JP2010114623A - 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 carrier supply 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 includes: one or more subcarrier frequencies 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 modulator for transmitting, to the OLT as an up-link signal, modulated light obtained by inputting, through the power splitter, CW light output from a WDM light source on the station side and having a plurality of wavelength components and modulating the CW light by the RF modulation signal. The OLT includes: a receiver including an optical receiver for converting the up-link signals respectively transmitted from each of the ONUs to electric signals as subcarrier-multiplexed up-link signals, and an RF demodulator compatible with the ONUs for demodulating the transmission signals of the ONUs from the electric signals based on the subcarrier frequencies 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. Therefore, 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 has an optical modulator mounted on the transmitters of the ONUs 20-1 to 20-n, and the CW light having the wavelengths λu1 to λun transmitted from the light source of the OLT 10 is received. The wavelength splitter 33 demultiplexes the wavelength and modulates the CW 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 CW light of wavelength λu1 are input to ONU 20-1, and the CW light of wavelength λu1 is modulated and returned 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, the carrierless type colorless ONU transmitter modulates the CW light of the wavelength demultiplexed corresponding to the wavelength splitter type shown in FIG. Unlike the configuration, a wavelength tunable filter is used to select CW light having an arbitrary wavelength from CW light having wavelengths λu1 to λun supplied from the OLT light source to each ONU. However, it is difficult to realize an inexpensive wavelength tunable filter that has high responsiveness and is capable of varying the selected wavelength in a wide band, and there are problems in realizing a colorless ONU corresponding to the power splitter type WDM-PON and the carrier wave supply system. It was.

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

  The 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 different from each other. At least one subcarrier frequency is assigned, and 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 plurality of wavelength components output from the WDM light source on the station side And a transmitter including an optical modulator that transmits the modulated light obtained by modulating the CW light using an RF modulation signal as an upstream signal to the OLT. The transmitted upstream signal is received as an upstream signal that is subcarrier multiplexed via a power splitter and converted into an electrical signal. Comprising a receiver for a receiver including a respective ONU corresponding RF demodulator for demodulating a transmission signal of each ONU from the electric signal based on the subcarrier frequencies allocated to each ONU.

  Each ONU optical modulator may include an optical amplifier that amplifies an upstream signal. The OLT may be configured to include a delay compensator that compensates for a delay difference caused by an upstream signal having a plurality of wavelength components caused by chromatic dispersion in an optical fiber transmission line, in front of the optical receiver.

  The OLT includes a wavelength demultiplexer that demultiplexes an upstream signal having a plurality of wavelength components into each wavelength component, and a receiver that supports each ONU, and each wavelength component demultiplexed by the wavelength demultiplexer. The upstream signal may be converted into an electrical signal by each ONU-compatible light receiver, and 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 CW light having a plurality of wavelength components output from a WDM light source on the station side are input via a power splitter, and the CW light is modulated with the RF modulation signal And an optical modulator that transmits the modulated light as an upstream signal to the OLT.

  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 optical modulator that generates an RF modulated signal obtained by modulating an RF carrier wave of a carrier frequency with a transmission signal and inputs CW light having a plurality of wavelength components output from a WDM light source on the station side via a power splitter is RF modulated. Modulated light obtained by modulating the CW light with the signal is generated and transmitted to the OLT as an upstream signal.

  The present invention generates an RF modulation signal obtained by modulating an RF carrier having a subcarrier frequency with a transmission signal in each ONU using different subcarrier frequencies, and for CW light having a plurality of wavelength components given from a WDM light source. And collectively modulating with an RF modulation signal to generate 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 carrier wave supply 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, 32 and a power splitter 34, respectively. The CW light (continuous light) of wavelengths λ1 to λn output from the WDM light source 11 of the OLT 10 arrives at each ONU without being demultiplexed. The optical modulators are mounted on the transmitters of the ONUs 20-1 to 20-n, and the upstream signals are generated by modulating the CW light of the wavelengths λ1 to λn supplied from the WDM light source 11 of the OLT 10 to each ONU. 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.

  In this embodiment, a WDM light source 11 is provided in the OLT 10, CW light of wavelengths λ 1 to λ n output from the WDM light source 11 is input to the optical fiber transmission line 31, and the ONU 20 via the power splitter 34 together with the downstream signal. Although the example of supplying to -1 to 20-n has been shown, the WDM light source 11 may be outside the OLT 10 or may be configured to supply to each ONU through a route different from the downstream signal. The same applies to other embodiments described below.

  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. This is a configuration that is cut out, amplified by the amplifier 23 and input to the optical modulator 24. The optical modulator 24 optically modulates CW light of wavelengths λ1 to λn with an RF modulation signal of subcarrier frequency fn and outputs modulated light. The filter 22 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 signals (modulated light) from the ONUs are merged by the power splitter 34, the modulation components of the subcarrier frequencies f1 to fn are subcarrier multiplexed with respect to the CW lights of wavelengths λ1 to λn, respectively. Become.

  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 corresponding to the modulated light having the wavelengths λ1 to λn. .

  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 colorless ONU corresponding to the power splitter type WDM-PON and the carrier wave supply system without using the wavelength tunable filter.

  Note that a wavelength tunable filter may be used instead of the WDM light source 11 by using a light source that outputs CW light of one wavelength and modulating the CW light of one wavelength at each ONU with an RF modulation signal having subcarrier frequencies f1 to fn. It is possible to realize a colorless ONU without using. On the other hand, as shown in FIG. 1, for example, in the ONU 20-n, the CW light of the wavelengths λ1 to λn is optically modulated at once with the RF modulation signal of the subcarrier frequency fn, and the RF demodulator of the center frequency fn of the OLT 10 is obtained. In 15-n, by demodulating the frequency fn component from the electrical signal corresponding to the modulated light of wavelengths λ1 to λn, it is possible to secure an SN ratio that is n times that of the configuration using one wavelength.

(Second Embodiment)
FIG. 5 shows a second embodiment of the optical communication system of the present invention.
In the present embodiment, when the optical fiber that is a transmission path between the OLT 10 and the ONUs 20-1 to 20-n is elongated, the optical loss increases and the influence of the chromatic dispersion of the optical fiber increases. It corresponds to.

  In the figure, the transmitters of the ONUs 20-1 to 20-n are the same as those in the first embodiment in FIG. 4 except that an optical amplifier 25 is disposed after the optical modulator 24. Instead of the optical modulator 24 and the optical amplifier 25, an optical modulator having an optical amplification function may be used.

  In the receiver of the OLT 10, in order to compensate for the delay difference generated in the upstream signal having a plurality of wavelength components due to the chromatic dispersion of the optical fiber transmission lines 31 and 32 and the power splitter 34, the delay compensation is provided in the front stage of the light receiver 12. A configuration is adopted in which a modulator 40 is disposed and modulated light whose delay is adjusted for each wavelength is input to the light receiver 12. Other configurations are the same as those of the first embodiment of FIG. For example, as illustrated in FIG. 6, the delay compensator 40 uses a wavelength demultiplexer 41, a delay line 42, and a wavelength multiplexer 43, and has a configuration in which a delay that differs for each wavelength is corrected by the delay line 42. Further, the delay compensator 40 may use a configuration using an optical circulator and a fiber grating that provides a wavelength-corresponding delay amount, or an optical fiber having the inverse dispersion characteristics of the optical fiber transmission lines 31 and 32.

  In this embodiment, the configuration corresponding to both the increase in optical loss and the chromatic dispersion of the optical fiber is shown. However, the optical amplifier 25 corresponding to the increase in optical loss and the delay compensation corresponding to the chromatic dispersion in the transmission line are shown. It is good also as a structure which arrange | positions the container 40 separately.

(Third embodiment)
FIG. 7 shows a third 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 of the center frequencies f1 to fn of the OLT 10 are the same in a one-to-one correspondence.

  The OLT 10 of this embodiment demultiplexes modulated light of wavelengths λ1 to λn input as an upstream signal into each wavelength by the wavelength filter 16, and each of the modulated light of each wavelength corresponds to an OSU (Optical Subscriber Unit: optical subscriber line). Terminal device) 17-1 to 17-n. 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.

  The first embodiment is configured to receive, for example, an RF frequency component of frequency fn from each modulated light of wavelengths λ1 to λn. In the present embodiment, for example, an RF frequency of frequency fn from the modulated light of wavelength λn is used. The configuration is such that the component is received, and the SN ratio of the received signal is superior to that of the first embodiment.

(Fourth embodiment)
In the first to third embodiments, the ONUs 20-1 to 20-n and the subcarrier frequencies f1 to fn of the RF carrier have a one-to-one correspondence, 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 third 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 26 to obtain a multiple RF modulation signal. On the other hand, in the OLT 10 as well, it is possible to increase the bandwidth allocated to each ONU by using an RF demodulator that corresponds to the center frequency for 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 the structural example of the delay compensator. The figure which shows 3rd Embodiment of the optical communication system of this invention. The figure which shows an example of the transmitter of ONU in 4th Embodiment of the optical communication system of this invention.

Explanation of symbols

10 OLT (Optical subscriber line terminal board)
DESCRIPTION OF SYMBOLS 11 WDM light source 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)
DESCRIPTION OF SYMBOLS 21 Multiplier 22 Filter 23 Amplifier 24 Optical modulator 25 Optical amplifier 26 Adder 31, 32 Optical fiber transmission line 33 Wavelength splitter 34 Power splitter 35 Wavelength multiplexer / demultiplexer 40 Delay compensator 41 Wavelength demultiplexer 42 Delay line 43 Wavelength Multiplexer

Claims (7)

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 subcarrier frequency different from each other, and an 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 a WDM light source on the station side And an optical modulator that inputs CW light having a plurality of wavelength components output from the power splitter and transmits the modulated light obtained by modulating the CW light with the RF modulation signal to the OLT as an upstream signal. With a transmitter,
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,
An optical communication system, wherein the optical modulator of each ONU includes an optical amplifier that amplifies the upstream signal. The optical communication system according to claim 1,
The OLT includes a delay compensator that compensates for a delay difference caused by chromatic dispersion of the optical fiber transmission line in the upstream signal having the plurality of wavelength components, in front of the optical receiver. Communications system. The optical communication system according to claim 1,
The OLT includes a wavelength demultiplexer that demultiplexes the upstream signal having the plurality of wavelength components into each wavelength component, and a receiver that corresponds to each ONU, and each of the wavelengths demultiplexed by the wavelength demultiplexer An optical communication system, wherein an upstream signal of a wavelength component 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;
CW light having a plurality of wavelength components output from the WDM light source on the station side is input via the power splitter, and modulated light obtained by modulating the CW light with the RF modulation signal is transmitted as an upstream signal to the OLT. An ONU transmitter comprising: an optical modulator. The OLT receiver of the optical communication system according to claim 1,
A 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 optical modulator that inputs CW light having a plurality of wavelength components output from the WDM light source on the station side via the power splitter generates modulated light obtained by modulating the CW light with the RF modulation signal, and An uplink signal transmission method for an ONU, wherein the signal is transmitted to the OLT as a signal.

Images