Article comprising a planar optical waveguide with optically...

Details Article comprising a planar optical waveguide with optically... Article comprising a planar optical waveguide with optically...

1999-09-20

2001-03-27

Spyrou, Cassandra (Department: 2872)

Optical waveguides

Planar optical waveguide

C385S142000, C385S130000

Reexamination Certificate

active

06208792

ABSTRACT:

FIELD OF THE INVENTION
This application pertains to articles (e.g., an all-optical fiber switch for an optical fiber communication system) that comprise an optical waveguide (typically a planar optical waveguide) with optically non-linear core.
BACKGROUND
Switching of optical pulses is an essential functionality of substantially any practical optical fiber communication system. Current technology limits practical electronic switching speeds to about 40 Gbit/s. Thus, in order to attain single channel bit rates higher than about 40 Gbit/s, it is necessary to develop the ability to switch and process optical pulses at speeds substantially higher than 40 Gbit/s.
This application discloses means for ultra fast switching and/or processing (collectively “switching”) of optical pulses, exemplarily permitting sub-picosecond switching times.
Japanese Kokei Patent Application No. Hei 3 [1991]-21934 discloses nonlinear optical devices comprising Ge, As, S and Se-containing chalcogenide nonlinear material.
All cited references are incorporated herein by reference.
SUMMARY OF THE INVENTION
All-optical switching (i.e., switching of an optical signal pulse with an optical control pulse) in principle can be made ultra-fast.
Typically, signal and control light propagate together through an optical waveguide comprising an optically nonlinear core material. Of particular interest herein are planar optical waveguides.
The refractive index n of a nonlinear material is conventionally expressed as n
0
+n
2
I, wherein I is the optical intensity (in W/cm
2
), n
2
is the nonlinear refractive index (in cm
2
/W), and n
0
is the conventional linear refractive index. Similarly, the nonlinear attenuation &agr; of a material is expressed as &agr;
0
+&agr;
2
I, wherein &agr;
2
is the nonlinear attenuation (in cm/W), and &agr;
0
is the conventional linear attenuation (in cm
−1
). It will be understood that typically the above parameters are wavelength-dependent.
Using the fact that an all-optical switching device of the type that is of interest herein typically utilizes a phase shift of order &pgr;, it can be deduced that such a device requires a waveguide of length L equal to about &lgr;/2n
2
I, where &lgr; is the optical wavelength in vacuum. In fiber devices L can be quite long, but in planar waveguide devices L desirably should be no more than about 1 cm. Furthermore, devices of interest herein will typically operate at a wavelength at or near 1.55 &mgr;m, exemplarily in the range 1.45-1.65 &mgr;m. For the sake of concreteness, in the discussion below it will be assumed that &lgr;=1.55 &mgr;m. Still furthermore, a reasonable light intensity I is about 1 GW/cm
2
, and an acceptable attenuation ao is less than about L
−1
.
For an operating wavelength at which the nonlinear attenuation of a given waveguide core material dominates, the above requirements lead to the inequality (&agr;
2
&lgr;/2n
2
)<1, and for a wavelength at which the linear attenuation dominates, the requirements lead to the inequality (&agr;
0
&lgr;/2n
2
I)<1. In both cases it is clearly desirable if n
2
is relatively large, typically more than several 100 times larger than the nonlinear refractive index of silica, designated n
2
(SiO
2
), which is about 2.8×10
−16
cm
2
/W at 1.55 &mgr;m. Furthermore, &agr; desirably is not more than about 1 cm
−1
.
We have carried out a theoretical analysis of the optical properties of some chalcogenide glasses and have determined that some such glass can meet the above recited requirements, and thus can be used as nonlinear core material in a planar waveguide for all-optical switching.
More specifically, the invention is embodied in an article that comprises a planar waveguide adapted for guiding light of vacuum wavelength &lgr; in the range 1.45-1.65 &mgr;m. The planar waveguide comprises a nonlinear core material having at &lgr; a refractive index n=n
0
+n
2
I, where n
0
is the linear refractive index, n
2
is the nonlinear refractive index, and I is the intensity of guided light in the waveguide.
Significantly, the nonlinear core material is a chalcogenide glass comprising selenium and a member of the group consisting of arsenic, germanium, and arsenic and germanium. Associated with the chalcogenide glass is an optical energy gap E
g
. See, for instance, R. Zallen, “The Physics of Amorphous Solids”, John Wiley and Sons, New York, 1983, especially p. 266. The chalcogenide glass further comprises one or more dopant elements selected from the group of elements whose presence in the chalcogenide glass results in a change in E
g
. The amount of the one or more dopant elements in the doped chalcogenide glass is selected such that E
g
is substantially equal to a two-photon energy 2h&ngr;, where h is Planck's constant and &ngr;=c/&lgr;, where c is the speed of light in vacuum, and the amount is furthermore selected such that the doped chalcogenide glass has a nonlinear refractive index n
2
greater than 200n
2
(SiO
2
), preferably greater than 400n
2
(SiO
2
), where n
2
(SiO
2
) is the nonlinear refractive index of vitreous silica at about 1.55 &mgr;m.
Exemplary dopant elements are tellurium, antimony, thallium, copper, silver and sulfur. Of the recited exemplary dopant elements, all but S reduce E
g
.
It should be understood that the prior art contains data on some of the optical properties of substantially any chalcogenide glass of interest herein, including data on some effects of doping. However, to the best of our knowledge, nothing in the prior art suggests a technique for evaluating the nonlinearity of a given chalcogenide glass and, significantly, nothing suggests the use of chalcogenide glass of sufficiently large nonlinearity as core material of a planar optical waveguide, the planar waveguide for instance being used for all-optical pulse switching or processing.


REFERENCES:
patent: 5732179 (1998-03-01), Caneau et al.
patent: 6108474 (2000-08-01), Eggleton et al.
patent: 3-21934 (1991-01-01), None
“Photonic Packet Switching”,Optical Networks—A Practical Perspective, Published by Morgan Kaufmann Publishers, Inc., pp. 515-531 (1998).
“The Physics of Amorphous Solids” by R. Zallen, published by John Wiley & Sons, pp. 266.
“Optical Oscillator Strengths and Excitation Energies in Solids, Liquids, and Molecules”, by S. H. Wemple,The Journal of Chemical Physics, vol 67, No. 5, pp. 2151-2168 (Sep. 1, 1977).

Affiliated with

Also associated with

Rating

Article comprising a planar optical waveguide with optically... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Article comprising a planar optical waveguide with optically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Article comprising a planar optical waveguide with optically... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2510724