OTDR type measurement system using remote excitation amplification
By synchronizing excitation light modulation with probe and return light timings, the system enhances gain in remote amplifiers, overcoming distance limitations in OTDR-type measurements, achieving extended sensing distances and reduced noise.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- OCC CORP
- Filing Date
- 2024-11-05
- Publication Date
- 2026-05-19
AI Technical Summary
Existing OTDR-type measurement systems face limitations in extending the distance of optical fiber sensing measurements due to the attenuation of excitation light over long distances, particularly beyond 100 km, leading to insufficient gain in remote excitation amplification repeaters.
The system employs intensity and phase modulation of excitation light to synchronize its input with the timing of probe pulse light and return light, increasing the instantaneous power at the optical amplifier without raising the average power, thereby enhancing the gain of remote amplifiers.
This approach allows for increased output power of amplification repeaters, extending the distance from the excitation light source to the repeater, and reduces noise and ASE emission, while maintaining accurate measurement performance.
Smart Images
Figure 2026081474000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical fields of optical fiber sensing and optical amplification relay.
Background Art
[0002] <Optical Fiber Sensing> Optical fibers are used not only as communication media but also as sensors. For example, when sound waves or vibrations are applied to an optical fiber, the light passing through the optical fiber is modulated, and by detecting the reflected light or transmitted light, environmental information such as sound and vibration in a remote location can be detected and measured. One representative such measuring device is called DAS (Distributed Acoustic Sensing). DAS is a measuring device that detects environmental information from the backscattered light of the light propagating through an optical fiber and is a type of OTDR (Optical Time Domain Reflectometry) measuring device. DAS can measure vibrations, strains, etc. at each point through which the probe pulse light passes by analyzing Rayleigh backscattered light. In addition, BOTDR, which analyzes Brillouin backscattered light, is also known.
[0003] An OTDR type measuring device outputs probe pulse light toward an optical fiber serving as a sensor, and the backscattered light generated in the optical fiber propagates in the opposite direction to the probe pulse light, returns to the measuring machine, is detected, and measures the state of the optical fiber at the location where the backscattered light is generated.
[0004] OTDR is widely used today as a tool for confirming the integrity of optical fiber lines used as transmission paths for communication signals, such as losses and reflections, and has been studied for use as a measuring device for optical fiber sensing since its early days.
[0005] <Combination of Optical Fiber Sensing and Optical Amplification Repeater> Due to transmission losses in optical fibers, the sensing signal light is attenuated, thereby limiting the measurable distance. Therefore, a technique to compensate for this loss using an optical amplifier is disclosed, for example, in Patent Document 1. The most widely used optical amplifier today is the EDFA (Er-doped fiber amplifier).
[0006] In OTDR type measuring instruments, the probe pulse light and the backscattered light generated in the optical fiber propagate in opposite directions in a bidirectional transmission across a single fiber. Therefore, a typical configuration for an amplification repeater is to separate the light in each direction using a circulator, amplify each signal, and then combine them using a circulator.
[0007] <Remote excitation method> When transmitting optical signals over long distances via optical fiber cables, the transmission loss in the optical fiber causes attenuation of the optical signal, limiting the communication distance. Therefore, optical amplifier repeaters, which use an optical amplifier in between to compensate for the loss, are effective.
[0008] In a typical optical amplifier configuration, the source of the excitation light for exciting the EDF is located in close proximity to the EDF. A typical example of an excitation light source is a semiconductor laser. This semiconductor laser is driven by commercial power.
[0009] However, it is often necessary to install optical amplification repeaters in locations where commercial power is difficult to obtain, such as underwater cables. One solution in such cases is remote excitation, in which excitation light is sent from a land-based light source to the repeater via optical fiber. This is a well-known technique that is widely used in practice, as described in, for example, Non-Patent Documents 1 and 2.
[0010] For remote excitation, the excitation wavelength used for EDFAs (Er-doped Fiber Amplifiers) is 1.48 μm, which allows for long-distance transmission using communication optical fibers. The 0.98 μm excitation wavelength, which is currently the mainstream for EDFs, is not used for remote excitation because the attenuation associated with optical fiber transmission is greater than that of 1.48 μm.
[0011] Although 1.48 μm excitation light is attenuated when transmitted over long distances, in remote excitation methods, the excitation light is sent to a remote repeater by transmitting it with a high enough power to compensate for this attenuation. It is empirically known that the excitation light power of 1.48 μm is about 5-10 mW (7-10 dBm) for the EDF to achieve a practical gain. This is also explained in Non-Patent Literature 1 (p. 42, 1st column).
[0012] In a typical configuration of conventional remote excitation, excitation light of about 1W (+30dBm) is transmitted from a land-based light source to excite an EDF located about 100km away. The typical transmission loss at a wavelength of 1.48μm in a 100km communication optical fiber is about 20dB, so the power that reaches the repeater is about +10dBm. An excitation power of +10dBm is close to the minimum value at which a practical amplification gain can be obtained, and at even greater distances, it becomes difficult to deliver sufficient excitation light power.
[0013] As explained in Figure 2.2-2 of Non-Patent Document 2, the excitation light for remote excitation may be wavelength-multiplexed with the signal light at the land terminal station and transmitted on the same wire, or the signal light and excitation wavelength may be transmitted on separate wires from the land terminal station to the optical amplifier and combined just before the EDF in the remote excitation optical amplifier.
[0014] When signals are transmitted through the same fiber, a phenomenon called stimulated Raman scattering occurs in the optical fiber, where some of the energy of the excitation light is transferred to the signal light, i.e., optical amplification occurs. While this phenomenon can be actively utilized, when transmitting the excitation light over longer distances, it is undesirable for energy to be lost, so it is preferable to transmit it through separate fibers. [Prior art documents] [Patent Documents]
[0015] [Patent Document 1] U.S. Patent No. 7595865 [Patent Document 2] Japanese Patent Application Publication No. 09-113941 [Non-patent literature]
[0016] [Non-Patent Document 1] Development of a Submarine Remote Excitation Optical Amplification System Implemented Between Okinawa Main Island and Miyako Island, Tomoyoshi Kataoka et al., NTT Technical Journal, June 2005. [Non-Patent Document 2] Optical Submarine Cables (Book), 2.2.2 Transmission Distance Extension Technology for Non-Relay Transmission Systems, Optical Submarine Cable Writing Committee (This section was written by Hidenori Taga), May 2010. [Overview of the project] [Problems that the invention aims to solve]
[0017] In a measurement system combining an OTDR-type measuring instrument and a remote excitation amplification relay, we aim to enable optical fiber sensing measurements by remotely exciting an EDF located at a very great distance from the land terminal and relaying the optical signal, which was difficult with conventional remote excitation amplification configurations. A very great distance refers to a distance significantly exceeding 100 km, for example.
[0018] The distance from the land-based terminal station to the repeater in a remote excitation system is limited by the maximum power of the excitation light and the transmission loss. The transmission medium with the lowest transmission loss is transverse single-mode optical fiber, but the cross-sectional area of its optical waveguide (core) is 80 μm². 2 The power output is extremely small. Therefore, when the input optical power increases, the power per unit cross-sectional area becomes very high, making it easier for problems to occur such as light leakage from the optical fiber and thermal degradation of the coating. Currently, around 10W is considered the practical limit.
[0019] The present invention has been made in view of the above circumstances, and in a measurement system using an OTDR type measuring instrument and a remote excitation amplification repeater, it is possible to increase the gain of a remote amplifier without increasing the output power of the excitation light. As a result, the output power of the amplification repeater is increased, and the distance between the excitation light source and the amplification repeater is extended.
Means for Solving the Problems
[0020] The OTDR type measurement system using remote excitation amplification according to the present invention includes an OTDR type measuring instrument that outputs probe pulse light to an optical fiber, analyzes the scattered return light from the optical fiber, and measures the ambient environmental information at the scattering points of the optical fiber, the optical fiber, an amplification repeater disposed in the middle of the optical fiber and including an optical amplifier that compensates for attenuation of the signal light (i.e., the probe pulse light and the return light) of the OTDR type measuring instrument, a light source for the excitation light required by the optical amplifier, and an optical fiber that delivers the excitation light from the source to the amplification repeater. In the OTDR type measurement system, an intensity modulation means for the excitation light is provided, and the intensity and phase of the excitation light are adjusted such that the excitation light is strongly input to the optical amplifier at the timing when the signal light of the OTDR type measuring instrument passes through the optical amplifier.
Effects of the Invention
[0021] According to the present invention, in a measurement system using an OTDR type measuring instrument and a remote excitation amplification repeater, it is possible to increase the output power of the amplification repeater and extend the distance from the excitation light source to the amplification repeater.
Brief Description of the Drawings
[0022] [Figure 1] It is a configuration diagram of the first embodiment. [Figure 2] It is a diagram for explaining the timing of the probe pulse light passing through the optical amplification repeater and the excitation light of the amplifier for the probe pulse light. [Figure 3] It is a diagram for explaining the timing and waveform of the return light passing through the optical amplification repeater and the excitation light of the amplifier for the return light. [Figure 4] This is an example of a configuration using remote excitation amplification relay in a long-distance measurement system using an OTDR type detector. [Figure 5] Figure 4 is an explanatory diagram of the intensity waveform of the reflected light at each point. [Figure 6] This is a diagram illustrating the configuration of the second embodiment. [Figure 7] This is a diagram showing a modified example of the second embodiment. [Figure 8] This is a diagram illustrating the configuration of the third embodiment. [Modes for carrying out the invention]
[0023] <First Example> Figure 1 illustrates the configuration of the first embodiment. The dotted line within the land terminal contains the components added by the present invention, while the rest is a conventionally known configuration. First, the conventional configuration will be described.
[0024] The OTDR type measuring instrument 4 is, for example, a DAS. The total length of cables 3a and 3b between the land terminal station 1 and the amplifier repeater 2 of interest is, for example, 180 km, and the cable 3c further away from the amplifier repeater 2 of interest is approximately 90 km. Environmental information of these cables, such as vibration, is measured by the DAS. Here, cables 3a, 3b, and 3c are cables containing optical fiber cores as shown in Figure 1, but may also contain other optical fiber cores or electrical wires.
[0025] The probe pulse light 7 emitted by the DAS travels far away, continuously returning Rayleigh backscattered light to the DAS, and by the time it reaches the amplified repeater 2, it has been significantly attenuated due to transmission loss.
[0026] In the amplified repeater, the probe pulse light 7 from the OTDR type measuring instrument 4 is separated from the return light 8 by the circulator 10a, amplified by the EDF 12a, then combined with the return light 8 by the circulator 10b, and sent out for sensing on the next cable 3c.
[0027] The return light 8 from cable 3c, which is further away than the repeater under consideration, is separated from the probe pulse light 7 by circulator 10b in the amplified repeater 2, amplified by EDF 12b, then combined with the probe pulse light 7 by circulator 10a, and sent to the OTDR type measuring instrument 4.
[0028] The excitation light for the amplifier repeater 2 is also transmitted from the land terminal station 1 through optical cables 3a and 3b. Although it is significantly attenuated due to transmission loss, the excitation power necessary for amplification is still delivered.
[0029] While there are several variations in the configuration of the excitation light source, the core technology for a 10W-class transverse single-mode fiber output light source involves bundling the output from a transverse multimode high-power semiconductor laser into a double-clad optical fiber amplifier for excitation.
[0030] In this embodiment, we will first explain a configuration in which the output of the seed light source 5 with an excitation light wavelength is split by a 3dB coupler 30, input to the aforementioned high-power optical amplifier 6, and amplified to near the upper limit of power that can be input to the transmission optical fiber before being output.
[0031] Since the practical optical power that can be input to a transverse single-mode optical fiber is considered to be limited to about 10W (+40dBm), multiple cores are used to send excitation light to amplifiers at long distances. In this example, one core is allocated for the probe pulse light amplifier and one core for the return light amplifier, and each is used to send 10W of excitation light power. However, the loss coefficient for single-mode optical fiber transmission with an excitation light wavelength of 1.48μm is typically about 0.2dB / km, so the power of excitation light 9a and 9b after 180km transmission is attenuated to about +4dBm (2.5mW), and it is difficult to obtain sufficient gain even when input to an EDF.
[0032] The above is a description of the conventional configuration.
[0033] <Components added in this invention> In this invention, in addition to the conventional configuration described above, a portion of the probe pulse light from the OTDR type measuring instrument 4 is branched by a coupler 20 at the land terminal station 1, then received by a modulation signal generator 21, the ping rate of the probe pulse light 7 is extracted as a clock, and intensity modulation synchronized with that clock is applied to the excitation light. As a result, even if the time-averaged value of the optical power is the same, the instantaneous optical power can be increased by the pulse occupancy rate (duty ratio).
[0034] In the configuration shown in Figure 1, the ping rate was set to 350 Hz (period approximately 2.9 ms), and the pulse width of probe pulse light 7 was set to 50 ns. Therefore, the duty cycle of probe pulse light 7 is extremely small at 0.0017%.
[0035] <Amplification of probe pulsed light> Figure 2 shows an example of the intensity waveforms of the probe pulse light 7 and the excitation light 9a of the probe pulse light optical amplifier 12a before and after the amplification repeater 2. The intensity of the probe pulse light 7 is localized on the time axis. Therefore, if the probe pulse light 7 is excited only while passing through the EDF 12a, the gain for the probe pulse light 7 can be increased even if the time-averaged power is the same.
[0036] The phase of the intensity-modulated signal at the land station is optimally adjusted so that the probe pulse light 7 and the excitation light 9a overlap in the EDF 12a. Specifically, the intensity-modulated waveform of the excitation light 9 has a rise and fall time of 300 μs each, and a flat portion of 200 μs. In terms of half-width, this pulse shape is approximately 500 μs. The ping rate is 350 Hz (period approximately 2.9 ms), so the duty cycle is 17.5%. After applying this intensity modulation to the excitation light 9, when amplified by the high-power amplifier 6 in Figure 1, the peak value of the pulse intensity becomes approximately 5.7 times the average value. Therefore, by matching the timing of the probe pulse light 7 passing through the amplifier repeater 12a with the timing of the excitation light 9a pulse passing through, the excitation power when the probe pulse light 7 passes through was increased to approximately +10 dBm, while the average power of the excitation light is +4 dBm.
[0037] <Amplification of reflected light> Figure 3 shows an example of the intensity waveforms of the return light 8 and the excitation light 9b of the return light optical amplifier 12b before and after the amplified repeater 2. The intensity waveform of the return light 8 is strongest at the moment the probe pulse light 7 enters the next optical fiber transmission path, and then gradually decreases. Figure 3 schematically shows the waveforms at timing 1 when the return light 8 begins to enter the repeater 2 and timing 2 when it finishes passing through.
[0038] Here, Figures 4 and 5 illustrate how the pulse occupancy rate of the return light 8 decreases at repeaters far from the land terminal station 1. As shown in Figure 4, the measurement system is assumed to consist of three cable sections and two amplified repeaters. The length of one cable section (denoted as span in Figures 4 and 5) is, for example, 90 km. In other words, amplified repeater 2 in Figure 1 is the second repeater from the measuring instrument in Figure 4. The first amplified repeater from the measuring instrument is close to the land terminal station and can be sufficiently excited using conventional techniques, so it is omitted in Figure 1.
[0039] The reflected light waveforms at points A, B, and C in Figure 4 are schematically shown in Figure 5.
[0040] At point A, which is close to the OTDR detector, the reflected light has a signal for most of the probe pulse emission period (ping rate). On the other hand, at point C, the amplifier repeater furthest from the OTDR detector, the reflected light output waveform only contains reflected light from spans farther away than itself, meaning that reflected light is present for less than 1 / 3 of the probe pulse emission period (ping rate). Thus, since the reflected light 8 is also localized on the time axis, by intensity modulating the excitation light 9b to EDF12b so that it is input only when the reflected light 8 is present, a higher gain can be achieved even with the same time-averaged power.
[0041] <Optimal waveform of excitation light for backlight amplification> Since the waveform of the return light 8 is such that the intensity is strongest at the time of emission of the probe pulse light 7 into the next cable section 3c, and gradually weakens thereafter, it is better to make the intensity waveform of the excitation light the opposite. That is, the rising part of the return light 8 weakens the excitation light 9b, and as the return light 8 weakens, the excitation light 9b is strengthened. By doing so, the excitation light can be made more localized in the part where gain is required, and even with the same average power, a higher gain can be obtained.
[0042] Specifically, the intensity modulation waveform of the excitation light was set as a waveform with a duty ratio of about 40% as shown in FIG. 3, amplified by the high-power amplifier in FIG. 1, and sent to the remote amplification repeater. By matching the phase of the excitation light waveform with the timing when the return light passes through the amplification repeater, even when the average power of the excitation light is +4 dBm, the power at the time of passage of the probe pulse light could be increased to about +8 dBm.
[0043] <Further improvement obtained when the ping rate is sufficiently lower than the upper limit value> In this embodiment, an example was described in which the ping rate, that is, the emission frequency of the probe pulse light 7, was set to 350 Hz. This value is almost the upper limit for a cable length of 270 km. Since the time required for light to travel back and forth through the 270 km optical fiber is about 2.7 milliseconds, the probe pulse light 7 is emitted at a period of about 2.9 milliseconds with a margin (standby) time of about 0.2 milliseconds (T_pause in FIG. 5).
[0044] In DAS and the like that measure vibrations applied to the optical fiber at high speed, this ping rate is the measurement sampling rate, so a fast ping rate is often desired. On the other hand, for applications such as monitoring slow loss fluctuations, the ping rate can be slow. That is, T_pause can be made larger, for example, about 2.3 milliseconds. Combined with the time of about 2.7 milliseconds required for light to travel back and forth through the 270 km optical fiber, it is 5 milliseconds, that is, 200 Hz.
[0045] By widening the T_pause in this way, the duty cycle of both the probe pulse light 7 and the return light 8 is further reduced, making it easier to obtain the effects of the present invention. For example, as described above, if the pulse width of the excitation light for amplifying the return light from cable 3c is 500 μs and the ping rate is 200 Hz, the duty cycle can be reduced to 10%, so even with the same time-averaged power as the continuous light, the instantaneous excitation power can be increased by almost 10 times, and the gain can be increased accordingly.
[0046] <Measuring instruments suitable for optical amplification relay> The OTDR type measuring instrument to which this invention is effective is only that which does not use the intensity (power) of the reflected light as the measured value, such as DAS and BOTDR. Because DAS measures by detecting the phase change of the reflected light, and BOTDR measures by detecting the frequency change of the reflected light, slight changes in the intensity of the reflected light do not directly affect the measured value. Therefore, even if gain modulation is performed to reduce the difference between high and low power points of the reflected light, it does not affect the measured value.
[0047] <Transfer function from excitation light intensity modulation to optical amplifier gain modulation> Here, we discuss the transfer function by which the intensity modulation of the excitation light is converted into the gain modulation of the optical amplifier. In this embodiment, an EDFA is used as an example of the optical amplifier. In the case of an EDFA, it is known that the modulation bandwidth is about 20 kHz, depending on the conditions. For excitation light intensity modulation at frequencies higher than 20 kHz, the gain modulation decreases.
[0048] In the case of an OTDR type measuring instrument like the present invention, the ping rate is limited by the length of the optical fiber being measured. Once one probe pulse is output, the next probe pulse cannot be output until it reaches the far end of the optical fiber and the reflected light generated near the far end returns to the measuring instrument. It is necessary to wait for the time it takes for the light to travel back and forth through the optical fiber. Specifically, if the optical fiber length is 100 km, the upper limit of the ping rate is approximately 1 kHz. Since the present invention relates to excitation light modulation to an optical amplifier located more than 100 km away, the ping rate is typically several hundred Hz, which is sufficient to modulate the gain of the optical amplifier. Furthermore, in the present invention, the excitation light is subjected to intensity modulation with a somewhat complex waveform, with a duty cycle less than 0.5, while the ping rate is used as the period. In other words, it has harmonic components. Some degree of attenuation occurs in these harmonic components, causing distortion in the gain modulation waveform. For this reason, it is desirable that the intensity modulation waveform of the excitation light be a waveform that slightly emphasizes the harmonic components.
[0049] <Noise reduction effect> A secondary effect of this invention is noise reduction. This is because the gain of the optical amplifier is modulated by modulating the intensity of the excitation light, so the generation of ASE (Amplified Spontaneous Emission) optical noise emitted by the optical amplifier is reduced during periods when the gain is low.
[0050] Referring again to Figures 4 and 5, for example, at point C, the gain of the return light amplifier at point C is only necessary when the return light from Span #3 passes through, and no gain is needed at other times. By applying this gain modulation, the output of ASE light is suppressed except during the time when the return light from Span #3 passes through. As a result, the superposition of ASE light from the amplifier at point C is suppressed during the time when the return light from Spans #1 and #2 at point A passes through, and the degradation of measurement performance caused by ASE light superposition is suppressed.
[0051] <Second Example> A modified version of the excitation light source in the first embodiment will be explained using Figures 6 and 7. Since only the configuration of the excitation light source differs from the first embodiment, other parts are omitted.
[0052] In the first embodiment, the excitation light source is realized by a combination of an excitation light source 5 that outputs continuous light and intensity modulators 22a and 22b, but in the second embodiment, direct modulation of semiconductor lasers 23a and 23b is used.
[0053] The most widely used excitation source for remote excitation today is a semiconductor laser with a wavelength of approximately 1.48 μm. A semiconductor laser is a type of diode in terms of its electronic circuitry. By passing a forward current through the diode, the photo-semiconductor is excited, the light is amplified, and the laser oscillates. Modulating this forward current modulates the intensity of the laser output light. This is called direct modulation and is one of the widely used intensity modulation techniques.
[0054] When the laser oscillation is stopped and restarted by modulating the injection current into a semiconductor laser, the wavelength of the output light fluctuates significantly, which can lead to undesirable effects. In this application, a perfect extinction ratio is not required, so it is desirable to keep the lower limit of the injection current modulation within the range where the laser oscillation does not stop, that is, to modulate the output power by varying the current strength within the range of current above the laser oscillation threshold.
[0055] If direct modulation of a semiconductor laser can be used as the excitation light source, it can be implemented more economically than using an intensity modulator. Depending on the required excitation wavelength and output power, there may be cases where the direct modulation method of a semiconductor laser cannot be used or is difficult to implement, in which case a configuration using an intensity modulator can be used.
[0056] As shown in Figure 6, the directly modulated light from semiconductor lasers 23a and 23b may be transmitted as is, or, if a high-power optical amplifier in that wavelength band is available, it may be amplified by the high-power optical amplifier 6 as shown in Figure 7 before transmission.
[0057] <Third Example> In the first embodiment, the waveforms of the excitation light were optimized separately for the probe pulse light amplifier and the return light amplifier, but as shown in Figure 8, the waveforms may be made common. Furthermore, the excitation light 9 may be delivered to the amplifier repeater 2a via a single fiber and then branched at the 3dB coupler 14 in the amplifier repeater 2a for excitation. This allows the optical intensity modulators at the land terminal stations to be consolidated into a single unit. However, in this configuration, it becomes impossible to adjust the phase difference between the excitation light for the probe pulse light and the excitation light for the return light by adjusting the phase of the drive electrical signal of the intensity modulator, so the phase may be adjusted to some extent by inserting an optical fiber delay line of appropriate length.
[0058] The same applies to the second embodiment, in which the directly modulating semiconductor lasers may be combined into a single unit.
[0059] <Different variations not shown in the illustrations> In the first embodiment, the ping rate of the probe pulse light is obtained by splitting a portion of the probe pulse light, receiving it, and extracting the clock signal. However, if this signal can be obtained directly from an OTDR type measuring instrument, the signal can be used as is without splitting the probe pulse light and extracting the clock signal.
[0060] The light intensity modulator 22 may also be placed on the output side of the high-power amplifier 6. However, in this configuration, the input waveform of the high-power amplifier 6 is continuous light (CW light), so the effect of making the peak power value several times higher than the time-averaged output power of the high-power amplifier 6 cannot be obtained, and the energy efficiency is poor.
[0061] Even in systems where the probe pulse light 7 and the return light 8 are transmitted through separate core wires, the ingenuity of the present invention is effective and the desired results can be obtained.
[0062] In the examples, an EDFA (Er-doped fiber amplifier) was used as the optical amplifier. Currently, EDFA is the only optical amplifier for which remote excitation is practical, but similar effects can be obtained with other types of laser amplifiers by introducing the mechanism of the present invention. [Explanation of Symbols]
[0063] 1. Land-based terminal equipment 2,2a Amplifier Repeater 3a, 3b, 3c cable 4 OTDR type measuring device 5. Excitation light source (seed light source) 6. High-power amplifier 7. Probe pulsed light 8. Reflected light 9,9a,9b Excitation light 10a, 10b Optical Circulator 11a, 11b Optical bandpass filters (OBPF) 12a, 12b Erbium-doped optical fiber (EDF) 13a, 13b Excitation light / signal light WDM filter 14 3dB coupler 20 Branch Coupler 21 Modulated signal generation period 22a, 22b, 22c Light intensity modulator 23a, 23b Semiconductor laser (excitation light source) 30 3dB coupler
Claims
1. An OTDR type measuring instrument that outputs probe pulse light to an optical fiber, analyzes the scattered return light from the optical fiber, and measures ambient environmental information at the scattering point of the optical fiber, The optical fiber, An amplification repeater is placed in the middle of the optical fiber and is equipped with an optical amplifier that compensates for the attenuation of the signal light of the OTDR type measuring instrument (i.e., the probe pulse light and the return light), The light source for the excitation light required by the optical amplifier, Optical fiber that delivers the excitation light from the light source to the amplifier repeater In an OTDR type measurement system, which consists of the following, The system includes means for modulating the intensity of the excitation light, The intensity and phase of the excitation light are adjusted so that the excitation light is strongly input to the optical amplifier at the timing when the signal light of the OTDR type measuring instrument passes through the optical amplifier. An OTDR-type measurement system using remote excitation amplification.
2. The probe pulse light and the return light are transmitted bidirectionally through the same optical fiber core. The aforementioned amplifier repeater is A component that can perform wave splitting and combined wave operation based on direction, such as with a circulator, The system comprises the optical amplifier for the probe pulse light and the optical amplifier for the return light, The system involves splitting the signal in each direction, amplifying each signal, and then combining them again in the same direction. An OTDR type measurement system using remote excitation amplification as described in claim 1.
3. The probe pulse light and the return light are transmitted in opposite directions through separate optical fiber cores. The aforementioned amplifier repeater includes: The optical amplifier for the probe pulse light is located in the probe pulse light transmission optical fiber. The optical amplifier for the return light is inserted into the optical fiber for the return light transmission, Furthermore, the return light from the probe pulse optical transmission optical fiber is decoupled by a decoupler and combined with the return light transmission optical fiber by a multiplexer. An OTDR type measurement system using remote excitation amplification as described in claim 1.
4. For the excitation light used in the return light amplifier, the intensity-modulated waveform should have a small rising edge and a large falling edge. An OTDR type measurement system using remote excitation amplification according to any one of claims 1 to 3.
5. The intensity modulation means for the excitation light is an intensity modulator. An OTDR type measurement system using remote excitation amplification as described in claim 1.
6. The intensity modulation means for the excitation light is direct modulation of the semiconductor laser that generates the excitation light. An OTDR type measurement system using remote excitation amplification as described in claim 1.