Optical communication system and optical output device

Abstract

This optical communication system includes an optical line terminal (OLT) and a plurality of optical network units (ONU) connected to the OLT. The OLT notifies the plurality of ONUs of the power of an optical signal received from the ONU. Each ONU includes: an optical output unit that outputs an optical signal; and a control unit that controls, in accordance with the power notified from the OLT, the power of the optical signal output from the optical output unit.

Description

Optical communication system and optical output device

[0001] This invention relates to an optical communication system and an optical output device.

[0002] In an optical subscriber network, the Optical Network Unit (ONU) installed on the subscriber side transmits a certain amount of light to the Optical Line Terminal (OLT) on the other side. Therefore, if the distance between the ONU and the OLT is short, the power of the light input from the ONU becomes excessive, resulting in the ONU consuming surplus power.

[0003] Furthermore, in a PON system, the OLT receives light from multiple ONUs, resulting in variations in the power of the light received from each ONU. Therefore, the OLT uses a limiting amplifier (LA) to smooth out these variations in light power. Consequently, if the ONU transmits light of constant power, it leads to increased power consumption in the OLT. Therefore, a solution to this problem is needed.

[0004] Nogawa, Katsurai, Nakamura, Kamitsuna, Otomo, “10 Gbit / s Burst Mode Receiving IC Technology”, NTT Technical Journal, Vol.9, No.3, pp.31-35, 2011.1

[0005] The present invention aims to provide a technology that can reduce the power consumption of ONUs and OLTs.

[0006] One aspect of the present invention is an optical communication system comprising an OLT and a plurality of ONUs connected to the OLT, wherein the OLT notifies the plurality of ONUs of the power of the optical signal it receives from the ONUs, and the ONUs comprise an optical output unit that outputs an optical signal and a control unit that controls the power of the optical signal output from the optical output unit in accordance with the power notified by the OLT.

[0007] The present invention makes it possible to reduce the power consumption of the ONU and OLT.

[0008] This figure shows an example configuration of the optical communication system 1 according to this embodiment. This figure shows an example configuration of the ONU 2 and OLT 3 according to this embodiment. This is a sequence diagram showing the operation of the ONU 2 and OLT 3 according to this embodiment. This figure shows the optical output unit 21 according to the first embodiment. This is a graph showing an example of the relationship between the magnitude of the current injected into the SOA and the gain by the SOA. This figure shows an example of the reflectivity of the DBR. This shows an example of the reflectivity of the DBR and an example of the power spectrum of the optical signal output from the light source 211. This figure shows the optical output unit 21 according to the second embodiment. This is a graph showing the power of the optical signal received by the OLT in a conventional optical communication system. This is a graph showing the power of the optical signal received by the OLT 3 in the optical communication system 1 of this embodiment.

[0009] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the embodiments described below.

[0010] Figure 1 shows an example configuration of the optical communication system 1 according to this embodiment. The optical communication system 1 includes a plurality of ONUs 2 and OLTs 3. The optical communication system 1 shown in Figure 1 includes three ONUs 2-1 to 2-3, but it may also include two or four or more ONUs 2.

[0011] Each of the ONU2 units and the OLT3 unit transmits and receives optical signals.

[0012] Figure 2 shows an example configuration of ONU2 and OLT3 according to this embodiment. ONU2 includes an optical output unit 21, a branching unit 22, an optical receiving unit 23, and a control unit 24.

[0013] The optical output unit 21 outputs an optical signal to the branching unit 22. The branching unit 22 outputs the optical signal input from the optical output unit 21 to the OLT 3. The branching unit 22 outputs the optical signal input from the OLT 3 to the optical receiving unit 23. The optical receiving unit 23 receives the optical signal from the OLT 3 via the branching unit 22.

[0014] The control unit 24 controls the power of the optical signal output from the optical output unit 21.

[0015] The OLT3 comprises an optical output unit 31, a branching unit 32, an optical receiving unit 33, and a control unit 34.

[0016] The optical output unit 31 outputs an optical signal to the branching unit 32. The branching unit 32 outputs the optical signal input from the optical output unit 31 to a specific ONU 2. The branching unit 32 outputs the optical signal input from the ONU 2 to the optical receiving unit 33. The optical receiving unit 33 receives the optical signal from the ONU 2 via the branching unit 32. The optical receiving unit 33 may level the power of the optical signals received from each ONU 2. If the power of the optical signals received from the ONU 2 is below the minimum receiving sensitivity, the optical receiving unit 33 may perform amplification or equalization processing.

[0017] The control unit 34 causes the optical output unit 31 to output an optical signal containing power information of the optical signal received by the optical receiving unit 33. The optical signal output here is received by each ONU 2. After receiving the optical signal from the OLT 3, the ONU 2 controls the power of the optical signal output from the optical output unit 21 based on the power information of the optical signal contained in the optical signal.

[0018] Figure 3 is a sequence diagram showing the operation of the ONU 2 and OLT 3 according to this embodiment. The optical output unit 21 of the ONU 2 outputs an optical signal to the OLT 3 (step S21). The optical signal output by the ONU 2 here includes information for identifying the ONU 2 as the output source. The power of the optical signal output by the ONU 2 here is a predetermined magnitude.

[0019] The optical receiving unit 33 of the OLT3 receives an optical signal from the ONU2 (step S31). The optical receiving unit 33 measures the power of the received optical signal (step S32). The control unit 34 outputs an optical signal containing information on the measurement result of the power of the received optical signal to the optical output unit 31 (step S33). Here, the ONU2, which is the output destination of the optical signal, is identified based on the information for identifying the ONU2 included in the optical signal received in step S31.

[0020] The optical receiving unit 23 of the ONU2 receives an optical signal from the OLT3 (step S22). The control unit 24 of the ONU2 controls the power of the optical signal output from the optical output unit 21 (step S23). The control unit 24 controls the power of the optical signal output from the optical output unit 21 based on the power of the optical signal output in step S21 and the power of the optical signal received by the OLT3, as indicated by the information contained in the optical signal received from the OLT3. The ONU2 communicates with the OLT using the optical signal with the power controlled in step S23.

[0021] For example, the control unit 24 controls the optical output unit 21 so that the power of the optical signal output from the optical output unit 21 is equal to the minimum receiving sensitivity of the OLT 3 plus the line loss experienced by the optical signal output to the OLT 3. In step S21, the power of the output optical signal is G １ Therefore, the power of the optical signal received by OLT3 is G ２ In this case, the line loss experienced by the optical signal output from ONU2 to OLT3 is G １ -G ２ Therefore, the power of the optical signal output in step S21 is G １ Therefore, the information contained in the optical signal received from OLT3 indicates that the power of the optical signal received by OLT3 is G ２ Therefore, when the minimum receiving sensitivity of OLT3 is M, the control unit 24 determines that the power of the optical signal output from the optical output unit 21 is M + (G １ -G ２ The optical output unit 21 is controlled so that the result is as follows.

[0022] The power of the optical signal output from the optical output unit 21 may be an amount equal to the minimum receiving sensitivity of the OLT 3 plus the line loss experienced by the optical signal output to the OLT 3, plus a predetermined amount.

[0023] Each ONU2 performs the operations in steps S21 to S23, and the OLT3 performs the operations in steps S31 to S33 for each ONU2, thereby making the power of the optical signals output from each ONU2 uniform when they are received by the OLT3.

[0024] In the above description, the control unit 24 calculates the power of the optical signal to be output from the optical output unit 21 from the power of the optical signal output in step S21 and the power of the optical signal received by the OLT 3, as indicated by the information contained in the optical signal received from the OLT 3, and controls the optical output unit 21 to output an optical signal of the calculated power. However, the calculation of the power of the optical signal to be output from the optical output unit 21 may be performed by the control unit 34 of the OLT 3. In this case, the power of the optical signal output from the ONU 2 in the initial state is stored in the OLT 3 in advance, and the control unit 34 calculates the power of the optical signal to be output from the optical output unit 21 from the stored power of the optical signal output from the ONU 2 in the initial state and the power of the optical signal received by the optical receiver 33, and causes the optical output unit 31 to output an optical signal containing the calculation result information. In this case, the control unit 24 of the ONU 2 controls the optical output unit 21 based on the calculation result contained in the optical signal received from the OLT 3, and causes the optical output unit 21 to output an optical signal with the power indicated by the calculation result.

[0025] The configuration of the optical output unit 21 will be described in detail below. Figure 4 is a diagram showing the optical output unit 21 according to the first embodiment. The optical output unit 21 according to the first embodiment includes a light source 211 and a power adjustment unit 212.

[0026] The light source 211 outputs an optical signal of constant power. The light source 211 is, for example, a distributed feedback laser (DFB). The light source 211 may be any other type of laser. The power adjustment unit 212 adjusts the power of the optical signal output from the light source 211. The power adjustment unit 212 is, for example, a semiconductor optical amplifier (SOA). Figure 5 is a graph showing an example of the relationship between the magnitude of the current injected into the SOA and the gain obtained by the SOA. By changing the magnitude of the current injected into the SOA, the gain obtained by the SOA changes. The control unit 24 controls the current injected into the SOA included in the optical output unit 21 based on the relationship between the magnitude of the current injected into the SOA and the gain obtained by the SOA. This allows the control unit 24 to change the power of the optical signal output from the optical output unit 21.

[0027] The power adjustment unit 212 is, for example, a distributed Bragg reflector (DBR) and a heater. Figure 6 shows an example of the reflectivity of a DBR. A DBR is a reflector whose reflectivity varies depending on the wavelength of the optical signal, and when the temperature is increased, the reflection spectrum redshifts due to the thermo-optic effect. Figure 6 shows an example of the power spectrum of an optical signal output from a light source 211. The optical signal output from the light source 211 has a power maximum point at a specific wavelength due to the oscillation spectrum of the light source 211. By setting the power maximum point of the optical signal output from the light source 211 to a point where the rate of change of the DBR's reflection spectrum is high, and the control unit 24 controls the output of the heater, the reflectivity of the optical signal output from the light source 211 by the DBR can be controlled. As a result, the control unit 24 can change the power of the optical signal output from the optical output unit 21.

[0028] Instead of a DBR, other components with different reflectivity depending on the wavelength may be used. For example, a ring resonator can also be used to produce different reflectivity depending on the wavelength.

[0029] The power adjustment unit 212 may be a Mach-Zehnder interferometer, and the power of the optical signal output from the light source 211 may be adjusted by the phase control of the Mach-Zehnder interferometer. Alternatively, the power adjustment unit 212 may be an optical modulator, and the power of the optical signal output from the light source 211 may be adjusted by the electric field absorption effect of the optical modulator.

[0030] This allows the optical output unit 21 to adjust the power of the optical signal it outputs.

[0031] Furthermore, the power adjustment unit 212 may also include both an SOA and a DBR. The DBR may be other components with different reflectivity depending on the wavelength. In this case, the DBR transmits the optical signal according to the wavelength of the optical signal output from the light source 211, and the SOA amplifies the transmitted optical signal. At this time, the optical signal output from the light source 211 is directly modulated, and switching is performed between a 0-level oscillation mode and a 1-level oscillation mode. Figure 7 shows an example of the reflectivity of the DBR and an example of the power spectrum of the optical signal output from the light source 211. When the optical signal is directly modulated, due to the carrier plasma effect, the power spectrum of the optical signal in the 1-level oscillation mode becomes a blue-shifted version of the power spectrum of the optical signal in the 0-level oscillation mode. The reflection spectrum of the DBR or the power spectrum of the optical signal is adjusted so that the reflectivity of the DBR differs between the wavelength at which the power spectrum of the optical signal in the 1-level oscillation mode is maximum and the wavelength of the power spectrum of the optical signal in the 0-level oscillation mode.

[0032] The detuned-loading effect of the DBR reduces the α parameter and improves the relaxation oscillation frequency (fr). Therefore, it is expected that the ONU2 duration will be increased and the modulation speed will be increased. Furthermore, even when the power adjustment unit 212 consists of a DBR and a heater, the detuned-loading effect can be expected to increase the modulation speed of the ONU2.

[0033] Figure 8 shows an optical output unit 21 according to the second embodiment. The optical output unit 21 according to the second embodiment includes a plurality of light sources 211-1 to 211-N (where N is an integer of 2 or more) and a switch 213.

[0034] In the second embodiment, the light sources 211 output optical signals with different powers. For example, the light sources 211 are lasers with different lengths of active layers. The switch 213 may output an optical signal via a single-mode waveguide among the optical signals output from the plurality of light sources 211-1 to 211-N. Since the relaxation oscillation frequency (fr) is almost constant regardless of the active layer length, the modulation band can be maintained. Also, if the photon lifetime is appropriately designed to adjust the damping effect, a flat small-signal response can be obtained at the current where fr is maximum.

[0035] FIG. 9 is a graph showing the power of the optical signal received by the OLT in a conventional optical communication system. Three ONUs are connected to the OLT, and the transmission distances between the OLT and each ONU are different. The graph shown in FIG. 6 has the power P of the optical signal on the vertical axis out , and the horizontal axis shows the positions of the ONU and the OLT. On the horizontal axis, the length between each ONU and the OLT indicates the transmission distance between each ONU and the OLT. When the distance between the ONU and the OLT is short, as described above, the power of the optical signal received by the OLT is much larger than the minimum reception sensitivity of the OLT, and surplus energy is being used. Also, since the powers of the optical signals received by the OLT from each ONU are different, it is necessary to smooth the power.

[0036] FIG. 10 is a graph showing the power of the optical signal received by the OLT 3 in the optical communication system 1 of this embodiment. In this embodiment, since the powers of the optical signals output by each ONU 2 are set to be equal at the OLT 3, the OLT 3 receives optical signals with equal powers from each ONU 2. Therefore, the OLT 3 does not need to smooth the power of the optical signal received from the ONU 2, and the power consumption of the OLT 3 can be reduced. Also, when the optical output unit 21 of each ONU 2 includes a light source 211 and a power adjustment unit 212, and the power adjustment unit 212 is an SOA, since the SOA amplifies, the light source 211 may output a smaller power than the light source included in a conventional ONU. Thereby, the power consumption in the ONU 2 can be reduced.

[0037] The processing of the control unit 24 and / or control unit 34 in the above-described embodiment may be implemented by a computer using software. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. Here, "computer system" includes hardware such as the OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and storage devices such as hard disks built into a computer system. Moreover, "computer-readable recording medium" may also include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside a computer system that acts as a server or client in such a case. Furthermore, the above-mentioned program may be for implementing a part of the above-mentioned function, or it may be a program that can implement the above-mentioned function in combination with a program already recorded in the computer system, or it may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0038] 1 Optical communication system, 2 ONU, 21 Optical output unit, 211 Light source, 212 Power adjustment unit, 213 Switch, 22 Branching unit, 23 Optical receiving unit, 24 Control unit, 3 OLT, 31 Optical output unit, 32 Branching unit, 33 Optical receiving unit, 34 Control unit

Claims

1. An optical communication system comprising an OLT and a plurality of ONUs connected to the OLT, wherein the OLT notifies the plurality of ONUs of the power of the optical signal it receives from the ONUs, and the ONUs each comprising an optical output unit that outputs an optical signal and a control unit that controls the power of the optical signal output from the optical output unit according to the power notified by the OLT.

2. The optical communication system according to claim 1, wherein the optical output unit comprises a light source that outputs an optical signal of constant power, and a power adjustment unit that adjusts the power of the optical signal output from the light source, the power adjustment unit is a semiconductor optical amplifier, and the control unit controls the magnitude of the current injected into the semiconductor optical amplifier.

3. The optical communication system according to claim 1, wherein the optical output unit comprises a light source that outputs an optical signal of constant power, and a power adjustment unit that adjusts the power of the optical signal output from the light source, the power adjustment unit is a reflector having different reflectances depending on the wavelength, and the control unit controls the reflectance of the reflector.

4. An optical output device comprising: an optical output unit that outputs light; a power adjustment unit that adjusts the power of the light; and a control unit that controls the power adjustment unit.

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