JP2008227994A - Optical transmission apparatus and optical transmission method - Google Patents

Abstract

【Task】
When a wavelength multiplexed optical signal having a narrow wavelength interval is amplified by an optical amplifier, the optical signal is greatly deteriorated due to a nonlinear effect generated inside the optical amplifier.
[Solution]
The wavelength multiplexed optical signal is separated into two signal groups having a wavelength interval twice as large as the original wavelength interval, and each signal group is amplified by an optical amplifier.
[Selection] Figure 6

Description

  The present invention relates to a transmission apparatus and a transmission method for transmitting wavelength-multiplexed optical signals.

  In an optical communication system, in order to reduce system cost while expanding communication capacity, a wavelength division multiplexing optical transmission technique is generally applied in which a plurality of signal lights having different wavelengths are bundled and communicated with one optical fiber. In an actual system, an optical fiber amplifier is installed on the transmission path to compensate for the loss of the optical signal that occurs in the optical fiber that is the transmission path between two distant points. A plurality of signal lights having different wavelengths are collectively amplified without being converted into.

  FIG. 1 shows a general network configuration using a wavelength division multiplexing optical transmission system. As a network configuration, an access 1 for providing an FTTH (Fiber To The Home) service using an OLT (Optical Line Terminal) device 1-2 or an ONU (Optical Network Unit) device 1-3 to a local unit subscriber. -4, edge 1-6 for aggregating communications from local unit subscribers in a regional group using a plurality of L2 (Layer 2) switches 1-5, and communications aggregated by L2 switch in city units Consists of a metro 1-7 to be aggregated and a core 1-8 for efficiently transmitting long distances between large cities for large-capacity communications aggregated in city units. In this network, an OADM (Optical Add Drop Multiplexer) device 1-1 is an optical transmission system that is used to collect communications scattered over a relatively wide area in one place.

  FIG. 2 is a general configuration example of the OADM device 1-1. The OADM device 1-1 performs optical amplification on the light intensity attenuated when transmitting through the transmission line (optical fiber) 2-1, or has a sufficiently large light intensity when transmitting to the transmission line 2-1. Optical amplifying unit 2-2 for performing optical amplification, branching and inserting for extracting a desired signal from a plurality of wavelength-multiplexed optical signals, or for wavelength-multiplexing a desired signal and bundling it again into a plurality of signal groups In order to properly convert the signal branched from the unit 2-5 and the branch insertion unit 2-5 to the subscriber signal accommodated in the OADM device 1-1, or to appropriately convert the signal from the subscriber signal In addition, the transponder unit 2-3 for wavelength multiplexing at the add / drop unit, and the supervisory control unit 2 for performing supervision control on the optical amplifying unit 2-2, the add / drop unit 2-5, and the transponder unit 2-3. -4.

  The optical amplifying unit 2-2 performs optical amplification on the receiving side optical amplifying unit for performing optical amplification on the signal light intensity received from the transmission line, and on the signal light intensity received from the add / drop unit. The transmission side optical amplifying unit for sending out to the transmission line. Further, the add / drop unit 2-5 also performs wavelength addition on the signal light received from the transponder unit and the add / drop unit on the branch side for performing wavelength branching on the signal light from the optical amplifier on the receiving side. It is comprised from the branch insertion part of the insertion side.

  In the OADM device 1-1 in FIG. 2, the signal light propagates along the path indicated by the dotted line 2-7 with respect to the signal light, and is transmitted to the monitor control light 2-4-1 mounted on the monitor control unit 2-4. On the other hand, the supervisory control light propagates as indicated by the solid line 2-6. That is, the supervisory control light 2-4-1 is separated by the optical amplifying unit 2-2, and input to the supervisory control light processing unit 2-4-1 mounted on the supervisory control unit 2-4. The signal light 2-7 is optically amplified by the optical amplifying unit 2-2 and then input to the add / drop unit 2-5. Note that the signal light flow 2-7 and the supervisory control light flow 2-6 are described only in the input direction, but the same signal flows in the output direction.

  FIG. 3 is a diagram for explaining wavelength-multiplexed light of the wavelength-multiplexed signal group 3-2 and the supervisory control signal 3-1. In a general OADM device 1-1, communication of signals used for control and monitoring between a plurality of wavelength-multiplexed signal groups 3-2 carrying actual communication data and the remote OADM devices 1-1 is performed. There is a supervisory control signal 3-1 for realizing. FIG. 3 shows 32 wavelength-multiplexed signal wavelength groups 3-2 and one monitor control signal 3-1 wavelength, and the monitor control signal 3-1 is the short wavelength side of the signal wavelength group 3-2. However, when the monitoring control signal 3-1 is arranged on the long wave side or when a plurality of monitoring control signals 3-1 are arranged, the signal wavelength is wavelength-multiplexed with a numerical value other than 32. Sometimes it is.

  In the general OADM device 1-1, a function of extracting a desired signal from a plurality of optical signals or wavelength-multiplexing a desired signal and bundling it again into a plurality of signal groups is performed in the branching insertion unit 2-5. Is called. Further, regarding the communication of the monitoring control signal between the remotely arranged OADM devices 1-1, for example, only the monitoring control signal is branched from the wavelength multiplexed light in the monitoring control signal branching unit arranged in the input part of the optical amplification unit, In addition, a supervisory control signal is inserted with respect to the signal wavelength in the supervisory control signal insertion unit arranged at the output of the optical amplifier.

  FIG. 4 is a diagram for explaining branch insertion for the supervisory control signal in the optical amplifying unit 2-2 constituting a part of the wavelength multiplexing apparatus. In the optical amplifying unit 2-2, a supervisory control signal branching unit 4-4 for branching the supervisory control signal and the signal is mounted inside, and the signal and the supervisory signal are input before the signal amplifying unit 4-3 that performs signal amplification Separate control signals. Also, a monitoring control signal insertion unit 4-5 for inserting a monitoring control signal into the signal is mounted inside the optical amplification unit 2-2, and the optically amplified signal after passing through the signal amplification unit and the monitoring control are installed. Combine the signals.

  As described with reference to FIG. 2, regarding the signal light, the signal light propagates along a route indicated by 2-7, and the supervisory control light propagates as indicated by 2-6. That is, the supervisory control light 2-6 is branched by the supervisory control signal branching unit 4-4 mounted on the optical amplifier 4-2, and is input to the supervisory control unit 2-4. Further, the signal light 2-7 is not branched by the supervisory control signal branching unit 4-4 but is input to the signal amplifying unit 4-3 and optically amplified. Note that the signal light flow 2-7 and the supervisory control light flow 2-6 are described only in the input direction, but the same signal flows in the output direction.

In the case of increasing the communication capacity handled by the OADM device 1-1 having such a general configuration example,
1) A method of increasing the width of the wavelength band accommodated in the OADM device 2) A method of increasing the signal speed (bit rate) per wavelength accommodated in the OADM device 3) A method of increasing the wavelength density without changing the wavelength band accommodated in the OADM device There are three.

  Among them, with respect to 1), in order to widen the width of the wavelength band, it is necessary to expand the amplification band of the optical amplifying unit and expand the wavelength band handled by the add / drop unit and the transponder unit. For example, if the amplification band of the optical amplification unit is expanded, it is necessary to achieve a wider range of gain flatness within the wavelength band required for the optical amplification unit, and the specifications required for the optical amplification unit are drastically severe. It becomes. In addition, the required light emission wavelength for the optical transmission unit for emitting light in the transponder unit needs to be realized in a wider range, and the required specifications as in the optical amplification unit become drastically strict. Furthermore, depending on the type of transmission line (optical fiber), there is a phenomenon in which the optical fiber is non-linear in the vicinity of the zero dispersion wavelength where the chromatic dispersion is zero. In some cases, the expanded wavelength band cannot be used depending on the type of optical fiber.

  2) is a method of increasing the signal speed (bit rate) per wavelength while maintaining the width of the wavelength band as it is. This has little effect on the amplification band or add / drop unit of the optical amplification unit, but the signal waveform increases because the influence of the wavelength dispersion of the optical fiber increases by four times the increase in bit rate as the signal speed increases. The effect of deterioration is dramatically increased. Further, since the reception sensitivity is deteriorated in proportion to the bit rate as the signal speed is increased, a function for compensating for the reception sensitivity deterioration by the increase of the bit rate is required. In general, this sensitivity degradation compensation includes a method of increasing the correction capability of the error correction function installed in the transponder unit, and the wavelength dispersion of the transmission line to compensate for the influence of the wavelength dispersion of the optical fiber. Therefore, a method for executing dispersion compensation design that cancels the characteristics in more detail is required, which raises a problem of an increase in the price of the entire system.

  Furthermore, with regard to 3), in order to increase the wavelength density, it is not necessary to widen the amplification band of the optical amplifying unit, but the wavelength multiplexed light density inside the optical amplifying unit increases, so that the optical fiber is formed inside the optical amplifying unit. The influence of nonlinearity becomes remarkable, and it leads to signal waveform deterioration due to the interaction between wavelengths due to nonlinear effects such as four-wave mixing and cross-phase modulation effect. In general, the optical amplifying unit 2-2 is composed of an optical fiber in the same manner as the transmission line, and a special substance (erbium) is added to the optical fiber, and a predetermined laser beam is applied to the added optical fiber from the outside. By inputting, an optical signal passing through the optical fiber to which erbium is added is optically amplified. The optical fiber accommodated in the optical amplifying unit 2-2 is sufficiently shorter than the length of several tens of meters and the length of several tens of kilometers of the optical fiber used in the transmission path. However, the optical fiber for amplification used in the optical amplifying unit 2-2 optically amplifies the optical signal by confining the optical signal at a high density by narrowing the width (core system) of the path through which the optical signal passes. The amplification efficiency is improved.

  Therefore, the optical fiber for amplification uses an optical fiber that is sufficiently shorter than a normal optical fiber. However, since the optical signal is confined at a high density, it cannot be ignored compared to the transmission line. Non-linear effects occur. Furthermore, since the strongest light intensity is generated inside the optical amplifier in the entire optical transmission apparatus, signals that are wavelength-multiplexed at a higher density in order to increase the wavelength density are generated inside the optical amplifier. The generated nonlinear effect may be dominant.

  FIG. 5 is a diagram showing an optical level diagram when high-density wavelength multiplexing is realized in the general OADM device configuration example shown in FIG. A represents the light intensity of the signal optically amplified by the transmission-side optical amplifying unit 5-2 when being transmitted to the transmission line 5-1, and B represents the transmitted signal light intensity propagates through the transmission line. Represents the intensity of the optical signal after attenuation. Further, C is the light intensity for transmitting the attenuated optical signal intensity to the add / drop unit 5-5 after optical amplification by the optical amplifier unit 5-2 on the receiving side, and D is transmitted. It represents the signal light intensity at which the optical signal is lost due to the insertion loss of the add / drop unit 5-5.

  In this light level diagram, the place where the light intensity is the highest is the output section of the light amplification section 5-2 on the receiving side, that is, C. This is because the upper limit input limit of light intensity is generally +3 dBm or more in the add / drop unit, which is sufficiently larger than the upper limit input limit to the transmission path. Further, the lowest point of the optical level diagram is the place that most affects the optical SNR, and D is sufficiently larger than B in order to prevent the optical SNR degradation from being dominant due to the insertion loss generated in the add / drop section. This is because it needs to be large.

  This is a phenomenon that appears particularly prominently in the OADM device 1-1. That is, the OADM device 1-1 has a function of optically branching and inserting wavelength-multiplexed light as an optical signal in the add / drop unit 2-5 of FIG. 2, but the insertion loss of the add / drop unit is large. In general, the insertion loss of the branch insertion section is 10 to 15 dB. This is a loss that is comparable to the insertion loss of the transmission line 5-1. If the signal light intensity of C is not increased in FIG. 2-3, the light intensity of D is significantly reduced. The light intensity will be comparable. In order to avoid this, in order to increase the light intensity of D, the light intensity of C, that is, the light amplification section (reception side) that performs light amplification from B to C tends to require a large light amplification degree and light output intensity. It is in. Further, in A, there is an upper limit input limit due to a nonlinear effect generated in the optical fiber as a transmission line, which is generally −5 dBm / ch to 0 dBm / ch per wavelength, and the upper limit input to the add / drop unit. Lower than the limit.

  From these facts, the point where the highest signal light intensity is required is C, and the optical signal density tends to be highest in the C output, that is, the optical amplifying unit (receiving side) that performs optical amplification from B to C. There is a reason why the nonlinear effect generated in the optical amplifier is larger than the nonlinear effect generated in the transmission line. On the other hand, in Patent Document 1, waveform shaping is performed by inputting a signal having a large light intensity to the nonlinear fiber, but in addition to the waveform shaping effect, four-wave mixing and mutual phase generated in the nonlinear fiber are performed. In order to reduce signal waveform degradation due to interaction between wavelengths such as modulation effects, the odd numbered wavelength multiplexed light and even numbered wavelength multiplexed light are separated and widened before being input to the nonlinear fiber. By inputting into the nonlinear fiber in the state of the wavelength interval, the interaction between wavelengths generated inside the nonlinear fiber is reduced.

  In other words, expecting the waveform shaping effect due to the nonlinear effect generated inside the nonlinear fiber, high signal light is input to the nonlinear fiber, but if it is input to the nonlinear fiber in a wavelength multiplexed state in order to input high signal light Inter-wavelength interaction occurs between wavelength multiplexed signals, and signal waveform deterioration occurs. Therefore, the wavelength chill interaction is reduced by separating the odd-numbered wavelength multiplexed light and the even-numbered wavelength multiplexed light immediately before the wavelength multiplexed signal is input to the nonlinear fiber.

JP 2004-198926 A

  However, in Patent Document 1, the target for reducing the interaction between wavelengths is the nonlinear optical fibers 12-1 and 12-2 for performing waveform shaping of the optical signal, and the inside of the nonlinear optical fibers 12-1 and 12-2. A waveform shaping effect due to a nonlinear effect is expected for each optical signal. That is, the object is to reduce the interaction between wavelengths while maintaining the generation amount of the self-nonlinear effect. In this case, the nonlinear effect generated inside the optical amplifier 11 for transmitting the optical signal to the nonlinear optical fibers 12-1 and 12-2 is not mentioned.

  Further, in the optical transmission system using the OADM device 1-1, the influence of the output light intensity of the optical amplifier 11 on the optical SNR of the system is important. By keeping the output intensity of the optical amplifier 11 high, the OADM device 1- No mention is made that the optical SNR of an optical transmission system using 1 can be kept high.

  In the present invention, the interleaver method is used to reduce the nonlinear effect generated in the optical amplifier, which becomes a problem when increasing the wavelength multiplexed light handled by the OADM device 1-1 using the method 3). The problem is solved by amplifying light to a desired light intensity without increasing the density of wavelength multiplexed light input into the optical amplifier.

  For this reason, even-numbered wavelength-multiplexed light and odd-numbered wavelength-multiplexed light are first separated from a plurality of wavelength-multiplexed optical signals input from the transmission path using a device that realizes an interleaver function. As a result, the signal density of the optical signal input from the transmission path can be reduced to ½. Next, the optical signal wavelength with the signal density reduced to ½ is separately input to the even-numbered wavelength-multiplexed optical amplifier or the odd-numbered wavelength-multiplexed optical amplifier, and the signal density of the optical signal is changed. Light amplification is performed while keeping it low.

  According to the present invention, since the optical signal density inside the optical amplifier is kept low, the waveform deterioration effect due to the nonlinear optical effect generated in the optical amplifier can be kept low.

  FIG. 6 illustrates a wavelength division multiplexing optical transmission system (OADM) having a wavelength branching / inserting function in an interleaver system according to the present invention. FIG. 6 is a block diagram of the OADM apparatus of FIG. 2 in which an even-numbered wavelength multiplexed light and an odd-numbered wavelength multiplexed light are multiplexed by an interleaver 6-6 before optically amplifying the wavelength multiplexed light output from the transmission line 6-1. After separating the light or performing optical amplification in the optical amplifying unit 6-2 and before sending an optical signal to the transmission line, even-numbered wavelength multiplexed light and odd-numbered wavelength multiplexed light in the interleaver unit Communication capacity expansion is realized by providing a function of multiplexing light.

  In FIG. 6, in addition to the interleaver unit 6-6, an add / drop unit for extracting a desired signal from a plurality of wavelength-multiplexed optical signals or for wavelength-multiplexing a desired signal and bundling it again into a plurality of signal groups. 6-5, in order to properly convert the signal branched from the add / drop unit 6-5 to the subscriber signal accommodated in the OADM device 1-1, or to appropriately convert the signal from the subscriber signal , A transponder unit 6-3 for wavelength multiplexing at the add / drop unit, and a supervisory control unit 6-6 for monitoring and controlling the optical amplifying unit 6-2, the add / drop unit 6-5, and the transponder unit 6-3. It is composed of four.

  Here, the optical amplifying unit 6-2, the add / drop unit 6-5, and the monitoring control unit 6-4 are separately prepared for odd-numbered wavelength multiplexed light or even-numbered wavelength multiplexed light. That is, after being branched into odd-numbered or even-numbered wavelength multiplexed light by the interleaver unit 6-6 or before being inserted into odd-numbered or even-numbered wavelength multiplexed light by the interleaver unit 6-6, The function of the odd-numbered wavelength multiplexed light is realized in the odd-numbered (odd) wavelength-multiplexed light amplifying unit 6-2o, the add / drop unit 6-5o, and the supervisory control unit 6-4o. The function is realized in the optical amplifier 6-2e for wavelength-multiplexed light having an even number (even), the add / drop unit 6-5e, and the supervisory control unit 6-4e.

  Further, since the interleaver unit 6-6 needs to handle not only the signal wavelength but also the monitor control light at the same time as the odd-numbered or even-numbered wavelength multiplexed light, the odd-numbered monitor control light is an odd number. The wavelength-multiplexed wavelengths are assigned at the same wavelength intervals as the signal light for use. Further, the even-numbered supervisory control light is assigned a wavelength-multiplexed wavelength at the same wavelength interval as the even-numbered signal light. By assigning supervisory control light to the signal light at the same wavelength interval as the signal light in this way, the supervisory control light is branched and inserted into the odd-numbered wavelength signal group and the even-numbered wavelength signal group simultaneously with the signal light. It becomes possible.

  In the embodiment of FIG. 6, as the interleaver unit method, the wavelength-division multiplexed signal light is divided and divided into the odd-numbered signal light and the even-numbered signal light in two parts, but the interleaver unit method is used. The effect can also be satisfied by performing the division or multiplexing into 4 divisions or 8 divisions.

  In the OADM device 1-1 in FIG. 6, the signal light for the odd-numbered wavelength propagates along the path indicated by the dotted line 2-7o, and the signal light for the even-numbered wavelength is indicated by the dotted line 2-7e. The signal light propagates along such a path. Further, as shown by the solid line 2-6o, the odd-numbered supervisory control control unit 2-4-1o for the odd-numbered wavelength mounted on the odd-numbered supervisory control unit 6-4o is provided. With respect to the monitoring control light processing unit 2-4-1e for the even-numbered wavelength mounted on the even-numbered monitoring control unit 6-4e, the light is propagated, as shown by the solid line 2-6e. The supervisory control light propagates.

  That is, the odd-numbered supervisory control light 2-4-1o and the even-numbered supervisory control light 2-4-1e are wavelength-separated into an odd-numbered side and an even-numbered side by the interleaver 6-6, and then the odd-numbered supervisory control light The light 2-4-1o is separated by the odd-numbered side optical amplifier 6-2o and input to the monitoring control light processing unit 2-4-1o mounted on the monitoring control unit 6-4o. The even-numbered monitoring control light 2-4-1e is separated by the even-numbered optical amplifier 6-2e and input to the monitoring control light processing unit 2-4-1e mounted on the monitoring control unit 6-4e. Is done. The signal light flows 2-7o and 2-7e and the monitoring control light flows 2-6o and 2-6e are described only in the input direction, but the same signal flows in the output direction.

  Further, in the embodiment of FIG. 7, there is a branching / inserting section 6-5 that does not perform regenerative repeat of the optical signal when connecting between the OADM apparatuses 1-1, and compensates only the optical fiber passing loss with the optical amplifier. An OADM device 1-1 that does not perform is also conceivable. In this case, in the OADM device 1-1, there is no branching / inserting unit 6-5 in a portion sandwiched between the interleaver units 6-6, and the optical amplifying unit 6-2o for even-numbered signals and What is necessary is just to arrange | position the optical amplification part 6-2e for the signal for odd numbers. Further, similarly to the OADM device 1-1 in FIG. 5, the monitoring control unit 6-4e for odd number signals and the monitoring control unit 6-4o for even number signals are respectively for odd numbers. The optical amplifying unit 6-2o and the even-numbered optical amplifying unit 6-2e are separately monitored and controlled.

  In this case, similarly to the OADM device 1-1 in FIG. 5, the monitoring control wavelengths used in the monitoring control unit 6-4 are the odd-numbered optical amplifier 6-2o and the odd-numbered optical amplifier 6. -2e are wavelength-separated and multiplexed independently of each other, and therefore have the same wavelength arrangement as the odd-numbered signal wavelength and the even-numbered signal wavelength. In the OADM device 1-1 in FIG. 7, the signal light propagates along the path indicated by 2-7o for the signal light for the odd-side wavelength, and the signal light for the even-side wavelength is indicated by 2-7e. The signal light propagates along the path. Further, as shown by 2-6o, the odd-numbered monitoring control light propagates to the monitoring control light 2-4-1o for the odd-numbered wavelength mounted in the odd-numbered monitoring control unit 6-4o. The even-numbered monitoring control light 2-4-1e for the even-numbered wavelength mounted on the even-numbered monitoring control unit 6-4e propagates as shown by 2-6e. To do.

  That is, the odd-numbered supervisory control light 2-4-1o and the even-numbered supervisory control light 2-4-1e are wavelength-separated into an odd-numbered side and an even-numbered side by the interleaver 6-6, and then the odd-numbered supervisory control light The light 2-4-1o is separated by the odd-numbered side optical amplifier 6-2o and input to the monitoring control light processing unit 2-4-1o mounted on the monitoring control unit 6-4o. The even-numbered monitoring control light 2-4-1e is separated by the even-numbered optical amplifier 6-2e and input to the monitoring control light processing unit 2-4-1e mounted on the monitoring control unit 6-4e. Is done.

  The odd-numbered signal light 2-7o and the even-numbered signal light 2-7e are separated into odd-numbered and even-numbered wavelengths by the interleaver 6-6, and the even-numbered signal light 2-7o is even-numbered. The odd-numbered signal light 2-7e is amplified by the odd-numbered optical amplifier 2-2e. The signal light flows 2-7o and 2-7e and the monitoring control light flows 2-6o and 2-6e are described only in the input direction, but the same signal flows in the output direction.

  FIG. 8 is a diagram for explaining the wavelength separation method of the interleaver 6-6 used in this embodiment. The signal groups # 1, # 2,..., # 31, and # 32 represent the wavelength-multiplexed signal group 8-1 before performing the interleaver, and for example, at a certain frequency interval such as a 50 GHz interval. They are regularly arranged. On the other hand, in the interleaver unit 6-6, odd numbers are regularly arranged at a certain frequency interval such as a 100 GHz interval such as # 1, # 3, # 5,... # 29, # 31. Only signal group 8-2 and only even numbers that are regularly arranged at a certain frequency interval such as 100 GHz interval such as # 2, # 4, # 6,..., # 30, # 32. It has a function of separating the signal group 8-3. The signal groups such as # 1, # 2,... May be assigned as signal wavelengths, or may be assigned as monitoring control signal wavelengths.

  For the supervisory control light 2-4-1 for the odd-numbered system described in FIGS. 6 and 7, for example, the odd-numbered supervisory control light flow 2-6o and the odd-numbered side in the interleaver 6-6. The signal light flow 2-7o of the interleaver 6-6 must be output to the port that multiplexes and outputs the signal light of the odd-numbered wavelength side, and input to the same odd-numbered optical amplifier 6-5o. There is. Similarly, the even-number side monitor control light flow 2-6e and the even-number signal light flow 2-7e are multiplexed with the even-numbered wavelength signal light of the interleaver 6-6 for output. It is necessary to output it and input it to the same even-numbered optical amplifier 6-5e.

  Therefore, if the supervisory control light 2-4-1o is added to the signal light set to the odd numbered wavelength arrangement, the odd numbered wavelength arrangement 8-2 is also applied to the supervisory control light 2-4-1o. Must be set to Further, the wavelength accuracy required for the supervisory control light 2-4-1o is equal to the wavelength accuracy of the signal light arranged at odd numbers, that is, the wavelength indicated by the reference numeral 8-2 in FIG. 8 for the signal light. It needs to be arranged at the wavelength of the interval. Similarly, if the supervisory control light 2-4-1e is added to the signal light set to the even-numbered wavelength arrangement, the even-numbered wavelength arrangement 8- Must be set to 3. Further, the wavelength accuracy required for the supervisory control light 2-4-1e is equal to the wavelength accuracy of the signal light arranged at the even number, that is, the wavelength indicated by the reference numeral 8-3 in FIG. 8 for the signal light. It needs to be arranged at the wavelength of the interval.

  By arranging the signal light wavelength and the monitoring control light wavelength on the same number in this way, it becomes possible to input to the same device of the odd number or even number, and the signal light and the monitoring control light are managed correctly. be able to. Specifically, the monitor control light wavelength when the signal light wavelength is arranged as 1573.714 nm, 1574.540 nm, 1575.368 nm,..., For example, 1573.888 nm is used. It suffices if it matches the wavelength defined by 714 nm ± 0.8 nm × N (N is an integer). In addition, as a monitoring control light wavelength when arranged as 1574.127 nm, 1574.954 nm, 1575.782 nm, etc., for example, 1574.127 nm ± 0.8 nm × N, such as 1573.301 nm. It suffices if it matches the wavelength defined by (N is an integer). In the wavelength exemplified here, the wavelength interval before the interleaving is 0.4 nm, and the wavelength interval between the even and odd signal groups after the interleaving is 0.8 nm. That is, if the wavelength interval of the wavelength multiplexed signal light before passing through the interleaver is N / 2, the wavelength interval of each wavelength multiplexed signal light after passing through the interleaver is N.

  FIG. 9 is a diagram for explaining a block configuration of the interleaver unit 6-6. The interleaver unit 6-6 includes a demultiplexing side 6-6-1 having one input and two outputs, or a multiplexing side 6-6-2 having two inputs and one output, as shown in FIG. Thus, for example, a signal group 9-1 regularly arranged at a certain frequency interval such as a 50 GHz interval and two signal groups 9-2, 9 regularly arranged at a certain frequency interval such as a 100 GHz interval -3 is multiplexed and separated.

  FIG. 10 is a diagram for explaining the problem of crosstalk on the demultiplexing side 6-6-1 of the demultiplexing side interleaver. The interleaver partial wave side 6-6-1 separates the wavelength multiplexed light from the input port 10-7 into odd numbered wavelength multiplexed light and even numbered wavelength multiplexed light. At this time, the even-numbered wavelength multiplexed light is mixed in the even-numbered output section, and the even-numbered wavelength multiplexed light is mixed in the odd-numbered output section. In other words, in addition to the odd-numbered wavelength multiplexed light intensity P10-2, the even-numbered wavelength multiplexed light intensity q10-3 is mixed in the odd-numbered wavelength output port 10-1. Similarly, in addition to the even-numbered wavelength multiplexed light intensity Q10-6, the odd-numbered wavelength multiplexed light intensity p10-5 is mixed into the even-numbered wavelength optical output port 10-4.

For this reason,
(Formula 1)
Odd number wavelength output port 10-1 = P + q
Even numbered wavelength output port 10-4 = Q + p
That is, the light intensity is observed. This mole light is determined by the optical characteristics of the optical device that realizes the interleaver function. Here, when P = 0, the even-numbered wavelength multiplexed light intensity q10-3 is observed at the odd-numbered wavelength output port 10-1 even though there is no odd-numbered wavelength multiplexed light. The In this case, the subsequent optical amplifying unit does not have permission for optical amplification because there is originally no wavelength-multiplexed light intensity that is input, but in the above case, it receives the light intensity of the mole light q10-3. Since the optical amplification is erroneously permitted, the optical amplifier malfunctions.

The relationship among P, Q, p, and q is P >> p, q, and Q >> p, q when the even-numbered and odd-numbered signal lights are not zero.
(Formula 2)
P-XTp = p
Q-XTq = q
It is. XT is a numerical value that defines the amount of crosstalk, and actually has a value of about 25 dB. Here, XTp is a difference between the signal light intensity P output from the output port 10-1 having the odd numbered wavelength and the signal light intensity p observed from the output port 10-4 having the even numbered wavelength. Similarly, XTq is the difference between the signal light intensity Q output from the even-numbered wavelength output port 10-4 and the signal light intensity q observed from the odd-numbered wavelength output port 10-1.

  In this embodiment, in order to reduce the influence of the mole light, as shown in FIG. 11, the variable attenuators 11-1 and 11-3 and the wavelength resolution of the demultiplexing side 6-6-1 of the interleaver unit are reduced. The light intensity monitors 11-2 and 11-4 are respectively arranged at the odd numbered wavelength output port 10-1 and the even numbered wavelength output port 10-4.

  Specifically, the variable attenuator 11-is disposed immediately after the interleaver 6-6-1 for separating the odd-numbered wavelength and the even-numbered wavelength, and attenuates the output light intensity from the interleaver 6-6-1. 1 and 11-3, and light intensity monitors 11-2 and 11-4 with wavelength resolution capable of observing the light intensity for each wavelength passing through the variable attenuator output. Here, the positions of the variable attenuators 11-1 and 11-3 and the light intensity monitors with wavelength resolution 11-2 and 11-4 are in the order shown in FIG. 11, but this is the reverse order, that is, with wavelength resolution. The order of the light intensity monitors 11-2 and 11-4 and the variable attenuators 11-1 and 11-3 may be used. The variable attenuators 11-1 and 11-3 realize a loss addition function for preventing an optical signal from being output from the odd numbered wavelength output port 10-1 or even numbered wavelength output port 10-4. Is to do.

  FIG. 12 shows the internal structure of the light intensity monitors 11-2 and 11-4 with wavelength resolution. The light intensity monitor with wavelength resolution is a band-pass filter shape and a variable wavelength filter 12-1 capable of changing the center frequency, a photodiode 12-2 for monitoring the light intensity, a predetermined center frequency, From the control unit 12-3 that monitors the light intensity of the corresponding frequency by changing the center frequency of the wavelength tunable filter 12-1 and monitoring the light intensity at a predetermined frequency of the input light intensity 12-4. Composed.

  As a wavelength tunable filter that varies the center frequency, for example, a commercially available filter can be used. For example, a wavelength tunable filter that can change the center frequency by changing the temperature is commercially available.

Since the light intensity monitors 11-2 and 11-4 with wavelength resolution can simultaneously monitor the signal light intensity and the signal frequency, the signal light intensities for a plurality of odd-numbered wavelengths are P1, P2, P3,. Assuming that 1, 2, 3,... N corresponds to the wavelength number of the odd numbered wavelength, the signal light intensity (total signal light intensity) for the odd numbered wavelength can be obtained by calculation. Similarly, when the signal light intensity for a plurality of even-numbered wavelengths is Q1, Q2, Q3,... Qn (1, 2, 3,... N corresponds to the wavelength number of even-numbered wavelengths). The signal light intensity (total signal light intensity) for even-numbered wavelengths can be obtained by calculation.
(Formula 3)
P = P1 + P2 + ... + Pn
Q = Q1 + Q2 + ... + Qn
Thus, the presence / absence of an odd wavelength signal can be detected using the light intensity P, and the presence / absence of an even wavelength signal can be detected using the light intensity Q.

  Specifically, thresholds for identifying the presence / absence of light intensity with respect to the light intensity P and Q are set to THP and THQ, for example. In the case of P> THP and Q> THQ, the detected signal light intensities are both greater than the threshold value, and therefore, it indicates a state where both odd and even wavelengths exist. On the other hand, in the case of P <THP and Q <THQ, both are smaller than the threshold value, and thus represent a state where neither odd wavelength nor even wavelength exists. As described above, by comparing the light intensity P and the light intensity Q with the threshold values THP and THQ, it is possible to detect the presence of odd wavelengths and even wavelengths.

  In the configuration of the interleaver demultiplexing unit 6-6-1 shown in FIG. 11, when there is no odd wavelength or even wavelength (P = 0 or Q = 0), the output of the odd number wavelength is shown in FIG. Processing for preventing the output of the mole light p10-5 having the signal intensity P10-2 and the mole light q10-3 having the signal intensity Q10-6 from being output from the port 10-1 and the output port 10-4 having the even-numbered wavelength. A flowchart is shown. In FIG. 13, the light intensity monitors 11-2 and 11-4 with wavelength resolution are used to monitor the light intensity for the odd numbered wavelength output port 10-1 and the light intensity monitor for the even numbered wavelength output port 10-4, respectively. I do. Then, the light intensity P is calculated using Equation 3 from the light intensity observed by the light intensity monitor with wavelength resolution 11-2. Further, the light intensity Q is calculated from the light intensity observed by the light intensity monitor with wavelength resolution 11-4 using Equation 3 (130).

  Further, the light intensity P obtained by the above calculation is compared with a predetermined threshold value THP, and the variable attenuator 11-1 is set to the maximum loss when P <THP. No optical signal is output from 1 (131). Further, the light intensity Q obtained by the above calculation is compared with a predetermined threshold THQ, and the variable attenuator 11-4 is set to the maximum loss when P <THQ, so that the even-numbered wavelength output port 10- No optical signal is output from 4 (132). With this operation, when there is no odd-numbered signal wavelength 10-2 or even-numbered signal wavelength 10-6, p10-3 and q10-5, which are respective mole lights, are input to the subsequent optical amplifier. Can be prevented.

The figure for demonstrating an example of the schematic structure of the whole network with which this invention is applied. The figure for demonstrating an example of schematic structure of a general wavelength division multiplexing optical transmission system Diagram for explaining an example of an interleaver system in a wavelength division multiplexing system The figure for demonstrating an example of a structure of the optical amplifier in a wavelength division multiplexing system Diagram for explaining optical level diagram in wavelength multiplexing system The figure for demonstrating an example of a schematic structure of a wavelength division multiplexing system The figure for demonstrating another example of the schematic structure of a wavelength division multiplexing system The figure for explaining an example of the wavelength in the interleaver system in the wavelength division multiplexing system Diagram for explaining an example of an interleaver system in a wavelength division multiplexing system Diagram for explaining the optical signal strength in the interleaver system in the wavelength division multiplexing system Diagram for explaining an example of an interleaver system in a wavelength division multiplexing system Diagram for explaining an example of the internal structure of a light intensity monitor with wavelength resolution Example of processing flow diagram for reducing the effects of molelight

Explanation of symbols

1-1: OADM, 1-2: OLT device, 1-3: ONU device, 1-4: access, 1-5: L2 switch, 1-6: edge, 1-7: metro, 1-8: core 2-1: Transmission path (optical fiber), 2-2: optical amplifier, 2-3: transponder unit, 2-4: supervisory control unit, 2-4-1: supervisory control light, 2-5: branch insertion 2-7: Flow of monitoring control light, 2-7: Flow of signal light, 3-1: Monitoring control signal, 3-2: Signal wavelength group, 4-1: Transmission path (optical fiber), 4- 2: optical amplifier, 4-3: signal amplification unit, 4-4: supervisory control signal branching unit, 5-1: transmission path, 5-2: optical amplification unit, 5-5: branching insertion unit, 6-1 Transmission path (optical fiber), 6-2: optical amplification unit, 6-3: transponder unit, 6-4: supervisory control unit, 6-5: branch insertion unit, 6-6: interleaver unit, 6-6 1 : Demultiplexing side, 6-6-2: multiplexing side, 7-1: transmission path (optical fiber), 7-2: optical amplification unit, 7-3: transponder unit, 7-4: monitoring control unit, 7 -5: add / drop unit, 7-6: interleaver unit, 7-7: variable attenuating unit, 8-1: before interleaver, 8-2: odd-numbered optical signal wavelength, 8-3: even-numbered signal Wavelength, 9-1: Pre-interleaver wavelength, 9-2: Odd-numbered optical signal wavelength after interleaver, 9-3: Even-numbered optical signal wavelength after interleaver, 9-4: Odd-numbered light before interleaver Signal wavelength, 9-5: even-numbered optical signal wavelength before interleaver, 9-5: wavelength after interleaver, 10-1: output port for odd-numbered wavelength, 10-2: wavelength-multiplexed light intensity P for odd-numbered 10-3: Even-numbered wavelength multiplexed light intensity (more light), 10-4: Even-numbered wavelength Power port, 10-5: odd-numbered wavelength multiplexed light intensity (more light) p, 10-6: even-numbered wavelength multiplexed light intensity Q, 10-7: input port, 11-1: variable attenuator, 11-2 : Light intensity monitor with wavelength resolution, 11-3: Variable attenuator, 11-4: Light intensity monitor with wavelength resolution.

Claims (3)

In an optical transmission device that relays wavelength-multiplexed optical signals,
A wavelength separation unit that separates a wavelength-multiplexed optical signal having a wavelength interval of N between individual signals into a first wavelength-multiplexed optical signal and a second wavelength-multiplexed optical signal having an individual wavelength interval of 2N; ,
A first monitoring light separating unit for separating first monitoring light from the first separated wavelength multiplexed optical signal;
A second monitoring light separating unit for separating second monitoring light from the second separated wavelength multiplexed optical signal;
A first optical amplification unit that amplifies the first wavelength division multiplexed optical signal that has passed through the first monitoring light separation unit;
A second optical amplification unit that amplifies the second wavelength multiplexed optical signal that has passed through the second monitoring light separation unit;
A first monitoring light processing unit that receives and processes the first monitoring light from the first monitoring light separation unit and outputs a third monitoring light;
A second monitoring light processing unit that receives and processes the second monitoring light from the second monitoring light separation unit and outputs a fourth monitoring light;
A first monitoring light multiplexing unit that combines the first wavelength-multiplexed optical signal from the first optical amplification unit and the third monitoring light;
A second monitoring light combining unit that combines the second wavelength-multiplexed optical signal from the second optical amplification unit and the fourth monitoring light;
The wavelength multiplexed optical signal from the first supervisory optical multiplexer and the wavelength multiplexed optical signal from the second supervisory optical multiplexer are wavelength multiplexed so that the individual signals of the respective wavelength multiplexed optical signals are alternately arranged. A transmission apparatus comprising: a wavelength multiplexing unit. The optical transmission device according to claim 1,
The first monitoring light multiplexing unit uses a wavelength that does not collide with the wavelength of each signal included in the second wavelength multiplexed optical signal, as the wavelength of the third monitoring light,
The second monitoring light multiplexing unit uses, as the wavelength of the fourth monitoring light, a wavelength that does not collide with the wavelength of each signal included in the first wavelength multiplexed optical signal. . The optical transmission device according to claim 2,
A first light intensity monitoring unit that monitors the magnitude of the first wavelength multiplexed optical signal output from the wavelength demultiplexing unit;
A second light intensity monitoring unit that monitors the magnitude of the second wavelength multiplexed optical signal output from the wavelength demultiplexing unit;
A first variable attenuator capable of controlling the amount of attenuation, which attenuates the magnitude of the first wavelength-multiplexed optical signal output from the wavelength separator;
A second variable attenuator capable of controlling the amount of attenuation, which attenuates the magnitude of the second wavelength-multiplexed optical signal output from the wavelength separation unit;
When the intensity of the first wavelength-multiplexed optical signal monitored by the first light intensity monitoring unit is smaller than a predetermined value, the first wavelength-multiplexed light is attenuated by the first variable attenuator. When the intensity of the second wavelength-multiplexed optical signal monitored by the second light intensity monitoring unit is smaller than a predetermined value after blocking the optical signal, the second variable attenuator An optical transmission apparatus comprising: a control unit configured to block the second wavelength division multiplexed optical signal.

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