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Chapter 5:
Electronic and Opto-electronic Properties of High-Speed Phase Shifters
High-speed phase shifters consisting of electro-refraction optical waveguides are the most essential functional blocks of integrated MZ optical modulators used in high-capacity optical networks. This chapter firstly deals with the physics of phase modulation and related matters relevant to high-speed phase shifters. It is stated that free-carrier plasma refraction is most suitable to phase shifters used for quasi-zero-chirp optical modulation in broad spectral ranges without temperature regulation. This chapter focuses on high-speed carrierdepletion phase shifters based on free-carrier plasma refraction. The plasmarefraction phase shifters are classified primarily into two types, lateral and vertical, according to the configuration of the PN junction. The last part of this chapter presents the design and modeling of the carrier-depletion PN-junction phase shifters in two schemes. The first scheme is described as a semi-analytical method comprising the optical simulation of the mode field in a phase-shifter waveguide (described in Chapter 4) and the analytical modeling/ calculation of the plasma refraction using the abrupt PN-junction model and mode-field confinement factor. The semi-analytical model serves as a versatile tool for understanding the operational principles of PN-junction phase shifters and proofing new design concepts of phase shifters without time-consuming, massive computing tasks. The other scheme is a computational method performed for the accurate design and modeling of phase shifters on a siliconphotonics platform after the proof of concept is completed.
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