Micro resonators shaped as rings or disks coupled to optical waveguides offer the possibility of highly integrated, compact photonic integrated circuits. Building blocks of such circuits, such as ring resonator band stop filters have been realized in several different technologies. But all these approaches have a common drawback. In order to keep the Q factor of the micro resonator high, the radius should be many times the operating wavelength. This makes the resonator multi moded and many closely spaced resonances are supported. As a result the free spectral range of the filter is narrow. Although this could be desirable for some specific applications, in general it is undesirable since it is not possible to filter a specific wavelength over a band of wavelengths. We resolve this difficulty using a hybrid integration technology. For this purpose we use the coupling between a GaAs epilayer removed from its substrate and a polymer channel waveguide as shown in Figure 1. In our previous work we demonstrated the coupling between a GaAs epilayer and a polymer channel waveguide. The structure formed this way is an asymmetric directional coupler, and works as a narrow band filter. In other words coupling in this structure is very wavelength selective. But to see this coupling epilayer does not have to be long and straight. It can be shaped as either a ring or a disk. Shaping the epilayer as a ring or a disk introduces another condition to see the coupling. This is the resonance condition of the mode excited in the ring.
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