Microwave photonic filters (MPFs) are key components for radio frequency (RF) signal processing. Most reported MPFs with high performance are implemented by using optical fiber and discrete optoelectronic devices. In order to reduce the volume of the filter, a number of microring resonator (MRR) based MPFs in silicon have been reported recently. Nevertheless, the full width at half maximum (FWHM) bandwidth of most of these MPFs are wider than 2 GHz and the peak rejection ratios are generally lower than 30 dB because of the trade-off between the bandwidth and the rejection of the adopted MRR.
In order to improve the performance of the filter, several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang and Yuan Yu, proposed and experimentally demonstrated a silicon-on-insulator based widely tunable MPF, which is implemented by using an under-coupled MRR assisted by two cascaded tunable Mach-Zehnder interferometers (MZIs), as the Fig1. In the experiment, the MPF achieves an ultrahigh peak rejection of exceeding 60 dB, a full width at half maximum bandwidth of 780 MHz and a frequency tuning range of 0-40 GHz even when the propagation loss of the MRR is 1.65 dB/cm, as the Fig2. To the best of our knowledge, this MPF demonstrates ultrahigh peak rejection and narrow bandwidth simultaneously in SOI for the first time with MRR of such propagation loss and avoids using external electrical devices to improve the rejection. The proposed scheme might be valuable towards the large scale silicon-based photonic integration.
Fig.2. (a) MPF with ultrahigh peak rejection. (b) The tenability of the filter.
On 19 March 2018, this work was published on Optics Letters with the title of Silicon-on-insulator-based microwave photonic filter with narrowband and ultrahigh peak rejection. The work is supported by National Natural Science Foundation of China (61501194), Natural Science Fund for Distinguished Young Scholars (61125501), Hubei Provincial Natural Science Foundation of China (2015CFB231, 2014CFA004), the Fundamental Research Funds for the Central Universities (HUST: 2016YXMS025), and Director Fund of WNLO. Full text can be viewed by
https://doi.org/10.1364/OL.43.001359
