JP5220499B2 - Optical pulse tester - Google Patents

Description

  The present invention relates to a subscriber line terminal unit (ONU: Optical Network Unit) on each user's home side from an optical line terminal (OLT) in a PON (Passive Optical Network) system via an optical splitter. The present invention relates to an optical pulse tester for measuring the optical loss and the position of a fault point in an optical fiber line.

  In recent years, the speed of optical access systems such as FTTH (Fiber To The Home) has been remarkably increased, and about 100 times faster and wider bandwidth has been realized in the last 5 years. Has been done. As a method for realizing high-speed broadband optical access networks, PON is a system capable of high-speed data transmission / reception with a plurality of subscriber homes without providing a special relay device in the middle of the transmission path. The system has been put into practical use.

  This PON system is a transmission method in which one optical fiber is branched from an OLT by an optical splitter and shared by ONUs installed in a plurality of user homes, and the OLT sharing and optical fiber cost can be kept low. Is possible. The PON system includes B-PON (Broadband-PON), GE-PON (Gigabit Ethernet (registered trademark) -PON), G-PON (Gigabit-PON), etc., depending on the difference in frame and transmission speed. However, the basic configuration is such that the OLT and the ONU at each user's house are connected via an optical splitter.

  In such an optical access system, not only the introduction cost per user but also the operation cost is important, and a system having both high speed and economy is required. Therefore, a system that can monitor the branched optical line between the OLT and the plurality of ONUs at low cost is also expected in order to reduce the operation cost. Note that these technologies can also be used as in-building communication technologies.

FIG. 6 is a schematic configuration diagram of an optical branch monitoring system disclosed in Patent Document 1 below. As shown in the figure, the optical branch monitoring system 100 of Patent Document 1 below is an optical multi-branch communication system in which a communication company station including a transmission device 101 that is an OLT and a plurality of ONUs 102 are connected by an optical splitter 103. In the optical branch line monitoring system for monitoring each branch line 1a _{1 to} 1a ₈ , each ONU 102 includes FBGs 102-1 to 102-8 that reflect the unique monitoring wavelength light respectively assigned to each ONU 102. The control unit 104 emits each monitoring wavelength light so that the intensity of each monitoring wavelength light at the input end of each of the FBGs 102-1 to 102-8 is less than the minimum reception intensity of the ONU 102. Then, the transmission apparatus 101 monitors each line while sequentially outputting the monitoring wavelength assigned to each ONU 102 by the OTDR 105, and a photo counting method capable of detecting light with high sensitivity is proposed for the light detection of the OTDR 105.

Also, as a system different from the above system, an optical filter that reflects the same monitoring wavelength and the same monitoring wavelength to each ONU, instead of assigning a unique monitoring wavelength to each ONU and an FBG that reflects the unique monitoring wavelength. A method of using is also considered. If this method is used, the light source wavelength on the OLT side may be one wavelength, and there is an advantage that an inexpensive monitoring system can be realized. In this case, it is necessary to operate by changing the optical fiber length from the optical splitter to each ONU so that the reflection positions of the optical splitters are different.
JP 2005-192138 A

  However, in the above-described conventional method, the method of assigning the unique monitoring wavelength light and the FBG reflecting the unique monitoring wavelength light to each former ONU requires a light source and an FBG having a plurality of wavelengths. There is a problem that the configuration becomes expensive and the operation cost increases accordingly.

  Further, in the latter method using an optical filter that reflects the same monitoring wavelength light and the same monitoring wavelength light for each ONU, a high positional resolution of about 1 m or less is required for the management and operation of the optical fiber length to each ONU. Therefore, high-sensitivity, highly stable light that can cope with improvement in positional accuracy by shortening the monitoring wavelength light, and reduction in the detection level of monitoring wavelength light by shortening the monitoring wavelength light and optical branching by the optical splitter There is a problem that signal detection is necessary and the system configuration is expensive.

  Further, in order to improve the positional accuracy in searching for an optical line fault point in an optical multi-branch communication system, it is necessary to shorten the pulse of the monitoring wavelength light. The limit is 3 ns per pulse (resolution: 80 cm), and position accuracy beyond this cannot be realized.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide an inexpensive optical pulse tester capable of accurately measuring the position of a fault point in a laid optical fiber line with high positional accuracy. To do.

In order to achieve the above object, the optical pulse tester according to claim 1 is configured such that the subscriber line terminal equipment 2 and the plurality of subscriber line terminators 3 branch and connect the optical signal by the optical splitter 5 in a one-to-many manner. In the optical multi-branch communication system, the test light is incident on the optical fiber 6 to be measured from the subscriber terminal station side, reflected from the optical filter 4 installed immediately before the subscriber terminal side, and the subscriber In an optical pulse tester that receives and detects the return light that returns to the line end station device side and measures the optical loss and fault point position of the measured optical fiber,
A modulation signal generator 11b that outputs a peak pulse modulation signal that modulates the test light into a peak pulse and a rectangular pulse modulation signal that modulates the test light into a rectangular pulse, and a modulation signal from the modulation signal generation unit A light source 11a that emits test light modulated according to the above, and when measuring the position of the obstacle point, the test light modulated by the peak-shaped pulse modulation signal output from the modulation signal generator is used. A light source unit that emits the test light modulated by the rectangular pulse modulation signal output from the modulation signal generator when the light loss is emitted from the light source and the optical loss of the optical fiber 6 to be measured is measured. 11 and
Filter means 14 for extracting only the optical signal of the test light from the return light from the optical fiber to be measured;
Photodetection means 15 for photoelectrically converting the optical signal of the test light extracted by the filter means;
A signal processing control unit 16 that performs processing control related to measurement of a fault point position of the optical fiber to be measured based on an electrical signal photoelectrically converted by the light detection unit;
It is comprised from these.

The optical pulse tester according to claim 2 is the optical pulse tester according to claim 1, wherein the signal processing control unit 16 terminates the subscriber line when the test light is emitted to the optical fiber 6 to be measured. The reflection level of the return light from the device 3 and the reference reflection level that is the reflection level of the return light from the subscriber line terminating device when the optical fiber to be measured of the optical multi-branch communication system set in advance is in a normal state Compare with the data,
When the measured reflection level of the return light is within a predetermined range with the reference reflection level data as a reference, it is determined that the measured optical fiber is in a normal state .

  According to the optical pulse tester of the present invention, when measuring the position of a fault point in an optical fiber to be measured, the spatial resolution is improved by using a pointed pulse with a narrower pulse width than that of a rectangular pulse, thereby achieving higher accuracy. It is possible to measure the position of the obstacle. Moreover, since a general differential circuit is used for the modulation of the pointed pulse, an optical pulse tester having a low system configuration can be provided.

  Furthermore, when measuring the position of a fault point, test light modulated into a peak pulse can be selected, and when measuring optical loss, test light modulated into a rectangular pulse can be selected. By switching to an optimal waveform according to the above, a highly reliable optical line test can be performed.

  When performing an optical line test in an optical multi-branch communication system in which one-to-many branch connection such as a PON system is performed instead of a one-to-one connection, when measuring the position of a fault point with each ONU By using test light modulated with a pointed pulse, it is possible to accurately measure the position of the obstacle point with high positional accuracy, and to improve the labor and work efficiency of the test.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing a configuration of an optical pulse tester according to the present invention and a PON system using the same device, and FIG. 2 shows a peak-shaped pulse modulation signal in a modulation signal generation unit of the optical pulse tester. FIG. 3A is a circuit diagram showing an example of a differentiation circuit to be generated, FIG. 3A is an explanatory diagram showing a rectangular pulse waveform used at the time of optical loss measurement, and FIG. 3B is a pointed shape used at the time of measuring a fault point position. FIG. 4 is an explanatory diagram showing a pulse waveform, FIG. 4 is an explanatory diagram showing a measurement waveform when measured with a rectangular pulse and a pointed pulse, and FIG. 5 is a diagram illustrating another embodiment of the optical pulse tester according to the present invention. It is explanatory drawing which shows the example which was.

  The optical pulse tester of this example makes test light having a predetermined pulse width incident on an optical fiber to be measured and returns light (backscattered light or Fresnel reflected light) returning from the optical fiber to be measured. In an optical pulse tester that performs optical line tests such as measuring optical loss and fault point position of the optical fiber under test by receiving light, a rectangular pulse modulation signal that measures optical loss and a pointed shape that detects the fault point position A modulation signal generator that generates a pulse modulation signal is used, and high accuracy is achieved by using test light modulated with a pointed pulse modulation signal when performing an optical line test to measure the position of the fault point of the optical fiber under measurement. In addition, the position of the fault point of the optical fiber is measured.

  First, the configuration of the optical pulse tester according to the present invention will be described with reference to FIGS. As shown in FIG. 1, the optical pulse tester 1 of this example includes a light source unit 11, a branching unit 12, an optical amplification unit 13, a filter unit 14, a light detection unit 15, a signal processing control unit 16, a storage unit 17, and a display. Means 18 and operating means 19 are provided and connected to the optical fiber 6 to be measured via an optical terminal 20 provided at a predetermined location of the device.

  In the following description, the optical pulse tester 1 of this example includes a plurality of OLTs 2 that are subscriber line terminal devices and an optical filter 4 that reflects the test light from the optical pulse tester 1 immediately before. A description will be given of an example used for an optical line test in a PON system in which an ONU 3 as a subscriber line termination device is optically branched by an optical splitter 5.

  The light source unit 11 includes a light source 11a that emits test light to the optical fiber 6 to be measured, and a modulation signal generating unit 11b that modulates the test light emitted from the light source 11a according to the type of optical line test.

  The light source 11a is composed of, for example, an LD (Laser Diode), and is modulated based on a modulation signal (rectangular pulse modulation signal or peak pulse modulation signal) from a modulation signal generation means 11b described later when performing an optical line test. The pulsed test light is emitted. In optical communication in the PON system, for example, wavelengths for communication (1.31 / 1.49 / 1.55 μm) and pumping (0.98 / 1.48 μm) are used, so these wavelengths are different. Test light having a wavelength (1.65 μm, 0.78 μm) is emitted.

  When a modulation command (rectangular pulse modulation command or peak pulse modulation command) is input from the control unit 16c, the modulation signal generation unit 11b receives a rectangular pulse modulation signal or a peak for modulating the optical pulse of the test light into a rectangular pulse. A cusp-shaped pulse modulation signal for modulation into a head-shaped pulse (triangular wave) is output.

  That is, when measuring the optical loss of the optical fiber 6 to be measured, the modulation signal generating unit 11b outputs a test light based on this command when a rectangular pulse modulation command for modulating the optical pulse to the rectangular pulse is output from the control unit 16c. A rectangular pulse modulation signal for modulating the signal into a rectangular pulse is output to the light source 11a. Further, when detecting the position of the fault point of the optical fiber 6 to be measured, a peak-shaped pulse modulation command is output from the control means 16c to modulate the peak-shaped pulse. A pulse-shaped pulse modulation signal for modulating the signal to the light source 11a is output to the light source 11a.

The generation circuit of the rectangular pulse modulation signal in the modulation signal generation means 11b is the same as the configuration of the pulse generation circuit (not shown) provided in the existing optical pulse tester 1, and the rectangular pulse modulation command from the control means 16c. Based on the above, a rectangular pulse modulation signal is output to the light source 11a at a predetermined generation timing.
In addition, the peak-shaped pulse modulation signal generation circuit is configured by a general differentiation circuit as shown in FIG. 2, for example, and the peak-shaped pulse modulation signal is generated at a predetermined generation timing based on the peak-shaped pulse modulation command from the control means 16c. The head-shaped pulse modulation signal is output to the light source 11a.

  Here, the waveform pulse generated by each modulation signal will be described. The rectangular pulse modulated by the rectangular pulse modulation signal is the same as that conventionally used as shown in FIG. 3 (a), with a pulse width of 10 ns and a minimum resolution of 1.6 m, and a pulse width of 3 ns and a minimum resolution of 80 cm. It is. On the other hand, as shown in FIG. 3B, the pulse width of the pointed pulse is narrower than that of the rectangular pulse (resolution at 1.5 dBdown is 80 cm or less).

  Therefore, when a rectangular pulse is emitted and a waveform is displayed based on the return light, for example, a waveform A (dotted line in the figure) as shown in FIG. 4 is displayed. Further, when a peak-shaped pulse is emitted and a waveform is displayed based on the return light, a waveform B (solid line in the figure) as shown in FIG. 4 is displayed, for example. As can be confirmed from the waveform in the figure, the waveform obtained by the rectangular pulse is vague and the position of the optical filter 4 installed immediately before the ONU 3 is not clearly displayed, whereas the waveform obtained by the pointed pulse The position of each optical filter 4 is accurately displayed.

In this way, since the pulse width of the pointed pulse is narrower than that of the rectangular pulse as in the past, it is possible to increase the resolution further than the rectangular pulse when measuring the fault point position, and more accurate. It becomes possible to measure the position of the obstacle.
In addition, using a pointed pulse reduces the overshoot and undershoot of the received light signal compared to the case of using a rectangular pulse, so the fall behind the reflection point in the measured waveform is mitigated, and false detection can be eliminated. There are also advantages.

  The branching unit 12 is composed of, for example, an optical directional coupler such as a 3 dB coupler, and returns from the optical fiber 6 to be measured as the test light emitted from the light source 11a is incident on the optical fiber 6 to be measured. Light (backscattered light and Fresnel reflected light) is led to the optical amplifying means 13.

  The optical amplifying unit 13 amplifies the return light derived from the branching unit 12 in a direct light state and outputs the amplified light to the filter unit 14.

  The filter means 14 is a filter that transmits only light having a predetermined wavelength of incident light, and returns light of test light output from the light source 11a (in this example, 1.65 μm light modulated in a rectangular pulse and a cusp). Only the optical signal of 0.78 μm light modulated into a head pulse is transmitted, and the transmitted optical signal is output to the light detection means 15.

  The light detection means 15 is composed of, for example, an APD (Avalanche Photo Diode), receives and detects an optical signal transmitted through the filter means 14, converts it into an electrical signal (photoelectric conversion), and performs signal processing control on the converted electrical signal. To the unit 16.

  The signal processing control unit 16 includes an A / D conversion unit 16a, an addition processing unit 16b, and a control unit 16c. The signal processing control unit 16 performs various processing controls related to the optical line test based on the electrical signal from the light detection unit 15. Yes.

  The A / D conversion unit 16a performs A / D conversion on the electrical signal output from the light detection unit 15, and outputs the converted electrical signal to the addition processing unit 16b.

  The addition processing unit 16b performs processing of the electrical signal output from the A / D conversion unit 16a (simple addition, average addition, and filter processing of these addition results as necessary), and is obtained by this processing. The processing data is output to the control means 16c.

  The control means 16c is comprised with the microcomputer comprised, for example with CPU, ROM, RAM, etc. Based on the processing data obtained by the addition processing means 16b, the control means 16c generates waveform data to be displayed on the display means 18 and displays waveforms such as auto search processing for event points (for example, fault point positions) existing in the waveform. Modulation command (rectangular pulse modulation command or pointed pulse modulation) to modulate to test light (rectangular pulse or pointed pulse) suitable for the type of optical line test selected by control, eg user settings Command) and control of switching the display waveform displayed on the display means 18 and the like, various controls necessary for driving the optical pulse tester 1 are performed.

  Further, the control means 16c obtains the return light reflection level data based on the processing data output from the addition processing means 16b and the return light reference reflection level data that is the normal state reflection level stored in the storage means 17. Comparison is made to determine whether or not the return light reflection level measured when the reference reflection level data is used as a reference is within a predetermined range (can be arbitrarily set). It is determined that it is in a state. Further, the control means 16c controls the display means 18 to output the contents of this determination result.

  The storage means 17 is composed of, for example, a rewritable semiconductor memory such as ROM or RAM, an HDD, and the like. The reflection level of the return light from the filter 4 (two-point loss between the peak level and the noise level) is stored as reference reflection level data in a state where the position of each ONU 3 is associated with the reflection level. The storage unit 17 also stores drive control data necessary for driving each part of the optical pulse tester 1.

  The reference reflection level data stored in the storage means 17 need not be measured at the time of installation when accurate information such as the distance of the optical fiber to be installed and the installation position of the ONU 3 is known. It is also possible to input a numerical value directly from the operation means 19 and store this value as reference reflection level data.

  The display means 18 is composed of a display device such as a liquid crystal display, for example, and displays and displays display information such as waveform display based on waveform measurement of the optical path test and various setting contents when the device is driven, under the control of the control means 16c. ing.

  The operation means 19 drives / stops the apparatus, selects an optical line test, sets parameters relating to the test, and selects / switches test light depending on the type of optical line test (that is, selects / switches a modulation signal according to the test contents). ), Which is constituted by various operation keys used when operating the optical pulse tester 1 such as switching of the display waveform displayed on the display means 18, and outputs an operation signal accompanying the key operation to the control means 16c. .

  When measuring the optical loss using the optical pulse tester 1 described above, the user connects to the measured optical fiber 6 via the optical terminal 20 in order to measure the optical loss of the measured optical fiber 6. The rectangular pulse test light is selected by the operating means 19 in order to emit rectangular pulse test light suitable for the measurement of optical loss.

  When rectangular pulse test light is selected, a rectangular pulse modulation command is output from the control means 16c to the modulation signal generating means 11b, and a rectangular pulse modulation signal is output from the modulation signal generating means 11b to the light source 11a based on this command. To do. Then, the modulated rectangular pulse test light is emitted to the optical fiber 6 to be measured, and the return light (back scattered light) of the test light is led out to the optical amplifying means 13 by the branching means 12.

  The derived return light is subjected to photoelectric conversion by the light detection means 15 after the filter processing in the filter means 14, and further the A / D conversion means 16a performs A / D conversion of the photoelectrically converted electric signal, and is added based on this digital signal. Based on the processing data added by the processing means 16b, the display contents subjected to the waveform display processing are displayed on the display means 18.

  Further, when the failure point position is measured using the optical pulse tester 1 described above, the user connects the optical pulse tester 1 to the optical fiber 6 to be measured in the same manner as described above, and then measures the failure point position. In order to emit a suitable pointed pulse test light, the operating means 19 selects the pointed pulse test light.

  When the test light of the peak-shaped pulse is selected, a peak-shaped pulse modulation command is output from the control unit 16c to the modulation signal generating unit 11b, and based on this command, the peak-shaped pulse modulation is performed from the modulation signal generating unit 11b. A signal is output to the light source 11a. Then, the modulated pointed pulse test light is emitted to the optical fiber 6 to be measured, and the return light (Fresnel reflected light) of the test light is led to the optical amplifying means 13 by the branching means 12.

  The derived return light is subjected to photoelectric conversion by the light detection means 15 after the filter processing in the filter means 14, and further the A / D conversion means 16a performs A / D conversion of the photoelectrically converted electric signal, and is added based on this digital signal. Based on the processing data added by the processing means 16b, the display contents subjected to the waveform display processing are displayed on the display means 18.

  In this way, the optical pulse tester 1 described above, when measuring the optical loss, modulates the modulation signal generating means 11b so as to emit the rectangular pulse test light suitable for measuring the optical loss of the optical fiber 6 to be measured. Then, a rectangular pulse modulation signal is output to the light source 11a, and the test light modulated by the modulation signal is emitted to the optical fiber 6 to be measured. When measuring the position of the fault point, the modulation signal generating means 11b emits a pointed pulse modulated signal so as to emit test light of a peaked pulse suitable for measuring the position of the fault point of the optical fiber 6 to be measured. Is output to the light source 11a, and the test light modulated by the modulation signal is emitted to the optical fiber 6 to be measured.

  This makes it possible to use a pointed pulse with a narrower pulse width than the rectangular pulse when measuring the position of the obstacle, thus improving the spatial resolution compared to the conventional measurement of the position of the obstacle point in the rectangular pulse and providing more accurate obstacles. The point position can be measured. In addition, since a general differential circuit is used for the modulation of the pointed pulse, the optical pulse tester 1 having a low system configuration and capable of detecting light with high accuracy and high stability can be provided. .

  By the way, in the above-described embodiment, when the polarization characteristic of the backscattered light that is the return light becomes a problem, the optical path between the light source 11a and the branching means 12, the optical path between the branching means 12 and the optical terminal 20, and the branching. By inserting a polarization scrambler that randomly changes the polarization into any of the optical paths between the means 12 and the optical amplification means 13, it is possible to perform measurement independent of the polarization characteristics.

  In the above description, the optical pulse tester 1 of this example is connected to the OLT 2 which is a subscriber line terminal station device and the ONU 3 which is a plurality of subscriber line terminal devices via a branch optical fiber transmission line using the optical splitter 5. However, the present invention is not limited to this. For example, as shown in FIG. 5, the test light is output by connecting to the optical fiber 6 to be measured, By receiving the return light of the output light, it is possible to detect the optical loss and the fault point position of the optical fiber as in the above embodiment.

  Further, in the above-described embodiment, the optical pulse tester 1 has been described with an example in which the optical amplifying means 13 is provided. However, the optical amplifying means 13 is attenuated when the laying distance of the optical fiber 6 to be measured is long. Since it is a means for amplifying light to improve sensitivity, it is particularly used when it can be used only in a place where the laying distance is short or sufficient sensitivity can be secured without attenuation of the return light from the optical fiber 6 to be measured. do not have to.

  As mentioned above, although the best form in this invention was demonstrated, this invention is not limited with the description and drawing by this form. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

It is a schematic block diagram which shows the structure of the optical pulse tester based on this invention, and the PON system using the apparatus. It is a circuit diagram which shows an example of the differentiation circuit which generates the peak-shaped pulse modulation signal in the modulation signal generation part of the optical pulse tester. (A) It is explanatory drawing which shows the rectangular pulse waveform used at the time of optical loss measurement. (B) It is explanatory drawing which shows the peak-shaped pulse waveform used at the time of the measurement of an obstruction point position. It is explanatory drawing which shows the measurement waveform at the time of measuring with a rectangular pulse and a peak-shaped pulse. It is explanatory drawing which shows the example which used the optical pulse tester based on this invention with the other form. It is explanatory drawing which shows schematic structure of the conventional optical branch line monitoring system.

Explanation of symbols

1 ... Optical pulse tester 2 ... Subscriber line terminal equipment (OLT)
3. Subscriber line termination unit (ONU)
DESCRIPTION OF SYMBOLS 4 ... Optical filter 5 ... Optical splitter 6 ... Optical fiber to be measured 11 ... Light source part (11a ... Light source, 11b ... Modulation signal generation means)
DESCRIPTION OF SYMBOLS 12 ... Branch means 13 ... Optical amplification means 14 ... Filter means 15 ... Light detection means 16 ... Signal processing control means (16a ... A / D conversion means, 16b ... Addition processing means, 16c ... Control means)
17 ... Storage means 18 ... Display means 19 ... Operation means 20 ... Optical terminal

Claims (2)

The subscriber terminal device in an optical multi-branch communication system in which a subscriber line terminal device (2) and a plurality of subscriber line terminators (3) are branched and connected in a one-to-many manner with an optical splitter (5). The test light is incident on the optical fiber to be measured (6) from the side, and the return light reflected from the optical filter (4) installed immediately before the subscriber termination device side and returning to the subscriber line terminal device side is returned. In the optical pulse tester that detects the light loss and the position of the fault point of the optical fiber to be measured by detecting the received light,
A modulation signal generator (11b) for outputting a peak pulse modulation signal for modulating the test light into a peak pulse and a rectangular pulse modulation signal for modulating the test light into a rectangular pulse; A light source (11a) that emits test light modulated based on the modulation signal, and when the position of the obstacle point is measured, it is modulated by the peak-shaped pulse modulation signal output from the modulation signal generator When the test light is emitted from the light source and the optical loss of the optical fiber to be measured (6) is measured, the test light modulated by the rectangular pulse modulation signal output from the modulation signal generator is A light source unit (11) emitting from the light source;
Filter means (14) for extracting only the optical signal of the test light from the return light from the optical fiber to be measured;
A light detection means (15) for photoelectrically converting the optical signal of the test light extracted by the filter means;
A signal processing control unit (16) that performs processing control related to measurement of a fault point position of the optical fiber to be measured, based on the electrical signal photoelectrically converted by the light detection unit;
An optical pulse tester comprising: The signal processing control unit (16) has a reflection level of return light from the subscriber line terminating device (3) when the test light is emitted to the optical fiber to be measured (6), and the preset level. Compared with the reference reflection level data, which is the reflection level of the return light from the subscriber line termination device when the optical fiber under test of the optical multi-branch communication system is in a normal state,
Claim wherein the reference reflection level data the measured return light reflection level when a reference is in if it was within a predetermined range, wherein said measured optical fiber is determined to be in a normal state The optical pulse tester according to 1 .

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