Abstract: A light return loss measurement method and system with an optical time domain reflectometer (OTDR) which displays an output of an arithmetic circuit. The method and system permits measurement of the light return loss over an arbitrary interval of an optical fiber. The system's arithmetic circuit calculates light return loss across a measurement interval set in a display waveform data by dividing a predetermined light return loss and integrating the measured waveform by multiplying the set interval by a light interception correction constant. The integration performed is a quadrature of various sections of an optical fiber. The light return loss measurement method and system also permits easy calibration of the light return loss in the OTDR.

Abstract: The present invention provides light frequency control apparatus comprising a light pulse signal generating mechanism for generating a light pulse signal of a standard frequency; a light frequency shifting mechanism for circulating this light pulse signal a predetermined number of times, delaying this light pulse signal at each cycle thereby sequentially shifting and outputting the aforementioned light pulse signal; an extracting mechanism for extracting a light pulse signal in the second half of a cycle from the output of the light frequency shifting mechanism; and a polarization control mechanism inserted into the light frequency shifting mechanism for controlling the angle of polarization of the light pulse signal circulating in the light frequency shifting mechanism based on the amount of attenuation of the light pulse signal outputted by the extracting mechanism.

Abstract: The present invention provides light frequency control apparatus comprising a light pulse signal generating mechanism for converting continuous light into a light pulse signal, and outputting this light pulse signal; a light signal generating mechanism for repeatedly generating at predetermined cycles, a light signal, in which a light frequency component therein is shifted to form a staircase shape based on the number of cycles of a loop within which the light pulse signal circulates; and a dummy light generating mechanism for generating dummy light at a timing such that the level of the light signal becomes zero, and supplying this dummy light to the light amplifying mechanism. The aforementioned loop is formed from a light amplifying mechanism for amplifying the light pulse signal outputted from the light pulse signal generating mechanism, light delay mechanism for delaying the light pulse signal a fixed amount; and frequency shifting mechanism for shifting the frequency of the light pulse signal.

Abstract: A reference light generating mechanism generates reference light, a light frequency component of which varies in a stepped manner at fixed intervals, repeatedly at pre-specified cycles, and generates a timing signal in accordance with this variance. A detecting mechanism detects a frequency difference between a reference light frequency freely selected from among the light frequency component and a feedback light frequency of feedback light fed back so as to conform to the reference light frequency, and synchronizes this with a timing signal, and an output light generating mechanism generates output light, the light frequency of which is controlled in accordance with the frequency difference, and conducts the feedback of this output light to the detecting mechanism as feedback light.

Abstract: A light frequency shifter repeatedly generates, at predetermined cycles, an optical signal, an optical frequency component of which varies in a stepped manner at fixed intervals, and timing generating circuit generates timing signals corresponding to this variation. Detecting mechanisms synchronize, with the timing signal, a frequency difference between a reference light frequency freely selected from the light frequency component and a feedback light frequency of feedback light fed back so as to conform to this reference light frequency, and detect this. Light frequency-regulated light source extracts an output optical signal circulating within a closed loop circuit controlling the light frequency in accordance with the frequency difference described above, and supplies this to a light output terminal, and feeds back a portion of the output optical signal to the detecting mechanism as the feedback light described above.

Abstract: An apparatus for measuring a distortion position of an optical fiber is disclosed. A light source generates continuous light with frequency f.sub.0 and injects the continuous light into a far-end of an optical fiber to be measured. An optical coupler divides the outgoing continuous light from a near-end of the optical fiber. An optical amplifier amplifies output light from the optical coupler. A first optical switch generates a first optical pulse by switching output light from the optical amplifier. An optical frequency shifter generates a second optical pulse having frequency components (f.sub.0 +f.sub.m) based on the first optical pulse from the first optical switch. A second optical switch injects the second optical pulse into the near-end of the optical fiber. A display displays outgoing continuous light with frequency f.sub.0 from the near-end of the optical fiber via the optical coupler and the second optical switch.