Hybrid lasers and modulator on silicon in the near- and mid-infrared region
Date of Issue2017-07-31
School of Electrical and Electronic Engineering
The tremendous developments of the silicon photonics nowadays make it possible to build a series of powerful components within the same chip. The use of the advanced Complimentary-metal-oxide-semiconductor (CMOS) technology opens up many possibilities for new applications including the communications, processing and displays, etc., which is traditionally limited by the electronic interconnect. Many photonic components such as the modulator and detector are studied for many years with much improved performances, while a reliable electrically pumped light source is less developed at this stage. With the wafer bonding technology, it is possible to combine the high performance conventional diode laser with silicon photonics and fulfill the requirements for large scale silicon photonic integration in the near-infrared (NIR) region. In addition, besides the studies in the NIR region, the silicon is inherently transparent to 8.5 um. As a result, it is potential and rewarding to apply the concept of silicon photonics for the mid-infrared (MIR) applications, which is less developed now and requires a further investigation. In this thesis, we build the platform for the evanescent hybrid diode laser working at ~1.55 um. The design, fabrication and characterization of the device are developed to realize the device on the Si-on-insulator (SOI) platform. Several laser configurations are explored in order to be compatible with other components on the same chip. A single-wavelength laser is desired for the communication hence the hybrid III-V/Si laser with laterally coupled Bragg grating on Si waveguide is proposed and demonstrated. The lateral grating can be fabricated by CMOS-compatible inline lithography, which avoids the use of expensive and time-consuming electron beam lithography. The device works at room temperature with the single-side-suppression-ratio (SMSR) of 20 dB and the threshold current density is 1.54 kA/cm2. In the next, the noise properties of the hybrid diode laser are also studied. The investigation of relative intensity noise (RIN) provides a guideline to design the configuration for a low noise value, and the device under optical injection locking shows a reduced phase noise. Both studies are important for the further development of the device. Besides the exploration of the hybrid diode laser on SOI platform, the hybrid QCL structure is investigated in details to use the advanced CMOS technology for the MIR SOI platform. QCL is chosen as the MIR gain material which is already proven as a powerful tool for the spectroscopy, sensing and free-space communications, etc. The entire route to develop the hybrid QCL on SOI is presented, including the fabrication procedures, the Au-Au bonded device with designed wafer, plasma assisted wafer bonding technique and finally the hybrid QCL device. No such device is demonstrated when the work was initialized. The hybrid QCL is expected to be an important component for MIR SOI platforms. Furthermore, due to the increased electro-absorption effect in Si at MIR wavelength, a suitable MIR optical modulator is still missing. In addition, the increased loss in SiO2 also limits the development of a high performance optical modulator. On the other hand, the graphene is already shown with excellent electronic and optical properties, which is potential for ultrafast and broadband optical modulator at MIR region. Here we demonstrate the double-layer-graphene based optical modulator on SOI at 4.7 um, which opens up the possibility of modulating light in MIR Si platform. The modulation efficiencies are 0.031dB/um and 0.046 dB/um for straight and slot waveguides, respectively. Therefore, the integration of hybrid QCL and graphene-based optical modulator may find applications in MIR SOI platform in the near future.
DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics