Three - University of Arkansas Physics Department

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CLE0'98. Conference on Lasers and Electro-Optics, Vo1.6, p 173,1998
TUESDAY AFfERNOON / CLE0'98 / 173
The Isotropic nature of photorefractlve
screening solltons and the Interactlomi
between them
Honpng Meng, Gregory J. Salamo,
Mordechai Segev,' Physics Department,
University of Arkansas Fayetteville, Arkansas
72701
Studies on the incoherent' and coherent2-'
collisions between photorefractive screening
solitons in both one and two transverse dimensions
have been reported recently. These studies
report on the fusing and repulsion of coherent
solitons, as well as on the birth of
additional solitons. Interestingly, these studies
have been able to ignore the role of the twodimensional
anisotropic nature of the photorefractive
material. In this paper we present
experimental evidence demonstrating that the
photorefractive-index perturbation responsible
for the formation of individual photorefractive
screening solitons and the behavior of
coherent coUisions between them is isotropic,
even though the photorefractive medium is
inherently anisotropic. The evidence is based
on three independent observations.
CTuM60 Fig. 1. (a10 Shows the individual
beam profiles at the entrance face in the horizontallvedcal
plane to be 11wm; (blg) Shows the
individual diffracted beam profiles at the exit face
in the horizontaUvertical plane to be 50 bm: (clh)
Shows theindividual trapped beam profilesat the
exit face in the horizontallvertical plane to be 1 I
bm; (dli) Shows the resulting 1 I-wrn beam from
the collision between both beams colliding in the
horizontal/vertical plane when the phase between
them is 0'; and (elj) Shows the two 1 l-pm beams
after collision in the horizontallvertical plane
when the phase between them is 180". The soliton
to background intensity ratio was 10 in each case.
CTuM60 Pig. 2. Plot of the increment in the
scaled separation due to repulsion (180" phase
difference) between the two solitons measured at
the exit face of the crystal as a function of the
scaled initial separation at the entrance face. The
collision is observed to be identical in the vertical
and horizontal planes.
Fist, a circular beam of diameter 1 I pm at
the input face of an SBN:60 crystal [any one of
the four individual profiles in Figs. ](a) and
l(f)], which would normally diffract to a circular
beam of approximately 50 pm [Figs. I (b)
and l(g)] in diameter, was trapped to form a
circularly symmetric beam of 11-pm diameter
at the output face [Figs. l(c) and l(h)].
Second, Fig. 1 also shows theoutput profiles
of two initially parallel solitons with 0' relative
phase propagating simultaneously through the
crystal. The diameter of each beam is 1 I p
and the separation between the two beams at
the input face is 18 pm. Two configurations
were studied: one with the two beams colliding
in horizontal plane or plane containing the
c axis [Fig, l(d)j, and another with the two
beams coliding in the vertical plane or plane
perpendicular to the caxis [Fig. 1 (i)]. The same
external field was applied along the cdirection
in both cases. Independent ofwhether the collision
is in the horizontal or vertical planes, the
two incident solitons fuse together into a single
circularly symmetric soliton of the same 1 1 -
pm diameter.
Third, when the collision occurs with v
relative phase between the two circular incident
beams, they are trapped and repel each
other so that their separation increases at the
exit face. In addition to the fact that each
trapped beam has an identical circularly syrnmetric
1 1-pm profile at the exit face, the repulsive
force or the separation between the two
solitons at the exit face is also identical, independent
of whether the collision occurs in
horizontal [Fig, l(e)] or vertical planes [Fig.
l(j)]. Figure 2 shows aplot ofthe change in the
scaled separation (repulsion) between the two
solitons at the output face as a function of the
scaled separation (repulsion) between the two
solitons at the output face as a function of the
scaled initial separation, for collisions in both
the horizontal and vertical planes. The data
demonstrates that independent of whether the
collision is in the horizontal or vertical plane,
there is no difference in the repulsive force.
*Department of Elecaical Engineering, Princeton
University, Princeton, New Jersey 08544
1. M. Shih and M. Segev, Opt. Lett. 21,1538
(1996).
2. G.S. Garcia-Quirino, M.D. Iturbe-
Castillo, V.A. Vysloukh, J.J. Sanchez-
Mondragon, S.I. Stepanov, G. Luto-
Martines G.E. Torres-Cisneros. Opt. Lett.
22,154 (1997).
3. W. Krolikowski and S.A. Holmstsrom,
Opt. Lett. 22,369 (1997).
4. H. Meng, G. Salamo, M. Shih, M. Segev,
Opt. Lett. 22,448 (1997).
Contmllable Y-Junctions in a
photorefractlve BTO crystal by computer
generated holograms based on dark
spatlal solitons
C.M. G6mez-Sarabia, J.A. Andrade-Lucio,
M.D. Iturbe-Castillo, S. Perez-Mbrquez,'
G.E. Torres-Cisneros,' Institute Nacional de
Astrofisica, Optica y Electrdnica Apartado
Postal 51/216, 72000 Puebla, Pue. Mexico;
E-maik diturbe@naoep,mx
The use of dark spatial solitons to generate
optical Y-junctions1,' has been proved experimentally.
This optical device is based on the
ability of dark solitoil to guide a second beam
by the refractive-index changes photoinduced
in a nonlinear medium.'
A dark soliton is a zone of zero irradiance
distribution immersed on a uniform bright
background. Experimentally, such a perturbation
is carried out using amplitude or phase
masks. An amplitude obstacle, for example a
wire, positioned in front of the bcam produces
an even number of dark spatial solitons, i.e.,
their widths, highly depends on the characteristics
of the initial beam profile.
Theoretically, given an initial beam profile,
it is possible to know which will be the soliton
solutions to the nonlinear Schroedinger equation
(NLSE).' Experimentally, only the formation
of identical solitons has been reported.
In this paper we report the generation of an
asymmetric Y-junction by an hologram ob-
Chhf61 Fig, 1. Images and profiles for the
pump beam: (a) input, (b) output, and (c) output
with 1.8 kV applied.