JP3615476B2 - Optical access system, access node device, and user node device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology of an optical wavelength multiplex access system that establishes communication with an access node device without placing an expensive light source in a user node device (ONU: Optical Network Unit) at a subscriber's home.
[0002]
[Prior art]
In an optical access system, cost reduction is essential, and there are many configurations such as a passive double star (PDS) system or a user node device that does not include a light source and modulates and reflects unmodulated light from the access node device. It is being considered. In the future, there is a strong demand for the realization of an optical access system with higher capacity and lower cost, such as the Internet and video services.
[0003]
[Problems to be solved by the invention]
Among the above-described conventional technologies, the most studied PDS system achieves cost reduction with a capacity of 50 to 150 Mbit / s by a technology such as TCM (Time Compression Multiplexing) / TDMA (Time Division Multiple Access). ing. Since the TCM technology for single-fiber bidirectional transmission requires twice the transmission speed, no high-speed study corresponding to the recent Gigabit Ethernet class has been announced.
[0004]
In addition, a method of looping unmodulated light without providing a light source in the user node device is conceivable, and it is easy to increase the speed. However, it is difficult to reduce the cost because two optical fibers are required.
[0005]
Further, in the study of direct reflection on the same fiber, the wavelength of the CW (Continuous Wave) light and the reflected light is the same, so that significant transmission degradation due to interference with Rayleigh scattered light becomes a problem. There is also a high-speed modulation limit of optical elements used for reflection.
[0006]
An object of the present invention is to provide an optical access system, an access node device, and a user node device that can be realized at a low cost of the entire system. An object of the present invention is to provide an optical access system, an access node device, and a user node device that enable a network configuration excellent in service responsiveness and maintainability. It is an object of the present invention to provide an optical access system, an access node device, and a user node device that can achieve high network reliability. An object of the present invention is to provide an optical access system, an access node device, and a user node device that can constitute a highly stable network.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, in the present invention, the access node device includes a light source of unmodulated light (CW light), and the CW light is transmitted to the user node device. An oscillator that oscillates at a frequency Δf and a frequency modulator are provided. The CW light is modulated to shift the frequency (= wavelength) of the optical signal from the CW light by Δf, and then modulated with uplink data and sent back to the access node device. .
[0008]
As an oscillator, for example, high stabilization can be achieved at low cost by using a clock of a retiming circuit extracted from a received signal. In the access node device, only the upstream signal shifted by the frequency Δf is extracted by the optical filter to cut the near-end reflected light of the CW light.
[0009]
By adopting such a configuration, an expensive light source is not required for the user node device, and the single system bidirectional transmission can be realized with high stability and high speed by the frequency shift of the CW light, thereby realizing the cost reduction of the entire system. In addition, since the optical signal from each user node device can be wavelength-multiplexed as it is in the access node device, a transparent system directly connected to the wavelength from the user node device to the center node can be configured stably and economically. A network configuration with excellent maintainability is possible. In addition, the active system and the standby system can be easily configured by two optical signals generated by the user node device, and high reliability of the network can be achieved. In addition, the optical signal output from each user node device can be controlled without causing excessive optical loss on the access node device side, and a highly stable network can be configured.
[0010]
That is, a first aspect of the present invention includes an access node device that accommodates a subscriber and a user node device installed in a subscriber's house, and an optical fiber is provided between the access node device and the user node device. This is an optical access system that performs bidirectional transmission using a single core.
[0011]
Here, the present invention is characterized in that the access node device is modulated with the light source of the CW light having a wavelength different from the optical signal modulated with the downlink data addressed to the user node device, and the downlink data. A means for combining the optical signal and the CW light and transmitting the optical signal to the optical fiber; and an optical filter for transmitting an optical signal arriving from the user node device and having a frequency of Δf away from the frequency of the CW light. The user node apparatus separates the CW light from the optical signal modulated by the downlink data coming from the access node apparatus and the optical signal combined with the CW light, and the separation by the separating means. There is provided means for causing the frequency of the CW light to be shifted by a frequency Δf, and means for externally modulating the CW light having undergone the frequency Δf transition with upstream data.
[0012]
As a result, an expensive light source is not required for the user node device, and the single system bidirectional transmission can be performed with high stability and high speed by the frequency shift of the CW light, so that the cost of the entire system can be reduced. In addition, since the optical signal from each user node device can be wavelength-multiplexed as it is in the access node device, a transparent system directly connected to the wavelength from the user node device to the center node can be configured stably and economically. A network configuration with excellent maintainability is possible.
[0013]
The means for making the transition can be realized, for example, by including an oscillator having a frequency Δf and a frequency modulator that causes the CW light to make a frequency Δf transition by the oscillation frequency Δf of the oscillator. At this time, an N-multiplier that multiplies the clock signal of the retiming circuit in the user node device by N may be provided as the oscillator.
[0014]
Also, a plurality of N user node devices are connected to one access node device, and the access node device has a CW light having an N channel wavelength different from an optical signal modulated with downlink data addressed to the user node device. And an optical filter that transmits optical signals that are separated from the frequency of the CW light having the wavelength of the N channel by Δf from optical signals arriving from a plurality of N user node devices.
[0015]
In addition, a ring transmission path including at least two of the access node devices may be provided, or at least two of the ring transmission paths may be connected in a multiplexed manner. Thereby, the network scale can be easily expanded.
[0016]
The access node apparatus includes an optical filter that transmits an optical signal arriving from the user node apparatus and having a frequency that is + Δf apart from the frequency of the CW light and a signal that is −Δf apart, and the user node apparatus includes the optical filter A means for transitioning the frequency of the CW light separated by the means for separating the frequency + Δf and −Δf; and a means for externally modulating the CW light subjected to the frequency + Δf and −Δf transition with upstream data. You can also.
[0017]
With such a configuration, working and spare optical fibers are provided between the access node device and the user node device and between the access node devices, and the signal separated by + Δf and the signal separated by −Δf. Any one of the received signals may be an optical signal transmitted through the working optical fiber, and the other may be an optical signal transmitted through the spare optical fiber.
[0018]
As a result, the active system and the standby system can be easily configured by the two optical signals generated by the user node device, and high reliability of the network can be achieved.
[0019]
According to a second aspect of the present invention, there is provided an access node device, and the feature of the present invention is that a light source of CW light having a wavelength different from that of an optical signal modulated by downlink data addressed to a user node device, Means for combining an optical signal modulated with downlink data and the CW light and transmitting the optical signal to an optical fiber; and an optical signal arriving from the user node device and transmitting an optical signal whose frequency is Δf away from the frequency of the CW light And an optical filter to be provided.
[0020]
A third aspect of the present invention is a user node device, which is characterized in that an optical signal obtained by combining an optical signal modulated by downlink data coming from an access node device and CW light is combined. Means for separating the CW light from the light, means for making a frequency Δf transition of the frequency of the separated CW light, and means for externally modulating the CW light subjected to the frequency Δf transition with upstream data.
[0021]
The means for making the transition can be configured to include, for example, an oscillator having a frequency Δf and a frequency modulator that causes the CW light to make a frequency Δf transition by the oscillation frequency Δf of the oscillator. At this time, the oscillator can be configured easily and inexpensively by providing an N-multiplier that multiplies the clock signal of the retiming circuit in the user node device as the oscillator.
[0022]
The access node device includes a light source of non-modulated light (CW light) having an N channel wavelength different from an optical signal modulated with downlink data addressed to the user node device, and a plurality of N user node devices. An optical filter that transmits an incoming optical signal having a frequency of Δf away from the frequency of the CW light having the N-channel wavelength may also be provided. Thereby, a plurality of user node devices can be accommodated in one access node device.
[0023]
The access node apparatus includes an optical filter that transmits an optical signal arriving from the user node apparatus and having a frequency that is separated from the frequency of the CW light by + Δf and a signal that is separated by −Δf. You can also. In this case, it is desirable that the user node apparatus includes a means for causing the frequency of the CW light separated by the separating means to transition between frequency + Δf and −Δf. As a result, a highly reliable optical access system using the working and spare optical fibers can be constructed.
[0024]
The access node apparatus preferably includes means for adjusting the intensity of the CW light transmitted according to the intensity of the optical signal coming from the user node apparatus. Thereby, control of optical signal output from each user node apparatus can be controlled without giving excessive optical loss on the access node apparatus side, and a highly stable network can be configured.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the optical access system according to the embodiment of the present invention will be described with reference to FIG. 1, FIG. 3, FIG. 4, FIG. FIG. 1 is a block diagram of an optical access system according to the first embodiment of the present invention. FIG. 3 is a block diagram of an optical access system according to the second embodiment of the present invention. FIG. 4 is a diagram showing an example of an access transfer network to which the present invention is applied. FIG. 5 is a block diagram of an optical access system according to the third embodiment of the present invention. FIG. 7 is a block diagram of an optical access system according to the third and fourth embodiments of the present invention.
[0026]
As shown in FIG. 1, the present invention includes an access node device A-1 that accommodates subscribers, and a user node device (ONU: Optical Network Unit) ONU-1 installed in the subscriber's home. This is an optical access system that performs bi-directional transmission between the device A-1 and the user node device ONU-1 using a single optical fiber F-1.
[0027]
Here, the feature of the present invention is that the access node apparatus A-1 includes a CW light source 1 that is unmodulated light having a wavelength different from that of the optical signal modulated by the downlink data addressed to the user node apparatus ONU-1. The optical signal modulated with the downlink data and the CW light are combined and transmitted to an optical fiber, and the optical signal arriving from the user node apparatus ONU-1 is light whose frequency is Δf away from the frequency of the CW light. And an arrayed waveguide grating (AWG) 2 serving as an optical filter that transmits the signal, and the user node device ONU-1 is modulated by the downlink data coming from the access node device A-1 A band demultiplexer 3 for separating the CW light from an optical signal obtained by combining the signal and the CW light, and the CW separated by the band demultiplexer 3 There is provided means for changing the frequency of the light by a frequency Δf and an external modulator 6 for externally modulating the CW light having the frequency Δf changed with upstream data.
[0028]
The means for making the transition includes an oscillator 5 having a frequency Δf and a frequency modulator 4 for causing the CW light to make a frequency Δf transition by the oscillation frequency Δf of the oscillator 5.
[0029]
As shown in FIG. 3, an N multiplier 8 that multiplies the clock signal of the retiming circuit 7 in the user node device ONU-1 by N can be provided instead of the oscillator 5.
[0030]
As shown in FIG. 5, a plurality of N user node devices ONU-1 to ONU-n are connected to one access node device A-1, and the access node device A-1 is connected to the user node devices ONU-1 to ONU-. a multi-wavelength light source 9 which is a CW light source having an N-channel wavelength different from the optical signal modulated by the downlink data addressed to n, and the N-channel wavelength of the optical signal arriving from the user node devices ONU-1 to ONU-n. It is also possible to provide an arrayed waveguide diffraction grating (AWG) 10 as an optical filter that transmits an optical signal separated by Δf from the frequency of the CW light.
[0031]
As shown in FIG. 4A, the optical access system of the present invention includes a ring transmission line including access node devices A-1, A-2, and A-3, and can be applied to an access transfer network. Further, as shown in FIG. 4B, at least two ring transmission lines can be connected in a multiplexed manner.
[0032]
As shown in FIG. 7, the access node device A-1 is an optical signal arriving from the user node device ONU-n that transmits a signal whose frequency is + Δf apart from the frequency of the CW light and a signal that is −Δf apart. The user node device ONU-n includes an arrayed waveguide diffraction grating 11 as a filter. The user node device ONU-n has two systems of oscillators 5 that perform frequency + Δf and −Δf transitions of the frequency of the CW light separated by the band splitter 3 and frequency modulation And an external modulator 6 of two systems for externally modulating the CW light whose frequency is shifted by + Δf and −Δf with upstream data, and between the access node device A-1 and the user node device ONU-n A working optical fiber and a spare optical fiber are provided between the access node apparatuses A-1 to An, and the signals separated by + Δf and the signals separated by −Δf are provided. Either one may be an optical signal transmitted through the working optical fiber, and the other may be an optical signal transmitted through the spare optical fiber.
[0033]
A wavelength-specific optical output monitor circuit 12 and a wavelength-specific optical output control circuit 13 for adjusting the intensity of the CW light transmitted according to the intensity of the optical signal arriving from the user node apparatus ONU-n may be provided.
[0034]
In the following, embodiments of the present invention will be described in more detail.
[0035]
(First Example)
A first embodiment of the present invention is shown in FIGS. FIG. 1 uses an arrayed waveguide grating (AWG) 2 widely used in a WDM system for multiplexing of CW light and downstream optical signals and for demultiplexing upstream signals in the access node device A-1. .
[0036]
Only the upstream signal shifted by the frequency Δf can be extracted by this arrayed waveguide grating 2 to cut the near-end reflection of the CW light. The user node device ONU-1 includes an oscillator 5 that oscillates at a frequency Δf and a frequency modulator 4, and modulates the band-demultiplexed CW light by the frequency modulator 4 and then externally modulates it with an upstream data signal. FIG. 2 shows the relationship between the wavelength arrangement at this time and the upstream optical signal subjected to frequency shift (wavelength conversion).
[0037]
(Second embodiment)
A second embodiment of the present invention is shown in FIG. FIG. 3 shows a method of using a retiming signal as an oscillator that oscillates at a frequency Δf in the user node device ONU-1. The user node device ONU-1 is provided with a retiming circuit 7 for clock extraction in a normal transmission / reception circuit. A specific configuration example is shown in which an N multiplier 8 that multiplies the clock signal from the retiming circuit 7 is provided, and the frequency modulator 4 is modulated by the N multiplied signal. Although FIG. 3 shows a configuration using the optical circulator 14 in the optical transceiver, the configuration of the band splitter 3 and the optical isolator 15 may be used as shown in FIG.
[0038]
(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. FIG. 4A shows an example of an access-transfer network to which the present invention is applied, and FIG. 4B shows a case where rings are further multiplexed. FIG. 5 shows a configuration of an access node and n user node devices ONU. The access node A-1 is provided with a multi-wavelength light source that is not modulated (CW light) at a plurality of different wavelengths, and is transmitted from the center node to each user node device ONU via the upper ring of FIG. From the multi-wavelength light source, the CW lights having different wavelengths are multiplexed by the arrayed waveguide diffraction grating (AWG) to the respective user node devices ONU and transmitted to the respective optical fibers.
[0039]
The configuration of the user node apparatus ONU shown in FIG. 5 is the same as that in FIG. 1 or FIG. FIG. 6 shows an example of wavelength arrangement at that time, and a downstream optical signal directed to the user node apparatus ONU includes a downstream wavelength region from the center node and a region of CW light from the multi-wavelength light source. The upstream optical signal from each user node apparatus ONU is shifted from the original CW light by Δf. Of these, FIG. 7 describes only the nth user node device ONU. In FIG. 7, only the CW light and the modulated upstream signal are described.
[0040]
Using a sine wave as a frequency modulation waveform in the user node apparatus ONU, the modulation index is set to about 1 to 2.5, and an optical signal shifted by + Δf and −Δf with respect to the wavelength is generated in the CW light. An example of an optical spectrum at this time is shown in FIG. In the access node, as shown in FIG. 7, one of the optical signals shifted by + Δf and −Δf is used as a working signal, and one is used as a spare signal.
[0041]
(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIGS. Usually, since the distance between the access node apparatus A-1 and each user node apparatus ONU is different and the optical loss varies, it is necessary to control the respective optical outputs. In the fourth embodiment, means for demultiplexing one optical signal on the access node A-1 side among the plurality of optical signals generated in the user node apparatus ONU of the third embodiment is arranged as shown in FIG. Performed by a waveguide diffraction grating (AWG) 11, the output of the demultiplexed optical signal is detected by a wavelength-specific light output monitor circuit 12, and is provided with a wavelength-specific light output control circuit 13 for CW light. The CW light output can be controlled for each wavelength to a predetermined output according to the output of the circuit 12. As an example of the wavelength for the wavelength-specific light output control circuit 13, a signal that is 2Δf away from the CW light can be used as shown in FIG. An optical signal shifted by Δf for the standby optical signal may be used for optical output control.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the cost of the entire system. In addition, a network configuration excellent in service responsiveness and maintainability becomes possible. Furthermore, high reliability of the network can be achieved. In addition, a highly stable network can be configured.
[Brief description of the drawings]
FIG. 1 is a block diagram of an optical access system according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a relationship between a wavelength arrangement of a downstream optical signal and a frequency-shifted upstream optical signal.
FIG. 3 is a block diagram of an optical access system according to a second embodiment of the present invention.
FIG. 4 is a diagram showing an example of an access transfer network to which the present invention is applied.
FIG. 5 is a block diagram of an optical access system according to a third embodiment of the present invention.
FIG. 6 is a diagram showing the relationship between wavelength arrangement of downstream optical signals and upstream optical signals subjected to frequency conversion.
FIG. 7 is a block diagram of an optical access system according to third and fourth embodiments of the present invention.
FIG. 8 is a diagram illustrating a relationship between a downstream CW optical signal and a frequency-shifted upstream optical signal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 CW light source 2, 10, 11 Array waveguide diffraction grating 3 Band splitter 4 Frequency modulator 5 Oscillator 6 External modulator 7 Retiming circuit 8 N frequency multiplier 9 Multi-wavelength light source 12 Optical output monitor circuit according to wavelength 13 Wavelength Separate optical output control circuit 14 Optical circulator 15 Optical isolators A-1, A-2, A-3, A-4 User node devices ONU-1 to ONU-n Access node devices

Claims (14)

An optical access system comprising an access node device accommodating a subscriber and a user node device installed in the subscriber's house, and bi-directionally transmitting between the access node device and the user node device using a single optical fiber In
The access node device
A light source of CW (Continuous Wave) light that is unmodulated light having a wavelength different from that of an optical signal modulated by downlink data addressed to the user node device;
Means for combining the optical signal modulated with the downlink data and the CW light and sending them to an optical fiber;
An optical filter that transmits an optical signal having a frequency of Δf away from the frequency of the CW light by an optical signal arriving from the user node device;
The user node device is
Means for separating the CW light from the optical signal modulated by the downlink data coming from the access node device and the optical signal combined with the CW light;
Means for causing a frequency Δf transition of the frequency of the CW light separated by the separating means;
Means for externally modulating the CW light having a frequency Δf transition with upstream data ;
An optical access system comprising: means for transmitting the output light of the means for external modulation to the optical fiber as an upstream optical signal addressed to the access node . The means for transition is:
An oscillator of frequency Δf;
The optical access system according to claim 1, further comprising: a frequency modulator that causes the CW light to transition at a frequency Δf by an oscillation frequency Δf of the oscillator. The user node device includes a retiming circuit that extracts a clock of the downlink data,
It said oscillator optical access system <br/> claim 2 comprising N times frequency divider for outputting the extracted clock signal of the retiming circuit N times to. A plurality of N user node devices are connected to one access node device,
The access node device
A light source of non-modulated light (CW light) having an N channel wavelength different from an optical signal modulated by downlink data addressed to the user node device;
The optical access system according to claim 1, further comprising: an optical filter that transmits optical signals that are separated from the frequency of the CW light having the wavelength of the N channel by Δf from optical signals that arrive from a plurality of N user node apparatuses. The access node device includes an optical filter that transmits an optical signal arriving from the user node device and having a frequency that is + Δf apart from a frequency of the CW light and a signal that is −Δf apart from the frequency of the CW light.
The oscillator is a sine wave oscillator;
The frequency modulator is configured to generate an optical signal including a component having a frequency Δf transition in the positive direction and a component having a frequency Δf transition in the negative direction with respect to the frequency of the CW light by frequency-modulating the CW light. Yes,
The light according to claim 2, wherein the external modulating means is configured to modulate an optical signal including a component having a frequency Δf transition in the positive direction and a component having a frequency Δf transition in the negative direction with upstream data. Access system. The access node apparatus uses one of the signal separated by + Δf and the signal separated by −Δf, which arrives from the user node apparatus via the optical fiber, as an active signal, and the other as a backup signal. 5. The optical access system according to 5. CW light , which is unmodulated light having a wavelength different from that of the optical signal modulated by the downlink data addressed to the user node device, is generated as an optical signal used by the user node device to change the frequency by Δf and used for modulation of the uplink data. A light source to
Means for combining the optical signal modulated with the downlink data and the CW light and sending them to an optical fiber;
An access node device comprising: an optical filter that transmits an optical signal arriving from the user node device and having a frequency of Δf away from the frequency of the CW light. Means for separating the CW light from the optical signal obtained by combining the optical signal modulated with the downlink data coming from the access node device and the CW light;
Means for transitioning the frequency of the separated CW light by a frequency Δf;
A user node apparatus comprising: means for externally modulating CW light having a frequency Δf transition with uplink data. The means for transition is:
An oscillator of frequency Δf;
9. The user node device according to claim 8, further comprising: a frequency modulator that causes the CW light to transition at a frequency Δf by an oscillation frequency Δf of the oscillator. A retiming circuit for extracting a clock of the downlink data;
The oscillator user node apparatus <br/> claim 9 further comprising a N-fold frequency divider for outputting the extracted clock signal of the retiming circuit N times to. A light source of CW light that is unmodulated light having an N channel wavelength different from an optical signal modulated by downlink data addressed to the user node device;
The access node apparatus according to claim 7, further comprising: an optical filter that transmits optical signals arriving from a plurality of N user node apparatuses each having a frequency of Δf away from the frequency of the CW light having the wavelength of the N channel. 8. The access node apparatus according to claim 7, further comprising an optical filter that transmits an optical signal arriving from the user node apparatus and having a frequency that is + Δf apart from the frequency of the CW light and a signal that is −Δf apart. 9. The user node apparatus according to claim 8, further comprising means for causing the frequency of the CW light separated by the separating means to undergo frequency + Δf and −Δf transitions. 8. The access node apparatus according to claim 7, further comprising means for adjusting the intensity of the CW light transmitted according to the intensity of an optical signal coming from the user node apparatus.

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