JPH1141179A - Star-shaped optical subscriber system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an error of a reception signal due to multiple reflection. SOLUTION: When an optical network unit(ONU) 2-n has the longest transmission distance with an optical subscriber unit(OSU) 1 among ONU2-1 to 2-n, an optical attenuator 5 with an attenuation amount to coincide with a reception level of a signal of the ONU2-n in an OSU1 is installed in a star coupler 3 by other ONUS 2-1, 2-2. Consequently, a signal level of multipath reflected light of the ONU2-2 with the highest signal level becomes equal to or lower than the signal levels of each of the ONUs 2-1 to 2-n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
(Passive Double Star)
With regard to star type optical subscriber systems such as systems,
The present invention relates to a configuration for preventing a system operation failure due to multiple reflected light.

[0002]

2. Description of the Related Art A star-type optical subscriber system has been considered as a system capable of high-speed, wide-band communication by laying an optical fiber cable to a subscriber's house. At present, such a star type optical subscriber system includes P
A DS system is being considered.

Conventionally, documents relating to such a PDS system include, for example, [a] Y. TAKIGWA et al: “ATM based
Passive Double Starsystem offering B-ISDN,
N-ISDN ", and POTS" GLOBCOM '9
3, pp. 14-18 Dec. 1993 [b] OKUMURA et al: “ATM based o
ptical access network providing multiple service
s "6TH INTERNAL WORKS
HOP ON OPTICAL ACCESS NET
WORK, pp.7.5-1,7.5-9 Oct.1994.

The conventional star-type optical subscriber system disclosed in the above-mentioned documents and the like is configured as follows. FIG.
It is a block diagram of the conventional star type optical subscriber system. The illustrated star optical subscriber system is a PDS system. This PDS system is an OSU (Optical Subscriber Unit) that is an intra-office device (station-side network termination device).
1 and ONUs (Optical Network Units) 2-1 to 2-n, which are a plurality of subscriber-side devices (subscriber-side network terminating devices), are connected via an optical fiber 4 via a star coupler 3;
This is a communication system in which one transmission path is shared by a plurality of users.

In such a PDS system, a signal (downlink signal) from the station inside device (hereinafter, referred to as OSU) 1 to each of the subscriber side devices (hereinafter, referred to as ONU) 2-1 to 2-n is a common signal. Are received by each of the ONUs 2-1 to 2-n, and each of the ONUs 2-1 to 2-n receives P by a polling request from the OSU 1 specified for each PDS cell.
A DS cell is sent (up signal). In OSU1, each O
In order to avoid collision of burst signals from the NUs 2-1 to 2-n, the delay time due to the transmission distance at the time of connection is measured for each of the ONUs 2-1 to 2-n, and the signal from each of the ONUs 2-1 to 2-n is measured. The cell transmission timing of the OSU 1 is controlled in accordance with the transmission delay so that the reception timing of the cell becomes constant. The transmission distance between the OSU 1 and each of the ONUs 2-1 to 2-n is specified to be a maximum of 10 km.

[0006]

However, the PDS
A major problem in realizing the system is the effect of multiple reflected light on the upstream signal. That is,
Due to the difference in transmission distance between the OSU 1 and each of the ONUs 2-1 to 2-n, etc., the reception level at the OSU 1 greatly differs for each of the ONUs 2-1 to 2-n. Need.
For signals from ONUs that are short from the OSU1, the reception level at the OSU1 is large and an optical connector or the like is not shown. OSU1 and ONU2-1 to 2-n
The level of the reflected light generated in the optical circuit or the like cannot be ignored.
The level of the reflected light exceeds the threshold, which is another ONU2
When overlapping with the transmission signals from -1 to 2-n occurs, a case may occur where signals from the other ONUs 2-1 to 2-n cannot be received.

For this reason, it is necessary to take measures such as reducing the reflection at the optical components so as not to exceed the reception threshold level of the OSU1. Such a problem is described, for example, in Kajiwara et al., “Regarding Optical Multiple Reflection Characteristics in PDS,” Spring Meeting B-977, IEICE, 1996. Design conditions become difficult.

[0008] In view of the above, in the star type optical subscriber system, it has been desired to implement a specific measure for preventing an error of a received signal due to multiple reflection.

[0009]

The present invention employs the following structure to solve the above-mentioned problems. <Structure of Claim 1> In a star-type optical subscriber system in which a plurality of subscriber-side devices are branched into a star-type optical transmission line and connected to an office-side device, an optical branching unit for branching into a star-type is provided. A star-type optical device comprising an optical attenuator having an attenuation corresponding to the signal level of each subscriber side device so as to average the signal reception level of the station side device between the subscriber side device. It is a subscriber system.

<Explanation of Claim 1> The star type optical subscriber system in the invention of claim 1 is, for example, a passive double star system, but is not limited to this, and has a single star configuration. Optical subscriber system. Also, the optical branching unit is a star coupler in a passive double star system,
If it is a single star configuration, it is a station inside device. Further, the optical attenuator may be installed anywhere between each optical network unit and the optical branching unit.

According to the first aspect of the present invention, the optical reception level in the station inside apparatus can be averaged, and as a result, the error of the received signal due to the multiple reflection can be reliably prevented. Can be. In addition, since only an optical attenuator is added as a configuration for obtaining such an effect, there is an effect that design is easy and there is almost no increase in cost due to this. Further, since the received signal level in the station inside device is averaged, the effect that the dynamic range of the received signal can be small even in the station inside device can be obtained.

<Structure of Claim 2> According to Claim 1, the attenuation of the optical attenuator is a value corresponding to the transmission distance between the subscriber unit and the station inside device. System.

<Description of Claim 2> According to the invention of Claim 2, since the attenuation of the optical attenuator is determined by the transmission distance between the subscriber unit and the station inside device, the attenuation of the optical attenuator can be easily and accurately determined. You can decide the amount.

<Structure of Claim 3> In Claim 1 or 2, the optical splitter is a star coupler in a passive double star system, and the optical attenuator is provided in the star coupler. An optical subscriber system.

<Explanation of Claim 3> In the invention of claim 3, the star type optical subscriber system is a passive double star system, and an optical attenuator is provided in a star coupler. As a result, as a passive double star system, there is an effect that an error of a received signal due to multiple reflection can be surely prevented without adding a new configuration to a subscriber side device or a station inside device.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. << Specific Example >><Configuration> FIG. 1 is a configuration diagram showing a specific example of the star type optical subscriber system of the present invention. The illustrated system shows a PDS system. This PDS system includes an OSU1 which is an intra-office device and an ONU2 which is a plurality of subscriber-side devices.
-1 to 2-n are connected by an optical fiber 4 via a star coupler 3, and one transmission line is shared by a plurality of users. These configurations are the same as those in the related art.

Each of the ONUs 2-1 to 2-n is connected to a star coupler 3 to which an optical attenuator 5 having an attenuation corresponding to a transmission distance from each OSU 1 is added. For example, in the illustrated example, each transmission distance is ONU2
-1 is 5 km, ONU2-2 is 2 km, ONU2-n
Is 10 km, the attenuation of the optical attenuator 5 is the lowest in signal level (the distance from the OSU 1 is long).
The ONU2-n level is replaced with other ONU2-1 to 2-n-
The value is determined so that the signal level of 1 matches.

<Operation> FIG. 3 is an explanatory diagram showing a comparison between the present embodiment and a case where an optical attenuator is not added. FIG. 3A shows a case where an optical attenuator is not added, and a difference occurs in a reception level in the OSU 1 due to a difference in transmission distance between each of the ONUs 2-1 to 2-n and the OSU 1. On the other hand, as shown in (b), when the optical attenuator 5 is added, the signal level of each of the ONUs 2-1 to 2-n is equal to the signal level of the ONU 2-n having the longest transmission distance. Therefore, the ONU with the highest signal level
The multiple reflection light of 2-2 is also kept lower than the signal level of each of the ONUs 2-1 to 2-n. As a result, the signal level of the multiple reflected light does not reach the OSU1 reception threshold,
No signal error occurs due to the collision between the reflected light and the signal.

<Effects> As described above, according to this specific example, in the PDS system, each of the ONUs 2-1 to 2-n
Each time, an optical attenuator 5 corresponding to the level difference is added between the star coupler 3 and the ONUs 2-1 to 2-n, so that the optical reception level in the OSU 1 can be made uniform. An error in the received signal due to multiple reflection can be reliably prevented. Also, in this specific example,
Since the configuration is such that the optical attenuator 5 is merely added to a general PDS system, there is an effect that the design is easy and there is almost no cost increase.

In the above example, the PDS system has been described as the star type optical subscriber system. However, the present invention is not limited to this. Can be applied to

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a specific example of a star type optical subscriber system according to the present invention.

FIG. 2 is a configuration diagram of a conventional star type optical subscriber system.

FIG. 3 is an explanatory diagram showing an effect of a specific example of the star type optical subscriber system of the present invention in comparison with a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 OSU (Inside station apparatus) 2-1 to 2-n ONU (Subscriber side apparatus) 3 Star coupler 4 Optical fiber 5 Optical attenuator

Claims (3)

[Claims] 1. A star optical subscriber system in which a plurality of subscriber-side devices are branched into a star-type optical transmission line and connected to an office-side device, wherein the star-type optical branching unit; A star type, wherein an optical attenuator having an attenuation amount according to the signal level of each subscriber side device is provided between the subscriber side device and the signal reception level of the station inside device so as to be averaged. Optical subscriber system. 2. The star type optical subscriber system according to claim 1, wherein the attenuation of the optical attenuator is a value corresponding to the transmission distance between the subscriber side device and the office side device. 3. The star type optical subscriber system according to claim 1, wherein the optical branching unit is a star coupler in a passive double star system, and an optical attenuator is provided in the star coupler. .