Two-dimensional photonic bandgap defect
laser
0.
Painter,
R.
K.
Lee,
A.
Yariv,
and
A.
Scherer
California Institute
of
Technolqgy,
Electrical
Engineering,
MS
196-98,
Pasadena, CA
91125,
USA
E-mail:
opainter@cw. ealtech.
edu
J.
D.
O’Brien,
I.
Kim,
and
P.
D.
Dapkus
University
of
Southern California, Department
of
Eleetrieoi
Engineering,
Los
Angeles, CA
90089
With the maturation of crystal
growth
dong with the nanofabrication of semiconductors, there has been
strong interest in creating optical microcavities for spontaneous emission control. The Vertical Cavity
Surface
Emitting Laser(VCSEL) was the
first
device to
shrink
the optical mode to sizes
on
the order of the
wavelength of light[l]. Subsequently, the microdisk laser was developed which
uses
total internal reflection
to
form high-Q whispering gallery modes[2].
In
this
work
we form
a
new type of optical microcavity
using
twcdimensional photonic crystals embedded in
a
half wavelength thick waveguide. Modes localized
to
a
single defect in the photonic crystal can be theoretically shown
to
have mode volumes
as
small 2(X/2n)3[3].
The flexibility in design of the photonic crystal enables one to tailor the device for vertical emission
or
for
coupling into
an
in-plane waveguide. The added versatility in being able
to
etch the laser cavity may
also
help develop low threshold laser
sources
in material systems in which high index contrast epitaxial
mirrors
do not
exist.
Two dimensional(2D) photonic crystals have been fabricated and characterized
in
a
variety
of
semicon-
ductor materials, however they are not effective, by themselves, in
confining
optical modes in the third
direction.
In
order to localize the light in
all
directions
we
use
a
combination of
a
microdisk type structure
and
a
2D photonic crystal.
A
thin dielectric slab is used for total-internal reflection of the light in the
vertical direction, and
a
hexagonal array of
air
holes
forms
the 2D photonic crystal which provides in-plane
localization. The microcavity structures are fabricated in the
InGaAsP
material system in order to reduce
non-radiative
surface
recombination.
Gain
is
provided by four strained
InGaAsP
quantum
wells
(QW)
separated by quaternary barriers. The emission wavelength of the QWs
are
designed for 1.55pm
at
room
temperature.
The optical cavity itself
is
created by removing
a
single hole in the photonic crystal, thereby forming
an optical mode locslized
to
the defect region[4]. The modes
of
the defect cavity have
been
analyzed
previously[3] and
consist
of
a
pair of doubly degenerate
x
and y dipole modes. The electric field intensity
of the y-dipole mode
is
shown in Figure
1.
The
laser
cavities were optidy pumped with
a
85Onm
diode laser beam focused to approximately
a
4pm
spot covering the defect region. The photoluminescence
was
collected from above using
a
microscope
ob-
jective and then
run
through
a
spectrometer.
Pulsed
lasi
action was observed
at
a
substrate temperature
of 143K.
A
spectrum
of
the laser line
just
above threshold
is
shown in Figure
2
along with
a
plot of power
at
the lasing wavelength
versus
absorbed pump power. The relatively large threshold pump power
can
be
attributed to the
lsck
of thermal heat-sinking in the undercut membranes, which has
so
far
limited lasing
action
to
low temperature, pulsed operation.
CPD2
1-2
Two-Dimensional photonic bandgap
...,
0.
Painter,
et.
al.
0000
00000
Figure
1:
2D slice through the middle
of
the slab showing the electric field ampli-
tude
of
the y-dipole mode.
0.9
’
Punv
-.
P,
CmW
7
4
6
e
7
Punv
Pem.
P,
CmW
(a)
GL
curve
showing the
(b)
Spectrum
of
the laser line just above
power
at
the
laser
wavelength
threehold.
The linewidth
is
approximately
’
vereue
the
absorbed
pump
0.2nm
(resolution limit
of
spectrometer).
Power.
Figure
2:
Sile mode defect laser
at
a
substrate temperature
of
143K
References
[l]
J.
L. Jewell,
J.
P.
Harbison,
A.
Scherer,
Y.
H.
Lee, and L.
T.
Flora, “Vertical-Cavity SurfaceEmitting
Lasers:
Design, Growth, Fabrication, Characterization,” lEEE Journal
of
Quantum Electronics
27,
[2]
A.
F.
J.
Levi,
S.
L. McCall,
S.
J.
Pearton, and
R.
A.
Logan, “Room Temperature Operation
of
Submicrometre
Radius
Disk Laser,” lEEE Electronics Letters
29,1666-1667 (1993).
[3]
0.
Painter,
J.
VuEkovid, and
A.
Scherer, “Defect Modes
of
a
Two-Dimensional Photonic Crystal
in
an
Optically Thin Dielectric Slab,” Journal
of
the Optical Society
of
America
B
16,
275-285 (1999).
[4]
P.
R
Vieneuve,
S.
Fan,
and
J.
D. Joannopoulos, “Microcavitiea
in
photonic crystals: Mode symmetry,
tunabiity, and coupling efficiency,” Physical Review
B
54,7837-7842
(1996).
1332-1346 (1996).