Optical Switch and Optical Modulation in Silicon Photonics Devices

• Main Authors: Mao-TengHsu, 徐懋騰
• Other Authors: Ricky-Wenkuei Chuang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/78860435890555739414

博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 101 === The main purpose of our research is that we want to fabricate the high operating speed, high modulation depth and low operating power consumption silicon optical waveguide modulator and optical switch. In the field of our silicon optical waveguide modulators, we start this research from a simply structure device, and then we try to change the device structure in order to improve the device characteristic in following devices. We had designed and fabricated five different silicon optical waveguide modulator structures. In our first device structure, we have successfully demonstrated silicon p+–p––n+ (p–i–n) waveguide modulators fabricated on SOI substrates utilizing the index modulation technique. The efficiency of the modulator depends critically on the core width, available dopant concentrations of both p+ and n+ doped regions, and driving current. By using the spin-on-dopant technique, both p- and n- regions can be conveniently defined without the need of relying on cumbersome implantation procedure. The highest modulation depth achieved was ~4.15% for a 7-mm-long device operating at a forward bias current density of 5 mA/mm. In our second device structure, we have successfully demonstrated a working silicon three-terminal transistor-based waveguide modulator; most of all, the dependencies of the modulation depth on the relative device dimensions and applied biasing signals of different frequencies were studied in full detail. Based on our results, the enhancements in the modulation depth of the devices were clearly observed as their rib waveguide widths or modulation lengths became respectively wider or longer. Furthermore, incorporating a third terminal with different applied VGS’s did help to reduce the rise and fall times of the modulators. Finally, adding trenches close to the edges of the rib inevitably impeded the carriers flow, thereby limiting the efficiency of carrier depletion or accumulation during the actual device operation. In our third device structure, the design of MMI-MZI modulators with dimensions of 6000 × 40 μm was proposed, fabricated and analyzed. The operation of these devices was based on the carrier injection effect, from which an approximate extinction ratio of 28.3 dB was obtained using BPM simulation. As for the device measurements, when the driving power was set at 0.2 W, the first π phase shift was observed. Finally, the optical response measurements indicated that the rise/fall times determined for MMI-MZIs with the three different MLs of 460, 960 and 1960 μm were 56/84, 52/84 and 76/88 ns, respectively. Finally, the 3-dB roll-off frequency ( f3dB ) of greater than 6 MHz was also determined via the frequency response measurement. In our fourth device structure, A new three-termina1 transistor is proposed as a modulation structure for Mach­Zehnder interferometric optical modulators fabricated on SOS (silicon-on-silicon) substrates. The concept of the equivalent circuits was used to better understand the performance of these three­terminal devices. Our experimental results showed that an approximately 0.75 W (or 50mA IS current) of Switching power is needed to initiate the first π phase shift and With this input power applied, an excess of 25 dB extinction ratio is achieved. Furthermore, the optical response measurements obtained earlier also indicated that the rise and fall times measured from these device are in the neighborhood of 8.5 and 7.5μs, respectively. Finally, the 3dB roll-off frequency (f3dB) was also measured with values in the excess of 400kHz for the modulators with the phase Shifters of three different lengths. The insensitivities of the devices temporal and frequency responses toward the phase shifter length are in fact predominantly attributed to the slow thermo-optic effects. In our fifth device structure, the design of the double injection field effect transistor (DIFET) based MZI modulators with three different phase shifter lengths was proposed, fabricated, and analyzed. According to the experimental results obtained, the highest extinction ratio achieved was in the excess of 17 dB. Furthermore, the optical response measurements indicated that the rise/fall times determined for MZIs with the three different modulation lengths of 500, 1000 and 2000 μm were 44/60 ns, 48/64 ns, and 50/54 ns, respectively. Finally, the 3dB roll-off frequency (f3dB) of more than 10.5 MHz was also determined via the frequency response measurement. We have successfully designed and fabricated a cascaded MMI-based 2 × 2 SiO2 /SiON/SiO2 optical waveguide switch utilizing the thermo-optic effect. Our FD-BPM simulation and subsequent device characterization results matched rather well with one another. The minor discrepancy between the simulation and experimentation data appeared to be due to a slightly changing thermo-optic coefficient of SiON film during the actual device operation, whereas a constant TO coefficient of SiON was assumed instead in carrying out the simulation. Our experimental results have demonstrated that a minimal heating power of ~0.89 W is required to start the optical switching with the highest extinction coefficient of higher than 12 dB. Finally, the dynamic response measurement conducted on our devices clearly indicates the rise and fall times thereby obtained are around 314 μs.