On Nov 16, 2009, at 1:50 AM, 蒙自明 wrote:
Dear Steven and all:
I am a new user of Meep. What I want to ask is about:
How can I determine the time-average input power and record the
time-average output power at some position?
According to the part "Units and Nonlinearity in Meep" on the
website, the input power is approximately proportional to the square
of current amplitude(J^2). Is that a time-average correlation?
This is exactly true for a linear system. If you multiply J by 2, the
resulting fields multiply by 2, by linearity.
Further, in the nonlinear situation recording time-average power
seems problematic. Has this been fixed?
Why is this problematic?
The key thing in a nonlinear system is to define precisely what you
want to do. The optical bistability results are usually for CW
(constant amplitude) incident fields. If you have a CW field (or a
field whose amplitude is changing very slowly, like a narrowband
gaussian), computing average power is no problem: you just output the
flux every timestep for one period, for example. There are lots of
other ways to do it as well, e.g. for a narrowband Gaussian you can
ask Meep to compute the Fourier-transformed flux at the center
frequency, and work backwards from that to get the Gaussian amplitude
and any other characteristic you want.
Steven
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