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Core Replacement

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

  • 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

See the entire Fabrication Process

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