RU2384955C1 - Fibre-optic information transmission system - Google Patents

Abstract

FIELD: physics, communications.

SUBSTANCE: invention relates to optical communication engineering and can be used in designing bus transmission systems and intra-object data collection and control local systems. Invention involves using a set of fibre-optic adjustable delay lines for generating one aggregate serial stream from parallel information streams, where data and a clock signal are transmitted at different optical radiation wavelengths. An adjustable fibre-optic delay line also serves for synchronisation phase adjustment at the receiving end.

EFFECT: simplification of time multiplexing and demultiplexing of transmitted digital streams.

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Description

The invention is a device and relates to the field of information transmission systems, can be used for trunk and object fiber-optic systems for transmitting digital information via optical cables, and relates to the data link layer of the transmission system (sub-level of access control to the medium).

To increase the amount of information transmitted through the transmission channels, compression of the transmitted signals is used. Known fiber optic transmission systems with wave (spectral) multiplexing (WDM). In [1], a block diagram of a fiber-optic transmission system with spectral multiplexing (multiplexing) is presented. The system consists of sequentially installed: an optical multiplexer having n optical inputs (λ ₁ -λ _n ), an optical amplifier, a fiber optic transmission path (fiber line), a second optical amplifier, an optical demultiplexer with n optical outputs (λ ₁ -λ _n )

The advantage of the system is the independence of compaction from the type of transmitted traffic (SDH, PDH, IP, ATM or others). Each optical carrier frequency is generated by an independent laser radiation source and can transmit a digital signal stream generated in accordance with the methods used in various synchronous information transmission technologies .

A wave compression system (WDM) with n transmission channels has the following disadvantages.

1. Limited temperature range during operation. The limitation of the temperature range is associated with a high dependence of the parameters of optical multiplexers and demultiplexers with the number of spectral channels more than 4 on temperature. The best foreign optical demultiplexers and multiplexers with more than 4 channels number operate in the temperature range of at least 0 ° C and no more than 70 ° C [2]. In the same temperature range, the required frequency stability is ensured by high-quality single-frequency (DFB) laser diodes made on the basis of quantum heterostructures with an integrated Bragg grating used in WDM transmission systems [3].

2. Reducing the distance between the repeaters with an increase in the number of transmission channels (wavelengths of optical carriers). One of the parameters that determine the allowable distance between repeaters is the power of the transmitted optical signals. However, if a certain threshold of power is exceeded, nonlinear effects can appear in the optical fiber, which can lead to communication failure [4]. First of all, it is:

- nonlinear refraction - a phenomenon that is determined by the dependence of the refractive index of the core of the optical fiber on the intensity of the electric field E;

- stimulated inelastic scattering - a phenomenon in which an optical wave transfers part of its energy to a nonlinear medium as a result of interaction with molecules;

- modulation instability - the phenomenon of modulation of a stationary wave state under the influence of nonlinear and dispersion effects;

- parametric processes - phenomena caused by the interaction of optical waves with the electrons of the outer shells (four-wave mixing, harmonic generation and parametric amplification).

In addition, it should be noted that there are “weak points” in the optical fiber where, when a certain power density is exceeded, an optical discharge can be initiated, which causes the process of core material destruction. Such weak points are fiber ends, places of welded and mechanical joints. A particular danger to fiber-optic communication systems is the fact that, having arisen at a “weak point”, the optical discharge propagates along the optical fiber towards the optical radiation in the form of a destruction wave at a speed of approximately 1 m / s [5]. At the same time, many kilometers of optical cable, as well as passive and active elements of the fiber-optic communication system, will be destroyed. In this regard, restrictions on the value of the maximum signal power in the optical fiber are adopted. In accordance with the G.692 standard, with the simultaneous use of many sources of the optical signal, the total power in the optical fiber should be no more than 19 dBm [6, 7]. Thus, the power budget of each transmission channel is reduced n times by reducing the power level of information signals.

3. The transmitted streams of digital information should be formed only by synchronous message transfer technologies, i.e. contain synchronization signals in its structure. External synchronization is impossible due to the presence of chromatic dispersion in the optical fiber, information signals and synchronization signals will propagate at different radiation wavelengths and therefore have different propagation times (different delays in the fiber optic path). As a result, a desynchronization will occur in the transmission system.

Time division multiplexed information transmission (TDM) systems are known.

In [8], a block diagram of a fiber-optic communication system with temporary information compression is presented, which provides transmission from 4 to 24 E1 streams (technology of plesiochronous digital hierarchy, PDH) and digital streams using Ethernet 10 / 100TX and RS232 technologies. The system consists of Super-Nail type multiplexers / demultiplexers (RTK 34.5) connected by a single-fiber optical cable. Multiplexers / demultiplexers have interface units for interfacing with E1, Ethernet 10 / 100TX, RS232 channels and an optical channel. Moreover, transmission and reception are carried out at a speed of 100 Mbit / s at different wavelengths of optical radiation - 1.31 (transmission) and 1.55 μm (reception).

The system can operate in an extended temperature range, provides the maximum possible distance between repeaters. The synchronization of the transmitted information is carried out by introducing equalization bits into the transmitted information stream. The system can be performed on a domestic optoelectronic component base.

The main disadvantages of the system are the low transmission rate limited by PDH technology and equal to 565 Mbit / s, and the need to “expand” the entire structured stream to isolate even its smallest part (for example, a low-speed RS232 stream).

In [9], a fiber-optic transmission system with temporary (and, if necessary, wave) information compression is presented, which uses the technology of plesiochronous digital hierarchy (PDH) and synchronous digital hierarchy (SDH) to transmit information.

The system consists of sequentially installed block converting the input signal into a pulse-code sequence (channel-forming block), performing sampling, quantization, linear (or non-linear, if necessary) coding and noise-resistant coding, a block of temporary grouping of component signals (frames / tribes) PDH of the required level hierarchy, the interface block of component (tribal) signals arriving at the temporary multiplexing SDH, performing input / output, local cross-coupling , SDH multiplexing unit, which logically generates the STM-N module of the required hierarchy level, an optical interface unit that converts the logical pulse sequence into the STM-N physical sequence (performs all the necessary transformations to form the headers: sectional, multiplexed, and path (path), as well as interface coding) of the transmitting unit, which modulates the carrier radiation source (laser) and linear coding of the wave block is multiplexed WDM (an optional unit is used only if necessary), a powerful optical amplifier (booster), which amplifies the optical digital sequence to the level required to create the necessary total power budget, an optical linear amplifier, which carries out optical signal amplification at the overlap (span or regeneration) section , an optical preamplifier that amplifies the input signal at the receiving end, a WDM demultiplexer (when using a wave multiplexing unit), about optical receiver that receives the signal, the optical interface unit that converts the physical sequence equivalent to the STM-N module into a logical pulse sequence and performs conversions on decoding the interface code and interpretation of the headers: sectional, multiplexed and path (path), SDH demultiplexing unit logical decomposition of the pulse sequence of the STM-N module and allocation of component signals (tribes) of the required level of the PDH hierarchy , an interface block of component (tribal) signals, a block for disassembling a group signal (frame / tribe) PDH of the accepted hierarchy level to the required one, for example, Е1, and highlighting the desired time slot, a block for converting a pulse-code sequence into an output signal performing noise-proof decoding and restoration discretized, quantized and codified signal. In duplex transmission, it is necessary to have a double set of equipment for transmitting and receiving operations at both ends.

SDH technology differs from PDH in that it does not use alignment bits to synchronize the transmitted information, but special fields in the structure of transmitted information packets — synchronous transport modules of various levels (from STM-1 to STM-256). The main advantage of SDH technology is the ability to isolate encapsulated tribes of SDH, PDH or other technologies without expanding the entire structured digital stream.

The system can operate in an extended temperature range, provides the maximum possible distance between repeaters. It provides information transfer rates up to 40 Gbit / s (STM-256 level).

The synchronization of the transmitted information is carried out by introducing equalization bits into the transmitted information stream.

The main disadvantage of the system is the complexity of forming and disbanding synchronous transport modules, especially for hierarchy levels STM-64 and STM-256. The information flow rate for STM-64 modules is 10 Gb / s, for STM-256 modules it is 40 Gb / s. When switching from the speed of STM-16 2.5 Gbit / s modules to 10 Gbit / s, technological difficulties arise in creating electronic components for this frequency range. The domestic electronic industry does not currently have the technology for the production of microcircuits for this frequency range. Thus, with the development of transmission speeds of more than 2.5 Gbit / s, a technological dependence on foreign manufacturers appears.

Closest to the technical solution to the proposed information transmission system is a fiber-optic information transmission system (interface for transmitting discrete information through an optical channel), described in [10].

The device consists of M transmitting units, a first group of M transceiver optical modules, an optical combiner with a transmission matrix M X1, a fiber optic path, a spectrally selective coupler with a transmission matrix 1X M, a second group of M transceiving optical modules and M receiving units.

Each transmitting unit consists of an input buffer two-port N-bit register, the inputs of which are connected to N lines of the N-bit input data bus, a synchronization device, (N + 1) semiconductor laser transmitting optoelectronic modules, (N + 1) fiber-optic delay lines made in the form of segments of optical cables of fixed length, an optical combiner with a transmission matrix (N + 1) X1.

Each receiving unit consists of an optical splitter with a 1X N transmission matrix, a set of fiber-optic delay lines of (N + 1) delay lines made in the form of segments of optical cables of a fixed length, a set of (N + 1) receiving optoelectronic modules, an output two-port N-bit buffer register, the outputs of which are connected to the lines of the output N-bit data bus, a device for generating clock pulses, consisting of a D-trigger, a pulse shaper and a time delay device.

The interface, which is a transmission system, operates as follows.

The semiconductor laser transmitting optoelectronic modules of each transmitting optoelectronic unit convert the electrical signals at the output of the input buffer register and the synchronization signal at the output of the clock generator into optical signals and direct these signals to the input poles of the set of fiber optic delay lines. The optical clock signal has a minimum delay determined by the length of the connecting cables. We will consider it equal to 0. With the interval Δt, 2Δt, ... N Δt - signals from the first, second, etc. are delayed. Nth optoelectronic transmitting modules.

The output poles of a set of fiber optic delay lines are connected to the input poles of the optical combiner. The combiner generates a group optical signal directed to the output of the transmitting unit.

The group optical signals of the optoelectronic transmitting units are sent to M transceiver optical modules that convert the wavelength of the optical radiation of the transmitting optoelectronic modules into a spectral range with a frequency spacing equal to Δν × M.

The output signals of the transceiver optical modules are combined by an optical multiplexer (spectrally selective optical combiner) and sent to the transmission path (fiber optic path) and then to the input optical pole of the spectrally selective splitter (optical demultiplexer). A spectrally selective splitter acts as a switch, distributing a single information flow between consumers (subscribers) depending on the wavelength of the optical signal. Local optical information flows are directed to the inputs of M receiving transceiving optical modules, which restore signals and convert the wavelength to its original state. The output optical poles of the transceiver optical modules are connected to the input optical poles M of the receiving optoelectronic units.

Each group optical signal is directed to the input optical pole of each receiving optoelectronic unit. This signal is fed to the optical input of the splitter with a transmission matrix 1X (N + 1) and then through fiber-optic delay lines to the optical inputs (N + 1) of the optoelectronic receiving optical modules.

The set of delay lines is structurally similar to the set located in the transmitting unit, but in the synchronization channel, the delay is maximum and equal to (Δt · N-τ), where τ is the time interval that takes into account the speed of the component base used. In the transmission channel of the first bit of information, the delay is Δt · (N-1), the second is Δt · (N-2), and so on. The most significant bit of information has a minimum delay.

The electrical outputs of the N receiving optoelectronic modules are connected to the lines of the input port of the buffer register. The output of the (N + 1) -th receiving module is connected to the input of the clock generation circuit, the output of which is connected to the register control input and the synchronization output line.

The disadvantages of the considered information transfer system (information transfer interface) are the following:

- the scope is limited, since the use of spectral multiplexing to form an aggregate optical signal limits the temperature range during operation (the typical range of operating temperatures of multiplexers for 4 channels is from 0 to 70 ° C, for mobile and deployable systems, the temperature range during operation should be within from -40 to + 70 ° C);

- there is a restriction on the power of the optical spectral components of the group signal associated with the possibility of the influence of nonlinear effects in the optical fiber on the quality of communication (according to G.692 recommendations, the total power of all channels should be no more than 19 dBm), the power limit leads to a limitation of the interval between repeaters in communication lines;

- the need to use technologically sophisticated spectrally selective splitters and combiners of foreign production, since the domestic industry has not mastered the technology of their production;

- low transmission speed due to the limited speed of discrete components of digital technology (the maximum clock frequency for domestic registers and triggers is 400 MHz, which allows you to organize a transmission system with a speed of not more than 400 Mbit / s in one channel).

The proposed fiber-optic information transmission system solves the problem of increasing the power of the optical signal in the transmission channels to increase the maximum distance between repeaters, increase the speed of information transfer, provide the possibility of using mainly domestic optoelectronic component base, provide the ability to work in an extended temperature range, and enable digital transmission streams that do not contain service fields in their structure that provide synchronization increase in the share of the payload in the structure of the digital stream.

The essence of the invention lies in the fact that in a device containing a sequentially installed transmitting unit, a fiber optic path, a receiving unit, and the transmitting unit contains an input N-bit data bus for connecting N information sources, N + 1 transmitting optoelectronic modules, N fiber optical delay lines, the optical inputs of which are connected to the optical outputs of N transmitting optoelectronic modules, a spectrally selective optical combiner, the first input of which is connected to the output of the (N + 1) -th optical the electronic module, the synchronization device, the receiving unit contains an optical splitter, the first receiving optoelectronic module receiving information data, the optical input of which is connected to the first output of the splitter, the second receiving optoelectronic module receiving synchronization signals, the optical input of which is connected to the second output of the splitter through fiber optical delay line, a device for generating clock pulses, output N bit data bus,

- a powerful optical amplifier, sequentially installed chromatic dispersion compensator and a preliminary optical amplifier are introduced, the optical input of a powerful optical amplifier connected to the output of the transmitting unit, and the output to the input optical pole of the fiber optic path, the input optical pole of the chromatic dispersion compensator connected to the output optical the fiber optic path, and the optical output of the pre-amplifier is connected to the optical input of the receiving unit, in The input unit contains (N + 1) pulse shapers, an optical combiner with an N × 1 transmission matrix, and the inputs of N pulse shapers are connected to the lines of the input N-bit data bus, and the outputs to N transmitting optoelectronic modules, the input (N + 1) - of the first pulse shaper is connected to the output of the synchronization device, and the output to the input of the (N + 1) -th transmitting optoelectronic module, N fiber-optic delay lines are configured to delay time, N optical inputs of the optical combiner are connected to optical outputs of N delay lines, and the optical output of the combiner is connected to the second input of a spectrally selective optical combiner having a 2 × 1 transmission matrix, two electronic amplifiers, N electronic keys, are introduced into the receiving unit, and the input of the first electronic amplifier is connected to the output of the first receiving optoelectronic module and the output to the switched inputs of N electronic keys, the input of the second electronic amplifier is connected to the output of the second receiving optoelectronic module, and the output to the input of the sync forming device pulses - and is connected to the output synchronization line, N-outputs of the clock generation device are connected to the control inputs of N electronic keys, and the outputs of electronic keys are connected to the output N lines of the data bus, the spectrally selective splitter installed at the input of the receiving unit has a transmission matrix 1 × 2, for the possibility of adjusting the delay time, all fiber-optic delay lines consist of sequentially installed length of optical cable of a fixed length, two optical lenses, the distance between which can be changed by the regulation mechanism and the mode field diameter transducer.

The drawing (see figure 1) shows a structural diagram of a device that implements the proposed invention.

The device comprises sequentially installed transmitting unit 1, a powerful optical amplifier 2, a fiber optic path 3, a chromatic dispersion compensator 4, a preliminary optical amplifier 5 and a receiving unit 6.

The transmitting unit 1 forms an optical aggregate digital stream. This stream is directed to the input of a powerful optical amplifier 2, which increases the power of optical signals to a maximum value. The maximum power value is limited by the threshold of nonlinear phenomena in the optical fiber of the fiber optic path 3. At the output of the fiber optic path 3, a chromatic dispersion compensator 4 is installed, which is a segment of a special fiber with a large negative dispersion that compensates for the positive chromatic dispersion in the optical fiber of the fiber optic path 3. The preliminary optical amplifier 5 increases the power of the optical signal to ensure its conversion of the optoelectron receiving modules installed in the receiving unit 6.

The inputs of the transmitting unit 1 (see Fig. 2) are the lines of the N-bit input data bus 7 connected to the inputs of the N-pulse shapers 8. The transmitted digital streams are sent to the data bus line 7, the clock frequency of these streams is generated by the synchronization device 9. Pulses synchronization generated by the synchronization device 9, are fed to the input of the (N + 1) th pulse shaper 10. From the outputs of the pulse shapers 8 and 10, signals representing pulses of a given duration are fed to the electrical inputs of the transmitting optoelectronic modules. Moreover, the N first transmitting optoelectronic modules 11 convert information signals into optical pulsed signals at an optical radiation wavelength λ _d , and synchronization signals (N + 1) by the transmitting optoelectronic module 12 are converted into optical pulses at an optical radiation wavelength λ _s .

Signals with a wavelength of optical radiation λ _{d are} routed through N fiber-optic delay lines 13 to the inputs of the optical combiner 14 with a transmission matrix N × 1.

Signals with a wavelength of optical radiation λ _{s are} sent to the first input of a spectrally selective combiner 15, its second input is connected to the output of the optical combiner 14, optical signals with a wavelength λ _d are present at this output. The output of the transmitting unit is the output of a spectrally selective combiner 15 with a 2 × 1 transmission matrix, the output will contain optical signals with radiation wavelengths λ _d and λ _s .

Fiber optic delay lines 13 have the ability to tune the delay time. They consist of two parts - a constant delay line (see Fig. 3), which is a segment of an optical cable of fixed length 16 (the delay of the optical signal is proportional to the length of the optical fiber of the cable) and a tunable delay line 17.

Tunable delay lines consist of sequentially installed input optical single-mode fiber 18, two optical lenses 19 and 20, a field diameter transducer of mode 21 (see Fig. 4). Optical lenses can be gradient (see figa) or spherical (see fig.4b). The lenses are installed at a certain distance from each other, which can be changed by the regulation mechanism 22. The first lens acts as a collimator of optical radiation. A collimator converts a diverging beam of optical radiation from the end face of a single-mode fiber 18 into a parallel beam. A parallel optical beam of infrared optical radiation from the first lens 19 is directed to the second lens 20, spaced from the first at a distance d. The second lens 20 forms an image of the output end face of the input single-mode optical fiber at the input optical pole of the mode field diameter transducer 21. Due to lens manufacturing errors, the image size of the end single-mode fiber end face projected at the input optical pole of the mode field diameter transducer 21 will exceed its true dimensions . To reduce the introduced optical losses, the converter 21 reduces the image size of the output end of the input optical fiber 19 to its true size at the output pole of the converter.

A decrease in the mode field diameter (image size) is achieved using a special optical fiber by thermal diffusion of the impurity doping the core of the optical fiber into its cladding [11].

The delay of the optical signals is adjusted using the regulation mechanism 22, which changes the distance between the lenses, while changing the geometric path of the optical signal and its delay time.

The input of the receiving unit is the input of a spectrally selective coupler 23 with a transmission matrix 1 × 2 (see figure 5). The first output of the splitter, tuned to a wavelength of optical radiation λ _d , is connected to the optical input of the first receiving optoelectronic module 24, the output of which is connected to the input of the first electronic amplifier 25, the output of which is connected to the switched inputs of N electronic keys 26.

The second output of the splitter 23, tuned to a wavelength of optical radiation λ _s , is connected to the optical input of the second receiving optoelectronic module 27 through a fiber optic delay line 28. The design of this delay line is similar to the delay lines of the transmitting unit. The output of the second receiving optoelectronic module is connected to the input of the second electronic amplifier 29, the output of which is connected to the synchronization output line 30 and the input of the clock generator 31. The N outputs of the clock generator 31 are connected to the control inputs of the N electronic keys 26, the outputs of these keys are connected to the output lines N-bit data bus 32.

We show the operation of the device with a specific example.

As an example, the diagrams presented in Fig.6 illustrates the process of transmitting 4 digital streams connected to the lines of the input 4-bit data bus (N = 4).

For transmission over a fiber-optic channel, the digital stream undergoes an interface conversion to optimize the passage through the communication line (linear coding). For transmission over optical cables, they most often use a linear code without returning to zero (NRZ).

Figure 6 presents the diagrams of the pulses of synchronization of digital streams and the diagrams of digital streams of information (CPU _1- CPU ₄ ) in the linear code NRZ (the first 4 bits of each stream are presented on the diagrams). In the NRZ code, the signal of the logical unit is generated by a pulse whose duration is equal to the duration of the bit interval (the period of the clock clocks generated by the synchronization device 9). Logical zero corresponds to no signal.

Pulses of digital information flows and clock pulses are sent to pulse shapers 8 and 10, structurally made according to one scheme.

The pulse shapers 8 and 10 convert the linear NRZ code into a bipolar code with RZ returning to zero, while they format (normalize) the pulse duration. In the RZ code, the presence of an impulse corresponds to a logical unit, the absence corresponds to a logical zero. If we denote the duration of the bit interval (the repetition period of the synchronization pulses) T _s , then at the output of the (N + 1) -th synchronization pulse shaper 10, pulses must be received at a level of 0.1 equal to t _c , which is determined by the expression (see Fig. 6)

where N is the bit width of the data bus (the number of digital transmitted information streams), in the considered example N = 4.

Shapers of data pulses (with numbers 1 ÷ N) 8 must generate pulses, the duration of which t _d at the level of 0.1 is determined by the expression (see Fig.6)

In the microsecond and nanosecond ranges, pulse shapers can be constructed according to well-known schemes on TTL and LVTTL logic microcircuits [12].

The schemes of pulse shapers in the picosecond range are also known and can be performed on a domestic component electronic base [13-14] using pulse avalanche-key diodes and transistors.

The electrical pulses generated by the shapers 8 and 10 are converted by means of transmitting optoelectronic modules 11 and 12 into optical pulse signals. Moreover, the transmitting optoelectronic module 12 generates optical synchronization signals with a wavelength of λ _s , and modules 11 generate optical data signals with a wavelength of λ _d . Optical data signals λ _d and synchronization λ _{s are} sent to the input of a spectrally selective combiner 15, see figure 2. Moreover, the optical data signals are combined using fiber-optic delay lines 13 and the optical combiner 14 into a single digital optical stream.

Each of the fiber optic delay lines 13 consists of a constant delay line 16, built on a piece of optical cable of a fixed length, and a tunable delay line 17, see Fig.3.

Optical cables of fixed length 16 delay the signals for a time τ _k , depending on the length of the cables L, and

where n is the refractive index of the core of the optical fiber,

c is the speed of light in vacuum.

Tunable delay lines 17 adjust the delay of the signals by changing the distance between the two lenses. The delay value of the optical signal τ _p in this case can be calculated by the formula

where L _SK - the length of the optical connecting cables;

n is the refractive index of the core of the optical fiber;

d is the distance between the lenses;

n _d is the refractive index of the medium filling the gap between the lenses.

Optical cable lengths 16 and delay values of controlled lines 17 are selected so as to provide a shift delay between the signals in the channels of transmission by an amount τ _k, defined by the formula

where T _with - the duration of the bit interval;

N - bit width of the data bus (the number of digital transmitted information streams).

The optical pulse stream formed at the output of the transmitting unit is sent to the optical transmission channel, which consists of a high-power optical amplifier 2 (booster), a fiber optic path 3, a chromatic dispersion compensator 4, a preliminary optical amplifier 5, connected in series, see Fig. 1.

Powerful optical amplifier 2 is designed to increase the power of transmitted signals to a maximum level. The higher the power of these signals, the greater the distance can be set between the signal regenerators, that is, to increase the maximum possible length of the fiber optic path 3 (span length).

The transmission medium in the optical cable of the fiber optic path 3 is, as a rule, a standard single-mode optical fiber (SMF). One of the characteristics of an optical fiber is chromatic dispersion; for a standard single-mode fiber, the chromatic dispersion at a wavelength of optical radiation of 1.55 μm is 17 ps / (nm · km). The presence of chromatic dispersion leads to a broadening of pulsed optical signals propagating along the fiber optic path. Pulse broadening can lead to errors in the transmission of information. To compensate for the positive chromatic dispersion in the proposed device, a compensator 4 is used, made of a special optical fiber (DSF type) with a large negative dispersion of the order of minus 100 ps / (nm · km). The DSF length of the optical fiber is selected from the condition for obtaining the final small negative dispersion, and in the presence of phase self-modulation in the standard optical fiber, conditions are created for the soliton mode of propagation of pulses (propagation without distortion). Since the DSF optical fiber introduces additional optical losses, a preliminary optical amplifier 5 is installed at the input of the receiving unit 6 to amplify the optical signals.

A spectrally selective coupler 23, installed at the input of the receiving unit, divides the group optical signal from the fiber optic path into two components - with a wavelength of optical radiation λ _d and λ _s . Optical signals with a wavelength of optical radiation λ _{d are} sent to the receiving optoelectronic module 24, converted into electrical pulses, amplified by an amplifier 25, and routed through electronic pulse keys 26 to the output data bus lines 32. The control inputs of the keys 26 are connected to the terminals of the clock generation device 31.

Synchronization pulses received by the receiving optoelectronic module 27 and amplified by the amplifier 29 are received at the input of the clock generation device 31. Optical pulses with an optical wavelength λ _c emitted by a spectrally selective coupler 23 are received at this module. Before reaching the input optical pole of module 27 optical pulses from the output of the splitter 23 are delayed by a delay line 28, the design of which is similar to the design of the previously considered delay lines 13.

The synchronization pulses propagate at a wavelength of optical radiation other than the wavelength at which the data is propagated. This leads to the fact that the propagation delay of the data in the transmission channel will be different due to chromatic dispersion from the propagation delay of the synchronization signals. Despite the obtained time shift, using the delay line 28, you can always make sure that the midpoints of the synchronization clocks correspond to the midpoints of the data bit intervals. In this case, the electrical synchronization pulse from the output of the amplifier 29 is supplied to the control input of the 1st electronic key at a time when an electrical pulse of data of the 1st digital stream from the output of the amplifier 25 is present at its input, see Fig. 5. An electrical synchronization pulse from the 1st output of the clock generation device is supplied to the control input of the 2nd electronic key at a time when an electric pulse of data of the 2nd digital stream is present at its input. An electrical synchronization pulse from the 2nd output of the clock generation device is supplied to the control input of the 3rd electronic key at a time when an electric pulse of data of the 3rd digital stream is present at its input. An electrical synchronization pulse from the 3rd output of the clock generation device is supplied to the control input of the 4th electronic key at a time when an electric pulse of data of the 4th digital stream is present at its input.

The electrical synchronization pulses of the channels are generated by the device 31 from the electrical pulses supplied to the input of the device from the output of the amplifier 29. Channel sync pulses with a delay Δτ equal to each other equal to

For relatively low information transfer rates, the channel sync pulse shaping device may be a pulse counter that counts synchronization pulses. For higher speeds exceeding the speed of discrete digital microcircuits, the device can be made in the form of a broadband delay line with taps.

The designs of such delay lines are known, for example, they can be delay lines made on strip lines [13], or silicon delay lines, for example, type DS1020-15 with a minimum step of 150 ps, described in [15].

Pulse electronic keys for relatively low speeds can be performed on logic circuits. For higher speeds, the keys can be made on pulse switching diodes. One of such schemes of an ultrafast key (selection device) of an open type is presented in [12]. The parameters of high-speed diodes operating in the picosecond range are presented in [16].

As keys, you can also use chips from National Semiconductor. This company produces electronic switches of the DS25CP102 type, intended for use as dividers or multiplexers for routing or switching high-speed signals in telecommunication equipment at a speed of 3.125 Gbit / s [17].

Key outputs are data output bus lines. On the lines of this bus we will have restored digital streams in the RZ code. For decoding digital streams, synchronization pulses integrated into information streams (for PDH, SDH and the like transmission technologies) or synchronization pulses output via line 30 can be used, see FIG. 5.

As shown above, the present invention solves the following tasks:

- increasing the power of the optical signal in the transmission channels to increase the maximum distance between the transponders;

- increase the speed of information transfer;

- ensuring the possibility of using mainly domestic optoelectronic component base;

- providing the ability to work in an extended temperature range;

- providing the possibility of transmitting digital streams that do not contain service fields in their structure that provide synchronization;

- increase in the structure of the digital stream of the share of the payload.

The temperature range during operation of the prototype device is limited mainly by the temperature dependence of the transmission coefficients of a spectrally selective splitter and combiner. The best foreign spectrally selective splitters and combiners (optical demultiplexers and multiplexers) for the number of transmission channels of more than 4 operate in the temperature range from 0 to 70 ° C [2].

The proposed device uses spectrally selective combiner and splitter for two wavelengths of optical radiation. A two-channel spectrally selective splitter (combiner) can be made using alloy technology, the temperature during operation of such a splitter is in the range from minus 40 to 70 ° C [18]. This temperature range corresponds to the 1U execution group according to GOST RV 20.39.414.1-97 and can significantly expand the scope of the proposed device, for example, the proposed device can be used in systems for collecting, managing and processing information of mobile deployable complexes.

For the prototype device, the transmission rate is limited by the speed of the buffer register chips and D-flip-flops. Today, the fastest circuits are microcircuits made on the elements of emitter-coupled logic [19]. Of the domestic microcircuits, the fastest registers and triggers are buffer 6-bit parallel registers of the 1500IR150 type and D-triggers of the 1500TM130 type, their maximum clock frequency is 400 MHz, the data pulse settling time is 0.6 ns, i.e. the minimum pulse duration can be 1.25 ns [19].

Based on the principle of operation of the prototype, the bit stream velocity B _i at each fixed wavelength of optical radiation λ _i is determined from the expression

where N is the number of bits of the buffer registers;

Δτ _p - the duration of the pause between pulses at the output of the optical adder of each transmitting unit;

Δτ _and is the minimum pulse duration (we assume Δτ _p = Δτ _and );

i is the number of the transmitting block (i = 1 ÷ M), M is the number of transmitting blocks and the number of wavelengths of the aggregate signal in the transmission channel, determined by the expression

where B is the desired speed of the transmission channel.

As shown above, restrictions on the value of the maximum signal power in the optical fiber are adopted. In accordance with the G.692 standard, with the simultaneous use of many sources of the optical signal, the total power in the optical fiber should be no more than 19 dBm [6, 7].

Due to the limitation of optical power in the optical fiber, when using M wavelengths, the maximum power of each channel P _i can be no more

where P _max is the maximum power in the optical fiber according to the recommendations of G.692.

In the logarithmic form P _i = P _max -10lg M (dBm)

The maximum power in the channels determines the power budget.

The proposed device uses two transmission channels, one for transmitting data, the other for transmitting synchronization signals. Obviously, already at M> 2 we get a gain in the power budget.

If we assume that the analog device is built on registers 1500 ИР150 and triggers 1500ТМ130, then Δτ _p = Δτ _and = 2.5 ns. Using formula (6), we determine the information flow rate at each fixed wavelength of optical radiation. It will be equal to 342.8 Mbps. Thus, for the fastest domestic component base, the gain in power will be obtained at a transmission speed of more than 685.6 Mbit / s. With increasing speed of the transmission channel, this gain will increase, since in the prototype device, the number of wavelengths used in the aggregate signal increases.

The ability to transmit digital streams that do not contain synchronization fields in their structure and increase the share of the payload in the transmitted digital stream follows from the principle of operation of the proposed device.

The possibility of increasing the speed of information transfer and the use of domestic electronic component base will be shown with a specific example.

Consider the example of constructing the proposed device, designed to transmit optical signals at a speed of 10 Gbit / s with maximum use of the domestic component base (to implement a prototype device at the same speed, a transmission system with 30 optical wavelengths would be needed). Note that the domestic industry has not yet produced optical multiplexers / demultiplexers for 30 channels.

Suppose there are four digital streams at the input of the transmission system that share a common clock. The speed of each stream is 2.5 Gbit / s.

Assume that the pulses are transmitted in the NRZ code. Shapers must convert the NRZ code to RZ code with a pulse duration calculated by the formula (1). For a speed of 2.5 Gbit / s, the pulse duration should be equal to 100 ps.

Pulse shortening can be obtained using a circuit built on a diode with charge accumulation (domestic diodes of the type KD524, KD528, KD630) described in [13] on page 250 (Fig. 7.13b). The circuit allows you to shorten the input pulse to a duration of 100 ps (with a leading edge of 40 ps and a trailing edge of about 30 ps) with an amplitude of pulses up to 50 V. The principle of operation of the circuit is based on the property of the diode with charge accumulation to sharply restore the reverse resistance when switching from direct conduction to closed state.

To convert electric pulses into optical radiation, domestic high-frequency laser modules DMP0131-23, produced by NPF DILAZ, with a modulation frequency range up to 16 GHz can be used [21].

Fiber delay lines should provide a time shift of signals in data channels equal to 100 ps. The signal in the second channel should be delayed relative to the signal in the first channel by 100 ps, the signal in the third channel should be delayed relative to the signal in the second channel by 100 ps, etc. A relative delay of 100 ps is ensured by delay lines built on optical fibers with a length different by Δl. The value of Δl in m can be calculated by the formula

where Δτ is the relative delay, (Δτ = 10 ^-10 s);

c is the speed of light in vacuum;

n is the refractive index of the core of the optical fiber.

Substituting the parameter values into formula (10), we obtain the value of the step of changing the length of the optical fibers for fiber-optic delay lines. This value will be equal to 30 mm, that is, the optical fibers in the delay lines should differ by 30 mm (the error in the manufacture of fixed delay lines is eliminated by the adjustable section).

2-channel optical combiners, 2-wave spectrally-selective splitters and combiners, optical amplifiers are produced by the domestic industry with parameters corresponding to foreign samples.

The generated optical group signal containing the transmitted data is sent to the receiving optoelectronic module 19. The optical signal is a sequence of pulses following with a period of 100 ps. The pulse front is 30–40 ps. To convert optical pulses into electric ones, a receiving optoelectronic module with a time constant of less than 30-40 ps will be needed. These requirements are met by high-speed fiber-optic InGaAs / InP PIN photodetectors (receiving modules) manufactured by NPF DILAZ with a time constant of about 30 ps and a passband at the level of minus 3 dB-16 GHz [21].

To sort the pulses by the transmission channels, electronic keys and a device for generating channel clock pulses are needed. As such a device, a broadband delay line of electrical signals can be used. As shown above, designs of delay lines with taps are known, for example, they can be delay lines described in [13].

Fig. 8.15 in [13] shows the block diagram of the recorder, into which a cable delay line is introduced, providing a sampling frequency of 1 GHz and picosecond resolution.

Pulse electronic keys can be made on pulse switching diodes. One of such schemes of an ultrafast key (selection device) of an open type is presented in [13]. The parameters of high-speed domestic diodes operating in the picosecond range are presented in [16].

Thus, the proposed device, a fiber-optic system for transmitting information with time and wave compaction, differs from the prototype device in its extended temperature range during operation, a large value of optical power in the transmission channels, and the ability to transmit signals without fields responsible for synchronization (the relative payload level). It is possible to implement a device with a transmission rate of 10 Gbit / s on a domestic component base without using high-speed electronic multiplexers / demultiplexers of the STM-64 level, which can only be built on a foreign component base.

Literature

1. Naniy O.E. Fundamentals of technology of spectral multiplexing of transmission channels (WDM). Lightwave Russian edition, No. 2, 2004. 47-52 c.

2. Information from the site http://www.cisco.com.

3. Information from the site http://www.fti-optronic.com.

4. Slepov N.N. Modern technologies of digital fiber-optic communication networks. - M .: Radio and communications, 2000 .-- 468 p.

5. Bufetov I.A., Dianov E.M. Optical discharge in optical fibers. Lightwave Russian edition, No. 4, 2004. 50-51 p.

6. Nekuchaev A., Yusupaliev U. Symbolic data transmission over fiber optic links. Patent - Russian, what next? Electronics. The science. Technics. Business (NTB): Communications and Telecommunications, No. 6, 2001.

7. ITU-T Rec. G.692 - Optical interfaces for multi-channel systems with optical amplifiers (10.98).

8. Catalog of products manufactured by Russian Telephone Company, Novosibirsk, Russia, catalog version dated 08/05/2008 (available at http://www.rus-telcom.ru/).

9. Fiber-optic technology: history, achievements, prospects / Collection of articles edited by Dmitriev SA, Slepova NN - M.: Publishing House "Connect", 2000. - 376 p.

10. RF patent for the invention No. 2289207 "Interface for transmitting discrete information via an optical cable."

11. Information from the site http://www.b-tech.ru/index.asp?rid=1869

12. Pukhalsky G.I., Novoseltseva T.Ya. Design of discrete devices on integrated circuits: Reference. - M.: Radio and Communications, 1990. - 304 p.

13. Picosecond pulsed technique / V.N. Ilyushenko, B.I. Avdochenko, V.Yu. Baranov and others; under. ed. V.N. Ilyushenko. - M.: Energoatomizdat, 1993 .-- 368 p.

14. Small-sized pump generators of semiconductor lasers / V.N. Legky, I. D. Mitsenko, B. V. Galun. - Tomsk: Radio and communications. Tomsk Department, 1990 .-- 216 p.

15. Information from the site http://www.terraelectronica.ru/pdf/MAX/DS1020-15.pdf.

16. Information from the site http://www.niipp.ru/Russian/products/S_impulse.htm.

17. Information from the site /http://kazus.ru/lenta/view/0_7058_0.html.

18. Information from the site http://user.rol.ru/~optcom/.

19. Shilo V.L. Popular Digital Chips: A Guide. - M.: Radio and Communications, 1987 - 352 p.

20. R. Fridman “Fiber-optic communication systems”, Technosphere, Moscow, 2003, p. 280.

21. Information from the site http://www.dilas.ru/.

Claims (1)

A fiber optic information transmission system comprising sequentially mounted transmitting unit, fiber optic path, receiving unit, the transmitting unit containing an input N-bit data bus for connecting N information sources, N + 1 transmitting optoelectronic modules, N fiber-optic delay lines whose optical inputs are connected to the optical outputs of N transmitting optoelectronic modules, a spectrally selective optical combiner, the first input of which is connected to the output of the (N + 1) -th optoelectronic module, synchronization device, the receiving unit contains an optical splitter, the first receiving optoelectronic module receiving information data, the optical input of which is connected to the first output of the splitter, the second receiving optoelectronic module receiving synchronization signals, the optical input of which is connected to the second output of the splitter through fiber an optical delay line, a device for generating clock pulses, an output N bit data bus, characterized in that a powerful optical the first amplifier, sequentially installed chromatic dispersion compensator and a preliminary optical amplifier, the optical input of a powerful optical amplifier connected to the output of the transmitting unit, and the output to the input optical pole of the fiber optic path, the input optical pole of the chromatic dispersion compensator connected to the output optical pole of the fiber optical path, and the optical output of the pre-amplifier is connected to the optical input of the receiving unit, (N + 1) forms are introduced into the transmitting unit pulse generators, an optical combiner with a transmission matrix N × 1, the inputs of N pulse shapers connected to the lines of the input N-bit data bus, and the outputs to N transmitting optoelectronic modules, the input of the (N + 1) -th pulse shaper connected to the output of the synchronization device and the output to the input of the (N + 1) -th transmitting optoelectronic module, N fiber-optic delay lines are configured to delay time, N optical inputs of the optical combiner are connected to the optical outputs of N delay lines, and the optical output of the combiner is connected to the second input of a spectrally selective optical combiner having a 2 × 1 transmission matrix, two electronic amplifiers, N electronic keys, are introduced into the receiving unit, the input of the first electronic amplifier being connected to the output of the first receiving optoelectronic module, and the output being switched the inputs of N electronic keys, the input of the second electronic amplifier is connected to the output of the second receiving optoelectronic module, and the output to the input of the clock generation device and connected to the output the bottom line of synchronization, the N-outputs of the clock generator are connected to the control inputs of N electronic keys, and the outputs of the electronic keys are connected to the output N-bit data bus lines, the spectrally selective splitter installed at the input of the receiving unit has a 1 × 2 transmission matrix, for Possibilities for controlling the delay time All fiber-optic delay lines consist of sequentially installed lengths of optical cable of fixed length, two optical lenses, the distance between which can be changed by the regulation mechanism and the transducer of the mode field diameter.

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