Nano-scale Si doped Si-rich SiOx/ Si-rich SiNx/Si-rich SiCx ring waveguide based all-optical modulator using linear free-carrier absorption and nonlinear Kerr effect
Date Issued
2014
Date
2014
Author(s)
Su, Sheng-Pin
Abstract
In this thesis, we simulate, fabricate and analyze the Si-QD doped Si-rich SiOx/ Si-rich SiCx/ Si-rich SiNx micro-ring waveguide resonator based all-optical modulator using linear free-carrier absorption and nonlinear Kerr effect.
In the chapter 2, by integrating with a ring-resonator waveguide, the Si quantum dot doped SiOx strip-loaded waveguide based free-carrier absorption modulator with enhanced FCA loss modulation is demonstrated by different pumping wavelengths. The micro-ring waveguide resonator induced a dark-comb like throughput transfer function in wavelength domain, in which function with a Q-factor of 6×103 can be blue-shifted by varying the photo-excited electron-hole plasma density. When transmitting optical data stream at the central wavelength of any notch in the dark-comb throughput function, the output data-stream can be inverted by pumping the micro-ring waveguide resonator to up-shift the notch away from its original wavelength. As a result, this maximize the extinction ratio of output data stream. The largest FCA loss and highest free-carrier density can be enhanced up to 3.44 cm-1 and 9.29×1016 cm-3, respectively, at excitation intensity as high as 6.7 W/cm2. By adding the micro-ring waveguide resonator, the modulation depth can be further enhanced from 52.5% to 63.5% by up-shifting the transfer function of the micro-ring waveguide resonator with the photo-excited e-h plasma. The maximal wavelength of the transmittance notch shift can be up to 0.033 nm under the same pumping intensity at wavelength of 1563.42 nm. The excited free-carriers inside the micro-ring waveguide resonator is obtained to be ~5.25×1015 cm-3. The pumping wavelength dependent transmission notch linewidth is broadened from 0.26 nm to 0.3 nm when the ring waveguide resonator is pumped by 325-nm HeCd laser.
Due to the speed of FCA based modulator is limited by the carrier lifetime which the modulation speed of SiOx:Si-QD is ~ 1 μs. As a result, the ultrafast nonlinear optical Kerr effect is employed in the following work.
In the chapter 3, the ultrafast optical Kerr switch with a Si-rich SiC micro-ring resonator is demonstrated. In addition, the nonlinear refractive index of Si-rich SiC at telecommunication wavelengths is firstly estimated by the resonance red-shift, which is still unknown in the literature. With the 12 Gbit/s NRZ-OOK optical pump data-stream, the Si-rich SiC micro-ring resonator shows a great applicability in the real optical communication system. From the maximal inverted probe signal, the red-shift of resonance dip is 0.07 nm corresponding to refractive index change of 1.2×10-4. By the red-shift of resonance dip, the nonlinear refractive index of Si-rich SiC is estimated to be n2=3.14×10-13 cm2/W, which is several orders magnitude larger than that in SiC. From the analyses of XPS and the RSS, the excessive Si concentration of 37.2% which exist in the form of Si-QDs is observed. The existence of Si-QDs buried in the Si-rich SiC matrix can effectively result in a huge enhancement on the nonlinear refractive index, which can be explained by the quantum confinement effect. From the BPM analysis under single-mode condition, the waveguide width and height of 600 nm and 300 nm is determined. The fabricated micro-ring waveguide resonator is obtain with Q=22800 and the transmittance drop of nearly 60% at a wavelength of 1551.08 nm.
In the chapter 4, the 12 Gbit/s optical Kerr switch has been demonstrated with a Si-rich SiN micro-ring resonator in the first time. The Si-rich SiN with excessive Si of 23.4% is grown by PECVD process with fluence ratio of [SiH4]/[NH3] equals 0.9. The fabricated mirco-ring resonator of Q=11000 is observed, which provides a field enhancement inside the micro ring resonator. By introducing the 12 Gbit/s NRZ-OOK data stream as the optical pump format, the ultra-fast response up to 83 ps of the Si-rich SiN micro-ring resonator shows a great applicability in the real-world optical communication system. The SNR is degraded from 9.66 dB to 5.32 dB after the wavelength conversion. According to the ultrafast response of nonlinear Kerr effect, the nonlinear refractive index of Si3N4:Si-QD at near-infrared wavelengths for optical telecommunications is instantly modified by the input optical data stream to cause the red-shift on the resonance of the micro-ring, thus providing a high-speed optical switch up to 12 Gbit/s via the cross-wavelength amplitude modulation effect. By analyzing the resonance dip red-shift of 0.13 nm corresponding toδn=2.2×10-4, the nonlinear refractive index of the Si-rich SiN is estimated as n2=δn/Ir=2.17×10-13 cm2/W, which is one order and two orders of magnitude larger than that in Si and SiN, respectively.
Subjects
矽量子點
環形共振腔
光波導
自由載子吸收
克爾效應
全光調變器
非歸零開關鍵控
Type
thesis
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