JP3376957B2 - Apparatus and method for measuring chromatic dispersion of optical fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for measuring the chromatic dispersion characteristic of an optical fiber. The invention particularly relates to a method and a device for measuring the chromatic dispersion characteristics of installed optical fibers.

[0002]

2. Description of the Related Art The wavelength dispersion characteristic of an optical transmission line in a long-distance, large-capacity optical transmission system is an important characteristic that determines the transmission speed. Therefore, in order to realize an optimized long-distance, large-capacity optical transmission system, it is important to measure the chromatic dispersion characteristics of the installed optical fiber. Until now, the technology of chromatic dispersion characteristics was not suitable for measuring the chromatic dispersion of the installed optical fiber.

In measuring the chromatic dispersion characteristic of an optical fiber, pulsed light of different wavelengths is made incident on one end of the optical fiber to be measured, and this is taken out at the other end of the optical fiber to measure the phase difference and delay time of the pulsed light. The chromatic dispersion characteristic of the optical fiber is measured by sequentially performing this operation for pulsed lights having different wavelengths.

FIG. 7 shows an example of a conventional method of measuring the wavelength dispersion characteristic of an optical fiber. FIG. 7A shows a configuration for measuring the wavelength dispersion characteristic of a long optical fiber, in which measurement pulsed light is input from one end of an optical transmission unit of an optical fiber having a length of 40 km or more, An optical receiver at the other end of the optical fiber receives the pulsed light transmitted through this optical fiber and measures the wavelength dispersion characteristic of the optical fiber. In this case, the entrance end and the exit end of the optical fiber are at the same position, that is, the light transmission unit and the light reception unit are at the same position, and the light transmission unit and the light reception unit synchronize the transmission and reception of the pulsed light. It is assumed that In the method of measuring the chromatic dispersion characteristics shown in FIG. 7A, since the entrance end and the exit end of the optical fiber need to be provided at the same place, the measurement is performed on the optical fiber before installation, and the optical fiber after installation is measured. It is not suitable for measuring the chromatic dispersion characteristics of fibers.

Next, the configuration shown in FIG. 7 (b) shows a method for measuring the chromatic dispersion characteristics of the laid optical fiber. Here, the optical transmitter for injecting the pulsed light and the light for extracting the pulsed light are used. Since the optical transmitter and the optical receiver are located at a position distant from each other, it is necessary that the optical transmitter and the optical receiver are synchronized with each other. It is necessary to transmit the synchronization signal from one end of the optical fiber under test to the optical reception unit at the other end of the optical fiber to be measured, and to provide the synchronization signal reception unit in the optical reception unit.

Further, in the method of measuring wavelength dispersion of an optical fiber disclosed in Japanese Unexamined Patent Publication No. 8-334436, a reflection mirror or an amplifier is installed at the far end of the optical fiber, and pulsed light of different wavelength is made incident on the optical fiber. The phase difference and the delay time of the pulsed light that is reciprocated and taken out at one end of the optical fiber are measured, and the chromatic dispersion characteristic is measured by changing the wavelength light and repeating it sequentially. This method is shown in FIG.
Although it is not necessary to separately provide a synchronization signal transmission line as in (b), it is for measuring the propagation delay characteristics of pulsed light that has reciprocated in the optical fiber. If the laying distance of the optical fiber is long, the measurement light is used. There is a problem of large attenuation. Further, pulsed light of the same wavelength travels back and forth through the same optical fiber, which causes a problem that the interaction between the forward light and the backward light cannot be ignored.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems and does not require a separate synchronization signal transmission line for measuring the chromatic dispersion characteristics of a laid optical fiber transmission line, and also provides a round-trip pulse light. It is an object of the present invention to provide a method and apparatus for measuring chromatic dispersion characteristics of an optical fiber transmission line in which no mutual interaction occurs. It is another object of the present invention to superimpose wavelength identification information on incident pulsed light to facilitate measurement of chromatic dispersion characteristics performed by a receiver.

The present invention relates to an apparatus and method for measuring chromatic dispersion characteristics of an optical fiber in a laid optical fiber transmission line. Here, the feature of the present invention is that the wavelength of the pulsed light extracted at the other end of the optical fiber is converted into pulsed light of a specific constant wavelength different from the wavelengths of the transmitted pulsed light of a plurality of wavelengths. It is to be folded back at one end of the fiber.

That is, a first aspect of the present invention relates to an apparatus for measuring chromatic dispersion characteristics of an optical fiber, which is provided at one end of the optical fiber and which transmits a pulsed light of a different wavelength to the optical fiber. Measuring means including an optical receiver for measuring the chromatic dispersion characteristic of the optical fiber from the pulsed light received from the optical fiber, and receiving the pulsed light propagating through the optical fiber provided at the other end of the optical fiber, Pulsed light wavelength conversion means for converting the received pulsed light into pulsed light of a certain constant wavelength and transmitting it through the optical fiber, wherein the optical receiver is the pulsed light of the constant wavelength transmitted from the other end of the optical fiber. It is characterized by including means for measuring the propagation delay characteristics of the pulsed light of different wavelengths transmitted from.

Further, the optical transmitter is provided with wavelength # 1 to wavelength # 1.
The pulsed light wavelength conversion means does not superimpose the received pulsed light of the wavelengths # 1 to #N with the wavelength of the received pulsed light. It is preferable to include means for converting the pulsed light of wavelength #R and transmitting it.

Further, it is preferable that the optical transmission section includes means for superimposing a wavelength identification signal on the pulsed light to be transmitted.

Further, the measuring means or the pulsed light wavelength converting means may include a circulator as a light distributing means for separating the transmitted pulsed light and the received pulsed light of the pulsed light.

Further, a second aspect of the present invention relates to a method for measuring the wavelength dispersion characteristic of an optical fiber, in which pulsed lights of different wavelengths are sequentially incident from one end of the laid optical fiber, and the other end of the optical fiber. The pulsed light received by the above is converted into pulsed light of a certain specific wavelength that does not overlap with the wavelength of the pulsed light and is returned to one end of the optical fiber, and the propagation delay of the pulsed light of the specific wavelength extracted at one end of the optical fiber The characteristic is measured to measure the chromatic dispersion characteristic of the optical fiber.

From one end of the laid optical fiber, pulsed lights of different wavelengths are incident and transmitted. For this wavelength,
Pulse lights of N wavelengths from 1 to N are generated and sequentially transmitted. At the other end of the optical fiber,
The pulsed light has a specific constant wavelength (R) that does not overlap with the wavelengths of .about.N, is incident on the optical fiber again, and is transmitted to one end of the optical fiber. At one end of the optical fiber, the pulsed light of the constant wavelength is extracted, and the propagation delay characteristic of the transmitted pulsed light of each wavelength is measured. Since the pulsed light is converted to a specific wavelength and transmitted in the return path and chromatic dispersion does not occur, the delay time in the return path is constant. When measuring the propagation delay of the extracted pulsed light for each wavelength, the delay time on the return path is common.Therefore, if the delay time on the return path is canceled, the propagation delay time caused by chromatic dispersion on the outbound path can be detected. , The wavelength dispersion characteristic of the optical fiber can be obtained from the relationship with each wavelength. The chromatic dispersion value is the propagation delay time /
Given by wavelength spacing / transmission line distance, typically (ps
/ Nm / km).

[0014]

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 shows the configuration of the first embodiment.

At one end of the laid optical fiber 3, the optical transmitter 11 for injecting pulsed light of different wavelengths into the optical fiber 3 and the propagation delay characteristics of the pulsed light received from the optical fiber are measured, and the wavelength dispersion of this optical fiber is measured. A measuring device 1 is provided as a measuring unit including a light receiving unit 12 for obtaining characteristics. On the other hand, at the other end of the optical fiber 3, the measuring instrument 2 is used as a pulsed light wavelength converting means for receiving the pulsed light propagating through the optical fiber 3, converting the received pulsed light into pulsed light having a certain fixed wavelength, and entering the pulsed light into the optical fiber. Is provided. Here, the measuring device 1 includes an optical transmitter 11 and an optical receiver 1.
2 and an optical coupler 13 that causes the pulsed light from the optical transmitter to enter the optical fiber 3 and separates the pulsed light from the optical fiber 3 into the optical receiver 12. In addition, the optical transmitter 1
1 includes a variable wavelength light source 111 and an optical modulator 112. Further, the optical receiver 12 includes a measuring unit that measures the propagation delay time of the received pulsed light and measures the chromatic dispersion characteristic of the optical fiber 3.

Further, the measuring device 2 separates the pulsed light from the optical fiber 3 into an optical coupler 21 which makes the pulsed light incident on the optical fiber 3 and an optical / optical converter 21 which converts the pulsed light from the optical coupler 21 into an electric signal. The electrical conversion circuit 22 and the electrical / optical conversion circuit 22 converts the signal converted by the optical / electrical conversion circuit 22 into pulsed light of wavelength R and makes it enter the optical fiber 3 via the optical coupler 21.
And an optical conversion circuit 23.

Next, the operation of the configuration shown in FIG. 1 will be described with reference to FIG.
A description will be given with reference to (a) and (b).

The optical transmitter 11 sequentially generates optical signals of wavelengths # 1 to #N from the variable wavelength light source 111, and the optical modulator 11
2, the phase T is modulated into pulsed light having a constant phase, and the pulsed light is incident on the optical fiber 3 laid via the optical coupler 13 and propagated. This transmitted pulsed light is as shown in FIG. The phase information of the transmitted pulsed light is separately provided to the optical receiver 12 as a synchronization signal. The pulsed light propagating through the optical fiber 3 is transmitted by the measuring instrument 2 via the optical coupler 21.
It is given to the electric conversion circuit 22 and converted into an electric signal. The converted electric signal is converted into pulsed light of wavelength #R by the electric / optical conversion circuit 23, and is incident on the optical fiber 3 via the optical coupler 21 and propagated. The pulse signal of wavelength #R propagated through the optical fiber 3 is received by the optical receiver 12 via the optical coupler 13. The propagation delay (D12, D1N) for each wavelength of # 1 to #N is calculated between the respective pulsed lights from the delay time between the pulsed light corresponding to the wavelength # 1 from the measuring instrument 21 and the pulsed light of another wavelength. It can be detected by canceling the phases. The return propagation delay is equal because the wavelength #R is constant in all pulsed lights. Therefore, the return propagation delay is canceled by detecting the delay time of each pulsed light. The chromatic dispersion characteristic of the optical fiber can be obtained from the relationship between the detected propagation delay time for each wavelength and the wavelength. The chromatic dispersion value is represented by propagation delay time / wavelength interval / propagation distance, and the unit is generally ps / nm / km.

The measurement accuracy can be improved by performing this measurement a plurality of times and averaging the measured values.

In this embodiment, it is not necessary that the input and output ends of the optical fiber are close to each other, and it is provided at one end of the optical fiber 3 on which the measuring device 1 having the optical transmitter and the optical receiver is laid. Accurate chromatic dispersion measurement can be performed by simply installing a measuring device 2 provided at the end with a means for converting pulsed light of each wavelength into pulsed light of a specific constant wavelength.

(Second Embodiment) FIG. 3 shows the configuration of the second embodiment. In the second embodiment, the optical transmitter 11
In addition, a wavelength identification signal circuit 113 for generating and superimposing wavelength identification information on the transmission pulsed light of each wavelength output from the optical transmission unit 11 is provided.

Next, the operation of the second embodiment will be described with reference to FIG.

The optical transmitter 11 includes a variable wavelength light source 111, an optical modulator 112, and a wavelength identification signal circuit 113,
The wavelength tunable light source 111 generates light of wavelengths # 1 to #N,
The optical modulator modulates the pulsed light with a constant phase (T) into the laying optical fiber 3 through the optical coupler 13. The wavelength identification signal circuit 113 outputs f to the pulsed light with wavelengths # 1 to #N.
The optical modulator 112 generates a wavelength identification modulated signal of 1 to fN.
Alternatively, the variable wavelength light source 111 is used for superimposition. The transmission pulsed light on which the wavelength identification signal is superimposed is shown in FIG.
The measuring instrument 2 is composed of an optical coupler 21, an optical / electrical converting circuit 22, and an electrical / optical converting circuit 23. As shown in FIG. F1
While maintaining the wavelength identification signal of up to fN, it is converted into pulsed light of wavelength #R and folded back by the laying optical fiber 3. Optical receiver 1
2 is the propagation delay of each wavelength,
It is detected by canceling the phase between the respective pulsed lights from the difference in delay time between the one pulsed light and the pulses of other wavelengths. The pulsed light of each wavelength can be identified by detecting the wavelength identification signal. By detecting the wavelength identification signal superimposed on the pulsed light, it is easy to prevent error measurement in chromatic dispersion measurement.

(Third Embodiment) Next, the configuration of the third embodiment is shown in FIG. The third embodiment differs from the second embodiment in that the optical couplers 13 and 21 are changed to circulators 14 and 24, and the light source is a variable wavelength light source to a plurality of fixed wavelength light sources 11.
4 _1-114 point was changed to _N and are different. Further, by providing a plurality of fixed wavelength light sources 114 _{1 to} 114 _N as the light source, the optical modulators 115 _{1 to} 115 _N and the wavelength identification signal circuits 116 _{1 to} 116 _N are respectively fixed wavelength light source 1
_N of 14 _{1 to} 114 _N are provided, and these wavelengths #
The pulse lights 1 to #N are multiplexed by the multiplexer 117 and are incident on the laying optical fiber 3 via the circulator 14.

The third embodiment has an advantage that the influence of light reflection can be reduced by using a circulator. In addition, the measurement accuracy is improved by using N light sources, optical modulators, and wavelength identification signal circuits, respectively, and by using a fixed wavelength light source, it is possible to stabilize the wavelength compared to a variable wavelength light source. There is an advantage that the measurement accuracy can be improved.

The light generated in the wavelength #. 1 to # N from the fixed wavelength light source 114 ₁ to 114 _N, the optical modulator 115 _1-115
It is modulated into a synchronous pulsed light with a constant phase by _N , and is added to the multiplexer 117.
Are multiplexed and transmitted by the laying optical fiber 3. At this time, the wavelength identification signal circuits 116 _{1 to} 116 _N generate f1 to fN.
The wavelength identification modulated signal of is superimposed on the pulsed light of wavelengths # 1 to #N. The phase signal is separately provided to the optical receiver 12 as a synchronization signal. The optical receiver 12 detects the propagation delay for each wavelength from the delay time difference between the pulse light of wavelength # 1 from the measuring instrument 2 and the pulse light of each wavelength. The pulsed light of each wavelength can be identified by detecting the wavelength identification signal.
The measuring device 2 is a circulator 24, an optical / electrical conversion circuit 2
2. Equipped with an electrical / optical conversion circuit 23, wavelengths # 1 to #
The pulsed lights up to N are converted into pulsed lights of wavelength #R while transmitting the wavelength identification signals of f1 to fN, and transmitted by the laying optical fiber 3.

[0028]

As described above, according to the invention of the present application, the wavelength dispersion characteristics of the laid optical fiber can be measured between remote places with a simple structure. Further, it is possible to prevent the error measurement from occurring by superimposing the wavelength identification signals.
Further, the use of the circulator enables more accurate measurement.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the measurement operation of the first embodiment of the present invention.

FIG. 3 is a diagram showing the configuration of a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the measurement operation of the second embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of a third embodiment of the present invention.

FIG. 6 is a diagram for explaining the measurement operation of the third embodiment of the present invention.

FIG. 7 is a diagram illustrating a conventional method of measuring the wavelength dispersion characteristic of an optical fiber.

[Explanation of symbols]

1, 2 Measuring device 3 Optical fiber 11 Optical transmitting unit 12 Optical receiving unit 13, 21 Optical coupler 14, 24 Circulator 22 Optical / electrical converting circuit 23 Electric / optical converting circuit 111 Wavelength variable light source 112 Optical modulator 113 Wavelength identifying signal circuit 114 _{1 to} 114 _N fixed wavelength light source 115 _{1 to} 115 _N optical modulator 116 _{1 to} 116 _N wavelength identification signal circuit 117 multiplexer

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Claims (5)

(57) [Claims] 1. A light which is provided at one end of an optical fiber and in which pulsed light of different wavelengths is sequentially incident on the optical fiber and light for measuring chromatic dispersion characteristics of the optical fiber from pulsed light received from the optical fiber. Each time the measuring means including a receiving section and the other end of the optical fiber, the pulsed light propagating through the optical fiber is received, the received pulsed light is converted into pulsed light of a certain constant wavelength and transmitted through the optical fiber. And a pulsed light wavelength conversion means, the optical receiving unit, a means for measuring the propagation delay characteristics of pulsed light of different wavelengths transmitted from the pulsed light of the constant wavelength transmitted from the other end of the optical fiber. A chromatic dispersion measuring device for an optical fiber transmission line, comprising: 2. The optical transmission unit includes means for sequentially generating pulsed light of N different wavelengths from wavelength # 1 to wavelength #N, and the pulsed light wavelength conversion means includes the received wavelength # 1. ~
2. The chromatic dispersion measuring apparatus for an optical fiber according to claim 1, further comprising means for converting pulsed light having a wavelength of #N into pulsed light having a wavelength #R that does not overlap the wavelength of the received pulsed light and transmitting the pulsed light. 3. The optical fiber chromatic dispersion measuring apparatus according to claim 1, wherein the optical transmission unit includes means for superimposing a wavelength identification signal on the pulsed light to be transmitted. 4. The wavelength of the optical fiber according to claim 2, wherein the measuring means or the pulsed light wavelength conversion means includes a circulator as a light distributing means for separating the transmitted pulsed light and the received pulsed light of the pulsed light. Dispersion measuring device. 5. A pulsed light having a different wavelength is sequentially incident from one end of the laid optical fiber, and the pulsed light received at the other end of the optical fiber is received.
And the wavelength of the pulsed light is converted into pulsed light of a certain specific wavelength that is not superposed and folded back at one end of the optical fiber, and the light from the propagation delay characteristics of the pulsed light of the specific wavelength extracted at one end of the optical fiber A method for measuring chromatic dispersion of an optical fiber for measuring chromatic dispersion characteristics of the fiber.