JPH01250803A - Interferometer - Google Patents

Abstract

PURPOSE:To constitute an optical phase detecting means without using any polarization beam splitter and to simplify an optical system and to decrease the number of components by providing diffraction gratings, polarizers, detectors, etc. CONSTITUTION:A polarized light beam is incident on diffraction gratings 46 and 48 and four of diffracted light beams outputted by the grating 48 are supplied to four polarizers 50a-50d. The diffracted light beams form interference fringes when passing through the polarizers 50a-50d and images of the interference fringes are formed on photodetectors 52a-52d. Those detectors 52a-52d perform photoelectric conversion corresponding to the light and dark of the interference fringes incident on the detectors 52a-52d. For the purpose, the angles of polarization of the polarizers 50a-50d are selected properly to obtain photoelectric conversion signals of four phases which are 90 deg. out of phase of periodic variation in light intensity due to the movement of a corner cube prism 16. Those signals are further divided electrically and counted by a normal counter to know the relative movement quantity of the prism 16, and the optical phase detecting means 44 can be constituted and the optical system is simplified and reduced in the number of components.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention supplies measurement light and reference light generated from a light beam such as a laser beam onto the same optical path, and mutually positions them onto a plurality of optical paths. This invention relates to an improvement in an interferometer that measures changes in the optical path length of measurement light by dividing it with a phase difference.

[Conventional technology]

As an example of an interferometer, there is a laser interferometer that obtains four-phase signals as shown in FIG. 6, for example.

In FIG. 6, a laser light source 10 generates a laser beam 12 containing an S-polarized component and a P-polarized component, and a polarizing beam splitter 14 and a corner cube 16 as a moving reflector are disposed on the optical path of the laser beam 12.

The polarizing beam splitter 14 causes the P-polarized component of the laser beam 12 to travel straight, and reflects the S-polarized component in a direction perpendicular to the incident beam. In order to obtain a reference light by reflecting this reflected light back to the polarizing beam splitter 14,
A corner cube prism 18 as a fixed reflector is attached to the polarizing beam splitter 14.

Further, on the optical path reflected by the corner cube prism 16, a 1/2 wavelength plate 20. A beam splitter 24, a polarizing beam splitter 26, and a 7-axis detector 28 are arranged in this order.

Beam splitter 24 has a part polarizing beam splitter 2
6, and the rest is reflected in a direction perpendicular to the incident beam. On the optical path of the laser beam reflected from the beam splitter 24, a quarter wavelength plate 32, a polarizing beam splitter 34, and a 7-photodetector 36 are sequentially arranged. Polarizing beam splitter 34 polarizes the incident beam P
The polarized light is made to travel straight and is supplied to the 7 Otodetector 36,
Reflects the polarized light in a direction perpendicular to the incident beam. A seven-point detector 38 is arranged on the optical path of this reflected beam.

On the other hand, the polarizing beam splitter 26 causes the P-polarized light component of the incident beam to proceed straight to the photodetector 28, and reflects the S-polarized light component in a direction perpendicular to the incident beam, and supplies the reflected light to a photodetector 30 disposed on the optical path thereof. In the above configuration, the P polarized light component of the laser beam 12 generated by the laser light source 10 is sent to the corner cube prism 16 by the polarizing beam splitter 14, and the S polarized light component is sent to the corner cube prism 18. The laser beam reflected by each of the corner cube prisms 16 and 18 is returned to the polarizing beam splitter 14 again, and exits from the polarizing beam splitter 14 through the same optical path. The laser beam reflected from the corner cube prism 18 becomes a reference light, the laser beam reflected from the corner cube prism 16 becomes a measurement light, and the reference light and measurement light interfere on the optical path exiting the polarizing beam splitter 14. The interference fringes change depending on the amount of movement of the corner cube prism 16 in the optical path direction. The corner cube prism 16 is attached to a moving member to measure length, distance, etc.

When the light beam from the polarizing beam splitter 14 passes through the half-wave plate 20, the polarization directions of the measurement light and the reference light are rotated by 45 degrees, and then the light beam is split into two directions by the beam splitter 24. In the light beam split in the straight direction by the beam splitter 24, the P-polarized light beam further travels straight through the polarizing beam splitter 26, and the S-polarized light beam perpendicular to this beam heads toward the 7-photodetector 30.

7 Laser beam (interference light) for Otodetector 28
If is 0 degrees, the interference light received by the 7-otodetector 30 has a deviation of 180 degrees.

On the other hand, the laser beam reflected by the beam splitter 24 is given a phase delay to either the reference light or the measurement light by the 174 wavelength plate 32, and is further split into two directions whose polarization planes are perpendicular to each other by the polarizing beam splitter 34. The interference fringes are supplied to seven detectors 36 and 38, respectively.

The interference light supplied to the 7-otodetectors 36 and 38 is
Since the 174 wavelength plate 32 is disposed in the optical path, there are phase delays of 90 degrees and 270 degrees with respect to 0 degrees of the 7-wavelength detector 28.

Therefore, 7 Oto detectors 28, 36, 30, 38
sequentially outputs four-phase photoelectric conversion signals having a phase shift of 90 degrees.

Two sets of electrical signals with a phase shift of 180 degrees after charging conversion of each of the 7 Otodetectors are processed by a subtracter (not shown) to remove the DC bias component of the signal (if there is a DC bias component, interference fringes may be counted incorrectly). As shown in Figure 7, the amplitude is doubled and the phase is 9.
Generates a double number with 0 degree difference. By electrically dividing this double sign and counting it with a normal counter, the amount of movement of the corner cube prism 16 can be determined.
Therefore, length, distance, etc. can be known.

Regarding this type of interferometer, Japanese Patent Application Laid-Open No. 62
There is -70720.

[Problems to be Solved by the Invention] However, in the conventional interferometer, the beam splitter 24 and the polarizing beam splitter 26 are used to split the interference light into four
Since it is necessary to have a structure that divides the light beam into two directions and provides a phase difference of 90 degrees, there is a problem in that there is a limit to the miniaturization of the device and also leads to an increase in cost.

The present invention has been made in view of the actual state of the prior art described above, and it is an object of the present invention to provide an interferometer with a simplified configuration and miniaturization.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention includes a light source that generates a light beam, splitting the light beam from the light source into each of a constant reflector and a moving reflector, light splitting means for emitting the reference light reflected by the fixed reflector and the measurement light reflected by the movable reflector onto the same optical path; and an optical phase detection means for obtaining a plurality of charge conversion signals having phase differences,
In an interferometer that counts interference fringes by processing each signal, a diffraction grating outputs a plurality of diffracted lights with respect to the light beam from the light splitting means, and each of the diffracted lights obtained by the diffraction grating. a plurality of polarizers that are inserted into the optical path of the light beam and arranged so that their outputs have a predetermined phase difference, and a plurality of 7-photodetectors that photoelectrically convert interference light obtained through each of the polarizers. It is set up (1).

[Function] The diffraction grating causes the light beam from the light splitting means to be diffracted in, for example, four directions, and polarizers having different polarization angles are disposed in the optical path of each of the diffracted lights. Since each of the interference lights goes up to 7 Otodetectors and is photoelectrically converted, by arranging the outputs of the polarizers so that the phase differs by 90 degrees, optical phase detection can be performed without using a beam splitter or a polarizing beam splitter. means can be configured.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing an embodiment of a laser interferometer according to the present invention, and FIG. 2 is a perspective view showing details of the optical phase detection means (44) in the embodiment of FIG. 1. In this embodiment, the same reference numerals are given to the same parts as in FIG. 6, and the explanation thereof will be omitted, and different configurations will be explained.

In FIG. 1, there is a lens 40174 on the optical path of the output beam of the polarizing beam splitter 14 as a light splitting means.
A wavelength plate 42 and an optical phase detection means 44 are arranged in this order.

When the diameter of the light beam from the polarizing beam splitter 14 is large, the lens 40 separates the light beam from the optical phase detection means 44.
Used to narrow down to Otodetector.

Therefore, if the beam diameter from the polarizing beam splitter 14 fits within seven detectors, there is no need to provide it. Furthermore, the 174 wavelength plate 42 functions to convert the reference light (S polarized light) and measurement light (P polarized light) of the light beam supplied from the lens 40 into circularly polarized light that is rotated in opposite directions.

As shown in FIG. 2, the optical phase detection means 44 includes a
fIIJl and second diffraction grating 4 that diffracts the light beam from wavelength plate 42 in a plurality of directions (four directions in this embodiment)
Polarizers 50a to 50d are arranged in the optical path of the four diffracted lights obtained by the diffraction grating 6 and the diffraction grating 48, and are set at different polarization angles. It is configured to include seven photodetectors 52a to 52d, each of which outputs a corresponding photoelectric conversion signal.

Next, the operation of the embodiment with the above configuration will be explained.

A light beam 12 of linearly polarized light (including an S-polarized light component and a P-polarized light component) emitted from the laser light source 10 is split by a polarizing beam splitter 14 into S-polarized light and P-polarized light, respectively.
The S-polarized light beam is reflected by the corner cube prism 18, and the P-polarized light beam is reflected by the corner cube prism 16, and returned to the polarization beam splitter 14 as reference light and measurement light, respectively. is emitted from the polarizing beam splitter 14. At this time, since the corner cube prisms 16 and 18 are at different distances from the polarizing beam splitter 14, there is a difference in optical path length between the S-polarized beam and the P-polarized beam.

The light beams sent out on the same axis from the polarizing beam splitter 14 have their beam diameters adjusted by the lens 40, and then, when passing through the 174-wave plate 42, the S-polarized light and the P-polarized light become circularly polarized light with opposite rotations. . The polarized light beam is incident on diffraction gratings 46 and 48 which are stacked so that the gratings are perpendicular to each other, and four of the diffracted lights output from the diffraction grating 48 are supplied to polarizers 50a to 50d. be done. The diffracted light forms interference fringes when passing through the polarizers 50a to 50cl, and the interference fringes form the 7-photodetector 52a.
The image is formed at ~52d. 7 Otodetector 52a to 52d
performs charging conversion according to the brightness and darkness of the interference fringes entering each light. As the corner cube prism 16 moves,
The light intensity on the photodetector 52 changes periodically as shown in FIG.

Therefore, by appropriately selecting the polarization angles (easy transmission axes) of the polarizers 50a to 50d, the phase of the periodic change in light intensity due to the movement of the corner cube prism 16 can be adjusted to 90°.
It is possible to obtain four-phase charging conversion signals that are shifted by degrees.

These 4-phase signals whose phases are shifted by 90 degrees are respectively converted into O degree signals.
90 degree signal, 180 degree signal, 9.270 degree signal, as shown in Figures 4 and 5, (0°-180°) and (90°
” -270°), two signals with a DC bias component removed and with a phase difference of 90 degrees are obtained. This signal is further electrically divided and counted by an ordinary counter. By this, it is possible to know the amount of relative movement of the corner cube prism 16. In the above explanation, a laser interferometer was used as an example, but the reference light (reference light) and measurement light (detection light) are the same with a difference in optical path. It can be widely applied to devices configured to output light on the optical axis, separate this light beam into a plurality of optical paths with different phases, and process signals between each optical path.In addition, in the above embodiment, two In this embodiment, the diffraction gratings are stacked so that the gratings are perpendicular to each other, but they may be configured as one piece.

Furthermore, in this example, a four-phase type example was shown, but
It is possible to use any phase such as 3-phase, 6-phase, 8-phase, etc. In addition, the 174-wave plate 46 can be installed at a position other than the one shown in the figure, such that it can be installed immediately before any two of the polarizers 50a to 50d, and the optical axis direction of the crystal of the 174-wave plate 46 can be set in the S-polarized direction or in the P-polarized direction. It may be arranged to match the direction. Further, as the polarizer 50, a polarizer, a polarizing beam splitter, a Woerlaston prism, etc. can be used.

[Effect of the invention 1 As explained above, according to the present invention, the optical phase detection means can be configured without using a beam splitter or a polarizing beam subrifter, so it is possible to simplify the optical system and reduce the number of parts. , it is possible to easily miniaturize the device and make it multi-phase.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
A perspective view showing details of the optical detection means 44 in the embodiment shown in the figure, FIG. 3 is a light intensity detection characteristic diagram in the configuration shown in FIG. 1,
4 and 5 are waveform explanatory diagrams showing subtraction processing of four-phase signals in an embodiment of the present invention, and FIG. 6 is a configuration diagram showing a conventional interferometer. 10... Laser light source 14... Polarizing beam splitter 16.18... Corner cube prism 42
...1/4 wavelength plate 44...Optical phase detection means
46.48...Diffraction grating 50a~50cl...
・Polarizer 52a to 52d...7 Oto Detector Patent applicant Tokyo Seimitsu Co., Ltd. Figure 1 Figure 3 Figure 4 Figure 5 Figure 6\

Claims (1)

[Claims] (1) A light source that generates a light beam, and the light beam from the light source is divided into a fixed reflector and a moving reflector, and the reference light reflected by the fixed reflector and reflected by the moving reflector. and an optical phase detection means for obtaining a plurality of photoelectric conversion signals having a predetermined phase difference from each other from the light beam emitted from the light splitting means, An interferometer that counts interference fringes by processing each signal includes a diffraction grating that outputs a plurality of diffracted lights with respect to the light beam from the light splitting means, and each of the diffracted lights obtained by the diffraction grating. It includes a plurality of polarizers that are inserted into an optical path and arranged so that their outputs have a predetermined phase difference, and a plurality of photodetectors that photoelectrically convert interference light obtained through each of the polarizers. An interferometer characterized by: