Photonic Crystal Narrow Pass-band Filtersa
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Photonic Crystal Narrow Pass-band Filters Zhengbiao Ouyang, Haishan Liu, Jingzhen Li Solid State Photonics Laboratory, College of Scientific Researches, Shenzhen University, Shenzhen 518060, China ABSTRACT We present a photonic crystal narrow pass-band optical filter, which is made of two pieces of photonic crystals with different photonic band gaps. Our numerical investigations show that this kind of structure is feasible for narrow pass-band optical filtering. The pass-band may be less than 0.1nm in the infrared communication frequency band. In ideal cases, the optical transmission in the pass band is very close to 1. This means a very low insert energy loss. INTRODUCTION High quality narrow pass-band filters are one kind of the key elements for precision optical information acquiring and processing systems and for large-capacity, high-speed optical communication systems. Traditionally, prism dispersion, bulk-grating dispersion, Bragg fiber grating reflection, arrayed waveguide grating diffraction interference, single-mode fiber transmission, multi-layer interference, and optical resonance can lead to narrow pass-band filtering [1,2]. Usually, it is difficult to keep very narrow pass-band, high pass-band transmission, low cost, and small device volume at the same time. We present a photonic crystal narrow pass-band optical filter, which is made of two pieces of 1D photonic crystals [3] with different photonic band gaps. Our numerical investigations show that this kind of structure is feasible for narrow pass-band optical filtering. The pass band may be less than 0.1nm in the infrared communication frequency band. In ideal cases, the optical transmission in the pass band is very close to 1. This means a very low insert energy loss. It is greatly superior to other kind of narrow pass-band optical filters. Unlike multi-layer interference filters, it only needs a small number of layers to obtain the same filtering effect. So the cost can be lowed considerably. Comparing to other kind of narrow pass-band filters, it is small in volume since the size of it is only of the order of a few wavelengths. This kind of photonic crystal narrow band optical filter may find applications in dense wavelength division multiplexing (DWDM) for optical communications and in remote sense and measurement. THEORETICAL MODEL The photonic bandgap narrow pass-band filter investigated in this paper is made of two different 1D photonic crystals, each of which has a different period length (lattice constant), each period of the photonic crystal is made of two high contrast dielectric layers, as shown in figure 1. The numbers of periods of the two crystals are the same. A linear dielectric material with K9.4.1
n1 n0
n0
wave in
wave out
n2 Figure 1. The schematic of photonic bandgap narrow-pass band filter. refractive index n0 surrounds the whole structure. Each of the photonic crystal has a different
photonic bandgap. The whole structure has a combined photonic bandgap in which a narrow pass-band may open when the operating parameters are
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