A groove is created in the fiber core by selective chemical etching and filled with another material.
The goal is to efficiently couple light into the material deposited onto the etched
section and then back into the unetched fiber section in order to guide light through the polymer waveguide.
The material is deposited onto the fiber through standard spin coating.
The spinning process coupled with surface forces spreads a uniform
layer of polymer onto the flat surface of the fiber and forces a thicker
layer into the fiber groove. The polymer in the groove acts as a waveguide.
Waveguide dimensions are dependent on many factors, such as polymer viscosity,
spin speed, spin ramp time, and the profile of the removed core.
In this research polymethyl methacrylate (PMMA) is used
as a host polymer with the azo dye DR1 as the guest
chromophore. We chose this mixture because it is
readily available and offers proof of concept. (Click here for information on mixing polymers)
We varied the viscosity by increasing the solvent volume from 60 to 150 mL while
holding the spin rate to ~2000 rpm.
Fiber Cross-Section
PMMA
DR1 azo dye
Methy Ethyl Ketone
Clorobenzene
Loss
8g
0.6g
37.5ml
112.5ml
1.6dB
8g
0.6g
30ml
90ml
36dB
8g
0.6g
15ml
45ml
∞
Top View of Power Profile
Transition region at 10microns.
Thicker polymer on flat allows the light to spread out within the polymer
layer on the flat surface of the fiber.
Low loss requires the polymer on the flat to not support a guided mode
Cross-Sectional View
Top image is the thicker layer
Thicker polymer has a continual spreading of power away from the core region
Lπ length as a function of polymer thickness over the core.
Lπ is related to the device efficiency
Trade-Offs
Thicker layer in core corresponds to thicker polymer on flat surface
Thicker layer in core has higher efficiency
Thickness on flat must be low to couple light back into the fiber
