Optical generation of highly stable millimeter and terahertz waves is proposed and experimentally demonstrated. The optical-fiber-path-induced phase fluctuation is identically transferred to a 40 MHz intermediate frequency by using dual-heterodyne phase error transfer, then canceled by a phase-locked loop. Based on the scheme, highly stable signals within the frequency range from 25 GHz to 1 THz are generated, and the phase jitter is decreased from 2.05 rad to 4.7 mrad in the frequency range from 0.01 Hz to 1 MHz. For 1 THz, the residual phase noise reaches -60 dBc/Hz at 1 Hz frequency offset from the carrier, and the relative timing jitter is reduced to 0.7 fs.
We report on a versatile optical frequency-modulated continuous-wave interferometry technique that exploits wideband phase locking for generating highly coherent linear laser frequency chirps. This technique is based on an ultra-short delay-unbalanced interferometer, which leads to a large bandwidth, short lock time, and robust operation even in the absence of any isolation from environmental perturbations. In combination with a digital delay-matched phase error compensation, this permits the achievement of a range window about 60 times larger than the intrinsic laser coherence length with a 1.25 mm Fourier transform-limited spatial resolution. The demonstrated configuration can be easily applied to virtually any semiconductor laser.
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