InP Based Photonic Integrated Circuits And Their Fabrication Processes

Since 1970s, the progress of epitaxial technology for Indium Phosphide (InP) based material system has enabled the long-life, high reliability semiconductor active devices to mature, which has laid the foundation for a leap-forward development of optical communication. The energy band structure of indium phosphide and its quaternary compounds can be tailored by varying its composition, which provides a great deal of flexibility for the realization of a variety of photonic devices. Hence, InP based integrated photonic devices has been investigated very widely.The subject of this thesis is to use InP and its quaternary compounds to fabricate low-cost, high reliability integrated photonic devices for dense wavelength division multiplexing (DWDM), tunable lasers and fiber-to-the-home (FTTH) applications. The theory and fabrication processes of InP based integrated photonics devices are developed in order to lay a foundation for the future development of other related photonic devices.With the growing demand of the optical network bandwidth, DWDM systems have been deployed very widely. DWDM can simultaneously multiplex and demultiplexe dozens of wavelengths, hence, the planar waveguide demultiplexer has been widely used in DWDM systems. While arrayed waveguide grating is preferable for silica based devices, echelle grating demultiplexer is more suitable for InP based devices, because of its small size and better scalability to higher-channel count. The state-of-art InP based demultiplexing device reported in the literature is a 44-channel optical channel monitor based on the integration of an echelle grating demultiplexer and a waveguide detector array. While the device achieves a high degree of integration, it has drawbacks, particularly the large insertion loss due to the passband-flatening method it uses. This thesis presents a novel passband-flattened Optical Channel Monitor (OCM) device based on integration of an echelle grating demultiplexer and slab waveguide detectors. It provides a wide channel passband without suffering from any loss penalty, and the device is more compact compared to the channel waveguide based detector approach. Numerical simulation demonstrated the high-performance of the proposed device.Another type of photonic integrated devices that the thesis focuses on is the design and development of novel monolithicly integrated tunable lasers. The thesis presents a single-electrode tuned mode-hop-free laser based on ring coupled laser structure. We also proposed a novel ring coupled laser which use a half-wave coupler. Compared to dual-coupler ring coupled lasers, the merit of single-coupler ring coupled lasers is free spectrum range of the device can be enlarged due to the incorporation of a strong Vernier effect in this structute, which could greatly relax the restrictions on the ring radius. We believe the proposed laser will take the single ring filted tunable lasers into practice.The thesis also proposed a novel monolithic di/triplexer design. The diplexer uses a ring cavity laser as the upstream transmitter and a 2x2 coupler of the ring also serves as a demultiplexer for up and down stream signals, simultanously. A bi-level etched structure is employed here as the coupler. The merit of the bi-level coupler is its compact footprint and low requirement for photolithography resolution. Moreover, the thesis also introduces an echelle grating to demulplex the two down stream signals so that the proposed diplexer can be extended to a triplexer.Finally, we systematiclly investigated the fabrication processes for photonic integrated devices, including lithography, dry and wet etching, planarization, metal sputtering, lift-off, chemical mechanical polishing and so on. A robust dry etching recipe which can achieve a vertical and smooth etched facet is obtained. Besides, the thesis also presents a method to planarize the ridge waveguide of lasers. It uses a thin spin-on polymer film to obtain the planarization which is robust to the non-uniformity of the film thickness and the speed of etch back. With the developed processes, we succesfully fabricated and experimentally demonstrated V-coupled cavity lasers.