JP3018606B2 - Optical pulse tester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pulse tester for measuring the loss and break position of an optical fiber using optical homodyne light reception.

[0002]

2. Description of the Related Art Next, the construction of a conventional optical pulse tester will be described with reference to FIG. The configuration of FIG. 8 is a configuration using homodyne light reception. 8, reference numeral 21 denotes a coherent light source whose optical frequency is stabilized, 2 denotes an optical splitter, 3 denotes an optical pulse modulator, 5 denotes an optical splitter, 6 denotes an optical multiplexer, 7 denotes a photodetector, and 8 denotes a signal processing unit. Reference numeral 10 denotes an optical fiber, and reference numeral 25 denotes a timing generator. As a technique similar to that of FIG. 8, there is Japanese Patent Application No. 2-260246.

The light source 21 continuously emits coherent light having a stable optical frequency, and the optical splitter 2 splits the light emitted from the light source 21 into signal light 11 and local light 12. The optical pulse modulator 3 performs optical pulse modulation on the signal light 11 with a signal from the timing generator 25 and emits the signal light 11 as an optical pulse signal 13. The optical splitter 5 splits the backscattered light 14 from the optical fiber 10 to the optical multiplexer 6. The optical multiplexer 6 multiplexes the backscattered light 14 from the optical fiber 10 and the local light 12, and the photodetector 7 performs optical homodyne detection on the signal light multiplexed by the optical multiplexer 6. The signal processing unit 8 amplifies, A / D-converts, averages, and displays the signal that has been subjected to the optical-electrical conversion by the photodetector 7.

[0004]

In FIG. 8, when the backscattered light 14 from the optical fiber 10 is measured using the light source 21 having good coherency, the intensity noise of the backscattered light 14 increases and the measured waveform becomes Due to the occurrence of distortion, the accuracy and accuracy are not sufficient for measuring the loss and break position of the optical fiber.
FIGS. 6A and 6B show models of measured waveforms when a light source having good coherency is used.

The present invention uses a coherent light source whose optical frequency can be changed, changes the optical frequency of continuous coherent light with a signal from a timing generator, and modulates the pulse frequency with the timing of changing the optical frequency and the optical pulse modulator. Give the appropriate time relationship between the timings to apply,
The intensity noise generated by the coherent light is made uncorrelated for each optical pulse or for each unit with a plurality of optical pulses as one unit, signals having uncorrelated intensity noise are averaged, and the measurement waveform due to the intensity noise is calculated. An object is to provide an optical pulse tester that reduces distortion.

[0006]

In order to achieve this object, according to the present invention, a variable frequency light source 1 for emitting continuous coherent light and a coherent light of the light source 1 are converted to a signal light 11.
And an optical splitter 2 that splits the signal light 11 into a local light 12 and a signal light 11 split by the optical splitter 2 into a signal 1 from a timing generator 4.
6, an optical pulse modulator 3 for generating an optical pulse signal 13 by pulse modulation, an optical splitter 5 for extracting backscattered light 14 generated when the optical pulse signal 13 enters the optical fiber 10, and an optical splitter 5 An optical multiplexer 6 for multiplexing the backscattered light 14 branched by the optical splitter 2 and the local light 12 branched by the optical splitter 2, a photodetector 7 for homodyne detection of the light combined by the optical multiplexer 6, A signal processing unit 8 for amplifying, A / D converting, and averaging the signal optical-to-electrically converted by the photodetector 7 and changing the optical frequency of the light source 1 every time a signal 15 is output from the timing generator 4 The optical fiber 10 is measured, and the light source 1 is measured.
The noise component of the measured data is averaged by adding the data measured while changing the optical frequency of the data.

[0007]

Next, the construction of the optical pulse tester according to the present invention will be described with reference to FIG. FIG. 1 is different from FIG. 8 in that the signal 15 of the timing generator 4 is connected to the light source 1, and the rest is the same as FIG. FIG. 1 shows a case where homodyne light reception is used.
As the optical pulse modulator 3, a modulator that shifts an optical frequency and a pulse modulation such as an acousto-optic device is used.

Next, an example of the configuration of the light source 1 shown in FIG. 1 will be described with reference to FIG. There are various types of frequency-variable light sources 1. For example, model names 120-01 to 04 of Lightwave can be used. 2A is a counter and 1B is D / A.
The converter, 1C is an amplifier, and 1D is a light emitting element. The signal 15 from the timing generator 4 enters the counter 1A,
The counter 1A counts up. The output of the counter 1A is converted by the D / A converter 1B and amplified by the amplifier 1C. For the light emitting element 1D, for example, a laser diode is used. Each time the signal 15 from the timing generator 4 is input, the counter 1A is counted up by the signal 15.
The counter value is converted by the D / A converter 1B, and the light-emitting element 1
Change the drive current of D.

Next, the relationship between the driving current of the light emitting element 1D and the light emitting frequency will be described with reference to FIG. FIG. 3 is a diagram when a laser diode is used for the light emitting element 1D. The horizontal axis is the drive current, and the vertical axis is the light emission frequency. When the driving current is Ia, the light emission frequency becomes fa and the driving current becomes Ib
At this time, the emission frequency becomes fb. For example, drive current
When 40mA is changed from 40mA to 40.02mA, the emission frequency becomes 230TH
It becomes 230 THz + 10 MHz from z. Therefore, when the counter 1A is counted up by the signal 15 every time the signal 15 from the timing generator 4 is input, the counter value increases each time, and the light emitting frequency of the light emitting element 1D becomes 10 MHz.
It increases by z.

Next, another example of the configuration of the light source 1 in FIG. 1 will be described with reference to FIG. 4 is a Peltier element, and the other elements are the same as those in FIG. FIG. 4 shows a light emitting element 1D mounted on a Peltier element 1E. Each time a signal 15 from the timing generator 4 is output, the counter 1A is counted up by the signal 15, and the output of the counter 1A is changed to D / D.
The optical frequency of the light emitting element 1D is changed by changing the current flowing through the Peltier element 1E after conversion by the A converter (1B).
The relationship between the ambient temperature of the light emitting element 1D and the light emission frequency is similar to FIG. ○, and the light emission frequency of the light emitting element 1D can be changed by changing the ambient temperature of the light emitting element 1D.

Next, the timing of the signals 15 and 16 of the timing generator 4 and the timing of the backscattered light 14 will be described with reference to FIG. 5A is the timing of the signal 15, and FIG.
6 is the timing of FIG. 5, and FIG. The region a in FIG. 5 is a portion where the optical frequency of the light emitted from the light source 1 is fa, and the region b is a portion where the optical frequency is fb.
In FIG. 5A, the light pulse modulator 3 emits light by the width of the pulse. At Tc in FIG. 5, the signal processing unit 9 finishes securing the output signal from the photodetector 8.

As shown in FIG. 5, the timing generator 4
Is the signal 1 after the signal processing unit 9 secures the data at Tc.
5 is sent to the light source 1. The light source 1 receives the signal 15 from the timing generator 4 and changes the optical frequency from fa to fb. FIG. 5 illustrates fa and fb, but in practice, the accuracy can be improved by increasing the number of samples. The timing generator 4 sends the signal 1 to the optical pulse modulator 3 after the optical frequency of the light emitted from the light source 1 changes from fa to fb.
Send 6. The optical pulse modulator 3 pulse-modulates the signal light 11 whose optical frequency becomes fb by the signal 16. Thereafter, the operation of FIG. 5 is repeated to change the optical frequency and
Averaging the data of.

Next, the principle of reducing the distortion of the measured waveform by averaging will be described with reference to FIGS. FIG. 6A shows the measured waveform when the optical frequency is fa, and FIG. 6A shows the measured waveform when the optical frequency is f.
It is a measurement waveform in the case of b. Since there is no correlation between the data in FIG. 6A and FIG. 6A, the variation of the data has a Gaussian distribution as shown in FIG. 7 if the number of measurements is sufficiently large.
Since the average value of the data variation at the distance L having a Gaussian distribution faithfully reproduces the information of the optical fiber 10 having the backscattered light 14, FIG.
By averaging (a), a waveform with little distortion can be obtained as shown in FIG.

[0014]

According to the present invention, since the light frequency of the light source is changed for each light pulse or for a plurality of light pulses as one unit, the intensity of the backscattered light generated due to the high coherency of the light source. Noise is uncorrelated between data measured at different optical frequencies, and averaging the measured uncorrelated data can improve accuracy and accuracy in measuring loss and breakpoint locations of optical fibers.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical pulse tester according to the present invention.

FIG. 2 is a configuration diagram of a light source 1 of FIG.

FIG. 3 is a diagram illustrating a relationship between a driving current of a light emitting element 1D and a light emitting frequency.

FIG. 4 is another configuration diagram of the light source 1 of FIG.

5 is a timing chart of the signal 15, the signal 16, and the backscattered light 14. FIG.

FIG. 6 is a measurement waveform chart when optical frequencies are different.

FIG. 7 is a diagram showing data variations when the number of measurements is sufficiently large.

FIG. 8 is a configuration diagram of an optical pulse tester according to the related art.

[Explanation of symbols]

 Reference Signs List 1 light source 1A counter 1B D / A converter 1D light emitting element 1E Peltier element 2 optical splitter 3 optical pulse modulator 4 timing generator 5 optical splitter 6 optical multiplexer 7 photodetector 8 signal processing unit 10 optical fiber 11 signal Light 12 Local light 13 Optical pulse signal 14 Backscattered light 15 Signal 16 Signal

Continuation of the front page (56) References JP-A-4-138330 (JP, A) JP-A-62-217135 (JP, A) JP-A-62-123327 (JP, A) JP-A-63-154922 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/02 G01J 9 / 04,11 / 00

Claims (1)

(57) [Claims] 1. A frequency-variable light source (1) for emitting continuous coherent light, and a first optical splitter (B) for splitting the coherent light of the light source (1) into a signal light (11) and a local light (12). 2) and
Optical pulse modulation of the signal light (11) split by the first optical splitter (2) with the first signal (16) from the timing generator (4) to obtain an optical pulse signal (13) Device (3) and a second optical splitter (5) for extracting backscattered light (14) generated by making the optical pulse signal (13) incident on the optical fiber (10).
And an optical multiplexer (6) for multiplexing the backscattered light (14) split by the second optical splitter (5) and the local light (12) split by the first optical splitter (2). , A photodetector (7) for homodyne detection of the light multiplexed by the optical multiplexer (6), and amplifying, A / D conversion and averaging of the signal optical-electrically converted by the photodetector (7) A signal processing unit (8) for performing the second operation from the timing generator (4).
The optical fiber (10) is measured by changing the optical frequency of the light source (1) every time the signal (15) is output, and the measured data is added by changing the optical frequency of the light source (1) and adding the measured data. An optical pulse tester characterized by averaging noise components.