JP5138237B2 - Optical sampling apparatus and optical sampling method - Google Patents

Description

  The present invention relates to an optical sampling technique, and more particularly to a technique for measuring the polarization state of signal light that fluctuates at high speed in an ultrahigh-speed optical communication system.

  In an ultrahigh-speed optical communication system with a transmission rate per channel of 40 gigabits per second or more, management of optical fiber dispersion characteristics, particularly polarization mode dispersion, is an important issue. In a normal optical fiber, the core diameter deviates from an ideal circle due to various external factors such as heat, tension, and pressure, birefringence exists inside the core, and polarization mode dispersion occurs. Polarization mode dispersion, which fluctuates at a high speed due to changes in these external factors, is a major transmission capacity limitation factor in an ultrahigh-speed optical communication system. In evaluating and compensating this polarization mode dispersion, it is indispensable to measure the polarization state of signal light that fluctuates at high speed.

A polarization state measuring device using a polarizer and a wave plate is known and has already been commercialized. In this method, the signal light that is the light to be measured is branched into four and then received through a spatial optical system composed of a polarizer, a wave plate, etc., and the amplitude of the X polarization component of the signal light, the Y polarization The amplitude of the component and the phase difference between the X polarization component and the Y polarization component are obtained (see Non-Patent Document 1).
However, since the measurement rate of this polarization state measuring device is 3500 per second or more, it is not possible to measure the polarization state of signal light that fluctuates at high speed in the optical transmission line or optical device of the ultrahigh-speed optical communication system. Is possible.

  In addition, as a technique related to optical sampling, by observing the linear correlation between the signal light and the local light emission pulse, the intensity modulation component and the frequency modulation component of the signal light are observed simultaneously with the pulse width of the local light pulse as time resolution Techniques are known (see, for example, Patent Document 1 and Patent Document 2).

JP-A-9-162808

JP 2004-132719 A

Hewlett-Packard Japan, “Optical measuring instrument catalog 1998-1999”, p. 80-84, 1998

  An object of this invention is to provide the technique which can measure the polarization state of the optical signal which fluctuates at high speed.

  An optical sampling device according to an aspect of the present invention has a period slightly different from the repetition period of signal light, the pulse width is shorter than the pulse width of signal light, and an X polarization component and a Y polarization component in a measurement system Sampling pulse generating means for generating optical pulses having substantially the same, means for separating the signal light and sampling pulse into X polarization component and Y polarization component, respectively, and the polarization separated signal light, A branching unit that branches the Y polarization component of the sampling pulse into a first Y polarization component and a second Y polarization component, and any one of the signal light and the second Y polarization component of the sampling pulse. A first delay unit that delays a predetermined time, inputs the signal light and the X polarization component of the sampling pulse, and shifts one phase of the signal light and the X polarization component of the sampling pulse by π / 2. The 90-degree hybrid is inputted with the signal light and the first Y polarization component of the sampling pulse, and the phase of any one of the signal light and the first Y polarization component of the sampling pulse is shifted by π / 2. Two optical 90-degree hybrids and the second Y-polarized component of the sampling light and the second Y-polarized component of the sampling light. Receiving the third optical 90-degree hybrid that shifts one of the phases by π / 2, the signal light from the first optical 90-degree hybrid, and the X polarization component of the sampling pulse; The first and second balanced optical receivers that output two currents respectively, and the signal light from the second optical 90-degree hybrid and the first Y polarization component of the sampling pulse. The third and fourth balanced optical receivers outputting the third and fourth currents, respectively, and the signal light from the third optical 90-degree hybrid and the second Y polarization of the sampling pulse 5th and 6th balanced optical receivers that receive components and output 5th and 6th currents, respectively, and arithmetic processing that performs arithmetic processing on the current values of the first to sixth currents And an apparatus. The present invention is not limited to an apparatus, and can also be established as an invention of a method realized by the apparatus.

  According to the present invention, the polarization state of an optical signal that fluctuates at high speed can be measured. That is, it is possible to realize optical sampling for detecting an interference effect that is a linear correlation between the X polarization component and the Y polarization component of the sampling pulse for each of the X polarization component and the Y polarization component of the signal light. The amplitude and phase of the X polarization component and the Y polarization component of the light can be observed.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an optical sampling apparatus according to the first embodiment of the present invention. The optical sampling apparatus according to the present embodiment includes a sampling pulse generating means 1, polarization separating elements 2-1 and 2-2, branching elements 3-1 and 3-2, a delay means 4-2, To third optical 90-degree hybrids 5-1 to 5-3, first to sixth balanced light receivers 6-1 to 6-6, and first to sixth low-pass filters 7-1. -7-6, first to sixth numerical means 8-1 to 8-6, and an arithmetic processing unit 9.

  The sampling pulse generator 1 generates a sampling pulse having a period 1 / (f + Δf) obtained by adding an offset Δf to a repetition period 1 / f of repetitive signal light (hereinafter simply referred to as “signal light”). . This sampling pulse has both the X-polarized wave component and the Y-polarized wave component almost uniformly with respect to the XY coordinates that are connected to the measurement system. Here, the setting of the offset Δf is changed according to the signal light to be observed, but the signal is observed as follows depending on the value of the offset Δf. Increasing the offset Δf increases the number of signal pulses that can be observed (displayed), but each observed signal pulse becomes coarse. On the other hand, if the offset Δf is decreased, the signal light can be observed finely, but the number of signal pulses that can be observed decreases. These relationships are in a trade-off relationship with respect to a certain memory (the number of samplings). That is, for an arbitrary signal light, in order to increase the magnification of the measurement result (that is, the fineness of observation of the signal light), the offset Δf may be decreased. For this reason, in the present invention, although depending on the time resolution and spatial resolution of the measurement system, high-speed measurement at the sub-pico level is possible.

  The sampling pulse that is a local light emission pulse output from the sampling pulse generating means 1 is a polarization separation element 2-1, and the signal light is a polarization separation element 2-2. And the Y polarization component. As the polarization separation elements 2-1 and 2-2, for example, polarization elements such as a polarization beam splitter, rutile, and calcite can be used. These polarization beam splitting elements convert the incident signal light and sampling pulse into a polarization component (X polarization) in the reference direction (0 degree direction) and a polarization component (Y polarization in the 90 degree direction with respect to the reference direction). ).

The Y polarization component of the sampling pulse separated by the separation element 2-1 is branched into a first Y polarization component and a second Y polarization component by the branching unit 3-1, and the Y polarization component of the signal light is first Y polarization component in the branch unit 3 2 and is split into a second Y polarization component. The phase of the first Y-polarized wave component of the sampling pulse is corrected by correcting means 4-1, which will be described in detail later, and the second Y-polarized wave component of the sampling pulse is delayed by a predetermined time by delay means 4-2. The Here, the delay means 4-2 delays the second Y-polarized component of the sampling pulse, but controls the relative time delay between the sampling pulse and the signal light. Instead of the second Y polarization component, the second Y polarization component of the signal light may be delayed for a predetermined time. Further, the same action can be realized by branching the X polarization component instead of the Y polarization component into the first and second polarization components and providing delay means for one of them.

The X polarization component of the signal light and the X polarization component of the sampling pulse separated by the polarization separation elements 2-1 and 2-2 enter the first optical hybrid 5-1, and the X polarization component of the signal light. The phase of either the wave component or the X polarization component of the sampling pulse is shifted by π / 2 in the first optical hybrid 5-1.
Further, the first Y polarization component of the signal light and the first Y polarization component of the sampling pulse are incident on the second optical hybrid 5-2, and the first Y polarization component of the signal light and the sampling are sampled. The phase of any one of the first Y polarization components of the pulse is shifted by π / 2 by the second optical hybrid 5-2.
The second Y-polarized component of the signal light and the second Y-polarized component of the sampling pulse are incident on the third optical hybrid 5-3 and sampled with the second Y-polarized component of the signal light. The phase of any one of the second Y polarization components of the pulse is shifted by π / 2 by the third optical hybrid 5-3.
The first to third light 90-degree hybrids 5-1 to 5-3 are known to be realized by, for example, a spatial optical system using a half mirror and a polarization separation element or an integrated optical circuit. .

  Output lights from the first to third optical hybrids 5-1 to 5-3 are received by the first to sixth balanced optical receivers 6-1 to 6-6. The outputs from the first to sixth balanced optical receivers 6-1 to 6-6 are the first to sixth low-pass filters 7-1 to 7 that are set to the repetition period of the sampling pulse. After waveform equalization at -6, it is digitized by the first to sixth digitizing means 8-1 to 8-6 and then input to the arithmetic processing unit 9. The arithmetic processing unit 9 performs arithmetic processing as described below on the six input digital signals, that is, the six current values generated in the first to sixth balanced optical receivers, The amplitude and phase of the X polarization component and Y polarization component of the signal light are obtained.

ここで、ａ_sx（ｔ）、ａ_sy（ｔ）は信号光のＸ、Ｙ偏波成分の振幅であり、φ_sx（ｔ）、φ_sy（ｔ）は信号光のＸ、Ｙ偏波成分の位相である。
一方、上記条件を満たす基準方向に対して４５度方向を向く単一偏波面を有したサンプリングパルスの偏波状態は、次式で表される。

ここで、ａ_p（ｔ）、φ_pはサンプリングパルスのＸ、Ｙ偏波成分の振幅とＸ、Ｙ偏波成分の位相であり、ｔ₀はパルスの中心位置である。上記条件３より両者の中心周波数をω₀と置く。 Next, the operation of the optical sampling apparatus of the present embodiment configured as described above will be described.
The sampling pulse needs to satisfy the following conditions. These conditions and the action of the optical hybrid are the same as those of the conventional optical sampling technology (see, for example, Patent Document 1 and Patent Document 2).
(Condition 1) The intensity of the signal light hardly changes within the time of the pulse width of the sampling light pulse.
(Condition 2) The frequency of the signal light hardly changes within the time of the pulse width of the sampling light pulse.
(Condition 3) The center frequency of the sampling light matches the center frequency of the signal light.
From the above conditions 1 and 2, it is necessary to prepare a sampling light pulse sufficiently shorter than the required time resolution in order to measure the polarization state of the signal light that fluctuates at high speed. When the above conditions are satisfied, it will be described below that the amplitude and phase of the X polarization component and Y polarization component of the signal are correctly detected by the optical sampling device of the present invention.
First, the polarization state of the signal light is expressed by the following equation.

Here, a _sx (t) and a _sy (t) are the amplitudes of the X and Y polarization components of the signal light, and φ _sx (t) and φ _sy (t) are the X and Y polarization components of the signal light. Is the phase.
On the other hand, the polarization state of the sampling pulse having a single polarization plane facing the direction of 45 degrees with respect to the reference direction satisfying the above condition is expressed by the following equation.

Here, a _p (t) and φ _p are the amplitudes of the X and Y polarization components and the phases of the X and Y polarization components of the sampling pulse, and t ₀ is the center position of the pulse. From condition 3 above, the center frequency of both is set to ω ₀ .

When the relative phase difference between the X and Y polarization components of the signal light is δ _xy (t), the Jones vector indicating the polarization state of the signal light at an arbitrary time is the above three parameters {a _sx (t), a _sy (t), δ _xy (t)} is uniquely determined.
At this time, current values P ₁ (t) and P ₂ (t) of currents output from the first and second balanced optical receivers 6-1 and 6-2 through the first optical hybrid 5-1. ) Is expressed as follows.

FIG. 2 shows a flow for obtaining the (instantaneous) amplitudes of the X polarization component and the Y polarization component using the above current values, and a flow for obtaining the phase of the X polarization component and the Y polarization component. 3 shows. The measured values P ₁ (t) to P ₆ (t) in FIGS. 2 and 3 are output from the first to sixth numerical means 8-1 to 8-6, and are as follows. Will be explained. 2 and 3 are all executed by the arithmetic processing unit 9.

となる。
同様に、第２の光ハイブリッド５−２を介して第３及び第４のバランス型光受信器６−３、６−４から出力される電流の電流値Ｐ₃（ｔ）、Ｐ₄（ｔ）より求められる信号光のＹ偏波成分の振幅ａ_sy（ｔ）は、

となる（ステップＡ１３、Ａ１４、Ａ２２、Ａ３２、Ａ４２）。 As shown in FIG. 2, the amplitude of the X-polarized wave component is that of the sampling pulse and the signal light output from the first and second balanced optical receivers 6-1 and 6-2 via the first optical hybrid. The current values P ₁ (t) and P ₂ (t) of the X polarization component are respectively squared (steps A11 and A12), added (step A21), and obtained by taking the square root (step A31). (Step A41). Therefore, the amplitude a _sx (t ₀ ) of the X polarization component of the signal light is

It becomes.
Similarly, current values P ₃ (t) and P ₄ (t) of currents output from the third and fourth balanced optical receivers 6-3 and 6-4 via the second optical hybrid 5-2. The amplitude a _sy (t) of the Y polarization component of the signal light obtained from

(Steps A13, A14, A22, A32, A42).

Next, the phase of the X polarization component and the phase of the Y polarization component are obtained as shown in FIG.
First, current values P ₁ (t) and P ₂ (t) of currents output from the first and second balanced optical receivers 6-1 and 6-2 through the first optical hybrid 5-1. Current values P ₃ (t) and P ₄ (t) of currents output from the third and fourth balanced optical receivers 6-3 and 6-4 via the second optical hybrid 5-2. Current values P ₅ (t) and P ₆ (t) of currents output from the fifth and sixth balanced optical receivers 6-5 and 6-6 via the third optical hybrid 5-3. The first to third arc tangents (arc tangents) are calculated with respect to the result (steps B11 to B13). For example, current values P ₁ (t) and P ₂ (t) of currents output from the first and second balanced optical receivers 6-1 and 6-2 through the first optical hybrid 5-1. From this, the phase difference φ _sx (t) −φ _p between the phase φ _sx (t) of the X polarization component of the signal light and the phase φ _p of the X polarization component of the sampling pulse is obtained,

となる（ステップＢ１１）。

(Step B11).

となる（ステップＢ１２）。式（６）において、φ_offは第１の光ハイブリッドと第２の光ハイブリッド間の光路差によって生じる相対的な位相差であり、補正手段４−１で補正された位相分である。この第１の光ハイブリッドと第２の光ハイブリッド間の光路差によって生じる相対的な位相差φ_offは、測定開始前に予め求めておく必要がある。この位相差は、例えば、Ｘ−Ｙ座標に対して４５°傾いた直線偏波を信号光として入力することで予測することができる。 Then, current values P ₃ (t) and P ₄ (t) of currents output from the third and fourth balanced optical receivers 6-3 and 6-4 via the second optical hybrid 5-2. From this, the phase difference φ _sy (t) −φ _p between the phase φ _sy (t) of the Y polarization component of the signal light and the phase φ _p of the Y polarization component of the sampling pulse is obtained,

(Step B12). In Expression (6), φ _off is a relative phase difference caused by an optical path difference between the first optical hybrid and the second optical hybrid, and is a phase component corrected by the correcting unit 4-1. The relative phase difference φ _off caused by the optical path difference between the first optical hybrid and the second optical hybrid needs to be obtained in advance before the start of measurement. This phase difference can be predicted, for example, by inputting a linearly polarized wave tilted by 45 ° with respect to the XY coordinates as signal light.

An optical path difference corresponding to the delay τ is provided between the second optical hybrid and the third optical hybrid, and the phase change per unit time (instantaneous frequency) is determined from the amount of phase change caused by the optical path difference (time delay). Further, the phase of the Y polarization component is obtained. The optical path difference between the first optical hybrid and the second optical hybrid is corrected by φ _off , and the phase of the X polarization component can be obtained based on the phase of the Y polarization component obtained above.

Since the optical path difference between the first, second, and third optical hybrids is related by φ _off and τ, the relative position caused by the optical path difference between the first optical hybrid and the third optical hybrid. The phase difference need not be considered directly.

Also, current values P ₅ (t) and P ₆ (t) of currents output from the fifth and sixth balanced optical receivers 6-5 and 6-6 via the third optical hybrid 5-3. The phase difference φ _sy (t + τ) −φ _p between the phase φ _sy (t + τ) of the Y polarization component of the signal light and the phase φ _p of the Y polarization component of the sampling pulse is expressed as follows (step) B13).

The calculation for obtaining the Jones vector [a _sx (t), a _sy (t) exp {iδ _xy (t ₀ )] representing the polarization state of the signal light from the equations (3) to (6) is performed as follows. .

First, δ _xy (t ₀ ) is calculated as in the following equation from Equations (5) and (6).

Further, the following equation is obtained from the equations (6) and (7) (step B3).

This is the amount of change in the phase of the Y polarization component at the time delay τ and corresponds to the instantaneous frequency. Then, by integrating this instantaneous frequency (step B4), the phase φ _sy (t) of the Y polarization component of the signal light is obtained (step B5). Further, the phase φ _sx (t) of the X polarization component of the signal light is also calculated from the equation (8) according to the equation (9) (step B6).

  Therefore, the amplitude and phase of the X and Y polarization components of the signal light can be obtained by performing the arithmetic processing as described above.

なる計算を行うことにより、強度変調成分Ｉ（ｔ₀）を得ることができる。 From the amplitudes a _sx (t) and a _sy (t) of the X and Y polarization components of the signal light obtained by the above arithmetic processing,

By performing this calculation, the intensity modulation component I (t ₀ ) can be obtained.

In this embodiment, when the signal light is only X-polarized light, φ _sy (t ₀ + τ) −φ _sy (t ₀ ) cannot be obtained. However, before the signal light is input, the polarization rotator is turned on. By using it, such a situation can be avoided.

An optical sampling apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a schematic configuration of an optical sampling device according to the second embodiment of the present invention. In this embodiment, even when the time delay provided by the variable delay means 10 is set to 0, the relative phase difference caused by the optical path difference between the first optical hybrid and the second optical hybrid is not zero. For this reason, although φ _off is omitted in FIG. 4, it is necessary to consider φ _off in this embodiment as well as in the first embodiment. In FIG. 4, the same components as those in FIG.

The sampling pulse generator 1 generates a sampling pulse having a period 1 / (f + Δf) obtained by adding an offset Δf to a signal light repetition period 1 / f.
The sampling pulse that is a local light emission pulse output from the sampling pulse generating means 1 is a polarization separation element 2-1, and the signal light is a polarization separation element 2-2. And the Y polarization component. The separated X polarization component of the sampling pulse and the X polarization component of the signal light are incident on the first optical hybrid 5-1. The Y polarization component of the sampling pulse delayed by the variable delay means 10 for a predetermined time and the Y polarization component of the signal light not delayed are incident on the second optical hybrid 5-2.

  Output lights from the first and second optical hybrids 5-1 and 5-2 are received by the first to fourth balanced optical receivers 6-1 to 6-4. The output currents from the first to fourth balanced optical receivers are the first to fourth low-pass filters 7-1 to 7-4 whose cutoff frequency is set to about the repetition period of the sampling pulse. After the waveform equalization, it is digitized by the first to fourth digitizing means 8-1 to 8-4 and then input to the arithmetic processing unit 9.

The operation of the optical sampling device according to this embodiment configured as described above will be described.
When the time delay provided by the variable delay means 10 is set to zero, the output currents from the first to fourth balanced optical receivers are the first to fourth balanced lights in the first embodiment. This corresponds to the current values P ₁ (t) to P ₄ (t) of the output current from the receiver. Therefore, Formula (3)-Formula (6) are obtained.

Next, when the time delay of the variable delay means 10 is set to τ, the output currents from the third and fourth balanced optical receivers 6-3 and 6-4 are the fifth in the first embodiment. And the current values P ₅ (t) and P ₆ (t) of the output current from the sixth balanced optical receivers 6-5 and 6-6. Therefore, equation (7) is obtained.

  The arithmetic processing unit 9 performs arithmetic processing on the six current values input in two steps as described above, and obtains the amplitude and phase of the X polarization component and Y polarization component of the signal light. However, since the X polarization component of the signal light can be obtained without depending on the delay time τ, it is obtained in the same manner as in the first embodiment as shown in FIG.

  Next, in the second embodiment, the first measurement value (first measurement in FIG. 6: time delay 0) and the second measurement value (second measurement in FIG. 6: time delay τ) ) To match the time axis. Therefore, the amplitude waveform of the X polarization component of the signal light is obtained from each of the first measurement value and the second measurement value (step B72), the amplitude waveforms are compared, and the time that is most correlated is obtained. Ask. Then, based on the time, the time axis of the first measurement value and the second measurement value are matched to associate the first measurement value with the second measurement value (step B8). The subsequent processing is the same as in FIG.

  Hereinafter, the polarization mode dispersion vector for measuring the polarization mode dispersion vector of the birefringent medium using the complex amplitude of the X polarization component and the Y polarization component calculated in the arithmetic processing of the first and second embodiments. The measurement method of will be described.

  In an optical communication system composed of continuous birefringent media, the influence of overall polarization mode dispersion can be evaluated as the sum of PMD vectors of individual birefringent media.

The polarization mode dispersion vector is defined as the Stokes vector in the Stokes space (Poincare sphere), the direction is parallel to the Stokes vector indicating the slow main polarization state of the output light from the birefringent medium, and the magnitude is the group The delay amount τ.

The polarization motion when the optical frequency u is changed is expressed by the following equation.

The PMD vector is expressed by the following equation from Equation (12).

The signal light in a certain polarization state is input to the medium birefringent medium, and the polarization state of the output light on the output side is [x _out (t), y _out (t)], and the output is expressed as a function of the time. If the result of Fourier transform of the polarization state of light is [x _out (ω), y _out (ω)], this can be regarded as a Jones vector in the frequency space. If this is converted into a Stokes vector, the polarization state of the output light in the Stokes space can be obtained as a function of frequency.

In the present invention, in the arithmetic processing of the first and second embodiments, the complex amplitudes {a _sx (t), a _sy (t) of the X polarization component and the Y polarization component of the signal light shown in Expression (1). , Φ _sx (t), φ _sy (t)}, that is, [x _out (t), y _out (t)] can be completely measured for the polarization state of the output light. Therefore, the Stokes vector S indicating the polarization state of the output light from the birefringent medium is measured by measuring the complex amplitude of the X-polarized component and the Y-polarized component of the output light from the medium birefringent medium and its time change. The change amount dS / dω of S can be obtained, and the PMD vector τ can be obtained from the equations (13) and (14) using these values.

  As described above, the optical sampling device according to the present embodiment can measure the polarization state of an optical signal that fluctuates at high speed. Further, it is possible to realize optical sampling by detecting an interference effect that is a linear correlation between the signal light and the sampling pulse, and at the same time as measuring the waveform of the signal light, it is possible to measure the polarization state of the signal light.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements.
In addition, for example, even if some structural requirements are deleted from all the structural requirements shown in each embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the effect of the invention Can be obtained as an invention.

It is a figure which shows schematic structure of the optical sampling apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the flow for calculating | requiring the (instantaneous) amplitude of a X polarization component and a Y polarization component. It is a figure which shows the flow for calculating | requiring the phase of a X polarization component and a Y polarization component. It is a figure which shows schematic structure of the optical sampling apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the flow for calculating | requiring the (instantaneous) amplitude of a X polarization component and a Y polarization component. It is a figure which shows the flow for calculating | requiring the phase of a X polarization component and a Y polarization component.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sampling pulse generation means 2-1, 2-2 ... Polarization separation element 3-1, 3-2 ... Branch element 4-1 ... Correction means 4-2 ... Delay means 5-1-5-3 ... Light 90 Degree hybrids 6-1 to 6-6... Balance type light receivers 7-1 to 7-6... Low pass filters 8-1 to 8-6.

Claims (9)

Sampling that generates a light pulse having a period slightly different from the repetition period of the signal light, the pulse width being shorter than the pulse width of the signal light, and having the X polarization component and the Y polarization component in the measurement system almost evenly. Pulse generating means;
Means for separating the signal light and the sampling pulse into an X polarization component and a Y polarization component, respectively;
Branching means for branching the Y polarization component of the polarization separated signal light and the sampling pulse into a first Y polarization component and a second Y polarization component;
Delay means for delaying any one of the signal light and the second Y polarization component of the sampling pulse for a predetermined time;
A first optical 90-degree hybrid that inputs the signal light and the X-polarized component of the sampling pulse, and shifts the phase of either the signal light or the X-polarized component of the sampling pulse by π / 2;
The signal light and the first Y polarization component of the sampling pulse are input, and the second light 90 degrees that shifts the phase of either the signal light or the first Y polarization component of the sampling pulse by π / 2 Hybrid and
The signal light and the second Y polarization component of the sampling pulse are input after the delay means, and the phase of either the signal light or the second Y polarization component of the sampling pulse is π / A third 90 degree light hybrid that shifts by two;
First and second balanced optical receivers that receive the signal light from the first optical 90-degree hybrid and the X-polarized component of the sampling pulse and output first and second currents, respectively;
Third and fourth balanced optical receivers that receive the signal light from the second optical 90-degree hybrid and the first Y polarization component of the sampling pulse and output third and fourth currents, respectively. And
Fifth and sixth balanced optical receivers that receive the signal light from the third optical 90-degree hybrid and the second Y polarization component of the sampling pulse and output fifth and sixth currents, respectively. And
An optical sampling device comprising: an arithmetic processing device that performs arithmetic processing on the current values of the first to sixth currents. The optical sampling device according to claim 1, wherein the arithmetic processing unit is:
Output current values from the first to sixth balanced optical receivers are respectively P ₁ (t ₀ ), P ₂ (t ₀ ), P ₃ (t ₀ ), P ₄ (t ₀ ), P ₅ (t ₀ ), P ₆ (t ₀ )
The first current value P ₁ (t ₀ ) and the second current value P ₂ (t ₀ ) are summed to a square, and the third current value P ₃ (t ₀ ) and the fourth current value P ₄ (t ₀ ) is summed to the square, and the amplitudes of the X polarization component and the Y polarization component of the signal light are calculated based on the two square sums.
The first current value P ₁ (t ₀ ) is divided by the second current value P ₂ (t ₀ ), and the third current value P ₃ (t ₀ ) is divided into the fourth current value P ₄ (t _0). ), The fifth current value P ₅ (t ₀ ) is divided by the sixth current value P ₆ (t ₀ ), and the X polarization component and Y of the signal light are divided based on the three divided values. An optical sampling device that calculates a phase of a polarization component. It has a repetition period and slightly different periods of the signal light is shorter than the pulse width of the pulse width of the signal light, to generate optical pulses having substantially equal and the X polarization component and the Y polarization component in the measurement system Sampling pulse generating means;
Means for separating the signal light and the sampling pulse into an X polarization component and a Y polarization component, respectively;
A first optical 90-degree hybrid that inputs the signal light and the X-polarized component of the sampling pulse, and shifts the phase of either the signal light or the X-polarized component of the sampling pulse by π / 2;
A second optical 90-degree hybrid that inputs the signal light and the Y-polarized component of the sampling pulse, and shifts the phase of either the signal light or the first Y-polarized component of the sampling pulse by π / 2;
Arranged before the first optical 90-degree hybrid or the second optical 90-degree hybrid, the delay amount for delaying either the X-polarized component or the Y-polarized component of the signal light or the sampling pulse can be switched. Variable delay means;
First and second balances for receiving the signal light from the first optical 90-degree hybrid and the X polarization component of the sampling pulse and outputting first, second, fifth and sixth currents, respectively. Type optical receiver,
Third and fourth balances that receive the signal light from the second optical 90-degree hybrid and the Y-polarized component of the sampling pulse and output third, fourth, seventh, and eighth currents, respectively. Type optical receiver,
An optical sampling device comprising: an arithmetic processing device that performs arithmetic processing on the current values of the first to eighth currents. The optical sampling device according to claim 3, wherein the arithmetic processing unit includes:
The current values of the first to eighth currents output from the first to fourth balanced optical receivers according to the switching of the variable delay means are respectively Q ₁ (t ₀ ) and Q ₂ (t ₀ ). , Q ₃ (t ₀ ), Q ₄ (t ₀ ), Q ₅ (t ₀ ), Q ₆ (t ₀ ), Q ₇ (t ₀ ), Q ₈ (t ₀ ),
The first current value Q ₁ (t ₀ ) and the second current value Q ₂ (t ₀ ) are summed to a square, and the third current value Q ₃ (t ₀ ) and the fourth current value Q ₄ (t ₀ ) is summed to the square, and the amplitudes of the X polarization component and the Y polarization component of the signal light are calculated based on the two square sums.
The first current value Q ₁ (t ₀ ) is divided by the second current value Q ₂ (t ₀ ), and the third current value Q ₃ (t ₀ ) is divided into the fourth current value Q ₄ (t _0). ), The fifth current value Q ₅ (t ₀ ) is divided by the sixth current value Q ₆ (t ₀ ), and the seventh current value Q ₇ (t ₀ ) is divided into the eighth current value. An optical sampling device characterized in that the phase of the X polarization component and the Y polarization component of the signal light is calculated based on the divided value and Q ₈ (t ₀ ). An optical pulse having a slightly different repetition period of the signal light, a pulse width shorter than the pulse width of the signal light, and having the X polarization component and the Y polarization component in the measurement system substantially evenly;
The signal light and the sampling pulse are separated into an X polarization component and a Y polarization component, respectively.
Branching the Y polarization component of the polarization separated signal light and sampling pulse into a first Y polarization component and a second Y polarization component;
Either the signal light or the second Y polarization component of the sampling pulse is delayed for a predetermined time;
The phase of either the signal light or the X polarization component of the sampling pulse is shifted by π / 2,
The phase of either one of the signal light and the first Y polarization component of the sampling pulse is shifted by π / 2,
The phase of either one of the signal light and the second Y polarization component of the sampling pulse delayed by either one is shifted by π / 2,
Converting the X-polarized component of the signal light and the sampling pulse whose phase is shifted to one of the current values of the first and second currents;
Converting the first Y-polarized component of the signal light and the sampling pulse whose phase has been shifted to the current values of the third and fourth currents,
Converting the signal light and the second Y-polarized component of the sampling pulse whose phase has been shifted to the current values of the fifth and sixth currents,
An optical sampling method comprising: performing predetermined arithmetic processing on the current values of the first to sixth currents to obtain the amplitude and phase of the X polarization component and the Y polarization component of the signal light. 6. The optical sampling method according to claim 5, wherein the arithmetic processing is performed.
Output current values from the first to sixth balanced optical receivers are respectively P ₁ (t ₀ ), P ₂ (t ₀ ), P ₃ (t ₀ ), P ₄ (t ₀ ), P ₅ (t ₀ ), P ₆ (t ₀ ), the first current value Pl (t ₀ ) and the second current value P ₂ (t ₀ ) are squared and summed, and the third current value P ₃ (t ₀₎ ) And the fourth current value P ₄ (t ₀ ), and the amplitudes of the X polarization component and the Y polarization component of the signal light are calculated based on the two square sums.
The first current value P ₁ (t ₀ ) is divided by the second current value P ₂ (t ₀ ), and the third current value P ₃ (t ₀ ) is divided into the fourth current value P ₄ (t _0). ), The fifth current value P ₅ (t ₀ ) is divided by the sixth current value P ₆ (t ₀ ), and based on these three divided values, the X polarization component of the signal light and the Y An optical sampling method comprising calculating a phase of a polarization component. An optical pulse having a slightly different repetition period of the signal light, a pulse width shorter than the pulse width of the signal light, and having the X polarization component and the Y polarization component in the measurement system substantially evenly;
The signal light and the sampling pulse are separated into an X polarization component and a Y polarization component, respectively.
Delay either signal light or sampling pulse X polarization component and Y polarization component so that the delay amount can be switched,
The phase of either the signal light or the X polarization component of the sampling pulse is shifted by π / 2,
The phase of either one of the signal light and the Y polarization component of the sampling pulse is shifted by π / 2,
Converting the X-polarized component and the Y-polarized component of the signal light and the sampling pulse whose phase has been shifted to a current value;
An optical sampling method for obtaining the amplitude and phase of the X polarization component and Y polarization component of the signal light based on the current value,
When the delay amount is set to 0, the signal light whose phase is shifted and the X polarization component of the sampling pulse are converted into current values of the first and second currents, and Converting the Y-polarized component of the signal light and the sampling pulse whose phase is shifted to the current values of the third and fourth currents,
When the delay amount is set to a predetermined delay amount, the signal light whose phase is shifted and the X-polarized component of the sampling pulse are converted into current values of fifth and sixth currents, And, the Y-polarized component of the signal light and the sampling pulse whose phase is shifted in any one of them is converted into current values of seventh and eighth currents,
An optical sampling method, wherein arithmetic processing is performed on the current values of the first to eighth currents corresponding to the delay amount. The optical sampling method according to claim 7, wherein the arithmetic processing is performed.
The current values of the first to eighth currents output from the first to fourth balanced optical receivers inputted in two times according to the switching of the variable delay means are respectively Q ₁ , ( t ₀ ), Q ₂ (t ₀ ), Q ₃ (t ₀ ), Q ₄ (t ₀ ), Q ₅ (t ₀ ), Q ₆ (t ₀ ), Q ₇ (t ₀ ), Q ₈ (t ₀ )), the first current value Q ₁ (t ₀ ) and the second current value Q ₂ (t ₀ ) are summed to a square, and the third current value Q ₃ (t ₀ ) and the fourth current value The value Q ₄ (t ₀ ) is summed to the square, and the amplitudes of the X polarization component and the Y polarization component of the signal light are calculated based on the two summed square values.
The first current value Q ₁ (t ₀ ) is divided by the second current value Q ₂ (t ₀ ), and the third current value Q ₃ (t ₀ ) is divided into the fourth current value Q ₄ (t _0). ), The fifth current value Q ₅ (t ₀ ) is divided by the sixth current value Q ₆ (t ₀ ), and the seventh current value Q ₇ (t ₀ ) is divided into the eighth current value. The optical sampling method is characterized in that the phase of the X polarization component and the Y polarization component of the signal light is calculated based on the divided value and Q ₈ (t ₀ ). 8. The optical sampling method according to claim 5, wherein the amplitude and phase of the X polarization component and Y polarization component of the signal light calculated as a function of time, that is, the X polarization component and the Y polarization component are calculated. An optical sampling method comprising: transforming a complex amplitude into a function of frequency by Fourier transform, and calculating a PMD vector based on the value.

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