JP2015100027A - Optical amplification device, and gain setting method of optical amplification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that extension of an OLT-ONU distance and increase of a splitter branch number are requested more than a light receiving range of OLT.SOLUTION: An optical amplification device includes: a first multiplexer/demultiplexer for distributing a downlink signal from the OLT to a downlink coupler and an uplink signal from a second uplink coupler to the OLT, respectively; a second multiplexer/demultiplexer for distributing an uplink signal from the ONU to a first uplink coupler; an optical level monitor for monitoring an optical level of the uplink signal branched by the first uplink coupler; a delay unit connected to the first uplink coupler for delaying the uplink signal; an optical amplifier connected to the delay unit for amplifying the uplink signal; a waveform monitoring part connected to the downlink coupler for monitoring a distance measurement signal; and a gain control part connected to the optical level monitor and the waveform monitoring part for controlling a gain of the optical amplifier.

Description

  The present invention relates to an optical amplifying device for amplifying an upstream optical signal of a passive network optical system and a gain setting method for the optical amplifying device.

  Due to a significant increase in communication traffic, optical fiber communication has become widespread in order to realize a wider band and a longer distance. One system for realizing an optical access network that connects a center station and a subscriber by an optical fiber is a PON system. A PON system consists of a single optical fiber terminal unit (OLT) and a plurality of optical network unit units (ONUs) connected by a single optical fiber and an optical splitter. This is a system in which facilities such as an OLT and an optical splitter are shared among subscribers. As typical PON standards, EPON (Ethernet (registered trademark) PON) standardized by IEEE 802.3ah, ITU-T G. There are GPON (Gigabit Capable PON) standardized by 984 and 10G-EPON (10 Gigabit-Ethernet PON) standardized by IEEE 802.3av. The upstream frame transmitted from the ONU to the OLT in the PON and the downstream frame transmitted from the OLT to the ONU are multiplexed by wavelength division multiplexing (WDM). In the downstream frame, the same data is transmitted from the OLT to all ONUs connected by optical fibers. The ONU that has received the data refers to the destination information included in the signal, discards frames other than the one addressed to itself, and transfers only the frame addressed to itself to the user apparatus. On the other hand, the upstream frame is multiplexed and communicated by time division multiple access (TDMA) using burst transmission in which ONU transmits data at a specified time in accordance with transmission permission from OLT.

  In the PON system, it is necessary to keep the optical level of the upstream burst signal output from the ONU within the light receiving sensitivity range of the OLT at the optical input unit of the OLT. However, since the upstream burst signal output from each ONU has different losses depending on the transmission distance to the OLT and the number of branches in the optical splitter, a difference occurs in the optical input level to the OLT. Therefore, when SOA is used as a means for extending the transmission distance of the PON system, the optical output level of the SOA is monitored, and the SOA gain is adjusted according to the optical level of each upstream burst signal, so that the light of each upstream burst signal can be obtained. The level is within the light receiving sensitivity range in the optical receiver having the OLT. Regarding the adjustment of the SOA gain when applying SOA to the PON system, Patent Document 1 describes the dynamic of the optical input level to the SOA by avoiding saturation in the SOA when the optical input level to the SOA becomes excessive. It describes a technique for expanding the range.

JP 2012-019353 A

  Conventionally, when SOA is applied to a PON system, the SOA optical output level is monitored and the SOA gain adjustment unit is used to adjust the SOA gain in accordance with the optical level of each upstream optical burst signal. I was giving feedback. However, in this method, it takes time to stabilize the gain, and during that time it is impossible for the OLT to correctly receive the optical burst signal from the ONU, leading to a decrease in transmission efficiency.

  On the other hand, when the SOA gain is applied to the PON system as a fixed value in order to suppress a decrease in transmission efficiency, the dynamic range of the SOA becomes a problem. When the technique disclosed in Patent Document 1 is used as a countermeasure, the size of the apparatus increases as the number of peripheral devices of the SOA, such as a device that adjusts the optical input level to the SOA, increases. In addition, when a clamp (level compressor) is used as a device for adjusting the optical input level, waveform distortion due to the rising / falling waveform of the optical waveform occurs.

  The above-described problem is that the first multiplexer / demultiplexer that distributes the downlink signal from the station-side optical line terminator to the downlink coupler and the uplink signal from the second uplink coupler to the station-side optical line terminator, A second multiplexer / demultiplexer for distributing the upstream signal from the subscriber network terminating device to the first upstream coupler, an optical level monitor for monitoring the optical level of the upstream signal branched by the first upstream coupler, A delay unit that is connected to the upstream coupler and delays the upstream signal; an optical amplifier that is connected to the delay unit and amplifies the upstream signal; a waveform monitoring unit that is connected to the downstream coupler and monitors the distance measurement signal; A gain control unit that is connected to the level monitor and the waveform monitoring unit and controls the gain of the optical amplifier, and the gain control unit holds the optical level when the waveform monitoring unit detects the distance measurement signal Reset the range, A new optical level range is acquired based on the upstream burst signal from a number of optical subscriber network termination devices, and the gain of the optical amplifier is adjusted to the optical level of the received burst signal based on the acquired optical level range. This can be solved by an optical amplifying device that switches between the two.

  A first multiplexer / demultiplexer that distributes a downlink signal from the station-side optical line terminator to the downlink coupler and an uplink signal from the second uplink coupler to the station-side optical line terminator, and an optical subscriber network; A second multiplexer / demultiplexer that distributes the upstream signal from the termination device to the first upstream coupler, an optical level monitor that monitors the optical level of the upstream signal branched by the first upstream coupler, and a first upstream coupler. A delay unit connected to delay the upstream signal; an optical amplifier connected to the delay unit for amplifying the upstream signal; a waveform monitoring unit connected to the downstream coupler for monitoring the distance measurement signal; and an optical level monitor; A gain control unit configured to include a gain control unit that is connected to the waveform monitoring unit and controls the gain of the optical amplifier, the step of receiving a distance measurement signal, and a plurality of burst signals , Light Measuring the Le, obtaining a light level range, based on the light level range obtained, and determining the light level to switch the gain, the gain setting method of an optical amplifier including a can be solved.

  It is possible to suppress a decrease in transmission efficiency by performing high-speed multistage gain switching.

It is a block diagram of an optical access network. It is a block diagram of an optical amplification part. It is a figure explaining the optical loss by transmission distance and a branch. It is a figure explaining the optical output level and ONT optical input level of ONU. It is a graph of SOA optical input level and OLT optical input level. It is a timing chart of each signal in the upstream optical amplifier. 3 is a look-up table for SOA gain switching. It is a flowchart of the gain setting of SOA using a look-up table. It is a timing chart which shows the update of a level monitor value for every burst signal. It is a flowchart of the gain setting example of SOA using a calculation formula.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples.
A configuration of an optical access network using the PON system 10 will be described with reference to FIG. In FIG. 1, the optical access network includes the Internet 20 and a PON system 10. The PON system 10 includes an OLT 90, a trunk optical fiber 105, an optical amplification device (optical amplification unit) 101, a splitter 106, a branch fiber 107, and an ONU 102.

  Subscriber terminals (including personal computers (PCs) and telephones) accommodated in the optical access network are connected to a public communication network (here, the Internet 20), which is a higher-level communication network, via the PON system 10, and data Send and receive. The ONU 102 accommodates subscriber terminals.

  N (specifically, 32) ONUs 102 can be connected to the OLT 90 via one main optical fiber 105, each optical splitter 106, and a plurality of branch optical fibers 107. In FIG. 1, three (n = 3) ONUs 102 are illustrated. Each of the ONUs 102 is different in the transmission distance from the OLT 90 and the optical splitter 106 passing through. ONU # 1 (102-1) has a transmission distance of 2 km from the OLT 90. The optical splitter between the OLT and the ONU is only the 8-branch optical splitter 106-1. ONU # 2 (102-2) has a transmission distance of 20 km from the OLT 90. The optical splitter between the OLT and the ONU is an 8-branch optical splitter 106-1 and a 2-branch optical splitter 106-2. ONU # 3 (102-3) has a transmission distance of 40 km from the OLT. The optical splitter between the OLT and the ONU is an 8-branch optical splitter 106-1 and a 4-branch optical splitter 106-3. In addition, (XXkm) described in the lower part of each ONU in the drawing is a transmission distance between the OLT 90 and the ONU 102.

  The downstream signal 103 transmitted from the OLT 90 toward the ONU 102 is broadcast to all the ONUs 102. On the other hand, the upstream signal 104 transmitted from the ONU 102 toward the OLT 90 transmits burst data in a time zone (time slot) individually designated by the ONU 90 from the OLT 90. The upstream signal 108 becomes a multiplexed signal 104 by the splitter 106.

  At this time, the longer the transmission distance is, or the greater the number and number of branches of the optical splitter that passes through, the greater the loss of the optical signal. For this reason, the light level at the upstream signal input unit of the optical amplification unit 101 decreases as the loss increases. The optical amplifying unit 101 appropriately amplifies the optical signal from each ONU 102 so as to be within the reception sensitivity of the OLT. Thereby, the optical amplifying unit 101 enables communication between the ONU 102 and the OLT 90.

Example 1 describes an optical amplification unit that employs automatic gain switching using a lookup table.
With reference to FIG. 2, the configuration of the optical amplification unit will be described. In FIG. 2, an optical amplifying device (optical amplifying unit) 101 includes a multiplexer / demultiplexer (WDM) 201, a waveform monitoring unit (pattern monitor) 202, a gain control unit (gain control) 203, and a semiconductor optical amplifier (SOA). ) 204, SOA 205, gain control 206, delay unit (guard time delay) 207, optical level monitor 208, coupler 209, coupler 210, WDM 211, and optical level monitor 212. ing.

  The WDM 201 sends a downstream optical signal transmitted from the OLT side to the coupler 213. On the other hand, the WDM 201 sends the upstream signal from the coupler 214 to the OLT side. The pattern monitor 202 monitors the downlink signal and the uplink signal branched by the couplers 213 and 214, and detects the distance measurement signal and the burst signal. The pattern monitor 202 detects that the optical output signal of the SOA 205 is lost. The gain control 203 controls the gain of the SOA 205 based on the upstream signal level detected by the light level monitor 212 and the detection pattern of the pattern monitor 202. The SOA 204 amplifies the downstream signal. The SOA 205 amplifies the upstream signal. The gain control 206 controls the gain of the SOA 204 based on the downstream signal level detected by the optical level monitor 208.

  The guard time delay 207 delays the upstream optical signal. The optical level monitor 208 monitors the downstream optical output signal level. The coupler 209 branches the output light of the SOA 204 into the WDM 211 and the optical level monitor 208. The coupler 210 branches the upstream signal from the WDM 211 to the guard time delay 207 and the optical level monitor 212. The WDM 211 sends an upstream signal from the ONU side to the coupler 210. The WDM 511 sends the downstream signal from the coupler 209 to the ONU side. The optical level monitor 212 monitors the upstream optical input signal level.

  With reference to FIG. 3, the transmission loss of ONU # 1 (102-1), ONU # 2 (102-2), and ONU # 3 (102-3) shown in FIG. 1 is demonstrated. Here, ONU transmission loss includes loss due to transmission distance and loss due to branching. When optical loss in an optical fiber is a general value, 0.5 dB for a transmission distance of 1 km, and optical loss in an optical splitter is an ideal value, a loss of 3 dB / N for the number of branches of 2 N The loss generated in the upstream optical signal from each ONU is as follows.

  The loss due to ONU # 1 transmission distance (2 km) is 1 dB, the loss due to branching (8 branches) is 9 dB, and the total loss is 10 dB. Similarly, the loss due to ONU # 2 transmission distance (20 km) is 10 dB, the loss due to branching (16 branches) is 12 dB, and the total loss is 22 dB. The loss due to ONU # 3 transmission distance (40 km) is 20 dB, branching (32 The loss due to branching is 15 dB, and the total loss is 35 dB.

  With reference to FIG. 4, the optical output level of each ONU and the optical input level to the OLT reflecting the transmission line loss described in FIG. 3 when the gain of the optical amplifying unit 101 is fixed to zero will be described. In FIG. 4, the optical output level of the ONU is in the range of +4 to −1 dBm according to the 1000BASE-PX10 standard defined in IEEE 802.3ah. ONU # 1 is the maximum optical output level (4 dBm), ONU # 2 is the intermediate optical output level (1.5 dBm), and ONU # 3 is the minimum optical output level (-1 dBm). The value obtained by subtracting the transmission line loss from the optical output level is the optical input level to the OLT. That is, the optical input level from the ONU # 1 to the OLT is -6 dBm, the optical input level from the ONU # 2 to the OLT is -20.5 dBm, and the optical signal from the ONU # 3 to the OLT. The optical input level is -36 dBm.

  The optical input level of the OLT 90 when the gain of the SOA 205 is variable will be described with reference to FIG. In FIG. 5, the light receiving sensitivity of the OLT is set to −6 dBm to −27 dBm according to the 1000BASE-PX10 standard defined in IEEE 802.3ah. The OLT optical input level of the optical signals from ONU # 1 (−6 dBm) and ONU # 2 (−20.5 dBm) is within the light receiving sensitivity range of the OLT even when the gain of the SOA 205 is 0 dB. However, the optical input level (-36 dBm) of ONU # 3 is outside the light receiving sensitivity range of the OLT. In order to make the OLT optical input level of the optical signal from ONU # 3 within the light receiving sensitivity range of the OLT, a gain in the SOA is required to be 9 dB.

  Accordingly, the values required for the gain of the SOA 205 are 9 dB and 0 dB, and the gain is 0 dB when the optical input level to the SOA 205 is within the range of −6 dBm to −27 dBm, and the gain is 9 dB when it is −27 dBm or less. The number of gain switching stages is two stages of 0 dB and 9 dB.

  The timing of the coupler 210 input, the guard time delay 207 output, the SOA 205 output, and the SOA 205 gain will be described with reference to FIG. In FIG. 6, the optical input to the coupler 210 is measured by the optical level monitor 212. If the measurement result is an upstream burst signal 601 with a low light level, the gain level (604) of the SOA 205 is increased. After the gain of the SOA 205 is stabilized, the upstream burst signal 602 output from the guard time delay 207 is amplified by the SOA 205 and output. Thereafter, when the pattern monitor 202 detects that the optical output signal of the SOA 205 is lost, the gain of the SOA 205 is returned to the minimum value.

  On the other hand, when the optical input level to the optical coupler 210 is high, the SOA gain level (608) remains low. Note that t1 in FIG. 6 is the light level detection time. t2 is a gain switching time. t3 is the detection time of the SOA output decrease.

  The lookup table will be described with reference to FIG. In FIG. 7, a lookup table 70 is a matrix of maximum light levels 71 and minimum light levels. The contents will be described using a cell having a maximum light level of −16 dBm and a minimum light level of −41 dBm. This cell holds GMAX = 14 dB, GMIN = 0 dB, Pa = −27 dBm, N = 2. Here, GMAX is the maximum gain value, GMIN is the minimum gain value, Pa is the light level at which the gain is switched, and N is the number of switching stages. Note that the N = 3 cell further holds GMID (intermediate gain), and Pa becomes Pa1 and Pa2. The look-up table 70 is held by the gain control 203.

  The gain setting process will be described with reference to FIG. In FIG. 8, this flowchart starts gain adjustment as a detection trigger for the distance measurement signal. The optical amplifying unit 101 starts measuring the elapsed time t after starting the gain adjustment (S702). The optical amplifying unit 101 resets the maximum level PMAX and the minimum level PMIN of the level monitor values held so far (S703). The optical amplification unit 101 detects the upstream burst signal (S704). The optical amplifying unit 101 measures the optical level with the optical level monitor 212 (S705). The optical amplifying unit 101 sets the level monitor value P of the measured upstream optical signal to the maximum level (PMAX) and the minimum level (PMIN) (S706). The optical amplifying unit 101 determines whether “0” continues for 5 bits or more in the signal monitored by the pattern monitor 202 (S707). If Yes, the optical amplification unit 101 determines that the upstream burst signal has ended, and clears the level monitor value P (S708). Here, the reason for determining that the burst signal ends when “0” is 5 bits or more is that IEEE 802.3ah stipulates that an 8B10B code is used in the optical transmission section, and as long as data exists from the code conversion rule. This is because “0” continues only up to 4 bits. In other PON standards, when a different code is used for the transmission section, the end of the burst signal and determination are appropriately changed.

  The optical amplifying unit 101 detects an upstream burst signal from the next ONU 102 (S709). The optical amplifying unit 101 measures the optical level of the upstream burst signal with the optical level monitor 212 (S710). The optical amplifying unit 101 compares the level monitor value P with PMAX (S711). If the level monitor value P is larger than PMAX (Yes), the optical amplifying unit 101 updates the value of PMAX (S712). In step 711, when the optical level monitor P is equal to or lower than PMAX (No), the optical amplifying unit 101 compares with PMIN (S713). If the level monitor value P is smaller than PMIN. The optical amplifying unit 101 updates the value of PMIN (S714). In step 713, when the level monitor value P is equal to or greater than PMIN, the optical amplifying unit 101 holds the values of PMAX and PMIN without updating them.

  After step 712, after step 714, when the result in step 713 is No, the optical amplifying unit 101 determines whether the specified time of the distance measurement operation is longer than the elapsed time t from the start of gain adjustment (S715). If t is shorter than the specified time of the distance measurement operation (Yes), the optical amplifying unit 101 determines that the ranging operation is still in progress, and proceeds to step 707. In step 715, when t is equal to or longer than the specified time of the distance measurement operation, the optical amplifying unit 101 determines that the ranging operation is completed, and the maximum SOA 205 is determined from the look-up table 70 of the gain control 203 from PMAX and PMIN. If there is a gain (GMAX), a minimum gain (GMIN), an intermediate gain (GMID), a gain switching stage number N, and a gain switching light level Pa are read (S716). The optical amplifying unit 101 starts control for switching the gain for each burst signal (S717) and ends.

  In the case of the condition of FIG. 4, since the maximum level is −6 dBm and the minimum level is −36 dBm, GMAX = 9 dB, GMIN = 0 dB, Pa = −27 dBm, and N = 2 from the lookup table 70. When the values of the maximum light level and the minimum light level, or both, become intermediate values of the coordinates, the optical amplifying unit 101 calculates each gain, the number of gain steps, and the gain switching light level from the coordinates of the value with a large one-step light level. Make a reading decision.

  With reference to FIG. 9, the transition for each burst signal of the level monitor value of the burst signal will be described. In FIG. 9, the figure shows the optical input of the optical monitor 212, the optical monitor signal, the PMAX value, and the PMIN value from the top. The PMAX value and the PMIN value are reset by detecting the distance measurement signal. When the optical monitor signal exceeds the threshold and exceeds the held PMAX value, the PMAX value is updated. Further, when the optical monitor signal is less than the threshold value and less than the held PMIX value, the PMIX value is updated.

  The optical level monitor 212 monitors the average value of each upstream burst signal, and the value of the maximum level (PMAX) and the minimum level (PMIN) of the upstream burst signal after elapse of tm when the optical level monitor value is stabilized after detection of the upstream burst signal. Is compared with the light level monitor value and updated.

Example 2 describes multistage gain switching using computation. In the second embodiment, the configuration of the optical amplification unit is as shown in FIG.
With reference to FIG. 10, the flow of SOA gain setting using a calculation formula will be described. In FIG. 10, the operation from the start of measurement of t (S1002) to the comparison of the distance measurement time and the gain adjustment time t (S1015) is the same as the distance measurement time from the start of measurement of t (S702) in FIG. This is the same as the comparison of gain adjustment time t (S715). Therefore, explanation is omitted.
After determining PMAX and PMIN, the optical amplifying unit 101 obtains the number of gain switching stages using Equation 1 (S1016).
N ≧ (PMAX−PMIN) / (OLT light receiving range) (Expression 1)
Here, N is a positive integer (rounded up after the decimal point).

  When the gain switching stage number N is 3, for each gain, the optical amplifying unit 101 has G1 = 0 dB, G2 = (OLT light receiving range) × (N−2), G3 = (OLT light receiving range) × (N−1). (S1017). The optical amplifying unit 101 starts gain switching with the optical level monitor from the obtained gain (S1018), and ends.

  Specifically, if PMAX is −6 dBm, PMIN is −50 dBm, and the OLT light reception level is −6 dBm to −27 dBm, the OLT light reception range is 21 dB. When N is 3, G2 is 21 dB from G1 = 0 dB, G2 = (OLT light receiving range) × (N−2), and G3 = 42 dB from G3 = (OLT light receiving range) × (N−3). It becomes. The light levels to which the gains obtained from the above are applied are −6 dBm to −27 dBm for G1 = 0 dB, −28 dBm to −48 dBm for G2 = 21 dB, and −49 to −50 dBm for G3 = 42 dB. It can be within the light receiving range.

  According to the above-described embodiment, it is possible to suppress a decrease in transmission efficiency by performing high-speed multistage gain switching. Also, the transmission efficiency is higher than that of the successive approximation type.

  DESCRIPTION OF SYMBOLS 10 ... PON system, 20 ... Internet, 90 ... OLT, 102 ... ONU, 105 ... Trunk optical fiber, 101 ... Optical amplification device (optical amplification part), 102 ... ONU, 106 ... Splitter, 107 ... Branch line fiber, 201 ... Total Demultiplexer (WDM), 202 ... Waveform monitoring unit (pattern monitor), 203 ... Gain control, 204 ... Semiconductor optical amplifier (SOA), 205 ... SOA, 206 ... Gain control unit (gain control), 207 ... Delay device ( Guard time delay), 208... Optical level monitor, 209... Coupler, 210... Coupler, 211.

Claims (5)

A first multiplexer / demultiplexer that distributes a downlink signal from the station-side optical line terminator to the downlink coupler, and an uplink signal from the second uplink coupler to the station-side optical line terminator;
A second multiplexer / demultiplexer that distributes the upstream signal from the optical network unit to the first upstream coupler;
An optical level monitor for monitoring the optical level of the upstream signal branched by the first upstream coupler;
A delay unit connected to the first upstream coupler and delaying the upstream signal;
An optical amplifier connected to the delay device and amplifying the upstream signal;
A waveform monitoring unit connected to the downstream coupler and monitoring a distance measurement signal;
A gain control unit that is connected to the optical level monitor and the waveform monitoring unit and controls a gain of the optical amplifier; and
When the waveform monitoring unit detects a distance measurement signal, the gain control unit resets the optical level range to be held, and based on upstream burst signals from the plurality of optical subscriber network termination devices, a new optical level is obtained. An optical amplifying apparatus characterized by acquiring a range and switching the gain of the optical amplifier in accordance with the optical level of a received burst signal based on the acquired optical level range. The optical amplification device according to claim 1,
The gain control section switches the gain of the optical amplifier based on a table that holds the light level range and the switching light level. The optical amplification device according to claim 1,
The gain control unit sets an optical level for switching a gain based on the optical level range and a light receiving range of the station side optical network unit. The optical amplification device according to claim 1,
The waveform monitoring unit is further connected to the second upstream coupler and monitors the end of a burst signal. A first multiplexer / demultiplexer that distributes a downlink signal from the station-side optical line terminator to the downlink coupler, and an uplink signal from the second uplink coupler to the station-side optical line terminator;
A second multiplexer / demultiplexer that distributes the upstream signal from the optical network unit to the first upstream coupler;
An optical level monitor for monitoring the optical level of the upstream signal branched by the first upstream coupler;
A delay unit connected to the first upstream coupler and delaying the upstream signal;
An optical amplifier connected to the delay device and amplifying the upstream signal;
A waveform monitoring unit connected to the downstream coupler and monitoring a distance measurement signal;
A gain control unit connected to the optical level monitor and the waveform monitoring unit to control the gain of the optical amplifier, and comprising:
Receiving a distance measurement signal; and
Measuring a light level for a plurality of burst signals;
Obtaining a light level range;
Determining a light level for switching the gain based on an acquired light level range, and a gain setting method for an optical amplifying apparatus.

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