Optical communications – Transmitter and receiver system – Including optical waveguide
Reexamination Certificate
2000-03-17
2004-02-17
Chan, Jason (Department: 2633)
Optical communications
Transmitter and receiver system
Including optical waveguide
C398S139000, C398S142000, C398S146000, C398S178000, C398S200000, C398S214000, C385S005000, C385S009000, C385S032000, C385S050000
Reexamination Certificate
active
06694103
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to nonlinear integrated and fiber optics and more specifically to completely optical switches and optical transistors and can be used in fiber-optic optical communications, in optical logical schemes and in other fields, where all-optical switching, amplification, controlling and modulation optical radiation is need.
BACKGROUND ART
The method of self-switching of unidirectional distributively coupled waves (UDCW) is known [A. A. Maier, “The method of signal switching in tunnelly-coupled optical waveguides”, USSR PATENT No1152397 (September 1982);
Byull. Izobret
. (46) 300 (1988); A. A. Maier.
Physics
-
Uspekhi
vol.38 (No 9) pp.991-1029 (1995)]. The method consists in a sharp change of a ratio of intensities (and phases) of the waves at output of tunnel-coupled optical waveguides (TCOW) caused by a small variation of intensities or phases of these waves at the input of the TCOW. Due to given method the earlier unknown class of optical transistors was suggested. The important advantage of the fiber optical transistor is convenience of its junction with optical fiber communication lines. The phenomenon of self-switching is accompanied by auto-synchronization of waves, i.e. alignment of phases of waves at the output of TCOW in so-called midpoint of self-switching [(A. A. Maier.
Physics
-
Uspekhi
v.38 (No 9) 991-1029 (1995)].
As one from perspective variants of the optical transistor the so-called discrete optical transistor was proposed [A. A. Maier.
Sov. J. Quantum Electron
. v.17, p.1013 (1987)], in which as pump the sequence of super-short pulses is used.
If the dispersion is essential in fiber-optic waveguide, that takes place in long fiber-optic waveguides, the optimum shape for supershort pulses is soliton shape.
It is known that, while propagating along the fiber-optic waveguide, even over large distances, the soliton pulses do not diffuse (broaden), saving the form sech(t), since for them the nonlinear compression is compensated by dispersion diffusing. Therefore solitons are perspective for transfer of recordly large information contents.
The fact that solitons can be switched completely as a unit, thus providing complete self-switching, i.e., high effective gain for the discrete optical transistor [A. A. Maier
Sov. J. Quantum Electron
. v.17, p.1013 (1987)], is of even greater importance for us. It is explained by the fact that a soliton propagating along the fiber optic waveguide retains a uniform phase temporal profile, i.e., for all points of the soliton, its phase is nearly the same and depends only on the longitudinal coordinate z. Self-switching occurs near the self-switching midpoint M, corresponding to the unit modulus of the elliptic function, through which the output intensity is expressed. At this point, the output wave amplitudes and phases at the output of the zeroth and the first waveguides are equal, and the characteristic rate of change (i.e., the sensitivity to small variations of input powers and phases) is maximum.
The closest to the proposed method is the method (S. Trillo, S. Wabnitz, E. M. Wright, G. I. Stegeman.
Optics Lett
. 1988, 13, 672-674) of switching of pulses close to the second-order solitons (when input intensities a
00
2
=3.63, a
10
2
=0) in cubic-nonlinear TCOW.
Defects of this method are the rather high energy of solitons fed into the waveguides, and also small sharpness and depth of the switching.
DISCLOSURE OF THE INVENTION
Technical aim of the invention is a decreasing of energy of solitons fed into the waveguides, and also increase of sharpness and depth of switching, and gain of optical transistor.
In the first variant of the method for switching, amplification and modulation of unidirectional distributively coupled pulses and waves they feed radiation in the form of pulses with different maximum intensity |a
k0
2
| into the input of at least one of tunnel-coupled optical waveguides, having nonlinearity and the second-order dispersion,
the put task is solved by that
as the pulses they use fundamental solitons or fundamental soliton-like pulses with amplitude and shape near to that of fundamental solitons, maximum intensity |a
k0
2
| of which lies in the range from 0.6I
M
to 1.4I
M
, here I
M
is critical intensity, thereto I
M
=(2÷8)K/|&thgr;|, where
a
k0
is input pulse amplitude in soliton normalization, k is number of waveguide,
K is coefficient of tunnel coupling in soliton normalization averaged over the length of tunnel coupling of the waveguides,
&thgr; is arithmetic average nonlinear coefficient of the tunnel-coupled optical waveguides in soliton normalization.
As a rule, I
M
=(5÷7)K/|&thgr;|. In particular cases I
M
=(5.5÷6.5)K/|&thgr;|, and I
M
=(5.9÷6.1)K/|&thgr;|.
As a rule, as the pulses fed into input of waveguide they use fundamental solitons or fundamental soliton-like pulses with amplitude and shape near to that of fundamental solitons, maximum intensity |a
k0
2
| of which is in the range from 0.9I
M
to 1.1I
M
. In special cases said maximum intensity |a
k0
2
| lies in the range from 0.99I
M
to 1.01I
M
. In particular cases the |a
k0
2
| is in the range from 0.995I
M
to 1.005I
M
.
The nearness of pulse amplitude to the amplitude of the fundamental soliton consists in that they use pulses with amplitude 0.5<a
k0
<1.5.
In particular the length of tunnel coupling of the waveguides is more or equal to half of the beat length of transfer of radiation power between the waveguides in linear regime. The beat length of transfer of radiation power between the waveguides in linear regime is meant as the length of the tunnel-coupling, at which the transfer of energy from zero waveguide to the first waveguide takes place, provided that radiation is fed only into the zeroth waveguide and nonlinear factor is equal to zero, i.e. for feeding optical radiation, square of intensity of which is by the order of magnitude less than square of the critical intensity. Very sharp switching takes place with the length of tunnel coupling of the waveguides is more than or equals three lengths of transfer of radiation power between the waveguides in linear regime.
In particular case, all said pulses are fed into the input of only one of said tunnel-coupled optical waveguides.
In particular case, the tunnel-coupled optical waveguides are made as dual-core fiber optic waveguides.
In the second variant of the method, consisting in that they feed pump optical radiation in the form of pulses with maximum intensity |a
k0
2
| into the input of at least one of tunnel-coupled optical waveguides, having cubic nonlinearity and dispersion of the second order,
the put task is solved by that
into the input of another or of the same waveguide they feed radiation with variable intensity and/or maximum intensity and/or phase, thereto maximum intensity |A
5
2
| of this radiation is at least in ten times less than maximum intensity |a
k0
2
|, and as the pulses fed into the input of zero waveguide they use fundamental solitons or fundamental soliton-like pulses with amplitude and shape near to that of fundamental solitons, maximum intensity of which lies in the range from 0.6I
M
to 1.4I
M
, here I
M
is critical intensity, thereto I
M
=(2÷8)K/|&thgr;|, where:
a
k0
is input pulse amplitude in soliton normalization, k is a number of waveguide,
K is coefficient of tunnel coupling of the waveguides in soliton normalization averaged over the length of tunnel coupling,
&thgr; is arithmetic average nonlinear coefficient of two waveguides in soliton normalization.
As a rule, I
M
=(5÷7)K/|&thgr;|. In particular cases I
M
=(5.5÷6.5)K/|&thgr;|, and I
M
=(5.9÷6.1)K/|&thgr;|.
The nearness of the pulse amplitude to th
Chan Jason
Cleomen Ltd.
Collard & Roe P.C.
Sedighian M. R.
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