LIGHT BASE BAND OSCILLATOR USING SEMICONDUCTOR LASER

摘要

PURPOSE:To cause the self-excited oscillation of alight base band and then to measure the length or a faulty point of an optical fiber from the frequency of the above-mentioned self-excited oscillation, by making a laser beam incident to an end of the optical fiber and feeding positively the returned beam back to a semiconductor laser. CONSTITUTION:The DC bias is set for a seminconductor laser 11 through a setting circuit 12 to perform a laser oscillation. The beam sent from the laser 11 is made incident to an end of an optical fiber 14 through a beam splitter 13. The laser beam propagates into the fiber 14, returns by Fresnel reflection, is reflected by the splitter 13 and made incident to a photodetector 15 to be converted into an electric signal. This electric signal passes through a band pass filter 16 and is then amplified by an amplifier 17 to be positively fed back to the laser 11. In this case, the sum of the phase change in the fiber 14 and the phase change of an electric circuit system including the detector 15 though the laser 11 becomes an integer-fold value of the period of the self-excited oscillation.