Post-Processing-Free Multi-Bit Extraction From Chaotic Laser Diode With CFBG Feedback

Multi-bit extraction from a chaotic external-cavity laser diode with mirror feedback is a common way to generate ultrafast physical random numbers. Unfortunately, to overcome the randomness defect caused by external-cavity resonance, i.e., time delay signature (TDS), complicated post-processing methods are required. These methods are usually operated offline and thus limit the real-time extraction of random numbers. In this letter, we experimentally demonstrate random number generation by multi-bit extraction without any other post-processing (i.e., post-processing-free multi-bit extraction) from a chaotic laser diode under dispersive feedback of a chirped fiber Bragg grating. The dispersive feedback can provide additional frequency-dependent delay and induce external-cavity modes with irregular mode separation, which depresses the TDS of laser chaos and improves its physical randomness. In experiments, after quantizing the randomness-improved laser chaos with an 8-bit analog-digital convertor, 160-Gbps physical random numbers with verified randomness are obtained by extracting four least significant bits (LSBs) at 40-GS/s sampling rate. Compared with the conventional mirror-feedback scheme, this proposed scheme can extract two more LSBs at the same sampling rate. More importantly, it paves the way for realizing the real-time generation of ultrafast random numbers using multi-bit extraction from laser chaos.