JPH06167418A - Optical pulse tester - Google Patents

Abstract

PURPOSE:To provide a tester capable of measuring the distance up to a breaking point or a discontinuous point with high accuracy when optical fibers different in refractive index are subjected to cascade connection. CONSTITUTION:An optical pulse tester is equipped with a section setting means 20 for setting the section of an optical fiber 10 to be measured, a refractive index setting means 19 for setting the refractive index of the section and a memory means 21 allowing the section and the refractive index to correspond to each other to store them and the refractive indexes set at every section different in refractive index of the optical fiber 10 to be measured are adapted to calculate a distance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a fault point of an optical fiber to be measured by injecting an optical pulse into the optical fiber to be measured and detecting an optical signal returning to a pulse incident end of the optical fiber to be measured. More specifically, the present invention relates to an optical pulse test apparatus for performing a search and a loss measurement, and particularly to an optical pulse test apparatus capable of measuring a distance to a break point or a discontinuous point with high accuracy when optical fibers having different refractive indexes are cascaded.

[0002]

2. Description of the Related Art FIG. 6 shows the configuration of a conventional optical pulse test apparatus. The configuration and operation of the conventional optical pulse test apparatus will be described with reference to FIG. The pulse generator 11 generates a pulse signal (electrical signal) based on a command from the control unit 26, and sends the pulse signal to the light source 12. The light source 12 receives the pulse signal from the pulse generator 11, generates an optical pulse, and sends the optical pulse to the optical path control means 13. The optical path control means 13 acts so as to guide the light pulse sent from the light source 12 to the fiber under measurement 10 and guide the reflected light returning from the fiber under measurement 10 to the light receiver 14. A known half mirror, an optical directional coupler, an ultrasonic light deflector, or the like is used for the optical path control means 13. A control signal for controlling the optical path is given from the control unit 26. The light receiver 14 converts the reflected light from the measured optical fiber 10 into an electric signal and sends the electric signal to the processing unit 15.
The processing unit 15 includes an A / D converter, a display controller, and the like, and receives the optical pulse to the optical fiber 10 to be measured and then receives the optical receiver 14.
The locus is displayed on the display 27 by associating the electric signal output by the device with time. An example of the display is shown in FIG. The refractive index setting means 29 is prepared for the operator of this apparatus to input the refractive index (N), and includes a rotary encoder,
A keyboard or the like is used. In the conventional device, only one refractive index can be set for one measurement. The marker setting means 28 is prepared so that the operator of the apparatus can set the marker at a desired position on the locus drawn on the display unit 27. A rotary encoder and [→] [←] keys are used. The control unit 26 controls the entire apparatus and calculates the distance.

The operation of the conventional optical pulse test apparatus thus constructed will be described. The operator inputs the refractive index (N) of the measured optical fiber 10, and the display unit 27 displays
A trajectory as shown in FIG. 2 is drawn. Marker setting means 2
By the operation of 8, the marker is placed at the desired position on the trajectory. The distance (L) from one end where the optical pulse is incident on the optical fiber 10 to be measured to the position where the marker is placed is calculated by the control unit 26, and is numerically displayed at a predetermined location on the display unit 27. The following formula is used to calculate the distance.

L = (C / N) · (T / 2) (1) L: The position where the marker is placed from one end where the optical pulse is incident on the optical fiber 10 to be measured. Distance to: C: Speed of light (about 300,000 km / sec) N: Refractive index of the optical fiber under test T: Time for the optical pulse to reciprocate the distance L of the optical fiber under test

[0005]

The optical fiber 10 to be measured.
If L is a single refractive index, the accuracy of the distance (L) is guaranteed even in the conventional device. In long-distance transmission, a plurality of optical fibers are cascade-connected by fusion or the like. If the refractive index (N) of all optical fibers is the same, the accuracy of measuring the distance (L) is guaranteed even in the conventional device. However, if the manufacturers and manufacturing lots of optical fibers differ, the refractive index (N) varies from 0.1% to 0.5%. for that reason,
Optical fibers with different refractive indices (N) are connected
The accuracy of the obtained distance is not guaranteed when the measurement is performed by a conventional device in which only a single refractive index can be set. For example, when optical fibers having different refractive indexes of 0.5% are cascade-connected, a measurement error of 50 m occurs at 10 km.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and comprises section setting means (20) for setting a section of an optical fiber to be measured, and a refractive index of the section. And a storage means (21) for storing the sections and the refractive indexes in association with each other, each section having a different refractive index of the optical fiber (10) to be measured. Then, the set refractive index is applied to the distance calculation.

[0007]

The distance calculation is performed by applying the refractive index set for each section based on the section information of the optical fiber to be measured and the refractive index set by the operator of the apparatus.

[0008]

FIG. 1 is a block diagram showing an embodiment of the present invention. Elements having the same functions as the constituent elements of the prior art shown in FIG. 6 are designated by the same reference numerals. An embodiment of the present invention will be described below with reference to the drawings.

[Structure] The pulse generator 11 includes a controller 16
A pulse signal (electrical signal) is generated based on the command of 1, and the pulse signal is sent to the light source 12.

The light source 12 receives the pulse signal from the pulse generator 11, generates an optical pulse, and sends the optical pulse to the optical path control means 13.

The optical path control means 13 functions so as to guide the optical pulse sent from the light source 12 to the fiber 10 to be measured and guide the reflected light returning from the fiber 10 to be measured to the light receiver 14. A control signal for controlling the optical path is given from the control unit 16. A known half mirror, an optical directional coupler, an ultrasonic light deflector, or the like is used for the optical path control means 13. The purpose of installing the optical path control means 13 is that the reflected light from the optical fiber 10 to be measured is the light source 12.
The purpose of this is to prevent the light receiver 14 from being saturated by the Fresnel reflected light that occurs at the connection point (connector connection) between the device and the fiber 10 to be measured. For this purpose, an optical path control technique as disclosed in JP-A-3-87627 can be applied.

Here, the technique disclosed in Japanese Patent Laid-Open No. 3-87627 will be outlined. Amplifies the reflected light from the first optical terminal and the first optical terminal that emits an optical pulse in the oscillating state to the optical fiber to be measured, which exhibits three states of oscillation, amplification, and attenuation related to light according to the magnitude of the excitation component. Alternatively, an optical element having a second optical terminal that allows passage in an attenuated state is provided. Further, a light receiving means for receiving the reflected light that has passed through the second optical terminal of the optical element and converting it into an electric signal is provided.
The excitation component of the optical element is oscillated at the first timing,
An optical pulse is emitted from the first optical terminal to the optical fiber under measurement. At the second timing, the optical element is set in the attenuated state and the Fresnel reflection reflected at the near end of the device is masked, so that the light receiving means can be prevented from being saturated. Furthermore, at the third timing, the optical element is set to the amplification state, and the desired reflected light is optically amplified,
It can be guided to the light receiving means. That is, unlike the above-mentioned ultrasonic optical deflector, instead of changing the optical path, generation of an optical pulse, masking of unnecessary reflection pulse, and amplification are performed by one optical element.

The light receiver 14 converts the reflected light from the optical fiber 10 to be measured into an electric signal, and processes the electric signal.
Send to 5.

The processing unit 15 includes an A / D converter, a data memory, a display controller, etc., receives an electric signal output from the photodetector 14 after the light pulse is emitted to the optical fiber 10 to be measured, and responds to time. Along with this, the locus is displayed on the display device 17.
An example of the display is shown in FIG.

Sampling interval (t) during A / D conversion
Is kept accurate and constant based on the output signal of a crystal oscillator (not shown) provided in the device. Sampling is started after a lapse of a predetermined time from the light pulse emission, and each sampling point (Sm) (m = 1, 2, 3, ... M)
The magnitude of the reflected pulse corresponding to is obtained by A / D conversion. The sampling points (Sm) and the magnitudes are associated with each other and stored in a data memory (not shown). In this case, each sampling point (S
A method such that m) is used as an address of the data memory may be adopted. That is, the relationship between the sampling interval (t), the number of samples (m), and the round-trip time (T) of the optical pulse is as shown in equation (2). T = t × m (2) T: round-trip time of optical pulse t: sampling interval m: number of samples

The refractive index setting means 19 is prepared for the operator of this apparatus to input the refractive index (N).
Rotary encoder, numeric keypad, [↑] [↓]
Keys etc. are used. The section setting means 20 sets a predetermined section and inputs the refractive index corresponding to the section.

The marker setting means 18 is prepared so that the operator of the apparatus can set a marker at a desired position on the locus drawn on the display unit 17. A rotary encoder, [→] [←] key, etc. are used.

The control unit 16 is composed of a CPU, a memory and the like, and controls the entire apparatus and calculates the distance.

The section setting means 20 has a certain connection point (start point) when fibers under measurement having different refractive indexes are connected.
And to set a connection point (end point) adjacent thereto. The refractive index setting means 1 sets the refractive index corresponding to the section.
Enter by 9. The section setting means 20 includes a section counter for determining the order of sections.

The storage means 21 stores the sections (start point and end point) input by the section setting means 20 and the refractive index setting means 1.
The refractive index input by 9 is associated and stored.
The memory table is shown in FIG.

[Operation] The operation of the optical pulse test apparatus of the present invention thus constructed will be described. Even in an optical fiber transmission line in which a plurality of optical fibers having different refractive indexes (N) are cascade-connected, specifications such as length and refractive index of each optical fiber are often clarified at the time of installation. In such a case, the section and the refractive index are set in advance before the measurement. There are two modes for setting the section and the refractive index. Less than,
The mode of each setting and the distance calculation method will be described.

[First Mode] Setting Distance as Section Information FIG. 4 is a flow chart showing a procedure for setting a starting point and an ending point of a section by distances (known numerical values). A mode of setting the section and the refractive index will be described with reference to FIG. (Step 1) The section counter included in the section setting means 20 is preset to "1" (k = 1). (Step 2) The distance (Lk) that is the end point of the section is input from the section setting means 20. (Step 3) The refractive index (Nk) of the section (k) is
It is input from the refractive index setting means 19. (Step 4) From the set end point distance (Lk) and refractive index (Nk), the sampling point (Sm) corresponding to the end point position of the section, that is, the starting point of the section corresponds to the number of the sampling point. It is calculated using the following formula. Sm = Lk × Nk × 2 / (C × t) (3) Sm: sampling point corresponding to the end point of the section C: speed of light (known) t: sampling interval (known) (Step 5) section Number (section counter value: k),
The end point (Lk) of the distance, the refractive index (Nk), and the sampling point (Sm) are stored in the storage means 21 in association with each other as shown in FIG. The distance (Lk) at the end point and the sampling point (Sm) are expressed by the equation (3).
The distance (Lk) at the end point does not have to be stored in the storage unit 21 because the relation is associated with. (Step 6) When setting the refractive index in the next section (k + 1), the process branches to Step 7 and the section counter is incremented by 1 (k + 1) to return to Step 2 (input of the end point) and the subsequent section information and refraction Set the rate sequentially. Otherwise,
The setting is completed and the measurement can be started.

Next, a method of calculating the distance when the section is set by the distance will be described. Operate the marker setting means 18,
The marker M is placed at the position where the distance should be calculated (see FIG. 2).
The control unit 16 identifies the number of the sampling point where the marker M is placed. The position is taken as the Sxth sampling point. Next, the section in which the marker M is placed is identified using Expression (4). Sm-1 ≦ Sx <Sm (4) Sm-1: Sampling point corresponding to the end point of the section (k-1) immediately before the section where the marker M is placed Sm: The section (k-1) ), The sampling point corresponding to the end point of the section (k), that is, the sampling point corresponding to the marker M and the sampling point corresponding to the end point of each section can be compared to identify. The distance to the marker (M) is calculated by the equation (5). Lx = (t * (Sm-1)) / 2+ (C * t * (Sx-Sm-1)) / (N * 2) (5) In addition, it shows in the memory table of FIG. It is also possible to perform the distance calculation using the “distance (Lk)” that is stored. In that case, the following formula applies: Lx = Lk-1 + (C * t * (Sx-Sm-1)) / (N * 2)

[Second Mode] Inputting section information by placing a marker on the displayed locus FIG. 5 shows a marker on the locus (see FIG. 2) displayed on the screen of the display unit 17. It is a flow diagram which shows the procedure which puts it and sets a section. A mode of setting the section and the refractive index will be described with reference to FIG. (Step 1) The section counter included in the section setting means 20 is preset to "1" (k = 1). (Step 2) A marker is placed at the end point of the section. The section setting means 20 gives an instruction to confirm the end point (for example, pressing the RETURN key). (Step 3) The refractive index (Nk) of the section (k) is
It is input from the refractive index setting means 19. (Step 4) The control means 16 obtains the sampling point (Sm) corresponding to the end point of the section. (Step 5) Section number (section counter value: k),
The refractive index (Nk) and the sampling point (Sm) corresponding to the position where the marker is placed are stored in the storage means 21 as shown in FIG.
As shown in FIG. (Step 6) When setting the refractive index in the next section (k + 1), the process branches to Step 7 and the section counter is incremented by 1 (k + 1) to return to Step 2 (input of the end point) and the subsequent section information and refraction Set the rate sequentially. Otherwise,
The setting is completed and the measurement can be started.

A procedure for calculating the distance to the desired position of the optical fiber 10 to be measured using the section information and the refractive index set as described above will be described. Marker setting means 18
Is operated to place the marker M at the position where the distance should be calculated (see FIG. 2). The control unit 16 identifies the number of the sampling point where the marker M is placed. The position is taken as the Sxth sampling point. Next, the section in which the marker M is placed is identified using Expression (4). Sm-1≤Sx <Sm (4) The distance to the marker (M) is calculated by the equation (6). L = L1 + L2 + L3 ... + Lx = (C * t * S1) / (2 * N1) + (C * t * S2) / (2 * N2) + (C * t * S3) / (2 * N3) : + (C × t × (Sx−Sm−1)) / (2 × Nk) ··· (6) L: The position where the marker is placed from one end where the optical pulse is incident on the optical fiber 10 to be measured. Distance L1, L2, L3: Distance of each section Lx: Distance from the start point of the section where the marker is placed to the marker position C: Speed of light (about 300,000 km / sec) Nk: Marker M is placed Refractive index of section S1, S2, S3: Sampling point corresponding to end point of section Sx: Sampling point corresponding to marker position t: Sampling interval Based on equation (6), set the refractive index for each section Apply this to calculate the distance, and then calculate the sum of the distances in each section to determine the distance to the point where the marker is placed. It can be obtained in. The controller 16 performs these calculations.

[0026]

The section setting means 20 for setting the section of the optical fiber to be measured, the refractive index setting means 19 for setting the refractive index of the section, and the section and the refractive index are associated with each other. Even if optical fibers having different refraction indexes are connected in cascade, the storage means 21 for storing is used to calculate the distance by applying the set refraction index to each section of the optical fiber 10 to be measured. Since this is set, the accuracy of the distance calculation is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical pulse test apparatus of the present invention.

FIG. 2 is a diagram showing an example of a screen display of the optical pulse test apparatus.

FIG. 3 is a memory table showing an example of storing section information and a refractive index.

FIG. 4 is a flow chart of setting a refractive index using a section as distance information.

FIG. 5 is a flowchart for setting a refractive index while designating a section with a marker.

FIG. 6 is a block diagram showing a configuration of a conventional optical pulse test apparatus.

[Explanation of symbols]

 10 optical fiber to be measured 11 pulse generator 12 light source 13 optical path control means 14 light receiver 15 processing section 16 control section 17 display section 18 marker setting means 19 refractive index setting means 20 section setting means 21 storage means

Claims (1)

[Claims] 1. An optical pulse is incident on a measured optical fiber (10) to receive Fresnel reflected light or backscattered light from the measured optical fiber, and the received optical signal is converted into an electric signal, In an optical pulse test apparatus for measuring the characteristics of an optical fiber to be measured, section setting means (20) for setting the section of the optical fiber to be measured, and refractive index setting means (1) for setting the refractive index of the section.
9) and a storage unit (21) that stores the sections and the refractive index in association with each other, and stores the optical fiber to be measured from the section information and the refractive index and the electric signal stored in the storage unit. An optical pulse test apparatus characterized in that characteristics are calculated.