SU1322093A1 - Method of checking variations of fibre light guides in length - Google Patents

Abstract

This invention relates to a measurement technique. The purpose of the invention is to improve the accuracy of monitoring changes in the length of optical fibers and simplify the method of control by eliminating the influence of fluctuations. The goal is achieved by the fact that in the method of controlling changes in the length of the optical fiber (BC), including alternating modulation of the intensity of optical radiation of wavelengths and a reference electric signal, transmitting modulated optical radiation through the BC, highlighting the envelope of the radiation transmitted by the BC, measuring phase shift between the radiation envelope and the reference signal and the measurement of the difference in phase shifts for the radiation of the first and second wavelengths, the change of which determines the change in the length of the sun, a and l in Biranne requirements of equality of the temperature derivative of the group refractive index of the core material N sun when A and .. Furthermore, a time delay is introduced into the reference signal by passing it through a fiber optic channel. 1 hp ff, 2 un. with (L

Description

The invention relates to a measurement technique, in particular, to the field of measuring the length of optical fibers (BC) by optical means and can be used in the manufacture of fiber optic cables and control of the relative change in their lengths, as well as in the development of sun-based sensors and devices wiring reference and heterodyne signals. ABOUT

The purpose of the invention is to improve the accuracy of control of changes in the length of the aircraft and simplify the method of control.

Fig. 1 shows a two-channel reference signal wiring device 5 in Fig. 2, a device for measuring the difference in lengths of the measured aircraft relative to the reference aircraft.

Dual channel wiring device

(ft is the length difference (alignment accuracy) of the measured and reference aircraft, which, in order to obtain a positive effect due to) alignment of BS lengths, must generally satisfy the requirement of Irffl I. The phase shift of the measured and reference signals is equal to

t nn - F,

2 | (ML

,

etc

(3)

where v,

etc

gprg

-,

etc.

The change in Φ phase shift with a change in and

 4F

on j

expressed as

-4N.

(four)

where 4N N (j) - Ы (Д).

In expression (4) there is no member,

The reference signal associated with the phase shift of the signal consists of two phases in electronic units. This is due to the photodetectors 1 and 2, the two so that controlled photodetectors 3 and 4, d / ltpd f

H p p depends on f and not all three V-shaped splitters 5-7,

sit from

(....

0

  0). Isa f 0). Izna and, accordingly, to a change in phase H (4) on

th -AlAN,

ABOUT

(3)

for transmitting the optical transmitter 8 to change the length t of the measured BC to LT radiation in two optical fibers leads to a change in the phase F,, (2) the BC and BC, one of which serves in

as the reference switch 9, the generator 10 of the reference signal and the phase meter 11.

The device for measuring the difference in lengths of the measured BC relative to the reference BC consists of two photodetectors 12 and 13 for receiving a signal from the reference fiber optical fiber BC and the measured fiber optical fiber BC. whose length differs from the length of the BC to it (f must be measured), the radiation splitter 14, the optical transmitter 15, the wavelength switch 16 of the optical transmitter, the generator 17 of the reference signal and the phase meter 18.

The method is as follows.

Measuring 4 d and dN, c and f, we will determine df from (5). 35 The reference signal wiring works as follows.

The radiation of the optical transmitter 8 is modulated by the reference electrical signal of the frequency f of the generator 10. From the code of the transmitter 8, the modulated radiation is transmitted through. Y-splitters 5-7, optical fibers of the sun and sun, enters the entrance

40

Photodiode 1 and 2 dyes, from the outputs of which the electrical signals are received In the case when the modulated optical radiation is passed once through the measured and reference air, the phases of the reference and measured signals at the input are determined by the relations

2ift - 2JifN (I ::. T). j

tlCP

,,.,(one}

2 ... ep-.np. .

(2)

where H-per I P-i phase shift of the signal in the optical transmitter, the photodetector of the reference channel and the photodetector of the measuring channel;

(ft is the length difference (alignment accuracy) of the measured and reference aircraft, which, in order to obtain a positive effect due to) alignment of BS lengths, must generally satisfy the requirement of Irffl I. The phase shift of the measured and reference signals is equal to

 nn - F,

2 | (ML

,

etc

(3)

,

etc.

phase shift when changing and,

 4F

on j

expressed

-4N.

 with a phase shift of the signal in these blocks. This is due to d / ltpd f

H pp depends on f and is not dependent on the phase shift of the signal in electronic units. This is due to the fact that d / ltpd f

sit from

(....

0

  0). A change in the length t of the measured BC on LT leads to a change in the phase of Φ ,,, (2)

on and accordingly to change

phase (4) on

-

th -AlAN,

ABOUT

(3)

Measured 4 d and the value of dN, c and f, determine from (5) the value of df. The reference signal wiring works as follows.

The radiation of the optical transmitter 8 is modulated by the reference electrical signal of the frequency f of the generator 10. From the code of the transmitter 8, the modulated radiation is transmitted through. Y-splitters 5-7, optical fibers of the sun and sun, enters the entrance

dy photodetectors 1 and 2, from the outputs of which electrical signals are supplied to the consumer. The modulated radiation reflected on the BC outputs, and BC (inputs of the photoreceivers 1 and 2) through the BC, splitter 5 and through the BC., Splitter 6 is fed to the inputs of the photoreceivers 3 and 4, from the outputs of which the electrical signals are one as a reference, the other is the measured is fed to the phase meter 11. The switch 9 changes the wavelength of the optical transmitter L to L, thereby changing the phase shift of the reference and measured signals, which is recorded by the phase meter. After determining the difference of the phase shifts by i and L per 31322093

switch 9 changes D to D, (/ | in

Choice of L

the proposed device is the working wavelength). The change during the operation of the device of the length of the measured sun relative to the reference sun g. On a to g (l) is monitored by the change in the difference in phase shifts determined during operation by switching to a.

The length difference measurement device operates as follows.

The transmitter 15 radiation is modulated by the reference electric signal of the frequency f of the generator 17. From the transmitter 15 output, the modulated radiation | 5 through the splitter 14 and the AF and BCj optical fibers to the inputs of the photodetectors 12 and 13. The reference (from the output of the photoreceiver 12) and measured (from the output photodetector 13) electric signals are fed to the phase meter 18, which records the phase shift of these signals. Conversion 16 changes / 1, by D, by changing the shift of the reference and measured signals, which is recorded by 25 phase meters 18. From the phase difference of AJ and, 1, it is determined. After determining the phase difference, the switch 1 6 changes to D 1

and

flying (7), it is determined the dependence of the temperature

dN dn,

-; - And - (p - indicator prelo

dl dl

core material) from d. C does not require wideband equipment when implemented, that optical radiation modulated by a signal with a fixed frequency. This makes it possible to reduce the transmittance of the optical transmitter and photo-modulators and, accordingly, the magnification of the df measurement. Thus, when the transmittance of the photovoltage is five times the signal / w ratio, the accuracy of the measurement of the phase (T) increases approximately by a factor. In addition, the setting of the frequency g and the optical length D of the optical transmitter due to the large time delays (more than the difference of the electrical length and measurement channels) is eliminated for precise measurements of the non-frequency frequencies f.

From (1) - (5) it follows that inconsistencies (/ AI will give

instead of the sun, the next sun is put, from-30

 -T.G. measurement errors 34 equal to

the length of which is the length of the sun

measured similarly. The lengths of BC2 light guides must be preliminarily rough with the length of the reference AF fiber with an accuracy of not less than 35 max satisfying the requirement

f.i,

2) MN. ,,. .

--- cfi / f. Relational

L /

sif measurement errors are equal

tl N 4l 4N

1 dT lm

21,

(6)

40

since the phase meter measures the phase shifts and the difference of these shifts within 2.

Using formulas (1) - (5), it can be shown that the described method eliminates the influence on the measurement accuracy df of the temperature instability of the group refractive index N.

From (2) - (5) it follows that a change in the temperature of the measured BC by if T with respect to the temperature of the reference BC c leads to an error: f measurement l (5 equal to

Z / ffl d. ..., „2i (frrdN ,,. DN.,. Л

--- 5- (lU.sHt c-laf l,) - 5- (d,) J X

X cAT oh so

dN,. dN,, t () - nt 1

dT

Choice of L

, and Л, satisfying (7), is determined by the type of dependence of temperature derivatives

dN dn,

-; - And - (p - index of refraction

dl dl

core material) from d. The method does not require the implementation of the development of broadband equipment, since the optical radiation is modulated by a signal with a fixed frequency f. This makes it possible to reduce the bandwidth of the modulating frequencies of the optical transmitter and photodetectors and, accordingly, to increase the measurement accuracy of df. Thus, with a decrease in the transmittance of the photodetector by five times, the signal-to-noise ratio, as well as the accuracy of the phase measurement (V and RT), will approximately double. In addition, the influence on the measurement accuracy of the instabilities of the frequency f of the master oscillator and the optical length D of the optical transmitter, due to the large difference in time delays (large difference in electrical lengths) of the reference and measurement channels, is eliminated.

From (1) - (5) it follows that instabilities (/ AI will lead to

f.i,

2) MN. ,,. .

--- cfi / f. Relative

L /

sif measurements respectively

(eight)

tl N 4l 4N

1 dT lm

0

g (9)

1 and ut f

In the case of temperature instability of the laser wavelength, the expression (8) is written in the form

C / I dN dA

Hg -

 Jidn d

dT

,

(10) and in the case of instability c / L caused by c / T, in the form

dN dA d, dl

.

(eleven)

It is obvious that with exact equality of the lengths of the measured and reference BC (cff 0) errors,, j, and t are equal to zero.

Pris / G 3 m, G 500 m, df 0.1m, 1 50 ° С, N 1.47; dN / dA 0.03 1 / μm, 0.5 μm; Aj 0.9 m N (A,) 1.49; N (A,) 1.465. 0.14 (14%). At 5.10 5 MHz,

df f, c / r

f 500 M and idl

 0.1 M in -: 167 times less error about T

The known device simplifies the measurement method without requiring additional measurements excluding the phase instabilities of the electronic pps blocks. This is due to the fact that, in the method, the control over the change in the length of the aircraft is made by changing the phase H which does not contain the phase shift of the signals in the electronic units

Since the temperature change

fO

Claims (2)

1. A method of monitoring changes in the length of optical fibers, which successively modulate the intensity of an optical signal of a wavelength L with a reference electric signal, passes a modulated optical signal through a light guide, extracts an electrical signal proportional to the absorbing optical signal, the transmitted optical fiber, measuring - - - nCLJid. tH VJlXtt-Ult; 1 V OV- i WDVy / J, j I l-J CT, C I-L 4N group refractive index “phase shift between the signal envelope, unambiguously associated with the change in the L, the transmitted fiber, and the reference signal; the proposed method can also be used as a method for controlling the temperature of changes in the electric scrap, as well as the difference in the phase shifts, the change in which determines the change in the length of the fiber, and the length of the optical fibers. In the case of Q and y with the fact that, for the purpose of the normal Sun, the relationship between the temperature change in L electrical length The accuracy of the control, simplification of the method, measurement is also performed for the optical signal of the second wavelength 2 modulated by the same 25 reference signal, the wavelengths A and Aj are chosen from the requirement that the temperature derivative of the group refractive index N of the core material of the fiber is equal for, / and Sun L and 1 has the form. LCH and + (). (12) where / s1 is caused by the change in the IT temperature of the sun, o (8-10. measured by N, J-, It should be noted that taken on a working 2. Method POP.1, characterized in that the time delay of the reference signal is entered, the skip length L not necessarily equal to or D. Measurement is important when it is built-35 through a fiber-optic channel, a scientific research institute based on the VS wiring device having a common optics transmitter of reference and heterodyne signals, when the main destabilizing factor leading to the output phases 1-1 disconnected is the difference 40 with a measuring channel and the length of the fiber corresponding to the signal delay in the measured optical fiber. temperature regimes and different partial channels. Invention Formula 1. A method of controlling changes in the length of optical fibers, which successively modulate the intensity of an optical signal of a wavelength L with a reference electric signal, passes a modulated optical signal through a light guide, extracts an electrical signal proportional to the absorbing optical signal transmitted through the optical fiber, measuring k ni nCLJid. tH VJlXtt-Ult; 1 V OV- i WDVy / J, j I l-J CT, C I-L „Phase shift between the signal envelope, The accuracy of the control, the simplification of the method, the measurement is also performed for the optical signal of the second wavelength 2 modulated by the same reference signal, the wavelengths A and Aj are chosen from the requirement that the temperature derivative of the group refractive index N of the core material of the fiber is equal for, / and Ё «/ dl - dN. . UT; - -iTUj;  dT 2. Method POP.1, characterized in that the time delay of the reference signal is entered, the skip it through a fiber optic channel having a common optical transmitter it through a fiber optic channel having a common optical transmitter with a measuring channel and the length of the fiber corresponding to the signal delay in the measured optical fiber. BCf BCz 1 2 Editor A. Sabo Compiled by E.Glazkova Tehred A. Kravchuk Order 2853/36 Circulation 677 Subscription  VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 Proofreader G. Reshetnik