Abstract: In a measurement requiring a high space resolution using S-BOTDR, a pulse train composed of a plurality of pulses having the interval between the pulses longer than the phonon lifetime is interpulse-code-modulated. A Golay code is used for the interpulse code modulation to eliminate the sidelobes of the correlation in using a technique of correlation. In a technique without using correlation, an Hadamard matrix is used for the interpulse code modulation and the resultant matrix is inverted in the signal processing.

Abstract: In a measurement requiring a high space resolution using S-BOTDR, a pulse train composed of a plurality of pulses having the interval between the pulses longer than the phonon lifetime is interpulse-code-modulated. A Golay code is used for the interpulse code modulation to eliminate the sidelobes of the correlation in using a technique of correlation. In a technique without using correlation, an Hadamard matrix is used for the interpulse code modulation and the resultant matrix is inverted in the signal processing.

Abstract: An apparatus for measuring the characteristics of an optical fiber is provided. An optical pulse generator generates, from a coherent light, first and second optical pulses having a time interval which is equal to or shorter tan a life time of an acoustic wave in the optical fiber. A detector couples the coherent light with a Brillouin backscattered light which includes first and second Brillouin backscattered lights belonging to the first and second optical pulses respectively, thereby generating an optical signal. The detector further converts the optical signal into an electrical signal. A signal processor takes the sum of the electrical signal and a delay electrical signal which is delayed from the electrical signal by a delay time corresponding to the time interval, thereby generating an interference signal, and finds the characteristics of the optical fiber based on the interference signal.

Abstract: A silica-based optical fiber includes a core and a cladding that is formed on an outer circumference of the core. The core includes three or more layers including a layer doped with at least one of germanium and fluorine, and a concentration of the germanium or the fluorine in each of the layers is controlled in such a manner that a Brillouin gain spectral peak is spread into a plurality of peaks on a Brillouin gain spectrum. With this scheme, an optical fiber is provided, which has stable characteristics in the longitudinal direction, and which has a high SBS threshold so that generation of the SBS can be effectively suppressed.

Abstract: A silica-based optical fiber includes a core and a cladding that is formed on an outer circumference of the core. The core includes three or more layers including a layer doped with at least one of germanium and fluorine, and a concentration of the germanium or the fluorine in each of the layers is controlled in such a manner that a Brillouin gain spectral peak is spread into a plurality of peaks on a Brillouin gain spectrum. With this scheme, an optical fiber is provided, which has stable characteristics in the longitudinal direction, and which has a high SBS threshold so that generation of the SBS can be effectively suppressed.

Abstract: An apparatus for measuring the characteristics of an optical fiber is provided. An optical pulse generator generates, from a coherent light, first and second optical pulses having a time interval which is equal to or shorter tan a life time of an acoustic wave in the optical fiber. A detector couples the coherent light with a Brillouin backscattered light which includes first and second Brillouin backscattered lights belonging to the first and second optical pulses respectively, thereby generating an optical signal. The detector further converts the optical signal into an electrical signal. A signal processor takes the sum of the electrical signal and a delay electrical signal which is delayed from the electrical signal by a delay time corresponding to the time interval, thereby generating an interference signal, and finds the characteristics of the optical fiber based on the interference signal.

Abstract: A plastic optical fiber includes having a first core, a second core having a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refactive index difference n1 between the first core and the clad are in a range that satisfies the expressions Y≧−1.134X+1.0518 (1), and X≦−1.4842Y2+1.1097Y+0.7097 (2), and provided that Y<0.4 or X≧0.76 and that coordinate pairs X=0.8 and Y=0.35 as well as X=0.8 and Y=0.45 are excluded. The plastic optical fiber can have a high transmission power and a wide bandwidth. A cable and an optical transimission device can each include this plastic optical fiber.

Abstract: The present invention relates to a plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core; wherein a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refractive index difference n1, between the first core and the clad are in a range where the following Expressions

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: An impedance element is disclosed which is formed with an electro-elastic surface wave transducing device composed of a substrate for the propagation of an elastic surface wave and an electro-elastic surface wave transducer disposed on the substrate for converting an electrical signal into an elastic surface wave or vice versa. The impedance element has a frequency-impedance characteristic that it exhibits a sufficiently high impedance in a predetermined frequency band but a sufficiently low impedance in the other frequency bands.Further, a band-rejection filter is disclosed which includes the abovesaid impedance element and has a band-rejection filter characteristic dependent upon the frequency-impedance characteristic of the impedance element.