KR100898327B1 - Compensation method of nonlinear error of interferometer by the angular alignment of a wave plate - Google Patents

Abstract

The present invention relates to a nonlinear error compensation method of an interferometer by angular alignment of the waveplate to compensate for nonlinear errors by rearranging the waveplate so that the nonlinear error of the interferometer is minimized. Means for achieving this, including a first polarized light splitter and interfering the light incident through the double-pass interference, the second and third polarized light splitter and a half-wave plate and a quarter wave plate combined CLAIMS 1. A nonlinear error compensation method of an interferometer for obtaining an interference signal through a signal detector, comprising: a first step of measuring optical characteristics of first, second, and third polarized light splitters in a matrix form; Obtaining a rotation matrix of the half wave plate and the quarter wave plate; A third step of obtaining a nonlinear error using a matrix of the first, second, and third polarized light splitters, and a rotation matrix of the half wave plate and the quarter wave plate; A fourth step of calculating a minimum angular alignment value of the half-wave plate and the quarter-wave plate from the nonlinear error for each rotation angle of the half-wave plate and the quarter-wave plate; And a fifth step of compensating and rotating the half-wave plate and the quarter-wave plate by the minimum angle alignment value by the minimum angle alignment value. According to the present invention, it is possible to construct an interferometer having high resolution and accuracy through nonlinear error compensation.

Homodyne interferometer, optical interferometer, nonlinear error compensation, wave plate alignment

Description

Compensation method of nonlinear error of interferometer by the angular alignment of a wave plate}

The present invention relates to a nonlinear error compensation method of the interferometer through the angle alignment of the wave plate, and more particularly, the interferometer through the angle alignment of the wave plate for compensating the nonlinear error by rearranging the wave plate to minimize the nonlinear error of the interferometer Nonlinear error compensation method.

Laser interferometers are very good at measuring precision displacement and have been used as sensors in measuring precision displacement over the past decades. Recently, with the rapid development of nanotechnology, the demand for such a precision displacement measurement sensor is expanding and its field of application is also diversifying.

In the case of semiconductor manufacturing process equipment, a lithography equipment can be mentioned as a representative example. A precision sensor capable of emitting a control signal to determine an accurate position is one of the key components, and therefore a laser displacement sensor with high accuracy is essential. Element. In addition, laser displacement sensors play an important role in LCD and PDP manufacturing processes. Recently, such a precise displacement measurement technique is indispensable in implementing bio-technology, and has become a core technology.

Therefore, the higher the resolution and accuracy of the laser displacement sensor, the better it will be able to produce better products in the industry where it is applied.

In addition, the homodyne interferometer used as a kind of interferometer is very simple in the configuration of the optical system and the configuration of the light detector part is not complicated, so the process of extracting the phase value from the interference signal of laser light is also very simple. It also has a high resolution (sub-nanometer) that can be used as a precision displacement sensor.

However, the homodyne interferometer has a disadvantage in that it is sensitive to noise and alignment of the optical system because the intensity of the interference fringe is used as a signal.

The error factors of the laser interferometer include the instability of the laser frequency as a light source, the alignment error, the influence of vibration, the change of the air refractive index according to the temperature change, and the measurement error according to the air flow.

Ultimately, however, the nonlinear error and noise of the interferometer itself are important factors for achieving high resolution, and the error caused by the nonlinearity generated by the interferometer is the biggest limitation in the measurement, especially when high resolution and absolute measurement accuracy are required in a short measurement range. have.

Nonlinear errors in displacement measurements using homodyne interferometers are mainly due to factors such as polarization leakage (wave plate, beam splitter, polarizer instability) in the optical system.

1 is a graph showing a nonlinear error of an interferometer, and FIG. 2 is a Lissajous graph of an interferometer having a nonlinear error. As shown in Fig. 1, the relationship between the phase and the displacement in the homodyne interferometer is linear (1) in the ideal case, but nonlinear (3) in the real case. Typical homodyne interferometers have a magnitude of nonlinear error of about 3-4 nm.

Also, as shown in Fig. 2, the Lissajous graph of an interferometer having a nonlinear error is circular 5 in an ideal case, but elliptical 7 in an actual case.

As a conventional method for reducing such a nonlinear error, a compensation method by selecting a gain value according to the performance of an elliptical fitting method or a polarization beam splitter has been proposed.

Elliptic curve fitting is a method for compensating for nonlinearity errors in homodyne interferometers. When the signal from the interferometer is plotted in a lissajou graph, it is an ellipse rather than a perfect circle equation. Therefore, the elliptic curve fitting can be used to calculate the exact phase value, thereby reducing the nonlinearity error. However, the elliptic curve fitting must first calculate the coefficient values of the elliptic equation with the measured values obtained through the measurement. Therefore, there is a disadvantage that it takes a lot of time for this to be difficult to apply to real-time position control.

 The compensation method by selecting a gain value according to the performance of the polarized light splitter is a method of reducing the nonlinear error by adjusting the gain value in the photo detector according to the performance of the polarized light splitter. However, since this method selects the gain value by using a signal before one period, compensation is not possible in real time.

The present invention is to solve the above problems, an object of the present invention to minimize the non-linear error of the non-linear interferometer through the angle alignment of the wave plate for rearranging the angle of the wave plate in accordance with the optical characteristics of the polarizing light splitter An error compensation method is provided.

As a means for achieving the above object,

It includes a first polarized light splitter and interferes the light incident through the double pass interference unit, and the interference signal is transmitted through the second and third polarized light splitters and a signal detector in which the half wave plate and the quarter wave plate are combined. A nonlinear error compensation method of an interferometer comprising: a first step of measuring optical characteristics of first, second, and third polarized light splitters and obtaining them in a matrix form; Obtaining a rotation matrix of the half wave plate and the quarter wave plate; A third step of obtaining a nonlinear error using a matrix of the first, second, and third polarized light splitters, and a rotation matrix of the half wave plate and the quarter wave plate; A fourth step of calculating a minimum angular alignment value of the half-wave plate and the quarter-wave plate from the nonlinear error for each rotation angle of the half-wave plate and the quarter-wave plate; And a fifth step of compensating and rotating the half-wave plate and the quarter-wave plate by the minimum angle alignment value by the minimum angle alignment value.

In addition, the optical characteristics of each polarizing ray splitter include: first measuring means for measuring light reflected from the light splitter by the light transmitted from the light source and transmitted through the rotating first polarizer; Second measuring means for measuring the light transmitted from the light splitter and the light reflected from the first, second and third polarized light splitters to be measured; A third measurement means for measuring the light transmitted through the second polarizer rotating the light transmitted from the first, second, and third polarized light splitters; and the Jones matrix according to the transmission and reflection obtained by using the polarization ratio measured from the second polarizer. to be.

In addition, the Jones matrix is expressed according to reflection and transmission.

에 따르는 행렬인 것이 특징이다. 이때 t는 빛의 투과율, r은 빛의 반사율, p는 P편광, s는 S편광, c는 크로스토크(crosstalk)를 나타낸다.

It is characterized by a matrix according to. Where t is light transmittance, r is light reflectance, p is P polarized light, s is S polarized light, and c is crosstalk.

,In addition, the rotation matrix of the quarter wave plate and the half wave plate is the Jones matrix according to the following equation,

,

는 각도 정렬오차인 것이 특징이다.here,

Is an angle alignment error.

The interferometer may be a homodyne interference optical system, a phase displacement interference optical system, or a heterodyne interference optical system.

In addition, the minimum angle alignment value is

에 따라 계산되고, 여기서, E_nonlinear는 비선형오차를, ψ_QWP1은 기준팔(reference arm)의 사분파장판의 회전각도를, ψ_QWP2는 측정팔(measurement arm)의 사분파장파의 회전각도를, ψ_QWP3은 검출부의 사분파장판의 회전각도를, 그리고 ψ_HWP 는 검출부의 반파장판의 회전각도를 각각 나타내는 것이 특징이다.

Where E _nonlinear is the nonlinear error, ψ _QWP1 is the angle of rotation of the quadrant plate of the reference arm, and ψ _QWP2 is the angle of rotation of the quarter wave of the measurement arm, ψ _QWP3 represents the rotation angle of the _quarter- wave plate of the detector, and ψ _HWP represents the rotation angle of the half-wave plate of the detector.

According to the present invention, it is possible to construct an interferometer having high resolution and accuracy through nonlinear error compensation.

Real-time compensation is also possible in systems requiring high resolution.

It can also be used in all applications requiring precise position control, such as manufacturers of displacement measurement sensors, manufacturers of semiconductors, LCDs, and PDP equipment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to components of each drawing, the same reference numerals are used for the same components as much as possible even if they are shown in different drawings.

In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

First, the configuration and operation of the interferometer will be described and the nonlinear error compensation method of the interferometer will be described.

(Configuration of Interferometer)

3 is a block diagram showing the configuration of an interferometer according to the present invention. The interferometer according to the present invention includes an interference part 100 that largely interferes with light generated from the light source 30, and a signal detection part 200 that detects an interference signal from the light emitted from the interference part 100. It is done by

The interference unit 100 includes a light source 30, a first polarized light splitter PBS1, and a polarization changing unit 40.

Light generated by the light source 30 is spectroscopically transmitted and reflected by the first polarized light splitter PBS1. The polarization changing means 40 changes the polarization state of each of the transmitted light and the reflected light by the double pass method.

The polarization changing means 40 is a light transmitted through the first and second quarter wave plates (QWP1, QWP2) and the first and second quarter wave plates (QWP1, QWP2) are installed perpendicular to the transmitted light and reflected light, respectively. The first and second reflecting mirrors 41 and 42 for reflecting back to the first and second quarter wave plates QWP1 and QWP2 are included. In addition, the polarization change means 40 further comprises a corner cube (CC) for changing the traveling direction of the light. The corner cube CC is disposed to face the first quarter wave plate QWP1 around the first polarized light splitter PBS1.

The signal detector 200 includes a right-angle prism 50 that vertically changes the light emitted from the interference unit 100, a third quarter wave plate QWP3 that changes the polarization state of the light, and the polarized light. And a light splitter (NPBS) that reflects or transmits light.

In addition, the signal detection unit 200 is provided by the second polarized light splitter (PBS2) and the second polarized light splitter (PBS2) that receives the light transmitted from the light splitter (NPBS) and separates the light according to the polarization component again. And first and second photodetectors D1 and D2 for detecting the separated light, respectively. In addition, the signal detector 200 separates the half-wave plate (HWP) for changing the polarization state of the light reflected from the light splitter (NPBS) and the light passing through the half-wave plate (HWP) according to the polarization component And third and fourth photodetectors D3 and D4 for detecting the reflected light and the transmitted light separated from the third polarized light splitter PBS3 and the third polarized light splitter PBS3, respectively. In addition, the first to fourth photodetectors D1 to D4 collect interference signals from the data collection unit 60, respectively, and detect the phase from the phase detector 70 from the interference signals.

(Operation of interferometer)

In the interferometer according to the invention, the light source 30 is a frequency stabilized He-Ne laser and produces light rays having a wavelength of 632.8 nm. In this case, the light beam is incident on the first polarized light splitter PBS1 at an angle of 45 degrees. Accordingly, the light beam irradiated to the first polarized light splitter PBS1 is divided into transmitted light (P component) and reflected light (S component) polarized at a 45 ° angle.

The divided transmitted light and the reflected light pass through the first and second quarter wave plates QWP1 and QWP2, respectively, and are reflected by the first and second reflectors 41 and 42, respectively. Pass through the splitter plates QWP1 and QWP2. At this time, since the first and second quarter wave plates QWP1 and QWP2 are aligned at 45 ° angles, the first and second quarter wave plates QWP1 and QWP2 are linearly transmitted and reflected light. The polarization state is changed to circularly polarized light while passing through). The circular flat light is again passed through the first and second quadrant plates QWP1 and QWP2, and the polarization state is changed to the original linear flat light. In particular, the linear polarization at this time is changed to linear polarization perpendicular to the original linear polarization component.

On the other hand, the light rays passing through the second quarter wave plate QWP2 are reflected by the corner cube CC again to be returned to the first polarized light splitter PBS1. Since the linearly polarized light returned in this way is converted into a vertical polarization component, the linearly polarized light is transmitted or reflected by the first quarter wave plate QWP1. At this time, the light transmitted by the first polarization ray splitter PBS1 is reflected because the polarization is vertically changed, and the reflected light is transmitted because the polarization is vertically changed. Similarly, after passing through the first and second quarter wave plates QWP1 and QWP2, they are reflected by the first and second reflecting mirrors 41 and 42, and after passing through the first and second quarter wave plates QWP1 and QWP2, 1 is incident to the polarizing light splitter PBS1 and exits from the interference part 100.

The light emitted from the interference part 100 is redirected by the rectangular prism 50. The polarized light passes through the combination process of the NPBS, the second and third polarized light splitters PBS2 and PBS3, the third quarter wave plate QWP3 and the half wave plate HWP. 0 °, 90 °, 180 °, and 270 °. These interference signals are detected by four first to fourth photodetectors D1 to D4, respectively. The detected interference signal is collected by the data collector 60, and the phase detector 70 detects the phase of each interference signal.

Nonlinear Error Compensation Method of Interferometer

4 is a flowchart illustrating a nonlinear error compensation method according to the present invention. As shown in FIG. 4, the first polarized light splitter PBS1 includes a first polarized light splitter PBS1 and interferes the incident light through the double pass type interference part 100, and the second and third polarized light splitters In the nonlinear error compensating method of an interferometer, which obtains an interference signal through a signal detector 200 combining PBS2, PBS3) and a half wave plate (HWP) and a quarter wave plate (QWP), the first, second and third polarization beam splitters ( A first step (S100) of measuring optical characteristics of the PBS1) to obtain a matrix; Obtaining a rotation matrix of the half-wave plate (HWP) and the quarter-wave plate (QWP) (S200); A third step (S300) of obtaining a nonlinear error using a matrix of the first, second, and third polarized light splitters PBS1, PBS2, and PBS3, and a rotation matrix of the half-wave plate HWP and the quarter-wave plate QWP; A fourth step (S400) of calculating a minimum angle alignment value of the half wave plate (HWP) and the quarter wave plate (QWP) from the nonlinear error for each rotation angle of the half wave plate (HWP) and the quarter wave plate (QWP); And a fifth step (S500) of compensating the half-wave plate (HWP) and the quarter-wave plate (QWP) by the minimum angle alignment value and rotating it by the minimum angle alignment value.

5 is a schematic view showing the configuration of measuring means for measuring the optical properties of the polarizing light splitter according to the present invention. As shown in FIG. 5, the first step S100 measures the optical characteristics of the first, second, and third polarized light splitters PBS1, PBS2, and PBS3 to obtain a Jones matrix. To obtain the Jones matrix, the characteristic measuring means as shown in FIG. 5 is used. Measurement of the optical characteristics through such a characteristic measuring means is performed as follows. In this specification, the measurement using the first polarized light splitter PBS1 has been described, and the second and third polarized light splitters PBS2 and PBS3 also measure optical characteristics in the same manner.

The light obtained by transmitting the light generated from the light source 30 'through the rotating first polarizer 10 is incident to the light splitter NPBS.

The reflected light split by the light splitter NPBS is measured by the first measuring means M1, and the transmitted light is incident on the first polarized light splitter PBS1 which is the measurement target. The light reflected from the first polarized light splitter PBS1 is measured by the second measuring means M2, and the transmitted light is incident on the rotating second polarizer 20. The light transmitted through the second polarizer 20 is measured by the third measuring means M3. In this case, the first and second polarizers 10 and 20 use a Glentomson polarizer having a polarization resolution of 1: 10000, and the first, second and third measuring means M1, M2, and M3 use photodiodes.

Thus, the Jones matrix according to the transmittance (T) and the reflectance (R) using the polarization ratio measured when the reflectance and the transmittance are maximum with the first, second, and third measuring means (M1, M2, M3) 1] can be obtained.

Where t is light transmittance, r is light reflectance, p is P polarized light, s is S polarized light, and c is crosstalk.

In the present invention, the Jones matrix of the polarized light splitter PBS is characterized as described above. This is to consider all polarization leakage components generated as light passes or reflects through the polarized light splitter PBS.

For the present invention, as a result of measuring optical characteristics of an arbitrary polarization splitter (PBS), a Jones matrix as shown in Equation 2 can be obtained.

The second step S200 is to obtain a rotation matrix of the half wave plate HWP and the quarter wave plate QWP. The rotation matrix of the wave plate is obtained by using the Jones matrix of the wave plate. In general, the Jones matrix W _o of the wave plate is expressed by Equation 3.

In addition, the rotation matrix W of the wave plate is obtained by multiplying R before and after the Jones matrix W _{o as} shown in [Equation 4].

는 파장 지연오차(phase retardance error)를,

는 회전각도를 각각 나타낸다.Here, R is a rotation matrix for the rotation angle (ψ), Γ is a relative phase change according to the polarization component,

Phase retardance error,

Represents the rotation angle, respectively.

Substituting the values corresponding to the half wave plate (HWP) and the quarter wave plate (QWP) into the variables of Equation 4, respectively, can be obtained as shown in Equations 5 and 6 below. . [Equation 5] represents the rotation matrix of the quarter wave plate (QWP), and [Equation 6] represents the rotation matrix of the half wave plate (HWP).

The third step (S300) is a step of obtaining a nonlinear error. The nonlinear error is generally known, and the nonlinear error of the interferometer can be obtained by calculating the nonlinear degree of phase information obtained from the interferometer. When the experiment is performed to prove the present invention, in order to obtain a nonlinear error due to the angle alignment of the wave plate, the wave plate is rotated at a constant angle within 0.5 ° and the nonlinear error according to the angle alignment value is obtained through calculation.

The fourth step S400 is a step of calculating a minimum angle alignment value from the nonlinear error calculated in the third step S300. That is, since the nonlinear error of the wavelength plate varies according to the optical characteristics of the first polarized light splitter PBS1, the minimum angle alignment value is calculated by assuming the nonlinear error of each wavelength plate as a function of the angle error.

Therefore, the minimum angle alignment value

으로 나타낼 수 있다. 여기서, E_nonlinear는 비선형오차를, ψ_QWP1은 기준팔(reference arm)의 사분파장판의 회전각도를, ψ_QWP2는 측정팔(measurement arm)의 사분파장파의 회전각도를, ψ_QWP3은 검출부의 사분파장판의 회전각도를, 그리고 ψ_HWP 는 검출부의 반파장판의 회 전각도를 각각 나타낸다. 즉, 각 파장판의 회전각에 따라 비선형오차의 크기가 달라지게 되는데, 제 1, 2, 3 편광광선분할기(PBS1,PBS2,PBS3)에 기인하는 편광 누설 성분에 의한 비선형 오차가 최소가 되도록 하는 파장판의 회전 정렬 각도값을 계산하게 되는 것이다.

It can be represented as Where E _nonlinear is the nonlinear error, ψ _QWP1 is the rotation angle of the quadrant plate of the reference arm, ψ _QWP2 is the rotation angle of the quarter wave of the measurement arm, and ψ _QWP3 is The rotation angle of the _quarter wave plate and ψ _HWP represent the rotation angle of the half wave plate of the detection unit, respectively. That is, the magnitude of the nonlinear error varies according to the rotation angle of each wave plate. The nonlinear error caused by the polarization leakage components due to the first, second, and third polarization ray splitters PBS1, PBS2, and PBS3 is minimized. The angle of rotation alignment of the wave plate is calculated.

The fifth step (S500) is a step of aligning the calculated rotation angle by applying the rotation angle of each wave plate calculated in the fourth step (S400) to the actual interferometer.

In addition, in the preferred embodiment of the present invention, the above-described compensation method is applicable to homodyne interference optical system, phase shift interference (PSI) optical system or heterodyne interference optical system.

(Preferred embodiment)

In a preferred embodiment of the present invention it is carried out under the following conditions.

The light source is a frequency stabilized He-Ne laser, has a wavelength of 632.8 nm, and has an intensity fluctuation of about 1%.

2) The wave plate has a wavelength delay error of 1/250 [rad].

3) The polarized light splitter PBS is incomplete and has a polarization crosstalk component.

FIG. 6 is a graph showing nonlinear errors assuming ideal cases of a polarization splitter and a wave plate. As shown in FIG. 6, it can be seen that non-linear errors are almost absent except for calculation errors when the incompleteness and alignment error of the polarizing beam splitter and the wave plate are not considered. However, using the above-described Equation 1 to Equation 6, the nonlinear error is obtained as follows by setting the angular displacement to 0.5 °. In the graph, "X" represents displacement and "Y" axis represents nonlinear error.

7 is a graph showing a nonlinear error measured in consideration of alignment errors of a polarizing beam splitter and a wave plate according to the present invention. As shown in FIG. 7, it can be seen that the peak-to-valley (PV) value is about 3 nm, which is close to the value of the nonlinear error of the conventional interferometer. In addition, it can be seen that the nonlinear error is a periodic signal and includes a sinusoidal high order (PV) component.

8A to 8D are graphs illustrating nonlinear errors according to angle changes of the first to third quarter wave plates and the half wave plate according to the present invention. In general, the alignment angle is 45 ° for the quarter wave plate used in the interferometer, and the alignment angle for the half wave plate is 22.5 °. However, each wave plate shows a different magnitude of nonlinear error according to the rotation angle, as shown in FIGS. 8A to 6D.

In the case of the quadrature wave plates QWP1 to QWP3 in Figs. 8A to 8C, nonlinear errors of about 0.2 nm are shown for an angle error of 0.5 °. However, in the case of the half-wave plate (HWP) of Figure 8d shows a non-linear error value of about 0.3 ~ 0.4 nm for the same angle error. It can be seen that the half wave plate (HWP) is more sensitive than the quarter wave plate (QWP1 ~ QWP3) to the angle change. 8A to 8C, the "Y" axis represents a nonlinear error, and the "X" axis represents the rotation angle of the wave plate, respectively.

Figure 9a is a graph showing the displacement according to the angle change of the quarter wave plate of the measuring arm and the half-wave plate of the light detection unit, Figure 9b is a graph showing the displacement according to the angle change of the quarter wave plate of the reference arm and the half-wave plate of the light detector 9C is a graph showing the displacement according to the angle change of the quarter wave plate and the half wave plate of the light detector. As shown in FIGS. 9A to 9C, nonlinear errors were measured in consideration of the case where the half-wavelength plates HWP had errors at the same time than the quarter-wavelength plates QWP1 to QWP3.

FIG. 9A illustrates the displacement of the first quarter wave plate QWP1 and the half wave plate HWP of the light detector 200 with respect to the angle change. The rotation angle of the first quarter wave plate QWP1 is 59 ° and the half wave. When the lamella (HWP) is 23.1 °, it has a value of about 1.1 nm as the minimum nonlinear error value.

FIG. 9B is a measurement of the displacement of the second quarter wave plate QWP2 and the half wave plate HWP of the light detector 200 with respect to the angle change, and the rotation angle of the second quarter wave plate QWP2 is 29 ° and the half wave. It can be seen that when the lamellae HWP is 23.1 °, it has a value of 1.3 nm as the minimum nonlinear error value.

FIG. 9C is a measurement of the displacement with respect to the angle change of the half wave plate HWP and the third quarter wave plate QWP3 of the light detector 200. The rotation angle of the third quarter wave plate QWP3 is 23.2 ° and the half wave. It can be seen that when the lamellae HWP is 23.2 °, it has a minimum nonlinear error value of about 1.7 nm.

을 이용하여 비선형 오차가 최소가 되도록하는 각 사분파장판 (QWP)및 반파장파(HWP)의 회전각도 정렬값을 다음 [수학식7]과 같이 계산한다.The minimum nonlinear error value thus obtained is expressed as a function of angular error.

Calculate the rotation angle alignment value of each quarter wave plate (QWP) and half wave wave (HWP) to minimize the nonlinear error by using Equation (7).

Here, QWP1 to QWP3 represent first to third quarter wave plates, and HWP represents half wave plates.

Thus, it can be seen that each wave plate must be aligned with a new rotational alignment angle according to the optical characteristics of the first, second, and third polarized light splitters PBS1, PBS2, and PBS3, rather than the known angles.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

      1 is a graph showing the nonlinear error of an interferometer.

2 is a Lissajous graph of an interferometer with nonlinear error.

3 is a block diagram showing the configuration of an interferometer according to the present invention.

4 is a flowchart illustrating a nonlinear error compensation method according to the present invention.

5 is a schematic view showing the configuration of measuring means for measuring the optical properties of a polarized light splitter according to the present invention.

FIG. 6 is a graph showing nonlinear errors assuming ideal cases of polarizing beam splitters and wave plates. FIG.

7 is a graph showing a nonlinear error measured in consideration of alignment errors of a polarization splitter and a wave plate according to the present invention.

8A to 8D are graphs showing nonlinear errors according to angle changes of the first to third quarter wave plates and the half wave plate according to the present invention.

Figure 9a is a graph showing the displacement according to the angle change of the quarter wave plate of the measuring arm and the half wave plate of the light detector.

Figure 9b is a graph showing the displacement according to the angle change of the quarter wave plate of the reference arm and the half wave plate of the light detector.

Figure 9c is a graph showing the displacement according to the angle change of the quarter-wave plate and half-wave plate of the light detector.

Explanation of symbols on the main parts of the drawings

10: first polarizer 20: second polarizer

30, 30 ': light source 40: polarization changing means

41: first reflector 42: second reflector

50: right angle prism 60: data collector

70: phase detector 100: interference

200: signal detector CC: corner cube

D1: first photodetector D2: second photodetector

D3: third photodetector D4: fourth photodetector

HWP: Half-wave plate M1: First measuring means

M2: second measuring means M3: third measuring means

PBS1: first polarized light splitter PBS2: second polarized light splitter

PBS3: Third polarized light splitter QWP: Quad wave plate

QWP1: first quarter wave plate QWP2: second quarter wave plate

QWP3: Third quarter wave plate NPBS: Light splitter

Claims (6)

It includes a first polarized light splitter (PBS1) and interferes the light incident through the double pass interference unit 100, the second and third polarized light splitters (PBS2, PBS3) and half-wave plate In the non-linear error compensation method of the interferometer to obtain the interference signal through the signal detection unit 200 combined with (HWP) and the quarter wave plate (QWP), A first step (S100) of measuring optical characteristics of the first, second and third polarized light splitters (PBS1) to obtain a matrix; A second step (S200) of obtaining a rotation matrix of the half wave plate (HWP) and the quarter wave plate (QWP); A third step of obtaining a nonlinear error using a matrix of the first, second, and third polarized light splitters PBS1, PBS2, and PBS3, and a rotation matrix of the half wave plate HWP and the quarter wave plate QWP (S300). ); A fourth step S400 of calculating a minimum angle alignment value of the half-wave plate HWP and the quarter-wave plate QWP from the nonlinear error of each rotation angle of the half-wave plate HWP and the quarter-wave plate QWP; ); And A fifth step (S500) of compensating and rotating the half-wave plate (HWP) and the quarter-wave plate (QWP) by the minimum angle alignment value by the minimum angle alignment value (S500). Nonlinear error compensation method of interferometer through angular alignment. The method of claim 1, The optical characteristics of each of the polarized light splitters PBS1, PBS2, and PBS3 may be configured to measure light reflected from the light splitter NPBS by light transmitted from the light source 30 ′ and passing through the rotating first polarizer 10. First measuring means (M1); Second measuring means (M2) for measuring the light reflected from the first, second and third polarized light splitters (PBS1, PBS2, PBS3) which are the light transmitted from the light splitter (NPBS); A polarization ratio measured from the third measuring means (M3) for measuring the light transmitted through the second polarizer 20 which rotates the light transmitted from the first, second and third polarized light splitters (PBS1, PBS2, PBS3); Nonlinear error compensation method of the interferometer through the angle alignment of the wave plate, characterized in that the Jones matrix according to the transmission and reflection obtained by using. The method of claim 2, The Jones matrix is represented by Equation 8 according to the reflection (R) and the transmission (T).

Nonlinear error compensation method of the interferometer by angular alignment of the wave plate, characterized in that the matrix according to. Where t is light transmittance, r is light reflectance, p is P polarized light, s is S polarized light, and c is crosstalk. The method of claim 1, The rotation matrix of the quarter wave plate (QWP) and the half wave plate (HWP) is a Jones matrix according to the following Equations 9 and 10, respectively.

here,

Nonlinear error compensation method of the interferometer through the angle alignment of the wave plate, characterized in that the angle alignment error. The method of claim 1, The interferometer is a homodyne interference optical system, a phase displacement interference optical system or a heterodyne interference optical system characterized in that the nonlinear error compensation method of the interferometer by angular alignment of the wavelength plate. The method of claim 1, The minimum angle alignment value

Where E _nonlinear is the nonlinear error, ψ _QWP1 is the angle of rotation of the quadrant plate of the reference arm, and ψ _QWP2 is the angle of rotation of the quarter wave of the measurement arm, ψ _QWP3 represents the rotation angle of the _quarter wave plate of the detector, and ψ _HWP represents the rotation angle of the half wave plate of the detector, respectively.

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