RU2264692C1 - Fiber-optic network - Google Patents

Abstract

FIELD: optical communications.

SUBSTANCE: couplers incorporated in fiber-optic network data exchange bus in the form of optical fiber loop from first to last one are characterized in reducing gain. As a result, in the course of network operation optical power of receivers is independent of number assigned to receiving and transmitting terminals.

EFFECT: reduced variations in power supplied to terminal receivers.

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Description

The invention relates to fiber optic information transmission systems and can be used in airborne information exchange systems.

A known optical fiber network containing a data bus, made in the form of two parallel optical fibers, N-terminals with an optical transmitter and a receiver each, located along the bus and N-1 a pair of optical couplers, a transmitter and a receiver of the first terminal are connected to the bus through the ends of the optical fibers , and the transmitters and receivers of the second and subsequent terminals through the corresponding couple of couplers. In addition, the receiver of the first terminal and the transmitter of the remaining terminals are connected to one bus fiber, and the transmitter of the first terminal and the receivers of the other terminals to another bus fiber. All taps have equal branch coefficients for the bus [1, 2].

A disadvantage of the known technical solution is the large power difference of the optical signals supplied from different transmitters to the receiver of the first terminal, the dynamic range of which limits the number of terminals in the network.

In addition, since the first terminal acts as an active repeater in the bus between two fibers, the reliability of the communication line as a whole is determined by the reliability of its “bottleneck” - the repeater.

,

,

,...,

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. [3]Known fiber optic network containing N terms with an optical receiver and transmitter each, and a data bus in the form of a light guide ring. The ring includes N directional optical couplers through which terminals are connected to the bus. The taps in the ring from the last to the first (by the hour) are made with decreasing branch (transmission) coefficients in a harmonic sequence:

,

,

, ...,

,

. [3]

Moreover, in order to equalize the optical power at the receivers, the transmitters in the terminals from the first to the last have powers that decrease in approximately the same harmonic sequence (i.e., the transmitter of the terminal corresponding to the first coupler has a power N / 2 times that of the transmitter last terminal).

и первому ответвителю с коэффициентом ответвления

. Таким образом циркуляция оптической мощности по кольцу приводит к перекоси (в N раз) по принимаемой мощности при обмене данными между двумя любыми терминалами. Что и является основным недостатком известного технического решения.However, the alignment of optical power occurs in “pieces”: when transmitting from a terminal with the i-th number to terminals with large serial numbers, we get one optical power level at the receivers, and when transmitting to terminals with numbers less than i, we get another one, N times smaller. The latter is due to the circulation of power along the ring and a jump-like decrease in the branch power when switching along the ring from the last N-th coupler with a branch coefficient

and the first coupler with a branch coefficient

. Thus, the circulation of optical power along the ring leads to a skew (N times) in received power during data exchange between any two terminals. Which is the main disadvantage of the known technical solution.

A known fiber-optic network containing N terminals with an optical receiver and transmitter each, and a data bus in the form of a light guide loop, the first and second branches of which are connected by the first input and output ports via (N-1) directional optical couplers, the first terminal is connected with the bus through the beginning and end of the light guide loop, and the second and subsequent terminals are connected to the bus through the second input ports of the first and subsequent, respectively, in the order of their placement along the bus, taps in the first branch and second outputs e ports of taps in the second branch of the loop, all terminal transmitters connected to the first branch of the loop, and all receivers to the second branch of the loop [4].

This device is taken as a prototype. The disadvantage of the prototype is the large difference in the power of the optical signals supplied to the terminal receivers from the transmitters located at the beginning and at the end of the bus, due to the loss of optical power during the passage of signals along the bus on taps with equal branch coefficients. In addition, due to branch losses, prototype receivers located at the beginning and end of the bus are in significantly different reception conditions for the minimum input power level. It is fundamentally impossible to exclude or reduce these losses, since they ensure the passive bus performance. With equal branch coefficients, such as those of the prototype, they lead to unreasonably high requirements for the dynamic range and sensitivity of the receivers and, as a result, to the possibility of errors in data transmission during transitions from low to high signal levels and vice versa.

The present invention solves the problem of reducing the difference (ratio) of the power supplied to the receivers of the terminals from the transmitters located in different places of the fiber-optic bus, as well as the alignment of the optical power supplied to the receivers located in different places of the bus.

To achieve this technical result, a fiber optic network contains N terminals with an optical receiver and transmitter each, and a data bus in the form of a light guide loop. The first and second branches of the loop are connected by the first input and output ports along (N-1) directional optical couplers. The first terminal is connected to the bus through the beginning and end of the light guide loop, and the second and subsequent terminals are connected to the bus through the second input ports of the first and subsequent, respectively, in the order of their placement along the bus, couplers in the first branch and second output ports of the couplers in the second branch of the loop. All terminal transmitters are connected to the first branch of the loop, and all receivers are connected to the second branch of the loop. Unlike the prototype, in the branches of the loop, the couplers from the first to the last are made with decreasing transfer coefficients from the first input to the second output ports and from the second input to the first output ports.

Due to the presence of distinctive features in the proposed network, the optical powers supplied to the receivers of different terminals are aligned, and the power difference at the receivers from the transmitters of different terminals is reduced.

,

,

,

,...,

.The difference in optical power reaches its minimum when the couplers in the branches of the loop are made with decreasing transfer coefficients in a harmonic sequence:

,

,

,

, ...,

.

In this case, there is no difference in optical powers, and power weakened by N ² times is applied to the receivers regardless of the number of the transmitting and receiving terminals.

Figure 1 shows a diagram of the proposed fiber optic network.

Figure 2 shows a diagram of a directional optical coupler.

The fiber optic network (Fig. 1) contains a data bus made in the form of a light guide loop 1. In the first branch 2 and the second branch 3 of the light loop 1 are included by the first input 19 and output 20 ports (see Fig. 2) according to (N -1) directional optical couplers 4, 5, 6, 7 and 8, 9, 10, 11, respectively. N terminals 12, 13, ..., 16 are connected to the data exchange bus with an optical transmitter 23 and a receiver 24 each, and the transmitter 23 and the receiver 24 of the first terminal 12 are connected to the bus through the beginning 17 and the end 18 of the light guide loop 1, and the transmitter 23 and the receiver 24 of the second terminal 13 through the second input 21 and output 22 ports of the couplers 4 and 8, respectively, and the transmitters and receivers of the third terminal 14 through the second input 21 and the second output 22 of the couplers 5 and 9, etc. All transmitters 23 of the terminals are connected with the first branch 2 of the light guide loop 1, and all receivers 24 with the second branch 3 of the loop 1.

Taps 4, 5, 6 in the first branch 2 of loop 1 have transmission coefficients α (Fig. 2) from the first input port 19 to the second output port 22 and from the second input port 21 to the first output port 20, equal to α ₄ = 1/2 , α ₅ = 1/3, α ₆ = 1/4, ... Similarly, taps 8, 9, 10 in the second branch 3 have transmission coefficients α ₈ = 1/2, α ₉ = 1/3, α ₁₀ = 1 / 4, ... etc., decreasing along the tire in a harmonic sequence. The latter in branches 2, 3 answered 7, 11 have transmission coefficients α ₇ = α ₁₁ = 1 / N. Thus, a couple of couplers with transmission coefficients α = 1 / i are connected with the i-th network terminal in the order of their placement along the bus.

Works fiber optic network (figure 1) as follows. One of the terminals, for example, terminal 12, performs the functions of a network controller and controls the operation of the terminals according to the well-known exchange protocol, for example, according to GOST 26765.52-87 (not considered in the application). In this case, the optical radiation from the transmitter 23 of one of the terminals is introduced into the branch 2 of the light guide loop 1 and propagates along the branch 2 to turn 25 of the loop, where it enters the second branch 3 of the light guide loop 1. In this case, the power P of the optical radiation from the transmitter of the ith terminal enters to branch 2 weakened i times in accordance with the branch coefficient α of the coupler into the light guide loop. Further propagating along branch 2 and encountering couplers on its propagation path, the power is additionally attenuated first (i + l) / i times, then (i + 2) / (i + l) times, etc. On the last coupler 7, the optical power is attenuated N / (N-1) times. Thus, by turning 25 loops, the optical power is weakened N times (i × (i + 1): i × (i + 2) :( i + 1) × ... × (N-1) :( N -2) × N: (N-1) = N) regardless of the number i of the transmitting terminal. Propagating along the second branch 3 of loop 1, optical radiation is extracted by couplers to the receivers of 24 terminals. Meeting the couplers on the propagation path along the second branch 3, the optical power is additionally attenuated, first N / (N-1) times (on the coupler 11), then (N-1) / (N-2) times, etc. So the optical radiation approaches the j-terminal coupler N ² / j times (N × N: (N-1) × (N-1) :( N-2) × ... × (j + 2) : (j + 1) × (j + 1): j = N ² / j) and, therefore, the receiver 24 of the jth terminal receives optical power attenuated by a factor of N through the light guide loop 1 ((N ² : j) × j = N ² ) regardless of the number j of the receiving terminal.

Let us show, for an example of a line with N = 6, that a decrease in the power drop at the line receivers occurs in the general case, when the transmission coefficients decrease arbitrarily (the reduction sequence is not harmonic).

Let the couplers be placed along the bus with the following transmission coefficients α: 1/3; 1 / 3.3; 1 / 3.8; 1 / 4,5; 1/5, in decreasing order. Then the optical signal from the second terminal 13 will reach the turn 25 of the loop weakened by 9.39 times (3: 1 × 3.3: 2.3 × 3.8: 2.8 × 4.5: 3.5 × 5: 4 = 9.39). And since the power of the optical signal from the last terminal 7 is introduced into the bus weakened by 5 times, the difference (ratio) of power will be 9.39 / 5 = 1.88. At the same time, in the prototype, with equal branch coefficients, for example 1/3, the power will be weakened by 15.2 times, and the difference will be 15.2 / 3 = 5.06. In the case of a transmission coefficient equal to 1/4, the power attenuation in the prototype will be 12.4, and the difference is 3.16. If the transfer coefficient is taken to be 1/5 or less, then the ratio of power input to the bus from the first and second terminals will be more than 4, against 2 for the same terminals in the example of the claimed device.

Note: All the above calculations are performed without taking into account losses at the connection of bus elements and losses due to attenuation in the optical fiber. The current level of development of fiber-optic technology allows even single-mode fibers to be connected at a loss level of 0.01 dB with an attenuation coefficient of about 0.15 dB / km, and the coupler’s own losses on coupled waveguides are less than 0.05 dB. In on-board and local networks of small length with the number of terminals less than 100, these losses can be ignored.

Sources of information

1. M.B. Miller, N. E. Lewis. Linear Fiber Optic Databus for Aircraft, - Avionics, 1988, april, p. 26-29.

2. PCT patent W 083/03327, H 04 B 9/00.

3. England patent No. 2154091, 1985, H 04 B 10/00.

4. V.P. Klimov. Designing airborne multiplex communication channels. M .: Publishing House of the Moscow Aviation Institute, 1993, pp. 161-162.

Claims (2)

1. A fiber optic network containing N terminals with an optical receiver and transmitter each and a data bus in the form of a light guide loop, the first and second branches of which are connected by the first input and output ports via (N-1) directional optical couplers, the first terminal is connected with the bus through the beginning and end of the light guide loop, and the second and subsequent terminals, respectively, through the second input ports of the first and subsequent in the order they are placed along the bus couplers in the first branch and the second output ports of the couplers t swarm branch of the loop, with all terminal transmitters connected to the first branch of the loop, and all receivers connected to the second branch of the loop, characterized in that in the branches of the loop the couplers from the first to the last are made with decreasing transmission coefficients from the first input to the second output port and from the second input to the first output ports. 2. The network according to claim 2, characterized in that the couplers in the lines and branches of the loop are made with decreasing transmission coefficients in a harmonic sequence.

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