RU2423000C1 - Double passive fibre-optic network - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: double passive fibre-optic network has a bidirectional bus made from optical fibre, two central control nodes (controller), multiple user nodes of a first and a second network, guided X-couplers and three-port optical circulators. Transmission to the first network is carried out at wavelength 1, and to the second at wavelength 2 (2ëá1). The guided X-couplers, in the order of their arrangement in the bus from the first to the second controller, have increasing branching coefficient at wavelength 1 for transmission to the first network and decreasing branching coefficient at wavelength 2 for transmission to the second network. ^ EFFECT: increase in number of user nodes serviced by a network while reducing requirements for the dynamic range of 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 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 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 Pth 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 [Razl / 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, 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 working 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. Известна волоконно-оптическая линия связи, содержащая трехпортовые оптические циркуляторы на концах линии, в которой реализована дуплексная (двунаправленная) передача по единственному оптическому волокну [8]. По аналогии с известной линией связи можно предложить двойную сеть с использованием трехпортовых оптических циркуляторов для организации дуплексной передачи в первой и второй сетях по одной единственной двунаправленной шине с ответвителями. Однако оптимизация такой двойной сети с признаком выполнения ответвителей с коэффициентами ответвления из гармонической последовательности:

- невозможна и в этом случае по выше указанной причине.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:

. 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. 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 branch coefficients from a harmonic sequence:

- impossible in this case for the above reason.

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 with optical transmitter and receiver each, a bi-directional bus made of optical fiber and many directional X-couplers, connected to the bus by a pair of its ports. Subscriber units are optically coupled to the bus via directional X-couplers. 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, three-port optical circulators are introduced into the dual network in terms of the number of nodes in the first and second networks. Each X-bus coupler is connected by a pair of its branch ports to a pair of three-port optical circulators, one of which is connected by optically decoupled ports to the transmitter and receiver of the corresponding subscriber unit of the first network with the possibility of transmission in the direction of the first central control unit. And another circulator from the pair is connected by optically decoupled ports to the transmitter and receiver of the corresponding node of the second network with the possibility of transmission in the direction of the second central control node. The transmitters and receivers of the first and second central control nodes are optically coupled to the bus via three-port optical circulators located at said opposite ends of the bus. The directional X-couplers, in the order of their arrangement on the bus 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.

The invention is illustrated by drawings.

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

.

Figure 5 shows a functional diagram of a three-port optical circulator.

. Приемники узлов для увеличения развязки сетей (снижения перекрестных помех) могут быть снабжены избирательными фильтрами (не показаны) на принимаемую длину волны. В рассматриваемом варианте исполнения это длина волны λ₁ и длина волны λ₂.Double passive fiber-optic network Figure 1 contains a bi-directional bus 1 of optical fiber, the first and second central control nodes (controllers) 2 and 3, many subscriber nodes 11, 12, 13, 14 of the first network and many subscriber nodes 15, 16, 17, 18 of the second network, directional X-couplers 4, 5, 6, 7, connected by a pair of their ports to bus 1, and three-port optical circulators 21, ..., 28. Transmitters T and receivers R of the first and second central control nodes 2 and 3 optically coupled to bus 1 via three-port optical circulators 19 and 20 located at opposite ends 9 and 10 of tire 1, respectively. The transmitter T and receiver R of each of the subscriber units 11, ..., 14 of the first network are optically connected to the bus 1 through the corresponding circuit from the three-port optical circulator 21, ..., 24 and the X-coupler 4, ..., 7 with the possibility of transmission in the direction of the first central control node 2. The transmitter T and receiver R of each of the subscriber nodes 15, ..., 18 of the second network are optically connected to the bus 1 through the corresponding circuit from the three-port optical circulator 25, ..., 28 and the X-coupler 4, ..., 7 with the possibility of transmission in the direction second central administration present node 3. All transmitters T subscriber nodes 11, ..., 14 and first controller are sent at the wavelength λ 2 of the first network _1. All transmitters T of the subscriber units 15, ..., 18 and the second controller 3 transmit at a wavelength

. 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 wavelength λ ₁ and wavelength λ ₂ .

In the functional diagram of the directional X-coupler of FIG. 2, ports 31 and 32 are for connection to bus 1, and branch ports 33 and 34 are for communication with circulators. The directional X-couplers 4, 5, 6, 7 have a spectrally dependent branch coefficient α _i (λ), where i is the serial number of the branch in the bus 1 in the direction from the first central control unit 2 to the second central control unit 3. In FIG. .1 coupler 4 has serial number 1, coupler 5 has number 2, etc., the last one in bus 1, coupler 7 has number N. Branch coefficients α _i (λ) increase with increasing serial number i of the coupler at wavelength λ ₁ and decrease at a wavelength of λ ₂ in accordance with the following recursion nt formulas:

;

;

,

,

, где δ_i ⁽¹⁾ [дБ/км] - погонное затухание оптического волокна на участке длиной

[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 шины в отсутствие потерь в сети (δ_i=0), позволяющие получить максимальное число абонентских узлов.where δ _i - total losses in the area between (i-1) and i taps;

where δ _i ⁽¹⁾ [dB / km] is the specific attenuation of the optical fiber over a length

[km], δ _i ⁽²⁾ [dB] - excess losses of the coupler i, δ _i ⁽³⁾ [dB] - total losses in the connections of optical fibers in the mentioned 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 four 5 6 7 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 defined energy potential (budget) network: φ = 10 lg [P _rad / P _pore]. 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.

, где

- потери вносимые оптическим циркулятором 19; потенциал за первым в шине ответвителем (поз.4) равен

, где δ₁ - суммарные потери на участке от циркулятора 19 до первого ответвителя (поз.4) в шине (включая избыточные потери ответвителя 4); потенциал за вторым ответвителем (поз.5) равен

, где δ₂ - потери на участке от первого ответвителя до второго (включая избыточные потери ответвителя 5), тогда для потенциала за i ответвителем можно написать:We present the derivation of formulas (5). Consider the change in the energy potential φ, along bus 1 in the first network. The potential at the end of bus 9 is

where

- losses introduced by the optical circulator 19; the potential behind the first coupler in the bus (item 4) is

where δ ₁ is the total loss in the section from the circulator 19 to the first coupler (item 4) in the bus (including excess coupler losses 4); the potential behind the second coupler (item 5) is

, where δ ₂ is the loss in the area from the first coupler to the second (including excess losses of the coupler 5), then for the potential beyond 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 P _then at the receiver. Then, for the potential φ _{R of the} receiver R associated with the i coupler, we can write:

where δ ⁽⁴⁾ is the loss introduced by the circulator connected to the i coupler.

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 10 шины 1 во второй сети;

- суммарные потери на участке от второго центрального управляющего узла 3 до N ответвителя (поз.7) в шине.Where

- potential at the end 10 of bus 1 in the second network;

- total losses in the area from the second central control unit 3 to the N coupler (pos. 7) in the bus.

,

,

- суммарные потери на участке от N ответвителя (поз.7) до (N-1) ответвителя (поз.6); и для потенциала

имеем:Where

- total losses in the area from the N coupler (pos. 7) to the (N-1) coupler (pos. 6); and for potential

we have:

For potentials at the receivers R 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 insertion loss of the circulator 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 0.002 0.0021 0.0016 0.001 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 (Figure 3), 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-couplers 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.

Three-port optical circulators 21, ..., 28 (FIG. 1) are also broadband devices, the production of which has been mastered by the industry in the same transparency bands. In the invention with the above-described X-couplers (Figure 3), the first network uses circulators 19, 21, ..., 24 with a central wavelength of 1550 nm of the operating range, and the second network uses circulators 20, 25, ..., 28 with a central wavelength 1310 nm. A three-port optical circulator is a device whose operation is based on the gyrotropic properties of ferrites: in particular, nonreciprocal 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 ports (circulate) of the device [8]. In the functional diagram of FIG. 5, transmission is possible only from port 51 to port 52 and from port 52 to port 53. Therefore, in the network of FIG. 1, optically isolated circulator ports 51 and 53 are used for communication with the transmitter T and receiver R at all nodes of the network, respectively. .

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 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, pp. 469-478]. Let us describe their work using the example of the first network. The central node OLT (Optical Line Terminal) 2 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 bus 1. 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) of signals intended for different subscriber nodes 11, 12, ..., 14. The transmitter T of the central node 2 operates at a fixed wavelength, for example , Λ ₁ = 1550 nm and the radiation flow passes through optical circulator 19 to the bus 1. X-couplers 4 Where evenly distributed, 5, ..., 7, and circulators 21, ..., 24 to the receivers R-sites 11, 12, ..., 14 The second stream (similar to the upstream in PON) from the subscriber units 11, ..., 14 to the receiver R of the central node 2 is formed by synchronous access with time division TDMA (Time Division Multiplexing Access) signals from the transmitters T of the subscriber units 11, 12, ..., 14 in bus 1. Radiation from transmitters T is introduced into bus 1 through circulators 21, ..., 24 and taps 4, 5, 6, 7. In this case, the transmission is carried out at the same wavelength λ ₁ = 1550 nm and an individual schedule is set for each subscriber unit 11, 12, ..., 14, taking into account the distance of the node from the receiver R of the central node 2.

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, ..., 14 are transmitted at different wavelengths λ ₁₁ , λ ₁₂ , ..., λ _{1N of the} tunable laser of the transmitter T of the central node 2. Receivers R of the subscriber units 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 2 is carried out at the same wavelength λ ₁ by synchronous access with time division TDMA.

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 known PON networks with a tree architecture in saving optical fiber, ease of monitoring during operation of the network. 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

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

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

5. X.-G. Unger. Planar 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; edited by prof. V.P. Shuvalova. - M: Hotline - 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 (3)

1. A double passive fiber-optic network containing the first and second networks with the first and second central control nodes (controllers), respectively, and a plurality of subscriber nodes with optical receiver and transmitter each, a bi-directional bus made of optical fiber and a plurality of directional X-couplers included in the bus with a pair of its ports, subscriber nodes are connected to the bus through directional X-couplers, the first and second central control nodes are located at opposite ends of the bus, and the transmission wavelengths are the subscriber nodes of the first network are different from the transmission wavelengths by the subscriber nodes of the second network, characterized in that three-port optical circulators are introduced into it according to the number of nodes in the first and second networks, each X-bus coupler is connected by a pair of its branch ports with a pair of three-port optical circulators the taps in the order of their placement in the bus 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 transmission wavelengths in the second network. 2. 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 α _i (λ ₂ ) at a transmission wavelength λ ₂ in the second networks 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. 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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