Analyzing photonic crystal fiber dispersion, bend loss, and coupling efficiency with MODE Solutions

Step 1: Construct the photonic crystal fiber model with easy-to-use CAD editor

The layout editor shows all of the simulation objects. Objects can be moved and resized with simple mouse movements, and complicated structures can be constructed easily from the simulation object library which contains dozens of pre-defined components, and the material database which contains broadband material dispersion data for many common materials including semiconductors, dielectrics and metals.

Step 2: Calculate the near-field modal profile of the photonic crystal fiber and the propagation loss

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.  Easily:

• search over refractive index range to locate fundamental mode of interest, and
• explore modal data as each mode found is expressed in terms of field profile, propagation loss, and effective index

Step 3: Determine the far-field radiation profile of the photonic crystal fiber

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

• intricate spatial detail of the far field mode profile can be observed by plotting the field on a logarithmic scale

Step 4: Calculate the dispersion of fundamental photonic crystal fiber mode

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

Step 5: Determine the coupling efficiency of a Gaussian beam to the fundamental mode

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.

• using a 10 micron beam waist radius Gaussian aligned to the center of the fiber, a 87% coupling efficiency results
• the overlap analysis window shows the Gaussian beam has a modal area of 311 micron² while the large-area photonic crystal fiber has a modal area of 561 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 74%

Step 6: Automate simulation and analysis - measure total bend loss as a function of fiber radius of curvature

The built-in Parameter Sweep and Optimization framework can be used to perform parameter sweeps and optimize designs.

• a parameter sweep is performed as a function of the bend radius of curvature
• the total fractional bend loss (i.e. propagation loss + bend loss) is plotted on a logarthmic 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 decreases below 10 centimeters