JP2000329652A - Apparatus and method for measurement of wavelength dispersion of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring method, for a wavelength dispersion characteristic, in which an interaction between back pulsed light and forth pulsed light is not generated by a method wherein an optical wavelength conversion means is installed at the other end of an optical fiber, received pulsed light is converted into pulsed light at a set wavelength which is different from the wavelength of the pulsed light and the pulsed light is turned up and transmitted to one end of the optical fiber. SOLUTION: Light signals at wavelengths #1 to #N are generated sequentially from a variable-wavelength light source 111 in an optical transmission part 11, and they are modulated, by an optical modulator 112, to pulsed light at a constant phase so as to be incident and propagated on an optical fiber 3. The propagated pulsed light is given to a photoelectric conversion circuit 22 via an optical coupler 21, a converted electric signal is converted, by an photoelectric conversion circuit 23, into pulsed light at a wavelength #R, and the pulsed light is propagated in the optical fiber 3 so as to be received by an optical reception part 12. A propagation delay at every wavelength is detected in such a way that a phase between beams of pulsed light is offset on the basis of the delay time between pulsed light corresponding to the wavelength #1 from a measuring device 2 and pulsed light at other wavelengths, and a wavelength dispersion characteristic can be obtained on the basis of a relationship between the respective wavelengths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for measuring the chromatic dispersion characteristics of an optical fiber. The present invention particularly relates to a method and apparatus for measuring the chromatic dispersion characteristics of an installed optical fiber.

[0002]

2. Description of the Related Art The chromatic 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 and large-capacity optical transmission system, it is important to measure the chromatic dispersion characteristics of the installed optical fiber. The technique of the chromatic dispersion characteristics up to now has not been suitable for measuring the chromatic dispersion of an installed optical fiber.

In the measurement of the chromatic dispersion characteristics of an optical fiber, pulse lights of different wavelengths enter one end of an optical fiber to be measured, are taken out at the other end of the optical fiber, and the phase difference and delay time of the pulse light are measured. This operation is sequentially performed for pulsed lights having different wavelengths to measure the chromatic dispersion characteristics of the optical fiber.

FIG. 7 shows an example of a conventional method for measuring the chromatic dispersion characteristics of an optical fiber. FIG. 7A shows a configuration for measuring the chromatic dispersion characteristics of a long optical fiber, in which a pulse light for measurement is input from an optical transmitter at one end 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 pulse light transmitted through the optical fiber and measures the chromatic dispersion characteristics of the optical fiber. In this case, the input end and the output end of the optical fiber are at the same location, that is, the optical transmission unit and the optical reception unit are at the same location, and the optical transmission unit and the optical reception unit synchronize transmission and reception of pulsed light. It is assumed that it has been taken. In the method of measuring the chromatic dispersion characteristic shown in FIG. 7A, since the input end and the output end of the optical fiber must be provided at the same place, the measurement is performed on the optical fiber before the installation, and the light after the installation is It is not suitable for measuring the chromatic dispersion characteristics of a fiber.

Next, the configuration shown in FIG. 7 (b) shows a method for measuring the chromatic dispersion characteristics of the laid optical fiber. In this case, an optical transmitter for receiving pulse light and a light for extracting pulse light are shown. Since the receiving unit is located at a distance from the receiving unit, the optical transmitting unit and the optical receiving unit need to be synchronized, and a transmission line for a synchronization signal is provided separately from the laid optical fiber. It is necessary to transmit a synchronization signal to the optical receiver from one end to the other end of the optical fiber to be measured on the path, and to provide the optical receiver with a synchronization signal receiver.

In the method of measuring chromatic dispersion of an optical fiber disclosed in Japanese Patent Application Laid-Open No. 8-334436, a reflection mirror or an amplifier is installed at the far end of the optical fiber, and pulsed light having a different wavelength is incident on the optical fiber. The pulse light extracted at one end of the optical fiber is reciprocated and the phase difference and the delay time are measured, and the chromatic dispersion characteristics are measured by sequentially repeating the change with the wavelength light. This method is illustrated in FIG.
Although it is not necessary to separately provide a transmission line for a synchronization signal as in (b), the transmission delay line measures the propagation delay characteristics of the pulsed light traveling back and forth in the optical fiber. There is a problem that the attenuation of the light is large. In addition, the pulse light having the same wavelength reciprocates in the same optical fiber, and there is a problem that the interaction between the outward light and the backward light cannot be ignored.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem, and does not require a separate transmission line for a synchronization signal for measuring the chromatic dispersion characteristics of an installed optical fiber transmission line. It is an object of the present invention to provide a method and an apparatus for measuring the chromatic dispersion characteristics of an optical fiber transmission line in which no interaction between them occurs. Another object of the present invention is to superimpose wavelength identification information on incident pulse light to facilitate measurement of chromatic dispersion characteristics performed by a receiving unit.

The present invention relates to an apparatus and a method for measuring the chromatic dispersion characteristics of an optical fiber in an installed 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 a pulsed light of a specific constant wavelength different from the wavelength of the transmitted pulsed light of a plurality of wavelengths, and the light is converted to light. It is to be folded 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 having 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 pulse light received from the optical fiber, and receiving the pulse light transmitted through the optical fiber provided at the other end of the optical fiber; Pulse light wavelength conversion means for converting received pulse light into pulse light of a certain wavelength and transmitting the pulse light with the optical fiber, wherein the light receiving unit is configured to transmit the pulse light of the certain wavelength transmitted from the other end of the optical fiber. And means for measuring the propagation delay characteristics of the pulsed light for different wavelengths transmitted from the optical disc.

[0009] The optical transmission unit may include a wavelength # 1 to a wavelength # 1.
Means for sequentially generating pulse light of N different wavelengths up to N, wherein the pulse light wavelength converting means does not superimpose the received pulse light of wavelengths # 1 to #N on the wavelength of the received pulse light. It is preferable to include a means for converting the light into pulse light of wavelength #R and transmitting the light.

[0010] It is preferable that the optical transmitter includes means for superimposing a wavelength identification signal on the pulse light to be transmitted.

Further, the measuring means or the pulse light wavelength converting means may include a circulator as light distribution means for separating transmission pulse light and reception pulse light of pulse light.

Further, a second aspect of the present invention relates to a method for measuring the chromatic dispersion characteristics of an optical fiber, in which pulse lights of different wavelengths are sequentially incident from one end of the laid optical fiber, and the other end of the optical fiber. The pulse light received at step (b) is converted into pulse light of a specific wavelength that is not superimposed on the wavelength of the pulse light, is turned back to one end of the optical fiber, and propagation delay of the pulse light of the specific wavelength extracted at one end of the optical fiber. The characteristic is measured, and the chromatic dispersion characteristic of the optical fiber is measured.

[0013] From one end of the laid optical fiber, pulse lights of different wavelengths are incident and transmitted. As this wavelength,
Pulse light of N wavelengths from 1 to N is generated and transmitted sequentially. At the other end of the optical fiber, the extracted pulse light is
The pulse light is converted into a pulse light having a specific constant wavelength (R) which does not overlap with the wavelengths of .about.N. At one end of the optical fiber, the pulse light having the predetermined wavelength is extracted, and the propagation delay characteristic of the pulse light for each transmitted wavelength is measured. The pulse light is converted to a specific wavelength on the return path and transmitted, and no chromatic dispersion occurs. Therefore, the delay time on the return path is constant. When the propagation delay of the extracted pulse light for each wavelength is measured, the delay time on the return path is common, so if the delay time on the return path is canceled out, the propagation delay time caused by the chromatic dispersion on the outward 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 represented by the propagation delay time /
Given by wavelength spacing / transmission path distance, it is generally (ps
/ Nm / km).

[0014]

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, an optical transmitter 11 for inputting pulsed light of different wavelengths to the optical fiber 3 and a propagation delay characteristic of the pulsed light received from the optical fiber are measured, and the chromatic dispersion of the optical fiber is measured. A measuring device 1 is provided as measuring means including an optical receiving unit 12 for obtaining characteristics. On the other hand, the other end of the optical fiber 3 receives the pulse light propagated through the optical fiber 3, converts the received pulse light into pulse light of a certain wavelength, and converts the received pulse light into a pulse light wavelength converting means which enters the optical fiber. Is provided. Here, the measuring device 1 includes an optical transmitting unit 11 and an optical receiving unit 1.
2 and an optical coupler 13 for inputting the pulse light from the optical transmission unit to the optical fiber 3 and separating the pulse light from the optical fiber 3 to the optical reception unit 12. Also, the optical transmission unit 1
1 includes a variable wavelength light source 111 and an optical modulator 112. The optical receiving unit 12 includes a measuring unit that measures the propagation delay time of the received pulsed light and measures the chromatic dispersion characteristics of the optical fiber 3.

Further, the measuring device 2 separates the pulse light from the optical fiber 3 and inputs the pulse light into the optical fiber 3, and a light / optical converter for converting the pulse light from the optical coupler 21 into an electric signal. An electric / electrical conversion circuit 22, which converts the signal converted by the optical / electrical conversion circuit 22 into pulse light having a wavelength R, and inputs the pulsed light to the optical fiber 3 via the optical coupler 21.
A light conversion circuit 23;

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

The optical transmitter 11 sequentially generates optical signals of wavelengths # 1 to #N from the wavelength tunable light source 111,
2, the phase T is modulated into a constant pulse light, and is incident on the laid optical fiber 3 via the optical coupler 13 and propagated. This transmission pulse light is as shown in FIG. The phase information of the transmitted pulse light is separately provided to the optical receiver 12 as a synchronization signal. The pulse light that has propagated through the optical fiber 3 is transmitted to the optical
The electric signal is supplied to the electric conversion circuit 22 and converted into an electric signal. The converted electric signal is converted into pulse 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 of the wavelengths # 1 to #N is calculated based on the delay time between the pulse light corresponding to wavelength # 1 from the measuring device 21 and the pulse light of another wavelength. Detection can be performed by canceling the phases. The return path propagation delays are equal because the wavelength #R is constant for all pulsed lights. Accordingly, the return propagation delay is canceled by detecting the delay time of each pulse light. The wavelength dispersion characteristic of the optical fiber can be obtained from the relationship between the detected propagation delay time and the wavelength for each wavelength. The chromatic dispersion value is represented by propagation delay time / wavelength interval / propagation distance, and the unit is generally ps / nm / km.

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

In this embodiment, the input and output ends of the optical fiber do not need to be close to each other, and are provided at one end of the optical fiber 3 on which the measuring device 1 having the optical transmitting section and the optical receiving section is laid. At the end, an accurate chromatic dispersion measurement can be performed with a configuration in which only the measuring device 2 provided with means for converting pulse light of each wavelength into pulse light of a specific constant wavelength is installed.

(Second Embodiment) FIG. 3 shows the configuration of the second embodiment. In the second embodiment, the optical transmitter 11
Further, a wavelength identification signal circuit 113 for generating and superimposing wavelength identification information on transmission pulse 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 transmission unit 11 includes a variable wavelength light source 111, an optical modulator 112, and a wavelength identification signal circuit 113.
Light of wavelengths # 1 to #N is generated from the wavelength variable light source 111,
The optical modulator modulates the pulse light into a pulse light having a constant phase (T) and enters the laid optical fiber 3 via the optical coupler 13. The wavelength identification signal circuit 113 converts the pulse light of wavelengths # 1 to #N into f
An optical modulator 112 generates a wavelength discrimination modulation signal of 1 to fN.
Alternatively, they are superposed by the wavelength variable light source 111. FIG. 4A shows the transmission pulse light on which the wavelength identification signal is superimposed.
The measuring device 2 includes an optical coupler 21, an optical / electrical converting circuit 22, and an electric / optical converting circuit 23. As shown in FIG. 4B, the measuring device 2 has pulsed light of wavelengths # 1 to #N. To f1
While retaining the wavelength identification signal of .about.fN, it is converted into a pulse light of wavelength #R, and folded back by the laid optical fiber 3. Optical receiver 1
2 is the propagation delay for each wavelength,
Detection is performed by canceling the phase between each pulse light from the difference in delay time between one pulse light and a pulse of another wavelength. Identification of the pulsed light of each wavelength is made possible by detecting the wavelength identification signal. By detecting the wavelength identification signal superimposed on the pulse light, it is easy to prevent error measurement in chromatic dispersion measurement.

(Third Embodiment) Next, the configuration of a 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 that the light source is changed from a wavelength variable 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 light sources, the optical modulators 115 _{1 to} 115 _N and the wavelength identification signal circuits 116 _{1 to} 116 _N are respectively connected to the fixed wavelength light source 1.
14 _{1 to} 114 _N are provided corresponding to N, and these wavelengths #
The configuration is such that pulse lights 1 to #N are multiplexed by a multiplexer 117 and are incident on the laid optical fiber 3 via a circulator 14.

The third embodiment has the advantage that the use of a circulator can reduce the influence of light reflection. In addition, measurement accuracy is improved by using N light sources, optical modulators, and N wavelength identification signal circuits, respectively. By using a fixed wavelength light source, the wavelength can be stabilized as compared with a variable wavelength light source. There is an advantage that measurement accuracy can be increased.

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
The light is modulated into a synchronous pulse light having a constant phase at _N ,
And transmitted by the laid optical fiber 3. F1~fN the wavelength identification signal circuit 116 ₁ -116 _N that time
Is superimposed on the pulse lights 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 device 2 and the pulse light of each wavelength. The pulse 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. It has an electric / optical conversion circuit 23, and has wavelengths # 1 to #
The pulse light up to N is converted into pulse light of wavelength #R and transmitted through the laid optical fiber 3 while holding the wavelength identification signals of f1 to fN.

[0028]

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

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a measurement operation according to the first embodiment of the present invention.

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

FIG. 4 is a diagram illustrating a measurement operation according to a second embodiment of the present invention.

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

FIG. 6 is a diagram illustrating a measurement operation according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a conventional method for measuring the chromatic dispersion characteristics of an optical fiber.

[Explanation of symbols]

DESCRIPTION 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 conversion circuit 23 Electric / optical conversion circuit 111 Wavelength variable light source 112 Optical modulator 113 Wavelength identification 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

Claims (5)

[Claims] 1. An optical transmission unit provided at one end of an optical fiber for inputting pulsed light of different wavelengths to the optical fiber, and an optical receiver for measuring a wavelength dispersion characteristic of the optical fiber from the pulsed light received from the optical fiber. Measuring means including a portion, a pulse light provided at the other end of the optical fiber, receiving the pulse light transmitted through the optical fiber, converting the received pulse light into a pulse light of a certain wavelength, and transmitting the pulse light through the optical fiber Wavelength conversion means, wherein the optical receiving unit includes means for measuring propagation delay characteristics of pulse light of different wavelengths transmitted from the pulse light of the constant wavelength transmitted from the other end of the optical fiber. Characteristic chromatic dispersion measuring device for optical fiber transmission line. 2. The optical transmission unit includes means for sequentially generating pulse lights of N different wavelengths from wavelength # 1 to wavelength #N, wherein the pulse light wavelength conversion means receives the received wavelength # 1. ~
2. The optical fiber chromatic dispersion measuring apparatus according to claim 1, further comprising means for converting pulse light having a wavelength of #N into pulse light having a wavelength of #R which does not overlap with the wavelength of the received pulse light and transmitting the pulse light. 3. The optical fiber chromatic dispersion measuring apparatus according to claim 1, wherein the optical transmission unit includes a unit that superimposes a wavelength identification signal on the pulse light to be transmitted. 4. The wavelength of an optical fiber according to claim 2, wherein said measuring means or said pulse light wavelength converting means includes a circulator as light distribution means for separating transmission pulse light and reception pulse light of pulse light. Dispersion measurement device. 5. A pulsed light having a specific wavelength which is sequentially incident from one end of an laid optical fiber and has a different wavelength, and the pulsed light received at the other end of the optical fiber is not superimposed on the wavelength of the pulsed light. And returning the optical fiber to one end of the optical fiber, and measuring the chromatic dispersion characteristic of the optical fiber from the propagation delay characteristic of the pulse light of the specific wavelength extracted at one end of the optical fiber.