Ultra-compact on-chip one dimensional nanobeam cavity for simultaneous temperature sensor and bandstop filter at 2 μm waveband

Abstract

Optical sensors with compact size are key components in on-chip highly dense integrated devices. An ultra-compact one dimensional photonic crystal nanobeam cavity (1D-PhC-NBC) structure with the functionalities of both sensing and filtering is proposed. To confine the light into center of cavity to obtain a fundamental resonant mode and filter out the light belonging to other frequency band at the same time, the structure consists of one 1D-PhC-NBC sensor (1D-PhC-NBCS) and one 1D-PhC-NBC filter (1D-PhC-NBCF). In the region of 1D-PhC-NBCS, the waveguide width is tapered from the center to the end and the size of air holes is kept the same. In the region of 1D-PhC-NBCF, the waveguide width and the size of air holes are the same. The 1D-PhC-NBCF is serially located on the behind of 1D-PhC-NBCS to obtain the desired resonant peak. With three dimensional finite-difference time-domain (3D-FDTD) simulation, the results show that an optimal resonant frequency of air mode and mirror strength are achieved when the semi-major and semi-minor axes are equal to 0.38 μm and 0.14 μm, and the width of waveguide is tapered from 1.07 μm to 0.83 μm, respectively. The fundamental resonant peak of 1940.85 nm is obtained in 1D-PhC-NBCF when the semi-major axis of 0.27 μm and semi-minor axes of 0.08 μm are chosen. The sensitivity of 198.09 nm/RIU is achieved with the increase of temperature. The size is about a half of the previous reported nanobeam structure due to the that filter at one side of the structure. Particularly, the minimum size of the proposed structure is only 12.6 μm × 1.1 μm. Therefore, it is a promising method to construct highly integrated sensor arrays for on-chip applications.