All-silicon omnidirectional mirrors based on one-dimensional photonic crystals

Abstract : We report on the fabrication of monolithic omnidirectional mirrors based on one-dimensional photonic crystals. The mirrors are comprised of chirped and unchirped multiple layers of microporous silicon. Porosities have been chosen to achieve an optimal low refractive index nL∼1.5 and a high refractive index nH∼2.55. Unchirped structures, centered in the near-infrared, exhibit an omnidirectional reflection band of 100 nm, in agreement with the calculated photonic band structure. Chirped structures exhibit an enlarged omnidirectional stop band (340 nm). Given the possibility of easily tailoring the optical thickness of porous silicon, this material is shown to be very practical for engineering omnidirectional mirrors.