JP5414373B2 - Optical access network, optical communication method, and optical subscriber unit - Google Patents

Description

  The present invention relates to an optical access network, an optical communication method, and an optical subscriber unit.

  In recent years, with the increase of data communication traffic including the Internet, an optical access network using a time division multiplexing (TDM) technique has been spreading. In particular, in Japan and North America, high-speed access is realized by introducing services such as IEEE-compliant GE-PON (Gigabit Ethernet Passive Optical Network) and ITU-T-compliant G-PON (Gigabit-capable Passive Optical Network). ing.

  FIG. 1 is a block diagram showing a configuration example of an optical access network in GE-PON or G-PON. In this optical access network, optical subscriber units (ONU: Optical Network Unit) 1-1 to 1-N (N is a plurality) arranged in each subscriber, and a accommodating station device 2 arranged in the accommodating station. Are coupled through a common optical fiber 4 using a power splitter 3. In an actual optical access network, downlink signals transmitted from the accommodating station device 2 to the optical subscriber units 1-1 to 1-N and transmitted from the optical subscriber units 1-1 to 1-N to the accommodating station device 2 are transmitted. A different wavelength is assigned to each upstream signal, and bidirectional transmission is performed on the same optical fiber 4. Here, only the upstream signal transmission configuration is shown.

  Each of the optical subscriber units 1-1 to 1-N stores a data signal to be transmitted in a frame and transmits it to the accommodating station device 2. Frames transmitted from the optical subscriber units 1-1 to 1 -N are combined in the power splitter 3. Here, in order to avoid frame collision, the timing at which each optical subscriber unit 1-1 to 1-N transmits a frame is controlled by the accommodating station device 2. Therefore, the frames combined by the power splitter 3 are multiplexed in the time axis direction without overlapping each other as shown in the illustration of FIG.

  In GE-PON and G-PON, such a multiplexing technique is used to share a high-speed line rate of 1 Gb / s or more among a plurality of subscribers. According to the configuration of this optical access network, since the optical fiber 4 that couples the accommodation station device 2 and the power splitter 3 is shared, a high-speed optical access system can be realized at low cost.

  Consider making this optical access network longer or multi-branched. Increasing the distance of the optical fiber and increasing the number of branches of the power splitter 3 increase the optical loss from the accommodation station device 2 to the optical subscriber units 1-1 to 1-N. The technology to overcome it is common. A representative technique is a technique for increasing the reception sensitivity.

  FIG. 15 is a block configuration diagram illustrating an example in which reception sensitivity is increased by using a coherent optical detection technique as a configuration example of the optical subscriber units 1-1 to 1-N illustrated in FIG. An example of this configuration is disclosed in Patent Document 1, for example. The optical subscriber unit 1 includes a light source 11, a duplexer 12, a modulator 13, a circulator 14, and a receiver 15. The upstream signal modulates the output of the light source 11 with the data signal in the modulator 13 and is transmitted to the accommodation station via the circulator 14. On the other hand, the downlink signal transmitted from the accommodation station is received by the receiver 15 via the circulator 14. At that time, the receiver 15 performs coherent optical detection using a part of the output of the light source 11 demultiplexed by the demultiplexer 12. As a coherent optical detection method, homodyne optical detection or heterodyne optical detection can be used. Similarly, the upstream signal transmitted to the accommodation station can be received by coherent optical detection. According to this configuration, by sharing the light source used for uplink signal transmission and the light source used for coherent light detection, the reception sensitivity can be enhanced with a simple configuration.

  However, the configuration example shown in FIG. 15 multiplexes data signals transmitted / received by subscribers in the wavelength axis direction using wavelength division multiplexing (WDM) technology, as described in Patent Document 1. It is aimed to do. Patent Document 1 does not consider application to TDM technology.

  In order to apply coherent optical detection to GE-PON or G-PON based on TDM technology, the extinction ratio is very large as the modulator 13 of the optical subscriber unit 1 in the configuration example shown in FIG. Things are needed. If the extinction ratio of the modulator 13 is small, even if it is a time during which the optical subscriber unit 1 does not transmit a frame (non-transmission time), the optical power is output, albeit slightly. At that time, it collides with a frame transmitted by another optical subscriber unit, and the performance of the uplink signal is deteriorated due to interference noise. If the output of the light source 11 is turned off, interference can be avoided, but during that time, it becomes impossible to monitor the control frame for controlling the TDM system sent from the accommodating station apparatus 2 in the downlink signal.

  As described above, in the optical subscriber unit 1 having the configuration shown in FIG. 15, when the downstream signal is monitored, the optical power is transmitted to the optical access network, and the quality of the upstream signal output from the other optical subscriber unit is improved. It will deteriorate. Here, the application to GE-PON and G-PON has been described as an example, but the same problem can occur in any optical access network using a power splitter.

JP 2007-49597 A

  The present invention has been carried out under such a background. In an optical access network in which a plurality of optical subscriber units are accommodated by a receiving station device via a common optical transmission line, coherent optical detection is performed on a downstream signal. It is an object of the present invention to provide an optical access network, an optical communication method, and an optical subscriber unit that can monitor a downstream wavelength without degrading the performance of an upstream signal output from another optical subscriber unit. To do.

  According to a first aspect of the present invention, in an optical access network having a plurality of optical subscriber units and a receiving station unit that accommodates the plurality of optical subscriber units via a common optical transmission line, a plurality of optical subscriber units Each subscriber unit is a light source that continuously outputs light of a specific wavelength, a receiver that receives an optical signal by coherent optical detection using a part of the output of the light source, and the output of the light source is modulated by a data signal. And an optical access network comprising: a modulator for interrupting the input or output of the modulator so as not to interfere with an optical signal of another optical subscriber unit through a common optical transmission line Is done.

  According to a second aspect of the present invention, there is provided an optical communication method in which a plurality of optical subscribers and a receiving station that accommodates the plurality of optical subscribers communicate via a common optical transmission line. Each subscriber receives an optical signal by coherent optical detection using a part of the output of a light source that continuously outputs light of a specific wavelength, modulates the output of the light source with a data signal, and uses a common optical transmission line. There is provided an optical communication method characterized in that the output of modulation or the output of a light source used for modulation is blocked as necessary so as not to interfere with optical signals of other optical subscribers.

  According to a third aspect of the present invention, in an optical subscriber unit, a plurality of subscribers are respectively arranged in a plurality of subscribers of an optical access network connected to a receiving station via a common optical transmission line. A light source that outputs light of a specific wavelength, a receiver that receives a portion of the output of the light source by coherent optical detection, a modulator that modulates the output of the light source with a data signal, and a modulator There is provided an optical subscriber unit characterized by having a circuit breaker for blocking input or output.

  According to the present invention, it is possible to monitor a downstream wavelength without deteriorating the performance of an upstream signal output from another optical subscriber unit while performing coherent optical detection on the downstream signal.

It is a figure which shows the structural example of the optical access network which concerns on the 1st Embodiment of this invention. FIG. 2 is a block diagram illustrating a configuration example of an optical subscriber unit in the optical access network illustrated in FIG. 1. FIG. 3 is a block diagram showing a configuration example different from the configuration example shown in FIG. 2 of the optical subscriber unit in the optical access network shown in FIG. 1. FIG. 4 is a block diagram showing still another configuration example of the optical subscriber unit in the optical access network shown in FIG. 1 different from the configuration examples shown in FIGS. 2 and 3 respectively. FIG. 5 is a block diagram showing still another configuration example of the optical subscriber unit in the optical access network shown in FIG. 1 different from the configuration examples shown in FIGS. It is a block diagram which shows the structural example of the optical access network which applied the WDM technique to the existing network with which a accommodation station and a some subscriber are couple | bonded via a power splitter. It is a figure which shows an example of the WDM-PON wavelength arrangement | positioning used for the optical access network shown in FIG. FIG. 7 is a diagram illustrating an example of a correspondence relationship between an upstream wavelength and a downstream wavelength and a usage state in the optical access network illustrated in FIG. 6. It is a block diagram which shows the structural example of the optical subscriber apparatus using a coherent optical detection technique, and an optical access network using the same. It is a figure which shows an example of the wavelength arrangement | positioning used with the optical access network shown in FIG. FIG. 10 is a block diagram of an optical subscriber unit used in place of the optical subscriber unit in the optical access network shown in FIG. 9. FIG. 12 is a block configuration diagram of an optical subscriber unit different from the configuration shown in FIG. 11 used in place of the optical subscriber unit in the optical access network shown in FIG. 9. FIG. 13 is a block configuration diagram of an optical subscriber unit different from the configuration shown in FIGS. 11 and 12 used in place of the optical subscriber unit in the optical access network shown in FIG. 9. FIG. 14 is a block diagram of an optical subscriber unit different from the configuration shown in FIGS. 11 to 13 used in place of the optical subscriber unit in the optical access network shown in FIG. 9. It is a block block diagram which shows the example which raises reception sensitivity using a coherent optical detection technique as a structural example of the optical subscriber apparatus shown in FIG.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration example of an optical access network according to the first embodiment of the present invention. Here, as described in the section “Background Art”, a configuration example in GE-PON or G-PON will be described. This optical access network uses a power splitter 3 to connect a plurality of optical subscriber units 1-1 to 1-N and a plurality of optical subscriber units 1-1 to 1-N on a common optical transmission line. And a receiving station apparatus 2 that receives the data via an optical fiber 4. The timing at which each optical subscriber unit 1-1 to 1-N transmits a frame is controlled by the accommodating station device 2. The accommodating station apparatus 2 transmits a control frame for controlling the TDM system included in the downlink signal, and each optical subscriber unit 1-1 to 1-N monitors its control frame, thereby transmitting its own transmission frame. You can know the timing.

[Configuration example 1 of optical subscriber unit]
FIG. 2 is a block diagram showing a configuration example of the optical subscriber units 1-1 to 1-N in the optical access network shown in FIG. The optical subscriber unit 1 includes a light source 11, a duplexer 12, a modulator 13, a circulator 14, a receiver 15, and a circuit breaker 16.

  The light source 11 continuously outputs light having a specific wavelength. The duplexer 12 demultiplexes a part of the output of the light source 11. The modulator 13 modulates the output of the light source 11 with a data signal. The circulator 14 transmits the uplink signal output from the modulator 13 toward the accommodation station apparatus 2 and outputs the downlink signal transmitted from the accommodation station apparatus 2 to the receiver 15. Instead of the circulator 14, a 3 dB coupler can be used. The receiver 15 performs coherent optical detection on the downstream signal using a part of the output of the light source 11 demultiplexed by the demultiplexer 12. As a coherent optical detection method, homodyne optical detection or heterodyne optical detection can be used. The circuit breaker 16 blocks the output of the modulator 13 in accordance with a disable signal. Here, an example in which the circuit breaker 16 is disposed on the output side of the modulator 13 is shown, but the circuit breaker 16 is disposed on the input side of the modulator 13 and the output of the light source 11 input to the modulator 13 is blocked. You can also

  As the circuit breaker 16, an attenuator that can take a sufficient amount of attenuation can be used. The Disable signal supplied to the circuit breaker 16 is a signal indicating that the optical subscriber unit 1 is in a non-transmission time. This signal is generated by monitoring a control frame from the accommodation station device 2.

  By interrupting and releasing the optical signal output from the modulator 13 by the circuit breaker 16, interference with the optical signal of another optical subscriber unit on the optical transmission line 4 of the optical access network shown in FIG. Can be prevented. On the other hand, since the output of the light source 11 is not turned off, coherent reception is possible even during the non-transmission time, and the control frame from the accommodation station apparatus 2 can be monitored.

[Configuration example 2 of optical subscriber unit]
FIG. 3 is a block diagram showing another configuration example of the optical subscriber units 1-1 to 1-N in the optical access network shown in FIG. The optical subscriber unit 1 is different from the configuration example shown in FIG. 2 in that the circuit breaker is configured by a semiconductor optical amplifier (SOA) 17. As a drive signal for the semiconductor optical amplifier 17, an enable signal indicating that the optical subscriber unit 1 is transmitting time is used instead of the disable signal. That is, the drive current of the semiconductor optical amplifier 17 is modulated by the Enable signal. When the drive current does not flow, the semiconductor optical amplifier 17 completely absorbs the optical signal output from the modulator 13. That is, when the Enable signal is off, the output of the modulator 13 can be cut off. The semiconductor optical amplifier 17 may be disposed on the input side of the modulator 13 to block the output of the light source 11 input to the modulator 13.

[Configuration example 3 of optical subscriber unit]
FIG. 4 is a block diagram showing still another configuration example of the optical subscriber units 1-1 to 1-N in the optical access network shown in FIG. The optical subscriber unit 1 is largely different from the configuration examples shown in FIGS. 2 and 3 in that the modulator and the circuit breaker are constituted by the same semiconductor optical amplifier 18. By modulating the drive current of the semiconductor optical amplifier 18 with the transmission signal, the semiconductor optical amplifier 18 can have both functions of a modulator and a circuit breaker. Here, the transmission signal is a signal obtained by inputting the data signal to the switch 19 and turning the switch 19 from off to on in accordance with the enable signal being turned off to on (disable signal being turned on to off). When the port for driving the semiconductor optical amplifier 18 is divided into a data signal port and a bias port, a data signal and an Enable signal are input to each.

[Configuration example 4 of optical subscriber unit]
FIG. 5 is a block diagram showing still another configuration example of the optical subscriber units 1-1 to 1-N in the optical access network shown in FIG. The optical subscriber unit 1 is different from the configuration example shown in FIG. 3 in that a light source and a modulator are configured by a light source 20 that is directly modulated by a data signal to generate an FSK (Frequency Shift Keying) signal. As the light source 20 that generates the FSK signal, for example, a distributed feedback laser diode (DFB-LD) can be used.

  Since the FSK signal is modulated by frequency conversion, even when the data signal is off, the light source 20 outputs optical power that is almost the same as when it is on. For this reason, a big problem does not arise in reception of a downstream signal. However, if the spread of the optical spectrum by FSK modulation is large, the performance of the received downlink signal deteriorates. Therefore, it is desirable to use MSK (Minimum Shift Keying) with the smallest modulation index.

[Effect obtained by the first embodiment]
In the first embodiment described above, the optical subscriber units 1 and 1-1 to 1-N receive the downlink signal by the coherent optical detection method, while the uplink signal is other than its own transmission timing. Is blocked so that the light from the light sources 11 and 20 does not go out. Thereby, it is possible to receive the downlink signal with high sensitivity without deteriorating the performance of the uplink signal output by another optical subscriber unit while constantly monitoring the downlink signal. Further, by modulating the drive currents of the semiconductor optical amplifiers 17, 18, and 21, the function can be given to the semiconductor optical amplifiers 17, 18, and 19 without separately providing a circuit breaker. Further, if the FSK signal is generated by directly modulating the light source 20 with the data signal, the function of the light source 20 can be provided without providing a modulator separately.

[Second Embodiment]
The present invention can also be implemented in a WDM-PON in which WDM technology is applied to an optical access network. Before describing such an embodiment, WDM-PON will be described.

[WDM-PON]
With regard to WDM-PON in which WDM technology is applied to an access network, WDM-PON, which is being studied by various research institutes, can be subscribed without accelerating the electrical circuit by assigning one wavelength to one subscriber. The service bandwidth per person can be increased.

  It is expected that a provider providing a service using GE-PON or G-PON will consider using an existing network with a power splitter as a premise for introducing WDM-PON. This is because, if this is possible, the cost required for changing the existing network can be omitted. In addition, it is considered that it is desired to realize an ONU that does not depend on the wavelength, that is, a single-type (colorless) ONU. This is because when a plurality of types of ONUs having different transmission wavelengths and reception wavelengths are used, convenience is greatly reduced.

  FIG. 6 is a block diagram showing a configuration example of an optical access network in which a WDM technique is applied to an existing network in which a accommodating station and a plurality of subscribers are coupled via a power splitter. This optical access network includes optical subscriber units (ONUs) 31-1 to 31 -N arranged in each subscriber, and an optical terminal unit (OLT) 32 arranged as a receiving station device in the receiving station. And have. The optical subscriber units 31-1 to 31 -N are coupled to the optical fiber 34, which is a common optical transmission path, by the power splitter 33 disposed outside the accommodating station, and are accommodated in the optical terminator 32. Each of the optical subscriber units 31-1 to 31-N includes a transmitter 41, a receiver 42, a wavelength tunable filter 43, a multiplexer / demultiplexer 44, a detector 45, and a control circuit 46. The optical termination device 32 includes a wavelength multiplexer / demultiplexer 51 and N optical subscriber line units (OSUs) 52-1 to 52-N.

  The transmitter 41 can change the transmission wavelength, and in combination with the wavelength variable filter 43 that selects the reception wavelength, the optical subscriber units 31-1 to 31-N are made colorless. In order to make the optical subscriber units 31-1 to 31 -N colorless, it is necessary to consider the selection of the multiplexer / demultiplexer 44.

  FIG. 7 is a diagram illustrating an example of a WDM-PON wavelength arrangement. In FIG. 7, an upward arrow and a downward arrow indicate an upstream signal and a downstream signal, respectively. A dotted line indicates a wavelength position. In the figure, the upstream wavelength and the downstream wavelength are divided into different wavelength bands. In the case of this wavelength arrangement, it is desirable to use as the multiplexer / demultiplexer 44 a low-loss optical filter that collectively multiplexes and demultiplexes the wavelength bands of the upstream signal and downstream signal. An optical coupler may be used instead of the optical filter.

  FIG. 8 is a diagram illustrating an example of a correspondence relationship between the upstream wavelength and the downstream wavelength and a usage state. As shown in the figure, it is convenient to determine the correspondence between the upstream wavelength and the downstream wavelength according to the order of decreasing wavelength numbers, that is, the order of shorter wavelengths, but any combination is possible.

  In the optical access network shown in FIG. 6, the optical subscriber units 31-1 to 31-N coupled to the power splitter 33 need to assign unused wavelengths to the transmitter 41 and the receiver 42 therein. For example, the optical subscriber units 31-1 to 31- (N-1) are coupled to the power splitter 33, and the combinations of wavelength numbers 1 to N-1 are already in use as shown in FIG. Assume that the subscriber unit 31-N is coupled. In this case, the combination of wavelength numbers N is an unused wavelength.

  In order to detect this unused wavelength, first, according to the wavelength sweep control signal from the control circuit 46, the transmission wavelength of the wavelength tunable filter 43 is swept in accordance with the downstream wavelength. Next, a part of the signal photoelectrically converted by the receiver 42 is sent to the detector 45, the optical power is measured, and the measurement result is sent to the control circuit 46. In the control circuit 46, if the optical power is smaller than or below a certain value, the upstream wavelength of the transmitter 41 is set to a wavelength corresponding to the downstream wavelength at this time by the wavelength setting control signal. Further, the control circuit 46 sends an output control signal to the transmitter 41 to output an optical signal from the transmitter 41. On the other hand, if the optical power measured by the detector 45 is greater than or greater than a certain value, the control circuit 46 further sweeps the transmission wavelength of the wavelength tunable filter 43 and performs the operation up to now.

  By using a coherent optical detection technique instead of the wavelength tunable filter, it is possible to demultiplex the downstream signal. If the coherent optical detection technique is used, in addition to improving the reception sensitivity, it is possible to demultiplex a WDM signal having a very narrow wavelength interval, which is difficult to demultiplex using a wavelength tunable filter.

  FIG. 9 is a block diagram showing a configuration example of optical subscriber units 61-1 to 61-N using a coherent optical detection technique and an optical access network using the same. An example of this configuration is disclosed in Patent Document 1, for example. In this optical access network, an optical subscriber unit 61-1 to 61-N arranged in each subscriber and an optical terminator 62 as a accommodating station device arranged in the accommodating station are used by using a power splitter 63. Coupled via a common optical fiber 64. The optical subscriber units 61-1 to 61-N replace the transmitter 41, the receiver 42, the wavelength tunable filter 43 and the multiplexer / demultiplexer 44 shown in FIG. 6, respectively, with the light source 11, the demultiplexer 12, and the modulator. 13 has a circulator 14 and a receiver 15. The optical terminator 62 includes light sources 71-1 to 71-N, duplexers 72-1 to 72-N, modulators 73-1 to 73-N, a multiplexer 74, a circulator 75, a duplexer 76, and a receiver. Having the units 77-1 to 77-N. The light source 71-i, the demultiplexer 72-i, the modulator 73-i, and the receiver 77-i (i = 1 to N) correspond to the optical subscriber line device 52-i shown in FIG.

  The optical subscriber units 61-1 to 61-N modulate the output of the light source 11 with the data signal by the modulator 12 and transmit it to the optical termination device 62 via the circulator 14. On the other hand, the downstream signal transmitted from the optical terminal device 62 is received by the receiver 15 via the circulator 14. At this time, the receiver 15 performs coherent optical detection using a part of the output of the light source 11 demultiplexed by the demultiplexer 12. As a coherent optical detection method, homodyne optical detection or heterodyne optical detection can be used.

  In the optical terminator 62, the downstream signal is modulated by the modulators 73-1 to 73-N with the outputs of the light sources 71-1 to 71-N having different wavelengths, respectively, and multiplexed by the multiplexer 74, and the circulator 75. It is transmitted to the subscriber side via On the other hand, the upstream signals transmitted from the optical subscriber units 61-1 to 61-N are received by the receivers 77-1 to 77-N via the circulator 75 and the duplexer 76. At this time, the receivers 77-1 to 77-N use a part of outputs of the corresponding light sources 71-1 to 71-N demultiplexed by the corresponding demultiplexers 72-1 to 71-N, respectively. , Coherent light detection. As a coherent optical detection method, homodyne optical detection or heterodyne optical detection can be used as in the optical subscriber units 61-1 to 61-N.

  In this configuration example, the light source 11 shares the light source used for uplink signal transmission from the optical subscriber units 61-1 to 61-N and the light source used for coherent optical detection. As a result, the reception sensitivity can be increased with a simple configuration.

  FIG. 10 is a diagram showing an example of wavelength arrangement used in the optical access network shown in FIG. In the optical access network shown in FIG. 9, unlike the case where the wavelength tunable filter 43 is used in the optical subscriber units 31-1 to 31-N as shown in FIG. 6, the combination of the upstream wavelength and the downstream wavelength is not arbitrary. , Are uniquely determined as illustrated in FIG. Since the upstream wavelength is used for reception of the downstream wavelength, the correspondence between both wavelengths must be close to each other as shown in FIG. Although the case where heterodyne optical detection is performed is shown here, the upstream wavelength and the downstream wavelength are the same when homodyne optical detection is performed.

  Consider executing the wavelength setting method disclosed in Patent Document 1 in the optical access network shown in FIG. Here, a case where the optical subscriber unit 61-1 detects an unused wavelength will be described as an example. In the optical subscriber unit 61-1, it is necessary to sweep the output wavelength of the light source 11 in order to detect an unused wavelength. The wavelength is incident on the optical fiber 64 via the modulator 13 and the circulator 14. At that time, if any of the other optical subscriber units 61-2 to 61-N, for example, the optical subscriber unit 61-N is accommodated and connected to the optical terminator 62 using the same wavelength and is communicating with each other. To do. In this case, the output wavelength of the optical subscriber unit 61-1 becomes interference noise, and the quality of the upstream signal of the optical subscriber unit 61-N deteriorates. In the worst case, the connection with the optical termination unit 62 is lost. There is a possibility of disconnection.

  An embodiment for solving such a problem will be described below.

[Configuration example 1 of optical subscriber unit]
FIG. 11 is a block diagram of an optical subscriber unit 61 used in place of the optical subscriber units 61-1 to 61-N in the optical access network shown in FIG. In this optical subscriber unit 61, instead of the transmitter 41, the receiver 42, the wavelength tunable filter 43, and the multiplexer / demultiplexer 44 shown in FIG. 6, a light source 81, a demultiplexer 12, a modulator 13, a circulator 14, a reception Device 15 and circuit breaker 16. The receiver 15 and the detector 45 and the control circuit 46 shown in FIG. 6 constitute a means for sweeping the wavelength output from the light source 81 and detecting an unused received wavelength from the received output of the receiver 15. 6 sets the detected unused reception wavelength as a wavelength output from the light source 81 and constitutes a means for releasing the interruption by the circuit breaker 16. The circuit breaker 16 may be disposed on the input side of the modulator 13 to block the output of the light source 11 input to the modulator 13.

[Detection of unused wavelengths]
The detection of unused wavelengths by the optical subscriber unit 61 will be described. The unused wavelength is detected in a state where the circuit breaker 16 is operated by the output control signal from the control circuit 46 shown in FIG. Then, the wavelength output from the light source 81 is swept by the wavelength setting signal of the control circuit 46. A part of the output of the light source 81 is demultiplexed by the demultiplexer 12 and supplied to the receiver 15. The receiver 15 performs coherent optical detection on the downstream signal. An unused wavelength can be detected by sending the output of the receiver 15 to the detector 45 shown in FIG. 6 and measuring the optical power. Since the transmission wavelength is determined at the same time when the reception wavelength is determined, the wavelength sweep signal shown in FIG. 6 is not necessary. When the transmission / reception wavelength is determined, the control circuit 46 shown in FIG. 6 fixes the output wavelength of the light source 81 to the determined transmission wavelength by the wavelength setting signal. The control circuit 46 also releases the interruption by the circuit breaker 16 by the output control signal.

[Operation after wavelength setting]
After the transmission / reception wavelength is determined, the wavelength output from the light source 81 is fixed to a specific value by the wavelength setting signal from the control circuit 46 shown in FIG. The light source 81 continuously outputs light at the fixed wavelength (specific wavelength). The duplexer 12 demultiplexes a part of the output of the light source 11. The modulator 13 modulates the output of the light source 81 with a data signal. The circulator 14 transmits the upstream signal output from the modulator 13 toward the accommodating station device 2 and outputs the downstream signal transmitted from the optical terminal device 32 to the receiver 15. The receiver 15 performs coherent optical detection on the downstream signal using a part of the output of the light source 11 demultiplexed by the demultiplexer 12. After the wavelength is set, the wavelength used is different for each optical subscriber unit 61, so that it is not necessary to operate the circuit breaker 16. As the circuit breaker 16, an attenuator that can take a sufficient amount of attenuation can be used.

[Configuration example 2 of optical subscriber unit]
FIG. 12 is a block diagram of another optical subscriber unit 61 used in place of the optical subscriber units 61-1 to 61-N in the optical access network shown in FIG. The optical subscriber unit 61 is different from the configuration example shown in FIG. 11 in that the circuit breaker is constituted by the semiconductor optical amplifier 17. The on / off of the output control signal for driving the semiconductor optical amplifier 17 is reversed when an attenuator is used. The semiconductor optical amplifier 17 may be disposed on the input side of the modulator 13 to block the output of the light source 11 input to the modulator 13.

[Configuration example 3 of optical subscriber unit]
FIG. 13 is a block diagram of still another optical subscriber unit 61 used in place of the optical subscriber units 61-1 to 61-N in the optical access network shown in FIG. The optical subscriber unit 61 is largely different from the configuration examples shown in FIGS. 11 and 12 in that the modulator and the circuit breaker are constituted by the same semiconductor optical amplifier 18. By modulating the drive current of the semiconductor optical amplifier 18 with the transmission signal, the semiconductor optical amplifier 18 can have both functions of a modulator and a circuit breaker. Here, as the transmission signal, the data signal and the output control signal from the control circuit 46 shown in FIG. 6 are input to the switch 19, and the switch 19 is turned off when the interruption is performed, and the switch 19 is turned on when the interruption is released. This is the signal obtained. When the port for driving the semiconductor optical amplifier 18 is divided into a data signal port and a bias port, a data signal and an output control signal are input to each.

[Configuration example 4 of optical subscriber unit]
FIG. 14 is a block diagram of still another optical subscriber unit 61 used in place of the optical subscriber units 61-1 to 61-N in the optical access network shown in FIG. The optical subscriber unit 61 is different from the configuration example shown in FIG. 13 in that a light source and a modulator are configured by a light source 82 that generates an FSK signal by a wavelength setting signal modulated by a data signal. As the light source 82 for generating the FSK signal, for example, a distributed feedback laser diode can be used. However, if the spread of the optical spectrum by FSK modulation is large, the performance of the received downlink signal deteriorates. Therefore, it is desirable to use MSK having the smallest modulation index.

[Effect obtained by the second embodiment]
According to the second embodiment described above, in the configuration using the coherent optical detection method in the WDM-PON, the optical subscriber unit 61 detects the unused wavelength so that the light source in the optical subscriber unit 61 is detected. Even if the emission wavelength of 81 or 82 is swept, the performance of the uplink signal output by another optical subscriber unit is not deteriorated. Further, by modulating the drive currents of the semiconductor optical amplifiers 17, 18, and 21, the function can be given to the semiconductor optical amplifiers 17, 18, and 19 without separately providing a circuit breaker. Further, if the FSK signal is generated by directly modulating the light source 82 with the data signal, the function of the light source 82 can be provided without providing a modulator.

1-1 to 1-N, 31-1 to 31-N, 61-1 to 61-N, 61 Optical subscriber unit 2 Accommodating station device 3, 33, 63 Power splitter 4, 34, 64 Optical fiber 11, 20 , 71-1 to 71-N, 81, 82 Light source 12, 72-1 to 72-N, 76 Demultiplexer 13, 73-1 to 73-N Modulator 14, Circulator 15 Receiver 16 Breaker 17, 18 , 21 Semiconductor optical amplifier 32, 62 Optical termination device (accommodating station device)
DESCRIPTION OF SYMBOLS 41 Transmitter 42 Receiver 43 Wavelength variable filter 44 Multiplexer / demultiplexer 45 Detector 46 Control circuit 51 Wavelength multiplexer / demultiplexer 52-1 to 52-N Optical subscriber line apparatus 74 Multiplexer

Claims (6)

In an optical access network having a plurality of optical subscriber units and a receiving station unit that accommodates the plurality of optical subscriber units via a common optical transmission line,
Each of the plurality of optical subscriber units is
A light source that continuously outputs light of a specific wavelength;
A receiver for receiving an optical signal by coherent optical detection using a part of the output of the light source;
A modulator for modulating the output of the light source with a data signal;
A circuit breaker that cuts off the input or output of the modulator so as not to interfere with the optical signal of another optical subscriber unit in the common optical transmission line,
The plurality of optical subscriber units are assigned different wavelengths so that each signal is wavelength-multiplexed on the common optical transmission line,
In at least some of the plurality of optical subscriber units,
Means for sweeping the wavelength output by the light source in a state where the input or output of the modulator is interrupted by the circuit breaker, and detecting an unused reception wavelength from the reception output of the receiver;
And setting a detected unused reception wavelength as a wavelength output from the light source, and a means for releasing the interruption by the circuit breaker.
An optical access network characterized by that. In an optical communication method of an optical access network in which a plurality of optical subscriber devices and a receiving station device that accommodates the plurality of optical subscriber devices communicate via a common optical transmission line,
Each of the plurality of optical subscriber units is
The optical signal is received by the receiver by coherent optical detection using a part of the output of the light source that continuously outputs light of a specific wavelength,
The light source output is modulated by a modulator using a data signal,
So as not to interfere with the optical signal of the common optical transmission path in other optical subscriber units, blocked as required input or output of the modulator by the circuit breaker,
The plurality of optical subscriber units are assigned different wavelengths so that each signal is wavelength-multiplexed on the common optical transmission line,
At least some of the plurality of optical subscriber units are:
By sweeping the wavelength of the output of the light source while interrupting the input or output of the modulator by the circuit breaker detects a reception wavelength of the unused reception output of the receiver,
The reception wavelength of the detected unused and sets the output to wavelengths above Symbol light source, an optical communication method and cancels the blocking by the blocking device. In the optical subscriber unit respectively disposed in the plurality of subscribers of the optical access network in which a plurality of subscribers are connected to the accommodating station via a common optical transmission line,
A light source that continuously outputs light of a specific wavelength;
A receiver for receiving an optical signal by coherent optical detection using a part of the output of the light source;
A modulator for modulating the output of the light source with a data signal;
A circuit breaker for cutting off the input or output of the modulator,
The light source is a light source whose output wavelength is variable,
Means for sweeping the wavelength output by the light source in a state where the input or output of the modulator is interrupted by the circuit breaker, and detecting an unused reception wavelength from the reception output of the receiver;
An optical subscriber unit comprising: a detected unused reception wavelength set as a wavelength output by the light source; and a means for releasing the blocking by the circuit breaker.   4. The optical subscriber unit according to claim 3, wherein the circuit breaker comprises a semiconductor optical amplifier.   5. The optical subscriber unit according to claim 3, wherein the circuit breaker and the modulator are constituted by the same semiconductor amplifier. In the optical subscriber unit respectively disposed in the plurality of subscribers of the optical access network in which a plurality of subscribers are connected to the accommodating station via a common optical transmission line,
A variable length light source that is directly modulated with a data signal to generate an FSK signal ;
A receiver for receiving an optical signal by coherent optical detection using a part of the output of the variable length light source;
A circuit breaker for cutting off the output of the variable length light source;
Have
Means for sweeping the wavelength output by the variable length light source in a state where the output of the variable length light source is blocked by the circuit breaker, and detecting an unused reception wavelength from the reception output of the receiver;
Means for setting a detected unused reception wavelength as a wavelength to be output by the variable-length light source, and canceling the interruption by the circuit breaker;
An optical subscriber unit comprising:

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