INTEGRATED TURNKEY SOLITON MICROCOMBS
4.4 Supplementary information: Additional measurements Different types of microcombs in the injection locking systemDifferent types of microcombs in the injection locking system
1520 1540 1560 1580 Wavelength (nm)
Power (20 dB/div)
1520 1540 1560 1580
Wavelength (nm)
Power (20 dB/div)
-0.2 0 0.2
20 dB RBW 50 kHz
Frequency (GHz +19.787 GHz) RF powerRF power
20 dB RBW 50 kHz
Frequency (GHz +19.787 GHz)
-0.2 0 0.2
a
b
Breather soliton
Chaotic comb
1520 1540 1560 1580
Wavelength (nm)
Power (20 dB/div)
c Soliton crystal
Figure 4.8: Optical and electrical spectra of different microcomb types. (a-b) Optical spectra of breather solitons and a chaotic comb. Inset: Electrical beatnote signals. (c) Optical spectrum of a soliton crystal state.
of the turnkey soliton state to consist of multiple solitons. By carefully tuning the phase and controlling the MI gain, it is still possible to obtain a turnkey single soliton state, as shown in the third case (Fig. 4.7c).
4.4 Supplementary information: Additional measurements
Time (100 ms/div) 0
20 40
Frequency (MHz +19.750GHz) 0 1
Comb power (a.u.)
0 1RF power (a.u.)
Time (2 ms/div) 0
1
Comb power (a.u.)
Time (2 ms/div) 0
1
Comb power (a.u.)
a
b
Frequency decreasing Frequency increasing
c
Figure 4.9: (a) Turnkey generation of a chaotic comb. Upper panel: Comb power evolution. Lower panel: Spectrograph of RF beatnote power. (b-c) Comb power evolution when the pump laser frequency is driven from blue to red (b) and red to blue (c).
It is also possible to operate our system in different types of microcomb states under certain feedback phase and laser driving frequency. Fig. 4.8 shows the experimental spectra of breather solitons, a chaotic comb and a soliton crystal state, respectively.
The turnkey generation of the chaotic comb is further shown in Fig. 4.9a. The broad and noisy RF spectrum indicates that it is not mode-locked.
Tuning of turnkey soliton microcomb system
To further explore the performance of the turnkey soliton microcomb system, the frequency of the pump laser is driven by a linear current scan (Fig. 4.9b,c). The scan speed of the driving frequency is around 0.36 GHz/ms, estimated from the wavelength-current response when the laser is free running. When the laser is scanned across the resonance, feedback locking occurs and pulls the pump laser frequency towards the resonance until the driving frequency is out of the locking band. As shown in Fig. 4.9b, the power steps indicate that soliton states with different soliton numbers can be accessed as we tune the driving current. It is worth noting that the soliton microcombs can be powered-on when the laser is scanned from red-detuned side (Fig. 4.9c), which seldom happens under conventional pumping,
except in cases of an effectively negative thermo-optic response system [8]. The comb evolution during laser scanning is a useful tool to assess the robustness of the turnkey soliton generation.
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