JP4924900B2 - PON optical communication system using optical code division multiple access - Google Patents

Description

  The present invention relates to a PON (Passive Optical Network) optical communication system using optical code division multiple access (optical CDMA).

  Between an optical subscriber line station side device (Optical Line Terminal: hereinafter referred to as “station side device OLT”) and a plurality of optical subscriber line termination devices (Optical Network Unit: hereinafter referred to as “home side device ONU”), There is an optical communication system that performs two-way communication via an optical fiber communication network.

  In this optical communication system, an optical fiber communication network having a single star configuration in which each of the station side device OLT and each home side device ONU is radially connected by a single optical fiber has been put into practical use. In this network configuration, the configuration of the system and communication equipment becomes simple, but one home-side device ONU occupies one optical fiber, and this optical fiber is directly connected to the station-side device OLT by wiring. Must. Therefore, if the home-side apparatus ONU has N stations, N optical fibers that are directly connected from the station-side apparatus OLT are required, and it is difficult to reduce the price of the optical communication system.

  On the other hand, a PON (Passive Optical Network) system has been put to practical use as an optical communication system in which one optical fiber connected by wiring from the station side device OLT is shared by a plurality of home side devices ONU. This PON system is one of low-cost access methods for optical subscribers applied to FTTx such as FTTH (Fiber To The Home) and FTTB (Fiber To The Building).

  In this PON system, a passive optical branching device (hereinafter also simply referred to as “optical splitter”) that branches and multiplexes a signal that is passively input without requiring external power supply, and a station side device OLT. Are connected via an optical fiber such as a single mode fiber having a single propagation mode.

  In one optical communication system, there are usually a plurality of home-side devices ONU, and optical fibers branched by an optical splitter are provided in accordance with the number of home-side devices ONU.

  The station-side apparatus OLT and the N-station home-side apparatus ONU are based on 1-to-N transmission connected via an optical fiber and an optical splitter. Thereby, many home side apparatuses ONU can be allocated with respect to one station side apparatus OLT, and the whole installation cost can be held down.

  In such a PON system, since the N-side home device ONU shares one station-side device OLT, data transmission is performed so that signals do not collide by time division multiplexing from the home-side device ONU to the station-side device OLT. Do. Since the home apparatus ONU transmits data by transmitting optical signals only during the period allocated by the station apparatus OLT, the station apparatus OLT receives intermittent signals (a number of signals) from the N station home apparatus ONU. A group of signals including 0 and 1 (referred to as an optical burst signal) is transmitted.

  By the way, an optical communication system is known in which a light source is not provided in the home device ONU by supplying light from the station device OLT through an optical fiber as a light source of the home device ONU (see Patent Document 1 below). ).

  In addition, there is a desire to further improve upstream signal traffic in a PON system or the like.

Therefore, it has been proposed to apply optical code division multiple access (optical CDMA) in a PON system or the like (see Patent Document 1 below). If this optical CDMA system is used, an upstream optical signal output from each home-side apparatus ONU is encoded using a spreading code, so that an optical transmission line such as an optical fiber can be transmitted at a plurality of times with the same wavelength at the same time. Can be shared by optical signals. Therefore, it is possible to superimpose an upstream optical signal from another home-side apparatus ONU on the slot assigned to the home-side apparatus ONU.
JP 2003-298533 A

  However, the configuration described in Patent Document 1 requires a downstream optical fiber line from the station-side apparatus OLT to the home-side apparatus ONU and an upstream optical fiber line from the home-side apparatus ONU to the station-side apparatus OLT. For this reason, a PON optical communication system capable of reducing the number of optical fiber cores is desired.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a PON optical communication system using optical code division multiple access, which can reduce the number of optical fiber cores by sharing upstream and downstream optical fiber lines.

According to the optical communication system of the present invention, the station side device combines a light source that emits light of a plurality of (n) wavelengths and the light of the plurality of (n) wavelengths and transmits the combined light. And an optical multiplexing / demultiplexing unit that demultiplexes light of a plurality (n) of wavelengths received from the apparatus.
The home side device is configured to demultiplex a plurality of (n) wavelengths of light transmitted from the station side device for each wavelength, and to each light demultiplexed by the light demultiplexing unit. An optical delay / encoding unit that optically encodes the optical delay and an optical multiplexing unit that combines the lights output from the optical delay / encoding unit, The combined light is sent to the station side device through the optical signal line, and the station side device receives the light of the home side device for each light demultiplexed by the optical multiplexing / demultiplexing unit. An optical reverse delay unit that applies a delay opposite to the delay applied by the delay / encoding unit is provided.

  According to this configuration, the station-side device obtains a multi-wavelength optical signal that is optically delayed and encoded by the home-side device through a single-core optical signal line, and applies a reverse delay to the multi-wavelength optical signal for decoding. Thus, information on the home device can be obtained.

FBG can be used for one or both of the optical delay element of the optical delay / encoding unit and the optical delay element of the optical reverse delay unit.

  Also, according to the optical communication system of the present invention, it is possible to perform encoding using light of a single wavelength. That is, to the station side device, a light source that emits light of a single wavelength, an optical multiplexing unit that transmits the light of the single wavelength and takes out the light received from the home side device, and the light for time An optical switching unit that separates optically, and the home-side device demultiplexes the light of a single wavelength transmitted from the station-side device, and the optical demultiplexing unit demultiplexes the light. A time delay is provided to each of the light, an optical delay / encoding unit that optically encodes, and an optical multiplexing unit that combines the lights output from the optical delay / encoding unit, The light combined by the optical multiplexing unit is to be sent to the station side device through the optical signal line, the station side device, for each light temporally separated by the optical switching unit, An optical reverse delay unit that applies a delay opposite to the delay applied by the optical delay / encoding unit of the home-side apparatus;

  Even with this configuration, the station-side device obtains the multi-wavelength optical signal encoded by the home-side device through a single optical signal line, and decodes the multi-wavelength optical signal to obtain information on the home-side device. Obtainable.

  As described above, according to the present invention, it is possible to improve the uplink communication quality of the conventional PON system and improve the bit error rate (BER) characteristics and the multiplicity. In addition, cost reduction per line is an indispensable condition for the PON system, but by installing an upstream data line as an optical CDMA system, a high-cost and complex multi-wavelength ultrashort pulse light source must be installed only in the station side device OLT. Can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  <Embodiment 1>

  FIG. 1 shows a configuration of an optical CDMA-PON optical communication system (hereinafter referred to as “optical communication system”) in which a station side device OLT and a plurality of home side devices ONU (ONU1, ONU2,...) Are connected by optical fibers. FIG.

  The optical communication system includes a station side device OLT provided in a control station side station building, a home side device ONU provided in each of a plurality of subscriber homes, and a station side device OLT and each home side device ONU via an optical splitter 5. And an optical fiber 4 connected between the two.

  The home-side device ONU is a device for enjoying the optical network service, and is installed in the subscriber's home. The home device ONU is connected to a terminal device such as a personal computer via a broadband router.

  The optical splitter 5 does not require any external power supply, and passively branches or multiplexes signals input from the optical fiber 4 connected to one side to the optical fiber 4 connected to the other side. It is formed by a star coupler that outputs. Thereby, many home side apparatuses ONU can be allocated with respect to one station side apparatus OLT, and the whole installation cost can be held down.

  This optical communication system including the station side device OLT and the home side device ONU is, for example, GE-PON (Gigabit Ethernet-Passive Optical) which incorporates Gigabit Ethernet (Ethernet is a registered trademark) technology and realizes high-speed access section communication. Network) system. According to this GE-PON system, uplink communication is performed in units of variable length frames from the home device ONU to the station device OLT. A signal obtained by converting this frame into an optical signal is referred to as an “optical burst signal”.

  The station side device OLT includes an optical CDMA light source 11 that irradiates a plurality of (n) wavelengths of light λ1 to λn, an upper layer circuit 12 for controlling communication contents with the home side device ONU, and an upper layer circuit 12. An electrical / optical converter (E / O) 13 that converts the downstream electrical signal into an optical signal with wavelength λd, combines the light with wavelengths λ1 to λn and the light with wavelength λd, and sends them to the optical fiber 4. , A wavelength division multiplexing (WDM) 14 that separates optical signals from wavelengths λ1 to λn received from the home-side apparatus ONU for each wavelength, an optical amplifier 15 that amplifies each separated upstream optical signal, and each upstream An optical demultiplexer 16 that demultiplexes an optical signal and distributes the optical signal to the optical reverse delay / CDMA decoder 17 and an optical / electrical device that converts the optical signal output from the optical reverse delay / CDMA decoder 17 into an electrical signal. A converter (O / E) 18 is provided. The optical amplifier 15 may be omitted.

  The optical reverse delay / CDMA decoder 17 is provided corresponding to the number m of the home-side apparatuses ONUs, and these are referred to as decoders DEC1 to DECm. Each decoder DEC is composed of an optical device such as a fiber black grating (FBG) or an ADE wave guide grating (AWG), and details thereof will be described later.

  FIG. 2 is a diagram showing a specific configuration of the optical CDMA light source 11 installed in the station side apparatus OLT. The optical CDMA light source 11 includes n laser diodes (LD1 to LDn) for irradiating light of wavelengths λ1 to λn, an optical multiplexer 11a, and an external modulator (EA) for inputting a control signal (short pulse). ) 11b. This optical CDMA light source 11 condenses laser diodes (LD1 to LDn) for irradiating light of wavelengths λ1 to λn into one by an optical multiplexer 11a, and outputs light at a predetermined timing by an external modulator (EA) 11b. Waveform shaping by passing the signal. The laser diode LD is constituted by, for example, a mode-locked laser diode (MLLD). The external modulator 11b is configured by a modulator using an optical crystal such as LiNbO3 (lithium niobate).

  Returning to FIG. 1, the home-side apparatus ONU includes a wavelength separation unit 21 that separates light of wavelengths λ1, λ2,... Λn and light of wavelength λd transmitted from the station-side apparatus OLT, and separated light of wavelength λd. An optical / electrical converter (O / E) 22 that converts a signal into an electrical signal, an upper layer circuit 23 for controlling communication contents with a home-side apparatus ONU, and light of wavelengths λ1, λ2,. The optical delay and CDMA encoding unit 24 applies time delay and performs encoding, and an optical multiplexer 25 that combines the encoded optical signals with time delay.

  Hereinafter, a signal transmission / reception procedure in the downlink direction and the uplink direction of signals between the home-side apparatus ONU and the station-side apparatus OLT will be briefly described.

  In the station-side apparatus OLT that has received a signal from the Internet network, a predetermined bridge process is performed in order to specify a logical link to be relayed. At this time, the station side device OLT adds information such as a synchronization bit part including a logical link identifier and a GE-PON header to the frame signal, and converts it into an optical signal of wavelength λd by the electrical / optical converter 13, The data is sent to the wavelength multiplexing unit 14. This downstream optical signal is an optical continuous signal that is transmitted through the optical fiber 4 to all home-side apparatuses ONU in the same way as broadcast, and is not interrupted.

  On the other hand, the signals from the wavelengths λ1 to λn of the optical CDMA light source 11 of the station side device OLT are modulated with a single pulse, and then superposed together with the optical signal of the wavelength λd by the wavelength multiplexing unit 14, and are transmitted to each home side device ONU. Sent.

  The optical signal sent to the optical fiber 4 is branched by the optical splitter 5 and sent to each home-side apparatus ONU via the optical fiber 4 of each branch line.

  In the home-side apparatus ONU, the wavelength-multiplexed light is separated into light of wavelength λd and light of wavelengths λ1 to λn by the wavelength separation unit 21. The light of wavelength λd is supplied to an upper layer circuit 23 through an optical / electrical converter (O / E) 22, is signal-processed, and is transmitted to a terminal device such as a personal computer via a broadband router.

  In the home apparatus ONU, the wavelengths λ1, λ2,... Λn transmitted from the station apparatus OLT are separated by the wavelength demultiplexing unit 21, and the optical delay / CDMA code is separated from the separated wavelengths. In accordance with a command from the higher layer circuit 23, the conversion unit 24 performs optical code division multiple access (optical CDMA) encoding to generate an optical burst signal, and transmits the optical burst signal to the station side apparatus OLT via the optical fiber 4. .

  Since the optical burst signal is multiplexed and transmitted on the optical fiber 4 via the optical splitter 5, the optical signal received by the station side device OLT is the optical burst signal from the plurality of home side devices ONU. Contains.

  Conventionally, these optical burst signals are controlled to be transmitted in time division so as not to compete with each other in time. In this control, when data is transmitted from the station-side device OLT to each home-side device ONU, a period slot during which an upstream optical signal may be transmitted is allocated to each home-side device ONU and is notified as a control frame. Is done. Therefore, in the same optical communication system, the upstream optical signal transmitted from each home-side apparatus ONU can avoid contention.

  However, in the present invention, as described later, the upstream optical signal is encoded by the optical delay / CDMA encoding unit 24. Therefore, even if optical signals from different home-side apparatuses ONU compete in time, It is characterized in that it can be separated and taken out by the side device OLT.

  In the station-side apparatus OLT, the received light of wavelengths λ1, λ2,... Λn is separated by the wavelength multiplexing unit 14, and the light of each separated wavelength is decoded by the optical reverse delay / CDMA decoding unit 17, The signal is converted into an electric signal, and the signal is passed to the upper layer circuit 12.

  In this way, mutual communication between the home-side apparatus ONU and the station-side apparatus OLT is performed.

  FIG. 3 is a block diagram illustrating a configuration example of the optical delay / CDMA encoding unit 24 provided in the home-side apparatus ONU. Hereinafter, for the sake of simplicity, the description will be made assuming that the number “n” of the wavelengths λ1, λ2,... Λn is 4, but the number is not limited to this in the practice of the invention.

  The optical delay / CDMA encoding unit 24 includes an optical circulator CR disposed in the transmission path of each optical signal having wavelengths λ1, λ2, λ3, and λ4 separated by the wavelength separation unit 21, and a time for each optical signal. FBGs 1 to 4 for applying a general delay are provided. An FBG is called an optical fiber Bragg grating, and forms a diffraction grating having a periodic refractive index change in the core of an optical fiber, and serves as an optical reflector that Bragg reflects only light of a specific wavelength. This is an optical element having a function. The wavelength of light that causes reflection is determined by the period of the diffraction grating and the refractive index of the optical fiber.

  In the case of this embodiment, the arrangement of the diffraction gratings in each of the FBGs 1 to 4 is the wavelengths λ1, λ2, λ3, and λ4 from the side closer to the optical circulator CR. This arrangement is unique to the home-side apparatus ONU1, and is different from the arrangement of the other home-side apparatuses ONU2, 3, and 4 (described later).

  Since the diffraction gratings in each of the FBGs 1 to 4 are arranged in the order of the wavelengths λ1, λ2, λ3, and λ4, the delay times of the wavelengths λ2, λ3, and λ4 are two times and three times that of the wavelength λ1, respectively. 4 times.

  Further, the optical delay / CDMA encoding unit 24 includes an intensity modulator 26 for performing intensity modulation of optical intensity “0” or “1” on each optical signal. The states of these intensity modulators 26 are given based on commands from the upper layer circuit 23.

  As described above, the FBG and the intensity modulator 26 can perform spread coding of an optical signal in both time and intensity regions for each optical signal.

  The spread-encoded optical signal is multiplexed by the optical multiplexer 25 and transmitted to the station side device OLT.

  FIG. 4 is a block diagram showing the operation of the optical reverse delay / CDMA decoder 17 in the decoder DEC1 corresponding to the home apparatus ONU1 in the station apparatus OLT (illustration of the optical amplifier 15 and the optical demultiplexer 16). Is omitted).

  The decoder DEC1 includes an optical circulator CR arranged in the transmission path of each optical signal having the wavelengths λ1, λ2,... Λ4 separated by the wavelength multiplexing unit 14, and FBG5 for multiplying each optical signal by a time delay. 8 is provided. The decoder DEC1 includes an optical multiplexer 17a that combines the optical signals that have passed through the optical circulators CR into one. The optical signal passing through the optical multiplexer 17a is separated by a filter and decoded. The optical multiplexer 17a is not necessarily essential, and the optical multiplexer 17a may be omitted and each optical signal that has passed through each optical circulator CR may be decoded as it is.

  The arrangement of the diffraction gratings in each of the FBGs 5 to 8 has wavelengths λ4, λ3, λ2, and λ1 from the side closer to the optical circulator CR. Therefore, the delay times of the wavelengths λ3, λ2, and λ1 are twice, three times, and four times the delay time of the wavelength λ4, respectively.

  The arrangement of the diffraction gratings of the FBGs 5 to 8 is opposite to the arrangement of the diffraction gratings in the FBGs 1 to 4 of the home-side apparatus ONU1 shown in FIG. 3, and the light of each wavelength delayed by the home-side apparatus ONU1. Can give delays in reverse order. Thereby, at the output of the optical multiplexer 17a of the station side apparatus OLT, it is possible to obtain a single optical signal waveform in which optical signals of respective wavelengths are temporally superimposed.

  FIG. 5 is a block diagram illustrating a configuration example of the optical delay / CDMA encoding unit 24 of the home-side apparatus ONU2. The optical delay / CDMA encoding unit 24 includes an optical circulator CR disposed in the transmission path of each optical signal having wavelengths λ1, λ2,. FBGs 1 to 4 for applying a significant delay.

  In the case of this embodiment, the way of arranging the diffraction gratings in each of the FBGs 1 to 4 is different from the case of FIG. That is, the wavelengths λ4, λ1, λ2, and λ3 from the side closer to the optical circulator CR.

  The optical delay / CDMA encoding unit 24 includes an intensity modulator 26 for performing on / off intensity modulation of the optical intensity “0” or “1” for each optical signal. The states of these intensity modulators 26 are given based on commands from the upper layer circuit 23.

  As described above, the FBG and the intensity modulator 26 can perform spread coding of an optical signal in both time and wavelength regions for each optical signal.

  The spread-encoded optical signal is multiplexed by the optical multiplexer 25 and transmitted to the station side device OLT.

  FIG. 6 is a block diagram showing the operation of the decoder 2 of the optical reverse delay / CDMA decoding unit 17 corresponding to the home-side apparatus ONU2 of the station-side apparatus OLT.

  The decoder 2 includes an optical circulator CR disposed in the transmission path of each optical signal having wavelengths λ1, λ2, λ3, and λ4 separated by the wavelength separation unit 14, and an FBG 5 that applies a time delay to each optical signal. To 8 and an optical multiplexer 17a that combines the optical signals that have passed through these optical circulators CR into one.

  The arrangement of the diffraction gratings in each of the FBGs 5 to 8 is the wavelength λ3, λ2, λ1, λ4 from the side closer to the optical circulator CR.

  The arrangement of the diffraction gratings of the FBG is opposite to the arrangement of the diffraction gratings of the FBGs 1 to 4 of the home-side apparatus ONU2 shown in FIG. 5 and is reverse to the light of each wavelength delayed by the home-side apparatus ONU. Delays can be given in order. Thereby, at the output of the optical multiplexer of the station side apparatus OLT, it is possible to obtain a single optical signal waveform in which optical signals of respective wavelengths are temporally superimposed.

  The waveform of each part of the optical signal of the optical communication system described above will be described using a timing chart. In each timing chart, the horizontal axis represents time t, and the vertical axis represents light intensity.

  First, FIG. 7A shows light source light emitted from the optical CDMA light source 11 installed in the station side apparatus OLT. The light source light passes through an external modulator (EA) at a predetermined timing and is waveform-shaped. The waveform shaped waveform (a) is shown in FIG. 7B.

  8 shows the output waveforms (b1) to (b4) of the wavelength demultiplexing unit 21 and the output waveforms (c1) to (c1) of the optical encoding unit 24 corresponding to FIG. 6 is a timing chart showing c4) and an output waveform (d) of the optical multiplexer 25. The arrangement of the diffraction gratings in each of the FBGs 1 to 4 of the optical encoding unit 24 is the wavelength λ1, λ2, λ3, λ4 from the side closer to the optical circulator CR, so the delay of the waveform (c1) of the wavelength λ1 is one. The delay becomes larger as the waveforms (c2) to (c4) of the wavelengths λ2, λ3, and λ4 are the smallest. Therefore, the output waveform (d) of the optical multiplexer 25 is in the order of wavelengths λ1, λ2, λ3, λ4 in terms of time.

  8 shows the output waveforms (b1) to (b4) of the wavelength demultiplexing unit 21 and the output waveforms (c1) to (c1) of the optical encoding unit 24 corresponding to FIG. 6 is a timing chart showing c4) and an output waveform (d) of the optical multiplexer 25. The arrangement of the diffraction gratings in each of the FBGs 1 to 4 is the wavelength λ4, λ1, λ2, λ3 from the side closer to the optical circulator CR. Therefore, the delay of the wavelength λ4 is the smallest, and the wavelengths λ1, λ2, λ3 The delay is large. Therefore, the output waveform (d) of the optical multiplexer 25 is in the order of wavelengths λ4, λ1, λ2, and λ3 in terms of time.

  Here, the input times of the waveforms (b1) to (b4) passing through the wavelength separation unit 21 of the home side apparatus ONU1 and the input times of the waveforms (b1) to (b4) passing through the wavelength separation unit 21 of the home side apparatus ONU2 Is shifted in time. The reason why the time is shifted in this way is that the light propagation time from the master station side device OLT to each home side device ONU differs depending on the length of the optical fiber after passing through the optical splitter 5. Although the time lag is shifted by a time corresponding to the smallest delay time of FGB, this is not particularly meaningful.

  FIG. 9 (e) shows optical signals output from the respective home devices ONU 1 and ONU 2 and combined by the optical splitter 5. As shown in the figure, the optical burst signals output from the home devices ONU1 and ONU2 are partially overlapped. The combined optical signal is input to the station side device OLT.

  Waveforms (g1) to (g4) in FIG. 9 (DEC1) indicate optical signals of respective wavelengths to which time delays are given by the FBGs 5 to 8 of the decoder 1 of the station side apparatus OLT. An optical signal of wavelength λ1 is shown in (g1) to an optical signal of wavelength λ4 in (g4). As a result of the delay, the optical signals of the four wavelengths are aligned at the same time. An optical signal obtained by combining the optical signals of these wavelengths by the optical multiplexer 17a is shown in (h). The decoder 1 also gives a predetermined delay to optical signals of each wavelength received from a home-side device other than the ONU 1, for example, the ONU 2, but the optical signal obtained as a result of the combination has all four wavelengths. They are not aligned at the same time. Therefore, there is no possibility that information from a home side device other than the ONU 1 is erroneously taken in.

  FIG. 9 (DEC2) is a timing chart showing optical signals of respective wavelengths given time delays by the FBGs 5 to 8 of the decoder 2 of the station side apparatus OLT. An optical signal of wavelength λ1 is shown in (g1) to an optical signal of wavelength λ4 in (g4). As a result of the delay, the optical signals of the four wavelengths are aligned at the same time. An optical signal obtained by combining the optical signals of these wavelengths with an optical multiplexer is shown in (h). The decoder 2 gives a predetermined delay to each wavelength optical signal received from the home side device other than the ONU 2, for example, the ONU 1, but all four wavelengths are obtained as a result of the multiplexing. They are not aligned at the same time. Therefore, there is no possibility that information from a home side device other than the ONU 2 is erroneously taken in.

  In this way, even when a plurality of optical burst signals are temporally superimposed at the same time and input at the station-side apparatus OLT input stage, these superimposed signals are received by separate decoders of the decoder 17. Separated and extracted as independent signals. Therefore, each home-side apparatus ONU can handle more information than an optical communication system that performs upstream optical communication using a time slot.

  <Embodiment 2>

  Next, a system configuration in which light having a single wavelength λ1 is transmitted from the station-side device OLT to each home-side device ONU, and the home-side device ONU modulates using the light having the wavelength λ1 will be described.

  FIG. 10 is a schematic diagram showing a configuration of an optical communication system in which a station side device OLT and a plurality of home side devices ONU are connected by an optical fiber. The overall configuration of the optical communication system neckwork is the same as that described with reference to FIG.

  Referring to FIG. 10, the station side device OLT includes an optical CDMA light source 31 that emits light of one wavelength λ1, and an external modulator that shapes a waveform by passing an optical signal from the optical CDMA light source 31 at a predetermined timing. (EA) 32, an upper layer circuit 33 for controlling communication contents with the home-side apparatus ONU, and an electric / optical converter (E / O) that converts an electric signal from the upper layer circuit 33 into an optical signal of wavelength λd 34, a wavelength division multiplexing (WDM) 35 that multiplexes the light of wavelength λ1 and the light of wavelength λd and transmits them to the optical fiber 4 and separates the upstream optical signal of wavelength λ1 received from the home-side apparatus ONU. , An optical amplifier 36 that amplifies the upstream signal of wavelength λ1 separated by the wavelength multiplexing unit 35, an optical switch 37, an optical reverse delay / CDMA decoding unit 38, and an optical / electrical unit that converts the decoded optical signal into an electrical signal. Converter (O / ) Is equipped with a 39. The optical amplifier 36 may not be provided.

  The home-side device ONU has a wavelength separation unit 41 that separates the light of wavelength λ1 and the light of wavelength λd transmitted from the station-side device OLT, and the optical / electrical device that converts the separated optical signal of wavelength λd into an electrical signal. A demultiplexer 44, an upper layer circuit 43 for controlling communication contents with the converter (O / E) 42, the home-side apparatus ONU, an optical demultiplexer 44 for demultiplexing light of wavelength λ1 into n light beams An optical delay / CDMA encoder 45 that applies time delay to the light of wavelength λ 1 and performs encoding, an optical modulator 46 that turns on / off each optical signal supplied from the optical delay / CDMA encoder 45, The optical multiplexer 47 is configured to multiplex the optical signals that have passed through the modulation element 46.

  FIG. 11 is a block diagram illustrating a configuration example of the optical delay / CDMA encoding unit 45 of the home-side apparatus ONU1. The optical delay / CDMA encoding unit 45 includes an optical circulator CR disposed in the transmission path of each optical signal having the wavelength λ1 demultiplexed by the optical demultiplexer 44, and a time delay for each optical signal. FBG1-4 to hang are provided.

  In the case of the present embodiment, the arrangement of the diffraction gratings in each of the FBGs 1 to 4 is different for each FBG. FBG1 arranged in the order of wavelengths λ1, λ2, λ3, λ4, FBG2 arranged in the order of wavelengths λ4, λ1, λ2, λ3, and wavelengths λ3, λ4, λ1, λ2 The FBG 3 is arranged in the order of wavelengths λ2, λ3, λ4, and λ1. This arrangement is a common arrangement for all the home devices ONU1 to ONUm.

  The optical signals delayed by the FBGs 1 to 4 are turned on and off by four optical modulation elements 46 at “1” and “0”, and the output optical signals of the optical modulation elements 46 are combined into one by an optical multiplexer 47. Is done. As the optical configuration of the light modulation element 46, a known configuration such as an electro-optic modulation element can be adopted.

  This optical modulation element 46 can code-modulate an optical signal by a combination of which of the four optical channels is turned on and which is turned off. Information on this code is given based on a command (ctrl) from the upper layer circuit 43.

  As described above, the optical signals can be delayed and encoded by the FBGs 1 to 4 and the optical modulation element 46. The encoded optical signal is multiplexed by the optical multiplexer 47 and transmitted to the station side apparatus OLT.

  FIG. 12 is a block diagram showing an operation in the optical reverse delay / CDMA decoding unit 38 of the station side apparatus OLT corresponding to the home side apparatus ONU1.

The optical reverse delay / CDMA decoding unit 38 includes an optical switch 37 that switches the transmitted light of the wavelength λ1 in a time-sharing manner, and an optical circulator CR that is arranged in each optical transmission path switched by the optical switch 37. , FBGs 5-8 for multiplying each optical signal by a time delay. The optical reverse delay / CDMA decoder includes an optical / electrical converter (OE) as a demodulator that converts each optical signal that has passed through the optical circulator CR into an electrical signal.
The configuration of the optical switch 37 includes various examples such as a matrix type optical switch and a Mach-Zehnder type optical switch. Further, the optical switch may be constituted by a micro electro mechanical systems (MEMS) of a mirror drive type of a mechanical optical switch or an optical switch using an optical waveguide of an electronic optical switch using an electro-optic effect. Note that it is necessary to specify the switching start time of the optical switch 37. For this specification, if the station-side apparatus OLT detects the pulsed light that has entered the first burst signal, the optical switch is correspondingly detected. The switching of 37 may be started.

  The arrangement of the diffraction gratings in each of the FBGs 5 to 6 is different for each FBG. That is, from the side closer to the optical circulator CR, FBG 5 arranged in the order of wavelengths λ 4, λ 3 λ 2, λ 1, FBG 6 arranged in the order of wavelengths λ 3, λ 2, λ 1, λ 4, arranged in order of wavelengths λ 2, λ 1, λ 4, λ 3 The FBG 7 is arranged, and the FBG 8 is arranged in the order of wavelengths λ1, λ4, λ3, and λ2.

  The arrangement of the diffraction gratings of the FBG is opposite to the arrangement of the diffraction gratings of the FBGs 1 to 4 of the home-side apparatus ONU1 shown in FIG. 11, and the reverse order is applied to each light delayed by the home-side apparatus ONU1. Can give a delay. Thereby, in the station side apparatus OLT, each optical signal can be made to correspond temporally.

  These optical signals are simultaneously converted into electric signals by an optical / electrical converter (OE), and a parallel modulation signal can be taken out.

  FIG. 13 is a block diagram illustrating a configuration example of the optical delay / CDMA encoding unit 45 of the home-side apparatus ONU2. The optical delay / CDMA encoding unit 45 is different from the configuration of the optical delay / CDMA encoding unit of the home-side apparatus ONU1 shown in FIG.

  FIG. 14 is a block diagram showing the operation of the optical reverse delay / CDMA decoding unit 38 of the station side apparatus OLT. This figure shows the optical reverse delay / CDMA decoding of the station side apparatus OLT shown in FIG. Although it is exactly the same as the block diagram of the unit 45, the extracted code is a code corresponding to “1011” encoded by the home-side apparatus ONU2.

  The waveform of each part of the optical signal described above will be described using a timing chart. In each timing chart, the horizontal axis represents time t, and the vertical axis represents light intensity.

  First, FIG. 15A shows light source light emitted from the optical CDMA light source 31 installed in the station side apparatus OLT. This light source light is light having a single wavelength λ1. This light source light passes through the external modulator (EA) 32 at a predetermined timing and is waveform-shaped. FIG. 15B shows the waveform shaped waveform (a).

  16 (ONU1) includes output waveforms (b1) to (b4) of the optical demultiplexer 44 of the home-side apparatus ONU1 corresponding to FIG. 11, output waveforms (c1) to (c4) of the light modulation element 46, and 6 is a timing chart showing an output waveform (d) of the optical multiplexer 47. The output waveforms (c1) to (c4) of the light modulation element 46 are subjected to ON, ON, OFF, ON code modulation by the light modulation element 46. (d) is an array of “1, 1, 0, 1” at that time.

  16 (ONU2) includes output waveforms (b1) to (b4) of the optical demultiplexer 44 of the home-side apparatus ONU2 corresponding to FIG. 13, output waveforms (c1) to (c4) of the light modulation element 46, and 7 is a timing chart showing an output waveform (d) of the optical multiplexer 47. The output waveforms (c1) to (c4) of the light modulation element 46 are subjected to ON, OFF, ON, ON code modulation by the light modulation element 46. (d) is an array of “1, 0, 1, 1” at that time.

  Here, the input time of light passing through the wavelength separation unit 41 of the home-side apparatus ONU1 and the input time of light passing through the wavelength separation unit 41 of the home-side apparatus ONU2 are different from each other. The reason for this time shift is that the station side apparatus OLT controls the optical burst signals from the home side apparatus ONUs so that they are transmitted in time division so that they do not compete with each other in time ( This is different from the first embodiment). In the same optical communication system, the upstream optical signal transmitted from each home-side apparatus ONU can avoid contention.

  FIG. 17E shows an upstream optical signal from each home-side apparatus ONU multiplexed by the optical splitter 5. The combined optical signal is input to the station side device OLT.

  FIG. 17 (ONU1) shows an optical signal of each wavelength whose time delay is returned by the decoder 38 of the station side apparatus OLT with respect to the modulation of “1, 1, 0, 1” in the home side apparatus ONU1. It is a timing chart which shows. The optical signals of the respective wavelengths are aligned at the same time and become parallel signals. Optical signals of wavelength λ1 are shown in (g1) to (g4).

  FIG. 17 (ONU2) shows optical signals of respective wavelengths whose time delay is returned by the decoder 38 of the station side apparatus OLT with respect to the modulation of “1, 0, 1, 1” in the home side apparatus ONU2. It is a timing chart which shows. The optical signals of the respective wavelengths are aligned at the same time and become parallel signals. Optical signals of wavelength λ1 are shown in (g1) to (g4).

  Thus, at the stage of the station side device OLT input, even if a plurality of optical burst signals are temporally superimposed on the optical signal from the plurality of home side devices ONU2, they are superimposed on each other. Are separated by separate decoders of the decoder 17 and extracted as independent signals. Therefore, each home-side apparatus ONU can handle more information than an optical communication system that performs upstream optical communication using a time slot.

  In the optical CDMA communication system, the optical reverse delay / CDMA decoding unit and the O / E circuit receive a plurality of simultaneous burst optical signals, so that signals from the long-distance home-side device ONU and the short-distance home-side device ONU are received. If they overlap, a perspective problem occurs and the signal cannot be read. In order to solve this problem, the station side device OLT has a function of determining the training period and controlling the optical transmission power of the home side device ONU at the start of communication.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. For example, the number of wavelengths handled by the home-side apparatus ONU and the station-side apparatus OLT is not limited to 4, and the way of arranging the diffraction gratings of the FBGs is not limited to that shown in the figure.

It is the schematic which shows the structural example of the optical communication system which connected the station side apparatus OLT which concerns on Embodiment 1 of this invention, and several home side apparatus ONU with the optical fiber. It is a figure which shows the specific structure of the optical CDMA light source 11 installed in the station side apparatus OLT. It is a block diagram which shows the structural example of the optical delay and the CDMA encoding part 24 provided in the home side apparatus ONU1. FIG. 11 is a block diagram showing an operation in the decoder DEC1 corresponding to the home apparatus ONU1 of the optical reverse delay / CDMA decoder 17 in the station apparatus OLT. It is a block diagram which shows the structural example of the optical delay and the CDMA encoding part 24 provided in the home side apparatus ONU2. FIG. 10 is a block diagram showing an operation in the decoder DEC2 corresponding to the home apparatus ONU2 of the optical reverse delay / CDMA decoder 17 in the station apparatus OLT. FIG. 4 is a waveform diagram showing a light source light A irradiated from an optical CDMA light source 11 installed in a station side device OLT and an optical signal waveform B that has been waveform-shaped by passing through an external modulator (EA) at a predetermined timing. 6 is a timing chart showing optical signal waveforms of respective parts of the home-side apparatus ONU1 corresponding to FIG. 3 and optical signal output waveforms of respective parts of the home-side apparatus ONU2 corresponding to FIG. Waveforms (e) of optical signals output from the respective home-side devices ONU1 and ONU2 and combined by the optical splitter 5, and waveforms (g1) to (g4) of optical signals of respective parts of the decoder DEC1 corresponding to the home-side device ONU1 ), The waveform (h) of the optical signal obtained by combining these optical signals by the optical multiplexer 17a, and the waveform (g1) to (g4) of the optical signal of each part of the decoder DEC2 corresponding to the home-side apparatus ONU2. 4 is a timing chart showing the waveform (h) of an optical signal obtained by combining these optical signals by an optical multiplexer 17a. It is the schematic which shows the structural example of the optical communication system which connected the station side apparatus OLT which concerns on Embodiment 2 of this invention, and several home side apparatus ONU with the optical fiber. It is a block diagram which shows the structural example of the optical delay and the CDMA encoding part 45 provided in the home side apparatus ONU1. FIG. 11 is a block diagram showing the operation of the optical reverse delay / CDMA decoding unit 38 in the station side apparatus OLT. It is a block diagram which shows the example of a structure of the optical delay and CDMA encoding part 45 provided in the home side apparatus ONU2. FIG. 11 is a block diagram showing the operation of the optical reverse delay / CDMA decoding unit 38 in the station side apparatus OLT. FIG. 6 is a waveform diagram showing a light source light A having a wavelength λ1 emitted from an optical CDMA light source 11 installed in a station side device OLT and an optical signal waveform B which has been waveform-shaped by passing through an external modulator 32 at a predetermined timing. 6 is a timing chart showing optical signal waveforms of respective parts of the home-side apparatus ONU1 corresponding to FIG. 3 and optical signal output waveforms of respective parts of the home-side apparatus ONU2 corresponding to FIG. Waveforms (e) of optical signals output from the respective home devices ONU1 and ONU2 and combined by the optical splitter 5, waveforms (g1) to (g4) of optical signals received from the home devices ONU1, and the home side 6 is a timing chart showing waveforms (g1) to (g4) of optical signals received from the device ONU2.

Explanation of symbols

4 Optical fiber 5 Optical splitter 11 Optical CDMA light source (multiple wavelengths)
12, 23, 33, 43 Upper layer circuit 13, 34 Electrical / optical converter (E / O)
14, 35 Wavelength multiplexing unit 15, 36 Optical amplifier 16, 44 Optical demultiplexer 17, 38 Optical reverse delay / CDMA decoding unit 18, 39, 22, 42 Optical / electrical converter (O / E)
21, 41 Wavelength separation unit 24, 45 Optical delay / CDMA encoding unit 25, 47 Optical multiplexer 26, 46 Optical modulation element 31 Optical CDMA light source (single wavelength)
32 External modulator 37 Optical switch CR Optical circulator OLT Station side device ONU Home side device

Claims (4)

A plurality of home-side devices and station-side devices are connected by an optical signal line including an optical splitter, and an optical code division multiple access (optical CDMA) system is adopted for uplink data transmission from the home-side device to the station-side device. A PON optical communication system,
The optical signal line is composed of a single-core optical fiber,
The station-side device includes a light source that emits light of a plurality of wavelengths, and an optical multiplexing / demultiplexing unit that multiplexes and transmits the light of the plurality of wavelengths and demultiplexes light of the plurality of wavelengths received from the home-side device. And
The home-side device demultiplexes light of a plurality of wavelengths transmitted from the station-side device for each wavelength, and sets a time delay for each light demultiplexed by the light demultiplexing unit. And an optical delay / encoding unit that optically encodes and an optical multiplexing unit that multiplexes each light output from the optical delay / encoding unit, and is multiplexed by the optical multiplexing unit Transmitting light to the station side device through the optical signal line,
The station side device has an optical reverse delay unit that applies a delay opposite to the delay applied by the optical delay / encoding unit of the home side device to each of the lights demultiplexed by the optical multiplexing / demultiplexing unit An optical communication system. 2. The optical communication system according to claim 1 , wherein FBG is used for one or both of the optical delay element of the optical delay / encoding unit and the optical delay element of the optical reverse delay unit. A plurality of home-side devices and station-side devices are connected by an optical signal line including an optical splitter, and an optical code division multiple access (optical CDMA) system is employed for uplink data transmission from the home-side device to the station-side device A PON optical communication system,
The optical signal line is composed of a single-core optical fiber,
The station side device includes a light source that emits light of a single wavelength, an optical multiplexing unit that transmits the light of the single wavelength and extracts light received from the home side device, and temporally transmits the light. A light switching unit for separating,
The home-side device demultiplexes light of a single wavelength transmitted from the station-side device, and gives a time delay to each light demultiplexed by the light demultiplexing unit. An optical delay / encoding unit that optically encodes and an optical multiplexing unit that combines the lights output from the optical delay / encoding unit, and combines the light combined by the optical multiplexing unit. , Is sent to the station side device through the optical signal line,
The station-side device includes an optical reverse delay unit that applies a delay opposite to the delay performed by the optical delay / encoding unit of the home-side device for each light temporally separated by the optical switching unit. An optical communication system comprising: 4. The optical communication system according to claim 3 , wherein an FBG is used for one or both of the optical delay element of the optical delay / encoding unit and the optical delay element of the optical reverse delay unit.

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