We demonstrate here for the first time generation of tunable terahertz (THz) radiation based on photomixing continuous wave (CW) radiation of the DFB laser with fixed wavelength and self-sweeping Er-doped fiber one operating near 1560 nm. The latter sequentially generates longitudinal modes with duration of several milliseconds and regular hopping between them. In this case signal accumulation of THz radiation within generation of each mode can be performed to increase signal-to-noise ratio (SNR). We demonstrated the possibility of designing a spectrometer with spectral resolution down to 50 MHz in the tuning range of ~5 GHz near the central frequency of 100 GHz. The proposed approach can be useful in the development of spectroscopic systems, millimeter-wave lidars, and telecom devices.
In this work, a self-sweeping Yb-doped fiber laser generating quasi-CW radiation is demonstrated. The laser is based on a ring configuration allowing to form running and standing waves in separate sections of the cavity. The laser generates a sequence of single-frequency (linewidth of ~0.7 MHz) ultra long (~1 ms) rectangular pulses. The laser frequency changes from pulse to pulse by one inter-mode spacing (~10 MHz). The laser signal intensity is quasi-CW signal accompanied by regular bursts generating during frequency change, and the intensity never drops to zero. The features can be useful for long term averaging when measuring weak signals.
We present results on the first demonstration of self-sweeping effect in a ring Er-doped fiber laser. Reverse self-sweeping (with decreasing wavelength) in a range of ~0.1 nm was obtained. Typical sweeping rate was 4 pm/s, which is sufficiently slower as compared with earlier reported fiber lasers. Dual longitudinal mode self-sweeping (similar to reported earlier in linear cavity Er-doped fiber laser) is obtained. The laser generates sequentially long overlapping pulses. Frequency of each subsequent pulse increases by one inter-mode spacing. However, the typical duration of dual-mode operation is ~10 ms, which is one order longer than in previous works. We demonstrated that increase in pump power causes deceleration of sweeping and elongation of dual-mode pulses up to 500 ms. The developed source can be used for fiber sensor interrogation.
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