Study On Symmetical Photonic Crystal Filter With Air Defect

Photonic crystal has an important extremely application in microwave,optical communication,solar cell fields for which can selectively transmit the light waves and have the characteristics of small volume, low optical loss and easy integration; Photonic crystal filter can filter out the special wavelength of light wave, which has a very good application prospect in the field of optical communication mainly to detect the channel wavelength in DWDM system. In one-dimensional photonic crystal introducing liquid crystal, LiNb O3, BGO medium defect layer, then through the magneto- optical, electro-optic, thermo-optic or acoustic-optic effect changing the material refractive index of medium layer, the wavelength of defect mode can be tuning, which can realize tunable filter; But these tunable filter methods by introducing defect have a lot of limitations, such as poor tuning controllability, low transmittance, instable FWHM, high optical loss; Compared with this photonic crystal contained defect layer, using one dimensional binary photonic crystal with mirror symmetry canrealize filter also and can reduce the absorption of light for without defect layer which composed by third kind dielectric material. If the air defect layer is introduced, it will realize tunable filter by changing the thickness of air layer using ultra-micro mechanical technology. Based on this, this paper puts forward two kinds structures to realize the single channel or dual channel filter in optical communication band using the air defect layer and one-dimensional mirror symmetrical photonic crystal. The main research contents are summarized as follows:(1) Based on propagation of optical wave in photonic crystal, we deduce the optical transmission matrix of multilayer dielectric media and further derive the optical transmission matrix of one-dimensional asymmetric and symmetric photonic crystal; At last, we derive the reflectance and transmittance expression when the optical wave propagate respectively in three kinds of photonic crystals.(2) We design a kind of Mirror symmetrical photonic crystal filter structure with air defect, the expression is(H/L)N/D/(L/H)N. Adjust the structure parameters, then we simulate the photonic band gap characteristics. The range of band gap is 1220nm- 2100 nm, and appear a transmission peak at 1547.33 nm,which show that this structure can be used for single channel filtering in optical communication C-band. The effects of air layer thickness, incident angle,temperature and refractive index on the filter performance are studied separately.The results show that by changing the thickness of air layer can realize Linearly tunable filter with stable FWHM and high transmittance, and by changing theangle of incidence can realize nonlinear tunable filter of optic communication O,E, S, C band; Through the thickness of medium layer making up each other can realize the same filter characteristics.(3) We propose a kind of composite Mirror symmetrical photonic crystal filter structure with air defect, the expression is(H/L)N/D/(A/D/A)M/D/(L/H)N,select the structure parameters, then simulate and appear a transmission peak respectively at 1528.98 nm, 1564.74 nm. This structure can be used for dualchannel filtering in optical communication S, C band. The results showed as follows: tuning the thickness can achieve dual channel linearly tunablt filter;with the incident angle increases, the locations of the two transmission peaks have blue shift, and the changing of incident angle will lead to separation of two modes wave(TE/TM), show that angle tunable filter is suitable for double channel filtering of polarized light. And by changing the refractive index,thickness of dielectric layer, temperature can realize tunable filter also. when the periods number M change, the number of channels change, the number of channels is M+1, so this structure can realize the multi-channel filter in the near infrared band.