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. 2022 Mar 16;13:1388. doi: 10.1038/s41467-022-29049-2

Fig. 3. Experimental setup and results of high-purity THz carriers generation.

Fig. 3

a A master-slave optical injection-locking-based THz carrier generation scheme. The two DFB lasers are injection-locked as slaves by the master OFCG. The polarization state and injection strength are controlled and optimized by a polzarization controller (PC) and a variable optical attenuator (VOA), respectively. The output OFCG-locked two-tone signal passes through the port 3 of the circulator. The wavelength of each DFB tone is tuned by the thermal tuning current of the integrated heater, and the intensity is controlled with the injection current. The two-tone signal with separation of 408 GHz is then amplified, band-pass filtered, and polarization-aligned before being photomixed at the UTC-PD, generating a 408-GHz signal with broadband modulation. The signal is propagated over 10.7-meter distance before being detected and down-converted by a Schottky Barrier Diode (SBD)-based subharmonic mixer. An electrical spectrum analyzer (ESA) is used t monitor the down-converted intermediate frequency (IF) signal. b The optical spectra of the DFB-2 laser wavelength shifted between 1556 nm and 1560 nm, driven by injection current changing between 20 mA and 100 mA. The laser intensity varies accordingly. c The optical spectra of the two lasers and the OFC. The laser wavelengths are set to 1555.375 nm and 1558.975 nm with 3.3 nm (408 GHz) separation, spanning over 41 comb lines of 9.951 GHz comb-spacing from the MLL-based OFC. d The electrical spectra of the IF signal with and without the injection locking. The IF signal drifts around 10 GHz when free-running, shown as the blue trace. After being injection-locked to the OFC, the linewidth of the IF signal is much narrower and the power is 10 dB higher than the free-running case, shown as the red trace. e The single-sideband (SSB) phase noise as a function of comb-injection powers. The SSB phase noise decreases at higher injection power, particularly observable from the phase noise floors at >100 kHz frequency offset.