Page 145 - Maxwell House

POYNTING's THEOREM 125

We postpone these pictures discussion until the next chapter. It is worthwhile to point out that
according to preliminary tests, the data stream along an optical fiber with eight different OAM
beams can reach up to 2.5 Terabits per second (equivalent to 66 DVDs per second). So far, the
latest distance record is 1.1 km. Furthermore, it was experimentally proved the possibility to
distinguish 16 different OAM modes thereby giving a chance to double this capacity. A
preliminary test in free space validated the transfer 32 Gigabits per second over the air in mm
wavelength range. In 2016 laser OAM beams have been sent through a record-breaking 143 km
between two islands in the Canaries encoding and decoding a short message: "Hello World!"
The primary purpose of the test is to check how the different OAM modes survived so much
time traveling in the turbulent atmosphere.

3.1.9 Collecting the Results

Now, we can pull all results together in a compact diagram

(3.22)

Hint: Poynting’s theorem is universal and very powerful tool to control and cross-check
any simulation, analytical or especial numerical. A power conservation check based on
a rigorous Poynting’s theorem analysis allows determining the accuracy of the
numerical convergence. Sometimes this effect is due to the pure or not consistent to the
computer model meshing. Change and use variable meshing or simply increase the
mesh density, repeat the simulation and compare results.

If you detected any troubles checking your results against Poynting’s theorem, the
significant computational errors have been made or some discrepancies hurt your
computer model. Good idea is to check first the unit dimensions of all values and their
consistency. The next step is to check energy and power distribution in all or critical
elements of your model and apply the common sense to getting values and your
engineering intuition. Pay attention to power dissipated and reactive energy stored in
these elements, balance power transmitted out and into different regions of the model.
Keep in mind that visualizing plots of EM fields without energy or power indication
might be misleading. For example, their magnitudes may be surprisingly high while
there is no or very low transmitted or radiated power in the system. The reason might
lurked into resonance behavior of the circuit storing large reactive energy or sharp edge
phenomenon influence.