| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 101 === Silicon-on-insulator (SOI) has been widely utilized in high-speed and low-power electronics these few years due to its high refractive index to significantly reduce the component size and processing compatibility with complementary metal oxide semiconductor (CMOS), which advantages the developing of optoelectronic integrated circuits. Mach-Zehnder directional coupler (MZDC) is composed by two directional couplers connected with a short phase delay length. Compared with the multimode interferometer (MMI), MZDC owns the advantage of any splitting ratio and wavelength independence. In this thesis, different ratios from MZDC will be designed and demonstrated in the wavelength range from 1530 nm to 1565 nm.
In the digital communication applications, the Digital Video Broadcasting replaces traditional analog transmission. We digitized the television transmission system with the existing passive optical network system. Then a SOI based 95/5 splitting ratio MZDC was used to replace the fiber coupler for facilitating the integration of optoelectronic integrated circuits. For downstream signal, a 5% MZDC ratio was routed to the user and 95% was reserved for the upstream transmission, which was illustrated using direct modulated injection locking scheme in thesis. We successfully demonstrated the SOI based MZDC practically applied onto optical communication systems.
Differential Phase Shift Keying (DPSK) modulation system requires relatively low laser spectral quality, and then owns more tolerance for chromatic dispersion and polarization mode dispersion besides the extended transmission distance. Different from the amplitude demodulation, DPSK receiving is constructed by the delayed interferometer.
Using the 100-ps optical phase difference, corresponding to a path difference of 8689.6 μm, and two couplers through the MMI and MZDC, a delayed interferometer demodulator was demonstrated for 10 Gb/s DPSK demodulation. Meanwhile, the characteristic optical isolation from the delayed interferometer output is strongly dependent on the optical propagation loss and MZDC ratios. Because of the tunable laser source tunability, 50/50 ratios from MMI and MZDC were utilized to demonstrate the DPSK isolation as 9 dB only between 1550 to 1552 nm wavelengths.
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