Biomedical Engineering Reference
In-Depth Information
6.5 optical Fiber Simulation and comparison
to experimental results
An. optical. iber. has. a. deined. geometry. and. a. well-known. refractive. index.. herefore,. it. is. ideal. for.
.wavefront.aberration.experiments.and.corresponding.simulations..For.the.experiments,.we.chose.a mul-
timode.iber.made.of.fused.silica..he.polymer.iber.jacket.was.carefully.stripped.of.using.a.scalpel.and.
the.remaining.glass.iber.was.mounted.in.immersion.oil.(Zeiss;.
n
0
=
.
.at.23°C)..A.transmitted.light.
image.of.the.iber.is.shown.in.Figure.6.7;.its.outer.diameter.was.measured.to.be.71.μm..he.refractive.
index.of.fused.silica.for.the.used.wavelength.of.632.8.nm.(HeNe.Laser).is.1.49,.thus.the.diference.in.the.
values.of.refractive.index.is.expected.to.be.∆ = −
1 518
n
c
0 02.
..he.wavefront.measurement.and.subsequent.
Zernike-mode.extraction.were.performed.using.Equation.6.7..Again,.details.on.data.acquisition.and.the.
setup.can.be.found.in.the.work.by.Schwertner.et.al..(2004).
he.experimental.results.and.the.corresponding.simulations.are.shown.in.
Figure.6.8
.
.Since.the.con-
denser.lens.was.equipped.with.a.correction.collar,.it.was.feasible.to.compensate.for.the.remaining.static.
fraction. of. the. aberration. due. to. the. refractive. index. mismatch.. his. occured. because. a. dry. lens. was.
used.to.focus.into.an.oil-based.sample..As.a.result.of.this.compensation.adjustment,.the.experimental.
data.contain.the.ield-dependent.part.of.the.aberration.only.
For. the. simulations,. the. refractive. index. diference. of. ∆ = −
=
.
.
of.the.immersion.medium,.the.measured.iber.diameter.of.71.μm,.the.position.of.the.focal.spot.15.μm.
below.the.bottom.of.the.iber,.the.NA.0.5,.and.a.ield.of.view.of.130.μm.were.used.corresponding.to.the.
parameters.of.the.experiment..he.core.of.the.optical.iber.is.visible.in.Figure.6.7..It.was.not.included.
in.the.simulations.since.this.doped.region.has.only.a.small.diference.in.refractive.index.and.the.core.
volume.can.be.neglected.compared.to.the.volume.of.the.whole.iber.
he.experimental.results.for.the.iber.simulation.are.shown.in.the.lower.part.of.
Figure.6.8
.and.agree.well.
with.the.experimental.results.shown.in.the.upper.part.of.the.igure..he.main.features.of.the.measured.
n
c
0 028
.
1 518
,. the. refractive. index.
n
0
FIGuRE 6.7
Transmitted.light.microscope.image.of.the.optical.iber.used.for.the.interferometric.wavefront.mea-
surements..A.diameter-measurement.bar.indicates.the.scale;.this.value.was.used.for.the.simulations.
