KR100734855B1 - Passive Optical Network System for Optical Subscriber Expansion - Google Patents

Abstract

The present invention relates to a passive optical network system including an OLT and at least one ONU, wherein the downlink signal from the OLT to the ONU is transmitted through a first path and the uplink signal from the ONU to the OLT is transmitted through a second path. A first coupler; A second coupler having one end connected to each end of the first path and the second path of the first coupler and the other end respectively transmitting the uplink signal and the downlink signal through one path; A downlink optical amplifier positioned on the first path to compensate for the loss of the downlink signal; And an uplink optical amplifier positioned on the second path to compensate for the loss of the uplink signal. The uplink optical amplifier includes an uplink optical amplifier and a downlink optical amplifier. It provides a method of compensating for the loss to extend the number of optical subscribers in a passive optical network system.

Passive Optical Subscriber Network, Optical Amplifiers, WDM Couplers

Description

Passive optical network system for extension of optical subscriber unit

1 is a diagram illustrating a PON structure and an operating principle of the PON.

2 is a view showing the concept of a method for extending the number of optical subscribers using the optical amplifier according to the present invention.

3 is a view showing a PON structure for each optical amplification when the wavelength of the up, down signal according to the present invention is different.

4 is a diagram illustrating a PON structure for solving the uplink signal burst mode characteristic according to the present invention.

5 illustrates a PON structure for amplifying a downlink signal using a pump light according to the present invention.

6 is a diagram illustrating a PON structure for amplifying a downward direction signal by placing an optical amplifier according to the present invention in front of an OLT transmitter.

7 is a flowchart illustrating a method of extending the number of optical subscribers using an optical amplifier according to the present invention.

The present invention relates to a passive optical network (PON) system, and more particularly, to an apparatus and method for extending the number of optical subscribers of a passive optical network (PON) system using an optical amplifier.

The PON system is composed of one optical line terminal (OLT) provided at the service provider side and a plurality of optical network unit (ONU) provided at the user side. Data transfer in the PON system takes place between the OLT and the ONU.

The OLT is located in the distribution center and provides the ability to connect the subscriber network with the metro backbone network. The ONU is located near the subscriber to provide broadcast, voice and data services to the subscriber. In downlink transmission (OLT to ONU), PON is a point-to-multipoint network, and in uplink transmission (ONU to OLT), it has a multipoint-to-point network structure.

In the PON, one OLT and a plurality of ONUs are connected in a tree structure by an optical splitter. In the case of downstreaming of data, the optical signal data modulated by the Tx (transmitter) of the OLT proceeds along the transmission path, and the optical power is distributed by 1: N in the optical distribution unit and received in each ONU.

Since downlink transmission has a point-to-multipoint structure, broadcasting has a characteristic of broadcasting and is set to select a signal corresponding to each ONU among the same optical signals received from the ONU.

Each ONU has a receiver capable of receiving an optical signal and a transmitter capable of transmitting the optical signal.

On the other hand, in upstream, since the optical signals transmitted from each ONU may overlap each other after the optical distribution unit, it is necessary to adjust them. To this end, by using a media access control (MAC) function, the time allocated to each ONU is allocated so that the optical signals from each ONU do not overlap each other.

Therefore, since the optical signal transmitted from the ONU is transmitted at a specific time, it has a characteristic of burst mode and is set so as not to overlap each other in time. In OLT, an uplink signal is received using a burst mode receiver (BRx). The optical signal originating from each ONU has different optical powers depending on the distance between the ONU and the optical divider. Therefore, the BRx of the OLT is designed to operate normally in a wide input power dynamic range.

The basic operating principle of the PON system has been described above. The number of subscribers connected to the PON is proportional to the number of ONUs that can be connected and is therefore determined by the number of branches of the optical distribution unit.

In PON, the distance between the OLT and the ONU can be guaranteed up to 20 km, and transmission distances over 20 km cannot be achieved. The biggest influence on the transmission performance is optical loss in the transmission path. In the PON, the optical loss of the optical fiber line and the loss due to the number of branches of the optical distribution are the main causes.

In order to increase the number of splitting units in the optical distribution unit in order to expand the number of ONUs connected to the PON, the optical loss becomes large and transmission performance cannot be secured. For example, in the case of using the 1:32 optical splitter, the optical loss due to the split ratio is 15 dB, and the other optical losses are about 3 to 5 dB. Therefore, the loss in the optical splitter reaches 18 to 20 dB. In current PON technology, it is known that up to 1:32 light distribution can be used.

It is an object of the present invention to provide an apparatus and method for expanding the number of ONUs that can be simultaneously connected in a PON system using an optical amplifier.

One embodiment of a passive optical network system using an optical amplifier according to the present invention for achieving the above technical problem, in the passive optical network system consisting of an OLT and at least one ONU, the first signal from the OLT to the ONU A first coupler transmitting through a path and transmitting an uplink signal from the ONU to the OLT through a second path; A second coupler having one end connected to each end of the first path and the second path of the first coupler and the other end respectively transmitting the uplink signal and the downlink signal through one path; A downlink optical amplifier positioned on the first path to compensate for the loss of the downlink signal; And an upward direction optical amplifier positioned on the second path to compensate for the loss of the upward signal.

One embodiment of a passive optical network system using an optical amplifier according to the present invention for achieving the technical problem, in the passive optical network system consisting of an OLT and at least one ONU, located in the ONU and upward from the ONU to the OLT An uplink optical amplifier that amplifies while maintaining the burst mode characteristics of the signal; A first coupler transmitting a downlink signal from the OLT to the ONU through a first path and transmitting an uplink signal from the ONU to the OLT through a second path; A second coupler having one end connected to each end of the first path and the second path of the first coupler and the other end respectively transmitting the uplink signal and the downlink signal through one path; And a downward direction optical amplifier positioned on the first path to compensate for the loss of the downward signal.

One embodiment of a passive optical network system using an optical amplifier according to the present invention for achieving the technical problem, in the passive optical network system consisting of an OLT and at least one ONU, located in the ONU and upward from the ONU to the OLT And an upward optical amplifier for maintaining and amplifying a burst mode characteristic of the signal; and a downward optical amplifier positioned at the OLT and amplifying the downward signal.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating a PON structure and an operating principle of the PON.

In the PON, one OLT 100 and a plurality of ONUs 110, 120, 130, and 140 are connected in a tree structure by an optical splitter 150. In FIG. 1, in case of downstream 160 of data, optical signal data modulated at Tx (transmitter) of the OLT 100 proceeds along a transmission path, and the optical power is 1: N in the optical distribution unit 150. Is distributed at each ONU.

Since downlink transmission has a point-to-multipoint structure, broadcasting has a characteristic of broadcasting and is set to select a signal corresponding to each ONU among the same optical signals received from the ONU. In each ONU, there is a receiver capable of receiving an optical signal and a transmitter capable of transmitting the optical signal, as shown in the internal diagram of the OLT 100.

In order to expand the number of ONUs of the PON network, a method of increasing the number of splitting of the optical distribution unit 150 may be used. In this case, an optical amplifier is used to compensate for the optical loss.

2 is a view showing the concept of a method for extending the number of optical subscribers using the optical amplifier according to the present invention.

In the PON structure, the bidirectional optical amplifier 210 is located in the premises communication room 220 (Main distribution frame, MDF) together with the optical distribution unit 150. In the bidirectional optical amplifier 210, both uplink and downlink optical signals can obtain a constant optical gain.

 By the gain of the optical amplifier, the optical loss in the optical distribution unit 150 is compensated, thereby ensuring transmission performance. As the number of branches in the optical distribution increases, the optical gain of the optical amplifier must be greater. As the optical gain increases, the number of branches of the light distribution unit can be 1000 or more, and thus a large number of ONUs can be connected.

In current PON technology, the uplink and downlink signals have different wavelengths. For example, in Ethernet-PON, 1310nm is used for uplink transmission and 1490nm and 1550nm for downlink transmission. In reality, there is no optical amplifier that can amplify the wavelength of the uplink signal and the downlink signal. Therefore, it is necessary to use different optical amplifiers in the uplink signal and the downlink signal.

3 is a view showing a PON structure for each optical amplification when the wavelength of the up, down signal according to the present invention is different.

In FIG. 3, uplink and downlink are optically amplified using different optical amplifiers. WDM couplers 310 and 320 for separating the wavelength of the uplink signal and the downlink signal, an optical amplifier 330 for the uplink signal, and an optical amplifier 340 for the downlink signal. If the wavelengths of the up and down signals are different, optical amplification for each is required.

In the PON system, since downlink transmission is broadcasting in a point-to-multipoint structure, an optical signal having a uniform optical power is transmitted as shown in the downlink transmission signal 160 of FIG. 1. Therefore, since the optical amplifier for the down signal has a constant input optical power, there is no particular problem in the control.

On the other hand, since uplink transmission is a multi-point-to-point structure, each ONU is controlled so as not to overlap each other in the time domain, and thus has an optical signal form of a burst mode such as the uplink transmission signal 170 of FIG. 1. . Each burst has a different optical power depending on the light loss experienced from each ONU.

When this type of burst optical signal enters the input of the optical amplifier, it should be possible to obtain the output of the optical amplifier having the same shape as the input. In reality, however, such optical amplifiers do not exist. In order to improve this problem, the structure of the PON may be configured as shown in FIG. 4.

4 is a diagram illustrating a PON structure for solving the uplink signal burst mode characteristic according to the present invention.

For downlink transmission, optical amplification is performed in the optical amplifier 440 in the premises communication room 470. WDM couplers 450 and 460 separate wavelengths of an uplink signal and a downlink signal. The optical amplification for the upstream signal is made within the ONU.

There is an Rx (receiver) and a BTx (burst mode transmitter) in the ONU1 410, and the output of the BTx is amplified and output by the optical amplifier 420. A wavelength division coupler 430 is required to separate the upward direction signal and the downward direction signal amplified by the ONU.

Although the output of the burst mode is output from the BTx, since the optical power of the burst is constant and the ONU senses the time for driving the BTx, the control of the optical amplifier 420 can be easily performed by the control unit 480. Each ONU should have the same structure as ONU1.

In the PON structure, power is not supplied to the MDF 470. This is because there is an additional cost for power supply.

5 illustrates a PON structure for amplifying a downlink signal using a pump light according to the present invention.

In FIG. 5, the power supply of the optical amplifier 520 in the MDF 550 is not required in the PON having the structure shown in FIG. 4. In the optical amplifier, a part of the optical amplifier that requires power supply is a pump light (510), which is configured to be supplied to the optical amplifier 520 through the optical path along with the downlink transmission signal in the OLT.

The optical amplifier 520 can be operated by the pump light 510 supplied from the OLT without the power supply of the MDF 550.

6 is a diagram illustrating a PON structure for amplifying a downward direction signal by placing an optical amplifier according to the present invention in front of an OLT transmitter.

In FIG. 5, the down-signal optical amplifier 610 in the MDF is placed in front of the transmitter (Tx) in the OLT, and the up-signal optical amplifier is placed in front of the transmitter (BTx) in the ONU in order to maintain the burst mode characteristic of the uplink signal. .

7 is a flowchart illustrating a method of extending the number of optical subscribers using an optical amplifier according to the present invention.

The uplink signal and the downlink signal are separated from the WDM coupler (S700).

The number of subscribers connected to the PON system is expanded by amplifying the separated uplink and downlink signals, respectively, to compensate for the loss generated in the optical splitter (S710).

Although the preferred embodiments of the present invention have been described above by way of example, the scope of the present invention is not limited to these specific embodiments, and may be appropriately changed within the scope of the claims.

As described above, it is possible to connect a large number of subscribers to a single PON network at the same time using an optical amplifier, thereby reducing the service cost and the network management cost.

The present invention is applicable to all PON structures as well as Ethernet PON, and the optical amplifier can operate regardless of the burst mode characteristic of the optical signal transmitted from the subscriber to the OLT.

Claims (6)

In a passive optical network system comprising an optical line terminal (OLT) and at least one optical network unit (ONU), Transmits a downlink signal from the optical fiber termination device (OLT) to the optical fiber subscriber device (ONU) through a first path and cancels an uplink signal from the optical fiber subscriber device (ONU) to the optical fiber termination device (OLT). A first coupler transmitting through two paths; A second coupler having one end connected to each end of the first path and the second path of the first coupler and the other end respectively transmitting the uplink signal and the downlink signal through one path; A downlink optical amplifier positioned on the first path to compensate for the loss of the downlink signal; And And an uplink optical amplifier positioned on the second path to compensate for the loss of the uplink signal. The method of claim 1, The first coupler, the second coupler, the uplink optical amplifier, and the downlink optical amplifier are located in an internal communication room including an optical distribution unit for demultiplexing the downlink signal and multiplexing the uplink signal. Optical network system. A passive optical network system consisting of an optical path termination unit (OLT) and at least one optical path subscriber unit (ONU), An upward optical amplifier positioned in the optical path subscriber unit ONU and maintaining and amplifying a burst mode characteristic of an upstream signal from the optical path subscriber unit ONU to the optical path termination unit OLT; Transmits a downlink signal from the optical fiber termination device (OLT) to the optical fiber subscriber device (ONU) through a first path and cancels an uplink signal from the optical fiber subscriber device (ONU) to the optical fiber termination device (OLT). A first coupler transmitting through two paths; A second coupler having one end connected to each end of the first path and the second path of the first coupler and the other end respectively transmitting the uplink signal and the downlink signal through one path; And A downlink optical amplifier positioned on the first path to compensate for the loss of the downlink signal; Passive optical network system comprising a. The method of claim 3, wherein The downlink optical amplifier, the first coupler and the second coupler are located in an internal communication room having an optical splitter for demultiplexing the downlink signal and multiplexing the uplink signal. The method of claim 3, wherein And a pump light located at the optical path termination device (OLT) to activate the downward optical amplifier. A passive optical network system consisting of an optical path termination unit (OLT) and at least one optical path subscriber unit (ONU), An upward direction optical amplifier positioned at the optical path subscriber unit ONU and maintaining and amplifying a burst mode characteristic of an upward signal from the optical path subscriber unit ONU to the optical path termination unit OLT; and And a downward direction optical amplifier positioned at the optical path termination device (OLT) and amplifying the downward signal.

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