Abstract:
A data/audio multiplex transmission system comprising an audio modulator to modulate an input audio signal and output the modulated audio signal, an optical pulse signal generator to generate an optical pulse signal for carrying a LAN data, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the LAN data and the modulated audio signal, an optical fiber to propagate the optical signal output from the optical pulse signal generator, an opto-electric converter to convert the optical signal propagated on the optical fiber into an electric signal, a filter to extract a predetermined band out of the output signal from the opto-electric converter, an audio demodulator to demodulate the audio signal out of the output from the filter, and a data transmitter to transmit the LAN data included in the output signal from the opto-electric converter for a LAN.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority to Japanese Patent Application No. 2002-112809, filed Apr. 16, 2002, the entire contents of which are incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    This invention generally relates to a system, method, and apparatus for multiplex-transmitting a data and audio, and more specifically relates to a data/audio multiplexer/demultiplexer which gives an additional function for multiplexing/demultiplexing audio signal to an optical transceiver which transmits and receives a data through optical fibers, data/audio multiplex transmission system, and methods thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    Internet access through the medium of an optical fiber called FTTH (Fiber To The Home) has been utilized. In the FTTH, an apparatus to convert a format and protocol of a transmission data is disposed between an optical fiber and a LAN or computer. Such apparatus is generally called a media converter.  
           [0004]    Also, well-known is a configuration in which a dedicated telephone is connected to a terminal adapter which interconverts between an audio signal and an IP data, the terminal adapter being connected to a LAN (Local Area Network) terminal (e.g. 10/100 BASE-T) of an ADSL (Asymmetric Digital Subscriber Line) modem or media converter.  
           [0005]    A conventional media converter is used exclusively for data transmission and thus it is required to provide a separate telephone line to use the usual telephone service.  
           [0006]    Needless to say, when an audio signal is transmitted as a digital data on an access line (an ADSL line or optical fiber of FTTH) for connecting to the Internet, a telephone line is unnecessary. However, to perform this operation, it is necessary to connect a microphone and speaker for telephonic communication with a computer and to install audio service control software to process a telephone signal. Another method is to provide a dedicated terminal adapter to intermediate between audio signals and IP data. Such terminal adapter is a sort of alternate of the audio service control software on computer.  
         SUMMARY OF THE INVENTION  
         [0007]    A data/audio multiplexer/demultiplexer according to the invention comprises a data receiver connectable with a LAN, an audio modulator to modulate an input first audio signal and to output the modulated audio signal, an optical pulse signal generator to generate an optical pulse signal for carrying first data signal from the LAN received by the data receiver, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the first data signal and the modulated audio signal, an opto-electric converter to convert an input optical signal carrying second audio signal and second data signal into an electric signal, a filter to extract a predetermined band out of the signal output from the opto-electric converter, an audio demodulator to demodulate the second audio signal out of the output from the filter, and a data transmitter connectable to the LAN to output the second data signal included in the output signal from the opto-electric converter for the LAN.  
           [0008]    With the above configuration, telephonic communication is superimposed on a data communication line. That is, there is no need to provide a dedicated terminal adapter or another telephone line for telephonic communication.  
           [0009]    Preferably, the optical pulse signal generator comprises an amplitude modulator to analog-modulate the pulse amplitude of the first data signal from the LAN received by the data receiver with the modulated audio signal and an electrooptic converter to convert the output signal from the amplitude modulator to an optical signal. With this configuration, telephonic communication is superimposed on a data communication line with low-cost means.  
           [0010]    Preferably, the data/audio multiplexer/demultiplexer according to the invention further comprises a telephone connector to connect a telephone wherein the first audio signal enters the audio modulator through the telephone connector from the telephone and the second audio signal output from the audio demodulator is applied to the telephone through the telephone connector. With this configuration, an existing telephone is easily connected to the apparatus.  
           [0011]    Preferably, the data transmitter comprises a waveform shaper to shape a pulse waveform of the output signal from the opto-electric converter. With this configuration, distortion of a pulse waveform due to the audio multiplex is improved.  
           [0012]    A data/audio multiplexing/demultiplexing method according to the invention comprises an audio modulating step for modulating a first audio signal and outputting the modulated audio signal, an optical pulse signal generating step for generating an optical pulse signal for carrying first data signal input from a LAN, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the first data signal and the modulated audio signal, an opto-electric converting step for converting an input optical signal carrying second audio signal and second data signal into an electric signal, a band extracting step for extracting a predetermined band from the electric signal obtained in the opto-electric converting step, an audio demodulating step for demodulating the second audio signal from the signal having the band extracted in the band extracting step, and a data transmitting step for transmitting the second data signal included in the electric signal obtained in the opto-electric converting step for the LAN.  
           [0013]    With the above configuration, telephonic communication is superimposed on a data communication line. That is, there is no need to provide a dedicated terminal adapter or another telephone line for telephonic communication.  
           [0014]    Preferably, the optical pulse signal generating step comprises a pulse amplitude modulating step to analog-modulate pulse amplitude of the first data signal input from the LAN with the modulated audio signal obtained in the audio modulating step and an electrooptic converting step to convert the pulse signal whose amplitude was modulated in the pulse amplitude modulating step into an optical signal. With this configuration, telephonic communication is superimposed on a data communication line with low-cost means.  
           [0015]    Preferably, the data transmitting step comprises a waveform shaping step to shape a pulse waveform of the second data signal included in the electric signal obtained in the opto-electric converting step. With this configuration, distortion of a pulse waveform due to the audio multiplex is improved.  
           [0016]    A data/audio multiplex transmission system according to the invention comprises an audio modulator to modulate an input audio signal and to output the modulated audio signal, an optical pulse signal generator to generate an optical pulse signal for carrying a LAN data, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the LAN data and modulated audio signal, an optical fiber to transmit the optical signal output from the optical pulse signal generator, an opto-electric converter to convert the optical signal propagated on the optical fiber into an electric signal, a filter to extract a predetermined band from the output signal from the opto-electric converter, an audio demodulator to demodulate the audio signal from the output from the filter, and a data transmitter to transmit the LAN data included in the output signal from the opto-electric converter for the LAN.  
           [0017]    Preferably, the optical pulse signal generator comprises an amplitude modulator to analog-modulate pulse amplitude of the LAN data signal with the modulated audio signal and an electrooptic converter to convert the output signal from the amplitude modulator into an optical signal. With this configuration, telephonic communication is superimposed on a data communication line with low-cost means.  
           [0018]    Preferably, the data transmitter comprises a waveform shaper to shape a pulse waveform of the output signal from the opto-electric converter. With this configuration, distortion of a pulse waveform due to the audio multiplex is improved.  
           [0019]    A data/audio multiplex transmission method according to the invention comprises an audio modulating step to modulate an input audio signal and to output the modulated signal, an optical pulse signal generating step to generate an optical pulse signal for carrying a LAN data, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the LAN data and modulated audio signal and to output the generated optical pulse signal onto an optical transmission medium, an opto-electric converting step to convert the optical signal propagated on the optical transmission medium into an electric signal, a band extracting step to extract a predetermined band from the electric signal obtained in the opto-electric converting step, an audio demodulating step to demodulate the modulated audio signal from the signal having the band extracted in the band extracting step, and a data transmitting step to transmit the LAN data included in the electric signal obtained in the opto-electric converting step for the LAN.  
           [0020]    Preferably, the optical pulse signal generating step comprises a pulse amplitude modulating step to analog-modulate pulse amplitude of the LAN data with the modulated audio signal and an electrooptic converting step to convert the pulse signal whose amplitude is modulated in the pulse amplitude modulating step into an optical signal and to output the optical signal on to the optical transmission medium. With this configuration, telephonic communication is superimposed on a data communication line with low-cost means.  
           [0021]    Preferably, the data transmitting step comprises a waveform shaping step to shape a pulse waveform of the LAN data included in the electric signal obtained in the opto-electric converting step. With this configuration, distortion of a pulse waveform due to the audio multiplex is improved. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:  
         [0023]    [0023]FIG. 1 shows a schematic block diagram of an explanatory embodiment according to the invention; and  
         [0024]    [0024]FIG. 2 shows an example of output waveform from an AM modulator  40 . 
     
    
     DETAILED DESCRIPTION  
       [0025]    Explanatory embodiments of the invention are explained below in detail with reference to the drawings.  
         [0026]    [0026]FIG. 1 shows a schematic block diagram of an explanatory embodiment according to the invention. A media converter  10  installed in a user&#39;s set connects to a media converter  16  at a telephone switching station through optical fibers  12  and  14 . The optical fiber  12  transmits a signal from the media converter  10  to the media converter  16 , and the optical fiber  14  transmits a signal from the media converter  16  to the media converter  10 .  
         [0027]    First, the transmission of a data D 1  and audio signal V 1  from the user&#39;s house to the telephone switching station is explained below.  
         [0028]    The media converter  10  comprises a telephone modular jack  22  to connect with a telephone  20  to be used for a fixed telephone network and a 10/100 BASE-T terminal  24  to connect with a LAN. Although it is not illustrated in the drawing, a user&#39;s personal computer connects to the 10/100 BASE-T terminal  24  directly or through a LAN.  
         [0029]    A modulator  26  modulates an audio signal V 1  from the telephone  20  using a sine-wave signal of frequency f0 from a local oscillator  28 . Any modulation mode of AM, FM, and PM is applicable. In this embodiment, since an audio signal is multiplexed through analog intensity modulation on an optical pulse signal of 100 Mbit/s or 10 Mbit/s on the optical fibers  12  and  14 , it is preferable to shift components in a low frequency area including the direct current of an audio signal toward a higher frequency area. The bandwidth of a telephone signal is 4 kHz and so the oscillation frequency f0 of the local oscillator  28  should be 4 kHz or more, preferably 8˜10 kHz.  
         [0030]    A buffer amplifier  32  in an Ethernet (Trademark) transceiver  30  amplifies a signal carrying a data D 1  from a user&#39;s computer, and a driver  34  applies an output signal from the amplifier  32  to an AM modulator  40  with a predetermined voltage or current. The driver  34  is sometimes omitted or integrated with the buffer amplifier  32 . An output Va from the modulator  26  is also applied to the AM modulator  40  as a modulating signal. The AM modulator  40  modulates amplitude of the data signal output from the driver  34  with the modulated audio signal Va from the modulator  26 . FIG. 2 shows an example of output waveform from the AM modulator  40 . In FIG. 2, although RZ transmission is illustrated as an example of a data transmission system to make it easily understandable, an NRZ transmission system or the other pulse signal transmission systems are also applicable. Furthermore, it is also possible to utilize a different pulse signal transmission system for each of the electric stage and optical stage.  
         [0031]    The AM modulator  40  comprises for example a variable gain amplifier to amplify the output signal from the driver  34  with a gain that varies according to the output level from the modulator  26 . In other words, the AM modulator  40  multiplexes the modulated audio signal Va from the modulator  26  with the data signal to be transmitted for the telephone switching station.  
         [0032]    An LD driver  42  drives a laser diode (LD)  44  according to the output from the AM modulator  40 . The LD  44  generates an optical pulse signal for carrying the data D 1  and whose amplitude is modulated by the modulated audio signal Va and outputs the generated optical pulse signal onto the optical fiber  12 . Ideally, the output waveform from the LD  44  becomes equivalent to the waveform example shown in FIG. 2. That is, the output signal from the AM modulator  40  is converted to an optical signal by the LD driver  42  and LD  44 . It is also applicable that the LD driver  42  comprises such a function to convert from NRZ to RZ or from NRZ to RZ.  
         [0033]    As described above, the multiplexed data D 1  and audio signal V 1  propagates on the optical fiber  12  and enters the media converter  16  on the telephone switching station side.  
         [0034]    In the media converter  16  at the telephone switching station, a photodiode  62  converts the optical signal from the optical fiber  12  into an electric signal. The output from the photodiode  62  is applied to a limiter  64  and to a bandpass filter (BPF)  66  which extracts the modulated audio signal Va. The limiter  64  is disposed to flatten the pulse amplitude fluctuated by the modulated audio signal Va. If such consideration is unnecessary, the limiter  64  can be omitted. It is also applicable to dispose a waveform shaper to shape the pulse signal waveform instead of the limiter  64 .  
         [0035]    The output from the limiter  64  enters a buffer amplifier  74  of an Ethernet transceiver  72 . The buffer amplifier  74  amplifies the output signal from the limiter  64 , and a driver  76  outputs the output signal from the amplifier  74  according to a predetermined voltage or current onto the IP network. The driver  76  is sometimes omitted or integrated with the buffer amplifier  74 . An IP data signal carrying the data D 1  is output from the driver  76  for the IP network.  
         [0036]    The BPF  66  extracts the modulated audio signal Va out of the output from the photodiode  62 . A demodulator  68  demodulates the output from the BPF  66  using a sine wave output signal of frequency f0 from a local oscillator  70  to restore the audio signal V 1 . The restored audio signal V 1  is applied to a telephone switching equipment  60 . The telephone switching equipment  60  outputs the received audio signal V 1  for a telephone network.  
         [0037]    As described above, the data D 1  and audio signal V 1  are transmitted from the user&#39;s set to the telephone switching station.  
         [0038]    Next, the transmission of a data D 2  and audio signal V 2  from the telephone switching station to the user&#39;s set is explained below. This operation is practically identical to the transmission of the data D 1  and audio signal V 1  from the user&#39;s set to the telephone switching station.  
         [0039]    The telephone switching equipment  60  applies a telephone audio signal V 2  input from the telephone network to a modulator  84  in the media converter  16  at the telephone switching station. The modulator  84  modulates the audio signal V 2  from the telephone switching equipment  60  with the sine wave signal of frequency f0 from the local oscillator  70 . The modulation mode can be any one of AM, FM and PM.  
         [0040]    A buffer amplifier  78  in the Ethernet transceiver  72  amplifies a signal from the IP network for carrying the data D 2 , and a driver  80  applies the output signal from the amplifier  78  according to a predetermined voltage or current to an AM modulator  82 . The driver  80  is sometimes omitted or integrated with the buffer amplifier  78 . An output Vb from the modulator  84  is also applied to the AM modulator  82  as a modulating signal. The AM modulator  82  modulates amplitude of the data signal output from the driver  80  with the modulated audio signal Vb from the modulator  84 . In other words, the AM modulator  82  multiplexes the modulated audio signal Vb from the modulator  84  with the data signal to be transmitted for the user&#39;s set.  
         [0041]    An LD driver  86  drives a laser diode (LD)  88  according to the output from the AM modulator  82 . The LD  88  generates an optical pulse signal for carrying the data D 2  and whose amplitude is modulated by the modulated audio signal Vb and outputs the generated optical pulse signal onto the optical fiber  14 . That is, the output signal from the AM modulator  82  is converted into an optical signal by the LD driver  86  and LD  88 .  
         [0042]    As described above, the multiplexed data D 2  and audio signal V 2  propagates on the optical fiber  14  and enters the media converter  10  in the user&#39;s set.  
         [0043]    In the media converter  10  in the user&#39;s set, the photodiode  46  converts the optical signal from the optical fiber  14  into an electric signal. The output from the photodiode  46  is applied to the limiter  48  and to the bandpass filter (BPF)  50  which extracts the modulated audio signal Vb. The limiter  48  is disposed to flatten the pulse amplitude fluctuated by the modulated audio signal Vb. If such consideration is unnecessary, the limiter  48  can be omitted. It is also applicable to dispose a waveform shaper to shape a pulse signal waveform instead of the limiter  48 .  
         [0044]    The output from the limiter  48  enters a buffer amplifier  36  in the Ethernet transceiver  30 . The buffer amplifier  36  amplifies the output signal from the limiter  48 , and a driver  38  outputs the output signal from the amplifier  36  according to a predetermined voltage or current for a LAN in the user&#39;s set. The driver  38  is sometimes omitted or integrated with the buffer amplifier  36 . An IP data signal for carrying the data D 2  is output from the driver  38  for the user&#39;s LAN.  
         [0045]    The BPF  50  extracts the modulated audio signal Vb out of the output from the photodiode  46 . A demodulator  52  demodulates the output from the BPF  50  with the sine wave output signal of frequency f0 from the local oscillator  70  to restore the audio signal V 2 . The restored audio signal V 2  is applied to the telephone  20  through the modular jack  22 .  
         [0046]    As described above, the data D 2  and audio signal V 2  are transmitted from the telephone switching station to the user&#39;s set.  
         [0047]    As already mentioned, the drivers  34 ,  38 ,  76 ,  80  in the transceivers  30  and  72  can be omitted. Also, the limiters  48  and  64  can be omitted. Obviously, it is possible to use LPFs instead of the BPFs  50  and  66 .  
         [0048]    Although an embodiment applied for FTTH is explained here, the invention is applicable to the other access systems such as an access line of Ether-VPN.  
         [0049]    In the embodiment shown in FIG. 1, although the two optical fibers  12  and  14  are connected between the media converters  10  and  16  to make it easy to understand, it is also applicable to use a single optical fiber bidirectionally. For instance, by assigning a different wavelength to each of the up and down flows, an up signal light and a down signal light can be easily separated.  
         [0050]    Furthermore, it is obvious that data terminals such as a computer can be directly connected to the media converters  10  and  16 . That is, the LAN claimed in the present invention includes the data terminals as well.  
         [0051]    In the above embodiment, although the audio signal and data signal are multiplexed in the electric state, it is also applicable to convert the data into an optical state first and then modulate the pulse amplitude of the optical pulse signal with a modulated audio signal.  
         [0052]    As readily understandable from the aforementioned explanation, according to the invention, data communication represented by the Internet and existing telephone are efficiently united. Furthermore, it is possible to continue the telephone service without canceling the previous telephone service and without paying doubly for the telephone service. Since the invention is realized by merely adding a few low-cost parts to a media converter, the production cost can be kept very low.  
         [0053]    While the invention has been described with reference to the specific embodiment, it will be apparent to those skilled in the art that various changes and modifications can be made to the specific embodiment without departing from the spirit and scope of the invention as defined in the claims.