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.

Light waves in thin films and integrated optics.

Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 A × 100 A × 100 A GaAs/Ga 0.8 Al 0.2 As quantum box, and 15 times for Ga 0.47 In 0.53 As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm2and 62 A/cm2for GRINSCH GaAs/(Ga 0.8 Al 0.2 As-Ga 0.4 Al 0.6 As) and Ga 0.47 In 0.53 As/(Ga 0.28 In 0.72 As 0.6 P 0.4 -InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.

Gain and the threshold of three-dimensional quantum-box lasers

The prism coupler, known from experiments on integrated optics, can be used to determine the refractive index and the thickness of a light-guiding thin film. Both parameters are obtained simultaneously and with good accuracy by measuring the coupling angles at the prism and fitting them by a theoretical dispersion curve. The fundamentals and limitations. of this method are discussed, its practical use, and mathematical procedures for the evaluation.

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Measurement of Thin Film Parameters with a Prism Coupler

Publisher Summary A refractive index can be increased by ion implantation by changes in density and structure, by the addition of high-polarizability impurity ions, by a reduction of the plasma effect that increases the index and that is most important in the wavelength region far from the energy gap, and by absorption changing in the index in the region of the gap, that is, via the Kramers–Kronig relation. This chapter discusses the optical properties of implanted semiconductors, electrooptic components formed by ion implantation, general principles that determine most luminescent systems, effects of implantation temperature, luminescence centers in LiF-Mg-Ti radiation dosimeters, and use of line spectra in defect studies. In the LiF system, the luminescence bands are broad, and if alternative versions of the same complex exist, they cannot be resolved from the spectra. The addition, by implantation, of ions with incomplete inner electron shells opens up new possibilities as the lattice distortions of the free-ion energy levels are strongly perturbed by the defects in the neighborhood of the ion.

Optical Effects of Ion Implantation

This paper reviews the present knowledge on tantalum pentoxide (Ta 2 O 5 ) thin films and their applications in the field of microelectronics and integrated microtechnologies. Different methods used to produce tantalum oxide layers are described, emphazing elaboration mechanisms and key parameters for each technique. We also review recent advances in the deposition of Ta 2 O 5 in the particular field of microelectronics where high quality layers are required from the structural and electrical points of view. The physical, structural, optical, chemical and electrical properties of tantalum oxide thin films on semiconductors are then presented and essential film parameters, such as optical index, film density or dielectric permittivity, are discussed. After a reminder of the basic mechanisms that control the bulk electrical conduction in insulating films, we carefully examine the origin of leakage currents in Ta 2 O 5 and present the state-of-the-art concerning the insulating behaviour of tantalum oxide layers. Finally, applications of tantalum oxide thin films are presented in the last part of this paper. We show how Ta 2 O 5 has been employed as an antireflection coating, insulating layer, gate oxide, corrosion resistant material, and sensitive layer in a wide variety of components, circuits and sensors.

Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications

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 hexamethyldisiloxane These films are smooth, tough, pinhole-free, transparent from 04 μm to 075 μm, and exhibit very low loss (<004 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

Thin Organosilicon Films for Integrated Optics

We consider thin film light guides consisting of a transparent film of high refractive index deposited on a substrate of lower index. The propagation of light in such a two-dimensional transmission medium can be described within the limits of geometrical optics by an effective index of refraction N. Its value depends on the film thickness. Therefore, a light beam in the thin film guide is refracted or totally reflected at a step of film thickness. We discuss these phenomena (Snell’s law) and demonstrate them experimentally, using ZnS films on glass as guides. As applications, we show a thin film prism and thin film lenses for guided light beams. By properly choosing the film thicknesses at both sides of the step, one can obtain an unusually large positive or negative wavelength dispersion of the refraction or, if desired, achromatic refraction.

Geometrical optics in thin film light guides

We demonstrate a new and simple method of forming light-guiding interconnections in an integrated optical circuit. This involves bridging the devices with a thin film having tapered ends that form naturally during the deposition process. Experiments show that there is no specific requirement for the thickness, refractive index, or relative position of the bridging film. A theory of composite waveguides provides an understanding of these interconnections.

Formation of light-guiding interconnections in an integrated optical circuit by composite tapered-film coupling.

Attention is drawn to the properties of Ta2O5 film which make it attractive as a new dielectric medium for use in integrated optical circuitry. The Ta2O5 film discussed was formed by thermally oxidizing sputtered β-tantalum films in an oxygen atmosphere. Measurements showed that these films will support propagation of coherent red (6328-A.) light with a loss of 0.9 dB cm−1 and coherent blue (4880-A) light with a somewhat higher loss of 4.1 dB cm−1. From measurements of the coupling angle at which propagation of the various modes takes place, refractive indices for the TE and TM modes at 6328 A, 5145 A, and 4880 A were obtained. The loss mechanisms are discussed, and it is shown that most of the loss is due to scattering during the internal reflections at the air–oxide and oxide–substrate film surfaces. A small fraction of the loss appears to occur in the interior of the film. With Ta2O5 it is demonstrated for the first time that optical circuit components can be formed for use in integrated optics by employing existing thin-film technology. The basic process steps include the pattern generation of the β-Ta followed by thermal oxidation of the pattern. Experimental studies of propagation in straight and curved waveguides are described. It was found that the losses in pattern generated waveguides are of the order of 5 dB cm−1 to 7 dB cm−1, with the excess loss due to scattering from the waveguide edges. It is concluded that improvements in the smoothness of the boundaries of circuit elements are desirable to reduce transmission losses in pattern generated film.

R. J. Martin

Papers

Thin Organosilicon Films for Integrated Optics

Geometrical optics in thin film light guides

Formation of light-guiding interconnections in an integrated optical circuit by composite tapered-film coupling.

Optical propagation in sheet and pattern generated films of ta(2)o(5).