We designed and fabricated a silicon nitride (Si3N4) micro ring resonator filter coupled with a straight waveguide grating coupler in the visible wavelength range. The key parameters of the micro ring resonators, including the waveguide crosssection size, bending radius, coupling spacing as well as the linewidth and period of the grating coupler, are optimized to obtain an resonant output in the range of 730~780nm. Then, Si3N4 micro-ring resonators with different parameters are patterned by electron beam lithography (EBL), inductively coupled plasma etching (ICP) and other processes. At last, the filtered light peaks and the free spectral range of the micro ring resonator are characterized, which are found to be tunable by varying the cross section of the waveguide and the radius of the ring. In addition, by replacing SiO2 with Polyvinyl alcohol (PVA) resin as the upper cladding of the device, the flatness of the top surface of the device can be further improved with a simplified process. Our study lays a foundation for the heterogeneous integration of different materials with COMS compatible silicon nitride platform.
The rapid development in the field of optoelectronic integration requires highly efficient coupling between optical fibers and on-chip waveguides. Here, we report an efficient vertical grating coupler which is compatible with COMS process and suitable for silicon nitride photonic integration. The optimized design, fabrication and optical characterizations are presented in details for a silicon nitride waveguide grating coupler. The preliminary results show that the output power of the optimal device structure is 0.25dBm, in good agreement with the simulation result. The fully etched waveguide design needs only one-step etching, which greatly simplifies the fabrication process. Meanwhile, spin coating of Ma2400 series photoresist is innovatively used instead of evaporating SiO2 as the cladding layer of the device, which offers an efficient and economic way to obtain a flat top surface for integration of other devices. Our study provides an alternative method for the heterogeneous integration of functional devices on the COMS compatible silicon nitride platform.
The readily accessible commercial electron beam lithography (EBL) has high-accuracy and mask-free characteristics which enable fast exploration of novel on-chip devices. However, current EBL technique would be challenging to solve the dilemma between high accuracy and large writing field. Here we report an effective recipe to fabricate such multiscale photonic devices. It is realized by improving the standard procedure of stitching small writing fields with alignment markers. The key is the small patterns stitching and exposure alignment process. We divide the large design structure into several small patterns and take pictures of their corresponding alignment markers by the EBL instrument itself with exactly the same parameters used in the subsequent e-beam exposure. As such, the exposure alignment errors caused by calibration procedures are completely eliminated. We precisely write the divided patterns to desired locations by their surrounding markers and finally achieve gapless and precise stitching within the whole photonic circuit. The protocol is demonstrated by a Mach-Zehnder Interferometer (MZI) structure on a 200nm thick Si3N4 chip, in which nano-scale grating coupler have been clearly developed. Compared with traditional EBL technique, the connection accuracy of a waveguide between adjacent writing fields has been significantly improved to be less than 10 nm even without a laser interferometric stage. Moreover, due to the stitching mechanism, the maximum chip size for exposure becomes limitless and could reach up to the entire wafer. Our technique greatly expands the fabrication size of EBL while maintaining its high resolution and opens more opportunities to the development of integrated photonic circuits.
On chip light source is an indispensable component in the silicon based-photonic circuits. The emerging transition metal dichalcogenides, a prototype of van der Waals materials that features direct bandgap electronic structures, high exciton binding energy and wide compatibility with different substrates, offer opportunities for implementing novel light emitting devices. Here, we demonstrate an electrically pumped nanoemitter consisting of an atomically thin p-n junction with WS2 monolayer as the channel material and ionic liquid as the gating dielectric. Strong and stable electroluminescence can be realized by adjusting the voltages of the source and drain electrodes. Meanwhile, the p-n junction can be driven back and forth between source and drain leading to a moving light spot with controlled position. Our results provide a new approach toward highly tunable light emitting devices based on TMDCs which could enable the integration with the photonic chips for a wide range of biomedicine, sensing and lighting applications.
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