Diamond, with its transparency window up to 20μm that covers the entire molecular vibration fingerprint region, shows great potential in the application of integrated photonic devices with wavelengths exceeding 15μm. However, the relatively low refractive index of diamond poses a challenge in designing mid-infrared diamond devices with small size and high transmission rate.In this work, the authors used the inverse design method to design a mid-infrared diamond waveguide beam splitter with a wavelength of 15 μm. The device size is 15μm×15μm, and the total transmission rate is higher than 95%. The inverse design is based on the gradient descent algorithm, which can effectively optimize the distribution of dielectric constants between the input and output waveguides of the waveguide beam splitter to achieve any power allocation ratio between 0 and 100%. In addition, the authors have also fully studied and quantitatively analyzed the dependence of the inverse design algorithm on the structural parameters of the mid-infrared diamond waveguide beam splitter. The above research results have opened up a new way for designing compact and efficient mid-infrared diamond photonic devices.

Figure 1: Structural diagram of the designed suspended waveguide beam splitter

Figure 2: Implementation of different power allocation ratios for the mid-infrared diamond waveguide beam splitter

Article link: https://doi.org/10.1364/OL.526023