The measuring method of the optical lengths and delays fiber optic cable, and other passive fiber optic elements
(57) Abstract:The invention relates to measuring technique and can be used in fiber-optic technology in cable industry in the manufacture of optical fibers and cables, in measurement techniques in the creation and study of fiber-optic sensors, and so on, the Purpose of the invention is to simplify the measurement process. For implementing the inventive method used a linear dependence of the phase shift of the modulated optical signal on the optical fiber on the modulation frequency f. Given the possibility of measuring the phase difference to measure the shift from phase to phase only up to 2, it is proposed to implement a way to change the frequency of an electrical signal for modulating the intensity passing through the light guide optical radiation. When this is fixed with two frequencies f1and f2corresponding to two consecutive "zero" timing difference of the phases of the signals in the channels dual-channel measuring device without including the channels of the measured optical fiber or other passive fiber optic element. Then fix two consecutive reference f3and f4corresponding to two of posledovatelnogo. Then the desired measured optical length of the fiber is calculated by the expression LISM= C(1/f4-f3-1/f2-f1), and the delay of the signal measured in the passive fiber optic element is calculated by the expression where C is the speed of light. 3 Il. The invention relates to a measurement technique, namely the measurement of characteristics of optical fibers, and can be used in the manufacture of optical fibers in fiber optic technology, measurement technology in the creation and calibration of delays on the basis of optical fibers and passive fiber-optical elements (optical couplers, fiber optic switches, and so on), when you create, study and calibration of fiber-optic sensors of different physical quantities, and may also find application in optical instrumentation for measuring refractive index different transparent media (liquid, gaseous, and so on).Closest to the invention may be a method in which an intensity modulated harmonic electrical signal optical signal is divided into two optical signals. Each of these two signals injected into individual optical channel, and the output of each of etiolirovannyh signals at the outputs of these optical channels.In the first of optical channels include the measured optical fiber, and thus there is a possibility by introducing a special reflector to install the reflector on the first measurement stage on the input side of the measured sun, and in the second stage measurement at the output end of the measured sun.The second channel is an adjustable variable optical delay is a combination of movable and fixed reflective prisms that provide a change in optical length of the second channel. This provided the ability to accurately measure changes in the length of the second channel, which used a Michelson interferometer (with a count of interference fringes), the reflective mirror of one arm which is rigidly connected with the movable prism of the second channel.Measurement of the optical length of the armed forces this device is produced as follows. First reflector mounted on the input end of the measured sun, the movement of the movable elements of both channels to achieve a zero reading on the zero-organ installed at the outlets of the channels (align the optical lengths of the two channels). When this counter Michelson interferometer associated with the second channel set in n is ltate what readings zero-body in General will be different from zero due to the change of the optical length of the first channel on a dual optical length measured sun. Then the movement of the movable prisms of the second channel again achieve zero countdown to zero-the body (i.e., again align the optical length of the first and second channels), and the counter of the Michelson interferometer to change the interference pattern to determine the variation of the optical length of the second channel, i.e. the measured fiber.The accuracy of this method in fact is limited only by the sensitivity of the zero-body, locking the coincidence of the phases of the envelopes of the modulated signals in the channels.The disadvantage is the use of the second channel variable optical delay.The method of measuring optical lengths (delays) fiber optic cable, and other passive fiber optic components according to the invention is based on the use of intensity modulated harmonic electric signal optical radiation, which is divided into two light flux, each of which is injected into your optical channel. In one of the specified channels in the measurement process include the measured optical fiber; the radiation output of each channel is introduced into the phase comparator, fixing the zero value of the difference of the phases of the envelopes of the modulated signals in the channels.This is achieved in that for measuring the optical lengths of the optical fibers are first pre-set value is equivalent to the optical difference of the lengths of the channels measured without connecting element, which change the frequency of the modulating signal and remember the two values of frequency f1and f2the modulating signal in which the phase comparator detects two adjacent consecutive zero values of the differences between the phases. Then in one of the channels measured include passive fiber optic element, increasing the optical length of the channel to the length of the measured element, again thus change the frequency of the modulating signal and memorize two new frequency f3and f4the modulating signal in which the phase comparator fixes for two new adjacent consecutive zero reference of the differences between the phases. The desired value of the optical length of the passive fiber optic element is calculated by the expression:
L=C - where C is the speed of light.The delay value of the signal measured in the passive fiber optic element is calculated by the expression:
The method consists in the following. The method of measuring optical lengths and C intensity modulated optical radiation from time t can be represented by the formula:
I=I=+Iosin( t+ao)=I=+Iosin(2 f+ ), (1) where I=- constant component of optical radiation;
Iothe amplitude of the modulated light;
o- initial phase modulated signal;
f - frequency modulated signal.Thus the relation is valid:
f= C, (2) where is the wavelength of the modulating signal (electric signal);
C is the speed of propagation of electromagnetic waves.In addition, the optical length L of the optical element is the product of the geometric length of the light path in the element on the medium refractive index n of this element.L=nl, (3) where l is the geometrical path length of light in the element.Equivalent optical length of any optical channel is defined by the sum of the optical lengths of all components of the channel elements.The invention is illustrated in Fig.1-3.According shown in Fig.1 the scheme of direct intensity modulated harmonic signal optical radiation, the intensity of which is determined by the expression (1), the beam splitter D (for example, a translucent mirror, prismatic cube or the endoscope about the ka, but with less in comparison with the input radiation intensities and amplitudes.Each of these two intensity modulated light stream is introduced into a separate optical channel (two channel). Channels can be created on the basis of passive elements, as a purely optical, and on the basis of fiber-optical elements, and can be the difference between the equivalent optical lengths in a very wide range (e.g. from 0 to 103-104m).The radiation output of each channel is introduced into the phase comparator K, which provides fixation with high precision matching of the phases of the envelopes (equal to zero phase difference) entering modulated signals. In the channel (for example 1) include the measuring element through the light contacts a and b (light connectors, as shown in Fig.2, or connect these terminals are short-circuited to each other as shown in Fig.1.First, consider the case shown in Fig.1.If the optical channels I and II have the same optical length, intensity modulated signals in optical form are received at the comparator in the same phases, see the zero reading of the comparator. If the optical Cana is showing can be associated with the difference of the lengths of the channels and the frequency of the modulating signal in the following proportions.The difference between the optical lengths of the channels L1equal to the wavelength of the modulating radiation = (where f is the frequency of the modulating radiation) which corresponds to the phase difference between signals input to the comparator is equal to 2 = 360about.Arbitrary as the difference between the optical lengths of the channels L corresponds to the phase difference signals to the comparator are equal , i.e., L1== __ 2= 360o.From here you can make a proportion:
_ = or
= 2 = 2 = 2 i.e. = 2 (4)
According to expression (3) L=ln, then
Expressions (4) and (5) relate the values of the differences between the phases of the signals at the outputs of the channels with equivalent optical difference of the lengths or simply geometric lengths of the channels and the frequency of the modulating signal. In practice seems to be more convenient to use the expression (4), especially in cases when it is required to determine the delay in the channels.The expression (4) shows a linear dependence on f, if L is constant. As follows from expression (4) is the numerical value of L determines the angle dependence of the phase difference of the frequency f. The difference of the lengths of the channels may be formed, for example, included in one of the channels of the optical fiber great length.This corresponds to the wavelength of the modulating signal
= = = 300 m, i.e. the length of the fiber several times greater than the wavelength of the modulating signal. According to expression (4) is the phase difference introduced by the considered fiber is:
= 2 = 2=5,252=10,5=1890< / BR>But all existing measures of difference of phase measure phase shifts only within 0-360about(or -180about-+180about). As a result, the phase meter comparator, not capturing the value 10=1800aboutthat will indicate the value of the difference of the phases of the channels 90aboutthat can equally match the phase shifts equal to 90 and 450, and 810 and 1170aboutand so on, i.e., occurs the ambiguity of the reference phase shift.If you change the frequency f of the modulating signal and make it, say, f=1.2 MHz=1,2 106Hz. This corresponds to the wavelength of the modulating radiation:
= = 250 m
I.e. the wavelength is decreased, and these wavelengths on at phases , brought under consideration by the fiber (L 1575 m) in this case is
= 2 = 2=6,32=22,6=2268< / BR>In this case, the phase meter comparator will register values of the phase difference equal to 108aboutthat can mean both 108aboutand 468aboutand 828aboutand so on, i.e., again the uncertainty and ambiguity of reference.The authors have measured the dependence of f for multimode fiber fiber type quartz-quartz h μm with a gradient profile of the refractive index for different geometrical length l of the fiber. These dependencies are shown in Fig.3, fully confirmed the correctness of linear dependence for dierent values of l (which is the same and L) for any passive optical elements.This circumstance, as well as the possibility according to the expression (4) changes the value specified by the value of f changes and the achievement of the values that are multiples of 2 , which phase meter comparator registers with a high degree of accuracy, as "zero" values, eliminates all ambiguity measurement of phase shifts, and thus the measurement of the optical length of the fibre or other passive fiber-optic element as about the situation of the difference of the lengths of optical channels, in yet included measuring element. This modulated according to expression (1) optical radiation will enter the beam splitter D when closed short optical connectors a and b. Let this phase meter comparator To showing some (non-zero) value . Changing the value of the frequency f of the modulating signal (for example, increasing it), you can find the first value of the frequency f1, wherein the phase comparator To fix the first "zero" value, which may correspond to any value of the difference of phases1=2 K, where K=0,1,2,3.... (K - integers). According to expression (4) is an equality
1=2K = 2
(6) where K is the undefined value; L is the optical difference of the lengths of the channels.Continuing a smooth change in frequency in the same direction can be found next (neighboring) incremental value of frequency f2corresponding to the next consecutive "zero" reading of the comparator:
2= 2(K+1) = 2
Taking the difference of the expressions (7) and (8) we get:
2-1=2 (K+1)-2 K=2 . But at the same time:
2-1= (f2-f1)2 i.e., 2 = (f2-f1)2 (8) or L =
Expression (8) gives the value of the equivalent optical is Alov, for example, in the I channel, measured include passive fiber optic element with the desired optical length LISM. For this element include between the optical connectors a and b (Fig.2), i.e., the optical difference of the lengths of the channels L increased by the value of LISMand ie became L+LISM. Let this phase meter comparator To shows again some new (non-zero) value .Changing the value of the frequency f of the modulating signal (e.g., increasing), it is possible to find again the value of frequency f3, wherein the phase comparator To detect a new "zero" value that corresponds to some value of the difference of phases3=2 m, where m=0,1,2,3....According to expression (4) is an equality:
3= 2m 2
(9) where m is the undefined value.Continuing the smooth change of the frequency f in the same direction, you can find the next (adjacent) incremental value of frequency f4corresponding to the next consecutive "zero" reading of the comparator:
4= 2(m+1) = 2
Taking the difference of the expressions (10) and (9), we obtain
4=2 (m+1)-2 m=2 .And at the same time
i.e. 2 = (fins LISMmeasured element:
LISM=C - .(12)
As can be seen from expression (12), LISMdetermined only by the values of the measured frequencies f1f2f3and f4the value of fundamental constants and error fixing "zeros" of the phase comparator.Were made of real measurement of the optical length of the optical fibers using phase comparator, the retention value of the difference of phase at the resonant frequency of 1 MHz (after frequency conversion) error in phase is less than 0,001aboutwhen choosing a frequency f1-f4in the range of 1-10 MHz. The change in the phase difference by 0.001abouteven at long lengths of optical fibers corresponds to a change of frequency of 3.5 Hz.This change of frequency in this frequency range is easily secured a modern electron-counting frequency. The value of the speed of light With a known with an error of about 3 to 10-0that does not limit the measurement accuracy in the calculation according to expression (12).On the evaluation, the error in the determination of the optical lengths of the expression (12) is not greater than 0.005 m for the implementation of the proposed method there is no need for precision, adjustable is ilokano-optical elements in a wide range from 0 to 104mThe method can be applied in the study and the development of fiber-optic sensors that change their optical length at the external impacts. The method can be applied also to estimate the index of refraction of transparent liquids, if instead of the measured optical fiber between the optical element contacts a and b of Fig.2 to include a cuvette with a pre-known geometric length l, frequency f1and f2to measure when an empty cell, and the frequency f3and f4when fluid-filled ditch. Then, according to expression (12) we can calculate the value of LISMand the refractive index n in this case can be calculated from the expression (3) for a known value of l.Because you can write the well-known relation with the passage of light of the optical length of the optical fiber element=LISM/ , it may be obtained from the expression (12):
= - This expression is calculated to calculate the delay time measured in the passive fiber optic element. The MEASURING METHOD of the OPTICAL LENGTHS AND DELAYS FIBER optic cable, AND OTHER PASSIVE FIBER OPTIC ELEMENTS, consists in the fact that two optical light flux, each of which is introduced into the corresponding optical channel, in one of the channels in the measurement process includes measuring element, the radiation output of each channel is introduced into the phase comparator, fix the zero value of the difference of the phases of the envelopes of the modulated signals in the channels, characterized in that, to simplify the measurement process, the pre-change the frequency of the modulating signal, fix two adjacent consecutive zero values of the phase difference and the corresponding frequencies f1and f2the modulating signal, set the value of the equivalent optical difference of the lengths of optical channels without connecting the measured element, after turning in one of the optical channels of the measured optical fiber element change the length of the modulating signal, and recording the two new adjacent consecutive zero values of the phase difference and remember the two values of frequency f3and f4the modulating signal and the desired value of the optical length L of the fiber-optical element is calculated by the expression
< / BR>where C is the speed of light,
and the delay value of the signal measured in the passive fiber optic element is calculated by the expression
FIELD: measurement technology.
SUBSTANCE: according to method of contact-free optical measurement the object is placed between laser radiation source and photoreceiver. Power of laser radiation P is measured and compared with preset level of power P0 . Laser radiation is optically scanned into beam of parallel rays at the area where object finds its place and size of object is found from size of shade of object onto photoreceiver while correcting time of exposure from value of difference (P0-P). Device for realizing the method has laser, beam-splitting plate, short-focused cylindrical lens, output cylindrical lens, collimating lens, CCD, data processing unit, photoreceiving threshold unit.
EFFECT: improved precision of measurement.
5 cl, 1 dwg
FIELD: physics; measurement.
SUBSTANCE: invention is related to method, and also to device for measurement of component amount coming from surrounding gas atmosphere and received by parts in process of thermochemical treatment of metal parts. Sample, lengthwise size of which considerably exceeds its cross size, is exposed to gas atmosphere impact. Change of sample length in time in lengthwise direction is measured, being the result of component transfer from gas atmosphere, and measured change of length is used for determination of component amount that was transferred from gas atmosphere to sample. Method is performed isothermally or at changing temperature, at that change of length resulted from temperature change is compensated in calculations. In order to realise the method, device is used that incorporates clamp for sample used in method, system of length measurement for registration of sample length change in time in longitudinal direction, and also computing unit. Method provides possibility to obtain much more accurate data on amount of component coming from gas atmosphere and received by parts.
EFFECT: obtainment of much more accurate data on amount of component coming from gas atmosphere and received by parts.
14 cl, 11 dwg, 1 ex
FIELD: measurement equipment.
SUBSTANCE: method for contactless measurement of small objects sizes is realised with the help of device, comprising zoom, which is arranged in the form of single fixed, and also the first and second movable components. Considered object is placed in back focal plane of zoom. In back focal plane of zoom fixed component there are two calibrated frames arranged. Object image is subsequently matched with images of two frames, and position of movable component is fixed in process of this matching. Calculation of object size is carried out by two fixed positions of movable component, by size of frames and structural parametres of zoom.
EFFECT: provision of high accuracy of small objects linear dimensions measurement.
3 cl, 2 dwg
FIELD: machine building.
SUBSTANCE: pulse heat source with action time of where R - piping radius, d - wall thickness, a -temperature conductivity is installed on pulse heat source piping according to the method for determining the thickness of deposits on inner surface of piping, and temperature change is determined at the distance l=(2.5-3.5)d from the heating source. The device for determining the thickness of deposits on inner surface of piping is equipped with generator of current radio pulses, amplifier, analogue-to-digital converter, computing device, indicator of deposit thickness and indicator of deposit heat conductivity; at that, output of current radio pulse generator is connected to induction coil; amplifier input is connected to temperature sensor output; amplifier output is connected to input of analogue-to-digital converter; output of analogue-to-digital converter is connected to input of computing device; outputs of computing device are connected to indicators.
EFFECT: possibility of monitoring the deposits of small thickness and possibility of monitoring the pipes during performance of preventive actions when the process is stopped and pipes are dehydrated.
2 cl, 7 dwg
SUBSTANCE: silicon monocrystalline microheater is used as a displacement sensor and the value of heat lost from the microheater to a heat receiver serves as the measuring signal. The microheater has the shape of a variable section beam, the wide part of which is a resistor and has a region of opposite conduction type, and the narrow part is form of current leads having low-resistivity silicon regions and a silicide coating, wherein the end of the current leads is in form of a platform for forming metal contacts. Displacements vary from 5 to 800 mcm and measurement accuracy is equal to ±20 nm.
EFFECT: high accuracy and stability of sensor readings.