SU1503040A1 - Device for measuring group delay time - Google Patents

Abstract

The invention can be used to measure the group delay time of a fiber optic communication link (FOCL) with spatially separated inputs and outputs. The purpose of the invention is to expand the functionality by measuring the group delay time of a fiber optic link with spatially separated inputs and outputs. For this purpose, frequency dividers 2 and 5, low-pass filter 3 and time selector 4 are entered into the device, and control pulse generator 14, a second crystal oscillator 16, time selector 15 and divider 17 on the receiving side. through the filter 3 is connected to the first input of the time selector 4, the second input of which is connected through the divider 5 to the input of the filter 3. The second crystal oscillator 16 is connected via a time selector 15 to one input of the divider 17, the other inputs of which and the time selector 15 are connected Respectively with the inputs of the imaging device 14. In addition, the device contains the first crystal oscillator 1, the LED 6, through serially connected input unit 7, fiber optic 8, interference filter 9, photodiode 10, low pass filter 11, limiter amplifier 12 and phase detector 13, connected to the indicator 18. 2 Il.

Description

47

Phie.1

3150

An example of this is related to radar technology and is used, in particular, to measure the group latency of fiber-optic communication lines, whose inputs and outputs are located at geographically dispersed points.

The aim of the invention is to expand the use area by measuring the group delay time — fiber-optic communication lines with spaced inputs and outputs.

Figure 1 shows a block diagram of a device for measuring a group lag time; in fig. 2 - timing charts of the device.

The device contains on the transmitting side a crystal oscillator 1, the output of which is through frequency divider 2 .p connected to the input of the low-pass filter 3, the output connected to the first input of the time selector 4, the second input of which is also connected to the input of the lowpass filter 3 through the additional divider 5 frequencies per t, the output of the time selector 4 through the series-connected LED 6 and the radiation input unit 7 are connected to the input of the fiber-optic communication line 8, and on the receiving side an interference filter 9 which output via a serially connected photodiode 10, a low-pass filter 11 and a limiting amplifier 12 connected simultaneously to the inputs of the phase detector 13 and the driver 14 of the control pulses, the first output of which is connected to one input of the time selector 15, another input connected to the output of the crystal oscillator 16, the output of the time selector 15 is connected to the first input of the counter divider 17 of the frequency, the second input of the control pulses 14 connected to the second output, and the code of the counter divider 17 of the frequency n Connected to the second input of the phase detector 13, the output of which is connected to the indicator 18.

The device works as follows.

On the transmitting side, at the output of the frequency divider 5 per m, a signal (Fig. 2a) is formed from the harmonic signal of the crystal oscillator 1 with the frequency pL, which passes through the frequency divider 2 at n, which is characterized by forward and reverse stroke. This signal arrives at the second input of the time selector 4 and opens it only for the duration of the forward pulse,

At this time, the harmonic signal (Fig. 2b) with the frequency Sic of the output of the low-pass filter 3 is fed through the time selector 4 to the input of the LED 6 and modulates the intensity of its luminous flux according to a harmonic law. In this case, the intensity modulated light flux (signal) at the output of the LED 6 has the form of a signal in Fig. 2b and, without regard to the initial phase shifts, is analytically described by the expression

 (1 + McosQt) cos CO ,, t: I cos W-t +

 gp

+ - | - cos (co, -C) (W (. + n) t, (1)

where I is the maximum intensity (amplitude) of the light flux; COf - circular frequency of the light

flow.

With the passage of the signal (1) for the duration of the forward pulse (Fig. 2a) through the fiber-optic link 8, its spectral components undergo phase shifts, which are transferred to the envelope. Consequently, the instantaneous intensity of the modulated light flux at the output of the fiber-optic link 8 can be expressed as follows.

MIn ,, g

I, 1, cos () + --- COS (Cje -I) t 1 - G n

  COS L (Uc + n) t-tfiJ, (2)

where (n - phase shift at frequency

radiation C0 (.; (f,, H g phase shift at the frequency

(COP) and (Q (. + Q) respectively. Since cos (Q, -Q) t-Cf, -fcos (cJc + C) t -Cp, 2cos (co, t -) eos (Qt.) ,

then the inflation (2) can be represented as

I, I, cos () MI, cos (

X COs (Qt 4).

Considering that Q soz, m (zhns to believe

.-M g: C |); ----- UCf

 2

After simple transformations we get

, cos (COc, t-lj)) ri + Ncos (Qt +

-HH). (3)

From the comparison of expressions (3) and. (1) it can be seen that with the fulfillment of the condition WIA S2..CO. the envelope of the intensity-modulated light flux at the output of the fiber-optic communication line acquires an additional shift (C).

The signal (3) passes through the interference filter 9 and enters the photodiode 10, where the optical signal is converted into an electrical one with the formation of a photocurrent at its output, that is, e. voltage (fig.2g) with frequency Q, which is implemented using low-pass filter 11

and (Qt + uLf). (four)

From the foregoing, it follows that the group lag time estimates are based on the value of ucf based on the emission from Aui / Q.

The signal (4), after being limited in amplitude in the limiting amplifier 12, has the form of a signal (FIG. 2 e) and is fed to the first input of the detector 13,

With the arrival of the first pulse of the signal Q-lag time, containing nala (Figure 2d), the former 14 is controlled by the transmitting side of the first quartz;

These pulses are generated by a pulse (Fig. 2e), fed by the 1st to the selector 15, and keep the latter in the open state for the duration of the forward pulse of the signal (Fig. 2a). At the end of the direct stroke of the signal pulse (Fig. 2a), the shaper 14 produces a pulse (Fig. 2g), which arrives at the frequency divider 17 times to preset it in a certain state before the next forward stroke of the pulse (Fig. .2a). At the same time, 17 frequencies are input to the counter divider

During each forward stroke of the selector 15, a harmonic signal is received (Fig. 2h) from the output of the reference crystal oscillator 16 of the frequency.

030406

At the output of the frequency counter 17, a signal is generated (Fig. 2i), which is used as a reference and is fed to the second input of the phase detector 13.

However, as can be seen from the diagrams, the signal (Fig. 2i) at the output of the counter of the frequency divider 17, Q, is delayed with respect to the first pulse of the measuring signal (Fig. 2e) at the output of the limiting amplifier 12, those. does not coincide with the beginning of the delayed signal. J5 The magnitude of this delay will be determined by the number recorded in the counter 17 frequency divider and is within plus or minus one oscillation frequency of the oscillator frequency of the generator 20 of the 16, which practically characterizes the systematic measurement error due to the divergence of the frequencies of the generators 1 and 16 for the measurement time (the time duration of the forward stroke 25 of the signal pulse in Fig. 2a), which can be averaged over the measurement time and subtracted from the result of the indicator 18.

Thus, in the device for

The 30 group lag time measurements (TSS) are enhanced in functionality, which allows measuring the GDT of spatially separated objects while maintaining the high accuracy of the GDT measurement.

35

Claims (1)

Invention Formula A device for measuring a group oscillator, an LED, the output of which through the radiation input unit is connected to the fiber-optic input, a communication line, the output of which is connected on the receiving side to the input of the interference filter, the output connected to the input of the photodiode, the output of which is connected to the first input of the phase detector through the low-pass filter and the limiting amplifier, the output of which is connected to the indicator, in order to expand the field of use by measuring the group time delays in fiber-optic communication lines with separated inputs and outputs, are additionally inserted on the transmitting side two frequency dividers, a low-pass filter and a temporary selector, and on the receiving side a driver for controlling pulses, a second crystal oscillator, a temporary selector and a counter frequency divider, with the first frequency divider on the transmitting side connected to the output of the first KBapueBorq generator, and output simultaneously to the inputs of the low-pass filter and the second frequency divider, which are connected to the corresponding inputs of the time selector, the output connected to the LED, and on the receiving side i -fuifuum Well the driver of control pulses is connected simultaneously to the output of the amplifier of the limiter, the output of the generator of control pulses is connected to the first input of the time selector, the second input connected to the output of the second crystal oscillator, the output of the time selector is connected to the first input of the counter frequency divider, the second input of which connected to the second output of the driver control pulse, and the output of the counter frequency divider connected to the second input of the phase detector. | U UTJUUf J