JP2711104B2 - Optical pulse tester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a device to be measured by transmitting an optical pulse signal to an optical fiber to be measured and detecting an optical pulse signal output from the optical fiber to be measured. The present invention relates to an optical pulse tester for searching for a fault point of an optical fiber and measuring a loss.

[Prior Art] Conventionally, an optical pulse signal was sent to an optical fiber to be measured, reflected light returning from the optical fiber to be measured was taken out, and the optical fiber to be measured was tested. 16
There is an optical pulse tester as disclosed in Japanese Patent No. 1633.
The outline is shown in FIG. In the figure, reference numeral 10 denotes a pulse generator that generates a pulse signal, 20 denotes an optical output unit that generates an optical pulse signal, and 30 sends the optical pulse signal to the optical fiber 40 to be measured, and returns reflected light. In this example, a directional coupler is used as means for switching an optical path for taking out light. 51 is a photoelectric converter for converting reflected light into an electric signal, 52 is a variable resistance attenuator, 53 is an amplifier, 60 is an A / D converter for converting the electric signal into a digital signal, and 90 is a display unit. , 100 are data processing units.

 Next, this operation will be described.

The optical pulse signal emitted from the optical output unit 20 is incident on the optical fiber to be measured 40 from one end thereof via the switching means 30. At this time, backscattering due to Rayleigh scattering and reflection such as Fresnel occur in the optical fiber 40 to be measured. These reflected lights return to the switching means 30 again after a time corresponding to the reciprocating propagation distance from the incident one end to the point where the reflection has occurred, are sent out to the photoelectric converter 51, and are converted into electric signals.
This electric signal is supplied to an amplifier 53 via a variable resistance attenuator 52, amplified, and converted into a digital signal by an A / D converter 60. This digital signal is processed by the data processing unit 100 as the amount of light reflection corresponding to the propagation distance, and the display unit 90
Will be displayed. This display example is shown in FIG.

Ordinate level in FIG. 5, the horizontal axis the distance to the reflection point from the incident end of the optical fiber under test 40, F ₀ is the Fresnel reflection occurring at the incident end of the optical fiber under test 40, F ₁ at the other end The resulting Fresnel reflection. Characteristic A is backscattered light,
The inclination is due to the optical transmission loss of the optical fiber 40 to be measured.

In the above operation, the variable resistance attenuator 52 is provided for adjusting the loss due to the state of the end face or the connection state of the measured optical fiber 40, the level fluctuation due to the fluctuation of the output level of the optical output unit 20, and the like. It did not set the input level range.

Conventionally, in the field of measurement of electric circuits, there has been a network analyzer for inputting a frequency-swept electric signal to a circuit to be measured and analyzing and measuring an output signal output through the circuit to be measured. In this network analyzer, the analysis result is displayed on a coordinate with the horizontal axis representing frequency and the vertical axis representing level. In this case, in order to secure a dynamic range, measurement was performed while varying the level range of the output signal from the circuit under test input to the network analyzer.

[Problems to be solved by the invention]

In the optical pulse tester as described above, the measurement is performed in a single measurement covering the entire measurement range of the optical fiber 40 to be measured. However, since the measurement range is wide, the linearity is not good, and the level error and the distance error are poor. Was occurring. Furthermore, as the optical fiber lengthens, the measurement range of the optical pulse tester has become insufficient. In recent years, optical components have made remarkable progress, the output level of light and the level at which light can be received have been reduced, the light receiving sensitivity has been improved, and the dynamic range of the optical system has been widened. For this reason, the measurement range of the optical pulse tester is
53, which has been limited by electric circuits such as the A / D converter 60. That is, there is a problem that the characteristics of the measured optical fiber 40 can be measured at a time and displayed on one display screen only in a range corresponding to the dynamic range of the electric circuit. Moreover, each electric circuit is designed not to saturate at a high input level, and the S / N ratio cannot be sufficiently considered.

Also, in the case of a network analyzer in the field of measurement of electric circuits, since the electric network whose characteristics do not fluctuate over time is measured, the frequency sweep on the horizontal axis is stopped and the input level range is varied. Could be measured. However, in the optical pulse tester, there is a time difference according to the distance of the measured optical fiber 40 between when the optical pulse is transmitted to the measured optical fiber 40 and when the signal is received from the measured optical fiber 40. Since the signal processing cannot be performed during the time difference and the time difference (that is, the distance) is one of the measurement items, there is a technical difficulty that the network analyzer does not have.

The present invention has been made to solve these problems, and its purpose is to measure the overall characteristics with good linearity and S / N ratio even for an optical fiber to be measured over a long distance to obtain a wide dynamic range. Another object of the present invention is to provide an optical pulse tester that can be displayed on one display screen.

[Means for solving the problem]

An optical pulse tester according to the present invention receives an optical output unit 20 that converts a periodic electric pulse signal into an optical pulse signal and outputs the signal to an optical fiber to be measured, and an optical signal output from the optical fiber to be measured. An optical input unit 50 that converts the analog electric signal output from the optical input unit into a digital signal, and outputs the digital electric signal. Converter 60
And comparing the digital signal with a predetermined level, outputting match time information when the digital signal becomes equal to the specified level as the control information to the optical input unit to switch the amplification degree. The control unit 70, the output level of the A / D converter from the rise time information (0) to the coincidence time information (t ₀ ) for the first electric pulse signal (P ₀ ), and amplification of the optical input unit And the current matching time information (from t ₀ ) for the electric pulse signals (P ₁ , P ₂ , P ₃ ) from the next time
t ₁ , t ₁ to t ₂ , t ₂ to t ₃ ), the output level of the A / D converter and the amplification of the optical input unit are connected on the same time axis, and from the optical fiber under test And a data processing unit 80 that calculates and outputs an optical signal to be output.

[Action]

According to the present invention, an optical signal output from an optical fiber to be measured is converted into an analog electric signal by an optical input unit, amplified, and further converted into a digital signal by an A / D converter.
The control section compares the digital signal with a predetermined level range. Further, the control unit controls the range of the amplification degree of the optical input unit based on the result, and stores in the data processing unit the digital signal falling within the designated level range and the control amount when the optical input unit is controlled each time. Then, based on the stored data, the data is output as characteristics of the optical fiber to be measured.

〔Example〕

FIG. 1 is a view showing an embodiment of the present invention, in which an optical pulse signal is incident from one end of an optical fiber to be measured, and the reflected light reflected from the optical fiber to be measured is returned to the same end to be measured. An example is shown below. FIG. 2 is a diagram showing signal waveforms and operation contents of main parts in FIG. FIG.
FIG. 2 is a diagram showing the contents of data processing in FIG. 1. In these figures, reference numerals 10 to 40, 51, 53, 60 and 90 are the same as those of the conventional optical pulse tester. Reference numeral 50 denotes an optical input unit including the photoelectric converter 51, the amplifier 53, a limiting unit 54 and a level varying unit 55 described later. The limiting means 54 is means for limiting the level of the digital signal c output from the A / D converter 60 so as not to become too large as compared with a predetermined level range, and in this example, is an analog gate circuit. Note that the limiting means 54 may be constituted by an optical switch and arranged before the photoelectric converter 51. Level varying means 55 is a means for varying the level, in this example, the attenuation _{AT 0, AT 1, AT 2} , AT 3 (AT 0> AT
_1> is AT _2> variable resistor attenuator take values AT _3). This means may be constituted by a variable gain amplifier. In any case, it can be considered as amplification range switching (amplification switching), which is the ratio between the input level and the output level. A control unit 70 controls the limiting unit 54, the amplification degree switching unit (hereinafter referred to as "level varying unit") 55, and a data processing unit 80 described later, and is constituted by main parts indicated by the following reference numerals 71 to 76. . 71
Is a range memory in which an optimum level range is stored in advance. This level range is determined by the amplifier 53 and A /
This is the level range that can be output when the D converter 60 and the like operate optimally in consideration of their linearity, dynamic range, S / N ratio, and the like. 72 is a comparator, the A / D
The digital signal c output from the converter 60 and the range memory
Comparing the level range from 71, and outputs the time information d ₁ when the digital signal c exceeds the level range (when it is the lower limit of the level range in this example). 73 is a trigger counter is reset for respective periods by receiving the periodicity of the electric pulse signal from the pulse generator 10, and outputs the fine time information d ₂ of the cycle. 74 is a recording start detection unit, 75 is a recording stop memory, 76 is a recording time generation unit,
Reference numeral 76 denotes a range memory 7 based on the time information (d ₂ , d ₁ ) from the Toruga counter 73 and the comparator 72.
The time within the level range set to 1, that is, the time valid as data is detected and the recording time information f is output. Reference numeral 78 denotes a start setting unit which, based on the periodic electric pulse signal and the recording time information f from the pulse generation unit 10, indicates that valid data of the digital signal c has become data over the entire length of the measured optical fiber 40. It detects and outputs start information g. 77 is level control means, time information
Based on the d ₁ and the start information g, and outputs the control information e for controlling the level variable unit 55. This control information e
Is to designate one of the attenuation AT ₀ to AT ₃ of the level varying means, in this embodiment, is intended for switching sequentially from the maximum attenuation value AT ₀ to the minimum attenuation AT _3. Reference numeral 80 denotes a data processing unit, which is composed of main parts indicated by the following reference numerals 81 to 86. Reference numerals 81 and 82 denote wave memories, each of which stores valid data of the digital signal c alternately in correspondence with the measurement time (that is, the recording time information f). 83 is a range data memory, control information e in correspondence to the measured time based on, and stores the attenuation of the level variable unit 55 (either AT ₀ ~AT _3). Numeral 84 denotes an arithmetic unit which calculates each data from the range data memory 83 and the wave memory 81 or 82 in accordance with the measurement time. Reference numeral 85 denotes a memory control unit that controls the memories 81 to 83 and the arithmetic unit 84 to connect the measurement times and stores the data over the entire length of the measured optical fiber 40 in the display memory 86 in accordance with the distance. . That is, the measured optical fiber 40 is displayed on the display section 90.
Are displayed on one screen.

In the above configuration, the control unit 70 and the data processing unit 80 include a CPU, a memory, a digital circuit for generating timing, and the like.

Next, a series of operations of this embodiment will be described with reference to FIG. 1 and FIG.

As shown in FIG. 2 (a), the pulse generator 10
When the electrical pulse signal a (P ₀ , P ₁ , P ₂ , P ₃ , P ₄ ,...) Is transmitted to the optical output unit 20, the optical pulse signal
The reflected light that has entered the optical fiber 40 and reflected in the measured optical fiber 40 returns with a delay corresponding to the distance, and is converted into an electric signal b by the photoelectric converter 51 (see FIG. 2 (b)). .
This period T is selected to be longer than the time required for the optical pulse signal to reciprocate the entire length of the optical fiber 40 to be measured. The waveform of the electric signal b is the same as that described in the related art. By the way, just before the electric pulse signal a (P ₀ ) is output from the pulse generator 10, as shown in FIG.
73 pulses d ₂ is outputted initialized is made from, the limiting means 54 ON (signal passing state), the AT ₀ level varying means 55 is a maximum attenuation, the wave memory 81 to a write state, wave memory Reference numeral 82 denotes a read state (see FIGS. 2 (e), (h) and (i)). Moreover, the range memory 71, when the AT ₀ of the maximum attenuation is set (referred to as L _MIN) the lower limit of the value of the level range A / D converter 60 and the like to operate optimally is stored I have. The reason that only the lower limit value is set as the level range in this way is as follows.
Most of the characteristics of the electric signal b shown in FIG.

The operation from the initial state will be described below with reference to FIGS.
A description will be given along the timing and operation of each waveform shown in the figure.

(A) The electric signal b is supplied to the limiting means 54, the level varying means 5
The signal is applied to an A / D converter 60 via the amplifier 5 and the amplifier 53 and is converted into a digital signal c. On the other hand, the trigger counter 73 is reset to zero by the first pulse P ₀ from the pulse generator 10 (see FIG. 2A). Time information at this time
recording time generating unit 76 which receives the d ₂ via a recording start detection section 74 sends a rise of the recording time information f (see FIG. 2 (f)), the range data memory 83 from the control information e possible to store the control amount AT ₀ level obtained to start, data from the digital signal c is the wave memory 81
The storage of D ₀ (see FIGS. 2 (c) and (d ₁ ) and FIGS. 3 (a) and 3 (b)) is started.

(B) A comparator 72 comparing the digital signal c with a value L _MIN output as a level range from the range memory 71.
Is the value of the level of the digital signal c as shown in FIG.
When the time _falls below L _MIN , the matching time information t ₀ is output as the time information d ₁ (see FIG. 2 (d ₁ )).

Note that this matches the time information t ₀ is used as time to first when the electric pulse signal (P ₀₎ rise time information (0) from the time information d ₁ (t ₀₎ is output. The level control means 77 receiving this time information d ₁ (t ₀ )
during the period from t ₀ to the pulse generator 10 sends out a next electrical pulse signal (P _1), and sends control information e consisting attenuation AT ₁ to level varying means 55 and range data memory 83, controls each (See FIG. 2 (e)).

Here, AT ₀ −AT ₁ = R is the optimum output range of the A / D converter 60.

(C) On the other hand, the recording stop memory 75 which receives the time information d ₁
Is compared with the time information d ₂ from the trigger counter 73 and the time t ₀
To confirm and store, and sends the to the recording time generating unit 76 and the recording start detection section 74 t ₀ becomes information at the same time. Recording time generating unit 76 stops the operation of storing range data memory 83 and the wave memory 81 to t ₀ becomes time.

Range data memory 83 and the wave memory 81 is between (FIG. 2 (see f)) in association with measurement time stores the attenuation AT ₀ and data D ₀ (Figure 2 this time t ₀ (h ) And FIGS. 3 (a) and 3 (b)).

This completes the measurement for the first cycle. Next, measurement in the second and subsequent cycles is performed.

(D) The recording start detector 74 is provided with a recording stop memory 75
More information t ₀ have undergone earlier, after the trigger counter 73 is re-zero-reset (pulse P ₁ after generation) is adapted to output information t _0. Receiving this output, the recording time generator 76 stores the control amount AT ₁ and the data of the digital signal c from the control information e in the range data memory 83 and the wave memory 81 again after the time t ₀ from the generation of the pulse P _1. and stores the D _1. Level of the digital signal c is compared with the range memory 71, and stores the data D ₁ of the up outputs a coincidence time information t ₁ as its time information d ₁ if they match the lower limit value L _MIN level range. (FIG. 2) (c), (e),
(H), see FIGS. 3 (a) and 3 (b)). The recording time information f output from the recording time generating section 76 in this manner is as shown in FIG. 2 (f).

(E) The limiting means 54 cuts off the signal measured in the previous cycle based on the recording time information f. That is, pulse P ₁
OFF the circuit just in time t ₀ from the generator, and to ON later (see FIG. 2 (c)).

(F) In this manner, after performing the same operation as in the above (e) for the third and subsequent cycles, the start setting unit 78 adds up the recording time information f and determines a predetermined optical fiber under test 40. When the time corresponding to the entire length has been reached, completion of measurement is detected, start information g is output, and the next measurement is started (see FIG. 2 (g)). In this example, in order to measure the characteristics of the measured optical fiber 40 overall length, since the attenuation amount output by the level control means 77 is required four levels AT ₀ to AT _3, electric pulse signal (P _0, P ₁ ...) Are output, and the measurement is completed (see FIG. 2 (c)).

Here, AT ₁ -AT ₂ = AT ₂ -AT ₃ = R is set.
Although it is not necessary that the level resolution is constant, the level resolution by the A / D converter 60 can be used uniformly and efficiently.

(G) When the start information g is output, the initial setting similar setting is made again, the level varying means 55 AT ₀ of the maximum attenuation, respectively write state by the wave memory 82 and 81 is reversed, read state (FIG. 2 (e),
(H), (i)). The next pulse P ₄ in this state is outputted, a new measurement is started.

(H) In addition, the memory controller 85 receiving the start information g this time, the wave memory 81 and range data each data D from the memory 83 ₀ to D ₃ and the attenuation AT ₀ to AT ₃ leading to the arithmetic unit Calculate with 84 and calculate the value.
It is stored in the display memory 86 corresponding to the distance of 40 (second
(See FIG. (J)).

(I) By displaying the contents of the display memory 86 on the display unit 90, the measured optical fiber is measured for each electric pulse signal (P ₀ , P ₁ , P ₂ , P ₃ ...) By dividing the distance. 40 characteristics can be displayed on one screen.

However, in this example, this can be displayed after the measurement is completed.
This is after the elapse of four cycles of the pulse signal a (see FIG. 2 (k)). The digital signals c are alternately stored in the wave memories 81 and 82 so that data during the next four cycles is not lost.
Therefore, a single wave memory may be used if data is to be extracted and measured every four cycles. In this case, while data is missing, the previous data is held and displayed. Further, the period T of the pulse signal a is set to be longer than the time for the light to propagate through the entire length of the optical fiber 40 to be measured, and the operation (h) is performed during the time when the measurement is not substantially performed within the four periods of the measurement. , May be displayed from the next cycle after four cycles.

In the above example, when data of only a certain length of the measured optical fiber 40 is required, the digital signal c corresponding to one cycle of the optical pulse and the attenuation may be stored and output. . In such a case, the arithmetic unit 84 and the display memory 86 are unnecessary.

In the above (e), it is also possible to use an optical switch for the switching means 30 and to cause the optical switch to perform the operation of the limiting means 54. That is, based on the optical switch recording time information f, pulse P ₁ generated from the time only the light output unit 20 of t ₀ ON the connection between the optical fiber to be measured 40, the light input portion 50 measured optical fiber Turn off the connection with 40. ON and OFF after t ₀
Is reversed (see FIG. 2 (c)).

The optical switch as the limiting unit 54 and the switching unit 30 prevents the optical input unit 50 and the A / D converter 60 from saturating due to an excessive level when measurement is not being performed, and affecting the level being measured. It is for doing.

Although the description of the above example does not include the delay time of each component, it is necessary to consider this point in implementation. For example, in the above operation (d), the recording start detection unit 74
Trigger counter 73 is re-zero after reset the had been (pulse P ₁ after the generation) to output the information t _0, the delay time τ Tosureba considering information [t ₀ -τ] Output it. However, the range data memory 83 and the wave memory 81 store the control amount AT ₁ and the data of the digital signal c from the control information e, respectively, at time t ₀ after the pulse P _{1 is} generated.
D ₁ must be remembered. Also,
It is necessary for the measuring device to be calibrated in consideration of the delay time at the initial time.

If a precise optical attenuator is manufactured, it may be provided in the photoelectric converter 51 instead of the level varying means 55.

Furthermore, in the above example, an optical pulse signal was incident from one end of the measured optical fiber 40, and the reflected light reflected from the measured optical fiber and returned to the same end was measured.
An optical pulse signal can be input from one end of the measured optical fiber 40, and the loss, delay time, and the like of the measured optical fiber 40 can be measured by receiving the optical signal output to the other end. In this case, it is necessary to directly connect the optical output unit 20 and the photoelectric converter 51 with the measured optical fiber 40.

〔The invention's effect〕

An optical pulse tester according to the present invention receives an optical output unit 20 that converts a periodic electric pulse signal into an optical pulse signal and outputs the signal to an optical fiber to be measured, and an optical signal output from the optical fiber to be measured. An optical input unit 50 that converts the analog electric signal output from the optical input unit into a digital signal, and outputs the digital electric signal. With the converter 60,
A control unit that compares the digital signal with a predetermined level and outputs matching time information when the digital signal becomes equal to the specified level to the optical input unit as the control information to switch an amplification degree 70, the output level of the A / D converter from the rise time information (0) to the coincidence time information (t ₀ ) for the first electric pulse signal (P ₀ ), and the amplification degree of the optical input unit. , For the next and subsequent electric pulse signals (P ₁ , P ₂ , P ₃ ), the current match time information (t ₀ to t ₁ ,
The output from the optical fiber to be measured by connecting the said A / D converter output level and the light input portion amplification degree of from t ₁ to t ₃₎ from t _2, t ₂ on the same time axis A data processing unit 80 that calculates and outputs an optical signal is provided.In accordance with the level change, the amplification degree of the preceding stage is switched so that the output level of the A / D converter falls within the optimum range. A wider dynamic range than before can be obtained, and even a long-distance fiber can be measured over its entire length with good directivity and good S / N ratio, and the result can be displayed on one screen. Furthermore, since the A / D converter can be used effectively, there is also an effect of improving the measurement resolution.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing signal waveforms and operation contents of main parts in FIG. 1, and FIG. 3 is a diagram showing data processing contents in FIG. Figure, 4th
FIG. 5 is a diagram showing a conventional example, and FIG. 5 is a display example when measurement is performed in the conventional example of FIG. In the figure, 10 is a pulse generating unit, 20 is an optical output unit, 30 is a switching unit, 40 is an optical fiber to be measured, 50 is an optical input unit, 51 is a photoelectric converter, 52 is a variable resistance attenuator, 53 is an amplifier, 54 is a limiting means, 55 is a variable level means, 60 is an A / D converter, 70 is a control unit, 71 is a range memory, 72 is a comparator, 73 is a trigger counter, 74 is a recording start detection unit, and 75 is a recording stop. Memory, 76 is a recording time generation unit, 77 is a level control unit, 78 is a start setting unit, 80 and 100 are data processing units, 81 and 82 are wave memories, 83 is a range data memory, 84 is a calculator, and 85 is a memory control unit. , 86 is a display memory, 90 is a display unit, a is a pulse signal, b is an electric signal, c is a digital signal, d ₁ and d ₂ are time information, e is control information, f is recording time information, and g is start information. It is.

Claims (1)

(57) [Claims] An optical output section for converting a periodic electric pulse signal into an optical pulse signal and outputting the converted signal to an optical fiber to be measured;
An optical input unit (50) for receiving an optical signal output from the optical fiber to be measured, converting the optical signal into an analog electric signal, and receiving control information from the outside, switching the amplification degree and outputting the same;
An A / D converter (60) that converts an analog electric signal output from the optical input unit into a digital signal and outputs the digital signal, and compares the digital signal with a predetermined level to determine that the digital signal is A control unit (70) that outputs coincidence time information when the level becomes equal to the set level as the control information to the optical input unit and switches the amplification degree; and a rise time for the first electric pulse signal (P ₀ ). The output level of the A / D converter from the information (0) to the coincidence time information (t ₀ ) and the amplification degree of the optical input unit, and the electric pulse signals (P ₁ , P ₂ , P ₃ ) From the previous match time information to the current match time information (t ₀ to t ₁ ,
The output from the optical fiber to be measured by connecting the said A / D converter output level and the light input portion amplification degree of from t ₁ to t ₃₎ from t _2, t ₂ on the same time axis An optical pulse tester comprising: a data processing unit (80) for calculating and outputting an optical signal.