Injection Locking and Noise Reduction of Resonant Tunneling Diode Terahertz Oscillator

TL;DR

This paper demonstrates that injection locking significantly reduces the linewidth and noise of a resonant tunneling diode terahertz oscillator, aligning with theoretical models and improving spectral stability.

Contribution

It provides experimental validation of injection locking effects on linewidth and noise reduction in resonant tunneling diode terahertz oscillators, confirming theoretical models.

Findings

Linewidth reduced to less than 120 mHz from 4.4 MHz

Locking range proportional to injection amplitude

Noise component decreases with increased injection amplitude

Abstract

We studied the injection-locking properties of a resonant-tunneling-diode terahertz oscillator in the small-signal injection regime with a frequency-stabilized continuous THz wave. The linewidth of the emission spectrum dramatically decreased to less than 120 mHz (HWHM) from 4.4 MHz in the free running state as a result of the injection locking. We experimentally determined the amplitude of injection voltage at the antenna caused by the injected THz wave. The locking range was proportional to the injection amplitude and consistent with Adler's model. As increasing the injection amplitude, we observed decrease of the noise component in the power spectrum, which manifests the free-running state, and alternative increase of the injection-locked component. The noise component and the injection-locked component had the same power at the threshold injection amplitude as small as $5\times10^{-4}$ of the oscillation amplitude. This threshold behavior can be qualitatively explained by Maffezzoni's model of noise reduction in general limit-cycle oscillators.