Search

The traditional Optical Time Domain Reflectometry (OTDR) technology uses back Rayleigh scattering power for fiber detection. In transmission lines with optical amplifier, Erbium-Doped Fiber Amplifiers (EDFA) are mostly used to compensate for the loss of signal light and extend the transmission distance of the signal light. Since the EDFA amplifies the signal, it will generate spontaneous radiation noise, and the continuous accumulation of noise will rapidly decrease the signal-to-noise ratio measured by the OTDR. The paper mainly expounds the principle of Coherent Optical Time Domain Reflectometry (C-OTDR) technology. The detected signal optical power is concentrated to the intermediate frequency by the coherent detection method, and most of the noise can be filtered out by band-pass filtering the frequency signal. It can continuously extend the detection distance through the EDFA. We also propose to use the frequency shift keying method to eliminate the optical surge problem caused by the cascade of multi-stage repeaters in long-distance transmission of submarine cables. Through the development of self-developed coherent optical time domain reflectmeter, the actual test of C-OTDR technology in the simulated submarine cable multi-span transmission system has reached 3 000 km, which fully meets practical conditions.

Objective To explore the clinical features, genetic characters and the importance of prenatal diagnosis in spinocerebellar ataxia 3 (SCA3) patients. Methods SCA3/ATXN3 gene was determined by using PCR and segmental analysis techniques in 2 patients among a SCA3 Chinese Han family which included 9 patients in four generations. One patient was the proband's fetus. The clinical characters were also documented and analyzed in this family. Results There were 9 patients in this family with autosomal dominant inheritance feature. The initial symptoms in all affected members except the fetus were the gait disorders accompanied by dysphasia. Inability of upward gaze and bilateral Barbinski's signs were noted in proband. The onset age became earlier from generation to generation in this family which was around 50 year⁃old, 40 to 45 year⁃old, 28 year⁃old in generation Ⅰ, Ⅱ and Ⅲ, respectively. CAG repeats in SCA3/ATXN3 allele were 77 in proband, as well as in the fetus, while the normal SCA3/ATXN3 allele CAG repeats were less than 44. Conclusion SCA3 is the most frequent subtype of SCA in Asian. Unsteadiness of gait are first noted in most patients accompanied by other different symptoms and signs. Genetic anticipation was found in SCA3. But gene analysis revealed less dynamic mutation frequence in this family. Since there was no effective treatment in SCA3, hereditary consultation and prenatal diagnosis play an important role in disease prevention and hereditary. DOI：10.3969/j.issn.1672⁃6731.2012.03.010