Time delay signature (TDS) of a semiconductor laser subject to dispersive optical feedback from a chirped fibre Bragg grating (CFBG) is investigated experimentally and numerically. Different from mirror, CFBG provides additional frequency-dependent delay caused by dispersion, and thus induces external-cavity modes with irregular mode separation rather than a fixed separation induced by mirror feedback. Compared with mirror feedback, the CFBG feedback can greatly depress and even eliminate the TDS, although it leads to a similar quasi-period route to chaos with increases of feedback. In experiments, by using a CFBG with dispersion of 2000ps/nm, the TDS is decreased by 90% to about 0.04 compared with mirror feedback. Furthermore, both numerical and experimental results show that the TDS evolution is quite different: the TDS decreases more quickly down to a lower plateau (even background noise level of autocorrelation function) and never rises again. This evolution tendency is also different from that of FBG feedback, of which the TDS first decreases to a minimal value and then increases again as feedback strength increases. In addition, the CFBG feedback has no filtering effects and does not require amplification for feedback light.

We propose a combined attenuation and high-resolution fault measurement method using chaos optical time-domain reflectometry (OTDR). Utilizing the pulsemodulated chaotic light and correlation operation, this technique realizes fiber attenuation measurement and a distance-independent spatial resolution simultaneously. We demonstrate a proof-of-concept experiment for measurements of a single-mode fiber (G.652) and a fiber link consisting of a single-mode fiber (G.652) and a conventional (62.5-m) multimode fiber. The measurement results show that different attenuation coefficients can be measured, and the coefficients agree well with the values obtained by using conventional OTDR. A 0.6-m resolution is achieved with a data acquisition bandwidth of 200 MHz.

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Rationale:Accessory spleen torsion is a rare cause of the acute abdomen. The complications of accessory spleen torsion, such as intestinal obstruction, are rarer. We herein report a case of colonic obstruction caused by accessory spleen torsion because of the unusual condition.Patient concerns:A 15-year-old patient presented with acute intestinal obstruction with signs of peritoneal irritation. Abdominal computed tomography (CT) and ultrasonography examinations revealed a soft tissue mass in the left midabdomen. Systemic inflammatory response syndrome (SIRS) was observed in this case.Diagnoses:The diagnosis of peritonitis and colonic obstruction secondary to accessory spleen torsion was made. Pathologic examination showed infracted splenic tissue.Interventions:We performed emergency laparotomy and found that accessory spleen torsion pressured against splenic flexure and descending colon, and caused colon obstruction. The patient underwent accessory splenectomy and enteral decompression.Outcomes:At 6 months follow-up, the patient recovered well with perfect digestion.Lessons:Accessory spleen torsion and its complications are extremely rare. This entity should be considered in differential diagnosis of acute abdomen. However, in case of acute abdomen with critical clinical situation, emergency surgical intervention is necessary for timely diagnosis and treatment.

Evaluating entropy rate of high-dimensional chaos and shot noise from analog raw signals remains elusive and important in information security. We experimentally present an accurate assessment of entropy rate for physical process randomness. The entropy generation of optical-feedback laser chaos and physical randomness limit from shot noise are quantified and unambiguously discriminated using the growth rate of average permutation entropy value in memory time. The permutation entropy difference of filtered laser chaos with varying embedding delay time is investigated experimentally and theoretically. High resolution maps of the entropy difference is observed over the range of the injection-feedback parameter space. We also clarify an inverse relationship between the entropy rate and time delay signature of laser chaos over a wide range of parameters. Compared to the original chaos, the time delay signature is suppressed up to 95% with the minimum of 0.015 via frequencyband extractor, and the experiment agrees well with the theory. Our system provides a commendable entropy evaluation and source for physical random number generation.PACS numbers: