RU2339929C1 - Optical reflectometer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: reflectometer consists of a pulse former, one of the inputs of which is connected to the output of a microcontroller, and the output of which is connected to a source of optical radiation, Y-shaped optical splitter, the input/output of which is optically connected to the socket of the output optical connector of the reflectometer, and the output of which is optically connected a photodetector, the output of which is connected to the input of an analogue commutator, the control input of which is connected to one of the outputs of the microcontroller, and the output of which is connected to the input of a comparator and the input of a pulse stretcher, the input of which is connected to one of the outputs of the microcontroller, and the output of which is connected to the analogue input of an analogue-to-digital converter, the digital outputs of which are connected to the inputs of the microcontroller. A piece of optical fibre with given length is inserted into the positive feedback circuit, optically connected to the output of the source of optical radiation and the second input of the Y-shaped optical splitter. The output of the comparator is connected to one of the inputs of the microcontroller and to the second input of the pulse former.

EFFECT: increased accuracy of measuring the distance to the position of local irregularities in a fibre-optic tract.

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Description

The invention relates to the field of measuring technology, communication technology and optoelectronics and can be used to diagnose fiber optic paths in the production of optical fibers and fiber optic cables, when laying and operating fiber-optic communication lines. It is most advisable to use a device for monitoring fiber-optic paths of onboard local fiber-optic communication networks and information transfer. Such networks are characterized by a short length of connecting lines (up to 1 km) and a large number of crossings through various compartments. At the transition points, local optical inhomogeneities can occur due to the clamping or bending of the optical fiber. Finding places of heterogeneity must be carried out with extreme accuracy.

A known device for the diagnosis of fiber optic paths [1]. The device consists of two microcontrollers, a pulse shaper, a semiconductor radiation source, an optical coupler, 2 optical connectors, 2 photodetectors, a switch, a programmable attenuator, a comparator, a pulse expander, an analog-to-digital converter, a control panel, a digital indicator and a reprogrammable constant constant storage device. The device allows you to measure the reflection loss from the inhomogeneities of the fiber optic path (reflection coefficients) and the distance to the places of inhomogeneities.

The operation of the device lies in the fact that a short optical pulse is applied to the input of the controlled fiber optic path and the parameters of the pulse signals converted by a photodetector installed at the output of the coupler are measured so that this photodetector receives an optical backscattering signal. The optical pulses reflected from the inhomogeneities of the fiber optic path are converted by the photodetector into electrical pulses, are extracted at a predetermined level by the comparator and fed to one of the inputs of the high-speed microcontroller. The microcontroller selects a given pulse (in the order of its arrival), sets the time delay during which the entire train of pulses reflected from inhomogeneities ends, and with the help of a pulse shaper and a semiconductor optical radiation source forms a new optical pulse probing the fiber optic path. The distance to the place of the analyzed heterogeneity is determined by the frequency of the self-oscillating process that occurs due to repetitions of the process of formation of a new probe pulse upon receipt of a given reflected pulse. By the amplitude of the reflected pulse, the reflection coefficient (reflection loss) from the investigated inhomogeneity is measured.

The disadvantages of the device are:

1. Low resolution and accuracy of measuring the distance to the location of the heterogeneity. The measurement accuracy is limited by the time it takes to perform one operation of the microcontroller that registers the signal at the output of the comparator, for a microcontroller operating at a clock frequency of 150 MHz, the error in measuring distance is about 4 meters.

2. The device does not provide measurement of the attenuation of the optical signal along the fiber optic path.

A device is known, which is an optical reflectometer [2, p.27]. The device contains an optical module and a base module. The optical module consists of a pulse generator, a laser diode, an optical coupler, a photodetector, an amplifier, an optical connector, a photocurrent amplifier, and an analog-to-digital converter. The base module consists of a microprocessor and a display. The device generates an optical probe pulse directed to the fiber optic path and analyzes the backscattering radiation at the output of the coupler.

The device allows you to measure the attenuation of the optical signal along the fiber optic path and the distance to the places of heterogeneity.

The disadvantages of the device are the low accuracy of measuring distances with increasing duration of the probe optical pulses and the low dynamic range of measurements with decreasing their duration.

With a decrease in the duration of the probe pulse, the accuracy of distance measurement increases, but the power of the reverse Rayleigh scattering decreases.

The Rayleigh backscattering coefficient q in dB is determined by the formula [2, p. 41]

where t _and is the duration of the pulse probing the fiber in ns.

At a pulse duration of t _and = 2 ns (resolution over a length of 0.5 m), the coefficient of reverse Rayleigh scattering will be q = -77 dB, at t _and = 10 ns (resolution over a length of 2 m), q = -70 dB.

A device for an optical reflectometer is known which is closest in its technical essence to the invention [3]. The device allows you to measure the reflected optical power, reflection loss (reflection coefficients) and the distance to the location of the local heterogeneities of the fiber optic path.

The device includes a pulse shaper, a semiconductor radiation source, a Y-shaped optical splitter, two optical connectors, two photodetectors, an analog switch, a comparator, a programmable attenuator, two microcontrollers, a programmable frequency counter-divider, two digital keys, an analog key, a pulse expander, electronic delay line, analog-to-digital converter (ADC), indicator, control panel and reprogrammable read-only memory.

The device determines the distance to the place of local heterogeneities by measuring the frequency of self-oscillations. Moreover, the frequency of self-oscillations is determined by the delay of the optical signal in the nodes of the device and the delay associated with the propagation of the optical signal from the input end of the optical fiber to the location of the local inhomogeneity and vice versa.

The disadvantages of the device are:

1. The device does not provide a measurement of the attenuation of the optical signal along the fiber optic path.

2. The low accuracy of measuring the distance to the location of local heterogeneity associated with the instability of the frequency of self-oscillations. The frequency instability is due to the instability of the signal delay in the nodes of the device.

The signal passes through the following nodes included in the oscillatory circuit (feedback circuit):

- optical connector;

- Y-shaped optical splitter;

- photodetector;

- switch;

- comparator;

- counter divider;

- delay line (the signal in the delay line is delayed n times depending on the length of the fiber optic path);

- electronic key;

- pulse shaper;

- radiation source.

Depending on the length of the path, the electrical pulse from the output of the counter-divider frequency can be delayed in the delay line n times. This is necessary so that the new probe pulse does not overlap the pulses reflected from the path inhomogeneities initiated by the previous probe pulse. In connection with the remark made, it is obvious that the instability of the signal delay in this case will also increase n times.

To delay electrical pulses, delay lines of the following types are used [4]:

- distributed (coaxial or strip);

- with lumped parameters (built on L, C chains);

- ultrasonic (waveguide wire, waveguide tape, on volumetric acoustic waves, on surface acoustic waves);

- electronic digital (silicon or hybrid).

Strip delay lines with linear inductance L ₁ and linear capacitance C ₁ are characterized by high stability and broadband. The wave impedance of such a line W is independent of frequency and is determined by the formula [5]

where L ₀ = l·L ₁ , is the total inductance;

С ₀ = l · С ₁ - total capacity;

l is the length of the line.

The signal delay T is determined by the formula

An indispensable condition for the operation of such a delay line is the coordination of its resistances at the input and output. With pulsed signals at the input of the delay line, the matching problem becomes difficult due to the presence of stray capacitances at the input and output ends of the line. Mismatch of the line leads to spurious re-reflections of the signal from the ends of the line, which are unacceptable for the correct operation of the device.

Another disadvantage of such a delay line is the difficulty in calculating its parameters, since the geometric dimensions of the line depend on the transmitted wavelength of the electric signal [6]. In the case of pulsed signals, we are dealing not with a single radiation wavelength, but with a whole spectrum of wavelengths.

Based on the foregoing, we can conclude that it is impossible to use such delay lines in the device in question.

When using a coaxial delay line, the question also arises of matching the wave impedance of a coaxial cable in a wide band of transmitted frequencies. In addition, the attenuation of a signal in a coaxial cable depends on the signal frequency and has a value of about 0.1 dB / m for a frequency of 100 MHz (corresponding to a pulse front duration of the order of 10 ns) [6]. With a fiber optic path length of 1 km, the length of the coaxial delay line should be at least 3 km (due to the double passage of the line with an optical signal and the difference in the speed of light propagation in the optical fiber and the electromagnetic wave in the coaxial cable). With a length of 3 km, the signal attenuation in such a delay line will be 300 dB ( ^10-15 times). Such a delay line in the device cannot be used.

Delay lines with lumped parameters (on L, C or R, C chains) cannot be used in the device in question due to the following disadvantages:

- L, C chains distort the shape of the pulse signals;

- R, C chains lead to fast attenuation of the signal and also distort the shape of the pulse signals (tighten the front).

Ultrasonic delay lines cannot be used in the device in question because of their insufficient broadband. A bandwidth of at least 300 MHz is required; a bandwidth of not more than 10 MHz is provided [7].

Electronic digital delay lines can be performed on discrete elements (standby multivibrators), integrated elements (hybrid and silicon). The most stable parameters of the above have silicon integrated delay lines. The greatest success in their production was achieved by Dallas Semiconductor. The company produces integrated silicon delay lines of the DS1000 - DS1045 type with a delay time of 4 to 500 ns. The coefficient of instability of the delay time in the entire temperature range and the range of supply voltages is 1% [8].

Let the device in question control the inhomogeneities in the fiber optic path with a length l = 1 km. The signal delay time must be at least

where n is the refractive index of fused silica (n≈1.5);

s is the speed of light in vacuum (s = 3 · 10 ⁸ m / s).

The component of the error in measuring the distance to the location of the inhomogeneity Δl associated with the instability of the delay Δτ can be found by the formula

or Δl = cΔτ or

where t _p is the propagation time of the signal in the fiber optic path;

δl and δτ are the relative reduced values of the errors.

Since the instability of silicon delays (jitter) is 1%, when they are used in the device for monitoring a fiber optic path 1 km long, the maximum error in measuring the distance to the location of the inhomogeneity will be 30 m, unless special statistical processing methods using probabilistic methods and confidence intervals.

The proposed device solves the problem of providing the possibility of measuring the attenuation of the optical signal along the fiber optic path and the task of increasing the accuracy of measuring the distance to the location of local inhomogeneities in the fiber optic path.

The essence of the invention lies in the fact that in an optical reflectometer containing a pulse shaper, one of the inputs of which is connected to the output of the microcontroller, and the output is connected to a semiconductor source of optical radiation, a Y-shaped optical splitter, the input / output of which is optically connected to the outlet of the output optical connector OTDR, and the output is optically connected to the optical input of the photodetector, the output of which is connected to the input of an analog switch, the control input of which is connected to one of the outputs m of the microcontroller, and the output is connected to the input of the comparator and the input of the pulse expander, the input of which is connected to one of the outputs of the microcontroller, and the output is connected to the analog input of the analog-to-digital converter, the digital outputs of which are connected to the inputs of the microcontroller, which is connected to a personal computer, an optical segment is introduced fiber of a given length, optically coupled to the output of a semiconductor optical radiation source and a second input of a Y-shaped optical splitter, and the output of the comparator is connected to ne of the inputs of the microcontroller and to a second input of the pulse shaper.

In the drawings (see figure 1) shows a structural diagram of the proposed reflectometer.

The reflectometer consists of:

- microcontroller 1;

- pulse shaper 2;

- semiconductor optical radiation source 3;

- a piece of optical fiber of a given length 4;

- comparator 5;

- analog switch 6;

- photodetector 7;

- Y-shaped optical splitter 8;

- sockets of the output optical connector 9;

- pulse expander 10;

- analog-to-digital Converter 11;

- personal computer 12.

OTDR operates as follows.

When the OTDR power is turned on, execution of the program recorded in the resident program memory of the microcontroller 1 begins. At one of the outputs, the microcontroller 1 generates a voltage pulse (plot 1, figure 2), which is fed to the first input of the pulse shaper 2.

Shaper 2 on the front of the signal at its input generates a pulse of the pump current of the semiconductor radiation source 3 with a given duration (plot 2, figure 2).

The semiconductor optical radiation source 3 generates an optical pulse. The pulse is directed into the segment of the optical fiber 4, is delayed in it for a time τ ₀ , depending on its length L

where n is the refractive index of the fiber core;

c is the speed of light in vacuum.

Further, having passed the optical Y-shaped splitter 8 and the socket of the optical connector 9, the optical pulse is directed to the input of the measured fiber optic path.

Backscattering radiation, consisting of Rayleigh scattering and Fresnel reflections from local inhomogeneities, is directed by an optical Y-shaped splitter 8 to the optical input of the photodetector 7.

It should be noted that Fresnel reflections from junctions or large local inhomogeneities (clamps, kinks, cracks in the optical fiber) are significantly higher in power level compared to the Rayleigh scattering signal.

For example, the coefficient of reverse Rayleigh scattering at a pulse duration of t _and = 2 ns (resolution over a length of 0.5 m) is -77 dB, with a pulse duration of t _and = 10 ns (resolution over a length of 2 m) is -70 dB (see formula (1)).

The Fresnel reflection coefficient for optical connectors is from -30 to -50 dB [2, p. 41].

The output voltage of the photodetector 7 is fed to the input of the analog switch 6 (plot 3, figure 2). In the initial state, the switch 6 is in the off state and does not pass the signal. The microcontroller 1 at three time intervals τ ₁ , τ ₂ , τ ₃ generates three pulses in succession: a reset pulse of the pulse expander 10 (plot 4, figure 2), an analog switch on pulse 6 (plot 5, figure 2), an ADC conversion trigger 11 (plot 8, figure 2). The time of generation of the switching pulse of the analog switch τ ₂ and the duration of this pulse Δτ determine the location of the controlled area of the fiber optic path and its size

where l _i is the distance from the beginning of the fiber optic path to the beginning of the controlled area;

Δl is the size of the controlled area.

The values of τ ₁ , τ ₂ , τ ₃ , Δτ are set programmatically.

The reset pulse of the pulse expander prepares the pulse expander for the arrival of the next measured pulse. Typically, pulse expanders are constructed according to a diode-capacitor storage circuit [10]. When a reset pulse is applied, a key circuit, made on field-effect transistors, discharges the storage capacitor.

The switching pulse of the analog switch controls the transmission channel of the switch, which behaves like a resistor, the resistance of which can change many times when the control voltage changes. When a control pulse is applied, the channel resistance tends to zero. The plot of the voltage pulse at the output of the analog switch 6 is presented on the plot 6, see figure 2. This pulse is converted by a pulse expander 10 into a quasi-constant level, which is recorded by the ADC 11. The value of the pulse amplitude is digitally transmitted to the microcontroller. A pulse expander is necessary to simplify the design of the OTDR, since its use allows you to significantly reduce the cost of the device due to the use of a low-frequency ADC and a relatively low-frequency microcontroller.

After the backscattering signal ends (the end time of this signal is determined by the length of the fiber optic path), the microcontroller 1 generates a new pulse arriving at the first input of the pulse former 2. The measurement process is repeated, while the ADC digitally integrates (accumulates) the signal from the selected fiber optical path.

By programmatically shifting the opening moment of the analog switch, the OTDR examines the entire fiber optic path according to the described algorithm. According to the data obtained, a personal computer 12, connected to the microcontroller 1, builds a reflectogram of the path (the dependence of the signal level on distance). The slope of the reflectogram measures the attenuation of the signal along the path.

If there is a local heterogeneity in the studied area of the tract (plots 1, 2, 3, 4 in Fig. 3), it can be an optical connector or a crack in the optical fiber, then the backscattering signal will increase sharply due to Fresnel reflection. The signal will exceed the trip level of the comparator and a voltage pulse will appear at its output. This pulse is simultaneously fed to one of the inputs of the microcontroller 1 and to the second input of the pulse shaper 2 (diagrams 1 and 5, figure 3).

Entering the input of the shaper 2, the pulse excites the next probing optical pulse.

So that the train of backscattering signals reflected from the previous probe pulse does not overlap with the new signals, it is necessary that the condition

;where τ ₀ is the delay of the optical signal in the length of the optical fiber 4

;

τ _here is the signal transit time along the fiber optic path in one direction.

Coming to the input of the microcontroller, the pulse from the output of the comparator causes an external interruption of the main program. The microcontroller proceeds to execute the interrupt processing routine. The routine performs the following tasks:

- prohibits new interrupts.

- supports auto-oscillation process.

Note: to maintain self-oscillations, the microcontroller opens the analog switch after a time interval τ ₄ (see diagram 3 in Fig. 3) from the moment the comparator output signal arrives at the time Δτ and passes the pulse converted by the photodetector from the signal reflected from the investigated inhomogeneity that arose from the probe optical pulse initiated by the output pulse of the comparator. The pulse from the output of the analog switch is fed to the input of the comparator, initiating the next probing pulse. Self-oscillations with a period T _{i are} excited under the control of a microcontroller subroutine.

- Measures the period of self-oscillations - T _i .

- Transmits information about the period of self-oscillations to a personal computer.

- After measuring the period of auto-oscillations, it stops auto-oscillations (does not open the analog switch through τ ₄ ) and exits to the main program.

The main program generates a pulse at the first input of the pulse shaper, thereby exciting a probing optical signal, selects the next controlled area of the fiber optic path, changing the opening moment of the analog switch τ ₄ by the time Δτ, and accumulates the signal scattered from the selected region of the fiber optic path . The process of monitoring sections of the fiber optic path continues according to the algorithm described above.

All information about the fiber optic path is transmitted to a personal computer. The computer program calculates the distances to the locations of the detected inhomogeneities according to the period of self-oscillations and builds a trace trace. The steepness of the traces of the trace can be used to determine the attenuation of the optical signal in these areas.

It should be noted that, since there is no need to determine the distances to the locations of local inhomogeneities from the trace, a relatively long pulse of optical radiation can be used as a probe. In this case, the dynamic range of measurements sharply increases (according to the logarithmic law in accordance with formula 1).

Let us evaluate the characteristics of the proposed reflectometer.

When the i-th local heterogeneity is detected, self-oscillations are excited. The self-oscillation period T _i consists of the following components

;where τ ₀ is the delay of the optical signal in the length of the optical fiber 4

;

t _SL is the delay of the optical signal in the connecting lines (in the segments of the optical fiber between the splitter and the output optical connector, between the splitter and the photodetector);

τ _i is the delay of the optical signal during the propagation time from the beginning of the fiber optic path to the i-th local inhomogeneity and vice versa;

t _f - signal delay in the photodetector;

t _com - signal delay in the analog switch;

t _to - signal delay in the comparator;

t _fi - signal delay in the pulse shaper;

_uu t - signal delay in a semiconductor source of optical radiation.

The distance from the beginning of the fiber optic clock to the studied i-th local inhomogeneity can be found by the formula

where c is the speed of light in vacuum;

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

Taking into account formulas (11) and (12), the distance to the location of the i-th local heterogeneity can be found by the formula

Let us evaluate the accuracy of measuring the distance to the location of the heterogeneity. The accuracy of measuring the distance to the location of optical inhomogeneities will be determined by the stability of the refractive index along the length of the optical fiber, the error in measuring the period of self-oscillations, and the stability of signal delays at the nodes of the reflectometer. Taking into account possible parameter errors, formula (13) can be represented as follows

можно с достаточной степенью точности (менее 0,05%) заменить на следующее

[12]. В связи со сделанным замечанием и пренебрегая величинами второго порядка малости, формулу (14) можно представить в следующем видеDue to the fact that the instability of the group refractive index along the length of the optical fiber, as a rule, does not exceed 0.36% [11], the expression

with a sufficient degree of accuracy (less than 0.05%) can be replaced by the following

[12]. In connection with the remark made and neglecting the values of the second order of smallness, formula (14) can be represented in the following form

where δl _i is the relative error of measuring the distance to the location of the i-th heterogeneity;

δn is the relative value of the instability of the group refractive index along the length of the optical fiber (it does not depend on the device, it is a parameter of the control object).

Given that there is no correlation between the parameters, formula (15) can be rewritten

The first part of the formula depends on the characteristics of the reflectometer nodes, the second part reflects the instability of the group refractive index along the optical fiber of the controlled fiber-optic path (object of control).

We estimate the parameters included in formula (16) for a specific example.

Let the length of the measured fiber optic path be 1 km, the heterogeneity is located at a distance of 500 m from the beginning of the path, then the period of self-oscillations will be equal to

The error in measuring the period of self-oscillations will be found based on the stability value of the quartz resonator of the clock generator of the microcontroller, equal to 10 ^-6

ΔT _i = 15 · 10 ^-6 = 0.015 ns.

Note: the stability of a quartz resonator without the use of temperature control is about 10 ^-6 [13, p. 292], when using a thermostat, the stability is 10 ^-8 .

The refractive index of the core of the optical fiber depends on temperature and deformation in accordance with the formula [14, p. 44]:

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

Δn is the change in the refractive index;

- частная производная по температуре, характеризующая изменение плотности кварцевого стекла;

- the partial derivative with respect to temperature, characterizing the change in the density of quartz glass;

δn is the change in the refractive index due to photoelasticity.

The first term of formula (18) takes into account a change in the density of glass, the second term takes into account the effect of photoelasticity due to fiber deformation.

Let us consider in more detail the first term of formula (18), which takes into account the change in the density of quartz glass depending on temperature. Assuming that there are no deformations, we rewrite (18) as follows

where Δn is the change in the refractive index of the core of the optical fiber due to temperature changes;

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

ΔT is the change in temperature.

The minus sign indicates that with increasing temperature, the density of fused silica decreases [15].

Let the temperature range of the OTDR operation be from -20 to + 70 ° С, then

Then

On the other hand, with increasing ambient temperature, the length of the optical fiber segment increases due to thermal expansion. The coefficient of thermal expansion for fused silica is 0.4 · 10 ^-6 ° C ^-1 [16, p. 110]. When the temperature changes by 90 ° C, the signal delay in the optical fiber segment 2 km long will increase by Δτ ₀ = 0.36 ns.

Thus, the total delay in a 2-km-long optical fiber segment, when the ambient temperature changes by 90 ° С, will change by Δτ ₀ = -0.25 ns.

The value of Δt _SL can be neglected, since the length of the optical connecting lines is less than 0.01% of the length L of the length of the optical fiber.

The joint instability of the delays of the photodetector (photodiode with a transimpedance amplifier) Δt _f and the semiconductor source of optical radiation Δt _u is no more than 1 ns [17].

The value of Δt _com can be neglected, since the switch in the open state represents a short jumper with an ohmic resistance of about 10 Ohms (the inductance of the jumper can be ignored).

When using a comparator type AF011 B [18], the instability of the signal delay t _k will be no more than 0.05 ns.

The pulse shaper along the signal front can be represented in the form of a differentiating R, C chain and a comparator. If you use highly stable resistors and capacitors, then the main instability of the signal delay will be the comparator. The comparator delay instability was analyzed above. It can be assumed that t _phi = 0.05 ns.

Substituting the parameter values in the first part of formula 16, we find the error in measuring the distance to the place of optical inhomogeneity due to the nodes of the reflectometer

Note: as shown above, the error in measuring the distance to the location of the inhomogeneity due to fluctuations in the group refractive index of the material of the core of the optical fiber is 3.6 · 10 ^-3 .

The error in measuring the location of the inhomogeneity due to the nodes of the reflectometer in the example under consideration will be 0.1 m. The best foreign reflectometers provide a measurement accuracy of not more than 1.0 m [19, p. 53].

In this case, the duration of the probe pulse can be several microseconds, since the measurement error does not depend on the pulse duration. By increasing the duration of the probe pulses, the dynamic range of measurements can be increased.

Thus, the objective of the invention is achieved - the accuracy of measuring the distance to the locations of inhomogeneities is increased, it is possible to measure changes in the attenuation of optical signals along the fiber optic paths with an increased dynamic range of measurements compared to analogs.

Information sources

1. Yakovlev M.Ya., Tsukanov V.N. Diagnostic device for fiber-otic tracts. Patent for the invention of Russia No. 2180436 dated 10.31.2000, Bull. No 7 on March 10, 2002

2. Listvin A.V., Listvin V.N. Reflectometry of optical fibers. - M.: LESARart, 2005, 208 p.

3. Yakovlev M.Ya., Tsukanov V.N. Optical time domain reflectometer. Patent for the invention of Russia No. 2214583 dated April 12, 2002, Bull. No. 29 dated 10/20/2003

4. Electronics: Encyclopedic Dictionary / Ch. ed. V.G. Kolesnikov. - M .: Owls. Encyclopedia, 1991 .-- 668 p.

5. Yitzhoki Ya.S., Ovchinnikov N.I. Pulse digital devices. M., "Sov. Radio", 1973.

6. Izyumova T.I., Sviridov V.T. Waveguides, coaxial and strip lines. M., "Energy", 1975.

7. Boritko S.V. Development of low-frequency broadband delay lines for surface acoustic waves. "Electromagnetic waves and electronic systems", 2004, v. 8, No. 5.

8. Materials of the site http://www.itis.spb.ru/DALLAS/delay.htm.

9. Skating rink VB, Goncharov A.V. Optical parameters of detachable optical connectors. Photon Express 21, December 2000

10. Magrachev Z.V. Single-ended analog transmitters. M., "Energy", 1974.

11. International Telecommunication Optical Fiber Union Standard, G.652.

12. Bronstein I.N., Semendyaev K.A. Math reference. M., "Science", 1964.

13. Measurements in electronics: Reference book / V.A. Kuznetsov et al .; Ed. V.A. Kuznetsova. - M .: Energoatomizdat, 1987.

14. Fiber Optic Sensors / T. Okosi et al., Ed. T. Okosi: Per. with japan. - L .: Energoatomizdat, 1990.

15. Guloyan Yu.A. Physico-chemical properties and characteristics of glasses. Windows, doors, stained-glass windows, No. 4, 2005.

16. Enokhovich A.S. Handbook of Physics and Technology: Textbook. The manual for students. - M .: Education, 1989.

17. Information of Avangard-opton CJSC (St. Petersburg, Kondratyevsky pr., 72) about VOKS (fiber-optic synchronization channel) from www.avangard.org/uploaded/voks.pdf.

18. Dvornikov O. et al. Microcircuit AF011 B for high-precision time measurements // Chip News, 2003, No. 7. (Electronic version at: www.chipinfo.ru/literature/chipnews/200307/5.html).

19. Svintsov A.G. Reflectometric methods for measuring the parameters of the fiber optic link. Photon Express 4, June 2006

Claims (1)

An optical reflectometer containing a pulse shaper, one of the inputs of which is connected to the output of the microcontroller, and the output is connected to a semiconductor source of optical radiation, a Y-shaped optical splitter, the input / output of which is optically connected to the socket of the output optical connector of the reflectometer, and the output is optically connected to the optical the input of the photodetector, the output of which is connected to the input of the analog switch, the control input of which is connected to one of the outputs of the microcontroller, and the output is connected to the input of the com of the parator and the input of the pulse expander, the input of which is connected to one of the outputs of the microcontroller, and the output is connected to the analog input of the analog-to-digital converter, the digital outputs of which are connected to the inputs of the microcontroller, which is connected to a personal computer, characterized in that a piece of optical fiber of a given length is introduced optically connected to the output of the semiconductor optical radiation source and the second input of the Y-shaped optical splitter, and the output of the comparator is connected to one of the inputs of the microcon troller and with the second input of the pulse shaper.

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