JP5079659B2 - Optical access system - Google Patents

Description

  The present invention relates to an optical access system that enables a telephone call during a power failure.

  In recent years, optical access services that can transmit large amounts of information at high speed have been provided. The current optical access service is provided using a one-to-many connection network called a PON (Passive Optical Network) system.

  The PON system is a cost-effective system because an optical fiber transmission line and an intra-station device are shared by a plurality of users.

  FIG. 9 is a block diagram showing a configuration example of this PON system. In this example, the intra-station apparatus 201 and a plurality of user apparatuses 202 are connected via an optical fiber 203 and a power splitter 204.

  In order to be shared by a plurality of users, time division multiplexing technology is used for downlink communication from the intra-station device 201 to the user device 202, and time division multiple access technology is used for uplink communication from the user device 202 to the intra-station device 201. It has been. User multiplexing of up to 32 users is possible.

  The optical access service using the PON system has a large number of users and can provide a broadband service at a low cost. Therefore, the number of users is expected to increase further in the future, and is attracting attention as an infrastructure of a communication system.

  By the way, in an optical access system using an optical fiber transmission line such as a PON system, it is difficult to supply power to a user apparatus performed in a network using a conventional metallic cable. Therefore, in an emergency in which power supply from the AC power supply in the house is impossible, power supply to the user device 202 may be performed by an uninterruptible power supply (UPS).

  The backup by the uninterruptible power supply is currently limited to about 3 to 4 hours, and is not in a situation where it can sufficiently function as a lifeline in an emergency.

  In response to this problem in the optical access system, Patent Document 1 discloses a method of performing only a call using a small amount of power that can be supplied by optical power feeding. Specifically, in a downlink call, the photodiode is received in the no-bias mode, and the sound is reproduced by a high impedance speaker.

  For uplink communication, a voice-light intensity direct modulator is used, and a loop-back configuration is adopted in which the light transmitted from the in-station device is directly converted into a sound, that is, a light intensity change proportional to the sound pressure change and turned back. In this way, uplink communication is realized.

  However, with the method using Patent Document 1, user multiplexing cannot be realized in the currently used PON system. This is because current user devices that receive time-division multiplex connections and provide high-speed Internet connection services require 5 W to 10 W of power, whereas the power that can be optically fed is about 1 mW per user device. This is because the power is minute.

  In optical communication, methods for realizing user multiplexing generally include wavelength multiplexing, time division multiplexing, and frequency multiplexing.

  In any of these methods, it is necessary to realize user multiplexing using a passive device in order to enable uplink communication at the time of a power failure in the user's home. It is necessary to provide a passive device in the user apparatus or in a branch part.

  In the wavelength multiplexing system, 32 WDM filters having different transmission bands are required. A WDM filter is generally expensive, and if one user apparatus is provided, the user apparatus becomes expensive, so that it is not suitable for an optical access service that provides a service at a low cost.

  Similarly to the wavelength multiplexing method, the frequency multiplexing method requires 32 frequency filters each having a different transmission frequency. Although the frequency filter is inexpensive, the user apparatus requires an oscillator that oscillates a specific frequency and a system that controls each oscillation frequency, and power supply for these systems is required.

  In the time division multiplexing method, a system for controlling the oscillation of the upstream signal is required, and power supply for that is required.

  That is, in order to provide an optical access system that can be used at a power failure at a low cost, it is necessary to construct a system that does not use power in the user's home after using the frequency multiplexing system and the time division multiplexing system.

  In downlink communication, by using a passive device, even in the event of a power failure, it is possible to communicate by user multiplexing according to the above-described method, but as a multiplexing method that can adopt a passive device and use an inexpensive device, There is a frequency multiplexing method. In the case of the frequency multiplexing method, it is necessary to control the frequency of each user apparatus. This method is disclosed in Non-Patent Document 1, for example.

JP-A-11-154915 IEICE 2007 Society Conference B-8-12

  Thus, in the conventional system, there is a problem in the uplink signal multiplexing system, and it is not possible to provide an optical access system that can communicate during a power failure.

  The present invention has been made in view of such a problem, and an object thereof is to provide an optical access system capable of communication even during a power failure.

In the optical access system of the present invention, the intra-station device and the user device are connected via an optical transmission line and a power splitter, the downstream signal light is user-multiplexed by frequency multiplexing technology, and the upstream signal light is oscillated from the intra-station device. An optical access system that is modulated in a device and returned to an intra-station device, wherein a user apparatus inputs an upstream signal light and modulates the signal light by using an audio signal; and a downstream signal extraction means for extracting a carrier wave of light, enter the upstream signal light modulated by an audio signal from the audio modulator section, have rows modulated by using a carrier wave extracted by the extraction means with respect to the signal light, light and a modulating means for outputting to the transmission line, station apparatus receives an uplink signal light modulated by the carrier wave and the audio signal of the downstream signal light folded back from the user apparatus, the downstream signal light Demodulated based on the carrier wave, characterized in that it has a receiving means for separating a signal of each user device.

  According to the present invention, it is possible to provide an optical access system capable of making a call even if a user's home is out of power, for example.

Hereinafter, an optical access system according to an embodiment of the present invention will be described with reference to the drawings. This optical access system is, for example, a PON (Passive Optical
Network) system.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration example of an optical access system according to an embodiment of the present invention. In this optical access system, the intra-station device 11 and the N user devices 12-1 to 12-N (hereinafter simply referred to as the user device 12 when there is no need to distinguish them individually, the same applies to other cases). Are connected via an optical fiber 13 and a power splitter 14.

  This optical access system has a loopback configuration in which uplink signal light (unmodulated light) transmitted from the in-station device 11 is modulated according to the audio signal in the user device 12 and then returned to the in-station device 11 in uplink communication. It has been adopted. User multiplexing in downlink signals and uplink signals is realized by a frequency multiplexing method.

  In FIG. 1, the in-station device 11 includes a downstream signal oscillating unit 21, a modulating unit 22, N carrier wave oscillating units 23-1 to 23 -N corresponding to the respective user devices 12, an upstream signal oscillating unit 24, The signal receiving unit 25 includes a directional multiplexing / demultiplexing unit 26 that separates oscillation and reception of the upstream signal, and a multiplexing / demultiplexing unit 27 that demultiplexes the upstream signal and the downstream signal.

  The user apparatus 12-1 includes a downlink signal reception unit 31, a frequency selection unit 32, a demodulation unit 33, an audio reproduction unit 34, a carrier wave extraction unit 35, a carrier wave modulation unit 36, an audio modulation unit 37, and uplink and downlink of upstream signal light. A directional multiplexing / demultiplexing unit 38 for multiplexing / demultiplexing and a multiplexing / demultiplexing unit 39 for multiplexing / demultiplexing the upstream signal and the downstream signal are configured.

  The frequency selection unit 32 uses a predetermined carrier frequency assigned to the user device 12-1 (that is, a carrier frequency different from other user devices 12 connected to the same in-station device 11 (hereinafter referred to as a carrier frequency fcn). The carrier extraction unit 35 selects a carrier frequency excluding the audio signal band within the band of the carrier frequency fcn selected by the frequency selection unit 32.

  Since the user devices 12-2 (not shown) to 12-N have the same configuration as the user device 12-1, the illustration and description thereof are omitted. Note that the carrier frequency selected by the frequency selectors of the user devices 12-2 to 12-N is also referred to as a carrier frequency fcn.

  The power splitter 14 demultiplexes the downstream signal light or the upstream signal light transmitted from the intra-station device 11 to the optical fiber 13 to the optical fiber 13 to which each user device 12 is connected. The power splitter 14 also mixes the upstream signal light transmitted from each user device 12 and transmits it to the optical fiber 13.

(Downlink signal transmission)
The downlink signal transmission from the in-station apparatus 11 to each user apparatus 12 will be described. In the modulation unit 22 of the in-station device 11, the light oscillated by the downstream signal oscillating unit 21 is modulated by a signal having a maximum of N carrier frequencies, and is transmitted as a downstream signal light via the multiplexing / demultiplexing unit 27. It is sent out to the fiber 13. Downstream signal light transmitted to the optical fiber 13 reaches each user device 12 via the power splitter 14.

  The downlink signal light reaching each user apparatus 12 is received by the downlink signal receiving section 31 via the multiplexing / demultiplexing section 39 in each user apparatus 12, and is photoelectrically converted there.

  Of the downlink signal photoelectrically converted by the downlink signal receiving unit 31, only the downlink signal having the carrier frequency fcn assigned to the user device 12 is transmitted through the frequency selection unit 32 to the demodulation unit 33 and the carrier extraction unit 35. Entered. The downlink signal input to the demodulator 33 is then demodulated into an audio signal and output as audio via the audio reproduction unit 34.

  In this way, downlink signals that are user-multiplexed by the frequency multiplexing method are transmitted and received.

  The carrier extraction unit 35 to which the downlink signal having the carrier frequency fcn assigned to the user is input, the voice within the band of the carrier frequency fcn selected by the frequency selection unit 32 from the input downlink signal light. A carrier frequency component excluding the signal band is selected (extracted).

(Uplink signal transmission)
Next, uplink signal transmission from the user apparatus 12 toward the in-station apparatus 11 will be described. The light (unmodulated light) oscillated by the upstream signal oscillating unit 24 of the intra-station device 11 is transmitted as upstream signal light to the optical fiber 13 via the directional multiplexing / demultiplexing unit 26 and the multiplexing / demultiplexing unit 27, and is then supplied to the power splitter 14. Each user apparatus 12 is reached via

  The upstream signal light that has reached each user apparatus 12 is input to the audio modulation section 37 via the multiplexing / demultiplexing section 39 and the directional multiplexing / demultiplexing section 38 in each user apparatus 12.

  In the audio modulation unit 37, the audio signal is directly converted into an optical signal, and the upstream signal light subjected to the modulation of the audio signal is input to the carrier wave modulation unit 36. An optical microphone is one of devices that can directly convert an audio signal into an optical signal.

  The carrier modulation unit 36 uses the carrier frequency excluding the band of the audio signal within the band of the carrier frequency fcn extracted by the carrier extraction unit 35 as described above when receiving the downlink signal, and converts it to the upstream signal light at the optical stage. Apply modulation. In this way, by performing modulation using the carrier frequency fcn unique to the user apparatus 12, uplink signal light having a carrier component specific to the user apparatus 12 is generated.

  The carrier wave modulation unit 36 can be constituted by a modulator having an electro-optic effect, which is made of, for example, lithium niobate (LiNb03).

  The upstream signal light modulated by the carrier modulation unit 36 is transmitted to the optical fiber 13 via the directional multiplexing / demultiplexing unit 38 and the multiplexing / demultiplexing unit 39, and reaches the intra-station apparatus 11 via the power splitter 14.

  The upstream signal light reaching the in-station device 11 is input to the upstream signal receiving unit 25 via the multiplexing / demultiplexing unit 27 and the directional multiplexing / demultiplexing unit 26, and is subjected to photoelectric conversion. Since the uplink signal has a carrier component specific to the user apparatus 12, the uplink signal is separated into signals for each user apparatus 12 by demodulating based on the carrier component.

  In this way, transmission / reception of an uplink signal that is user-multiplexed by the frequency multiplexing method is realized.

  As described above, the intra-station device 11 employs a loopback configuration in which the unmodulated uplink signal is transmitted to the user device 12, and the user device 12 modulates the uplink signal with the audio signal and returns to the intra-station device 11, Since the loopback configuration is mainly constructed using passive devices, an upstream signal can be transmitted even during a power failure.

  Further, the intra-station device 11 transmits a downlink signal that has been user-multiplexed by the frequency multiplexing method to the user device 12, and the user device 12 receives the downlink signal that has been transmitted using a passive device, and the user receives the downlink signal from the downlink signal. Since the carrier wave assigned to the device 12 is extracted, and the uplink signal is further modulated by the carrier frequency component and turned back to the in-station device 11, the user device 12 is provided with an oscillator that oscillates a specific frequency or individual Even if a system for controlling the oscillation frequency is not provided, it is possible to perform user multiplexing of uplink signals by frequency multiplexing. As a result, it is possible to provide an inexpensive optical access system that can be used in the event of a power failure (for example, an optical access system that can make a call even if a user's home loses power).

  In the above description, the carrier modulation unit 36, the audio modulation unit 37, and the directional multiplexing / demultiplexing unit 38 of the user apparatus 12 are configured separately. Can be configured with devices.

  FIG. 2 is a diagram illustrating a configuration example of a reflective modulator used in place of the carrier wave modulation unit 36, the audio modulation unit 37, and the directional multiplexing / demultiplexing unit 38. This modulator has the same configuration as an LN (LiNb03) MZ (Mach-Zehnder Interferometer) type modulator.

  It terminates at the pair of optical waveguides 51 and 52 and is folded back to the Y-branch optical waveguide 53. At the end of the optical waveguide 51, there is provided a diaphragm 54 in which the reflecting mirror vibrates with sound. The light reflected by the diaphragm 54 becomes an optical signal whose phase changes according to sound (sound pressure). On the other hand, the end of the optical waveguide 52 on the opposite side is fixed by a reflecting mirror 55, and light of a certain phase is reflected (the path is common, and the phases of the incident wave and the reflected wave are reversed) )

  Accordingly, the phase change occurs in the optical waveguide 51 on the diaphragm 54 side, and the optical waveguide 52 on the fixed end side is multiplexed in a state where there is no phase change, similarly to intensity modulation using the electro-optic effect. The light whose intensity is modulated by the sound (sound pressure) is output.

  In the above description, the wiring from the frequency selection unit 32 is divided into the carrier extraction unit 35 and the demodulation unit 33. However, since a modulator having an electro-optic effect generally requires almost no current, the carrier extraction unit 35 By taking the high impedance side, modulation to the upstream signal is possible without loss of downstream signals.

[Second Embodiment]
FIG. 3 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention. In this optical access system, an intra-station apparatus 101 and N user apparatuses 102 are connected via an optical fiber 13 and a power splitter 14.

  In this optical access system, as in the case of the example of FIG. 1 (that is, the first embodiment), in the upstream communication, the upstream signal light transmitted from the in-station device 101 is received by the user device 102 in accordance with the audio signal. A loop-back configuration is used in which the signal is modulated and returned to the intra-station apparatus 101. On the other hand, the user multiplexing of the uplink signal is realized by the time division multiplexing method unlike the case of the first embodiment.

  In FIG. 3, the intra-station apparatus 101 includes a downlink signal oscillating unit 111, a modulating unit 112, N carrier wave oscillating units 113-1 to 113-N, an upstream signal oscillating unit 114, an upstream signal receiving unit 115, an upstream signal receiver It comprises a directional multiplexing / demultiplexing unit 116 that separates oscillation and reception, a multiplexing / demultiplexing unit 117 that demultiplexes upstream and downstream signals, and a transmission timing adjustment unit 118. The transmission timing adjusting unit 118 is connected to the upstream signal oscillating unit 114 and the upstream signal receiving unit 115.

  The user apparatus 102-1 includes a downlink signal reception unit 121, a frequency selection unit 122, a demodulation unit 123, an audio reproduction unit 124, an audio modulation unit 125, and a directional multiplexing / demultiplexing unit that multiplexes and demultiplexes upstream and downstream of upstream signal light. 126, and a multiplexing / demultiplexing unit 127 for multiplexing / demultiplexing the upstream signal and the downstream signal. That is, functions corresponding to the frequency selection unit 32 and the carrier wave extraction unit 35 of the user device 12 illustrated in FIG. 1 are excluded from the user device 102-1.

  Since the user devices 102-2 (not shown) to 102-N basically have the same configuration as the user device 102-1, the illustration and description thereof are omitted.

(Downlink signal transmission)
Downlink signal transmission from the in-station apparatus 101 to the user apparatus 102 is basically the same as the example of FIG. 1 (first embodiment), the downlink signal oscillation unit 111 to the carrier wave oscillation unit 113 of the in-station apparatus 101, and Since it is performed based on the downlink signal reception unit 121 to the audio modulation unit 125 of the user apparatus 102, the description thereof is omitted.

(Uplink signal transmission)
The uplink signal transmission from the user apparatus 102 to the intra-station apparatus 101 will be described. As for the upstream signal light, the directional multiplexing / demultiplexing unit 116 and the multiplexing / demultiplexing unit 117 are generated by the upstream signal light generated by the upstream signal oscillating unit 114 at the timing according to the control of the transmission timing adjusting unit 118 in the in-station apparatus 101. And sent to the optical fiber 13. The upstream signal light (unmodulated signal light) transmitted to the optical fiber 13 reaches each user apparatus 102 via the power splitter 14.

  FIG. 4 is a diagram schematically showing the upstream signal light transmitted from the intra-station apparatus 101. Thus, the upstream signal light is transmitted as a pulse signal with a predetermined time interval (that is, transmission interval Ts). The transmission interval Ts is determined by the distance between the intra-station device 101 and the user device 102 that is farthest away.

  The upstream signal light that has reached the user apparatus 102 is input to the audio modulation section 125 via the multiplexing / demultiplexing section 127 and the directional multiplexing / demultiplexing section 126 of the user apparatus 102.

  In the audio modulation unit 125, the input upstream signal light is modulated with the audio signal, and is transmitted to the optical fiber 13 through the directional multiplexing / demultiplexing unit 126 and the multiplexing / demultiplexing unit 127, and is transmitted through the power splitter 14 in the station. The device 101 is reached.

  The uplink signal light that has reached the intra-station device 101 is input to the uplink signal receiving unit 115 via the multiplexing / demultiplexing unit 117 and the directional multiplexing / demultiplexing unit 116, subjected to photoelectric conversion, and is controlled by the transmission timing adjusting unit 118. Pulse signals are collected at different timings.

  FIG. 5 is a diagram schematically showing an uplink signal received by the intra-station apparatus 101. As shown in FIG. Thus, the uplink signal from a certain user apparatus 102 (in this example, user apparatuses 102-1 and 102-N) is shifted at a constant interval (time Td in the example of FIG. 5) with a certain interval (in FIG. 5). In the example, it is received at the transmission interval Ts).

  That is, when the distance between the user apparatuses 102-1 to 102-N and the intra-station apparatus 101 is long in the order from the smallest branch number, the first uplink signal S102- from the user apparatus 102-1 When the time at which 1-1 is received is used as a reference, the first uplink signal S102-2-1 from the user apparatus 102-2 arrives at the in-station apparatus 101 with a delay of time Td2 from that time. The time Td2 is a time corresponding to the difference in distance between the user apparatuses 102-1 and 102-2 and the intra-station apparatus 101. Similarly, the first uplink signal S102-N-1 from the user apparatus 102-N arrives at the intra-station apparatus 101 with a delay of time TdN from the reference time. The time TdN is also a time corresponding to a difference in distance between the user apparatuses 102-1 and 102-N and the intra-station apparatus 101. Since unmodulated signal light is transmitted from the intra-station device 101 at intervals of time Ts, when signals are collected every time Ts from the first uplink signal from each user device 102, each user device 102 PAM (Pulse Amplitude Modulation) can be obtained.

  In FIG. 5, an uplink signal from the user apparatus 102-1 and a part of the pulse signal from the user apparatus 102-N are indicated by arrows. Further, a signal obtained as a result of collecting uplink signals from the user apparatus 102-N is also schematically shown.

  That is, the upstream signals can be separated into signals for each user apparatus 102 by collecting and demodulating received signals at regular intervals while shifting the timing. The timing for collecting the signals is controlled by the transmission timing adjustment unit 118. By taking a comprehensive line of the PAM-modulated signal, a transmitted voice signal can be obtained (restored).

[Third Embodiment]
FIG. 6 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention. In this optical access system, an intra-station device 151 is provided instead of the intra-station device 101 of FIG.

  The in-station device 151 is provided with M sets of the uplink signal oscillating unit 114, the uplink signal receiving unit 115, and the directional multiplexing / demultiplexing unit 116 of the in-station device 101 shown in FIG. The upstream signal oscillators 114-1 to 114-M oscillate light having different wavelengths λ. Further, a multiplexing / demultiplexing unit 161 is provided between the directional multiplexing / demultiplexing unit 116 and the multiplexing / demultiplexing unit 117. The other parts are the same as in FIG.

  The maximum service length of the optical access system is usually 20 km, and the minimum service length is 0 distance. It takes about 100 nsec for the light to travel by 20 km. For example, in the case of the example of FIG. 3 (ie, the second embodiment), since the loopback configuration is adopted, the uplink signal is transmitted from the in-station apparatus 101, returned by the user apparatus 102, and returned to the in-station apparatus 101. Takes up to about 200 nsec. That is, when a service is provided for all distances from 0 to 20 km using the second embodiment, the uplink signal transmission interval Ts is 200 nsec. Since the received signal is PAM modulated, the sampling rate of the signal at this time is 1/200 nsec = 5 kSPS.

  Since a voice signal used in a telephone is generally from 300 Hz to 3.4 kHz, a necessary sampling rate is 6.8 kSPS. That is, in the second embodiment, services cannot be provided over the entire area.

  Therefore, in the example of FIG. 6 (that is, the third embodiment), the sampling rate of the PAM modulation signal is increased by transmitting pulse signals of a plurality of wavelengths as upstream signals, and the service can be applied over the entire region. It is.

  FIG. 7 is a diagram schematically showing the upstream signal light transmitted from the intra-station device 151. In FIG. 7, M = 2, two signals of wavelength λ1 (the optical signal oscillated by the upstream signal oscillating unit 114-1), and signal of wavelength λ2 (the light oscillated by the upstream signal oscillating unit 114-2). Signal) is transmitted at the transmission interval Ts. The signal of wavelength λ2 is delayed (shifted) by the time Tdd of {(nth (= 2) th wavelength-1) / M (= 1/2) × transmission interval Ts} from the transmission of the signal of wavelength λ1. Sent).

  FIG. 8 is a diagram schematically showing an uplink signal received by the intra-station device 151. Thus, the uplink signal from a certain user apparatus 102 (in this example, the user apparatus 102-N) is received at regular intervals. Then, for the received uplink signal, the uplink signal can be separated into signals for each user apparatus 102 by collecting signals corresponding to the transmission interval Ts and transmission timing for each wavelength λ. By taking a comprehensive line of the collected signals, a transmitted voice signal can be obtained (restored).

  By configuring the upstream signal with signals of M wavelengths λ in this way, the sampling rate can be increased M times. For example, when two wavelengths λ are used, the obtained sampling rate is 10 KSPS, and a sampling rate sufficient for propagation of a voice signal in a telephone can be obtained.

It is a block diagram which shows the structural example of the optical access system which concerns on embodiment of this invention. FIG. 2 is a diagram illustrating a configuration example of a reflective modulator used in place of the carrier wave modulation unit, the audio modulation unit, and the directional multiplexing / demultiplexing unit in FIG. 1. It is a block diagram which shows the other structural example of the optical access system which concerns on embodiment of this invention. It is the figure which showed typically the upstream signal light transmitted from the in-station apparatus shown in FIG. It is the figure which showed typically the upstream signal received by the intra-station apparatus shown in FIG. It is a block diagram which shows the other structural example of the optical access system which concerns on embodiment of this invention. It is the figure which showed typically the upstream signal light transmitted from the in-station apparatus shown in FIG. It is the figure which showed typically the upstream signal received by the intra-station apparatus shown in FIG. It is a figure which shows the structural example of a PON system.

Explanation of symbols

  11 Intra-station equipment, 12 User equipment, 13 Optical fiber, 14 Power splitter, 21 Downstream signal oscillator, 22 Modulator, 23 Carrier oscillator, 24 Upstream signal oscillator, 25 Upstream signal receiver, 26 Directional multiplexing / demultiplexing section , 27 multiplexing / demultiplexing unit, 31 downlink signal receiving unit, 32 frequency selecting unit, 33 demodulating unit, 34 audio reproducing unit, 35 carrier extracting unit, 36 carrier modulating unit, 37 audio modulating unit, 38 directional multiplexing / demultiplexing unit, 39 multiplexer / demultiplexer, 51 optical waveguide, 52 optical waveguide, 53 Y-branch optical waveguide, 54 diaphragm, 55 reflector, 101 in-station device, 102 user device, 114 upstream signal oscillator, 115 upstream signal receiver, 116 directivity Multiplexing / demultiplexing unit, 117 multiplexing / demultiplexing unit, 118 transmission timing adjustment unit, 125 voice modulation , 126 Directional multiplexing / demultiplexing unit, 127 Combined / demultiplexed unit, 161 Combined / demultiplexed unit

Claims (1)

The intra-station device and the user device are connected via an optical transmission line and a power splitter, the downstream signal light is user-multiplexed by frequency multiplexing technology, and the upstream signal light is oscillated from the intra-station device and modulated in the user device. In the optical access system folded back to the in-station device,
The user device is
An audio modulation unit that inputs the upstream signal light and modulates the signal light using an audio signal;
Extraction means for extracting the carrier wave of the downstream signal light ;
Enter the upstream signal light modulated by the audio signal from the audio modulator section, have rows modulated by using a carrier wave extracted by the extracting means relative to the signal light, and outputs to the optical transmission line modulation means And
The intra-station device is
The upstream signal light modulated by the downlink signal light carrier and the audio signal that has been returned from the user apparatus is received, demodulated based on the downstream signal light carrier, and separated into signals for each user apparatus. An optical access system comprising a receiving means.

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