Distributed meandering resonator add-drop filters in silicon photonic integrated circuits design, fabrication and analysis

Add-drop filters (ADF) based on meandering loop mirrors (MLMs) and resonators based on MLMs are designed, fabricated, and analyzed using silicon integrated photonics circuit (Si-PIC) technology for operation in the standard near-infrared (near-IR) telecommunication band. Optical waveguides, directional couplers, MLMs, meandering resonators (MRs), antisymmetric meandering resonators (AMRs), and symmetric meandering resonators (SMRs) with symmetric and antisymmetric directional couplers are utilized as a function of the directional coupler length to scan the desired near-IR telecommunication band. A silicon on insulator (SOI) platform is used to realize strip waveguides in transverse electric (TE) mode polarized single mode configuration. The structures' design is based on numerical simulations using a photonics design kit and resulting geometry of the structures were incorporated into the photonics layout for fabrication by e-beam lithography. After the writing of the silicon strip waveguide, and before oxide deposition, the photonic structures were imaged with scanning electron microscopy (SEM) to physically characterize the fabricated devices. Surface gratings are used to couple in and out of these photonic structures with single mode optical fibers. The excitation source for the spectral measurement of the device transmission is a tunable laser operating in the 1500 – 1580 nm wavelength range. The transmission signals in logarithmic (dB) scale are detected in the same experimental region using calibrated near-IR photodetectors. The data is acquired by a control and data acquisition computer. The experimentally measured transmission spectra are analyzed. To make the results more reader friendly, the spectra are color coded: port number 1,2,3 are utilized as outputs and colored as green, blue, and red, respectively. The reflection and transmission intensities are v plotted in logarithmic (dB) scale. The free spectral range (FSR), quality factor (Q-factor), mode split, insertion loss (IL), extinction ratio (ER), and slope rate (SR) are deduced from experimentally measured spectra. To understand the actual spectral response, we first analyzed the spectra. Since the input and outputs of the devices had to be connected to the grating couplers, to couple in and out from the optical fibers, the measurement responses are always modulated by the grating coupler responses. First, we analyzed the wavelength dependence of a DC, one of the basic elements used in our designs. Then we look at the MLM spectral response, which incorporates a directional coupler. After developing the understanding of directional coupler and the MLM, we moved to the analysis of the spectral responses of more complex structures with ADF, MLM, DC- MR, DC-SMR, DC-RMR, SC-MR, and DC-AMR. The general response of a tunable mirror is observed for the MLMs. DC-MR shows the behavior of a Fabry-Pérot resonator with power distributed according to the coupling constants. DC-RMR shows the behavior of RE-MZI. SC-MRs show the typical Fabry-Pérot response. The DC-AMRs show the typical spectra like the coupled resonator induced transparency (CRIT), the analogue of the electromagnetically induced transparency (EIT) spectral responses. Whereas the DC-SMRs show the mode split Fano resonance spectral responses. The figures of merits (FOMs) are given as the best result achieved for each design. The devices themselves have almost no insertion loss and the loss mechanism almost directly comes from the surface grating couplers -in and out- for all structures. SC-MR has an FSR of 1.6 nm with a best Q-factor of 19000, has an extinction ratio of 23 dB and a slope rate of 163 dB/nm. SC-MR has an FSR of 1.1 nm with a best Q-factor of 12000, has an extinction ratio of 30 dB and a slope rate of 307 dB/nm. DC-SMR has an FSR of 2.05 nm with a best Q-factor of 10000, a mode split of 1.1 nm, has an extinction ratio of 27 dB and a slope rate of 450 dB/nm. DC-AMR has an FSR of 1.83 nm with a best Q-factor of 40000, a mode split of 0.1 nm, has an extinction ratio of 33 dB and a slope rate of 872 dB/nm. DC-RMR has an FSR of 3.6 nm with a best Q-factor of 8000, a mode split of 1.1 nm, has an extinction ratio of 29 dB and a slope rate of 183 dB/nm. In all of our designs we introduced a subsection of a waveguide with a specific length, if the vi round-trip optical path length is increased by increasing the length of the subsection, these devices can even be used for dense wavelength division multiplexing (DWDM) applications, which should have a spacing of 0.2 nm at 1550 nm. These results show that proposed devices, ADF-MLM, ADF resonators are good candidates for WDM applications, but still further modifications are required to be used as novel integrated photonic elements for optical communication, computation, and sensing.