JPS6057777B2 - optical transmission equipment - Google Patents

Description

[Detailed description of the invention] The present invention connects a center and a plurality of terminals with a single wire,
The present invention provides an optical transmission device that performs bidirectional transmission by using a plurality of wavelengths.

Conventionally, as a method for connecting a center and multiple terminals in an optical fiber transmission system, as shown in Figure 1 a and b,
Possible methods include connecting each terminal and the center using separate lines, using a directional coupler, or using a duplexer. The individual connection method shown in Figure 1a allows for a large optical output and does not require a splitter or demultiplexer, but it requires an input light source for each line and has the disadvantage of requiring a large amount of transmission fiber. have.

Furthermore, in the case of bidirectional transmission, a fiber of the same distance is required, or devices such as a splitter or a duplexer are required. Further, the same figure shows a case where a directional coupler is used, and 7 indicates a center configuration, and 8 to 14 indicate terminal portions constituted by branches having a four-terminal configuration.

A part of the optical signal 15 output from the center 7 is branched into a fiber 17 at the terminal section 8, and the rest is transmitted to the terminal section 9. On the other hand, part of the optical signal input from the fiber 16 is transmitted to the terminal section 9 and the rest to the fiber 17. In other words, a part of the optical signal of the fiber 16 that should be input to the fiber 15 is transmitted to the fiber 17, so not only is the loss of the transmitted optical signal very large, but also the input signal of the fiber 16 and the output signal of the fiber 17 are In the case of signals in the same frequency band, the terminal unit 8 cannot transmit and receive signals at the same time for this reason. Furthermore, the input optical signal from the fiber 16 is transmitted to the terminal portions 9, 10...
...Since it is also received by 14 etc., it also has the drawback of crosstalk. In order to eliminate such drawbacks, the applicant has
We have already proposed an optical transmission device that can perform two-way transmission without crosstalk by connecting multiple terminals in series using multiple wavelengths.

A part of the device is shown in FIG. 18 is λ.

It is a central station that has a transmitting and receiving section for wavelength bands up to λ6, and 19 to 25 are wavelength bands λ0 to λ. The terminal station has transmitting and receiving sections, and these are sequentially connected. λ sent from the central station. - λ6 signals are taken out at the terminal station 19, and at the same time, the signals in the λ1 wavelength band emitted from this station are superimposed on the extracted signals in the λ2 to λ6 wavelength bands. In this way, the terminal stations 19 to 25 can each individually transmit and receive signals of λ1 to λ6.
However, even with this configuration, when the distance between terminals becomes long, the transmitted optical power decreases as the distance from the central station increases, and the optical output particularly decreases as the terminal station 25 is reached. Another disadvantage is that the transmission band decreases as the distance from the input end increases.

The present invention has been made to solve the above-mentioned drawbacks.
An object of the present invention is to provide an optical transmission device in which the optical output does not decrease even when the transmission distance becomes long, the transmission band does not decrease, and crosstalk does not occur.

The present invention will be described below with reference to the drawings and embodiments.

The configuration of the present invention will be described with reference to FIG. 3, taking as an example the case of a light source in four wavelength bands.

28 is a central station having a signal generation source in the wavelength band λ1 to λ, and a receiving device for signals in the same wavelength band, and 29, 30, 31,
32 is a demultiplexer having input and output terminals for each wavelength band of λ1, λ3, λ4, and λ2.

Each branching filter and the central station are connected in series by optical fibers to form a closed circuit. FIG. 4a shows an example of a duplexer that constitutes each terminal section 29 to 32, in which 37 to 40 are fiber inputs,
Output ends 41 to 44 are lens systems, and 45 is a bandpass filter, the filter characteristics of which are shown in FIG. 4b. Now, r1 and R2 incident from fiber 37
The optical signals in the R2 wavelength band are made into parallel beams by the lens 41, and the R2 wavelength band signal is reflected by the filter 45 and transmitted to the fiber 40. The r1 wavelength band signal passes through the filter 45 and is transmitted to the fiber 39. On the other hand, the r1 wavelength band signal incident from the fiber 38 is similarly filtered into the filter 4.
5 and is combined with the R2 wavelength band signal and transmitted to fiber 40. Note that the characteristics of the filter shown in FIG. 4b may be such that it reflects only signals in a predetermined wavelength band other than the present embodiment. The configuration shown in FIG. 4a can also be obtained using a self-converging lens. In Fig. 3, λ1,
The relationship between λ2, λ3, and λ is λ1, λ2, λ3, and λ4.

Optical signals in the input 1 and λ3 wavelength bands are sent out in a direction 35, and optical signals in the λ2 and λ4 wavelength bands are sent out in the opposite direction 36. Of the λ1 and λ3 signals sent from the central station 28, the λ1 wavelength band optical signal is split into the fiber 34 at the terminal station 29, and a new λ1 wavelength band optical signal is input from the fiber 33 to the terminal station 29. The transmitted optical signal in the λ3 wavelength band and l are transmitted to the terminal station 30. Similarly, the terminal station 30 inputs and outputs an optical signal in the λ3 wavelength band, in the opposite direction, the terminal station 31 inputs and outputs a λ4 wavelength band signal, and the terminal station 32 inputs and outputs a λ2 wavelength band signal. In this way, bidirectional communication is possible between the central station and each terminal station, and since each terminal station transmits only its own wavelength band, it goes without saying that there is no crosstalk between each terminal station. Since light is transmitted in both directions from the central station, the optical transmission distance from the central station to each terminal station is halved compared to that in FIG. 2, and the drop in optical output is halved.

Usually, there are more signals sent from the central station than from each terminal station, so a wide band is required.
However, if the central station transmits optical signals in only one direction, the transmission band becomes narrower for later terminals as the distance between terminal stations becomes longer. By transmitting more signals, the signal distance from the central station is halved, allowing for a wider band. Similarly, as the distance increases, the optical output decreases, but this can also be prevented. Furthermore, even if there is a disconnection at any point, all signals from the central office will not be lost. By the way, for example, if the multi-wavelength band optical signal transmitted from the central station has the wavelength characteristics shown in FIG. Therefore, no matter how well a filter with good characteristics is used to separate the signals, signal overlap occurs and the S/N ratio decreases.

Similarly, S/
A decrease in N occurs. However, as shown in Figure 3, λ1
By transmitting the λ2 and λ4 wavelength band signals from one side and the λ2 and λ4 wavelength band signals from the other side, the wavelength bands of the optical signals transmitted in one direction no longer overlap, and the filter characteristics are not as strict. Even if there is no signal interference, signal interference due to overlapping wavelength bands, that is, a reduction in S/N does not occur. Such features become more effective as the number of wavelength bands increases. As explained above, according to the present invention, since multiple wavelength band signals are transmitted from the central station to both sides of the closed loop, it is possible to prevent a decrease in light output at terminal stations located far from the central station, and also to prevent transmission Not only can the band be widened, but crosstalk between terminal stations will not occur. Furthermore, according to the present invention, signal interference due to overlapping wavelength bands is eliminated, and even if the transmission body is cut at any point, all signals from the central station will not be weakened or cut off.

[Brief explanation of drawings]

FIGS. 1A and 1B are block diagrams of a conventional optical transmission device, FIG. 2 is a block diagram of an optical transmission device already proposed by the applicant, and FIG. 3 is an embodiment of the optical transmission device of the present invention. Configuration diagram, Figure 4A,
5b is a configuration diagram of a terminal station according to the present invention and a filter characteristic diagram of the terminal station, and FIG. 5 is a characteristic diagram of a plurality of wavelength band signals. 28... Central station, 29-32... Terminal station, 33, 34, 37-40... Optical fiber, 41-44... Lens system, 45 ····filter.

Claims (1)

[Scope of Claims] 1. A central station that transmits and receives a plurality of wavelength band signals and a plurality of terminal stations that transmit and receive respective wavelength band signals are connected by a transmission body to form a closed loop, An optical transmission device characterized in that the central station performs both transmitting and receiving functions at each of the starting end and the terminating end of the closed loop. 2. The optical transmission device according to claim 1, wherein the signals transmitted at the starting end and the ending end of the closed loop are signals in wavelength bands adjacent to each other.