JP4110765B2 - Light emitting / receiving composite unit and displacement detection device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical unit that obtains a signal using polarized light using a semiconductor laser as a light source, and more particularly to a structure of a so-called “lattice interference displacement detector” that detects displacement using interference by diffracted light. is there.
[0002]
[Prior art]
The displacement detection device used in the field of semiconductor manufacturing or the like includes, for example, a device (so-called so-called “solid scale” on which scales are recorded, and detection means that electrically detects the amount of displacement in the linear movement direction of the scale. Linear encoders) are known.
[0003]
An apparatus (such as a hologram encoder) that detects displacement using interference of diffracted light obtained by a diffraction grating can be cited as an apparatus that enables detection with high accuracy and high resolution.
[0004]
FIG. 4 shows an example a of the configuration of a conventional displacement detection device, which is composed of three parts: a light irradiation part b, an optical path control and test part c, and a light receiving part d.
[0005]
In the light irradiation part b, a semiconductor laser LS is used as a light source, and a first converging lens L1 and a first polarizing beam splitter PBS1 are arranged. As for the optical path control and the test part c, the first reflecting mirrors R1a and R1b, the reflective diffraction grating RG, the second converging lenses L2a and L2b, the first λ / 4 wavelength plate (quarter wavelength) Plate) WP1a, WP1b, and further second reflection mirrors R2a, R2b are arranged.
[0006]
For the light receiving part d, a transflective mirror HM, a second polarizing beam splitter PBS2, a third polarizing beam splitter PBS3, a second λ / 4 wavelength plate WP2, and photodetectors PD1 to PD4 are arranged. .
[0007]
The light emitted from the semiconductor laser LS is converted into convergent light by the first converging lens L1, and then polarized and separated by the polarization beam splitter PBS1 to become two lights (see the light beams LFa and LFb), one of which is a reflection mirror. The optical path is changed by R1a and reaches the reflective diffraction grating RG, and the other optical path is changed by the reflecting mirror R1b and reaches the reflective diffraction grating RG. Here, “polarization separation” means that the incident light beam is separated into a P-polarized component and an S-polarized component.
[0008]
A second converging lens is used for each light beam that is diffracted at least higher than the first order, which has the same sign (the same sign is the same) in the reflection type diffraction grating RG attached to the test part (linear scale or the like). After passing through each of L2a and L2b, after the respective polarization directions are rotated by 90 degrees by the λ / 4 wave plates WP1a and WP1b and reflection mirrors R2a and R2b arranged at the angular positions corresponding to the diffraction angles, the same as the forward path Following the optical path in the reverse direction, the first polarization beam splitter PBS1 is reached.
[0009]
Since the light reaching the polarization beam splitter PBS1 is in a state in which the polarization direction is rotated by 90 degrees with respect to the original direction, the light is emitted in a direction different from the incident direction in the forward path and is transmitted through the semi-transmissive mirror HM. Head for. Then, the amount of light reaching the translucent mirror HM is divided into two, one of the divided lights reaches the polarization beam splitter PBS3, and the other light passes through the λ / 4 wavelength plate WP2 and then enters the polarization beam splitter PBS2. Reach.
[0010]
The mounting posture of the polarization beam splitter PBS3 is arranged around the optical axis around the optical axis and at an angle of about 45 degrees with respect to the polarization direction of the reached light beam.
[0011]
The light beams polarized and separated by the polarization beam splitter PBS2 reach the photodetectors PD1 and PD2, respectively, and the light intensity is converted into an electric quantity. Further, the light beams polarized and separated by the polarization beam splitter PBS3 reach the photodetectors PD3 and PD4, respectively, and the light intensity is converted into an electric quantity.
[0012]
The operation principle of this example is as follows.
[0013]
The two light beams LFa and LFb having different polarization directions (or polarization states) separated by the polarization beam splitter PBS1 are reflected and diffracted by the reflection type diffraction grating RG to be diffracted light of the same sign, and λ / 4 By the wave plates WP1a and WP1b and the reflection mirrors R2a and R2b, the forward path is returned to the polarization beam splitter PBS1 and mixed as a light beam whose polarization direction is rotated by approximately 90 degrees.
[0014]
At that time, since the two mixed light beams are divided by two from the semiconductor laser LS having the same polarization component, the two lights interfere with each other even in different polarization directions.
[0015]
Now, when the reflection type diffraction grating RG is moved in the direction in which the gratings are aligned relative to other optical systems (for example, the direction indicated by the arrow A in FIG. 4), the lights mixed by the polarization beam splitter PBS1 interfere with each other. However, intensity changes occur at a pitch corresponding to the diffraction order for each polarization direction. By separating the intensity change due to the interference into a plurality of polarization components, the photodetectors PD1 to PD4 can detect light intensity distributions having different phases. That is, by detecting this change in light intensity, the amount of movement of the reflective diffraction grating RG can be detected with a resolution obtained by multiplying the diffraction grating pitch by the inverse of the diffraction order and the inverse of the number of diffractions by a factor of two. Can do. Furthermore, since the intensity change obtained by the photodetectors PD1 to PD4 has a shape very close to a sine wave, it is possible to obtain a high resolution by a method of interpolating the detection waveform.
[0016]
In such a displacement detection device using diffracted light interference, for example, a reflective diffraction grating is created with a hologram, etc., and the obtained sine wave signal is further divided to achieve resolution of the order of nm (nanometers). It is also possible to do.
[0017]
[Problems to be solved by the invention]
However, the conventional displacement detection device has the following problems due to the necessity of assembling the light-emitting component, the light-receiving component, or the optical component separately manufactured in the manufacturing process.
[0018]
-When assembling the equipment, it is necessary to make precise adjustments for the finishing accuracy of each part or variation in characteristics, so complicated processes are required and it is difficult to reduce the cost.
[0019]
-A large space is required for adjustment, fastening and fixing of each part, and it is therefore difficult to reduce the size of the device.
[0020]
-Since an adhesive must be used for the final fixing after precision adjustment, the adhesion state is likely to be influenced by the surrounding environmental changes, etc., and there is a possibility that the adjustment part may be displaced due to environmental changes or changes over time. There is.
[0021]
Accordingly, an object of the present invention is to provide a highly reliable light receiving / emitting composite unit suitable for miniaturization and weight reduction at low cost, and a displacement detection device using the interference of diffracted light while mounting the unit. To do.
[0022]
[Means for Solving the Problems]
In order to solve the above-described problems, a light receiving / emitting composite unit according to the present invention includes a light emitting element and a plurality of return lights that detect light emitted from the light emitting element and returned to the unit through an external optical system. The light receiving element is arranged on the same substrate or member, and the polarized light that separates the light emitted from the light emitting element constituting the light branching part (or the light branching part including the light splitting part) into one prism. A separation film and a light branching film for branching the return light returned to the unit through the external optical system, and a converging or diverging lens for the output light and the return light, and an arbitrary direction from the polarization state of the return light This structure has a structure in which diffractive members for separating and diffracting the polarized light components in different directions are integrally formed.
[0023]
Further, the displacement detection device according to the present invention includes a light receiving / emitting composite unit manufactured with an integral structure as described above, a test part including a diffraction grating as an external optical system for the unit, and a light receiving / emitting composite unit. A polarizing member for changing the polarization state by receiving the diffracted light from the diffraction grating after the reflection, and a reflecting member for reflecting the light passing through the polarizing member and returning it in the reverse direction (direction toward the diffraction grating) It is a thing.
[0024]
Therefore, according to the present invention, the light-emitting element, the light-receiving element, the polarization separation film that separates the emitted light from the light-emitting element constituting the light branching portion, and the emitted light have returned to the unit through the external optical system. By integrating a single prism, lens, and diffractive member with a light branching film that branches the return light, it is easy to adjust the position of each part, and it is suitable for cost reduction, size reduction, and weight reduction. High-intensity light emitting / receiving composite unit and a displacement detection device using the same can be manufactured.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration example of a displacement detection device using a light receiving / emitting composite unit (or light transmission / reception unit) according to the present invention, which is applied to a lattice interference type displacement detection device.
[0026]
As can be seen from the structural comparison with FIG. 4, most of the components of the optical system are housed in the light receiving / emitting composite unit 1, and the two light beams emitted after being polarized and separated in the unit. LFa and LFb reach the first reflecting members (reflecting mirrors R1a and R1b) constituting the external optical system ET, respectively, and undergo an optical path change. These first reflecting members are necessary for reflecting the light emitted from the light receiving / emitting composite unit 1 toward a reflection diffraction grating RG, for example, a hologram grating (volume type phase hologram or the like) having high diffraction efficiency. It is a thing.
[0027]
Each light reaching the reflection type diffraction grating RG used in the detected part such as a linear scale is input to the grating at a short distance (the difference in the optical path length in the grating is reduced, and the error in the wavelength of the original signal is generated). In this case, after diffracting at the first or higher order, the polarizing member (λ / 4 wavelength plates WP1a and WP1b) and the second reflecting member (reflecting mirror R2a) are respectively passed through the converging lenses L2a and L2b. R2b). That is, the light beam LFa reaches the reflecting mirror R2a via the λ / 4 wave plate WP1a after being diffracted by the reflective diffraction grating RG, and the light beam LFb is λd after being diffracted by the reflective diffraction grating RG. / 4 It reaches the reflecting mirror R2b through the / 4 wavelength plate WP1b. The λ / 4 wave plates WP1a and WP1b have a role of changing the polarization state upon receiving the diffracted light from the reflection type diffraction grating RG, and rotate the polarization direction by 90 degrees as described above. Further, the reflecting mirrors R2a and R2b have a role of reflecting the light whose polarization state has been changed and returning it in the reverse direction, and each of the reflected light travels back and forth in the reverse direction. 1 is reached (becomes the return light to the unit).
[0028]
FIG. 2 shows a configuration example of the light emitting / receiving composite unit 1 and shows a main part of the internal structure.
[0029]
The light receiving / emitting composite unit 1 has a light source 3, a light branching unit 4, lens groups 8_1 to 8_3, a diffractive member 5 (5_1, 5_2), and a light receiving unit 6 (6_1 to 6) with respect to the housing member (or sealing member) 2. 6_4), a λ / 4 wavelength plate 11 is provided to form an integrated structure.
[0030]
The light source 3 is used as a measurement light source (or a light emitting unit) in application to the displacement detection device. The light emitting element 3a (for example, a semiconductor laser is used) is fixed on the semiconductor substrate 7 having a reflection surface 7a with respect to light emitted from the element. That is, the reflecting surface 7a serves as an optical path changing unit that changes the light emitted from the light emitting element 3a in a direction along the set optical axis of the light source 3 (vertical direction in the figure), and raises the light upward in the figure. Work. The semiconductor substrate 7 is fixed to the inner bottom surface of the housing member 2.
[0031]
The receiving member 6 is housed in the housing member 2, and a plurality of light receiving elements 6_1 to 6_4 are formed on the semiconductor substrate 6a in order to detect light that has passed through the diffraction member 5 (5_1, 5_2). Although not clearly shown in the figure, the light emitting element 3a or the semiconductor substrates 6a and 7 are electrically connected to an electrode member for wiring that leads from the housing member 2 to the outside, for example, by wire bonding or the like. .
[0032]
The housing member 2 on which the semiconductor substrates 6a and 7 are arranged and fixed is provided with a cover member 8 for covering and sealing the opening, whereby the light source 3, the light receiving unit 6, and the diffraction member 5 are packaged. . For example, a transparent plastic material is used for the cover member 8, and a plurality of lenses 8_1 to 8_3 are formed. In other words, the lens 8_1 is a converging lens disposed on the optical axis of the light source 3, and light emitted from the light emitting element 3a and then reflected by the reflecting surface 7a passes through the λ / 4 wavelength plate 11 to the lens. The incident light that has passed through the lens is emitted out of the unit through a polarization separation film described later. Further, the lenses 8_2 and 8_3 are provided for converging (or diverging) the return light from the external optical system ET shown in FIG.
[0033]
The cover member 8 is provided with the λ / 4 wavelength plate 11 in the vicinity of the lens 8_1. The composite prism 9 that constitutes the light branching unit 4 and includes the λ / 4 wavelength plate 10, and further, the polarization separation disposed near the lenses 8_2 and 8_3 in order to separate the polarization components of the branched return light. The diffractive optical elements 5_1 and 5_2 are fixed.
[0034]
That is, the λ / 4 wavelength plate 11 and the diffractive optical elements 5_1 and 5_2 are fixed to the inner surface side of the cover member 8, and the diffractive optical elements 5_1 and 5_2 constitute the diffractive member 5. The diffractive optical element 5_1 is provided for the lens 8_2, and diffracted light by the element is detected by the light receiving elements 6_1 and 6_2. The diffractive optical element 5_2 is provided for the lens 8_3, and the diffracted light from the element is detected by the light receiving elements 6_3 and 6_4.
[0035]
A composite prism 9 is mounted and fixed on the upper surface of the cover member 8, and includes a polarization splitting film 9a, a light branching film 9b for branching the return light beam, and a total reflection surface 9c. That is, the polarization separation film 9a and the light branching film 9b constitute the light branching section 4, and the polarization separation film 9a is disposed on the optical axis of the light source 3 at a position corresponding to the lens 8_1, The light branching film 9b is disposed at a position corresponding to the lens 8_2. The total reflection surface 9c is disposed at a position corresponding to the lens 8_3.
[0036]
Thus, the lens and the diffractive optical element are arranged between the composite prism 9 and the light receiving unit 6.
[0037]
A λ / 4 wavelength plate 10 (corresponding to the WP2) is disposed immediately behind the light branching film 9b (on the total reflection surface 9c side), and light passing through the wavelength plate among the return light. It reaches the total reflection surface 9c.
[0038]
In this example, the return light beam that has returned to the unit 1 through the external optical system ET is divided into two by the light branching film 9b. However, the number of branches is not limited to this, but at least two. What is necessary is just to comprise so that it may branch to the above and may be guide | induced to the diffractive optical element for polarization separation. Further, the position of the diffractive optical element may be any position as long as it is between the light branching film 9 b and the total reflection surface 9 c and the light receiving unit 6.
[0039]
Thus, the operation of this configuration is as follows.
[0040]
First, the light emitted from the light emitting element 3a is reflected by the reflecting surface 7a of the semiconductor substrate 7 and undergoes an optical path change. Then, the reflected light becomes circularly polarized light by the λ / 4 wavelength plate 11 and becomes convergent light by the convergent lens 8_1 disposed on the cover member 8, and reaches the polarization separation film 9a of the composite prism 9.
[0041]
The light beams LFa and LFb separated into the linearly polarized light components by the polarization separation film 9a are diffracted by the reflection type diffraction grating RG of the external optical system ET shown in FIG. Rotated approximately 90 degrees to return light and enter the respective composite prisms 9 (the light beam LFb enters from the upper side of FIG. 2 and the light beam LFa enters from the left side of FIG. 2), and enters the polarization separation film 9a again. Come back.
[0042]
Since each return light beam has a phase difference of 90 degrees with respect to the polarization state incident and separated from the light source 3, it is directed to the light branching film 9b and the total reflection surface 9c while being mixed. The λ / 4 wavelength plate 10 disposed in the composite prism 9 has a function of further providing phase information by changing linearly polarized light to circularly polarized light.
[0043]
The light beams branched by the light branching film 9b and the total reflection surface 9c are converged by the converging lenses 8_2 and 8_3 of the cover member 8, and then separated into polarization components by the corresponding diffractive optical elements 5_1 and 5_2. Diffracted at different angles. The diffracted light reaches the corresponding light receiving elements 6_1 to 6_4.
[0044]
Note that the diffractive optical elements 5_1 and 5_2 for separating the polarization can be manufactured using a semiconductor lithography technique or the like as a diffractive optical element having a grating period shorter than the emission wavelength of the light source 3, for example. In the example, since the number of branches is 4, for example, the light beams separated with the polarization directions set to 0 degrees, 45 degrees, 90 degrees, and 135 degrees (45-degree intervals) are respectively transmitted to the light receiving elements 6_1 to 6_4. It is the composition which becomes.
[0045]
With respect to each light beam incident on each light receiving element 6_1 to 6_4, information on the amount of movement related to the reflective diffraction grating RG is included as a change in the amount of received light due to interference of higher-order diffracted light. The amount of movement of the diffraction grating RG can be obtained by appropriately performing a known calculation process on the detection signal received in step S4 and converted into an electrical signal.
[0046]
In this example, when a semiconductor laser is used as the light emitting element 3a, the polarized light separation film disposed on the composite prism 9 due to the emitted light being linearly polarized light parallel to the mounting surface. The λ / 4 wavelength plate 11 is used so that polarization separation can be performed with an appropriate amount of light at 9a, but not limited to this, the configuration shown in FIG. 3 (the posture of the semiconductor substrate 7 on which the light emitting element 3a is mounted) (Positioning rotated at an angle θ of about 45 degrees in the mounting surface to the housing member 2) is possible.
[0047]
FIG. 3 is a plan view of the light source and the light receiving unit viewed from the optical axis direction. In the light receiving / emitting composite unit 1, the light emitting element 3a (semiconductor laser) and the reflecting surface 7a are removed with the cover member 8 and the composite prism 9 removed. 2 shows the positional relationship between the semiconductor substrate 7 on which is mounted and the semiconductor substrate 6a constituting the light receiving unit 6.
[0048]
When the light receiving / emitting composite unit 1 is viewed from the optical axis direction of the light source 3 and the light receiving unit 6, the straight line “LN1” indicates a straight line (light emitting axis) including the light emitting direction (emission direction) of the light emitting element 3a. (The set optical axis of the light source is a direction orthogonal to the paper surface). Further, the straight line “LN2” is the center of each of the light receiving elements 6_1 to 6_4 (shown by a broken line in the drawing) formed on the semiconductor substrate 6a (light receiving center, that is, the optical axis of each element and the light receiving surface). A straight line passing through (intersection point) is shown and extends in the longitudinal direction of the semiconductor substrate 6a. The angle “θ” represents an angle formed by the straight line LN1 and the straight line LN2, and is an angle of 45 degrees (or approximately 45 degrees).
[0049]
According to this arrangement, the emitted light deflected from the light emitting element 3 a by the reflecting surface 7 a (starting up in the optical axis direction of the light source 3 by changing the optical path) is approximately 45 degrees according to the mounting angle of the semiconductor substrate 7. Since the light reaches the polarization separation film 9a with a polarization angle and is separated into a P-polarized component and an S-polarized component having substantially the same light amount, uneven separation of the luminous flux can be prevented.
[0050]
For the semiconductor substrate 6a on which the light receiving elements 6_1 to 6_4 are formed, in addition to the light receiving circuit, a detection signal amplification circuit (current voltage conversion amplification circuit, etc.), a calculation circuit related to the detection signal, and the like are integrally formed. By doing so, it is possible to improve the detection accuracy by improving the S / N ratio (signal-to-noise ratio), for example, the size of the entire apparatus, and the cost.
[0051]
Note that the above-described configuration is merely an example of the present invention. For example, the semiconductor substrates 6a and 7 are disposed and fixed on the inner bottom surface of the housing member 2, but the same function is achieved by the present invention. The structure is not limited to this structure as long as it is based on the gist, and the converging lenses 8_1 to 8_3 and the like formed integrally with the cover member 8 also have a structure in which equivalent optical components are substituted as their functions. Various embodiments can be mentioned.
[0052]
And according to the above-described light emitting / receiving composite unit 1 and the displacement detection device using the same, the following advantages are obtained.
[0053]
First, in the conventional displacement detection apparatus, as shown in FIG. 4, in the optical path from the light source LS to the polarization beam splitter PBS1 and the optical path from the beam splitter to the photodetectors PD1 to PD4, individual optical components are provided. Therefore, for example, it is necessary to fix each part to a base part such as an optical base, and adjustment of the positional relationship of each part is troublesome. There is no such inconvenience.
[0054]
That is, as in the present invention, when an optical component (such as an optical element) is packaged and integrally formed in a semiconductor sealing structure, the polarization separation diffractive optical element for separating the polarization component related to the return light beam 5_1 and 5_2 are placed in the optical path, and the light-emitting element 3a and the light-receiving elements 6_1 to 6_4 can be arranged in a plane, and the integrally formed optical components are moved or adjusted by changing their mounting postures. It can be easily manufactured by fixing later. In particular, a semiconductor element is precisely placed and fixed in a connected semiconductor sealing part having, for example, a silicon wafer or a reference part on the position, and an electronic component (such as a light emitting element or a light receiving element) after fixing. After that, the optical component is placed at a predetermined position, and after detecting the state of the light flux from the light emitting element to the light receiving element and the amount of light, the position of the optical component is finely adjusted and fixed. However, it can be easily realized by using existing technology (for example, realized by an optical system or the like in a head device (optical pickup or the like) for an optical disk). Therefore, adjustment and assembly processes can be easily performed using semiconductor manufacturing equipment.
[0055]
In this way, by integrally forming the parts in the semiconductor sealing structure, adjustment becomes extremely easy, and it is possible to reduce the size and weight of the shape and mass, and at the same time, it has been proven in semiconductor manufacturing. A certain high reliability is guaranteed.
[0056]
Furthermore, a compact configuration can be realized by using a diffractive optical element for polarization separation.
[0057]
【The invention's effect】
As is apparent from the above description, according to the inventions according to claims 1 and 3, polarized light that separates the light emitted from the light emitting element , the light receiving element, and the light emitting element constituting the light branching portion into two. Precise position adjustment is possible by integrating a single prism, lens, and diffractive member with a light splitting film that splits the return light that has been returned to the unit through the external optical system. It is easy, and it is not necessary to make a large arrangement space for the parts, so it is suitable for downsizing. Since each part is confined in the same housing member, it is difficult to be affected by environmental changes and changes over time, so that the occurrence of misalignment can be prevented and the reliability of the unit can be improved.
[0058]
According to the invention which concerns on Claim 2 or Claim 4, a compact structure can be implement | achieved by arrange | positioning a diffraction member between an optical branching part and a light receiving element, and the polarization component of return light can be isolate | separated.
[0059]
According to the inventions according to claims 5 and 6, polarization separation (separation into P-polarized light and S-polarized light) can be performed with a substantially uniform light amount.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of a lattice interference type displacement detection apparatus using a light receiving / emitting composite unit according to the present invention.
FIG. 2 is a diagram showing an example of a configuration of a light receiving / emitting composite unit according to the present invention.
FIG. 3 is a plan view for explaining an arrangement example of a light source and a light receiving unit in the light emitting / receiving composite unit.
FIG. 4 is a diagram illustrating a configuration example of a conventional grating interference type displacement detection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light reception / emission composite unit 1, ET ... Displacement detection device, 3 ... Light source, 3a ... Light emitting element, 4 ... Light branching part, 5, 5_1, 5_2 ... Diffraction member, 6 ... Light receiving part, 6_1 to 6_4 ... Light reception Element, 8_1 to 8_3 ... lens, 9 ... prism, 9a ... polarization separation film, 9b ... light branching film, ET ... external optical system, RG ... diffraction grating, R2a, R2b ... reflection member, WP1a, WP1b ... polarization member

Claims (6)

A plurality of light receiving elements for detecting a light emitting element and return light from which the emitted light emitted from the light emitting element returns to the unit through the external optical system are disposed on the same substrate or member,
A polarization splitting film that separates the light emitted from the light emitting element constituting the light branching portion into two and a light branching film that branches the return light that has returned to the unit through the external optical system. Is provided,
A converging or diverging lens for the outgoing light and return light, and a diffractive member for separating a polarization component in an arbitrary direction from the polarization state of the return light and diffracting it in different directions, and these members A combined light receiving and emitting unit characterized by having an integrally formed structure. In the light emitting / receiving composite unit according to claim 1,
A diffractive member is disposed between the light branching portion and the light receiving element. A plurality of light receiving elements for detecting a light emitting element and return light from which the emitted light emitted from the light emitting element returns to the unit through the external optical system are disposed on the same substrate or member,
A polarization splitting film that separates the light emitted from the light emitting element constituting the light branching portion into two and a light branching film that branches the return light that has returned to the unit through the external optical system. Is provided,
A converging or diverging lens for the outgoing light and return light, and a diffractive member for separating a polarization component in an arbitrary direction from the polarization state of the return light and diffracting it in different directions, and these members A light receiving and emitting composite unit having a structure formed integrally;
A polarizing member for changing the polarization state by receiving the diffracted light emitted from the test part including the diffraction grating and the diffraction grating after being emitted from the light receiving / emitting composite unit, and reflecting the light passing through the polarizing member in the reverse direction An external optical system including a reflecting member for returning is provided. In the displacement detection apparatus according to claim 3,
A displacement detecting device, wherein the diffractive member is disposed between the light branching portion and the light receiving element. In the light emitting / receiving composite unit according to claim 1,
The light emitted from the light emitting element is configured to reach the polarization separation film after undergoing an optical path change in the direction along the set optical axis,
When viewed from the optical axis direction of the light source including the light emitting element and the light receiving unit including the light receiving element, a straight line including the light emitting direction of the light emitting element and a straight line passing through the center of each light receiving element constituting the light receiving unit Are arranged so as to form an angle of approximately 45 °. In the displacement detection apparatus according to claim 3,
The light emitted from the light emitting element in the light receiving / emitting composite unit is configured to reach the polarization separation film after undergoing an optical path change in the direction along the set optical axis,
When the light receiving / emitting composite unit is viewed from the optical axis direction of the light source including the light emitting element and the light receiving unit including the light receiving element, each light receiving unit constituting the light receiving unit and a straight line including the light emitting direction of the light emitting element. A displacement detecting device, wherein the straight line passing through the center of the element is arranged at an angle of approximately 45 °.

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