JP2003106942A - Device for measuring polarized wave mode dispersion and distribution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently measure polarized wave mode dispersion PMD at each position L in an optical fiber 18. SOLUTION: Information of light a propagating at each position L in the optical fiber 18 is obtained by utilizing backward scattered light b generated in the optical fiber 18. Furthermore, a light source part 10 for emitting a plurality of pulselike light a1 , a2 having wavelengths λ1 , λ2 different from each other at a fixed measurement period TS and a light wave synthesizer 14 for synthesizing each light a1 , a2 emitted from the light source part into one light a are adopted to incorporate a plurality of light pulses a1 , a2 having different wavelengths in one measurement period TS for the light a entering the optical fiber 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to measurement of polarization mode dispersion PMD in an optical fiber, and more particularly, to polarization mode dispersion PMD measurement at each position from one end to the other end of the optical fiber. The present invention relates to a distribution measuring device.

[0002]

2. Description of the Related Art In an optical communication system using an optical fiber as a transmission medium, since an optical pulse signal is attenuated or its waveform is disturbed in the process of being transmitted through the optical fiber, a repeater is installed every 120 to 150 km. is doing. In each repeater, the incident optical pulse signal is converted into an electric signal, amplified, further waveform-shaped, converted into an optical pulse signal again, and emitted to an optical fiber.

However, in recent years, an optical amplifier which directly amplifies an optical pulse signal transmitted through an optical fiber has been put into practical use, and has been adopted in place of the above-mentioned repeater. By using this optical amplifier, it is possible to communicate an optical pulse signal over a distance of, for example, 10,000 km without using a repeater. However, although the optical amplifier has a function of amplifying the optical pulse signal, it does not have a waveform shaping function for the optical pulse signal.

A major cause of disturbance of the optical pulse signal waveform during transmission over a long distance optical fiber is polarization mode dispersion of the optical fiber itself, in addition to noise. This polarization mode dispersion will be described. Figure 9
As shown in (a), a difference occurs in the transmission speed of the optical components 2a and 2b of the optical pulse signal transmitted in the optical fiber 1 which are orthogonal to each other. This difference in transmission speed is caused by deformation or refraction of the corresponding optical fiber, which causes a difference in refractive index within the cross section of the optical fiber.

Therefore, the optical pulse signal is transmitted to the optical fiber 1.
In the process of being transmitted through the inside, the orthogonal light components 2a, 2
A phase difference Δφ or a delay time Δτ between the optical components 2a and 2b occurs in b. As a result, as shown in FIG.
When the total pulse width W of the optical pulse signal 2 spreads in the process of being transmitted in the optical fiber 1 and the phase difference Δφ between the optical components 2a and 2b becomes one wavelength (Δφ = 2π), the optical pulse signal 2 The total pulse width W of 2 is doubled (2 W). The increase in the pulse width W of the optical pulse signal 2 causes a disadvantage that the frequency of the optical pulse signal 2 applied to the optical fiber 1 is limited.

Therefore, it is very important to measure the polarization mode dispersion PDM in the optical fiber 1 used in the optical communication system. Specifically, the optical pulse signal 2 incident from one end 1a of the optical fiber 1 is transferred to the other end 1b.
When it reaches, it is necessary to measure and confirm the delay time Δτ or the phase difference Δφ between the optical components 2a and 2b.

A general measurement procedure using the Jones matrix (JMM) method of the polarization mode dispersion PDM in the optical fiber 1 will be described with reference to FIG. In this Jones matrix method, a test optical pulse signal 3a is incident on one end 1a of the optical fiber 1 and transmitted through the optical fiber 1 and output to the other end 1b of the optical fiber 1. The signal 3b is received.

The polarization state of the test optical pulse signal 3a applied to the one end 1a of the optical fiber 1 is set to three polarization states of 0 °, 45 ° and 90 ° with respect to the reference axis,
The detection state of the optical pulse signal 3b received by the other end 1b of the optical fiber 1 is set to 0 °, 45 °, 90 °, and 4 (circularly polarized).
Set to type. Then, 0 °, 45 °, 90 on the incident side
The light intensity of the optical pulse signal 3b is measured in four types of detection states for each polarization state of °.

Therefore, the measurement is carried out with a total of 12 combinations. Let the light intensity (incident light intensity) of the light pulse signal 3a in each polarization state be _X00 , _X45 , _X90 (= [X]), and the light intensity (emission light intensity) of the light pulse signal 3b in each detection state. Is defined as Y ₀₀ , Y ₄₅ , Y ₉₀ , Y _R (= [Y]), the equation (1) is obtained.

[0010] In the formula, [S] is the light intensity on the input side X ₀₀ , X ₄₅ , X
₉₀ (= [X]) and output side light intensity Y ₀₀ , Y ₄₅ , Y ₉₀ ,
It is referred to as a Stokes parameter [S] indicating a relationship with Y _R (= [Y]). When the Stokes parameter [S] is obtained, the Jones vectors J ₀₀ , J ₄₅ , J ₉₀ , and J _R of each output light (each detection state) are obtained from the Stokes parameter [S]. Furthermore, each of these Jones vectors J ₀₀ , J ₄₅ ,
One Jones Matrix T from J ₉₀ , J _R
Ask for.

The Jones Matrix T described above
The wavelength of the incident optical pulse signal 3a is changed by the minute wavelength Δλ and is calculated by the same calculation method. That is, two wavelengths lambda _1, Jones matrix T in lambda ₂ (lambda
₁ ) and T (λ ₂ ) are calculated. From these two matrix values T (λ ₁ ) and T (λ ₂ ) the other end 1b of the optical fiber 1
Delay time Δτ between the optical components 2a and 2b in
Alternatively, the polarization mode dispersion PDM having the phase difference Δφ can be obtained.

[0012]

However, the method of measuring the polarization mode dispersion PDM of the optical fiber by the above-mentioned procedure still has the following problems to be improved.

That is, in addition to a total of 12 kinds of measurement conditions including three kinds of polarization states for making the test optical pulse signal 3a incident and four kinds of detecting states for taking out the optical pulse signal 3b, Since data of two types of wavelengths λ ₁ and λ ₂ are required, a total of 24 measurements must be performed. Therefore, the measurement work time is significantly increased.

In the method shown in FIG. 10, only the polarization mode dispersion PDM at the other end 1b of the optical fiber 1 to be measured can be measured. For example 1000
It is considered that various deformations and stresses are applied on the way in the long-distance optical fiber 1 exceeding km. It is considered that the polarization mode dispersion PDM suddenly changes at such a position, but there is no way to understand the changes in the polarization mode dispersion PDM occurring at the midway position in the optical fiber 1.

The present invention has been made in view of such circumstances, and the polarization mode dispersion at each position in the optical fiber can be measured by utilizing the backscattered light generated in the optical fiber. It is an object of the present invention to provide a polarization mode dispersion distribution measuring device that can significantly reduce the measurement processing time.

[0016]

In order to solve the above-mentioned problems, a polarization mode dispersion distribution measuring apparatus of the present invention is a light source section for emitting a plurality of pulsed lights having different wavelengths at a predetermined measurement cycle. And a multiplexer that combines the lights emitted from the light source unit, and a polarization that selectively polarizes the lights combined by the combiner into three different polarization planes and makes them incident on the optical fiber to be measured. And the backscattered light emitted from the optical fiber to be measured and receiving the backscattered light at 0 °, 45 °,
An analyzer capable of selectively extracting 90 ° and circular detecting components, and a demultiplexer that demultiplexes each detecting component emitted from the analyzing device into a plurality of original light beams having different wavelengths. And a plurality of light receiving units for receiving each light demultiplexed by the demultiplexer and converting it into a signal corresponding to the light intensity, and a plurality of A for converting the signals output from the plurality of light receiving units into digital data. A D / D converter and a polarization mode dispersion distribution calculator that calculates the polarization mode dispersion at each position of the optical fiber to be measured based on each data output from each of the plurality of A / D converters. There is.

In the polarization mode dispersion distribution measuring apparatus configured as described above, the measurement control unit has a total of 12 polarization states and light analysis states adopted when the Jones matrix (JMM) method is used. The combination is sequentially instructed to the polarizer and the analyzer for each measurement cycle. Further, a plurality of pulsed lights having different wavelengths are applied to the optical fiber to be measured within each measurement period. Therefore, the required number of measurements was reduced to 24, which is a half of the conventional number, to 12 times. As a result, the measurement processing time can be significantly reduced.

Further, the light incident from one end of the optical fiber to be measured is not detected at the other end side but is detected by the backscattered light output from the one end side. The backscattered light is
Since it is the reflected light at each position in the optical fiber to be measured, it is possible to equivalently detect the optical state at each position. Strictly speaking, the backscattered light received at one end is transmitted through the double path, so it is necessary to correct the reception level. From the optical state at each position and the optical state at one end, the polarization mode dispersion PDM at each position in the measurement target optical fiber can be obtained.

Another aspect of the present invention is the polarization mode dispersion distribution measuring apparatus of the above-mentioned aspect, wherein the light source section emits a plurality of pulsed lights having different wavelengths at different times within the measurement cycle. .

According to another invention, in the polarization mode dispersion distribution measuring apparatus of the above invention, the light source section emits a plurality of pulsed lights having different wavelengths at the same timing.

Another invention is the polarization mode dispersion distribution measuring apparatus of the above-mentioned invention, wherein the light source section emits two pulsed lights having different wavelengths.

Further, in the polarization mode dispersion distribution measuring apparatus of another invention, a wavelength tunable light source section for emitting a plurality of pulsed lights having different wavelengths and temporally shifted from each other in a predetermined measurement cycle. And a polarizer that selectively polarizes the light emitted from the variable wavelength light source unit into three different polarization planes based on an external instruction to enter the optical fiber to be measured, and a rearward light emitted from the optical fiber to be measured. An analyzer capable of receiving scattered light and selectively extracting each of the 0.degree., 45.degree., 90.degree. And circular detecting components of the backscattered light, and each detecting light emitted from the analyzer. From the start time of the measurement cycle, a demultiplexer that demultiplexes the component into light of each wavelength, multiple light receiving units that receive each light demultiplexed by the demultiplexer and convert it into a signal corresponding to the light intensity, The signals output from multiple light-receiving units are digitally converted at fixed time intervals. Of polarization mode dispersion (PMD) at each position of the optical fiber to be measured based on each of the plurality of A / D converters that convert the optical fiber into the data and the respective data output from each of the plurality of A / D converters. The wave mode dispersion distribution calculation unit and the total of 12 combinations of the polarization state and the detection state are sequentially instructed to the polarizer and the analyzer for each measurement cycle, and after the total 12 combinations are instructed, the polarization mode is calculated. And a measurement control unit for instructing the dispersion distribution calculation unit to calculate polarization mode dispersion.

In the polarization mode dispersion distribution measuring apparatus configured as described above, since the wavelength tunable light source section which emits light having a plurality of pulse waveforms having different wavelengths and temporally shifted from each other is adopted, A multiplexer is not required, and the entire device can be simplified.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a schematic configuration diagram of a polarization mode distribution measuring apparatus according to a first embodiment of the present invention. Light source unit 10
As shown in FIG. 2, the wavelength λ has a pulse width W.
The semiconductor laser 11 for emitting the semiconductor laser 11a for emitting the _first light pulses a ₁ in a certain measurement period T _S, the light pulses a ₂ wavelength lambda ₂ having a pulse width W at a certain measurement period T _S
b and are incorporated. Each semiconductor laser 11a, 11b
Each optical pulse a _1, a ₂ of the pulse width W emitted from the measurement period T _S, the deviation amount t _S of the emission timing of each optical pulse a _1, a ₂ is driven and controlled by the drive circuit 13. Drive circuit 1
3 starts the conversion start timing signals d ₁ and d ₂ to the timing control unit 28 at the respective start times of the measurement cycle T _S.
Is sent.

[0025] Each optical pulse a ₁ emitted shifted by a minute time t _S from the light source unit 10, a ₂ is being multiplexed into one light a in the next multiplexer 14, incorporated the following polarizer 15a It is incident on the deflected polarizer 15. This polarizer 15 is used in the measurement controller 2
Based on the instruction from 7, the angle of the polarizer 15a is adjusted so that the incident light a is 0 °, 45 °, 9 ° with respect to the reference direction.
Each polarization state of 0 ° is controlled.

In the polarizer 15, the polarization directions are 0 °, 45 °, 9
The light a controlled to one of 0 ° passes through the optical branching device 16 as it is and is incident on the one end 18a of the optical fiber 18 to be measured via the connector 17. The light a incident from the one end 18a is transmitted in the optical fiber 18 toward the other end 18b. Backscattered light b is predominant in the process in which the light a is transmitted through the optical fiber 18. The backscattered light b is emitted from the one end 18a of the optical fiber 18 and the connector 1
It is incident on the optical splitter 16 via 7. The backscattered light b is split by the optical splitter 16 and is incident on the analyzer 19.

In this analyzer 19, an analyzer 20 and a 1/4 are provided.
A wave plate 21 is incorporated. The analyzer 19 adjusts the angle of the analyzer 20 or selects the ¼ wavelength plate 21 based on the instruction from the measurement control unit 27, and the incident backscattered light b is 0 ° with respect to the reference direction. , 45 °, 90 °, or circular polarization (analysis) light components are extracted.

The light component in each detection direction of the backscattered light b extracted by the analyzer 19 is divided by the next demultiplexer 22 into _two backscattered light having the original wavelengths λ ₁ and λ ₂ , respectively. The light is split into lights b ₁ and b ₂ .

The backscattered lights b ₁ and b ₂ having the respective wavelengths λ ₁ and λ ₂ demultiplexed by the demultiplexer 22 are respectively received by the light receiving section 2.
The signal is converted into a signal corresponding to the light intensity by 3a and 23b, amplified by each amplifier 24a and 24b to a predetermined level, and then input to each A / D converter 25a and 25b.

As shown in FIG. 2, the A / D converters 25a and 25b receive a fixed time interval t _{d when the} conversion start timing signals d ₁ and d ₂ from the timing controller 28 are input.
The synchronization with the clock, the input each data value of the digital d [lambda] ₁₁ the signals _{are, Dλ 12, Dλ 13, ...} , Dλ 21, Dλ
₂₂ , Dλ ₂₃ , ... Each A / D converter 25a, 2
5b converted data values Dλ ₁₁ , Dλ ₁₂ , Dλ ₁₃ ,
, Dλ ₂₁ , Dλ ₂₂ , Dλ ₂₃ , ... Are input to the next polarization mode dispersion distribution calculation unit 26. Therefore, each of the data values Dλ ₁₁ , Dλ ₁₂ , Dλ ₁₃ , ..., Dλ ₂₁ , Dλ ₂₂ ,
Dλ ₂₃ , ... Are each position L in the optical fiber 18 to be measured (each distance position L ₁ , L ₂ , L ₃ from the one end 18a,
The light intensity Y of the light pulse in

For example, the polarization mode dispersion distribution calculator 26, which is a small computer, includes the A / D converters 25a and 25b.
Data value Dλ ₁₁ under each of the 24 types of measurement conditions (combination of polarization state, detection state, wavelength state) input from
Dλ ₁₂ , Dλ ₁₃ , ..., Dλ ₂₁ , Dλ ₂₂ , Dλ ₂₃ , ... Are temporarily stored, and based on the calculation instruction e from the measurement control unit 27, each distance from one end in the optical fiber 18 to be measured. For example, the light components 2a, 2 at the positions L ₁ , L ₂ , L ₃ , ...
The polarization mode dispersions PDM ₁ , PDM ₂ , PDM ₃ , ... Comprising the delay time Δτ or the phase difference Δφ generated between b are calculated.

Specifically, when the light source section 10 emits _one optical pulse a ₁ having a single wavelength λ ₁ , the polarizer 15 is set to three polarization states of 0 °, 45 °, and 90 ° (A = 1. ~ 3)
The optical signals X001, X451, and X901 (= [X] ₁ ) converted into the electric signals of the polarizer 15 in the case of setting are previously measured and stored in the storage unit. Similarly, the polarizer 15 when the other light pulse a ₂ of single wavelength λ ₂ is emitted from the light source unit 10 is set to three polarization states (A = 1 to 3) of 0 °, 45 °, and 90 °. Polarizer 15 when
Each optical signal X002, X452, when converted into each electric signal of
X902 (= [X] ₂ ) is measured in advance and stored and held in the storage unit.

Then, twelve kinds of data values Dλ of each wavelength λ ₁ and λ ₂ at each distance position L ₁ , L ₂ , L ₃ , ...
_{From 1} (= [Y] ₁ ) and Dλ ₂ (= [Y] ₂ ), the Stokes parameters [S] ₁ and [S] ₂ for each wavelength λ ₁ and λ ₂ satisfying the above-mentioned equation (1) are calculated. calculate. Each wavelength λ ₁ ,
Stokes parameters for each _{λ 2 [S] 1, [} S] 2
Then, from the Stokes parameters [S] ₁ and [S] ₂ , the Jones vectors J ₀₀ and J ₄₅ of the output light (each detection state) for each wavelength λ ₁ and λ ₂ are obtained.
Find J ₉₀ and J _R. Furthermore, these wavelengths λ ₁ and λ ₂
Each Jones Vector J ₀₀ , J ₄₅ , J ₉₀ , J
Each of _R wavelength lambda _1, lambda ₂ every respective one of Jones matrix T (λ _1), obtaining the T (λ _1). The matrix values T (λ ₁ ), T for each wavelength λ ₁ , λ ₂
From (λ ₁ ), the polarization mode dispersion PMD including the delay time Δτ or the phase difference Δφ generated between the optical components 2a and 2b at the corresponding distance position L of the optical fiber 18 to be measured is calculated.

When the polarization mode dispersion PMD at one distance position L is obtained, the polarization mode dispersion PMD at each distance position is calculated by the same procedure.

In this way, the optical fiber 1 to be measured
Each distance position L from one end 18a of 8 ₁, L₂, L₃To ...
Each polarization mode dispersion PMD in₁, PMD₂, PMD₃,
... is calculated. Figure 4 shows the calculated polarization mode dispersion PM
It is a figure which shows an example of the distribution characteristic in the optical fiber 18 of D.
It

The measurement control unit 27 including a computer is
Prior to the start of this polarization mode dispersion distribution PMD measurement,
For the drive circuit 13 of the light source unit 10, each optical pulse a ₁ ,
The width W of a ₂ , the measurement cycle T _S , and the deviation amount t _S of the emission timing of each optical pulse a ₁ , a ₂ are set.

When the above-mentioned preparation process is completed, the measurement control section 27 determines the three polarization states of 0 °, 45 °, and 90 °, and 0.
Twelve combinations in total of four detection states of °, 45 °, 90 °, and circle (polarization) are sequentially instructed to the polarizer 15 and the detector 19 for each measurement cycle T _S, and a total of 12 combinations. After instructing the combination, the polarization mode dispersion distribution calculation unit 26 is sent a polarization mode dispersion calculation instruction e.

The detailed operation of the measurement control unit 27 will be described with reference to the flowchart of FIG. First, the polarization state and the detection state will be defined. As shown in FIG. 3, the polarization state A = 1
Is 0 ° polarized light, the polarization state A = 2 is 45 ° polarized light, and the polarization state A = 3 is 90 ° polarized light. In addition, the detection state B =
1 is set to 0 °, polarization state B = 2 is set to 45 °,
The polarization state B = 3 is 90 ° analysis, and B = 4 is circular analysis (polarization) using a ¼ wavelength plate.

When the process is started, the polarizer 15 for the light a incident on the optical fiber 18 is sent in S (step) 1.
The polarization state of is initialized (A = 1). And the polarizer 1
The polarization state of No. 5 is set to A (S2). Next, in S3, the detection state of the detector 19 for the backscattered light b output from the optical fiber 18 is initialized (B = 1). Then, the light detection state of the light detector 19 is set to B (S4).

Next, an optical pulse is sent to the drive circuit 13 of the light source section 10.
Su a₁, A₂The output finger instruction is output (S5). Then,
As shown in FIG. 2 from the light source unit 10, when the pulse width W is very small
Interval t _SOf a pair of optical pulses a whose output timing is shifted by₁,
a₂Is output. A pair of light pulses a₁, A₂Is output
Then, from the drive circuit 13 to the A / D converters 25a and 25b.
Change command to d₁, D₂Is sent. As a result, constant
Each A / D converter 2 is synchronized with the clock of the time interval td.
Each data value Dλ from 5a and 25b₁₁, Dλ₁₂, Dλ₁₃,
…, Dλ_{twenty one}, Dλ_{twenty two}, Dλ_{twenty three}, ... are output.

The measurement controller 27 controls the polarization mode dispersion distribution.
For each wavelength λ₁, Λ₂Each data value for
Dλ₁₁, Dλ₁₂, Dλ₁₃, ..., Dλ_{twenty one}, Dλ_{twenty two}, D
λ_{twenty three}, And the reading instruction e of ... Is transmitted (S6). as a result,
The polarization mode dispersion distribution calculation unit 26 calculates the polarization state A and the analysis state.
In one measurement condition consisting of combination [AB] with state B
Each wavelength λ₁, Λ₂Each data value for₁₁, Dλ₁₂,
Dλ₁₃, ..., Dλ_{twenty one}, Dλ _{twenty two}, Dλ_{twenty three}Open reading of
Start.

Then, when the measurement cycle (period) T _S elapses from the output start time of the pair of optical pulses a ₁ and a ₂ (S
7), it is determined that the measurement process for the backscattered lights b ₁ and b _{2 under} one measurement condition is completed, and in S8, the detection state for the backscattered light b is updated (B = B + 1).

When the updated detection state B does not exceed 4 (S9), the process returns to S4, and the backscattered lights b ₁ and b ₂ for the measurement conditions using the updated detection state B are measured. Start the measurement process.

If the post-update detection state B exceeds 4 in S9, the measurement processing for changing the detection state for one polarization state has been completed four times, so in S10, the optical fiber 18 Update the polarization state for the light a incident on (A
= A + 1).

If the updated polarization state A does not exceed 3 (S11), the process returns to S2, and the measurement process for the backscattered lights b ₁ and b _{2 under} the measurement conditions using the updated polarization state A is performed. To start.

When the updated polarization state A exceeds 3 in S11, the respective wavelengths λ ₁ and λ for 12 combinations [AB] of the three polarization states A and the four detection states B in total. Each data value for ₂ Dλ ₁₁ , Dλ ₁₂ , Dλ ₁₃ , ..., D
Since the reading processing of λ ₂₁ , Dλ ₂₂ , Dλ ₂₃ , ... Has been completed, the polarization mode dispersion P at each position L of the optical fiber 18 to be measured is instructed to the polarization mode dispersion distribution calculator 26.
The calculation instruction e of MD ₁ , PMD ₂ , PMD ₃ , ... Is output.

When the polarization mode dispersion calculation instruction e is input from the measurement control section 27, the polarization mode dispersion distribution calculation section 26 receives one end 1 of the optical fiber 18 to be measured according to the procedure described above.
The polarization mode dispersions PMD ₁ , PMD ₂ , PMD ₃ , ... At the distance positions L ₁ , L ₂ , L ₃ , ... From 8a are calculated. Then, the calculation result is output.

In the polarization mode dispersion measuring apparatus configured as described above, the output from the light source unit 10 and the multiplexer 14
The light a incident from the one end 18a of the optical fiber 18 to be measured via the polarizer 15 is detected by the backscattered light b output from the one end 18a side instead of being detected by the other end 18b. There is.

The back scattered light b is the optical fiber 1 to be measured.
Since it is the reflected light at each of the distance positions L ₁ , L ₂ , L ₃ , ... Within 8 the light state at each position L can be equivalently detected.
Then, each data value Dλ ₁₁ , D under each measurement condition of the backscattered light b at each distance position L ₁ , L ₂ , L ₃ , ...
_{λ 12, Dλ 13, ...,} Dλ 21, Dλ 22, Dλ 23, ... reads, using these data values, each distance position in the optical fiber 18 to be measured _{L 1, L 2, L 3} , ... The respective polarization mode dispersions PMD ₁ , PMD ₂ , PMD ₃ , ... Therefore, the polarization mode dispersion PMD of the optical fiber 18 to be measured can be measured in more detail.

Further, the measurement control unit 27 has a total of 12 combinations of the three polarization states of the polarizer 15 and the four analysis states of the analyzer 19 which are adopted when the Jones matrix (JMM) method is used. Is sequentially instructed to the polarizer 15 and the analyzer 19 for each measurement cycle T _S. Further, a pair of optical pulses a ₁ , which have different wavelengths λ ₁ and λ ₂ in each measurement period T _S and whose emission timings are deviated by a minute time t _S ,
The light a obtained by multiplexing a ₂ is applied to the optical fiber 18 to be measured. Then, the backscattered light b is separated by the demultiplexer 22 into two backscattered lights b ₁ and b ₂ having respective original wavelengths λ ₁ and λ ₂ .

Therefore, different wavelengths λ₁, Λ₂of
The same measurement cycle T for light calculation _SCan be done within
So, the required number of measurements is now 24 times, which is half the previous number, and 12 times.
Fell. As a result, polarization mode dispersion PMD measurement processing
The time can be greatly reduced.

[0052] In the first embodiment apparatus shown in Second Embodiment FIG. 1, a pair of optical pulses a _1, a ₂ output from the light source unit 10, such emission timing is shifted by a minute time t _S Controlled to. However, as shown in FIG. 5, it is also possible to control the emission timings of the optical pulses a ₁ and a ₂ to be the same.

(Third Embodiment) FIG. 6 is a schematic configuration diagram of a polarization mode distribution measuring apparatus according to a third embodiment of the present invention. The same parts as those of the polarization mode distribution measuring apparatus of the first embodiment shown in FIG. 1 are designated by the same reference numerals. Therefore,
Detailed description of the overlapping parts will be omitted.

In the device of the third embodiment, the light source unit 1
Within 0, different wavelengths lambda _1, respectively, lambda _2, ..., the light pulses a _1, a ₂ with lambda _N, ..., to emit a _{N N (N>}
3) The semiconductor lasers 11a, 11b, ..., 11 _N are incorporated. The multiplexer 14 has N optical pulses a ₁ , a ₂ ,
..., a _N is combined into one light a.

The light a synthesized by the multiplexer 14 is the polarizer 1
5, it is incident on the optical fiber 18 to be measured through the optical branching device 16. The backscattered light b of the optical fiber 18 is incident on the demultiplexer 22a via the optical branching device 16 and the photodetector 19. The demultiplexer 22a demultiplexes the incident backscattered light b into N backscattered lights b ₁ , b ₂ , ..., B _N having original wavelengths λ ₁ , λ ₂ , ..., λ _N components, respectively. To wave.

Each wavelength λ ₁ branched by the demultiplexer 22a,
, each backscattered light b ₁ , b ₂ , ..., Having a λ ₂ , ..., λ _N component
b _N is converted into a signal corresponding to the light intensity by each of the light receiving sections 23a, 23b, ..., 23 _N , and then the A / D converter 2
5a, 25b, ..., 25 _N.

Each A / D converter 25a, 25b, ... 25 _N
Is a constant time interval t when each conversion start timing signal d ₁ , d ₂ , ... d _N from the timing control unit 28 is input.
_{At d} , each input signal is converted to each digital data value D
λ ₁₁ , Dλ ₁₂ , Dλ ₁₃ , ..., Dλ ₂₁ , Dλ ₂₂ , Dλ ₂₃ ,
, Dλ _N1 , Dλ _N2 , Dλ _N3 , ... Each A / D
.. 25 _N converted by the converters 25a, 25b, ... 25 _N , Dλ ₁₁ , Dλ ₁₂ , Dλ ₁₃ , ..., Dλ ₂₁ , Dλ ₂₂ , Dλ
₂₃ , ..., Dλ _N1 , Dλ _N2 , Dλ _N3 , ... Are input to the next polarization mode dispersion distribution calculation unit 26.

The polarization mode dispersion distribution calculator 26 has N wavelengths λ ₁ , λ ₂ , ..., λ _N designated by the measurement controller 27.
Using a pair of wavelengths λ _a and λ _b of
The calculation processing of the polarization mode dispersion PMD for each distance position L of the measurement target optical fiber 18 is performed.

In the polarization mode dispersion distribution measuring apparatus configured as described above, the measurement control unit 27 sequentially selects a plurality of pairs of wavelengths having different wavelength regions, and instructs the polarization mode dispersion distribution calculation unit 26. By doing so, FIG.
, The polarization mode dispersion PMD at each wavelength λ in the optical fiber 18 is calculated, and the polarization mode dispersion P
The wavelength characteristics of MM can be obtained.

Further, the polarization mode dispersion PMD is measured not only for a combination of adjacent wavelengths of _a pair of wavelengths λ _a and λ _b but also for a combination of arbitrary wavelengths as shown in FIG. 7B. be able to.

As described above, the polarization mode dispersion distribution measuring apparatus of the third embodiment can obtain various wavelength characteristics in the polarization mode dispersion PMD of the optical fiber 18 to be measured.

(Fourth Embodiment) FIG. 8 is a schematic configuration diagram of a polarization mode distribution measuring apparatus according to a fourth embodiment of the present invention. The same parts as those of the polarization mode distribution measuring apparatus of the first embodiment shown in FIG. 1 are designated by the same reference numerals. Therefore,
Detailed description of the overlapping parts will be omitted.

In the third embodiment device, a variable wavelength light source part 30 is provided instead of the light source part 10 in the first embodiment device of FIG. 1, and the multiplexer 14 is removed. In the tunable wavelength light source unit 30, the semiconductor laser 3 in which the oscillation wavelength λ is arbitrarily variably set within a predetermined wavelength range by the drive circuit 13a
1 is incorporated.

Then, the measurement control unit 27 causes the drive circuit 13a.
In addition, when an emission command of light having a plurality of pulse waveforms having different wavelengths and temporally different from each other is sent, the same wavelength is output from the wavelength variable light source unit 30 within the measurement cycle T _S shown in FIG. has a pulse width W, different wavelength λ from each other, and one light a generation time had a pair of pulse waveform shifted by a minute time t _S is emitted. One light a emitted from the variable wavelength light source unit 30 is directly incident on the polarizer 15. The subsequent operation is the same as that of the first embodiment device of FIG.

Therefore, it is possible to obtain substantially the same operational effect as the polarization mode dispersion distribution measuring apparatus of the first embodiment described above. Further, in this embodiment device, it is not necessary to use a multiplexer.

[0066]

As described above, in the polarization mode dispersion distribution measuring apparatus of the present invention, the information on the light propagating at each position in the optical fiber is utilized by utilizing the backscattered light generated in the optical fiber. It has gained. Further, a plurality of light pulses having different wavelengths are incorporated into the light entering the optical fiber within one measurement cycle. Therefore, the polarization mode dispersion PMD at each position in the optical fiber can be measured, and the measurement processing time can be significantly shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a polarization mode dispersion distribution measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a time chart showing the measurement operation of the polarization mode dispersion distribution measurement apparatus of the first embodiment.

FIG. 3 is a flowchart showing the operation of a measurement control unit incorporated in the polarization mode dispersion distribution measuring apparatus of the first embodiment.

FIG. 4 is a diagram showing the characteristics of polarization mode dispersion measured by the polarization mode dispersion distribution measurement apparatus of the first embodiment.

FIG. 5 is a diagram showing a waveform of light emitted from a light source unit in the polarization mode dispersion distribution measuring apparatus according to the second embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of a polarization mode dispersion distribution measuring apparatus according to a third embodiment of the present invention.

FIG. 7 is a diagram showing wavelength characteristics of polarization mode dispersion measured by the polarization mode dispersion distribution measuring apparatus of the third embodiment.

FIG. 8 is a diagram showing a schematic configuration of a polarization mode dispersion distribution measuring apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a diagram for explaining polarization mode dispersion.

FIG. 10 is a diagram for explaining the measurement principle of polarization mode dispersion using the Johnson matrix method.

[Explanation of symbols]

10 ... Light source parts 11a, 11b, 11 _N ... Semiconductor lasers 13, 13a ... Driving circuit 14 ... Multiplexer 15 ... Polarizer 16 ... Optical splitter 18 ... Optical fiber 19 ... Analyzer 22, 22a ... Splitter 23a , 23b, 23 _N ... Light receiving parts 24a, 24b, 24 _N ... Amplifying parts 25a, 25b, 25 _N ... A / D converter 26 ... Polarization mode dispersion distribution computing part 27 ... Measurement control part 28 ... Timing control part 30 ... Variable wavelength light source

Claims (5)

[Claims] 1. A light source section (1) for emitting a plurality of pulsed lights having different wavelengths at a predetermined measurement cycle (T _S ).
0) and a multiplexer (14) for multiplexing the lights emitted from the light source unit.
A polarizer (15) which selectively polarizes the lights combined by the multiplexer into three different polarization planes and makes the polarized light enter the measurement target optical fiber (18), and exits from the measurement target optical fiber. Received backscattered light (b) is received, and the backscattered light is 0 °, 45 °, 90 °.
And an analyzer (19) capable of selectively extracting each of the detection components of a circle, and demultiplexing each of the detection components emitted from the analysis device into the plurality of original light beams having different wavelengths. A demultiplexer (22), a plurality of light receiving units (23a, 23b) for receiving each light demultiplexed by the demultiplexer and converting it into a signal corresponding to the light intensity, and outputs from the plurality of light receiving units A plurality of A / D converters (25a, 25b) for converting the generated signals into digital data, and each of the measurement target optical fibers based on the respective data output from the plurality of A / D converters A polarization mode dispersion distribution measuring device comprising: a polarization mode dispersion distribution calculation unit (26) for calculating the polarization mode dispersion (PMD) at the position (L). 2. The polarization mode dispersion distribution measurement according to claim 1, wherein the light source unit emits a plurality of pulsed lights having wavelengths different from each other at different times within the measurement cycle. apparatus. 3. The polarization mode dispersion distribution measuring apparatus according to claim 1, wherein the light source section emits a plurality of pulsed lights having different wavelengths at the same timing. 4. The polarization mode dispersion distribution measuring device according to claim 1, wherein the light source unit emits two pulsed lights having wavelengths different from each other. 5. A wavelength tunable light source section (30) for emitting a plurality of pulsed lights having different wavelengths and shifted in time at a predetermined measurement cycle (T _S ), and the tunable light source section. A polarizer (15) that selectively polarizes the light emitted from the three different polarization planes based on an external instruction and makes the polarized light enter the optical fiber (18) to be measured.
And 0 °, 45 °, 90 ° of the backscattered light by receiving the backscattered light (b) emitted from the optical fiber to be measured.
And a detector (19) capable of selectively extracting each of the detection components of a circle, and a demultiplexer (D) for demultiplexing each of the detection components emitted from the detector into light of each wavelength ( 22), a plurality of light receiving sections (23a, 23b) for receiving each light demultiplexed by the demultiplexer and converting it into a signal corresponding to the light intensity, and a constant time interval from the start time of the measurement cycle. A plurality of A / D converters (25a, 25b) for converting the signals output from the plurality of light receiving units at (t _S ) into digital data
And a polarization mode dispersion distribution calculation unit that calculates polarization mode dispersion (PMD) at each position (L) of the measurement target optical fiber based on each data output from the plurality of A / D converters. (26) and sequentially instructing the polarizer and the analyzer of a total of 12 combinations of the polarization state and the detection state for each measurement cycle, and after instructing the total of 12 combinations, the polarization A polarization mode dispersion distribution measuring apparatus comprising: a measurement control unit (27) for instructing a mode dispersion distribution calculating unit to calculate polarization mode dispersion.