JPH04161803A - Two-dimensional light phase information detector - Google Patents

Abstract

PURPOSE:To achieve measurement of a wave front and a phase difference and the like at a high accuracy by performing a parallel processing of first and second two-dimensional signals from a photoheterodyne interference means to obtain a phase difference. CONSTITUTION:First reading light obtained as an input sample light IN1 from a photoheterodyne interferometer impinged into the side of a photoconductor of an LCLV26a to be collimated is impinged into the side of a liquid crystal of an element 26a through a half mirror 26b and the reflected light thereof is impinged into a half mirror 30. On the other hand, an IN2 from the interferometer having an optical plane arranged therein is impinged into the side of the photoconductor of an LCLV 28b while a second reading light is impinged into the liquid crystal side of an element 28a through a half mirror 28b and the reflected light thereof is impinged into the half mirror 30. Two pieces of binary coded light information are made incident on the liquid crystal side of an LCLV32a and a third reading light is impinged likewise. An output light reflected with the liquid crystal is turned to a logic OR signal as the sum of pieces of information sliced. The signal is integrated with a CCD array 34 and converted into an electric charge corresponding to a phase difference of intensity modulation light from the interferometer. The use of a coherent light source as the reading light enables the prevention of the formation of an interference fringe.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-dimensional optical phase detection device using optical heterodyne interferometry.

[Conventional technology]

As a conventional device for detecting two-dimensional optical phase information with high precision, there is, for example, a high-precision interference measurement device. FIG. 6 is a diagram showing the configuration of an optical heterodyne interferometer as an example.

As shown in the figure, the optical heterodyne interferometer is constructed using a Twyman Green interferometer. The beam expander 2 expands the diameter of the laser beam having the frequency fo and makes it incident on the beam splitter 4 .

The laser light incident on the beam splitter 4 is split into two optical paths that travel in directions perpendicular to each other.

The laser beam (reference beam) that has traveled upward in the drawing passes through a frequency shifter 10 and is reflected by a reference mirror 6. In this case, the frequency of the reference light is changed to f by the frequency shifter 10.
It shifts from o to fo+2f.

On the other hand, the laser light (measuring light) that has traveled to the right side of the drawing is reflected by the sample mirror 8. These two laser beams reflected by the reference mirror 6 and sample mirror 8 (
The reference light and measurement light are combined again by the beam splitter 4, enter the observation lens 12, and form an interference image in front of it.

In this case, only the reference light is given a frequency shift. Therefore, an interference image formed on a predetermined observation surface by the reference light and measurement light is converted into a signal on a temporal carrier frequency. The phase difference of this signal on the time axis has a two-dimensional distribution on a predetermined observation plane, and the phase difference between the signal detected by the reference photoelectric detector 16 and the signal detected by the measurement photoelectric detector 14. can be electrically detected by the phase meter 18. The two-dimensional distribution of the phase difference on the time axis of the signal detected by the phase meter 18 is the two-dimensional distribution of the optical phase difference (i.e. optical path difference) between the reference light and measurement light reflected by the reference mirror 6 and sample mirror 8. It corresponds to the distribution of

[Problems to be Solved by the Invention] However, the above-mentioned optical heterodyne interferometer has the disadvantage that mechanical operation of the measurement photoelectric detector 14 is essential, and high-speed measurement cannot be performed.

Therefore, an object of the present invention is to provide a device that detects two-dimensional optical phase information in parallel using heterodyne interferometry.

[Means to solve the problem]

In order to achieve the above object, in the two-dimensional optical phase information detection device according to the present invention, (a) first and second two-dimensional optical phase information are detected by a first
and (b) first and second optical heterodyne interference means for converting the first and second two-dimensional signals from the first and second optical heterodyne interference means into a second two-dimensional signal, respectively; (c) mutual conversion of the two-dimensional binary optical information from the first and second binary converting means; (d) an integrating means for integrating the two-dimensional AND optical signal outputted from the calculating means;

[Effect]

Each of the first and second two-dimensional signals output from the first and second optical heterogain interference means is a two-dimensional distribution of light that has been intensity-modulated at a predetermined frequency. Note that by projecting this light onto a screen or the like provided on a predetermined observation surface, a striped pattern flowing on the screen can be observed. The first and second binarization means perform predetermined threshold processing on the first and second two-dimensional signals. That is, the first and second two-dimensional signals are binarized according to their two-dimensional intensity distribution. The obtained two-dimensional binary optical information is converted into a two-dimensional logical product optical signal by a calculation means. The obtained two-dimensional AND optical signal at each point has a time width equal to the phase difference at each corresponding point of the first and second two-dimensional signals, and is different from these two-dimensional signals. It is a periodic pulse signal that is repeated at the same period. Therefore, if this periodic pulse signal (logical product optical signal) is integrated at each point, the phase difference at each point of the first and second two-dimensional signals can be detected in parallel as the intensity. .

〔Example〕

Before describing specific embodiments, the configuration and operation of the two-dimensional optical phase information detection apparatus of the present invention will be specifically described with reference to FIGS. 1 and 2.

As the first optical heterodyne interference means 22, the conventional optical heterodyne interferometer shown in FIG. 6 can be used. In this case, the two-dimensional optical phase information corresponds to the unevenness distribution of the sample mirror 8.

Therefore, the unevenness distribution of the sample mirror 8 is converted into a first two-dimensional signal on a predetermined temporal carrier frequency and projected onto the threshold element 26. The threshold element 26 is the first two
This is a value conversion means, and uses, for example, a nonlinear etalon gate array.

The signal light INI shown in FIG. 2 shows the intensity change of the first two-dimensional signal when focusing on one point on the threshold element 26, and it can be seen that the signal light INI changes sinusoidally. .

Here, the principle of heterodyne interferometry for converting two-dimensional optical phase information into a two-dimensional signal will be briefly explained.

The measurement light from the sample mirror 8 and the reference light from the reference mirror 6 at an arbitrary point X on the observation surface (that is, the surface of the threshold element 26) at time t are expressed as follows.

U (xS t)=uo (x) ・exp
fi [2πf t+φo(x)])U (XS
t)"u (x) ・r
“exp fi [2π
(f o +2f) t + φ, co)
Here, U and φ. (X) represents the amplitude and phase of the measurement light, respectively. Also, U and φ (x)
r represents the amplitude and phase of the reference light, respectively. Therefore, the intensity of light detected at point X is given by the following equation.

1 (x 1t) −” o+Ur 1−u
(x) ヰu (x)”tenr 2uo (x) ・ur (x)cos [4πf
t+φ −φo(x) As can be seen from this equation, the intensity of the detection light changes sinusoidally at the frequency 2f of the difference between the measurement light and the reference light, and its phase φ −φ. (X) is the optical phase difference (phase difference as a light wave or optical path length difference in units of wavelength) between both laser beams. In other words, the optical phase difference between both laser beams can be converted into a phase difference between intensity-modulated temporal carrier waves.

The above explanation relates to the conversion of the phase difference along the X-axis, or the phase difference of intensity modulation is converted from the optical phase difference using the same principle regarding the y-axis direction, which is perpendicular to the X-axis in the observation plane. The conversion to 61 is possible. As a result, two-dimensional optical phase information can be converted into a two-dimensional signal on a predetermined temporal carrier frequency.

The first light output from the first optical heterodyne interference means 22
The two-dimensional signal is binarized at a predetermined light intensity value by the threshold element 26 and converted into two-dimensional binarized optical information. The signal light TH1 shown in FIG. 2 shows the intensity change of the two-dimensional binarized destination information regarding one point on the threshold value element 6.

On the other hand, the second optical heterodyne interference means 24 also utilizes an optical heterodyne interferometer similar to that shown in FIG. However, as two-dimensional optical phase information, an optical flat serving as a reference plane is placed at the position of the sample mirror 8. In this case, the second two-dimensional 2D corresponding to the unevenness distribution of the optical flat
The a-coded optical information is a second wave on a predetermined temporal carrier frequency.
The signal is converted into a two-dimensional signal and projected onto the threshold element 28, which is the second binarization means. In this case, assuming that there is no inclination of the optical flat, the phase of the signal light IN2 indicating the intensity change of the second two-dimensional signal when focusing on one point on the threshold element 28 will be different from that of other points on the threshold element 28. Match the phase of each point. Therefore, the signal light TH indicating the intensity change of the two-dimensional binary optical information regarding one point on the threshold element 28
2 also substantially match at each point on the threshold element 28.

The two-dimensional binary optical information emitted from each threshold element 26 and 28 is combined by a half mirror 30 and enters a logic element 32. This logic element 32 is an arithmetic means, and is composed of, for example, a nonlinear etalon gate array. This logic element 32 calculates the logical product at each point of the two-dimensional binary optical information from each threshold value element 26.28 (signal light AND).
, gives a two-dimensional conjunctive optical signal.

The two-dimensional AND optical signal emitted from the logic element 32 is
The light enters an integrating element 34, which is composed of a CCD array or the like, and is integrated there. In other words, the two-dimensional logical product optical signal emitted from the logic element 32 is flattened for each point, and the phase difference between the first and second two-dimensional optical phase information is changed between the first and second two-dimensional optical phase information. It is detected as a charge distribution corresponding to the phase difference of the target signal. In other words, this charge distribution etc.
It corresponds to the unevenness distribution.

In the explanation of FIG. 1, the unevenness distribution of the sample mirror with respect to the optical flat was detected. By arranging these two-dimensional optical phase information, it is possible to obtain a phase difference distribution between these two-dimensional optical phase information.

Further, first and second optical heterodyne interference means 22.2
4 may be constituted by one optical heterodyne interferometer. In this case, a sample mirror and an optical flat are placed separately at the position of the sample mirror 8. If the threshold elements 26 and 28 are placed side by side on the observation surface of the optical heterodyne interferometer, two-dimensional binarized optical information can be obtained by each threshold element. Thereafter, the unevenness distribution of the sample mirror 8 can be detected as a phase difference using a configuration similar to that shown in FIG.

Furthermore, it is not necessary that the sample mirror 8 of FIG. 1 be planar. For example, if the sample mirror 8 has a curvature, a lens or the like may be placed between the sample mirror 8 and the beam splitter 4.

Similarly, the threshold elements 26, 28, logic element 32, etc. do not necessarily need to be formed in a planar shape.

As the above-mentioned binarization means and calculation means, in addition to the nonlinear etalon gate array, for example, a spatial light modulation tube (MSLM),
A two-dimensional optical bistable device using a liquid crystal spatial light modulation tube (LCLV) or the like can be used. Furthermore, it goes without saying that various two-dimensional photodetecting devices other than a CCD array can be used as the integrating means.

Preferred embodiments of the present invention will be described in detail below.

FIG. 3 is a diagram showing a two-dimensional optical phase information detection device of the first embodiment.

In the case of the illustrated embodiment, the LCLV25a is used as the binarization means.
, 28a and a half mirror 26b128b, an LCLV 32a and a half mirror 32b were used as calculation means, and a CCD array 34 was used as an integration means.

Light from an optical heterodyne interferometer in which a sample mirror is arranged is incident on the side surface of the LCLV 26a on the photoconductor side.

The collimated first readout light enters the liquid crystal side of the LCLV 26a via the nozzle mirror 26b. The output light reflected by the liquid crystal enters the half mirror 30 as two-dimensional binary optical information.

On the other hand, light from an optical heterogain interferometer equipped with an optical flat is incident on the surface of the LCLV 28a on the photoconductor side. The collimated second readout light enters the liquid crystal side of the LCLV 28a via the half mirror 28b. The output light reflected by the liquid crystal enters the nof mirror 30 as two-dimensional binary optical information. LCLV26
The two-dimensional binary optical information from a and 28a is LCLV3
The light is incident on the photoconductor side surface of 2a. The collimated third readout light is transmitted to the LCL via the half mirror 32b.
It enters the liquid crystal side of V32a. The output light reflected by the liquid crystal becomes a two-dimensional AND optical signal obtained by slicing the sum of each two-dimensional binary optical information by a predetermined threshold value. LCL
The two-dimensional logical product optical signal from V28a is integrated by the CCD array 34, and is converted into a phase difference of the intensity modulated light from the optical heterodyne interferometer, and therefore a difference in unevenness between the sample mirror and the optical flat (phase difference in wavelength units). converted into the corresponding charge. In this case, if incoherent light sources are used as the first and second readout lights (for example, the polarization planes of each readout light are orthogonal), LCLV3
It is possible to easily prevent the two-dimensional binary optical information incident on the photoconductor side of 2a from interfering with each other and forming an interference pattern.

FIG. 4 is a perspective view of the two-dimensional optical phase information detection device of the second embodiment.

In the case of the second embodiment, nonlinear etalon gate arrays 26 and 28 were used as the binarization means, a nonlinear etalon gate array 32 was also used as the calculation means, and a CCD array 34 was used as the integration means. Light from an optical heterodyne interferometer with a sample mirror is incident on a nonlinear etalon gate array 26. Light from an optical heterodyne interferometer with an optical flat is incident on a nonlinear etalon gate array 28. The subsequent logical product operation and integration are the same as in the case of FIG. 1 or FIG. 3, so the details will be omitted.

FIG. 5 is a sectional view showing a part of the nonlinear etalon gate array 26, 28, 32, which is a two-dimensional optical bistable device. Briefly, a structure in which a Zn5e layer is sandwiched between dielectric multilayer films is uniformly formed on a glass substrate.

〔Effect of the invention〕

As explained above, according to the two-dimensional optical phase information detection device of the present invention, the first and second two-dimensional signals from the optical heterodyne interference means are processed in parallel, and the first and second two-dimensional signals are processed in parallel.
The phase difference of dimensional signals is obtained. Therefore, highly accurate wavefront measurement, phase difference measurement, etc. can be realized at high speed.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the configuration of the two-dimensional optical phase information detection device of the present invention, FIG. 2 is a diagram for explaining the operation of the two-dimensional optical phase information detection device of FIG. 1, and FIG. A diagram showing the configuration of a two-dimensional optical phase information detection device according to the first embodiment, FIG.
A diagram showing the configuration of a two-dimensional optical phase information detection device according to an embodiment,
FIG. 5 is a diagram showing the structure of a nonlinear etalon gate array used in the two-dimensional optical phase information detection device of FIG. 4, and FIG. 6 is a diagram showing a conventional optical heterodyne interferometer. 22... first optical heterodyne interference means, 24...
Second pre-heterodyne interference means, 26...first binarization means, 28...second binarization means, 32...calculation means, 34...integration means. Representative Patent Attorney Yoshiki Hase Configuration of two-dimensional optical phase information detection device Fig. 1 Fig. 4 W/4 λ/2 person/4 nonlinear etalon gate array Fig. 5 Optical heterotine wafer meter Fig. 6

Claims (1)

[Claims] First and second two-dimensional optical phase information that converts the first and second two-dimensional optical phase information into first and second two-dimensional signals on predetermined temporal carrier frequencies, respectively. an optical heterodyne interference means; first and second two-dimensional signals for converting the first and second two-dimensional signals from the first and second optical heterodyne interference means into two-dimensional binary optical information, respectively; digitization means; arithmetic means for providing a two-dimensional AND optical signal between the two-dimensional binary optical information from the first and second binarization means; and an output from the arithmetic means. A two-dimensional optical phase information detection device comprising: an integrating means for integrating the two-dimensional logical product optical signal.