Phase Control of Terahertz Waves Using Injection-Locked Resonant Tunneling Diode Oscillator

Controlling the phase of terahertz (THz) waves is necessary for various applications, particularly beam steering with phased arrays. Resonant tunneling diodes (RTDs) are promising candidates for compact THz sources, and injection-locking phenomenon can be used to control the phase of RTD oscillators. In this study, we experimentally demonstrate the phase control of an injection-locked RTD oscillator. We fabricated an RTD oscillator with a slot antenna and developed a device package that reduces external THz feedback to obtain continuous frequency tuning. The free-running frequency varied from 380.5 to 386.7 GHz over a bias range of 0.61 to 0.65 V. To measure the phase of RTD oscillator, we constructed a heterodyne detection system in which all signals were well synchronized to achieve good phase measurement accuracy. The frequency of the RTD oscillator was locked to an injection signal of 383.2 GHz from an external source, and the phase was controlled by the bias voltage under the injection locking. The measured phase changed from −81° to +73° within the locking range. The bias-voltage dependence of the phase change reasonably agreed with the theoretical expectation.