JP4111163B2 - Abnormal light detection and blocking device - Google Patents

Description

The present invention relates to abnormal light detecting blocking device that put the star optical network, such as the PON system.

  The center station and a plurality of subscribers are connected to the passive optical splitter by a center station terminal device, so-called OLT (Optical Line Terminal), and each subscriber terminal device, so-called ONU (Optical Network Unit), by an optical fiber. In an optical transmission system that is a star-type optical network, a so-called PON (Passive Optical Network) system, if any ONU (Optical network unit) outputs abnormal light to the optical network, the entire network may be down.

  In the PON system, each ONU can output the signal light to the OLT toward the OLT only at a timing permitted by the OLT. In the PON system, TDM (Time Division Multiplexing) is used for transmission of downstream signals, and TDMA (Time Division Multiple Access) is used for transmission of upstream signals. That is, the OLT dynamically assigns time slots that do not overlap each other to each ONU for uplink signals to the center station. Abnormal light is light that the ONU outputs to the optical fiber at an unacceptable timing. Causes of abnormal light generation include errors in the timing of sending signal light to the optical fiber, and continuous light output due to a failure of the light source or its drive circuit.

As an apparatus for monitoring such abnormal light, each upstream signal is transmitted to the center station via another communication line, and the validity of the signal is verified at the center station. In the case of abnormal light, each ONU and optical coupler Patent Document 1 discloses a configuration for blocking the extraordinary light on the optical fiber between the two.
JP-A-11-98078

  In the configuration described in Patent Document 1, it is necessary to prepare a communication line different from the PON system that transmits the output light of each ONU to the center station. Further, when a plurality of optical splitters are connected in multiple stages, the configuration becomes complicated.

The present invention, in a PON system, and an object thereof is to provide a detection and blocking can Ru extraordinary light detecting blocking device abnormal light with a simpler configuration.

The abnormal light detection / blocking device according to the present invention is a star type optical network in which a plurality of subscribers partially share an optical fiber transmission line and communicate with a center station. An abnormal light detection / blocking device arranged between an optical transmission line and an abnormal light detection / blocking device arranged between the subscriber terminal device and the optical transmission line, and in normal operation from the subscriber terminal device to the center station An optical switch that passes the upstream light and the downstream light from the center station to the subscriber terminal device, and monitors the upstream light, and controls the optical switch when the upstream light is abnormal light. A monitoring device that blocks the passage of the upstream light, and an optical coupler that divides the upstream light and supplies the upstream light to the monitoring device, and the optical switch is configured to pass the upstream light and the downstream light. 1 and the upstream light Blocked, characterized in that the downstream optical in the second state and the optical switch capable of switching to forward to the monitoring device.

  According to the present invention, it is possible to prevent abnormal light that causes network disconnection from being output to the star network. This improves the reliability of the star network.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an ONU which is an embodiment of the present invention. The ONU 10 of this embodiment is connected to the OLT 14 of the center station via the optical fiber 12 and is connected to the computer (PC) 18 via the LAN cable 16 (and hub). As a data communication device connected to the ONU 10, there is a so-called home gateway other than the PC 18. The optical fiber 12 is connected to the optical fiber connection terminal 20 of the ONU 10, and the LAN cable 16 is connected to the data input terminal 22 and the data output terminal 24. The optical fiber 12 represents an optical transmission line that connects the ONU 10 and the OLT 14 in the PON system.

  Uplink data Dup output from the PC 18 is input to the LAN receiver 26 via the data input terminal 22. The LAN receiving device 26 includes, for example, a preamplifier and a conversion device that converts a frame configuration of LAN data into a data frame configuration on the optical fiber 12. The output data of the LAN receiver 26 is applied to the drive circuit 30 via the rate adjustment buffer 28. The drive circuit 30 drives the laser diode 32 according to the data from the buffer 28. As a result, the laser diode 32 outputs an optical signal having the wavelength λ1 that carries the upstream data Dup. In the PON system, laser beams having different wavelengths are used for upstream and downstream. Here, the wavelength of the light that carries the upstream signal is λ1, and the wavelength of the light that carries the downstream signal is λ2.

  The output signal light from the laser diode 32 is input to a wavelength division multiplexing (WDM) optical coupler 36 via a normally closed optical switch 34. The upstream signal light output from the WDM optical coupler 36 reaches the OLT 14 of the center station via the optical fiber connection terminal 20 and the optical fiber 12. Between the WDM optical coupler 36 and the optical fiber connection terminal 20, an optical demultiplexer 38 that branches a part of the upstream signal light is disposed. The optical demultiplexer 38 is composed of, for example, a 1 × 2 optical coupler. The upstream signal light branched by the optical demultiplexer 38 is supplied to the monitor device 40. The function of the monitor device 40 will be described later.

  The OLT 14 outputs, to the optical fiber 12, downlink signal light having a wavelength λ <b> 2 that carries downlink data Ddown directed to the PC 18 and a control command for the ONU 10. The downstream signal light is input to the WDM optical coupler 36 via the optical fiber connection terminal 20. The WDM optical coupler 36 supplies the downstream signal light having the wavelength λ <b> 2 to the light receiver 42. The light receiver 42 converts the downstream signal light into an electrical signal. The output of the light receiver 42 is applied to the monitor device 40 and the LAN transmitter 44. The LAN transmission device 44 includes a waveform shaping device, a conversion circuit that converts the data frame configuration of the output electrical signal of the light receiver 42 into a LAN data frame configuration, a preamplifier, and the like. The LAN transmission device 44 supplies the downlink data Ddown carried by the output electric signal of the light receiver 42 to the PC 18 via the LAN cable 16. The monitor device 40 takes in the control command for the ONU 10 and the control command for the optical switch 34 among the output electric signals of the light receiver 42.

  The ONU 10 has a configuration in which an optical switch 34, an optical demultiplexer 38, and a monitor device 40 are added to an existing ONU. The drive circuit 30, the laser diode 32, and the optical switch 34 function as an upstream light generator defined in the claims. Hereinafter, the function of detecting and blocking abnormal light by the added optical switch 34, optical demultiplexer 38, and monitor device 40 will be described in detail.

  The situation where the communication between other ONUs and the OLT 14 is obstructed includes the case 1 in which the upstream signal light is output to both the permitted time slot and the unauthorized time slot, and the signal light to the permitted time slot. There are a case 2 in which the upstream signal light is output in an unauthorized time slot without outputting, and a case 3 in which the laser diode 32 outputs continuous light. These abnormal lights can be detected by examining whether or not upstream light having the wavelength λ1 exists in a time slot that is not permitted by the ONU 10. In general, cases 1 and 3 can be detected by monitoring the optical power of the light having the wavelength λ 1 output to the optical fiber 12. The former detection method can identify the case 2, but the latter method cannot identify the case 2.

  Most of the upstream light having the wavelength λ 1 output from the laser diode 32 reaches the OLT 14 through the optical switch 34, the WDM coupler 36 and the optical fiber 12, but a part is demultiplexed by the optical demultiplexer 38. Input to the monitor device 40. The monitor device 40 confirms whether the upstream light from the optical demultiplexer 38 corresponds to any of cases 1, 2, and 3. As described above, the monitor device 40 detects whether the upstream light from the optical demultiplexer 38 is also present in a time slot that is not permitted, or the upstream light from the optical demultiplexer 38. Whether or not the light is abnormal is determined based on whether or not the power is larger than the optical power that should be. The monitor device 40 can know the time slot assigned to the ONU 10 for transmitting the upstream signal from the OLT 14 from the control signal from the OLT 14 included in the output signal of the light receiver 42. For example, the monitor device 40 or its function is included in a CPU (not shown) that controls the ONU 10.

  If it is determined that the light is abnormal, the monitor device 40 opens the optical switch 34. Thereby, it is possible to completely prevent abnormal light from being output to the optical fiber 12. In order to facilitate understanding of the operation, the configuration example in which the optical switch 34 is connected to the output side of the laser diode 32 is shown in FIG. 1, but of course, an electric switch is arranged between the drive circuit 30 and the laser diode 32. However, when abnormal light occurs, the electrical switch may be opened. When the signal carrying the data Dup is superposed, the operation of the drive circuit 30 itself is stopped when the abnormal light is generated, and the laser diode 32 never emits light, that is, the upstream light is not emitted from the optical fiber 12. It is also possible that the output is never performed.

  To recover from the abnormal light blocking state, for example, a method of forcibly resetting the ONU 10 by turning off the power and turning it on again, and a method of transmitting an optical switch closing command or an uplink signal transmission restart command from the OLT 14 to the ONU 10 There is. In the former case, the optical switch 34 is initialized and enters a closed state. In addition, when the optical switch closing command is transmitted from the OLT 14 to the ONU 10, the monitor device 40 takes in the control command from the output signal of the light receiver 42, and the control command is the optical switch closing command or the uplink signal transmission restart command. The optical switch 34 is closed. Compared with sending a forced reset command from the OLT 14 to the ONU 10, it can be used earlier. Of course, any method is premised on the generation of abnormal light being stopped.

  Further, the optical switch 34 may be disposed between the WDM coupler 36 and the optical demultiplexer 38 or between the optical demultiplexer 38 and the optical fiber connection terminal 20. In this case, since it becomes impossible to receive the downstream signal light, there is no method for recovery other than manual forced reset. The optical demultiplexer 38 may be disposed between the optical switch 34 and the WDM coupler 36.

  FIG. 2 shows a schematic block diagram of a configuration example of the monitor device 40. The light receiver 50 converts the upstream light from the optical demultiplexer 38 into an electrical signal. The A / D converter 52 converts the output of the light receiver 50 into a digital signal and applies it to the microprocessor 54. The microprocessor 54 receives an output signal of the light receiver 42, particularly a control signal. The microprocessor 54 determines from the output digital signal of the A / D converter 52 whether or not the upstream light is present in a time slot other than the permitted time slot, and the upstream light is transmitted to the time slot other than the permitted time slot. Is present, the optical switch 34 is opened. The microprocessor 54 also controls opening / closing of the optical switch 34 in accordance with a control command from the OLT 14 obtained from the output of the light receiver 42. In this configuration, all cases 1, 2, and 3 can be detected and abnormal light can be completely prevented, but the configuration of the monitor device 40 becomes complicated.

  FIG. 3 shows a schematic block diagram of the monitor device 40 that determines whether or not the upstream light is abnormal light based on the optical power. The power monitor 60 measures the optical power of the upstream light from the optical demultiplexer 38, and the integrating circuit 62 displays the measurement result of the power monitor 60 within a predetermined period, for example, one period of upstream signal allocation. Integrate. The switch control circuit 64 compares the integration result of the integration circuit 62 within the predetermined period with a predetermined threshold, and determines that the upstream light is abnormal light when the integration result exceeds the predetermined threshold. The threshold value is set to, for example, the optical power in the longest period that can be assigned to the uplink signal in a normal state, or an optical power slightly larger than this. In the case of abnormal light, the switch control circuit 64 opens the optical switch 34. The switch control circuit 64 also controls opening and closing of the optical switch 34 in accordance with a control command from the OLT 14 obtained from the output of the light receiver 42. With this configuration, it is not possible to detect whether upstream light is present in an unauthorized time slot.

  The integration period of the integration circuit 62 may be a period other than the band allocation period specified by the OLT 14. If it is normal, there should be no upstream light within such a period. If the optical power can be detected within this period, it can be determined that abnormal light is being output.

  FIG. 4 shows a schematic block diagram of a second embodiment of the present invention. The same components as those in the embodiment shown in FIG.

  In the ONU 10 a of the embodiment shown in FIG. 4, a 2 × 2 optical coupler 70 is arranged instead of the optical demultiplexer 38. The optical coupler 70 can branch the upstream light output from the laser diode 32 and the downstream light from the OLT 14. The branched upstream light and downstream light are input to the monitor device 72. The configuration of the monitor device 72 basically includes the configuration shown in FIG. 2 or FIG. 3, but includes a light receiver that converts downstream light into an electrical signal. The monitoring device 72 monitors the upstream light from the optical coupler 70 in the same manner as the monitoring device 40. When the upstream light is abnormal light, the monitoring device 72 opens the optical switch 34. Further, the monitor device 72 converts the downstream light from the optical coupler 70 into an electrical signal, and analyzes a control command from the OLT 14 included in the electrical signal. When the control command from the OLT 14 is a command for instructing closing of the optical switch 34, the monitor device 72 closes the optical switch 34 in accordance with the command.

  FIG. 5 shows a schematic block diagram of a third embodiment of the present invention. The same components as those in the embodiment shown in FIG.

  In the ONU 10 b of the embodiment shown in FIG. 5, an optical demultiplexer 74 that branches downstream light is provided between the WDM coupler 36 and the light receiver 42, and the downstream light split by the optical demultiplexer 74 is monitored 76. Entered in. The monitor device 76 has the same configuration and function as the monitor device 72. The monitor device 76 monitors the upstream light from the optical demultiplexer 38 in the same manner as the monitor device 40. If the upstream light is abnormal light, the monitor device 76 opens the optical switch 34. The monitor device 76 converts the downstream light from the optical demultiplexer 74 into an electrical signal, and analyzes the control command from the OLT 14 included in the electrical signal. When the control command from the OLT 14 is a command for instructing closing of the optical switch 34 or an uplink signal transmission restart command, the monitor device 76 closes the optical switch 34 according to the command.

  FIG. 6 shows a schematic block diagram of the fourth embodiment of the present invention. In this embodiment, the abnormal light detection / blocking function is arranged outside the existing ONU. This embodiment is useful for adding an extraordinary light blocking detection function to an existing ONU.

  The ONU 110 includes an optical fiber connection terminal 112 and a LAN terminal 114. A computer 116 is connected to the LAN terminal 114 directly or via a hub. The ONU 110 has a configuration in which, for example, the optical switch 34, the optical demultiplexer 38, and the monitor device 40 are excluded from the ONU 10.

  The optical fiber connection terminal 112 of the ONU 110 is connected to the OLT 124 of the center station via the normally closed optical switch 118, the 2 × 2 optical coupler 120, and the optical fiber 122. Similar to the optical fiber 12, the optical fiber 122 represents an optical transmission line in the PON system. The 2 × 2 optical coupler 120 branches upstream light from the ONU 110 toward the OLT 124 and downstream light from the OLT 124 toward the ONU 110. The upstream light branched by the optical coupler 120 is input to the monitor device 126. The light receiver 128 converts the downstream light branched by the optical coupler 120 into an electrical signal, and the output electrical signal of the light receiver 128 is input to the monitor device 126. The monitor device 126 has the same configuration as that shown in FIG. 2 or 3 except for the function that operates in synchronization with the ONU 110. The monitor device 126 is connected to the ONU 110 via the synchronization signal line 130 for the synchronization operation with the ONU 110.

  In this embodiment, upstream light output from the fiber connection terminal 112 of the ONU 110 is input to the optical coupler 120 via the optical switch 118. The optical coupler 120 outputs most of the upstream light from the optical switch 118 to the optical fiber 122 and applies the rest to the monitor device 126. The monitor device 126 detects whether the upstream light from the optical coupler 120 is also present in a time slot where the optical coupler 120 is not permitted, or determines whether the upstream optical power is greater than a predetermined threshold value. It is determined whether the light is abnormal light. When it is determined that the upstream light is abnormal light, the monitor device 126 opens the optical switch 118. Thereby, it is possible to completely prevent abnormal upstream light from being output to the optical fiber 122. However, in this embodiment, the optical switch 118 also blocks downstream light from the OLT 124 to the ONU 110.

  To recover from the abnormal light blocking state, an optical switch closing command is transmitted from the OLT 124 to the monitor device 126. This optical switch closing command is transmitted to the monitor device 126 using, for example, a downstream signal light from the OLT 124 to the ONU 110. A command that is not used by the ONU 110 may be used as the switch control command. Downstream signal light output from the OLT 124 is input to the light receiver 128 via the optical fiber 122 and the optical coupler 120. The light receiver 128 converts the downstream signal from the OLT 124 into an electrical signal and applies the electrical signal to the monitor device 126. The monitor device 126 closes the optical switch 118 in accordance with the optical switch closing command included in the output electric signal of the light receiver 128. Thereby, the upstream light output from the ONU 110 can pass through the optical switch 118 and can reach the OLT 124 via the optical coupler 120 and the optical fiber 122.

  When determining whether or not the light is abnormal by measuring the optical power, the monitoring device 126 does not need to establish synchronization with the ONU 110.

  FIG. 7 shows a schematic block diagram of a fifth embodiment of the present invention. The embodiment shown in FIG. 7 is also a modification of the embodiment shown in FIG. 6, and the same components as those in the embodiment shown in FIG.

  An optical switch 140 is disposed instead of the optical switch 118, and a 1 × 2 optical coupler 142 that branches only upstream light is disposed instead of the 2 × 2 optical coupler 120. The optical switch 140 includes a common contact C and two contacts A and B that are selectively connected to the common contact C. The contact A is connected to the fiber connection terminal 112 of the ONU 110, the contact B is connected to the light receiver 144, and the common contact C is connected to the 1 × 2 optical coupler 142 that demultiplexes the upstream light. The upstream light branched by the optical coupler 142 is applied to the monitor device 146. In the optical switch 140, the contact A is normally connected to the common contact C, and the contact B is connected to the common contact C when abnormal light is blocked.

  When the contact A is connected to the common contact C, the upstream light output from the ONU 110 can reach the OLT 124, and the downstream light output from the OLT 124 can reach the ONU 110. The optical coupler 142 outputs most of the upstream light from the optical switch 140 to the optical fiber 122 and applies the rest to the monitor device 146. The monitor device 146 detects whether or not the upstream light from the optical coupler 142 is also present in a time slot that is not permitted, or whether or not the optical power of the upstream light is greater than a predetermined threshold value. Determine whether it is light. The ONU 110 notifies the monitor device 146 of the time slot permitted for the uplink signal. When the monitor device 146 determines that the upstream light is abnormal light, the monitor device 146 switches the common contact C of the optical switch 140 to the contact B. Thereby, it is possible to completely prevent abnormal upstream light from being output to the optical fiber 122.

  When the contact B of the optical switch 140 is connected to the common contact C, the upstream light output from the ONU 110 is blocked by the optical switch 140, but the downstream light output from the OLT 124 is input to the light receiver 144 by the optical switch 140. . The light receiver 144 converts the downstream light into an electrical signal and applies it to the monitor device 146. Accordingly, the ONU 110 cannot receive a signal from the OLT 124, but the monitor device 146 can receive a signal from the OLT 124, for example, a control command.

  When it is desired to recover from the abnormal light blocking state, the OLT 124 transmits an optical switch switching command to the monitor device 126. The downstream signal light that carries the optical switch switching command output from the OLT 124 is input to the light receiver 144 via the optical fiber 122, the optical coupler 142, and the optical switch 140. The light receiver 144 converts the downstream signal light from the OLT 124 into an electrical signal and applies the electrical signal to the monitor device 146. The monitor device 146 connects the common contact C of the optical switch 140 to the contact A in accordance with the optical switch switching command included in the output electrical signal of the light receiver 144. Thereby, the upstream light output from the ONU 110 can pass through the optical switch 140 and can reach the OLT 124 via the optical coupler 142 and the optical fiber 122.

  When determining whether or not the light is abnormal by measuring the optical power, the monitor device 146 does not need to establish synchronization with the ONU 110.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of the first embodiment of the present invention. 3 is a schematic configuration block diagram showing a configuration example of a monitor device 40. FIG. 3 is a schematic configuration block diagram showing a second configuration example of the monitor device 40. FIG. It is a schematic block diagram of the second embodiment of the present invention. It is a schematic block diagram of the third embodiment of the present invention. It is a schematic block diagram of the fourth embodiment of the present invention. It is a schematic block diagram of the fifth embodiment of the present invention.

Explanation of symbols

10, 10a, 10b: ONU
12: Optical fiber 14: OLT
16: LAN cable 18: Computer (PC)
20: optical fiber connection terminal 22: data input terminal 24: data output terminal 26: LAN receiver 28: buffer 30: drive circuit 32: laser diode 34: optical switch 36: WDM coupler 38: optical demultiplexer 40: monitor device 42: light receiver 44: LAN transmitter 50: light receiver 52: A / D converter 54: microprocessor 60: power monitor 62: integration circuit 64: switch control circuit 70: 2 × 2 optical coupler 72: monitor device 74: Optical demultiplexer 76: Monitor device 110: ONU
112: Optical fiber connection terminal 114: LAN terminal 116: Computer 118: Optical switch 120: 2 × 2 optical coupler 122: Optical fiber 124: OLT
126: monitor device 128: light receiver 130: synchronization signal line 140: optical switch 142: 1 × 2 optical coupler 144: light receiver 146: monitor device

Claims (4)

In a star-type optical network in which a plurality of subscribers partially share an optical fiber transmission line and communicate with a center station, the subscriber terminal device (110) and the optical transmission line (122) of the star-type optical network An abnormal light detection and blocking device disposed between,
Arranged between the subscriber terminal device (110) and the optical transmission line (122), and when normal, upstream light from the subscriber terminal device (110) to the center station (124), and the center An optical switch ( 140) that passes downstream light from the station (124) to the subscriber terminal device (110);
A monitor device ( 144, 146) that monitors the upstream light and controls the optical switch ( 140) to block the passage of the upstream light when the upstream light is abnormal light;
Optical coupler (142) for branching the upstream light and supplying it to the monitoring device (144, 146)
And
The optical switch switches between a first state in which the upstream light and the downstream light pass and a second state in which the upstream light is blocked and the downstream light is transferred to the monitoring device (144, 146). An abnormal light detection / blocking device , characterized by being an optical switch that can be used. The monitoring device ( 144, 146) includes a determination device (54) for determining whether or not the upstream light exists in a period other than the upstream optical transmission permission period of the subscriber terminal device (110). The abnormal light detection blocking device according to claim 1 . The abnormal light detection / blocking device according to claim 1 , wherein the monitoring device ( 144, 146) includes a power measuring device (60, 62) for measuring the optical power of the upstream light in a predetermined period. The monitoring devices ( 144, 146) have a function (54, 64) for receiving a transmission resumption command transmitted by the downstream light from the center station (124), and according to the transmission resumption command, The abnormal light detection / blocking device according to claim 1 , wherein the optical switch ( 140) is controlled to pass the upstream light.

Images