In recent years, several groups have investigated the use of Proximal Spatial Light modulation (PSML) as an alternative fiber optic imaging technique. In PSLM, the light exiting the distal end of the fiber optic endoscope can be focused, without any distal micro-optics or micro-mechanics, on any point within the Field Of View (FOV) via spatial modulation of the light before it is coupled in at the endoscope’s proximal end. In previous work, we reported on the custom design of a Coherent Fiber Bundle made with soft glasses (as opposed to the commercially available optical fibers used by other groups) to be used with PSLM. In this paper we present the results of the numerical characterization of the Coherent Fiber Bundle fabricated according to our design. We investigate the CFB’s modal propagation characteristics as well as its imaging properties (FOV and point spread function). Our numerical characterization also takes into account fabrication induced defects such as variations in core size, core shape (ellipticity) and lattice constant. Realistic values for the defects were obtained via SEM images of the fabricated CFB’s cross section. We find that noise on the wave front of the field exiting the distal end of the CFB causes a much larger deterioration of the point spread function than amplitude noise. And while we find that variations in core shape have the largest impact on the CFB’s propagation characteristics, our results indicate that this negative impact could be negated if the elliptical cores were aligned along a common axis.
In this paper we studied the photosensitivity and scatter properties of several types of photopolymers that are used in the
printing industry. We applied different measurement methodologies to experimentally characterize both the absorption
and scatter properties of the photopolymers. In a first part we measured the absorption spectra of different unexposed
photopolymers in the range between 350 and 1600 nm. From these spectra we calculated the absorbance coefficients.
After this, we repeated this procedure for the cured material which we obtained by illuminating the photopolymers with a
laser source. We investigated the absorption properties for different illumination times in the range between 0 and 2000
ms. From these measurements we could calculate for the different materials the difference in absorbance between the
cured and the non-cured material. Depending on the material the absorbance of the non-cured material was a factor 20 to
60 higher compared to the absorbance of the cured material. These results were used as input for the optical model.
In a next step we measured the BTDF for the different materials and calculated the scatter angle at 1/e2. As a result we
obtained scatter angles between 2° and 6°. In a last step we verified and confirmed these differences in scatter behavior
by measuring the MTF of a real imaging system that included the photopolymer.
With the ever-increasing prevalence of minimally invasive procedures (MIP) in the medical world, the designing of
endoscopes, essential in MIP, becomes more and more challenging. As the continuous and ubiquitous need for
miniaturization is starting to outmatch the possibilities offered by the combination of conventional fibre optics and
micro-optics, novel approaches are necessary in order to ensure the advancement of endoscopy and consequently of MIP.
In conventional fibre bundles the phase-relation between cores is not conserved during the propagation of an electrical
field and as such extra micro-optics at the distal end are necessary in order to be able to focus or scan the exiting light or
achieve a certain field of view (FOV). In this paper we analyze the requirements and constraints for a multi-core optical
fibre (MCF) which conserves the phase relationship between the cores. With such a phase conserving MCF, focusing
and scanning light at the distal end could be done by shaping the wavefront through adaptive optics before coupling the
light into the fibre therefore making extra micro-optics superfluous.
Using numerical and mode solving simulations we investigate the relationship between the size, the period and the
numerical aperture of the cores on the one hand and the focal point and field of view on the other hand. We show that
there is a non-circumventable trade-off between intercore crosstalk and the FOV. In addition, we determine the effects
on the focusing ability and on the FOV of deviations of core size and period, due to fabrication errors. Using this
knowledge, we propose two designs for the phase conserving MCF. The first design allows for focusing and scanning the
exiting light but is sensitive to deviations in core size and separation. The second design is less sensitive to fabrication
errors but can only focus and not sweep.
The propagation of coherent light through a heterogeneous medium is an often-encountered problem in optics. Analytical
solutions, found by solving the appropriate differential equations, usually only exist for simplified and idealized
situations limiting their accuracy and applicability. A widely used approach is the Beam Propagation Method in which
the electric field is determined by solving the wave equation numerically, making the method time-consuming, a
drawback exacerbated by the heterogeneity of the medium. In this work we propose an alternative approach which
combines, in an iterative way, optical ray-tracing simulation in the software ASAP™ with numerical simulations in
Matlab in order to model the change in light distribution in a medium with anisotropic absorption, exposed to partially
coherent light with high irradiance. The medium under study is a photosensitive polymer in which photochemical
reactions cause the local absorption to change as a function of the local light fluence. Under continuous illumination, this
results in time-varying light distributions throughout the irradiance process. In our model the fluence-absorption
interaction is modelled by splitting up each iteration step into two parts. In the first part the optical ray-tracing software
determines the new light distribution in the medium using the absorption from the previous iteration step. In the second
part, using the new light distribution, the new absorption coefficients are calculated and expressed as a set of
polynomials. The evolution of the light distribution and absorption is presented and the change in total transmission is
compared with experiments.
We present an enhanced out-of-plane coupling component for Printed Circuit Board-level optical interconnections.
Rather than using a standard 45° micro-mirror to turn the light path over 90° we introduce a curvature in the
mirror profile and incorporate an extra cylindrical micro-lens for beam collimation. Both modifications enable
an increase in coupling efficiency and are extensively investigated using non-sequential ray tracing simulations in
combination with Matlab optimization algorithms. The resulting design is fabricated using Deep Proton Writing
and experimental characterization of the geometrical properties and measured coupling efficiencies are presented.
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