Increase Phase Velocity by Losing Power ?

AI Thread Summary
The discussion centers on the relationship between phase velocity and power loss in waveguides, as described in Snyder's "Optical Waveguide Theory." It states that while phase velocity can exceed the speed of light in the cladding, this occurs only when there is a loss of power to radiation. The participants express confusion about how losing energy correlates with an increase in phase velocity, emphasizing that the power loss results from achieving a high phase velocity rather than causing it. An analogy is made to driving too fast around a bend, where increased speed leads to energy loss. Understanding this relationship is crucial for comprehending waveguide behavior and energy dynamics.
Jeffrey Yang
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I just read some words from the book Optical Waveguide Theory by Snyder, Allan W., p226. It says that

"However, although it is possible for the phase velocity of a mode to exceed the maximum speed of light in the cladding (of waveguide), c/n_cl, this cannot occur without losing power to radiation"

My question is how to understand this? Why losing power can increase the phase velocity of the wave?
 
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The loss of power is the result of setting up such a high phase velocity wave, it is not the cause of the high velocity.
 
Simon Bridge said:
The loss of power is the result of setting up such a high phase velocity wave, it is not the cause of the high velocity.

Thanks for your reply. I still cannot understand the internal relationship between "losing energy" and "change of phase velocity", could you please explain more about this?
 
If you make the phase velocity too fast, some of the light inevitably escapes.
It's like if you try to drive too fast around a bend you lose some power to skidding... going fast has more energy but you are also losing energy.
 

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