US20020044274A1 - Apparatus and method for measuring optical characteristics and recording medium - Google Patents
Apparatus and method for measuring optical characteristics and recording medium Download PDFInfo
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- US20020044274A1 US20020044274A1 US09/975,557 US97555701A US2002044274A1 US 20020044274 A1 US20020044274 A1 US 20020044274A1 US 97555701 A US97555701 A US 97555701A US 2002044274 A1 US2002044274 A1 US 2002044274A1
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- wavelength light
- modulating frequency
- modulating
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- variable wavelength
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/335—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face using two or more input wavelengths
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/333—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face using modulated input signals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/338—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by measuring dispersion other than PMD, e.g. chromatic dispersion
Definitions
- the present invention relates to measuring chromatic dispersion characteristic of a DUT (Device Under Test) such as an optical fiber, and more specifically relates to technology for measuring without being influenced by a contraction/extension of the DUT.
- DUT Device Under Test
- the present invention relates to measuring chromatic dispersion characteristic of a DUT (Device Under Test) such as an optical fiber, and more specifically relates to technology for measuring without being influenced by a contraction/extension of the DUT.
- FIG. 4 shows a constitution of its measuring system.
- the measuring system is divided into a light source system 10 and a characteristics measuring system 20 .
- a variable wavelength light source 12 in the light source system 10 changes a wavelength to generate light with a wavelength of ⁇ x (variable wavelength light).
- a fixed wavelength light source 13 fixes a wavelength to generate light with a wavelength of ⁇ 0 (fixed wavelength light).
- ⁇ 0 is a wavelength which provides the minimum chromatic dispersion in a DUT 30 .
- the variable wavelength light and the fixed wavelength light are modulated with a frequency of f respectively by an optical modulator 15 a , and an optical modulator 15 b , and are composed by a multiplexer 16 .
- the frequency f is provided by power supplies for modulating, which are omitted in the drawing.
- Light composed in the multiplexer 16 enters into the DUT 30 .
- the light transmitted through the DUT 30 enters an optical demultiplexer 21 of the characteristics measuring system 20 .
- the optical demultiplexer 21 separates the transmitted light through the DUT 30 into light with the wavelength of ⁇ x and light with the wavelength of ⁇ 0.
- An optical/electrical converter for measuring 22 a and an optical/electrical converter for reference 22 b respectively apply optical/electrical conversion to the light with the wavelength of ⁇ x and the light with the wavelength of ⁇ 0, and a phase comparator 24 detects a phase difference between an output from the optical/electrical converter for measuring 22 a and an output from the optical/electrical converter for reference 22 b.
- the transmitted light with the wavelength of ⁇ x is affected by the chromatic dispersion and the contraction/extension of DUT 30 .
- the transmitted light with the wavelength of ⁇ 0 is affected only by the contraction/extension of DUT 30 . This is because ⁇ 0 is the wavelength which provides the minimum chromatic dispersion in DUT 30 .
- detecting the phase difference between the transmitted light with the wavelength of ⁇ x and the transmitted light with the wavelength of ⁇ 0 removes the affect of contraction/extension of DUT 30 .
- a purpose of the present invention is to provide an apparatus and the like for measuring the chromatic dispersion when the modulating frequency for the variable wavelength light source and the modulating frequency for the fixed wavelength light source for reference are different.
- the phase difference between the phase of variable wavelength light component and the phase of signal having the first modulating frequency includes the affect of contraction/extension and the like of the device under test.
- the phase difference between the phase of fixed wavelength light component and the phase of signal having the second modulating frequency includes only the affect of contraction/extension and the like of the device under test.
- the “true phase difference” here is a phase difference when the affect of contraction/extension of device under test is removed.
- the present invention as described in claim 2 is the optical characteristics measuring apparatus as claimed in claim 1, wherein the phase comparing unit is provided with: a variable wavelength light phase comparing unit for obtaining a phase difference between the variable wavelength light component and the signal having the first modulating frequency; a fixed wavelength light phase comparing unit for obtaining a phase difference between the fixed wavelength light component and the signal having the second modulating frequency; a phase difference converting unit for converting the phase difference calculated by the fixed wavelength light phase comparing unit to what corresponding to the first modulating frequency; and a true phase difference calculating unit for calculating a true phase difference from the phase difference calculated by the variable wavelength light phase comparing unit and the converted result of the phase difference converting unit.
- the optical characteristics measuring apparatus as claimed in claim 1 further includes a characteristics calculating unit for calculating group delay or chromatic dispersion of the device under test from the true phase difference.
- an optical characteristics measuring method for measuring characteristics of light transmitted thorough a device under test includes: a variable wavelength light generating step for generating variable wavelength light; a fixed wavelength light generating step for generating fixed wavelength light; a variable wavelength light modulating step for receiving a signal having a first modulating frequency, and modulating the variable wavelength light with the first modulating frequency; a fixed wavelength light modulating step for receiving a signal having a second modulating frequency, which is different from the first modulating frequency, and modulating the fixed wavelength light with the second modulating frequency; a composite light generating step for entering composite light composed of the variable wavelength light and the fixed wavelength light into the device under test; a wavelength component extracting step for extracting a fixed wavelength light component and a variable wavelength light component from transmitted light transmitted from the device under test; and a phase comparing step for measuring a true phase difference between the variable wavelength light component having the first modulating frequency and the signal having the first modulating frequency based on the variable wavelength light component, the fixed wavelength light component
- the present invention as described in claim 5, is a computer-readable medium having a program of instructions for execution by the computer to perform an optical characteristics measuring process for measuring characteristics of light transmitted thorough a device under test.
- the optical characteristics measuring process includes: a variable wavelength light generating processing for generating variable wavelength light; a fixed wavelength light generating processing for generating fixed wavelength light; a variable wavelength light modulating processing for receiving a signal having a first modulating frequency, and modulating the variable wavelength light with the first modulating frequency; a fixed wavelength light modulating processing for receiving a signal having a second modulating frequency, which is different from the first modulating frequency, and modulating the fixed wavelength light with the second modulating frequency; a composite light generating processing for entering composite light composed of the variable wavelength light and the fixed wavelength light into the device under test; a wavelength component extracting processing for extracting a fixed wavelength light component and a variable wavelength light component from transmitted light transmitted from the device under test; and a phase comparing processing for measuring a true phase difference between the variable wavelength light component having the first modulating frequency and
- FIG. 1 is a block diagram showing a constitution of an optical characteristics measuring apparatus relating to an embodiment of the present invention
- FIG. 2 is a drawing showing a principle of an operation of the embodiment of present invention
- FIG. 3 is a flowchart showing an operation of the embodiment of present invention.
- FIG. 4 is a block diagram showing a constitution of an optical characteristics measuring apparatus of prior art.
- FIG. 1 is a block diagram showing a constitution of an optical characteristics measuring apparatus relating to an embodiment of the present invention.
- the optical characteristics measuring apparatus relating to the embodiment of the present invention includes a light source system 10 connected with one end of a DUT 30 , and a characteristics measuring system 20 connected with the other end of DUT 30 .
- the DUT 30 is what transmits light such as an optical fiber.
- the light source system 10 is provided with a variable wavelength light source 12 , a fixed wavelength light source 13 , power supplies for modulating 14 a and 14 b , optical modulators 15 a and 15 b , and a multiplexer 16 .
- the variable wavelength light source 12 generates variable wavelength light whose wavelength changes.
- the variable wavelength light source 12 sweeps the wavelength ⁇ x of variable wavelength light.
- the fixed wavelength light source 13 generates fixed wavelength light whose wavelength is fixed. It is desirable that the wavelength of fixed wavelength light is fixed to the wavelength ⁇ 0, which provides the minimum chromatic dispersion in DUT 30 .
- the power supply for modulating 14 a generates an electrical signal having a first frequency of fmx.
- the power supply for modulating 14 b generates an electrical signal having a second frequency of fm 0 .
- the optical modulator 15 a modulates the variable wavelength light with the first frequency fmx.
- the optical modulator 15 a receives the electrical signal generated by the power supply for modulating 14 a to obtain the first frequency fmx.
- the optical modulator 15 b modulates the fixed wavelength light with the second frequency fm 0 .
- the optical modulator 15 b receives the electrical signal generated by the power supply for modulating 14 b to obtain the second frequency fm 0 .
- the optical modulators 15 a and 15 b include lithium niobate (LN). As long as they can modulate light, they do not necessarily include LN.
- the multiplexer 16 composes the variable wavelength light with the fixed wavelength light to generate composite light, and enters it into the DUT 30 .
- the composite light provided for the DUT 30 is transmitted through the DUT 30 .
- the light which has been transmitted through the DUT 30 is referred as transmitted light.
- the characteristics measuring system 20 is provided with an optical/electrical converter 22 , a detector 23 , a variable wavelength light phase comparator 24 , a fixed wavelength light phase comparator 25 , a phase difference converter 26 , a true phase difference calculator 27 , and a characteristics calculator 28 .
- a phase comparing means comprises the variable wavelength light phase comparator 24 , the fixed wavelength light phase comparator 25 , the phase difference converter 26 , and the true phase difference calculator 27 .
- the optical/electrical converter 22 applies optical/electrical conversion to the transmitted light.
- the detector 23 extracts a variable wavelength light component modulated with the first frequency fmx, and a fixed wavelength light component modulated with the second frequency fm 0 from an electrical signal obtained by applying optical/electrical conversion to the transmitted light.
- the variable wavelength light phase comparator 24 measures a phase difference between a phase ⁇ x of the variable wavelength light component and a phase ⁇ x′ of an electrical signal including the first frequency fmx generated by the power supply for modulating 14 a .
- the fixed wavelength light phase comparator 25 measures a phase difference between a phase ⁇ 0 of the fixed wavelength light component and a phase ⁇ 0 ′ of an electrical signal including the second frequency fm 0 generated by the power supply for modulating 14 b .
- the phase difference converter 26 converts the phase difference ⁇ 0 ⁇ 0 ′ calculated by the fixed wavelength light phase comparator 25 into what corresponding to the first modulating frequency fmx.
- the true phase difference calculator 27 obtains a true phase difference between the variable wavelength light component having first modulating frequency fmx and the electrical signal including the first modulating frequency fmx from the phase difference ⁇ x ⁇ x′ calculated by the variable wavelength light phase comparator 24 , and the converted result of phase difference converter 26 .
- the “true phase difference” here is a phase difference when the affect of contraction/extension of DUT 30 is removed.
- the characteristics calculator 28 calculates the group delay or the chromatic dispersion of the device under test from the true phase difference.
- a group delay characteristic is obtained from a relationship between the true phase difference and the first modulating frequency fmx.
- the chromatic dispersion characteristic is obtained by differentiating the group delay characteristic by the wavelength.
- phase comparing means comprising the variable wavelength light phase comparator 24 , the fixed wavelength light phase comparator 25 , the phase difference converter 26 , and the true phase difference calculator 27 obtains the true phase difference which excludes the affect of contraction/extension of DUT 30 while referring to FIG. 2.
- the phase ⁇ x of variable wavelength light component is a sum of the phase ⁇ x′ of electrical signal including the first frequency fmx generated by the power supply for modulating 14 a , a phase difference ⁇ due to the chromatic dispersion, and a phase difference ⁇ ex caused by the contraction/extension of DUT 30 .
- ⁇ xt is a phase of the variable wavelength light component when there is no affect of the contraction/extension of DUT 30 . Relationship among ⁇ x, ⁇ x′, ⁇ xt and the like is described in FIG. 2 ( a ).
- the variable wavelength light phase comparator 24 is provided with ⁇ x and ⁇ x′, and obtains ⁇ x ⁇ x′. However, ⁇ ex is not obtained. Thus, the true phase difference ⁇ is not obtained.
- ⁇ e 0 which is a difference between the phase ⁇ 0 of fixed wavelength light component and the phase ⁇ 0 ′ of electrical signal having the second frequency fm 0 generated by the power supply for modulating 14 b is caused by the contraction/extension of DUT 30 , and is not affected by the chromatic dispersion.
- FIG. 2 ( b ) shows a relationship among ⁇ 0 , ⁇ 0 ′ and the like.
- the fixed wavelength light phase comparator 25 is provided with ⁇ 0 and ⁇ 0 ′, and obtains ⁇ 0 ⁇ 0 ′.
- Both ⁇ ex and ⁇ e 0 are caused by the contraction/extension of DUT 30 . Thus, they have the relationship shown in the FIG. 2 ( c ), for example.
- the phase difference converter 26 uses the relationship to calculate ⁇ ex from ⁇ e 0 . It converts the phase difference ⁇ 0 ⁇ 0 ′ calculated by the fixed wavelength light phase comparator 25 to what corresponding to the first modulating frequency fmx.
- the true phase difference calculator 27 receives ⁇ x ⁇ x′ from the variable wavelength light phase comparator 24 , and ⁇ ex from the phase difference converter 26 to obtain the true phase difference ⁇ .
- the variable wavelength light source 12 of light source system 10 changes wavelength to generate light with the wavelength of ⁇ x (variable wavelength light).
- the fixed wavelength light source 13 fixes wavelength to generate light with the wavelength of ⁇ 0 (fixed wavelength light).
- the ⁇ 0 is a wavelength which provides the minimum chromatic dispersion in DUT 30 .
- the variable wavelength light is modulated by the optical modulator 15 a with the first frequency fmx, and the fixed wavelength light is modulated by the optical modulator 15 b with the frequency fm 0 (S 10 ), and they are composed by the multiplexer 16 (S 12 ).
- the power supply for modulating 14 a provides the optical modulator 15 a with the first frequency fmx.
- the power supply for modulating 14 b provides the optical modulator 15 b with the second frequency fm 0 .
- the light composed by the multiplexer 16 is provided for the DUT 30 .
- the light transmitted through the DUT 30 is provided for the optical/electrical converter 22 of characteristics measuring system 20 .
- the optical/electrical converter 22 applies optical/electrical conversion to the transmitted light to provide for the detector 23 (S 14 ).
- the detector 23 extracts the variable wavelength light component and the fixed wavelength light component from the transmitted light which is applied with the optical/electrical conversion (S 16 ).
- the variable wavelength light component is provided for the variable wavelength light phase comparator 24 .
- the fixed wavelength light component is provided for the fixed wavelength light phase comparator 25 .
- the electrical signal generated by the power supply for modulating 14 a is provided for the variable wavelength light phase comparator 24 .
- the electrical signal generated by the power supply for modulating 14 b is provided for the fixed wavelength light phase comparator 25 .
- the variable wavelength light phase comparator 24 obtains the phase difference between the phase ⁇ x of variable wavelength light component and the phase ⁇ x′ of electrical signal including the first frequency fmx generated by the power supply for modulating 14 a (S 20 ). Then, the fixed wavelength light phase comparator 25 obtains the phase difference between the phase ⁇ 0 of fixed wavelength light component and the phase ⁇ 0 ′ of electrical signal including the second frequency fm 0 generated by the power supply for modulating 14 b (S 22 ). The fixed wavelength light phase comparator 25 provides the phase difference converter 26 with ⁇ 0 ⁇ 0 ′, that is ⁇ e 0 . The phase difference converter 26 calculates ⁇ ex from ⁇ e 0 (S 24 ).
- the true phase difference calculator 27 receives ⁇ x ⁇ x′ from the variable wavelength light phase comparator 24 , receives ⁇ ex from the phase difference converter 26 , and obtains the true phase difference ⁇ (S 26 ). Finally, the characteristics calculator 28 uses the true phase difference ⁇ to obtain the group delay or the chromatic dispersion of DUT 30 (S 28 ).
- a computer provided with a CPU, a hard disk, and a medium reading apparatus (such as a floppy disk and a CD-ROM) reads a medium storing a program for realizing the individual parts described above in the medium reading apparatus, and installs the program on the hard disk.
- a medium reading apparatus such as a floppy disk and a CD-ROM
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Abstract
Description
- 1 . Field of the Invention
- The present invention relates to measuring chromatic dispersion characteristic of a DUT (Device Under Test) such as an optical fiber, and more specifically relates to technology for measuring without being influenced by a contraction/extension of the DUT.
- 2 . Description of the Related Art
- When chromatic dispersion characteristic of a device under test (DUT) such as an optical fiber are measured, it is desirable to measure while eliminating the influence of a contraction/extension of the DUT. A technology for measuring without being influenced by the contraction/extension of the DUT is described in Publication of Japanese Patent Laid-Open No. H01-291141.
- FIG. 4 shows a constitution of its measuring system. As described in FIG. 4, the measuring system is divided into a
light source system 10 and acharacteristics measuring system 20. A variablewavelength light source 12 in thelight source system 10 changes a wavelength to generate light with a wavelength of λx (variable wavelength light). A fixedwavelength light source 13 fixes a wavelength to generate light with a wavelength of λ0 (fixed wavelength light). λ0 is a wavelength which provides the minimum chromatic dispersion in aDUT 30. The variable wavelength light and the fixed wavelength light are modulated with a frequency of f respectively by anoptical modulator 15 a, and anoptical modulator 15 b, and are composed by amultiplexer 16. The frequency f is provided by power supplies for modulating, which are omitted in the drawing. - Light composed in the
multiplexer 16 enters into theDUT 30. The light transmitted through theDUT 30 enters anoptical demultiplexer 21 of thecharacteristics measuring system 20. Theoptical demultiplexer 21 separates the transmitted light through theDUT 30 into light with the wavelength of λx and light with the wavelength of λ0. An optical/electrical converter for measuring 22 a and an optical/electrical converter forreference 22 b respectively apply optical/electrical conversion to the light with the wavelength of λx and the light with the wavelength of λ0, and aphase comparator 24 detects a phase difference between an output from the optical/electrical converter for measuring 22 a and an output from the optical/electrical converter forreference 22 b. - The transmitted light with the wavelength of λx is affected by the chromatic dispersion and the contraction/extension of
DUT 30. The transmitted light with the wavelength of λ0 is affected only by the contraction/extension ofDUT 30. This is because λ0 is the wavelength which provides the minimum chromatic dispersion inDUT 30. Thus, detecting the phase difference between the transmitted light with the wavelength of λx and the transmitted light with the wavelength of λ0 removes the affect of contraction/extension ofDUT 30. - However, it is required to provide the
optical modulator 15 a and theoptical modulator 15 b with the same frequency for modulating. In other words, it is impossible to set the frequency for modulating in theoptical modulator 15 a and the frequency for modulating in theoptical modulator 15 b different from each other. - A purpose of the present invention is to provide an apparatus and the like for measuring the chromatic dispersion when the modulating frequency for the variable wavelength light source and the modulating frequency for the fixed wavelength light source for reference are different.
- According to the present invention as described in
claim 1, an optical characteristics measuring apparatus for measuring characteristics of light transmitted thorough a device under test includes: a variable wavelength light source for generating variable wavelength light; a fixed wavelength light source for generating fixed wavelength light; a variable wavelength light modulating unit for receiving a signal having a first modulating frequency, and modulating the variable wavelength light with the first modulating frequency; a fixed wavelength light modulating unit for receiving a signal having a second modulating frequency, which is different from the first modulating frequency, and modulating the fixed wavelength light with the second modulating frequency; a composite light generating unit for entering composite light composed of the variable wavelength light and the fixed wavelength light into the device under test; a wavelength component extracting unit for extracting a fixed wavelength light component and a variable wavelength light component from transmitted light transmitted from the device under test; and a phase comparing unit for measuring a true phase difference between the variable wavelength light component having the first modulating frequency and the signal having the first modulating frequency based on the variable wavelength light component, the fixed wavelength light component, the signal having the first modulating frequency, and the signal having the second modulating frequency; wherein characteristics of the device under test is obtained from the true phase difference. - With the optical characteristics measuring apparatus constituted as described above, the phase difference between the phase of variable wavelength light component and the phase of signal having the first modulating frequency includes the affect of contraction/extension and the like of the device under test. On the other hand, the phase difference between the phase of fixed wavelength light component and the phase of signal having the second modulating frequency includes only the affect of contraction/extension and the like of the device under test. Thus, it is possible to remove the affect of contraction/extension and the like of the device under test from the phase difference between the phase of variable wavelength light component and the phase of signal having the first modulating frequency by taking into account of the phase difference between the phase of fixed wavelength light component and the phase of signal having the second modulating frequency. In other words, a true phase difference is measured. Also, the first modulating frequency may be different from the second modulating frequency.
- The “true phase difference” here is a phase difference when the affect of contraction/extension of device under test is removed.
- The present invention as described in claim 2, is the optical characteristics measuring apparatus as claimed in
claim 1, wherein the phase comparing unit is provided with: a variable wavelength light phase comparing unit for obtaining a phase difference between the variable wavelength light component and the signal having the first modulating frequency; a fixed wavelength light phase comparing unit for obtaining a phase difference between the fixed wavelength light component and the signal having the second modulating frequency; a phase difference converting unit for converting the phase difference calculated by the fixed wavelength light phase comparing unit to what corresponding to the first modulating frequency; and a true phase difference calculating unit for calculating a true phase difference from the phase difference calculated by the variable wavelength light phase comparing unit and the converted result of the phase difference converting unit. - According to the present invention as described in claim 3, the optical characteristics measuring apparatus as claimed in
claim 1 further includes a characteristics calculating unit for calculating group delay or chromatic dispersion of the device under test from the true phase difference. - According to the present invention as described in
claim 4, an optical characteristics measuring method for measuring characteristics of light transmitted thorough a device under test includes: a variable wavelength light generating step for generating variable wavelength light; a fixed wavelength light generating step for generating fixed wavelength light; a variable wavelength light modulating step for receiving a signal having a first modulating frequency, and modulating the variable wavelength light with the first modulating frequency; a fixed wavelength light modulating step for receiving a signal having a second modulating frequency, which is different from the first modulating frequency, and modulating the fixed wavelength light with the second modulating frequency; a composite light generating step for entering composite light composed of the variable wavelength light and the fixed wavelength light into the device under test; a wavelength component extracting step for extracting a fixed wavelength light component and a variable wavelength light component from transmitted light transmitted from the device under test; and a phase comparing step for measuring a true phase difference between the variable wavelength light component having the first modulating frequency and the signal having the first modulating frequency based on the variable wavelength light component, the fixed wavelength light component, the signal having the first modulating frequency, and the signal having the second modulating frequency; wherein characteristics of the device under test is obtained from the true phase difference. - The present invention as described in claim 5, is a computer-readable medium having a program of instructions for execution by the computer to perform an optical characteristics measuring process for measuring characteristics of light transmitted thorough a device under test. The optical characteristics measuring process includes: a variable wavelength light generating processing for generating variable wavelength light; a fixed wavelength light generating processing for generating fixed wavelength light; a variable wavelength light modulating processing for receiving a signal having a first modulating frequency, and modulating the variable wavelength light with the first modulating frequency; a fixed wavelength light modulating processing for receiving a signal having a second modulating frequency, which is different from the first modulating frequency, and modulating the fixed wavelength light with the second modulating frequency; a composite light generating processing for entering composite light composed of the variable wavelength light and the fixed wavelength light into the device under test; a wavelength component extracting processing for extracting a fixed wavelength light component and a variable wavelength light component from transmitted light transmitted from the device under test; and a phase comparing processing for measuring a true phase difference between the variable wavelength light component having the first modulating frequency and the signal having the first modulating frequency based on the variable wavelength light component, the fixed wavelength light component, the signal having the first modulating frequency, and the signal having the second modulating frequency; wherein characteristics of the device under test is obtained from the true phase difference.
- FIG. 1 is a block diagram showing a constitution of an optical characteristics measuring apparatus relating to an embodiment of the present invention;
- FIG. 2 is a drawing showing a principle of an operation of the embodiment of present invention;
- FIG. 3 is a flowchart showing an operation of the embodiment of present invention; and
- FIG. 4 is a block diagram showing a constitution of an optical characteristics measuring apparatus of prior art.
- The following section describes an embodiment of the present invention referring to drawings.
- FIG. 1 is a block diagram showing a constitution of an optical characteristics measuring apparatus relating to an embodiment of the present invention. The optical characteristics measuring apparatus relating to the embodiment of the present invention includes a
light source system 10 connected with one end of aDUT 30, and acharacteristics measuring system 20 connected with the other end ofDUT 30. TheDUT 30 is what transmits light such as an optical fiber. - The
light source system 10 is provided with a variablewavelength light source 12, a fixedwavelength light source 13, power supplies for modulating 14 a and 14 b,optical modulators multiplexer 16. The variablewavelength light source 12 generates variable wavelength light whose wavelength changes. The variablewavelength light source 12 sweeps the wavelength λx of variable wavelength light. The fixedwavelength light source 13 generates fixed wavelength light whose wavelength is fixed. It is desirable that the wavelength of fixed wavelength light is fixed to the wavelength λ0, which provides the minimum chromatic dispersion inDUT 30. The power supply for modulating 14 a generates an electrical signal having a first frequency of fmx. The power supply for modulating 14 b generates an electrical signal having a second frequency of fm0. Theoptical modulator 15 a modulates the variable wavelength light with the first frequency fmx. Theoptical modulator 15 a receives the electrical signal generated by the power supply for modulating 14 a to obtain the first frequency fmx. Theoptical modulator 15 b modulates the fixed wavelength light with the second frequency fm0. Theoptical modulator 15 b receives the electrical signal generated by the power supply for modulating 14 b to obtain the second frequency fm0. Theoptical modulators multiplexer 16 composes the variable wavelength light with the fixed wavelength light to generate composite light, and enters it into theDUT 30. - The composite light provided for the
DUT 30 is transmitted through theDUT 30. The light which has been transmitted through theDUT 30 is referred as transmitted light. - The
characteristics measuring system 20 is provided with an optical/electrical converter 22, adetector 23, a variable wavelengthlight phase comparator 24, a fixed wavelengthlight phase comparator 25, aphase difference converter 26, a truephase difference calculator 27, and acharacteristics calculator 28. A phase comparing means comprises the variable wavelengthlight phase comparator 24, the fixed wavelengthlight phase comparator 25, thephase difference converter 26, and the truephase difference calculator 27. - The optical/
electrical converter 22 applies optical/electrical conversion to the transmitted light. Thedetector 23 extracts a variable wavelength light component modulated with the first frequency fmx, and a fixed wavelength light component modulated with the second frequency fm0 from an electrical signal obtained by applying optical/electrical conversion to the transmitted light. - The variable wavelength
light phase comparator 24 measures a phase difference between a phase φx of the variable wavelength light component and a phase φx′ of an electrical signal including the first frequency fmx generated by the power supply for modulating 14 a. The fixed wavelengthlight phase comparator 25 measures a phase difference between a phase φ0 of the fixed wavelength light component and a phase φ0′ of an electrical signal including the second frequency fm0 generated by the power supply for modulating 14 b. Thephase difference converter 26 converts the phase difference φ0−φ0′ calculated by the fixed wavelengthlight phase comparator 25 into what corresponding to the first modulating frequency fmx. The truephase difference calculator 27 obtains a true phase difference between the variable wavelength light component having first modulating frequency fmx and the electrical signal including the first modulating frequency fmx from the phase difference φx−φx′ calculated by the variable wavelengthlight phase comparator 24, and the converted result ofphase difference converter 26. The “true phase difference” here is a phase difference when the affect of contraction/extension ofDUT 30 is removed. Thecharacteristics calculator 28 calculates the group delay or the chromatic dispersion of the device under test from the true phase difference. A group delay characteristic is obtained from a relationship between the true phase difference and the first modulating frequency fmx. The chromatic dispersion characteristic is obtained by differentiating the group delay characteristic by the wavelength. - The following section describes a principle for how the phase comparing means comprising the variable wavelength
light phase comparator 24, the fixed wavelengthlight phase comparator 25, thephase difference converter 26, and the truephase difference calculator 27 obtains the true phase difference which excludes the affect of contraction/extension ofDUT 30 while referring to FIG. 2. - The phase φ x of variable wavelength light component is a sum of the phase φx′ of electrical signal including the first frequency fmx generated by the power supply for modulating14 a, a phase difference φ due to the chromatic dispersion, and a phase difference φex caused by the contraction/extension of
DUT 30. φxt is a phase of the variable wavelength light component when there is no affect of the contraction/extension ofDUT 30. Relationship among φx, φx′, φxt and the like is described in FIG. 2 (a). The variable wavelengthlight phase comparator 24 is provided with φx and φx′, and obtains φx−φx′. However, φex is not obtained. Thus, the true phase difference φ is not obtained. - On the other hand, φe0, which is a difference between the phase φ0 of fixed wavelength light component and the phase φ0′ of electrical signal having the second frequency fm0 generated by the power supply for modulating 14 b is caused by the contraction/extension of
DUT 30, and is not affected by the chromatic dispersion. This is because the wavelength λ0 of fixed wavelength light generated by the fixedwavelength light source 13 is fixed to a value which provides the minimum chromatic dispersion inDUT 30. FIG. 2 (b) shows a relationship among φ0, φ0′ and the like. The fixed wavelengthlight phase comparator 25 is provided with φ0 and φ0′, and obtains φ0−φ0′. - Both φex and φe0 are caused by the contraction/extension of
DUT 30. Thus, they have the relationship shown in the FIG. 2 (c), for example. Thephase difference converter 26 uses the relationship to calculate φex from φe0. It converts the phase difference φ0−φ0′ calculated by the fixed wavelengthlight phase comparator 25 to what corresponding to the first modulating frequency fmx. - The true
phase difference calculator 27 receives φx−φx′ from the variable wavelengthlight phase comparator 24, and φex from thephase difference converter 26 to obtain the true phase difference φ. - The flowchart in FIG. 3 describes the operation of embodiment of present invention. The variable wavelength
light source 12 oflight source system 10 changes wavelength to generate light with the wavelength of φx (variable wavelength light). The fixedwavelength light source 13 fixes wavelength to generate light with the wavelength of λ0 (fixed wavelength light). The λ0 is a wavelength which provides the minimum chromatic dispersion inDUT 30. The variable wavelength light is modulated by theoptical modulator 15 a with the first frequency fmx, and the fixed wavelength light is modulated by theoptical modulator 15 b with the frequency fm0 (S10), and they are composed by the multiplexer 16 (S12). The power supply for modulating 14 a provides theoptical modulator 15 a with the first frequency fmx. The power supply for modulating 14 b provides theoptical modulator 15 b with the second frequency fm0. - The light composed by the
multiplexer 16 is provided for theDUT 30. The light transmitted through theDUT 30 is provided for the optical/electrical converter 22 ofcharacteristics measuring system 20. The optical/electrical converter 22 applies optical/electrical conversion to the transmitted light to provide for the detector 23 (S14). Thedetector 23 extracts the variable wavelength light component and the fixed wavelength light component from the transmitted light which is applied with the optical/electrical conversion (S16). The variable wavelength light component is provided for the variable wavelengthlight phase comparator 24. The fixed wavelength light component is provided for the fixed wavelengthlight phase comparator 25. The electrical signal generated by the power supply for modulating 14 a is provided for the variable wavelengthlight phase comparator 24. The electrical signal generated by the power supply for modulating 14 b is provided for the fixed wavelengthlight phase comparator 25. - The variable wavelength
light phase comparator 24 obtains the phase difference between the phase φx of variable wavelength light component and the phase φx′ of electrical signal including the first frequency fmx generated by the power supply for modulating 14 a (S20). Then, the fixed wavelengthlight phase comparator 25 obtains the phase difference between the phase φ0 of fixed wavelength light component and the phase φ0′ of electrical signal including the second frequency fm0 generated by the power supply for modulating 14 b (S22). The fixed wavelengthlight phase comparator 25 provides thephase difference converter 26 with φ0−φ0′, that is φe0. Thephase difference converter 26 calculates φex from φe0 (S24). The truephase difference calculator 27 receives φx−φx′ from the variable wavelengthlight phase comparator 24, receives φex from thephase difference converter 26, and obtains the true phase difference φ (S26). Finally, thecharacteristics calculator 28 uses the true phase difference φ to obtain the group delay or the chromatic dispersion of DUT 30 (S28). - With the embodiment of present invention, it is possible to obtain the group delay or the chromatic dispersion of
DUT 30 by removing the affect of contraction/extension ofDUT 30 and the like when the first modulating frequency fmx and the second modulating frequency fm0 are different from each other. - The embodiment described above is also realized as follows. A computer provided with a CPU, a hard disk, and a medium reading apparatus (such as a floppy disk and a CD-ROM) reads a medium storing a program for realizing the individual parts described above in the medium reading apparatus, and installs the program on the hard disk. This method also realizes the function described above.
- With the present invention, it is possible to obtain characteristics of a device under test by removing an affect of contraction/extension of the device under test when the first modulating frequency and the second modulating frequency are different from each other.
Claims (5)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2000313392A JP2002122514A (en) | 2000-10-13 | 2000-10-13 | Light characteristic measuring device, method and recording medium |
JP2000-313392 | 2000-10-13 |
Publications (2)
Publication Number | Publication Date |
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US20020044274A1 true US20020044274A1 (en) | 2002-04-18 |
US6433865B1 US6433865B1 (en) | 2002-08-13 |
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US09/975,557 Expired - Fee Related US6433865B1 (en) | 2000-10-13 | 2001-10-12 | Apparatus and method for measuring optical characteristics and recording medium |
Country Status (6)
Country | Link |
---|---|
US (1) | US6433865B1 (en) |
JP (1) | JP2002122514A (en) |
CA (1) | CA2358723C (en) |
DE (1) | DE10150539A1 (en) |
FR (1) | FR2815408B1 (en) |
GB (1) | GB2372101B8 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7016023B2 (en) | 2003-02-21 | 2006-03-21 | Agilent Technologies, Inc. | Chromatic dispersion measurement |
US10404397B2 (en) * | 2015-12-23 | 2019-09-03 | Adva Optical Networking Se | Wavelength division multiplexed telecommunication system with automatic compensation of chromatic dispersion |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7206516B2 (en) * | 2002-04-30 | 2007-04-17 | Pivotal Decisions Llc | Apparatus and method for measuring the dispersion of a fiber span |
US6724468B2 (en) * | 2002-07-31 | 2004-04-20 | Agilent Technologies, Inc | Single sweep phase shift method and apparatus for measuring chromatic and polarization dependent dispersion |
US10093843B2 (en) | 2013-10-15 | 2018-10-09 | Enrad Ltd. | Elastomer and/or composite based material for thermal energy storage |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CA1195138A (en) * | 1983-06-06 | 1985-10-15 | Paul J. Vella | Measuring chromatic dispersion of fibers |
JPS63210743A (en) * | 1987-02-27 | 1988-09-01 | Anritsu Corp | Wavelength dispersion measuring instrument |
EP0614074B1 (en) * | 1992-08-25 | 1998-05-13 | Kabushiki Kaisha Toshiba | Optical wavelength measuring instrument |
JP2994531B2 (en) * | 1993-07-06 | 1999-12-27 | ケイディディ株式会社 | Optical wavelength dispersion measurement method and apparatus |
US5969806A (en) * | 1997-06-30 | 1999-10-19 | Tyco Submarine Systems Ltd. | Chromatic dispersion measurement in a fiber optic cable |
-
2000
- 2000-10-13 JP JP2000313392A patent/JP2002122514A/en not_active Withdrawn
-
2001
- 2001-10-09 GB GB0124223A patent/GB2372101B8/en not_active Expired - Fee Related
- 2001-10-12 DE DE10150539A patent/DE10150539A1/en not_active Ceased
- 2001-10-12 FR FR0113170A patent/FR2815408B1/en not_active Expired - Fee Related
- 2001-10-12 US US09/975,557 patent/US6433865B1/en not_active Expired - Fee Related
- 2001-10-12 CA CA002358723A patent/CA2358723C/en not_active Expired - Fee Related
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7016023B2 (en) | 2003-02-21 | 2006-03-21 | Agilent Technologies, Inc. | Chromatic dispersion measurement |
US10404397B2 (en) * | 2015-12-23 | 2019-09-03 | Adva Optical Networking Se | Wavelength division multiplexed telecommunication system with automatic compensation of chromatic dispersion |
Also Published As
Publication number | Publication date |
---|---|
FR2815408A1 (en) | 2002-04-19 |
CA2358723A1 (en) | 2002-04-13 |
GB0124223D0 (en) | 2001-11-28 |
CA2358723C (en) | 2005-11-22 |
GB2372101B (en) | 2003-01-22 |
GB2372101A8 (en) | 2005-09-21 |
JP2002122514A (en) | 2002-04-26 |
FR2815408B1 (en) | 2005-03-11 |
GB2372101B8 (en) | 2005-09-21 |
US6433865B1 (en) | 2002-08-13 |
GB2372101A (en) | 2002-08-14 |
DE10150539A1 (en) | 2002-05-02 |
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