Arrays of fiber pigtails can be used to project and receive light. Unfortunately, most fiber pigtail arrays are not aligned well enough for coherently combining different optical beams. This imprecision stems in part from misalignment between the optical fiber and the endcap spliced to the end of the optical fiber. The endcap is often polished, curved, or patterned, causing the light emitted by the endcapped fiber to refract or diffract as it exits the endcap. This refraction or diffraction shifts the apparent position of the beam waist from its actual position. Measuring this virtual beam waist position before and after splicing the endcap to the fiber increases the absolute precision with which the fiber is aligned to the endcap. This increase in absolute precision reduces the deviation in virtual beam waist position among endcapped fibers, making it easier to produce arrays of endcapped fibers aligned precisely enough for coherent beam combining.

A device for measuring the parameters of phase elements and dispersion of optical fibers, characterized in that it contains: a light source, serially connected to fiber optic coupler, one of whose arms constitutes a part of the reference arm, and whose second arm constitutes a part of the measurement arm of the device, and a motorized linear stage is mounted on the arm of the device. One of the arms of the device is connected to at least one detector, and at least one collimator is placed in at least of the arms of the device, at least before the phase element. A method of measuring the parameters of the phase element and the dispersion of optical fibers is conducted in two stages, wherein the first stage assumes the calibration of the device and the second stage is the proper measurement.

A method is described for selecting fibers meeting requirements of a second minimum bandwidth at a second wavelength based on differential mode delay data measured at a first wavelength different from the second wavelength. The method comprises measuring the differential mode delay (DMD) data for the multimode fiber at the first wavelength, wherein the DMD data comprises output laser pulse data as a function of the radial position of an input laser pulse having the first wavelength; selecting the multimode fiber based on meeting requirements of the second minimum bandwidth at the second wavelength based on a second set of criteria, comprising a second criterion comprising: the radial dependence of the differential mode delay data measured at the first wavelength being within a pre-determined tolerance of a pre-determined reference function constructed by concatenating two or more even-order polynomials having the form:

[00001]${\left(r\right)}_{\mathrm{ref},k}=c_{0,k}+{c_{1,k}\left(\frac{r}{a}\right)}^2+{c_{2,k}\left(\frac{r}{a}\right)}^4.$

In this invention, a novel technique is introduced to measure chromatic dispersion (CD) in optical fibers. This technique is based on a relatively low-frequency optoelectronic oscillation (OEO) to provide fast, precise and low cost method for CD measurement that can be implemented easily in commercial instruments. In addition, another technique is presented to compensate for fiber thermal fluctuations during measurement which is based on a second simultaneously oscillating OEO. The proposed setup is implemented to measure the CD in normal single mode fibers with lengths of 40 km, 10 km, 1 km. Moreover, it is implemented to measure CD in 400 m of nonzero dispersion shifted fiber to test the system ability to resolve small chromatic delays. The proposed setup can resolve delays less than 0.1 ps/nm (which can be further improved by increasing the oscillation frequency) and measure CD with precision as low as 0.005 ps/nm.km as low as 20 seconds over a wavelength range from 1500 to 1630 nm. Further improvements may be possible by slightly better system design.

A method of characterizing a multimode optical fiber results in a measure of estimated modal bandwidth (EMB) that is independent of the bandwidth of the light used in the characterization. The method includes propagating pulses of light along the multimode optical fiber at prescribed radial positions relative to an optical axis of the multimode optical fiber and detecting output pulses from the multimode optical fiber corresponding to the pulses of light propagated along the multimode optical fiber at the prescribed radial positions relative to the optical axis of the multimode optical fiber. An estimated modal bandwidth of the multimode optical fiber is calculated in a manner that accounts for chromatic dispersion of the multimode optical fiber.

In some examples, an apparatus receives a first measurement of a plurality of wavelength channels obtained at a first location of an optical medium, and a second measurement of the plurality of wavelength channels obtained at a second location of the optical medium. The apparatus computes a value relating to dispersion in the optical medium by correlating the first measurement and the second measurement.

The invention relates to a method for qualifying the actual effective modal bandwidth of a multimode optical fiber over a predetermined wavelength range, comprising the steps of: carrying out (30) a Dispersion Modal Delay (DMD) measurement of the multimode optical fiber at a single wavelength to obtain an actual DMD plot; generating (32) at least two distinct modified DMD plots from the actual DMD plot, each modified DMD plot being generated by applying to the recorded traces a temporal delay t that increases in absolute values with the radial offset value r.sub.offset, each modified DMD plot being associated with a predetermined bandwidth threshold (S1; S2); for each modified DMD plot, computing (33) an effective modal bandwidth as a function of said modified DMD plot and comparing (34) the computed effective modal bandwidth (EMBc.sub.1; EMBc.sub.2) with the bandwidth threshold value to which the modified DMD plot is associated; (35) qualifying the actual effective modal bandwidth as a function of results from the comparing step.

A method is used to select a multimode fiber meeting requirements of a first minimum bandwidth at a first wavelength and a second minimum bandwidth at a second wavelength different from the first wavelength. Differential mode delay (DMD) data is measured for the multimode fiber at the first wavelength. The DMD data comprises output laser pulse data as a function of the radial position of an input laser pulse having the first wavelength. The DMD data is transformed into mode group space, to obtain relative mode group delay data as a function of mode group. The multimode fiber is selected based on meeting requirements of the first minimum bandwidth at the first wavelength based on a first set of criteria, comprising a first criterion using as input the measured differential mode delay (DMD) data for the multimode fiber measured at the first wavelength. The multimode fiber is selected based on meeting requirements of the second minimum bandwidth at the second wavelength based on a second set of criteria, comprising: a second criterion using as input the relative mode group delay data. A related system is also described.

An optical characteristic inspection circuit includes, in order, an optical input element, an optical splitter circuit including a resistor, a first optical circuit to be inspected connected to one output of the optical splitter circuit, a second optical circuit to be inspected connected to another output of the optical splitter circuit, and a photodetector that detects an intensity of light transmitted through the first optical circuit to be inspected and an intensity of light transmitted through the second optical circuit to be inspected. Therefore, the present invention can provide an optical characteristic inspection circuit capable of reducing man-hours required for optical characteristic inspection.

A Fourier-transformer performs Fourier transform on a filter coefficient output from an adaptive equalizer which comprises a finite impulse response filter of N taps (N represents an integer of 2 or more) in a time direction. An eigenvalue sum calculator integrates a frequency-differentiation result of the Fourier-transformed filter coefficient and a complex conjugate of the Fourier-transformed filter coefficient to calculate a matrix, and calculates a sum of two eigenvalues of the matrix. A proportionality factor calculator calculates a proportionality factor for frequency from the sum of the two eigenvalues.