JP3079703B2 - TDMA optical transmission 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 TDMA optical transmission system and, more particularly, to an optical separation circuit of a TDMA optical transmission system using a star coupler for branching a transmission line.

[0002]

2. Description of the Related Art Conventionally, this type of TDMA (Time D
In an optical transmission system of the multiplex multiple access (vision multiple access) system, the optical transmission path is separated by a star coupler, and the optical signal from the parent device of the central station is separated into a star by the star coupler. A terminal device is connected to each separation destination, and each terminal device sequentially communicates in a time zone determined by a burst signal from the parent device. There are many types of star couplers for branching and connecting a plurality of optical transmission lines. For example, a twist / fusion method using coupling between tapered fibers is typical. Generally, the star coupler and each terminal device are connected by a transmission line using an optical fiber, but the distance between them varies, and therefore, the delay time and amplitude characteristics of the optical signal differ.

[0003]

As described above, in the conventional example, since the distance from the star coupler to each terminal device at the separation destination is various, a burst signal is transmitted from each terminal device by TDMA transmission or the like. In the case where the master device receives the data via the communication device, there is a problem that the amplitude of the received data is not determined, which complicates the optical receiving circuit.

[0004]

According to the present invention, there is provided a TDMA optical transmission system comprising: a terminating device; and an optical demultiplexer using a star coupler for separating one optical transmission line from the terminating device into a plurality of transmission lines. And a plurality of terminal devices connected to the end of each transmission path separated by the optical separation unit.
In the optical transmission system, the optical separation unit includes the star coupler and a plurality of optical variable attenuators that vary the amplitude of an optical signal connected to each signal line separated by the star coupler by a control signal from the outside. And transmitting an optical signal from the terminating device connected to each of the optical variable attenuators to the transmission line on the terminal device side, and measuring a delay time of the transmission line on the terminal device side by an optical response signal from the terminal device. A plurality of delay time measuring circuits, an output signal of each of the delay time measuring circuits, a maximum delay time detecting circuit for detecting a maximum delay time among them, an output signal of each of the delay time measuring circuits, A plurality of delay time comparison circuits for comparing the output signal of the delay time detection circuit and outputting each of the control signals for controlling the amount of light attenuation determined from the delay time difference.

[0005]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. Here, a case where optical ping-pong transmission, which is an example of the TDMA system, is performed in a system in which a subscriber line is separated into N lines by a star coupler will be described as an example. The portion shown by the dotted line is the light separating section 8 which characterizes the present invention. The burst signal output from the terminating device 7 to the optical transmission line 700 is separated into N transmission lines by the star coupler 6, and after passing through the optical variable attenuators 3-1 to 3-N, respectively, the delay time measuring circuit 2- 1 to 2-N. Each delay time measurement circuit 2-1
In to 2-N, it detects the input timing of the burst signal as the time T _1. Each delay time measuring circuit 2-1 to 2
-N are transmitted through the optical transmission line 100, respectively.
-1 to 100-N and output to the terminal devices 1-1 to 1-N
To reach. Since the lengths of the respective optical transmission paths differ in the arrival time, there is a time difference depending on the terminal device. The terminal devices 1-1 to 1-N that have received the burst signal output the folded burst signal and again transmit the transmission lines 100-1 to 100-1 to 10-N.
0-N, delay time measuring circuits 2-1 and 2-2, respectively.
-N. Each of the delay time measurement circuits detects this input timing as Tn (1 ≦ n ≦ N), and the detection time T
_The value .DELTA.Tn (1.ltoreq.n.ltoreq.N) obtained by counting the difference from ₁ is used as the maximum delay time detecting circuit 5 and the corresponding delay time comparing circuit 4.
-1 to 4-N are output. Delay time comparison circuits 4-1 to 4
-N is the value ΔTn entered, compares the maximum delay time [Delta] T _max, which is input from maximum delay time detecting circuit, to calculate the time difference ΔT _max -ΔTn, optical variable attenuator 3-1 to this as a control signal Output to 3-N. Since the delay time of the optical signal is proportional to the attenuation, the attenuation of the variable optical attenuator (3-1 to 3-N) is controlled by this control signal and input to the star coupler 6 and the terminating device 7. The amplitude of the burst signal of each of the terminal devices (1-1 to 1-N) has a constant value.

[0006]

As described above, according to the present invention, the attenuation of the optical attenuator set for each transmission line is automatically set in accordance with each distance difference in consideration of the distance difference between the transmission lines, and the termination device is provided. Since the amplitude of the input burst signal is constant, the AGC peripheral circuit and the like in the optical receiving unit inside the termination device are simplified, so that there is an effect that the device can be reduced in size and cost as a whole.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

[Explanation of symbols]

 1-1 to 1-N terminal device 2-1 to 2-N delay time measurement circuit 3-1 to 3-N variable optical attenuator 4-1 to 4-N delay time comparison circuit 5 maximum delay time detection circuit 6 star Coupler 7 Termination device 8 Optical separation unit 100-1 to 100-N, 700 Optical transmission line

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04B 10/00 H04J 14/08 H04J 3/00 H04L 12/44

Claims (1)

(57) [Claims] 1. A terminating device, a light separating unit using a star coupler for separating one optical transmission line from the terminating device into a plurality of transmission lines, and each transmission line separated by the light separating unit In the TDMA type optical transmission system including a plurality of terminal devices connected to the end of the optical coupler, the optical demultiplexing unit transmits the amplitude of the optical signal connected to the star coupler and each signal line separated by the star coupler. A plurality of variable optical attenuators that can be varied by an external control signal;
A plurality of optical variable attenuators connected to each of the optical variable attenuators for transmitting an optical signal from the terminating device to a transmission line on the terminal device side and measuring a delay time of the transmission line on the terminal device side by an optical response signal from the terminal device A delay time measurement circuit, a maximum delay time detection circuit that receives an output signal of each of the delay time measurement circuits and detects a maximum delay time among them, an output signal of each of the delay time measurement circuits, and the maximum delay time A plurality of delay time comparing circuits for comparing the output signal of the detection circuit and outputting each of the control signals for controlling the optical attenuation determined from the delay time difference. system.