RU2155449C1 - Digital optical signal transmission line - Google Patents

Abstract

FIELD: quantum radio engineering and optical communication, applicable in equipment of fiber-optic, laser space, atmospheric and other communication lines. SUBSTANCE: transmission line has an amplifier-modulator, laser, laser power stabilizer, two matching devices, optical signal transmitting medium, photodetector, preamplifier, automatic gain control, optimal filter, clock frequency recovery device. The concept of the claimed invention is in the fact that additionally cut in the known transmission line are two signal converters, N phase regenerators, (N-1) preamplifiers, amplifier - pumping generator, signal conditioning device, which allow separation of noise sources by phase regenerators, this results in reduction of probability of error in transmission of signal over the line, and, consequently, in increase of the energy potential and length of the transmission line. As compared with the immediate analogues, the transmission line has a higher energy potential by 3 to 8 dB, which makes it possible to increase the length of the connecting lines of local networks and the length of the regeneration section of main and intrazone communication networks. EFFECT: reduced cost of equipment of communication systems and networks. 3 dwg

Description

 The invention relates to the field of quantum radio engineering and optical communication and can be used in the equipment of fiber-optic and laser space communication lines.

 A known transmission line of a digital optical signal (Fig. 1), a prototype of the proposed technical solution, which contains an amplifier modulator 1, a laser generator 2, a device for stabilizing the power of the laser 3, matching devices 4 and 6, the transmission medium of the optical signal 5, photodetector 7, preliminary amplifier 8, amplifier 9, automatic gain control (AGC) 10, solver 11, clock recovery device 12 (Miki T. At al // Review ECL - 1978-76, N 5 / 6- P. 676-692) .

 A disadvantage of the known digital optical signal transmission line is its short length.

 The aim of the proposed technical solution is to increase the length of the transmission line of the digital optical signal.

 This goal is achieved by the fact that the known transmission line includes two signal converters, N shaping filters, N phase regenerators, (N-1) pre-amplifiers, a pump driver, a signal conditioning apparatus.

 A diagram of the proposed digital optical signal transmission line is shown in FIG. 2. The transmission line contains the following blocks: amplifier-modulator 1, laser generator 2, laser power stabilization device 3, first matching device 4, transmission medium of the optical signal 5, second matching device 6, photodetector 7, first pre-amplifier 8, amplifier 9, AGC device 10, clock frequency recovery device 12, first signal converter 13, first shaping filter 14, first phase regenerator 15, second signal converter 16, signal conditioning device 17, amplifier-shaped pump 18, Nth shaping filter 19, Nth phase regenerator 20, Nth preamplifier 21, and also (N-2) shaping filters identical to the first 14, (N-2) phase regenerators identical to the first 15, (N-2) preamplifiers identical to the first 8 in terms of design and structure (the numerical values of the parameters of their elements may vary and are selected from the condition of the minimum probability of transmission error).

 The principle of operation of the proposed digital optical signal transmission line is as follows.

An input digital signal in NRZ format is fed to the input of the first signal converter 13, in which it is converted into a signal of one of the following types:
a) a sinusoidal phase-modulated (0-π) signal, the carrier frequency ω _{n of} which is significantly and an integer number of times higher than the clock frequency (Fig. 3a);
b) a sequence of alternating pulses and pauses, the number and duration of which are equal and the duration is much less than the clock interval. When changing the transmitted character ("0" or "1"), the pulses and pauses are interchanged;
c) a bi-pulse signal (Fig. 3c), in which the transmission of the "1" symbol in the interval 0 - T corresponds to the transmission of the pulse in the interval 0 - 0.5T and the pause in the interval 0.5T - T, and the transmission of the symbol "0" in the interval T - 2T corresponds to the transmission of a pause in the interval T - 1.5T and a pulse in the interval 1.5T - 2T.

 The signal from the output of the first signal converter 13 is amplified by the amplifier-modulator 1 to the level necessary to modulate the laser generator 2, the optical power at the output of which is maintained at a predetermined level using the laser power stabilization device 3. The optical signal from the output of the laser generator 2 through the first matching device 4 enters the transmission medium of the optical signal 5, the output of which through the second matching device 6 is fed to the input of the photodetector 7. Next, the signal through the first forming filter 14, providing the maximum signal to noise ratio at its output, is fed to the input of the first phase regenerator 15.

 Since the sequence of alternating pulses and pauses, as well as the bi-pulse signal (Fig. 3b, c, solid line), up to high-order spectral components, correspond to a sinusoidal signal with on-off (0-π) phase modulation (Fig. 3b, c, dashed line) then, for the regeneration of such signals, the principle of regeneration of a phase-modulated signal can be used. To this end, a pump signal is supplied to the second input of the phase regenerator 15, the frequency of which is twice the carrier frequency of the equivalent phase-modulated signal, and the power is sufficient to change the parameter of the diode or transistor over a wide range. At the output of the phase regenerator 15, a sinusoidal signal is generated, the phase of which, up to the probability of a regeneration error, takes two values 0 or π depending on the transmitted symbol. Thus, the phase noise of the signal coming from the output of the photodetector 7 is suppressed. Amplitude noise is not suppressed, but it does not affect the transmission characteristics of the information contained in the phase of the signal.

 As a phase regenerator, a degenerate parametric amplifier can be used, which uses the nonlinear capacitance of locked semiconductor p-n junctions, which is tuned to a small gain, and therefore is absolutely stable and has high stability of its characteristics. Due to the small losses in the nonlinear capacitance, the level of additional noise generated by the phase regenerator is negligible. In addition to the parametric amplifier, a similar device operating on the nonlinear active conductivity of a diode or transistor can be used.

 The signal from the output of the first phase regenerator 15 is amplified by the first pre-amplifier 8 and fed to the input of the second shaping filter and then to the input of the second phase regenerator, designed to suppress noise, the sources of which are located in the first pre-amplifier 8, etc. Finally, the signal goes to the input of the N-th shaping filter, the N-th phase regenerator and the N-th pre-amplifier, from the output of which the signal goes to the input of the amplifier 9, which amplifies the signal to the level necessary for processing it by non-linear devices.

 Since the phase regeneration process is independent of the signal level, the signal can be regenerated in the first amplification stages at a low signal level. This allows you to separate the noise sources with regenerators, without allowing the addition of their capacities. Therefore, in contrast to the prototype, it is not the addition of noise powers, but the addition of the error probabilities of each regenerator, which leads to a significant decrease in the probability of transmission errors of the digital signal over the line.

From the output of amplifier 9, the signal is supplied to the inputs of the devices: signal generation 17, clock recovery 12 and AGC 10, as well as to the input of the pump driver 18. Amplitude noise is suppressed in the signal conditioning device 17 and the signal is restored to the probability of a regeneration error, formed at the output of the first signal converter 13, which is fed to the input of the second signal converter 16, where the original shape and amplitude of the signal are restored, as well as its temporal location at the clock int the ervale. In a clock recovery device, a clock signal is extracted from a digital signal supplied to its input. The clock signal is fed to the second input of the pump driver 18, in which, depending on the type of signal at the output of the signal converter 13, the clock frequency of a sequence of pulses and pauses (Fig. 3b) or a bi-pulse signal (Fig. 3c) or carrier frequency is extracted ω _{n a} sinusoidal phase-modulated signal and the formation of pump signals that are fed to the second inputs of the phase regenerators and to the second input of the signal conditioning device 17. Control signals are generated in the AGC device, arriving at the second inputs of the amplifier 9 and photodetector 7 to automatically change the gain of the amplifier 9 and the avalanche gain of the photodetector 7. When using pin-photodetectors in the photodetector, the AGC signal is not applied to the photodetector.

 The number of shaping filters, phase regenerators, and pre-amplifiers (number N) depends on the amplification and noise characteristics of the pre-amplifiers, which are selected from the condition of minimum probability of signal transmission error on the line. The signal at the output of the last pre-amplifier should be large enough so that the signal-to-noise ratio at the output of amplifier 9 significantly exceeds the value corresponding to a given error probability.

 The phase regenerator contains a notch filter of the pump frequency, which prevents the pump signal from entering the pre-amplifier, which can significantly change the amplification and noise characteristics of this amplifier.

 The first shaping filter and the first phase regenerator are included at the junction of the photodiode and the first transistor of the amplifier. Therefore, it is advisable to construct blocks 7, 14, 15 and 8 in the form of an optoelectronic integrated circuit in order to reduce dimensions, spurious parameters, increase operational reliability and resistance to mechanical stress.

 The positive effect of using the proposed digital optical signal transmission line is to increase its length compared to the prototype by an amount determined by the ratio Δl = ΔE / α, where ΔE is the increase in energy potential (dB), α is the attenuation of 1 km of the optical signal transmission medium (dB / km). The increase in energy potential depending on the parameters of the transmission line is 3-8 dB. (See Attachment).

The economic effect of using the proposed digital optical signal transmission line can be estimated by the example of the construction of a transport communication network, in which the proposed transmission line is used as a communication trunk (SL). Suppose that the network uses three types of optical cables (OK) with different attenuations, and therefore different maximum SL lengths - l ₁ , l ₂ , l ₃ - and accordingly different prices of 1 km OK - C ₁ , C ₂ , C ₃ . In this case, the relative reduction in the cost of OK ΔC / C when using the proposed transmission line compared with the prototype due to the possibility of using more relatively cheap OK is determined by
ΔC / C = (ΔE / E′C _ok lΔl) (l $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ ΔC ₁₂ + l $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ ΔC ₂₃ ),
where ΔC ₁₂ = C ₂ -C ₁ ; ΔC ₂₃ = C ₃ -C ₂ ;
E 'is the average attenuation in OK SL;
C _ok - average price of 1 km OK;
l is the average length of the trunk on the network;
Δl - the spread of the lengths of the trunk on the network.

Assuming ΔE = 3-8 dB; E '= 30 dB; C _ok = C ₂ ; ΔC ₁₂ = ΔC ₂₃ = ΔC _approx ; Δl = l ₃ - 0.5l ₁ ; l = 0.5 (l ₃ + 0.5l ₁ ); l ₂ / l ₁ = l ₃ / l ₂ = 1.5, we obtain
ΔC / C = (0.15-0.35) ΔC _ok / C _ok
If the prices for OK are C ₁ = 2000 cu; C ₂ = 2500 cu; C ₃ = 3000 oz e. for 1 km, then C _ok = 2500 cu, and ΔC _ok = 500 cu In this case, ΔC / C = 0.03 - 0.07. In absolute terms, the economic effect of using the proposed transmission line in the considered example at an annual cost of OK of 100 million cu makes 3 - 7 million cu

где A₁ = 2q₀Δf(I_c+I_T)I $\genfrac{}{}{0ex}{}{\text{-2}}{\text{c}}$ ; A₂ = 2q₀ΔfI|y₁|²I $\genfrac{}{}{0ex}{}{\text{-2}}{\text{c}}$ g^-2;
β = g²|y_выx+y_вx|^-2; I_c = q₀η(hν)^-1P_c;
P_е - мощность оптического сигнала на входе фотодетектора;
I_т - темновой ток фотодиода;
Δf - полоса пропускания тракта усиления;
I - расчетный ток транзистора, определяющий его шумовые характеристики (в полевых транзисторах приблизительно равен току стока);
g - крутизна характеристики передачи транзистора;
y_вх, y_вых - входная и выходная проводимости транзистора;
y₁ - проводимость цепи на стыке фотодиода и первого транзистора;
M - коэффициент лавинного усиления фотодиода;
x - шумовой параметр лавинного фотодиода;
η - - квантовая эффективность фотодиода;
hν - энергия фотона;
q₀ - заряд электрона.APPENDIX
The signal-to-noise ratio at the input of the prototype decider is determined by the ratio

where A ₁ = 2q ₀ Δf (I _c + I _T ) I $\genfrac{}{}{0ex}{}{\text{-2}}{\text{c}}$ ; A ₂ = 2q ₀ ΔfI | y ₁ | ² I $\genfrac{}{}{0ex}{}{\text{-2}}{\text{c}}$ g ^-2 ;
β = g ² | y _vx + y _vx | ^-2 ; I _c = q ₀ η (hν) ^-1 P _c ;
P _e is the power of the optical signal at the input of the photodetector;
I _t is the dark current of the photodiode;
Δf is the bandwidth of the amplification path;
I is the calculated current of the transistor, which determines its noise characteristics (in field-effect transistors, it is approximately equal to the drain current);
g is the transconductance slope of the transistor;
y _in , y _out - input and output conductivity of the transistor;
y ₁ is the conductivity of the circuit at the junction of the photodiode and the first transistor;
M is the avalanche gain coefficient of the photodiode;
x is the noise parameter of the avalanche photodiode;
η - is the quantum efficiency of the photodiode;
hν is the photon energy;
q ₀ is the electron charge.

где S $\genfrac{}{}{0ex}{}{\text{-1}}{\text{0}}$ = A₁M^x+A₂M^-2(1-β^-1)^-1.
Вероятность ошибки передачи сигнала в предлагаемой линии передачи

где S₁ ^-1 = A₁M^x; S₂ ^-1 = A₂M^-2; S $\genfrac{}{}{0ex}{}{\text{-1}}{\text{3}}$ = A₂M^-2β^-1; S $\genfrac{}{}{0ex}{}{\text{-1}}{\text{4}}$ = A₂M^-2β^-2,...
Поскольку K₂ представляет собой малую величину, 10^-9-10^-11, то приведенный выше ряд быстро сходится уже при β ≥ 1,1, что позволяет выражение для K₂ ограничить двумя первыми слагаемыми. Для подавления влияния шумов всех транзисторов, кроме первого, в прототипе необходимо выбрать β ≥ 10, а в предлагаемой линии передачи β ≥ 1,1. Определяя M из условия минимума K₁ и K₂ и пренебрегая малыми величинами, получим выражение для увеличения энергетического потенциала в предлагаемой линии передачи по сравнению с прототипом при заданной вероятности ошибки передачи

где

β₁, β₂ - значения β, рассчитанные для прототипа и предлагаемой линии передачи соответственно;
n - показатель степени функции, аппроксимирующей вольт-амперную характеристику транзистора I=auⁿ, 1 < n < 2.The probability of signal transmission errors in the prototype

where s $\genfrac{}{}{0ex}{}{\text{-1}}{\text{0}}$ = A ₁ M ^x + A ₂ M ^-2 (1-β ^-1 ) ^-1 .
The probability of signal transmission errors in the proposed transmission line

where S ₁ ^-1 = A ₁ M ^x ; S ₂ ^-1 = A ₂ M ^-2 ; S $\genfrac{}{}{0ex}{}{\text{-1}}{\text{3}}$ = A ₂ M ^-2 β ^-1 ; S $\genfrac{}{}{0ex}{}{\text{-1}}{\text{4}}$ = A ₂ M ^-2 β ^-2 , ...
Since K ₂ is a small value, 10 ^-9 -10 ^-11 , the above series quickly converges already at β ≥ 1.1, which allows the expression for K ₂ to be limited to the first two terms. To suppress the influence of noise of all transistors, except the first, in the prototype it is necessary to choose β ≥ 10, and in the proposed transmission line β ≥ 1.1. Determining M from the minimum conditions K ₁ and K ₂ and neglecting small quantities, we obtain an expression for increasing the energy potential in the proposed transmission line compared to the prototype for a given probability of transmission error

Where

β ₁ , β ₂ - β values calculated for the prototype and the proposed transmission line, respectively;
n is the exponent of the function approximating the current-voltage characteristic of the transistor I = au ⁿ , 1 <n <2.

Э = (3,3 - 7,8) дБ, а при использовании фотодиодов с x = 2,4 ΔЭ достигает 16 дБ.Existing avalanche photodiodes have x = 0.7 - 1, and for long-wavelength ranges, x = 2.4 is possible. Therefore, for x = 0.7 -1, n = 1.25 - 1.5; β ₁ = 10; β ₂ = 1.1 increase in energy potential

E = (3.3 - 7.8) dB, and when using photodiodes with x = 2.4, ΔE reaches 16 dB.

Claims (1)

 A digital optical signal transmission line comprising a modulator amplifier, a laser generator, a laser power stabilization device, an optical signal transmission medium, first and second matching devices, a photo detector, a preliminary amplifier, an amplifier, an automatic gain control device, a clock recovery device, and an amplifier output -modulator is connected to the first input of the laser generator, the first output of which is connected to the input of the first matching device, the output of which is connected is connected to the input of the optical signal transmission medium, the output of which is connected to the input of the second matching device, the output of which is connected to the first input of the photodetector, the second output of the laser generator is connected to the input of the laser power stabilization device, the first output of which is connected to the first input of the amplifier-modulator, and the second the output is connected to the second input of the laser generator, the output of the amplifier is connected to the input of the clock recovery device and the input of the automatic gain control device, the output which is connected to the first input of the amplifier and the second input of the photodetector, characterized in that it includes the first and second signal converters, N shaping filters, N phase regenerators, (N-1) pre-amplifiers, a pump driver, a signal conditioning apparatus, the input of the transmission line is the input of the first signal converter, the output of which is connected to the second input of the amplifier-modulator, the output of the photodetector is connected to the input of the first shaping filter, the output of each of N shaping filters connected to the first input of the corresponding phase regenerator, the output of which is connected to the input of the corresponding pre-amplifier, the output of the N-th pre-amplifier is connected to the second input of the amplifier, the output of which is connected to the first input of the pump driver and the first input of the signal conditioning device, the output of which is connected with the input of the second signal converter, the output of which is the output of the transmission line, the output of the clock recovery device is connected to the second input house-shaper amplifier pump, the first and second outputs of which are connected respectively to the second inputs of each of the N phase regenerator and a second input of the signal device.

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