When propagating through periodically structured media, i. e. photoniccrystals, optical waves will be modulated with the periodicity. As a result,the dispersion of waves will no longer behave as in a free space, and so calledfrequency band structures appear. Under certain conditions, waves may beprohibited from propagation in certain or all directions, corresponding topartial and complete bandgaps respectively. Here we report a new fascinatingphenomenon associated with the partial gaps, that is, deflection of opticalwaves. This phenomenon will render novel applications in manipulating lightflows.
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