JPS6177737A - Optical pulse tester - Google Patents

Abstract

PURPOSE:To perform optical pulse testing by a compact, high-performance tester, by using a semiconductor laser device as a light source, which emits light pulses, and operating the semiconductor laser as a light detector by switching means during the period when the light pulses are transmitted. CONSTITUTION:A semiconductor laser device is used as a light source 11. The light pulses from the light source 11 are directly inputted to an optical fiber to be measured 13. One end of the laser device 11 is connected to an electric pulse generator 18 through a load resistor 17. The other end of the laser device 11 is grounded. Only when the light pulses are emitted from the laser device 11, the driving pulses are imparted from the generator 18. During the other period, the bias voltage of the laser device 11 is made to be zero or negative value, so that the laser device 11 can detect light. A connecting point 19 of the laser device 11 and the load resistor 17 is connected to a signal processor 15. The back scattering light from the fiber 13 is returned to the laser device 11. The light current from the laser device 11, which is the light detector, is processed by the processor 15 and displayed on a display device 16. Thus the light pulse test can be performed by a compact, high-performance tester.

Description

Detailed Description of the Invention "Industrial Application Field" This invention injects a light pulse into one end of an optical fiber, detects the backscattered light of the optical fiber, and searches for fault points and measures losses in the optical fiber. Related to optical pulse testing equipment that performs such operations.

"Prior Art" Conventionally, this type of optical pulse tester has been constructed as shown in FIG. That is, a light pulse from a light source 11 passes through an optical directional coupler 12 and enters one end of an optical fiber 13 to be measured. The backward Rayleigh scattered light generated in the optical fiber 13 to be measured enters the photodetector 14 via the optical directional coupler 12fe. The scattered light converted into an electrical signal by the photodetector 14 is processed by a signal processor 15, and is supplied to a display section 16 to display an observed waveform.

As described above, the conventional optical pulse tester is always provided with the optical directional coupler 12 and the photodetector 14 for separating the transmitted optical pulse and the backscattered light.

As the optical directional coupler 12, a beam splitter type directional coupler shown in FIG. 2A or an ultrasonic deflector type directional coupler shown in FIG. 2B is used. These optical directional couplers have a large insertion loss and a large volume, making it difficult to make the optical pulse tester compact and high-performance. Furthermore, since the optical directional coupler 12 and the highly sensitive photodetector 14 are very expensive, they are also expensive to install as an optical pulse tester.

``Means for Solving the Problems'' According to the present invention, a semiconductor laser is used as a light source that emits light pulses, and during the period of receiving backscattered light from the optical fiber under test after emitting light pulses, The bias of the semiconductor laser is controlled so that it acts as a photodetector. The semiconductor laser when acting as a photodetector detects backscattered light from the optical fiber to be measured, and uses this detection output as a measurement signal to search for fault points in the optical fiber to be measured, measure loss, etc. With this configuration, there is no need for an optical directional coupler or a dedicated photodetector.

"Embodiment" FIG. 3 shows an embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals. In this invention, a semiconductor laser is used as the light source 11. A light pulse from the light source 11 is directly incident on the optical fiber 13 to be measured. One end of the semiconductor laser 11 is connected to an electric pulse generator 18 through a load resistor 17, and the other end of the semiconductor laser is grounded.

In this example, only when the semiconductor laser 11 emits a light pulse, a driving pulse is applied from the electric pulse generator 18, and the bias voltage of the semiconductor laser 11 is set to zero or negative, and the semiconductor laser 11 detects the light. be made possible. A connection point 19 between the semiconductor laser 11 and the load resistor 17 is connected to the signal processor 15, and the signal processor 1 converts the light detected by the semiconductor laser 11 into an electrical signal.
Supply to 5.

A positive voltage pulse is applied from the electric pulse generator 18 to the semiconductor laser 11 as shown in FIG. 4A, and a light pulse 21 is generated as shown in FIG. 4B.

The optical pulse 21 is input to one end of the optical fiber 13 to be measured. Backscattered light 22 from the optical fiber 13 returns to the semiconductor laser 11 again. At that time, semiconductor laser 1
Since the voltage applied to IJ is zero (or negative), the semiconductor laser 11 acts as a photodetector, and the incident backward ray IJ-scattered light is converted into an electrical signal.

The semiconductor laser 11 emits light when a forward voltage is applied to the PN junction, absorbs light when a reverse voltage is applied, and becomes a photodetector. Therefore, when the semiconductor laser 11 is at zero bias, a photocurrent flows through the semiconductor laser 11 due to backscattered light.
This is observed as a voltage change between the terminals of the semiconductor laser 11 at the connection point 19. The backscattered signal thus converted into an electrical signal is processed by the signal processor 15 and displayed on the display section 16.

The time chart If of the above operation is shown in FIG. FIG. 4A shows an electric pulse controlling light emission/detection, FIG. 4B shows an emitted light pulse 21 and backscattered light 22 from the optical fiber 13,
At both ends of the optical fiber, there is a Fresnel reflected pulse 2 at the input end.
3, a forward drop voltage pulse 25 during radiation through the optical fiber 13, and a backscattered signal 26 are obtained.

As shown in FIG. 5, an analog switch 27 is inserted between the connection point 19 and the signal processor 15, and the analog switch 27 is controlled by the output of the delay control circuit 2B. The delay control circuit 28 is supplied with electrical pulses from the electrical pulse generator 18 . A time chart 11 of this device is shown in FIG. In order to eliminate the Fresnel reflection at the input end of the fiber (pulse 23 in FIG. 6B) from being input to the signal processor 15, the sixth
As shown in FIG. A, when the reflected light 23 is incident on the semiconductor laser 11, a slight positive voltage E0 is applied to prevent light absorption from occurring. That is, no scattered light is detected in this state. When detecting light, the detection sensitivity is improved by setting the bias of the semiconductor laser 11 to a slightly negative potential -E2. Generation of the electric pulses and control of the electric bias shown in FIG. 6 are performed by the electric pulse generator 18, and the electric pulses are also supplied to the delay control circuit 29, which senses the electric pulses. Then, after a delay of a certain time T1, a gate signal 31 is generated, and the analog switch 27 is turned on with the gate signal 31.
Let it be N. The optical pulse 21 from the semiconductor laser 11 and the backscattered light 22 from the optical fiber 13 to be measured are shown in FIG. 6B.
However, the backscattered signal input to the signal processor 15 becomes as shown in Figure 6. In this way, unnecessary voltage components are removed compared to the case of FIG. 4C.

7 and 8 show experimental data observed on the display section 16 according to the embodiment shown in FIG. 5.

Each semiconductor laser 11 has a wavelength λ of 1.31 μm.
This is the data when using a 1.56 μm one. Further, as the optical fiber 13 to be measured, a single mode fiber having a length of about 11 Kx is used. FIG. 7A and FIG. 8A are data corresponding to FIG. 6, respectively, and it can be confirmed that the fiber length is about 11 km. FIG. 7B and FIG. 8B are logarithmically transformed diagrams of FIG. 7A and FIG. 8, and it was confirmed that the optical pulse test of the optical fiber can be performed up to about 20 KII from the slope of the straight line.

``Effects of the Invention'' As explained above, according to the present invention, a semiconductor laser used as a light source is used as a photodetector when no light is emitted, which has been indispensable in optical pulse testers. This method has the advantage that a photodetector such as an optical directional coupler or Ge-APD can be removed, the insertion loss of the optical directional coupler is zero, and a compact high-performance optical pulse tester can be manufactured. In addition, since expensive items such as an optical directional coupler and a Ge-APD photodetector are not used, it is possible to realize an optical pulse tester that is inexpensive and has low insertion loss since no optical directional coupler is used.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional optical pulse tester, Fig. 2 is a diagram showing a psychotropic coupler used in the conventional optical pulse tester, and Fig. 3 is an example of the optical pulse tester of the present invention. 4 is a time flowchart showing the operation example of FIG. 3, FIG. 5 is a block diagram showing an embodiment of the optical pulse tester pond of the present invention, and FIG. FIGS. 7 and 8 are time flow charts illustrating an example of the operation of FIG. 11: Semiconductor laser beam i, 12: Optical directional coupler, 13
: optical fiber to be measured, 14: photodetector, 15: signal processor, 16: display section, 17: load resistor, 18: electric pulse generator, 27: analog switch, 28: delay control circuit. Patent applicant: Representative of Nippon Telegraph and Telephone Public Corporation Takuo Kusano 17 O 2 Figure O 3 Figure IP 4 Figure + ■ 2i77 Figure point fiber moxibustion (kml 2t78 Length (km) Optical fiber & (km) This Nikko fiber moxibustion (km)

Claims (1)

[Claims] (1) Inject a light pulse into one end of the optical fiber under test, detect the Rayleigh scattered light from the optical fiber under test, and use the detection output as a measurement signal to at least search for fault points and measure loss in the optical fiber under test. In an optical pulse tester that performs one of the above, a semiconductor laser is used as a light source that emits the optical pulse, and while transmitting the optical pulse,
A light pulse characterized in that a bias voltage of the semiconductor laser is controlled by a switching means to cause the semiconductor laser to act as a photodetector, and a photocurrent of the semiconductor laser serving as the photodetector is used as the measurement signal. Test device.