JP4113869B2 - Optical delay - Google Patents

Description

  The present invention relates to an optical delay device for continuously changing a light delay amount (optical path length).

  As an optical delay device used in a Michelson interferometer or the like, it is necessary to continuously and repeatedly change the delay amount with the incident optical axis and the outgoing optical axis being equal.

  As this type of optical delay device, the following Patent Document 1 discloses a structure in which the amount of light delay is changed by rotating a logarithmic spiral mirror on the outer periphery.

JP 2000-206425 A

  FIG. 10 shows a schematic configuration of this optical delay device, and the logarithmic spiral mirror 1 can be rotated alternately in the directions of arrows H1 and H2 around the main axis 2 coinciding with the origin (center axis). The light Sa incident along the optical axis La perpendicular to the main axis 2 is reflected at a point Xa where the optical axis La and the reflecting surface 1a formed on the outer periphery of the logarithmic spiral mirror 1 intersect. The reflection direction has a property of always making a certain angle α with respect to the incident optical axis La.

  Therefore, as shown in FIG. 10, the planar mirror 3 is arranged so that the reflecting surface 3 a thereof is orthogonal to the optical axis Lb of the primary reflected light Sb from the logarithmic spiral mirror 1. The secondary reflected light Sc emitted from the point Xb on the reflecting surface 3a with respect to the reflected light Sb can be returned to the reflecting surface 1a of the logarithmic spiral mirror 1 along the optical axis Lb.

  The tertiary reflected light Sd emitted from the point Xa of the reflecting surface 1a of the logarithmic spiral mirror 1 with respect to the secondary reflected light Sc is emitted in the direction opposite to the incident light Sa along the optical axis La.

Here, as shown in FIG. 10, from the point X on the incident optical axis La when the logarithmic spiral mirror 1 is located at the angle θ to the incident optical axis La to the point Xa on the reflecting surface 1a of the logarithmic spiral mirror 1. Is a third order with respect to the light input from the point X, where A (θ) is the distance from the point Xa of the reflective surface 1a of the logarithmic spiral mirror 1 to the point Xb of the reflective surface 3a of the plane mirror 3 The optical path length P (θ) until the reflected light Sc returns to the point X is
P (θ) = 2 [A (θ) + B (θ)]
It becomes.

  Then, when the logarithmic spiral mirror 1 is rotated from the state of FIG. 10 in the H1 direction to an angle θa as shown in FIG. 11A, the distance between the points X and Xa is longer than A (θ). (Θa), the distance between the points Xa and Xb is B (θa) longer than B (θ), and the entire optical path length P (θa) is also longer than the optical path length P (θ) in the state of FIG. Become.

  Conversely, when the logarithmic spiral mirror 1 is rotated from the state of FIG. 10 in the H2 direction to an angle θb as shown in FIG. 11B, the distance between the points X and Xa is shorter than A (θ). A (θb), the distance between the points Xa and Xb is B (θb) shorter than B (θ), and the entire optical path length P (θb) is also based on the optical path length P (θ) in the state of FIG. Shorter.

  Therefore, by rotating the logarithmic spiral mirror 1 back and forth within a predetermined angle range, the optical path length can be continuously and repeatedly changed within the predetermined range.

  However, a curved surface structure in which the distance from the origin to the reflecting surface 1a varies in a logarithmic manner like the logarithmic spiral mirror 1 is difficult to manufacture, and the cost increases in order to obtain high accuracy.

  Further, since the reflecting surface 1a is a curved surface, the light beam that is reflected twice by the reflecting surface 1a and emitted is spread with respect to the incident light, and a Michelson interferometer or the like when beam spreading becomes a problem It becomes difficult to use, and its application is limited.

  Further, in the structure in which the logarithmic spiral mirror 1 is reciprocally rotated as described above, the logarithmic spiral mirror 1 is inevitably asymmetric with respect to the rotation axis (main shaft 2), and vibration occurs when the logarithmic spiral mirror 1 is reciprocally rotated at high speed. This occurs and the device is easily destroyed by this vibration. Therefore, it must be used in a low-speed operation that does not generate vibration (for example, a reciprocating operation of about several hundred Hz).

  An object of the present invention is to solve these problems, and to provide an optical delay device capable of repeatedly changing an optical path length at a high speed without causing a beam spread of emitted light at a low cost.

In order to achieve the above object, an optical delay device according to claim 1 of the present invention comprises:
It has a flat mirror body (22) having a reflecting surface formed on one surface side, and is configured to rotate the mirror body about an axis parallel to the reflecting surface, on a plane orthogonal to the axis. A rotating mirror (21) that receives incident light (Sa) incident along the reflecting surface,
It has a plurality of planar reflecting surfaces, receives primary reflected light (Sb) emitted from the rotating mirror with respect to the incident light, and is parallel to and spaced from the optical axis of the primary reflected light A first reflector (40) for emitting secondary reflected light (Sc) of the optical axis to the rotating mirror;
The third-order reflected light (Sd) emitted from the rotating mirror that has received the second-order reflected light with an optical axis parallel to the optical axis of the incident light is a planar shape orthogonal to the optical axis of the third-order reflected light. And a second reflector (50) for emitting the fourth-order reflected light (Se) having an optical axis that coincides with the third-order reflected light to the rotating mirror.
The fifth-order reflected light (Sf) is emitted from the rotating mirror that has received the fourth-order reflected light to the first reflector with an optical axis that matches the second-order reflected light, and the fifth-order reflected light is received. A sixth-order reflected light (Sg) is emitted from the first reflector to the rotating mirror with an optical axis coinciding with the first-order reflected light, and the incident light enters the rotating mirror that has received the sixth-order reflected light. The seventh-order reflected light (Sh) is emitted with an optical axis that coincides with the incident light, and the optical path length until the seventh-order reflected light is emitted with respect to the incident light is continuously increased by the rotation of the mirror body. It is characterized by being configured to change.

The optical delay device according to claim 2 of the present invention is the optical delay device according to claim 1,
The rotating mirror is
The mirror body (22), the fixed substrate (24, 25), the edge of the fixed substrate and the outer edge of the mirror body are connected and twisted in the length direction to deform the mirror body. A force is applied to the mirror body by a drive signal having a frequency corresponding to a natural frequency determined by the shaft (23) that is movably supported and the mirror body and the shaft, and the mirror body is reciprocated by the natural vibration. It has the rotation drive means (30, 31, 35) to move.

The optical delay device according to claim 3 of the present invention is the optical delay device according to claim 1 or 2,
The first reflector is any one of a corner mirror, a corner prism, a right angle mirror, and a right angle prism.

  As described above, the optical delay device of the present invention has a structure in which the first reflector and the second reflector reflect light on the planar reflecting surface, and is easy to manufacture including a rotating mirror, at low cost. Since it can be configured, and no beam divergence occurs, there is no problem even if it is used in the Michelson interferometer or the like, and the application is wide.

  In addition, since the optical path length is variable by reciprocatingly rotating the flat mirror body, the optical path length can be changed at high speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an optical delay device 20 according to an embodiment to which the present invention is applied.

  As shown in FIG. 1, the optical delay device 20 includes a rotating mirror 21, a first reflector 40, and a second reflector 50.

  The rotating mirror 21 has a flat mirror body 22 having a reflecting surface 22a for reflecting light on one surface side, and the mirror body 22 reciprocates around an axis 23 parallel to the reflecting surface 22a. It is comprised so that it may rotate.

The rotating mirror 21 is a so-called MEMS (Micro Electro Mechanical).
System) technology, and is configured in a small size and with high dimensional accuracy using a semiconductor substrate etching technology.

  FIG. 2 shows a specific configuration example of the rotating mirror 21. In FIG. 2, the mirror main body 22 is formed in a horizontally-long rectangular flat plate shape, and a reflection surface 22a is formed on one surface side thereof. Horizontally-long rectangular fixed substrates 24 and 25 are arranged in parallel above and below the mirror body 22.

  Between the lower edge center of the upper fixed substrate 24 and the upper edge center of the mirror body 22, and between the upper edge center of the lower fixed substrate 25 and the lower edge center of the mirror body 22, the shafts 23 are aligned with each other. , 23.

  The width and thickness of the shaft 23 are set so as to be torsionally deformed in a desired rotational angle range in the length direction and to return from the deformed state. By the torsional deformation of the pair of upper and lower shafts 23, The mirror main body 22 can reciprocate around the axis 23 with respect to the fixed substrates 24 and 25. However, the thickness of the shaft 23 is the same as the thickness of the mirror main body 22 and the fixed substrates 24 and 25.

  Further, the block formed integrally with the mirror main body 22, the fixed substrates 24 and 25 and the shaft 23 in this way has conductivity in order to electrostatically apply a rotational driving force.

  Here, two fixed substrates 24 and 25 separated from each other are used. However, two shafts are formed inside one fixed substrate formed in a frame shape by connecting both ends of the fixed substrates 24 and 25. A structure in which the mirror main body 22 is rotatably supported via 23 may be used.

  The fixed substrates 24 and 25 are fixed so as to overlap on spacers 27 and 28 provided in parallel to each other on one surface side of the supporting substrate 26 having an insulating property. In addition, electrode plates 30 and 31 are fixed at positions facing one end of the back surface of the mirror body 22 on one side of the support substrate 26.

  Then, between the pair of electrode plates 30 and 31 and the block including the mirror main body 22, the drive signal generator 35 drives the voltage levels to be inverted as shown in FIGS. 3A and 3B. Signals Va and Vb are applied.

  Due to the drive signals Va and Vb, electrostatic attraction force is alternately generated between the electrode plates 30 and 31 and both ends of the back surface of the mirror body 22, and the mirror body 22 reciprocates.

  The frequencies of the drive signals Va and Vb are set to values corresponding to the natural frequency of the mirror main body 22 determined by the shape and weight of the mirror main body 22, the spring constant of the shaft 23, and the like. A large rotation amplitude is obtained.

  Further, as described above, the rotating mirror 21 is formed to be very small and lightweight as a whole including the mirror main body 22 by the MEMS technology, and there is no element that limits the shape of the mirror main body 22. As in this example, it can be formed symmetrically with respect to the axis 23.

  Therefore, the mirror main body 22 can be reciprocated at a high speed at several hundred Hz to several tens of kHz without generating vibration.

  Here, in order to continuously and repeatedly vary the optical path length, the rotating mirror 21 is continuously reciprocally rotated. However, the rotating mirror 21 may be controlled so as to be stopped at an arbitrary angle. In that case, a constant voltage may be applied from the drive signal generator 35 to any one of the electrode plates.

  The structure of the rotating mirror 21 is not limited to the above-described one, and various shapes can be changed. The driving system is not limited to the electrostatic force described above, but includes a magnet and a coil. You may use the magnetic force obtained by using. Further, a mechanical force may be applied using a piezoelectric element or the like.

  As shown in FIG. 1, light Sa having an optical axis La parallel to a plane orthogonal to the axis 23 is incident on the end of the reflecting surface 22 a of the mirror body 22 of the rotating mirror 21.

  The primary reflected light Sb emitted from the rotating mirror 21 that has received the incident light Sa is incident on the first reflector 40.

  The first reflector 40 receives the primary reflected light Sb emitted from the rotating mirror 21 with respect to the incident light Sa, and the optical axis Lc parallel to and spaced from the optical axis Lb of the primary reflected light Sb. The secondary reflected light Sc is emitted to the rotating mirror 21. In this embodiment, as shown in FIG. 4, the outer shape of the first reflector 40 is a right isosceles triangle and has a predetermined thickness. A right angle prism having a thickness is used.

  The two end faces 40a and 40b orthogonal to each other of the right-angle prism have a property of totally reflecting light incident on the inside at a predetermined range angle from the end face 40c side along the opposite side of the right angle. In the state of such an angle range, the two end surfaces 40a and 40b form a reflecting surface. Therefore, in the following description, these two orthogonal end surfaces are referred to as reflecting surfaces 40a and 40b.

  In order to obtain more reliable reflection characteristics, a reflecting material may be coated on the reflecting surfaces 40a and 40b of the right-angle prism.

  From the rotating mirror 21 that has received the secondary reflected light Sc from the first reflector 40, the tertiary reflected light Sd of the optical axis Ld parallel to the optical axis La of the incident light Sa travels toward the second reflector 50. Are emitted.

  The second reflector 50 is made of, for example, a plane mirror, and receives the third-order reflected light Sd by a planar reflecting surface 50a orthogonal to the optical axis Ld, and matches the fourth-order reflected light Se with the third-order reflected light Sd. The optical axis Ld is returned to the rotating mirror 21.

  Accordingly, the rotating mirror 21 that has received the fourth-order reflected light Se emits the fifth-order reflected light Sf toward the first reflector 40 along the optical axis Lc that coincides with the second-order reflected light Sc. From the first reflector 40 that has received the secondary reflected light Sf, the sixth reflected light Sg is emitted toward the rotating mirror 21 along the optical axis Lb that coincides with the primary reflected light Sb, and the sixth reflected light Sg. The seventh-order reflected light Sh is emitted from the rotating mirror 21 that has received the light with the optical axis La coinciding with the incident light Sa.

  Here, the optical axes La and Ld are parallel to the end surface 40c of the first reflector 40, and the mirror main body 22 of the rotating mirror 21 has its reflecting surface 22a and the optical axis La as shown in FIG. , Ld is reciprocally rotated within a range of several degrees (eg, ± 3 °) around a predetermined value θ (eg, 41 °).

  In this embodiment, the optical axes La to Ld are included in the same plane. However, depending on the structure of the first reflector 40, the plane including the optical axes La and Lb and the optical axis Lc are included. , There may be a step between the plane including Ld.

In the case of the optical delay device 20 having the above configuration, the seventh-order reflection with respect to the light Sa incident from the point X on the optical axis La in a state where the reflection surface 22a of the mirror body 22 forms an angle θ with respect to the optical axis La. The total optical path length P (θ) until the light Sh returns to the point X is
P (θ) = 2 [A (θ) + B (θ) + C (θ) + D (θ) + Q (θ)]
It can be expressed as.

  Here, the optical path length A (θ) is the distance from the point X on the optical axis La to the point Xa where the reflecting surface 22a of the mirror body 22 and the optical axis La intersect, and the optical path length B (θ) is the point Xa. The optical path length C (θ) from the point Xc where the optical axis Lb and the end surface 40c of the first reflector 40 intersect is the distance from the point Xb where the optical axis Lb and the end surface 40c of the first reflector 40 intersect. The distance to the point Xd where the optical axis Lc and the reflecting surface 22a of the mirror body 22 intersect, and the optical path length D (θ), from the point Xd, the optical axis Ld and the reflecting surface 50a of the second reflector 50 intersect. This is the distance to the point Xe.

  Further, the optical path length Q (θ) is the sum of the optical path lengths from the point Xb to the point Xc through the reflecting surfaces 40a and 40b in the first reflector 40.

  Although the detailed equation of the optical path length is not shown here, the optical path length P (θ) is approximately approximated by a sine function relating to θ, and the change in the optical path length A (θ) is dominant among the optical paths. I know that.

  Therefore, for example, when the mirror main body 22 rotates clockwise from the state shown in FIG. 1 to the angle θa as shown in FIG. 5A, the optical path length A (θa) is greater than the optical path length A (θ). Since it becomes shorter, the entire optical path length P (θa) is also shorter than the optical path length P (θ).

  Conversely, when the mirror body 22 rotates counterclockwise to the angle θb as shown in FIG. 5B, the optical path length A (θb) becomes longer than the optical path length A (θ). The optical path length P (θb) is longer than the optical path length P (θ).

  FIG. 6 shows a change characteristic of the optical path length P (θ) when θ is changed in a range of ± 3 ° (based on an optical path length of −3 °). As is apparent from FIG. 6, when θ is changed in a range of ± 3 °, a change in the optical path length P (θ) of 1 mm or more can be obtained.

  By setting the initial position of the rotating mirror 21 and the relative position with respect to the first reflector 40, the change characteristic of the optical path length can be set as desired, for example, when the optical path length is maximized when θ is 0 °. Can be shaped.

  As described above, in the optical delay device 20 according to the embodiment, the first reflector 40 and the second reflector 50 for returning light to the mirror body 22 having a flat structure reflect the light on the planar reflection surface. Therefore, since the rotating mirror 20 is easily manufactured and can be configured at low cost, and there is no beam divergence, there is no problem even if it is used for a Michelson interferometer or the like, and the application is wide.

  In addition, since the optical path length is variable by reciprocatingly rotating the flat mirror body 22, the mirror body can be symmetrical with respect to the rotation axis, and the optical path length can be increased at high speed without generating vibration. Can be changed.

  In the optical delay device 20 described above, a right-angle prism is used as the first reflector 40. However, the first reflector 40 has a plurality of planar reflecting surfaces, and rotates with respect to the incident light Sa. The primary reflected light Sb emitted from the moving mirror 21 can be received, and the secondary reflected light Sc of the optical axis Lc parallel to and separated from the optical axis Lb of the primary reflected light Sb can be emitted to the rotating mirror 21. If so, the structure is arbitrary.

  For example, as the first reflector 40, a right angle mirror having two mutually orthogonal reflecting surfaces 40a 'and 40b' as shown in FIG. 7 may be used, and the optical delay device 20 may be configured as shown in FIG. .

  As the first reflector 40, as shown in FIG. 9A, a corner prism having three planar reflecting surfaces 40d, 40e, and 40f orthogonal to each other, or shown in FIG. 9B. As described above, a corner mirror having three planar reflecting surfaces 40d ', 40e', and 40f 'orthogonal to each other can be used, and a reflector having four or more planar reflecting surfaces can be used. .

  Further, in the above description, the incident light Sa is incident on the end of the reflecting surface 22a of the mirror body 22 far from the first reflector 40, and the secondary reflected light or 4 is used using almost the entire area up to the opposite end. The next reflected light is received, but conversely, the incident light Sa is incident on the end of the reflecting surface 22a of the mirror body 22 that is closer to the first reflector 40, and the almost entire area up to the opposite end is used. You may receive secondary reflected light and quaternary reflected light. Further, only a half region of the reflection surface 22a of the mirror body 22 may be used.

The figure which shows the structure of embodiment of this invention The figure which shows the structural example of the principal part of embodiment of this invention. Drive signal diagram of main part of embodiment of the present invention The perspective view of the principal part of embodiment of this invention Operation explanatory diagram of the embodiment of the present invention The figure which shows the change characteristic of the optical path length with respect to the mirror angle of embodiment of this invention The perspective view of the right angle mirror which can be used as the 1st reflector of this invention The figure which shows the optical delay device which used the right-angle mirror as a 1st reflector. Perspective view of corner prism and corner mirror usable as first reflector Schematic configuration diagram of conventional equipment Operation explanatory diagram of conventional equipment

Explanation of symbols

  20 …… Optical delay device, 21 …… Rotating mirror, 22 …… Mirror body, 22a …… Reflective surface, 23 …… Axis, 24, 25 …… Fixed substrate, 26 …… Support substrate, 27, 28 …… Spacer, 30, 31 ... Electrode plate, 35 ... Drive signal generator, 40 ... First reflector, 40a, 40b ... Reflective surface, 50 ... Second reflector, 50a ... Reflective surface

Claims (3)

It has a flat mirror body (22) having a reflecting surface formed on one surface side, and is configured to rotate the mirror body about an axis parallel to the reflecting surface, on a plane orthogonal to the axis. A rotating mirror (21) that receives incident light (Sa) incident along the reflecting surface,
It has a plurality of planar reflecting surfaces, receives primary reflected light (Sb) emitted from the rotating mirror with respect to the incident light, and is parallel to and spaced from the optical axis of the primary reflected light A first reflector (40) for emitting secondary reflected light (Sc) of the optical axis to the rotating mirror;
The third-order reflected light (Sd) emitted from the rotating mirror that has received the second-order reflected light with an optical axis parallel to the optical axis of the incident light is a planar shape orthogonal to the optical axis of the third-order reflected light. And a second reflector (50) for emitting the fourth-order reflected light (Se) having an optical axis that coincides with the third-order reflected light to the rotating mirror.
The fifth-order reflected light (Sf) is emitted from the rotating mirror that has received the fourth-order reflected light to the first reflector with an optical axis that matches the second-order reflected light, and the fifth-order reflected light is received. A sixth-order reflected light (Sg) is emitted from the first reflector to the rotating mirror with an optical axis coinciding with the first-order reflected light, and the incident light enters the rotating mirror that has received the sixth-order reflected light. The seventh-order reflected light (Sh) is emitted with an optical axis that coincides with the incident light, and the optical path length until the seventh-order reflected light is emitted with respect to the incident light is continuously increased by the rotation of the mirror body. An optical delay device configured to change to The rotating mirror is
The mirror body (22), the fixed substrate (24, 25), the edge of the fixed substrate and the outer edge of the mirror body are connected and twisted in the length direction to deform the mirror body. A force is applied to the mirror body by a drive signal having a frequency corresponding to a natural frequency determined by the shaft (23) that is movably supported and the mirror body and the shaft, and the mirror body is reciprocated by the natural vibration. 2. An optical delay device according to claim 1, further comprising a rotation drive means (30, 31, 35) for moving the optical delay device.   3. The optical delay device according to claim 1, wherein the first reflector is any one of a corner mirror, a corner prism, a right-angle mirror, and a right-angle prism.

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