Optical component comprising layers of porous silicon

Details Optical component comprising layers of porous silicon Optical component comprising layers of porous silicon

1995-12-04

1997-12-09

Dzierzynski, Paul M.

Optical: systems and elements

Light interference

Produced by coating or lamina

359586, 359589, G02B 528

Patent

active

056966296

DESCRIPTION:

BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of PCT/DE 94/00635 filed 8 Jun. 1994 and based in turn upon German National Application P 43 19 413.3 filed 14 Jun. 1993 under the International Convention.


BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an optical component comprised of transparent thin layers of different thicknesses and differing refractive indexes.
2. Description of Related Art
Such optical components have been known for a long time. Thus, for example, optical components have been used whose operation depends upon interference effects in thin layers. These include for example interference filters and mirrors. The geometric effect of a layer sequence which, inter alia, is composed of layers of two materials which have different refractive indexes is determined by an appropriate selection of the layer sequence and the optical thicknesses of the individual layers. The so-called optical thickness of the layer is the thickness of the layer multiplied by the refractive index. These optical thicknesses are usually whole fractions of the respective wavelengths which are selected for the filter or mirror. Thus a so-called Bragg reflector can be comprised of a periodic layer sequence of two layers with the greatest possible difference in refractive index and an optical layer thickness each of 1/4 of the respective wavelength for which the reflector has an optimum effect. In contrast thereto, there is a Fabry-Perot filter which has a somewhat modified layer sequence which provides a high transmission for a predetermined wavelength while for other wavelengths the filter is opaque. Optical components from layers with gradually varying refractive index are known as waveguides or as anti-reflection coatings.


SUMMARY OF THE INVENTION

It is an object of the invention to substitute another material for the layers of the materials customarily used.
This object is achieved according to the invention in that the layers are comprised of porous silicon.
The production of a layer system of porous silicon can be realized in different ways: for the production of porous silicon, the porosity and thus the optical characteristics of an individual layer can be affected in a very simple manner. starting material for the etching process give rise to a change in the microstructure and thus the optical characteristics. With the differently doped layers for the starting material, a variation in the level and also the kind of doping is conceivable. Thus, inter alia, the following doping sequences can be considered: Si/SiGe can produce a porous layer system. etching process for the microstructures can be used to produce layer systems according to the invention. The variation of the intensity of the illumination and also a change in the spectrum of the incident light are possible.
The processes mentioned under a) through d) can be combined with one another to field a layer system with the optimum optical characteristics.
The layer system of the invention depending upon the desired application can be varied and thus the emission characteristic or absorption characteristic of a light emitting component or photodetector (filter, antireflection coating) can be influenced. Thus a version of the optical component has thicknesses and refractive indexes of the layers forming an interference filter and can be utilized as such.
The filter effect is achieved by a periodic sequence of layers with different optical characteristics (dielectric functions). Depending upon the layer sequence, different kinds of filters are attainable (band pass, band blocking, Fabry-Perot filters), whereby the filter effects can be combinable also by the series positioning of different types of filters. Such filters are usable in optics and also for influencing the emission characteristics for light emitting components (for example colored flat imaging screens also of porous silicon) and as accessory filters for photodiodes, for example, in color cameras.
The special advantage of

REFERENCES:
patent: 4271210 (1981-06-01), Yoldas
patent: 4535026 (1985-08-01), Yoldas et al.
patent: 5218472 (1993-06-01), Jozefowicz et al.
J. G. wilder, "Porous Silicon AR Coating for Use at 248 nm or 266 nm", Applied Optics vol. 23, No. 10, pp. 1448-1449 15 May 1984.
"IR Spectroscopic ellipsometry: Instrumentation and applications in semiconductors" by Gilbert alcser, published in Thin Solid Films, 234 356-362 25 Oct. 1993.

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