Abstract:
An optical subscriber network system is disclosed, which comprises: a server bi-directional optical transmitter including a multiplexer to multiplexes communication data and broadcast data, a server laser diode to converts the multiplexed data into an optical signal, and a server photo diode receive communication data from a subscriber, wherein the server bi-directional optical transmitter transmits the upstream communication data; and a subscriber bi-directional optical receiver including a subscriber laser diode to transmit upstream communication data, a subscriber photo diode to receive the optical signal transmitted from the server bi-directional optical transmitter, and a demultiplexer to demultiplex and divide the multiplexed signal into communication data and broadcast data. In the optical subscriber network system, the optical transmitter and the optical receiver can transceive image signals and Ethernet communication signals in a two-way direction by means of a single laser diode and photo diode.

Description:
CLAIM OF PRIORITY 
     This application claims priority to an application entitled “Optical subscriber network system,” filed in the Korean Intellectual Property Office on Aug. 26, 2003 and assigned Serial No. 2003-59171, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical subscriber network system, and more particularly, an optical subscriber network system that supports broadcast and communication services using a fiber to the home (FTTH) network. 
     2. Description of the Related Art 
       FIG. 1  is a block diagram of a conventional optical subscriber network. As shown in  FIG. 1 , an optical subscriber network system providing broadcast/communication service includes an optical line terminal (hereinafter, referred to as an OLT), an optical network unit (hereinafter, referred to as an ONU), and an optical cable. The OLT converts broadcast data transmitted from a broadcaster into an optical signal to provide a user with broadcast service. It then transmits one tied optical signal. The ONU is a user-side apparatus and transmits information, which is received from the OLT, to a subscriber. The optical cable connects the OLT to the ONU. Operationally, the ONU receives a service requirement from a terminal of a service user. The ONU then provides a corresponding service. The broadcast/communication data, which is transmitted from the broadcaster, is transmitted to the ONU via the OLT, 
     In such an optical subscriber network system, when an optical signal is transmitted to a home, signals such as continuous Ethernet broadcast signals or video on demand (VOD) signals are transmitted to a subscriber in a single direction. A burst Ethernet communication signal is burst when it is transceived. Such directionality and continuity makes it difficult to transmit the two signals together. Therefore, broadcast signals in various channels are multiplexed by time division multiplexing (TDM). Then one optical wavelength is assigned to the multiplexed signal by a coarse wavelength division multiplexing (hereinafter, referred to as a CWDM). In this way, another optical wavelength is assigned to the Ethernet communication signal by the CWDM. By using such a CWDM method, a fiber to the home (FTTH) network is realized. 
     Shown in  FIG. 2  is a conventional FTTH optical subscriber network system, in which a bi-directional transceiving of a digital broadcasting and an Internet signal is possible. Such a network includes a server-side bi-directional optical transmitter  110  (hereinafter, referred to as an OLT) and a subscriber-side bi-directional optical receiver  120  (hereinafter, referred to as an ONU). The OLT  110  includes a first laser diode (hereinafter, referred to as a LD)  111  for transmitting digital broadcast data, a second LD  112  for transmitting downstream Internet data, a server-side photo diode (hereinafter, referred to as a PD)  113  for receiving upstream Internet data, a band-pass filter  114  which is installed in front of the server-side PD  113  and passes only the upstream Internet data, and an multiple optical waveguide element  115  for dividing each input/output data. The ONU  120  includes an multiple optical waveguide element  125  for dividing data inputted from the server-side bi-directional optical transmitter  110 , a first PD  121  for receiving the digital broadcast data inputted from the server-side bi-directional optical transmitter  110 , a second PD  122  for receiving the downstream Internet data inputted from the server-side bi-directional optical transmitter  110 , and a subscriber-side LD  123  for transmitting upstream Internet data. 
     The server-side PD  113  detects upstream Internet data  127  input from the subscriber-side. It enables a server computer to recognize the upstream Internet data  127 . The first LD  111  is a vertical cavity surface emitting laser (hereinafter, referred to as a VCSEL). The VCSEL modulates input digital broadcast data  116  into an optical signal and transmits the modulated optical signal the ONU  120 . The second LD  112  is a VCSEL having a wavelength different from the first LD  111 . The second LD  112  modulates downstream Internet data  117  into an optical signal and transmits the modulated optical signal the ONU  120 . 
     In addition, the subscriber-side LD modulates the upstream Internet data  127 . This data is transmitted from the subscriber-side to the server-side. The subscriber-side LD modulates this data into an optical signal and outputs it. Further, the subscriber-side LD forms a pair with the second PD  122  in the subscriber-side and enables bi-directional transceiving of an Internet signal. The first PD  121  detects and outputs the digital broadcast data  116  modulated into an optical signal by the first LD  111 . The second PD  122  detects the downstream Internet data  117  transmitted from the second LD  112  and converts it into data that can be recognized by a computer in the subscriber-side. 
     However, since such a conventional FTTH optical subscriber network system requires two optical signals (i.e. an optical signal for transmitting an image signal and an optical signal for transmitting an communication signal) the OLT  100  must transmit signals through the two LD  111  and  112 . It also requires an optical coupler, which is an optical waveguide element, for coupling the signals. Accordingly, the system manufacturing cost increases. Further, even when the two signals are received in the ONU  200 , the ONU  200  needs a coupler, which is an optical waveguide element, for dividing the two signals and the two PD  121  and  122 . Thus, the number of parts and the system manufacturing cost are increased. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to overcome or reduce the above-mentioned problems occurring in the prior art. One object of the present invention is to provide an optical subscriber network system, in which an optical transmitter and an optical receiver can respectively transceive an image signal and an Ethernet communication signal in a two-way direction using a single laser diode and photo diode. 
     According to the principles of the present invention an optical subscriber network system is provided, comprising a server bi-directional optical transmitter including a multiplexer to multiplexes communication data and broadcast data, a server laser diode to converts the multiplexed data into an optical signal, and a server photo diode receive communication data from a subscriber, wherein the server bi-directional optical transmitter transmits the upstream communication data; and a subscriber bi-directional optical receiver including a subscriber laser diode to transmit upstream communication data, a subscriber photo diode to receive the optical signal transmitted from the server bi-directional optical transmitter, and a demultiplexer to demultiplex and divide the multiplexed signal into communication data and broadcast data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a conventional optical subscriber network; 
         FIG. 2  is a block diagram of a conventional optical subscriber network system which supports a convergence service of broadcast and communication; 
         FIG. 3  is a block diagram of an optical subscriber network system which supports a convergence service of broadcast and communication according to an embodiment of the present invention; 
         FIG. 4  is a block diagram of an optical subscriber network system which supports a convergence service of broadcast and communication according to another embodiment of the present invention; and 
         FIG. 5  is a view showing a frame generated by an optical subscriber network system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment according to the present invention will be described with reference to the accompanying drawings. The same reference numerals are used to designate the same elements as those shown in other drawings. In the below description, many particular items, such as detailed elements of circuit, are shown, but these are provided for helping the general understanding of the present invention, it will be understood by those skilled in the art that the present invention can be embodied without particular items. For the purposes of clarity and simplicity, a detailed description of known functions and configuration incorporated herein will be omitted as it may make the subject matter of the present invention unclear. 
       FIG. 3  is a block diagram of an OLT  10  and an ONU  20  in an optical subscriber network system according to the present invention. The optical subscriber network system is realized in a FTTH network for providing a convergence service of broadcasting and communication. As shown in  FIG. 3 , the OLT  10  includes a RJ-45 connector  18  for connecting a server-side computer, an Ethernet switch  16 , a time division multiplexer (hereinafter, referred to as a TDM)  11 , a first laser diode (hereinafter, referred to as a LD)  12 , and a second photo diode (hereinafter, referred to as a PD)  13 . The Ethernet switch  16  is provided between a first PHY  15  and a second PHY  17 . The TDM  11  combines an Ethernet communication signal and multi-channel MPEG2 multi program transport stream (hereinafter, referred to as a MPTS) signals. It then multiplexes the combined signal. The LD  12  converts the multiplexed signal into an optical signal and transmits the converted signal to the ONU  20  through an optical fiber  30 . The PD  13  receives an Ethernet communication signal from the ONU  20  connected to a subscriber set-top box (not shown). The TDM  11  multiplexes the Ethernet communication signal and the MPTS signals. Moreover, it inserts the multiplexed signal into a time slot and constructs a time slot frame. 
     The ONU  20  includes a first PD  21 , a second LD  22 , a time division demultiplexer (hereinafter, referred to as a TDDM)  24 , a clock and data recovery (hereinafter, referred to as a CDR)  23 , a third PHY  25 , a fourth PHY  26 , an Ethernet switch  27 , a fifth PHY  28 , and a RJ-45 connector  29 . The first PD  21  receives the multiplexed signal. The second LD  22  transmits an Ethernet communication signal provided from a subscriber-side computer. The TDDM  24  demultiplexes the multiplexed signal received by the first PD  21  and provides multi-channel broadcast signal to a subscriber set-top box. The CDR  23  provides the TDDM  24  with a clock signal and reproduces the multiplexed signal. The third PHY  25  converts a signal (a type of a communication signal) from the TDDM  24 , e.g. from a media independent interface (hereinafter, referred to as a MII) signal, to a TX signal. The fourth PHY  26  converts a TX signal into a MII signal. The Ethernet switch  27  switches the MII signal from the fourth PHY  26  to provide the MII signal to a corresponding subscriber-side computer. The fifth PHY  28  converts the MII signal from the Ethernet switch  27  into a signal type which can be transmitted through a cable. The RJ-45 connector  29  connects a subscriber-side computer (not shown). 
     The first PHY  15  converts a RX signal generated by the second PD  13  into a MII signal. The second PHY  17  converts the MII signal into a multi level transmit-3 (hereinafter, referred to as a MLT-3) signal, which can be transmitted through an unshielded twisted pair (hereinafter, referred to as an UTP) cable. It then provides the MLT-3 signal to the RJ-45 connector  18 . Further, the second PHY  17  converts a MLT-3 signal from the RJ-45 connector  18  into a MII signal and provides it to the Ethernet switch  16 . The MII is an interface standard for 10 BaseT/100BaseTX media access control. The MII supports both a transmission rate of 2.5 Mhz for 10 BaseT transmission and a transmission rate of 25 Mhz for 100 BaseTX transmission. The MLT-3 is a method which lowers the frequency while maintaining a high-speed data communication speed. The Ethernet switch  27  performs the same function as a hub. It controls communication between a plurality of subscriber computers connected to the RJ-45 connector  29 . 
     The fourth PHY  26  converts the MII signal from the Ethernet switch  27  into a TX signal and outputs it to the second LD  22 . The TX signal output from the fourth PHY  26  is divided. Then the divided signal is input to an input terminal of the third PHY  25 . 
     Hereinafter, operation of the OLT  10  and the ONU  20  will be described. First, a process course of an downstream Ethernet communication signal will be described. In the OLT  10 , the Ethernet communication signal input through the RJ-45 connector  18  is converted into a MII signal via the second PHY  17  and the Ethernet switch  16 . The MII signal is input to the TDM  11 . Further, ‘n’ number of channels of the MPTSs, which are image signals, are input to the TDM  11 . The ‘n’ number of channels of the MPTSs and the MII high-speed Ethernet communication signal are multiplexed by the TDM  11 . The multiplexed signal is directly modulated by the first LD  12 . Then, the modulated signals are input to the first PD  21  in the ONU  20  through an optical fiber  300 . 
     Further, the signals are converted into electrical signals by the first PD  21  in the ONU  20 . The converted signals are input to the CDR  23 . Then, the signals are reproduced into electrical signals by the CDR  23 . The reproduced signals are input to the TDDM  24 . Herein, a clock is extracted from the CDR  23 , and provided to the TDDM  24 . The TDDM  24  divides the ‘n’ number of channels of the MPTSs and the high-speed Ethernet communication signal and then restores the signals. 
     Each MPTS signal is input to a broadcasting set-top box (not shown). Further, the MII Ethernet communication signal is input to the third PHY  25 . Then it is converted into a non return to zero inversion (NRZI) signal which is an FX signal. Thereafter, the NRZI signal is input to the fourth PHY  26 . For example, the FX signal is obtained by encoding an MII signal according to 100 Base-T standard, which is an electric signal, so that the signal can be transmitted through an optical fiber. 
     The MII signal output from the fourth PHY  26  is converted into a MLT-3 signal via the Ethernet switch  27  and the fifth PHY  28 . Then the converted signal is output as an Ethernet communication signal through the RJ-45 connector  29 . 
     Next, a process course of an upstream Ethernet communication signal is described. The Ethernet communication signal is input through the RJ-45 connector  29 , which connects a subscriber computer, in the ONU  20 . The input signal is converted into the NRZI signal, which is a FX signal, passing through the fifth PHY  28 , the Ethernet switch  27 , and the fourth PHY  26 . The NRZI signal is directly modulated by the second LD  22 . The third PHY  25  operates only when a signal is input to the third PHY  25 . Thus, the FX signal, which is outputted to the second LD  22 , must be divided. Then the divided signal must be also input to the third PHY  25 . 
     The Ethernet communication signal is transmitted to the OLT  1  through the second LD  22  and an optical fiber. It is then received by the second PD  13  in the OLT  10 . The received signal is transmitted to a server computer (not shown) through the RJ-45 connector  18  via the first PHY  15 , the Ethernet switch  16 , and the second PHY  17 . The Ethernet switch  16  performs the same function as a hub. It switches Ethernet data according to predetermined switching information. 
       FIG. 4  is a block diagram of an ONU  40  according to another embodiment of the present invention. As shown in  FIG. 4 , a TDDM  24  demultiplexes a signal, which is obtained by combining ‘n’ number of broadcast signals and a high-speed Ethernet communication signal, according to a clock of a CDR  23 . Further, the TDDM  24  outputs MPTS signals of ‘n’ number of divided channels to set-top boxes (not shown). It also provides an Ethernet switch  27  with a MII signal, which is a high-speed Ethernet communication signal. The Ethernet switch  27  outputs a MII signal, which is a high-speed Ethernet signal input through a RJ-45 connector  29  and a seventh PHY  28 , to a sixth PHY  45 . The sixth PHY  45  converts the MII signal input from the Ethernet switch  27  into an FX signal and then outputs the FX signal to a second LD  22 . 
     The sixth PHY  45  is operated only when a signal is input through an RX input pin. Thus, the input pin of the sixth PHY  45  to which a RX signal is input must be connected with an output pin of the sixth PHY  45  from which a TX signal is outputted. 
       FIG. 5  is a time slot frame  50  generated by multiplexing ‘n’ number of broadcasting signals and a high-speed Ethernet communication signal in a TDM according to the present invention. As shown in  FIG. 5 , the time slot frame  50  includes continuous time slots.  FIG. 5  shows the time slot frame  50  including ‘n’ number of MPTS broadcasting signals and one high-speed Ethernet communication signal. Further, a TDM may be designed so that ‘n’ number of MPTS broadcast signals and a plurality of high-speed Ethernet communication signals is included in one time slot frame. Such a time slot frame is demultiplexed by the TDDM  24  in the ONU  20 . The demultiplexed frame is divided into ‘n’ number of MPTS broadcast signals and one high-speed Ethernet communication signal. 
     Accordingly, in the present invention, the OLT  10  and the ONU  20  include a single LD and PD, respectively. The OLT  10  combines ‘n’ number of channels of MPTS broadcasting signals and a high-speed Ethernet signal input through a RJ-45 connector. It multiplexes them as a time slot signal, and transmits the multiplexed signal through the LD. Then, the ONU  20  receives the combined signal through a single optical receiver. It divides the received signal into ‘n’ number of channels of MPTS broadcasting signals and a high-speed Ethernet signal. The ONU  20  provides the high-speed Ethernet signal to the Ethernet switch. It also provides the ‘n’ number of channels of MPTS broadcasting signals to a set-top box (not shown) connected to the TDDM  24 . Further, when the high-speed Ethernet communication signal is transmitted, the ONU  20  outputs this signal, which is input from a subscriber computer connected to a RJ-45 connector, through the LD. The OLT  10  receives the high-speed Ethernet communication signal through an optical receiver. The OLT  10  transmits this signal to a server computer connected to a RJ-45 connector. 
     As described above, the OLT and the ONU of an optical subscriber network system according to the present invention do not require two LDs or an optical receiver in transceiving a high-speed Ethernet communication signal and a MPTS broadcast signal. Therefore, the optical subscriber network system has a reduced number of elements. 
     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.