JP3778183B2 - Master station apparatus in optical communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical communication system in which a master station and a plurality of slave stations are connected by an optical fiber via a passive optical splitter.
[0002]
[Prior art]
In a system for bidirectional communication between a master station and a plurality of slave stations using an optical data communication network, there is a network configuration in which the master station and each slave station are radially connected by a single optical fiber. It has been put into practical use (Single Star). This network configuration simplifies the system and equipment configuration, but since one slave station occupies one optical fiber (if the number of slave stations is N, N optical fibers are required), the system is low. It is difficult to make a price.
[0003]
Therefore, a PON (Passive Optical Network) system (also referred to as PDS (Passive Double Star)) in which one optical fiber is shared by a plurality of slave stations has been proposed. In this PON system, a master station and a passive optical branching unit are connected by an optical fiber, and an optical branching unit and a plurality of slave stations are connected by a plurality of optical fibers. Further, a configuration in which another optical branching device is inserted between the optical branching device and the plurality of slave stations is also employed.
[0004]
In the PON system, the downstream optical signal transmitted from the master station is distributed to all the slave stations, but only the slave station having the destination address takes in the optical signal. Further, the transmission time of each slave station is divided and assigned to the upstream optical signal transmitted from the slave station so that the slave stations do not collide with each other.
In the PON system, optical signals from a slave station installed near the master station or a slave station with few branches, and a slave station installed far from the master station or from a slave station that has passed multiple branches. The optical reception intensity at the master station is greatly different from that of the optical signal.
[0005]
This is because light is attenuated when propagating through the optical fiber and is further attenuated every time it passes through the optical branching unit.
On the other hand, an avalanche photodiode (APD) having an optical multiplication function may be used in the optical receiver of the master station. This APD can receive even weak optical signals with high sensitivity due to the multiplication of the reverse-biased PN junction. However, when a strong optical signal is input, the APD is easily saturated and can receive an accurate optical signal. Disappear.
[0006]
Therefore, in order to set the multiplication factor of the APD large for a weak input optical signal and small for a strong input optical signal, the bias voltage of the APD is adjusted.
For example, when a fixed resistor is inserted in series with an APD and a large current flows through the APD, a principle is used in which a bias voltage applied to the APD is reduced using a voltage drop of the resistor (referred to as a self-bias method). ).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-355218
[0008]
[Problems to be solved by the invention]
However, in the self-bias method, when the bias setting time is delayed due to the stray capacitance of the light receiving circuit, there is a large drop in the received intensity of the optical signal transmitted from each slave station in a time division manner in the PON system. In addition, there is a problem that the bias voltage cannot be quickly changed.
Although it is conceivable to measure the intensity of the optical signal from each slave station and feedback control the bias voltage of the APD (Patent Document 1), the rise time of the optical signal from each slave station is very short. In addition (because of about 1 nanosecond), the feedback loop has a time constant, so that there is a problem that it cannot sufficiently follow the rising of the received optical signal.
[0009]
Further, when a slave station newly joins the PON system, since the master station does not know the slave station, the transmission intensity of the upstream optical signal from the slave station is also increased in addition to the fact that the transmission time cannot be divided and allocated. Since it is not measured, there is also a problem that the master station cannot properly receive the upstream optical signal from the slave station.
For this reason, the reception of the upstream optical signal from the slave station is predicted during the period of recognizing the new subscriber station by polling from the master station, so that the reception intensity of the upstream optical signal is appropriately handled during this period. Therefore, there has been a demand for a master station apparatus in an optical communication system that can set the bias voltage.
[0010]
Therefore, the present invention provides an optical communication system in which a master station and a plurality of slave stations are connected by an optical fiber via an optical branching unit during a period in which reception of an upstream optical signal from the slave station is predicted. An object of the present invention is to provide a master station device in an optical communication system capable of appropriately setting the light receiving sensitivity of an APD.
Another object of the present invention is to connect a master station and a plurality of slave stations with an optical fiber via an optical splitter, and the master station specifies a time slot of an upstream optical signal from the slave station. In an optical communication system that determines the transmission time of an upstream optical signal, the detection sensitivity does not decrease even if there is a large difference in the optical reception intensity of the master station, and it is received without saturation even if there is a large optical input. It is to provide a master station apparatus in an optical communication system capable of performing the above.
[0011]
Still another object of the present invention is to connect a master station and a plurality of slave stations with an optical fiber via an optical branching unit, and the master station recognizes a slave station newly joined to the optical communication system. Therefore, in an optical communication system that polls the slave station, a bias voltage appropriately corresponding to the reception intensity of the uplink optical signal is applied during a period when reception of the uplink optical signal from the slave station is predicted. It is to provide a master station device in an optical communication system that can be set.
[0012]
[Means for Solving the Problems and Effects of the Invention]
  The master station apparatus in the optical communication system of the present invention is an avalanche photodiode that receives an upstream optical signal from a slave station.And a DC power source that supplies a bias power to the avalanche photodiode, and a reception control unit that changes the light receiving sensitivity of the avalanche photodiode in a plurality of stages, and the DC power source includes a switch circuit that switches different output voltages. The reception control unit sets a bias voltage to be applied to the avalanche photodiode by switching the switch circuit at a time before receiving the upstream optical signal from a specific slave station, and sets the light receiving sensitivity of the avalanche photodiode. To change(Claim 1).
  According to this configuration, the light receiving sensitivity of the APD can be changed in a plurality of stages (two or more stages) during a period in which the reception of the upstream optical signal from the slave station is predicted. Since any one of these steps is the light receiving sensitivity of the APD corresponding to the intensity of the upstream optical signal from the slave station, the light receiving sensitivity of the APD can be set appropriately.
  The DC power supply includes a switch circuit that switches between different output voltages, and the reception control unit sets a bias voltage to be applied to the APD by switching the switch circuit, so that an appropriate bias voltage can be quickly applied to the APD by switching the switch circuit. Can be given to.
[0013]
parentThe station apparatus may include a storage unit that stores in advance the reception intensity of the upstream optical signal from a specific slave station for each slave station (claims).2).
[0014]
According to this configuration, it is assumed that the reception intensity of the upstream optical signal from the slave station at the master station apparatus is temporally unchanged for each slave station. The reception intensity of the signal is measured in advance for each slave station and stored in the storage unit. Since the master station device is an optical communication system that determines the transmission time point of the upstream optical signal by designating the time slot of the upstream optical signal from the slave station, the period for receiving the upstream optical signal from a specific slave station can be predicted in advance Therefore, at the time before the reception, the light receiving sensitivity of the APD is set according to the reception intensity of the upstream optical signal of the slave station stored in the storage unit. As a result, the light receiving sensitivity of the APD can be set without time delay, so that even when there is a fast change and a large drop in the optical signal intensity of the master station device, it is possible to sufficiently follow.
[0015]
  In addition, the master station device applied to the optical communication system has a storage unit that stores in advance, for each slave station, the optimum bias voltage of the DC power supply corresponding to the reception intensity of the upstream optical signal from the specific slave station. (Claims)3).
  Claim2Description and claims3Differences from the described arrangement are claimed.2In the configuration described above, the reception intensity of the upstream optical signal from the slave station is measured in advance for each slave station and stored in the storage unit, and the upstream optical signal of the slave station stored in the storage unit is received at a predetermined point in time. Whereas the bias voltage is set according to the strength, the claim3In the configuration described above, the reception intensity of the upstream optical signal from the slave station is measured for each slave station, and the corresponding optimum bias voltage is stored in advance for each slave station, and stored in the storage unit at a predetermined time point. The bias voltage is set. As described above, there is no change in achieving the object of the invention of optimally setting the light receiving sensitivity of the APD only by the difference in the stage of data to be stored.
[0017]
  The DC power source includes a plurality of variable output voltage power sources and a switch circuit that switches between the power sources, and the reception control unit applies a bias voltage to the APD using one power source, The bias voltage is changed in accordance with the reception intensity of the next slave station received at the power source, and the bias voltage is switched by the switch circuit before the upstream optical signal from the next slave station is received. (Claims)4). With this configuration, since the “other power supply” can set a bias voltage according to the reception intensity of the next received slave station, switching of the switch circuit changes the next received slave station. An appropriate bias voltage corresponding to the reception intensity can be quickly applied to the APD. Further, by using a variable output voltage power supply, the number of steps of the output voltage change can be changed in an analog stepless manner or digitally in a stepwise manner.
[0018]
  If the optical communication system includes an unrecognized child station discovery period in which the parent station device polls each unrecognized child station to find a child station that is not recognized by the parent station device. The apparatus sets the bias voltage of the DC power supply in a plurality of stages in order to receive a response signal to the polling.5). At this time, the bias voltage may be set to be different for each unrecognized slave station discovery period.6), The unrecognized child station discovery period may be subdivided into a plurality of sections, and the subdivided sections may be set to have different bias voltages.7).
[0019]
According to these configurations, the master station apparatus knows in advance the period during which reception of a response signal to polling is predicted, but does not know the optimum bias voltage corresponding to the reception intensity of the signal. Therefore, the bias voltage is set in a plurality of stages (two or more stages) during the period in which the response signal for polling is expected to be received. Since any one of these steps is the optimum bias voltage corresponding to the reception intensity of the response signal, the response signal can be appropriately received when the bias voltage is set.
[0020]
  Further, the stage of the bias voltage for each of the subdivided sections in the unrecognized child station discovery period may be set so as to increase step by step.8).
  When polling all unrecognized slave stations at the same time during the unrecognized slave station discovery period, the master station device responds from a slave station installed near the master station or a slave station with few branches. A signal is received immediately after polling, and a response signal from a slave station installed at a location far from the master station or a slave station that has passed through a plurality of branches is received after polling. Therefore, the reception strength of the response signal received immediately after polling is high, and the reception strength of the response signal received after a while after polling is low.
[0021]
  Claim8According to the described configuration, the bias voltage is set so that the stage for each subdivided section in the unrecognized slave station discovery period is gradually increased. As a result, in a single unrecognized slave station discovery period, not only response signals from slave stations installed near the master station device but also response signals from slave stations installed far away are received. it can.
  Further, the time width of each of the plurality of sections to be subdivided may be set so as to change for each unrecognized child station discovery period.9).
[0022]
When the time width of each section subdivided in the unrecognized slave station discovery period is the same, and the unrecognized slave station discovery period is repeatedly applied to the optical communication system, for each unrecognized slave station discovery period Even if the bias voltage is set differently for each of the subdivided sections, the upstream optical signal may not be received between the subdivided sections. In addition, even in the next unrecognized slave station discovery period, the upstream optical signal cannot be received between the subdivided sections.
[0023]
  Claim9With this configuration, the time width of each of the plurality of sections to be subdivided is set so as to change for each unrecognized slave station discovery period. Therefore, the upstream optical signal is between the subdivided sections. Can solve the problem that can not be received.
  The master station apparatus in the optical communication system including the unrecognized slave station discovery period includes a detection unit for detecting that an upstream optical signal is received from a slave station that is not recognized by the master station. And when the reception of the upstream optical signal is detected by the detection unit, the change of the bias voltage of the DC power supply may be prohibited (claim).10). With this configuration, it is possible to prevent the reception of the upstream optical signal from being interrupted by changing the bias voltage while receiving the upstream optical signal from the slave station.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<Overall configuration of the present invention>
FIG. 1 is a block diagram showing a PON system. A PON system component in the station is called a master station or a master station device, and a PON system component in the subscriber's house is called a slave station. The PON system includes a master station 1, a plurality of slave stations 5, and optical branching devices 3a and 3b. The master station 1 and the optical branching device 3a are connected by a single-core optical fiber 2, and an optical branching device 3a. And optical branching unit 3b, optical branching unit 3a and slave station 5, and optical branching unit 3b and slave station 5 are connected by optical fiber 4, respectively. A single mode fiber is used as the optical fiber. Each of the optical branching devices 3a and 3b is configured by a star coupler.
[0025]
The downstream optical signal from the master station 1 to the slave station 5 and the upstream optical signal from the slave station 5 to the master station 1 are each composed of packets.
The master station 1 receives a packet sent from a host network (such as the Internet), sends it to the slave station 5 through an optical fiber, receives a packet sent from the slave station 5, and sends it to the host network have.
The master station 1 includes an optical transmission line termination device (OTL; Optical Line Terminals) serving as a connection end with the optical fiber 2, a layer 2 switch, and a broadband access router serving as a connection end of a higher-level network.
[0026]
The slave station 5 includes a personal computer installed in the house, an optical subscriber line terminal unit (ONU: Optical Network Unit) that transmits and receives broadband optical signals of the personal computer to the optical network, and the like.
Briefly describing the operation of the PON system, a downstream packet that enters the master station 1 from a higher-level network is subjected to predetermined processing by the layer 2 switch in the master station 1. And it transmits to an optical fiber through OLT. The optical signal transmitted to the optical fiber is branched by the optical branching devices 3a and 3b and transmitted to the slave station 5 connected to the optical branching devices 3a and 3b. And decrypt the packet.
[0027]
On the other hand, the upstream packet transmitted from the slave station 5 is transmitted to the master station 1 via the optical branching units 3a and 3b. In the master station 1, after predetermined processing is performed by the layer 2 switch, it is transmitted from here to the upper network via the broadband access router.
It is necessary to prevent uplink packets transmitted from the slave stations 5 from competing with each other in time. Therefore, when transmitting a packet from the master station 1 to the slave station 5, an upstream optical signal time slot (hereinafter simply referred to as "slot") is assigned to each slave station 5. The slave station 5 to which the slot is assigned transmits an uplink packet to the assigned slot. Therefore, contention for upstream packets between the slave stations 5 is avoided. Note that the clock must be shared between the master station 1 and the slave station 5, but the time adjustment of this clock is performed by including time information in the packet when performing packet communication. It can be carried out.
[0028]
The master station 1 receives uplink packets sequentially from each slave station 5, but the optical signal strength differs depending on the path of the optical fiber. For example, the length of the optical fiber is different for each slave station 5, and it differs depending on whether or not it passes through the optical branching unit 3b.
FIG. 2 is a graph for explaining the difference in the intensity of the uplink packet from each slave station 5, with the horizontal axis representing time and the vertical axis representing reception intensity. Packets 1 to 4 received from different slave stations 5 have different reception strengths.
[0029]
When a new slave station 5 joins the PON system, the master station 1 does not recognize the slave station 5 and therefore cannot allocate a slot to the slave station 5. As a result, the upstream optical signal from the slave station 5 cannot be received correctly.
For this reason, the master station 1 is a child that is not recognized by the master station 1 by the operation and polling in the period of receiving the upstream optical signal from the slave station 5 to which the slot is assigned (hereinafter referred to as “data period”). An operation is performed in an unrecognized child station discovery period (hereinafter referred to as “discovery period”) for finding the station 5.
[0030]
FIG. 3 is a time sequence diagram for explaining the overall operation of the master station 1. The master station 1 repeatedly performs the operation in the data period and the operation in the discovery period alternately. Hereinafter, the operation of the master station 1 in the data period will be described as a first embodiment of the present invention, and the operation of the master station 1 in the discovery period will be separately described as a second embodiment of the present invention.
<First Embodiment>
FIG. 4 is a block diagram showing the configuration of the PON system for explaining the master station 1 according to the first embodiment of the present invention.
[0031]
This PON system includes a master station 1, slave stations 51, 52, and 53, and optical branching devices 3a and 3b, and the master station 1 and the optical branching device 3a are connected by a single optical fiber 2. Between the splitter 3a and the slave station 51, between the optical splitter 3a and the optical splitter 3b, between the optical splitter 3b and the slave station 52, and between the optical splitter 3b and the slave station 53, respectively. They are connected by an optical fiber 4.
In this PON system, a slave station 51 is installed at a location closest to the master station 1, a slave station 52 is installed at a location closest to the next, and a slave station 53 is installed at a location farthest from the master station 1. To do. Further, the master station 1 determines the propagation delay time between the master station 1 and the slave station 51, the propagation delay time between the master station 1 and the slave station 52, and the propagation delay time between the master station 1 and the slave station 53. Assume that you know in advance.
[0032]
FIG. 5 is a block diagram showing a configuration of the optical transmission line termination device OLT in the master station 1 according to the first embodiment. The optical transmission line termination device OLT is provided with an APD that receives an upstream optical signal, and the received light signal of the APD is input to a post amplifier through a transimpedance amplifier 11 for converting a current signal into a voltage signal. . A variable voltage type DC power supply 12 for providing a bias voltage to the APD is provided.
[0033]
In principle, the voltage variable DC power supply 12 can employ a circuit in which the feedback voltage of the voltage variable DC-AC converter is variable. Specifically, a voltage variable type DC-DC converter power supply circuit (for example, Linear Technology LT1930 / LT1930A) developed for APD can be employed.
Further, an optical reception control circuit 13 for controlling the bias voltage of the APD is provided. The optical reception control circuit 13 includes a reception intensity storage unit 14 that stores reception intensity from the slave stations 51 to 53, and an optimum bias determination unit 15 that determines an optimum bias voltage based on the stored reception intensity. Yes.
[0034]
The functions described below of the optical reception control circuit 13, the reception intensity storage unit 14, and the optimum bias determination unit 15 are executed by a computer provided in the optical transmission line termination device OLT using a predetermined program. is there.
The optical reception control circuit 13 measures the intensity of light received from the slave stations 51 to 53 and stores the intensity information in the reception intensity storage unit 14. Although the measurement time is arbitrary, for example, the measurement is performed at a time determined once a day. In the measurement method, the intensity of light is determined by fixing the bias voltage of the APD to a certain value and measuring the current flowing through the APD at that time.
[0035]
FIG. 6 is a graph showing the relationship between the APD multiplication factor M and the reverse bias voltage. The optical reception control circuit 13 sets a large multiplication factor M for a small reception intensity and sets a small multiplication factor M for a strong input optical signal. Therefore, the optical reception control circuit 13 has a table that defines the relationship between the reception intensity and the optimum bias voltage of ADP based on this graph. The optical reception control circuit 13 adjusts the APD bias voltage using this table.
[0036]
The optimum bias determination unit 15 uses the intensity information stored in the reception intensity storage unit 14 and this table, and the optimum bias voltage for receiving the upstream optical signal from the slave station 51 is V1. It is assumed that the optimum bias voltage for receiving the upstream optical signal from the station 52 is V2, and the optimum bias voltage for receiving the upstream optical signal from the slave station 53 is V3.
FIG. 7 is a time sequence diagram for explaining the operation of the master station 1 according to the first embodiment.
[0037]
When the data period starts, the optical reception control circuit 13 transmits the packets 1 to 3 to the slave stations 51 to 53 based on the slots assigned to the slave stations 51 to 53, respectively. When receiving the packets 1 to 3, the slave stations 51 to 53 transmit the upstream packets 1 ′ to 3 ′ to the master station 1, respectively. At this time, the optical reception control circuit 13 receives the upstream packet 1 ′ during the time t12 to t13 based on the propagation delay time between the master station 1 and each of the slave stations 51 to 53. Sometimes packet 1 is transmitted to the slave station 51. Subsequently, in order to receive the upstream packet 2 ′ between times t 22 and t 23, the packet 2 is transmitted to the slave station 52 at time t 21. Next, in order to receive the upstream packet 3 ′ between times t 32 and t 33, the packet 3 is transmitted to the slave station 53 at time t 31. With the above operation, the mutual competition of the upstream packets 1 ′ to 3 ′ is avoided.
[0038]
As described above, the optical reception control circuit 13 can know in advance which time the uplink packet from which slave station 51 to 53 is received based on the slot assigned to the slave stations 51 to 53.
The optimum bias unit 15 determines a bias voltage in advance in accordance with the time when the uplink packet from the slave stations 51 to 53 is received. Then, the determined optimum bias voltage is set in the DC power supply 12 in a vacant time zone until the reception of the uplink packet from the previous slave station is completed and the uplink packet from the specific slave station is received.
[0039]
Specifically, when the packet 1 is transmitted, the optimum bias voltage between times t12 and t13 is determined as V1, and the DC power supply 12 is set so that the bias voltage becomes V1 before time t12. When the packet 2 is transmitted, the optimum bias voltage between times t22 and t23 is determined as V2, and the DC power supply 12 is set so that the bias voltage between times t13 and t22 becomes V2. Further, when the packet 3 is transmitted, the optimum bias voltage between times t32 and t33 is determined as V3, and the DC power supply 12 is set so that the bias voltage between times t23 and t32 becomes V3.
[0040]
With the above operation, the APD set with an appropriate bias can receive the upstream optical signal from the slave stations 51 to 53 with appropriate sensitivity. Since it is possible to cope with optical signals having various intensities inputted to the APD in time, the optical signal can be received without securing the S / N ratio and without being saturated.
In the above embodiment, the optical reception control circuit 13 adjusts the voltage of the voltage variable type DC power supply using the table that defines the relationship between the reception intensity and the optimum bias voltage of the APD. A plurality of fixed DC power supplies may be prepared and switched to one of the DC power supplies.
[0041]
FIG. 8 shows a circuit example in which the DC power sources 12 a and 12 b having two different voltages are switched by the switch circuit 16. The optimum bias determination unit 15 sets a threshold value for the upstream optical signal, compares the reception intensity of the slave stations 51 to 53 stored in the reception intensity storage unit 14 with the threshold value, and the reception intensity is higher than the threshold value. When the reception intensity is higher than the threshold value, a low bias voltage is determined. Then, the DC circuit 12a or 12b is selected by switching with the switch circuit 16 in accordance with the time when the upstream packets from the slave stations 51 to 53 are received. In this way, by switching the DC power supply by the switch circuit 16, it is not necessary to use a voltage variable DC power supply, and the circuit configuration of the DC power supply can be simplified.
[0042]
FIG. 9 shows a circuit block diagram in which a plurality of voltage variable type DC power supplies 12c and 12d having different voltages are prepared and switched to one of the DC power supplies 12c or 12d. In the optical reception control circuit 13, the optimum bias determination unit 15 determines the optimum bias voltage V 1 according to the uplink packet received from the slave station 51, and matches the uplink packet received from the next slave station 52. Next, the next optimum bias voltage V2 is determined. The optimum bias determination unit 15 supplies a signal corresponding to the determined optimum bias voltage V1 to one DC power supply 12c. While the upstream packet is received from the slave station 51 (for example, between times t12 and t13 in FIG. 7), a signal corresponding to the next optimum bias voltage V2 is supplied to the other DC power source 12d. The other DC power supply 12d stands by in a state where the optimum bias voltage V2 is set. The optimum bias determination unit 15 switches the switch circuit 16 before the upstream packet from the slave station 51 is finished and before the upstream packet is received from the next slave station 52 (between times t13 and t22). As a result, the supply of voltage from the other DC power supply 12d starts promptly. Since the other DC power supply 12d is in a standby state with the optimum bias voltage V2 set, the power supply voltage is stable.
[0043]
While the voltage is supplied from the other DC power supply 12d (between times t22 and t23), the optimum bias determination unit 15 sends the gate voltage signal corresponding to the next optimum bias voltage V3 to the one DC power supply. 12c. One DC power supply 12c stands by in a state where the optimum bias voltage V3 is set for the upstream optical signal from the next slave station 53. By repeating such a procedure, a stable bias voltage can always be supplied to the APD.
[0044]
FIG. 10 is a block diagram showing a configuration of the optical transmission line termination device OLT in the master station 1 having an optimum bias storage unit that stores an optimum bias voltage. Instead of the reception strength storage unit 14 described so far, an OLT including an optimum bias storage unit 17 that stores optimum biases V1 to V3 corresponding to the reception strengths of the slave stations 51 to 53 may be used. At this time, the optimum bias determination unit 15 selects the stored optimum bias voltage and sets the DC power supply 12.
[0045]
As described above, the master station 1 in the data period can appropriately and quickly set the light receiving sensitivity of the APD following the change in the reception intensity of the upstream optical signal from the slave stations 51 to 53. High sensitivity reception and strong input resistance can be realized at the same time.
Second Embodiment
FIG. 11 is a block diagram showing the configuration of the PON system for explaining the master station 1 according to the second embodiment of the present invention.
[0046]
This PON system includes a master station 1, slave stations 54, 55, and 56, and optical branching devices 3a and 3b, and the master station 1 and the optical branching device 3a are connected by a single-core optical fiber 2. Between the splitter 3a and the slave station 54, between the optical splitter 3a and the optical splitter 3b, between the optical splitter 3b and the slave station 55, and between the optical splitter 3b and the slave station 56, respectively. They are connected by an optical fiber 4. It is assumed that a slave station 54 is installed at a location closest to the master station 1 and a slave station 56 is installed at a location closest to the next.
[0047]
In this PON system, it is assumed that the master station 1 knows in advance the propagation delay time between the master station 1 and the slave station 55 and has received the upstream optical signal intensity from the slave station 55 in advance. Further, the slave stations 54 and 56 have just newly joined the PON system, and the master station 1 transmits the propagation delay time between the master station 1 and the slave stations 54 and 56 and the upstream light from the slave stations 54 and 56. Assume that the signal strength is not known. Therefore, during the data period, the master station 1 can receive the upstream optical signal from the slave station 55, but cannot receive the upstream optical signal from the slave stations 54 and 56 that cannot be specified.
[0048]
During the discovery period, the master station 1 transmits a packet X to the slave stations 54 and 56, and the slave stations 54 and 56 that have received the packet X return a return packet X ′ to the master station 1. Upon receiving this return packet X ′, the master station 1 recognizes the slave stations 54 and 56 based on this packet (hereinafter, these operations are collectively referred to as “polling”).
FIG. 12 is a time sequence diagram for explaining polling.
[0049]
Even if the master station 1 transmits the packet X to the slave stations 54 and 56, the master station 1 does not know the propagation delay time between the master station 1 and the slave stations 54 and 56, so the reception time of the return packet X ′ is determined. It cannot be predicted in advance. Further, since the reception strength from the slave stations 54 and 56 is not grasped, the optimum bias voltage when receiving the packet X ′ is not known.
FIG. 13 is a block diagram showing the configuration of the OLT in the master station 1 according to the second embodiment. The same components as those in FIG.
[0050]
The optical reception control circuit 13 includes a bias voltage adjustment unit 18 for adjusting to an optimum bias voltage corresponding to the reception intensity from the slave stations 54 and 56 not recognized by the master station 1.
The functions described below of the reception control circuit 13 and the bias voltage adjusting unit 18 are executed by a computer provided in the optical transmission line terminating device OLT using a predetermined program.
[0051]
The bias voltage adjustment unit 18 can set the bias voltage in a plurality of stages during the discovery period. In this description, it is assumed that the bias voltage adjusting unit 18 can set the bias voltage in three stages of V10, V20, and V30. Also, it is assumed that the optimum bias voltage for receiving the upstream optical signal given from the slave station 54 is V10, and the optimum bias voltage for receiving the upstream optical signal given from the slave station 56 is V20.
FIG. 14 is a time sequence diagram for explaining an example of the reverse bias voltage of the APD set in the discovery period, with the horizontal axis representing time and the vertical axis representing reverse bias voltage. The bias voltage V10 is set during the first discovery period, the bias voltage V20 is set during the next discovery period, and the bias voltage V30 is set during the next discovery period.
[0052]
FIG. 15 is a time sequence diagram for explaining another example of the APD reverse bias voltage set in the discovery period. The discovery period is subdivided into three sections t1, the bias voltage V20 is set in the first section t1, the bias voltage V30 is set in the next section t1, and the bias voltage V10 is set in the last section t1.
In this way, by setting the bias voltage in a plurality of stages in the discovery period, the optimum bias voltages V10 and V20 for receiving the packet can be obtained even if the reception strength of the packet from the slave stations 54 and 56 is not grasped in advance. Can be set. When the bias voltage is set, the upstream optical signals from the slave stations 54 and 56 can be received to recognize the slave stations 54 and 56.
[0053]
Accordingly, in the example of FIG. 14, the bias voltage V10 is set between the times t41 and t42, so that the upstream optical signal from the slave station 54 can be received during this time, and the bias voltage V20 is set between the times t43 and t44. Therefore, the upstream optical signal from the slave station 56 can be received during this period.
In the example of FIG. 15, since the bias voltage V20 is set between times t51 and t52, the upstream optical signal can be received during this time, and the bias voltage V10 is set between times t53 and t54. Therefore, the upstream optical signal from the slave station 54 can be received during this period.
[0054]
FIG. 16 is a time sequence diagram for explaining still another example of the reverse bias voltage of the APD set in the discovery period. The bias voltage V10 is set in the first interval t1, and the bias voltage is set in the next interval t1. V20 is set, and the bias voltage V30 is set in the last section t1.
When the packet X is transmitted to the slave stations 54 and 56 all at once, the master station 1 receives the reply packet X ′ from the slave station 54 immediately after the packet X is transmitted, and after receiving the reply packet X ′ for a while. After that, the reply packet X ′ from the slave station 56 is received. Further, since the slave station 54 is installed at a location closest to the master station 1, the reception strength of the packet from the slave station 54 is strong, and the slave station installed at a position far from the slave station 54 when viewed from the master station 1. The reception strength of the packet from 56 is weaker than the reception strength from the slave station 54.
[0055]
Therefore, as shown in FIG. 16, by increasing the bias voltage as the discovery period elapses, it is possible to receive a reply packet X ′ from the slave station 54 immediately after the discovery period starts in one discovery period. Instead, the reply packet X ′ from the slave station 56 can also be received after a while after the discovery period starts.
FIG. 17 is a time sequence diagram for explaining still another example of the APD reverse bias voltage set in the discovery period.
[0056]
The first discovery period is subdivided into three sections t1, the bias voltage V10 is set in the first section t1, the bias voltage V20 is set in the next section t1, and the bias voltage V30 is set in the last section t1. The
The next discovery period is subdivided into three sections t2, t3 and t1. The time width in each section is t2> t1> t3. The bias voltage V10 is set in the first interval t2, the bias voltage V20 is set in the next interval t3, and the bias voltage V30 is set in the final interval t1.
[0057]
Further, the next discovery period is subdivided into three sections t1, t2 and t3, the bias voltage V10 is set in the first section t1, the bias voltage V20 is set in the next section t2, and the bias is set in the last section t3. The voltage V30 is set.
For example, when receiving an optical signal from the slave station 54 at time t71 after each discovery period starts and receiving an optical signal from the slave station 56 at time t72, in the first discovery period shown in FIG. Since the bias voltage changes at times t71 and t72, the optical signals from the slave stations 54 and 56 cannot be received. In addition, when the discovery period composed of the three sections t1 is repeatedly applied, the optical signals from the slave stations 54 and 56 cannot be received at any time.
[0058]
However, as shown in FIG. 17, when the time widths of the three sections subdivided for each discovery period are changed, the bias voltage V10 is set at the time t71 of the second discovery period, and the third time The bias voltage V20 is set at time t72 of the discovery period. Therefore, the optimum bias voltage of the optical signal applied from the slave stations 54 and 56 can be set at an appropriate timing by a plurality of discovery periods in which the time widths of the three sections to be subdivided are different.
[0059]
FIG. 18 is a block diagram showing another configuration of the OLT of the master station 1 according to the second embodiment. In this figure, in addition to the configuration of FIG. 13, a sampling hold (S / H) circuit 19 and a monitor circuit are shown. 20 is provided.
An APD light reception monitor signal is input to the monitor circuit 20, and the monitor circuit 20 sequentially monitors (monitors) the APD light reception monitor signal. Threshold voltages Lv1 and Lv2 are input to the monitor circuit 20, and when the light reception monitor signal is not less than Lv1 and not more than Lv2, the APD determines that the upstream optical signal is received, and the light reception monitor signal Is output.
[0060]
The S / H circuit 19 is supplied with the bias voltage set by the bias voltage adjusting unit 16 and the light reception monitor signal output from the monitor circuit 20. When the light reception monitor signal is input, the S / H circuit 19 holds the bias voltage input at that time.
FIG. 19 is a time sequence diagram for explaining the bias voltage held by the S / H circuit 19.
[0061]
FIG. 6A is a time sequence diagram showing the bias voltage adjusted by the bias voltage adjusting unit 18, in which the bias voltage V4 is set between times t4 and t5, and the bias voltage V6 between times t5 and t6. Is set.
FIG. 4B is a time sequence diagram showing an APD light reception monitor signal input to the monitor circuit 20. Since the APD receives an optical signal between times t4 and t6, the APD light reception monitor signal is received. Is Lv1 or higher and Lv2 or lower. Accordingly, at this time, a light reception monitor signal is given to the S / H circuit 19.
[0062]
FIG. 4C is a time sequence diagram showing the bias voltage applied to the APD, where the bias voltage V4 is applied between times t4 and t6, and the bias voltage V6 is applied after time t6. This is because the light reception monitor signal is input to the S / H circuit 19 between the times t4 and t6, so that the bias voltage V4 at the time t4 continues to be held until the time t6.
Thus, by prohibiting the change of the bias voltage while the APD is receiving the upstream optical signal and holding the bias voltage, the bias voltage is changed while the upstream optical signal is received, and the light It is possible to prevent the reception of signals from being interrupted.
[0063]
As described above, the master station 1 in the discovery period does not know the reception intensity of the upstream optical signal from the slave station newly joined to the PON system and the propagation delay time between the slave station and the master station 1. However, it is possible to appropriately receive the upstream optical signal from the slave station by setting the bias voltage in a plurality of stages.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.
[0064]
For example, in this description, it has been described that a child station newly joined to the PON system is found during the discovery period. However, a child station that has just been turned on may be found during the discovery period. In addition, when each discovery period is subdivided, it has been described as subdividing into three sections. However, it is not necessary to limit to three sections, and subdividing into four sections is subdivided into five sections. May be.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an entire PON system.
FIG. 2 is a graph for explaining a difference in intensity of an upstream optical signal from each slave station 5;
FIG. 3 is a time sequence diagram for explaining the overall operation of the master station 1;
FIG. 4 is a block diagram showing a configuration of a PON system for explaining a master station 1 according to the first embodiment of the present invention.
FIG. 5 is a block diagram showing a configuration of an OLT in the master station 1 according to the first embodiment.
FIG. 6 is a graph showing the relationship between an APD multiplication factor M and a reverse bias voltage.
FIG. 7 is a time sequence diagram for explaining the operation of the master station 1 according to the first embodiment.
FIG. 8 is a block diagram illustrating a circuit example in which a DC power source having two different voltages is switched by a switch circuit 16;
FIG. 9 is a block diagram showing a circuit example in which two voltage-variable DC power sources having different voltages are prepared and switched by a switch circuit 16;
FIG. 10 is a block diagram illustrating a configuration of an OLT in the master station 1 including an optimum bias storage unit that stores an optimum bias voltage.
FIG. 11 is a block diagram showing a configuration of a PON system for explaining a master station 1 according to a second embodiment of the present invention.
FIG. 12 is a time sequence diagram for explaining polling;
FIG. 13 is a block diagram showing a configuration of an OLT in the master station 1 according to the second embodiment.
FIG. 14 is a time sequence diagram for explaining an example of a reverse bias voltage of APD set in a discovery period.
FIG. 15 is a time sequence diagram for explaining another example of the APD reverse bias voltage set in the discovery period;
FIG. 16 is a time sequence diagram for explaining still another example of the reverse bias voltage of the APD set in the discovery period.
FIG. 17 is a time sequence diagram for explaining still another example of the reverse bias voltage of APD set in the discovery period.
FIG. 18 is a block diagram showing another configuration of the OLT of the master station 1 according to the second embodiment.
FIG. 19 is a time sequence diagram for explaining a bias voltage held by an S / H circuit.
[Explanation of symbols]
1 Master station
2 Optical fiber
3a, 3b Optical splitter
4 Optical fiber
5,51-56 Slave station
11 Transimpedance amplifier
12 DC power supply
13 Optical reception control circuit
14 Reception strength storage
15 Optimal bias determination unit
16 Switch circuit
17 Optimal bias storage
18 Bias voltage adjuster
19 S / H (sampling hold) circuit
20 Monitor circuit
APD avalanche photodiode
Optical transmission line termination device for OLT master station
ONU Slave station optical subscriber line termination equipment

Claims (10)

The master station and multiple slave stations are connected via an optical fiber via an optical splitter, and the master station designates the time slot of the upstream optical signal for a specific slave station. In the optical communication system in which the transmission time point of the upstream optical signal is determined ,
An avalanche photodiode that receives the upstream optical signal from the slave station ;
A DC power supply for supplying a bias power to the avalanche photodiode;
A reception control unit that changes the light receiving sensitivity of the avalanche photodiode in a plurality of stages,
The DC power supply includes a switch circuit that switches between different output voltages,
The reception control unit sets a bias voltage to be applied to the avalanche photodiode by switching the switch circuit at a time before receiving an upstream optical signal from a specific slave station, and changes a light receiving sensitivity of the avalanche photodiode. A master station device in an optical communication system , characterized in that: Before the Kioya station apparatus, and the storage unit is provided for storing in advance for each slave station a reception intensity of the upstream optical signals from a particular slave station,
The reception control unit, by setting the bias voltage of the DC power source in response to the reception intensity of the upstream optical signals of the child station stored before term memory unit, to set a light receiving sensitivity of the avalanche photodiode The master station apparatus in the optical communication system according to claim 1, wherein The front Kioya station apparatus is provided with a storage unit for previously storing for each slave station the optimum bias voltage of the DC power supply in accordance with the reception intensity of the upstream optical signals from a particular slave station,
The reception control unit, by setting the bias voltage of the DC power supply based on the optimum bias voltage stored before term memory unit, and sets the receiving sensitivity of the avalanche photodiode, according to claim A master station device in the optical communication system according to claim 1 . The DC power supply is a plurality of power supplies having different output voltages,
The reception control unit applies a bias voltage to the avalanche photodiode using one power source, and changes the bias voltage according to the reception intensity of the slave station received next by another power source, 4. The master station apparatus in an optical communication system according to claim 2 , wherein the bias voltage is switched by a switch circuit at a time before receiving an upstream optical signal from the station. In an optical communication system in which a master station and a plurality of slave stations are connected by an optical fiber via an optical splitter,
An avalanche photodiode that receives the upstream optical signal from the slave station;
A DC power supply for supplying a bias power to the avalanche photodiode;
A reception control unit that changes the light receiving sensitivity of the avalanche photodiode in a plurality of stages by setting a bias voltage of the DC power supply;
In the optical communication system, an unrecognized slave station discovery period for finding a slave station that is not recognized by the master station by polling from the master station is included,
The reception control section, at unrecognized slave station discovery period to receive the upstream optical signal from unrecognized slave station, optical communication systems that and sets the bias voltage of the DC power supply in a plurality of stages Master station device. The unrecognized slave station discovery period is provided regularly,
6. The master station apparatus in an optical communication system according to claim 5 , wherein the reception control unit sets the bias voltage of the DC power supply at a different stage for each unrecognized slave station discovery period. The reception control unit, said subdividing the unrecognized slave station discovery period into a plurality of sections, and wherein the changing the bias voltage to each section in the unrecognized slave station discovery period, of claim 5, wherein A master station apparatus in an optical communication system. 8. The master station apparatus in an optical communication system according to claim 7 , wherein a change in bias voltage for each section in the unrecognized slave station discovery period causes a voltage value of the bias voltage to increase gradually. 8. The master station apparatus in an optical communication system according to claim 7 , wherein the reception control unit changes a time width of each of the plurality of subdivided sections for each unrecognized slave station discovery period. The master station device includes a detection unit that detects that an upstream optical signal has been received from a slave station that is not recognized by the master station,
The reception control unit when the reception of the upstream optical signal is detected by the detection unit, characterized in that to prohibit a change in the bias voltage of the DC power supply, to claim 5 of claim 9 A master station apparatus in the optical communication system described.

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