JP2014020878A - Characteristic analysis device and method for optical branch line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To individually measure the optical line loss characteristics of an existing out-of-station facility.SOLUTION: With respect to a fiber to be inspected in which light reflection filters are arranged at branch lower optical fibers branched by an optical splitter, two types of test rays of light having different wavelength are generated for analyzing the characteristics of each of the branch lower optical fibers from a branch point to the light reflection filters, and the respective test rays of light are encoded and multiplexed, and the multiplexed test rays of light are made incident to the fiber to be inspected, and probe rays of light returned from the branch lower optical fibers are extracted, and the probe rays of light having the wavelength of one type of test rays of light are extracted from the probe rays of light, and the probe rays of light are converted into currents, and converted into a digital signal, and the branch lower optical fiber corresponding to the digital signal is specified, and a Brillouin gain is analyzed from the specified digital signal, and measurement is repeatedly performed by changing the code, and the Brillouin gain characteristic distribution of each of the lower branch filters is acquired from the repeated measurement result.

Description

  The present invention relates to a characteristic analysis apparatus and a characteristic analysis method for an optical line such as an optical fiber, and more particularly to a case where an optical line after branching is analyzed.

  In an optical communication system using an optical line such as an optical fiber, an optical pulse line monitoring device is used to detect a failure of the optical line or to specify a failure position. The optical pulse line monitoring device utilizes the fact that backscattered light having the same wavelength as the light is generated and propagates in the reverse direction as the light propagates in the optical line. That is, when an optical pulse is incident on the optical line as test light, backscattered light continues to be generated until the optical pulse reaches the breaking point, and the end face of the optical line on which the return light having the same wavelength as the test light is incident. It is emitted from. By measuring the duration of the backscattered light, it is possible to specify the break position of the optical line. As a monitoring device based on this principle, an OTDR (Optical Time Domain Reflectometer) is typical.

  However, with regard to PON (Passive Optical Network) type optical branch lines, the OTDR installed in a telecommunications carrier equipment building uses a branch optical fiber (hereinafter referred to as “Branch Lower”) located on the user equipment side (lower side) from the optical splitter. It is difficult to individually identify loss information of an optical device connected to an optical line such as an optical fiber ”) or an optical device (reflection filter), an optical splitter, or a fiber connection component.

  That is, since the trunk optical fiber laid from the telecommunications carrier equipment building is branched into a plurality of optical fibers by the optical splitter, the test light is also uniformly distributed to the plurality of lower branch optical fibers by the optical splitter. After that, when the return light from each lower branch optical fiber returns to the incident end, the return light overlaps with the optical splitter. Therefore, from the OTDR waveform observed at the incident end, which branch lower optical fiber has failed. Cannot be identified. As described above, the existing OTDR is basically effective for measurement of one optical fiber, but cannot be applied as it is to a PON type optical branch line. Therefore, a technique for enabling application of OTDR to an optical branch line has been proposed (see Non-Patent Document 1 and Patent Document 1).

JP-A-7-87017

Y. Enomoto et al., "Over 31.5dB dynamic range optical fiber line testing system with optical fiber fault isolation function 32dB-branched PON", OFC2003 Technical Digest, paper ThAA3 (2003), pp. 608-610 H. Takahashi / et al /., "Individual Loss Distribution Measurement in 4-branched PON Using Pulsed Pump-Probe Brillouin Gain Analysis", OFC2012 Technical Digest, paper OTh3I.2 (2012)

  In Non-Patent Document 1, an optical filter that reflects test light is installed as a termination filter in front of a user device, and the intensity of reflected light from each user device is measured by high-resolution OTDR. According to the report, it is reported that an accuracy of 2 m can be obtained as a distance resolution in the branched optical fiber below the optical splitter.

However, in this technology, the fault core is identified and whether the fault location is the user device or the optical line is limited, and the position where the fault occurs in the lower branch optical fiber is specified. I can't.
In Patent Document 1, an arrayed waveguide diffraction grating type wavelength multiplexer / demultiplexer that uses multi-beam interference of light is used as an optical splitter, and the wavelength of the test light is switched by a wavelength tunable light source to select the optical line under test. Proposals have been made. This is because the wavelength of the tunable light source is swept, the wavelength of the reflected light is detected by the light reflection processing unit, and the wavelength of the test light is set by using the wavelength as a reference, and each optical line is associated with the wavelength of the test light. Individual monitoring can be realized.

  However, an optical branching device having a wavelength routing function typified by an arrayed waveguide grating type wavelength multiplexer / demultiplexer is generally expensive, and it is costly to use it in an access optical system that accommodates many subscribers. Difficult in terms. Furthermore, such optical components are highly temperature dependent and need to be added with a temperature adjustment function, which is not preferable because the cost required for constructing the system increases.

In Non-Patent Document 2, two test light pulses, a pump light pulse and a probe light pulse, are incident and the Brillouin gain at the collision position of both test lights is analyzed to measure the individual loss distribution of the lower core of the splitter. Technology is disclosed.
However, the Brillouin gain analysis using the pulse method can identify the lower branch optical fiber when there is a difference of 1 m or more in length for each individual lower branch optical fiber (that is, the resolution is 1 m or less). is there. This is because, in the pulse method, the sensitivity is significantly deteriorated when the pulse width is narrower than the phonon lifetime (˜1 m) of Brillouin scattering. Therefore, the method described in Non-Patent Document 2 cannot be measured when there is no difference in length between individual branched optical fibers equal to or larger than the pulse width of the test light. In other words, in actual equipment monitoring, in the case of a branched optical line when a place where user equipment such as an apartment is installed is adjacent, the difference in length of the branched optical fiber may be 1 m or less. Therefore, it cannot be measured by the pulse method.

  Therefore, in the PON type optical branch line, when monitoring the branch lower optical fiber from the optical splitter to the user equipment side and the equipment (optical devices such as optical splitters and fiber connection parts), a new optical device and optical line configuration are added. Without changing (without cost by changing existing equipment), it is possible to individually measure the optical line loss characteristics of existing off-site equipment (branch lower fiber and light reflection filter with different fiber lengths), There is a need for a technology that can measure even when the difference in length of the optical fiber below the branch is as short as 1 m or less (that is, the resolution is 1 m or more).

  The present invention was made in order to solve the above-described problems.When monitoring the branch lower optical fiber on the user apparatus side from the optical splitter and the apparatus, without changing the optical device or the optical line configuration newly, It is an object of the present invention to provide an optical branch line characteristic analysis device and a characteristic analysis method thereof capable of individually measuring optical line loss characteristics of existing off-site facilities.

In order to solve the above-described problems, the optical branch line characteristic analyzer according to the present invention is configured in the following manner.
(1) One optical fiber is branched from a first optical fiber to an Nth optical fiber by an optical splitter, and test light is supplied to the far end of the first to Nth branched lower optical fibers branched by the optical splitter. The light from the branch point by the optical splitter is connected to a fiber to be measured to which first to Nth single-wavelength reflection type optical filters that reflect and transmit light having a wavelength different from the wavelength of the test light are connected. An optical branch line characteristic analysis apparatus for analyzing optical line characteristics of an optical branch line having a minimum difference in length for an N-core branched lower optical fiber up to a filter having an optical fiber identification resolution or higher. Test light generating means for generating two different types of test lights, encoding means for encoding the two types of test lights having different wavelengths, and multiplexing means for combining the two types of encoded test lights And the combined A test light is incident on the fiber to be measured, and a circulator for extracting the probe light returned from the branch optical fiber below the optical splitter, and one wavelength of the two types of test light from the extracted probe light. Filter means for extraction, optical / electrical conversion means for receiving the probe light extracted by the filter means and converting it into current, analog / digital conversion means for converting the test light converted into current into a digital signal, The digital signal is decoded, the branch lower optical fiber is identified as the digital signal of the probe light, the Brillouin gain is analyzed from the identified digital signal, the sign is changed, and the measurement is performed. The Brillouin gain characteristics of each of the lower branch fibers of the optical splitter from the measurement results of repeated measurement A manner that and a processing means for acquiring fabric.

(2) In (1), the Brillouin gain analysis includes measurement of distortion in the optical medium.
(3) In (1), the optical line characteristic is at least one of an optical attenuation amount with respect to a distance, a position of a bending obstacle, a degree of bending, a position of a disconnection obstacle, and a temperature change amount with respect to the distance.

Moreover, the optical branch line characteristic analysis method according to the present invention is configured in the following manner.
(4) One optical fiber is branched from the first to the Nth optical fiber by the optical splitter, and the test light is supplied to the far end of the first to Nth branched lower optical fibers branched by the optical splitter. The light from the branch point by the optical splitter is connected to a fiber to be measured to which first to Nth single-wavelength reflection type optical filters that reflect and transmit light having a wavelength different from the wavelength of the test light are connected. Applied to the optical branch line characteristic analysis device for analyzing the characteristics of the optical branch line having the minimum difference in length for the N-core branched lower optical fiber to the filter having an optical fiber identification resolution or higher,
Two types of test light having different wavelengths are generated, each test light is encoded and combined, and the combined test light enters the fiber to be measured and returns from the branch optical fiber below the optical splitter. The probe light is extracted, one wavelength of the two types of test light is extracted from the probe light, the extracted probe light for one wavelength is converted into a current, and the converted current signal is converted into a digital signal. A method of converting and decoding the digital signal to analyze the characteristics of the optical branch line,
From the decoding result of the digital signal, specify which of the branch lower optical fibers is the probe light digital signal, analyze the Brillouin gain from the specified digital signal, change the sign, and repeat the above measurement The Brillouin gain characteristic distribution of each of the lower branch fibers of the optical splitter is obtained from the measurement results repeatedly performed.

  According to the present invention, in order to obtain the characteristic distribution of the individual branch optical fibers on the lower side of the optical splitter, the light reflection filter that reflects the test light wavelength at the end of the branch lower optical fiber is different from that of the lower branch optical fiber Because it only needs to be equipped, it can be measured accurately at low cost without replacing the current PON type optical line, and can be measured even when the required difference in length of the bottom optical fiber is 1 m or less (resolution is 1 m or more) ) Optical branch line characteristic analysis apparatus and method.

It is a block diagram which shows the structure of the analyzer which employ | adopts the characteristic-analysis method of the optical branch line which concerns on the 1st Embodiment of this invention. The flowchart which shows the flow of a process of the arithmetic processing unit used for 1st Embodiment. It is a block diagram which shows the structure of the analyzer which employ | adopts the characteristic-analysis method of the optical branch line which concerns on the 2nd Embodiment of this invention.

Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment.
(First embodiment)
FIG. 1 is a block diagram illustrating a configuration of an optical branch line characteristic analyzing apparatus according to the first embodiment. The apparatus shown in FIG. 1 (all other components excluding the fiber to be measured surrounded by a dotted line) can determine the Brillouin gain characteristic distribution received by the first test light in the fiber to be measured. .

In the first embodiment shown in FIG. 1, the continuous light output from the light source 11 is branched into two systems by the branch element 12 and further branched into two systems by the branch element 13.
One of the lights branched by the branch element 13 is referred to as first test light (probe light), and the other is referred to as second test light (pump light). The optical frequency of the first test light is shifted by f _B by the optical frequency changing means 17. Specifically, the optical frequency changing means 17 may be an external modulator having a function of changing the frequency of the modulation sideband according to the signal frequency from the sine wave generator 19 to be driven, and uses LiNbO ₃ . Any phase modulator, amplitude modulator, or SSB modulator may be used.

The first test light whose frequency has been changed by the optical frequency changing means 17 is incident on the optical modulator 18 and is subjected to coded modulation by the optical coding means 21. On the other hand, the second test light branched by the branch element 13 is optically amplified by the optical amplifier 14, then enters the optical modulator 15, and is subjected to encoding modulation by the optical encoding means 20. Specifically, a waveguide modulator using LiNbO ₃ driven by an arbitrary waveform can be used as the optical encoding means 20 and 21.

Here, the order of the optical frequency shift by the optical frequency changing unit 17 and the sine wave generator 19 and the optical encoding modulation by the optical modulators 15 and 18 and the optical encoding units 20 and 21 are arbitrary.
The encoded first test light and the encoded second test light are combined by the combining element 16, pass through the circulator 22, and enter the measured optical fiber 23. The measured optical fiber 23 includes an optical splitter 231, a branch lower optical fiber 232, and a light reflection filter 233 installed at the end of the branch lower optical fiber. The first test light and the second test light that are N-branched by the optical splitter 231 interact in the branched lower optical fiber 232, and the first test light undergoes Brillouin amplification. The first test light and the second test light that have undergone the Brillouin amplification reach the optical circulator 22 and are guided to the optical filter 24 by the optical circulator 22. The optical filter 24 extracts only the first test light. The first test light extracted here is combined with the unmodulated light branched by the first-stage branching element 12 and the multiplexing element 25 to receive the light. Is received by the device 26.

  The output current from the optical receiver 26 is converted into a digital signal by an analog / digital (A / D) converter 27 and then input to the arithmetic processing unit 28. The arithmetic processing unit 28 performs arithmetic processing of a Brillouin gain information separation method, a Brillouin gain analysis method, and a distribution measurement method for each branched optical fiber, which will be described below, on the input current value to obtain a loss distribution with respect to the distance. .

Next, the operation of the above-described optical line characteristic analyzing apparatus of the present embodiment will be described. The optical frequency changing unit 17, the optical encoding units 20 and 21, the optical receiver 26, and the measured optical fiber 23 need to satisfy the following conditions.
(Condition 1) The code φ _n (t) of the optical encoding means 21 for encoding the first test light and the code ψ _n (t) of the optical encoding means 20 for encoding the second test light are arbitrary The frequency difference f ₁ is always constant at time t, and the frequency difference is not constant at other times.
(Condition 2) The frequency shift by the optical frequency changing means 17 is equal to the difference frequency between the Brillouin frequency shift f _B and the intersymbol frequency difference f ₁ described in Condition 1.
(Condition 3) The code φ (t) of the optical encoding means 21 that encodes the first test light has a correlation of 1 at an arbitrary time t and a correlation of 0 at other times.
(Condition 4) The minimum fiber length difference of the branched lower optical fiber 232 to be the measured optical fiber 23 is equal to or greater than the optical fiber identification resolution ΔL.
(Condition 5) The band of the optical receiver 26 is a band that can receive the modulation band of encoding.

Here, the conditions 1 to 5 have the following meanings.
Condition 1 is a condition for acquiring Brillouin gain information only at an arbitrary position z.
When the code characteristics of the optical encoding means 20 and 21 are as described above, the frequency difference between the first test light and the second test light is always the Brillouin frequency by matching with the condition 2 at an arbitrary position z in the measured fiber 23. Since it is equal to the shift, it undergoes Brillouin amplification over the code length. Since the frequency difference between the first test light and the second test light fluctuates at other positions, the Brillouin amplification is not always performed over the code length. Therefore, the Brillouin gain at an arbitrary position z can be obtained by integrating over the code length of the first test light.

Condition 2 is a condition necessary for the first test light to undergo Brillouin amplification by the second test light.
Conditions 3 and 4 are conditions necessary for acquiring individual Brillouin gain information of the lower branch optical fiber 232.
When the code characteristics of the optical encoding means 20 and 21 are as described above, the code φ _n (t) generated by the optical or electrical stage of the first test light reflected and returned from the end of the lower branch optical fiber 232 By taking the correlation over the code length, it is possible to obtain the intensity of the first test light that has returned from any branch lower optical fiber 232.

Condition 5 requires that the band of the optical receiver 26 and the band of the A / D converter 27 be wider than the optical code modulation frequency in order to accurately measure the optical code.
An optical line characteristic analysis method using this embodiment when this condition is satisfied will be described.
Two test lights having different wavelengths (first test light, second test light) are used, the first test light is probe light, the optical frequency is f ₀ -f _B , the second test light is pump light, and the optical frequency f _0. Here, f ₀ is the optical frequency of the pump light, and f _B is the optical frequency shift amount due to Brillouin backscattering.

The encoded first test light and the encoded second test light are incident on the optical fiber 23 to be measured. Here, the first test light and the second test light are N-branched by the optical splitter 231.
(i) Brillouin gain analysis method When the frequency of the first test light (probe light) and the second test light (pump light) is different by f _B , Scattering occurs and the first test light undergoes amplification represented by equation (1).

ここで、α_Bはブリルアン増幅率、g_Bはブリルアン散乱係数、zは分岐下部光ファイバ入射端から第一試験光と第二試験光がインタラクションした位置までの距離、I_pump(z)は分岐下部光ファイバ入射端から距離zだけ離れた位置における第二試験光(ポンプ光)の強度である。

Where α _B is the Brillouin amplification factor, g _B is the Brillouin scattering coefficient, z is the distance from the incident end of the branched lower optical fiber to the position where the first test light and the second test light interact, and I _pump (z) is the branch This is the intensity of the second test light (pump light) at a position z away from the lower optical fiber incident end.

If the loss of the lower branch optical fiber core wire #i is α _i and the total loss when going back and forth through the lower branch optical fiber core wire #i is 1 / D _i , The intensity I _probe (2L _i ) of the first test light at the incident end of the optical fiber is expressed by Expression (2).

式（2）より、分岐下部光ファイバ入射端での第一試験光の強度I_probe(2L_i)は、I_pump(z)のみの関数となる。
ここで、I_pump(z)は、式(3)で表される。

From Expression (2), the intensity I _probe (2L _i ) of the first test light at the incident end of the branched lower optical fiber is a function of only I _pump (z).
Here, I _pump (z) is expressed by Equation (3).

よって、式(2)は、式(3)を用いると式(4)として表される。

Therefore, Expression (2) is expressed as Expression (4) when Expression (3) is used.

上記（4）式より、ブリルアン利得を解析することにより、インタラクションした場所までの損失を取得できる。
上記、各分岐下部光ファイバからの戻り光I_probe(2L_i)は、光スプリッタから光受信器までの光ファイバにより同じ損失を受ける。
よって、ブリルアン利得を解析すれば、線路損失を測定することができる。
(ii) 分布測定方法
第一試験光の符号化をφ_n(t)、第二試験光の符号化をψ_n(t)とすると、φ_n(t)とψ_n(t)は、ある時刻tのときのみ周波数差がf₁で一定であり、それ以外の時刻において周波数差が一定でない符号である。

By analyzing the Brillouin gain from the above equation (4), the loss up to the location where the interaction occurred can be obtained.
The return light I _probe (2L _i ) from each branch lower optical fiber is subjected to the same loss by the optical fiber from the optical splitter to the optical receiver.
Therefore, line loss can be measured by analyzing the Brillouin gain.
(ii) Distribution measurement method If the encoding of the first test light is φ _n (t) and the encoding of the second test light is ψ _n (t), then φ _n (t) and ψ _n (t) are The frequency difference is constant at f ₁ only at time t, and the frequency difference is not constant at other times.

Further, the code φ _n (t) of the first test light is a code in which the correlation is 1 only at a certain time t and the correlation is 0 at other times.

被測定光ファイバの入射端から分岐下部光ファイバ#a（1≦a≦Nの整数）の終端までの長さをL_aとする。符号化された第一試験光は、分岐下部光ファイバの終端に設置された光反射フィルタにより反射される。反射して戻ってきた第一試験光と第二試験光は対向伝搬し、被測定ファイバ中でインタラクションする。ここで、第一試験光の符号をφ₁〜φ_nまで変化させ、第二試験光の符号をψ₁〜ψ_nまで変化させる。
例えば、以下のように周波数変調した場合を考える。

The length from the incident end of the optical fiber under test to the end of the branch lower optical fiber #a (integer of 1 ≦ a ≦ N) and L _a. The encoded first test light is reflected by a light reflection filter installed at the end of the branched lower optical fiber. The first test light and the second test light that have returned after reflection propagate in opposite directions and interact in the measured fiber. Here, the sign of the first test light is changed from phi ₁ to [phi] _n, changing the sign of the second test light to ψ ₁ ~ψ _n.
For example, consider the case of frequency modulation as follows.

Δfは符号化の変調振幅、f_mnはn番目の変調周波数、θは初期位相である。このとき、φ_nとψ_nで符号化した第一試験光と第二試験光を被測定ファイバ中に入射した場合、周波数差が一定の位置が周期的に表れる。この間隔をd_mnとすると、

Δf is the modulation amplitude of encoding, f _mn is the nth modulation frequency, and θ is the initial phase. At this time, when the first test light and the second test light encoded by φ _n and ψ _n are incident on the fiber to be measured, a position where the frequency difference is constant appears periodically. If this interval is d _mn ,

この位置(相関ピーク位置)において、第一試験光と第二試験光は周波数差がブリルアン周波数シフトと等しくなるため、符号長に渡ってブリルアン増幅を受ける。ここで、式(7)より、変調周波数f_mnを変化させることで間隔d_mnが変わり、相関ピーク位置を変化できる。そのため、変調周波数f_mnを変化させ、測定を繰り返すことでブリルアン利得の分布情報を取得可能である。

At this position (correlation peak position), the first test light and the second test light are subjected to Brillouin amplification over the code length because the frequency difference is equal to the Brillouin frequency shift. Here, from the equation (7), the interval d _mn is changed by changing the modulation frequency f _mn , and the correlation peak position can be changed. Therefore, the Brillouin gain distribution information can be acquired by changing the modulation frequency f _mn and repeating the measurement.

(iii) Brillouin gain information separation method for branched optical fiber
When the time for the first test light to be reflected by the test light reflection filter 233 at the end of the branched optical fiber #a and reach the optical receiver 26 is t _da , it is expressed by Expression (8).

ここで、vは光ファイバ中の光速、L_aは入射端から分岐下部光ファイバ#aの終端の試験光反射フィルタ２３３までの距離である。
他の分岐光ファイバ#b（1≦b≦Nの整数）から戻ってきた第一試験光が光受信器２６に到達する時間t_dbは、式(9)で表される。

Here, v is the velocity of light in an optical fiber, the L _a is the distance from the incident end to the test light reflection filter 233 of the end of the branch lower optical fiber #a.
A time t _db when the first test light returned from the other branch optical fiber #b (an integer of 1 ≦ b ≦ N) reaches the optical receiver 26 is expressed by Expression (9).

よって、#a、#bから光受信器２６に戻る第一試験光の時間差は、式(10)で表される。

Therefore, the time difference between the first test lights returning from #a and #b to the optical receiver 26 is expressed by Expression (10).

L_a ≠ L_bのとき、異なる分岐光ファイバ#a、#bから反射されて戻ってきた第一試験光が光受信器２６に到達する時間が異なる。ここで、異なる分岐光ファイバ#a、#bから戻ってきた、符号化された第一試験光は、光スプリッタ２３１で合波される。異なる分岐光ファイバ#a、#bから戻ってきた第一試験光が光スプリッタ２３１で合波されるとき、符号の位相はずれている。受光側へ戻ってきた第一試験光は、以下の式で与えられる。

When L _a ≠ L _b, the time required for the first test light reflected and returned from the different branched optical fibers #a and #b to reach the optical receiver 26 is different. Here, the encoded first test light returned from the different branched optical fibers #a and #b is multiplexed by the optical splitter 231. When the first test lights returned from the different branch optical fibers #a and #b are combined by the optical splitter 231, the signs are out of phase. The first test light that has returned to the light receiving side is given by the following equation.

そこで、分岐#Nから戻ってきた第一試験光に合わせて、受光側で符号φ_Nnを生成する。

Therefore, the code φ _Nn is generated on the light receiving side in accordance with the first test light returned from the branch #N.

このとき、φ_an(t)と受光した信号の相関を取ることで、分岐#aの位置zでのブリルアン利得が得られる。また、φ_bn(t)と受光した信号の相関を取ることで、分岐#bの位置zでのブリルアン利得が得られる。つまり、受光側へ戻ってきた第一試験光I_dと符号φ_Nnの相関を取ることで、分岐下部ファイバ#a、#bのブリルアン利得情報を分離して取得可能である。

At this time, the Brillouin gain at the position z of the branch #a is obtained by correlating φ _an (t) with the received signal. Further, by obtaining a correlation between φ _bn (t) and the received signal, the Brillouin gain at the position z of the branch #b can be obtained. That is, the Brillouin gain information of the branched lower fibers #a and #b can be separated and acquired by obtaining a correlation between the first test light I _d returning to the light receiving side and the sign _φNn .

  Here, the resolution for separately identifying the branched lower optical fibers #a and #b is determined by the code characteristics of the encoded first test light. The encoded first test light is decoded by the correlation between the codes. A resolution (branching optical fiber identification resolution) ΔL for identifying the branched lower optical fibers #a and #b when encoded by the expression (5) is expressed by an expression (13).

このため、分岐下部光ファイバ#a、#bの識別分解能は、パルス幅ではなく、符号特性により決まるので、分岐下部光ファイバ#a、#bの識別分解能をフォノン寿命より短くすることが可能となる。式(13)より、Δfを50 MHz以上で変調することで、分岐下部光ファイバ#a、#bの識別分解能は1m以上を実現できる。

For this reason, the identification resolution of the lower branch optical fibers #a and #b is determined not by the pulse width but by the sign characteristics, so that the identification resolution of the lower branch optical fibers #a and #b can be made shorter than the phonon lifetime. Become. From equation (13), by modulating Δf at 50 MHz or higher, the discrimination resolution of the branched lower optical fibers #a and #b can be 1 m or higher.

  That is, it is possible to separate the first test light obtained on the light receiving side into information for each branched lower optical fiber by changing the initial phase and decoding. In addition, when using sine wave modulation, modulation resolution of Δf at 50 MHz or more can realize the identification resolution of the lower branch optical fibers #a and #b of 1 m or more, and about 1 cm by setting Δf to 5 GHz. The lower split optical fiber identification resolution can be realized.

FIG. 2 shows a flowchart for realizing the above processing in the arithmetic processing unit 28.
In FIG. 2, first, when a digitized probe signal is input (step S1), this probe signal is decoded to identify which branch lower optical fiber is the digital signal of the probe light. (Step S2) The Brillouin gain is analyzed from the identified digital signal (Step S3), the sign is changed (Step S4), and the above measurement is repeated. The Brillouin gain characteristic distribution is acquired (steps S5 and S6).

In the above embodiment, the case where the first test light and the second test light are encoded with a sine wave has been described, but the encoding can also be measured with a pseudo-random signal (PRBS).
When each of the measurement results (i) to (iii) and conditions 1 to 5 are satisfied, according to this embodiment, individual loss distribution measurement of the lower branch optical fibers #a and #b of the PON type optical branch line is performed. Measurement is possible only with the configuration of the existing off-site equipment (optical splitter 231, lower branch optical fiber 232, and light reflection filter 233 installed at the end of the lower branch optical fiber), and discrimination resolution of lower branch optical fibers #a and #b Can achieve measurement even when 1 m or more is realized, that is, when the difference in length of the branched lower optical fiber is 1 m or less.

(Second Embodiment)
FIG. 3 is a block diagram showing the configuration of the optical branch line characteristic analyzing apparatus according to the second embodiment. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals, and different parts will be described here.
In the apparatus shown in FIG. 3, a light source 31 is provided separately from the light source 11, and the optical encoding unit 29 modulates the waveform of the laser injection current of the light source 11 with an arbitrary code and delays it for a certain period by the delay control unit 30. The laser injection current is waveform-modulated with the same sign. The transmission light encoded and modulated by the light source 31 is sent to the multiplexing element 25, and is combined with the first test light from the optical filter 24, and is thereby received by the optical receiver 26 as a correlation waveform.

  That is, in the first embodiment, the correlation processing is performed by the arithmetic processing unit 27 after receiving the light, whereas in the second embodiment, the signal light that has been subjected to the delay code modulation by the light source 31 is combined with the multiplexing element. This is a method of performing correlation processing by light interference by combining with test light at 25. The light source 31 shown in FIG. 3 may be a light source that can be arbitrarily waveform-modulated by an injection current, like the light source 11.

  In addition, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some configurations may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different example embodiments may be combined as appropriate.

DESCRIPTION OF SYMBOLS 11 ... Light source 12, 13 ... Branch element 14 ... Optical amplifier 15, 18 ... Optical modulator 16, 25 ... Multiplexing element 17 ... Optical frequency change means 19 ... Sine wave generator 20, 21 ... Optical encoding means 22 ... Circulator 23 ... Fiber to be measured 231 ... Optical splitter 232 ... Lower branch optical fiber 233 ... Optical reflection filter 24 ... Optical filter 26 ... Optical receiver 27 ... A / D converter 28 ... Arithmetic processor 29 ... Optical encoding means 30 ... Delay Control means 31 ... Light source

Claims (4)

A single optical fiber is branched from a first optical fiber to an Nth optical fiber by an optical splitter, and the test light is reflected to a far end of the first to Nth branched lower optical fibers branched by the optical splitter; For a fiber to be measured to which first to Nth single wavelength reflection type optical filters that transmit light having a wavelength different from the wavelength of the test light are connected, from the branch point by the optical splitter to the optical filter. An optical branch line characteristic analyzing apparatus for analyzing optical line characteristics of an optical branch line having a minimum difference in length with respect to an N-core branched lower optical fiber having an optical fiber identification resolution or higher,
A test light generating means for generating two types of test light having different wavelengths;
Encoding means for encoding the two types of test light having different wavelengths;
A multiplexing means for multiplexing the encoded two kinds of test lights;
A circulator that makes the combined test light enter the fiber to be measured and extracts the probe light returned from the branch optical fiber below the optical splitter;
Filter means for extracting one wavelength of the two kinds of test light from the extracted probe light;
Light / electric conversion means for receiving the probe light extracted by the filter means and converting it into a current;
Analog-digital conversion means for converting the test light converted into the current into a digital signal;
The digital signal is decoded, the branch lower optical fiber is identified as the probe light digital signal, the Brillouin gain is analyzed from the identified digital signal, the sign is changed, and the measurement is performed. An apparatus for analyzing characteristics of an optical branch line, comprising: an arithmetic processing unit that obtains a Brillouin gain characteristic distribution of each of the lower branch fibers of the optical splitter from measurement results that are repeatedly performed and repeatedly measured.   2. The optical branch line characteristic analysis apparatus according to claim 1, wherein the Brillouin gain analysis includes measurement of distortion in an optical medium.   2. The optical branch line according to claim 1, wherein the optical line characteristic is at least one of an optical attenuation with respect to a distance, a position of a bending obstacle, a degree of bending, a position of a disconnection obstacle, and a temperature change amount with respect to the distance. Characteristic analysis device. A single optical fiber is branched from a first optical fiber to an Nth optical fiber by an optical splitter, and the test light is reflected to a far end of the first to Nth branched lower optical fibers branched by the optical splitter; For a fiber to be measured to which first to Nth single wavelength reflection type optical filters that transmit light having a wavelength different from the wavelength of the test light are connected, from the branch point by the optical splitter to the optical filter. Applied to an optical branch line characteristic analyzer for analyzing the characteristics of an optical branch line in which the minimum difference in length of the N-core branched lower optical fiber has an optical fiber identification resolution or higher,
Two types of test light having different wavelengths are generated, each test light is encoded and combined, and the combined test light enters the fiber to be measured and returns from the branch optical fiber below the optical splitter. The probe light is extracted, one wavelength of the two types of test light is extracted from the probe light, the extracted probe light for one wavelength is converted into a current, and the converted current signal is converted into a digital signal. A method of converting and decoding the digital signal to analyze the characteristics of the optical branch line,
Identify which branch lower optical fiber is the digital signal of the probe light incident from the decoding result of the digital signal,
Analyzing the Brillouin gain from the identified digital signal;
Repeat the above measurement by changing the sign,
A characteristic analysis method for an optical branch line, characterized in that a Brillouin gain characteristic distribution of each of the lower branch fibers of the optical splitter is obtained from measurement results obtained repeatedly.

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