RU2372726C2 - Double passive fibre-optic network - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: double passive fibre-optic network has a first and a second bidirectional bus made from optical fibre, first and second central control points (controllers), several subscriber points of the first network and several subscriber points of the second network, directional couplers of the first bus and directional couplers of the second bus. Transmitters of the first and second controllers are optically connected to the second bus through its ends. Receivers of the first and second controllers are optically connected to the first bus through its ends. Transmitters of subscriber points are optically connected to the first bus through corresponding directional couplers, and receivers - to the second bus through directional couplers. The first network transmits at wavelength λ₁, and the second - at wavelength λ₂ (λ₁≠λ₂). Directional couplers of each bus, in the order of their arrangement in the buses from one controller to the other, are made with increasing coupler coefficients at transmission wavelength λ₁ in the first network and with decreasing coupler coefficients at transmission wavelength λ₂ in the second network.

EFFECT: increased number of subscriber points in the networks with simultaneous reduction of requirements to dynamic range of used receivers.

3 cl, 4 dwg, 2 tbl

Description

The invention relates to the field of telecommunications, to passive fiber-optic networks with bus topology, and can be used in broadcast telecommunication 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 limitation in 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 Riesl is the radiation power introduced 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 [Rizl / Rpor] in logarithmic terms is called the energy potential of the network (or network budget) and determines the maximum possible number of serviced subscriber nodes in a passive network when the power from the transmitter is evenly distributed among the receivers of the 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, containing the first and second networks with the first and second central control nodes (controllers), respectively, and sets of subscriber nodes, the first and second bi-directional optical fiber buses and a plurality of directional 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 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 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 restriction on the number of subscriber nodes in each network, estimated by dependence (4) and increased requirements for the dynamic range of receivers in the network. In the analogue of [1] with unidirectional tires, these shortcomings 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.

The present invention solves the problem of 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 a plurality of subscriber nodes, the first and second bidirectional optical fiber buses and a plurality of directional couplers included in the first and second tires. 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 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 couplers of the second bus with the possibility of receiving transmission from the first and second central control nodes, respectively. In the first bi-directional 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. In the second bi-directional bus, the transmission wavelength of the first central control unit is different from the transmission wavelength of the second central control unit. Unlike the prototype, the directional couplers of each of the bidirectional buses in the order of their placement in the tires 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 couplers are made with branch coefficients α _i (λ ₁ ) at a transmission wavelength λ ₁ in the first network and α _i (λ ₂ ) at a transmission wavelength λ ₂ in the second network according to the following recurrence formulas:

;

;

;

;

,

,

where i - the serial number of the coupler in the first and second tire, N - number of taps in each tire, δ _i - total loss (dB) on the bus segment between (i-1) ^M and i ^M taps tire, including excessive loss of i ^th coupler .

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

The invention is illustrated by drawings, where:

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 .

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) 3 and 4, a lot of subscriber nodes 11, 12, 13, 14 of the first network and a plurality of subscriber units 21, 22, 23, 24 of the second network, directional couplers 5, 6, 7, 8 of the first bus 1 and directional couplers 15, 16, 17, 18 of the second bus 2. The transmitters T of the first and second controllers 3 and 4 are optically coupled with the second bus 2 through its ends 9 and 10. The receivers R of the first and second controllers 3 and 4 are optical and connected to the first bus through its ends 19 and 20. Transmitters T of subscriber units 11 and 21, 12 and 22, 13 and 23, 14 and 24 are optically connected to the first bus 1 through directional couplers 5, 6, 7, 8, respectively. The receivers R of the subscriber units 11 and 21, 12 and 22, 13 and 23, 14 and 24 are optically coupled to the second bus 2 through directional couplers 15, 16, 17, 18, respectively. All transmitters T of the subscriber units 11, 12, 13, 14 and the first controller 3 of the first network transmit at a wavelength of λ ₁ . All transmitters T of the subscriber units 21, 22, 23, 24 and the second controller 4 transmit at a wavelength of λ ₂ (λ ₂ ≠ λ ₁ ). The receivers of the nodes to increase the isolation of the networks (reduce crosstalk) can be equipped with selective filters (not shown) for the received wavelength. In this embodiment, it is a wavelength λ ₁ and a wavelength λ ₂ .

The directional couplers 5, 6, 7, 8 and 15, 16, 17, 18, the functional diagram of which is shown in FIG. 2, have a spectrally dependent branch coefficient α _i (λ), where i is the serial number of the location of the coupler in buses 1, 2 in the direction from the first controller 3 to the second controller 4. In Fig. 1, the couplers 11 and 21 are number 1, the couplers 12 and 22 are number 2, etc., the last couplers 14 and 24 in the buses are number N. Coefficients branches 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 recurrence formulas:

, где δ_i ⁽³⁾ [дБ/км] - погонное затухание оптического волокна на участке длиной l [км], δ_i ⁽²⁾ [дБ] - избыточные потери i ответвителя, δ_i ⁽³⁾ [дБ] - суммарные потери в соединениях оптических волокон на упомянутом участке. В таблице 1 приведены оптимальные коэффициенты ответвления α_i(λ) для ответвителей первой и второй шин в отсутствии потерь в сети (δ_i=0), позволяющие получить максимальное число абонентских узлов в сети.where δ _i - total losses in the area between (i-1) and i taps;

, where δ _i ⁽³⁾ [dB / km] is the linear 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 said section. Table 1 shows the optimal branch coefficients α _i (λ) for the first and second bus couplers in the absence of network losses (δ _i = 0), allowing to obtain the maximum number of subscriber nodes in the network.

Table 1 Pos. in figure 1 11 and 21 12 and 22 13 and 23 14 and 24 I one 2 3 ... ... N-2 N-1 N α _i (λ ₁ ) 1 / N 1 / N-2 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, which is determined by the energy potential (budget) of the network: φ = 101g [Riesl / Rpor]. At the same time, a reduction in the requirements on the dynamic range of the receivers used in the network is achieved - the result of a constant level of received power by the central and subscriber nodes.

We present the derivation of formulas (5). Consider the change in the energy potential φ _i along bus 2 in the first network. The potential at the end of bus 9 is φ; the potential behind the first coupler in the bus (key 15) is equal to φ ₁ = φ-δ ₁ + 101g (1-α ₁ ), where δ ₁ is the total loss in the area from controller 9 to the first coupler (key 15) in the bus ( including excess coupler losses); the potential behind the second coupler (pos. 16) is 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 for the i coupler, you can write:

The energy potential φ _R at the receiver R of each subscriber unit 11, ..., 14 is equal to zero - the condition for obtaining power Рпор at the receiver. Then the potential φ receiver _R, associated with the i ^th coupler, we can write:

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

Или для

Or for

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:

, где φ - потенциал на конце 10 шины 2 во второй сети;

- суммарные потери на участке от второго контроллера 4 до N^го ответвителя в шине (поз.18);

, где

- суммарные потери на участке от N^го ответвителя до (N-1)^го ответвителя; и для потенциала

имеем:

where φ is the potential at the end 10 of bus 2 in the second network;

- total losses in the area from the second controller 4 to the N- ^th branch in the bus (pos. 18);

where

- total loss of the section from ^{the first} coupler to N (N-1) ^th tap; and for potential

we have:

For potentials at the receivers 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, 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 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 the formulas (5); network energy potential

φ = 29.85 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 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 0.002 0.0021 0.0016 0.001 0.001

Among the known directional 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 31, 32 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 32 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 to 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} related 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 (Figure 3), it is always possible to achieve branch coefficients α _i (λ ₁ ) and α _i (λ ₂ ) corresponding to the data in Tables 1 and 2. Note that the considered taps are broadband devices, and ratios close to those indicated in tables 1 and 2 will be performed in two bands: 1550 ± 40 nm and 1310 ± 40 nm.

Spectrally dependent couplers are used in frequency multiplexing / separation devices (WDM-multiplexers), 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 the reduction of only two end nodes in the buses (FIG. 1) (see table 1). The best embodiment of the 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 transmitting relay from the second bus to the first; 2) as a broadcast access network. Moreover, the first and second networks of the dual network operate independently of one another.

The operation of the first and second networks in the claimed 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, pp. 469-478].

Let us describe their work using the example of the first network. The central node OLT (Optical Line Terminal) 3 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, ..., 14 in the second bus 2. In this case, any of the methods of flow formation known in PON technologies is used, for example, synchronous transmission with time division TDM (Time Division Multiplexing) signals intended for different subscriber units 11, 12, ..., 14. Transmitter T central unit operates at a fixed wavelength , E.g., λ ₁ = 1550 nm and the radiation flux is uniformly distributed taps 15, 16, ..., 18 and the receivers R-sites 11, 12, ..., 14. The second flow (similar to the upward flow in PON) from subscriber units 11, ..., 14 to the receiver R of the central node 3 is formed by the method of synchronous access with time division TDMA (Time Division Multiplexing Access) of signals from the transmitters T of the subscriber nodes 11, 12, ..., 14 in the first bus 1 (radiation from the transmitters is introduced into the bus by taps 5, 6, 7, 8). In this case, the transmission is carried out at the same wavelength λ ₁ = 1550 nm and an individual schedule is established for each subscriber unit 11, 12, ..., 14, taking into account the distance of the node from the receiver R of the central node 3.

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 nodes 11, 12, ..., 14 are transmitted at different wavelengths λ ₁₁ , λ ₁₂ , ..., λ _{1N of the} tunable laser of the transmitter T of the central node 3. Receivers R of the subscriber nodes 11, ..., 14 in this case are equipped with selective filters tuned to wavelengths λ ₁₁ , λ ₁₂ , ..., λ _1N , respectively. In the second stream, the transmission from the subscriber units 11, 12, ..., 14 to the receiver R of the central node 3 is carried out at the same wavelength λ ₂ by synchronous access with time division TDMA.

The claimed network, despite the bus architecture, 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, ease of monitoring during network operation and availability (protection of the schedule). Therefore, the industrial application of the invention will be a cost-effective alternative to known networks.

Used sources

1. Patent US 4089584, CL 385-24.

2. PCT Application WO 83/03327, Н04В 9/00, publ. 1983 year

3. Patent RU 2 264692, Н04В 10/12, publ. 2005 year

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

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

6. Telecommunication systems and networks: Textbook in 3 vol. 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.

Claims (3)

1. A dual passive fiber optic network containing 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 couplers included in the first and second buses, the first and second central control nodes are located at opposite ends of the buses, 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 bus ends, transmitters of subscriber units of the first and second networks are optically connected to the first bus through directional couplers of the first bus with the possibility of transmission in the direction of the first and second central control nodes, respectively, receivers of subscriber nodes of the first and second networks are optically connected to the second bus through directional couplers of the second buses with the possibility of receiving transmission from the first and second central control nodes, respectively, in the first bi-directional bus wavelength of the transmission waves of the subscriber the nodes of the first network are different from the transmission wavelengths by the subscriber nodes of the second network, in the second bidirectional bus, the transmission wavelength of the first central control unit is different from the transmission wavelength of the second central control unit, characterized in that the directional couplers of each of the bidirectional buses in the order they are placed in the 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 coefficient branches at the wavelengths of the gears in the second network. 2. The network according to claim 1, characterized in that the directional 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:

α _N (λ ₁ ) = α ₁ (λ ₂ ) = 1,
where i is the serial number of the coupler in the first and second buses; N is the number of taps in each network bus; δ _i - total loss (dB) on the bus section between the (i-1) th and ith bus couplers, including excess coupler losses. 3. The network according to claim 1, characterized in that the receiver of each node contains a selective filter for the received wavelength.

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