Extended Data Fig. 6: The RIN and linewidth measurement using a fiber-based isolator as a benchmark.

The isolation ratio is 50 dB. The reflected power is also set at 0.4% of the laser power. a, The RIN measurement over 8 MHz range under four different conditions: 1) isolator on, reflection off; 2) isolator on, reflection on; 3) isolator off, reflection off; 4) isolator off, reflection on. The isolator successfully protects the RIN of the laser. Only in the case of reflection on and isolator off, we observe the beatnote which corresponds to the external cavity FSR (similar to what is observed in the Extended Data Fig. 5). b, The linewidth measurement of the laser. We observe a similar phenomenon as compared to the LN-chip-based isolator case plotted in Fig. 4c. The isolator can protect the single mode operation and the linewidth of the laser. Without the isolator’s protection, the reflection would cause multimode oscillation with spectral spacing equal to the FSR of the external cavity formed between the DFB laser and the fiber reflector. In this measurement, the cavity FSR is 7.2 MHz. iso: isolator; ref: reflection.