We propose a simple route to obtain an ultrawide free spectral range (FSR) using a composite racetrack microring resonator (RMRR) with Fabry–Perot cavities. The presence of two Fabry–Perot cavities in the straight arm of the RMRR suppresses other peaks while yielding a single resonance dip with a high extinction ratio. A comprehensive, detailed mathematical description and finite difference time domain (FDTD) simulations investigate the proposed device performances. The modified RMRR yields an FSR value greater than 150 nm while retaining the unmodified ring resonator’s $Q$-factor. Other than its application in communications, the device also will be highly useful for sensing. FDTD simulations show a sensitivity of 185 nm/RIU, which is 2.6 times larger than the unmodified RMRR. The proposed device also enjoys compactness and a wide tunability range and has less fabrication complexity. The proposed sensor could be a strong candidate in optical communications, optical switching, and many other applications.

中文翻译：

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具有集成式Fabry-Perot腔的超宽FSR微环赛道谐振器，用于折射率传感

我们提出了一种简单的方法，即使用具有Fabry-Perot腔的复合跑道微环谐振器（RMRR）来获得超宽自由光谱范围（FSR）。RMRR直臂中存在两个Fabry-Perot腔会抑制其他峰，同时产生具有高消光比的单个共振谷。全面，详细的数学描述和时域有限差分（FDTD）仿真研究了拟议的器件性能。修改后的RMRR产生的FSR值大于150 nm，同时保留了未修改的环形谐振器的$ Q $-因素。除了在通信中的应用外，该设备还将对传感非常有用。FDTD仿真显示灵敏度为185 nm / RIU，比未修改的RMRR大2.6倍。所提出的装置还具有紧凑性和宽的可调范围，并且具有较少的制造复杂性。拟议中的传感器可能是光通信，光交换和许多其他应用中的强大候选者。