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Unidirectional Light Propagation Based On Coupling Between Photonic Crystal Waveguides And Cavity

Posted on:2019-05-20Degree:MasterType:Thesis
Country:ChinaCandidate:Y L DuanFull Text:PDF
GTID:2428330566495960Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
In the optical communication system,it is necessary to provide a light wave unidirectional transmitter in the light path in order to avoid the impact of the reflected light on the normal operation of the active device and to ensure the stability of the optical system.Photonic crystal is a new type of artificial crystal material,which is composed of different dielectric constant materials in the space,with photonic band gap and photonic local characteristics.Because of these two characteristics,and the characteristic of photonic crystals are easy to integrate,photonic crystals have a wide range of applications in many fields,such as optical filters.Because of its lattice constant and the working wavelength in an order of magnitude,photonic crystals become the preferred material for the preparation of integrated optical unidirectional transmission devices.At present,magnetic material or non-linear material is added to the photon crystal to realize unidirectional light propagation,using the magneto-optic effects of magnetic material or non-linear effect of nonlinear effect.But the former requires external magnetic field to achieve magneto-optic effects,and the latter requires high-power incident light to produce non-linear effects,both of them are not very convenient in practical applications.In order to overcome the shortcomings of the above two kinds of photonic crystals,it is found that breaking the symmetry of the spatial structure of the photonic crystal can realize the unidirectional light transmission by matching or mismatching the modes.Three unidirectional light propagation structure are designed and simulated in this paper.The unidirectional light propagation structure with square lattice Si rods is studied first.The lattice constant is 631.7nm and the radius of the rods is 0.2a.The W1 waveguide is along ?X direction,and is formed by removing a half row of rods,and the W2 waveguide is along XM direction,formed by removing part of two columns of rods.They are coupled together by the cavity which is formed by removing two central rods and replaced with one cavity rod of 0.19 a radii.By optimizing the structure,the transmission efficiency at the cavity mode of 1.55 um reaches about 0.969 in one direction while the light transmission is blocked in the opposite direction.The unidirectional light propagation structure with triangular lattice Si rods is also studied.The lattice constant equals 656 nm and the radius of the rods is 0.2a.Waveguides can also be achieved by removing a row of rods in one direction and removing one or two rods every other row in another direction.The cavity is made by removing two rods in the centre.By optimizing the structure,the transmission efficiency at the frequency of 193.5THz reaches about 0.582 in one direction while the light transmission is blocked in the opposite direction.The unidirectional light propagation structure with square lattice Si rods has better unidirectionality.The unidirectional light propagation structure with Si rods has high unidirectionality but the structure cannot stand high pressure and it costs high,so the unidirectional light propagation structure with air holes should be studied in order to overcome these disadvantages.The unidirectional light propagation structure with triangular lattice air holes is studied.The lattice constant is 439.1nm and the radius of the air holes is 0.36 a.By removing a row of air holes in one direction and removing one or two rods every other row in another direction,waveguide W1 and W2 can be achieved.The cavity is made by removing one air hole and shifting the two air holes outwards for a distance of 0.2a,respectively.By optimizing the structure,the transmission efficiency at the frequency of 193.5THz reaches about 0.904 in one direction while the light transmission is blocked in the opposite direction.COMSOL and RSoft were used to simulate and analyze the light propagation.The structure can be widely used in the future all-optical integrated circuits.
Keywords/Search Tags:Photonic crystal, Waveguide, Resonant cavity, Mode matching
PDF Full Text Request
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