MIAMI UNIVERSITY CENTER FOR NANOTECHNOLOGY
Modeling & Fabrication of Ridge Waveguides and their Comparison to Photonic Bandgap Structures
Kathleen Beddow, Meron Tekeste, Senthil Rajagopal, Jan M. Yarrison-Rice, Physics Department, Miami University
Modeling: Waveguides
Introduction
Optoelectronics is a field of technology involving the study and fabrication of microelectronic devices
that interact with light (photons). An optoelectronic device either contains or acts as a transducer, a
device that converts between electrical and optical signals. This technology provides the capacity to
generate, transport, and manipulate data at exceptional rates. Our study focuses upon the
characterization of both waveguides, specifically the Ridge Waveguide, and Photonic Bandgap
Structures with a goal to be able to fabricate the waveguides in house.
Fabrication of Ridge Waveguide
Fig. 4 Waveguide Modeling at
632.8nm wavelength:
a.) Straight Slab Waveguide:
Light Propagation with High
Power Loss
Total Internal Reflection
a.) Snell’s Law
•PBG structure will be fabricated via e-beam lithography and plasma etching.
b.)
1. Wafer Cut
to Size
2. Coat with
Negative
Photoresist
4. Expose to UV
light
5. Develop the
Resist
b.)Straight Ridge Waveguide
(1.3 micron Ridge): Light
Propagation with Minimal
Power Loss
b.
Fig. 1
•Although the HF solution will etch both the Si3N4 and SiO2, selectivity for the Si3N4 can be increased
by increasing the dilution of the HF solution. In doing this however, the etch rate is sacrificed, some of
which may be regained through elevation of temperature.
a.)
•Total Internal Reflection occurs as light travels from a higher to a lower index of refraction when the
refracted angle is equal to 90o or greater, which depends on the angle of incidence.
a.
•The fabrication of the Ridge Waveguide will be done through UV photolithography followed by
immersion of a slab waveguide in a dilute hydrofluoric acid (HF) solution for wet etching.
b.) Total Internal Reflection
Fig. 2
Optical Waveguide
c.)S-Ridge Waveguide, Curve
of Radius 900 micron: Light
Guidance
a.) Slab Waveguide
• Waveguide: Structural component of integrated optical
circuits having the ability to guide high frequency
electromagnetic waves due to different indices of
refraction.
Fig. 6
(Knotter, D. Martin et.al. "Selective Si3N4 etch in Single Wafer Application" Solid
State Phenomena” Vol.103-104 (2005): 103-106.)
b.) Ridge Waveguide
d.) S-Ridge Waveguide,
Curve of Radius 13 micron:
Light Loss
Si3N4 (n=2.02)
• Once fabrication has occurred, the waveguide will be characterized by measuring the input and
output power. This will allow us to determine the amount of light escaping as it travels down the
waveguide.
Radius of
Curvature:
13 micron
SiO2 (n=1.46)
Fig. 7
Setup for Measuring Light
Transmission through
Waveguide
Photonic Bandgap Structures (PBG)
Modeling: PBG
•Photonic Bandgap Structure: Substrate (e.g. Silicon Nitride) etched with periodic array of air pores is used
to create a photonic lattice.
3.5
Summary
2.5
2
R = 75nm
a
b
Silicon Nitride
n=2.02
y (micron)
0.8
Frequency (w a/2p c)
R
b.)
1.5
0.9
0.7
1.5
1
1
0.5
0.6
0.5
0.5
0.4
Fig. 5 Triangular Lattice PBG
Modeling at 632.8nm
wavelength:
0
0
0.3
0.5
1
1.5
2
2.5
x (micron)
3
3.5
4
4.5
5
a.) Triangular Lattice Straight
PBG Structure: Minimal Light
Loss, 92% Transmission
0.2
a
a = 257nm
b.) Triangular Lattice Curved
PBG Structure: Minimal Light
Loss, 94% Transmission
0.1
0
2
G
X
M
G
Fig. 3 a.) Triangular Lattice of PBG b.) Dispersion Graph
Amplitude
1.5
3
2
2.5
y (micron)
1
Air holes
n=1
b.) Etching Process
Experimental Characterization of Waveguide
• Ridge Waveguide: A slab waveguide with a “Ridge”
etched into the upper substrate, changing the effective
indices of refraction on either side, creating conditions for
Total Internal Reflection within the ridge area allowing for
guidance of light.
a.)
6. Add HF to Wet
Etch Wafer
7. Remove Resist
a.) Selectivity and Etch Rate of HF solution at various Dilutions
Radius of
Curvature:
900 micron
3. Add Glass Slide
with Ridge Pattern
in Chromium
1.5
2
1
1.5
0.5
1
•In examining the properties of these waveguides and PBG structures, their ability to guide and
contain light will be examined and compared.
0.5
0.5
1
1.5
2
2.5
x (micron)
3
3.5
4
4.5
•In addition to modeling ridge waveguides, the goal is to be able to fabricate these structures within
our facilities. This will be done through an wet etching process with HF.
1
435nm
0.5
435nm
0
-3
•We are studying the field of optoelectronics in an effort to model both ridge waveguides and
photonic bandgap structures.
-2
-1
0
s (micron)
1
2
3
•Once fabricated our waveguides will be characterized through a series of measurements to show
their effectiveness in containing light.