JP2008131592A - Optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication system capable of reducing crosstalk because of non-linear optical effect such as induced Raman scattering or the like in optical fiber thereby improving the signal quality of a video signal or the like which generates wavelength multiplex. <P>SOLUTION: An OLT (optical line termination) is provided with a frame scrutinization unit 16 which detects an idle signal which repeats periodical fixed bit pattern from a down signal to an ONU (optical network unit) and a dummy frame producer 17 which inserts the dummy frame filled with scramble data with respect to the idle signal detected by the frame scrutinization unit 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical communication system based on a passive optical network (PON) in which an optical video signal is wavelength-multiplexed with an optical communication signal.

  With the explosive spread of the Internet in recent years, higher speed and higher density in access optical transmission technology are expected more and more. In addition, the spread of access optical fibers has dramatically improved. From the viewpoint of efficient use of transmission lines, in addition to the wavelength signal light in the upstream 1310 nm and downstream 1490 nm bands used in the PON technology, Analog video distribution technology using wavelength signal light has been actively researched.

  In such a single-core bidirectional PON system in which a video signal is wavelength-multiplexed with such an optical communication signal, a downstream signal distributed from a station side device (OLT; Optical Line Terminal) is converted from an electrical signal by a distributed feedback FP laser. After being converted into an optical signal, it is transmitted in the optical transmission line by a carrier wave having an output of about 2 mW in the wavelength 1490 nm band. Also, the analog video signal of the video source in which AM modulation is applied to the optical signal carrier wave in the 1550 nm band is combined with the downstream signal by the optical multiplexer having wavelength selection property, and transmitted to the single-core trunk optical fiber.

  On the other hand, an upstream signal transmitted from a subscriber side device (ONU; Optical Network Unit) to the OLT is output after being modulated by a light source having a wavelength of 1310 nm, and the upstream signal from each ONU is multiplexed by an optical multiplexer. And transmitted to the trunk optical fiber. In the optical branching station connected to the trunk optical fiber, the analog video signal light and the downlink signal that have passed through the trunk optical fiber are demultiplexed for each wavelength and supplied to each ONU.

  In addition, with the demand for broadband by subscribers, a GE-PON (Gigabit Ethernet (registered trademark) -PON) system capable of gigabit transmission based on IEEE 802.3ah has been developed. For example, in an optical communication system using GE-PON disclosed in Patent Document 1, idle pattern data transmitted from the ONU to the OLT is converted into data transmitted as a low-level optical signal by the OLT. This eliminates data loss caused by collision of idle pattern data from other ONUs to which no bandwidth is allocated while ONUs and OLTs to which bandwidth is allocated transmit and receive data.

JP 2003-283522 A

  In a conventional optical communication system using PON, an idle signal of CSMA / CD (Carrier Sense Multiple Access with Collision Detection) method transmitted from the OLT to the ONU, that is, when there is no downlink data from the OLT to the ONU is transmitted. Since the idle pattern signal is a fixed bit pattern, the same pattern is repeated in the physical layer. When the same pattern is repeated in this way, a specific spectrum appears strongly in the optical signal as the physical layer.

  For example, when transmitting idle pattern data having a predetermined frequency (62.5 MHz) in the downstream 1490 nm band, if the idle signal and the analog video signal in the 1550 nm band are simultaneously conducted through the trunk optical fiber, the light wave in the wavelength 1490 nm band is transmitted through the optical fiber. The light wave having a wavelength of 1550 nm is emitted by stimulated Raman scattering due to the lattice vibration of quartz. The light wave having a wavelength of 1550 nm caused by the idle signal includes a fundamental harmonic of the predetermined frequency and its multiplied wave, and if a harmonic frequency component is generated in the vicinity of the video signal, it becomes an interference wave for the video signal. The video signal becomes distortion crosstalk (crosstalk) and degrades the video.

  In addition, although the system of patent document 1 converts idle pattern data into data transmitted as a low-level optical signal by OLT, the stimulated Raman scattering due to the idle signal as described above is not considered, Crosstalk caused by this cannot be prevented.

  The present invention has been made to solve the above-described problems, and reduces crosstalk caused by nonlinear optical effects such as stimulated Raman scattering in an optical fiber and improves signal quality of a wavelength-multiplexed video signal or the like. An object of the present invention is to obtain an optical communication system that can be used.

  An optical communication system according to the present invention includes a station-side device and a plurality of subscriber-side devices, and a single-core optical transmission path is provided between the station-side device and the subscriber-side device via an optical multiplexer / demultiplexer. In the connected optical communication system, the station side device detects a signal that repeats a periodic fixed bit pattern from the downlink signal to the subscriber side device, and the signal detected by the scrutiny unit is periodic. And a dummy data insertion unit for inserting dummy data having no periodicity instead of the fixed bit pattern.

  According to the present invention, the station side device detects a signal that repeats a periodic fixed bit pattern from the downlink signal to the subscriber side device, and the periodic fixing for the signal detected by the review unit Since a dummy data insertion unit for inserting dummy data having no periodicity instead of a bit pattern is provided, a non-linear optical effect is applied to a signal of a specific frequency (for example, an analog video signal using a signal light having a wavelength of 1550 nm). Since a signal (for example, a CSMA / CD idle signal using a light wave having a wavelength of 1490 nm) that repeats a periodic fixed bit pattern that has an influence becomes dummy data (for example, scrambled data) having no periodicity, The influence by the nonlinear optical effect can be suppressed. As a result, for example, crosstalk caused by nonlinear optical effects such as the stimulated Raman effect in a single optical transmission line can be reduced, and the signal quality of video signals and the like that are wavelength-multiplexed can be improved. .

Embodiment 1.
FIG. 1 is a diagram showing the configuration of an optical communication system according to Embodiment 1 of the present invention. The present invention is applied to a single-core bidirectional GE-PON system that wavelength-multiplexes a video signal with an optical communication signal. Show. The communication OLT (station side device) 1a and the video OLT 1b are connected to the upper side of the WDM coupler 4 through optical transmission lines 2a and 2b, respectively. Further, on the lower side of the WDM coupler 4, a 4-to-1 optical multiplexer / demultiplexer 7, a trunk optical fiber transmission line (single-core optical transmission line) 3 and a WDM coupler 5 are sequentially connected.

  The communication ONU 6a and the video ONU 6b are connected to the lower side of the WDM coupler 5 through an optical transmission path. The communication OLT 1 a is connected to a host device of the host network 9 via a GE-PON NNI (Network Node Interface) 8 that is a connection interface between the communication OLT 1 a and the host network 9.

  In the present invention, a signal transmitted from the higher level network 9 to the OLTs 6a and 6b via the OLTs 1a and 1b is set as a downstream signal, and is transmitted from the lower level devices of the lower level network to the higher level network 9 via the OLTs 6a and 6b and the OLTs 1a and 1b. This signal is assumed to be an upstream signal.

  The downstream signal A transmitted from the communication OLT 1a is transmitted through the optical transmission line 2a with an optical signal carrier wave of about +4 dBm (2 mW) from the output of the wavelength 1490 nm band. The video signal B transmitted from the video OLT 1b is an analog video signal of a video source in which AM modulation is applied to an optical signal carrier having a wavelength of 1550 nm. This video signal B is input to the WDM coupler 4 having wavelength selection property through the optical transmission line 2 b, and is combined with the downstream signal A from the communication OLT 1 a by the WDM coupler 4, and then through the optical multiplexer / demultiplexer 7. A single-core trunk optical fiber transmission line 3 is transmitted.

  The WDM coupler 5 demultiplexes the signal light of the downstream signal A and the signal light of the analog video signal B transmitted through the trunk optical fiber transmission line 3 for each wavelength, and transmits the downstream signal A and the video ONU 6b to the communication ONU 6a. To output a video signal B. The video ONU 6b receives the video signal B and reproduces the video. The upstream signal C transmitted from the communication ONU 6 a to the communication OLT 1 a is obtained by modulating the optical signal carrier wave in the wavelength 1310 nm band, and transmits the trunk optical fiber transmission line 3 through the WDM coupler 5.

  FIG. 2 is a block diagram showing the configuration of the communication OLT in FIG. In FIG. 2, the communication OLT 1 a includes an O / E conversion unit 10, a SERDES 12, an FPGA 14, and a GigaPHY 15. The O / E conversion unit 10 includes a WDM coupler 11, and demultiplexes an upstream signal C having a wavelength of 1310 nm from an optical signal propagating through the optical transmission line 2 a by the WDM coupler 11. The light is converted into an electrical signal and output to the SERDES 12. Further, the O / E conversion unit 10 converts the electrical signal from the higher-level network 9 input via the SERDES 12 into a downstream signal A having a wavelength of 1490 nm and outputs it to the optical transmission line 2a.

  The SERDES 12 is a serializer / deserializer that is a serial-parallel converter, and serializes an electrical signal from the upper network 9 or parallelizes a serial signal from the lower network. The PON LSI 13 is configured to perform PON control of the optical access system according to the first embodiment, and executes processing such as allocation of a communication band to the ONU.

  An FPGA (Field Programmable Gate Array) 14 is a device that can be reconfigured by programming. The FPGA 14 according to the first embodiment constitutes a PON control circuit, a frame scrutiny unit (scrutiny unit) 16, and a dummy frame generation unit (dummy data insertion unit) 17. A PON control circuit (not shown) relays signals between the PON LSI 13 and the GigaPHY 15 and sends idle pattern data. The frame scrutinizing unit 16 scrutinizes the frame of the downstream signal. The dummy frame generation unit 17 inserts a dummy frame. As idle pattern data, for example, there is a K28.5 pattern (00111111010) which is an Ethernet (registered trademark) idle signal.

  The GigaPHY 15 is configured to function as a physical layer of the communication OLT 1a, and converts an input upstream signal into a signal that conforms to the specification of the GE-PON NNI8 on the upper network 9 side, or converts a downstream signal into a frame scrutiny unit of the FPGA 14 16 is converted into a signal that can be handled.

  The frame scrutinizing unit 16 scrutinizes the frame of the downstream signal and controls the dummy frame generating unit 17 based on the result. For example, when the main signal IFG (Inter Frame Gap = MAC (Media Access Control) packet interval) in the downstream signal is checked and the byte size of the IFG is equal to or larger than a predetermined value (for example, 84 bytes), the idle pattern data during this period is video. It is determined that the signal is affected, and the dummy frame generation unit 17 is controlled to insert a dummy frame in the corresponding part.

  The dummy frame generator 17 inserts a dummy frame from the GE-PON NNI 8 side when idle pattern data is detected in the downstream signal by the frame scrutinizer 16. As a dummy frame, for example, the frame length is 72 bytes, DA (Destination Address) is broadcast, EtherType is 0x0800 (IPv4) broadcast frame (destination MAC address is all bit value 1), scramble data is filled Output to the PON LSI 13.

  In the present invention, scramble refers to conversion to a random pattern by scrambling encoding idle pattern data that is a fixed bit pattern. Thereby, generation | occurrence | production of the spectrum of the specific period by periodic idle pattern data is suppressed.

  In the scramble coding, the original signal sequence is converted into a different signal sequence according to a certain conversion rule, and the mark rate is approximately 1 regardless of the mark rate of the original signal sequence (probability of appearance of “1” of the digital code). A random signal sequence of / 2. For example, the idle pattern data is scrambled by taking the exclusive OR of the pattern generated by the dummy frame generation unit 17 and the original signal sequence.

  FIG. 3 is a block diagram showing the configuration of the ONU in FIG. In FIG. 3, the communication ONU 6 a includes an O / E converter 18, a SERDES 20, and a frame filter 21. The O / E conversion unit 18 includes a WDM coupler 19, which demultiplexes a downstream signal A having a wavelength of 1490 nm from an optical signal propagating through the optical transmission line by the WDM coupler 19. Is converted into an electrical signal and output to the SERDES 20. The O / E conversion unit 18 converts the electrical signal from the lower network input via the SERDES 20 into an upstream signal C having a wavelength of 1310 nm band and outputs the upstream signal C to the optical transmission line.

  The SERDES 20 is a serializer / deserializer, and serializes electrical signals from the lower network or parallelizes serial signals from the upper network 9. The frame filter 21 filters the dummy frame data so as not to pass through to the lower network side. For example, when a broadcast frame obtained by converting an idle signal is detected by the OLT 1a, filtering is performed on the broadcast frame.

Next, the operation will be described.
Parallel data serving as a downstream signal output from a PON control circuit (not shown) configured by the FPGA 14 is input to the frame review unit 16. The frame scrutinizing unit 16 checks the main signal IFG in the downstream signal, and determines that the idle pattern data during this period affects the video signal if the byte size of the IFG is greater than or equal to a predetermined value. Thereby, under the control of the frame scrutinizing unit 16, the dummy frame generating unit 17 inserts a dummy frame into the idle pattern data.

  FIG. 4 is a diagram for explaining dummy frame insertion processing. As shown in FIG. 4, the idle pattern data output from the PON control circuit has a unique bit pattern repeated at a cycle of 62.5 MHz. Therefore, when it is determined that the repetition of a predetermined value or more is detected in the main signal IFG check by the frame scrutinizing unit 16 and it is determined that the dummy frame needs to be inserted, the dummy frame generating unit 17 adds the dummy frame to the subsequent idle pattern data. Insert and fill the scramble data 22.

  In the example shown in FIG. 4, when idle pattern data is transmitted for 0.8 ns in the downstream signal transmitted at a transmission rate of 1.25 Gbps (when two fixed bit patterns of idle pattern data are consecutive), a dummy frame needs to be inserted. It is judged. Thereby, the dummy frame generation unit 17 inserts a broadcast frame as a dummy frame into the subsequent idle pattern data, scrambles the fixed bit pattern of the idle pattern data, and converts the scrambled data 22 that is a random pattern into the broadcast frame. To fill. In this way, the periodic fixed bit pattern of the idle pattern data is converted into scrambled data, and the frequency component resulting from the repetition of the fixed bit pattern is smoothed.

  The downstream signal filled with the scrambled data 22 is used as transmission data to the ONU to which the band is assigned by the PON LSI 13, serialized by the SERDES 12, and then converted into an optical signal having a wavelength of 1490 nm by the O / E converter 10. And output to the optical transmission line 2a. On the other hand, the downstream video signal is also output as a modulation signal from the video OLT 1b and is transmitted to the optical transmission line 2b as an optical signal having a wavelength of 1550 nm.

  These optical signals are wavelength multiplexed by the WDM coupler 4 and transmitted through the single-core trunk optical fiber transmission line 3 via the optical coupler 7. The transmitted optical signal is subjected to wavelength separation by the WDM coupler 5 and separated into an optical signal for data communication and an optical signal for video and then input to the communication ONU 6a and the video ONU 6b, respectively.

  In the ONU 6a, the downstream signal A having a wavelength of 1490 nm is demultiplexed from the optical signal propagating through the optical transmission line by the WDM coupler 19 in the O / E converter 18, and the signal light of the downstream signal A is converted into an electrical signal. Output to SERDES 20. In the SERDES 20, the serial data from the O / E conversion unit 18 is converted into parallel data and output to the frame filter 21.

  The frame filter 21 filters the dummy frame data so as not to pass through to the lower network side. For example, the SA (Source Address) of the received frame is detected, and if the SA is a broadcast address, it is determined that the SA is a broadcast frame filled with scrambled data 22, and is filtered by the frame filter 21 and discarded.

  While actual data is being transmitted, idle pattern data is not transmitted and no dummy frame is inserted. Therefore, the communication OLT 1a only needs to obtain the actual data of the data communication signal. Therefore, the frame filter 21 is not an essential configuration in the communication OLT 1a.

  In the video ONU 6b, the O / E converter converts the optical signal into an electrical signal, and outputs the electrical signal to a lower-level network device that reproduces the video signal. At this time, as described above, the frequency component of the idle pattern data that affects the video signal is smoothed and crosstalk superimposed on the analog video signal is improved, so that it is received by the video ONU 6b. The quality of the video signal can be improved.

Next, a CNR (Carrier-to-Noise Ratio) measurement result with respect to a ratio (idle pattern occurrence rate) of transmitting idle pattern data as a downlink signal by OLT will be described.
FIG. 5 is a graph showing a line spectrum by a simulated carrier signal simulating a video signal and an idle pattern. In the system shown in FIG. 1, the CNR measurement is performed under the condition that the output of the communication OLT 1a is +4.3 dBm, the analog video output of the video OLT 1b is +19 dBm, and the optical fiber length of the trunk optical fiber transmission line 3 is 10 km. .

  In addition, 1550 nm light (simulated carrier signal) simulating an analog video signal is modulated with a 50 MHz sine wave (modulation factor 5.6%) to measure CNR, and an optical fiber (not shown) in the video OLT 1b is used. It is amplified to +19 dBm with an amplifier (EDFA). The communication OLT 1a outputs only a fixed bit pattern of idle pattern data as an optical signal having a wavelength of 1490 nm (idle pattern occurrence rate 100%).

  As shown in FIG. 5, the CNR was measured from the intensity ratio between the simulated carrier signal modulated at 5.6% and the line spectrum caused by the idle pattern of the optical signal in the wavelength 1490 nm band from the communication OLT 1a. From FIG. 5, it can be seen that line spectra caused by the idle pattern are generated at 62.5 MHz, 125 MHz, and 187.5 MHz by inserting (sweeping) the modulation frequency. In particular, the line spectrum with a frequency of 62.5 MHz is close to the frequency 50 MHz of the simulated carrier signal, which causes crosstalk.

  FIG. 6 is a graph showing measurement results of CNR with respect to the idle pattern occurrence rate. FIG. 6 shows a CNR measurement result when the idle pattern occurrence rate is changed by performing the above-described processing and converting the fixed bit pattern of the idle pattern data into scrambled data in the communication OLT 1a.

  As shown in FIG. 6, it can be seen that the CNR is remarkably improved by lowering the idle pattern occurrence rate. For example, compared with the case where the idle pattern occurrence rate is 100%, when the idle pattern occurrence rate is 20%, the CNR based on the line spectrum of the frequency 62.5 MHz is 9.2 dB and the CNR based on the line spectrum of the frequency 125 MHz is 10.0 dB improvement.

  As described above, according to the first embodiment, the fixed bit pattern is periodically repeated in the communication data of the optical signal of the wavelength 1490 nm band multiplexed with the optical signal of the analog video signal of the wavelength 1550 nm band. The frame scrutinizing unit 16 for detecting the idle pattern data to be detected and the dummy frame generating unit 17 for inserting a dummy frame into the detected idle pattern data are provided. The resulting nonlinear optical effect in the optical fiber can be suppressed. As a result, crosstalk due to the nonlinear optical effect can be reduced, and the signal quality of a video signal or the like to be wavelength-multiplexed can be improved.

Embodiment 2. FIG.
FIG. 7 is a diagram showing a configuration of an optical communication system according to the second embodiment of the present invention. As in the first embodiment, a single-core bidirectional GE-PON system that wavelength-multiplexes a video signal with an optical communication signal. The case where it applies to is shown. In FIG. 7, the same or equivalent components as those in FIG.

  In FIG. 7, in the system of the second embodiment, unlike the system configuration shown in the first embodiment, a 4-to-1 optical multiplexer / demultiplexer (output reduction means) 23 is provided between the communication OLT 1a and the WDM coupler 4. Provided. The optical multiplexer / demultiplexer 23 is an optical multiplexer / demultiplexer having no wavelength selection property, and an optical signal propagating through the optical transmission path 2a passes through the optical multiplexer / demultiplexer 23, so that the optical signal output is reduced to a quarter. To do. For example, if the output of the communication OLT 1a is +4 dBm (2 mW), the optical multiplexer / demultiplexer 23 reduces the output to a sub mW of about 0.5 mW.

Next, similarly to the first embodiment, a CNR (Carrier-to-Noise Ratio) measurement result with respect to a ratio (idle pattern occurrence rate) of transmitting idle pattern data as a downlink signal by OLT will be described.
FIG. 8 is a graph showing the measurement result of CNR with respect to the idle pattern occurrence rate. In the system shown in FIGS. 1 and 7, the CNR measurement is performed in the same manner as in the first embodiment. The output of the communication OLT 1a is +4.3 dBm, the analog video output of the video OLT 1b is +19 dBm, and the trunk optical fiber transmission line 3 The optical fiber length is 10 km.

  In addition, 1550 nm light (simulated carrier signal) simulating an analog video signal is modulated with a 50 MHz sine wave (modulation factor 5.6%) to measure CNR, and an optical fiber (not shown) in the video OLT 1b is used. It is amplified to +19 dBm with an amplifier (EDFA). The communication OLT 1a outputs only a fixed bit pattern of idle pattern data as an optical signal having a wavelength of 1490 nm (idle pattern occurrence rate 100%). The CNR was measured from the intensity ratio between the simulated carrier signal modulated at 5.6% and the line spectrum caused by the idle pattern by the optical signal in the wavelength 1490 nm band from the communication OLT 1a.

  In FIG. 8, as in the first embodiment, in the communication OLT 1a, when the idle pattern occurrence rate is changed by performing the above-described processing and converting the fixed bit pattern of the idle pattern data into scrambled data. The measurement result of CNR is shown.

  The difference from the first embodiment is that the square plot is obtained by branching the output of the communication OLT 1a into four by the optical multiplexer / demultiplexer 23 shown in FIG. 7 and reducing the power level to the sub mW order. The diamond-shaped plot shows the case where the output of the communication OLT 1a is transmitted to the WDM coupler 4 without branching, as in FIG.

  As shown in FIG. 8, the CNR is improved by lowering the idle pattern occurrence rate, but it can be seen that the CNR is further improved by branching the output of the communication OLT 1a by the optical multiplexer / demultiplexer 23. . For example, when the idle pattern occurrence rate is 100%, the CNR due to the line spectrum of the frequency 62.5 MHz is improved by 10.2 dB in the case of no branch and 1 × 4 branch, and in the case where the idle pattern occurrence rate is 20% None and 1 × 4 branch, and 1 × 4 branch improves CNR by 10.6 dB.

  As described above, according to the second embodiment, since the optical multiplexer / demultiplexer 23 for reducing the output of the communication OLT 1a is provided, the idle pattern data that is wavelength-multiplexed with the optical signal of the wavelength 1550 nm band by the analog video signal. The power level of the optical signal in the wavelength 1490 nm band including can be reduced. As a result, the gain of the Raman effect using signal light in the wavelength 1490 nm band as the excitation light source is reduced, crosstalk superimposed on the analog video signal transmitted in the wavelength 1550 nm band is improved, and the quality of the video signal is improved. Can do.

  In the second embodiment, the optical multiplexer / demultiplexer 23 is connected to the output side (lower network side) of the communication OLT 1a. However, as shown in FIG. 9, the fixed attenuator (attenuator, output reduction) is shown. Means) 24 may be provided. The fixed attenuator 24 has a function of reducing the output of the communication OLT 1a to the sub-mW order, like the optical multiplexer / demultiplexer 23. Also with this configuration, the same effect as in the second embodiment can be obtained. The present invention is not limited to the optical multiplexer / demultiplexer 23 and the fixed attenuator 24 as long as it has a function of reducing the output of the communication OLT 1a to the sub-mW order.

  Furthermore, in the second embodiment, the example in which the optical multiplexer / demultiplexer 23 is provided in the configuration of the first embodiment has been described. However, the present invention is not limited to this, and the communication OLT 1a adds a dummy frame to the idle pattern data. It does not have to have the function of inserting. Alternatively, the optical multiplexer / demultiplexer 23 and the fixed attenuator 24 may be provided on the optical transmission line 2a that connects the communication OLT 1a and the WDM coupler 4.

It is a figure which shows the structure of the optical communication system by Embodiment 1 of this invention. It is a block diagram which shows the structure of communication OLT in FIG. It is a block diagram which shows the structure of ONU in FIG. It is a figure for demonstrating the insertion process of a dummy frame. It is a graph which shows the line spectrum by the simulation carrier signal which simulated the video signal, and an idle pattern. It is a graph which shows the measurement result of CNR with respect to an idle pattern generation rate. It is a figure which shows the structure of the optical communication system by Embodiment 2 of this invention. It is a graph which shows the measurement result of CNR with respect to an idle pattern generation rate. It is a figure which shows the other structure of the optical communication system by Embodiment 2. FIG.

Explanation of symbols

  1a OLT for communication (station side equipment), 1b OLT for video, 2a, 2b optical transmission line, 3 trunk optical fiber transmission line (single core optical transmission line), 4,5 WDM coupler, 6a ONU for communication, 6b video ONU, 7 Optical multiplexer / demultiplexer, 8 GE-PON NNI, 9 Host network, 10, 18 O / E converter, 11, 19 WDM coupler, 12, 20 SERDES, 13 PON LSI, 14 FPGA, 15 GigaPHY, 16 Frame scrutiny unit (scrutiny unit), 17 Dummy frame generation unit (dummy data insertion unit), 21 Frame filter, 22 Scramble data, 23 Optical multiplexer / demultiplexer (output reduction means), 24 Fixed attenuator (attenuator, output reduction means) ).

Claims (5)

In an optical communication system comprising a station-side device and a plurality of subscriber-side devices, wherein the station-side device and the subscriber-side device are connected by a single optical transmission line via an optical multiplexer / demultiplexer,
The station side device
A scrutinizing unit for detecting a signal that repeats a periodic fixed bit pattern from a downstream signal to the subscriber side device;
An optical communication system, comprising: a dummy data insertion unit that inserts dummy data having no periodicity in place of a periodic fixed bit pattern with respect to a signal detected by the examination unit.   2. The optical communication system according to claim 1, wherein an output reduction means for reducing the output level of the station side device is provided between the station side device and the optical multiplexer / demultiplexer.   3. The output reduction means is at least one of an optical multiplexer / demultiplexer without wavelength selection that branches the output of the station side device or an attenuator that reduces the output level of the station side device. Optical communication system. In an optical communication system comprising a station-side device and a plurality of subscriber-side devices, wherein the station-side device and the subscriber-side device are connected by a single optical transmission line via an optical multiplexer / demultiplexer,
An optical communication system comprising output reduction means for reducing the output level of the station side device between the station side device and the optical multiplexer / demultiplexer.   The output reduction means is at least one of an optical multiplexer / demultiplexer without wavelength selection for branching the output of the station side apparatus or an attenuator for reducing the output level of the station side apparatus. Optical communication system.

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