CS230331B1 - A method and apparatus for detecting multiple phase shifted interference signals in a laser interferometer - Google Patents

Abstract

The invention relates to laser interferometers. The essence of the invention is a method of detecting multiple phase-shifted interference signals, where light beams from the interferometer fed to the interference are gradually affected by dividing the intensities, passing through an optical medium with a different light propagation speed in two perpendicular directions and using a polarizing passage, or possibly reflecting the light beams at the optical interface, thereby achieving a change in the polarization state of the partial light beams with the desired phase difference, which after impacting the detectors create signals with a phase shift of π 2n. The invention is intended for laser interferometers.

Description

The invention relates to a method and device for detecting signals in a laser interferometer. A laser interferometer usually consists of a source of linearly polarized light, the interferometer itself and a detection unit for detecting interference signals.

At the output of the interferometer itself, an interference field is created, the state of which depends on the path differences of both branches of the interferometer. The impact of interfering beams of rays on photoelectric detectors creates interference signals in the detection unit, which are further processed in the evaluation electronics. The method of detecting interference signals largely determines the properties of the entire device, i.e. resolution, determination of the direction of movement, measurement reliability, etc.

The disadvantages of existing detection methods are mainly low resolution, low utilization of incoming light intensity, and the presence of a DC component in interference signals, which significantly contributes to the unreliability of the device.

These previous disadvantages are eliminated by a method of detecting multiple phase-shifted interference signals, e.g. n pairs of signals in quadrature, mutually phase-shifted by an angle --— from a laser interferometer with 2n high resolution and with elimination of the DC component of the signal, the essence of which is that the light beams from the interferometer itself, fed to the interference, are gradually affected by dividing the intensities, passing through an optical medium with a different light propagation speed in two perpendicular directions and using a polarizing passage, or possibly reflection of the light beams at the optical interface, thereby achieving a change in the polarization state of the partial light beams with the desired phase difference, which after impacting the detectors create signals with a phase shift —-— .

2n

The essence of the device is that it contains at least one, or more combined optical elements, consisting of a series-connected approximately non-polarizing splitter and a polarizing splitter, between which birefringent optical elements, for example retardation plates, are inserted, or these elements are placed in front of the approximately non-polarizing splitter. Another essence of the combined optical elements is that they consist of at least one series-connected polarization-asymmetric optical splitter and a polarizing splitter, between which birefringent elements, for example retardation plates, are inserted, or these birefringent elements are placed in front of the polarization-asymmetric optical splitter.

The device is supplemented in the path of orthogonally linearly polarized beams from the interferometer itself with an additional plate, possibly provided with a dielectric layer.

The outputs of the fourth and fifth detectors are connected to the input of the differential amplifier.

The outputs of the second and third, fourth and fifth detectors are connected via dividers to the inputs of the summing and differential amplifiers.

The advantage of the above method of detecting multiple phase-shifted signals, e.g., n pairs of signals in quadrature mutually phase-shifted by an angle -y—, is high resolution, i.e. full utilization of the intensity of the incoming light and removal of the DC component in interference signals.

The invention will be further explained by the attached drawing, where Fig. 1 schematically shows the arrangement of the detection unit with two pairs of signals in quadrature, Fig. 2 with four pairs, Fig. 3 with one pair of signals in quadrature and one in antiphase phase shifted by —-— and Fig. 4 shows another variant of the arrangement according to Fig. 2.

The principle of the method of detecting interference signals consists in dividing the interfering beams into sub-beams, which are acted upon by birefringent optical elements, thereby obtaining sub-beam interference fields. Suitable frequency directions are selected from each sub-beam interference field, for example by means of polarizing splitters, and these beams of light fall on photoelectric detectors. N pairs of signals are obtained, mutually phase-shifted by an angle —; while the signals of each pair are in £11

7Γ quadrature, i.e. phase shifted by —-— . If the detection unit is adapted to detect signals in antiphase, the DC component can be removed with an increased number of detectors by using differential amplifiers. In another variant, the DC component is removed by using a suitable combination of the sum and difference of the signals.

At the input of the detection unit, we express the polarized light of the unified beams by the Jones vector:

where:

ε _ν — Jones vector of the input unified bundles,

Ei — electric vector of the reference beam,

Ei — electric vector of the measuring beam.

For one pair of partial interference fields, which are obtained by the interference of the first two partial beams and the phase-shifted second two partial beams, assuming

El = El . θ ^ίφ , where φ is the phase shift between El and Ei, it follows:

w· - AI • A2 AN xK, · * ·“ · * M -

(Em+'ΐϊ)

where

T* **1 A1 » · · AN w **

are the Jones matrices of the optical elements in the path of the first partial interfering beam,

B1 • · f BN **· «**

are the Jones matrices of the optical elements in the path of the second partial interfering beam,

Ki, Ki', K2, Kz — constants.

Furthermore, the following applies to the Jones matrices of optical elements:

P* ^- *** - * A1 « A2 • ♦ » AN -» *·

oh oh 1-1

·<** * B1 • B2 « 9 < BN **««» «X - ·«-

(1-i)

O o d-i) (ni)

The light intensities of the first two partial interfering beams are given by the relations:

1, - / ί, · Z* . 1- kJ · E* 11 11 = _K * .ή ( ₁ , _cos/ , = 4^2= 'E,(1tsin?l

Both signals are therefore in quadrature, i.e. they have a phase shift of 90° with respect to each other. The same applies to signals in antiphase, which have a — sign.

For another pair of partial interference fields, which are obtained by the interference of two partial beams with a phase shift of θ, the following must hold:

with respect to the first pair of sub-beams, where n is the number of pairs of signals in quadrature, and assuming

*· *1 —» **· A1 A2 * « 9 AN * * «« -» P«>

r f Ί 2nd = L- ¹ « I 3 0 -

r** ·* 07 B2 9 · · SN Γ* Eats. 1«. •w —·

and further:

e ^l i 2q i

and* * r*“ ·Μ In 2 m (Ui) (1~i J»eQ i • • ♦ · BN 0 0 * aw *· #«* p. >

in

The light intensities of these partial interfering light beams are:

1 +cos(f+ 2. £/i-- ^K Í ^tE l · ^{1 +} sin

The phase shift of these interference signals is relative to the first pair of signals.

Pairs of partial interference fields are obtained in the detection unit by splitting the beam from the interferometer into partial beams and interfering the partial interference beams with different forms of polarization. In the following, the interference of three forms of polarization of the partial beams will be considered:

1. interference of circularly polarized beams of opposite orientation,

2. interference of circularly and linearly polarized beams,

3. interference of two linearly polarized beams with direct phase shift.

Now to the individual cases:

1. Interference of circularly polarized beams of opposite orientation

We will consider two variants, namely> a detection unit with four detectors and a detection unit with eight detectors. The additional first detector 4 is used to check for beam interruptions in the interferometer. The arrangement of the detection unit with four detectors is shown in Fig. 1.

The individual optical elements have the following values:

rotator 5: left-handed, phase shift S = 90°, i.e. rotation of the oscillation plane a = 45°, delay plates:

phase feed azimuth first 7: o = 90 ^: , Θ = 0° second 8: Oh = 180°, Θ = 45° third 12: δ = 90 ^cents , Θ = (P fourth 13: δ = 180°, Θ = 67.5'

first approximately non-polarizing divider 6:

^r v — ^R ±* Ti= ^R ,;

first and second polarizing dividers 9 and 14:

Γ _// ^Ο.99 _/ 0.01, ^0.01,^0.99

For the second and third detectors 10, 11, on which the light beams ai‘bt‘ and ai“bi“ fall, if we neglect the effect of the additional plate 1, the following applies:

A1

A2

A3

r ** A4 Λ5 i 1 1-1 1 1

~vr

-i 1 4 I * e H- ' ® 2.

1 o o

— - — ~ »» Γ ^- * * ·** ·«. 0 0 'οϊ Γ ; Τ Ί e ^l >t. 0 A1 A2 A3 A4 A5 w·“ *W r ^-1 0 1 0 0 e ^l τ

fce‘ f 0 , 1 1st o d 0 I VI 1 i - and? 1-1

J £ I e © where:

kS _r — phase shift caused by the first, approximately non-polarizing divider 6 upon reflection, its reflectivity in the plane perpendicular to the plane of incidence and

R„ — its reflectivity in the plane of incidence. For input unified beams the following applies:

7Γ * e

/Lil '1 Vz

F

• e ⁰ ir 1 ~e?

so their intensities are:

I ~ ¹ rc* £?

H tLy = “ý— · Rjl + cos /) ! ή -.1 £-J ~ 2 h ~~~2— * ~ ^c osf)

Further, at the output of the first differential amplifier 17, where the signal li is fed directly and the signal Ii' through the first resistor divider 19 in the ratio (we assume R, > R„), we have for the first resulting signal:

T i 2

Rh-cqs?

The resulting signal after the first differential amplifier 17 therefore does not contain a DC loop.

For the fourth and fifth detectors 15 and 16, on which the light beams a2 ^l b2 and a2"b2 are incident, the following applies:

'2 ^e

**ϊ Γ Ί Γ Ί 82 B3 04 B5 **·

^,e 2

^C 2 ^S 2 ^S 2- ^C 2

-ií e ^l * o í 7Γ

-£t r

Γ** r ^- * ““ί r** *> ť ;1f -i . X > 84 B5 0 0 c, with, e H- 0 'Γΰε'ζΓ o r 81 82 83 = * 2 . ΊΓ ** » jC r— L £L.T 0 /ř/e 2_J 0 1^ 0 e ^l 4

1-1 1 1

'^e ^l *

where:

kS _t — phase shift caused by the first approximately non-polarizing divider during passage, ' its transmittance in the plane perpendicular *1 to the plane of incidence,

T„ — its transmittance in the plane of incidence, „ where 3 is the azimuthal angle ϋζ—-coszyj a/2 of the fourth linear delay>2 — sin í t) of the ďov-ací plate 13.

Furthermore, if we assume:

c„- s ₉ = ^_ -£= : JI = o ^{2 2} KF' ^T ' we get:

£ £i i i

Jr.

2.

£1 £

-e ^ří /W £ l/Ď 'í e ^L Ť^ ⁺ e ' ^e ^Ce ¹ ΐ fh. * é ¹ ΐ ) o

Z ^íe ^Σ f tfW f R}

so the intensities are:

-j θ ·'* ~2 j =-Le _y ^l Z 2 ^z * ij ^T j. * ^T +( T,,- cos f* 2 f^T,, f > 4 * '* _c 2 r ^! z ⁼ ΊΓ ~-ít

Tl* ^T «+(T _f 'TJ cos'/>+2 før^ siaf

When using imperfect, that is, approximately non-polarizing dividers (T _x V, the signals Iz, 12* contain a certain component in phase and a certain component in antiphase.

If we transfer the signals I2, I2 ¹ to the second differential amplifier 18, we get for the third resulting signal:

l — i ~ í ^z - 1— '2 -fT,, r ₂ . _With iaf

Thus, the resulting signal after the second differential amplifier 18 does not contain a DC component and is exactly in quadrature with respect to the first signal.

The resolution of the detection unit (and interferometer) can be further increased by processing the electrical signals in additional amplifiers.

Let's assume that we have pairs of signals in quadrature, each pair of which has, in addition to the fundamental signal, a signal in antiphase, i.e.:

si = Ei ² R„ . cos φ; si' = Ei ² R„ . cos φ· ί ₂ =ε, ² f^T _l 'SLríf _í

We bring all signals to the same amplitude using additional amplifiers:

si = k cos p;

si' = k cos p;

k cos φ + k sin φ = k . γ2. sim(p + k cos — k sin φ = k . V2 . sin(— φ +

If we feed two signals of appropriate polarity to the next differential amplification stage, we get the following at the output:

S2 = k cos φ — (+ k sin φ) = = k . V2. cos(p -t- —ξ—| si = k cos φ — (— k sin p) = = k . V2 . sin(p + —ξ—)

S2 = k sin φ; sa' = k sin φ;

For two signals with the same amplitude:

^-) = k . \Í2 . COS (- φ + = k . 1/2 . COS (p + -í-)

This resulted in two signals in quadrature with a half phase shift compared to the original ones.

Similarly, further division of phase differences can be obtained by processing signals si, sz, si', S2 ¹ , S3, S3 ^l , si, si', but before feeding them to further differential amplifiers, it is necessary to adjust the amplitudes of all signals to the same level.

S5 = k . COS φ — 1 — k CCS ( φ +

S6 - k . sin φ — k sln^? -í- We have thus obtained two signals with a half phase difference with respect to signals S3 and st

In dividing the phase differences, it would be possible to continue. The limitation of the number of dividing stages will be due to the inaccuracies of the phase angles of the signals in quadrature, inaccuracies and fluctuations in the amplitudes of the individual signals, etc.

Therefore, for higher resolution of the device, it will be necessary to use optical phase angle division, supplemented by electronic division.

The arrangement of the detection unit with eight detectors is shown in Fig. 2.

)] = ^2c °s mm.cosU +-Í-)

Jl· ² “ ³ -/...... ^sin (' ⁺ -H

The optical elements have the following values: Rotator 5 has the same value as in the description of Fig. 1.

First, second and third, approximately non-polarizing divider 6, 21 and 31 j ^T i ^=R // > =°

Third, fourth, fifth and sixth polarizing divider 24, 29, 34 and 37

7^0.99, Τ^Ο,ΟΊ, R„^O,O1, Rj~»0.99

fifth 20 : δ - 180°, θ = 45° sixth 22 : δ = 90°, Θ = 0' ¹ seventh 23 : δ == 180°, Θ = 11.25° eighth 27 : δ = 90°, Θ = 0°

ninth 28 : δ tenth 30 : δ eleventh 32 : δ = twelfth 33 : δ = thirteenth 35 : δ = fourteenth 36 : δ =

180°, 180°, O Θ = 0° = 45° 90°, Θ = 0° 180°, Θ = 67.5° 90°, Θ = 0° 180°, Θ = 33.75'

For the second and third detectors 10, 11, on which the light beams a/bT and afb-i" fall, if we neglect the effect of the additional plate 1, the following applies:

⁰ 'S

W ^l T ^T ? ^R oo _r R _lf e ^l ž*

f— f* Γ* ** **Ί L. 1-1 Aΐ' Α2 r · · · Α7 =.··,, · Where αι' SS. 0 0 β 1 - - 0 ί

and for the intensities we get:

By feeding the signal li directly and Ii' through the first resistor divider 19 in the ratio - ----- to the first differential amplifier stage 17, we obtain for the first resulting signal:

I = L 'COS?

' RjT ¹

The signal after the first differential amplifier 17 does not contain a uniform component.

For the fourth and fifth detectors 15, 16, on which the light beams a5'bj' and a+bs' are incident, the following applies:

JL

X. -** ·* / jX* -«· ** 7-7 B1 B2 9 · · · B7 ™ · · ’ - 1 kcte Bl' =2 0 Q 1 1 ***» *· — *>*» *> ·* ,ο ι

i zz •x _Λ_ ^R í ^T ll ^f Vi ⁺ >3? «* t -Sir>.y.cos(S _T -S _R )>

' RJ„ ♦ Mrcos/r.-R.íi.]- ² 1/ ^- ¾¾L

By feeding the signals I?,, Iž“ to the second differential amplifier stage 18, we obtain for the third resulting signal:

^03 k - 2 l/R„ ^R j. ^T v ^T ± · cos ) · sin ?

For the sixth and seventh detectors 25 and 26, on which the light beams a3‘b3‘ and a3“b3“ are incident, the following applies:

and Where

1 '1-1 Γ Ί Γ Ύ >1 ** 'fc*. 1 1 ·». A1 to J A2 to • · · A7

Al' o O so the light intensities are:

Ύ* Z >E&Rfí ^ř 3'”2” cos/ -2C _z S ₂ sia.f 1 -(c£s* ) cos/+2 C _Z S _Z siilf

Signals b, Í3 ¹ If we choose are therefore in antiphase and their basic phase shift depends on C2, Sz.

we get:

. _ £?«Λ '3 ~ 2 ^{u cos} ^ ~ g) II 1tcos(iři £) I r'R h ^x 3 2 1 - -fa 005ý> ♦ -X 5in.y 2. ~~ J 1-~coS (/>+ -^) J

For the eighth and ninth detectors 38 and 39, which are affected by the light beams a6*b6‘ and as“b6“, the following applies:

The next procedure is the same as for the sixth and seventh detectors 25 and 26. In the expressions for

3- 2 I ^from we get for the light intensity:

The DC component of the signals from the sixth and seventh detectors 25, 26 is removed using the third differential amplifier 40 and from the eighth and ninth detectors 38 and 39 using the fourth differential amplifier 41, at the output of which we obtain the second and fourth resulting signals I02 and I04.

intensity, it is necessary to substitute T,T„ instead of R/R,,. By substituting

2. Interference of two beams, one of which is linearly and the other circularly or elliptically polarized

This type of interference provides an interference field that, for two perpendicular polarizations selected by a polarization divider, gives two signals in quadrature. Compared to the previous method, we can thus obtain twice as fine a phase angle division for the same number of detectors. The arrangement of a detection unit of this type with four detectors for signal detection is shown in Fig. 3.

Optical elements have the following values:

rotator 5 as equivalent to that described in Fig. 1, polarization asymmetric divider 42:

T^ = R„^0.12,

0.03, delay plates of the following reference numbers:

fifteenth 43 : S = 180°, Θ = 45° sixteenth 44 : δ = 180°, Θ 1 2 seventeenth 45 : δ = 90°, Θ = 45° eighteenth 48 : δ = 180°, Θ == 0° nineteenth 47 : δ = 180°, Θ = 45°

arctg

For the sixth and ninth detectors 25 and 39, if we neglect the influence of the additional plate 1, which is affected by the light beams ai‘bi and ai“bi, the following applies:

r Α1 Α2 .., r- Λ 6 ₌ 1 *1 0 7 7 i » - 'ς. s ₂ ~ 0 1 ⁰ J _t r~ J-sr 0 0 & » 7 ~ ^S F ^C 2. 0 0 fe,e 2^

If you set a condition where for ki, ka holds:

we get:

q^_EiC2

you you

and -0 }* 2k ₁₊ l(i 0 it 2 Her

and for intensities . _£ 2 Rs/^Rl p ♦ cos (/* V) + sira. (/ +

, _ _c 2 R„+Rj. ^E i —— where the polarization asymmetric divider 42 must meet the conditions:

^-(V/T )K _Z , R _(/ = f3+2/rJ R _i5 R„=ůj Rj^T,,

For the second and third detectors 10 and 11:

r· — —I ' - < *Ί 1 0 cost Í5ia/ 0 *- 1 A1 A2 • * · A5 — 0 0 ⁰ 2ζ 2 _C ÍSÍI2 ~ý~ cos -Έ- 1 0 i— < > k 2 2j -

?ΰ _β ^! ί ^τ

O

A1

A2

A5

For the case <5 = π we get:

I - ^{T l} $--2

Í3 = -^-5.(1-cos/) í,-#- T„(1^osf) hTo eliminate the DC component of all signals, we consider that we have the following signals available:

(pccs/J

R» ^1, Rj.

=ůi* fL·2 + + sira fy'* ·? ) _c 2 ' ^E 1 • Ea where Lz “ J j Lz > Lt

By dividing the signal I3 by the second resistor divider 54 in the ratio

Further, by adding I3 and Í3 ^l in the summing amplifier 49

Γζ R# t„ Rj.

and by subtracting the signal Í3 ^l in the fifth differential amplifier 48 we get:

L- í,-Ij = C ² -LcoiýWe assume that the DC component changes equally for all signals and we can therefore write:

and further by amplification in the ratio

Ri/j- Rj.

in the operational amplifier 50 and subtracting it from the signal li in the sixth differential amplifier 51 we get the second resulting signal I02:

R = (1 * Hl cos ť) · £/ = cos

2.” ^v + ^R 'Í ^R J ^L 1~ 3

- _R„+R.í.

and 9~ 1.

1+ k ₉ “>s(?+ ' ^E 1 fk^cosfy

-í>] ^l 02 =br, -k ^{R f} 'J. - To ₂ tf

COS (Ý + -Tf-)

Similarly, by subtracting the signal I2 from the value AsEpT^ in the seventh differential amplifier 52, we obtain the fourth resulting signal Ion ~

Further, by subtracting the resulting signals I02 and I03 in the eighth differential amplifier 53, we obtain the third resulting signal I03:

^! oí ⁼ l MR» i/2~co _S (/* £)

So we get the resulting signals:

/ _o ,(/ ₊ o+ř ₃ -^--T ₃ =u.

. _ 2 z ω i 77 \ ^l 02 (?*V ⁼ 'Φ ~ ' ^C ° ^S ~ ' í ₀₃ %) =b -V?ú-U ₂ -V7 ² ú)=ι/i: * ₂ · ^cos £) ^l 04 ' ^COS

The resulting signals are without a DC component and are shifted by —~—. One of the signals is created electronically by adding: cos [φ + —|

3. Interference of two beams of light with direct phase shift

As an example, we will give a detection unit with eight detectors for signal detection. The layout diagram is identical to Fig. 2, but different values are used for some of the polarization optics elements, while the effect of the additional plate 1 is neglected:

instead of the delay plates sixth 22 and seventh 23, the twentieth 55 is used: δ = 45°, Θ = 45° twenty-first 56: δ = 180°, 0=0° and instead of the delay plates thirteen 35 and fourteen 36, the twenty-second 57: 5 = 45°, Θ = 45° twenty-third 58: δ = 180°, 0 = 45°

The other optical elements of the detection unit are the same as in the first type of detection unit (Fig. 2J.

For the second and third detectors 10 and 11:

*Ί Γ ^- * A1 A2 • # * A7 *·»

O

O-1 ‘il. o e /#·

11Γ

1-1

1. 1 t -f-T

AND"·"

\í A2 • · « A7 — ·>-

0 0 0 э 1 0 0-7 —J [e‘* -V ?7T 0 e k- l/ÎVť o. _ÍT ~ 0 ^e-'T ^T

About 1 about

1-1 1

For the fourth and fifth detectors 15 and 16 we have:

I am a woman.

-7 1 1 1

About 1 1 About

/ňě' ť ^T θ - <r ± R Γ* S Bl B2 B7 *Ί 0 0 _ about /1 '/zé“ ^l T ^T !/φ 1 ** - - * « · - 0 1 >-» »·*

C

For the sixth and seventh detectors 25 and 20 the following applies:

For the values Cž = 1, S2 = 0 we get:

^l 3 ^R jl ^R D * ^{coS +} F^J ^l í ⁼ ¥ í-j]

For the eighth and ninth detectors 38 and 30 we have:

Bl

B7

About í| 1 About

. £ θ £ H Γη ~ í j —pz Ί--Π Γ r ✓ 0 I ^E / d and also -

Furthermore, for the values C-; = 0, Ss = 1, we obtain V >

mute: in '

Tg, Ί + cos /a, —

E^ in„ about

Ί*

Elimination of the DC component is the same as in the first case.

Examples of embodiments of devices for detecting interference signals, using the above method of detecting n pairs of signals in quadrature mutually phase-shifted by

7Γ angle — in a laser interferometer for 2n different forms of light polarization in the parts of the interfering beams, are shown in the figures.

Fig. 1 presents the case where orthogonally linearly polarized light beams are converted to counter-circularly polarized ones and the detection of interference signals is performed using two pairs of detectors. We assume a rectangular coordinate system x, y, z, where the z axis is the beam propagation axis and the planes of oscillation of the measuring beam a and the reference beam b fall on the x and y axes, respectively. In the path of the unified beam from the interferometer aobe itself, an additional plate 1 is first inserted under the Brewster angle for one polarization, the reflected beam c of the second polarization is reflected from the mirror 3 and falls on the first detector 4. In the path of the transmitted unified beam ab, a rotator 5 is placed before falling on the first approximately non-polarizing splitter 6. The reflected beam a'bi first passes through the first linear λ/4 delay plate 7, then the second linear A/2 delay plate 8 and on the first polarizing splitter 9 it is divided into the reflected beam ai'bi', falling on the second detector 10, and the transmitted beam ai"bi" falling on the third detector 11. The beam azbž passing through the first approximately non-polarizing splitter 6 first passes through the third linear λ/4 delay plate 12, then the quarter-linear A/2 by the delay plate 13 and on the second polarizing divider 14 it is divided into the reflected beam aSW incident on the fourth detector 15 and the transmitted beam a2"b2" incident on the fifth detector 16. The electrical signal from the second detector 10 arrives at the first differential amplifier 17, as well as the signal from the third detector 11 via the first resistive divider 19. The signals from the fourth detector 15 and the fifth detector 16 arrive at the second differential amplifier 13.

Fig. 2 is a similar case, but with twice the number of detector pairs. An additional plate 1 with a dielectric layer 2 is first inserted into the path of the unified beam from the interferometer, which reflects the beam c onto the first detector 4. A rotator 5 is placed in the path of the passing unified beam ab, through which the unified beam ab passes before impinging on the first approximately non-polarizing splitter 6. The reflected beam aibi first passes through the fifth linear λ/2 delay plate 20 and then impinges on the second approximately non-polarizing splitter 21, where it is divided into the reflected beam a3b3 and the transmitted beam ai'»4. The beam aobs first passes through the sixth linear λ/4 delay plate 22, then through the seventh linear λ/2 delay plate 23 and at the third polarizing splitter 24 it is divided into the transmitted beam a3 ^l b3', incident on the sixth detector 25 and into the reflected beam ag"b3" incident on the seventh detector 26. The beam a4b4 first passes through the eighth linear λ/4 delay plate 27, then through the ninth linear λ/2 delay plate 28 and at the fourth polarizing splitter 29 it is divided into the reflected beam a4'b4* incident on the second detector 10 and into the transmitted beam a4"b4" incident on the third detector 11. The beam a-di2 passing through the first approximately non-polarizing splitter 6 first passes through the tenth linear λ/2 delay plate 30 and then impinges on a third approximately non-polarizing splitter 31, where it is divided into a reflected beam ajbs and a transmitted beam aebs. The beam agbg first passes through the eleventh linear λ/4 delay plate 32, then through the twelfth linear λ/2 delay plate 33 and at the fifth polarizing splitter 34 is divided into the reflected beam ag'bg ⁶ incident on the fourth detector 15 and the transmitted beam ag"bg" incident on the fifth detector 16. The beam a first passes through the thirteenth linear λ/4 delay plate 35, then through the fourteenth linear λ/2 delay plate 36 and at the sixth polarizing splitter 37 is divided into the reflected beam as'b6', incident on the eighth detector 38 and the transmitted beam as''bs" incident on the ninth detector 39.

The electrical signal from the second detector 10 comes to the first differential amplifier 17, as does the signal from the third detector 11 through the first resistor divider 19. The signals from the sixth detector 25 and the seventh detector 26 come to the third differential amplifier 40. The signals from the fourth detector 15 and the fifth detector 18 come to the second differential amplifier 18. The signals from the eighth detector 38 and the ninth detector 39 come to the fourth differential amplifier 41.

Fig. 3 shows an example of a detection unit operating in one of two branches with two beams, one of which is linearly and the other circularly polarized. In the path of the unified beam from the interferometer aeba itself, an additional plate 1 with a dielectric layer 2 is first inserted, which reflects the beam c onto the first detector 4. In the path of the passing unified beam ab, a rotator 5 is placed, through which the unified beam ab passes before impinging on the polarization-asymmetric splitter 42. The reflected beam a«bi passes successively through the fifteenth linear λ/2 delay plate 43, then the sixteenth linear λ/2 delay plate 44 and then the seventeenth linear λ/4 delay plate 45 and finally impinges on the first polarizing splitter 9, where it is divided into the reflected beam ai'bi', impinging on the sixth detector 25, and the transmitted beam ai“bi”, impinging on the ninth detector 39. The beam azb? passing through the polarization-asymmetric divider 42, it first proceeds through the eighteenth linear λ/2 delay plate 4S, then through the nineteenth linear λ/2 delay plate 47 and falls on the second polarizing divider 14, where it is divided into the reflected beam azW, falling on the second detector 10, and the transmitted beam a2“b2 ^ťi , falling on the third detector 11. The signal from the third detector 11 is fed through the second resistive divider 54 to the fifth differential amplifier 48 and simultaneously to the summing amplifier 49, to which the signal from the second detector 10 also arrives. An operational amplifier 50 is included after the summing amplifier 49. The signal from the sixth detector 25 is fed to the sixth differential amplifier 51 and the signal from the ninth detector 39 arrives at the seventh differential amplifier 52. The output signals from the sixth and seventh differential amplifiers 51 and 52 arrive at the third differential amplifier 53.

Fig. 4 shows an example of a detection unit design, where in both branches, for one pair of detectors, direct phase p:shift of individual partial interfering beams is used. Fig. 4 is identical to Fig. 2 with the difference that in the beam path ajb3, instead of the sixth linear λ/4 delay plate 22 and the seventh linear λ/2 delay plate 23, the twentieth linear λ/8 delay plate 55 and the twenty-first linear λ/2 delay plate 56 are included, and in the beam path asbs, instead of the thirteenth linear λ/4 delay plate 35 and the fourteenth linear λ/2 delay plate 36, the twenty-second linear λ/8 delay plate 57 and the twenty-third linear 7/2 delay plate 38 are included.

The detection units for the three forms of light polarization mentioned above operate in such a way that the combined light beams ab from the interferometer itself are divided into partial light beams aibi, a?bz and, by the action of combined optical elements, they are converted to the desired form of polarization and, in turn, the desired phase shift between the individual partial beams is given. The combined optical elements consist of a series-connected approximately non-subordinating splitter, birefringent elements and a polarizing splitter. The approximately non-subordinating splitter in cooperation with the birefringent elements serves to divide the beam and to transform the form of polarization with the creation of the appropriate phase shift between the partial beams. The polarizing splitter selects two polarizations (usually orthogonally linear), which provide the desired interference signals. The function of the detection units is further explained directly on the basis of exemplary embodiments.

The principle of operation of the detection unit according to Fig. 1 is as follows: The unified beam aebň from the interferometer itself, which enters the detection unit, contains the measuring aa and the reference beam by which are orthogonally linearly polarized and have a common propagation axis. We assume a rectangular coordinate system x, y, z, where the z axis is the beam propagation axis. The electric field vectors of the measuring ae, respectively. reference beam ba fall into the respective axes and are denoted by E _x , E _y . The additional plate 1, located at the Brewster angle to the plane of oscillations of the reference beam, divides a small part c of the intensity of the measuring beam as, which after reflection from the mirror 3 falls on the first detector 4 and the obtained signal serves to check the beam interruption in the laser interferometer. The advancing beam ab passes through a left-handed rotator 5 with a delay angle of 90°, which rotates the planes of oscillation of the reference and measurement unified beams by 45°. At the first approximately non-polarizing splitter 6, the beam ab is divided into sub-beams aibi and asbx. The reflected beam aibi first passes through the first linear λ/4 delay plate 7 (δ = 90°, Θ 01), where it is converted into circularly polarized beams of opposite orientation (elliptically polarized with approximately the same azimuthal angle). The phase shift is set using the second linear λ/2 delay plate 8 (δ = 180°, Θ = 0). When the beam aibi hits the first polarizing splitter 0, it is split into beams ai'bi' and ai"bi", which have planes of oscillation perpendicular to each other, as a result of which the signals on the second and third detectors 16 and 11 are in antiphase and have a basic phase shift of zero. In the passing beam azbs, the functions of the optical elements, i.e. the third linear λ/4 delay plate 12 (δ = 90°, Θ = 0), the fourth linear λ/2 delay plate 13 (δ = 180°, Θ = 67.5°) and the second polarizing divider 14, similar to the arbi beam with the difference that by rotating the azimuth of the fourth linear λ/2 delay plate 13 to an angle Θ = 67.5°, it is achieved that the signals on the fourth and fifth detectors 15 and 16 are phase shifted by ττ/2 relative to the first pair of signals on the second and third detectors 10 and 11, while they are in antiphase with each other, The geometric arrangement of the optical elements remains in one plane. The above arrangement of the detection unit achieves full utilization of the beam energy from the interferometer and removal of the DC component using two signals in antiphase. As was derived, the resolution of the detection unit can be increased electronically. The DC component of the signals is removed using the first and second differential amplifiers 17 and 18, signals with the same level, but in antiphase from the second and third detectors 16, 11 and the fourth and fifth detectors 15, 16. The same signal level is achieved by the first resistive divider 19. The resulting signals Ιοί, I33 from the differential amplifiers 17 and 18 then no longer contain a DC component.

The principle of the detection unit in Fig. 2 is similar. The unified beam a or b from the interferometer itself first falls on an additional plate 1 with a dielectric layer 2, by means of which a small part c of it is divided to the first detector 4 for indicating the beam interruption in the laser interferometer. The special dielectric layers 2 on the additional plate 1 cause the additional plate 1 to have the same effect as in the previous case, i.e. that only a small part of the intensity of the measuring beam ae is reflected from one dielectric layer; The second dielectric layer on the opposite side of the plate represents an anti-reflection layer for both beams, the measuring a and the reference b. The passing beam ab then impinges on the left-handed rotator 5 (δ =·= 90°, a = 45°), where the plane of oscillations of the reference and measuring beams as a whole is rotated by 45°, and then on the first approximately non-polarizing splitter 6, where it is divided into partial beams aibi and a2b?„; in the path of these divided beams are placed the fifth and tenth linear λ/2 delay plates 20 and 30 (δ = 180°, Θ = 45°), which rotate the planes of oscillations by 90°, so that after double reflection, or passage through the second and third approximately non-polarizing splitters. 21 and 31, the original polarization state is preserved in the beams asbs and asbs as in the beam ab. Then, at beams aobs, aebs, conversion from orthogonal linearly polarized beams to circularly polarized beams of opposite orientation (for beams aeb4 and asbs to elliptically polarized with approximately the same azimuthal angle) was performed using the sixth, eighth, eleventh and thirteenth linear λ/4 delay plates 22, 27, 32 and 35 having the same value (δ = 90°, (j = 0°). By rotating the azimuth of the linear λ/2 delay plates located behind them, relative to the ninth linear λ/2 delay plate 28 (δ = 180°, Θ = 0°)

3 0 3 31.

By the angles: 11.25° for the seventh delay plate 23 (δ = 180°, Θ = 11.25°), 67.5° for the twelfth delay plate 33 (δ = 180°, Θ = 67.5°) and 33.75° for the fourteenth delay plate 36 (δ = 180°, Θ = 33.75°), it is achieved that the signals on the detectors are always phase-shifted by —, while being in antiphase with each other. The geometric arrangement of the optical elements remains in one plane. Again, full use of the beam energy from the interferometer itself is achieved and twice the resolution compared to the detection unit, where there are only two signals in quadrature. The DC component of the signals is also removed by means of two signals in antiphase. A further increase in resolution is again possible electronically. The DC component of the signals is removed in the same way as in the previous case. The signals in antiphase at the second and third, sixth and seventh detectors 10 and 11, 25 and 26, as well as at the fourth and fifth, eighth and ninth detectors 15 and 16, 38 and 39 are fed to the inputs of the first and third differential amplifiers 17 and 40 and the second and fourth differential amplifiers 18 and 41, at the output of which the resulting signals Ιοί, I02, I03 and I04 no longer contain a DC component. The same level of the signals is ensured by the first resistive divider 19.

Fig. 3 shows the case where a combination of circularly and linearly polarized light is created in one branch of the detection unit from the originally orthogonally linearly polarized beams from the interferometer itself. First, the orthogonally linearly polarized unified beam a or b from the interferometer itself passes through an additional plate 1 with dielectric layers 2, which, together with the first detector 4, serves to check for beam interruption. Then it passes through a left-handed rotator 5 (<S = 90°, a = 45°), where the system of orthogonally linearly polarized beams a and b is rotated by an angle of 45°. On the polarization-asymmetric splitter 42 with dielectric layers with the properties: T, = R,, = 0.12, T„ = R^ = 0.83, R„ = (3 + 2V2 jR^, the division into two partial linearly polarized unified beams atbi and ažbž occurs. In the path of the reflected partial beam aibi, in which the components of the linearly polarized light measuring ai and the reference bt make an angle of 135°, the fifteenth linear Λ/2 delay plate 43 (á = 180°, Θ = 45°) is placed first and behind it the sixteenth linear λ/2 delay plate 44 (<5 = 180°, Θ = —g—arctgf ), so that the planes of oscillations of the measuring ai and the reference beam bi are rotated so that one of them falls into the respective coordinate axis and the other is under 45°. The following seventeenth linear λ/4 delay plate 45 (ó = 90°, Θ = 45°) then causes the component of linearly polarized light below 45° to remain unchanged, while the second component is formed into circularly polarized light. On the first polarizing splitter 9, the light beam consisting of linearly and circularly polarized light is divided so that the incident light beams a2b? and ai“bi“ have a phase shift of +45° and —45° on the sixth detector 25 and the ninth detector 39; thus, we obtain two signals in quadrature. The passing partial linearly polarized beam a2b? first proceeds through the eighteenth linear λ/2 delay plate 46 (<? = = 180°, Θ = 0°) and the nineteenth linear λ/2 delay plate 47 (á = 180°, Θ = 45°), which serves to correct small phase shifts and to equalize the intensities, and then it falls on the second polarizing divider 14, where it is divided into beams a2'bž' and a2“b2 ^u , which fall on the second and third detectors 10 and 11, on which a signal with a basic zero shift of 0° is generated, and then a signal in antiphase, which is used to eliminate the DC component of the signals. The DC component of all signals is removed and a signal with a phase shift —~— is created using summing, operational and differential amplifiers. By subtracting the signal from the detector 10 from the signal from the detector 11 divided in the second resistive divider 54 using the fifth differential amplifier 48, we obtain the first resulting signal I01 (p + 0) with a basic phase shift of 0° and without a DC component. By adding up both input signals from input of the differential amplifier 48 in the summing amplifier 40, amplifying this signal in the ratio A3 = —- ~ in the operational amplifier 50 and subtracting this signal from the signal from the sixth detector 25 in the sixth differential amplifier 51 we obtain the second resulting signal I02 φ + —) with a phase shift—without a DC component. Similarly, by subtracting the signal from the ninth detector 39 from the output signal from the operational amplifier 50 in the seventh differential amplifier 52 we obtain the fourth resulting signal I04

with a phase shift and without a DC component. Finally, by subtracting the fourth resulting signal I04 j from the second resulting signal (I02 ~—J in the eighth differential amplifier 53, we obtain the third resulting signal I03 \φ + —x—) with a phase shift —-— without a DC component.

Fig. 4 shows an example of the use of direct phase shift in the detection unit, in contrast to Fig. 2, where the orthogonally linearly polarized beams are everywhere converted to counter-rotating circularly (elliptically) polarized beams. In Fig. 4, in both branches, always for one pair of detectors, namely for the sixth 23 and the seventh 26 and for the eighth 36 and the ninth 39, the light beams asln and asbs remain orthogonally linearly polarized at an angle of 45°. The twenty-second 2/4 linear delay plates 55 (<$ = 90°, Θ = —45°) and 57 (<S = 90°, Θ = 45°) perform a direct phase shift so that, with respect to the basic signal with a zero phase shift of 0 ^c on the second detector 10 (whereas the signal on the third detector 11 is in antiphase), the sixth detector 25 has a phase shift of 45 ³ (whereas the signal on the seventh detector 26 is in antiphase with respect to the signal on 25), the fourth detector 15 gives a signal shifted by 90 ² (whereas the signal on the fifth detector 16 is in antiphase with respect to it) and the signal from the eighth detector 38 has a phase shift of 135° (whereas the signal on the ninth detector 39 is in antiphase with respect to it). The other members of the polarizing optics adjust the polarization state so that the phase shifts and contrast of the interference signals can be established even when using only approximately polarizing splitters, the first 6, the second 21 and the third 31, which, however, similarly to the previous cases, are assumed to have the same properties (i.e. simultaneous layering).

Claims (6)

Subject 1. A method for detecting multiple phase-shifted interference signals in a laser interferometer, e.g., n pairs of signals in a quadrate 7Γver, phase-shifted relative to one another from a high-resolution laser interferometer and eliminating a DC signal component, The interference induced is gradually treated by dividing the intensities, passing through the optical medium with a different speed of light propagation in two orthogonal directions and using a polarizing passage, respectively. the reflection of the light beams at the optical interface, thereby achieving a change in the polarization state of the sub-beams with the desired phase difference, which upon impact on the detectors produces phase shift signals. 2. An apparatus for carrying out a method for detecting a plurality of phase-shifted interference signals according to claim 1, characterized in that it comprises at least one combined optical member consisting of a series-connected approximately non-polarizing divider (6, 21, 31) and a polarizing divider (9, 14, 24). 29, 34, 37) interposed with birefringent optical elements, for example delay pads (7, 8, 12, 13, 20, 22, 23, 27, 28, 30, 32, 33, 35, OF THE INVENTION 36, 43, 44, 45, 46, 47, 55, 56, 57, 58), or the birefringent optical elements are located in front of an approximately non-polarizing divider (8, 21, 31). Detection device according to Claim 2, characterized in that the combined optical elements consist of at least one series-aligned polarization-asymmetric optical splitter (42) and a polarizing splitter (9, 14) between which birefringent elements, for example delay plates (43, 44, 45, 46, 47) or the birefringent optical elements are located in front of the polarizing asymmetric optical divider (42). Detection device according to Claims 2 and 3, characterized in that it comprises in the path of orthogonally linearly polarized beams from its own interferometer (ao, bo) an additional plate (1), optionally provided with a dielectric layer (2). Detection device according to Claims 2, 3 and 4, characterized in that the outputs of the fourth and fifth detectors (15, 16) are connected to the input of the first differential amplifier (17). 6. A detection device according to claim 2, 3 or 4, characterized in that the outputs of the second and third, sixth and ninth detectors (10, 11, 25, 39) are connected via a resistive divider (54) to the inputs of the summation and differential amplifiers (48). 49, 50, 51, 52, 53).