1×4 Optical Demultiplexer And Notch Filter In Photonic Crystal Based On Self-collimation Effect

Since the photonic crystal was proposed by Yablonvitch and John in 1987,it has attracted extensive attention as a new type of material with unique ability to control light.Photonic crystals have the characteristics of the photonic band gap,polarization,photon localization,and self-collimation,etc.,which can effectively control the transmission of light.The self-collimation effect of photonic crystal allows light to propagate without diffraction in the photonic crystal without external conditions(such as line defect waveguide),which greatly reduces the difficulty of manufacturing photonic crystals Optical devices based on photonic crystals self-collimation effect have the advantages of small size,single material,and simple structure,which can play an important role in future optical communications and photonic integrated circuits.In this paper,the silicon-based photonic crystal with relatively mature technology is used,and the numerical simulation are carried out through the free semi-open source software packages MPB and MEEP developed by the Massachusetts Institute of Technology.Based on the plane-wave expansion(PWE)method,the MPB software package is used to analyze the dispersion of the photonic crystal,calculate the photonic band gap and the self-collimation frequency range of the photonic crystal;Based on the finite-difference time-domain(FDTD)method,MEEP software package simulates the transmission spectrum and magnetic field intensity distribution of photonic crystals.The research content and results of this paper are as follows:1.Photonic crystal 1×4 optical demultiplexer.Based on the photonic crystal self-collimation effect and light interference theory,the 1×4 optical demultiplexer of second band in air-hole type photonic crystal with two different polarization modes was designed and numerically simulated.The 1×4 optical demultiplexer consists of two cascaded Mach-Zehnder interferometers and an independent mirror.The self-collimation frequency range is calculated by MPB software,and the transmission spectrum and magnetic field intensity distribution of 1×4 optical demultiplexer are calculated by MEEP software.The simulation results indicate that by selecting the correct optical path length,the input SC beam with four evenly spaced frequencies can be demultiplexed into four output ports in the 1×4 OD.2.Photonic crystal notch filter.Based on the photonic crystal self-collimation effect and the Fabry Perot interferometer,the notch filter of second band in air-hole type photonic crystal with two different polarization modes was designed and numerically simulated.The photonic crystal notch filter consists of two parallel mirrors and a beam splitter.The notch filter can block the passage of light of a certain frequency without affecting the light of other frequencies.According to the theoretical transmission spectrum formula of the Fabry-Perot interferometer,the theoretical transmission spectrum formula of the notch filter is derived.The self-collimation frequency range is calculated by MPB software,and the transmission spectrum and magnetic field intensity distribution of notch filter are calculated by MEEP software.The simulation results indicate that changing the distance between the mirrors or the radius of the beam splitter can change the transmission spectrum.1×4 optical demultiplexer and notch filter of the second band with two different polarization modes in air hole type silicon-based photonic crystal are proposed for the first time in this paper.The second band photonic crystal device has the advantage of a larger air holes radius compared to the first band and is therefore easier to manufacture;the air hole type silicon-based photonic crystal is more mature than other photonic crystal production processes and is expected to be commercialized.Therefore,the photonic crystal device designed in this paper has lower manufacturing process difficulty and stronger practicability.The photonic crystal device designed in this paper is only a few tens of microns in size,with excellent performance,and is expected to be used in future optical communication systems and integrated optical circuits.