Time division multiple access over wavelength division multiplexed passive optical network

Provided is a time division multiple access over wavelength division multiplexed passive optical network (TDM-over-WDM-PON) system. According to the TDM-over-WDM-PON system, a downstream optical signal is separated according to a wavelength in a remote node, transmitted to an optical amplifying device located in subscriber equipment, amplified in the optical amplifying device, transmitted back to the remote node, and then transmitted to the subscriber equipment. Also, an upstream optical signal is transmitted to a wavelength converting device located in the subscriber equipment from the remote node, wavelength-converted in the wavelength converting device, returned back to the remote node, and then transmitted to a central office.

TECHNICAL FIELD

The present invention relates to a method of applying a wavelength division multiplexing technology to a time division multiplexing (TDM) passive optical network (PON).

The present invention is derived from research performed as an IT growth power technology development business of the Ministry of Information and Communication and the Institute of Information Technology Assessment (IITA), Republic of Korea [2007-S-014-01, Metro-Access Integrated Optical Network Technology].

BACKGROUND ART

In a gigabit Ethernet (GE)-passive optical network (PON), which is a type of a conventional time division multiplexing (TDM)-passive optical network (PON), a feeder fiber accepts the maximum 32 subscribers and provides a total bandwidth of 1 Gbps. A gigabit (G)-PON, which is another type of the conventional TDM-PON, is being developed, and accepts 64 subscribers and provides a total bandwidth of 2.6 Gbps downward and 1.2 Gbps upward. A transmission distance of the conventional TDM-PON is prescribed to 20 Km. It is expected that services requiring a high bandwidth, including an IPTV, will be in the mainstream within a few years, and accordingly, a fiber to the home (FTTH) optical network is being developed, and a GE-PON is currently provided. However, as the number of subscribers of the FTTH optical network increases, it is required to efficiently use an infrastructure of a conventional optical network. Also, the conventional optical network needs to be improved so as to provide an increased bandwidth to a subscriber.

A dense wavelength division multiplexing (WDM)-PON is widely known as a next generation optical network. The dense WDM-PON is being actively studied specifically in Korea, and a system having 1 Gbps per wavelength and 16 optical wavelength multiplexing structure is about to be commercialized. However, an optical transmission/reception module of the dense WDM-PON is much more expensive than that of the GE-PON, and thus it is not suitable to apply the dense WDM-PON to the FTTH optical network with a current price level. Also, in order to apply the dense WDM-PON, a remote node, and an optical terminal of a subscriber need to be exchanged. Accordingly, the WDM-PON is only applied to a few new subscribers who require a high bandwidth.

DISCLOSURE OF INVENTION

Technical Problem

The present invention provides a method and system which can remarkably reduce a feeder fiber line and enlarge a transmission distance between a central office (CO) and a terminal of a subscriber, by applying a wavelength division multiplexing (WDM) transmission method to a time division multiplexing-passive optical network (TDM-PON), between the CO and a remote node (RN).

Technical Solution

According to an aspect of the present invention, there is provided a remote node of a passive optical network located between a central office and subscriber equipment, the remote node comprising: a wavelength multiplexer which demultiplexes downstream optical signals received from the central office and multiplexes wavelength-converted upstream optical signals; and an optical circulator which transmits the demultiplexed downstream optical signals to an optical signal amplifying device and then transmits to the subscriber equipment an amplified downstream optical signals received from the optical signal amplifying device, and transmits the upstream optical signals to a wavelength converting device and then transmits to the wavelength multiplexer the wavelength-converted upstream received from the optical amplifying device.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: an optical amplification unit which receives a downstream optical signal from the remote node, amplifies the downstream optical signal, and then returns the downstream optical signal to the remote node; and a wavelength conversion unit which receives an upstream optical signal from the remote node, converts the upstream optical signal to a predetermined wavelength, and then returns the upstream optical signal to the remote node.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: a signal regeneration unit which receives a downstream optical signal from the remote node, restores the downstream optical signal to the original signal via timing re-arrangement and form restoration processes, and then returns the restored downstream optical signal to the remote node; and a wavelength conversion unit which receives an upstream optical signal from the remote node, converts the upstream optical signal to a predetermined wavelength, and then returns the converted upstream optical signal to the remote node.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: a first reflective semiconductor optical amplifier (RSOA) which amplifies a downstream optical signal received from the remote node; a coupler which splits the amplified downstream optical signal and transmits a part of the split downstream optical signal to the remote node; a signal conversion unit which converts an upstream optical signal received from the remote node to an electric signal; a second RSOA which amplifies another part of the split downstream optical stream, and modulates and outputs the amplified downstream optical stream by using the electric signal; and a WDM filter which transmits the downstream optical signal from the second RSOA to the remote node.

According to another aspect of the present invention, there is provided a central office in a passive optical network connected to subscriber equipment via a remote node, the central office comprising: a seed light source; a wavelength multiplexer which wavelength-divides a seed light; and a plurality of optical transmitters which modulate the wavelength-divided seed light to downstream optical signals containing downstream data, wherein wavelength multiplexer wavelength-multiplexes and outputs the downstream optical signals having different wavelengths modulated by the plurality of optical transmitters.

According to another aspect of the present invention, there is provided a method of transmitting an optical signal in a remote node of a passive optical network comprising a central office, the remote node, and subscriber equipment, the method comprising: a downstream transmission step wherein downstream optical signals are demultiplexed and are transmitted to an external optical amplifying device, and the downstream optical signals amplified by the optical amplifying device are received and then transmitted to the subscriber equipment; and an upstream transmission step wherein upstream optical signals are transmitted to an external wavelength converting device, and the wavelength-converted upstream optical signals are received from the wavelength converting device and then transmitted to the central office.

ADVANTAGEOUS EFFECTS

According to the present invention, by installing an additional apparatus to a subscriber while continuously using subscriber equipment and an optical splitter of a TDM-PON and by applying a WDM transmission method between a CO and a RN, a feeder fiber line can be remarkably reduced and a transmission distance between the CO and the subscriber equipment can be increased. Accordingly, high price, which is the main issue of a conventional WDM-PON, can be decreased, and a disadvantage of exchanging equipment so as to change TDM-PON to WDM-PON can be solved.

BEST MODE

According to an aspect of the present invention, there is provided a remote node of a passive optical network located between a central office and subscriber equipment, the remote node comprising: a wavelength multiplexer which demultiplexes downstream optical signals received from the central office and multiplexes wavelength-converted upstream optical signals; and an optical circulator which transmits the demultiplexed downstream optical signals to an optical signal amplifying device and then transmits to the subscriber equipment an amplified downstream optical signals received from the optical signal amplifying device, and transmits the upstream optical signals to a wavelength converting device and then transmits to the wavelength multiplexer the wavelength-converted upstream received from the optical amplifying device.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: an optical amplification unit which receives a downstream optical signal from the remote node, amplifies the downstream optical signal, and then returns the downstream optical signal to the remote node; and a wavelength conversion unit which receives an upstream optical signal from the remote node, converts the upstream optical signal to a predetermined wavelength, and then returns the upstream optical signal to the remote node.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: a signal regeneration unit which receives a downstream optical signal from the remote node, restores the downstream optical signal to the original signal via timing re-arrangement and form restoration processes, and then returns the restored downstream optical signal to the remote node; and a wavelength conversion unit which receives an upstream optical signal from the remote node, converts the upstream optical signal to a predetermined wavelength, and then returns the converted upstream optical signal to the remote node.

According to another aspect of the present invention, there is provided subscriber equipment in a passive optical network connected to a central office via a remote node, the subscriber equipment comprising: a first reflective semiconductor optical amplifier (RSOA) which amplifies a downstream optical signal received from the remote node; a coupler which splits the amplified downstream optical signal and transmits a part of the split downstream optical signal to the remote node; a signal conversion unit which converts an upstream optical signal received from the remote node to an electric signal; a second RSOA which amplifies another part of the split downstream optical stream, and modulates and outputs the amplified downstream optical stream by using the electric signal; and a WDM filter which transmits the downstream optical signal from the second RSOA to the remote node.

According to another aspect of the present invention, there is provided a central office in a passive optical network connected to subscriber equipment via a remote node, the central office comprising: a seed light source; a wavelength multiplexer which wavelength-divides a seed light; and a plurality of optical transmitters which modulate the wavelength-divided seed light to downstream optical signals containing downstream data, wherein wavelength multiplexer wavelength-multiplexes and outputs the downstream optical signals having different wavelengths modulated by the plurality of optical transmitters.

According to another aspect of the present invention, there is provided a method of transmitting an optical signal in a remote node of a passive optical network comprising a central office, the remote node, and subscriber equipment, the method comprising: a downstream transmission step wherein downstream optical signals are demultiplexed and are transmitted to an external optical amplifying device, and the downstream optical signals amplified by the optical amplifying device are received and then transmitted to the subscriber equipment; and an upstream transmission step wherein upstream optical signals are transmitted to an external wavelength converting device, and the wavelength-converted upstream optical signals are received from the wavelength converting device and then transmitted to the central office.

Mode for Invention

Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 1is a diagram illustrating a time division multiple access over wavelength division multiplexed passive optical network (TDM-over-WDM-PON), according to an embodiment of the present invention;

Referring toFIG. 1, the TDM-over-WDM-PON includes a central office (CO), a remote node (RN)200, and a subscriber equipment300.

An optical line terminal (OLT)100installed in the CO includes a protocol processor110, a plurality of transmitters and receivers (TRx)120, and a wavelength multiplexer130. The protocol processor110switches downstream data going down to the subscriber and upstream data coming up from the subscriber, and processes a transmission protocol. The plurality of TRx120transmits and receives an optical signal, and the wavelength multiplexer130wavelength-multiplexes and transmits different optical wavelengths of downstream optical signals received from the plurality of TRx120to one feeder fiber, and simultaneously wavelength-demultiplexes the wavelength-multiplexed upstream optical signals.

The RN200includes a wavelength multiplexer210, an optical circulator220, and an optical splitter230. The wavelength multiplexer210receives the wavelength-multiplexed downstream optical signals from the feeder fiber, demultiplexes the received downstream optical signals, and transmits the demultiplexed downstream optical signals to N optical fibers connected to the subscribers. Also, the wavelength multiplexer210receives N upstream optical signals according to each wavelength from the N optical fibers, wavelength-multiplexes the N upstream optical signals, and then transmits the N upstream optical signals to one feeder fiber. The optical circulator220transmits the received optical signal to an assigned output port, and the optical splitter230splits the received optical signal into M optical signals.

The subscriber equipment300includes a plurality of conventional TDM-PON optical network units (ONUs)310or optical network terminals ONTs, a wavelength conversion unit (WCU)320which converts and outputs an optical signal received from the conventional TDM-PON ONUs310to a predetermined dense WDM (DWDM) optical wavelength, an optical amplification unit (OAU)330which amplifies a strength of a received optical signal, and an additional signal unit380which transmits additional data which are not data from conventional TDM-PON subscribers to the CO.

Detailed operations of the TDM-over-WDM-PON according to the current embodiment of the present invention will now be described.

An optical signal transmitted from the wavelength multiplexer210of the RN200to the subscriber equipment300is input to the optical circulator220, circulated in the optical circulator220, and then output to the OAU330of the subscriber equipment300. The optical signal input to the OAU330of the subscriber equipment300is amplified, and re-input to the optical circulator220of the RN200. The optical signal input to the optical circulator220is circulated inside the optical circulator220, and then output through the optical splitter230. Upon receiving the optical signal, the optical splitter230of the RN200transmits the optical signal to the M ONUs310.

Meanwhile, the optical signals output from the M ONUs310gather in the optical splitter230, and are transmitted to the optical circulator220of the RN200. The optical signals input to the optical circulator220are circulated in the optical circulator220, and then transmitted to the WCU320of the subscriber equipment330. The optical signals input to the WCU320are converted to a predetermined wavelength, and then re-input to the optical circulator220. The optical signals re-input to the optical circulator220are circulated in the optical circulator220, and then transmitted to a predetermined port of the wavelength multiplexer210. The optical signals input to the wavelength multiplexer210are wavelength-multiplexed with other optical signals having different wavelength received from another port, transmitted to one feeder fiber, and then transmitted to the CO.

The WCU320of the subscriber equipment300may convert a received optical signal to an electric signal, re-convert the electric signal to an optical signal having a predetermined wavelength, and then output the optical signal. Alternatively, the WCU320may output the optical signal after converting the wavelength, without converting the optical signal into the electric signal.

FIG. 2is a diagram illustrating a CO and subscriber equipment300in a TDM-over-WDM-PON, according to other embodiments of the present invention.

Referring toFIG. 2, an OLT100installed in the CO includes a protocol processor110, an plurality of optical transmitters121, a plurality of optical receivers122, a first wavelength multiplexer131, a second wavelength multiplexer132, a first circulator133, a second circulator134, and a seed light source (SL source)134.

A seed light output from the SL source134is input to the first wavelength multiplexer131via the first circulator133. The first wavelength multiplexer131wavelength-divides the received seed light to have a plurality of optical wavelengths, and transits the divided optical wavelengths to the plurality of optical transmitters121. The optical transmitters121amplify the received seed light, modulate the seed light into downstream data received from the protocol processor110, and output an optical signal including the downstream data. The optical signals having different wavelengths output from the optical transmitters121are re-transmitted to the first wavelength multiplexer131. The first wavelength multiplexer131wavelength-multiplexes the received optical signals, and then transmits the optical signals to the first circulator133via one optical fiber. The first circulator133transmits the wavelength-multiplexed optical signals to the second circulator134. The second circulator134circulates the received optical signals, and transmits the optical signals to the RN200via a feeder fiber.

Also, wavelength-multiplexed upstream optical signals that come up from the RN200are transmitted to the second circulator134, circulated, and then transmitted to the second wavelength multiplexer132. The second wavelength multiplexer132demultiplexes the received upstream optical signals and transmits the demultiplexed upstream optical signals to the optical receivers122. The optical receivers122convert the received upstream optical signals to electric signals.

Generally, one optical transmitter121and one optical receiver122form a pair according to a wavelength, so as to form one TRx120. A reflective semiconductor optical amplifier (RSOA) or an SOA may combine with a circulator to from the optical transmitter121.

The SL source134may be a broadband light source (BLS) or a light source wherein a plurality of optical wavelengths are multiplexed. When the SL source134is a BLS, the wavelength of the seed light is divided (spectrum sliced) via the first wavelength multiplexer131, and each of the sliced seed light is input to the optical transmitter121. When the SL source134is the light source wherein a plurality of optical wavelengths are multiplexed, the wavelength of the seed light is divided (WDM demultiplexed) via the first wavelength multiplexer131, and each of the divided seed light is input to the optical transmitter121.

The OAU330of the subscriber300may include a circulator331and an amplifier332. An optical signal transmitted from the optical circulator220of the RN200is input to the circulator331of the OAU330, and then output to the amplifier332. The optical signal outputted from the amplifier332is input to the circulator331, circulated in the circulator331, and then output to the optical circulator220of the RN200.

FIG. 3is a diagram illustrating a RN200in a TDM-over-WDM-PON, according to an embodiment of the present invention.

Referring toFIG. 3, the RN200includes a wavelength multiplexer210, a first circulator221, a second circulator222, a first WDM filter223, a second WDM filter224, and an optical splitter230.

A downstream optical signal that is wavelength-demultiplexed and outputted from the wavelength multiplexer210is input to a first port of the first circulator221and output from a second port of the first circulator221. The downstream optical signal output from the second port of the first circulator221is input to a first port of the second circulator222and output from a second port of the second circulator222. The downstream optical signal output from the second port of the second circulator222is transmitted to an OAU330of subscriber equipment300. Then, the downstream optical signal is input to a first port of a circulator331of the OAU330, output to a second port of the circulator331, amplified by an amplifier332, input to a third port of the circulator331, and then output to the first port of the circulator331. The downstream optical signal output to the first port of the circulator331is input to the second port of the second circulator222, and then output to a third port of the second circulator222. Next, the downstream optical signal is input to a first port of the first WDM filter223, which classifies a DWDM wavelength band and an upstream optical wavelength (1310 nm band) used by a TDM-PON, and then output to a second port of the first WDM filter223.

Also, an upstream optical signal in a 1310 nm band input to a second port of the first WDM filter223via the optical splitter230is output to a third port of the first WDM filter223. The upstream optical signal is input to a first port of the second WDM filter224, and output to a second port of the second filter224. Then, the upstream optical signal is converted to an optical signal having a predetermined DWDM wavelength by the WCU320of the subscriber equipment300, re-input to the second port of the second WDM filter224, and output to a third port of the second WDM filter224. The optical signal output to the third port of the second WDM filter224is input to a third port of the first circulator221, and output to the first port of the first circulator221. The optical signal output to the first port of the first circulator221is input to a corresponding port of the wavelength multiplexer210. Then, the wavelength multiplexer210wavelength-multiplexes the received optical signal with other optical signals having different wavelengths, and transmits the optical signal to an OLT100via a feeder fiber.

FIG. 4is a diagram illustrating subscriber equipment300in a TDM-over-WDM-PON, according to another embodiment of the present invention.

Referring toFIG. 4, the structure of the TDM-over-WDM-PON according to the current embodiment is similar to that according to the previous embodiment inFIG. 3. However in the current embodiment, a signal regeneration unit (SRU)340is included in the subscriber equipment300, instead of the OAU330. An optical signal output from a second port of a second circulator222is input to the SRU340. The optical signal input to the SRU340is restored to the original signal via not only an optical amplification process, but also via timing re-arrangement and form restoration processes. The SRU340may convert the optical signal to an electric signal, perform the timing re-arrangement process, and then convert the electric signal back to the optical signal. Alternatively, the SRU340may perform signal arrangement and form restoration processes without converting the optical signal to an electric signal.

FIG. 5is a diagram illustrating subscriber equipment300in a TDM-over-WDM-PON, according to another embodiment of the present invention.

Referring toFIG. 5, the structure of the TDM-over-WDM-PON according to the current embodiment is similar to that according to the previous embodiment inFIG. 3. However in the current embodiment, an apparatus350including an RSOA is used instead of the WCU320, and an apparatus360including an RSOA is used instead of the OAU330.

Downstream optical signals in a DWDM wavelength band output from a second port of a second circulator222are input to a first RSOA361via a coupler362. Then, the downstream optical signals are amplified in the first RSOA361, and then re-input to the coupler362. A part of the downstream optical signals is input to the second port of the second circulator222, and a remaining part of the downstream optical signals is input to a first port of a third circulator353. The downstream optical signals input to the first port of the third circulator353is output a second port of the third circulator353, and then input to a second RSOA352. The downstream optical signal input to the second RSOA352operates as a seed light. In other words, the downstream optical signal is planarized and amplified in the second RSOA352, and then modulated and output by an electric signal output from a signal conversion unit351and an additional signal unit380. The downstream optical signal output from the second RSOA352is input to the second port of the third circulator353and output to a third port of the third circulator353. Then, the downstream optical signal is input to a first port of a third WDM filter354and output to a third port of the third WDM filter354.

Also, an upstream optical signal in a 1310 nm band output to a second port of a second WDM filter224is input to a second port of the third WDM filter354and output to a third port of the third WDM filter354. Then, the upstream optical signal is transmitted to the signal conversion unit351and then converted to an electric signal by the signal conversion unit351.

Such apparatuses350and360may be identically used irrelevant to a DWDM optical wavelength.

FIG. 6is a diagram for describing a method of simultaneously performing data transmission and broadcasting transmission services in a TDM-over-WDM-PON, according to an embodiment of the present invention.

Referring toFIG. 6, a broadcast signal transmitter150, which can add a broadcast signal, is included in an output port of a wavelength multiplexer130in a CO, the output port facing a subscriber direction. Also, a broadcast signal receiver240, which can extract a broadcast signal that is additionally transmitted, is included in an RN200.

The broadcast signal transmitter150performs phase modulation on a broadcast signal (BS)151included in a RF sub-carrier (SC)152, and outputs the BS151. The broadcast signal receiver240receives a part of an optical signal by splitting the optical signal by using a coupler250, receives a signal by receiving a reference signal (RS)243, performs phase modulation (PD) on the received signal, and converts the received signal to an electric signal. The phase of the RS243is adjusted so that the size of the received signal becomes the maximum.

FIG. 7is a diagram for describing a method of simultaneously performing data transmission and broadcasting transmission services in a TDM-over-WDM-PON, according to another embodiment of the present invention.

The method ofFIG. 7is almost similar to the method ofFIG. 6, except that a broadcast signal receiver390is installed in subscriber equipment300.