Polarization based integration scheme (POLIS)

One of the most fundamental problems to overcome in the integration of guided-wave photonic devices is the proper engineering and fabrication of the coupling between active and passive components. In this thesis a novel integration technique based on polarization manipulation, is presented. It is called Polarization based Integration Scheme (POLIS). Experimental results have shown that it is possible to design a layer structure on a substrate of indium phosphide (InP), which can guide light with one polarization, but absorbs light with the opposite polarization. The polarization in this case is a parameter that determines the material properties. Thus instead of changing the material the polarization state of the signal is changed to realize active and passive components. With polarization converters it is possible to obtain the required polarization, transparent or absorbent, in each component of the optical circuit. This creates the possibility to integrate lasers and detectors together with waveguides, switches and demultiplexers on one material. One such device, an integrated detector, is studied and experimentally demonstrated here. Transparency for one polarization and absorption for the other polarization at the same wavelength, is achieved with strain in a quantum well. The strain splits the heavy hole(hh) and the light hole(lh) subbands in the valence band, and thus the two transitions give absorption at different wavelengths. The hh transition is linked with transverse electric (TE) absorption, while the lh transition is primarily connected with transverse magnetic (TM) absorption. If compressive strain is applied to the quantum well the hh transition is at a higher wavelength than the lh transition. Therefore, the splitting of the subbands creates a wavelength region in which the TE-polarization is absorbed, while the TM-polarization is not. The crucial component for POLIS is the polarization converter. A model is developed for the mode propagation in a slanted side polarization converter based on double heterostructures. The model is extended to include absorption and propagation mismatch. Polarization converters on different double heterostructures (with and without quantum wells) have been designed and realized by three different processing techniques: electron beam, high resolution and contact optical lithographies. The realized converters can be described well with the model. From the fitting of the experimental results to the model the TE-absorption can be determined. This is an important parameter in the design of active devices. Several POLIS devices have been successfully realized, with reasonable device performances. This implies low losses for waveguides, quite good responsivity for detectors and wide wavelength separation between TE and TM emission peaks for LEDs. An integrated waveguide detector shows more or less the same results as expected from the individual components. Thus there is no appreciable performance penalty for the components due to the integration technology.