Terahertz Nonreciprocal Photonic Spin Manipulation with Light‐Magneto‐Joint Modulation

Abstract Nonreciprocal materials and devices play an irreplaceable role in isolating, routing, and multiplexing. However, in the terahertz (THz) band, their active control mechanisms are still limited. Herein, a THz nonreciprocal photonic spin transmission is demonstrated in the undoped InSb actively manipulated by a light‐magneto‐joint modulation method, in which THz cyclotron resonance of the photoinduced carriers is conjunctively excited by both pump laser and external magnetic field. Moreover, a diffusion model of photoinduced non‐equilibrium carriers and its nonreciprocal dispersion model of magnetized plasma are established to interpret the experimental observation. The results indicate that the light‐magneto‐joint modulation achieves a broadband amplitude‐phase modulation with a higher modulation depth (>2π rad phase shift), as well as an active nonreciprocal spin transmission with magnetic circular dichroism (>20dB) and the Faraday rotation effect (>90°) in InSb, which is more efficient and faster than the traditional thermal excitation. Furthermore, the demonstration in a single‐frequency THz transmission system shows that this light‐magneto‐joint modulation mechanism in InSb can be multifunctionally applied in active control, isolation, and polarization conversion.