JP2010114621A - Optical communication system, transmitter of onu, receiver of olt, and method of transmitting up-link signal of onu - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power splitter type WDM-PON without using a wavelength-variable filter, and a colorless ONU compatible with a self-emitting method. <P>SOLUTION: In the optical communication system, a station-side OLT and a plurality of user-side ONUs are connected through a power splitter and an optical fiber transmission path. Each ONU has one or more subcarrier frequencies different for each ONU allocated thereto, and includes: a transmitter including an RF modulation means to generate an RF modulation signal obtained by modulating an RF carrier of the subcarrier frequency with a transmission signal; and a light source for transmitting, as an up-link signal, modulated light having a wideband spectrum at a predetermined central wavelength and modulated by the RF modulation signal. The OLT includes: a receiver including an optical receiver for receiving, through the power splitter, the up-link signals respectively transmitted from each of the ONUs as subcarrier-multiplexed up-link signals to be converted to electric signals, and an RF demodulator compatible with each of the ONUs for demodulating the transmission signals of the ONUs from the electric signals based on the subcarrier frequencies allocated to each of the ONUs. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical communication system suitable for increasing the speed of an optical access system. The present invention also relates to an ONU transmitter, an OLT receiver, and an ONU upstream signal transmission method in an optical communication system.

  The speed of optical access systems has been remarkably high, and in the last five years, the speed and bandwidth have increased by a factor of 100. Gigabit-class broadband services are now commercially available for GE-PON (Gigabit Ethernet (registered trademark)-Passive Optical Network) systems. Provided economically with introduction. The next-generation PON technology approach to further increase the speed and bandwidth is mainly the time multiplexing (TDM) method that performs user multiplexing on the time axis, which is an extension technology, and the user multiplexing on the wavelength axis. There is a wavelength division multiplexing (WDM) system, and the latter is called WDM-PON.

FIG. 1 shows a configuration example of a WDM-PON system (Non-Patent Document 1).
In the figure, an OLT (Optical Line Terminal: optical subscriber line terminal board) 10 arranged on the station side and ONUs (Optical Network Unit: optical network termination devices) 20-1 to 20-n (on the user side) n is a natural number) is connected 1 to n through the optical fiber transmission line 31, the wavelength splitter 33 or the power splitter 34, and the n optical fiber transmission lines 32.

  In the wavelength splitter type WDM-PON of FIG. 1A, the downstream signals of wavelengths λd1 to λdn corresponding to the ONUs 20-1 to 20-n are demultiplexed by the wavelength splitter 33 and transmitted to each ONU. Further, the upstream signals of wavelengths λu1 to λun respectively output from the ONUs 20-1 to 20-n are wavelength-multiplexed by the wavelength splitter 33 and transmitted to the OLT 10.

  In the power splitter type WDM-PON of FIG. 1B, downstream signals of wavelengths λd1 to λdn corresponding to the ONUs 20-1 to 20-n are branched into n by the power splitter 34 and transmitted to each ONU. Each ONU selects and receives downlink signals of the corresponding wavelengths λd1 to λdn. Uplink signals of wavelengths λu1 to λun output from the ONUs 20-1 to 20-n are joined by the power splitter 34 and transmitted to the OLT 10.

The physical topology of WDM-PON is passive double star, and the optical fiber that is the transmission path is shared by multiple users, but since different wavelengths are assigned to each user, the logical topology is single star. It has become. For this reason, the service can be set and changed independently for each user without affecting other users while sharing the transmission path with the user.
K. Iwatsuki, J. Kani, H. Suzuki, and M. Fujiwara, "Access and Metro Networks based on WDM Technologies", IEEE J. Lightwave Technol., Vol. 22, No. 11, pp. 2623-2630, ( 2004)

  In WDM-PON, since a wavelength is fixedly assigned to each ONU, it is necessary to prepare ONUs having different transmission wavelengths for each user, and the convenience and maintenance operability for the user are lacking. For this reason, in order to realize an easy-to-use ONU without being aware of the wavelength, it is necessary to make the ONU as a single product so that the transmission wavelength of the ONU can be set from the station side (OLT side). This technology is called ONU's colorless technology.

  Colorless technology can be broadly divided into a self-luminous system and a carrier wave supply system. As shown in FIG. 2 (a), in the self-light emitting method, a light source having wavelength selectivity is mounted on the ONU itself, and the transmission wavelength of each ONU is set from the station side at the time of opening. Here, the transmitters of the ONUs 20-1 to 20-n transmit uplink signals having wavelengths λu1 to λun, respectively.

  As shown in FIG. 2 (b), the carrier wave supply system includes an ONU 20-1 to 20 -n transmitter in which an optical modulator is mounted, and the continuous light of wavelengths λu 1 to λun transmitted from the light source of the OLT 10 is received. The wavelength splitter 33 demultiplexes the wavelength and modulates the continuous light of each wavelength supplied to each ONU to generate an upstream signal. For example, a configuration is shown in which a downstream signal of wavelength λd1 and continuous light of wavelength λu1 are input to ONU 20-1, and the continuous light of wavelength λu1 is modulated and turned back as an upstream signal.

  FIG. 3 shows a system configuration example in which an existing PON (GE-PON) and a WDM-PON coexist. Here, since the optical splitter of the existing PON is a power splitter, the coexisting WDM-PON has a configuration using the power splitter 34 shown in FIG.

  In the figure, OLT (GE-OLT) and ONU (GE-ONU) corresponding to GE-PON, OLT (λ1 -OLT) and ONU (λ1 -ONU) occupying wavelength λ1 in WDM-PON, and WDM-PON The OLT (λ 2 -OLT) and the ONU (λ 2 -ONU) occupying the wavelength λ 2 are connected via a wavelength multiplexer / demultiplexer 35, an optical fiber transmission line 31, a power splitter 34, and an optical fiber transmission line 32. GE-PON is a bandwidth sharing service in which one wavelength is shared by a plurality of ONUs, and the bandwidth is temporally shared by a plurality of ONUs. The WDM-PON is a band occupation service in which one wavelength λ1 and λ2 is assigned to each ONU in a wavelength band different from that of the GE-PON, and a transmission rate can be set for each wavelength.

  In the power splitter type WDM-PON shown in FIG. 3, a transmitter of a self-luminous colorless ONU uses a method of changing the oscillation wavelength of a wavelength tunable light source or a light spectrum of a broadband light source using a wavelength tunable filter (wavelength (The center wavelength of the variable filter is the transmission wavelength). However, it is difficult to realize an inexpensive wavelength tunable filter that has high responsiveness and can vary the selected wavelength in a wide band, and has been a problem in realizing a self-luminous colorless ONU. Further, in the self-light-emitting method, it is necessary to monitor the wavelength from the station side and perform wavelength management so that the wavelength does not overlap with other ONUs, which has been a problem for flexible operation.

  The present invention relates to an optical communication system, an ONU transmitter, an OLT receiver, and an ONU upstream signal transmission capable of realizing a power splitter type WDM-PON and a colorless ONU corresponding to a self-light-emitting method without using a wavelength tunable filter. It aims to provide a method.

  A first invention is an optical communication system in which an OLT arranged on a station side and ONUs arranged on a plurality of users are connected via a power splitter and an optical fiber transmission line, and each ONU is provided for each ONU. And at least one different subcarrier frequency is assigned, and RF modulation means for generating an RF modulation signal obtained by modulating an RF carrier of the assigned subcarrier frequency with a transmission signal, and having a broadband spectrum at a predetermined center wavelength A transmitter including a light source that transmits the modulated light modulated by the RF modulation signal as an upstream signal, and the OLT receives the upstream signal transmitted from each ONU as an upstream signal that is subcarrier-multiplexed via the power splitter. Based on the subcarrier frequency assigned to each ONU Comprising a receiver including a respective ONU corresponding RF demodulator for demodulating a transmission signal of each ONU from the electrical signal.

  Further, instead of the OSU light source, an optical modulator is provided that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source, and transmits the modulated light obtained by modulating the CW light with an RF modulation signal as an upstream signal. May be. Also, instead of the OSU light source, CW light having a broad spectrum at a predetermined center wavelength is input from an external light source, the CW light is modulated with an RF modulation signal, and modulated light having only one side of the modulation spectrum is transmitted. You may provide the optical modulator transmitted as a signal.

  The OLT includes a wavelength demultiplexer that demultiplexes a broadband upstream signal into each wavelength component, and a receiver that supports each ONU, and each upstream signal of each wavelength component that is demultiplexed by the wavelength demultiplexer. An ONU-compatible light receiver may convert each signal into an electrical signal, and a demodulator may be demodulated by each ONU-compatible RF demodulator.

  According to a second aspect of the present invention, in the ONU transmitter of the optical communication system of the first aspect, at least one subcarrier frequency different from each other is assigned to each ONU, and RF carriers of the assigned subcarrier frequencies are transmitted. RF modulation means for generating an RF modulation signal modulated with a signal, and a light source for transmitting, as an upstream signal, modulated light obtained by modulating output light having a wide spectrum at a predetermined center wavelength with an RF modulation signal.

  Further, instead of the light source, an optical modulator may be provided that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source, and transmits the modulated light obtained by modulating the CW light with an RF modulation signal as an upstream signal. Good. Also, instead of the light source, CW light having a wide spectrum at a predetermined center wavelength is input from an external light source, the CW light is modulated with an RF modulation signal, and modulated light having only one side modulation spectrum is used as an upstream signal. An optical modulator for transmission may be provided.

  According to a third aspect of the present invention, in the OLT receiver of the optical communication system according to the first aspect, the upstream signal transmitted from each ONU is received as an upstream signal that is subcarrier multiplexed via the power splitter and converted into an electrical signal. A light receiver for conversion and an RF demodulator for each ONU that demodulates the transmission signal of each ONU from an electrical signal based on a subcarrier frequency assigned to each ONU.

  According to a fourth aspect of the present invention, in the upstream signal transmission method for an ONU of the optical communication system according to the first aspect of the present invention, the RF modulation means to which at least one subcarrier frequency different from each other is assigned to each ONU An RF modulation signal obtained by modulating an RF carrier wave having a carrier frequency with a transmission signal is generated, and modulated light modulated with the RF modulation signal is transmitted as an upstream signal from a light source having a broadband spectrum at a predetermined center wavelength.

  Further, instead of the light source, an optical modulator that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source may be used, and modulated light obtained by modulating CW light with an RF modulation signal may be transmitted as an upstream signal. Good. Also, instead of a light source, an optical modulator that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source is used to modulate CW light with an RF modulation signal and to have only one side modulation spectrum Light may be transmitted as an upstream signal.

  The present invention generates an RF modulated signal obtained by modulating an RF carrier having a subcarrier frequency with a transmission signal in each ONU that uses different subcarrier frequencies, and generates an RF modulated signal from a light source having a wide spectrum at a predetermined center wavelength. The modulated light modulated in step S1 is transmitted as an upstream signal. The uplink signal transmitted from each ONU is input to the OLT as an uplink signal that is subcarrier multiplexed via the power splitter. In the OLT, this upstream signal is converted into an electric signal, and the transmission signal of each ONU is demodulated from the electric signal based on the subcarrier frequency assigned to each ONU.

  In this way, by making the subcarrier frequency of the RF carrier correspond to each ONU and each RF demodulator of the OLT, the ONU and the RF modulator correspond one-to-one, and a power splitter type WDM without using a wavelength tunable filter. -A colorless ONU corresponding to the PON and the self-light-emitting method can be realized. Note that when the ONU is provided with RF modulation means made of an electronic circuit, an ONU that is overwhelmingly less expensive than when the ONU is provided with a wavelength tunable filter that is an optical module can be realized.

(First embodiment)
FIG. 4 shows a first embodiment of the optical communication system of the present invention.
In the figure, the OLT 10 arranged on the station side and the ONUs 20-1 to 20-n arranged on the plurality of user sides are connected in a one-to-n relationship via optical fiber transmission lines 31 and 32 and a power splitter 34, respectively. The Here, a configuration example of a transmitter of the ONUs 20-1 to 20-n and a receiver of the OLT 10 that receives an upstream signal corresponding to each ONU is shown, and a transmitter of the OLT 10 that is a downstream signal transmission system and the ONUs 20-1 to 20-1 The configuration of the 20-n receiver is omitted.

  The transmitter of the ONU 20-n superimposes the baseband transmission signal on the RF carrier having the subcarrier frequency fn by the multiplier 21, and the one-sideband and RF carrier component of the RF modulation signal output from the multiplier 21 by the filter 22. It is configured to cut out and input to a superluminescent diode (SLD) 25 having a broadband spectrum via an amplifier 23 and a bias T circuit 24. The SLD 25 of the ONU 20-n outputs a broadband modulated light modulated by an RF modulation signal having a subcarrier frequency fn. Note that the filter 23 may be omitted.

  Here, mutually different subcarrier frequencies f1 to fn are used for RF carriers on which baseband transmission signals are superimposed by the transmitters of the ONUs 20-1 to 20-n. Therefore, when the upstream signal (modulated light) from each ONU is merged by the power splitter 34, the modulated components of the subcarrier frequencies f1 to fn are subcarrier multiplexed with respect to the broadband light.

  The receiver of the OLT 10 converts the modulated light to be received into an electric signal by the light receiver 12, amplifies the amplified signal by the amplifier 13, and an RF demodulator 15 having center frequencies f 1 to f n corresponding to each ONU by the distributor 14. It is the structure distributed to -1 to 15-n. The RF demodulator 15-n having the center frequency fn extracts the baseband transmission signal transmitted from the ONU 20-n by demodulating the subcarrier frequency fn component from the electrical signal.

  In this way, the ONUs and RF modulators have a one-to-one correspondence by making the subcarrier frequencies f1 to fn of the RF carrier correspond to the ONUs 20-1 to 20-n and the RF demodulators 15-1 to 15-n of the OLT 10. Correspondingly, it is possible to realize a power splitter type WDM-PON and a colorless ONU corresponding to a self-luminous system without using a wavelength tunable filter.

(Second Embodiment)
FIG. 5 shows a second embodiment of the optical communication system of the present invention.
In the first embodiment, the SLD 25 is directly modulated with an RF modulation signal in each ONU. However, in this embodiment, an optical modulator 26 is used instead of the SLD 25, and a light source such as an SLD having an external broadband spectrum is used. The configuration is characterized in that the CW light input from is externally modulated. Other configurations are the same as those of the first embodiment.

(Third embodiment)
FIG. 6 shows a third embodiment of the optical communication system of the present invention.
In the second embodiment, an optical modulator 26 is used in each ONU and CW light input from an external light source is externally modulated. However, in this embodiment, an SSB (Single Sid Band) is used instead of the optical modulator 26. The optical modulator 27 is used to transmit modulated light having only one side of the modulated spectrum component as a downstream signal. Other configurations are the same as those in the first embodiment and the second embodiment.

  A normal optical modulator generates a modulation spectrum on both sides of the optical carrier (CW light) like a double sideband generated by AM modulation, but the SSB optical modulator 27 can obtain only one side of the modulation spectrum. When transmitting SCM modulated light generated by a normal optical modulator, the dispersion of the optical fiber affects the interference state of the modulation spectrum on both sides and causes waveform deterioration. However, the SSB optical modulator 27 is used. This has the effect of reducing waveform deterioration due to dispersion.

(Fourth embodiment)
FIG. 7 shows a fourth embodiment of the optical communication system of the present invention.
In this embodiment, the configuration of the OLT 10 of the first embodiment is changed, but the ONUs 20-1 to 20-n and the subcarrier frequencies f1 to fn of the RF carrier are made to correspond one-to-one, and thus the ONU 20- 1 to 20-n and the RF demodulators 15-1 to 15-n having the center frequencies f1 to fn of the OLT 10 are made to correspond one-to-one.

  The OLT 10 of this embodiment demultiplexes broadband modulated light input as an upstream signal into components of wavelengths λ1 to λn by the wavelength filter 16, and each of the modulated light of each wavelength corresponds to an OSU (Optical Subscriber Unit: optical subscriber). Line termination device) Input to 17-1 to 17-n. The modulated light of each wavelength is subcarrier multiplexed with components of subcarrier frequencies f1 to fn. For example, the receiver of the OSU 17-n converts the received modulated light having the wavelength λn into an electric signal by the light receiver 12, amplifies it by the amplifier 13, and inputs the amplified electric signal to the RF demodulator 15-n having the center frequency fn. It is the structure to do. The RF demodulator 15-n having the center frequency fn extracts the baseband transmission signal transmitted from the ONU 20-n by demodulating the frequency fn component from the electrical signal corresponding to the modulated light having the wavelength λn. In this embodiment, the configuration of the transmission system for the OSU downlink signal is also omitted.

  Further, the configurations of the OLT 10 and the OSU 17 of the present embodiment can be similarly applied to the second embodiment and the third embodiment.

(Fifth embodiment)
In the first to fourth embodiments, the ONUs 20-1 to 20-n and the subcarrier frequencies f1 to fn of the RF carrier are made to correspond one-to-one, so that the center frequencies f1 to the ONUs 20-1 to 20-n and the OLT 10 The RF demodulators 15-1 to 15-n of fn are made to correspond one-to-one.

  In the first to fourth embodiments, a plurality of subcarrier frequencies of the RF carrier to be assigned to each ONU are set, for example, a plurality of RF modulation signals in which a plurality of baseband transmission signals are superimposed on RF carriers having different subcarrier frequencies are multiplexed. Then, the CW light of wavelengths λ1 to λn is modulated with the multiple RF modulation signal. An example of an ONU transmitter is shown in FIG. In FIG. 8, RF modulation signals obtained by modulating baseband transmission signals a and b with RF carriers of subcarrier frequencies fa and fb are added by an adder 28 to form a multiplexed RF modulation signal. On the other hand, also in the OLT 10, by using an RF demodulator having a center frequency corresponding to a plurality of subcarrier frequencies for each ONU, it is possible to increase the bandwidth allocated to each ONU.

  Further, the subcarrier frequencies of a plurality of RF carriers assigned to each ONU are not fixed, but can be variably controlled by dynamically changing the subcarrier frequencies according to a control signal from the OLT. For example, by using OFDM (Orthogonal Frequency Division Multiplexing) as the modulation scheme of the ONU and assigning each frequency component of OFDM between the ONU and the RF demodulator of the OLT, fine control of band allocation becomes possible.

The figure which shows the structural example of a WDM-PON system. The figure which shows the structural example of the WDM-PON system using a colorless ONU. The figure which shows the system structural example in which the existing PON (GE-PON) and WDM-PON coexist. The figure which shows 1st Embodiment of the optical communication system of this invention. The figure which shows 2nd Embodiment of the optical communication system of this invention. The figure which shows 3rd Embodiment of the optical communication system of this invention. The figure which shows 4th Embodiment of the optical communication system of this invention. The figure which shows an example of the transmitter of ONU in 5th Embodiment of the optical communication system of this invention.

Explanation of symbols

10 OLT (Optical subscriber line terminal board)
DESCRIPTION OF SYMBOLS 12 Light receiver 13 Amplifier 14 Divider 15 RF demodulator 16 Wavelength filter 17 OSU (Optical subscriber line termination device)
20 ONU (Optical network terminator)
21 Multiplier 22 Filter 23 Amplifier 24 Optical Modulator 25 Super Luminescent Diode (SLD)
26 Optical modulator 27 SSB optical modulator 28 Adder 31, 32 Optical fiber transmission line 33 Wavelength splitter 34 Power splitter 35 Wavelength multiplexer / demultiplexer

Claims (11)

An optical subscriber line termination board (hereinafter referred to as “OLT”) disposed on the station side and an optical network termination device (hereinafter referred to as “ONU”) disposed on each of a plurality of users are connected to the power splitter and the optical fiber transmission line. In an optical communication system connected via
Each ONU is assigned at least one different subcarrier frequency for each ONU, and an RF modulation means for generating an RF modulation signal obtained by modulating an RF carrier wave of the assigned subcarrier frequency with a transmission signal, and a predetermined center wavelength A transmitter having a broadband spectrum and a light source that transmits the modulated light modulated by the RF modulation signal as an upstream signal,
The OLT receives the upstream signal transmitted from each ONU as a subcarrier multiplexed upstream signal via the power splitter and converts it into an electrical signal, and a sub-assignment assigned to each ONU. An optical communication system comprising: a receiver including an ONU-compatible RF demodulator that demodulates a transmission signal of each ONU from the electrical signal based on a carrier frequency. The optical communication system according to claim 1,
In place of the OSU light source, an optical modulator is provided that inputs CW light having a broad spectrum at a predetermined center wavelength from an external light source, and transmits the modulated light obtained by modulating the CW light with the RF modulation signal as an upstream signal. An optical communication system characterized by that. The optical communication system according to claim 1,
Instead of the OSU light source, CW light having a broad spectrum at a predetermined center wavelength is input from an external light source, the CW light is modulated by the RF modulation signal, and modulated light having only one side modulation spectrum is transmitted. An optical communication system comprising an optical modulator for transmitting as a signal. The optical communication system according to claim 1,
The OLT includes a wavelength demultiplexer for demultiplexing the broadband upstream signal into each wavelength component, and a receiver for each ONU, and the upstream signal of each wavelength component demultiplexed by the wavelength demultiplexer. An optical communication system, wherein the optical signal is converted into an electrical signal by each of the ONU-compatible light receivers and demodulated by the ONU-compatible RF demodulator. The ONU transmitter of the optical communication system according to claim 1,
RF modulation means for generating at least one subcarrier frequency different from each other for each ONU, and generating an RF modulation signal obtained by modulating an RF carrier of the assigned subcarrier frequency with a transmission signal;
An ONU transmitter comprising: a light source that transmits, as an upstream signal, modulated light obtained by modulating output light having a broadband spectrum at a predetermined center wavelength with the RF modulation signal. The transmitter of the optical communication system OSU according to claim 5,
Instead of the light source, an optical modulator is provided that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source, and transmits the modulated light obtained by modulating the CW light with the RF modulation signal as an upstream signal. An OSU transmitter characterized by the above. The transmitter of the optical communication system OSU according to claim 5,
Instead of the light source, CW light having a broad spectrum at a predetermined center wavelength is input from an external light source, the CW light is modulated by the RF modulation signal, and modulated light having only one side of the modulation spectrum is used as an upstream signal. An OSU transmitter comprising an optical modulator for transmission. The OLT receiver of the optical communication system according to claim 1,
A light receiver that receives the upstream signal transmitted from each ONU as an upstream signal that is subcarrier-multiplexed via the power splitter and converts it into an electrical signal;
An OLT receiver comprising: an RF demodulator corresponding to each ONU that demodulates a transmission signal of each ONU from the electrical signal based on a subcarrier frequency assigned to each ONU. The ONU upstream signal transmission method of the optical communication system according to claim 1,
RF modulation means to which at least one subcarrier frequency different from each other is assigned to each ONU generates an RF modulation signal obtained by modulating an RF carrier of the assigned subcarrier frequency with a transmission signal,
An upstream signal transmission method for an ONU, wherein modulated light modulated by the RF modulation signal is transmitted as an upstream signal from a light source having a broadband spectrum at a predetermined center wavelength. The ONU uplink signal transmission method according to claim 9,
In place of the light source, an optical modulator that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source is used, and modulated light obtained by modulating the CW light with the RF modulation signal is transmitted as an upstream signal. An ONU upstream signal transmission method characterized by The ONU uplink signal transmission method according to claim 9,
Instead of the light source, an optical modulator that inputs CW light having a wide spectrum at a predetermined center wavelength from an external light source is used, and the CW light is modulated by the RF modulation signal and only one side of the modulation spectrum is modulated. An ONU upstream signal transmission method characterized by transmitting light as an upstream signal.

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