JP2005055382A - Polarization dispersion measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the polarization dispersion of a subject with excellent precision by using the Jones matrix analysis method. <P>SOLUTION: The polarization dispersion measurement device comprises: a light frequency com generation part for generating the light frequency com composed of ≥n light frequency components with light frequency interval f; a polarization wave controller for controlling the state of the polarization and inputting the polarization into the subject; a demultiplexor for demultiplexing n light frequency components from the light frequency com transmitted through the subject; n polarimeters for measuring the polarization state of each frequency component demultiplexed by the demultiplexor; a measurement device controller for setting independent 3 polarization state on the Poincare sphere to the polarization controller; an operation part for calculating the polarization dispersion value of the subject by the operation of the Jones matrix of the subject from the relation between the input polarization state set by the polarization controller by the measurement device control part, and polarization state of each light frequency component measured by each polarimeter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polarization dispersion measuring apparatus for measuring polarization dispersion of a device used in a wavelength division multiplexing network or the network itself.

  The traffic flowing into the backbone network is steadily increasing due to the speeding up of the access means to the network accompanying the spread of xDSL and optical access services. On the other hand, routers and switches that handle increasing traffic are increasing in speed year by year to reach the gigabit range. In order to economically construct such a backbone network, wavelength division multiplexing (WDM) transmission technology has become effective.

  In addition to increasing the capacity of the link, by introducing path control (wavelength routing) in the optical domain, some wavelength channels are branched and inserted in order to achieve efficient traffic transfer and further economy. Optical add / drop technology and optical cross-connect technology that can freely set the path of an arbitrary wavelength channel are being developed.

  In such a wavelength division multiplexing network, it is an important issue to suppress the deterioration amount of each wavelength channel and make the wavelength channels uniform. Degradation of each wavelength channel is caused by transmission path loss, waveform degradation due to nonlinear optical effects in the high power region or crosstalk that induces nonlinear optical phenomena, and filtering effects of each wavelength channel due to wavelength dependence of multiplexers / demultiplexers and other devices. It is determined by various factors. Furthermore, in a high-speed network exceeding 40 Gbit / s, if the relay section becomes long, it is sensitive to signal degradation due to polarization dispersion and needs to be carefully designed.

  As a method for measuring polarization dispersion, a Jones matrix analysis method by B.L.Heffner has been proposed (Non-Patent Document 1). In this method, three independent polarization states are given on the input side of the object to be measured, and the Jones matrix T (η) of the object to be measured is obtained by measuring the output polarization state with respect to each input polarization state. The dependence of η is measured, and the polarization dispersion value of the object to be measured is calculated by taking the derivative with respect to the optical frequency of the solution of the eigenvalue problem using the Jones matrix T (η).

Here, a Jones matrix which is a 2 × 2 complex matrix is defined as Jout = T (η) · Jin with respect to a Jones vector J which is a 2 × 1 complex matrix representing the polarization state of light.
It is a matrix determined by That is, the Jones vector Jin representing the output polarization state is obtained by multiplying the Jones vector Jin representing the input polarization state by the Jones matrix T (η). This Jones matrix is composed of four independent parameters, one of which is a loss parameter, and can be effectively defined by three parameters. That is, the Jones matrix can be determined by measuring three output polarization states for three independent input polarization states. As a specific example, three independent polarization states of x polarization, y polarization, and 45 degree polarization with respect to the x and y axes shown in FIG. 12 are given on the input side of the object to be measured, and each output polarization state is obtained by a polarimeter. taking measurement. FIG. 13 shows the output polarization state measured for each input polarization state, and the parameters k ₁ , k ₂ , k ₃ , k ₄ representing the Jones matrix are
k ₁ = h _x / h _y ,
k ₂ = ν _x / ν _y ,
k ₃ = q _x / q _y ,
k ₄ = (k ₃ −k ₂ ) / (k ₁ −k ₂ )
The Jones matrix T (η) is defined as

Given in.
IEEE PHOTONIC TECHNOLOGY LETTERS, VOL.4, NO.9, Sep.1992, pp.1066-1069

  The Jones matrix analysis method for measuring polarization dispersion is a method of performing a differential operation at the optical frequency in the measurement principle, and the setting accuracy of the optical frequency directly affects the measurement accuracy of the polarization dispersion.

  On the other hand, with the conventional optical frequency setting means, it is difficult to determine the optical frequency of the test light with sub-GHz accuracy or less, and polarization dispersion cannot be measured with high accuracy. In addition, when a wavelength meter using the principle of the Michelson interferometer is used, there is a problem that a predetermined accuracy can be ensured but it is easily affected by fluctuations in environmental temperature. Furthermore, even with a configuration in which the wavelength of the test light is continuously changed, polarization dispersion is measured sequentially, so that it takes time for the number of channels.

  An object of the present invention is to provide a polarization dispersion measuring apparatus capable of measuring the polarization dispersion of a device under test with extremely high accuracy using the Jones matrix analysis method.

  The invention according to claim 1 calculates the Jones matrix of the device under test from the relationship between the input polarization state and the output polarization state of the device under test, and calculates the polarization dispersion value of the device under test from the result. In the measurement apparatus, an optical frequency comb generator for generating an optical frequency comb composed of n or more (n is an integer of 2 or more) optical frequency components at an optical frequency interval f, an optical frequency comb is input, and the polarization state is input A polarization controller to be controlled and input to the device to be measured, a demultiplexer for demultiplexing n optical frequency components from the optical frequency comb that has passed through the device to be measured, and each optical frequency demultiplexed by the demultiplexer N polarimeters for measuring the polarization state of the component, a measuring instrument controller for setting three independent polarization states on the Poincare sphere in the polarization controller, and an input polarization set by the polarization controller by the measuring instrument controller Status and each polarimeter It calculates the Jones matrix of the object to be measured from the relation between the polarization state of each optical frequency components measured, and a calculator for calculating the polarization dispersion value of the object to be measured from the result.

  Further, in the polarization dispersion measuring apparatus according to claim 1, an optical switch that selects one of n optical frequency components demultiplexed by a demultiplexer instead of n polarimeters is selected. And a polarimeter for measuring the polarization state of one optical frequency component, and the arithmetic unit accumulates the polarization state of each optical frequency component obtained by switching the optical switch under the control of the measuring instrument control unit, and the device under test The polarization dispersion value may be calculated (claim 2). Further, in place of the duplexer and the optical switch, a wavelength tunable filter that transmits one of the n optical frequency components output from the device under test is provided, and the arithmetic unit is tunable under the control of the measuring instrument controller. The polarization state of each optical frequency component obtained by switching the transmission wavelength of the filter may be accumulated, and the polarization dispersion value of the device under test may be calculated.

  Further, the duplexer and the optical switch according to claim 2 or the wavelength tunable filter according to claim 3 is arranged in front of the object to be measured, and one selected optical frequency component is input to the object to be measured. The optical frequency component that has passed through the object to be measured may be input to the polarimeter (claim 4).

  In addition, the duplexer and the optical switch according to claim 2 or the wavelength tunable filter according to claim 3 is arranged in front of the polarization controller, and one selected optical frequency component is passed through the polarization controller. It is good also as a structure which inputs into a to-be-measured object and inputs into the polarimeter the optical frequency component which passed the to-be-measured object.

  The optical frequency comb generator in the above polarization dispersion measuring apparatus includes a pulse light source that generates an optical pulse having a repetition frequency f, and a wide light outside the optical frequency component distribution region of the optical pulse while maintaining the repetition frequency f. It is good also as a structure provided with the SC light generation part which produces | generates a new optical frequency component in a frequency domain, and outputs as an optical frequency comb of the optical frequency space | interval f (Claim 6).

  The optical frequency comb generator generates a pulse light source that generates an optical pulse having a repetition frequency f / M (M is an integer of 2 or more), and a distribution of optical frequency components of the optical pulse while maintaining the repetition frequency f / M. A new optical frequency component is generated in a wide optical frequency region outside the area and output as an optical frequency comb having an optical frequency interval of f / M, and an optical frequency comb output from the SC light generating unit is thinned out A periodic transmission filter that outputs an optical frequency comb having an optical frequency interval f may be used.

  The optical frequency comb generator thins out and repeats a pulse light source that generates an optical pulse with a repetition frequency f / M (M is an integer of 2 or more) and an optical pulse with a repetition frequency f / M output from the pulse light source. A periodic transmission filter that outputs an optical pulse of frequency f, and a new optical frequency component generated in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse while maintaining the repetition frequency f. It is good also as a structure provided with the SC light generation part output as an optical frequency comb of the space | interval f (Claim 8).

  The optical frequency comb generator generates a pulse light source that generates an optical pulse having a repetition frequency Mf (M is an integer equal to or greater than 2) and an optical pulse having a repetition frequency Mf that is output from the pulse light source. A frequency divider that outputs an optical pulse of f, a new optical frequency component generated in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse while maintaining the repetition frequency f, and an optical frequency interval f It is good also as a structure provided with the SC light generation part which outputs as an optical frequency comb of this (claim 9).

  The optical frequency comb generator may include an optical frequency controller that controls the optical frequency interval between the optical peak of the predetermined reference light and the optical peak of the optical frequency comb closest thereto to be constant. (Claim 10).

  The polarization dispersion measuring apparatus of the present invention can measure the chromatic dispersion in the measured object with high accuracy by inputting the optical frequency comb output from the optical frequency comb generator to the measured object.

(First embodiment)
FIG. 1 shows a first embodiment of the polarization dispersion measuring apparatus of the present invention. In the figure, an optical frequency comb having a center optical frequency fc generated by the optical frequency comb generator 11 and n or more optical frequency components at an optical frequency interval f is input to the polarization controller 12 and controlled by the measuring instrument controller 13. The three polarization states of x-polarized light, y-polarized light, and 45-degree polarized light with respect to the x and y axes are set. The optical frequency comb set in this polarization state is input to the device under test 14. The optical frequency comb that has passed through the DUT 14 is demultiplexed into n optical frequency components of the optical frequency comb by the demultiplexer 15, and each optical frequency component is input to the polarimeters 16-1 to 16-n for measurement. The polarized state is input to the calculation unit 17.

  The calculation unit 17 is subject to the relationship between the input polarization state set by the polarization controller 12 by the measuring instrument control unit 13 and the output polarization state of each optical frequency component measured by each of the polarimeters 16-1 to 16-n. The Jones matrix of the measurement object 14 is calculated, and the polarization dispersion value of the measurement object 14 is calculated from the result.

  For example, when the optical frequency comb generator 11 generates optical frequency combs each having an accuracy of sub-GHz order at a frequency interval of 5 GHz, the Jones matrix of the DUT 14 can be measured at a frequency interval of 5 GHz. Therefore, the polarization dispersion of the device under test can be measured with extremely high accuracy by the Jones matrix analysis method for measuring the polarization dispersion of the device under test by performing a differential operation at the optical frequency.

  Further, when the wavelength multiplexing grid of the DUT 14 is f ′, the demultiplexing interval of the demultiplexer 15 may be f (f ′> f, for example, f ′ = 200 GHz, f = 25 GHz).

(Second Embodiment)
FIG. 2 shows a second embodiment of the polarization dispersion measuring apparatus of the present invention. A feature of the present embodiment is that, in the configuration of the first embodiment, instead of n polarimeters 16-1 to 16-n, one of the n optical frequency components demultiplexed by the demultiplexer 15 is used. An optical switch 21 to be selected and one polarimeter 22 for measuring the polarization state of the optical frequency component input through the optical switch 21 are provided. The measuring instrument control unit 23 performs switching control of the optical switch 21 and notifies the calculation unit 24 of the switching information. The calculation unit 24 accumulates the polarization state of each optical frequency component sequentially measured by the polarimeter 22 and calculates the polarization dispersion of the device under test 14.

(Third embodiment)
FIG. 3 shows a third embodiment of the polarization dispersion measuring apparatus of the present invention. The feature of this embodiment is that the wavelength tunable that transmits one of n optical frequency components output from the DUT 14 in place of the duplexer 15 and the optical switch 21 in the configuration of the second embodiment. The filter 25 is provided and the polarization state of the optical frequency component input through the wavelength tunable filter 25 is measured by the polarimeter 22. The measuring instrument control unit 23 controls the transmission wavelength of the wavelength tunable filter 25 and notifies the calculation unit 24 of the switching information. The calculation unit 24 accumulates the polarization state of each optical frequency component sequentially measured by the polarimeter 22 and calculates the polarization dispersion of the device under test 14.

(Fourth embodiment)
FIG. 4 shows a fourth embodiment of the polarization dispersion measuring apparatus of the present invention. The feature of this embodiment is that the branching filter 15 and the optical switch 21 in the second embodiment, or the wavelength tunable filter 25 in the third embodiment is arranged in front of the device under test 14, and light is applied to the device under test 14. In this configuration, one optical frequency component of the frequency comb is input, and the polarization state of the optical frequency component that has passed through the DUT 14 is measured by the polarimeter 22.

(Fifth embodiment)
FIG. 5 shows a fifth embodiment of the polarization dispersion measuring apparatus of the present invention. The feature of this embodiment is that the branching filter 15 and the optical switch 21 in the second embodiment, or the wavelength tunable filter 25 in the third embodiment is arranged in front of the polarization controller 12, and the light to be measured 14 is measured. In this configuration, one optical frequency component of the frequency comb is input, and the polarization state of the optical frequency component that has passed through the DUT 14 is measured by the polarimeter 22.

(First Configuration Example of Optical Frequency Comb Generation Unit 11)
FIG. 6 shows a first configuration example of the optical frequency comb generator 11. In the figure, the optical frequency comb generator 11 includes a mode-locked pulse light source 71 and an SC (super continuum) light generator (for example, an optical nonlinear medium) 72.

  The mode-locked pulse light source 71 generates a mode-locked light pulse having a repetition frequency f synchronized with a clock having a frequency f supplied from the optical frequency control unit 31. The optical frequency spectrum of the mode-locked light pulse is a combination of optical frequency components arranged at equal intervals at an optical frequency interval f on the optical frequency axis as shown in FIG. When this mode-locked light pulse is incident on the SC light generator 72, as shown in FIG. 7 (b), the optical frequency component of the mode-locked light pulse is maintained while maintaining the optical frequency interval f by the optical nonlinear effect in the medium. A new optical frequency component is generated in a wide optical frequency region outside the distribution region. The phases of these optical frequency components are all synchronized with the mode-locked light pulse in the time domain. As a result, output light that satisfies the conditions of the optical frequency comb generated by the optical frequency comb generator 11 of each of the above embodiments is output from the SC light generator 72.

Here, by combining the optical frequency comb and the reference light (not shown), the optical frequency spectrum becomes the reference light between the optical peaks of the optical frequency combs arranged at equal intervals f as shown in FIG. 7 (c). The light peak is generated. At this time, if the control of the optical frequency control unit 16 is performed so that the optical frequency interval fd between the optical peak of the reference light and the optical peak of the optical frequency comb closest _thereto is always kept constant, the optical frequency comb is included. The optical frequencies of all the optical frequency components to be held always maintain a constant optical frequency interval with respect to the reference light. Thereby, each optical frequency component of the optical frequency comb has a wavelength accuracy equivalent to that of the reference light. Further, if the optical frequency interval f _d is controlled to be shifted by Δf, each optical frequency component of the optical frequency comb can be shifted by Δf while maintaining the wavelength accuracy equivalent to that of the reference light. it can.

In addition, by using a light source with a configuration that locks the oscillation wavelength with respect to a molecular absorption line such as acetylene or cyan as the light source for generating the reference light, it is very high compared to the current wavelength meter of about ^10-7. Wavelength accuracy can be achieved.

(Second Configuration Example of Optical Frequency Comb Generation Unit 11)
FIG. 8 shows a second configuration example of the optical frequency comb generator 11. In the figure, the optical frequency comb generator 11 includes a mode-locked pulse light source 71, an SC light generator (for example, an optical nonlinear medium) 72, and a periodic transmission filter 73. The relationship among the mode-lock pulse light source 71, the SC light generator 72, and the optical frequency controller 31 is the same as that in the first embodiment shown in FIG. In this configuration example, a mode-locked light source 71 generates a mode-locked light pulse having a repetition frequency f / M, and an optical frequency comb having an optical frequency interval f / M output from the SC light generator 72 is used as a periodic transmission filter 73. Is thinned out and converted into an optical frequency comb having an optical frequency interval f.

(Third configuration example of the optical frequency comb generator 11)
FIG. 9 shows a third configuration example of the optical frequency comb generator 11. In the figure, the optical frequency comb generator 11 includes a mode-locked pulse light source 71, a periodic transmission filter 73, and an SC light generator (for example, an optical nonlinear medium) 72. In this configuration example, the order of the SC light generation unit 72 and the periodic transmission filter 73 in the second configuration example shown in FIG. A mode-locked light pulse having a repetition frequency f / M output from the mode-locked pulse light source 71 is thinned out by the periodic transmission filter 73, and a mode-locked light pulse having an optical frequency interval f is incident on the SC light generating unit 72. Thereby, the optical frequency comb of the optical frequency interval f is generated.

(Fourth configuration example of the optical frequency comb generator 11)
FIG. 10 shows a fourth configuration example of the optical frequency comb generator 11. In the figure, the optical frequency comb generator 11 includes a mode-lock pulse light source 71, a frequency divider 74, and an SC light generator (for example, an optical nonlinear medium) 72.

  As shown in FIG. 11A, the optical frequency comb is an optical frequency component arranged at equal intervals at an optical frequency interval f on the optical frequency axis. The phases of these optical frequency components are all synchronized, and as shown in FIG. 11 (b), the phases of the respective optical frequency components all coincide with each other at a certain moment. Since the optical frequency interval of each optical frequency component is f, coincidence of the phase of the optical frequency component is observed with a period of 1 / f on the time axis, and at this moment, all the optical frequency components strengthen each other and become large. Become power. Therefore, when the optical frequency comb generated by the optical frequency comb generator 11 is observed on the time axis, as shown in FIG. 11 (c), the pulse light becomes very narrow at a time interval of 1 / f.

  In this configuration example, a mode-locked light pulse having a repetition frequency Mf (for example, 25 GHz) output from the mode-lock pulse light source 71 is input to the frequency divider 74, and the repetition frequency f (for example, by thinning out the pulse light on the time axis). 5 GHz) mode-locked light pulse, which is incident on the SC light generator 72, thereby generating an optical frequency comb having an optical frequency interval f.

The figure which shows 1st Embodiment of the polarization-dispersion measuring apparatus of this invention. The figure which shows 2nd Embodiment of the polarization-dispersion measuring apparatus of this invention. The figure which shows 3rd Embodiment of the polarization-dispersion measuring apparatus of this invention. The figure which shows 4th Embodiment of the polarization-dispersion measuring apparatus of this invention. The figure which shows 5th Embodiment of the polarization-dispersion measuring apparatus of this invention. The figure which shows the 1st structural example of the optical frequency comb generation part 11. FIG. The figure which shows the optical spectrum of each part of the optical frequency comb generation part 11. FIG. The figure which shows the 2nd structural example of the optical frequency comb generation part 11. FIG. The figure which shows the 3rd structural example of the optical frequency comb generation part 11. FIG. The figure which shows the 4th structural example of the optical frequency comb generation part 11. FIG. The figure which shows the characteristic of the optical frequency comb which the optical frequency comb generation part 11 generate | occur | produces. The figure which shows the input polarization state set with a polarization controller. The figure which shows the polarization state of each optical frequency component measured with a polarimeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical frequency comb generation part 12 Polarization controller 13, 23 Measuring device control part 14 Device to be measured 15 Demultiplexer 16, 22 Polarimeter 17, 24 Calculation part 21 Optical switch 25 Wavelength variable filter 31 Optical frequency control part 71 Mode lock pulse Light source 72 SC light generating unit 73 Periodic transmission filter 74 Frequency divider

Claims (10)

In the polarization dispersion measuring apparatus that calculates the Jones matrix of the measurement object from the relationship between the input polarization state and the output polarization state of the measurement object, and calculates the polarization dispersion value of the measurement object from the result,
An optical frequency comb generator for generating an optical frequency comb composed of n or more (n is an integer of 2 or more) optical frequency components at an optical frequency interval f;
A polarization controller that inputs the optical frequency comb, controls the polarization state of the optical frequency comb, and inputs the polarization state;
A demultiplexer for demultiplexing n optical frequency components from the optical frequency comb that has passed through the device under test;
N polarimeters for measuring the polarization state of each optical frequency component demultiplexed by the demultiplexer, and a measuring instrument control unit for setting three independent polarization states on the Poincare sphere in the polarization controller;
The Jones matrix of the device under test is calculated from the relationship between the input polarization state set by the polarization controller by the measuring instrument controller and the polarization state of each optical frequency component measured by each polarimeter, and the result A polarization dispersion measuring apparatus, comprising: a calculation unit that calculates a polarization dispersion value of the object to be measured. In the polarization dispersion measuring apparatus according to claim 1,
Instead of the n polarimeters, an optical switch that selects one of the n optical frequency components demultiplexed by the duplexer, and one that measures the polarization state of the selected one optical frequency component With a polarimeter,
The calculation unit is configured to accumulate a polarization state of each optical frequency component obtained by switching the optical switch under the control of the measuring instrument control unit and calculate a polarization dispersion value of the device under test. Polarization dispersion measuring device. In the polarization dispersion measuring apparatus according to claim 2,
In place of the branching filter and the optical switch, a wavelength tunable filter that transmits one of n optical frequency components output from the device under test is provided,
The calculation unit is configured to accumulate the polarization state of each optical frequency component obtained by switching the transmission wavelength of the wavelength tunable filter under the control of the measuring instrument control unit, and calculate the polarization dispersion value of the device under test. There is a polarization dispersion measuring apparatus. The duplexer and the optical switch according to claim 2 or the wavelength tunable filter according to claim 3 is arranged in front of the device under test, and one selected optical frequency component is input to the device under test. The polarization dispersion measuring apparatus, wherein the optical frequency component that has passed through the device under test is input to the polarimeter. The duplexer and the optical switch according to claim 2 or the wavelength tunable filter according to claim 3 is arranged in front of the polarization controller, and one selected optical frequency component is passed through the polarization controller. A polarization dispersion measuring apparatus, characterized in that an optical frequency component that has been input to the device under test and passed through the device under test is input to the polarimeter. In the polarization dispersion measuring apparatus according to any one of claims 1 to 5,
The optical frequency comb generator is
A pulsed light source that generates a light pulse having a repetition frequency f;
SC light generation that generates a new optical frequency component in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse and outputs it as an optical frequency comb with an optical frequency interval f while maintaining the repetition frequency f And a polarization dispersion measuring apparatus. In the polarization dispersion measuring apparatus according to any one of claims 1 to 5,
The optical frequency comb generator is
A pulse light source that generates an optical pulse having a repetition frequency f / M (M is an integer of 2 or more);
While maintaining the repetition frequency f / M, a new optical frequency component is generated in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse, and output as an optical frequency comb having an optical frequency interval f / M. An SC light generating unit,
A polarization dispersion measuring apparatus comprising: a periodic transmission filter that thins out an optical frequency comb output from the SC light generation unit and outputs the thinned optical frequency comb as an optical frequency comb at an optical frequency interval f. In the polarization dispersion measuring apparatus according to any one of claims 1 to 5,
The optical frequency comb generator is
A pulse light source that generates an optical pulse having a repetition frequency f / M (M is an integer of 2 or more);
A periodic transmission filter that thins out optical pulses with a repetition frequency f / M output from the pulse light source and outputs optical pulses with a repetition frequency f;
SC light generation that generates a new optical frequency component in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse and outputs it as an optical frequency comb with an optical frequency interval f while maintaining the repetition frequency f And a polarization dispersion measuring apparatus. In the polarization dispersion measuring apparatus according to any one of claims 1 to 5,
The optical frequency comb generator is
A pulse light source that generates an optical pulse having a repetition frequency Mf (M is an integer of 2 or more);
A frequency divider that M-divides an optical pulse with a repetition frequency Mf output from the pulse light source and outputs an optical pulse with a repetition frequency f;
SC light generation that generates a new optical frequency component in a wide optical frequency region outside the optical frequency component distribution region of the optical pulse and outputs it as an optical frequency comb with an optical frequency interval f while maintaining the repetition frequency f And a polarization dispersion measuring apparatus. In the polarization dispersion measuring apparatus according to any one of claims 1 to 5,
The optical frequency comb generation unit includes an optical frequency control unit that controls an optical frequency interval between an optical peak of predetermined reference light and an optical peak of an optical frequency comb closest thereto to be constant. Characteristic polarization dispersion measuring device.

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