WO2009078608A2

WO2009078608A2 - Optical network system for providing wireless broadband services

Info

Publication number: WO2009078608A2
Application number: PCT/KR2008/007202
Authority: WO
Inventors: Byoung Whi Kim; Bong Tae Kim
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2007-12-14
Filing date: 2008-12-05
Publication date: 2009-06-25
Also published as: WO2009078608A3; KR101404107B1; KR20090063834A; CN101946429A

Abstract

An optical network system for providing wireless broadband services is provided. The optical network system may include an optical line terminal (OLT); and at least one optical network unit (ONU), wherein the OLT broadcasts downlink data to the ONU with the aid of a light source and the ONU transmits data to the OLT through a predetermined optical wavelength. Therefore, it is possible to easily identify what terminal has transmitted an optical signal to a center based on the wavelength of the optical signal and to reduce the consumption of optical fibers between the center and a number of access points (APs).

Description

OPTICAL NETWORK SYSTEM FOR PROVIDING WIRELESS

BROADBAND SERVICES

Technical Field

[1] The present invention relates to an optical network system for providing wireless broadband services.

[2] The present invention is based on research (Project No.: 2007-S-014-01, Project

Title: Metro- Access Integrated Optical Network Technology) conducted as part of Information Technology (IT) Growth Power Technology Development Project launched by Ministry of Information and Communication and Institute for Information Technology Advancement (HT A).

[3]

Background Art

[4] Due to recent developments in wireless transmission technology, the speed of transmitting wireless data has rapidly increased. High-Speed Downlink Packet Access (HSDPA) can support an uplink speed of 2 Mbps and a downlink speed of 14.4 Mbps, Wireless Broadband (WiBro) can support an uplink speed of 6 Mbps and a downlink speed of 19.97 Mbps, and WiBro-Evolution (Wibro-Evo) whose development is underway is expected to support an uplink speed of 50 Mbps and a downlink speed of 50 Mbps.

[5] In order to keep up with such an increase in the amount of data transmitted by wireless terminals, the performance of wired transmission networks must be improved.

[6] Conventional wireless techniques (such as WiBro) supporting the transmission of large amounts of wireless data are generally characterized by using different transmission media for uplink data and downlink data. That is, downlink data may be transmitted to a plurality of access points (APs), and the APs wirelessly transmit the downlink data to a plurality of subscriber terminals. On the other hand, uplink data is wirelessly transmitted to a plurality of APs by a plurality of subscriber terminals. Then, the uplink data collected by the APs is transmitted to a center, to which the APs are point-to-point connected, in a wired manner.

[7] However, when used in an area in which a plurality of APs are densely populated, conventional wireless techniques supporting the transmission of large amounts of wireless data may require the use of a considerable number of optical fibers due to the point-to-point connections between a center and the APs.

[8]

Disclosure of Invention Technical Problem

[9] The present invention provides a wavelength division multiplexing (WDM) optical network system which can reduce the consumption of optical fibers by efficiently connecting a plurality of access points (APs) and a center.

[10]

Technical Solution

[11] According to an aspect of the present invention, there is provided an optical network system including an optical line terminal (OLT); and at least one optical network unit (ONU), wherein the OLT broadcasts downlink data to the ONU with the aid of a light source and the ONU transmits data to the OLT through a predetermined optical wavelength.

[12] According to the present invention, a center may broadcast data to a plurality of APs with the aid of a single light source, and the APs may transmit data to the center through a predetermined optical wavelength. Therefore, it is possible to reduce the consumption of optical fibers between the center and the APs by using dense WDM (DWDM) to transmit uplink data. In addition, an optical transmitter/receiver apparatus that can be used in each of the APs may be able to operate independently of the wavelength of light. Therefore, it is possible to establish a WDM optical network capable of efficiently connecting the center and the APs. Brief Description of the Drawings

[13] The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

[14] FIG. 1 illustrates a block diagram of an optical network system according to an exemplary embodiment of the present invention;

[15] FIG. 2 illustrates a spectrum diagram of unpolarized light emitted from a seed light module;

[16] FIG. 3 illustrates a spectrum diagram of polarized light emitted from a seed light module;

[17] FIG. 4 illustrates a diagram of various wavelengths that can be used in the optical network system shown in FIG. 1 ;

[18] FIG. 5 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[19] FIG. 6 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[20] FIG. 7 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention; [21] FIG. 8 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[22] FIG. 9 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[23] FIG. 10 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[24] FIG. 11 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention;

[25] FIG. 12 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention; and

[26] FIG. 13 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention.

[27]

Best Mode for Carrying Out the Invention

[28] The present invention will hereinafter be described in detail with reference to the accompanying drawings in which exemplary embodiments of the invention are shown.

[29] FIG. 1 illustrates a block diagram of an optical network system according to an exemplary embodiment of the present invention. Referring to FIG. 1, the optical network system may include an optical line terminal 200, a remote node (RN) 300, and a plurality of optical network units (ONUs) 400- 1 through 400-N.

[30] The OLT 200 may include a seed light module 210, an optical transmitter 220, a first circulator 250, a second circulator 260, a plurality of optical receivers 230- 1 through 230-N, and an optical wavelength demultiplexer 240. The optical transmitter 220 may transmit an optical signal including downlink data. The optical transmitter 220 may be a reflective semiconductor optical amplifier (RSOA). The seed light module 210 may provide seed light to the optical transmitter 220. The first circulator 250 may transmit the seed light to the optical transmitter 220 and may transmit a downlink optical signal provided by the optical transmitter 220 to the second circulator 260. The second circulator 260 may transmit the downlink optical signal to an external optical fiber and may transmit an uplink optical signal to the optical wavelength demultiplexer (DMUX) 240. The optical receivers 230- 1 through 23On may receive the uplink optical signal. The optical wavelength demultiplexer 240 may demultiplex an uplink optical signal into a plurality of wavelengths.

[31] The RN 300 may include an optical wavelength multiplexer/demultiplexer 310. The optical wavelength multiplexer/demultiplexer 310 may receive a multiplexed downlink optical signal from the OLT 200, and may demultiplex the received multiplexed downlink optical signal. In addition, the optical wavelength multiplexer/demultiplexer 310 may receive a plurality of optical signals having different wavelengths from the ONUs 400-1 through 400-N, and may multiplex the received optical signals.

[32] The ONUs 400- 1 through 400-N may include a plurality of optical receivers 420- 1 through 420-N, respectively, a plurality of optical transmitters 410-1 through 410-N, respectively, and a plurality of optical filters 430-1 through 430-N, respectively. Each of the optical receivers 420- 1 through 420-N may receive a downlink optical signal and may restore downlink information from the received downlink optical signal. Each of the optical transmitters 410-1 through 410-N may convert uplink data into an optical signal and may output the optical signal. The optical filters 430-1 through 430-N may transmit a downlink optical signal to the optical receivers 420- 1 through 420-N, respectively. In addition, the optical fibers 430-1 through 430-N may transmit a plurality of uplink optical signals respectively provided by the optical transmitters 410-1 through 410-N to the RN 300.

[33] The operation of the OLT 200 will hereinafter be described in detail.

[34] Multiplexed light provided by the seed light module 210 may be input to a second port of the first circulator 250, and may be output from a first port of the first circulator 250. The multiplexed light output from the first port of the first circulator 250 may be input to the optical transmitter 220 as seed light. The optical transmitter 220 may amplify the seed light, and may modulate the amplified seed light based on downlink data. Thereafter, the optical transmitter 220 may output the modulated seed light as a downlink optical signal. The downlink optical signal output by the optical transmitter 220 may be input to the second port of the first circulator 250, and may be output from a third port of the first circulator 250. The downlink optical signal output from the third port of the first circulator 250 may be input to a third port of the second circulator 250, and may be output from a first port of the second circulator 250. The downlink optical signal output from the first port of the second circulator 260 may be transmitted to an external optical fiber. A plurality of multiplexed uplink optical signals provided by the ONUs 400- 1 through 400-N may be input to the first port of the second circulator 260, and may be output from the second port of the second circulator 260. The uplink optical signals output from the second port of the second circulator 260 may be input to the optical wavelength demultiplexer 240. The optical wavelength demultiplexer 240 may demultiplex the uplink optical signals input thereto. The demultiplexed uplink optical signals may be input to the optical receivers 230- 1 through 230-N, respectively. The optical receivers 230- 1 through 230-N may convert the demultiplexed uplink optical signals input thereto into electric signals and may thus restore uplink data.

[35] The operation of the ONUs 400-1 through 400-N will hereinafter be described in detail.

[36] An optical signal provided by the RN 300 may be input to the optical receivers 420-1 through 420-N through the optical filters 430- 1 through 430-N and may be converted into an electric signal. Thereafter, downlink data may be restored from the electric signal. The optical transmitters 410-1 through 410-N may transmit a plurality of uplink optical signals including uplink data to the RN 300 through the optical filters 430-1 through 430-N.

[37] FIGS 2 and 3 illustrate spectrum diagrams of light emitted from a seed light module.

Referring to FIG. 2, light emitted from a seed light module may be unpolarized light into which wavelengths with a wide spectral width are multiplexed. On the other hand, referring to FIG. 3, light emitted from a seed light module may be polarized light into which wavelengths with a narrow spectral width are multiplexed.

[38] FIG. 4 illustrates a diagram of various wavelengths that can be used in the optical network system shown in FIG. 1. Referring to FIG. 4, a downlink optical wavelength band and an uplink optical wavelength band satisfy the free spectral range (FSR) properties of the optical wavelength multiplexer/demultiplexer 310 of the RN 300.

[39] FIG. 5 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 5 is similar to the exemplary embodiment of FIG. 1 except that a plurality of ONUs 400-1 through 400-N may include a plurality of RSOAs 410-1 through 410-N, respectively, instead of optical transmitters. More specifically, referring to FIG. 5, the ONUs may include a plurality of optical couplers 440-1 through 440-N, respectively, the RSOAs 410-1 through 410-N, respectively, and a plurality of optical receivers 420- 1 through 420-N, respectively. A downlink optical signal provided by an RN 300 may be input to each of the ONUs 400-1 through 400-N. Each of the optical couplers 440- 1 through 440-N may divide a downlink optical signal input thereto into two portions, and may transmit one of the two portions to a corresponding RSOA and the other portion to a corresponding optical receiver. A downlink optical signal input to each of the optical receivers 420-1 through 420-N may be converted into an electric signal, and downlink data may be restored from the electric signal. An optical signal input to each of the RSOAs 410-1 through 410-N may be flattened by the corresponding optical receiver, and the flattened optical signal may be used as uplink light. The RSOAs 410-1 through 410-N may modulate flattened light based on uplink data, and may output the modulated light to the RN 300. Since a downlink optical signal is used as seed light for driving the RSOAs 410-1 through 410-N of the ONUs 400- 1 through 400-N, there is no need to provide seed light. Since a downlink optical signal is used as uplink light, uplink light may have the same wavelength as that of downlink light. Therefore, since there is no need to satisfy the FSR of an optical wavelength multiplexer/demultiplexer 310 of the RN 300, it is possible to perform demultiplexing at various points in an optical network system. In addition, since the RSOAs 410-1 through 410-N generate an uplink optical signal by flattening, amplifying and modulating a downlink optical signal, it is possible to configure an optical transmitter independently of the wavelength of light.

[40] FIG. 6 illustrates a block diagram of an optical network system according to an exemplary embodiment of the present invention. The optical network system shown in FIG. 6 is similar to the optical network system shown in FIG. 5 except that a feeder section between an OLT 200 and an RN 300 is constituted by two separate optical fibers, and that an uplink optical signal and a downlink optical signal are transmitted through different optical fibers. For this, in the exemplary embodiment of FIG. 6, the RN 300 may include a second circulator 260, whereas, in the exemplary embodiment of FIG. 5, the OLT 200 includes the second circulator 260. Referring to FIG. 6, a downlink optical signal provided by the OLT 200 may be input to a third port of a circulator 320, and may be output from a first port of the circulator 320. An uplink optical signal output from an optical wavelength multiplexer/demultiplexer 310 of the RN 300 may be input to the first port of the circulator 320, and may be output from a second port of the circulator 320.

[41] FIG. 7 illustrates a block diagram of an optical network system according to an exemplary embodiment of the present invention. The optical network system shown in FIG. 7 is similar to the optical network system shown in FIG. 5 except that an optical wavelength multiplexer/demultiplexer 310 include a plurality of optical power splitters 330-1 through 330-N for different wavelengths. More specifically, referring to FIG. 7, a downlink optical signal obtained by demultiplexing performed by the optical wavelength multiplexer/demultiplexer 310 is split into M portions by each of the optical power splitters 330-1 through 330-N. The M portions may be input to M ONUs 400- 1 through 400-M. A plurality of uplink optical signals provided by the M ONUs 400-1 through 400-M may be gathered by each of the optical power splitters 330-1 through 330-N, and may then be multiplexed along with other optical signals by the optical wavelength multiplexer/demultiplexer 310. The result of the multiplexing may be output to the OLT 200.

[42] FIG. 8 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 8 is similar to the optical network system shown in FIG. 7 except that a feeder section between an OLT 200 and an RN 300 is constituted by two separate optical fibers. Referring to FIG. 8, since the feeder section between an OLT 200 and an RN 300 is constituted by two separate optical fibers, a circulator 320 separating an uplink optical signal and a downlink optical signal may be installed in the RN 300.

[43] FIG. 9 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 9 is similar to the optical network system shown in FIG. 5 except that a seed light module 210 of an OLT 200 uses an external modulator 270, instead of using an RSOA, to generate a downlink optical signal.

[44] FIG. 10 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 10 is similar to the optical network system shown in FIG. 5 except that a seed light module 210 of an OLT 200 uses a semiconductor optical amplifier (SOA) 280, instead of using an RSOA, to generate a downlink optical signal.

[45] FIG. 11 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 11 is similar to the optical network system shown in FIG. 10 except that the optical network system shown in FIG. 11 includes a plurality of first and second RNs 300- 1 and 300-2 and can thus enable demultiplexing to be performed at various points in the optical network system shown in FIG. 11.

[46] More specifically, referring to FIG. 11, the first RN 300-1 may include an optical add/drop multiplexer (OADM) 330-1, which adds or drops first through k-th wavelengths A _/through A _k and allows the transmission of other wavelengths. The second RN 300-2 may include an OADM 330-2, which adds or drops (k+l)-th through p-th wavelengths A _k+1 through A _p and allows the transmission of other wavelengths. Even though only two RNs are illustrated in FIG. 11, the optical network system shown in FIG. 11 may include more than two RNs.

[47] The first RN 300-1 may also include a wavelength division multiplexing (WDM) multiplexer/demultiplexer 310-1, which multiplexes or demultiplexes the first through k-th wavelengths A _/ through A _k . Likewise, the second RN 300-2 may also include a WDM multiplexer/demultiplexer 310-2, which multiplexes or demultiplexes the (k+l)-th through p-th wavelengths A _k+1 through A _p . A plurality of optical signals added by the OADM 330-1 or 330-2 may be transmitted to an OLT.

[48] FIG. 12 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 12 is similar to the optical network system shown in FIG. 11 except that the optical network system shown in FIG. 12 is of a ring-type whereas the optical network system shown in FIG. 11 is of a linear type.

[49] Referring to FIG. 12, a first RN 300-1 may drop only certain wavelengths from downlink light provided by an SOA 280 of an OLT 200, and an OADM 330-1 of the first RN 300-1 may demultiplex the dropped wavelengths. Thereafter, the results of the demultiplexing may be transmitted to a plurality of ONUs 400-1 through 400- K. A plurality of optical signals provided by the ONUs 400-1 through 400-K may be multiplexed by a WDM multiplexer/demultiplexer 310-1, and some wavelengths may be added to the result of the multiplexing by the OADM 330-1. Thereafter, an optical signal obtained by the addition performed by the OADM 330-1 may be transmitted to a second RN 300-2. An OADM 330-2 of the second RN 300-2 may drop some wavelengths from the optical signal received by the second RN 300-2, and a WDM multiplexer/demultiplexer 310-2 may demultiplex the resulting optical signal. The results of the demultiplexing may be transmitted to a plurality of ONUs 400-k+l through 400-p. A plurality of optical signals provided by the ONUs 400-k+l through 400-p may be multiplexed by the WDM multiplexer/demultiplexer 310-2, and some wavelengths may be added to the result of the multiplexing by the OADM 330-2. Thereafter, an optical signal obtained by the addition may be transmitted to a third RN (not shown) or to a WDM demultiplexer 240 of the OLT 200.

[50] FIG. 13 illustrates a block diagram of an optical network system according to another exemplary embodiment of the present invention. The optical network system shown in FIG. 13 is similar to the optical network system shown in FIG. 5 except that each of a plurality of ONUs 400- 1 through 400-N includes a switch (not shown) and a plurality of downlink ports (not shown) and may thus be able to be connected to a plurality of subordinate terminals.

[51]

Industrial Applicability

[52] The present invention can be suitable for use in the transmission of data between a center and a plurality of access points (APs) in a wireless optical network system such as WiBro supporting the transmission of large amounts of data.

[53] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

[54]

[55]

Claims

[1] An optical network system comprising: an optical line terminal (OLT); and at least one optical network unit (ONU), wherein the OLT broadcasts downlink data to the ONU with the aid of a light source and the ONU transmits data to the OLT through a predetermined optical wavelength.

[2] The optical network system of claim 1, wherein the OLT includes an optical transmitter transmitting a downlink optical signal including downlink data, a seed light module providing seed light to the optical transmitter, a first circulator transmitting the seed light to the optical transmitter and transmitting the downlink optical signal to a second circulator, the second circulator transmitting the downlink optical signal to an external optical fiber and transmitting an uplink optical signal to an optical wavelength demultiplexer, the optical wavelength demultiplexer demultiplexing the uplink optical signal into a plurality of wavelengths, and at least one optical receiver receiving the uplink optical signal.

[3] The optical network system of claim 1, further comprising a remote node (RN) which includes an optical wavelength multiplexer/demultiplexer demultiplexing a downlink optical signal provided by the OLT and multiplexing a plurality of optical signals having different wavelengths provided by the ONU.

[4] The optical network system of claim 3, wherein the optical wavelength multiplexer/demultiplexer has a sufficient free spectral range (FSR) to handle a downlink optical wavelength band and an uplink optical wavelength band that are different.

[5] The optical network system of claim 1, wherein the ONU includes an optical receiver receiving a downlink optical signal and restoring downlink data from the downlink optical signal, an optical transmitter converting uplink data into an optical signal and transmitting the optical signal, and an optical filter transmitting the downlink optical signal to the optical transmitter and transmitting an uplink optical signal provided by the optical transmitter to an RN between the ONU and the OLT.

[6] The optical network system of claim 1, wherein the ONU includes a plurality of optical transmission modules that can be used independently of the wavelength of light.

[7] The optical network system of claim 6, wherein the ONU includes a reflective semiconductor optical amplifier (RSOA), which serves as an optical transmitter, receives one part of a downlink optical signal output by an RN between the ONU and the OLT, flattens the received downlink optical signal, modulates the flattened downlink optical signal based on uplink data, and outputs the modulated downlink optical signal to the RN, and an optical receiver, which receives another part of the downlink optical signal output by the RN, converts the received downlink optical signal into an electric signal, and restores downlink data from the electric signal.