Study Of Silicon Photonic Crystal Modulator

Silicon has long been the optimal material for microelectronics. Building photonic devices in silicon bears the advantage of being compatible to complementary metal-oxide-semiconductor fabrication technology, which can lead to monolithic integration of microelectronic and photonic devices on a single chip. Electrically driven optical modulation in silicon photonics typically relies on the free-carrier plasma dispersion effect of silicon materials. The achievable modulation speed, bandwidth and switching voltage are limited. By contrast, electrical-optical (EO) polymers offer very high Pockels coefficient with extremely fast response speed, and large bandwidth and low modulation voltage can be expected. Conventional polymer waveguides generally have large cross-section, and result in weak light confinement. The slottd guide mode has the highest intensity in the low-index polymer material, and this character is desirable for modulation purpose.However, the size of modulators is limited by conventional waveguide structures with millimeter interaction length. With the progress of nanofabrication technologies, there has been a great interest in the controlling the propagation of light in photonic crystals periodically structured at a scale comparable to, or slightly smaller than the wavelength. Photonic crystal waveguide can constrain the light due to the forbidden band. Utilizing the line defect or dot defect in the photonic crystals, we can control the propagation of light in certain directions and localizing light in the cavity.Combining the photonic crystals, slot waveguide, and EO modulation, we propose the new designs of optical modulators. This thesis makes innovative theoretical works mainly in the following four aspects:1. We proposed a new silicon modulator based on the horizontal photonic crystal slotted slab, in which the horizontal slotted slab is used to confine the beam vertically while the photonic crystal line-defect waveguide is employed to constrain the beam horizontally and slow down the group velocity of the light. The modulation is realized by controlling the EO effect of the polymer filled in the slot.2. We propose a new compact silicon modulator based on a slotted photonic crystal nanobeam cavity, and its optical characters are analyzed. The slot lies in both the cavity and the distributed Bragg reflectors region. This results in an ultrasmall modal volume and large quality factor. The modulator is operated in the transverse electrical (TE) like mode. The modulation is realized by controlling the EO effect of the polymer filled in the slot and holes.3. We came up with a new silicon modulator utilizing horizontal slotted photonic crystal nanoridge cavities. The resonance mode is strongly constrained horizontally by the photonic mirrors and vertically by the horizontal slot. The modulator is operated in the transverse magnetic (TM) like mode. If the EO polymer filled in the slot is employed to achieve fast modulation, analysis shows that a modulator with a bandwidth of 100GHz, a low switch voltage and a tiny length can be obtained.4. Considering the one dimensional or two dimensional photonic crystal and horizontal or vertical slot structures, we synthetically analyze the characters of formal-proposed structures. Compared with the horizontal slotted cavity, the vertical slotted cavity shows a larger quality factor. This mostly due to that the presence of vertical slot worsens more heavily the origin performance of resonant cavities. However, the large aspect ratio of horizontal slotted waveguide makes it a challenge in fabrication process.The work of this thesis mostly focuses in the device proposal, design and simulation. Partial demonstration of these devices is still underway. The proposed modulator is very promising for applications in future optoelectronic systems.