RU2423797C1 - Double passive fibre-optic network - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: double passive fibre-optic network has first and second fibre-optic bidirectional buses, first and second central control units (controllers), multiple subscriber points of the first network and multiple subscriber points of the second network, directed X-couplers of the first bus and directed X-couplers of the second bus, as well as paired and non-paired optical circulators. Transmission to the first network is carried out at wavelength λ₁, and to the second at wavelength λ₂ (λ₁ ≠ λ₂). The directed X-couplers, in the order of their arrangement in the buses from the first to the second controller, have an increasing branching coefficient at wavelength λ₁ for transmission to the first network and a decreasing branching coefficient at wavelength λ₂ for transmission to the second network.

EFFECT: high reliability of the network owing to possibility of switching to operation on a standby bus in case of default in the first bus, more subscriber points serviced by the network.

6 cl, 6 dwg

Description

The invention relates to the field of telecommunications, to passive fiber-optic networks with bus topology. And it can be used in broadcast telecommunication access networks, as well as in local data exchange networks.

In the field of telecommunications, passive networks are understood to mean networks in which the transmission of an optical signal between a central control unit (controller) and a plurality of subscriber units is carried out by passive components.

Known passive fiber optic network containing the first and second unidirectional buses made of optical fiber and many directional couplers included in the first and second buses, a central control node (controller) of the network and many subscriber nodes. Subscriber unit transmitters are optically coupled to the first bus via directional couplers of the first bus, and receivers to the second bus through directional couplers of the second bus. The transmitter of the controller is optically coupled to the end of the second bus, and the receiver to the end of the first bus. All bus couplers have equal branch coefficients [1].

A disadvantage of the known network is the lack of redundant buses to maintain the network's operability in the event of default (fiber breakage), as well as the limitation on the number N of serviced subscriber nodes in the network, which is determined by the smallest transmission coefficient in the network. In the first bus, this will be the transmission coefficient K _N - from the transmitter of the subscriber unit connected to the last N coupler in the bus to the controller receiver. In the second bus - transmission coefficient equal to the mentioned K _N , from the transmitter of the controller to the receiver of the last subscriber unit:

where α is the branch coefficient.

Expression (1) has a maximum at α = 1 / (N-2):

If P _rad is the radiation power injected into the fiber, and Rpor is the threshold sensitivity of the receiver, then, obviously, the lowest transmission coefficient in the network should satisfy the inequality:

From (2) and (3) we obtain the following estimate of the number N in an idealized (lossless) network:

The ratio [F _rad / P _pore] in logarithmic expression is called potential energy network (or network budget) and determines the maximum possible number of serviceable subscriber units in a passive network when the transmitter of the power is distributed uniformly in the receivers of subscriber nodes. As we see from (4), the known network is almost three times inferior to this parameter. In addition, the network places high demands on the dynamic range of receivers used in the network due to differences in bus transfer coefficients for different subscriber nodes.

A double fiber optic network is known, comprising the first and second networks with the first and second central control nodes (controllers), respectively, and sets of subscriber nodes, the first and second bidirectional optical fiber buses and a plurality of directional X-couplers included in the first and second buses. The first and second central control nodes are located at opposite ends of the tires. The transmitters of the central control nodes are optically connected to the second bus, and the receivers to the first bus through the aforementioned opposite ends of the buses. The transmitters of the subscriber units of the first and second networks are optically connected to the first bus via directional X-couplers of the first bus with the possibility of transmission in the direction of the first and second central control nodes, respectively. The receivers of the subscriber units of the first and second networks are optically connected to the second bus via directional X-couplers of the second bus with the possibility of receiving transmission from the first and second central control nodes, respectively. The transmission wavelength in the first network is different from the transmission wavelength in the second network [2].

Different operating wavelengths in the first and second networks can reduce crosstalk while transmitting in the first and second networks.

This technical solution is taken as a prototype.

…,

Этот прием использован в известной пассивной волоконно-оптической сети обмена данными с однонаправленной петлевой шиной [3]. Нетрудно видеть, что в двойной сети с двунаправленными шинами такое техническое решение не проходит, так как полностью нарушает работу одной из сетей.The prototype has the same drawbacks as the analog with unidirectional buses: the lack of redundant buses to maintain the network in the event of default (fiber breakage), as well as the restriction on the number of subscriber nodes in each network, estimated by dependence (4) and increased requirements for dynamic range of receivers on the network. The last drawback in the analogue [1] with unidirectional tires can be eliminated by the execution of directional couplers in the tires with decreasing branch coefficients in the order they follow in the tires towards the controller. For an idealized (lossless) network, the couplers in this case are executed with branch coefficients from a harmonic sequence: 1,

...

This technique was used in the well-known passive fiber-optic data exchange network with a unidirectional loop bus [3]. It is easy to see that in a dual network with bi-directional buses this technical solution does not work, as it completely disrupts the operation of one of the networks.

…,

невозможна и в этом случае по вышеуказанной причине. Кроме того, в такой сети будет отсутствовать резервирование.Known fiber-optic communication line containing three-port optical circulators at the ends of the line, which implements duplex (bidirectional) transmission over a single optical fiber [8]. By analogy with the well-known communication line, it is possible to offer a double network using three-port optical circulators for organizing duplex transmission in the first and second networks on a single bi-directional bus with couplers. However, the optimization of such a double network with a sign of the execution of taps with the coefficients of the branches from the harmonic sequence: 1,

...

impossible in this case for the above reason. In addition, there will be no redundancy in such a network.

The present invention solves the problem of backup in case of default, as well as increasing the number of subscriber nodes in networks, while reducing the requirements for the dynamic range of receivers used, and expanding the arsenal of technical means in the field of telecommunications.

To achieve this technical result, a double passive fiber-optic network contains the first and second networks with the first and second central control nodes (controllers), respectively, and the sets of subscriber nodes, the first and second bidirectional optical fiber buses and a plurality of directional X-couplers included in the first and the second bus with a pair of its ports, the subscriber nodes are optically connected to the buses through directional X-couplers. Each node of the first and second networks includes the first optical transmitter and receiver. The first and second central control nodes are located at opposite ends of the bus. The transmission wavelengths by the subscriber nodes of the first network are different from the transmission wavelengths by the subscriber nodes of the second network. Unlike the prototype, many optical circulators and a second transmitter with a receiver for each node of the first and second network are introduced into the dual network. The optical circulator is made with at least one pair of optically isolated ports. Directional X-couplers in pairs along one coupler from the first and second buses are connected by branch ports to pairs of optical circulators, and in each of these connections two pairs of optically isolated ports, one from each circulator, are used. Another pair of optically isolated ports, the circulator is connected to two other circulators from the above set. The first transmitter with the receiver and the second transmitter with the receiver of the subscriber unit of the first network are optically connected through the optically decoupled ports of one of the last two pairs of circulators, respectively, to the first and second bus with the possibility of transmission in the direction of the first central control unit. The first transmitter with the receiver and the second transmitter with the receiver of the subscriber unit of the second network are optically connected through the optically isolated ports of the second of the last two pairs of circulators, respectively, to the first and second bus with the possibility of transmission in the direction of the second central control unit. The central control unit is optically coupled to the first and second buses via three circulators, the first of which is connected by one pair of optically decoupled ports to the ends of the first and second bus of the site, and the other pair of optically decoupled ports by the first circulator connected to the second and third circulators. The optically isolated ports of the second circulator are connected to the first transmitter and the second receiver, and the third circulator to the second transmitter and the first receiver of the central control unit.

According to a special case of execution, directional X-couplers in the order of their placement in the first and second buses from the first central control unit to the second are made with increasing branch coefficients at the mentioned transmission wavelengths in the first network and with decreasing branch coefficients at the transmission wavelengths in the second network .

According to a special case of execution, directional X-couplers are made with branch coefficients α _i (λ ₁ ) at a wavelength of λ ₁ transmission in the first network and α _i (λ ₂ ) at a wavelength of λ ₂ transmission in the second network according to the following recurrence formulas:

;

;

where i is the serial number of the coupler in the bus, N is the number of couplers in the bus, δ _i are the total losses (dB) on the bus section between (i-1) and i bus taps, including excess losses of the i taps.

According to a special case of execution, the receiver of each node contains a selective filter for the received wavelength.

According to a special case of execution, all circulators are made with four ports.

According to a special case of execution, the circulators associated with the transmitters and receivers of the nodes are made with three ports, and the rest of the set with four ports.

The invention is illustrated in the drawings of Figures 1-5.

Figure 1 shows a block diagram of a dual passive fiber optic network.

Figure 2 shows a functional diagram of a spectrally dependent directional coupler.

Figure 3 shows a schematic representation of a directional coupler on two connected optical waveguides.

Figure 4 shows graphs of the beating of power along homogeneous coupled waveguides for two wavelengths λ ₁ ≠ λ ₂ .

Figure 5 shows a functional diagram of a three-port optical circulator (with one pair of optically isolated ports).

Figure 6 shows a functional diagram of a four-port optical circulator (with two pairs of optically isolated ports).

Double passive fiber-optic network Figure 1 contains the first and second bi-directional buses 1 and 2 of optical fiber, the first and second central control nodes (controllers) 10 and 20, many subscriber nodes 11, 12, 13 of the first network and many subscriber nodes 21 , 22, 23 of the second network, directional X-couplers 3, 4, 5, connected by a pair of their ports to bus 1, and directional X-couplers 6, 7, 8, connected by a pair of their ports to bus 2. Directional X-couplers 3 and 6, 4 and 7, 5 and 8 (one coupler from the first and second bus) are connected by ports from branches with pairs of optical circulators 14 and 24, 15 and 25, 16 and 26, moreover, in each of these compounds two pairs of optically isolated ports are used, one from each circulator (in Fig. 6 these are ports 2 and 4). Another pair of optically isolated ports (in FIG. 6 these are ports 1 and 3) circulators 14 and 24 are connected to pairs of circulators 17, 18 and 27, 28, respectively. Circulators 15 and 25 with circulators 35, 36 and 45, 46 are connected in a similar way, and circulators 16 and 26 with circulators 37, 38 and 47, 48. Circulators 17, 18, 27, 28, ..., 47, 48 can be as three-port ( see Figure 5), and four-port (see Figure 6), although the network is functionally enough three-port. The first transmitter T ₁ with receiver R ₁ and the second transmitter T ₂ with receiver R _{2 of the} subscriber units 11, 12, 13 of the first network are optically connected through optically isolated ports (in Fig. 6 these are ports 1 and 3) of the circulators 17, 18, 35, 36, 37, 38, respectively, with the first and second bus 1 and 2 with the possibility of transmission in the direction of the first central control unit 10. The first transmitter T ₁ with receiver R ₁ and the second transmitter T ₂ with receiver R _{2 of the} subscriber units 21, 22, 23 networks are optically connected through optically isolated circulator ports 27, 28, 45, 46, 47, 48, respectively the first and second bus 1 and 2 with the possibility of transmission in the direction of the second central control node 20. The central control node 10 is optically connected to the first 1 and second 2 buses through three circulators 30, 43, 44. The first circulator 30 is connected by one pair of optically decoupled ports with the ends 9 and 19 of the first 1 and second 2 buses, and another pair of optically isolated ports, the first circulator 30 is connected to the second 44 and third 43 circulators. The optically isolated ports of the second circulator 44 are connected to the first transmitter T ₁ and the second receiver R ₂ , and the third circulator 43 to the second transmitter T ₂ and the first receiver R _{1 of the} central control unit 10. The central control unit 20 is optically connected to the first 1 and second 2 buses by means of three circulators 50, 54, 55. The first circulator 50 is connected by one pair of optically decoupled ports to the ends 29 and 39 of the first 1 and second 2 buses, and the other pair of optically decoupled ports by the first circulator 50 connected to the second 54 and third 55 circulator ami. The optically isolated ports of the second circulator 54 are connected to the first transmitter T ₁ and the second receiver R ₂ , and the third circulator 55 to the second transmitter T ₂ and the first receiver R _{1 of the} central control unit 20.

All transmitters T _{1 of the} subscriber units 11, 12, 13 and the first controller 10 of the first network transmit at a wavelength of λ ₁ . All transmitters T _{1 of the} subscriber units 21, 22, 23 and the second controller 20 transmit at a wavelength of λ ₂ (λ ₂ ≠ λ ₁ ). Receivers R nodes to increase the isolation of networks (reduce crosstalk) can be equipped with selective filters (not shown) at the received wavelength. In this embodiment, it is wavelength λ ₁ and wavelength λ ₂ .

On the functional diagram of the directional X-coupler of Figure 2, ports 31 and 32 are intended to be included in buses 1 and 2, and branch ports 33 and 34 are for communication with circulators. The directional X-couplers 3, 4, 5, 6, 7, 8 have a spectrally dependent branch coefficient α _i (λ), where i is the serial number of the location of the coupler in buses 1 and 2 in the direction from the first central control unit 10 to the second central control node 20. In Fig. 1, taps 5, 8 have serial number 1, etc., taps 4, 7 are number 1 / N-1, taps 3, 6 are number N. The branch coefficients α _i (λ) increase with increasing serial number i of the coupler at a wavelength of λ ₁ and decrease at a wavelength of λ ₂ in accordance with the following recurrent formulas:

;

;

where δ _i - total losses in the area between (i-1) and i taps; δ _i = δ _i ⁽¹⁾ · l + δ _i ⁽²⁾ + δ _i ⁽³⁾ , where δ _i ⁽¹⁾ [dB / km] is the attenuation of the optical fiber over a section of length l [km], δ _i ^{( 2)} [dB] is the excess loss of the coupler i, δ _i ⁽³⁾ [dB] is the total loss in the connections of the optical fibers in the said section. Table 1 shows the optimal branch coefficients α _i (λ) for bus couplers in the absence of network losses (δ _i = 0), allowing to obtain the maximum number of subscriber nodes.

Table 1 Pos. in figure 1 5, 8 4, 7 3, 6 i one 2 3, ... ..., N-2 N-1 N α _i (λ ₁ ) 1 / N 1 / N-1, 1 / N-2, ... ... 1/3 1/2 one α _i (λ ₂ ) one 1/2, 1/3, ... ..., 1 / N-2 1 / N-1 1 / N

The number N is equal to the theoretical limit for passive networks defined energy potential (budget) network: φ = 10lg [P _rad / P _pore]. At the same time, a reduction in the dynamic range requirements used in the network of receivers is achieved, a result of the constancy of the level of received power by the central and subscriber nodes.

, где δ⁴ - потери, вносимые оптическими циркуляторами 30 и 44; потенциал за первым в шине ответвителем (поз.5) равен

, где δ₁ - суммарные потери на участке от циркулятора 30 до первого ответвителя (поз.5) в шине (включая избыточные потери ответвителя 5); потенциал за вторым ответвителем (не показан) равен φ₂=φ₁-δ₂+10lg(1-α₂), где δ₂ - потери на участке от первого ответвителя до второго (включая избыточные потери второго ответвителя), тогда для потенциала за i ответвителем можно написать:We present the derivation of formulas (5). Consider the change in the energy potential φ _i along bus 1 in the first network. The potential at the end of bus 9 is

where δ ⁴ - losses introduced by the optical circulators 30 and 44; the potential behind the first coupler in the bus (pos. 5) is equal to

where δ ₁ is the total loss in the area from the circulator 30 to the first coupler (item 5) in the bus (including excess coupler losses 5); the potential behind the second coupler (not shown) is equal to φ ₂ = φ ₁ -δ ₂ + 10lg (1-α ₂ ), where δ ₂ is the loss in the section from the first coupler to the second (including excess losses of the second coupler), then for the potential beyond i the coupler can be written:

The energy potential φ _R at the receiver R _{1 of} each subscriber unit 11, 12, 13 is zero - the condition for obtaining the power P _then at the receiver. Then, for the potential φ _{R of the} receiver R ₁ associated with the i coupler, we can write:

where δ ⁽⁴⁾ is the losses introduced by the circulators connected to the i coupler (for the coupler under number 1 (item 5) these are circulators 16, 37).

Expression (6) taking into account equation (7) we bring to the form:

.Substituting the expression for φ _i-1 from (7) into the last equation, we obtain the first of the recurrence formulas (5):

.

во второй сети можно написать:For energy potentials

in the second network you can write:

,

,

- потенциал на конце 29 шины 1 во второй сети;

- суммарные потери на участке от второго центрального управляющего узла 20 до N ответвителя (поз.3) в шине 1.Where

- potential at the end 29 of bus 1 in the second network;

- total losses in the area from the second central control unit 20 to the N coupler (item 3) in bus 1.

,

,

- суммарные потери на участке от N ответвителя (поз.3) до (N-1) ответвителя (поз.4); и для потенциала

имеем:Where

- total losses in the area from the N coupler (item 3) to (N-1) the coupler (item 4); and for potential

we have:

For potentials at the receivers R _{2 of the} second network, we write:

Performing transformations with equations (8) and (9) similar to the above transformations with equations (6) and (7), we arrive at the formula:

.

.

, и окончательно получаем вторую из рекуррентных формул (5):Assuming that the excess losses of the coupler do not depend on its number i of the direction of transmission and wavelength, we have

, and finally we get the second of the recurrence formulas (5):

.

.

Table 2 shows the optimal branch coefficients in the network with the same total losses in bus sections 1 between adjacent couplers: δ ₁ = δ ₂ = ... δ _N = 1 dB (section length l _i = 1 ... 2 km; δ _i ⁽¹⁾ = 0.2 ... 0.3 dB; δ _i ⁽²⁾ = 0.3 dB; δ _i ⁽³⁾ = 0.3 dB) calculated by formulas (5) and the energy potential in the first and second networks φ = 30, 85 dB (calculated by formulas (7), (6) taking into account the introduced losses by circulators δ ⁽⁴⁾ = 0.5 dB).

table 2 i one 2 3 four 5 6 7 8 9 10 eleven 12 α _i (λ ₁ ) 0.001 0.0013 0.0016 0.0021 0.0026 0.0033 0.0042 0.0053 0.0067 0.0085 0.011 0.014 α _i (λ ₂ ) one 0.443 0.260 0.171 0,120 0,087 0,065 0,049 0,037 0,029 0,022 0.017 i 13 fourteen fifteen 16 17 eighteen 19 twenty 21 22 23 24 α _i (λ ₁ ) 0.017 0,022 0,029 0,037 0,049 0,065 0,087 0,120 0.171 0.260 0.443 one α _i (λ ₂ ) 0.014 0.011 0.0085 0.0067 0,053 0,042 0.0033 0.0026 0.0021 0.0016 0.0013 0.001

Among the known directional X-couplers that meet the requirements of the invention, it is worth highlighting couplers arranged according to the principle of coupled waveguides. A diagram of such a coupler is shown in FIG. 3. Optical waveguides 41, 42 located parallel to each other interact with each other by decreasing external fields. The interaction of the waveguides leads to the fact that the power of the mode of one waveguide is partially transferred to the mode of another waveguide. The power transmitted to the mode of the waveguide 42 has the form [5, p.231-236]:

where F ₁ is the power at the input port of the waveguide 31; Δβ = (β ₁ -β ₂ ) / 2,

β ₁ , β ₂ are the phase propagation constants of the modes of the waveguides 31, 32, respectively; c is the coupling coefficient between the waveguide modes (the coupling coefficient c has an inverse exponential dependence on the distance d between the waveguides and inversely proportional dependence on the wavelength λ).

Figure 4 presents graphs of the runout of power F ₂ along the waveguide for two wavelengths λ ₁ = 1550 nm and λ ₂ = 1310 nm and normalized power F ₁ = 1. The beat lengths l ₁ , l ₂ at wavelengths λ ₁ , λ _{2 are} correlated as follows:

l ₁ : l ₂ ≈λ ₁ : λ ₂ = 1550 / 1310≈1.28. The graphs clearly show that by varying the values of c, Δβ and the bond length L (Fig.3Z), it is always possible to achieve branch coefficients α _i (λ ₁ ) and α _i (λ ₂ ) corresponding to tables 1 and 2. Note that the considered X - taps are broadband devices, and ratios close to those indicated in tables 1 and 2 will be performed in two transparency bands: 1550 ± 40 nm and 1310 ± 40 nm.

Optical circulators 14, ..., 55 (FIG. 1) are also broadband devices, the production of which has been mastered by industry in the same transparency bands. In the invention with the above-described X-couplers (Figure 3), the first network uses circulators 14, ..., 18, 35, 36, 37, 38, 30, 43, 44 with a central wavelength of 1550 nm in the operating range, and in the second network circulators 24, ..., 28, 45, ..., 48, 50, 54, 55 with a central wavelength of 1310 nm. An optical circulator is a device whose operation is based on the gyrotropic properties of ferrites: in particular, non-reciprocal rotation of the plane of polarization (Faraday effect) of an electromagnetic wave in waveguides made of ferrite single crystals. As a result, optical radiation can only be transmitted in a strictly defined sequence between the device ports (circulate) [8]. In the functional diagram of the three-port circulator of FIG. 5, transmission is possible only from port 1 to port 2 and from port 2 to port 3, ports 1 and 3 are optically isolated. The optical fiber 52 is designed for bi-directional transmission, the optical fibers 51 and 53 for unidirectional transmission. Therefore, in the network of Figure 1, port 1 of the three-port circulator is used for communication with the transmitter T, and port 3 with the receiver R in all nodes of the network. In the functional diagram of the four-port circulator of FIG. 6, transmission is possible only from port 1 to port 2, from port 2 to port 3, from port 3 to port 4 and from port 4 to port 1. All optical fibers 61, ..., 64 are designed for bi-directional transmission . Ports 1 and 3, as well as 2 and 4 are optically isolated, transmission between them is impossible for any direction of the radiation flux in the optical fibers 61, ..., 64.

Spectrally dependent couplers are used in spectral (frequency) multiplexing / separation devices (the so-called coarse WDM multiplexing), for which they tend to have coefficients α (λ ₁ ) = 1, α (λ ₂ ) = 0. As follows from expression (10) and graphs, this is possible only if phase synchronism is observed: Δβ = 0. The latter is difficult to implement in practice, and therefore WDM-multiplexers always have excess losses that reduce the level of the optical signal at the receivers of networks using WDM-multiplexing. And, as a result, the number of subscriber nodes is reduced in proportion to the losses introduced. At the same time, the indicated drawback of the couplers does not significantly affect the total number of subscriber units in the invention, since it leads to a reduction of only the two extreme subscriber units in the buses (Fig. 1) (see Table 1). The best embodiment of the X-coupler in the invention is a coupled waveguide coupler obtained from optical fibers by fusion (see, for example, [7]).

The claimed dual network can be used: 1) as a data exchange network between subscriber nodes, in this case the controllers perform the functions of transmit transmitters in networks; 2) as a broadcast access network. Moreover, the first and second networks of the dual network operate independently of one another. In both cases of using a dual network, controllers 2, 3 can be eliminated by replacing them with optical fiber amplifiers [4], and one of the subscriber nodes in each of the networks can perform their functions of managing the first and second networks. In this case, the double passive network will have extreme broadband, without the restrictions that repeaters introduce with the conversion of the transmitted signals from optical to electrical and vice versa.

The operation of the first and second networks in the dual network of Fig. 1, as broadcast access networks, is based on the same principle as the operation of networks known as PON (Passive Optical Networks) [4 p. 469-478]. Let us describe their work using the example of the first network. The central node OLT (Optical Line Terminal) 10 receives data from the backbone networks through the connection interfaces SNI (Service Node Interfaces) and forms the first stream (similar to the downstream in PON) to the subscriber nodes ONU (Optical Network Unit) 11, 12, 13 in bus 1. In this case, any of the methods of flow formation known in PON is used, for example, synchronous transmission with time division TDM (Time Division Multiplexing) signals intended for different subscriber nodes 11, 12, 13. The transmitter T _{1 of the} central node 10 operates on a fixed length waves, for example, λ ₁ = 1550 nm, and the radiation current passes through optical circulators 44, 30 to bus 1, where it is evenly distributed by X-couplers 5, 4, 3 and circulators 16-37, 15-35, 14-17 to receivers R _{1 of the} subscriber units 13, 12, 11. The second the stream (similar to the upstream in PON) from the subscriber units 11,12,13 to the receiver R _{1 of the} central node 10 is formed by synchronous access with time division TDMA (Time Division Multiplexing Access) signals from the transmitters T _{1 of the} subscriber units 11, 12, 13 in bus 1. Radiation from T ₁ transmitters is introduced into bus 1 through circulators 18-14, 36-15, 38-16 and taps 3, 4, 5. When this transmission is carried out at the same wavelength λ ₁ = 1550 nm and each subscriber node 11, 12, 13 sets an individual schedule taking into account the distance of the node from the receiver R _{1 of the} central node 10.

In the claimed network, it is also possible to transmit frequency-time packets of signals [6 p. 250]. In the first stream, the temporary positions of the signals intended for different subscriber units 11, 12, 13 are transmitted at different wavelengths λ ₁₁ , λ ₁₂ , ..., λ _{1N of the} tunable laser of the transmitter T _{1 of the} central node 10. Receivers R _{1 of the} subscriber units 11, ..., 13 in this case, they are equipped with selective filters tuned to wavelengths λ ₁₁ , λ ₁₂ , ..., λ _1N, respectively. In the second stream, transmission from subscriber nodes 11, ..., 13 to the receiver R _{1 of the} central node 10 is carried out at the same wavelength λ ₁ by synchronous access with time division TDMA.

When the optical fiber of the first bus 1 is broken, the first and second networks go to work with the backup second bus 2. Transmission in this case is carried out by the second transmitters T ₂ nodes, and the reception by the second receivers R ₂ . Otherwise, the operation of networks is no different from the above work with the first bus 1.

The claimed network, despite the bus topology, can be considered as a variant of the PON network. That is, it is fully compatible with hardware and software products released by the industry for PON technology.

On the other hand, the invention has an advantage over the well-known PON networks with a tree architecture in saving optical fiber, increased reliability due to redundancy and ease of monitoring during network operation. Therefore, the industrial application of the invention will be a cost-effective alternative to known access networks.

Used sources:

1. Patent US 4089584, CL. 385-24.

2. PCT Application WO 83/03327, H04B 9/00, 1983, publ.

3. Patent RU 2264692, H04B 10/12, 2005, publ.

4. Freeman R. Fiber-optic communication systems. 2nd supplemented ed .: Per. from English Ed. N.N.Slepova - M .: Technosphere, 2004

5. X.-G. Unger. Plenary and fiber optical waveguides / Per. from English V.V.Shevchenko - M .: Mir, 1980.

6. Telecommunication systems and networks: Textbook in 3 vols. Volume 3. - Multiservice networks; under the editorship of prof. V.P. Shuvalova. - M .: Hot line - Telecom, 2005

7. Patent US 4834481, G02B 6/28, 1989.

8. Rudov Yu.K., Zingerenko Yu.A., Orobinsky S.P., Mironov S.A. The use of optical circulators in fiber-optic transmission systems // Elektrosvyaz, 1999, No. 6, p. 36-37.

Claims (6)

1. A double passive fiber optic network containing the first and second networks with the first and second central control nodes, respectively, and a plurality of subscriber nodes, the first and second bi-directional optical fiber buses and a plurality of directional X-couplers included in the first and second bus pair ports, subscriber nodes are optically connected to the buses through directional X-couplers, the first and second central control nodes are located at opposite ends of the buses, each node of the first and second networks includes the first is an optical transmitter and receiver, and the transmission wavelengths by the subscriber nodes of the first network are different from the transmission wavelengths by the subscriber nodes of the second network, characterized in that a plurality of optical circulators and a second transmitter with a receiver are introduced for each node of the first and second network, the optical circulator is made with at least one pair of optically decoupled ports, directional X-couplers in pairs along one coupler from the first and second buses are connected by branch ports to pairs of optical circulators, each pair of these connections uses two pairs of optically decoupled ports, one from each circulator, and the other a pair of optically decoupled ports, the circulator is connected to two other circulators from the set, the first transmitter with a receiver and the second transmitter with the receiver of the subscriber unit of the first network are optically connected through optically decoupled ports of one of the last two pairs of circulators, respectively, with the first and second bus with the possibility of transmission in the direction of the first central control unit la, and the first transmitter with the receiver and the second transmitter with the receiver of the subscriber unit of the second network are optically connected through the optically decoupled ports of the second of the last two pairs of circulators, respectively, to the first and second bus with the possibility of transmission in the direction of the second central control unit, each central control unit is optically connected with the first and second buses by means of three circulators, the first of which is connected by one pair of optically decoupled ports to the ends of the first and second buses of the node placement, etc. The first pair of optically decoupled ports is connected to the second and third circulators, the optically decoupled ports of the second circulator are connected to the first transmitter and second receiver, and the third circulator to the second transmitter and first receiver of the unit. 2. The network according to claim 1, characterized in that the directional X-couplers in the order of their placement in the first and second buses from the first central control node to the second are made with increasing branch coefficients at the mentioned transmission wavelengths in the first network and with decreasing branch coefficients at transmission wavelengths in the second network. 3. The network according to claim 1, characterized in that the directional X-couplers are made with branch coefficients α _i (λ ₁ ) at a transmission wavelength λ ₁ in the first network and branch coefficients α _i (λ ₂ ) at a transmission wavelength λ ₂ in the second network according to the following recurrence formulas:

where i is the serial number of the coupler in the bus, N is the number of couplers in the bus, δ _i are the total losses (dB) on the bus section between (i-1) and i bus taps, including excess losses of the i taps. 4. The network according to claim 1, characterized in that the receiver of each node contains a selective filter for the received wavelength. 5. The network according to claim 1, characterized in that all the circulators are made with four ports. 6. The network according to claim 1, characterized in that the circulators associated with the transmitters and receivers of the nodes are made with three ports, and the rest of the aforementioned set with four ports.

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