        The Ring Resonator
        ------------------

Introduction
-------------

This example shows how a travelling-wave ring-resonator can be modelled in FIMMPROP. This is a Quasi-2D propagation in X/Z. 

* Start FIMMWAVE
* Open the project: RingResonator.prj

The project consists of two FIMMPROP components:
1. A FIMMPROP Layout - "Ringresonator"
2. A FIMMPROP scanner - "scanner"

* From the list of components on the main panel of FIMMWAVE, select Ringresonator.

As you can see, this is an FPLayout device in which the ring resonator is defined by the insertion of 4 shapes, two rectangular waveguides, defining the input and output, and the two circles that make up the ring. To view the properties of these shapes left click on the Edit Layout button on the toolbar.

Before calculating the propagation of the light in this device FIMMWAVE has to discretize this Layout into a sequence of RWG waveguides. To define the ring accurately we need to discretise it into a large number of RWGs so that the shape is retained. This number has been set to 60. (Solver options/Edit Solver parms/Generator options/Max slices)

Since we have a closed loop, points exist in the ring where light will be propagating
in the x-direction. Therefore, a lot of modes (including many evanescent modes) will be
needed to model this problem. In this example, 80 modes has been found to be just
sufficient.

* Select View\Optical Field\XZ Profile from the menu of the "Ringresonator" component
  window. Press Ok when the "View Z field Profile box appears".

After approximately 5 minutes (on an 800MHz PC), a field plot will appear showing light
resonating in the ring with light being dropped in the receiving waveguide.
You can see how much light is being dropped by inspecting the S-Matrix coefficients.

* Select View\S-Matrix from the component's menu.
* Select the L->L radio button.

Here it can be seen that ~69% of the light is being dropped into the fundamental mode
of the receiving waveguide (from mode 1 on the left-hand side to mode 2 also on the
left hand side).

The FIMMPROP Scanner can be set up to perform a wavelength scan of the power dropped. 
Here it has already been set up; the wavelength is parameterised with a variable "wavelength".

* Select "Scanner" from the list of objects on the main panel of FIMMWAVE.
* Select Scan\Start from the general scanner panel
* When the mode coefficients panel appears, remove all the modes from the list box on
  the right-hand side of the panel.
* Now in the box marked "input", ensure that "LHS mode" is selected.
* Next to the "input" box, in the text box entitled "mode (N1-N2), ensure that the
  value is 1.
* Likewise, in the box marked "Output", change the selection to "LHS" (i.e. we want to
  observe modes which get reflected back out of the device).
* Underneath the box marked "Output", in the textbox entitled "mode (N1-N2)", enter 2
  (i.e. we are interested in the power reflected back into the fundamental mode of the
  receiving waveguide.)
* Press the ===> button. This will enter the desired S-Matrix coefficient into the list.
* Press Ok. The scan will now start.

The scan will take a few minutes (depending on processor speed).
When the results appear you should see a resonance curve showing the peak at around
lambda = 1.57 microns.

