Revision for More Precise Self-Image Principle
Date Issued
2009
Date
2009
Author(s)
Chang, Ching-Hsiang
Abstract
Nowadays, silicon photonic waveguides have been developed quickly because their devices are suitable for the fabrication of photonic integrated circuits (PICs) and they have small sizes from the property of high index contrast (HIC) between silicon (Si~3.46) and silica (SiO2~1.44). Silicon photonic waveguides also have widely used, such as optical filters, optical switches, optical directional couplers and power splitter.urthermore, a multimode interference (MMI) coupler is an important element in various PICs, like optical switches, resonator filters, arrayed-waveguide grating (de)multiplexers and (polarization) power splitters. MMI couplers have the advantages of their compactness and simplicity and the working function is easier. MMI is from a straight thought, it is called self-image principle. To speak it briefly, self-image principle is to divide an input optical profile into every existing mode, this step is almost like the Fourier transform and then analyzes the interference of each mode.owever, there still are drawbacks in MMI devices with HICs materials and small size structure. Because in order to get the self-image length, which is based on two assumptions:a) The “effective” width W_e, we can approximate as the physical width W_m, i.e., W_e=W_m.b) The angle of incident is very small, i.e., k_yv^2≪k_0^2 n_r^2.owever, in small and HIC MMI devices, the self-image length is not the exact length of N-fold image and it will cause some power losses which reduce the output efficiency. Therefore, we drive the scalar wave equation and use perturbation method to correct the self-image length.n this work, it takes the 1×1 silicon on insulator (SOI) channel waveguide splitter to test and verify our revised method. The three-dimensional beam propagation method (3D-BPM) and TE polarization are utilized to simulate the analysis. From the theory and according to the fabrication of photonic integration circuits (PICs), we chose the photoresist on the top of waveguide to manipulate the propagation constants. And then it will take 1×2 SOI channel waveguide for the case of power splitter.rom our simulation results, it shows that the efficiency is larger with the modified structure than that with the original one. As a result, the method in this paper can be helpful for improving the efficiency. Because the method in this paper is a new concept, we hope this method can improve much more efficiency in MMI devices and find other applications in PICs in the future.
Subjects
photonic integrated circuits(PICs)
high index contrast(HIC)
multimode interference(MMI)
self-image principle
perturbation method
3-D beam propagation method (3-D BPM)
Type
thesis
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