Design and optimization of diamond mid-infrared phase shifter

Herein, the mid-infrared (7.7-13.7 mu m) diamond-based phase shifter was designed and optimized by finite-element analysis. The ridge-shaped diamond waveguide is designed and doped to form the internal p-n structure, and the internal carrier distribution is changed by applying forward and reverse voltages to change the effective refractive index to achieve the effect of pi-phase shift. The results show that when p-doping concentration is 4 x 1017 cm-3 and n doping concentration is 1 x 1018 cm-3, upon the reverse voltage (8 V) is applied, the change of the real part of effective refractive index (Delta R) is 1.6 x 10-5, and the length of the phase shifter (L) required to realize the pi-phase shift is 241 mm; upon the forward voltage (-8 V) is applied, Delta R increases to 3.2 x 10-4, and the length of the phase shifter required is shortened to 12.03 mm. Such a short length is relatively easy in industrial production. In order to make the refractive index distribution more uniform, the carrier concentration has been optimized as 1 x 1017 cm-3 for p-type and 4 x 1017 cm-3 for n-type, respectively.