JP3055287B2 - Subscriber optical network communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber optical network.

[0002]

2. Description of the Related Art There are proposals for a subscriber optical network, such as a system using a time division multiplex system and a system using wavelength multiplexing.

FIG. 4 is a diagram for explaining a first conventional example. In FIG. 4, a master station 401 includes a subscriber terminal 402 located in an office, a building, and the like, and an optical fiber 4.
03 tied. Downlink transmission light from the master station 401 is distributed to the subscriber terminal 402 by the star coupler 404, and conversely, upstream transmission light from the subscriber terminal 402 is joined by the star coupler 404, and
Sent to In this system, a time division multiple access system is used, and one-to-one communication between a master station 401 and a subscriber terminal station 402 is performed in a time division manner.

FIG. 5 is a diagram for explaining the conventional example of FIG. In FIG. 5, a master station 405 is connected to a subscriber terminal station 406 by an optical fiber 407 as in the first conventional example, but upstream and downstream communications are performed by different optical fibers. In this system, a wavelength multiplexing method is used. The wavelength division multiplexing transmission light from the master station 405 is separated in wavelength by the wavelength separation element 408, and the signal light having the wavelength previously allocated to each subscriber terminal station 406 is distributed to the subscriber terminal station 406. Conversely, the upstream transmission light transmitted from the subscriber terminal station 406 at the wavelength assigned to each subscriber terminal station 406 is combined (wavelength multiplexed) by the star coupler 409 and transmitted to the master station 405. The master station 405 implements one-to-one communication by separating the received light into signals corresponding to the respective subscriber terminal stations by using a wavelength separation element.

[0005]

In the first conventional example, it is necessary to increase the transmission speed in order to increase the transmission capacity or the number of subscribers.
There is a problem that it is expensive and the price of the whole system becomes expensive.

In the conventional example shown in FIG. 2, a wavelength multiplexing system is used. In order to realize this method, as described with reference to FIG. 5, it is necessary to control the wavelength separation element and the wavelength of the transmission light, and at present, the price of the entire system is high.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-cost subscriber optical network having a sufficient transmission capacity for a subscriber.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a communication system for a subscriber optical network using an optical fiber, wherein a frequency division multiple access system is used for upstream communication and a time division multiplex system is used for downstream communication. Subscriber optical network communication used
Communication system, the transmission light source of the subscriber station and the receiver
The optical beat spectrum width is wider than the signal bandwidth.
And a light source having a wide emission spectrum width .

Further , the present invention provides the above-mentioned optical network for subscribers.
In the wireless communication system, the transmission light source
It is characterized by using a netting diode.

[0010]

[0011]

According to the present invention , in a subscriber optical network using an optical fiber, since the frequency division multiplex access system is used for upstream communication, the transmission speed of the transmitter of the subscriber terminal does not become too high. In addition, since the time division multiplexing method is used for downlink communication, if a broadband service is to be provided, the downlink transmission speed increases, but a high-speed receiver is less expensive than a high-speed transmitter. Therefore,
Broadband services can be realized with inexpensive subscriber terminal equipment.

[0012]

Further , according to the present invention, in the transmitter of the subscriber terminal in the above-mentioned subscriber optical network, the transmitting light source receives the signal.
The spectral width of the optical beat in the transmitter is
Since use of broad light emission spectrum width of which widens to compare, it is possible to avoid optical beat noise occurs when a light source having a sharp emission spectrum, such as a laser light source used in the transmission source.

[0014]

The present invention will be described below in detail with reference to examples. FIG. 1A is a block diagram of a subscriber optical network to which the present invention is applied. This network uses a time division multiplexing method for downlink communication and a frequency division multiplexing access method for uplink communication. Downlink time division communication provides broadband services and high-speed circuit switching. In FIG. 1A, a semiconductor laser 103 placed in a master station 101 is used as a transmission light source for downlink communication. The semiconductor laser 103 is modulated by the time division multiplex signal and provides the above-mentioned broadband service in the broadcast mode.
According to recent optical communication technology, modulation in a band of 15 GHz or more is also possible. The transmission light from the master station 101 is distributed to the subscriber terminal station 102 by the star coupler 104, and the subscriber terminal station 102 receives the designated time slot of the time division multiplex signal according to the control frame. Considering the immediate demand for transmission capacity, it is considered that an optical subscriber system requires a larger bandwidth for downstream communication than for upstream communication. Also, compared to high-speed transmitters, high-speed receivers are less expensive.

For upstream communication, a super luminescent diode 105 located at the subscriber terminal 102 is used as a transmission light source. Super luminescent diode 10
5 has a wide optical spectrum, so that optical beat noise in the receiver of the master station 101 can be avoided without performing wavelength control of the light source. These superluminescent diodes 105 are modulated at a single carrier frequency. This not only reduces the cost of the subscriber terminal 102 but also avoids the effects of intermodulation distortion. That is,
By avoiding the frequency band where carrier frequency harmonics occur, it is not necessary to use a highly linear device for the transmitter of the subscriber terminal 102. FIG. 1B shows an example of subcarrier channel frequency allocation.

FIG. 2 is a diagram for explaining intermodulation distortion. When a device having low linearity is modulated by two carrier frequencies, a power spectrum shown in FIG. 2 is obtained. In FIG. 2, a power spectrum 20 of a carrier frequency is shown.
In addition to the power spectra 1, 202, there are power spectra 203, 204 of third-order intermodulation distortion. When modulated at a single carrier frequency, only harmonic distortion appears, and no intermodulation distortion appears. Harmonic distortion appears at a frequency that is an integral multiple of the carrier frequency, so there is no problem if the use of that band is avoided, but intermodulation distortion appears near the carrier frequency and affects the carrier-to-noise ratio of the signal.

In a system using a semiconductor laser as a transmission light source of the subscriber terminal station 102 and using a frequency multiplexing system for simultaneous transmission, the problem of optical beat noise in the receiver 106 of the master station 101 cannot be avoided. Therefore, in a system in which a semiconductor laser is used as the transmission light source of the subscriber station 102, some wavelength control of the transmission light source is necessarily required. In the third invention, a light source having a wide emission spectrum width, for example, a super luminescent diode is used in order to make wavelength control unnecessary. Since the emission spectrum width of the superluminescent diode is wide, even if a plurality of superluminescent diodes are used as the transmission light source of the subscriber terminal 102, the spectrum width of the optical beat at the receiver is very large compared to the signal band. Therefore, the level of noise due to the optical beat is low, and has little effect on the carrier noise ratio of the signal.

FIG. 3 shows a specific example of optical beat noise to show the effect of the third invention. FIG.
(A) is a block diagram of an experimental system. The two transmission light sources were modulated at 145 MHz and 155 MHz, respectively. The optical outputs from the transmitters were combined by an optical fiber coupler, and the received signals were observed by a spectrum analyzer. FIG.
(B)-(e) is the spectrum of the received signal observed by the spectrum analyzer. FIG. 3B shows a spectrum of a received signal when a superluminescent diode is used as a light source. Although the center wavelengths of the two superluminescent diodes are almost equal, FIG.
In (b), the effect of the optical beat is not seen at all. FIGS. 3C to 3E show spectra of received signals when a semiconductor laser is used as a light source. The wavelength difference between the two LDs is 0, 0.01, and 0.05 nm, respectively. The effect of the optical beat noise is particularly remarkable in FIG. 3C in which the wavelengths of the two semiconductor lasers are almost equal.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to only the embodiments. For example, although the embodiment has been described with reference to FIG. 1A showing a double star type fiber network, the present invention can be applied to a tree type fiber network. Further, an application using an optical amplifier is also possible.

[0020]

As described above, if the present invention is applied, it is possible to reduce the price of the subscriber terminal equipment and to provide the subscriber optical system having a sufficient transmission capacity to the subscriber. Network can be provided. Further, by using different frequencies for the uplink and downlink carriers, bidirectional communication can be easily performed. Also, by increasing the frequency multiplicity,
The number (transmission capacity) of subscriber terminal stations can be easily increased.

In addition, a single key is connected to a single transmitting light source of the subscriber terminal.
By allocating the carrier frequency, a high-linearity device is not required for the subscriber station in the subscriber optical network, so that the price of the subscriber station apparatus can be reduced.

The transmission light source of the subscriber terminal station emits light.
By using a light source having a wide torque width, it is not necessary to control the wavelength of the light source at the subscriber terminal in the subscriber network, so that the price of the subscriber terminal device can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the invention shown in FIG. 2;

FIG. 3 is a characteristic diagram for explaining the invention of FIG. 3;

FIG. 4 is a diagram showing a conventional first subscriber optical network.

FIG. 5 is a diagram showing a second conventional subscriber optical network.

[Explanation of symbols]

 101, 401, 405 Master station 102, 402, 406 Subscriber terminal station 103 Semiconductor laser 104, 404, 409 Star coupler 105 Super luminescent diode 106 Receiver 201, 202 Carrier spectrum 203, 204 Intermodulation distortion spectrum 403 , 407 Optical fiber 408 Wavelength separation element

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08

Claims (2)

(57) [Claims] A communication system for a subscriber optical network using an optical fiber, wherein a subscriber unit optical network communication using a frequency division multiplexing system for upstream communication and a time division multiplex system for downstream communication. In the system, the transmission light source of the subscriber station is provided with the optical beat scan at the receiver.
Emission spectrum whose spectral width is wider than the signal band
A subscriber-based optical network communication system characterized by using a light source having a wide torque width . 2. A transmission device according to claim 1, wherein said transmission light source is a super luminescent sensor.
2. The method according to claim 1, wherein a photodiode is used.
Subscriber-based optical network communication system.