Brillouin laser-driven terahertz oscillator up to 3 THz with femtosecond jitter

Abstract

The terahertz (THz) frequency range, spanning 0.1 to 10 THz, is a field ripe for innovation with vast, developing potential in areas like wireless communication and molecular spectroscopy. Our work introduces a dual-wavelength laser design that utilizes stimulated Brillouin scattering in an optical fiber cavity to effectively generate two highly coherent optical Stokes waves with differential phase noise inherently mitigated. To guarantee robust operation, the Stokes waves are optically injected into their respective pump lasers, which also serves to greatly improve the resulting coherence. The frequency difference between the two wavelengths is converted into THz waves through a uni-traveling-carrier photodiode. This innovative design facilitates the generation of THz waves with phase noise levels of less than -100 dBc/Hz, translating to timing noise below 10 attoseconds/sqrt(Hz) at 10 kHz Fourier frequency, over a carrier frequency range from 300 GHz to 3 THz. This development in phase noise reduction establishes a new benchmark in the spectral purity of tunable THz sources. Such advances are pivotal for applications to move beyond oscillator constraints.

Coherence enhancement between incoherent lasers based on passive phase compensation

“…Recently, the Brillouin laser-driven terahertz oscillator has been proposed to achieve remarkable results in the range of 300 GHz to 3 THz with low phase noise, by using an optical fibre cavity to generate two highly coherent optical Stokes waves, and then injecting the Stokes waves into two individual pump lasers [14]. It is noted that the performance is obtained by paying the cost of the need of high-quality and high-power pump lasers, and the precise control of the Brillouin chamber and the injection alignment.…”