Device and method for doubling the frequency of elecromagnetic radiation of a given frequency

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG.
2 illustrates diagrammatically a device embodying the invention for doubling the frequency of electromagnetic radiation input thereto.
As shown in FIG.
2, the device comprises a substrate 1 having a flat major surface 1a on which are formed successive first and second layers 2 and 3.
In the arrangement shown in FIG.
2 the first layer 2 is formed of a first active material having a plasma oscillation frequency equal or nearly equal to a given frequency desired to be doubled.
The various plasmon modes are discussed in a paper by E.
N.
Economou published in Physical Review 182 page 539 1969.
The second layer 3 is formed of a second material having a low absorption for electromagnetic radiation of twice the given frequency, the second layer having a mean thickness d.
gtoreq.
.
lambda.
i/4N.
sub.
B (where .
lambda.
i is the wavelength of electromagnetic radiation at the given frequency and N.
sub.
B is the refractive index of the second layer at the wavelength .
lambda.
i/2) so as to form a waveguide for frequency doubled electromagnetic radiation.
A further first layer 2 may be formed on the second layer 3 as shown in FIG.
As shown in FIG.
2, a major surface 5 of the second layer 3 may be formed, possibly by etching, with a periodic structure 6 in the form of sinusoidal corrugations or undulations having a period .
LAMBDA.
=.
lambda.
i/4N.
sub.
B (where .
lambda.
.
sub.
i is the wavelength of the incident electromagnetic radiation and N.
sub.
B is the refractive index of the waveguide second layer 3 at a wavelength of .
lambda.
i/2).
The further first layer 2' may be similarly corrugated as shown in FIG.
2.
The depth of the corrugations should be small, approximately .
lambda.
/10, to avoid scattering losses.
The periodic structure 6 shown in FIG.
2 is provided to provide optical feedback to give a directional output 8' and improve the efficiency and coupling of the frequency doubled (2) electromagnetic radiation.
In a particular example, the first layers 2 and 2' may be of mean thickness 1000