Tunable Lasers Phaselocked to Optical Frequency Comb
Win Indra, Zitong Feng, Meng Ding, Josef Vojtěch and Radan Slavík 


Fig. 4. Spectrum on the used OFC with total power of 0.5 mW and per-comb powers of 1.1 nW at 1530 nm, 2.3 nW at 1550 nm, and 3.7 nW at 1565 nm. 

Fig. 5.  Phase noise of beat signal between two tunable lasers with powers of 1 mW and 1-10 nW, respectively.

Fig. 6.  Phase noise of the beat signal between a tunable laser (power of 1 mW) and OFC with per-tone power of 1-10 nW at the wavelength of 1550  nm.

Fig. 7. Phase noise of the beat signal between a tunable laser (power of 1 mW) and OFC with per-tone power of 1 nW at the wavelength of 1550  nm for free-running laser (blue), when phaselocked using one double-integrator  (PI^2, blue), and using two double-integrators (PI^4, green). Measurement noise floor is also shown (grey, dashed). 

Fig. 8.  Phase Noise of beat signal of locking tunable laser to the OFC at different wavelengths with relevant OFC power set to 1 nW.

Fig. 9.  Phase noise jitter calculated from the measured phase noise of OFC-locked tunable laser (with per-tone power of 1 nW) when locked using PI^2 and PI^4 feedback controller. 

Fig. 10. Frequency error of OFC-laser beat signal with one double-integrator  (PI2) and two double-integrators (PI^4) using 1 s gate time, measured over 10 hours.

Fig. 11. Allan deviation calculated from the frequency counter data when a tunable laser is locked to the OFC using two double-integrators (PI^4)  and one double-integrator (PI^2), normalized to the laser carrier frequency (192 THz). 

Fig. 12. Fractional frequency instability of the beat signal at 1 s averaging times for various beat frequencies expected from our system and its comparison with the state-of-the art terahertz sources (adopted from [13]).