JP4553236B2 - Optical communication method and optical transmission apparatus - Google Patents

Description

  The present invention relates to an optical communication technique aimed at traffic control in a wavelength division multiplexing optical communication system or a time division multiplexing optical communication system, and more particularly to a downlink communication technique for one-to-n bidirectional optical communication.

  6 to 11 show conventional optical communication systems. FIG. 6 is a diagram for explaining a conventional optical communication system using a PON (Passive Optical Network). The optical network includes one parent node 10A, n child nodes 21 to 2n, and n branch star coupler 30. The parent node 10A and the star coupler 30 are one optical fiber 40, and n star couplers 30 are provided. The child nodes 21 to 2n are connected by n optical fibers 51 to 5n.

  Since communication from the parent node 10A to the child nodes 21 to 2n is generally referred to as “downlink communication” and communication in the opposite direction is referred to as “uplink communication”, the same expression is used in this specification. In addition, the present invention relates to downlink communication and does not depend on an uplink communication method in particular, and therefore only the downlink communication is described for convenience with respect to the prior art.

  Signals to the child nodes 21 to 2n are multiplexed and transmitted by time division multiplexing (TDM). That is, the signal transmitted from the parent node 10A is branched by the star coupler 30, and the same signal reaches all the child nodes 21 to 2n. Therefore, each of the child nodes 21 to 2n needs to have an ability to identify and receive only the signal addressed to the own node from the received signals.

  In the optical communication system using TDM-PON as described above, the optical fiber 40 from the parent node 10A to the star coupler 30 can be shared by a plurality of child nodes. Further, since the n child nodes 21 to 2n can be covered only by placing an optical transmission device including one optical transmitter in the parent node 10A, there is an advantage that a network can be constructed with a small capital investment.

  FIG. 7 is a diagram for explaining an optical communication system based on WDM-PON (Wavelength Division Multiplexing-PON). A major difference from the TDM-PON is that a wavelength filter 60 (in this case, n-channel) is used instead of the star coupler 30. In this network, one wavelength is assigned to each downlink communication for each of the child nodes 21 to 2n, and as shown in FIG. 8, optical transmitters Tx1 to Tx1 that transmit optical signals of the respective wavelengths λ1 to λn. Txn is prepared in the parent node 10B by the number n of the child nodes 21 to 2n, and the n-channel multiplexer 11 is also prepared. The signal is transmitted by WDM on the optical fiber 40 from the parent node 10B to the wavelength filter 60, and after being demultiplexed by the wavelength filter 60, the signal is distributed to each of the child nodes 21 to 2n.

  In this optical communication method using WDM-PON, since only the signal for the own node is transmitted to each of the child nodes 21 to 2n, not only the confidentiality of communication can be secured, but also the signal power is not branched. It can be transmitted to the child node with little power loss.

  FIG. 9 is a diagram for explaining an optical communication system based on WDM / TDM-PON (for example, see FIG. 1 of Patent Document 1 and FIG. 2 of Patent Document 2). The network configuration includes one parent node 10C, n child nodes 21 to 2n, and a wavelength filter 60 (in this case, n channels) as in the optical communication system using the WDM-PON, and the wavelength of the parent node 10C The filter 60 is a single optical fiber 40, and the wavelength filter 60 and n child nodes 21 to 2n are connected by n optical fibers 51 to 5n. Accordingly, only the optical signals having the assigned wavelengths λ1 to λn are transmitted to the child nodes 21 to 2n.

  In this optical communication system based on WDM / TDM-PON, an optical transmitter provided with a tunable light source as a light source, in which the optical transmission device of the parent node 10C can transmit optical signals having different wavelengths by the number n of the child nodes 21 to 2n. A signal of each of the child nodes 21 to 2n is provided and is time-division multiplexed and transmitted by switching the wavelengths λ1 to λn in time as shown in FIG.

  This optical communication system based on WDM / TDM-PON is a communication system having the characteristics of the optical communication systems based on TDM-PON and WDM-PON, but the number of optical transmitters prepared on the parent node 10C side is one. This is different from the optical communication system based on the WDM-PON in that only one piece is sufficient.

  Further, as shown in FIG. 10, in a bidirectional wavelength division multiplexing communication in which one wavelength is allocated to both the upstream communication and the downstream communication of each subscriber, an arrayed waveguide diffraction grating type optical multiplexer / demultiplexer ( AWG) 71 and 72, so that the wavelengths λ1 ′ to λn ′ for upstream communication and the wavelengths λ1 to λn for downstream communication are separated from each subscriber by the FSR of the AWGs 71 and 72. A technique for realizing one-core bidirectional wavelength division multiplexing communication using one optical fiber 41 between the parent node 10D and each of the child nodes 21 to 2n has been proposed (see, for example, Patent Document 3). . In FIG. 10, Tx1 to Txn are optical transmitters on the parent node 10D side, Rx1 to Rxn are optical receivers, Tx1 'to Txn' are optical transmitters on the child nodes 21 to 2n side, and Rx1 'to Rxn' are optical receivers. It is a vessel. FIG. 11 roughly shows the transmission spectrum of the AWG used at that time.

Japanese Patent Laid-Open No. 3-64136 Japanese Patent Laid-Open No. 10-229363 JP 2003-143084 A

  However, in the optical communication method using TDM-PON described in FIG. 6, since the signals for all the child nodes 21 to 2n are transmitted to all the child nodes, the reception device on the child node side is broken or malicious. There is a problem that there is a possibility that the confidentiality of communication may not be ensured when a human modifies a child node device. Further, since branching by the star coupler 30 branches the power of the optical signal, the number of branches n (= number of child nodes) is generally required in order to realize ultrahigh-speed transmission in which it is difficult to realize high minimum light receiving sensitivity. ) Must be reduced, and the economic effect is diminished. Another problem is that there is a limit to speeding up because one wavelength is shared by a plurality of child nodes.

  In addition, the optical communication method by WDM-PON described in FIGS. 7 and 8 requires an optical transmitter of the same number as the number of child nodes in the parent node, which causes an increase in capital investment and an increase in installation area. There is a problem of high costs.

  Further, in the optical communication method using WDM / TDM-PON described in FIG. 9, the effective communication speed is reduced to 1 / N (N: the number of child nodes during communication) compared to the WDM-PON method. For example, even if the number of optical transmitters is increased to 2 and the number of assigned nodes, that is, the number of child nodes to which bandwidth is allocated, is divided by half with each optical transmitter, the child nodes are fixed to each optical transmitter halfway. As a result, there is a problem that it is difficult to achieve the effect of expansion if the communicating child nodes are concentrated on one transmitter side. In addition, providing the same number of optical transmitters as the number of child nodes in the parent node has a problem that cost increases cannot be avoided.

  Furthermore, the bidirectional wavelength division multiplexing method described with reference to FIG. 10 requires a number of optical transmitters equal to the number of child nodes in the parent node, so that there is no problem that cost increases cannot be avoided. It remains a solution.

  An object of the present invention is to solve the above-described problems, and in downlink communication, the number of optical transmitters required for a parent node is less than the number of child nodes, thereby reducing the cost and achieving high-speed communication. It is to realize.

An optical communication method according to a first aspect of the present invention includes one opposing parent node and n (n: an integer of 3 or more) child nodes, and the parent node to the n child nodes. In the optical communication method in an optical network in which one different wavelength is fixedly assigned to each downstream optical signal transmitted to the downstream optical signal, the parent node has two wavelength variable light sources as the optical signal light sources. Less than n optical transmitters, and each of the optical transmitters is configured to allow the optical signals to have the same wavelength in such a way that two or more of the same wavelengths do not overlap at the same time and two or more of the different wavelengths overlap at the same time. And transmitting in the downstream direction.

  According to a second aspect of the present invention, in the optical communication method according to the first aspect, when a plurality of different optical signals are transmitted from a plurality of optical transmitters to the specific one child node at the same wavelength, The transmission timing of the optical signal is controlled so that a plurality of different optical signals do not arrive at the specific child node with time overlap.

An optical transmission device according to a third aspect of the present invention includes one opposing parent node and n child nodes (n: an integer of 3 or more), and the parent node to the n child nodes. An optical transmission device provided in the parent node of an optical network in which each different wavelength is fixedly assigned to each downstream optical signal transmitted to the downstream optical signal, wherein the variable wavelength light source is used as a light source of the optical signal In order to allow two or more and less than n optical transmitters, and the wavelength of the optical signal of each of the optical transmitters , the same wavelength must not overlap two or more at the same time, and different wavelengths can overlap two or more at the same time, And a transmitter controller that switches over time.

According to a fourth aspect of the present invention, in the optical transmission apparatus according to the third aspect , the transmitter control unit sends a plurality of different optical signals to a specific child node from a plurality of optical transmitters at the same wavelength. The transmission timing of the optical signal is controlled so that the plurality of different optical signals do not arrive at the specific one child node with a temporal overlap when transmitting the optical signal.

  According to the present invention, since the number of optical transmitters required for the parent node is less than the number of child nodes and two or more for downlink communication, the lower the number of the optical transmitters, the lower the cost. If the number is large, higher speed can be realized, and the balance between the two can satisfy both cost reduction and speedup of communication. Also, when a plurality of different optical signals for a specific child node are transmitted from a plurality of optical transmitters at the same wavelength, the transmission timing of the optical signal is prevented so as not to arrive at the child node with a temporal overlap. By controlling this, the child node can receive correctly. Furthermore, when transmitting optical signals from a plurality of optical transmitters to a specific child node, the optical signal transmission timing is controlled so that the optical signals arrive at the child node at the same wavelength at the same time. By doing so, the problem of transmission loss can be alleviated.

  The present invention relates to an optical network composed of one parent node and n child nodes, assigning different wavelengths to the child nodes one by one, and changing the communication time thereof, thereby increasing the communication speed. It is about the downlink communication which controls. By providing two or more and less than n optical transmitters each having a wavelength tunable light source as a light source for an optical signal, and changing the transmission wavelength allocation between the optical transmitters according to the destination child node, The child node bandwidth is controlled by the number of optical transmitters in the node. At this time, when a plurality of different optical signals for the same child node are transmitted from a plurality of optical transmitters with the same wavelength, the plurality of different optical signals arrive at the child node with time overlap. Therefore, accurate reception at the child node is enabled by controlling the transmission timing of each optical signal. In addition, by controlling the transmission timing of a plurality of optical signals so that a plurality of optical signals carrying the same signal and having the same wavelength arrive at one specific child node at the same time, the optical signal intensity of the child node is strengthened. This compensates for transmission loss and enables high frequency accommodation. This will be described in detail below.

  1-5 is a figure explaining Example 1 of this invention. First, the network configuration and its components will be described. As shown in FIG. 1, the optical network is composed of one parent node 10 and eight child nodes 21 to 28 and two communication nodes 81 and 82 facing each other, and the parent node 10 and child nodes 21 to 28 are arranged. Wavelength filter 60 (in this case, 8 channels) is arranged, and the parent node 10 and the wavelength filter 60 are one optical fiber 40, and the wavelength filter 60 and the eight child nodes 21 to 28 are eight. The optical fibers 51 to 58 are connected to each other. The parent node 10 is connected to the communication nodes 81 and 82 by one optical fiber 91 and 92, respectively. A different wavelength is fixedly assigned to each of the downstream optical signals of the child nodes 21 to 28, and the assigned wavelength of the child node k is expressed as λk (k: a natural number of 8 or less).

  As shown in FIG. 2, the parent node 10 includes two optical transmitters Tx1 and Tx2 each having one wavelength variable light source as a light source of optical signals, and one optical signal from each of the optical transmitters Tx1 and Tx2. The optical multiplexer 11 that multiplexes the optical fiber 40 and the transmitter control unit 12 that controls the allocated wavelength and the time of each of the optical transmitters Tx1 and Tx2 are provided as a downstream optical transmission device. Each of the child nodes 21 to 28 includes an optical receiver (not shown).

  First, consider a case where signals from the communication nodes 81 and 82 to the child nodes 21 to 28 are transmitted via the parent node 10. Signals D1, D2, D3, D4 addressed to the child nodes 21, 22, 23, 24 from the communication node 81, and signals D5, D6, D7, D8 addressed to the child nodes 25, 26, 27, 28 from the communication node 82. Is transmitted to the parent node 10 at the timing shown in FIG. At that time, in the parent node 10, the transmitter controller 12 assigns optical signals of λ5 to λ8 having four wavelengths to the optical transmitter Tx1, and assigns optical signals of four wavelengths of λ1 to λ4 to the optical transmitter 2, respectively. Send it. λ1 to λ8 are wavelengths of optical signals that carry the signals D1 to D8, respectively.

  As shown in FIG. 4, signals D1, D2, D5 addressed from the communication node 81 to the child nodes 21, 22, 25 are signals D1, D2, D5 addressed from the communication node 82 to the child nodes 26, 27, 28. Is transmitted to the parent node 10, optical signals with three wavelengths λ1, λ2, and λ5 are allocated to the optical transmitter Tx1, and optical signals with three wavelengths λ6, λ7, and λ8 are allocated to the optical transmitter Tx2. Send it.

  Next, as shown in FIG. 5, a situation is considered in which downlink signals addressed to the same child node are simultaneously transmitted from the two communication nodes 81 and 82 to the parent node 10. For example, downlink signals to the child node 22 are simultaneously transmitted from both communication nodes 81 and 82, which are defined as D21 and D22, the former is assigned to the optical transmitter Tx1, the latter is assigned to the optical transmitter Tx2, and transmission is performed. Shall be allowed to. At this time, if two different types of signals D2l and D22 arrive at the child node 22 with time overlap (arrive with an optical signal having the same wavelength λ2), the child node 22 can receive it accurately. Absent. Therefore, one of the signals, for example, D21 is stored in the buffer 13 of the parent node 10 by the transmitter control unit 12 so that there is no overlap in time when they reach the child node 22. Then, it may be transmitted later with an optical signal having a wavelength λ2. Or you may discard.

  In this embodiment, the amount of signals from the communication nodes 81 and 82 to the child nodes 21 to 28 via the parent node 10 is greatly increased. For example, in the two optical transmitters Tx1 and Tx2, the parent node In a situation where the signal entering 10 cannot be transmitted, the number of optical transmitters equipped with a wavelength tunable light source is increased to three or more, so that all the devices of the child nodes 21 to 28 are not added. There is also an advantage that more signals can be transmitted to the child node. That is, it becomes possible to transmit a higher speed downlink signal to the child node. However, the number of optical transmitters must be less than the number of child nodes.

  A second embodiment of the present invention will be described. As in the first embodiment, the optical network includes a parent node 10 and eight child nodes 21 to 28 facing the parent node 10, and a wavelength filter 60 (in this case, eight channels) is disposed between the optical nodes. The parent node 10 and the wavelength filter 60 are connected by one optical fiber 40, and the wavelength filter 60 and the eight child nodes 21 to 28 are connected by eight optical fibers 51 to 58, respectively.

  Also in the present embodiment, as shown in FIG. 2, the parent node 10 includes two optical transmitters Tx1 and Tx2 each having one wavelength variable light source as a light source of optical signals, and the optical transmitters Tx1 and Tx2. The optical multiplexer 11 that multiplexes the optical signal of the optical signal into one optical fiber 40 and the transmitter controller 12 that controls the allocated wavelength of each of the optical transmitters Tx1 and Tx2 and the time thereof are transmitted in the downstream optical transmission. Provide as a device. Each of the child nodes 21 to 28 includes an optical receiver (not shown).

  In this case, for example, it is assumed that the child node 23 is located very far from the parent node 10 and has a large loss when transmitting a downstream optical signal. Therefore, the wavelength variable light sources in the two optical transmitters Tx1 and Tx2 are controlled so that the signal D3 addressed to the child node 23 arrives at the child node 23 simultaneously with the optical signal of the same wavelength λ3. By transmitting, the intensity of the optical signal having the wavelength λ3 is increased. In this case, after accurately measuring the distance from the two optical transmitters Tx1 and Tx2 to the child node 23, the optical transmitters Tx1 and Tx2 are connected to the transmitter controller 12 so that the same signal reaches the child node at the same time. Control by. This method can solve the problem of large transmission loss.

  In the first and second embodiments, the case where there are eight child nodes and two optical transmitters exist in the parent node 10 has been described as an example. However, there are three or more optical transmitters (however, less than eight). In this case, the same may be performed with three or more optical transmitters.

It is explanatory drawing of the network structure in Example 1,2. It is explanatory drawing of the parent node structure in Example 1,2. It is explanatory drawing of the downlink communication operation | movement of Example 1. FIG. It is explanatory drawing of the downlink communication operation | movement of Example 1. FIG. It is explanatory drawing of the downlink communication operation | movement of Example 1. FIG. It is explanatory drawing of the optical communication system by the conventional TDM-POM. It is explanatory drawing of the parent node structure in WDM-POM. It is explanatory drawing of the optical communication system by the conventional WDM-POM. It is explanatory drawing of the optical communication system by the conventional TDM / WDM-POM. It is explanatory drawing of the network structure in a prior art (patent document 3). It is a characteristic view of the transmission spectrum of AWG used in a prior art (patent document 3).

Explanation of symbols

10, 10A to 10D: parent node, Rx1 to Rxn: optical receiver, Tx1 to Txn: optical transmitter, 11: optical multiplexer, 12: transmitter control unit, 13: buffer 21-2n: child node, Rx1 ′ ˜Rxn ′: optical receiver, Tx1 ′ to Txn ′: optical transmitter 30: n-branch star coupler 40: optical fiber 51-5n: optical fiber 60: wavelength filter 71, 72: optical waveguide multiplexing / demultiplexing type (AWG)
81, 82: Communication node 91, 92: Optical fiber λ1-λn: Wavelength of downstream optical signal λ1′-λn ′: Wavelength of upstream optical signal

Claims (4)

Each of the optical signals in the downlink direction is composed of one opposing parent node and n child nodes (n is an integer of 3 or more) and transmitted from the parent node to the n child nodes. In an optical communication method in an optical network in which different wavelengths are fixedly assigned one by one,
The parent node includes two or more and less than n optical transmitters having a wavelength tunable light source as a light source of an optical signal, and the optical signal has a wavelength equal to two or more at the same time by each of the optical transmitters , An optical communication method characterized by switching in time and transmitting in the downlink direction so as to allow two or more different wavelengths to overlap at the same time . The optical communication method according to claim 1,
When a plurality of different optical signals are transmitted from a plurality of optical transmitters to the specific one child node at the same wavelength, the plurality of different optical signals arrive at the specific child node with time overlap. An optical communication method characterized in that the transmission timing of the optical signal is controlled so as not to occur. Each of the optical signals in the downlink direction is composed of one opposing parent node and n child nodes (n is an integer of 3 or more) and transmitted from the parent node to the n child nodes. An optical transmission apparatus provided in the parent node of an optical network in which different wavelengths are fixedly assigned to each wavelength,
Two or more and less than n optical transmitters having a wavelength tunable light source as a light source of an optical signal, and the wavelength of the optical signal of each of the optical transmitters , the same wavelength must not overlap two or more at the same time, and different wavelengths can be simultaneously An optical transmission device comprising: a transmitter control unit that switches over time so as to allow two or more overlapping . The optical transmission device according to claim 3.
When the transmitter control unit transmits a plurality of different optical signals from a plurality of optical transmitters to the specific one child node at the same wavelength, the plurality of different optical signals are transmitted to the specific one child node. An optical transmission apparatus characterized by controlling the transmission timing of the optical signal so as not to arrive at a child node with time overlap .

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