Integration Properties Of Tir Optical Switch Array And Mmi Coupler

The integration of photonic device becomes more and more important due to the fast developing optical network. In this dissertation, we study the integration properties of two important photonic devices: optical switch array (the key component of optical network) and multirnode interference (MMI) coupler (it can realize many functions in optical signal processing). One purpose of this study is to enhance the integration ability of optical switch array, which can be realized by increasing the extinction ratio of the switch unit and optimize the array structure. The other purpose is to improve the compatibility between MMI coupler and most waveguide devices. This can be realized by adopting new interference structure.Current-injection total-internal-reflection (TIR) is applied to the switch due to its non-polarization dependent and high-speed property. Considering bandfilling, bandgap shrinkage and free-carrier absorption, the carrier-induced index change of GaAs is analyzed between 0.8|im~1.6jim. The asymmetrical Y-branch is optimized and the extinction ratio is increased more than lOdB. We bring forward perpendicular optical switch, which has strong integration potential. The distance between adjacent waveguide can be as small as 250(j.m. The extinction ratio of 25dB and crosstalk of 45dB is obtained in such a 4x4 array.Conventional MMI coupler is normally fabricated on deeply etched, high-index-contrast waveguide structure, while most other waveguide devices are weak-confined or gradual-bulge-edge structures. So the study on MMI coupler is the combination of MMI and weak-confined waveguide or MMI coupler and gradual-bulge-edge waveguide. The propagation-constant-error judgement method is brought out for the first time to analyze those modes in the MMI region. Results show that self-imaging can be improved by the introducing of weak-confined or gradual-bulge-edge waveguide. This means with the enhanced compatibility of MMI coupler, the performance can be improved at the same time:1. Further study shows that weak-confined MMI coupler reach the best performance under certain index contrast. An equation to solve this optimal index contrast is gained by decrease the propagation constant errors of high-order modes in the MMI region, which has the best resultcompared to other reported researches. For an optimized weak-confined 1x32 MMI splitter, the loss and uniformity are 0.026dB and O.OOSdB, respectively. As for the case of strong-confined one, the values are 1.443dB and 2.049dB, respectively.2. During the study on gradual-bulge-edge waveguide structure, we bring forward two new structures that can be applied to MMI coupler: grade-index-edge based on exponential function and waveguide with trapeziform cross-section. The first structure can nearly realize ideal self-imaging under appropriate condition, while the second structure has the advantage of easy fabrication. In the case of a 2-wavelength WDM, there is the contrast of about 50dB according to ideal self-imaging. The value of 50.7dB and 47dB are gained in the first and second structure, respectively, While in the case of conventional strong-confined structure, the contrast is only about 30dB.