Three - University of Arkansas Physics Department

Proceedings of SPIE - v 4217, p 235-238,2002
2000 International Conference on High-Density Interconnect and Systems packaging
Creating Optical Interconnects in Strontium Barium Niobate
Matthew Klotz and Gregory J. Salamo
Physics Department. University of Arkansas, Fayetteville, AR 7270 1
(501) 575-2506
salarno@comp.uark.edu
Mordechai Segev
Department of Electrical Engineering and Center for Photonics and Opto-Electronic
Materials (POEM), Princeton University, Princeton, New Jersey 08544
segev@ee.princeton.edu
ABSTRACT
In this paper we report on the use of soliton formation to create permanent waveguides by selectively reorienting
ferroelectric domains within the propagating light beam. For the experiment, the output of an argon-ion laser is
collimated andfocused to a spot size of I2 pm on the front face of a I cm cubic SBN:75 crystal. When a 3 kV/cm
electric field is applied to the crystal along the direction ofthe spontaneous polarization. the beam selffocuses 10 its
input diameter. The externalfield is then removed and a unifarm background beam that fills the crystal is swilched
on. The space charge field due to photoinduced screening charges is larger than the coercive field of' the
ferroelectric domains and causes the domains in the area of the incident beam to reverse their orientation. At
equilibrium, a new space charge field, due to the bound charge at the domain boundaries is locked in place. This
new field increases the index of refraction in only the area ofthe original soliton, so that a waveguide is formed
The waveguides are observed to have the same size as the original soliton, exhibit single mode behavior and last
indeI;nirely.
In oddition to crealing single and multiple waveguides, a coherent collision of two solitons was used 10
create several y-junctions in the crystal. Two mutually coherent, in phase beams were focused on the entrance face
ofthe crystal with a peak to peak separation of33 pm. As the applied electric field wus increased, the two beams
fused into one output beam, forming a yjunction. Following the procedure outlined above, several y-junctions were
fixed in the ctystal.
Key Words: Optical Interconnect, self-induced waveguides
Introduction
Optical spatial solitons [I] in photorefiactive crystals
[2] have shown potential to form graded index
waveguides which-can guide other beams [3,4]. A
soliton forms when a photoinduced index change in
the material exactly compensates for the difiaction of
the beam; i.e. the beam creates its own waveguide. In
photorefiactive materials, a screening soliton is
formed by the screening of an externally applied
electric field through the transport of photoinduced
carries [5]. The picture to the right ( Fig.l) is a top
view of a photorefractive crystal showing a lop
diameter incident laser beam difiacting as it
propagates from the entrance face to the exit face of an
unbiased crystal. Just below the difhcting picture, is a
top view when the crystal is biased and the laser beam
Fig.1. Top view showing an optical wire