The ability to manipulate and select optical modes effectively and accurately is strongly desired to enable single-mode operation. Microscale waveguide cavities support large numbers of closely spaced modes because their dimensions are typically much larger than the optical wavelengths. As a result, the stimulated emission outputs from these microscale waveguide cavities are subject to random fluctuations and instabilities caused by mode competition for limited gain. During recent decades, the effective manipulation and accurate selection of modes has been studied intensively to achieve single-mode operation.

Here, we report an optical system consisting of two directly coupled metal-cladded optical resonators that can realize a single-mode peak through control of the tuning between the resonant wavelengths of the two optical resonators. Additionally, the wavelength of the single-mode peak can be chosen via adjusting the angle of incident light. Furthermore, the linewidth and the power of single-mode output can be controlled completely by the thickness of resonator guide layer and the angle of incident light. Our demonstration of an optical-mode-selection system provides a way to realize optical information processing without the need for complex structures and specific materials. This optical system represents an important step toward integrated single-mode optical output. Therefore, this simple, effective, and tunable optical system has huge potential for applications in optical communications and the optical-sensor field.

FIG. 1. Wavelength tuning of the metal-cladded optical resonator. (a) Experimental setup. (b) Mode-selection system based on two chips. (c), (d) Optical-comb-spectrum experimental data for chip 1 and chip 2, respectively, at the different angles of incidence. (e) When the angle of incidence of chip 2 was adjusted and the angle of incidence of chip 1 remained fixed, the single-mode spectra shown were obtained from the mode-selection system based on the two chips at angles of incidence of 6.40°, 10.04°, 12.66° and 14.86°. (f) When the angle of incidence of chip 2 was 12.66°, we changed the angle of incident of chip 1, which resulted in the changes in the intensity of the single mode shown. (g) ATR peak characteristic.

This research was published in “Hailang Dai, Hong Yang, Zhuangqi Cao and Xianfeng Chen, Tunable single-mode output by optical-mode selection, Physical Review Applied, 19, 034046 (2023)”.

Link: https://doi.org/10.1103/PhysRevApplied.19.034046