JPH0222503A - Laser interference measuring instrument - Google Patents

Abstract

PURPOSE:To measure a long distance without generating unstable phase relation among four signals which are each pi/2 out of phase by providing 1st-3rd polarization beam splitters and four optical fibers. CONSTITUTION:The light from a laser light source 12 is separated by a polarizing film 18 into a P and an S component, which are made incident on a measuring mirror 20 and a reference mirror 22, whose reflected light components are recoupled by the 1st polarization beam splitter(BS) 16 and the coupled beam is split by a BS 24. Then the 2nd polarization BS 26 splits one light beam into a P and an S component by a polarizing film and has the optical axis of the projection of opposite-phase interference light at 45 deg. and the 3rd polarization BS 32 splits the other divided light component into a P and S component by a polarizing film and has the optical axis of the projection of opposite-phase interference light at 45 deg.. Then a 1/4-wavelength plate 28 which shifts the phase of light incident on the BS 32 90 deg. behind the light incident on the BS 26 is provided on the optical path between the BS 24 and BS 32 and light beams emitted from the BS 26 and BS 32 are made incident on terminals of optical fibers 46, 48, 50, and 52, thereby guiding their interference signal out of a case.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser interference measurement device, and more particularly to a laser interference measurement device constructed in a compact size using an optical fiber.

[Conventional technology]

FIG. 3 shows the structure of a conventional laser interference measurement device. In the figure, light emitted from a laser light source 10 is made into a parallel beam by a beam expander 12, and a right-angle prism 1
4, the direction is changed by 90°. The light emitted from the right-angle prism 14 enters the beam splitter 16 and passes through the measurement mirror 1.
8 and the reference mirror 20. The reflected light from the measurement mirror 18 and the reference mirror 20 enters the beam splitter 16 again, is recombined and output, passes through a magnifying lens 22, and projects interference fringes onto four photodiodes 24. The photodiode 24 converts the brightness of the interference fringes into an electrical signal, and when measuring the amount of movement, the amount of movement of the measuring mirror 18 is determined by counting the change in the brightness of the interference fringes corresponding to the amount of movement. .

[Problem that the invention seeks to solve]

In the conventional laser interference measurement device, one spot of interference fringes is projected onto four photodiodes 24, and the reference mirror 20 is tilted so that the phases of the four photodiodes 240 differ by π/2 to adjust the fringe spacing. Was. However, with this adjustment method, deviations in the fringe spacing and variations in the brightness of the interference fringes occur due to the vibration of the measuring mirror 18 and the surface properties of each mirror. This has the disadvantage that the phase relationship between signals that differ by π/2 becomes unstable.

Furthermore, in the conventional laser interference measurement device, the interference light emitted from the beam splitter 16 is transmitted to the photodiode 24.
Since light is directly received by the photodiode 24, the size of the device is limited by the outer diameter of the photodiode 24 even if other parts are miniaturized, and this has the drawback that miniaturization is not possible.

The present invention has been made in view of these circumstances, and proposes a compact laser interference measurement device that does not cause instability in the phase relationship of four signals whose phases differ by π/2 even when measuring long distances. The purpose is to

[Means for solving problems]

In order to achieve the above object, the present invention uses a corner cube prism for the measuring mirror and the reference mirror, and also divides the light from the Rede light source into a P component and an S component using a polarizing film. A first polarizing beam splitter is provided for making the light incident on the mirror and recombining the reflected light from the measurement mirror and the reference mirror, and a beam splitter is provided for splitting the light emitted from the first polarizing beam splitter into two directions. A second polarizing beam splitter with an optical axis tilted by 45 degrees is provided, which splits one of the lights split by the splitter into a P component and an S component using a polarizing film and outputs interference light of opposite phase. A third polarized beam splitter whose optical axis is tilted by 45 degrees is provided, which splits the other light into a P component and an S component using a polarizing film and emits interference light of opposite phase. a second in the optical path between the splitter and
The phase of the light incident on the third polarizing beam splitter is 90" with respect to the phase of the light incident on the third polarizing beam splitter.
A shifted A wavelength plate is provided, and the optical axis of the divided wavelength plate is the same as the polarization direction of either the P polarization or the S polarization of the first polarization beam splitter, and the light is emitted from the second and third polarization beam splitters. The laser interference measuring device is characterized in that the light is made incident on each end face of four optical fibers, and the interference signal is extracted from the case of the laser interference measurement device through these optical fibers.

[Effect]

In the present invention, four interference lights whose phases are shifted by π/2 can be extracted stably even in long distance measurements, so there is no error in long distance measurements, and each of the four optical fibers This interference light is applied to the end of each optical fiber, and the other end of each optical fiber is pulled out of the case of the interference device to electrically process the interference light. Therefore, the space inside the case is limited by the outer diameter of the optical fiber, and the size can be significantly reduced compared to the conventional laser interference measurement device, which is limited by the outer diameter of the photodiode.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a laser interference measurement device according to the present invention will be described in detail below with reference to the accompanying drawings.

In Fig. 1, lO is the case of the laser interference measurement device, 1
2 is a laser light source, 14 is a collimating lens, 16 is a polarizing beam subrifter having a polarizing film 18, 20 is a movable mirror consisting of a corner knife, and 22 is a reference mirror consisting of a corner knife.

Further, 22 is an optical system having an inverted telescope structure that focuses the light beam, 24 is a beam splitter, and 26 is a second polarizing beam splitter that splits one of the lights split by the beam splitter 24 into a P component and an S component; , 28 is a wavelength plate, 30 is a right-angle prism, and 32 is a third polarizing beam splitter that splits the other of the light split by the beam splitter 24 into a P component and an S component. Furthermore, 34 and 36 are right angle prisms, 38 to 44 are condenser lenses, and 46 to 52 are optical fibers.

The optical fibers 46 to 52 are sent to a processing circuit (not shown) outside the case 10 and electrically processed.

The operation of the laser interference measurement device according to the present invention configured as described above is as follows. First, the laser beam emitted from the Rade light source 12 is made into a parallel beam by the collimating lens 14 and enters the polarizing beam splitter 16 . Of the light incident on the polarizing beam splitter 16, the measurement light (
P component) passes through the polarizing/lighting film 18 and enters the movable mirror 20,
After the direction is changed by 180°, the beam enters the polarizing beam splitter 16 again. In addition, the reference light (S component) of the laser light is reflected by the polarizing film 18, changed direction by 180 degrees by the reference mirror 22, and exits again from the polarizing beam splitter 16.
and is recombined with the P component from the moving mirror 20.
The light beam emitted from the polarizing beam splitter 16 is focused by a lens optical system 22 having an optical system with an inverted telescope structure.
The beam enters the beam splitter 24. Beam splitter 2
The light incident on the polarizing beam splitter 26 is split, and one of the lights is incident on the second polarizing beam splitter 26. The P component of the light incident on the second polarizing beam splitter 26 passes through the polarizing film, is focused by the lens 38, and enters the end face of the optical fiber 46. Further, the S component reflected by the polarizing film by the second polarizing beam splitter 26 enters the right angle prism 34, and the S component light whose direction has been changed by 90 degrees by the right angle prism 34 is condensed by the lens 40 and sent to the optical fiber. The light is incident on the end face of 48.

Here, the interference lights entering the optical fibers 46 and 48 are the light that has passed through the polarizing film and the light that has been reflected, and therefore have opposite phases to each other.

Further, the other light split by the beam splitter 24 passes through the wavelength plate 28, has its direction changed by 90 degrees by the right angle prism 30, and enters the third polarizing beam splitter 32.

Since the light incident on the third polarizing beam splitter 32 has passed through the wavelength plate 28, its phase is shifted by 90° with respect to the light incident on the second polarizing beam splitter 26. The interference light (P component) on the transmitted side of the laser light incident on the third beam splitter 32 passes through the polarizing film, is further narrowed down by the lens 42, and enters the end face of the optical fiber 50. Further, the interference light (S component) reflected by the polarizing film of the third polarizing beam splitter 32 has its direction changed by 90° by the right angle prism 36, is focused by the lens 44, and enters the end face of the optical fiber 52. The interference light incident on the optical fibers 50 and 52 is the light that has passed through the polarizing film and the light that has been reflected, so they have opposite phases to each other.

According to the embodiment described above, in the second and third polarizing beam splitters 26 and 32, the optical axes of the transmitted light and the reflected light are orthogonal, so that the interference intensities have opposite phases. Also, the second
The third polarizing beam splitter 26.32 and the right-angle prism 34.36 are arranged on optical axes inclined at 45 degrees with respect to the S and P components, as shown in FIG. Further, a flea wave plate 30 is disposed on the reflection side optical path of the beam splitter 24, so that the phase of the reference light or measurement light is shifted by π/2 with respect to the transmission side optical path. This makes the phase π
The optical fiber 46 produces four interference lights shifted by /2.
The light is incident on the end faces of the optical fibers 46 to 52, and can be taken out to an electronic circuit (not shown) outside the case via optical fibers 46 to 52.

〔Effect of the invention〕

As explained above, according to the laser interference measurement device according to the present invention, by using optical components to generate four interference lights whose phases are shifted by π/2, the fringe interval can be maintained even when the movable mirror is moved over a long distance. Even if there is a deviation in the brightness of the interference fringes or a variation in the brightness of the interference fringes, the phase relationship between the four interference lights does not change.

In addition, the interference light is received by an optical fiber and sent to the laser interference measurement device and a separate processing circuit via the optical fiber.
The laser interference measurement device can be configured compactly.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the structure of the Rade interference measurement device according to the present invention, FIG. 2 is a perspective view showing the main parts of the laser interference measurement device according to the invention, and FIG. 3 is a diagram showing the conventional laser interference measurement device. FIG. 12... Rade light source, 16... Polarizing beam splitter, 20... Moving mirror, 22... Reference mirror, 2
4... Beam splitter, 26... Second polarizing beam splitter, 28... Wave plate, 32...
Third polarizing beam splitter, 46.52... optical fiber.

Claims (1)

[Scope of Claims] A first device that splits the light from the laser light source into a P component and an S component by a polarizing film and makes them incident on a measuring mirror and a reference mirror, and recombines the reflected light from the measuring mirror and the reference mirror. A polarizing beam splitter is provided to split the light emitted from the first polarizing beam splitter into two directions, and one of the lights split by the beam splitter is split into a P component and an S component by a polarizing film. A second polarizing beam splitter is installed to emit interference light with an opposite phase, and the other light split by the beam splitter is polarized by a polarizing film.
The third component splits into the S component and the S component and emits interference light of opposite phase.
A polarizing beam splitter is provided, and the phase of the light incident on the third polarizing beam splitter is adjusted in the optical path between the beam splitter and the third polarizing beam splitter with respect to the phase of the light incident on the second polarizing beam splitter. 90° shift 1
A /4 wavelength plate is provided, and the light emitted from the second and third polarizing beam splitters is
A laser interference measurement device characterized in that an interference signal is made incident on each end face of an optical fiber, and an interference signal is extracted from the case of the laser interference measurement device through the optical fiber.