Method of setting up duplex links in one fibre using optical signals operating in opposite directions and having same carrier wavelength with retroreflection control

FIELD: radio engineering, communication.

SUBSTANCE: method includes using an optical link which ends with bidirectional signal splitters designed to input/output information signals into the optical link; determining overall power of the reflected signal arriving at the input of an optical receiver; comparing said value with the maximum allowable noise power to select the information signal. By eliminating and/or redistributing, on the propagation path of the optical signal between the transmitter and the receiver, elements with a higher level of reflection or replacement thereof with elements with a lower level of reflection, overall power of the reflected signal arriving at the input of the optical receiver is obtained, which is sufficiently low for separating the information signal from the optical signal arriving at the input of the receiver, and the information signal is transmitted in opposite directions using one carrier wavelength for a specific optical link.

EFFECT: high efficiency of using fibre-optic links.

6 dwg, 2 tbl

The invention relates to techniques for fiber-optic communication and can be used in fiber-optic communication lines (FOCL) for the organization of multiple independent communication channels.

It is known (http://) using SFP+ modules for the organization of high-speed full-duplex channels with data transfer rates up to 10 Gbit/s In particular, WDM SFP+ modules are used for duplex communication channel in a single fiber. SFP+ modules support a feature that allows real-time to track the selected device parameters such as operating temperature, the bias current of the laser, the emitted optical power, received optical power, is also supported by the system alarm output settings outside of established tolerances.

The disadvantages of this method it is possible to recognize the low efficiency of the fibers, the impossibility of concurrent use of other devices on the same fibers.

It is known () the use of optical circulators for transmission over a single fiber and the wavelength of the two data flow in different directions. An optical circulator is a completely passive device, the principle of which is based on the effect of non-rotation of the polarization plane (the so-called Faraday effect). To send the data to ispolzuyutsya perpendicular to each other polarized plane. One of them is an optical signal in one direction and the other in the opposite direction.

The disadvantages of this method are quite high cost, determined by the value of the circulators, low efficiency, use of fibers (limited Windows of transparency of the optical circulators).

This decision was taken as the nearest equivalent.

The technical result obtained by the implementation of the developed technical solutions is to increase the efficiency of optical fibers by using optical signals, running in opposite directions and having the same carrier wavelength.

To achieve the technical result of the proposed use, a method of transmission of the information signal in single-fibre optic line in opposite directions using a single carrier wavelength, the implementation of which use optical communication line, ending a two-way dividers signals intended for input/output of information signals in an optical communication line, and pre-or during testing method to determine the total power of the reflected signal at the input of the optical receiver for specific optic line, compare at azanuy value with the maximum allocation information signal power and noise by removing and/or redistributing path the optical signal between the transmitter and receiver elements with a high level of reflection, or replace them with items with a lower level of reflection, get the total power of the reflected signal at the input of the optical receiver, small enough to highlight the information signal from the optical signal received at the input of the receiver and, as a consequence, the transfer of the information signal in opposite directions using a single carrier wavelength-specific optical communication lines.

Current schemes duplex channel require either two fibers or two carrier wavelengths for transmission and reception of the signal. However, these methods are ineffective, as for full-duplex communication channel requires a significant amount of scarce resources (optical fiber, the spectral range). For example, when using CWDM seals on these schemes can be arranged only eight full-duplex channels.

Consider the method does not require the use of any methods for the selective separation of signals (e.g., wavelength or polarization) for the separation of areas and expands the possibilities of their use for further condensation of the signals.

Creating a duplex channel with this method will not cause interference associated with look no further than volnovym offset because the channel will only use one carrier frequency, and not two, as in classical methods.

In addition, this method is fundamentally changes the circuit components (spectral multiplexing in optical fiber that enables high speed distributed networks over a single fiber in addition to the classical scheme "point to point".

The use of this method with the methods of wavelength-division multiplexing (WDM WDM, DWDM, etc. next LSG) leads to increased efficiency in the use of optical fibers in two times, and also increases the reliability of organized communication channels, reduces the cost of their organization due to the significant reduction of the required passive elements spectral multiplexing.

The result of application (depending on the use of spectral methods seal:

Note: in the table were compared with the traditional method (spectral multiplexing (LSG) single-fiber - 8-channel CWDM.

The method was tested on the operator's network for 3 years and has shown its effectiveness.

The basis for the proposed method was the assumption that the total power of the backward radiation, due to the physical properties of homogeneous fibers having standard characteristics is negligible.

For the technine level of the reflected signal in a homogeneous fiber has conducted a number of experiments, aimed at the measurement of the reflected signal at the point of entry of the radiation in a homogeneous fiber sufficiently large length.

The experiments conducted on the basic types of single-mode fibers showed that the level of the reflected signal is from 55 to 70 dB.

A rough calculation shows that the standard aperture single-mode fiber level of the reflected signal in the fiber length maximum usable length may not exceed a value of 55 dB.

According to the results of calculations and measurements, one can conclude the following:

The main power of the reflected signal appearing at the input in optical communication line when applying the optical signal occurs at the points of the line due to the increased reflection, while the share of power back radiation due to the physical properties of homogeneous fibers having standard characteristics is negligible.

Line points due to the increased reflection (hereinafter - reflecting elements can be, for example, mechanical detachable connections, and made passive optical elements (attenuators, CWDM components, and so on).

Thus, to transmit an optical signal of one length one single-mode fiber in two directions is enough noise from the reflected signal at the receiver input from the expressing elements of the line was small enough for a confident selection of the information signal.

Used calculation model (Figure 1) contains:

optical transmitter 1;

optical receiver 2;

- any bidirectional (transparent) device combining/separation signals (e.g., splitter) 3;

- fiber-optic communication line 4, which includes other devices seals;

reflective elements, including device combining/separation of the signals, the elements of the wave seal, detachable mechanical connection etc.

This scheme is sensitive to the effects of reflected signals, as the reflected signal passing through the device Association/division signals 3, falls not only on the insulator laser (transmitter 1), but also on the optical receiver 2.

The reflected signal level in the line in this diagram is the main and most significant component of the noise, and it must be below the minimum allowable level of noise of the optical receiver.

When designing channels DDM and/or their organization's existing communication lines according to the developed method pre-calculate the total power of the reflected signal at the input of the optical receiver caused all reflective elements positioned in the path of the signal transmitter.

The total capacity of the P_satrthe reflected signal is equal to the sum of the capacities of the reflected signals, arriving at the receiver input of each reflecting element on the way of the signal

In the circuit containing n reflective elements

$$P_{W\mathrm{about}tp}={\displaystyle \underset{i=1}{\overset{n}{\sum }}{P}_{W\mathrm{about}tpi}}$$, W,

where R_satr- the total power of the reflected signal at the input of the optical receiver.

P_{sotr i}- power of the reflected signal received at the input of the receiver from the i-th element.

Arriving at the receiver input optical power of the i-th reflecting element R_{sotr i}calculated from the logarithmic power level of the i-th reflecting element R_{sotr i}:

$$P_{W\mathrm{about}tp}=10\frac{p_{W\mathrm{about}tpi}}{10}$$, dBW,

which, in turn, is calculated as:

p_{sotr i}=p_East-A_i-A_{OTR i}-A_{arr i}, dBW,

where R_Eastthe signal level of the transmitter, dBW,

A_ioptical attenuation between the transmitter near the end and i-m is tragoudi element, dB,

And_{OTR i}optical attenuation reflection (return loss) of the i-th reflecting element, dB (from the specifications on the reflective element),

And_{arr i}optical attenuation between the i-th reflecting element and the receiver near the end in the opposite direction dB.

The logarithmic level of the total reflected signal at the receiver input is:

P_satr=10 lgP_satr, DBW.

When calculating the noise at the receiver input accepts the following assumptions:

1. The power reflected from the opposite end of the signal, given the large attenuation of the route (equal to twice the attenuation of the line), mistaken for a negligibly small value. So, for the line connection attenuation 15 dB (taking into account the attenuation of the y device) and the attenuation of reflections on mechanical connectors 16 dB power level reflected from the opposite end of the signal received at the input of the optical receiver is -46 dB, whereas the level of sensitivity of the receivers used for the communication with such attenuation, not less than -26 dB.

2. Noise power at the receiver input from the reflected signals of the second order reflections from reflections), take a negligibly small value. Thus, the estimated noise power at the receiver input from the reflected signals of the second order of 60 dB or more lower the e than the total power from the reflected signals of the first order.

3. Power reflection signal in homogeneous fiber mistaken for a negligibly small value (-55 dB).

The total noise power at the receiver input due to the above and for other reasons, take into account when comparing with the utmost level of noise at the receiver input.

The calculated power level P_satrthe reflected signal at the receiver input is compared with the maximum permissible sound power level of the receiver R_maxand receiver, regulated by the specification of the equipment (typically -40 dB -35...), taken with a margin of 3 dB (i.e. 50%) for other types of noise (including reflection from the far end, a reflection in a homogeneous fiber and noise from adjacent channels CWDM).

Must comply with the conditions under which:

P_{max W receiver}>R_{W neg}+3 dB.

Also, if hardware specifications regulated minimum logarithmic signal-to-noise ratio at the receiver input (R_{min SS}, dB),

P_{min SS}>R_receiver-R_satr-3 dB,

where R_receiver- the level of signal from the transmitter of the opposite terminal device at the receiver input.

These conditions must be met for all devices involved in the transmission of the information signal. All measurements and calculations performed to the desired wavelength.

According to the results of analysis is and depending on the elemental composition of the optical link exclude and/or redistribute path of the optical signal between the transmitter and receiver elements with a high level of reflection or replace their items with a lower level of reflection, getting the total power of the reflected signal at the input of the optical receiver, small enough to highlight the information signal from the optical signal received at the input of the receiver and, as a consequence, the transfer of the information signal in opposite directions using a single carrier wavelength-specific optical communication lines.

This scheme ensures stable operation of the channels in line with wave seal, and without it, and for this diagram is not important type of wave seal (WDM, CWDM, DWDM, HDWDM).

This scheme can be implemented without the use of wave seal, and with an additional seal (WDM, CWDM, DWDM).

In a preferred variant implementation of the method of the scheme n/2 duplex channels using a single carrier wavelength on a single channel in the network by using a wave seal can be implemented industrially, as shown in figure 2, where 5 indicated the wave seal.

The functionality of blocks and circuit elements of the organization full-duplex communication channels in a single fiber using one carrier frequency for reception and transmission:

1) Optical transmitter generates an optical of modelirovanie the information signal with a carrier frequency, allocated to a particular channel (the active element).

2) Optical receiver receives and processes the modulated optical information signal with a carrier frequency allocated to a particular channel (the active element).

3) Bidirectional (transparent) device combining/signal separation - separates/combines space optical signal transmission and reception, providing the division of flows (passive element).

4) Fiber-optic communication transmission medium optical information signal (passive element).

5) Wave seal - provides the ability to transmit one channel of the multiple data streams at different wavelengths (passive element).

The scheme works as follows. The optical transmitter 1 generates a modulated information signal with a carrier wavelength allocated to a particular channel. The signal is then fed to one of the outputs, bidirectional (transparent) device combining/splitting signals 3, passing through it, the signal falls in a wave seal 5, which at the same time and counter applies to both the receiving and the transmitting signal of this channel. Next, the signal is distributed over a linear path of fiber-optic communication line 4, the output from which it is fed to the common input dwon the identification of a (transparent) device combining/splitting signals 3, after passing through the wave seal 5.

In the device Association/division signals 3 information signal is divided into two parts. One part of the signal at the optical transmitter 1 and extinguished on the insulator laser, and the second is supplied to the optical receiver 2, which receives and processes the signal.

All passive elements of fiber-optic communication network should be transparent and, accordingly, to provide simultaneous transmission of signals in both directions. In the case of the use of this scheme in the network by using a wave seal 5 all bidirectional (transparent) optical combining/splitting 3 set outside distribution group signal and accordingly contribute to the attenuation of only the signal of one channel and not the whole line 4.

To measure the losses in the channel assemble the circuit shown in Figure 3. Initially, you must reset the optical power meter 2 from the optical radiation source 1. On the target device # 1 to one of the outputs of the combining/splitting signals 3 connect the optical radiation source 1 and the second output is immersed in the liquid 5 with a refractive index equal to the refractive index of fiber core.

On the target device # 2 to one of the output devices merge/split rings is fishing 3 connect the optical power meter 2, and the second end is also immersed in the liquid 5 with a refractive index equal to the refractive index of fiber core.

Skim reading from the optical power meter 2 corresponds to the losses in the channel. When the experiment requires that the optical radiation source 1 and the optical power meter 2 were set to the wavelength corresponding to the carrier wavelength in this channel.

When measuring the minimum level of the optical signal receiver from a given optical transmitter initially zero optical power meter 2 from the optical transmitter 1, used on the line. Assemble the circuit shown in Figure 4.

The optical transmitter 1 and the optical receiver 2 in active mode, connect directly through the test optical fiber 4. The fiber begins to wind on the core 3 with a diameter approximately equal to 6-7 mm, and when the link between transmitter 1 and receiver 2 is lost, the test fiber 4 slowly begin to twist from the core 3 until the connection is restored, after which the test fiber 4 is fixed in a predetermined position.

The optical receiver 2 is replaced by an optical power meter, which take readings. Since the optical transmitter 1 generates a modulated signal, the zeroing of the meter optical m is snasti from it may be error, equal to the amplitude of the optical signal.

For a more precise definition of the minimum acceptable signal level of the optical receiver 2 from the predetermined optical transmitter 1 is repeated measure 5-10 times and determine the arithmetic mean taken from measurements. This result will correspond to the desired parameter.

To measure the level of the reflected signal should be zero optical power meter 2 from the optical transmitter 1, used on the line. Assemble the circuit shown in Figure 5.

On the target device # 1 to one of the outputs of the combining/splitting signals 3 connect the optical transmitter 1 in the on state and the second output is immersed in the liquid 5 with a refractive index equal to the refractive index of fiber core.

On the target device # 2 to one of the outputs of the combining/splitting signals 3 connect the optical transmitter 1 in the off state, and the second output connect the optical power meter 2.

For a more precise definition of the level counter radiation without the reflected signal from the radiation source in the middle of the target device, repeat the measurement 5-10 times and determine the arithmetic average from the measurements taken.

On the target device # 2 of the optical transmitter 1 is transferred in turn the military state. Remove level measurement counter radiation reflected signal from the radiation source at the nearest target device 5-10 times and determine the arithmetic average from the measurements taken, and then subtract from the level counter signal with the received signal level of the counter signal without the echo signal, the result will be the desired value.

Below is the practical test of the proposed scheme. The tests made sample of the proposed scheme duplex communication channel in a single fiber using one carrier frequency for transmission and reception showed its performance and confirmed the achievement of this goal.

Was collected laboratory stand. As the wave of the seal used CWDM modules 1, collected on the basis of thin-film filters, as a device combining/splitting signals 2 used splitters with a division ratio of 50/50, the simulator line played two coils 4 with insertion attenuation 0.32 and 0.35 dB and two attenuator 3 to 10 dB each. Each attenuator 3 is connected through the connector FC APC 5. This type connectors directs the reflected signal so that it is displayed from the fiber. Terminal equipment connected via the connector type LC 6.

The tests were carried out using 4 duplex channels nanessa wavelengths 1310 nm, 1330 nm 1350 nm 1370 nm, respectively. The experimental design is shown in Fig.6.

The results are given in the measurement Protocol for the organization of a duplex communication channel in a single fiber using one carrier frequency for reception and transmission:

Given that for the selected SFP modules the receiver sensitivity is 40 dB, and guaranteed uptime is provided with a sensitivity of 37 dB (SFP 150 km Syoptec, 1 GB), the measurement results show the possibility of organizing a full-duplex channels at each of the selected wavelengths in the same fiber, which improves the efficiency of use of existing optical fiber and the spectral range.

Currently, the network operator is actively used about 50 of the communication channels constructed by the proposed method.

The mode of transmission of the information signal in single-fibre optic line in opposite directions using one carrier length in the wave, characterized in that use optical communication line, ending a two-way dividers signals intended for input/output of information signals in an optical communication line, and determine the total power of the reflected signal at the input of the optical receiver for specific optic line, compares the specified value with the maximum allocation information signal power and noise by removing and/or redistributing path of the optical signal between the transmitter and receiver elements with a high level of reflection, or replace them with items with a lower level of reflection, get the total power of the reflected signal at the input of the optical receiver little enough to highlight the information signal from the optical signal received at the input of the receiver and, as a consequence, the transfer of the information signal in opposite directions using a single carrier wavelength-specific optical communication line.