  Recent Brain-Machine Interfaces have shifted towards miniature devices that
are constructed from nanoscale components. While these devices can be implanted
into the brain, their functionalities can be limited, and will require
communication and networking to enable cooperation. One form of communication
for neuron stimulation is the use of light. A number of considerations needs to
be taken into account for the propagation and this includes diffraction,
scattering, absorption, as well as attenuation. These properties are not only
affected by the medium, but also by the cell's geometric shape. These factor
affects both the direction and amplitude of the light wave. This paper analyzes
the propagation path loss and geometrical gain, channel impulse and frequency
response for light propagation along the neural tissue. The total attenuation
depends on the propagation medium loss and geometrical gain, and the channel
response is highly dependent on the quantity of cells along the path.
Additionally, the optical properties of the medium also impacts on the time
delay at the receiver and the width the location of the detectors. Based on the
numerical analysis, spherical cells attenuate approximately 20% of the
transmitted power, which is less than the fusiform and pyramidal cells (35% and
65%, respectively).
