JP2007085981A - Method and instrument for measuring wavelength dispersion, and wavelength dispersion correction system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably and highly stably measure wavelength dispersion of a measured light pulse. <P>SOLUTION: This method has a process for controlling propagation or blocking of a process for shifting a frequency in one part of the measured light pulse, a process for changing one of the respective light pulses into a circular polarized light, a process for separating one changed into the circular polarized light into two orthogonal components, and for separating the other light pulse having a prescribed polarization direction into two orthogonal components, a switching process for switching the each light pulse to make the each light pulse get incident, the component by the component, and to make one of the components outgo, i.e. a process for receiving the light pulse outgoing from the first component switching process to be frequency-divided by a prescribed frequency, and a process for receiving the light pulse outgoing from the second component switching process to be frequency-resolved by the center frequency of the measured light pulse wherein a frequency resolved result is detected as an interference signal in the every component, and the wavelength dispersion is measured, based on each interference signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technical field such as a chromatic dispersion measuring device for measuring chromatic dispersion of an optical pulse, and in particular, a wavelength of an optical pulse propagating through an optical transmission line of an optical fiber network in a high-speed optical communication system having a transmission rate of several tens of Gbit / s. The present invention relates to a chromatic dispersion measuring apparatus for measuring dispersion, a chromatic dispersion correcting system including the measuring apparatus, and the like.

  In recent years, data communication has been shifting to one via an optical fiber, and along with this, the data transmission speed has been dramatically increased. In the near future, in such a high-speed optical communication system via an optical fiber, it is considered to use ultrashort optical pulses and communicate at a transmission rate of several tens of Gbit / s or higher, which is faster than the current transmission rate. Has been.

  By the way, when performing data communication in a high-speed optical communication system, there are always problems of crosstalk and transmission errors. However, as the data transmission speed increases, the width of each individual optical pulse and the interval between the optical pulses preceding and following each other are naturally increased. This becomes a very important issue because of the narrowing.

  The speed at which light travels through the material is determined by the refractive index of the material, and the higher the refractive index, the slower the light speed. In materials such as glass, semiconductors, and optical crystals, the refractive index changes depending on the frequency of light (wavelength in air), so the speed of light depends on the wavelength. It is known that due to the wavelength dependence of the refractive index, the waveform of the light pulse is distorted while the light pulse travels through the material, and the time width of the light pulse is increased. Thus, the characteristic that the speed of light differs according to the wavelength of light is hereinafter referred to as wavelength dispersion or simply dispersion.

  In this way, while traveling through the optical fiber, the waveform of the optical pulse is distorted or the time width of the optical pulse is widened. However, since the time width of the optical pulse is large at the conventional transmission speed, it is a particularly serious problem. It will not be. However, when the data transmission rate increases, crosstalk and transmission errors occur due to interference between the front and rear optical pulses. For this reason, simply trying to increase the transmission speed with the current technology cannot realize data communication at a higher speed.

  In order to remove (or control) chromatic dispersion in such a high-speed optical communication system, it is first necessary to measure the chromatic dispersion of various optical components used in the system and grasp the chromatic dispersion characteristics of each member. There is.

  For example, Patent Document 1 discloses a technique related to a heterodyne spectrum measuring instrument. According to this technique, a measured object is detected by detecting a phase difference between signal light and reference light using a probe light source and an optical coupler. It becomes possible to measure the chromatic dispersion.

Patent Document 2 discloses a technique for evaluating the frequency characteristics of an optical pulse using a nonlinear optical effect by transmitting the optical pulse through a two-photon absorption medium.
International Publication No. 2004/005974 Pamphlet JP 2003-28724 A

  The heterodyne spectrum measuring instrument described in Patent Document 1 described above is based on a single-wavelength interferometer that uses only a probe light source, and therefore, 1 × 3 in order to uniquely determine the phase difference caused by the object to be measured. Non-orthogonal three-component detection using a coupler. However, in the case of three-component detection, there is a problem that the apparatus configuration is complicated, the measurement accuracy is lowered, and the cost is increased.

  In addition, since the optical pulse evaluation method described in Patent Document 2 uses the nonlinear optical effect, when the transmission speed is 160 Gbit / s or higher, there is sufficient peak power. Can be applied because the pulse width is several ps (picosecond) or narrower than fs (femtosecond). For example, in the case of an optical pulse with a transmission speed of about several tens of Gbit / s, the pulse width Spreads to the order of several tens of ps, and the peak power is also lowered. Therefore, the efficiency due to the nonlinear optical effect is lowered, and sufficient chromatic dispersion cannot be measured.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a chromatic dispersion measuring method and the like that can reliably and highly stably measure the chromatic dispersion of an optical pulse.

  In order to solve the above-described problem, the invention according to claim 1 is a chromatic dispersion measuring method for measuring chromatic dispersion of an optical pulse to be measured. AO frequency shifter 12), measurement light pulse, measurement object switching step (SW0,1) for controlling propagation or blocking of the shifted light pulse whose frequency is shifted, and measurement light pulse or shifted light A circular polarization step (λ / 4 plate 15) for changing any one of the light pulses to circularly polarized light, and the circularly polarized one light pulse is separated into two orthogonal components, and a predetermined polarized light A separation step (polarization-independent beam splitter 17, polarizers 18 and 19) for separating the other optical pulse having a direction into two orthogonal components; and the measured optical pulse and the shifted optical pulse A first component switching step (SWmoni.) And a second component switching step (SWref.) For switching to enter and exit one of the incident components, and the first component A first frequency decomposition step (HF resonator 23moni. (Νx)) that receives the optical pulse emitted from the switching step (SWmoni.) And performs frequency decomposition at a predetermined frequency (νx); By switching the light pulse to be measured in the measurement object switching step (SW0, 1) and switching the component in the first component switching step (SWmoni.), Each of the measured light pulse and the shifted light pulse The first frequency decomposition step (HF resonator 23moni. (Νx)) for performing frequency decomposition for each component and the light pulse emitted from the second component switching step (SWref.). The cover A second frequency decomposition step (HF resonator 24ref. (Ν0)) for performing frequency decomposition at the center frequency of constant light pulse (ν0), which should be measured by the measurement object switching step (SW0,1). By switching the optical pulse and switching the component in the first component switching step (SWmoni.), The second frequency decomposition is performed for each component of the measured optical pulse and the shifted optical pulse. The result of the frequency decomposition in the frequency decomposition step (HF resonator 24ref. (Ν0)) and the first frequency decomposition step (HF resonator 23moni. (Νx)) is obtained for each component. The result of frequency decomposition in the step of detecting as an interference signal (detector 26moni. (Νx)) and the second frequency decomposition step (HF resonator 24ref. (Ν0)) is obtained for each component. Step of detecting as interference signal (detector 5Ref. And (.nu.0)), and the step of measuring the chromatic dispersion of said measured optical pulses on the basis of each said interference signal (measuring device 27), and having a.

  According to this, the optical pulse to be measured in the measurement object switching step (SW0, 1) is controlled to be switched to the measured light pulse or the shifted light pulse, or both optical pulses, and the first component switching step (SWmoni.). By switching each component, the frequency resolution can be performed for each orthogonal component for each of the optical pulse to be measured and the shifted optical pulse, so that the measurement of the chromatic dispersion of the optical pulse to be measured can be performed with high stability. Can be done. In addition, by sequentially switching the measurement object in the measurement object switching process and the first and second frequency decomposition processes, it is only necessary to detect the signal from the first frequency decomposition process and the signal from the second frequency decomposition process. Since the wavelength dispersion of the optical pulse can be measured, a general-purpose measuring device can be used, so that a simpler and lower cost measuring method can be provided.

  In order to solve the above-mentioned problem, the invention according to claim 2 is the chromatic dispersion measurement method according to claim 1, wherein the measured optical pulse is an optical pulse having a plurality of polarization components. A polarization component specifying step (polarization beam splitter 10 and polarization converter 11) for specifying the polarization component of the light and making it incident on the shift step.

  According to this, it is possible to measure the chromatic dispersion of each polarization component with an inexpensive and compact configuration for an optical pulse including a plurality of polarization components.

  In order to solve the above-mentioned problem, the invention according to claim 3 is the chromatic dispersion measuring method according to claim 1 or claim 2, wherein the first polarization direction control rotates the measured light pulse in a predetermined polarization direction. A step (λ / 2 plate 14) and a second polarization direction control step (λ / 2 plate 16) for rotating the shift light pulse in a predetermined polarization direction. After one of the light pulse and the shifted light pulse is rotated in the predetermined polarization direction, the one light pulse is changed to circularly polarized light. In the separation step, the other light pulse is the predetermined light pulse. After being rotated in the polarization direction, the other optical pulse is separated into two orthogonal components.

  According to this, since the measurement light pulse and the shift light pulse are rotated in a predetermined polarization direction through the first and second polarization direction control steps, the orthogonal two components can be acquired more accurately. Therefore, it is possible to reliably measure chromatic dispersion.

  In order to solve the above-mentioned problem, the invention according to claim 4 is the chromatic dispersion measuring method according to claim 1 or 2, wherein the measured optical pulse and the shifted optical pulse have a function of maintaining polarization. When propagating through the waveguide, each waveguide is provided so as to be rotatable around an axis, and one of the measured light pulse or the shifted light pulse is incident on the circular polarization step The optical waveguide that propagates the one optical pulse is rotated around the axis so that the one optical pulse has a predetermined polarization direction, and the other optical pulse is incident on the separation step. In this case, the waveguide that propagates the other optical pulse is rotated around the axis so that the other optical pulse has a predetermined polarization direction.

  According to this, since the waveguide is rotated around the axis and the light pulse to be measured and the shift light pulse are rotated in the predetermined polarization direction, the two orthogonal components can be obtained more accurately, and the wavelength can be obtained. It is possible to reliably measure the dispersion.

  In order to solve the above-mentioned problem, the invention according to claim 5 is the chromatic dispersion measurement method according to any one of claims 1 to 4, wherein the first frequency decomposition step (HF resonator 23moni). (νx)) is characterized in that frequency decomposition is performed by sweeping the predetermined frequency in at least a wavelength band in which chromatic dispersion of the optical pulse to be measured is to be measured.

  According to this, it is possible to perform measurement in a wide wavelength band that sufficiently covers the spread of the width of the optical pulse to be measured due to wavelength dispersion, not limited to a certain wavelength.

  In order to solve the above-mentioned problem, the invention according to claim 6 is the chromatic dispersion measuring method according to any one of claims 1 to 5, wherein the separation step is polarization independent of the polarization direction. The measurement light pulse and the shift light pulse are separated into two components using an independent beam splitter.

  According to this, the light can be reliably branched in two directions regardless of the polarization direction, and the branched light can be configured to overlap with high accuracy on the same axis in both paths.

  In order to solve the above problem, the invention according to claim 7 is the chromatic dispersion measurement method according to any one of claims 2 to 6, wherein the polarization component specifying step includes the optical pulse to be measured. A polarization beam splitter that separates the measured optical pulse into a vertical component and a horizontal component, and a polarization converter that polarizes one component of the measured optical pulse after the separation into the other component. It is characterized by specifying an ingredient.

  According to this, it is possible to reliably measure the chromatic dispersion of each polarization component with an inexpensive and compact configuration for an optical pulse including a plurality of polarization components.

  In order to solve the above-mentioned problem, the invention according to claim 8 is the chromatic dispersion measurement method according to any one of claims 1 to 7, wherein the shift step includes the frequency of the shifted optical pulse and the frequency. The frequency is shifted with respect to a part of the measured optical pulse so that the difference in frequency of the measured optical pulse is 0.8% to 1.2% of the pulse width of the measured pulse.

  According to this, the fluctuation of the light generated in the chromatic dispersion measuring device can be offset with high accuracy.

  In order to solve the above-mentioned problem, the invention according to claim 9 is a chromatic dispersion measuring apparatus for measuring the chromatic dispersion of the light pulse to be measured, and shift means for shifting the frequency with respect to a part of the light pulse to be measured ( AO frequency shifter 12), measurement light pulse, measurement object switching means (SW0, 1) for controlling propagation or blocking of the shift light pulse whose frequency is shifted, measurement light pulse or shift light A first optical element (λ / 4 plate 15) that changes any one of the pulses to circularly polarized light, and the one optical pulse that has been circularly polarized is separated into two orthogonal components, and a predetermined polarized light Separating means (polarization-independent beam splitter 17, polarizers 18, 19) for separating the other optical pulse having the direction into two orthogonal components, and the measured optical pulse and the shifted optical pulse First component switching means (SWmoni.) And second component switching means (SWref.) For switching to enter and emit one of the incident components, and the first component switching First frequency resolving means (HF resonator 23moni. (Νx)) that receives an optical pulse emitted from the means (SWmoni.) And performs frequency resolving at a predetermined frequency (νx). By switching the light pulse to be measured by the measurement object switching means (SW0, 1) and switching the component by the first component switching means (SWmoni.), Each of the measured light pulse and the shifted light pulse is obtained. Receiving the light pulses emitted from the first frequency resolving means (HF resonator 23moni. (Νx)) for performing frequency resolving for each component and the second component switching means (SWref.). The measured Second frequency resolving means (HF resonator 24ref. (Ν0)) for performing frequency decomposition at the center frequency of the optical pulse (ν0), which should be measured by the measurement object switching step (SW0,1). The second component that performs frequency decomposition for each component of the measured optical pulse and the shifted optical pulse by switching optical pulses and switching the components by the first component switching means (SWmoni.). The light from the frequency resolving means (HF resonator 24ref. (Ν0)) and the first frequency resolving means (HF resonator 23moni. (Νx)) is received as an interference signal for each component. The first detection means for detecting (detector 26moni. (Νx)) and the light from the second frequency resolving step (HF resonator 24ref. (Ν0)) are received and used as interference signals for each component. Second detection means for detection (detector 25ref. (Ν0)) A measuring means for measuring the chromatic dispersion of said measured optical pulses on the basis of each said interference signal (measuring device 27), and having a.

  In order to solve the above-mentioned problem, the invention described in claim 10 is the chromatic dispersion measuring device according to claim 9, wherein the measured optical pulse is an optical pulse having a plurality of polarization components. And a polarization component specifying unit for specifying the polarization component to be incident on the shift unit.

  In order to solve the above-mentioned problem, the invention according to claim 11 is the chromatic dispersion measuring apparatus according to claim 9 or 10, wherein the second optical element (rotating the measured optical pulse in a predetermined polarization direction) λ / 2 plate 14) and a third optical element (λ / 2 plate 16) for rotating the shift light pulse in a predetermined polarization direction, and the first optical element is formed by the second optical element. Either one of the measured light pulse after being rotated in the predetermined polarization direction or the shifted light pulse after being rotated in the predetermined polarization direction by the third optical element is a circle. The light is changed to polarized light, and the separation means separates the other light pulse into two orthogonal components after the other light pulse is rotated in the predetermined polarization direction by the second optical element or the third optical element. It is characterized by letting The

  In order to solve the above-described problem, the invention according to claim 12 is the chromatic dispersion measuring device according to claim 9 or 10, wherein the measured optical pulse and the shifted optical pulse have a function of maintaining polarization. Each of the waveguides is provided so as to be rotatable about an axis, and the one optical pulse of the measured optical pulse or the shifted optical pulse is incident on the first optical element. In this case, the waveguide for propagating the one optical pulse is rotated around the axis so that the one optical pulse has a predetermined polarization direction, and the other optical pulse is incident on the separating means. In this case, the waveguide for propagating the other optical pulse is rotated around the axis so that the other optical pulse has a predetermined polarization direction.

  In order to solve the above-mentioned problem, the invention according to claim 13 is the chromatic dispersion measuring device according to any one of claims 9 to 12, wherein the first frequency resolving means (HF resonator 23moni). (νx)) is characterized in that frequency decomposition is performed by sweeping the predetermined frequency in at least a wavelength band in which chromatic dispersion of the optical pulse to be measured is to be measured.

  In order to solve the above problem, according to a fourteenth aspect of the present invention, in the chromatic dispersion measuring apparatus according to any one of the ninth to twelfth aspects, the separation unit is a polarization that does not depend on the polarization direction. The measurement light pulse and the shift light pulse are separated into two components using an independent beam splitter.

  In order to solve the above-mentioned problem, according to a fifteenth aspect of the present invention, in the chromatic dispersion measuring apparatus according to any one of the tenth to fourteenth aspects, the polarization component specifying unit includes the measured optical pulse. A polarization beam splitter that separates the measured optical pulse into a vertical component and a horizontal component, and a polarization converter that polarizes one component of the measured optical pulse after the separation into the other component. It is characterized by specifying an ingredient.

  In order to solve the above-mentioned problem, the invention according to claim 16 is the chromatic dispersion measuring device according to any one of claims 9 to 15, wherein the shift means includes the frequency of the shifted optical pulse. The frequency is shifted with respect to a part of the light pulse to be measured so that the difference in frequency of the light pulse to be measured is 0.8% to 1.2% of the pulse width of the pulse to be measured. .

  In order to solve the above problem, the invention according to claim 17 is a chromatic dispersion correction system including a dispersion correction device (44) for correcting chromatic dispersion of an optical pulse propagating through an optical transmission line, and propagates through the optical transmission line. The chromatic dispersion measuring device (1) according to any one of claims 7 to 12, wherein a chromatic dispersion is measured using the optical pulse to be measured as the measured optical pulse, and a correction signal is based on the measured chromatic dispersion. Correction signal generating means for generating (Scom), correction signal transmitting means for transmitting the generated correction signal to the dispersion correction device, and the chromatic dispersion measuring apparatus that receives the correction signal and receives the correction signal. And the dispersion correction device for correcting the optical pulse propagating through the optical transmission line based on the above.

  According to this, the wavelength dispersion of the optical pulse propagating through the optical transmission line can be corrected with a reliable and simple configuration.

  In order to solve the above-mentioned problem, the invention according to claim 18 is the chromatic dispersion correction system according to claim 17, wherein the chromatic dispersion measuring device is an optical pulse propagating through the optical transmission line, and at least the The chromatic dispersion is measured using the optical pulse before correction by the dispersion correction device as the measured optical pulse.

  According to this, by measuring the chromatic dispersion of the optical pulse before correction, it is possible to reliably grasp the amount to be corrected and generate a correction signal.

  In order to solve the above-described problem, the invention according to claim 19 is the chromatic dispersion correction system according to claim 17 or 18, wherein the chromatic dispersion measuring device is an optical pulse propagating through the optical transmission line. Thus, chromatic dispersion is measured using at least the optical pulse corrected by the dispersion correction device as the optical pulse to be measured.

  According to this, by measuring the wavelength dispersion of the corrected optical pulse, it is possible to measure the correction accuracy, generate a correction signal based on this, and reduce it to the next correction.

  In order to solve the above-mentioned problem, the invention according to claim 20 is the chromatic dispersion correction system according to any one of claims 17 to 19, wherein an error of the optical pulse after correction by the dispersion correction device is detected. Error detection means (46) for detecting and transmitting to the chromatic dispersion measuring device as an error signal (Se), and the correction signal generating means of the chromatic dispersion measuring device adds the error signal received from the error detecting means to the error signal. Based on this, the correction signal (Scom) is generated.

  This makes it possible to perform chromatic dispersion correction with higher accuracy.

  In order to solve the above problem, the invention described in claim 21 is the chromatic dispersion correction system according to any one of claims 17 to 20, wherein a plurality of optical pulses are incident and the incident optical pulses are incident. Among them, it has a measured optical pulse switching means (N × 1 switch SW) for switching to emit one optical pulse as the measured optical pulse to the chromatic dispersion measuring device.

  According to this, by switching by the optical light pulse switching means to be measured, for example, each wavelength of the optical transmission line for performing wavelength multiplexing transmission is taken out by the fiber coupler, and a plurality of wavelength dispersion measuring devices can be used to measure a plurality of wavelengths. Since an optical pulse can be measured, even if there are a plurality of optical pulses, the measurement can be performed with a relatively compact system.

  In order to solve the above problem, according to a twenty-second aspect of the present invention, in the chromatic dispersion correction system according to the twenty-first aspect, the plurality of optical pulses are at least optical pulses before correction by the dispersion correction device or after correction. It includes an optical pulse.

  According to the present invention, frequency measurement is performed for each orthogonal component for each of the light pulse to be measured and the shift light pulse by sequentially switching the measurement object in the measurement object switching step and the first and second frequency decomposition steps. Therefore, it is possible to provide a chromatic dispersion measuring method capable of reliably measuring the chromatic dispersion of the optical pulse to be measured with good stability.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, this embodiment is a chromatic dispersion characteristic of an optical pulse propagating through an optical fiber transmission line such as an optical fiber network using wavelength division multiplexing, such as a trunk optical fiber transmission line between Tokyo and Osaka, a metro optical fiber network in an urban area, etc. 1 is an embodiment in which the present invention is applied to a chromatic dispersion measuring method, a chromatic dispersion measuring apparatus, and a chromatic dispersion correcting system using the chromatic dispersion measuring apparatus.

[Chromatic dispersion]
First, chromatic dispersion measured by the chromatic dispersion measuring apparatus 1 in the present embodiment will be described.

  In this embodiment, as described above, the spectral phase of the optical pulse propagating through the optical fiber transmission line is measured, and the characteristics of chromatic dispersion generated in the optical fiber transmission line are evaluated. In particular, the present embodiment will be described with reference to an embodiment suitable for evaluating chromatic dispersion characteristics of an optical fiber transmission line used in a high-speed optical communication system of about 10 GBit / s to 40 GBit / s.

  In order to evaluate the chromatic dispersion of the optical fiber transmission line, the frequency-wave number relationship, that is, the dispersion relationship is important. From this relationship, the speed at which light propagates through the optical fiber transmission line can be obtained. This speed refers to the speed at which the center of gravity of the light pulse moves, and is called “group speed”. The wavelength dependence of the group velocity represents chromatic dispersion.

  This group velocity is given as the slope (derivative coefficient) of the frequency-wavenumber characteristic curve. In vacuum and air, the frequency-wavenumber characteristic is a straight line, and the group velocity is constant regardless of the frequency. In a substance such as a metal, the frequency-wave number characteristic is not a straight line, and the group velocity changes according to the frequency. Since the optical fiber transmission path through which the optical pulse propagates is mainly formed of glass, chromatic dispersion occurs according to the characteristics of the glass, and the group velocity changes according to the frequency of the optical pulse (which may be referred to as wavelength). It will be.

  Here, since the optical pulse includes not only a single wavelength but also various wavelength components, if the group velocity depends on the wavelength, the width of the optical pulse increases as it propagates through the optical fiber transmission line, Signals are overlapped by optical pulses, causing crosstalk.

If the wavelength dispersion characteristic of this optical fiber transmission line is the dispersion parameter D, and the optical pulse width w and the spectral width Δλ of the light, the transmission distance L _D indicating the distance that the light has transmitted through the optical fiber transmission line having the dispersion parameter _D. Is expressed by the following Equation 1.

このような波長分散は、波長(または周波数)に応じて変化する群速度分散、及び二次、三次、…と次数毎に表記でき、光の電界の位相φを用いると、数式２に示す如く表すことができる。そして、分散パラメータＤとの関係は、数式３に示す関係を有する。なお、νは光の周波数であり、ｃは光の速度である。

Such chromatic dispersion can be expressed for each order, such as group velocity dispersion that changes according to wavelength (or frequency), and second order, third order,.... Can be represented. Then, the relationship with the dispersion parameter D has the relationship shown in Equation 3. Note that ν is the frequency of light and c is the speed of light.

  Therefore, in order to measure the chromatic dispersion, the frequency (wavelength) dependence of the phase of light, that is, the spectral phase φ (ν) may be measured.

ところで、光の周波数は非常に高く、電気的測定により光の電界の振動を測定することは、例えば、波長１５００ｎｍの光の周波数は２００ＴＨｚ（テラヘルツ）に相当し、現状の技術では不可能である。そこで、光の位相を測定する手段として、干渉計が用いられる。

By the way, the frequency of light is very high, and it is impossible to measure the vibration of the electric field of the light by electrical measurement, for example, the frequency of light having a wavelength of 1500 nm corresponds to 200 THz (terahertz). . Therefore, an interferometer is used as means for measuring the phase of light.

  In this interferometer, incident light is split in two directions by a beam splitter, and each light passes through an independent path and is then combined again. The phase difference due to the divided light propagating through each path can be measured as the intensity of the interference light after the combination.

Therefore, in the present embodiment, a part of the optical pulse propagating through the optical fiber transmission line is extracted, and an optical pulse obtained by shifting a part of the extracted optical pulse by Δν _AO with a frequency shifter (AOFS) is obtained. By using the interference fringe obtained by interfering with the original optical pulse by Fourier transform, the phase derivative of the original optical pulse can be obtained, and the group delay time can be measured.

  Hereinafter, it demonstrates more concretely using figures.

  FIG. 1A is a diagram illustrating a waveform of an optical pulse propagating through an optical fiber transmission line, and is a time waveform of an optical pulse with the horizontal axis representing time t and the vertical axis representing signal intensity I. In the example shown in the figure, it is assumed that the optical pulse repeats ON and OFF every 25 ps (40 Gbit / s). Here, by using the rising portion (ON state) of the signal intensity I as an absolute value and using the oscillating component as an exponential function, the general form of the optical pulse time waveform can be expressed by the following Equation 4. Note that φ (t) is generally called an optical pulse chirp and describes how the phase changes as a function of time. Here, the phase change caused by the optical fiber transmission line is described. Is shown.

更に、光パルス時間波形を空間依存性を除いて簡略化することにより、数式４を以下の数式５で示すことができ、同様にして、周波数をΔν_AOだけシフトさせた光パルスの光パルス時間波形は、以下の数式６で示すことができる。

Further, by simplifying the optical pulse time waveform by removing the spatial dependence, Equation 4 can be expressed by the following Equation 5, and similarly, the optical pulse time of the optical pulse with the frequency shifted by Δν _AO. The waveform can be expressed by Equation 6 below.

そして、上記数式５及び６を、ν₀を中心周波数としてフーリエ変換を行ない、以下の数式７、８で示す如く、絶対値で示されるパワースペクトルと指数関数で示される位相成分とにより構成された位相の関数として表すことができる。

Then, the above formulas 5 and 6 are subjected to Fourier transform with ν ₀ as the center frequency, and as shown in the following formulas 7 and 8, the power spectrum represented by the absolute value and the phase component represented by the exponential function are formed. It can be expressed as a function of phase.

これらフーリエ変換後の元の光パルスのスペクトルとフーリエ変換後の周波数シフトさせた光パルスのスペクトルを重ね合わせると以下の数式９で示すことができる。

When the spectrum of the original optical pulse after the Fourier transform and the spectrum of the optical pulse shifted in frequency after the Fourier transform are superimposed, it can be expressed by Equation 9 below.

ここで、図１（Ｂ）に光パルスの強度スペクトル波形を示す。同図は電界Ｒに対する周波数νの依存特性を示すものであり、実線で示す如く、周波数シフトしていない元の光パルスは中心周波数ν_０で電界Ｒが最大（ピーク）となるスペクトルを有することがわかる。一方、周波数をΔν_AOだけ微小シフトさせた場合（点線で図示）には、強度スペクトルのピークはシフトするが、波形は変化しないことがわかる。つまり、周波数を微小シフトさせても電界Ｒの値は変化がないため、絶対値で示される元の光パルスのパワースペクトルと周波数をΔν_AOだけ微小シフトさせた光パルスのパワースペクトルとは数式１０で示す如く近似することができる。

Here, FIG. 1B shows an intensity spectrum waveform of an optical pulse. This figure shows the dependence of the frequency ν on the electric field R. As shown by the solid line, the original optical pulse that has not been frequency shifted has a spectrum in which the electric field R is maximum (peak) at the center frequency ν _0. I understand. On the other hand, when the frequency is slightly shifted by Δν _AO (illustrated by a dotted line), the peak of the intensity spectrum is shifted, but the waveform is not changed. In other words, since the value of the electric field R does not change even if the frequency is slightly shifted, the power spectrum of the original optical pulse indicated by the absolute value and the power spectrum of the optical pulse whose frequency is slightly shifted by Δν _AO are expressed by Equation 10. Can be approximated as shown in FIG.

従って、上記数式９は、上記数式１０の近似式を用いて以下の数式１１で表すことができる。

Therefore, the formula 9 can be expressed by the following formula 11 using the approximate formula of the formula 10.

また、図１（Ｃ）に光パルスの位相の周波数νの依存特性を示す。測定対象である光ファイバー伝送路の光パルスは二次の分散を有しており、更に同図に示す如く上に凸形状を有する放物線で示されるように位相が変化する。周波数をΔν_AOだけ微小シフトさせた場合には図中点線で示す如く、位相もΔφだけシフトするのであるが、この位相のシフト量Δφの値は、周波数シフトしていない元の光パルス（図中実線）の微分した値と等価となる。従って、位相のシフト量Δφを周波数のシフト量Δν_AOで除算することにより、数式１２で示す如く群遅延時間τを求めることができる。

FIG. 1C shows the dependence characteristic of the phase ν of the optical pulse on the frequency ν. The optical pulse of the optical fiber transmission line to be measured has second-order dispersion, and the phase changes as shown by a parabola having an upward convex shape as shown in FIG. When the frequency is slightly shifted by Δν _AO , the phase is also shifted by Δφ, as indicated by the dotted line in the figure. The value of this phase shift amount Δφ is the original optical pulse that has not been frequency shifted (see FIG. It is equivalent to the differentiated value of the solid line. Therefore, by dividing the phase shift amount Δφ by the frequency shift amount Δν _AO , the group delay time τ can be obtained as shown in Equation 12.

なお、周波数のシフト量Δν_AOは、元の光パルスのパルス幅の約０．８％〜１．２％とするのが好適である。例えば、元の光パルスのパルス幅が４０Gbit／sである場合には、周波数のシフト量Δν_AOは約３００ＭＨｚ〜５００ＭＨｚ程度が好適であり、元の光パルスのパルス幅が１０Gbit／sである場合には、周波数のシフト量Δν_AOは約８０ＭＨｚ〜１２０ＭＨｚ程度が好適である。

The frequency shift amount Δν _AO is preferably about 0.8% to 1.2% of the pulse width of the original optical pulse. For example, when the pulse width of the original optical pulse is 40 Gbit / s, the frequency shift amount Δν _AO is preferably about 300 MHz to 500 MHz, and the pulse width of the original optical pulse is 10 Gbit / s. The frequency shift amount Δν _AO is preferably about 80 MHz to 120 MHz.

[Configuration and function of wavelength dispersion measuring apparatus 1]
Next, the configuration and function of the chromatic dispersion measuring apparatus 1 according to the present embodiment will be described with reference to FIG.

  FIG. 2 is a schematic configuration diagram of the chromatic dispersion measuring apparatus 1 according to the present embodiment.

As shown in the figure, the chromatic dispersion measuring apparatus 1 in this embodiment includes a polarization beam splitter 10, a polarization converter 11, an AO frequency shifter 12 as a shift means, a time delay circuit 13, and a switch SW as a measurement target switching means. ₀ , SW ₁ , λ / 2 plates 14 and 16 as second and third optical elements, λ / 4 plate 15 as first optical element, polarization-independent beam splitter 17 and polarizer 18 as separating means , 19, fiber couplers 20, 21, switch SW _moni (ν _x ) as first component switching means, switch SW _ref. (Ν ₀ ) as second component switching means, _HF as first frequency resolving means resonator _{23 moni (ν x), H} -F resonator 24 _ref as a second frequency decomposition _unit. (ν _0), the photodetector 25 _moni as a first detecting means ([nu _x) Photodetector 26 as a second detecting means _{ref. (Ν 0),} and functions to configured with a measuring device 27 as a computer that is configured to include a computer as measuring means. Note that an isolator for effectively preventing return light may be appropriately inserted into the chromatic dispersion measuring apparatus 1.

  As shown in FIG. 2, the chromatic dispersion measuring device 1 propagates through an optical fiber transmission line such as a trunk optical fiber transmission line between Tokyo and Osaka, a metro optical fiber network in an urban area, or an optical fiber network that uses wavelength division multiplexing transmission. A part of the optical pulse to be taken out is taken out by a fiber coupler and taken into the chromatic dispersion measuring apparatus 1 as a measured optical pulse in the chromatic dispersion measuring apparatus 1. In the example shown in FIG. 2, the optical pulse that is not extracted by the fiber coupler propagates through the optical fiber transmission line as it is.

  The polarization beam splitter 10 separates the optical pulse extracted by the fiber coupler into a horizontal polarization component and a vertical polarization component, and causes the horizontal polarization component to enter the switch SWp and the vertical polarization component to the polarization converter 11, respectively. Then, the polarization converter 11 switches the polarization component of the light propagating through the polarization maintaining fiber (PMF) from the polarization beam splitter 10 to polarize the vertical polarization component into the horizontal polarization, and switches it. Incident on SWp.

  Thereby, by aligning the optical pulse to be measured in one polarization direction, it is possible to measure each polarization component of the optical pulse propagating through the optical fiber transmission line with one chromatic dispersion measuring apparatus 1. More specifically, when an optical pulse from the polarization beam splitter 10 is selected by switching the switch SWp earlier than the polarization fluctuation time, the horizontal polarization component of the optical pulse is a measurement target to be measured. When an optical pulse from the polarization converter 11 is selected, a vertical polarization component of the optical pulse (which is converted into horizontal polarization by the polarization converter 11) is a measurement target. It can be a light pulse.

Note that the optical pulse to be measured is an optical pulse that transmits a specific wavelength channel using a wavelength variable filter (not shown) or the like, and the electric field is (E _in (t)).

  Further, the extracted optical pulse to be measured propagates in the polarization maintaining fiber in the chromatic dispersion measuring apparatus 1 except in the interferometer. This is because, in order to measure the frequency (wavelength) dependence of the phase of light with higher accuracy, it is preferable to use a polarization maintaining fiber capable of propagating light while maintaining the polarization of light.

AO frequency shifter 12 is used to partially shift amount .DELTA..nu _AO only the frequency shift of the measured light pulse selected by the switch _{SWp (E in (t))} . Note that the original measured optical pulse that has not been frequency-shifted is represented by an electric field (E ₀ (t)) as a zero-order optical pulse (measured optical pulse), and the measured optical pulse that has been frequency-shifted is the primary light (shifted). It is represented by an electric field (E ₁ (t)) as an optical pulse. In the following description, the original measured optical pulse that has not been frequency-shifted is referred to as a “zero-order optical pulse”, and the measured optical pulse that has been frequency-shifted is referred to as a “primary optical pulse”.

  That is, the relationship between the light intensity of the light pulse to be measured, the zeroth-order light pulse, and the zeroth-order light pulse selected by the switch SWp can be expressed by the following Equation 13.

時間遅延回路１３は、例えばレトロリフレクタで構成され、０次光パルスと１次光パルスの光路長を一致させるべく、１次光パルスの光路長を変化させるためのものである。なお、０次光パルスと１次光パルスの光路長が測定結果に影響しない程度に一致しているのであれば、時間遅延回路１３は必要ない。

The time delay circuit 13 is composed of, for example, a retroreflector, and is used to change the optical path length of the primary optical pulse so that the optical path lengths of the zero-order optical pulse and the primary optical pulse coincide with each other. Note that the time delay circuit 13 is not necessary if the optical path lengths of the zero-order light pulse and the first-order light pulse coincide with each other so as not to affect the measurement result.

The switches SW ₀ and SW ₁ are used to control the propagation or blocking of each light pulse when measuring the intensity of each of the zero-order light pulse and the first-order light pulse. Specifically, when measuring the 0-order light pulse ON the switch SW ₀ (propagation), the switch SW ₁ is turned OFF (opened cutoff), in measuring the primary light pulse, the switch SW ₀ OFF (blocking), as ON (propagate) the switch SW _1, leads to only one of the light pulses to be measured interferometer to (airborne region), and blocking the other light pulse, or both of light Guide the pulse into the interferometer for monitoring.

  Here, the behavior of each measured light pulse incident on the interferometer will be described. In the interferometer, an interference optical system for performing orthogonal two-component detection by polarization separation, polarization separation, and polarization selection is assembled, and the first member of the optical system is a λ / 2 plate. When each of the light pulses to be measured is incident on the (half-wave plate) 14 (and the λ / 2 plate 16), the light is emitted from the polarization maintaining fiber into the air.

An interference optical system for performing orthogonal two-component detection was constructed by air propagation. In FIG. 2, the propagation of light in the air propagation region is illustrated by a chain line, and all the light other than the air propagation region propagates in the polarization maintaining fiber. Then, the fluctuation of the light generated by being airborne in the interferometer, the phase difference in the H-F resonator _{23 moni (ν x) Δφ FT} (ν x) and H-F resonator 24 _ref. and configured to cancel the phase difference [Delta] [phi _FT in _{(ν 0) (ν 0)} . The phase difference Δφ _FT in each resonator and fluctuation removal using these phase differences will be described in detail later using Equations 31, 32, and 33. First, the λ / 2 plate 14 functions as a second optical element (first polarization direction control step) in the present embodiment, and the 0th-order optical pulse propagated from the AO frequency shifter 12 via the switch SW ₀ is After being inclined 45 degrees from the horizontal plane, it is guided to a quarter-wave plate 15 as the first optical element. Then, the λ / 4 plate 15 converts the reference light into circularly polarized light and then guides it to the polarization-independent beam splitter 17. When passing through the λ / 4 plate 15, the electric field of the zeroth-order light pulse can be expressed by the following formula 14. Hereinafter, in the two-stage description in parentheses in each numerical expression, the upper part indicates the horizontal polarization component, and the lower part indicates the vertical polarization component that is the orthogonal component.

なお、ここではλ／４板１５によって参照光を右回り円偏光としたが、左回りであってもよく、左回りとした場合には、位相の符号を変更すればよい。

Although the reference light is clockwise circularly polarized light by the λ / 4 plate 15 here, it may be counterclockwise, and if it is counterclockwise, the phase sign may be changed.

On the other hand, the λ / 2 plate 16 functions as a third optical element (second polarization direction control step) in the present embodiment, and transmits the primary light pulse propagated from the time delay circuit 13 via the switch SW ₁ to the horizontal plane. Inclined by 45 degrees and guided to the polarization-independent beam splitter 17. When passing through the λ / 2 plate 15, the electric field of the primary light pulse can be expressed by Equation 15 shown below.

そして、偏波無依存ビームスプリッタ（polarization independent）１７は、ポーラライザ１８、１９と共に分離手段として機能し、４５度の直線偏光とされた１次光パルスを２方向に分岐させ、一方の光束を反射してポーラライザ１８へ導くと共に、他方の光束を透過してポーラライザ１９へ導く。同様にして、円偏光とされた０次光パルスを２方向に分岐させ、一方の光束を透過してポーラライザ１８へ導くと共に、他方の光束を反射してポーラライザ１９へ導く。なお、ポーラライザ１８側（図２において偏波無依存ビームスプリッタ１７の右方向）を、水平偏光成分（ｃｏｓ成分）を検出するための経路Ｈとし、ポーラライザ１９側（図２において偏波無依存ビームスプリッタ１７の下方向）を、垂直偏光成分（ｓｉｎ成分）を検出するための経路Ｖとする。このように、偏波無依存ビームスプリッタ１７を分岐手段として用いることで、当該偏波無依存ビームスプリッタ１７を透過（又は反射）した０次光パルスと１次光パルスはその偏光によらず、何れの経路（Ｈ及びＶ）においても同軸上で重なるよう比較的容易に構成することができる。

The polarization independent beam splitter (polarization independent) 17 functions as a separating means together with the polarizers 18 and 19, branches the primary light pulse that is linearly polarized at 45 degrees in two directions, and reflects one light beam. Then, the light is guided to the polarizer 18 and the other light beam is transmitted to the polarizer 19. Similarly, the zero-order light pulse that has been circularly polarized is branched in two directions, one of the light beams is transmitted and guided to the polarizer 18, and the other light beam is reflected and guided to the polarizer 19. Note that the polarizer 18 side (the right direction of the polarization-independent beam splitter 17 in FIG. 2) is a path H for detecting the horizontal polarization component (cos component), and the polarizer 19 side (the polarization-independent beam in FIG. 2). A downward direction of the splitter 17) is defined as a path V for detecting a vertical polarization component (sin component). In this way, by using the polarization-independent beam splitter 17 as a branching unit, the zero-order optical pulse and the first-order optical pulse transmitted (or reflected) through the polarization-independent beam splitter 17 are not dependent on the polarization, Any of the paths (H and V) can be configured relatively easily so as to overlap on the same axis.

  In the path H, the electric field of the light after passing through the polarization-independent beam splitter 17 and before entering the polarizer 18 is the sum of the electric field of the light of the zeroth-order optical pulse and the electric field of the light of the first-order optical pulse. , Can be expressed by the following formula 16.

そして、経路Ｈにおいてポーラライザ１８は、偏波無依存ビームスプリッタ１７と共に分離手段として機能し、偏波無依存ビームスプリッタ１７からの０次光パルス及び１次光パルスのうち、所定偏光のみを最大透過してファイバーカプラー２０へ導く。本実施形態では、ポーラライザ１８は水平偏光成分を最大透過する角度を保持するよう構成した。すなわち、ポーラライザ１８を通過した光は、水平偏光成分のみであるとみなすことができる。ポーラライザ１８を通過後の光の電界を数式１７にて示す。

In the path H, the polarizer 18 functions as a separating unit together with the polarization-independent beam splitter 17, and transmits only predetermined polarization of the zero-order light pulse and the first-order light pulse from the polarization-independent beam splitter 17 to the maximum. To the fiber coupler 20. In the present embodiment, the polarizer 18 is configured to maintain an angle at which the horizontal polarization component is transmitted at the maximum. That is, the light that has passed through the polarizer 18 can be regarded as only a horizontal polarization component. The electric field of the light after passing through the polarizer 18 is represented by Expression 17.

一方、経路Ｖにおいても同様にして、偏波無依存ビームスプリッタ１７を経た後、ポーラライザ１９に入射する前の光の電界は、０次光パルスの電界と、１次光パルスの電界の和として、以下に示す数式１８で表すことができる。

Similarly, in the path V, the electric field of light after passing through the polarization-independent beam splitter 17 and before entering the polarizer 19 is the sum of the electric field of the zeroth-order optical pulse and the electric field of the first-order optical pulse. , Can be represented by Equation 18 shown below.

そして、経路Ｖにおいてポーラライザ１９は、偏波無依存ビームスプリッタ１７と共に分離手段として機能し、偏波無依存ビームスプリッタ１７からの０次光パルス及び１次光パルスのうち、所定偏光のみを最大透過してファイバーカプラー２１へ導く。本実施形態では、ポーラライザ１９は垂直偏光成分を最大透過する角度を保持するよう構成した。すなわち、ポーラライザ１９を通過した光は、垂直偏光成分のみであるとみなすことができる。ポーラライザ１９を通過後の光の電界Ｅｖを数式１９にて示す。

In the path V, the polarizer 19 functions as a separating unit together with the polarization-independent beam splitter 17, and transmits only the predetermined polarization of the zero-order light pulse and the first-order light pulse from the polarization-independent beam splitter 17 at the maximum. To the fiber coupler 21. In the present embodiment, the polarizer 19 is configured to maintain an angle at which the vertical polarization component is transmitted at the maximum. That is, the light that has passed through the polarizer 19 can be regarded as only a vertical polarization component. The electric field Ev of the light after passing through the polarizer 19 is expressed by Equation 19.

なお、ポーラライザ１８及び１９は、光パルスが有する全てのスペクトル帯域において、偏光特性が変化しないものとし、例えばpolarcor偏光板を用いる。

Polarizers 18 and 19 do not change polarization characteristics in all spectral bands of light pulses, and use, for example, polarcor polarizing plates.

  Further, when the light from each of the polarizers 18 and 19 is again incident on the polarization maintaining fiber and is incident on the fiber couplers 20 and 21, it is preferable to use a condensing lens (not shown). is there.

The fiber couplers 20 and 21 branch light from the polarizers 18 and 19 in two directions, respectively, and guide one to the switch SW _moni (ν _x ) _{. And} the other to the switch SW _ref. (Ν ₀ ) _. .

The switch SW _moni (ν _x ) and the switch SW _ref. (Ν ₀ ) are 2 × 1 optical switches, and the horizontal polarization component (cos component) of the path H from the fiber coupler 20 and the path V from the fiber coupler 21. of a vertical polarization component (sin component), respectively transmitting / blocking to by switching the respective components in time, later described to the two photodetectors _{25 moni (ν x), 26} ref. (ν 0) Only the horizontal polarization component (cos component) and the vertical polarization component (sin component) of the zero-order light pulse and the first-order light pulse can be individually detected.

The light having passed through the switch SW _moni (ν _x ) is _{incident on the HF} resonator 23 _moni (ν _x ) (High-Fineness Fabry-Perot Cavity), and the HF resonator 23 Frequency decomposition is performed by _moni (ν _x ) and Fourier transform is performed. The _HF resonator 23 _moni (ν _x ) is configured to be capable of adjusting the center frequency (hereinafter referred to as “resonance frequency”) ν _x of the resonator. Accordingly, by sweeping the center frequency ν _x of the resonator, the frequency band of the entire optical pulse to be measured can be detected (monitored) by the photodetector 25 _moni (ν _x ) (Photo detector).

On the other hand, the light that has passed through the switch SW _ref. The ([nu ₀₎ is made incident on H-F resonator 24 _ref. (Ν ₀₎ is the frequency resolution at the H-F resonator 24 _ref. (Ν ₀₎ Fourier Conversion is performed. In the _HF resonator 24 _ref. (Ν ₀ ), the resonance frequency is fixed to the center frequency ν ₀ of the 0th-order optical pulse (in other words, the center frequency ν _{0 of the} optical pulse to be measured), and is always 0th-order. The center frequency ν ₀ of the optical pulse can be detected (monitored) by the photodetector 26 _ref. (Ν ₀ ).

FIG. 3A shows the spectrum waveforms of the zero-order light pulse and the first-order light pulse, and the spectrum waveforms of the _HF resonator 23 _moni (ν _x ) and the _HF resonator 24 _ref. (Ν ₀ ). FIG. 3B shows the dependence characteristics of the phase ν of the zeroth-order optical pulse and the first-order optical pulse corresponding to FIG.

Thus, H-F resonator _{23 moni (ν x), 24} ref. (Ν 0) E H ^ FT (ν x) is the horizontal polarization component (cos component) output from, E _H ^ FT ( ν ₀ ) can be expressed by Equations 21 and 22 on condition of the following Equation 20.

また、Ｈ−Ｆ共振器２３_moni（ν_ｘ）、２４_ref.（ν_０）から出力される垂直偏光成分（ｓｉｎ成分）であるＥ_ｖ^FT（ν_ｘ）及びＥ_ｖ^FT（ν_０）は、上記数式２０を条件として、それぞれ数式２３、２４で表すことができる。

Also, E _v ^ FT (ν _x ) and E _v ^ FT (ν ₀ ), which are vertical polarization components (sin components) output from the _HF resonators 23 _moni (ν _x ) and 24 _ref. (Ν ₀ ) _. ) Can be expressed by Equations 23 and 24, respectively, with the above Equation 20 as a condition.

そして、光検出器２５_moni（ν_ｘ）は、第一検出手段として機能し、Ｈ−Ｆ共振器２３_moni（ν_ｘ）からの光パルスを受けて、０次光パルスと１次光パルスの水平偏光成分（ｃｏｓ成分）及び垂直偏光成分（ｓｉｎ成分）を検出し、それぞれについて、０次光パルスと１次光パルスによる干渉信号を検出する。なお、経路Ｈからの水平偏光成分（ｃｏｓ成分）を検出するか、経路Ｖからの垂直偏光成分（ｓｉｎ成分）を検出するかは、上述の如く第一成分切換手段として機能するスイッチＳＷ_moni（ν_ｘ）及び第二成分切換手段として機能するスイッチＳＷ_ref.（ν_０）によって制御することができる。また、光検出器２６_ref.（ν_０）も同様に第二検出手段として機能しＨ−Ｆ共振器２４_ref.（ν_０）からの光パルスを受けて、被測定光パルスの０次光パルスと１次光パルスの水平偏光成分（ｃｏｓ成分）及び垂直偏光成分（ｓｉｎ成分）を検出し、それぞれについて、０次光パルスと１次光パルスによる干渉信号を検出する。

The photodetector 25 _moni (ν _x ) functions as first detection means, receives the light pulse from the _HF resonator 23 _moni (ν _x ), and receives the zero-order light pulse and the first-order light pulse. A horizontal polarization component (cos component) and a vertical polarization component (sin component) are detected, and an interference signal due to the 0th-order light pulse and the first-order light pulse is detected for each. Whether the horizontal polarization component (cos component) from the path H is detected or the vertical polarization component (sin component) from the path V is detected is the switch SW _moni (functioning as the first component switching means as described above). ν _x ) and a switch SW _ref. (ν ₀ ) functioning as second component switching means. Similarly, the photodetector 26 _ref. (Ν ₀ ) also functions as a second detection means, receives the optical pulse from the _HF resonator 24 _ref. (Ν ₀ ), and receives the zero-order light of the measured optical pulse. The horizontal polarization component (cos component) and the vertical polarization component (sin component) of the pulse and the primary light pulse are detected, and the interference signal due to the zero-order light pulse and the primary light pulse is detected for each.

The interference signal of the horizontal polarization component (cos component) of the zero-order light pulse and the first-order light pulse detected by the light detector 25 _moni (ν _x ) is detected by Equation 25 and the light detector 26 _ref. (Ν ₀ ) _. The interference signals of the horizontal polarization component (cos component) of the zeroth-order light pulse and the first-order light pulse are shown in Equation 26 as light power, respectively.

光検出器２５_moni（ν_ｘ）によって検出された０次光パルスと１次光パルスの垂直偏光成分（ｓｉｎ成分）の干渉信号を数式２７に、光検出器２６_ref.（ν_０）によって検出された０次光パルスと１次光パルスの水平偏光成分（ｓｉｎ成分）の干渉信号を数式２８に、それぞれ光のパワーとして示す。

The interference signal of the vertical polarization component (sin component) of the zero-order light pulse and the first-order light pulse detected by the photodetector 25 _moni (ν _x ) is detected by Equation 27 and the photodetector 26 _ref. (Ν ₀ ) _. The interference signals of the horizontal polarization component (sin component) of the zeroth-order light pulse and the first-order light pulse that have been obtained are shown in Equation 28 as the light power.

測定対象切換手段としてのスイッチＳＷ_０、ＳＷ_１の双方をＯＮ（伝播）とすることにより、０次光パルスと１次光パルスの双方を干渉計内に取り入れ、０次項パルスのエネルギー成分（上記数式２５乃至数式２８におけるＥ_０として表記）と１次光パルスのエネルギー成分（上記数式２５乃至数式２８におけるＥ_１として表記）の双方の成分を含む上記各光の干渉信号を各光検出器にて取得することができる。

By turning on (propagating) both of the switches SW ₀ and SW ₁ as the measurement object switching means, both the zero-order light pulse and the first-order light pulse are taken into the interferometer, and the energy component of the zero-order term pulse (above) equation 25 to notation as E ₀ in equation 28) and the interference signal of each light containing both of the components of the energy components of the primary light pulse (denoted as E ₁ in the above equation 25 to equation 28) in each photodetector Can be obtained.

In Equations 25 to 28, the phase difference Δφ _FT (ν _x ) is the light frequency-resolved by the resonance frequency ν _x of the _HF resonator 23 _moni (ν _x ) as shown in Equation 29 below. The phase φ _FT (ν _x ) is obtained by subtracting the phase φ _FT (ν _x −Δν _AO ) of the light shifted by Δν _AO from the resonance frequency ν _x by the AO frequency shifter 12, and the phase difference Δφ _FT (ν _0), as shown in the following equation 30, H-F resonator 24 _ref. ([nu ₀₎ at the light frequency resolution center frequency [nu ₀ of the measured light pulse as the resonant frequency phase phi _FT ([nu ₀ ) is obtained by subtracting the phase φ _FT (ν ₀ −Δν _AO ) of the light shifted by Δν _AO by the AO frequency shifter 12 from the center frequency ν _{0 of the} optical pulse to be measured.

このようにして、各光検出器（光検出器２５_moni（ν_ｘ）、光検出器２６_ref.（ν_０））によって取得された信号を、測定手段としての測定装置２７に干渉信号データとして取り込んで、以下の数式３１及び数式３２に示す如くｃｏｓ成分とｓｉｎ成分の直交二成分として被測定光パルスの波長依存性（波長分散）を算出（測定）することができる。なお、測定装置２２はオシロスコープを含むものであれば、測定者が目視で干渉信号を確認できるので、より好適である。

In this way, the signals acquired by the respective photodetectors (the photodetectors 25 _moni (ν _x ) and the photodetectors 26 _ref. (Ν ₀ )) are transmitted as interference signal data to the measuring device 27 serving as a measuring unit. By taking in, the wavelength dependence (wavelength dispersion) of the light pulse to be measured can be calculated (measured) as two orthogonal components of the cos component and the sin component as shown in the following equations 31 and 32. Note that if the measurement device 22 includes an oscilloscope, the measurer can visually confirm the interference signal, which is more preferable.

上記数式３１及び数式３２に示す如く、一価関数である正接関数（tan）の逆関数でそれぞれの位相差を求めることにより、引数として負の無限から正の無限までの数値を取り得、ノイズが存在する状況下でも確実に位相差の一義的決定を行なうことが可能になる。

As shown in Equation 31 and Equation 32 above, each phase difference is obtained by the inverse function of the tangent function (tan), which is a monovalent function, so that a numerical value from negative infinity to positive infinity can be taken as an argument, and noise is It becomes possible to make an unambiguous determination of the phase difference even under existing conditions.

Then, the phase difference [Delta] [phi _FT ([nu in thus obtained "phase difference in the H-F resonator _{23 moni (ν x) Δφ FT} (ν x) " and "H-F resonator 24 _ref. (Ν _{0) 0} ) ”includes a component of phase fluctuation in the interferometer, and by obtaining the difference between these phase differences Δφ _FT (ν _x ) and Δφ _FT (ν ₀ ), the phase fluctuation in the interferometer The phase difference Δφ _FT-ST (ν _{x, 0} ) from which the component has been removed can be obtained as shown in Equation 33.

このようにして取得した位相差Δφ_FT-ST（ν_ｘ,0）は、図１（Ａ）〜（Ｃ）及び数式９乃至１２を用いて説明したように、周波数シフトしていない元の光パルスである０次光パルス（つまり、被測定光パルス）の微分値と等価であるため、ＡＯ周波数シフター１２によってシフトさせた周波数のシフト量Δν_AOで除算することにより、数式３４に示す如く群遅延時間τを求めることができる。

The phase difference Δφ _FT-ST (ν _{x, 0} ) obtained in this way is the original light that has not been frequency-shifted as described with reference to FIGS. 1 (A) to (C) and Equations 9 to 12. Since it is equivalent to the differential value of the 0th-order optical pulse (that is, the optical pulse to be measured), which is a pulse, by dividing by the shift amount Δν _AO of the frequency shifted by the AO frequency shifter 12, a group as shown in Equation 34 is obtained. The delay time τ can be obtained.

以上説明した如く、本実施形態における波長分散測定装置１によれば、光ファイバー伝送路を伝播する光パルスの一部である被測定光パルスを、周波数シフトしない０次光パルス（被測定光パルス）と、周波数シフトさせた1次光パルス（シフト光パルス）とに分離して、スイッチＳＷ_０、スイッチＳＷ_１を用いて測定すべき光パルスを切り替えつつ、それぞれを干渉計内に取り込むと共に、偏光分離による直交二成分（垂直成分と水平成分）検出を行ない、更に、検出された直交二成分をＨ−Ｆ共振器２３_moni（ν_ｘ）（第一周波数分解手段）及びＨ−Ｆ共振器２４_ref.（ν_０）（第二周波数分解手段）によって周波数分解を行なう際に、２×１光スイッチ（スイッチＳＷ_moni（ν_ｘ）及びスイッチＳＷ_ref.（ν_０））を設けたので、0次光パルスと１次光パルスのそれぞれについて、各共振器に各成分（垂直成分と水平成分）を分離して入力することができるので、被測定光パルスの波長分散の測定を確実に安定性よく行なうことができる。

As described above, according to the chromatic dispersion measuring apparatus 1 of the present embodiment, the measured optical pulse that is a part of the optical pulse propagating through the optical fiber transmission path is a zero-order optical pulse (measured optical pulse) that is not frequency-shifted. And the optical pulses to be measured using the switches SW ₀ and SW ₁ while being separated into frequency-shifted primary light pulses (shifted light pulses), and taking them into the interferometer and polarizing them. Quadrature two components (vertical component and horizontal component) are detected by separation, and the detected quadrature two components are further converted into _HF resonator 23 _moni (ν _x ) (first frequency resolving means) and _HF resonator 24. _ref. ([nu ₀₎ in performing the frequency decomposition by (second frequency decomposition unit), it is provided with the 2 × 1 optical switch (switch SW _moni ([nu _x) and the switch _{SW ref. (ν 0))} , 0 Since each component (vertical component and horizontal component) can be separated and input to each resonator for each of the optical pulse and the primary optical pulse, the measurement of the chromatic dispersion of the optical pulse to be measured is ensured with high stability. Can be done.

Further, by sequentially switching the objects to be measured by the switches SW ₀ , SW ₁ , SW _moni (ν _x ) and SW _ref. (Ν ₀ ), the resonance frequency ν _x and the optical pulse to be measured are measured by two resonators. The phase at the center frequency ν ₀ of the (zero order optical pulse) can be monitored (detected), and the zero order optical pulse can be detected by the photodetector 25 _moni (ν _x ) and the photodetector 26 _ref. (Ν ₀ ) _. Since the interference signal due to the primary light pulse can be detected for each component (vertical component and horizontal component), it is possible to realize highly accurate measurement of the chromatic dispersion of the light pulse to be measured.

  Furthermore, since it is possible to measure chromatic dispersion simply by detecting the signals from the two resonators, a general-purpose computer having two input terminals can be used as the measuring device 27, so that it is simpler and less expensive. A chromatic dispersion measuring apparatus can be provided.

  Further, an optical pulse propagating through the optical fiber transmission line to be measured is used as a measured optical pulse, and a part of the measured optical pulse itself is frequency-shifted by the AO frequency shifter 12 as a primary optical pulse. By interfering the remaining optical pulses that have not been frequency-shifted with the zeroth-order optical pulse, it is possible to perform orthogonal two-component detection and measure chromatic dispersion, so that it is simple without preparing other light sources. It becomes possible to measure the chromatic dispersion of an optical pulse with the apparatus configuration.

  Further, since the 0th-order light pulse and the 1st-order light pulse are rotated in the predetermined polarization direction via the λ / 2 plates 14 and 16, the orthogonal two components can be obtained more accurately and the chromatic dispersion can be obtained. Measurement can be performed reliably. Note that, as described in the present embodiment, the zero-order light pulse and the first-order light pulse are also propagated by the polarization maintaining fiber without passing through the λ / 2 plates 14 and 16, so that the fiber is rotated around the axis. A predetermined polarization direction may be obtained by rotating each.

Further, since the resonance frequency ν _x of the photodetector 25 _moni (ν _x ) can be swept (variable), the width of the optical pulse to be measured is not limited to a certain wavelength, and the width of the measured optical pulse is sufficiently widened by chromatic dispersion. It is possible to measure in a wide wavelength band that covers the range.

  Furthermore, in the interferometer, the polarization-independent beam splitter 17 is used to branch the zero-order light pulse and the first-order light pulse in two directions, so that it can be reliably branched in two directions regardless of the polarization direction. The branched light can be configured to overlap with high accuracy on the same axis in both the route V and the route H.

In order to cancel out the fluctuation of the light generated in the interferometer with high accuracy, for example, when the pulse width of the pulse to be measured is 40 Gbit / s, the frequency shift amount (0th order optical pulse by the AO frequency shifter 12). Δν _AO is preferably 0.8% to 1.2%, that is, about 300 MHz to 500 MHz, but the maximum value of the accurate frequency shift amount Δν _AO is The target phase stability is determined, and any value may be used as long as the phase fluctuation is equal to or less than the phase stability.

  In the above-described embodiment, the 0th-order optical pulse of the 0th-order optical pulse and the 1st-order optical pulse is incident on the interferometer as circularly polarized light using the λ / 4 plate 15, but the present invention is not limited to this. The primary light pulse may be incident on the interferometer as circularly polarized light using the λ / 4 plate 15.

In addition, the switch SW ₀ and the switch SW ₁ are used as the first component switching means and the second component switching means. However, the present invention is not limited to this, and the optical path lengths of the zero-order light pulse and the first-order light pulse are adjusted by the time delay circuit 13. After that, one 2 × 1 switch may be used as the first component switching means and the second component switching means.

  Even if the polarization converter 11 and the switch SWp are not used, two components from the AO frequency shifter 12 to the measuring device 27 described above are installed after each polarization beam splitter 10 for each change component. Although it is possible to measure each polarization component independently by the chromatic dispersion measuring device 1, if the polarization converter 11 and the switch SWp are used as described above, each polarization component can be measured by one chromatic dispersion measuring device 1. Since the components can be measured, the wavelength dispersion of both polarization components of the optical pulse propagating through the optical fiber transmission line can be measured with a cheaper and more compact device configuration.

[Configuration and function of wavelength dispersion correction system]
Next, the configuration and function of the chromatic dispersion correction system S using the chromatic dispersion measuring apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 4 is a schematic configuration diagram of the chromatic dispersion correction system S according to the present embodiment.

  As shown in FIG. 4, the chromatic dispersion correction system S in this embodiment includes a chromatic dispersion measurement apparatus 1, optical fiber networks 40 and 41, a pre-monitor fiber coupler 42, a post-monitor fiber coupler 43, a dispersion correction device 44, an Nx1 switch SW, A transmitter / receiver 45 and an error detector 46 are provided. In the system, the light pulse propagates between the constituent members via the polarization maintaining fiber.

  An optical pulse propagating through an optical fiber transmission line (optical transmission line) of the optical fiber network 40 on the terminal side of the fiber network 40 is a measured pulse, and the chromatic dispersion measurement apparatus 1 measures the chromatic dispersion of the optical pulse. . Then, with the dispersion correction device 42, the measurement result for the optical pulse to be corrected among the optical pulses propagating through the optical fiber transmission line of the fiber network 40 (hereinafter simply referred to as “corrected optical pulse”) Performs correction to generate chromatic dispersion having the same absolute value and the inverted sign, and receives the corrected optical pulse (hereinafter simply referred to as “corrected optical pulse”) by the transmitter / receiver 35. The correction optical pulse is transmitted from 45 to the optical fiber network 41, and the optical pulse restored by the correction can propagate in the optical fiber network 41 that has received the correction optical pulse. Hereinafter, specific procedures will be described with reference to the drawings.

  First, from the optical fiber network 40, an optical pulse transmitted through a specific wavelength channel using a wavelength tunable filter (not shown) among optical pulses propagating through the optical fiber transmission path is selected and extracted as a corrected optical pulse.

  The pre-monitor fiber coupler 42 branches the corrected optical pulse from the optical fiber network 40 in two directions, one of the corrected optical pulses after branching to the N × 1 switch SW, and the other corrected optical pulse by dispersion correction. Guide to device 44.

  The N × 1 switch SW functions as a measured optical pulse switching unit, and is an optical switch having N optical fiber connections on the incident side and one optical fiber connection on the output side of the N × 1 switch SW. On the incident side, one of the N incident fiber paths is selected and connected to the output path. The emission side is connected to an input port (not shown in FIG. 1) of the chromatic dispersion measuring apparatus 1. According to the example shown in FIG. 4, when the number of optical fiber connections on the incident side is 5 (N = 5) and the second incident fiber path from the left is connected to the output side as shown by the solid line in the figure, dispersion correction is performed. The chromatic dispersion can be measured by using the optical pulse (corrected optical pulse) before chromatic dispersion correction by the device 44 as the measured optical pulse. In addition, when the leftmost incident fiber path is connected to the output side as indicated by a one-dot chain line in the figure, the optical dispersion (corrected optical pulse) whose wavelength dispersion is corrected by the dispersion correcting device 44 is used as the measured optical pulse. Can be measured. In addition, the optical fiber transmission path of the path | route which extracted the optical pulse of a different wavelength channel and the branched optical fiber transmission path from a different optical fiber network can be connected to another incident fiber path | route. Further, the N × 1 switch SW receives the synchronization signal Ssy from the chromatic dispersion measuring device 1 through a cable or the like, thereby switching the path of the N × 1 switch SW in synchronization with the measurement by the chromatic dispersion measuring device 1. Can be done. Thereby, measurement evaluation of chromatic dispersion can be performed in a state where a specific path is identified.

  When the chromatic dispersion measuring apparatus 1 receives the measured optical pulse from the N × 1 switch SW, the chromatic dispersion measuring apparatus 1 measures the chromatic dispersion of the measured optical pulse. In addition, the specific chromatic dispersion measuring method in the chromatic dispersion measuring apparatus 1 is as described above.

  The chromatic dispersion measuring device 1 functions as a correction signal generation unit and a correction signal transmission unit, generates a dispersion correction signal Scom based on the measured chromatic dispersion, and transmits the generated dispersion correction signal Scom via a cable or the like. Transmit to the dispersion correction device 44. More specifically, the measuring device 27 including the computer of the chromatic dispersion measuring device 1 controls the control signal indicating the bias voltage to be applied to the dispersion correcting device 44 based on the measured chromatic dispersion or other As a control signal, a dispersion correction signal Scom is generated so as to generate chromatic dispersion having the same absolute value as that of the chromatic dispersion but having the opposite sign.

  The dispersion correction device 44 performs chromatic dispersion correction on the corrected optical pulse received from the pre-monitor fiber coupler 42 based on the dispersion correction signal Scom received from the chromatic dispersion measuring device 1, and the post-monitor fiber as the corrected optical pulse. Guide to coupler 43.

  In the post-monitor fiber coupler 43, the correction light pulse from the dispersion correction device 44 is branched in two directions, one of the correction light pulses after branching to the N × 1 switch SW, and the other correction light pulse to the transmitter / receiver 45. Lead. In this way, the corrected correction light pulse is made incident on the N × 1 switch SW, and measurement is performed again by the chromatic dispersion measuring device 1, so that the degree of correction performed by the dispersion correction device 44 remains. Correction accuracy such as the degree of chromatic dispersion (the chromatic dispersion remaining without being corrected) can be evaluated.

  The transmitter / receiver 45 generates a transmission optical pulse including the correction optical pulse from the post-monitor fiber coupler 43, guides the generated transmission optical pulse to the optical fiber network 41, and the optical fiber network 41 receiving the transmission optical pulse corrects the transmission optical pulse. It is possible to propagate the optical pulse restored by the above. The transmitter / receiver 45 converts the corrected light pulse into an electrical signal and transmits the data signal Sd to the error detector 46 via a cable or the like.

  The error detector 46 functions as an error detection unit, detects an error in the corrected optical pulse, and notifies the chromatic dispersion measuring device 1 of the error. More specifically, when the error detector 46 receives the data signal Sd transmitted from the transmitter / receiver 45, the error detector 46 measures an error such as a bit error rate, and cable the error signal Se to the chromatic dispersion measuring device 1 as the error signal Se. And so on. The chromatic dispersion measuring device 1 that has received the error signal Se functions as a correction signal generation unit, generates a dispersion correction signal Scom that reduces the error based on the error signal, and transmits the dispersion correction signal Scom to the dispersion correction device 44. . This makes it possible to perform chromatic dispersion correction with higher accuracy.

  Note that the chromatic dispersion correction can be performed not only in the above-described embodiment but also, for example, using only the correction light pulse as a measurement target. In this case, only the corrected optical pulse (corrected optical pulse) is used as a measurement target of the chromatic dispersion measuring apparatus 1, and the dispersion correcting device 44 may be controlled so that the remaining chromatic dispersion becomes as small as possible. Further, if the chromatic dispersion amount generated by the dispersion correction device 44 has been calibrated, the chromatic dispersion correction can be performed only by measuring the chromatic dispersion of the optical pulse to be corrected (the optical pulse before correction). However, from the viewpoint of high performance and maintenance management of the chromatic dispersion correction system S, as described in the above-described embodiment, both the corrected optical pulse and the corrected optical pulse are measured by the chromatic dispersion measuring apparatus 1. Preferably, each dispersion correction signal Scom is generated on the basis of both of these measured light pulses, and the corrected light pulse is corrected by the dispersion correction device 44.

(A) It is a figure which shows the waveform of the optical pulse which is propagating through the optical fiber transmission line. (B) A time waveform of an optical pulse. (C) It is a figure which shows the dependence characteristic of the frequency (nu) of the phase of an optical pulse. It is a schematic block diagram of the wavelength dispersion measuring apparatus 1 concerning this embodiment. (A) Spectral waveforms of the zero-order light pulse and the first-order light pulse, and spectrum waveforms of the _HF resonator 23 _moni (ν _x ) and the _HF resonator 24 _ref. (Ν ₀ ). (B) The dependence characteristic of the phase ν of the zeroth-order light pulse and the first-order light pulse on the frequency ν. It is a schematic block diagram of the wavelength dispersion measuring apparatus 1 concerning this embodiment.

Explanation of symbols

S wavelength dispersion correction system
DESCRIPTION OF SYMBOLS 1 Wavelength dispersion measuring apparatus 10 Polarization beam splitter 11 Polarization converter
12 AO frequency shifter 13 Time delay circuit 14, 16 λ / 2 plate 15 λ / 4 plate 17 Polarization independent beam splitter 18, 19 Polarizer 20, 21 Fiber coupler
25 _moni (ν _x ), 26 _ref. (Ν ₀ ) photodetector 23 _moni (ν _x ), 24 _ref. (Ν ₀ ) _HF resonator 27 measuring device SW ₀ , SW ₁ , SW _moni (ν _x ), SW _ref. (Ν ₀ ) Switch 40, 41 Optical fiber network 42 Fiber coupler for pre-monitoring 43 Fiber coupler for post-monitoring SW Nx1 switch 45 Transmitter / receiver 46 Error detector Scom Dispersion correction signal Ssy Synchronization signal Sd Data signal Se Error signal

Claims (22)

In a chromatic dispersion measuring method for measuring chromatic dispersion of a light pulse to be measured,
A shift step of shifting the frequency with respect to a part of the light pulse to be measured;
A measuring object switching step for controlling propagation or blocking of the measured optical pulse and the shifted optical pulse whose frequency is shifted;
A circularly polarizing step of changing either the light pulse to be measured or the shifted light pulse to circularly polarized light;
A separation step of separating one of the circularly polarized light pulses into two orthogonal components and separating the other light pulse having a predetermined polarization direction into two orthogonal components;
A first component switching step and a second component switching step of entering the measured light pulse and the shifted light pulse for each of the components, and switching to emit one of the incident components.
Receiving a light pulse emitted from the first component switching step and performing frequency decomposition at a predetermined frequency, wherein the light pulse to be measured is switched by the measurement object switching step; and The first frequency decomposition step of performing frequency decomposition for each of the components for each of the light pulse to be measured and the shifted light pulse by switching the component by a first component switching step;
A second frequency decomposition step of receiving the optical pulse emitted from the second component switching step and performing frequency decomposition at the center frequency of the measured optical pulse, the optical pulse to be measured by the measurement target switching step And the second frequency decomposition step of performing frequency decomposition for each of the components of the measured light pulse and the shifted light pulse by switching the component by the first component switching step,
Detecting the result of frequency decomposition in the first frequency decomposition step as an interference signal for each component;
Detecting the result of frequency decomposition in the second frequency decomposition step as an interference signal for each component;
Measuring chromatic dispersion of the light pulse to be measured based on each interference signal;
A chromatic dispersion measuring method comprising: In the chromatic dispersion measuring method according to claim 1,
In the case where the optical pulse to be measured is an optical pulse having a plurality of polarization components, there is provided a polarization component specifying step for specifying one polarization component and making it enter the shift step. Measuring method. In the chromatic dispersion measuring method according to claim 1 or 2,
A first polarization direction control step of rotating the measured light pulse in a predetermined polarization direction;
A second polarization direction control step of rotating the shift light pulse in a predetermined polarization direction,
In the circularly polarizing step, after one of the light pulse to be measured and the shifted light pulse is rotated in the predetermined polarization direction, the one light pulse is changed to circularly polarized light,
The method for measuring chromatic dispersion, wherein the separating step separates the other optical pulse into two orthogonal components after the other optical pulse is rotated in the predetermined polarization direction. In the chromatic dispersion measuring method according to claim 1 or 2,
The measured light pulse and the shifted light pulse propagate through a waveguide having a function of maintaining polarization, and each of the waveguides is provided to be rotatable around an axis; and
When the one light pulse of the light pulse to be measured or the shifted light pulse is incident on the circular polarization step, the waveguide that propagates the one light pulse is rotated about its axis to rotate the one light pulse. Rotate the light pulse to a predetermined polarization direction,
When the other optical pulse is incident on the separation step, the waveguide that propagates the other optical pulse is rotated around the axis so that the other optical pulse has a predetermined polarization direction. A chromatic dispersion measuring method characterized by the above. In the chromatic dispersion measuring method according to any one of claims 1 to 4,
The chromatic dispersion measuring method characterized in that the first frequency resolving step performs frequency decomposition by sweeping the predetermined frequency in at least a wavelength band in which chromatic dispersion of the optical pulse to be measured is to be measured. In the chromatic dispersion measuring method according to any one of claims 1 to 5,
The method for measuring chromatic dispersion, wherein the separating step separates the measured optical pulse and the shifted optical pulse into two components using a polarization-independent beam splitter that does not depend on the polarization direction. In the chromatic dispersion measuring method according to any one of claims 2 to 6,
The polarization component specifying step includes a polarization beam splitter that separates the measured optical pulse into a vertical component and a horizontal component, and a polarization that polarizes one component of the measured optical pulse after the separation into the other component. A chromatic dispersion measuring method, wherein a single polarization component of the measured optical pulse is specified by a converter. In the chromatic dispersion measuring method according to any one of claims 1 to 7,
The shift step includes a part of the measured optical pulse such that a difference between the frequency of the shifted optical pulse and the frequency of the measured optical pulse is 0.8% to 1.2% of the pulse width of the measured pulse. A chromatic dispersion measuring method, wherein the frequency is shifted with respect to. In a chromatic dispersion measuring device for measuring the chromatic dispersion of a light pulse to be measured,
Shift means for shifting the frequency with respect to a part of the light pulse to be measured;
A measuring object switching means for controlling propagation or blocking of the measured optical pulse and the shifted optical pulse whose frequency is shifted;
A first optical element that changes a light pulse of either the light pulse to be measured or the shifted light pulse to circularly polarized light;
Separating means for separating one of the light pulses that are circularly polarized into two orthogonal components and separating the other optical pulse having a predetermined polarization direction into two orthogonal components;
A first component switching unit and a second component switching unit configured to enter the measured light pulse and the shifted light pulse for each of the components, and to switch one of the incident components to emit the component;
First frequency resolving means for receiving an optical pulse emitted from the first component switching means and performing frequency decomposition at a predetermined frequency, wherein the optical pulse to be measured is switched by the measurement object switching means; and The first frequency resolving means for performing frequency resolving for each of the components of the measured light pulse and the shifted light pulse by switching the components by the first component switching means;
A second frequency resolving means for receiving the optical pulse emitted from the second component switching means and performing frequency decomposition at the center frequency of the measured optical pulse, the optical pulse to be measured by the measuring object switching step; And switching the component by the first component switching means, the second frequency resolving means for performing frequency decomposition for each of the components for each of the measured light pulse and the shifted light pulse,
First detection means for receiving light from the first frequency resolving means and detecting it as an interference signal for each component;
Second detection means for receiving light from the second frequency decomposition step and detecting as an interference signal for each component;
Measuring means for measuring chromatic dispersion of the light pulse to be measured based on each interference signal;
A chromatic dispersion measuring apparatus comprising: In the chromatic dispersion measuring apparatus according to claim 9,
In the case where the optical pulse to be measured is an optical pulse having a plurality of polarization components, there is provided a chromatic dispersion comprising polarization component specifying means for specifying one polarization component and making it incident on the shift means measuring device. In the chromatic dispersion measuring apparatus according to claim 9 or 10,
A second optical element that rotates the measured light pulse in a predetermined polarization direction;
A third optical element for rotating the shifted light pulse in a predetermined polarization direction,
The first optical element is the measured light pulse after being rotated in the predetermined polarization direction by the second optical element, or the shift after being rotated in the predetermined polarization direction by the third optical element. Change one of the light pulses to circularly polarized light,
The separating means separates the other optical pulse into two orthogonal components after the other optical pulse is rotated in the predetermined polarization direction by the second optical element or the third optical element. Chromatic dispersion measuring device. In the chromatic dispersion measuring apparatus according to claim 9 or 10,
The measured light pulse and the shifted light pulse propagate through a waveguide having a function of maintaining polarization, and each of the waveguides is provided to be rotatable around an axis; and
When the one optical pulse of the light pulse to be measured or the shifted light pulse is incident on the first optical element, the one of the light pulses propagating the one optical pulse is rotated around the axis and the one optical pulse is rotated. Are rotated so that the light pulse has a predetermined polarization direction,
When the other optical pulse is incident on the separating means, the waveguide that propagates the other optical pulse is rotated around the axis so that the other optical pulse has a predetermined polarization direction. A chromatic dispersion measuring apparatus. In the chromatic dispersion measuring device according to any one of claims 9 to 12,
The chromatic dispersion measuring apparatus, wherein the first frequency resolving means performs frequency decomposition by sweeping the predetermined frequency at least in a wavelength band in which chromatic dispersion of the optical pulse to be measured is to be measured. In the chromatic dispersion measuring device according to any one of claims 9 to 12,
The chromatic dispersion measuring apparatus, wherein the separating means separates the measured optical pulse and the shifted optical pulse into two components using a polarization-independent beam splitter independent of the polarization direction. In the chromatic dispersion measuring device according to any one of claims 10 to 14,
The polarization component specifying means includes a polarization beam splitter that separates the measured optical pulse into a vertical component and a horizontal component, and a polarization that polarizes one component of the measured optical pulse after the separation into the other component. A chromatic dispersion measuring apparatus characterized by specifying one polarization component of the measured optical pulse by a converter. In the chromatic dispersion measuring apparatus according to any one of claims 9 to 15,
The shift means includes a part of the measured optical pulse such that a difference between the frequency of the shifted optical pulse and the frequency of the measured optical pulse is 0.8% to 1.2% of the pulse width of the measured pulse. A chromatic dispersion measuring device characterized in that the frequency is shifted with respect to. In a chromatic dispersion correction system including a dispersion correction device for correcting chromatic dispersion of an optical pulse propagating through an optical transmission line,
The chromatic dispersion measuring apparatus according to any one of claims 7 to 12, wherein the chromatic dispersion is measured by using an optical pulse propagating through the optical transmission line as the measured optical pulse, based on the measured chromatic dispersion. A chromatic dispersion measuring device comprising: a correction signal generating means for generating a correction signal; and a correction signal transmitting means for transmitting the generated correction signal to the dispersion correction device;
The dispersion correction device that receives the correction signal and corrects an optical pulse propagating through the optical transmission line based on the correction signal;
A chromatic dispersion correction system comprising: The chromatic dispersion correction system according to claim 17,
The chromatic dispersion measuring device is an optical pulse propagating through the optical transmission line, and measures chromatic dispersion using at least an optical pulse before correction by the dispersion correction device as the measured optical pulse. Correction system. The chromatic dispersion correction system according to claim 17 or 18,
The chromatic dispersion measuring device is an optical pulse propagating through the optical transmission line, and measures chromatic dispersion using at least the optical pulse corrected by the dispersion correcting device as the measured optical pulse. Correction system. The chromatic dispersion correction system according to any one of claims 17 to 19,
An error detection means for detecting an error of the optical pulse after correction by the dispersion correction device and transmitting the error signal to the chromatic dispersion measuring device;
The chromatic dispersion correction system, wherein the correction signal generation means of the chromatic dispersion measuring device generates the correction signal based on the error signal received from an error detection means. The chromatic dispersion correction system according to any one of claims 17 to 20,
A plurality of optical pulses are incident, and a measured optical pulse switching unit is configured to switch so that one of the incident optical pulses is emitted as the measured optical pulse to the chromatic dispersion measuring device. Chromatic dispersion correction system. The chromatic dispersion correction system according to claim 21,
The chromatic dispersion correction system, wherein the plurality of optical pulses include at least an optical pulse before correction or an optical pulse after correction by the dispersion correction device.

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