In this example, we analyze the polarization dependence of an ARROW (anti-resonant
reflecting optical waveguide) structure in terms of propagation loss and far-field
modal profiles, and examine the frequency dependence of the dispersion and the
propagation loss as a function of wavelength from 780 to 980 nm. Finally, using
the built-in scripting environment, we calculate the sensitivity of coupling to the
low-loss TE mode using the fundamental mode of a SMF-28 fiber to lateral shifts of the
fiber.
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Step 1: Construct the ARROW waveguide 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 boundary conditions
- while symmetric or asymmetric boundary conditions can be used to selectively locate a mode with a specific polarization, we wish to compare the propagation loss for the different polarization states and so we choose to simulate the full structure
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Step 2: Sweep over refractive indices to locate the low-loss TE and TM modes
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MODE Solutions allows you to easily find the mode(s) of interest by scanning through a
specific refractive index range.
- to find the modes of interest, scan over refractive indices between the low-index core and the high-index cladding layers
- each mode found is expressed in terms of field profile, propagation loss, and effective index
- note that the TE-like mode has a propagation loss of 0.06X10-2 dB/cm while the TM-like mode has a value of 6.6 dB/cm
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Step 3: Determine the far-field radiation profile of the low-loss TE ARROW mode
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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.
- as expected, the mode diffracts much more strongly in the vertical direction owing to the tigher vertical confinement of mode in the vertical direction
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Step 4: Calculate the dispersion and the propagation loss of low-loss TE ARROW mode as a function of wavelength
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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 that there is a resonance in the total dispersion around 920 nm
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- a wavelength sweep from 780 to 980 nm shows that the propagation loss increases as the wavelength is increased and peaks around 920 nm owing primarily to the increased penetration of the longer wavelength into the lower cladding and lossy silicon substrate, and the reduced reflectivity of the mirror stack away from its 632 nm design wavelength
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Step 5: Automate simulation and analysis - determine the sensitivity of coupling a SMF-28 fiber to the TE-like ARROW 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 MODE Solutions, we first calculate the near-field mode profile of a SMF-28 fiber and calculate the coupling efficiency of this mode with the TE-like ARROW mode
- the plot to the left shows that a peak coupling efficiency of 8% is achieved when the two modes are perfectly aligned and this coupling efficiency falls off to about half that value for a 3 micron misalignment in both of the horizontal and vertical directions
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