JP6261825B1 - Optical communication apparatus and optical communication system - Google Patents

Abstract

The present invention is an optical communication device that operates as an optical subscriber line terminating device to which a plurality of subscriber side terminal devices can be connected, and a signal generator (transmission) that generates a signal to be transmitted to the plurality of subscriber side terminal devices. A signal generator (32), a transmission digital filter (33)), an optical resource allocated to each of the plurality of subscriber side terminal devices, and a transmission distance to each of the plurality of subscriber side terminal devices. An adjustment amount determination unit that determines an adjustment amount of the position of the signal point on the complex plane of the signal, a signal adjustment unit (34) that adjusts the position of the signal point on the complex plane of the signal based on the adjustment amount, and a signal And an optical signal generation unit (37) for converting the signal after the signal point is adjusted by the adjustment unit into an optical signal.

Description

  The present invention relates to an optical communication device and an optical communication system capable of communicating with a plurality of counterpart devices.

  A passive optical network system which is a form of an optical access network is also called a PON (Passive Optical Network) system. The PON system is composed of an optical subscriber line terminating device installed on the station side and one or more subscriber side terminal devices installed on the subscriber side. The optical subscriber line terminating device and each subscriber side The terminal device communicates via an optical transmission line such as an optical fiber. The optical subscriber line terminating device is also called OLT (Optical Line Terminal), and the subscriber side terminal device is also called ONU (Optical Network Unit). OLT and ONU are optical communication devices.

  The conventional optical access network uses optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), and time code division multiplexing (OCDM). Thus, high speed and large capacity are realized (for example, Patent Document 1). Patent Document 1 describes that in an optical access network to which wavelength division multiplexing is applied, the frequency bandwidth is adjusted and the frequency band is rearranged by changing the wavelength to be used.

  On the other hand, in preparation for the spread of the future 5G mobile phone system, the PON system is required to further increase the capacity, specifically, to realize a large capacity transmission of 100 Gb / s class. Accordingly, in IEEE 802.3ca, standardization of 100 G-EPON (Ethernet Passive Optical Network) for a transmission capacity of 100 Gb / s conforming to Ethernet (registered trademark) is being promoted.

  Digital coherent technology that has been developed for backbone optical networks can realize optical fiber transmission of 100 Gb / s at one wavelength, so it can be applied to next-generation optical access networks such as next-generation PON systems. It is done. In the following description, a method in which digital coherent technology is applied to the PON system is referred to as a coherent PON method.

JP 2014-187622 A

  The coherent PON system having a transmission capacity per wavelength of 100 Gb / s has a very large transmission capacity at the present time before the 5G mobile phone system is widely used, and the transmission capacity required by the ONU is smaller than 100 Gb / s. Redundant transmission capacity. Therefore, a mode in which one wavelength is shared by a plurality of ONUs can be considered.

However, when a plurality of ONUs using the same wavelength are connected to the OLT, the OLT needs to adjust the power of the output light in accordance with the ONU having the longest transmission distance. That is, the OLT needs to adjust the power of the output light so that the communication quality with the ONU having the longest transmission distance satisfies the prescribed requirements. Specifically, the OLT needs to adjust the power of the output light so that the bit error rate in the ONU having the longest transmission distance is equal to or less than the error correction limit of 3.8 × 10 ⁻³ . Therefore, when the difference between the distances from the OLT to each ONU is large, light having a power that provides a signal intensity greater than the minimum reception sensitivity reaches an ONU other than the ONU having the longest transmission distance. This means that the power consumption of the OLT when the ONU other than the ONU having the longest transmission distance communicates with the OLT is larger than necessary, and power is wasted.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an optical communication apparatus capable of suppressing power consumption.

In order to solve the above-described problems and achieve the object, the present invention is an optical communication device that operates as an optical subscriber line terminating device to which a plurality of subscriber-side terminal devices can be connected. A signal generation unit that generates a signal to be transmitted to the terminal device is provided. Further, the optical communication device includes a light resources allocated to each of the plurality of subscriber terminal equipment, the transmission distance to each of the plurality of subscriber terminal equipment, based on, in the complex plane of the signal An adjustment amount determination unit that determines an adjustment amount of the position of the signal point is provided. The optical communication device also includes a signal adjustment unit that adjusts the position of the signal point in the complex plane of the signal based on the adjustment amount, and an optical signal that converts the signal after the signal point is adjusted by the signal adjustment unit into an optical signal A generating unit. In addition, the adjustment amount determination unit, when the transmission distance to each subscriber-side terminal device assigned to the same polarization of the same wavelength is different, each subscriber-side terminal device assigned to the same polarization of the same wavelength When the transmission distance is the same, the adjustment amount is determined so that the intensity of the signal transmitted to the subscriber terminal apparatus with a short transmission distance is lower than the intensity of the signal transmitted to each subscriber terminal apparatus. .

  According to the present invention, there is an effect that an optical communication device capable of suppressing power consumption can be realized.

The figure which shows the structural example of the PON system which is an optical communication system comprised including the optical communication apparatus concerning embodiment The figure which shows the apparatus structural example of OLT and ONU which comprises the PON system concerning embodiment with the whole structure of a PON system The figure which shows an example of the method by which OLT concerning an embodiment allocates an optical resource to each ONU. The figure which shows the structural example of the optical transmitter / receiver with which OLT and ONU concerning embodiment are provided. The figure which shows the structural example of the optical transmission part of the optical transmitter / receiver with which OLT concerning embodiment is provided. The figure which shows the structural example of the optical receiver of the optical transmitter / receiver with which OLT concerning embodiment is provided. The figure which shows the structural example of the waveform shaping part contained in the optical receiver of the optical transmitter / receiver with which OLT and ONU concerning embodiment are equipped. The figure which shows the processing circuit which implement | achieves OLT and ONU concerning embodiment The figure which shows the control circuit which implement | achieves OLT and ONU concerning embodiment The figure which shows the 1st specific example of the PON system concerning embodiment The figure which shows an example of the constellation map of the optical signal which OLT transmits to each ONU in the PON system shown in FIG. The figure which shows the 2nd specific example of the PON system concerning embodiment The figure which shows an example of the constellation map of the optical signal which OLT transmits to each ONU in the PON system shown in FIG. The figure which shows the relationship between the transmission distance from OLT to ONU, and the minimum receiving sensitivity in the PON system concerning embodiment The figure which shows the relationship between I / Q imbalance parameter (theta) and power budget gain in the PON system concerning embodiment FIG. 3 is a sequence diagram showing an example of a data transmission operation in the downlink direction in the PON system according to the embodiment

  Hereinafter, an optical communication apparatus and an optical communication system according to embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of a PON system that is an optical communication system configured to include an optical communication apparatus according to an embodiment of the present invention.

The PON system 100 according to the present embodiment is compatible with the coherent PON system, and includes an OLT 1 and ONUs 2 ₁ to 2 ₄ . The OLT 1 corresponds to the optical communication apparatus according to the present invention. In the following description, when there is no need to distinguish the ONUs 2 ₁ to 2 ₄ , these may be described as ONU 2. The OLT 1 and each ONU 2 are connected via an optical transmission line and an optical coupler 3. In FIG. 1, the solid line indicates the downstream transmission direction, and transmission is from the OLT 1 to each ONU 2. A broken line indicates an upstream transmission direction, and transmission is performed from each ONU 2 to the OLT 1. Although the number of ONUs is 4 in FIG. 1, the number of ONUs is not limited to this. The number of ONUs may be 1 to 3 or 5 or more. In uplink transmission indicated by broken lines, it is assumed that signals from each ONU 2 toward OLT 1 are temporally burst-transmitted.

  Further, the PON system 100 according to the present embodiment makes the transmission capacity in the downlink direction variable. That is, the OLT 1 can change the transmission capacity in the downlink direction according to the transmission capacity required for each connected ONU 2.

  FIG. 2 is a diagram illustrating an example of device configurations of the OLT 1 and the ONU 2 configuring the PON system 100 according to the present embodiment, together with the overall configuration of the PON system.

As shown in FIG. 2, the OLT 1 includes a transmission capacity controller 11, optical transceivers 12 _{1 to} 12 _4, and an optical coupling demultiplexer 13. The optical transceivers 12 _{1 to} 12 ₄ use different wavelengths, but have the same internal configuration. In the following description, when there is no need to distinguish between the optical transceivers 12 _{1 to} 12 ₄ , these may be referred to as the optical transceiver 12.

  The transmission capacity controller 11 controls each optical transceiver 12 and adjusts the transmission capacity from the OLT 1 to each ONU 2.

The optical transceivers 12 _{1 to} 12 ₄ are optical transceivers having a transmission capacity of 100 Gb / s, and transmit and receive optical signals having different wavelengths. In this embodiment, the wavelength of the optical signal optical transceiver 12 ₁ to 12 ₄ is transmitted with each .lambda.1 -.lambda.4. The wavelengths of the optical signals received by the optical transceivers 12 _{1 to} 12 ₄ are wavelengths other than λ ₁ to λ _4, but the OLT 1 according to the present embodiment is characterized by the transmission operation. The description of the wavelength of the optical signal received by 12 is omitted.

The optical coupler / demultiplexer 13 combines the optical signals output from the optical transceivers 12 _{1 to} 12 ₄ to generate wavelength-multiplexed optical signals, and the ONUs 2 ₁ to 2 ₄ respectively output the optical signals. An optical signal in a state where a total of four waves are wavelength-multiplexed is demultiplexed for each wavelength. The optical coupler / demultiplexer 13 outputs the optical signal of each wavelength after demultiplexing to the optical transceivers 12 _{1 to} 12 ₄ that process the optical signal of each wavelength.

The ONUs 2 _{1 to} 2 ₄ include an optical transceiver 21. The optical transceiver 21 is an optical transceiver having a maximum transmission capacity of 100 Gb / s, and the transmission capacity is variable. In this embodiment, the ONUs 2 ₁ to 2 ₄ can select a transmission capacity from among three types of 25 Gb / s, 50 Gb / s, and 100 Gb / s. The maximum transmission capacity and selectable transmission capacity of the optical transceiver 21 are examples. The selectable transmission capacity types may be two types or four or more types. In the following description, for convenience of description, describes the ONU 2 ₁ and ONU # 1, describes the ONU 2 ₂ and ONU # 2, and wherein the ONU # 3 the ONU 2 _3, wherein ONU 2 ₄ a and ONU # 4 There is a case.

The optical transmission section between the OLT 1 and each ONU 2 is composed of an aggregation section, an optical coupler 3 and access sections # 1 to # 4. In the aggregation section, which is an optical transmission path between the OLT 1 and the optical coupler 3, a signal from each ONU 2 to the OLT 1 is transmitted in a wavelength division multiplexed state, and a signal from the OLT 1 to each ONU 2 is a wavelength. It is transmitted in a divided and multiplexed state. In access sections # 1 to # 4, which are optical transmission paths between the optical coupler 3 and each ONU 2, signals from each ONU 2 to the OLT 1 are transmitted without being multiplexed with other signals. A signal directed to the ONU 2 is transmitted in a multiplexed state. That is, when a signal directed from each ONU 2 to the OLT 1 is input, the optical coupler 3 performs wavelength division multiplexing and outputs the signal to the OLT 1, and a signal in a wavelength division multiplexed state from the OLT 1 to each ONU 2 is output. When input, it branches to each of the ONUs 2 ₁ to 2 ₄ .

FIG. 3 is a diagram illustrating an example of a method in which the OLT 1 according to the present embodiment allocates optical resources such as wavelength, polarization, and I / Q to each ONU 2. FIG. 3 shows an example of an optical resource allocation method when each of the ONUs 2 _{1 to} 2 ₄ uses the same transmission capacity. Further, FIG. 3, for each transmission capacity of each ONU 2 ₁ to 2 _4, OLT 1 indicates an assign which light resources to ONU 2 ₁ to 2 _4.

In FIG. 3, λ1 to λ4 indicate the wavelengths of optical signals transmitted by the optical transceivers 12 _{1 to} 12 ₄ of the OLT 1, respectively. XI represents an X-polarized I signal, XQ represents an X-polarized Q signal, YI represents a Y-polarized I signal, and YQ represents a Y-polarized Q signal. Further, # 1 to # 4 indicates ONU # 1 to # 4 That ONU 2 ₁ to 2 _4, respectively. “25 Gb / s / ONU” indicates that the transmission capacity per ONU 2 is 25 Gb / s. Similarly, “50 Gb / s / ONU” indicates that the transmission capacity per ONU 2 is 50 Gb / s, and “100 Gb / s / ONU” indicates that the transmission capacity per ONU 2 is 100 Gb / s. Indicates s.

  As shown in FIG. 3, when the transmission capacity of each ONU 2 is 25 Gb / s, the OLT 1 assigns λ1 XI to ONU # 1, assigns XQ of λ1 to ONU # 2, and YI of λ1 to ONU # 3. And YQ of λ1 is assigned to ONU # 4. Thus, when the transmission capacity of each ONU 2 is 25 Gb / s, the PON system 100 is in an operation mode that uses only one wavelength and does not use other wavelengths. Although one wavelength to be used is λ1, one wavelength to be used may be selected from λ2 to λ4.

  When the transmission capacity of each ONU2 is 50 Gb / s, OLT1 assigns XI and YI of λ1 to ONU # 1, assigns XQ and YQ of λ1 to ONU # 2, and assigns XI and YI of λ2 to ONU # 3 , XQ and YQ of λ2 are assigned to ONU # 4. Thus, when the transmission capacity of each ONU 2 is 50 Gb / s, the PON system 100 is in an operation mode that uses only two wavelengths and does not use other wavelengths. Note that the two wavelengths to be used may be selected from λ 3 and λ 4 as in the case where the transmission capacity of each ONU 2 is 25 Gb / s.

  When the transmission capacity of each ONU 2 is 100 Gb / s, the OLT 1 assigns XI, XQ, YI and YQ of λ1 to ONU # 1, assigns XI, XQ, YI and YQ of λ2 to ONU # 2, and ONU # 3 Is assigned XI, XQ, YI and YQ of λ3, and XI, XQ, YI and YQ of λ4 are assigned to ONU # 4. Thus, when the transmission capacity of each ONU 2 is 100 Gb / s, the PON system 100 is in an operation mode that uses all four wavelengths.

The allocation of optical resources shown in FIG. 3 is determined by the transmission capacity controller 11 of the OLT 1. That is, the transmission capacity controller 11, an optical resource allocation unit for allocating, based on the transmission capacity of each of the light resource ONU 2 ₁ to 2 ₄ to request to send data to each ONU 2 ₁ to 2 _4. Transmission capacity controller 11 determines the allocation of the light resource, the optical transceiver 12 ₁ to 12 ₄ of the determination result of the OLT 1, and notifies the ONU 2 ₁ to 2 ₄ in the optical transceiver 21. Notification from the transmission capacity controller 11 ONU 2 to 21 _{to 24} of the optical transceiver 21 is performed using one of the optical transceiver 12 ₁ to 12 _4, or two or more. In addition, the transmission capacity controller 11 uses one or more of the optical transceivers 12 _{1 to} 12 _{4 to} transmit information on the transmission capacity of each ONU 2 necessary for determining the allocation of optical resources. Obtain from ONU2.

In order to simplify the description, the optical resource allocation method when the transmission capacities of the ONUs 2 ₁ to 2 ₄ are the same has been described, but the transmission capacities of the ONUs 2 ₁ to 2 ₄ do not have to be the same. For example, when the transmission capacity of two ONUs 2 is 50 Gb / s and the transmission capacity of the remaining two ONUs 2 is 25 Gb / s, the operation mode uses two wavelengths. That is, the OLT 1 allocates the optical resources of each wavelength so that two ONUs can use them. For example, when the transmission capacity of two ONUs 2 is 50 Gb / s, the transmission capacity of one of the remaining two ONUs 2 is 25 Gb / s, and the transmission capacity of the other ONU 2 is 100 Gb / s, three wavelengths are set. It becomes the operation mode to use. That is, the OLT 1 allocates an optical resource of one wavelength to the ONU 2 having a transmission capacity of 100 Gb / s, and transmits the optical resources of two wavelengths among the remaining three wavelengths to the two ONUs 2 having a transmission capacity of 50 Gb / s and the transmission. Assigned to one ONU 2 with a capacity of 25 Gb / s.

  FIG. 4 is a diagram illustrating a configuration example of the optical transceiver 12 included in the OLT 1 and the optical transceiver 21 included in the ONU 2 according to the present embodiment. As shown in FIG. 4, the optical transceivers 12 and 21 include an optical transmitter 30 and an optical receiver 40. The optical transmitter / receiver 12 and the optical transmitter / receiver 21 are partially different in operation of the optical transmitter 30. Although details will be described later, the optical transmission unit 30 of the optical transceiver 12 performs processing for suppressing the optical power of the transmission signal.

  FIG. 5 is a diagram illustrating a configuration example of the optical transmission unit 30 of the optical transceiver 12 included in the OLT 1 according to the present embodiment. The optical transmission unit 30 of the optical transceiver 12 includes a transmission processing unit 31, a driver 36, and an optical signal generation unit 37. The transmission processing unit 31 includes a transmission signal generator 32, a transmission digital filter 33, and a signal adjustment unit 34. The signal adjustment unit 34 includes a waveform shaping unit 35. The optical signal generation unit 37 includes a light source 38 and an optical modulator 39. In FIG. 5, the electric signal is indicated by a broken line and the optical signal is indicated by a solid line.

  The transmission signal generator 32 generates a data signal to be transmitted to the opposing optical transceiver from the input transmission data, for example, 100 Gb / s transmission data. Specifically, the transmission signal generator 32 performs processing for error correction coding of transmission data, and furthermore, polarization multiplexed quaternary phase modulation called DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying), or DP A data signal is generated by performing a process of mapping transmission data to a symbol in accordance with a modulation method called polarization multiplexed 16-level amplitude phase modulation called -16QAM (Quadrature Amplitude Modulation). There are no particular restrictions on the specific processing contents and configuration of the transmission signal generator 32. The transmission signal generator 32 is realized by an encoder and a modulator. The transmission signal generator 32 and the transmission digital filter 33 constitute a signal generation unit that generates a signal to be transmitted to the ONU 2.

  The transmission digital filter 33 is realized by, for example, an FIR (Finite Impulse Response) filter. The transmission digital filter 33 performs a filtering process on the data signal generated by the transmission signal generator 32 to shape a spectrum in a desired frequency band. By shaping the spectrum on the transmission side, there is an advantage that the influence of interference with signals of adjacent wavelengths can be reduced. When designing a WDM system capable of realizing high frequency utilization efficiency, for example, the transmission digital filter 33 filters the data signal into a Nyquist shape, so that the OLT 1 can generate the data signal generated by each optical transceiver 12 at a high density. Can be multiplexed. On the other hand, when the channel is arranged with a fixed frequency grid such as 50 GHz intervals, the transmission digital filter 33 performs band limitation, so that the OLT 1 can suppress interference caused by frequency drift of the light source.

  An I / Q imbalance parameter to be described later is input to the signal adjustment unit 34. Based on the I / Q imbalance parameter input from the outside, the signal adjustment unit 34, for each of the X polarization and the Y polarization of the data signal output from the transmission digital filter 33, That is, the intensity of the I signal and the intensity of the Q signal are adjusted. The signal adjustment unit 34 outputs the adjusted data signal to the driver 36. In the signal adjustment unit 34, the waveform shaping unit 35 executes waveform shaping processing according to the I / Q imbalance parameter for the I signal and Q signal of each polarization, and adjusts the intensity of each signal. Each data signal after the intensity is adjusted is output to the driver 36. The driver 36 amplifies the intensity of each data signal input from the signal adjustment unit 34 until the intensity is such that the optical modulator 39 of the optical signal generation unit 37 can be driven.

  Although the waveform shaping unit 35 adjusts the intensity difference between the I signal and Q signal of each polarization, the driver 36 may perform the adjustment. In that case, the waveform shaping unit 35 may be omitted. When the driver 36 is configured to adjust the intensity difference between the I signal and Q signal of each polarization, the driver 36 operates as a signal adjustment unit. When the driver 36 operates as a signal adjustment unit, the driver 36 adjusts the intensity of the I signal and Q signal of each polarization according to the I / Q imbalance parameter.

  The optical signal generation unit 37 converts an electrical signal that is output from the signal adjustment unit 34 and amplified by the driver 36 into an optical signal. In the optical signal generator 37, the light source 38 sends out continuous light. The optical modulator 39 modulates the continuous light transmitted from the light source 38 based on the intensity-adjusted data signal input from the driver 36, and generates an optical signal as a transmission signal. The optical modulator 39 outputs the generated optical signal to the optical coupling demultiplexer 13.

  Although the optical transmitter 30 of the optical transceiver 12 provided in the OLT 1 has been described, the configuration of the optical transmitter 30 of the optical transmitter / receiver 21 provided in the ONU 2 is also the same. However, the optical transmitter 30 of the optical transceiver 21 does not adjust the intensity of each polarization I signal and Q signal of the data signal output from the transmission digital filter 33 based on the I / Q imbalance parameter. .

  FIG. 6 is a diagram illustrating a configuration example of the optical receiving unit 40 of the optical transceiver 12 included in the OLT 1 according to the present embodiment. The optical receiver 40 of the optical transceiver 12 includes a coherent receiver 41 and a reception processing unit 42. The reception processing unit 42 includes an ADC (Analog to Digital Converter) 43 and a waveform shaping unit 44. In FIG. 6, the optical signal is indicated by a solid line and the electric signal is indicated by a broken line.

  The coherent receiver 41 includes a light source, a polarization beam splitter, a beam splitter, a balanced photodiode, and the like. The coherent receiver 41 converts the received optical signal into an electrical signal by mixing and interfering the optical signal received from the ONU 2 via the optical transmission path with the continuous light generated by the light source.

  In the reception processing unit 42, the ADC unit 43, which is an analog-digital converter, performs sampling, quantization, and encoding on the electrical analog signal such as the DP-QPSK signal or the DP-16QAM signal input from the coherent receiver 41. And convert it to a digital signal. The ADC unit 43 outputs the DP-QPSK signal or the DP-16QAM signal converted into the digital signal to the waveform shaping unit 44.

  The waveform shaping unit 44 has the configuration shown in FIG. 7 and includes a dispersion compensation unit 45, a phase noise compensation unit 46, and an adaptive equalization unit 47. FIG. 7 is a diagram illustrating a configuration example of the waveform shaping unit 44 illustrated in FIG. 6. In the waveform shaping unit 44, the dispersion compensation unit 45 applies the dispersion effect generated during the optical fiber transmission to the frequency domain or time for the I and Q signals of X polarization and Y polarization input from the ADC unit 43. Equalize by region. The phase noise compensation unit 46 uses an algorithm such as a fourth power method for the difference between the frequency of the received optical signal and the frequency of the continuous light generated by the light source in the coherent receiver 41 and the influence of the phase noise generated during optical fiber transmission. Compensate. The adaptive equalization unit 47 performs polarization separation using an algorithm such as Constant Modulus Algorithm (CMA), and separates into signal components of each polarization.

  Although the optical receiver 40 of the optical transceiver 12 provided in the OLT 1 has been described, the optical receiver 40 of the optical transceiver 21 provided in the ONU 2 has the same configuration.

  Next, the hardware configuration of the OLT 1 according to the present embodiment will be described. The OLT 1 and the ONU 2 can all be realized by hardware. The light source 38 of the optical transmitter 30 shown in FIG. 5 can be realized by a semiconductor laser, and the optical modulator 39 can be realized by an LN (lithium niobate) modulator. Each of the other components is configured as a processing circuit, for example. In addition, a plurality of components may be configured as one processing circuit, and one component may be configured by a plurality of processing circuits.

  Even if the above processing circuit is dedicated hardware, a CPU (Central Processing Unit, a central processing unit, a processing unit, a processing unit, a microprocessor, a microcomputer, a processor, which executes a program stored in the memory and the memory, A control circuit including a DSP (Digital Signal Processor) may also be used. Here, the memory is, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory, or an EEPROM (Electrically Erasable Memory). A volatile semiconductor memory, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD (Digital Versatile Disk), and the like are applicable.

  When the above processing circuit is realized by dedicated hardware, the processing circuit is, for example, the processing circuit 101 shown in FIG. The processing circuit 101 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

When the above processing circuit is realized by a control circuit including a CPU, this control circuit is a control circuit having a configuration shown in FIG. 9, for example. As shown in FIG. 9 , the control circuit includes a processor 102 that is a CPU and a memory 103. When the processing circuit is realized by a control circuit, the processor 102 is realized by reading and executing a program stored in the memory 103 and corresponding to each process of each component. The memory 103 is also used as a temporary memory in each process performed by the processor 102.

  Each component configuring the OLT 1 or the ONU 2 may be partially realized by dedicated hardware and partially realized by a control circuit including a CPU.

  Subsequently, the operation of the PON system 100 according to the present embodiment will be described with a specific example.

FIG. 10 is a diagram illustrating a first specific example of the PON system 100 according to the present embodiment. The transmission capacity of each ONU 2 is 25 Gb / s. The allocation of optical resources to the ONUs 2 _{1 to} 2 ₄ (ONUs # 1 to # 4) is assumed to follow the allocation method shown in FIG. In FIG. 10, the length of the solid line connecting the OLT 1 and each ONU 2 represents the actual length of the transmission line between the OLT 1 and each ONU 2. Therefore, the transmission path between OLT1 and ONU # 1 and the transmission path between OLT1 and ONU # 4 are the transmission path between OLT1 and ONU # 2, and the transmission path between OLT1 and ONU # 3. Shorter than.

  In the PON system 100 having the configuration shown in FIG. 10, the OLT 1 adjusts the intensity of the optical signal transmitted to each of the ONUs 2 that use the same wavelength based on the difference in the length of the transmission path to each ONU 2. . The signal adjustment unit 34 shown in FIG. 5 adjusts the intensity of the optical signal.

  FIG. 11 is a diagram showing an example of a constellation map of optical signals transmitted from the OLT 1 to each ONU 2 in the PON system 100 having the configuration shown in FIG. In FIG. 11, a white circle indicates a signal point before the intensity is adjusted, and a black circle indicates an actual signal point, that is, a signal point after the intensity is adjusted. The signal point before the intensity adjustment corresponds to the signal point of the signal input to the signal adjustment unit 34 illustrated in FIG. 5, and the signal point after the intensity adjustment corresponds to the signal output from the signal adjustment unit 34. Corresponds to signal point.

As shown in FIGS. 3 and 10, for ONU # 1 and ONU # 2 to which X polarization is assigned, the transmission path from OLT1 to ONU # 1 is more than the transmission path from OLT1 to ONU # 2. short. For ONU # 3 and ONU # 4 to which Y polarization is assigned, the transmission path from OLT1 to ONU # 4 is shorter than the transmission path from OLT1 to ONU # 3. Therefore, as shown in FIG. 11, the OLT 1 assigns stronger signal strength to the XQ axis than to the XI axis, and assigns more power to the ONU # 2 that is longer-distance transmission than the ONU # 1. Further, the OLT 1 assigns a stronger signal strength to the YI axis than the YQ axis, and assigns more power to the ONU # 3 that is longer-distance transmission than the ONU # 4. Thus, the adjustment of the signal intensity assigned to each axis is performed by adjusting the position of the signal point on the complex plane of each of the X polarization and the Y polarization. Θ ₁ and θ ₂ shown in FIG. 11 are I / Q imbalance parameters, and are input to the signal adjustment unit 34 of the optical transceiver 12 constituting the OLT 1. The signal adjustment unit 34 adjusts the intensity of the X-polarized I signal and the Q signal based on θ ₁ and adjusts the intensity of the Y-polarized I signal and the Q signal based on θ ₂ . When the signal intensity of the I axis and the Q axis of the X polarization is equal, θ ₁ = 45 °. Similarly, θ ₂ = 45 ° when the Y-polarized I-axis and Q-axis signal intensities are equal. The I / Q imbalance parameter is generated by the transmission capacity controller 11. That is, the transmission capacity controller 11 is an adjustment amount determination unit that determines the adjustment amount of the position of the signal point on the complex plane of the signal transmitted to each ONU 2. In the following description, signal adjustment performed by the signal adjustment unit 34 may be referred to as I / Q imbalance modulation.

FIG. 12 is a diagram illustrating a second specific example of the PON system 100 according to the present embodiment. However, the description of ONUs 2 ₃ and 2 ₄ is omitted. The transmission capacity of each ONU 2 is 50 Gb / s. It is assumed that optical resources are allocated to the ONUs 2 ₁ and 2 ₂ (ONUs # 1 and # 2) according to the allocation method shown in FIG. In FIG. 12, as in FIG. 10, the length of the solid line connecting the OLT 1 and each ONU 2 represents the actual length of the transmission path between the OLT 1 and each ONU 2. Therefore, the transmission path between OLT1 and ONU # 1 is shorter than the transmission path between OLT1 and ONU # 2.

  FIG. 13 is a diagram showing an example of a constellation map of optical signals transmitted from the OLT 1 to each ONU 2 in the PON system 100 having the configuration shown in FIG. In FIG. 13, as in FIG. 11, white circles indicate signal points before the intensity is adjusted, and black circles indicate signal points after the intensity is adjusted.

As shown in FIG. 3 and FIG. 12, an ON signal is assigned to the ONU # 1, and a Q signal of each polarization is assigned to the ONU # 2. Further, the transmission path from OLT1 to ONU # 1 is shorter than the transmission path from OLT1 to ONU # 2. Therefore, as shown in FIG. 13, the OLT 1 assigns a stronger signal strength to the XQ axis than the XI axis, and assigns a stronger signal strength to the YQ axis than the YI axis, and ONU # 2 that is longer-distance transmission than the ONU # 1. Allocate more power for. However, θ ₁ = θ _{2 is} assumed.

FIG. 14 is a diagram showing the relationship between the transmission distance from the OLT 1 to the ONU 2 and the minimum reception sensitivity in the PON system 100 according to the present embodiment. The minimum receiving sensitivity is a receiving sensitivity at which the bit error rate reaches 3.8 × 10 ⁻³ . FIG. 14 shows the results obtained by simulation and experiment. The broken line indicates the simulation result, and the solid line indicates the experimental result. However, the modulation method is DP-QPSK, and the transmission capacity is 33 GBaud. As shown in FIG. 14, the minimum reception sensitivity is substantially constant at −31.5 dBm from the transmission distance of 50 km to 80 km assumed in the optical access network. Optimizing the power budget using I / Q imbalance modulation is effective in a region where the minimum reception sensitivity does not change with respect to such a transmission distance.

FIG. 15 is a diagram illustrating a relationship between the I / Q imbalance parameter θ and the power budget gain in the PON system 100 according to the present embodiment. FIG. 15 shows the results obtained by simulation and experiment. The broken line indicates the simulation result, and the solid line indicates the experimental result. As shown in FIG. 15, the power budget gain characteristic with respect to θ can be approximated by a quadratic function for both the I axis and the Q axis. Therefore, the characteristic of the I axis is G ₁ = a ₁ θ ² + b ₁ θ + c ₁ , the characteristic of the Q axis is G ₂ = a ₂ θ ² + b ₂ θ + c _2, and the power budget difference between ONU # 1 and ONU # 2 is In the case of ΔG, the I / Q imbalance parameter θ is expressed by the following equation (1). However, in the optical receiving unit 40 of the ONU 2, when the phase noise compensation unit 46 of the waveform shaping unit 44 performs compensation using the fourth power method, a range in which a signal in which the I component and the Q component are imbalanced can be compensated is π / 6. ≦ θ ≦ π / 3. Therefore, OLT 1 sets θ within this range.

  Next, an operation in which the OLT 1 transmits data to the ONU 2 will be described with reference to FIG. FIG. 16 is a sequence diagram illustrating an example of a downlink data transmission operation in the PON system 100 according to the present embodiment. Here, an operation example when the number of ONUs 2 connected to the OLT 1 is two will be described. Two ONUs 2 are referred to as ONU # 1 and ONU # 2. Further, it is assumed that the OLT 1 knows in advance the length of the transmission path between each ONU 2. For example, when the ONT # 1 is connected, the OLT 1 transmits a signal for measuring the transmission path length to the ONU # 1 and receives a response signal to the ONU # 1. Know the length of the transmission line. Specifically, the OLT 1 measures a required time from when a measurement signal is transmitted until a response signal is received, and calculates a transmission path length from the measured required time. The OLT 1 calculates the length of the transmission line with the ONU # 2 by the same method. The method by which the OLT 1 collects information on the length of the transmission path between each ONU 2 is not limited to this. The OLT 1 may receive input of information on the transmission path length to each ONU 2 from an administrator of the PON system 100 or the like.

  In downlink data transmission, first, each ONU 2 makes a request for downlink data transmission to the OLT 1 (steps S1-1 and S1-2). At this time, each ONU 2 notifies the OLT 1 of the downlink transmission capacity.

  Next, the OLT 1 confirms the availability of optical resources and allocates optical resources to each ONU 2 (step S2). Based on the transmission capacity notified from ONU # 1 and the transmission capacity notified from ONU # 2, OLT 1 allocates optical resources to be assigned to each ONU 2 so that the number of wavelengths to be used, that is, the number of optical transceivers to be used is reduced. decide. For example, when the total value of transmission capacities notified from ONU # 1 and ONU # 2 is 100 Gb / s or less, the OLT 1 converts each signal of XI, XQ, YI, and YQ that is not used into ONU # 1 and ONU # 2 are allocated according to the transmission capacity requested. In the OLT 1, the transmission capacity controller 11 performs allocation of optical resources.

  Next, the OLT 1 notifies the ONU # 1 and the ONU # 2 of the optical resource allocated in step S2 (steps S3-1 and S3-2). The ONU # 1 and the ONU # 2 that have received the notification of the optical resource set the optical transceiver for using the notified optical resource (steps S4-1 and S4-2). Completion notification is sent to the OLT 1 (steps S5-1 and S5-2).

  When the OLT 1 receives notification of setting completion from the ONU # 1 and ONU # 2, the OLT 1 sets an I / Q imbalance parameter (step S6). The OLT 1 determines the I / Q imbalance parameter based on the optical resource allocation result in step S2, the length of the transmission path to the ONU # 1, and the length of the transmission path to the ONU # 2. The OLT 1 allocates optical resources having the same wavelength to the ONU # 1 and the ONU # 2, and when the difference between the transmission path length to the ONU # 1 and the transmission path length to the ONU # 2 is large, the I signal strength and Q The I / Q imbalance parameter is set so that there is a difference in signal strength. For example, in the case of the second specific example shown in FIGS. 12 and 13, the OLT 1 has an XQ-axis signal strength that is greater than an XI-axis signal strength, and the YQ-axis signal strength is a YI-axis signal strength. The I / Q imbalance parameter is set so as to be larger. When the OLT 1 assigns different wavelengths to the ONU # 1 and ONU # 2, and when the difference between the transmission path length to the ONU # 1 and the transmission path length to the ONU # 2 is small, the I / Q IN Set the balance parameter θ = 45 °.

  When the setting of the I / Q imbalance parameter is completed, the OLT 1 transmits downlink data to the ONU # 1 and the ONU # 2 (steps S7-1 and S7-2). When transmitting downlink data, the OLT 1 adjusts the intensity on the I axis and the intensity on the Q axis of the signal to be transmitted according to the I / Q imbalance parameter set in step S6. The form of data transmission may be a stream type used in the current PON system or any other form. When ONU # 1 and ONU # 2 receive downlink data, they transmit a data transmission completion notification indicating that reception is complete to OLT1 (steps S8-1 and S8-2).

  As described above, in the PON system 100 according to the present embodiment, the OLT 1 uses each optical signal to be transmitted to each ONU 2 based on the optical resource allocation result for the ONU 2 and the length of the transmission path to each ONU 2. The signal intensity on the I axis and the signal intensity on the Q axis of the polarization were adjusted. Thereby, the power consumption when transmitting data to each ONU 2 can be adjusted according to the length of the transmission path, and when the same wavelength is assigned to a plurality of ONUs 2 having different transmission path lengths, The power of the signal transmitted to the ONU 2 having a short transmission path can be made smaller than the power of the signal transmitted to the ONU 2 having a long transmission path, and power consumption can be suppressed.

  The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 OLT, 2 _{1 to} 2 ₄ ONU, 3 optical coupler, 11 transmission capacity controller, 12, 12 _{1 to} 12 ₄ , 21 optical transceiver, 13 optical coupling demultiplexer, 30 optical transmission unit, 31 transmission processing unit, 32 Transmission signal generator, 33 Transmission digital filter, 34 Signal adjustment unit, 35, 44 Waveform shaping unit, 36 Driver, 37 Optical signal generation unit, 38 Light source, 39 Optical modulator, 40 Optical reception unit, 41 Coherent receiver, 42 Reception Processing unit, 43 ADC unit, 45 dispersion compensation unit, 46 phase noise compensation unit, 47 adaptive equalization unit, 100 PON system.

Claims (6)

An optical communication device that operates as an optical subscriber line terminating device capable of connecting a plurality of subscriber side terminal devices,
A signal generator for generating a signal to be transmitted to the plurality of subscriber-side terminal devices;
A light resources allocated to each of the plurality of subscriber terminal equipment, the transmission distance to each of said plurality of subscriber terminals, based on the position of the signal point in the complex plane of the signal An adjustment amount determination unit for determining the adjustment amount of
A signal adjustment unit that adjusts the position of a signal point in the complex plane of the signal based on the adjustment amount;
An optical signal generation unit that converts the signal after the position of the signal point is adjusted by the signal adjustment unit into an optical signal;
Equipped with a,
When the transmission distance to each subscriber-side terminal device assigned to the same polarization of the same wavelength is different, the adjustment amount determination unit is up to each subscriber-side terminal device assigned to the same polarization of the same wavelength. The amount of adjustment is determined so that the strength of the signal transmitted to the subscriber terminal device having a short transmission distance is lower than the strength of the signal transmitted to each subscriber terminal device when the transmission distance is the same. To
An optical communication device.   The adjustment amount determination unit, when the intensity of the signal transmitted to the subscriber side terminal device having a long transmission distance is the same transmission distance to each subscriber side terminal device assigned to the same polarization of the same wavelength The adjustment amount is determined so as to be the same as the intensity of the signal transmitted to each subscriber-side terminal device.
  The optical communication apparatus according to claim 1. An optical resource allocation unit that allocates optical resources for transmitting data to each of the plurality of subscriber-side terminal devices based on a transmission capacity requested by each of the plurality of subscriber-side terminal devices;
The optical communication apparatus according to claim 1 or 2, characterized in that it comprises a. The optical resource allocation unit allocates the optical resource so that the number of wavelengths to be used is reduced.
The optical communication apparatus according to claim 3 . The signal generating unit, the optical communication device according to claim 1, characterized in that it comprises a digital filter for limiting the signal band in any one of the four. An optical communication device according to any one of claims 1 to 5 ,
A plurality of subscriber-side terminal devices connected to the optical communication device;
An optical communication system comprising:

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