Biomedical Engineering Reference
In-Depth Information
Diffraction. resolution. reduction. is. obtained. when. the. input. plane. of. the. probe. is. rel-
atively. far. from. the. object. (far. ield. approximation),. and. then. the. light. distribution. on.
this.plane.resembles.the.light.distribution.over.the.imaging.lens.aperture..In.that.case.the.
diameter. of. the. iber.
D
. sets. the. maximal. spatial. frequency. transmitted. by. the. iber. and.
therefore.also.sets.the.spatial.resolution.obtainable.in.the.image.plane:
λ
V
D
δ
x
=
.
(26.4)
.
The. fact. that. there. are. multiple. cores. makes. this. equivalent. to. sampling. in. the. Fourier.
plane,. which. means. replication. in. the. image. plane. yields. limiting. restriction. over. the.
obtainable.ield.of.view:
=
λ
V
d
∆
x
.
(26.5)
.
where
Δ
x
.is.the.obtainable.ield.of.view.in.the.image.plane
d
.is.the.pitch.between.two.adjacent.cores.in.the.multi-core.probe
V
.can.be.evaluated.by.the.imaging.condition.of.Equation.26.1
The. resolution. in. microns. per. pixels. equals. the. obtainable. ield. of. view. divided. by. the.
number.of.pixels.
The. geometrical. limitation. is. obtained. when. the. distance. between. the. iber. and. the.
object.(
U
1
).is.relatively.small.(near.ield.approximation),.and.the.ield.of.view.is.limited.by.
the.diameter.of.the.iber.(
D
).while.the.pitch.between.two.cores.(
d
).determines.the.spatial.
sampling.resolution:
∆
x MD x Md
=
δ
=
.
(26.6)
.
where.
M
.is.the.demagniication.factor.of.the.proposed.imaging.system.and.it.equals.to
V
U U
M
=
.
(26.7)
+
.
1
2
For.the.fabricated.prototype.with.a.diameter.of.200.μm.(and.for.near.ield.approximation),.
the. obtainable. resolution. in. microns. per. pixels. depends. upon. the. distance. between. the.
two.adjacent.cores.and.equals.3.6.μm.
In.super.resolution.the.idea.is.to.encode.the.spatial.information.that.could.not.be.imaged.
with.the.optical.system.into.some.other.domain..We.want.to.transmit.it.through.the.system.
and.to.decode.it.(Zalevsky.and.Mendlovic.2004)..The.most.common.domain.in.which.to.
do.so.is.the.time.domain.
Therefore,. the. simplest. way. for. obtaining. resolution. improvement. in. the. proposed.
coniguration.is.as.follows:.In.the.case.of.far.ield.arrangement.(when.the.limiting.factor.is.
related.to.diffraction),.the.iber.itself.can.be.shifted.in.time..This.time.scanning.operation.
will. be. equivalent. to. generation. of. a. synthetically. increased. aperture,. similar. to. what.
happens.in.synthetic.aperture.radars.(SAR).(Fransceschetti.and.Lanari.1999).
