Three - University of Arkansas Physics Department

CLE0'98. Conference on Lasers and Electro-Optics Vo1.6, p 457-8,1998
THURSDAY AFTERNOON / CLE0'98 / 457
versi~tile imprinting of complicatedsoliton optical
circuitry, making bulk optical reconfigurable
waveguide componentspossible. In addition,
we expect these materials to support
two-dimensional spatial solitons, as do ferroelectric
photorefractive materials.
'Also at Univ. Studi dell'Aquila, Rome, Italy
""Univ. Studi dell'Aauila, Rome, Italv
Princeton University, Princeton, New Jersey
$Hebrew University, Jerusalem, Israel
1. M. Segev, A. Agranat, Opt. Lett. 22, 1299
(1997).
0 -' h~wijr3 '404r&%ii 2. A. Agranat, K. Hofmeister, A. Yarlv, Opt.
Im )m W Lett. 17,713 (1992).
Input Face Difhcted Output Soliton oup~t 3. M. Segev, M. Shih,G.C.Valley, J. 0pt.Soc.
Am B 13,706 (1996).
CThVl Fig. I. One-dimensional photographs and profiles of the 9-pm-wide FWHM input beam 4. See, e.g., K. Kos, H. Ming, G. Salamo, M.
(left), diffracted output beam at V = 0 (middle), and the self-trapped (soliton) output (right). The beam Shih, M. Segw, G.C. Valley, Phys. Rev. E
profiles are normalized to their maximum value in all cases. 53, R4330 (1996).
In our experiments, we use a laser beam
split into two orthogonal polarizations. The
transmitted beam, with polarization parallel to
that of the applied field (x direction), is focused
by a cylindrical lens onto the input face
of a KLTN crystal, with its narrow dimension
parallel to the xdirection. The sample is kept at
a constant temperature by a current controlled
Peltier junction. In a separate electro-opticinterferometric
experiment, we measure g, =
0.12 rn2C4, and nb = 2.2. The y-polarized
beam serves as the background beam: it is expanded,
recombined with the soliton beam,
and illuminates the crystal uniformly while
copropagating with the soliton-forming
x-polarized beam. We image the input-output
faces of the crystal on a CCD camera.
Figure 1 shows typical experimental results:
photographs and beam profiles at the input
face of the crystal (left) and at the output face
in the normal diffraction regime (middle; zero
voltage). A one-dimensional soliton forms
with the application of proper voltage (right).
In Fig. 1, the input beam is 9-@m FWHM, and
it diffracts to 29 pm with V = 0. The 9-pmwide
self-trapped (soliton) beam (right) forms
at 4 = 2.9, VIL 3 2 kV13.4 mm at T = 21°C.
To compare our experimental results with
the theory of solitons in photorefractive centrosymmetric
media,l we performed several
experiments. Keeping the input beam fixed, we
vary the intensity ratio and observe at which
applied voltage Vsteady-state solitons are observed.
We plot the existence points against the
predicted soliton existence curve.' Figure 2
shows such a comparison, for two difTerent
temperatures, at which E and $fl attain different
values. Several facts are evident. First, for
values of u, 1 1.5, the normalized width,
which is proportional to the applied voltage V,
has a linear dependence on t+, which is observed
in both theoretical and experimental
results. This dependence is unique to this type
of soliton and stands in contradistinction with
the dependence of Van I+, for screening solitons
that rely on the linear electro-optic effect
and at high intensity
ratios, A[ a: %; see Ref. 3). This confirms that
these solitons indeed rely on the quadratic
electro-optic effect. Another observation is
that, for both temperatures, the existence
curve flattens around u, = 1, which is consis-
(in that case, AS a