JP2013090143A - Optical subscriber-side device and optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mitigate an input dynamic range and a response speed required for an OLT optical receiver.SOLUTION: An ONU 1 includes: a reception signal intensity report unit 133 for measuring the reception intensity of a downward optical signal simultaneously transmitted from an OLT; based on the reception intensity of the downward optical signal measured by the reception signal intensity report unit 133, an LD drive condition controller 14 for controlling the transmission intensity of an upward optical signal transmitted to the OLT, to allow the reception intensity of an upward optical signal, burst received by the OLT, to be substantially constant irrespective of each ONU.

Description

  The present invention relates to a passive optical network configuration in which a plurality of optical subscriber side devices are connected to one optical station side device.

  As a typical network configuration of an optical access system, a single star configuration (Single Star Unit) in which an optical subscriber unit (Optical Network Unit: ONU) and an optical station side device (Optical Line Terminal: OLT) are connected one-to-one. SS) and a passive optical network (PON) configuration in which a plurality of ONUs are connected to one OLT.

  In the SS system, since the ONU can occupy the OLT, high-speed communication is possible, but there is a disadvantage that the apparatus cost is high. On the other hand, in the PON system, since a plurality of ONUs share one OLT and optical fiber equipment, the PON system is adopted in many optical access systems because it is economical.

  PON downlink transmission is a continuous mode, and signals to each ONU are transmitted in a time division multiplexing (TDM) manner. The downstream signal is broadcast to all ONUs, and each ONU selectively receives only the signal addressed to itself.

  On the other hand, in uplink transmission, each ONU transmits a signal at a timing designated by the OLT in order to avoid signal collision by time division multiple access (TDMA). Since the transmission distance between the ONU and the OLT is different for each ONU, the upstream signals from each ONU have a characteristic that they are intermittent with different strengths and phases, and the upstream signal is called a burst mode.

  The configuration of the ONU in the prior art is shown in FIG. The ONU 1 includes a WDM filter 11, an optical transmitter 12, and an optical receiver 13. The WDM filter 11 has a function of branching / combining optical signals having different wavelengths. In general, the PON system uses different wavelengths for the upstream signal and downstream signal, so the WDM filter 11 is used to prevent interference.

  The optical transmitter 12 includes a laser diode (LD) 121, an LD driver (LDD) 122, and an automatic power controller (APC) 123. The LD driver 122 drives the current flowing through the LD 121 based on the transmission signal and outputs a corresponding optical signal. The APC 123 has a function of controlling the output optical signal intensity of the LD 121 to be a constant value.

  The optical receiver 13 includes a photodiode (PD) 131, an equalizer amplifier (EQA) 132, and a received signal strength indicator (Received Signal Strength Indicator: RSSI) 133. The clock data regenerator (CDR) may be included in the optical receiver 13, but may be included in the logic circuit device 2 subsequent to the optical receiver 13 from the viewpoint of function sharing of the transmission apparatus.

  The received signal strength notification device 133 has a function of monitoring the strength of the photocurrent flowing through the PD 131. The equalizing amplifier 132 includes an impedance conversion amplifier (Transimpedance Amplifier: TIA) and an amplitude limiting amplifier (LIMitting Amplifier: LIA). The CDR has a clock recovery circuit (CRC) and an identification recovery circuit (DEC). The input optical signal to the optical receiver 13 is converted into a current signal by the PD 131, converted into a voltage signal in the TIA, and amplified in an LIA with an amplitude limited to a level that can be discriminated and reproduced by a subsequent CDR. In the CDR, the CRC extracts and reproduces the clock signal from the input signal, and the DEC discriminates and reproduces the input signal at the identification timing given by the reproduction clock, and sends the reproduction signal to the logic circuit device 2 in the subsequent stage.

“A Burst-Mode 3R Receiver for 10-Gbit / s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response Venue, IEEE Journal of Forest. 26, no. 1, pp. 99-107, January 2008.

The downstream signal is a continuous mode, and the optical signal intensity received by each ONU from the OLT is constant in principle, but is usually different for each user. For example, when subscribers A and B having different distances from the OLT are connected to the OLT in an arbitrary PON network, the optical signal strengths received from the OLT are P _{down_A} and P _{down_B} , respectively. P _{down_A} ≠ P _{down_B} , and P _{down_A} and P _{down_B} do not change in principle. However, it may change depending on the change in optical component performance over time.

  Since the upstream optical signal is in burst mode, the TIA and LIA that constitute the OLT optical receiver amplify burst signals with significantly different intensities without distortion, and the CRC needs to extract the clock signal from burst signals of different phases. is there. In this case, each receiving circuit needs to be optimized for each burst signal, but each circuit requires a certain response time.

  The uplink signal is TDMA, and if the response time of TIA or LIA is long, the uplink signal band, which is a shared resource, is wasted. Therefore, high-speed response performance is required for TIA and LIA. In addition, from the viewpoint of providing an uplink communication service, it is necessary to support a large transmission path loss for multi-branch support and wide-area accommodation, so that the TIA and LIA constituting the equalization amplifier have high sensitivity and wide range. Dynamic range reception performance is required.

  The upstream optical signal transmission processing in the ONU in the prior art is shown in FIG. It is assumed that the first ONU has a longer transmission distance from the OLT and a larger transmission path loss than the second ONU.

Time _{t 0} is the initial state, the time _{t 0} the power enters the first 1ONU and second 2ONU, it is assumed that from the time _{t 1} starts to operate normally. The LD driver 122 of the first ONU and the second ONU drives the LD 121 with a bias current _{Ibias_1} and a drive current _{idrv_1} .

The 1ONU is from time _{t 1} is allowed to transmit an uplink signal from the OLT. LDs 121 of the 1ONU has finished up until the time _{t 2, the} transmitted uplink data up to time _{t 3,} LDs 121 of the 1ONU until time _{t 4} ends the emission.

The 2ONU is from the time _{t 5} is allowed to transmit an uplink signal from the OLT. LDs 121 of the 2ONU has finished up until the time _{t 6,} and transmits the uplink data up to time _{t 7,} LDs 121 of the 2ONU until time _{t 8} ends the emission.

  FIG. 3 shows the reception processing of the upstream optical signal by the OLT in the prior art. Although the OLT optical receiver is different from the ONU optical receiver in that a burst signal is input, the configuration of the OLT optical receiver is not particularly shown because it is similar to the configuration of the ONU optical receiver.

Uplink data of the 1ONU from the time _{t 9} is inputted to the OLT of the optical receiver, after a certain response _time, between the _{t 10} to _{t 11,} receives a net _data, quenched by _{t 12.} Uplink data of the 2ONU from the time _{t 13} is input to the OLT of the optical receiver, after a certain response _time, during the period from _{t 14} to _{t 15,} it receives a net _data, quenched by _{t 16.}

  From FIG. 2, there is no difference between the first ONU and the second ONU in the optical signal power when the upstream optical signals of the first ONU and the second ONU are output from the ONU optical transmitter. This is because the bias current and drive current of the LD 121 are approximately the same between the first ONU and the second ONU.

  From FIG. 3, the optical signal power when the upstream optical signals of the first ONU and the second ONU are input to the optical receiver of the OLT, that is, the photocurrent flowing through the PD 131 is different between the first ONU and the second ONU, and Ircv1 and Ircv2 respectively. And Ircv1 <Ircv2. This is because the first ONU has a longer transmission distance from the OLT than the second ONU, and the transmission line loss to the OLT is larger.

  Therefore, for conventional OLT optical receivers, input optical signals having different intensities from the viewpoint of not only operating without error for a wide range of input power but also improving the utilization efficiency of the upstream band. In addition, high-speed response performance has been demanded.

  Therefore, in order to solve the above-described problems, an object of the present invention is to reduce the input dynamic range and response speed required for an optical receiver of an OLT.

  For downstream optical signals transmitted simultaneously from the optical station side device to a plurality of optical subscriber side devices, the transmission strength is the same for the plurality of optical subscriber side devices, but the reception strength is the transmission path loss for the plurality of optical subscriber side devices. Different to reflect the difference. Therefore, for the upstream optical signal transmitted from the plurality of optical subscriber side devices to the optical station side device, the transmission intensity is transmitted to the plurality of optical subscriber side devices so that the reception strength is the same for the plurality of optical subscriber side devices. It will be different to reflect the difference in road loss. That is, the transmission intensity of the upstream optical signal in each optical subscriber side apparatus is controlled based on the reception intensity of the downstream optical signal in each optical subscriber side apparatus.

  Specifically, the present invention is based on a reception intensity measurement unit that measures the reception intensity of a downstream optical signal that is simultaneously transmitted from the optical station side device, and a reception intensity of the downstream optical signal that is measured by the reception intensity measurement unit. By controlling the transmission intensity of the upstream optical signal transmitted to the optical station side apparatus, the reception intensity of the upstream optical signal burst-received by the optical station side apparatus is substantially constant regardless of each optical subscriber side apparatus. An optical subscriber-side apparatus comprising: a transmission intensity control unit configured to be an intensity.

  The present invention also measures an optical station side device that broadcasts a downlink signal simultaneously and a reception intensity of the downstream optical signal that is broadcast from the optical station side device, and is based on the measured reception strength of the downstream optical signal. Thus, by controlling the transmission intensity of each upstream optical signal to be transmitted to each of the optical station side devices, a plurality of lights each having substantially the same reception intensity of the upstream optical signal burst received by the optical station side device. An optical communication system comprising a subscriber-side device.

  According to this configuration, the reception intensity of the upstream optical signals transmitted from the plurality of optical subscriber side devices to the optical station side device is the same for the plurality of optical subscriber side devices. On the other hand, the required input dynamic range and response speed can be relaxed.

  In the present invention, the transmission intensity control unit controls the transmission intensity of the upstream optical signal transmitted to the optical station side device to be lower as the reception intensity of the downstream optical signal measured by the reception intensity measurement unit is higher. An optical subscriber side device characterized by the above.

  In the present invention, each of the plurality of optical subscriber-side devices controls a lower transmission intensity of the upstream optical signal to be transmitted to the optical station-side apparatus as the measured downstream optical signal reception intensity is higher. Is an optical communication system.

  According to this configuration, with respect to the upstream optical signal transmitted from the plurality of optical subscriber side devices to the optical station side device using the correlation that associates the reception strength of the downstream optical signal and the transmission strength of the upstream optical signal, the reception strength Can be made equal for a plurality of optical subscriber side devices.

  Further, the present invention provides an intensity correspondence storage unit that stores the transmission intensity of the upstream optical signal controlled by the transmission intensity control unit in correspondence with the reception intensity of the downstream optical signal measured by the reception intensity measurement unit. It is an optical subscriber side device further provided.

  Further, the present invention is characterized in that each of the plurality of optical subscriber side devices stores the transmission intensity of each upstream optical signal to be controlled, corresponding to the measured reception intensity of each downstream optical signal. It is an optical communication system.

  According to this configuration, by using the storage unit that associates the reception intensity of the downstream optical signal and the transmission intensity of the upstream optical signal, the reception intensity of the upstream optical signal transmitted from the plurality of optical subscriber side apparatuses to the optical station side apparatus is determined. Can be made equal for a plurality of optical subscriber side devices.

  The present invention can reduce the input dynamic range and response speed required for an OLT optical receiver.

It is a figure which shows the structure of ONU in a prior art. It is a figure which shows the transmission process of the upstream optical signal in ONU in a prior art. It is a figure which shows the reception process of the upstream optical signal in OLT in a prior art. It is a figure which shows the structure of ONU in this invention. It is a figure which shows the transmission process of the upstream optical signal in ONU in this invention. It is a figure which shows the reception process of the upstream optical signal in OLT in this invention. It is a figure which shows the operating condition in ONU in this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  The configuration of the ONU in the present invention is shown in FIG. The ONU 1 includes a WDM filter 11, an optical transmitter 12, an optical receiver 13, an LD drive condition controller 14, and an element operation condition storage table 15, and is connected to the logic circuit device 2. The optical transmitter 12 includes an LD 121, an LD driver 122, and an automatic power controller 123, and is connected to the logic circuit device 2. The optical receiver 13 includes a PD 131, an equalizing amplifier 132, and a received signal strength notification device 133, and is connected to the logic circuit device 2.

  The element operating condition storage table 15 is a storage element such as a nonvolatile memory, for example, and stores information associating the value of the photocurrent flowing through the PD 131 and the driving condition of the LD 121. The LD drive condition controller 14 is connected to each of the element operation condition storage table 15, the automatic power controller 123, and the reception signal strength notification device 133, and the photocurrent value of the PD 131 read from the reception signal strength notification device 133 is determined. Write to the element operation condition storage table 15, read the drive condition of the LD 121 set in the element operation condition storage table 15, and set the drive condition of the LD 121 to the automatic power controller 123.

  The above method uses a storage unit that associates the reception intensity of the downstream optical signal and the transmission intensity of the upstream optical signal. The following method associates the reception intensity of the downstream optical signal and the transmission intensity of the upstream optical signal. This is a method of using correlation. That is, a method of lowering the transmission intensity of the upstream optical signal is used as the reception intensity of the downstream optical signal is higher. Alternatively, a method of controlling the transmission intensity of the upstream optical signal in inverse proportion to the reception intensity of the downstream optical signal is used.

A method for controlling the transmission intensity of the upstream optical signal in inverse proportion to the reception intensity of the downstream optical signal will be described below. The transmission distance between the first 1ONU and OLT and _{L 1,} the transmission distance between the first 2ONU the OLT and _{L 2.} In the transmission / reception between the first ONU and the OLT, the reception strength is 1 / L ₁ (L ₁ > 1) times the transmission strength. In transmission / reception between the second ONU and the OLT, the reception intensity is 1 / L ₂ (L ₂ > 1) times the transmission intensity. When transmit power of the downlink optical signal is equally _{T down} against the 1ONU and second 2ONU, reception intensity at the 1ONU and second 2ONU downstream optical _{signals, R down_1 = T down / L} 1 and _{R down_2} = it is a T _down / _{L 2.} Reception intensity of the upstream optical signal, when it is equally _{R Stay up-against} the 1ONU and second 2ONU, transmission intensity at the 1ONU and second 2ONU upstream optical _{signal, T up_1 = R up × L} 1 and _{T up_2} = R _up × L ₂ . Therefore, T _up is determined with respect to R _down so that R _down × T _up = T _down × R _up = constant holds.

FIG. 5 shows upstream optical signal transmission processing in the ONU according to the present invention. It is assumed that the first ONU has a longer transmission distance from the OLT and a larger transmission path loss than the second ONU. Time _{t 0} is the initial state, the time _{t 0} the power enters the first 1ONU and second 2ONU, it is assumed that from the time _{t 1} starts to operate normally.

In the 1ONU, received signal strength notifier 133, outputs the input light current value _{I IN_1} from time _{t 1} for the first 1ONU. The LD drive condition controller 14 reads the input photocurrent value I in — ₁ from the received signal strength notifier 133 and writes it in the element operation condition storage table 15 by time t ₂ . LD driving condition controller 14 refers to the device operation condition storing table 15, the optimum bias current _{I Bias_1} and optimum driving current _{i Drv_1} the LDs 121, set to the automatic power controller 123 by time _{t 3.} As described above, the storage unit can be used, and the correlation between the uplink transmission optical signal intensity and the downlink reception optical signal intensity can also be used.

In the second ONU, the received signal strength notifier 133 outputs the input photocurrent value I _{in_2} for the second ONU from time t ₁ . The LD drive condition controller 14 reads the input photocurrent value I in — ₂ from the received signal strength notifier 133 and writes it in the element operation condition storage table 15 by time t ₂ . LD driving condition controller 14 refers to the device operation condition storing table 15, the optimum bias current _{I Bias_2} and optimum driving current _{i Drv_2} the LDs 121, set to the automatic power controller 123 by time _{t 3.} As described above, the storage unit can be used, and the correlation between the uplink transmission optical signal intensity and the downlink reception optical signal intensity can also be used.

The 1ONU is from time _{t 3} is allowed to transmit an uplink signal from the OLT. LDs 121 of the 1ONU has finished up until the time _{t 4,} and transmits the uplink data up to time _{t 5,} LDs 121 of the 1ONU until time _{t 6} ends the emission.

The 2ONU is from the time _{t 7} is allowed to transmit an uplink signal from the OLT. LDs 121 of the 2ONU has finished up until the time _{t 8,} and transmits the uplink data up to time _{t 9,} LDs 121 of the 2ONU until time _{t 10} ends the emission.

FIG. 6 shows reception processing of an upstream optical signal in the OLT according to the present invention. Uplink data of the 1ONU from the time _{t 11} is input to the OLT of the optical receiver, after a certain response _time, between the _{t 12} to _{t 13,} receives a net _data, quenched by _{t 14.} Uplink data of the 2ONU from the time _{t 15} is input to the OLT of the optical receiver, after a certain response _time, between the _{t 16} to _{t 17,} it receives a net _data, quenched by _{t 18.}

  As shown in FIG. 6, since the input photocurrent of the optical receiver of the OLT is substantially constant as Ircv1, the input dynamic range requirement for the optical receiver of the OLT can be relaxed. Further, since the required input dynamic range may be narrow, the response time required for optimizing the state of the optical receiver for burst signals having different input intensities can be shortened. As an example, the operating conditions of the first ONU and the second ONU in the present invention are shown in FIG. 7, and depend on the transmission distance of the optical fiber and the performance of components such as the LD 121 and the PD 131.

  In the ONU 1 in the present embodiment, the WDM filter 11 is used. However, the WDM filter 11 is not necessarily required, and the WDM filter 11 is not necessary when, for example, direction multiplexing (DDM) is used. In addition, although the number of ONUs has been described as an example, it is naturally possible to use three or more units.

  The optical subscriber side apparatus and the optical communication system according to the present invention can be applied to a PON that relaxes an input dynamic range and response speed required for an optical receiver of an OLT.

1: ONU
2: Logic circuit device 11: WDM filter 12: Optical transmitter 13: Optical receiver 14: LD driving condition controller 15: Element operating condition storage table 121: LD
122: LD driver 123: Automatic power controller 131: PD
132: Equalization amplifier 133: Received signal strength notification device

Claims (6)

A reception intensity measuring unit for measuring the reception intensity of the downstream optical signal transmitted from the optical station side device;
Based on the reception intensity of the downstream optical signal measured by the reception intensity measuring unit, the upstream station receives the burst received by the optical station side apparatus by controlling the transmission intensity of the upstream optical signal transmitted to the optical station side apparatus. A transmission intensity control unit that makes the reception intensity of the optical signal substantially constant regardless of each optical subscriber side device;
An optical subscriber-side apparatus comprising:   The transmission intensity control unit controls the transmission intensity of the upstream optical signal transmitted to the optical station side device to be lower as the reception intensity of the downstream optical signal measured by the reception intensity measurement unit is higher. The optical subscriber side apparatus according to claim 1. In correspondence with the reception intensity of the downstream optical signal measured by the reception intensity measurement unit, an intensity correspondence storage unit that stores the transmission intensity of the upstream optical signal controlled by the transmission intensity control unit,
The optical subscriber side device according to claim 1 or 2, further comprising: An optical station side device that simultaneously transmits downstream signals;
The reception intensity of the downstream optical signal transmitted from the optical station side apparatus is measured, and the transmission intensity of the upstream optical signal to be transmitted to the optical station side apparatus is determined based on the measured reception intensity of the downstream optical signal. By controlling each, a plurality of optical subscriber side devices each having substantially the same strength as the reception intensity of the upstream optical signal burst received by the optical station side device,
An optical communication system comprising:   The plurality of optical subscriber side devices each control the transmission intensity of the upstream optical signal to be transmitted to the optical station side device lower as the measured downstream optical signal reception intensity is higher, respectively. Item 5. The optical communication system according to Item 4.   The plurality of optical subscriber-side apparatuses respectively store transmission intensity of upstream optical signals to be controlled respectively corresponding to the measured reception intensity of downstream optical signals. Item 6. The optical communication system according to Item 5.

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