussed are: light-wave couplers and $m$-line spectroscopy, refraction and reflection of light in thin films, normal modes of the uniform, the graded and the metal-clad waveguides, optics in tapered films, theory of corrugated waveguides, and more importantly, physics of various thin-film optical devices and the method of the circuit formation.

Computer-aided design of thin-film optical devices

The paper describes a technique for the computer-aided design of optical devices which are structured from multilayer thin films. The method overcomes some of the disadvantages usually associated with the design of optical multilayer systems, such as a requirement for approximate initial designs and excessive computing time. Results are presented for both bandpass and bandstop optical filters. The design system has been planned to integrate with the requirements of a computer-controlled process for manufacturing optical devices.

Equal-phase-velocity propagation for the TE and TM modes of planar metal-clad optical waveguides

An asymmetrical four-layered metal-clad dielectric optical waveguide can support the TEN and TMN modes forN⩾0 with the same phase-velocity if the core thickness,t3, and the buffer layer thickness,t2, are suitably chosen. Only metals that have a negative real part ∈′1 of their complex permittivity\(\hat \in _{\text{1}} = \in '_1 - j \in ''_1 \)at optical frequencies are considered as the cladding material. It is shown that the application of a lossless approximation which set ∈″1=0 enables the development of a real expression which may be solved directly for the values oft2 andt3 that are required to achieve the equal-phase-velocity characteristic. Parametric plots for the guide dimensions are presented for representative waveguides and it is shown that an appropriate choice oft2 andt3 will reduce the absorption losses of the TE and TM modes to negligible levels. This property of the waveguide will find application in thin film optical devices such as polarization rotation modulators that require the simultaneous propagation of TE and TM polarized waves.

Automatic computer control of the manufacture of thin-film optical devices

This paper describes a project to investigate the feasibility of using a small digital computer to automatically control the manufacture of multilayer thin film optical interference devices. The manufacturing process and the computer control systems are described in detail and the results from a particular case study are presented. These results relate to the manufacture of a 5-layer antireflectance coating. The computer is shown to be able to control the process with precision and to have the potential for manufacturing devices toa consistent high quality.

1244. Electron beam, ion beam, X-ray optical techniques for fabricating surface-acoustic-wave and thin-film optical devices: H J Smith, Vide, 29 (173), 1975, 364–370

1244. Electron beam, ion beam, X-ray optical techniques for fabricating surface-acoustic-wave and thin-film optical devices: H J Smith, Vide, 29 (173), 1975, 364–370

Fabrication techniques for surface-acoustic-wave and thin-film optical devices : Henry I. Smith. Proc. IEEE, 62 (10) 1361 (October 1974)

Fabrication techniques for surface-acoustic-wave and thin-film optical devices : Henry I. Smith. Proc. IEEE, 62 (10) 1361 (October 1974)

Two-layered construction of integrated optical circuits and formation of thin-film prisms, lenses, and reflectors

We have demonstrated a new form of a two-layered construction of optical circuits. In this method, thin-film optical devices are covered by a single continuous layer of light-guiding film which serves as the interconnections as well as the input and output terminals. We also have demonstrated the construction of thin-film prisms, lenses, and a novel corner reflector in this type of structure.

Circuit theory for a class of anisotropic and gyrotropic thin-film optical waveguides and design of nonreciprocal devices for integrated optics

A circuit-theoretic treatment is presented for thin-film optical waveguides using a class of real anisotropic and gyrotropic materials. The analysis is based on the two-mode approximation in normal-mode theory. The terminal behavior of those guides is described by the 2 × 2 transmission matrix and expressions for matrix elements of six systems that are introduced as canonical elements in circuit synthesis are derived. Properties of canonical elements are discussed with particular attention on their reciprocity. Using the transmission matrix, we can treat the design of thin-film optical devices by a simple matrix operation familiar in conventional transmission-line circuit synthesis. As a typical application the design of various nonreciprocal integrated-optical devices is treated in detail. The desired response is synthesized by cascading selected canonical elements in an appropriate order. Examples include the gyrator, unidirectional mode converter, differential phase shifter, isolator, and circulator.

Fabrication techniques for surface-acoustic-wave and thin-film optical devices

The techniques of photolithography, electron lithography, X-ray lithography, ion bombardment etching, and liftoff are reviewed, and their advantages and disadvantages assessed from the point of view of fabricating surface-acoustic-wave and thin-film optical devices.

Macroscopic strain in facetted regions of garnet crystals

Morphological studies of Czochralski-grown gadolinium gallium garnet single crystals have revealed facetting characteristics identical to those observed in yttrium aluminium garnet. Accurate lattice parameter measurements made at various points within single crystals of these materials have been used to determine the strains associated with such facets. A possible explanation for the origin of the strain is proposed and the effect of facet imperfections upon the use of garnets in optical and magnetic thin film devices is discussed.

Thin Organosilicon Films for Integrated Optics

The continued development of integrated optics is heavily dependent upon the availability of materials that are suitable for the construction of thin-film optical circuitry and devices. We report here an investigation of new films made by an rf discharge polymerization process of organic chemical monomers. We concentrate our discussion on films prepared from vinyltrimethylsilane and hexamethyldisilbxane. These films are smooth, tough, pinhole-free, transparent from 0.4 microm to 0.75 microm, and exhibit very low loss (<0.04 dB/cm) for light-wave propagation. More importantly, experiments demonstrate the possibility of controlling the refractive index of the films either by the mixing of the two monomers before deposition or by chemical treatment after the film is deposited. The use of the prism-film coupler for studying the refractive index of each material is discussed in detail.

Light Waves in Thin Films and Integrated Optics

Integrated optics is a far-reaching attempt to apply thin-film technology to optical circuits and devices, and, by using methods of integrated circuitry, to achieve a better and more economical optical system. The specific topics discussed here are physics of light waves in thin films, materials and losses involved, methods of couplings light beam into and out of a thin film, and nonlinear interactions in waveguide structures. The purpose of this paper is to review in some detail the important development of this new and fascinating field, and to caution the reader that the technology involved is difficult because of the smallness and perfection demanded by thin-film optical devices.