Method and apparatus for measuring chromatic dispersion coefficient

Claim 3

A method as set forth in claim 1, wherein, in step (b), the calculated baseband characteristic closest to the actual baseband characteristic is obtained through a comparison of these two characteristics while sequentially varying the value of the provisional chromatic dispersion coefficient.

Claim 4

A method as set forth in claim 1, wherein, in step (b), the calculated baseband characteristic closest to the actual baseband characteristic is obtained through selection from a plurality of calculated baseband characteristics each having a corresponding provisional chromatic dispersion coefficient.

Claim 5

A method as set forth in claim 2, wherein the calculated baseband characteristic is defined by a theoretical approximation function H(f), that is; where a. denotes an amplitude of an i-th oscillation mode among n oscillation modes created in the optical spectrum of said input optical signal, f said modulation frequency, Δλ i a difference between the wavelength at the i-th oscillatin mode and the wavelength at a first oscillation mode, m said provisional chromatic dispersion coefficient, and L a length of the optical fiber to be measured.

Claim 6

A method as set forth in claim 3, wherein the calculated baseband characteristic is defined by a theoretical approximation fuction H(f), that is; where a i denotes an amplitude of an i-th oscillation mode among n oscillation modes created in the optical spectrum of said input optical signal, f said modulation frequency, Δλ i a difference between the wavelength at the i-th oscillation mode and the wavelength at a first oscillation mode, m said provisional chromatic dispersion coefficient, and L a length of the optical fiber to be measured.

Claim 7

A method as set forth in claim 4, wherein the chromatic dispersion coefficient is derived through computer simulation with the aid of a processor, the processor collecting and storing therein at least two data sets, in advance, a first data set available for specifying the theoretical approximation function function and a second data set available for specifying the actual baseband characteristic measured.

Claim 8

A method as set forth in claim 5, wherein the chromatic dispersion coefficient is derived through computer simulation with the aid of a processor, the processor collecting and storing therein at least two data sets, in advance, a first data set available for specifying the theoretical approximation function function and second data set available for specifying the actual baseband characteristic measured.

Claim 9

A method as set forth in claim 6, wherein said computer simulation is performed under a least square approximation method by employing an appreciation function AF, that is: where F k denotes the value of the actual baseband characteristic measured at the modulation frequency f k , and N a number of measuring points.

Claim 10

A method as set forth in claim 7, wherein said compute simulation is performed under a least square approximation method by empolying an appreciation function AF, that is: where F k denotes the value of the actual baseband characteristic measured at the modulation frequency f k , and N a number of measuring points.

Claim 15

An apparatus as set forth in claim 11, wherein said means are comprised, as a whole, of the following: an optical transmitter operative to modulate an optical signal with AC signals having different modulation frequencies and to launch the thus modulated optical signal, as an input optical signal, onto one end of an optical fiber to be measured; an optical receiver operative to detect a level of an output optical signal given from another end of the optical fiber at each of the modulation frequencies so as to measure an actual base baseband characteristic of the optical fiber; an optic spectrum analyzing part which functions to detect the wavelengths and amplitudes at each oscillation mode created in an optical spectrum of the input optical signal; and a data processing part which functions to derive a calculated baseband characteristic closest to the actual actual baseband characteristic measured in the optical reveiver, by using data concerning the modulation frequcney, the wavelength, and the amplitude produced from the optic spectrum analyzer, and a provisional chromatic dispersion coefficient and to set the provisional chromatic dispersion coefficient corresponding to the calculated baseband characteristic as the actual chromatic dispersion coefficient of the optical fiber.

Claim 16

An apparatus as set forth in claim 12, wherein said optical transmitter contains therein both an oscillator for producing the varialbe frequency AC signal and an electro-optic converter driven by the oscillator.

Claim 17

An apparatus as set forth in claim 13, wherein said electro-optic converter is provided with, at its output stage, an optical isolator.

Claim 18

An apparatus as set forth in claim 14, wherein an optical switch is located between said optical isolator and one end of the optical fiber, the optical switch operative to selectively supply the input optical signal to a spectroscope comprising said optical spectrum analyzing part or the optical fiber.

Claim 19

An apparatus as set forth in claim 12, wherein said optical receiver contains therein both an opto-electric converter for trasducing the receiving optical signal from the optical fiber to the corresponding electric signal and a selective level meter which is supplied with said electric signal so as to detect the level of the output optical signal at each said modulation frequency.

Claim 20

An apparatus as set forth in claim 16, wherein said opto-electric converter is provided with, at its input stage, an optical attenuator.

Claim 21

An apparatus as set forth in claim 12, wherein said optical spectrum analyzing-part contains therein both a spectroscope in which spectral decomposition is performed with respect to said input optical signal from said optical transmitter and an optical detector which interlocks with the spectroscope to detect both the wavelength and amplitude at each said oscillation mode.

Claim 22

An apparatus as set forth in claim 18, wherein both said spectroscope and said optical detector are formed, as an integral structure, with an optical spectrum analyzer.