The simple and effective optical filter is the significantly scientific and technical interest in optical signal processing and communication. Especially, the development of microsystem integration is limited in traditional optical filters, due to the complicated structure, small choice, large cost, etc. In this letter, we report an ultra-narrowband filter based on a metal-cladding resonant waveguide. Therein, the ultra-narrowband resonant mode is achieved based on the resonance screening of incident light and cavity modes. According to the experimental data, the full width at half maximum (FWHM) can reach less than 0.1 nm. Furthermore, the resonant peak of FWMH is determined by the thickness of the waveguide, and the resonant wavelength can be selected by changing the incident angle.

The device not only has the characteristics of the sizeable dynamic tuning range, narrow filter bandwidth, high transmittance, high sensitivity, and quality factor, but also has the advantages of simple structure, convenient control, easy fabrication and low cost. This new type of ultra-narrowband filter has broad application prospects in photonic integrated chips, chemical analysis, biosensing, medical diagnosis and other fields.

FIG. 1.  Filtering effect after adding broad-band filter and narrow-band filter to the optical path respectively. (a), (b) The effect of the 1.0-mm-thick waveguide filtering with broad-band filter and narrow-band filter. (c), (d) The effect of the 1.5-mm-thick waveguide filtering with broad-band filter and narrow-band filter.

FIG. 2. The number of filter peaks varies with the incident angle. (a) The effect of the 0.1-mm-thick waveguide filtering. (b) The effect of the 0.26-mm-thick waveguide filtering.

This research was published in “Hong Yang, Hailang Dai, and Xianfeng Chen, Ultra-narrowband filter based on the metal-cladding resonant waveguide, Optics Express, 30(26), 46861-46869 (2022)”.

Link: https://doi.org/10.1364/OE.475762