Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
2000-06-22
2002-04-23
Healy, Brian (Department: 2874)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S130000, C385S147000, C385S146000
Reexamination Certificate
active
06377741
ABSTRACT:
The invention concerns production means for the manufacturing of a wave guide, a bundle of wave guides, material consisting of wave guides, a screen consisting of wave guides together with the materials, the screens and the products which are made from these screens, or the above mentioned material.
One of these products is a mirror with a very high reflectance. Mirrors with a somewhat lower reflectance are known form the literature.
A. F. Harvey states on page 236 of “Coherent Light”, published by Wiley-Interscience in London in 1970, that mirrors with a high reflectance can be made by vapour deposition on a insulator of ¼−&lgr; layers of two dielectric media with different refractive indexes. Such multilayer mirrors do have the following 5 disadvantages:
1 ) Their bandwidth is limited. Harvey comments: Let n
i
be the refractive index of a layer of medium i and &Dgr;&lgr; the width of the band, at a distance of the media
1
and
2
of −(¼)&lgr;, &Dgr;&lgr;/&lgr;=(4/&pgr;)arc sin{(n
1
−n
2
)/(n
1
+n
2
)} yields. The bandwidth can be enlarged by varying the thickness of the layers. Harvey gives as an example the fact that a multilaser mirror consisting of 35 layers, in the wavelength domain 300 nm≦&lgr;≦830 nm, can have a reflectance greater than 0.9.
2) The power that these mirrors absorb is too much for some applications e.g. in high power lasers.
3) They do not reflect exclusively according to Snellius' law and thus scattering of light occurs.
Harvey gives as an example a 15 layer mirror designed for a wavelength of 1.06 &mgr;m, which transmits 0.05% reflects 99.34% and absorbs or scatters about 0.6%. Jeffrey W. Griffin et al show in Applied Optics (see vol 25, no.10, page 1532, 1986), that the scattering arises from two sources which cause surface scattering and volume scattering respectively. They state that volume scattering increases with the number of layers and they mention a 15 layer mirror, designed for a wavelength of 0.633 &mgr;m having a reflectance of 99% and a volume scattering of 1%. Therefore in practice the reflectance as a function of the number of layers has a maximum which is smaller than 1.
4) They do not have a sharply determinded cutoff wavelength. Therefore it is impossible to use these mirrors e.g. to cut off the spectrum of Nd-YAG laser in such a way that a smaller domain of the spectrum would be available in order to sharpen the focus of the Nd-YAG laser light.
5) Their applicability with respect to short wavelengths is limited due to the fact that at a certain wavelength the reflective ability of the normal reflection decreases as a function of the frequency.
The said invention, in most cases, does not have these disadvantages, or if so, to a lesser degree.
E.g. the wavelength domain having a high reflectance is not limited to the upper side but limits itself to the lowerside. There, the boundary is so sharp that it can be characterised by a cutoff wavelength, &lgr;
c
, and can be used e.g. to narrow the spectrum of a Nd-YAG laser. The power P absorbed by the mirror is considerably less than the power P
c
absorbed by a conventional multi-layer mirror. For a certain design of the mirror it is possible to estimate the magnitude of P with the help of P
c
.
Let A
e
be the surface area of the unit cell of the mirror and A
r
the surface area of the rim of the unit cell of the mirror: P≦(A
r
/A
e
)·P
c
is yielded.
A comparable relation holds also for P
s
; the power of the light that has been scattered by the mirror and P
cs
the power of the light that has been scattered by a conventional multi layer mirror. In some cases, depending upon the wavelength of the incident photons, it is realized that A
r
/A
e
≦10
−2
holds true. The field of application of the invented mirror is at the short wavelength side less limited than those of the metallic mirror and the multi layer mirror respectively. In the first case, this is caused by the fact that the reflectance is maximum at a 90° angle of incidence and in the second case it is caused by the fact that a less normal reflectance is mainly apparent at the outerwall, on the rim of the unit cell. The invention relates to a mirror consisting of various cells which either may or may not be of the same type.
If a mirror consists of a great number of identical cells then such a cell is called a unit cell. In practice a unit cell is built of at least two media whereof at least one corresponds with a wave guide. Such waveguides either may or may not be closed at one side and their length is at least equal to half of their cutoff wavelength &lgr;
c
, and preferably much longer than &lgr;
c
. The cutoff wavelength is defined as the largest wavelength of the radiation that can be transmitted by the waveguide. In order to prevent that the waves penetrate practically through the material within the wall of a waveguide, such a waveguide must have a length which is at least equal to five times the penetration depth &dgr;, of the material of which the wall of the waveguide consists. The penetration depth is defined in a longitudinal section of a wave guide. It is the distance from a point p in the wall of a waveguide to the innersurface of the wall of the waveguide. In point p the absolute value of the wavefunction &PSgr; of a photon transmitted by the waveguide has a value which is (1/e) times its value on the innersurface of the wall of the waveguide.
In a certain kind of unit cell, the simple unit cell medium 1 having refractive index n
1
is situated in the centre of a cross section of the cell, while medium 2 having refractive index n
2
is situated at the rim of that cross section coinciding exactly with the wall of the unit cell. Two kinds of simple unit cells are distinguished; type 1 being characterized by n
1
>n
2
and type 2 by n
2
>n
3
. Composed unit cells are also distinguished.
Such a unit cell has the property of having at least two different waveguides.
FIGS. 1A-N
shows some and by far not all of the possible examples of cross sections of unit cells. If it is, for whatever reason, important, e.g. to reduce costs, to minimize the amount of material of medium 2 then it is of advantage to make a cross section of both the outer periphery and the innerperiphery of a unit cell, and that the boundaries of medium 2 both should coincide with a regular hexagon.
The unit cells shown in the
FIGS. 1A-N
are all simple unit cells having the same property; in a cross section of the unit cell the periphery of medium 1 has either precisely 1, or precisely 2 or an infinite amount of points in common with a straight line.
Such unit cells are of importance for applications because in a cross section, the whole of medium 1 can be associated with exactly one cutoff wavelength. These cells are called specific unit cells.
The unit cells in the
FIGS. 1B
,
1
K and
1
L are all composed unit cells. The unit cell in
FIG. 1B
is an example of a unit cell having characteristic dimensions of 0.5&lgr;
ci
, where &lgr;
ci
is the cutoff wave length in medium i. With the proper design, a mirror consisting of such unit cells is suitable to reflect all electromagnetic radiation of wavelength &lgr; provided that &lgr;>&lgr;
ci
holds.
Conventional multi layer mirrors have structures of characteristic dimensions of 0.25&lgr;
i
, where &lgr;
i
the wavelength of the light in medium i in the mirror. In practice &lgr;
ci
≈&lgr;i holds. Therefore, the said invention can be made with greater precision than the corresponding conventional multi layer mirror, while the lower boundary of the wavelength domain is considerably lower than that of the conventional multi layer mirror. The unit cell shown in
FIG. 1K
can be used to make mirrors which allow for e.g. fifty percent transmittance. For instance, one waveguide can be used to transmit light while another waveguide is designed to reflect light. This unit cell is an example of a unit cell with more than 1 characteristic dimension. Mirrors consisting of various kinds of unit cells also belong to the invent
Healy Brian
Kenyon & Kenyon
LandOfFree
Wave guides and material comprising wave guides and its... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wave guides and material comprising wave guides and its..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wave guides and material comprising wave guides and its... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2850969