JP2010025913A - Wavelength dispersion measuring device and technique - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength dispersion measuring device and a technique thereof for measuring wavelength dispersion with sufficient accuracy without reflection at a receiving end, even if locations of the transmitting and receiving ends are different. <P>SOLUTION: The wavelength dispersion measuring device includes a process generating two light signals with different wavelength at a transmitting end of light transmission path, a process multiplexing the two light signals to transmit from the transmitting end of the light transmission path, a process transmitting wavelength dispersion measurement information containing wavelength of the measuring start signal based on generation of the light signals and the two light signals from the transmitting end to the receiving end, a process splitting the two light signals transmitted through the light transmission path to convert into electric signal, respectively, at the receiving end of the light transmission path. and a process measuring phase difference of the two signals with different converted wavelengths according to the measuring start signal of wavelength dispersion measurement information from the transmitting end to derive wavelength dispersion in the light transmission path from the measured phase difference and wavelength difference of the two signals of the wavelength dispersion measurement information which were measured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to chromatic dispersion measurement, and in particular, to a chromatic dispersion measurement apparatus and a chromatic dispersion measurement method for an optical communication apparatus such as a long-distance optical fiber transmission line where an input unit and an output unit are separated.

  In an optical fiber communication system where transmission speed increases and distance extension advances, chromatic dispersion compensation technology is an essential element. In particular, at a bit rate of 40 gigabits or more, wavelength distortion compensation is an indispensable technique because waveform distortion of an optical signal due to wavelength dispersion occurs even in a system with a transmission distance of about several tens of kilometers. Therefore, there is a need for a technique for accurately measuring chromatic dispersion in an optical fiber serving as a transmission line and compensating for waveform distortion caused by chromatic dispersion. Furthermore, in an optical fiber communication system, both ends of the transmission line are located at remote locations, and the chromatic dispersion of the optical fiber changes according to the external environment. Therefore, measurement and compensation of chromatic dispersion are performed at locations where the transmitter and receiver are separated. It must be possible even if it exists.

  In the conventional chromatic dispersion measuring device, when the input and output ends of the optical fiber to be measured such as the existing fiber on the field are not in the same place, a terminator or a circulator is provided to reflect the optical signal at the receiving end side, and at the transmitting end By receiving the return light, the chromatic dispersion of the optical fiber between two distant points was measured (for example, Patent Document 1). In addition, a method for measuring chromatic dispersion of an optical fiber to be measured from information on the intensity, average photocurrent, pulse shape, and light source frequency of a signal optically / electrically converted at the receiving end has been proposed (for example, Patent Document 2).

JP 2000-329653 A JP 2000-193558 A

  In the conventional chromatic dispersion measuring device, when the input and output ends of the optical fiber to be measured such as the existing fiber on the field are not in the same place, it is impossible to measure without reflecting by providing a terminator or a circulator. . However, in the method using the circulator, it is necessary to return the optical signal at the receiving end, and there is a problem that the system cannot be operated during the chromatic dispersion measurement. Further, even in the case of Patent Document 2, the chromatic dispersion of the optical fiber to be measured cannot be measured during system operation.

  The present invention has been made to solve the above problems, and a chromatic dispersion measuring apparatus and a chromatic dispersion measuring method for accurately measuring chromatic dispersion without reflection at the receiving end even when the transmitting and receiving ends are in different locations. The purpose is to provide.

  The present invention is a chromatic dispersion measuring apparatus for measuring chromatic dispersion in an optical transmission line, and an optical signal generating means for generating two optical signals having different wavelengths on the transmitting end side of the optical transmission line; A multiplexing unit configured to multiplex and transmit two optical signals, and from the transmission end side to the reception end side, a measurement start signal based on the generation of the optical signal by the optical signal generation unit and the two optical signals A measurement control means including a transmission path for transmitting chromatic dispersion measurement information including a wavelength is provided, and the two optical signals transmitted via the optical transmission path are demultiplexed on the receiving end side of the optical transmission path A demultiplexing unit, a photoelectric conversion unit that converts the two demultiplexed optical signals into electric signals, and a measurement start signal of chromatic dispersion measurement information from the transmitting end side, and the two different wavelengths converted The phase difference of the electrical signal is measured and this measured phase difference and the previous A wavelength dispersion measuring apparatus and method is characterized in that and a wavelength dispersion measuring means for determining the chromatic dispersion in the optical transmission line and a wavelength difference of wavelengths of the two signals of the wavelength dispersion measurement information.

  Furthermore, by providing a polarization beam splitter, the differential group delay time difference (DGD: Differential Group Delay), which is the first-order polarization mode dispersion, is measured, and the dispersion is achieved by providing three or more optical signals. If the slope coefficient or dispersion slope coefficient is known, the distance of the optical fiber to be measured is also measured.

  According to the present invention, it is possible to provide a chromatic dispersion measuring apparatus and method for accurately measuring chromatic dispersion without reflection at the receiving end even when the transmitting and receiving ends are in different places. In addition, since the measurement uses the delay difference between the frame pulses of transmission signals of two different wavelengths, the chromatic dispersion can be measured without affecting the main signal even during system operation.

Embodiment 1 FIG.
FIG. 1 shows a block diagram of a chromatic dispersion measuring apparatus according to an embodiment of the present invention. The chromatic dispersion measuring device according to the present invention is provided with H / W (hardware) provided respectively on the transmitting end side and the receiving end side for measuring the chromatic dispersion of the optical fibers F1 and F2 (measured) serving as optical transmission paths. And a computer that operates according to S / W (software) that controls the measurement units 10a and 10b, and further includes a network NW (a transmission path different from the optical transmission path). Measurement control units 20a and 20b having a communication function for communicating with each other. The measurement units 10a and 10b are respectively an SDH frame generation unit 11, an optical signal generation unit 12, a multiplexing unit 13 on the transmission side, a demultiplexing unit 14, a photoelectric conversion unit (O / E) 15, and an SDH frame synchronization unit on the reception side. 16, a chromatic dispersion measuring unit 17 is provided. One measuring unit is installed at the transmitting node and the other is installed at the receiving node, and the chromatic dispersion of the optical fibers F1 and F2, which are optical transmission lines, can be measured.

  The SDH frame generation unit 11 and the optical signal generation unit 12 constitute an optical signal generation unit, the SDH frame synchronization unit 16 and the chromatic dispersion measurement unit 17 constitute a chromatic dispersion measurement unit, and the measurement control units 20a and 20b and the network. NW constitutes a measurement control means. Further, FIG. 1 shows the respective wavelength dispersion measurement functions of the optical fibers F1 and F2 from the measurement unit 10a side to the measurement unit 10b side and in the opposite direction.

Hereinafter, chromatic dispersion measurement of the optical fiber F1 will be described as an example. When performing chromatic dispersion measurement, from the measurement control unit 20a on the transmission end side of the optical fiber F1 to the measurement control unit 20b on the reception end side via the network NW, Chromatic dispersion measurement information including wavelengths λ ₁ and λ ₂ of two optical signals having different wavelengths transmitted for measurement is transmitted.

The SDH frame generation unit 11 on the transmission side generates SDH frames for the wavelengths λ ₁ and λ ₂ . In the optical signal generation unit 12, the SDH signal (SDH frame signal) generated by the SDH frame generation unit 11 is optically modulated and combined by the multiplexing unit 13. When the modulated signal propagates through the transmission lines of the optical fibers F1 and F2, it is affected by the chromatic dispersion of the optical fiber and causes a group delay depending on the wavelength.

  When receiving the chromatic dispersion measurement information, the receiving side first separates and splits the multiplexed optical signal received by the demultiplexing unit 14 into the two different wavelengths described above, and then photoelectrically converts each optical signal. The unit 15 converts it into an electrical signal. Frame synchronization is performed by the SDH frame synchronization unit 16 for two electrical signals having different wavelengths, and a frame pulse generated by the frame synchronization is input to the chromatic dispersion measurement unit 17.

  The chromatic dispersion measuring unit 17 measures the delay difference between the two signals using the received frame pulse. If there is no chromatic dispersion in the optical transmission line, for example, the optical fiber F1, the timing of both signals is exactly the same, but in reality, due to the chromatic dispersion of the optical fiber F1, depending on the length of the optical fiber and the wavelength difference, There is a difference in timing between the two. The following equation is used to obtain chromatic dispersion from the estimated group delay time.

D _λ = nt (λ ₂ −λ ₁ )

Here, D _λ is chromatic dispersion, λ ₁ and λ ₂ are center wavelengths of two electric signals having different wavelengths, t is a bit interval, and n (n = 1, 2, 3,...) Is a bit shift number. . That is, nt is a group delay time difference (phase difference between two electric signals having different wavelengths). The wavelengths λ ₁ and λ ₂ can be obtained from chromatic dispersion measurement information.

  In this method, after SDH frame synchronization, a circuit (hardware) for measuring a group delay time is configured by an FPGA (Field Programmable Gate Array), and a PLL circuit is used for the FPGA circuit to measure the group delay. Time measurement accuracy can be improved.

FIG. 2 is a more detailed diagram of the hardware configuration on the receiving side of the chromatic dispersion measuring apparatus of FIG. Wavelengths λ ₁ and λ ₂ are extracted from the optical signal branched into two by the coupler 14a by band-pass filters (BPF) 14b and 14c, respectively. The extracted optical signal is optical / electrically converted by a photoelectric conversion unit (O / E) 15 and further branched into two. One electrical signal (wave) is clock recovered by clock extraction units (CDR) 161a and 161b, and SDH frames are synchronized by frame synchronizers 162a and 162b to generate frame pulses. The generated frame pulse is input to the chromatic dispersion measuring unit 17. The other electrical signal (wave) is directly input to the chromatic dispersion measuring unit 17 without passing through the clock extracting unit and the frame synchronizer.

The chromatic dispersion measurement unit 17 includes a low accuracy measurement unit 17a and a high accuracy measurement unit 17b. The low accuracy measurement unit 17a measures the chromatic dispersion by measuring the input delay difference of the frame pulse generated by the frame synchronization. That is, two frames pulses that arrive out destination of the frame pulse (towards the case of FIG. 2 lambda ₁₎ is operated the internal counter (not shown) from the other frame pulse (towards the case of FIG. 2 lambda ₂ after The delay time is obtained from the counter value until) arrives. The accuracy of chromatic dispersion measurement at this time corresponds to the reciprocal of the bit rate. For example, if the signal is 155.52 Mbps, the chromatic dispersion is measured with an accuracy of about 6.4 ns.

On the other hand, the signal that does not pass through the frame synchronizer among the signals that have been optically / electrically converted by the photoelectric conversion unit (O / E) 15 is used for high-accuracy chromatic dispersion measurement in the high-accuracy measurement unit 17b. FIG. 3 is a diagram showing an example of the circuit configuration of the hardware part of the high-precision measurement unit 17b of the chromatic dispersion measurement unit 17, and FIG. 4 is a timing chart for explaining the operation of the circuit of FIG. The circuit includes a clock input unit including a phase synchronization circuit (PLL) 171 that generates a plurality of clocks obtained by shifting a frame pulse, that is, a clock obtained by multiplying a clock (CLK) of 155.52 MHz by a predetermined multiple, respectively, by different phase amounts. , And λ ₁ and λ ₂ , respectively, are input from the first and second data input sections. The input side of the second data input unit includes an adjustment unit 172 that adjusts the delay based on the input delay difference measured by the low-precision measurement unit 17a.

  The input data is multiplied by x times by the PLL 171 and the clock of CLKn (n = 0, 1, 2, 3,..., K−1) is output. CLKn is a clock whose phase is shifted by 360 × (n / k) ° with respect to CLK0. FIG. 3 shows a circuit when x = 4 and k = 4. As shown in FIG. 4, CLK0 to CLK3 are 622.08 MHz (155.52 MHz × 4), and the respective phase differences are 90 °.

Input data (Data), which is an electrical signal of wavelengths λ ₁ and λ ₂ , is branched into four, and each is input to a first-stage T-FF (T-type flip-flop). Here, the data of the wavelength λ ₂ is adjusted so as to cancel out the bits corresponding to the delay based on the measurement result of the previously measured SDH frame. That is, the input data of the wavelengths λ ₁ and λ ₂ are adjusted to a delay difference of 1 bit or less for the SDH signal and input to the T-FF.

  The above CLK0 to 3 are input to each T-FF, and the operation timing is shifted by 90 °. CLK0 is input to the second T-FF. However, since the phase difference between CLK3 and CLK0 is only 90 °, there is a possibility that the timing may not be obtained depending on the arrangement and wiring situation inside the FPGA, and CLK2 that is opposite in phase to CLK0 is used. As a result, a phase difference of 270 ° can be obtained, and there is a margin in the placement and wiring. In this state, CLK0 cannot be input to all T-FFs as a gate signal (hit input data), so a third-stage T-FF is added. Here, CLK0 is input as a gate signal (input). Hit the data). Since the phase difference between CLK2 and CLK0 is 180 °, the timing margin is sufficient. After passing through the third stage T-FF, the timing comparison unit 173 measures a highly accurate chromatic dispersion value.

In the timing chart of the circuit of FIG. 3 shown in FIG. 4, D ₀ 0, D ₀ 1, D ₀ 2, and D ₀ 3 are branched into four and input data D ₀ 0 after passing through the first stage T-FF. −1d, D ₀ 1-1d, D ₀ 2-1d, D ₀ 3-1d are output data of the second stage T-FF, D ₀ 0-2d, D ₀ 1-2d, D ₀ 2-2d, D ₀ 3-2d is the output data of the third stage T-FF. Since the phase difference between CLK3 and CLK0 is only 90 °, that generates data _D 0 3-1d once _CLK2, be provided 180 ° phase difference _D 0 3-2d from D 0 3-1d it can. By generating data at CLK0 in the final stage T-FF, the timing of the first clock between the two clocks where the four-branched data changes from 0000 to 1111 becomes the phase delay to be measured, and the position relative to CLK0 The phase difference is 0 ° when 0000, 90 ° when 0001, 180 ° when 0011, and 270 ° when 0111.

In other words, the low accuracy measurement unit 17a can measure the delay difference only with an accuracy of how many clocks of 155 MHz. Therefore, in the high-accuracy measuring unit 17b, the clock (155 MHz CLK) is multiplied by the phase synchronization circuit (PLL) 171, and further, (0 °, 90 °, 180 °, 270 °) and a phase difference of 1/4 clock are provided. Increase measurement accuracy. FIG. 4 shows four clocks provided with a phase difference. Below this, the frame pulse (λ ₁ , λ ₂ ) is drawn, but here only the frame pulse (λ ₁ ) is focused.

In the first stage, the frame pulse is synchronized with CLK0 to CLK3 (clock transfer).
Since D ₀ 0 operates in synchronization with CLK 0, D ₀ 0 transitions to (L → H) when CLK 0 first changes (L → H) after the arrival of the frame pulse λ ₁ . Similarly, D ₀ 1 transitions to (L → H) after ¼ clock. D ₀ 2 transitions at a point where CLK ₂ first changes from (L → H) after the arrival of the frame pulse λ ₁ , and thus is a position returned by 3/4 clock from D ₀ 1. Similarly, D ₀ 3 transitions to (L → H) after 1/4 clock of D ₀ 2.

In the second stage, data synchronized with CLK0 to CLK3 is replaced with CLK0. Is the CLK0 and _{D 0 0} to note. D ₀ 0-1d changes to (L → H) when CLK ₀ changes to (L → H) after D _{0 0} changes to (L → H). Similarly, since the transition of _{D 0} 1 is an (L → H), where CLK0 changes and _{(L → H), D 0} 1-1d transitions to (L → H). Furthermore, D ₀ 2-1d changes to (L → H) when CLK ₀ changes to (L → H) after D _{0 2} changes to (L → H). Similarly, we want to consider D ₀ 3-1d at the end, but there is a problem here. There is only a ¼ clock margin after D ₀ 3 changes from (L → H) to when CLK0 changes from (L → H). In this case, the timing is very difficult, and circuit design with an FPGA or LSI is not easy. Therefore, synchronization is once performed at CLK2. Since there are 3/4 clocks from when D ₀ 3 changes from (L → H) to when CLK2 changes from (L → H), a sufficient timing margin can be obtained.

As a result, all signals other than D ₀ 3-1d are synchronized with CLK0. However, since D ₀ 3-1d is synchronized with CLK2, synchronization is performed again with CLK0 as the third stage. When the same operation as _heretofore, D 0 from the transition _D 0 3-1d is the (L → H) also 3-2d, 1/2 clocks until CLK0 changes and (L → H) Therefore, a sufficient circuit design is possible. The same operation is performed for the frame pulse λ2, and when all data is synchronized with CLK0, the timing is determined by the following method and the delay difference is measured.

  That is, paying attention to the rising edge (L → H) of 622.08 MHz CLK0, in FIG. 4, “0000” → “0000” → “0011” → “1111”. That is, “0011” during the transition from “0000” to “1111” is the measurement timing.

The timing comparator 173 obtains “0000”, “0001”, “0011”, and “0111” from the data of the wavelengths λ ₁ and λ ₂ . For example, when the wavelength λ1 is the wavelength λ2 in the "0001" is "0011", the wavelength lambda ₂ at a wavelength lambda ₁ is 90 degrees is 180 °, the phase difference (180 ° -90 ° = 90 ° , i.e. 622 The delay difference is 1/4 of 08 MHz.

  According to this method, it is possible to measure chromatic dispersion with an accuracy of x × k times that of the low-accuracy measurement unit 17a. For example, when the signal bit rate is 155.52 Mbps and x = 4 and k = 4, the measurement accuracy is about 6.4 ns / (4 × 4) = about 400 ps.

  The high-accuracy chromatic dispersion method by the high-precision measurement unit 17b is not limited to the four-branch input sequence in data input, and can be widely applied to multi-branch input sequences. Similarly, the multiplication of the internal PLL of the FPGA is not limited to four times.

  In the present invention, by transmitting information such as a measurement start signal and a transmission wavelength through a network, it is possible to accurately measure chromatic dispersion without reflection at the receiving end even when the transmitting and receiving ends are in different places.

  In addition, a phase synchronization circuit (PLL) provided on the receiving end side multiplies the input clock and generates a plurality of clocks whose phases are shifted by several tens of degrees. Using these clocks, signals of two different wavelengths are generated. Measurement accuracy can be improved by measuring the phase difference.

  In addition, by using the SDH (Synchronous Digital Hierarchy) frame pulse used for the normal communication of the optical waveguide for the measurement of the chromatic dispersion, the normal communication number is not affected even during the system operation. Chromatic dispersion can be measured. Note that SDH (Synchronous Digital Hierarchy) is a standard of the International Telecommunications Union (ITU-T) for optical communications widely used in Asia and Europe.

Embodiment 2. FIG.
FIG. 5 shows a block diagram of a chromatic dispersion measuring apparatus according to another embodiment of the present invention. The same or corresponding parts as those in the above embodiment are denoted by the same reference numerals and the description thereof is omitted. In FIG. 5, only the optical fiber F1 side from the measurement unit 10a to the measurement unit 10b is illustrated and described below. However, on the optical fiber F2 side, the direction of transmission and reception is opposite, but the same configuration is provided and the same operation is performed. Is done.

  The chromatic dispersion measuring apparatus of FIG. 5 is an apparatus having a polarization beam splitter (PBS) 22 on the receiving side, and measures differential group delay (DGD), which is first-order polarization mode dispersion. be able to. Also, a polarization rotator (STM1) 21 is placed on the transmission or reception side so that the maximum DGD can be accurately measured in a shorter time.

In the chromatic dispersion measuring apparatus shown in FIG. 5, a light intensity modulation signal having a wavelength λ ₂ , for example, output from the optical signal generation unit 12, which is sent by the optical fiber F 1, is separated into two optical signals by the polarization beam splitter 22. Each of the obtained two optical signals is converted into an electric signal by the photoelectric conversion unit 15. These electrical signals are input to the chromatic dispersion measuring unit 17 via the SDH frame synchronization unit 16.

  The chromatic dispersion measuring unit 17 further includes a cross correlation calculating unit 17c in addition to the low accuracy measuring unit 17a and the high accuracy measuring unit 17b (see FIG. 2). A differential group delay time difference (DGD), which is first-order polarization mode dispersion, is obtained by obtaining a cross-correlation between the two optical signals separated by the beam splitter 22. The low accuracy measurement unit 17a and the high accuracy measurement unit 17b of the chromatic dispersion measurement unit 17 obtain the above-described group delay time difference nt (phase difference) based on the differential group delay time difference (DGD), and then obtain the chromatic dispersion in the same manner.

  In addition, a polarization rotator 21 is provided on the optical transmission line on the transmission or reception side (reception side in FIG. 5), and the maximum differentiation is achieved in a shorter time by intentionally causing separation into the two main axes. The group delay time difference (DGD) can be accurately measured.

Embodiment 3 FIG.
FIG. 6 shows a block diagram of a chromatic dispersion measuring apparatus according to still another embodiment of the present invention. The same or corresponding parts as those in the above embodiment are denoted by the same reference numerals and the description thereof is omitted. The chromatic dispersion measuring apparatus in FIG. 6 uses an optical signal of three or more waves (showing three waves of λ ₁ , λ ₂ , and λ _{3 in} FIG. 6) to obtain a dispersion slope coefficient.

  G. of the International Telecommunication Union. The maximum value of the dispersion slope of the single mode fiber specified by 652 is specified as 0.093 ps / nm ^ 2 / km, and this value is used in the case of a measurement method using an optical signal of two wavelengths. As an expected value, it was necessary to use the wavelength interval between the two signals and the distance between the optical fibers to be measured (optical fibers F1 and F2).

  However, there is a problem that the chromatic dispersion value obtained from the expected value of the dispersion slope has a large error depending on the distance of the optical fiber to be measured.

  Therefore, by using optical signals of three or more waves, distance information of the optical fiber to be measured becomes unnecessary. Furthermore, when the dispersion slope coefficient is known, the distance of the optical fiber to be measured can be obtained.

  FIGS. 7A and 7B are diagrams for explaining the characteristics of the present invention. FIG. 7A shows a case of measurement using an optical signal of two wavelengths, and FIG. 7B shows a case of measurement using an optical signal of three wavelengths, for example. The left side of, shows the group delay time with respect to the wavelength, and the right side shows chromatic dispersion with respect to the wavelength. That is, in the case of measurement using an optical signal having two wavelengths, only two group delay times can be obtained as shown in FIG. 7A, and the dispersion slope cannot be obtained. Therefore, as shown in FIG. 7B, by using an optical signal having three or more wavelengths, two or more chromatic dispersion values are obtained, and a dispersion slope coefficient is obtained from a plurality of obtained chromatic dispersion values. The chromatic dispersion is obtained accurately without requiring distance information of the optical fiber to be measured.

  In FIG. 6, the operation between the SDH frame generation unit 11 on the transmission side and the SDH frame generation unit 16 on the reception side is basically the same as that of the above embodiment except that the number of optical signals is different. Therefore, although not shown in the figure, the configuration from the demultiplexing unit 14 to the SDH frame generation unit 16 in FIG. 6 has three configurations from the bandpass filter (BPF) 14 to the frame synchronizer 162 in FIG. Become. In addition to the above-described low-precision measurement unit 17a and high-precision measurement unit 17b, the chromatic dispersion measurement unit 17 obtains chromatic dispersion from a plurality of obtained chromatic dispersion values and further obtains the distance of the optical fiber to be measured. A length calculation unit 17d is further included.

  Then, as shown in FIG. 7B, the optical transmission line length calculation unit 17d obtains a dispersion slope coefficient from a plurality of chromatic dispersion values obtained by the low accuracy measurement unit 17a and the high accuracy measurement unit 17b. When the wavelength dispersion is accurately obtained without requiring the distance of the optical fiber to be measured, and the dispersion slope coefficient is stored in advance, the distance of the optical fiber to be measured is obtained.

  In the description of each of the above embodiments, the chromatic dispersion measurement information including the wavelength of the optical signal and the measurement start signal is described as being transmitted and received through the network NW (transmission path). It is also possible to transmit / receive using overhead.

  As the frame format, in addition to the SDH frame, G. of International Telecommunications Union (ITU-T). Any format including an optical transport network (OTN) frame defined in 709 can be used.

  It should be noted that the present invention is not limited to each of these embodiments, and it goes without saying that each of these embodiments and possible combinations of features are included.

It is a block diagram of the wavelength dispersion measuring apparatus by one embodiment of this invention. FIG. 2 is a more detailed diagram of a hardware configuration on the receiving side of the chromatic dispersion measuring apparatus in FIG. 1. It is a figure which shows an example of the circuit structure of the hardware part of the high precision measurement part of the chromatic dispersion measurement part of FIG. FIG. 4 is a timing chart for explaining the operation of the circuit of FIG. It is a block diagram of the wavelength dispersion measuring apparatus by another embodiment of this invention. It is a block diagram of the wavelength dispersion measuring apparatus by another embodiment of this invention. It is a figure for demonstrating the dispersion slope coefficient measuring system using the optical signal of three or more waves regarding the chromatic dispersion measuring apparatus of FIG.

Explanation of symbols

  10a, 10b measurement unit, 11 SDH frame generation unit, 12 optical signal generation unit, 13 multiplexing unit, 14 demultiplexing unit, 14a coupler, 14b, 14c band pass filter (BPF), 15 photoelectric conversion unit (O / E) 16 SDH frame synchronization unit, 17 chromatic dispersion measurement unit, 17a low accuracy measurement unit, 17b high accuracy measurement unit, 17c cross correlation calculation unit, 17d optical transmission line length calculation unit, 20a, 20b measurement control unit, 21 Polarization rotator, 22 Polarization beam splitter (PBS), 161a, 161b Clock extraction unit (CDR), 162a, 162b Frame synchronizer, 171 Phase synchronization circuit (PLL), 172 Adjustment unit, 173 Timing comparator, F1 , F2 optical fiber.

Claims (18)

A chromatic dispersion measuring device for measuring chromatic dispersion in an optical transmission line,
On the transmission end side of the optical transmission line,
Optical signal generating means for generating two optical signals having different wavelengths by framing them;
A multiplexing unit that multiplexes and transmits the two optical signals, and
From the transmission end side to the reception end side, provided is a measurement control means for transmitting chromatic dispersion measurement information including the measurement start signal based on the generation of the optical signal in the optical signal generation means and the wavelengths of the two optical signals,
On the receiving end side of the optical transmission line,
A demultiplexing unit that demultiplexes the two optical signals transmitted via the optical transmission path;
A photoelectric conversion unit that converts the two optical signals that have been demultiplexed into electrical signals;
According to the measurement start signal of the chromatic dispersion measurement information from the transmitting end side, the phase difference between the two converted electric signals having different wavelengths is measured, and the two signals of the measured phase difference and the chromatic dispersion measurement information are measured. Chromatic dispersion measuring means for obtaining chromatic dispersion in the optical transmission line from the wavelength difference of the wavelength,
A chromatic dispersion measuring apparatus comprising: The optical signal generating means on the transmitting end side is
A frame generator for generating respective frames for measuring chromatic dispersion of two optical signals;
An optical signal generation unit for generating the two optical signals by optical intensity modulation of the generated frame signal;
Including
The chromatic dispersion measuring means on the receiving end side is
A frame synchronization unit that regenerates a clock from two electrical signals having different wavelengths obtained by converting a frame signal of an optical signal into an electrical signal by the photoelectric conversion unit, and generates a frame pulse by performing frame synchronization based on the clock;
A phase difference between two electrical signals having different wavelengths is measured using a plurality of clocks obtained by shifting the clock generated by the phase synchronization circuit by a predetermined multiple and shifted by different phase amounts. A chromatic dispersion measuring unit for obtaining chromatic dispersion in the optical transmission line from the phase difference and the wavelength difference between the wavelengths of the two signals of the chromatic dispersion measurement information;
including,
The chromatic dispersion measuring apparatus according to claim 1. On the receiving end side of the optical transmission line,
A polarization beam splitter that separates one optical signal of the two optical signals from the optical transmission path into two optical signals;
The chromatic dispersion measuring means is
A mutual difference is obtained by obtaining a differential group delay time which is a first-order polarization mode dispersion by obtaining a cross-correlation of the two optical signals separated by the polarization beam splitter based on an electric signal converted by the photoelectric conversion unit. The chromatic dispersion measuring apparatus according to claim 1, further comprising a correlation calculation unit, and determining a phase difference based on the differential group delay time difference.   4. The chromatic dispersion measuring apparatus according to claim 3, wherein a polarization rotator for causing separation into two main axes is provided on an optical transmission line on a transmission side or a reception side. A chromatic dispersion measuring device for measuring chromatic dispersion in an optical transmission line,
On the transmission end side of the optical transmission line,
Optical signal generation means for generating three optical signals having different wavelengths by framing them;
A multiplexing unit that multiplexes and transmits the three optical signals; and
From the transmission end side to the reception end side, provided is a measurement control means for transmitting chromatic dispersion measurement information including the measurement start signal based on the generation of the optical signal by the optical signal generation means and the wavelengths of the three optical signals,
On the receiving end side of the optical transmission line,
A demultiplexing unit for demultiplexing the three optical signals transmitted via the optical transmission path;
A photoelectric conversion unit that converts the three optical signals that have been demultiplexed into electrical signals;
According to the measurement start signal of the chromatic dispersion measurement information from the transmitting end side, the phase difference of the three electrical signals having different converted wavelengths is measured, and the measured phase difference and the three signals of the chromatic dispersion measurement information are measured. Chromatic dispersion measuring means for obtaining a plurality of chromatic dispersion values in the optical transmission line from the wavelength difference of the wavelength, and further obtaining a dispersion slope coefficient from the obtained chromatic dispersion values;
A chromatic dispersion measuring apparatus comprising:   6. The chromatic dispersion measuring apparatus according to claim 5, wherein the chromatic dispersion measuring means stores a dispersion slope coefficient in advance and obtains the distance of the optical transmission line.   7. The chromatic dispersion measuring apparatus according to claim 1, wherein the measurement control means transmits / receives the chromatic dispersion measurement information using a network or the overhead of the optical signal formed into a frame.   The chromatic dispersion measuring apparatus according to any one of claims 1 to 7, wherein the same frame as that of normal transmission on the optical transmission line is used for optical transmission for chromatic dispersion measurement.   9. The chromatic dispersion measuring apparatus according to claim 8, wherein an SDH frame or an OTN frame is used as a frame former. A chromatic dispersion measuring method for measuring chromatic dispersion in an optical transmission line,
Framing and generating two optical signals having different wavelengths on the transmitting end side of the optical transmission path; and
Combining and transmitting the two optical signals from the transmission end side of the optical transmission path;
Transmitting from the transmitting end side to the receiving end side chromatic dispersion measurement information including the measurement start signal based on the generation of the optical signal and the wavelengths of the two optical signals;
Demultiplexing the two optical signals transmitted via the optical transmission path on the receiving end side of the optical transmission path and converting them to electrical signals, respectively;
According to the measurement start signal of the chromatic dispersion measurement information from the transmitting end side, the phase difference between the two converted electric signals having different wavelengths is measured, and the two signals of the measured phase difference and the two signals of the chromatic dispersion measurement information are measured. Obtaining chromatic dispersion in the optical transmission line from a wavelength difference between wavelengths;
A chromatic dispersion measuring method comprising: The step of generating an optical signal is
Generating respective frames for chromatic dispersion measurement of two optical signals;
A step of generating a light intensity modulation of the signal of the generated frame to generate the two optical signals;
Including
In the step of demultiplexing and converting to an electrical signal, the frame signal of the transmitted two optical signals is demultiplexed and further converted into an electrical signal,
The process of obtaining chromatic dispersion is
Regenerating a clock from the two electrical signals having different wavelengths and performing frame synchronization based on the clock to generate a frame pulse;
A phase difference between two electrical signals having different wavelengths is measured using a plurality of clocks obtained by shifting the clock generated by the phase synchronization circuit by a predetermined multiple and shifted by different phase amounts. Determining the chromatic dispersion in the optical transmission line from the phase difference and the wavelength difference between the wavelengths of the two signals of the chromatic dispersion measurement information;
The chromatic dispersion measuring method according to claim 10, comprising: Further comprising a step of separating one optical signal of the two optical signals from the optical transmission path into two optical signals by a polarization beam splitter at the receiving end side of the optical transmission path;
In the step of obtaining the chromatic dispersion, the first-order polarization mode dispersion is obtained by obtaining the cross-correlation of the two optical signals separated by the polarization beam splitter based on the electric signal converted by the photoelectric conversion unit. The chromatic dispersion measuring method according to claim 10, wherein a differential group delay time difference is obtained, and a phase difference is determined based on the differential group delay time difference.   13. The chromatic dispersion measuring method according to claim 12, further comprising a step of causing separation into two main axes by a polarization rotator on an optical transmission line on a transmission side or a reception side. A chromatic dispersion measuring method for measuring chromatic dispersion in an optical transmission line,
Framing and generating three optical signals having different wavelengths on the transmitting end side of the optical transmission path; and
Combining and transmitting the three optical signals from the transmission end side of the optical transmission path;
Transmitting from the transmitting end side to the receiving end side chromatic dispersion measurement information including the measurement start signal based on the generation of the optical signal and the wavelengths of the two optical signals;
Demultiplexing the three optical signals transmitted via the optical transmission path on the receiving end side of the optical transmission path and converting them to electrical signals, respectively;
According to the measurement start signal of the chromatic dispersion measurement information from the transmitting end side, the phase difference of the three electrical signals having different converted wavelengths is measured, and the measured phase difference and the three signals of the chromatic dispersion measurement information are measured. Obtaining a plurality of chromatic dispersions in the optical transmission line from the wavelength difference of the wavelengths, and further obtaining a dispersion slope coefficient from the obtained chromatic dispersion values;
A chromatic dispersion measuring method comprising:   The chromatic dispersion measuring method according to claim 14, wherein in the step of obtaining the dispersion slope coefficient, the dispersion slope coefficient is stored in advance, and the distance of the optical transmission line is obtained.   16. The chromatic dispersion measurement method according to claim 10, wherein in the step of transmitting chromatic dispersion measurement information, the chromatic dispersion measurement information is transmitted and received using an overhead of a network or framed optical signal.   The chromatic dispersion measuring method according to any one of claims 10 to 16, wherein the same frame as that of normal transmission in the optical transmission path is used for optical transmission for chromatic dispersion measurement.   The chromatic dispersion measuring method according to claim 17, wherein an SDH frame or an OTN frame is used as a frame former.

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