In this example, we analyze a commerically-available photonic crystal fiber
design. The goals of the current example are six-fold: we measure the
propagation loss, far field profile, dispersion, efficiency of coupling
(and sensitivity to misalignment) to the photonic crystal fiber mode with a
Gaussian beam and we examine the total loss experienced in a 90 degree bend
with the aim of determining the maximum radius of curvature that can be used
without the loss exceeding a threshold of 1 dB.
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Step 1: Construct the photonic crystal fiber model with easy-to-use CAD editor
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The layout editor shows all of the simulation objects.
Objects can be moved and resized with simple mouse movements.
- orange box shows the extent of the computation volume and the PML boundaries
- take advantage of photonic crystal fiber symmetry to reduce computation time
- use the array function to quickly create the triangular lattice
- make use of a Sellmeier material to account for material dispersion in real, industrial glasses
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Step 2: Calculate the near-field modal profile of the photonic crystal fiber and the propagation loss
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Integrated analysis routines facilitate data analysis and visualization. Choose from
drop-down menus which monitor you wish to analyze, and the field component of interest.
- search over refractive index range to locate fundamental mode of interest
- each mode found is expressed in terms of field profile, propagation loss, and effective index
- the calculated mode for the ideal structure has a loss of 7.1X10-8dB/km
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Step 3: Determine the far-field radiation profile of the photonic crystal fiber
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Built-in far-field projection routines enable you to project mode profiles onto a flat screen or onto a hemispherical surface, and integrate the profile over a specified angular cone or plane.
- large mode area photonic crystal fiber results in a very-low divergence angle beam in the far field
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- intricate spatial detail of the far field mode profile can be observed by plotting the field on a logarithmic scale
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Step 4: Calculate the dispersion of fundamental photonic crystal fiber mode
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Use built-in analysis routines to render complicated analysis simple. Perform a
frequency sweep and choose from a pull-down whether you wish to analyze the propagation
loss, effective index, group index, group delay, group velocity or dispersion as a
function of wavelength or frequency.
- a sweep versus frequency shows the total dispersion is about 20 ps/nm/km
- re-performing the calculation using a constant material index reduces the dispersion to about 1.2 ps/nm/km, illustrating that the majority of the dispersion arises from material dispersion
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Step 5: Determine the coupling efficiency of a Gaussian beam to the fundamental mode
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Extensive overlap analysis routines allow the end user to calculate the overlap integral
and coupling efficiency between the mode of interest and a Gaussian beam, another
waveguide mode, or data imported from another application such as ASAP 2005.
- using a 10 micron beam waist radius Gaussian aligned to the center of the fiber, a 88.1% coupling efficiency results
- the overlap analysis window shows the Gaussian beam has a modal area of 314 micron2 while the large-area photonic crystal fiber has a modal area of 581 micron2
- estimating the alignment sensitivity is as simple as putting in an offset (say, 5 microns in the x direction) which reduces the coupling efficiency to 73.5%
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Step 6: Automate simulation and analysis - measure total bend loss as a function of fiber radius of curvature
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The built-in scripting environment can be used to perform parameter sweeps, customize analysis, or automate both simulation and analysis to optimize device performance.
- ten automated simulations are performed as a function of the
bend radius of curvature
- the total bend loss (i.e. propagation loss + bend loss) is plotted on a
logarthimic scale as a function of radius of curvature
- calculate response shows that the total loss in the 90 degree bend increases very
rapidly when the radius of curvature approaches tens of centimeters
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